[ACTIVITY OF HYPOTHALAMIC-PITUITARY-ADRENAL AXIS OF PRENATALLY STRESSED MALE RATS IN EXPERIMENTAL MODEL OF DEPRESSION].

The hypothalamic-pituitary-adrenal (HPA) axis activity changes were examined in the adult, prenatally stressed male rats in the experimental depression model--the paradigm of "learned helplessness". It was shown that in males descending from intact mothers a depressive-like state was accompanied by an increase in HPA activity. The expression of corticotrophin-releasing hormone (CRH) in the hypothalamic paraventricular nucleus (PVN) increases, coupled with a rise in plasma levels of ACTH and corticosterone as well as in adrenal weight. At the same time in males born from mothers stressed during the last week of pregnancy we observed a decrease in activity of both the central (hypothalamus) and the peripheral (adrenal cortex) parts of regulation of this hormonal axis similar to that revealed for these animals in our previous study in "stress-restress" paradigm. It is concluded that prenatal stress modifies the sensitivity of animals to the inescapable intense stress impact, which manifests itself in a specific pattern of the HPA axis activity after stress load.

Activity of the Hypothalamic-Pituitary-Adrenal System in Prenatally Stressed Male Rats on the Experimental Model of Post-Traumatic Stress Disorder.

Using the experimental model of post-traumatic stress disorder (stress-restress paradigm), we studied the dynamics of activity of the hypothalamic-pituitary-adrenal system (HPAS) in adult male rats, whose mothers were daily subjected to restraint stress on days 15-19 of pregnancy. Prenatally stressed males that were subjected to combined stress and subsequent restress exhibited not only increased sensitivity of HPAS to negative feedback signals (manifested under restress conditions), but also enhanced stress system reactivity. These changes persisted to the 30th day after restress. Under basal conditions, the number of cells in the hypothalamic paraventricular nucleus of these animals expressing corticotropin-releasing hormone and vasopressin was shown to decrease progressively on days 1-30. By contrast, combined stress and restress in control animals were followed by an increase in the count of CRH-immunopositive cells in the magnocellular and parvocellular parts of the paraventricular nucleus and number of vasopressin-immunopositive cells in the magnocellular part of the nucleus (to the 10th day after restress). Our results indicate a peculiar level of functional activity of HPAS in prenatally stressed males in the stress-restress paradigm: decreased activity under basal conditions and enhanced reactivity during stress.

[STRESS-INDUCED PATTERNS OF THE HYPOTHALAMIC CRH AND VASOPRESSIN EXPRESSION IN FEMALE RATS IN A MODEL OF POSTTRAUMATIC STRESS DISORDER].

The neuroendocrine mechanisms underlying anxiety-like state development in cycling female rats with different plasma estradiol levels have been studied in a stress-restress paradigm, an animal model of posttraumatic stress disorder (PTSD). The effect of stress-restress on the hypothalamic expression of corticotropin-releasing hormone (CRH) and vasopressin was analyzed by quantitative immunocytochemistry. Stress-restress was found to increase CRH expression in the hypothalamic paraventricular nucleus (PVN) on the 10th post-restress day, but the level of CRH expression in the PVN restored to the basal values on the 30th post-restress day in all experimental groups. It was shown an increase in vasopressin immunoreactivity in the PVN from the 10th to the 30th post-restress days in female rats exposed to stress during the estrus phase (low plasma estradiol level). In summary, female rats with low plasma estradiol level exhibited the most significant changes in the hypothalamic neuroendocrine system following stress-restress exposure. It might be hypothesized that hyperactivity of the hypothalamic circuit of the central vasopressinergic system is one of the possible mechanisms underlying PTSD-like state development in female rats in a stress-restress paradigm.

Development of behavioral and hormonal disorders in prenatally stressed female rats on the model of posttraumatic stress disorder.

The dynamics of changes in behavioral and hormonal manifestations of a pathological state in mature female rats born by mothers exposed to daily restraint stress on days 15-19 of pregnancy were studied in the experimental model of posttraumatic stress disorder (stress-restress paradigm). Experiments demonstrated increased anxiety in control and prenatally stressed female rats after combined stress followed by restress. This parameter remained enhanced until day 10 after restress in control rats and day 30 in prenatally stressed animals. The severity of depression increased on days 1 and 10 after restress in prenatally stressed female rats. Basal activity of the pituitary-adrenocortical axis increased only in prenatally stressed female rats under these conditions. This parameter increased 1 day after restress and decreased after day 30. It was concluded that prenatal stress could increase the predisposition to post-stress mental pathologies in experimental animals, which are manifested in increased severity and duration of behavioral and hormonal impairments.

Selective effect of allopregnanolone on corticoliberin-induced anxiety.

We studied the effect of allopregnanolone on stress-induced anxiety caused by intranasal administration of corticoliberin to male Wistar rats. Active and passive rats were selected by their T-maze behavior and then were tested in elevated plus maze for initial anxiety level. Basing on test results, the animals were divided into following groups: active high-anxiety rats, active low-anxiety rats, and passive animals. Rats of the experimental subgroups received subcutaneous injection of allopregnanolone (0.2 mg/kg body weight), control animals received saline. In 30 min, all animals intranasally received corticoliberin (0.5 µg into each nostril) and then were tested in elevated plus maze. Passive animals demonstrated increased anxiety after corticoliberin administration against the background of allopregnanolone. Under the same conditions, low-anxiety rats demonstrated reduced anxiety, while in active high-anxiety animals, only an increase of motor activity was observed. Hence, the effect of allopregnanolone on anxiety level under stress conditions depends on individual typologic features of animal behavior.

[Modification of expression of neurohormones in hypothalamus of prenatally stressed male rats in model of posttraumatic stress disorder].

By the method of quantitative immunohistochemistry there has been studied expression of corticotrophin-releasing hormone (CRH) and vasopressin in hypothalamic paraventricular nucleus (PVN) of prenatally stressed rats in the experimental model of the posttraumatic stress disorder--the paradigm "stress-restress". The prenatal stress was modeled by immobilization of pregnant female rats for 1 h from the 15th to the 19th day of pregnancy. It has been shown that in sexually mature males--descendants of stressed mothers--a decrease in immunoreactivity to CRH and vasopressin is observed in the parvocellular and magnocellular PVN areas 10 days after the restress. In the control group males born by intact mothers the level of immunoreactivity to CRH was increased in both PVN areas, whereas with respect to vasopressin--in the magnocellular area. Only in the prenatally stressed males there is detected a decrease in the corticosterone level in the blood plasma 10 days after the restress. It is concluded that in the control group males themanifestation of the pathological state in the paradigm "stress-restress" consists in hyperactivation of the hypothalamic chain of regulation of the hypothalamo-pituitary-adrenocortical system, whereas in the prenatally stressed animals, on the contrary, there is observed a decrease in activity both of the central (PVN) and of the peripheral (adrenal cortex) chain of this hormonal axis.

Blockade of corticoliberin receptors prevents the development of post-stress psychopathology in rats with an active strategy of adaptive behavior.

Active and passive Wistar rats were subjected to single water immersions, after which they showed signs of post-stress depression. Administration on this background of the peptide CRH-R1 receptor blocker astressin prevented the development of behavioral deficit in active individuals but had no effect on the behavior of passive rats. These results lead to the conclusion that corticoliberin receptor blockers are effective in the treatment of post-stress depression only for individuals with an initially active behavioral strategy.

Changes in the adaptive behavior of active and passive wistar rats in a water immersion model of depression.

Animals with active and passive strategies of adaptive behavior were selected from a population of Wistar rats by testing in a T maze to measure the indexes of behavioral passivity and behavioral activity. After single (stress) or two (stress-restress) water immersions, individual changes in adaptive behavior were used to study the development of post-stress psychopathology and its interaction with the initial behavioral strategy. In the unavoidable aversive environment, active and passive rats developed different types of post-stress depression, only passive individuals fulfilling the criteria of post-traumatic stress disorder.

Expression of vasopressin in the hypothalamus of active and passive rats with poststress depression.

No interstrain differences were revealed in vasopressin concentration in the hypothalamus of control and treated active and passive rats with poststress depression. Changes in vasopressin immunoreactivity corresponded to variations in corticotropin-releasing hormone concentration observed in this model of depression. These data suggest that vasopressin contributes to the development of this experimental psychopathology.

Reactivity of the hypophyseal-adrenocortical system to stress in rats with active and passive behavioral strategies.

Rats with active (KHA) and passive (KLA) behavioral strategies showed no strain-related differences in basal corticosterone levels or in changes in corticosterone levels after exposure to mildly stressful stimuli. Only severe immobilization stress produced significant interstrain differences in the reactivity of the hypophyseal-adrenocortical system, as evidenced by the greater increase in blood corticosterone in KHA rats 30 min after stressing. The hormonal stress response in KHA rats was prolonged, as the elevated blood corticosterone level in these animals persisted longer than in KLA rats. The data provide evidence not only that the hypophyseal-adrenocortical systems have different sensitivities to severe stresses in these strains, but also that active and passive animals have different rates of inactivation of the stress reaction.

Adaptive behavior in active and passive rats after intranasal administration of corticotrophin-releasing hormone.

Rats with high (KHA) and low (KLA) rates of acquiring active avoidance reflexes were used to study the effects of intranasal administration of corticotrophin-releasing hormone on orientational-investigative behavior in an open field and anxiety in an elevated cross maze. Administration of the neurohormone induced opposite changes in the behavior of the rats of these lines in the two tests. In KLA rats, movement and investigative activity increased, while in KHA rats these behaviors decreased. In the elevated maze, KLA rats, unlike KHA rats, showed increases in the time spent in the open arms, which was evidence for a decrease in anxiety in these animals. Thus, intranasal hormone administration completely reproduced the effects seen after administration into the striatum. It is suggested that corticotrophin-releasing hormone is an endogenous factor for the detailed and appropriate correction of adaptive behavior.

Involvement of dopaminergic processes in the striatum during the effects of corticoliberin on the behavior of active and passive rats.

The effects of intranasal corticoliberin on behavior in the open field test were studied in rats with active and passive behavioral strategies (lines KHA and KLA); levels of dopamine and noradrenaline and their metabolites were measured in the striatum and hypothalamus. In KLA rats, administration of the neurohormone led to increases in motor and investigative activity, while decreases were seen in KHA rats. There were no interline differences in catecholamine levels in the hypothalamus, while dopamine levels in the KLA striatum nearly doubled and metabolite levels (DOPAC, HVA) were significantly lower than in KHA rats. Corticoliberin increased dopamine and noradrenaline levels in the hypothalamus of both rat lines, with significant decreases in the striatum. This decrease was more marked in KLA rats, probably due to the faster metabolism of transmitters in the presence of neurohormones, as indicated by the increase in metabolite levels in this structure.

Localization of corticoliberin receptors in the rat brain.

In situ hybridization was used to study the distribution of corticoliberin receptors of subtypes 1 and 2 (CL-R1 and CL-R2 respectively) in different structures of the rat brain. Levels of CL-R1 mRNA in the brain were significantly greater than levels of CL-R2 mRNA, and the most intense expression of the CL-R1 gene was seen in forebrain structures, especially various neocortical, archicortical, and paleocortical regions in the cerebellar cortex. In addition, significant levels of CL-R1 mRNA expression were noted in the red nucleus and the reticular nucleus of the tegmentum. Intense expression of CL-R2 mRNA was observed in structures of the olfactory system, corticomedial parts of the amygdala, fields CA1-CA4 of the hippocampus, the ventromedial hypothalamus, and several brain stem nuclei. Moderate levels of CL-R2 mRNA were seen in the dorsolateral neostriatum. These results provide evidence that corticoliberin receptors of both subtypes are widespread in the brain. The different patterns of expression of CL-R1 and CL-R2 in the brain probably provide the basis for the functional specificity of action of corticoliberin in brain structures.

Lipid peroxidation in the striatum of rats during stress after administration of cortisol.

Lipid peroxidation processes were studied in the striatum during stress in conditions of prior administration of cortisol. Three doses of cortisol (25 mg/kg, daily) had no significant effect on the levels of lipid peroxidation products six days after injections ended. However, lipid peroxidation responses to stress during this period in animals given cortisol were significantly stronger than in controls (there were decreases in the intermediate products of lipid peroxidation and increases in the quantities of Schiff bases). Thus, administration of hormone leads to long-term changes in one of the most important regulatory systems of the body--lipid peroxidation--and has sensitizing effects on changes in the levels of stress-induced lipid peroxidation products.

The neonatal glucocorticoid treatment-produced long-term changes of the pituitary-adrenal function and brain corticosteroid receptors in rats.

Two distinct periods of sensitivity to elevated glucocorticoid hormone levels during postnatal development of the pituitary-adrenal axis were studied. Wistar rats were injected subcutaneously (s.c.) with cortisol (1 mg/kg) on postnatal days 1-5 or 14-18. The steroid treatment during the first postnatal week resulted in a decrease of the morning basal and stress-induced plasma corticosterone levels in 30 day-old male rats, as well as in rats that were injected with cortisol on the third postnatal week. Stress-induced corticosterone levels in 90-day old cortisol-treated rats were determined in blood samples drawn from the tail vein before the restraint stress, immediately after the 20-min long stress, then 60 and 180 min afterwards. Only the rats treated with cortisol during the third week showed a prolonged stress-induced corticosterone secretion, with the highest corticosterone level in 180 min after the restraint stress. The early neonatal cortisol treatment had no effect on (3)H-corticosterone binding in all studied brain areas of the 90-day old rats. The rats treated with cortisol at the 14-17th postnatal days showed a significantly lower (3)H-corticosterone binding in the frontal cortex, hippocampus, and hypothalamus. These findings suggest that the third week of life in rats is more sensitive to elevated levels of corticosterone than the first one. The high level of glucocorticoids at this period has long-term effects on the efficiency of the negative feedback mechanisms provided by hypothalamus-pituitary-adrenal axis.

Involvement of the striatum in the central regulation of the hormonal functions of the gonads.

Studies reported here show that intrastriatal administration of corticoliberin to rats decreases the blood testosterone level. However, in conditions of chemical deficiency of dopaminergic transmission in the dorsal striatum induced by injection of 6-hydroxydopamine, the effect of this neurohormone did not appear. It is concluded that extrahypothalamic corticoliberin is involved in regulating the hormonal reproductive system acting via dopaminergic mechanisms.

Dopaminergic mechanisms of neostriatum in the regulation of adaptive behavior by corticoliberin.

A conditioned active avoidance response was developed in rats with high (KHA) and low (KLA) rates of learning and the effects of injection of corticoliberin into the dorsal striatum on orientational-investigative and avoidance behavior were studied in normal animals and after depletion of striatal dopamine by preliminary injection of 6-hydroxydopamine. These studies showed that corticoliberin, like 6-hydroxydopamine, produced similar trends in the animals' behavior. Their effects were mediated by opposite mechanisms in animals with initial active and passive learning strategies for adaptive behavior. The role of dopaminergic structures of the striatum in mediating the behavioral effects of corticoliberin is discussed.

Striatal mechanism of action of corticoliberin on behavior in dogs in conditions of dopamine deficiency.

This report describes studies of the interaction of the integrative dopaminergic and corticoliberin systems in the neostriatum during performance of situational food-related conditioned reflexes. Studies were performed in dogs with chemotrodes implanted in the substantia nigra and the head of the caudate nucleus. 6-Hydroxydopamine was injected into the substantia nigra at a dose of 50 microg, and 10 microg of corticoliberin was injected into the caudate nucleus. Blood cortisol and catecholamine levels were determined. Analysis of the result showed that an interaction takes place in the neostriatum between the corticoliberin and dopaminergic systems, and that in conditions in which dopaminergic structures are excluded, the efficacy of corticoliberin in the performance of behavioral acts decreases by 30-40%, i.e., complete expression of its regulatory role of motor situational conditioned reflexes is lost.

Modification of the behavioral effects of corticoliberin by early post-natal administration of corticosteroid hormones.

Experiments on rats in which hydrocortisone was given in the early postnatal period were used to study the effects of intrastriatal microinjection of corticoliberin on behavior in an open field test. Bilateral microinjection of corticoliberin into the neostriatum led to a sharp reduction in orientational-investigative activity. Rats given hydrocortisone in the first days of life had elevated movement activity, and the anxiogenic effect of corticoliberin was absent in these animals.

Neuroendocrine mechanisms of the formation of adaptive behavior.

The behavioral and neuroendocrine responses of the body to external changes are determined by genetically determined programs of individual development, and are established during pre- and post-natal ontogenesis. These responses, however, can be changed by stress or administration of corticosteroid hormones in "critical periods" of the body's development. Mineralo- and glucocorticoid receptors mediate the "inhibition" of particular neuroendocrine or neuromediator systems, promoting behavioral modification.