[Moving activity and wakefulness-sleep cycle changes in a mouse MPTP model of Parkinson's disease].

A group of mice with preliminary implanted (under general anesthesia) electrodes for cortical EEG and nuchal EMG was subjected to continuous baseline 24-hr video and digital polysomnographic recording with the 12/12 light/dark schedule, and then injected subcutaneously with 24 or 48 mg/kg of MPTP toxin or (the control group) saline. The recordings were continued for 2 weeks more. A significant increase in activity and the waking percentage as well as decrease in REM sleep and NREM sleep (tendency) during the dark period as compared to the baseline and control recordings was found. The effect was seen just on the 7th day following MPTP administration and became significant by the 14th day. The effect was more pronounced after 48 mg/kg injection than after 24. There were no changes during the light period. Morphological control revealed a 70% and 35% decreases in the amount of tyrosine hydroxylase positive neurons in substancia nigra/pars compacta after 48 and 24 mg/kg of MPTP, respectively, as compared to the saline group.

[Noradrenaline role in regulation of dopamine-producing neurons in rat arcuate nucleus].

Among most important functions of the neuroendocrine system is the regulation of reproduction, including the inhibitory control of prolactin secretion by dopamine (DA) synthesized in the arcuate nucleus (AN). Besides DA, noradrenaline (NA) contributes to this regulation though, in contrast DA, its concrete functional role remains to be uncertain. In the previous studies, it has been suggested that NA inhibits compensatory synthesis of DA in DA-producing neurons of AN under the failure of the dopaminergic system though no evidence were obtained. Therefore, the goal of this study was to specify the role of NA in the regulation of DA-producing neurons in AN. Two pharmacological models were used to this aim: a) switching off dopaminergic and noradrenergic neurons and their afferents in An or b) switching of only dopaminergic neurons and afferents that allowed us to recognize NA role in the complex catecholaminergic regulation of prolactin secretion. According to our data, the maintaining of the noradrenergic innervation of AN under the neurotoxin-induced failure of dopaminergic neurons resulted in the decrease of the expression of tyrosine hydroxylase (TH), the first enzyme ofDA synthesis, thereby enhancing DA deficit. This is considered as direct evidence of noradrenergic inhibitory control of TH expression in the neurons of AN.

[New concepts of pathogenesis, diagnosis, and treatment of neurodegenerative diseases].

Millions of patients all over the world suffer from chronic neurodegenerative diseases (NDD) (Parkinson's disease, Alzheimer's disease, Huntington disease, hyperprolactinemia, etc.) which result first in disability and then in fatal outcome. The key component of NDD pathogenesis is the degeneration of specific neurons leading with time to dysfunction, e.g. cognitive problems in Alzheimer's disease, disturbed motor behavior in Parkinson's disease, etc. Over the initial twenty-thirty years, NDD are developed as a preclinical condition, and their first symptoms appear only after degeneration of a greater part of specific neurons. The lag in the manifestation of NDD at the organismic level is explained by late triggering mechanisms of brain plasticity serving to compensate functional insufficiency of dying neurons. In this context, the appearance of initial symptoms is considered as a manifestation of irreversible degradation of the specific regulatory brain system and the exhaustion of compensatory resources of the brain that probably explains low efficiency of pharmacotherapy. This implies the necessity to develop preclinical diagnostics and preventive therapy aimed at arresting or at least slowing down of the neurodegenerative process and prolongation of the preclinical stage for many years. The development of preclinical diagnostics is based on a search for specific clinical forerunners of NDD and endogenous peripheral markers circulating in cerebrospinal fluid and blood. NDD diagnostics in the preclinical stage should be developed by identification of risk groups during prophylactic examination of healthy population based on detection of disease markers. The final diagnosis can be made by non-invasive neurovisualizing techniques. The new concept of NDD pathogenesis promotes further development of novel approaches to their diagnostics and treatment.

[Optimization of counting process of dopaminergic neurons in substantia nigra of parkinsonian mice].

Parkinson's disease (PD) results from degeneration of dopaminergic (DA-ergic) neurons of sunstantia nigra pars compacta (SNc). In experimental studies, this condition is modelled by administration of neurotoxin's precursor 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). The followed degeneration of DA-ergic neurons is estimated by cell counting. Cell counting with serial sections is exceedingly hard and expensive. Therefore this method is not used extensively in spite of its high precision. Widely known Konigsmark's formula (KF) allows not to count cells in all serial section, but only in sections selected at regular interval. However, its precision decreases with increasing the interval and other parameters. In given work we have developed mathematical method of approximation (MA) by improving of KF. MA allows reducing the time and chemical products expenses for processing and analysis of the material with maintenance of necessary counting precision. Two groups of C56/BL mice were used in this study. The first group received MPTP in a dose of 8 mg/kg with 1 week interval and showed 20% decrease in DA-ergic neurons in SNc. The second group received MPTP in a dose of 12 mg/kg four times with 2-h interval and showed 40 % decrease in DA-ergic neurons in SNc. Degeneration took place mostly in the middle part of SNc within rostra-caudal direction and led to rise of sharp differences in the number of neurons from section to section. These differences substantially decreased precision of FK (6 % error with counting in every 5th section), whereas precision of MA was sufficiently good (4% error with counting in every 7th section). Thus, we have developed MA, that allows us to decrease expenses of the time and chemicals for estimation of DA-ergic cells number in SNc of parkinsonian mice.

[Modeling of preclinical and early clinical stages of Parkinson's disease].

The first symptoms of Parkinson's disease manifest 20-30 years after the disease onset when the most dopaminergic neurons degenerated. Therefore, it is necessary to work out preclinical diagnostics and preventive treatment of this disease. Modeling of preclinical and early stages of Parkinson's disease was conducted in mice using 1-methyl-4-phenyl-1,2,3,6-tetrahydropiridine (MPTP). The changes in motor behavior were not observed in mice by 14 day after MPTP injections in dose 12 mg/kg two times with interval of two hours. In the striatum, the region of dopaminergic axon projection, the content of dopamine and number of dopaminergic axons decreased by 57% and 59%, respectively, i.e. there were no changes in dopamine in single axons. In the substantia nigra, the region of dopamine neuron localization, the content of dopamine did not change though the total number of neurons decreased by 28%. However the dopamine content in remained neurons was higher by 77% compared to the control that indirectly indicated the compensatory enhancement of dopamine synthesis. After the MPTP injections in dose 4x12 mg/kg, there were changes in motor behavior of mice in the most sensitive tests. In the striatum, the dopamine content and number of dopaminergic axons decreased by 75% and 68%, respectively. In the substantia nigra, there were no changes in dopamine content but the number of dopaminergic neurons decreased by 43%. The intraneuronal dopamine content increased by more than 70%. In conclusion, we constructed the models of preclinical stage (two-time MPTP injections) and transition phase from presymptomatic to symptomatic stage (four times of MPTP injections) of Parkinson's disease.

[Experimental modeling of functional deficiency of the nigrostriatal dopaminergic system in mice].

The dopaminergic nigrostriatal system is a key component of regulation of the motor behaviour. Cell bodies of dopaminergic DA-ergic neurons are located in the compact zone of the substantia nigra, and their axons are projected along the nigrostriatal tract to the striatum. This study was aimed to develop an experimental model of the functional insufficiency of the DA-ergic neurons of the nigrostriatal system without any manifestation of movement disorders, i.e., a model of presymptomatic stage of parkinsonism. This model has been developed with a single subcutaneous injection of a low dose of MPTP (12 mg/kg) which is converted in the brain into the MPP+, a neurotoxin of DA-ergic neurons. It has been shown that the MPTP injection on the 14th day is followed by: (a) absence of any sign of movement disorders; (b) no change in the DA content and the number of DA-ergic neurons in the substantia nigra; (c) substantial loss of DA in the striatum as a result of the degeneration of about 50% of DA-ergic axons. The absence of movement disorders under the substantial DA depletion and degradation of DA-ergic axons in the striatum is supposed to be a consequence of the turning on of the compensatory processes in the brain. Thus, we have developed the experimental model of presymptomatic stage of parkinsonism which is characterized by the degeneration of DA-ergic axons in the striatum without degradation of the neuron cell bodes in the substantia nigra.

[Effect of serotonin on the formation of neurons producing gonadotropin-releasing hormone in Wistar rats].

The effect of serotonin on the formation of neurons producing gonadotropin-releasing hormone (GnRH) during embryogenesis of Wistar rats was studied. The neurons producing GnRH were detected immunocytochemically on days 18 and 21 of embryonic development and on day 15 of postnatal development of rats with normal serotonin metabolism and rats in which the synthesis of serotonin was inhibited by p-chlorophenylalanine. The total number of GnRH neurons in serotonin deficiency was larger than in the case of its normal metabolism at all developmental stages studied. This is an indirect evidence for the inhibitory effect of serotonin on the formation ofGnRH neurons. To confirm the morphogenetic effect of serotonin, we studied the rate of formation of GnRH neurons by injecting bromodeoxyuridine in the formation period of these neurons. It was found that serotonin deficiency had no effect on the time of formation of GnRH neurons: over 97% of neurons formed on days 11 to 15 of embryonic development both in the experimental and control groups. Note that, in serotonin deficiency, the maximum number of GnRH neurons formed one day later than in the normal state. Thus, serotonin inhibits the proliferation of GnRH neuron progenitor cells and thereby has a morphogenetic effect on the development of these neurons.

[Development of serotonergic neurons of dorsal raphe nuclei in mice with knockout of monoamine oxidase A and 5-HT1A and 5-HT1B autoreceptor].

The morphological changes in the development of serotonergic neurons of the dorsal raphe nuclei in the medulla oblongata was studied by immunocytochemistry in mice with knockout of 1A and 1B serotonin autoreceptors as well as monoamine oxidase A. Serotonin autoreceptors regulate electric activity of serotonergic neurons as well as the synthesis and release of the neurotransmitter, while monoamine oxidase A catalyzes its degradation. These genetic modifications proved to have no effect on the number of serotonergic neurons in the medulla oblongata but induced morphofunctional changes. Decreased cell size and increased intracellular serotonin level were observed in the case of monoamine oxidase A deficiency, while excessive cell size and decreased intracellular serotonin level were observed in the case of autoreceptor deficiency. The data obtained confirm the hypothesis of autoregulation of serotonergic neurons in development.

[Monoamine synthesis by non-monoaminergic neurons: illusion of reality].

Apart from monoaminergic neurons possessing the whole set of enzymes of monoamine synthesis from the precursor amino acid, the neurons expressing individual enzymes of monoamine synthesis have been discovered in the mid-eighties. Most numerous monoenzymatic neurons express individual enzymes of dopamine (DA), thyrosine hydroxylase (TH) or aromatic L-amino acid decarboxylase (AADC). Functional characteristics and the functional significance of the monoenzymatic neurons have been evaluated in a series of our studies, mainly of the hypothalamic arcuate nucleus (AN), one of the most important DA-ergic centers of the brain. It has been demonstrated that the AN of rats contains numerous monoenzymatic neurons. Their portion among the neurons expressing enzymes of DA synthesis exceeded 99 % whereas it decreased continuously in postnatal period still reaching 50 % in adulthood. It was shown that the monoenzymatic neurons expressing complementary enzymes of DNA synthesis produce this neurotransmitter in cooperation. In this case, L-tyrosine is transformed to L-DOPA in TH containing neurons that is followed by L-DOPA release and uptake to AADC containing neurons with a semi-specific membrane transporter of large neutral amino acids for DA synthesis. Turning on the expression of enzymes of DA synthesis in non-dopaminergic neurons is an adaptive reaction under the functional insufficiency of DA-ergic neurons. So, hyperprolactinemia that is developed under the degeneration of DA-ergic neurons of the AN and the deficiency of DA, the prolactin-inhibiting neurohormone, was compensated in due time to increase in number of monoenzymatic neurons and the strengthening of cooperative synthesis of DA in the nucleus. The same compensatory cooperative synthesis if DA is supposed to be turned on under the degeneration of DA-ergic neurons of the nigrostriatal system that was manifested by appearance of the neurons expressing enzymes of DA synthesis in the deafferentiated striatum in rats. The expression of enzymes of DA synthesis in non-dopaminergic neurons is under the control by intercellular signals. e.g., catecholamines. Thus, numerous non-monoaminergic neurons in the brain expressing individual complementary enzymes of monoamine synthesis produce monoamines in cooperation that is a compensatory reaction to a functional insufficiency of monoaminergic neurons.

[Development of central and peripheral serotonin-producing systems in rats in ontogenesis].

The work deals with study of development of central and peripheral serotonin-producing systems in rat ontogenesis before and after formation of the blood-brain barrier. By the method of highly efficient liquid chromatography it has been shown that the serotonin level in peripheral blood before formation of the blood-brain barrier (in fetuses and neonatal rats) is sufficiently high for realization of physiological effect on target cells and organs. At the period of formation of the blood-brain barrier the serotonin level in brain sharply rises, whereas the serotonin concentration and amount in plasma and duodenum increase insignificantly. Completion of formation of the blood-brain barrier is accompanied by a significant increase of the serotonin content in duodenum, probably for maintenance of the high serotonin level in blood. To evaluate secretory activity, the mean rate of daily increment of the serotonin in the studied tissues was calculated. In brain, this parameter was maximal at the period of formation of the blood-brain barrier and then sharply fell, whereas in duodenum it rose markedly after completion of the barrier formation. In plasma this parameter decreased statistically significantly at the period of formation of the blood-brain barrier - from the 4th to the 16th postnatal days. This allows thinking that brain before formation of the blood-brain barrier is a most important source of serotonin in peripheral blood.

[Endocrine functions of the brain in adult and developing mammals].

The main prerequisite for organism's viability is the maintenance of the internal environment despite changes in the external environment, which is provided by the neuroendocrine control system. The key unit in this system is hypothalamus exerting endocrine effects on certain peripheral organs and anterior pituitary. Physiologically active substances of neuronal origin enter blood vessels in the neurohemal parts of hypothalamus where no blood-brain barrier exists. In other parts of the adult brain, the arrival of physiologically active substances is blocked by the blood-brain barrier. According to the generally accepted concept, the neuroendocrine system formation in ontogeny starts with the maturation of peripheral endocrine glands, which initially function autonomously and then are controlled by the anterior pituitary. The brain is engaged in neuroendocrine control after its maturation completes, which results in a closed control system typical of adult mammals. Since neurons start to secrete physiologically active substances soon after their formation and long before interneuronal connections are formed, these cells are thought to have an effect on brain development as inducers. Considering that there is no blood-brain barrier during this period, we proposed the hypothesis that the developing brain functions as a multipotent endocrine organ. This means that tens of physiologically active substances arrive from the brain to the systemic circulation and have an endocrine effect on the whole body development. Dopamine, serotonin, and gonadotropin-releasing hormone were selected as marker physiologically active substances of cerebral origin to test this hypothesis. In adult animals, they act as neurotransmitters or neuromodulators transmitting information from neuron to neuron as well as neurohormones arriving from the hypothalamus with portal blood to the anterior pituitary. Perinatal rats--before the blood-brain barrier is formed--proved to have equally high concentration of dopamine, serotonin, and gonadotropin-releasing hormone in the systemic circulation as in the adult portal system. After the brain-blood barrier is formed, the blood concentration of dopamine and gonadotropin-releasing hormone drops to zero, which indirectly confirms their cerebral origin. Moreover, the decrease in the blood concentration of dopamine, serotonin, and gonadotropin-releasing hormone before the brain-blood barrier formation after the microsurgical disruption of neurons that synthesize them or inhibition of dopamine and serotonin synthesis in the brain directly confirm their cerebral origin. Before the blood-brain barrier formation, dopamine, serotonin, gonadotropin-releasing hormone, and likely many other physiologically active substances of cerebral origin can have endocrine effects on peripheral target organs--anterior pituitary, gonads, kidney, heart, blood vessels, and the proper brain. Although the period of brain functioning as an endocrine organ is not long, it is crucial for the body development since physiologically active substances exert irreversible effects on the targets as morphogenetic factors during this period. Thus, the developing brain from the neuron formation to the establishment of the blood-brain barrier functions as a multipotent endocrine organ participating in endocrine control of the whole body development.

[Brain is a source of blood serotonin in rats during perinatal development].

The aim of this study was to test our hypothesis that the brain functions as an endocrine organ before the blood-brain barrier is formed. A model of drug-inhibited serotonin synthesis in the brain using a single stereotactic administration of p-chlorophenylalanine, an inhibitor of serotonin synthesis, was developed. The inhibitor dose inducing the maximum effect in the brain and no effect on serotonin synthesis in the periphery was experimentally selected. The concentration of serotonin and its metabolites (5-hydroxytryptophan and 5-hydroxy-indoleacetic acid) was studied by high performance liquid chromatography in the brain, duodenum, and blood (separately in plasma and platelets). The optimal p-chlorophenylalanine dose (200 mg/kg) was shown to induce a sharp decrease in the brain level of serotonin (70%), a moderate decrease in plasma (16%) and platelets (26%), and an insignificant decrease in the duodenum (12%). At the same time, this dose did not decrease the 5-hydroxytryptophan level in the intestine. This suggests that the decrease in the blood level of serotonin was due to the inhibition of its synthesis in the brain, whereas the decrease in the duodenum level of serotonin was due to the compensatory release to blood while its synthetic rate remained unaltered. Thus, the developing brain before the blood-brain barrier formation was shown to secrete serotonin into blood.

[Compensatory reaction during degeneration of arcuate nucleus dopaminergic neurons in rats].

The study has been carried out to verify the authors' hypothesis that degeneration of dopaminergic (DA-ergic) neurons of the hypothalamic tuberoinfundibular system and concomitant development of hyperprolactinemia are accompanied by involvement of compensatory synthesis of dopamine (DA) by non-dopaminergic neurons expressing single complementary enzymes of synthesis of this neurotransmitter. Degeneration of DA-ergic neurons was produced by a stereotaxic injection into the brain lateral ventricles of 6-hydroxydopamine (6-OHDA) - a specific neurotoxin of DA-ergic neurons. 14 and 45 days after the toxin administration there were determined concentration of prolactine in peripheral blood by methods of immunoenzyme and radioimmunological analyses as well as the DA amount in the arcuate nucleus by the method of highly efficient liquid chromatography with electrochemical detection. In a part of the animals, slices were prepared from the mediobasal hypothalamus (arcuate nucleus and medial eminence) and perfused with Krebs-Ringer medium; then the DA concentration was determined in the slices and in the incubation medium. 14 days after the neurotoxin administration there were revealed an increase of blood prolactine concentration and a decrease of DA concentration in the arcuate nucleus in vivo as well a decrease of the total DA amount in the slices and incubation medium in experiments in vitro. 45 days after the neurotoxin administration, all the above parameters returned to the normal level. This, the obtained data indicate that the hyperlactinemia and DA deficit appearing during degeneration of the arcuate nucleus DA-ergic neurons seem to be compensated due to an enhancement of DA synthesis by non-dopaminergic monoenzyme neurons of arctuate nucleus.

[Expression of the enzymes of dopamine synthesis in non-dopaminergic neurons: functional significance and regulation].

Dopamine(DA), the most widely distributed in the nervous system and functionally important chemical signal, is synthesized in DA-ergic neurons from L-tyrosine by means of two enzymes, tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC). Apart from the enzymes, specific DA transporter is an attribute of DA-ergic neurons. In the mid eighties of the last century, in addition to DA-ergic neurons, those expressing only one enzyme, TH or AADC, have been discovered. These "monoenzymatic" neurons occurred to be more numerous and more widely distributed in the brain compared to DA-ergic neurons that manifests their wide involvement to the brain functioning. It has been demonstrated that the monoenzymatic neurons expressing complementary enzymes of DA synthesis produce this neurotransmitter in cooperation. In this case, L-tyrosine is transformed to L-DOPA in TH containing neurons that is followed by L-DOPA release and uptake from the intercellular space to AADC containing neurons for DA synthesis. Moreover, the L-DOPA uptake to DA-ergic or serotoninergic neurons results either in the increase or the onset of DA synthesis in addition to serotonin, respectively. The expression of the enzymes of DA synthesis in non-dopaminergic neurons is one of the adaptive reactions serving to compensate the functional insufficiency of DA-ergic neurons. For instance, hyperprolactinemia and the deficiency of DA, prolactin-inhibiting hormone, which is developed under degeneration of DA-ergic neurons of the arcuate nucleus, are compensated with time due to the increase of the number of monoenzymatic neurons and cooperative synthesis of DA in the nucleus. It is supposed that the same compensatory cooperative synthesis of DA is turned on under the degeneration of DA-ergic neurons of the nigrostriatal system that is manifested by the appearance of non-dopaminergic neurons expressing enzymes of DA synthesis in the deafferentated striatum. The expression of the enzymes of DA synthesis in non-dopaminergic neurons is under the control by intercellular signals, catecholamines, neurotrophic (growth) factors and, perhaps, hormones. Thus, non-dopaminergic monoenzymatic neurons expressing enzymes of DA synthesis produce this neurotransmitter in cooperation that is a compensatory reaction under functional insufficiency of DA-ergic neurons, in neurodegenerative diseases, hyperprolactinemia and Parkinson's disease, in particular.

[Vasopressinergic neurons in rats during ontogenesis: reaction to salt-loading and its modulation by noradrenergic afferents].

Salt-loading in adult mammals stimulates vasopressin secretion by vasopressinergic neurons of the supraoptic nucleus that is under control by a number of hormones and neurotransmitters including noradrenalin. This study was aimed to determine at what period of ontogenesis the vasopressinergic neurons begin to respond to salt-loading and when the noradrenergic control of this process is switched on. Rats on the 21st embryonic day (E), the 3rd postnatal day (P) and P13 were salt-loaded, sometimes under simultaneous treatment with prasozin, an inhibitor of al -adrenoreceptors. Thereafter, the hypothalamic nuclei of the animals were processed for immunocytochemistry and in situ hybridization. Salt-loading provoked increased synthesis of vasopressin mRNA and, most probably, vasopressin itself in rats in all studied age groups. Under salt-loading, the intraneuronal content of vasopressin increased significantly at E21 and P3, whereas it did not change at P13. No change in the intracellular contents of vasopressin mRNA and vasopressin was observed in foetuses following salt-loading and treatment with prasozin though the same treatment provoked an increase of both parameters at P3. These data show that noradrenalin provides an inhibitory control of vasopressin expression at least since P3. Thus, vasopressinergic neurons begin to respond to salt-loading at the since P3. Thus, life by the increased expression of vasopressin that is postnatally under the inhibitory control by noradrenalin.

[Migration and differentiation of neurons producing gonadotropin-releasing hormone under conditions of serotonin excess in the brain of mouse embryos].

The work has been carried out on mice of the Tg8 line with knockout of gene of monoamineoxidase A with an increase of serotonin and noradrenaline content in the brain, and on mice of the C3H line with unchanged genome and normal concentration of monoamines. An immunocytochemical study has been performed of development of neurons producing gonadotropin-releasing hormone (GnRH) under conditions of excess of serotonin and noradrenaline in the mice in embryogenesis. The GnRH-neurons were revealed at the 18th day of embryonic development in telencephalon along trajectory of their migration from olfactory bulbs to the retrochiasmatic area. In telencephalon of mouse embryos of the Tg8 line, a redistribution of the GnRH-neurons along their migration trajectory was observed as compared with embryos of the C3H line mice. The percent of the GnRH-neurons in the Tg8 mouse embryos in caudal parts of the migration trajectory was lower than in rostral parts, the opposite distribution of the neurons being observed in the C3H line mouse embryos; at the excess of serotonin and noradrenaline in the Tg8 line mouse embryos, the total amount of GnRH-neurons in the brain was lower than in the C3H mice. In males of the Tg8 line mice under conditions of excess of serotonin and noradrenaline the optical density of neurons, which correlated with the GnRH concentration in the cell, was higher than in control mice. Thus, in the Tg8 mice under conditions of the serotonin and noradrenaline excess, migration of the GnRH-neurons to their final anlage in hypothalamus is accelerated as well as the total number of the GnRH-neurons decreases, which indicates a decrease of proliferation of cells-precursors and the earlier differentiation of neurons.

[Brain neurons partly expressing monoaminergic phenotype: distribution, development, and functional significance].

Besides the monoaminergic neurons possessing the whole set of the enzymes of monoamine synthesis from the precursor amino acid and the monoamine membrane transporter, the neurons partly expressing monoaminergic phenotype, one of the enzymes of monoamine synthesis and/or monoamine membrane transporter, have been discovered. The monoenzymatic neurons are widely distributed through the brain being even more numerous than monoaminergic neurons suggesting their important functional role. Most numerous monoenzymatic neurons express individual enzymes of dopamine (DA), tyrosine hydroxylase (TH) or aromatic L-amino acid decarboxylase (AADC). TH is enzymatically active in most monoenzymatic neurons converting L-tyrosine to L-DOPA. AADC is enzymatically active in all studied monoenzymatic neurons converting extracellular L-dihydroxyphenylalanine (L-DOPA) or 5-hydroxytryptophan captured from the extracellular space, to DA or serotonin, respectively. Monoenzymatic neurons expressing complementary enzymes of the DA synthetic pathway synthesize this neurotransmitter in cooperation. The cooperative synthesis of monoamines by non-monoaminergic neurons is believed to be a compensatory reaction under the functional insufficiency of monoaminergic neurons. In addition to monoenzymatic neurons, less numerous non-monoaminergic neurons expressing the serotonin membrane transporter but lacking all the enzymes or only rate-limiting enzymes of monoamine synthesis have been discovered. Although the functional significance of these neurons remains uncertain, they most probably represent a temporal store of serotonin captured within the brain either from the intercellular space or the cerebrospinal fluid. Thus, a substantial number of the brain neurons express partly the monoaminergic phenotype, probably, serving to compensate the functional deficiency of monoaminergic neurons.

[Changes in blood plasma volume in rats during ontogenesis].

The dynamics of blood plasma volume were studied for the first time in rats during ontogenesis. The significance of blood plasma volume is estimated in the transport of physiologically active substances to cells and target organs during development. The blood plasma volume was measured in male and female rats during embryogenesis on day 18 (E18), perinatal development on E21 and day of postnatal development (P3), and postnatal development on P15 and P30. Body mass was determined in the same animals and correlation was estimated between the blood plasma volume and body mass. The plasma volume increased 1.9-fold from E18 to E21, 1.4-fold from E21 to P3, 2.1-fold from P3 to P15, and 3.4-fold from P15 to P30. The body mass increased 5-fold from E18 to E21, 2-fold from E21 to P3, 2.3-fold from P3 to P15, and 3.2-fold from P15 to P30. The ratio of blood plasma to body mass was the highest on E18 (19%) and decreased twice by E21. This index varied from 5.4 to 4.8% during postnatal development. No sex-related differences in these indices were found in rats. The results obtained make it possible to determine the total content of physiologically active substances on the basis of their plasma concentration and, thereby, estimate the efficiency of secretory organs.