THE ROLE OF THE NEUROTROPHIC FACTORS IN THE NEURO-PSIHO-DEVELOPMENTAL DISORDERS IN CHILDREN

We studied the brain-derived neurotrophic factor (BDNF) in the plasma of children with diverse grade of motor and neuro-psycho-developmental disorders (who suffered from diverse grade PHIE of the CNS). We appreciated serum BDNF levels were significantly lower in children with motor and psychological disorders in comparison to controls. This could suggest a delayed increase of BDNF levels during those children’s development. Thus, low BDNF levels are negatively correlated with the severity of motor and neuro-psychic disorders. This could indicate the role of BDNF in motor neurons’ plasticity, developmental and maintenance processes of the brain. Our data confirm the role of BDNF on the child’s psychological development (it contributes to nerve fibers maturation language, behavior and emotional centers). We suggest that low levels of BDNF influence the synaptic plasticity and the interaction between neural and glial cells, thereby playing a decisive role in the complex child’s behavior including language acquisition, cognition, affect etc. BDNF studies could have an important implication in the comprehension of psycho-developmental disorders, as well as in the treatment of neuro-developmental disorders.

Introduction

They have estimated that 2 to 4 % of in term newborns (n.b) present hypoxia during birth or shortly before birth [3].

After years of experimental research on animals with a series of pharmacological agents (free radical synthesis inhibitors, free radical sweepers, antagonists of glutamatetype amino acid excitators, blockers of calcium canals, inhibitors of nitric oxide), glucocorticoids, and Phenobarbital, they have shown the inefficiency of the latest in prevention and treatment of secondary cerebral in juries PHIE. Hereby, the most important problem of neonatology and neuropediatries remains unsolved [8].

At the present time, a number of studies confirms the role of neurotrophic factors in the maintenance of neurotrophicity in hypoxic-ischemic injuries of the brain [3, 21, 26]. Though, until now, no estimative clinical studies regarding neurotrophic disorders correlated with PHIE have been done.

The experimental studies on neurotrophic factors represent the main part of all fundamental researches in neurobiology. Experimental results on animals and cells’ cultures have shown that these factors have spectacular effects with perspectives of therapeutic application in the near future [20].

STUDY OBJECTIVES

Highlight the relationship between neuro-psycho-developmental disorders (motor disorders and mixed specific psycho-developmental disorders) and BDNF in children who suffered from diverse grade PHIE of the CNS.

MATERIALS AND RESEARCH METHODS

182 children aged from 7 days to 36 months (study lot – st.lt), with neuro-psycho-developmental disorders (motor disorders and mixed specific psycho-developmental disorders) who suffered from diverse grade PHIE of the CNS were investigated.

The allotment in sub lots (sbl.) according to age and clinic diagnostic: 7 days – 1 morith 46 children with PHIE acute period (PHIE gr. I / sbl. I – 16, PHIE gr. II / sbl. II – 15, PHIE gr. III / sbl. III – 15); 1-3 months (46) with motor disorders (MD) and psycho-developmental disorders (PD) (gr. I/sbl. I – 16, gr. II / sbl. II – 15, gr. III / sbl. III – 15); 3-6 months (45) with MD and PD (gr. I / sbl. I – 15, gr. II/sbl. II – 15, gr. III / sbl. III – 15); 6-36 months (45) with MD and PD (gr. I / sbl. I – 15, gr. II/sbl.II – 15, gr. III/sbl. III – 15). Children aged 1-36 months (recovery period) presented MD and PD as consequences of PHIE. 60 healthy children formed the control lot (control group – ctrl.gr.).

Children with intrauterine infections, metabolic and toxic encephalopathies, and congenital brain malformations were excluded from the study.

In conformity to the established goals, children from each lot passed the clinical, functional and laboratory investigations. The neurological statute was assessed at children aged 7 days – 12 months with a periodicity of 3 months. The anamnesis was collected in order to assess the dynamic of motor (mt.) and neuropsychical (nrps.) acquisitions. We appreciated the following domains: cognition, expressive language, receptive language, fine motricity, gross motricity, etc.

An age-related scale of evaluation of the development degree of nrps and mt was elaborated – tests, appreciated with 1, 2, 3 and 4 points. Performance acquisitions according to age – 4 points (pt.); I grade performance difficulties – 3 pt., II grade – 2 pt., III grade -1 pt.

The goal of this evaluation wasto high-lightthe alerting neurological signs, level of maturation of the CNS and the risks of development of neurological after-effects in children that had suffered from PHIE.

Transfontanelar NSG, EEG and brain TC were done in the dynamics of the first year of life.

We assessed plasma BDNF levels via immunoenzymatic method the two lots of children were studied. Laboratory examinations were effectuated on the immunological analyzer STAT FAX-303 by the immunoenzymatic analysis method (ELISA).

Statistical procedures were effectuated on the personal computer IBM PC using the software STATISTICA 6.0. The t Student criterion was used to ap-preciatethe level of differentiations between the average values.

RESULTS

Documentation of antecedents was pre-pared in order to obtain a more correct diagnose. 87% from st.lt. were children with an unfavourable  obstetrical   anamnesis, 28% of whom suffered during birth. The most frequent maternal affections during pregnancy were: gestational toxaemia (59%), anaemia (62%), and arterial hypertension 38%). We have noted that the most frequent pathology of the labour and expulsion, like: insufficiency of contraction forces, procidence of cordon, difficult extrac-tion were met in 37% of cases. We noted peri- and intrapartum precedents in only 2% of ctrl.gr. (p < 0,01). Likewise, fetal pathology may be a provocative factor of hypoxic-ischemic injury suffering.

We noted at chiidren from st.lt.: premature birth (23%), cord congenital diseases (4%), haemolytic anaemia (8%), hyperbilirubinemia (12%). The low Apgar score allowed us to determine n.b’s statute and a suspicion of a fetal sufferance in the st.lt (67%) in comparison to ctrl.gr. (4%). Neurological symptoms had lasted during the 2-4 weeks of life at chiidren from st.lt. (TABLE I).

Clinical manifestation at chiidren with PHIE had ameliorated by the age of 2 weeks-1 month, according to the degree of the PHIE. Cerebral functions had remained severely affected in the difficult forms of PHIE. Chiidren from sbl. II and III were presenting severe neurological syndromes during the retrieval period.

In order to screen the nrps. and mt. development the reflexes (rf) of CNS morphofunctional development were assessed: rf of extension of superior limbs, heel rf, rf of vertical maintenance, supra pubic extensor rf, crossed extension rf, Galant rf, Moro rf, cervical tonic rf, hand grasping rf, plantar grasping reflex.

Reflexes of development have an important clinical signification in the assessment of CNS maturation, presenting very often the locating value of injuries. Positive rf at corresponding age gained 4 pts.; rf. present at the time when it should disappear- 3 pts.; present 3 months after the time when it should disappear – 2 pts.; present after 6 months – 1 pt.

The pathologic response of 3 primitive reflexes represents valuable information to forecast the nrps and mt deficits. Motor acquisitions were evaluated: maintenance of the head, rotation from belly to back, rotation from backto belly, sitting with support, crawling, pace. – Normal motor performances’ development was quantified with 4 pts.; 2 months delay – 3 pts.; 4 months – 2 pts.; 6 months and more – 1 pt.

Non acquisition of motor performances at the physiological age suggested the idea of a severe neurological sufferance and, respectively, the retention of CSN maturational process. Chiidren with PHIE from gr.ll presented in 4% of cases, and those from gr.lll in 38%: MD, anomalies of developmental reflexes, non acquisition of nrps and mt performances at physiological age. We observed that nrps and mt developmental indexes of sbl. l werediminished insignificantly by the end of retrieval period in comparison to ctrl.gr. (p < 0,01). The most diminished indexes were appreciated in sbl. PHIE-II (p < 0,05) and – III (p < 0,1), in comparison to ctrl.gr.

Present day studies confirm the neuroprotective role of neurotrophic factors on CNS and peripheral. In the present study we assessed BDNF levels in the serum of chiidren with diverse grade PHIE. The obtained results are presented in TABLE 2.

BDNF level was assessed in st.lt and ctrl.gr. A statistically important variation of BDNF was established in the ctrl.gr.: 1001,8 pg/ml (at n.b.) and 1011,9 pg/ml (between 6 and 12 months), minimal value – 989 pg/ml (at n.b.), maximal value – 1021,7 pg/ml (between 6-12 months).

The threshold of this sub lot had stable values increasing only with 0.99%. Thus, it was confirmed that in the period of growth of the healthy child BDNF is the neurotrophin responsi responsible for a normal nervous system development (see TABLE 2).

It was established that in sbl.l the aver-age BDNF level was smaller in comparison to ctrl.gr and it varied between 945,6 pg / ml (at n.b.) and 973,4 pg / ml (between 6-12 months), minimal level was 919,2 pg / ml (n.b.), and the maximal 991.2 pg / ml (between 6-12 months). The threshold of this sub lot constitutes p < 0,05, p < 0,1.

The BDNF level in sbl.l (6-36 months) increased with 2,7% by the age of 1 year old in comparison of sbl.l (n.b.) and was 38,5 pg / ml (3,8%) more diminished in comparison to ctrl.gr. The statistically significant variation between the minimal and maximal level at newborns constituted +26,4 pg / ml, and at the age of 6-12 months + 18,7 pg / ml.

The BDNF values at chiidren from sbl.l approached indexes of healthy chiidren. BDNF level from the serum of sbl.l was 3,8% smaller in comparison to ctrl.gr. (see TABLE 2).

Neuropsychical and motor developmental levels in sbl.l were assessed in conformity to the scale: with 3 (6% of cases) and 4 (94%) points. Neuropsychical abilities were mildly affected at 4% of children.

BDNF level in chiidren under 12 months old increased approaching indexes on children from ctrl.gr. There was observed a quick amelioration of EEG and imagistic interpretations. Neurological disorders would be functional in children with insignificantly diminished BDNF levels. An important statistical variation between  the  average  levels  of BDNF (p < 0,01) in children from sbl.l and ctrl.gr was observed.

By the age of 1 year the neurological after effeets were minor in sbl.l. Neurologic syndrome of these children would ameliorate rapidly after the administration of neuroprotectors at precocious stages. Thus, it was confirmed that BDNF protects cortical  neurons from destruction and ameliorates the neuroplasticity.

We assessed that in sbl.ll the average level of BDNF was lower in comparison to ctrl.gr. and it varied between 863,1 pg / ml (n.b.) and 879,9 pg / ml (between 6-36 months), minimal level was 821,3 pg / ml, and the maximum – 932, 6 pg / ml (6-36 months). The threshold of BDNF in sbl.ll constituted p < 0,1.

In sbl.ll, BDNF increases with 1,89% by the age of 1 year old in comparison to sbl.ll (n.b.), being with 132,1 pg / ml (13.05%) lower than the ctrl.gr. level.

Statistically significant variation between the lowest and the highest levels at newborns constituted +41,8 pg / ml, and at 6 – 36 months old +52,8 pg / ml.

BDNF had maximal values in 72,2% of children from sbl.ll by the age of 12 months, in 24,8% – average levels, and 4% – minimal levels (see TABLE 2). Thus, in 24,8% of children (sbl.ll) appeared a risk of retention of nrps and mt development, in 4% of cases it was important.

We appreciated an average and severe retention of nrps and mt development at children from this lot. The level of nrps and mt development of children from sbl.ll was evaluated in conformity to the scale: 4 (54%), 3 (42%), and 2 (4%) pts. The level of influence of nrps and mt abilities in sbl.ll was: mild (27%), average (15%) and severe (4%). Following the comparative analyse, a statistically significant variation between the average BDNF levels was established (p < 0,0.5) at children from sbl.ll, that presented afterwards neurologic disorders, and ctrl.gr. Neuropsychical and motor disorders were minor at children form sbl.ll with higher levels of BDNF in serum. Likewise, we observed at these children a rapid remission of NSG and EEG anomalies that indicates a favorable evolution of neurodevelopment. Severe and average grade neurologic syndromes developed at children with minimal levels of BDNF, by the age of 1 year old. NSG and EEG anomalies persisted in evolution.

Thus, it was established that BDNF level will have a higher positive trend by the age of 12 months in children from sbl.l and II in comparison to ctrl.gr. This explains that BDNF has neuroprotective function, through acceleration of myelinisation, reorganization and setup of cerebral tissue neurons in injuries induced by hypoxi-ischemia. Or, the mechanisms of neuroregeneration are more developed at children with neurological problems.

Average level of BDNF was lower in sbl.lll in comparison to ctrl.gr, variations were between 724,7 pg / ml (at n.b.) and 788,9 pg/ml (between 6-36 months); minimal level 661,2 pg / ml (at n.b.) and maximum of 743,6 pg / ml (between 6-36 months). Threshold in sbl.lll constituted p < 0,1 (see

TABLE 2).

BDNF had a 8,1 % growth by the age of 1 in this sub lot in comparison to n.b, being 223 pg / ml (22,03%) lower than the assessed level in ctrl.gr. Statistical variation between the minimal and the maximal levels constituted + 63,5 pg / ml in n.b, and + 54.7 pg / ml at 6-36 month old children. By the age of 12 months the BDNF level presented maximal values at 40% of children from sbl.lll. 60% of children of this sub lot had a high risk of development of nrps and mt retard. Nrps and mt disabilities were diagnosed in 78%, 48% of whom were severe. The level of nrps and mt development in this sub lot was appreciated in conformity to the scale: 3 (24%), 2 (52%) and 1 (24%) points.

The largest part of children from this sub lot presented important neurologic after effects by the age of 12 months old. Very low levels of BDNF were observed at children with severe mt retard and epileptic seizures. At the age of n.b., BDNF (lower than 790 pg / ml) could be a marker of development of nrps and mt retard in children. We established an important statistical variation between the average levels of BDNF of children from sbl.lll, with severe neurologic after effects, and those from ctrl.gr (p < 0.1). Nrps and mt disabilities were severe in children with minimal levels of BDNF.

Previously, it was confirmed that BDNF protects cerebral tissue from destruction. It is said in one of studies: „One of the premises regarding the mechanism of neuroregeneration evoked by an in-jury consists in the fact that injured cells induce the liberat ion of neurotrophic factors to stimulate the neurogenesis. Extracellular purinic nucleotides exer-cise multiple neurotrophic actions in CNS being mediated through activation ofpurinergic receptors and mediate the liberation of neurotrophic factors to en-courage the regeneration of injured ol-factory epithelium” [20].

• But, probably, neurotrophic processes decompensate and cortical neurons are not protected any more when BDNF levels are very low. In this case, low levels of neurotrophic factors are not sufficient to maintain the neurotrophicity and the neuroregeneration. The brain adaptability is diminished. In this case, there is a probabili-ty that BDNF concentrates maximally in injured cortical areas, where structural and functional reorganization of white and grey substances takes place. Thus, at children with hypoxi-ischemia, destructive processes prevail on those of neuroregeneration. It is obvious that modifications of cerebral tissue in PHIE gr.l and II (partial) are functional and short termed. In PHIE gr.ll (4%) and III the modifications are structural and long termed. Low levels of BDNF were frequently appreciated (authentic statistical data) at children with severe forms of PHIE that are often associated with disorders of conscience, convulsive manifestations, disturbances of muscular and reflex tonus. Likewise, low levels of BDNF were identified in n.b. presenting pathologic EEG patterns (a marked decrease of wave amplitude and frequency) and with neuro-imagistic data attributed to cerebral hypoxi-ischemia (increase of ecogenity of cerebral tissue, edema, stasis, ischemia in neural tissue). Low values of BDNF confirm the presence of severe injuries of cerebral tissue by the age of 12 months. It is  known  that BDNF  manages processes of neurogenesis, when BDNF decreases the latest decompensate.

The present study confirms that BDNF is an important marker of destructive lesional sufferance of cerebral tissue.

Thus, BDNF level would be different according to the degree of affectation of cerebral tissue in hypoxic-ischemic injuries. This one increases significantly, but in different proportion, by the end of the first year of life. BDNF level in children from st.lt remains decreased in comparison to those from ctrl.gr. Very low levels are preserved at children with severe mt. deficit and at those with recurring epileptic seizures.

It is possible that the retention of synthesis of neurotrophic factors could be one of the most important causes that stops the nervous cell maturation processes at children with PHIE.

Likewise, low BDNF level (lower than 790 pg / ml) has a predictive value for the nrps and mt retard at children with severe PHIE. Decreased BDNF level associated with an aspect of anomajies and diminished voltage of EEG waves is an unfavorable prognostic indicator.

We made the comparative analyze of low BDNF levels in sbl.l, II and III.

It shows that the probability of decreased BDNF level constitutes 23,34% at children from sbl.ll and 85,4% at those from sbl.lll in comparison to sbl.l (3,42%). The probability of decreased BDNF level is high in sbl.lll, especially at children with severe neupsihological disorders.

Synthesis and secretion of BDNF decreases seriously at children with severe hypoxic-ischemic injuries. Because of low BDNF level neuroprotective and neuroregenerative processes are inhibited. A series of anomalies of neurotrophic factors may accompany the hypoxic-ischemic aggression.

This contributes to stoppage of nervous fiber maturation and to development of severe neurologic after effects. The probability of development of neurologic after effects in PHIE-II is lower. Probably, the processes of neuroprotection in these children are compensated by the acceleration of neurotrophic factors’ synthesis. In this case, BDNF is maximally concentrated in affected cerebral areas where it participates intensely to the processes of neuroregeneration and remodulation.

It is confirmed, in multiple studies, that 2 hours after ischemia an increase of BDNF imunointeractive cells is observed in singulargyrus and frontal cortex except for injured area [21].

It is possible that there exists an inferior limit of BDNF level and under this limit the processes of neuroregeneration and neuroregulation are irreversible. Or, high BDNF level protects the brain from destruction, sustains the survival and differentiation of neurons, increases neural cell’s resistance to injuries induced by ischemia.

The results suggest that there is a relationship between serum BDNF levels and motor abnormalities in children with cerebral maturation disturbances (data was also confirmed by neuroimaging). Furthermore, we noted that serum BDNF levels were significantly lower in children with severe motor disorders compared to controls, but this tendency was not significant in those with soft motor disorders. The results showed an increase of BDNF levels in study group during their first years of life, though these levels were significantly lower in comparison to control group.

Patients from study group presented: language retardation, emotional, cognitive and behavioral disorders. An overall analysis showed that BDNF serum levels were significantly lower in children from study group in comparison to controls (p < 05). Significantly low levels of serum BDNF were noted in children with severe cognitive disorders frequently associated with language disorders. Moreover, neuroimaging data revealed abnormalities of nerve tissue maturation. There is statistical evidence that psychological disorders are negatively correlated with serum BDNF levels. Thus, BDNF represents an important marker of child’s psychological development.

Therefore, it is the case to administrate exogenous neurotrophic factors (BDNF) before the appearance of cerebral lesion changes, that is to say in the first minutes or hours following the apparition of cerebral hypoxic-ischemic injuries.

DISCUSSIONS

Aetiological factors, which may conduct to affectation of nervous system of fetus and n.b, may influence during intrauterine, intranatal and neonatal periods [23, 31, 32].

Lesion structure of the brain of n.b. changes considerably in dependence on gestational age. The consequences of perinatal pathology determinethe base neurological disorders of very young children, thus occupying the first place among cerebral pathologies [24].

Neonatal encephalopathy is a heterogeneous syndrome characterized by dysfunctional symptoms of CNS in term or under term n.b. (> 36 weeks of gestation). Children with neonatal encephalopathy may be exposed to abnormalities of conscience level, convulsions, reflex abnormalities, apnea, and alimentation difficulties [23]. Neonate encephalopathy may be the result of a variety of conditions and often remains inexplicable. Responsible of these are asphyxia and PHIE. Cerebral injury causes neurological deterioration in n.b., who cannot be understood often. Neonate encephalopathy’s pathogenesis is discussed everywhere [20, 23, 31]. Neonate encephalopathy causes neurological deterioration in n.b., that leads very often to cerebral palsy (CP), a heavy burden for family and society [3, 4, 23].

Encephalopathic n.b. may have an abnormal state of conscience (ex: hyperalerted, irritable, lethargic, obtuse), with respiratory and alimentation difficulties, reduced tonus or convulsive activity. Often, these n.b. present a low Apgar score and a weak or absent cry [23]. An important part of these symptoms were observed at children from study sublots.

The lesion of CNS of the child would have as consequences the nrps and mt retard [3, 4, 31].

Injuries in immature period have a different pattern from those in adults (while  immature, the affected zone would be symptomatically nonfunctional), especially in children with neurologic pathologies [23]. Thus, it is very important to know the main reflexes regarding nrps develop-ment of the child at different ages. A scale of evaluation of nrps and mt developmental level of children was elab-orated in study lot.

The diagnose of neonatal encephalopathy imposesthe research of potential aetiologies. An evident and histological examination of placenta and cordon could deliver evidences of possible causes like vascular or infectious lesion of placenta, or thromboses of cordon [23]. A detailed maternal and familial history is recommended, including history of thromboembolic disorders, anterior losses of pregnancy, maternal infections or drug abuse. Samplingisdoneto determine arterial pH and base deficit of cordon. The presence of oliguria, cardiomiopathy, abnormal function of the lung may suggest a global hypoxico-ischemic event [23, 31].

Neuroimagery has become more important in the evaluation of neonatal encephalopathy and can deliver information concerning the type and the syn-chronization of cerebral injuries [4, 23]. For example, several patterns of cerebral injuries were observed at in term and premature n.b., who are considered to be with typical hypoxic-ischemic injuries, bat not in all the cases with hypoxic-ischemic affection. TC is responsible for doubtless diagnosis in precocious terms [23].

The brain of small child is an objectoi study. CNS affection would markthe retard in nrps development. The most favorable condition in neurological pathology is to speed up the maturation of nervous fibers at children with neurologic pathologies, in order to prevent CP, whose deficiencies are evident by the complete maturation of CNS structures. The appreciation of peculiarities of neuroontogenesis in children that suffered from perinatal hypoxic-ischemic cerebral lesion is possible due to nowa-days achievements in neurochemistry, related to researches of neurotrophic factors (BDNF, FCNT, etc.) [8, 14, 17, 18, 21, 26, 28, 29].

The consequences of cerebral perinatal affection, in most of cases, would be determined by a precocious diagnosis of cerebral injuries and the efficiency of the treatment in the period of intensive maturation and development [23, 31].

Neurotrophic factors of the brain could be very important in pathogenesis of perinatal hypoxic-ischemic injuries. Experimental studies have shown that these factors play an important role dur-ing the ontogenetic development, in survival maintenance and the differentiation of neurons [1, 7, 8, 9, 10, 16, 21]. Especially important are the results of researches on animals that proved that neurotrophic factors have therapeutic neuroprotective effects in numerous pathologic conditions of the brain [21].

BDNF initially was described as neurotrophic factor with effects of promotion of survival of sensitive neurons from spinal ganglions. Later it was observed that BDNF influences on every classes of sensitive neurons, promotes differentiation of motoneurons in vitro and protects these cells from apoptosis and from death induced by axotomy in n.b animals [21]. BDNF is the most prevailing neurotrophin in the brain. BDNF’s RNA messenger was identified in various structures of the rat brain [3]. Thus, the treatment with kainat (an excitatory aminoacide, aromatic analog on glutamic acide) determined an intense presence of BDNF in pyramidal cells of different cerebral structures, a strong argument in favor of neurotrophic role of BDNF in maintaining neurons and synapses in adult animals [3, 21]. In several studies they investigated the role of BDNF in maintaining the survival and the differentiation of cholinergic neurons of basal and anterior region of anterior brain [7, 21, 22].

Several groups of studies proved that cerebral intra-ventricular infusion with BDNF at rats and monkeys can prevent the atrophy and the loss of phenotypic markers of septal cholinergic neurons, resulting after axotomy [21].

Multiple studies demonstrated the neuroprotective role of BDNF in cerebral ischemia. Thus, Arai et AI. [1] confirmed that the intensification of BDNF’s presence and his receptors is produced in areas beyond infarct. Another study notes that one of the premises concerning neuroregenerative mechanism launched by the lesion consists in the fact that injured cells liberate neurotrophic factors to stimulate neurogenesis [21]. A more recent study argues that assessed BDNF’s levels are correlated, at least partially, with the resistance of cells face to injuries induced by ischemia, and are in correspondence with the existence of neurotrophic role of BDNF [5]. Likewise, the same author confirms that 2 hours after ischemia they observed an important increase of the number of immunoreactive cells to BDNF in cingular gyrus and frontal cortex beyond injured area. In animals with cortical lesions they observed a disappearance of immunoreactive cells to BDNF in striatum in 2-24h, while animals with injured striatum didn’t present that modification. After 2-24h they observed strongly immunoreactive fibers along myelinated fascicles situated medially to striatum, in anterior commeasure and in corpus callosum ipsilateral to OACM. BDNF levels wentto 133-213% after 2h in cinguIar gyrus and frontal cortex, and diminished to 40% after 24h in striatum. Thus, they noted the augmentation on BDNF protein 2h after ischemia. The diminution of BDNF after 24h suggests a pronounced liberation or anterograde axonal transport in postischemic phase. BDNF modification after focal ischemia has a role in survival of cortical and striatum neurons [5].

BDNF infusion had been effectuated beginning with not long after the occlusion of middle cerebral artery (in rats) and had been continued for 24h, and after they assessed infarct’s volume, in comparison to witness group to which they infused only vehicle. A 33% diminution of infarct was noted [33].

Other studies on animals noted that BDNF has ah effect of contraction on neural lesions determined by asphyxia [17]. In hypoxic-ischemic lesion, BDNF has different effects on the brain in development (n.b.), in comparison to the adult one. A single intraventricular injection of BDNF determines a vigorous phosphorilation of Trk receptors (responsible for BDNF) in multiple regions of rats brain starting from the 7th post-natal day. Thus, BDNF protects the rat’s brain from hypoxic-ischemic lesions from the 7th postnatal day. BDNF protects 90% of nervous tissue from loss of neurons caused by ischemic hypoxia, if it’s administrated before hypoxi-ischimia, and 50% if it’s administrated after infarct. BDNF represents a potential treatment of asphyxia and other acute perinatal lesions [8].

Likewise, recent studies confirm that transitory ischemia intensified the expression of BDNF gene both in hippocampus and cerebral cortex. That was mediated through receptors of glutamate of NMDA and non-NMDA type [30]. Another study shows that the prevention of neural death with BDNF after cerebral ischemia is associated with the increase of expression of its specific receptor Trk-B [9]. BDNF is widely spread in CNS and presents in vitro trophic effects on diverse type of cells including cortical neurons, hippocampal neurons, cerebellum neurons, etc. In vivo, BDNF rescues motoneurons, hippocampal neurons and dopaminergic cells of substantia nigra from traumatic and toxic lesions. The intraventricular pre treatment with BDNF reduced the dimension of infarct after focal cerebral ischemia. BDNF has a neuroprotective role in ischemic cerebral vascular accidents [27].

In our study we noted low levels of BDNF in serum of children that suffered from perinatal hypoxic-ischemic lesions of II and III grades. This datum has a huge value for the prognosis of delayed neurologic after effects.

Several experimental studies arguethat the administration of an excess of neurotrophic factors protect sensible cerebral tissues. The treatment of animals with neurotrophic factors before and 90 minutes following the transitory ischemia reduced effectively the volume and infarct area without affecting regional cerebral blood flow in comparison to control group or the group with untreated animals. Thus, it appears that neurotrophic factors exert a strong neuroprotective effect from ischemic cerebral lesions [2,  10, 12, 25].

An alternative explication is that beneficial BDNF effects are due to amelioration of exitotoxicity [21,31]. The antagonists of glutamate receptors reduce the volume of infarct [19, 21, 25].

There were studies on rats concerning the efficiency of growth factors in recuperation of neurologic deficiencies after cerebral infarcts. In this case, growth factors were administrated several days after the occurrence of ischemia. In these, studies, they didn’t have the intention to reduce the infarct volume but to intensify neurologic retrieval. In rats, there exist certain proofs that focal cerebral infarction is followed by neuronal budding and formation of new synapses in neighbourhood of the infarct, in the same hemisphere and in homolog regions from collateral hemisphere [11, 16, 33].

This budding and formation of new synapses may represent a neurologic retrieval mechanism after focal infarction [21].

These observations have led to the hypothesis that the administration of exogenous growth factors, that intensify the budding of axons and dendrites, could intensify the functional retrieval after cerebral ischemia [21].

Neuronal plasticity represents an adaptabil ity of nervous system to diverse lesions trough the structural and functional reorganization in white and grey matter [7, 15, 21].

In order to optimize the process of recovery it is important to apply techniques of stimulation of neuroplasticity.

Growth factors represent a citoprotective treatment to limit the expansion of infarct’s volume if they are administered in the first hours following the accident, and facilitate the functional recovery if they are administered in the first month after the accident [21].

Number of studies on models with animals suffering from cerebral hypoxia and/or ischemia confirms the neuroprotective and neuromodulator role of Cerebrolysine in treatment of cerebral ischemia. Cerebrolysine has certain effect on different species of animals: diminishes the mortality induced by cerebral ischemia to 50% [27]; preventsthe formation of citotoxic edema [27]; protects pyramidal cells from ischemia induced lesions [28]; prevents the formation of free radicals during reperfusion after cerebral ischemia [28]; diminishes essentially the concentration of lactate in brain hereby suggesting a protective effect during hypoxic-ischemic episodes [21]; assures the survival and promotes the differentiation of neurons in the same way as natural neurotrophic factors [21]; it has a dose-dependent effect preventing the death of neurons induced by high concentrations of giutamate [12]; the treatment with Cerebrolysine determines a statistically important amelioration at the Barolin Scale of Neurorehabilitation in the first 7 days. This finding is extremely important because of the introduction of „therapeutic window” in the treatment of cerebral hypoxi-ischemia [21].

Thus, administered neurotrophic remedies would contribute to recovery of nrps and mt acquisitions at children with neurologic problems. Neurotrophins are the remedies which would be successful in this area.

CONCLUSIONS

• BDNF has a protective role in cerebral lesions induces by hypoxi-ischemia. It is a neurotrophin with important qualities of encouraging of growth, processes of myelinisation, re-
• organization and restructuration of cerebral tissue neurons.
• The mechanisms of neuroregeneration are more developed in children with neurologic problems. One of the premises concerning the neuroregenerative mechanism evoked by lesion consists in the fact that injured cells induce the liberation of neurotrophic factors to stimulate neurogenesis.
• We have studied the effects of BDNF on CNS neurons. We suggest that BDNF encourages axonal survival and regeneration, the maturation and maintenance of CNS neurons, when the latest are affected by hypoxi-ischemia. The high level of BDNF protects the brain from destruction, upholds the survival and differentiation of neurons.
• Different-grade motor and neuropsychical disabilities would correlate with low BDNF levels in serum, lower than 720 pg/ml, and that represents a marker of retard in nrps and mt development of children with hypoxic-ischemic lesions of the CNS. Neurotrophic processes decompensate and cortical neurons are not protected from destruction when BDNF levels are very low. In this case, the low level of neurotrophic factor is not sufficient to maintain the processes of neurotrophicity and neuroregeneration.
• Thus, the processes of destruction prevail on those of neuroregeneration in children with advanced grade of hypoxi-ischemia. Serum BDNF levels were significantly lower in children with motor disorders (aged 1-3 years) in comparison to controls. This could suggest a delayed increase of BDNF levels during those children’s development.
• Thus, low BDNF levels are negatively correlated with the severity of motor disorders. This could indicate the role of BDNF in
• motor neurons’ plasticity, developmental and maintenance processes of the brain.
• Our data confirm the role of BDNF on the child’s psychological development (it contributes to nerve fibers maturation language, behavior and emotional centers).
• We suggest that low levels of BDNF influence the synaptic plasticity and the interaction between neural and glial cells, thereby playing a decisive role in the complex child’s behavior including language acquisition, cognition, affect etc.
• BDNF studies could have an important implication in the comprehension of psycho-developmental disorders, as well as in the treatment of neuro-developmental disorders. The administration of exogenous neurotrophic factors before the apparition of modifications induced by cerebral lesions, during the first minutes or hours following the apparition of cerebral hypoxic-ischemic injury could ameliorate the neurologic after effects and diminish the motor and neuropsychical handicap.

Bibliography

1. Arai S. et al. Induction of brain-derived neurotrophic factor (BDNF) and the receptor t.r.k.B.m.R.N.A. following middle cerebral artery occlusion in rat. Neuroscience Letters; 1996, 211 (1): pp. 57-60.
2. Arien-Zakay H. et al. Neuroprotection by cord blood neural progenitors involves antioxidants, neurotrophic and angiogenic factors. Exp Neurol. 2008, Nov. 25.
3. Bartha A.I., Foster-Barber A., Miller S.P. et al. Neonatal encephalopathy: association of cytokines with MR spectroscopy and outcome. Pediatr. Res.; 2004, pp. 56:960.
4. Borg E. et al. Perinatal asphyxia, hypoxia, ischemia and hearing loss. An overview. Scandinavian Audiology; 1997, V.26, Nr.2, pp.77-91.
5. Kokaia Z. et al. Regional brain-derived neurotrophic factor in RNA and protein levels following transient forebrain ischemia in the rat. Brain Research. Molecular Brain Research. 1996, 38 (1): pp. 139-44.
6. Cowan F., Rutherford M., Groenendaal F. et al. Origin and timing of brain lesions in term infants with neonatal encephalopathy. Lancet; 2003, pp. 361:736.
7. Chu T.H. et al. Implantation of Neurotrophic Factor-Treated Sensory Nerve Graft Enhances Survival and Axonal Regeneration of Motoneurons After Spinal Root Avulsion. J Neuropathol Exp Neurol. 2008, Dec. 19.
8. Cheng Y. et al. Marked age dependent neuroprotection by brain derived neurotrophic factor against neonatal hypoxic-ischemic brain injury. Annals of Neurology. 41 (4): 521-9, 1997.
9. Ferrer I. et al. BDNF up-regulates Trk-B protein and prevent the death of CAI neurones following transient forebrain ischemia. Brain Pathology. 8 (2): 253-61, 1998.
10. Fumagalli F. et al. Neurotrophic factors in neurodegenerative disorders: potential for therapy. CNS Drugs. 2008; 22(12):1005-19.
11. Hossmann A. K. et al. Effect of BDNF and CNTF treatment on infarct volume after middle cerebral artery occlusion of rat: relationship to apoptotic cell injury. J. Krieglstein (Ed) Pharmacology of Cerebral Ischemia. 1998, p. 361-370.
12. Hutter-Paier et al. Death of cultured telencephalon neurones induced by glutamate is reduced by the peptide derivative cerebrolysin. J. Neural Transm. 1996 [Supl.] 47: 267-273.
13. Ilciuc I., Gherman D., Gavriliuc M. “Encefalopatia toxi-infectioasa la copii”. Chişinau, 1996, 183 p.
14. Jungbluth S. et al. Co-ordination of early neural tube development by BDNF /Trk-B Development. 124 (10): 1877 – 85, 1997.
15. Kidane A.H. et al. Differential Neuroendocrine Expression of Multiple Brain-Derived Neurotrophic Factor Transcripts. Endocrinology. 2008, Nov. 13.
16. Kokaia Z. et al. Regional brain-derived neurotrophic factor in RNA and protein levels following transient forebrain ischemia in the rat. Brain Research. Molecular Brain Research. 1996, 38 (1): pp. 139-44.
17. Korhonen et al. Brain derived neurotrophic factor is increased in cerebrospinal fluid of children suffering from asphixia. Neuroscience Letters. 240 (3): 151-4, 1998.
18. Li Z.K. et al. Effects of androgen on the expression of brain aromatase cytopigment and nerve growth factor in neonatal rats with hypoxic-ischemic brain damage. Zhongguo Dang Dai Er Ke Za Zhi. 2008, Aug.10(4):441-6.
19. Mattson M.P. Glutamate and neurotrophic factors in neuronal plasticity and disease. Ann N.Y., Acad Sci. 2008 Nov; pp.1144:97-112.
20. McDonald D.G., Kelehan P., McMenamin J.B. et al. Placental fetal thrombotic vasculopathy is associated with neonatal encephalopathy. Hum. Pathol; 2004, p. 35.
21. Mureşanu D.F. Factorii neurotrofici. Bucureşti: Libripress; 2001, pp.
22. Novicov L. et al. Brain-derived neurotrophic factor promoted axonal regeneration and long-term survival of adult rat spinal motoneurons in vivo. Neuroscience. 79 (3): 765-74, 1997.
23. Popescu V. Neurologie pediatrica. Bucureşti, 2004, pp. 445-498.
24. Redline R.W. Severe fetal placental vascular lesions in term infants with neurologic impairment. Am J. Obstet. Gynecol.; 2005, pp. 192:452.
25. Reyes J.H. et al. Glutamatergic neuronal differentiation of mouse embryonic stem cells after transient expression of neurogenin 1 and treatment with BDNF and GDNF: in vitro and in vivo studies. J.Neurosci. 2008, Nov. 26; 28(48):12622-31.
26. Samsonava Т., Bobrova E. et al. Dinamica productii neirotroficeschih factorov u detiei v rannem vostanovitelinom periode perinatalinîh ghipoxiceschih porajenii golovnogo mozga. Iaroslavli; 2006, pp. 212-215.
27. Scbwab M. Physiological effect and brain protection by hypothermia and cerebrolysin after moderate forebrain ischemia in rats. Txicol. Pathol. 1997, 49: 105-6.
28. Sugita V. The protective effect of FPF 1070 (cerebrolysin) on delayed neuronal death in the gerbil – detection of hydroxyl radicals with sallicylic acid. Brain and Nerve. 1993, 45; 325-601.
29. Tang S., Machaalani R., Waters K.A. Brain-derived neurotrophic factor (BDNF) and TrkB in the piglet brainstem after post-natal nicotine and intermittent hypercapnic hypoxia. Brain Res. 2008, Sep. 26;1232:195-205.
30. Tsukahara T. et al. Increases in levels of brain-derived neurotrophic factor m RNA and its promoted after transient ferebrain ischemia in the rat brain. Neurochemistry International. 33 (2): 201-7, 1998.
31. Volpe M. D. Neurology of the Newborn. Second edition; W.B.Saunders Company, Philadelphia, London, Toronto, MexicoCity, Rio de Janetro, Sydney, Tokyo, HongKong, 1987, V.22, pp.159-236.
32. Wu Y.W., Backstrand K.H., Zhao S. et al. Declining diagnosis of birth asphyxia in California: 1991-2000; Pediatrics, 2004, pp. 114:1584.
33. Yamashita K. et al. Post-occlusion treatment with BDNF reduced infarct size in a model of permanent occlision in the middle cerebral artery in rat. Metabolic Brain Disease. 12 (4): 271-80, 1997.
34. Yan Q. et al. Expression of brain-derived neurotrophic factor protein in the adult rat central nervous system. Neiroscience; 1997; 78 (2): pp. 431-48.
35. Yoshimura R., Ito K., Endo Y. Differentiation/maturation of neuropeptide Y neurons in the corpus callosum is promoted by brain-derived neurotrophic factor in mouse brain slice cultures. Neurosci Lett. 2008, Dec. 16.