Genetical aspects of hormonal modification of the stress reactivity. II. Modification in early ontogenesis of the stress reactivity of adult gray rats selected for behavior toward man

Inherited and modificational changes of the stress reactivity in two outbreed stocks of wild Norway rats trapped in nature and selected for behaviour were studied. During 18 generations the rats of one stock were selected for the lack of defensive behaviour in the glove test (tame), while in another stock the aggressiveness was maintained by the selection (aggressive). Interstock differences in the brain noradrenaline mechanisms were observed. The emotional stress reactivity of the tame animals was decreased, in comparison with the aggressive ones. Definitive stress reactivity of adult rats was modified by injections of hydrocortisone to their mothers on the 16 and 18 days of gestation. Hormonal treatment changed noradrenaline mechanisms and decreased the reaction to emotional stressor in aggressive rats. The modified level of the stress reactivity of aggressive rats was similar to the definitive level of the tame ones. Hormonal treatment did not modify stress reactivity in tame rats. Thus, the phenotype only emerging in aggressive rats, as a result of hormonal modification, is the inherited norm of the tame animals. However, due to rat selection for the lack of defensive behaviour towards the man, high corticosteroid level in the blood of pregnant females, an external developmental factor, in respect to the fetus, loses regulatory function during the development of the neuroendocrine mechanisms of the stress reaction.     

Hydrocortisone modification during intrauterine development of the activity of brain tyrosine hydroxylase in adult white rats

The activity of the key enzyme of catecholamine synthesis, tyrosine hydroxylase (TH), and the level of corticosteroids in blood were estimated in adult white rats in the normal state and after stress after their mothers were treated with hydrocortisone during pregnancy. The disturbance of the balance of corticosteroids during intrauterine development decreases the initial activity of TH in hypothalamus but increases it in the cortex of adult animals. Besides, after stress the increase in the level of corticosteroids in blood is less pronounced but the TH activation in hypothalamus is more distinct. Hence, the increase in the level of corticosteroids during intrauterine development induces long-term changes in the TH activity in brain which may be one of the causes of decrease in reactivity of adult animals after stress.     

Antidiuretic hormone content in the neurohypophysis of adult white rats after hydrocortisone administration in the early postnatal period

The age-related time-course of changes in arginine-vasopressin (AVP) content in the pituitary gland was studied in adult intact Wistar rats. In 60-day-old rats, the hormone content was measured before and after 24 h of water deprivation. In adult rats treated with a single injection of hydrocortisone at different times after birth, the content of AVP remained high in rats injected with hydrocortisone on day 2 or day 5 after birth, exceeding significantly the content of AVP in intact rats. The animals injected with hydrocortisone on day 9 or 15 manifested a more noticeable reduction in the hormone content, as was the case in intact rats. It is suggested that the first five days after birth is a critical period in the formation of the central regulation of AVP secretion with high sensitivity to short-term changes in corticosteroid balance.     

Changes in the mitotic activity and destruction of rat thymus lymphocytes following hydrocortisone administration at different hours of the day]

The 24-hour rhythm of mitoses was identical in the thymus lymphocytes of 30-day rats in control and in experimental animals 4 hours after injection of hydrocortisone. In the control rats the number of degenerating lymphocytes failed to alter in the course of 24 hours. Four hours after the hydrocortisone injection of degenerated cells increased sharply; however, the rate of the lymphocyte destruction was more significant at night and early in the morning than during the day and the evening.     

Reactivity of brain benzodiazepine receptors and individual sensitivity of rats to pentylenetetrazole

The individual sensitivity of the male Wistar rats to acute pentylenetetrazole injection was studied, the density and the affinity of benzodiazepine receptors in the cerebellar cortex for 3H-diazepam was measured. It was demonstrated that the reactivity of benzodiazepine receptors underlies the individual sensitivity to pentylenetetrazole. The animals with higher sensitivity were characterized by more intensive reaction than the control and resistant animals, i.e., by an decrease in the receptors density (the initial receptors density being equal in the sensitive, resistant, and control animals). Daily injections of a subconvulsive dose of pentylenetetrazole during 24 days increase the animal sensitivity to this substance, and this was accompanied by an increase in the reactivity of benzodiasepine receptors. Later on, the produced high sensitivity became somewhat lower but persisted for 6 months. The receptors density in this period reduced almost by half. In sensitive rats, a single low dose of pentylenetetrazole injected 6 months after treatment increased the density of benzodiazepine receptors. The age-matched controls, the same acute dose of pentylenetetrazole decreased both the receptor density and affinity of their binding. It is suggested that the increase in reactivity of benzodiazepine receptors is actualized via the intracellular metabotropic feedback mechanism.     

3H-uridine incorporation by small lymphocytes of tolerant rats: relationship to T and B lymphocytes.

Tissue tolerance was induced in neonatal rats by the intravenous injection of bone marrow cells from adult allogeneic rat donors. After 6 to 8 weeks, lymphoid cells from rats in which tolerance had been induced were tested for mixed lymphocyte reactivity (MLR), 3H-uridine uptake, and the relationship of uridine incorporation to B and T lymphocytes. Lymph node (LN) and spleen (SPL) cells from the adult inoculated rats showed no reactivity in the MLR or normal lymphocyte transfer reaction (NLTRx), indicating that the animals were tolerant. After in vitro exposure to 3H-uridine, an abundance of small lymphocytes (SL) from these same tolerant rats were heavily labeled, in contrast to nontolerant controls, where relatively few SL were heavily labeled. In order to determine whether the heavily uridine-labeled cells were T cells or B cells, lymphoid cells from the LN and SPL of tolerant animals were exposed to either rabbit anti-AKR brain serum or rabbit anti-rat Ig conjugated with ferritin. The results showed that the heavily uridine-labeled SL of the tolerant rats were mainly Ig-positive cells.     

Glucocorticoid-Induced Prenatal Modification of GABA-ergic Regulation of the Responsiveness of the Hypothalamo-Hypophyseal-Adrenocortical System to Stress in Rats

We studied the effects of introduction of exogenous glucocorticoids within the prenatal period (seven subcutaneous injections of hydrocortisone acetate, 50 mg/kg, daily, on the 15th–21st pregnancy days, or two injections on the 16th and 18th days) on the state of the hippocampal GABA-ergic system and the hypothalamo-hypophyseal-adrenocortical system (HHAS) of adult rats under conditions of acute stress (1-h-long immobilization): effects of pre-stress injection of an agonist of GABA_B receptors, baclofen (10 mg/kg, 30 min before immobilization), were also examined. The activity of glutamate decarboxylase and binding of ³H-GABA were the indices characterizing the state of the former regulatory system, while the content of catecholamines in the hypothalamus and the level of hormones of the adrenal cortex characterized the state of the latter system. Prenatal introduction of hydrocortisone acetate resulted in weakening of the adrenocortical reaction to acute stress in adult offspring males; post-stress changes in the noradrenaline level in the hypothalamus and the activity of glutamate decarboxylase in the hippocampus, as well as stress-related activation of GABA_B receptors, were absent in these animals. Adult females subjected to the prenatal influence of hydrocortisone acetate, vice versa, demonstrated a greater reaction of the adrenal cortex to stress; this occurred against the background of suppression of the activity of glutamate decarboxylase in the hippocampus and preserved activity of GABA_B receptors. Our study shows that modifying influences, which exogenous glucocorticoids applied within the prenatal period exert on the GABA-ergic regulation of the responsiveness of the HHAS to stress, are characterized in adult offspring of rats by a significant sex-related dependence. Neirofiziologiya/Neurophysiology, Vol. 37, No. 3, pp. 244–249, May–June, 2005.     

Glucocorticoids effects on exocrine pancreatic secretion in caerulein-induced acute pancreatitis in the rat.

The present work reports on exocrine pancreatic secretion in control rats, adrenalectomized rats and hydrocortisone-treated (10 mg/Kg/d) rats during 7 days, under normal conditions and after induction of acute pancreatitis with caerulein (20 micrograms/Kg) by 4 subcutaneous injections at hourly intervals. Pancreatic secretion was seen to be affected by the procedure of adrenalectomy, which led to a marked reduction in the secretion of proteins and amylase with respect to control values. This was probably due to the decrease occurring in the zymogen granules in the acinar cells of the exocrine pancreas, a phenomenon which also led to a decrease in pancreatic weight observed in these animals. Treatment with hydrocortisone induced a decrease in the secretion of proteins and amylase, as well as an increase in pancreatic weight. This agrees with the accepted hypothesis that large amounts glucocorticoids stimulate the synthesis and storage of proteins in the exocrine pancreas, reducing the secretory phase. The administration of high doses of caerulein under these conditions led to acute pancreatitis in the three groups of animals. This was paralleled by a dramatic decrease in protein and amylase secretion and by severe interstitial edema of the pancreas and by increases in serum amylase values. In the case of the animals treated previously with hydrocortisone, the latter were tripled with respect to the control animals. The conclusion is offered that since the storage of enzyme proteins is governed by glucocorticoids, which furthermore increase the sensitivity of the acinar cells to stimulation by secretagogues, the administration of these substances during the development of pancreatic lesions such as acute pancreatitis is highly compromising to the organism.     

Long-term effects of stress in critical periods of development on reactivity of adult female rats

Effects of stress during different periods of ontogeny, namely, the prenatal, prepubertal, or their combination (prenatal+prepubertal), on the indices of psychoemotional and tonic pain-related behaviors, as well as corticosterone reactivity after pain behavior were investigated in adult 90-day-old female Wistar rats. Our data show for the first time, the similarity of effects of prenatal (immobilization stress of a rat dam during the last week of pregnancy) and prepubertal (forced swimming, pain-related response in the formalin test) stresses on the indices under study, an increase in the time of immobility and in licking duration, but the difference between effects of combined stress on these indices. Pain-related response increased corticosterone in prepubertally stressed rats while in prenatally stressed rats, decreased it. In rats experienced combined stress, formalin-induced pain increased corticosterone as compared with that in prenatally, but not in prepubertally stressed rats. A positive correlation between pain-related reaction and stressed hormonal response was revealed in prepubertally stressed animals. So, long-term effects of stress during critical periods of ontogeny determine stress reactivity of behavioral and hormonal responses in adult female rats.     

Morphofunctional characteristics of the endocrine cells of the stomach following administration of hydrocortisone and L-thyroxine

Electron microscopy with application of specific fluorescent histochemical reaction of Falck, as well as some methods of impregnation made it possible to indentify enterochromaffin cells in the stomach of hyperthyroid rats and the rats after cortisone injection under the conditions ox hyperfunction of the thyroid gland. After 20 days of L-thyroxin injection, and after 10 days of hydrocortisone injection, preceded by L-thyroxin, the amount of enterochromaffin cells in the epithelial layer of the gastric mucosa were noted to increase that was accompanied by simultaneous increase of the number of secretory argyrophil granules in their cytoplasm. Simultaneous injection of L-thyroxin and hydrocortisone, while not decreasing statistically significant amount of the cells, produced degradation of their cytoplasm.     

Effect of repeated stress and administration of phenobarbital on the lymphoid tissue and on protein metabolism in the lymphocytes of infant and adult rats

Further study of the response to chronic stress stimulation in the early postnatal phase showed that the i.p. injection of physiological saline (stress stimulation) induced lymphopenia, a 50% decrease in the incorporation of 3H-leucine into isolated lymphocytes and a decrease in the weight of the thymus in 7-day-old male rats. No such changes were observed in adult animals. If repeated doses of phenobarbital were administered to stressed young rats, however, lymphopenia did not occur and the rate of the incorporation of 3H-leucine into isolated lymphocytes was not different from the control value; the protein content of the lymphocytes was significantly raised, however. In adult animals, phenobarbital increased the rate of incorporation of 3H-leucine into the lymphocytes. The repeated administration of phenobarbital reduced the weight of the thymus in both young and adult animals, but a decrease in spleen weight was recorded only in the young animals. A single i.p. injection of ACTH or dexamethasone caused lymphopenia and slowed down the incorporation of 3H-leucine into the lymphocytes of both young and adult animals. The results show that the striking decrease observed in the rate of the liver metabolism of corticosterone in suckling young rats not injured by repeated stress stimulation is accompanied by significant changes in the lymphoid tissue.     

Effect of prednisolone injections in early postnatal ontogeny on the circadian rhythm of corticosteroid function in adult rats

The effect of prednisolone injections during the early postnatal ontogenesis on the diurnal rhythm of corticosteroid function and stress reactivity in adult animals has been studied in rats. The injections of prednisolone to 7--9 days old rats resulted in the subsequent disturbance of diurnal rhythmicity in the suprarenal cortex functioning: the diurnal fluctuations of the content of 11-oxycorticosteroids in the blood plasma are smoothed out; the diurnal changes in the hormonal reaction to the stress stimulation disappear. This disturbance appears to be due to changes in the central mechanisms of the control of hypophysis-suprarenal system. The reactivity of this system per se suffered no changes.     

Changes in the reactivity of microvessels of the pia mater system of rats during ontogenesis

Changes in microvascular reactivity in pia mater system have been studied under conditions of bilateral occlusion of common carotid arteries in rats of different age groups. The studies were performed on the 7th, 30th, 45th and 90th day of the postnatal development. The occlusion of common carotid arteries lasted 6 min in week-old animals and 9 min in rats of other age groups. The phase character of microvascular reactivity has been determined. It has been found that dilation of arterioles depends on the age of the animal. So dilation of precortical arterioles averaged 20-25% of the initial level in 7-day-old animals and increased to 60-75% in 30- and 45-day-old animals. It has been determined that the smaller is the diameter of the vessels the more expressed is their reactivity. It has been shown that a steady reaction of compensatory adaptation in microvessels in characteristic only of adult animals.     

Function of the adrenal cortex during elaboration of the passive avoidance conditioned reflex in immature rats

Plasma 11-hydroxycorticosteroid (11-OHCS) levels were measured in 30-day-old rats by fluorometry during passive avoidance (PA) learning by means of a single electric footshock. In contrast to the data obtained in adult animals, pre-exposure of young rats for 7 days to the experimental environment (over 3 min daily) resulted in elevation of the basal 11-OHCS levels and in the lack of distinct changes in the hormonal background after placing the young rats into a chamber. As in previous experiments on adult rats, one day after PA learning the 11-OHCS levels were significantly lower in young rats displaying PA than in the animals which did not exhibit PA behavior. Five days after PA training these differences in adrenocortical reactivity disappeared, as was the case in adult animals.     

Contribution to histochemical distribution of non-specific cholinesterase activity in sensory ganglia of some mammals

The activity of non-specific cholinesterase was demonstrated histochemically in satellite cells of the spinal ganglia from adult rat, cat, rabbit and baboon. The spinal ganglia of newborn rats displayed distinct intraneuronal reactivity for non-specific cholinesterase while a low reactivity was observed in satellite cells. The spinal and trigeminal ganglia of adult mice contained satellite cells with non-specific cholinesterase reactivity only sporadically. Most of reaction product for non-specific cholinesterase activity (from low to high intensity) was found in perikarya of the neurons. Spinal and trigeminal ganglia of the same mice embryo exhibited diffuse staining for non-specific cholinesterase activity remaining in the spinal ganglia of newborn mice. The trigeminal ganglia of newborn mice exhibited, however, more differentiated pattern of the positive reaction for non-specific cholinesterase like adult animals. The pattern of histochemical distribution of non-specific cholinesterase activity in trigeminal and spinal ganglia from mice of various ages corresponds with morphological differentiation and maturation undergoing in a rostrocaudal wave. Intraneuronal presence of non-specific cholinesterase activity in sensory ganglia during development and in adult animals gives a new possibilities for explanation of the functional involvement of this enzyme in the nervous system.     

Effect of repeated stress on the function of pituitary-adrenal and immune systems in gray rats selected for behavior

Reaction of pituitary-adrenal axis to a 10-day immobilisation stress and a humoral immune response to subsequent injection of sheep red blood cells were investigated in gray rats selected for enhancement of decrease of aggressive behavior towards humans. It was show that pituitary-adrenal axis reaction of aggressive animals to repeated stress did not change during the experiment, while a decrease of stress-induced corticosterone level was observed already on day 5 of stress. Repeated stress led to enhancement of humoral immune response in aggressive rats, whereas it did not bring about any change in tame animals. based on the obtained data, it could be supposed that breeding of gray rats for domesticated behavior led a faster adaptation to repeated stress and the absence of stimulating influence on humoral immune response in tame rats.     

Changes in the activity of the brain renin-angiotensin system and in the functional state of the pituitary-adrenal system of rats under the influence of captopril]

While studying the effect of peroral captopril injections on the activity of renin-angiotensin system (RAS), the activity of angiotensin-converting enzyme (ACE) and angiotensin II content from anterior and mediobasal hypothalamus, medulla and adenohypophysis of intact rats has been established to decrease. Captopril administration decreases ACE activity which increases after hydrocortisone injection in rat medulla and striatum. Captopril results in no potentiation of hormonal effect in hypothalamus and in adenohypophysis where ACE activity decreases following hydrocortisone injection. A decrease in the RAS activity of brain structures and adenohypophysis induced by captopril administration to rats is accompanied by the inhibition of the activity in the pituitary-adrenal system. A decrease in ACTH level and in 11-hydroxycorticosteroids of the rat blood plasma has been determined after single captopril injection in the dosage of 10 and 50 mg/kg of body weight. Duration of the effect depends on the captopril dosage.     

Participation of the hypophyseal-adrenal cortex system in thrombin clearance during immobilization stress]

The examination carried out with thrombin marked by 131J resulted in a considerable increase of the thrombin clearance rate in healty male rats during the stress (caused by an immobilization lasting 30 minutes) and in an increase of thrombin deposits in the liver. A further increase of thrombin clearance occurred by the combination of immobilization and administration of ACTH. Contrary to ACTH the thrombin clearance is not stimulated in healthy animals by hydrocortisone. Thrombin clearance and thrombin deposits in the liver are lowered in adrenalectomized rats. In these animals the administration of ACTH does not result in an increase of thrombin clearance. The rate of thrombin clearance is normalized in adrenalectomized animals after administering hydrocortisone without as well as under conditions of stress. In adrenalectomized animals having received hydrocortisone as well as in healthy animals the administration of ACTH will results in an increase of thrombin clearance. From these experiments the conclusion can be drawn that ACTH will increase the intensity of thrombin clearance in stress and that hydrocortisone plays a transmitting part here.     

Interaction of chalones and glucocorticoid hormones in regulation of cell division

The action of hepatic chalone on cell proliferation in inoculated hepatoma 22a of mice was studied in the presence of a changed level of glucocorticoid hormones in experimental animals. Chalone was obtained from the liver of intact rats by ethanol precipitation. The intensity of cell proliferation in hepatoma was evaluated by the colcemide and autoradiography methods. Six hours after chalone injection c-mitosis in the tumor decreased 2.7-fold, and the DNA index 6.8-fold. It may be concluded that the preparation used contains both G1- and G2-chalones. Single or repeated injections of hydrocortisone to mice inhibits cell proliferation to a less degree than administration of chalone alone. Combination of hydrocortisone and chalone produces the same effect as injection of chalone alone. Adrenalectomy diminishes susceptibility of hepatoma cells to exogenous chalone. The degree of tumor proliferative activity in the adrenalectomized animals was half as much after chalone injection, as compared to that in intact animals. Thus, a certain level of glucocorticoid hormones in hepatoma tissue is necessary to reveal the action of chalones.