Prolactin response to immobilization stress and hemorrhage: the effect of hypothalamic deafferentations and posterior pituitary denervation.

The roles of posterior and anterolateral connections to the mediobasal hypothalamus (MBH) as well as innervation of the posterior pituitary in the PRL response to immobilization (IMO) and hemorrhage (HEM) were studied by means of surgical isolation, performed 6-9 days before stress exposure. Male rats bearing indwelling tail artery cannulae subjected to 120-min IMO reached peak PRL secretion in 5-20 min. HEM of 25% elicited a significant rise of PRL levels. A posterior cut in the MBH, performed without damaging the serotonergic fibers from the brain stem, attenuated the PRL response to 25% HEM, whereas the PRL elevation due to IMO remained unaffected. An anterolateral cut around the MBH eliminated both the IMO- and HEM-induced stimulation of PRL. Posterior lobe denervation reduced by about 27% the PRL response to IMO and eliminated the response to HEM. These results suggest the following conclusions. The neural structures located posteriorly to the MBH are involved in the transfer of signals triggering PRL secretion due to hypovolemia. Intact anterolateral pathways to the MBH and stalk-median eminence region are essential for the PRL-releasing activity under both stimuli. The posterior lobe may be an important link in the PRL stress response in male rats.

Specificity of the effect of repeated handling on sympathetic-adrenomedullary and pituitary-adrenocortical activity in rats.

The response of the pituitary-adrenocortical and sympathetic-adrenomedullary system to single and repeated handling was studied in rats. After repeated handling (14 days, 3 x 1 min daily or 1 day, 6 x 1 min at 30 min intervals) a reduction of plasma epinephrine and ACTH level was observed, while norepinephrine levels increased to the same extent as after the first handling. When repeatedly handled rats were handled by a different person, hormonal responses were altered: The reduction in the ACTH and epinephrine response was no longer apparent, whereas the norepinephrine response was potentiated. In the case of repeated handling over a short time period (3 hr) the last handling by a different person did not alter the reduced hormonal response. Behavioral habituation to repeated handling paralleled adaptation of plasma ACTH and epinephrine levels. The observed dissociation of plasma epinephrine and norepinephrine response suggests that different pathways control the response of the adrenal medulla and the peripheral sympathetic nervous system.

Effects of rewarding hypothalamic stimulation on plasma catecholamine levels in rats.

Plasma catecholamines were measured before, during and after exposure to lick-contingent rewarding hypothalamic stimulation, clock-triggered neutral hypothalamic stimulation, and licking maintained by water. Rewarding hypothalamic stimulation elicited a marked rise in plasma epinephrine levels which returned to baseline levels 3 min after the self-stimulation session. No changes in plasma epinephrine were observed under the latter two conditions. Increases in norepinephrine levels were more variable and seemed to correspond to motor activity being similar in the licking groups but unchanged with clock-triggered stimulation. These results indicate that stimulation of reward pathways may selectively influence adreno-medullary secretion.

Changes of plasma and adrenal catecholamines and corticosterone in stressed rats with septal lesions.

The effect of septal lesions on plasma catecholamine and corticosterone (B) levels has been studied in rats during single and 7 times repeated immobilization stress (IMO). Blood samples were obtained via a catheter in the tail artery or by decapitation. The increased circulating epinephrine (EPI) and norepinephrine (NE) levels observed in the initial phase of acute stress as well as the elevated baseline EPI level after six times repeated IMO are indicative of an enhanced response of the sympathetic adrenomedullary system after lesions of the septum. After decapitation of rats with septal lesions there was a significant increase in plasma NE one day after the sixth IMO and a block of EPI increase after the seventh IMO compared to sham-operated rats. The adrenocortical system was similarly found to be activated after septal lesions, exhibiting increased baseline plasma B levels. It has been suggested that the septal region affects the studied systems by exerting an inhibitory tonus. The removal of this inhibitory system results in an increase of adrenocortical and sympathetic-adrenomedullary activities.

Participation of "emotionality" in activation of the adrenal cortex of rats in some stress situations.

The present work attempts to interpret the relation between humoral and behavioral manifestations in rats under conditions of stress. The index of the humoral reaction to stress was plasma corticosterone levels. Initially, behavioral manifestations which are commonly subsumed under the term "emotionality" were studied. The methodological problems connected with measurement of emotionality led us to adopt instead the concept of "non-specific excitability" as proposed by J. Lat. Results are presented which point to a relationship between excitability of the animals and the activity of their adrenal cortex.

[The effect of chronic stress on the activity of the sympathetic-adrenomedullary system]. / Vplyv chronického stresu na aktivitu sympatiko-adrenomedulárneho systému.

Plasma levels of adrenaline (ADR) and noradrenaline (NA) belong to the best parameters of activity of the sympatho-adrenomedullary system (SAS). Introduction of a sensitive radioenzymatic method for the determination of catecholamines in small volumes of plasma (0.05 ml) and observing conditions of stressless blood collection by means of an indwelling catheter made in possible to determine basal plasma catecholamine levels and their dynamics during stress. Changes in plasma catecholamines were studied in acute and chronic stress (continual or intermittently repeated) in three stress models: 60-day hypokinesia, immobilization (IMO) repeated over 30 days, and 14-day or one-day handling of the rat for 1 minute. On first exposure to the given stressor the plasma levels of both catecholamines studied were increased. In the course of 60-day hypokinesia as well as during one- or 14-day handling plasma ADR levels returned to virtually resting values, plasma NA levels, however, remained at equally high values as recorded at the first exposure. During 30-day IMO basal values of ADR and NA in plasma were elevated, yet the catecholamine response to the last IMO was reduced compared to the first exposure. Under the effect of mild chronically acting stressors a dissociation was observed in the changes of plasma catecholamine levels: ADR failed to exhibit further increases, whereas NA kept significantly rising all over the period of the activity of the stressor. This differentiated activation of plasma catecholamines suggests the existence of different regulatory regions in the CNS.(ABSTRACT TRUNCATED AT 250 WORDS)

[Catecholamines in nuclei of the brains of the August strain rat during immobilization stress]. / Katekholaminy v iadrakh mozga krys linii Avgust pri immobilizatsionnom stresse.

Changes in epinephrine, norepinephrine and dopamine levels in different brain nuclei of the August rats were studied after 6.5-hr immobilization. The linkage between the BP dynamics under emotional stress and changes of catecholamines content was observed in epinephrinsynthetizing area A1, norepinephrinsynthetizing area A6 (locus Coeruleus) and dopaminsynthetizing area A9 (substantia nigra). Sharp increase of the BP in the August rats was related to obvious decrease of epinephrine content in A1, norepinephrine in locus coeruleus and dopamine in substantia nigra. The data obtained suggest that deficit of the catecholamines due to the metabolic changes during emotional stress may result in distutbances of the cardiovascular functions control in the August rats.

[Emotional stress-induced changes in catecholamines in the nuclei of the brains of rats differing in "open-field" behavior]. / Vyzvannye emotsional'nym stressom izmeneniia katekholaminov v iadrakh mozga krys, razlichaiushchikhsia po povedeniiu v "otkrytom pole".

The open-field test was used to study the role of initial emotionality in participation of brain catecholamines (CAs) in the BP control under emotional stress. The rats different in emotionality differed from each other in the level of CAs in single brain nuclei under normal conditions. Under stress, opposite CAs changes occurred in rats differing by their initial emotionality, in noradrenaline-synthetizing brain nuclei only. The neurochemical processes (features) which took part in the central BP control under stress were different in rats differing in their initial emotionality.

Corticosterone and prolactin responses to repeated handling and transfer of male rats.

The changes of plasma corticosterone and prolactin levels have been studied in rats after single, repeated or cross exposition to the moderate stressors: handling and transfer. The diminution of corticosterone and prolactin response has been found after repeated handling, but not after repeated transfer. The corticosterone level was significantly elevated in both cross-transfer and cross-handling groups and plasma prolactin level was significantly higher in the cross-handling animals. Both hormones manifested a parallel reaction to stress, prolactin being more difficult to obtain diminution of the reaction, corticosterone being more adaptable to repeated stress. It is concluded that the cross-adaptation between used stressful stimuli apparently could not be demonstrated, but, in contrast, the organism adapted to one stimulus possesses a greater corticosterone and prolactin reaction when being exposed to the new stimuli.

Stressfree administration of drugs by intraperitoneal cannulation in small laboratory animals.

A simple technique of chronic intraperitoneal cannulation in small laboratory animals has been described. It can be used for repeated i.p. administration of drugs without causing any remarkable disturbance to the animal as demonstrated by significantly less increase of corticosterone level compared to usual i.p. injection procedure. A simple device for producing a fixative ring on the cannula in order to hold the cannula in the proper place is described as well.

Repeated Maternal Deprivation Alters Behavioral Pattern and Attenuates Prolactin Response to Mild Stressor in Adult Male Wistar Rats.

OBJECTIVE: To evaluate the impact of repeated neonatal mother deprivation (RMD) of male rats on the behavioral parameters and response of prolactin to mild stress stimuli in the adulthood. METHODS: Afer birth, the pups of Wistar Porton Olac rats were crossfostered and their number was adjusted to 8 per litter (4 males and 4 females). They were removed from the dam for 6 hours daily on postnatal day 6, 7, 8 and for 12 hours daily on postnatal day 12, 13, 15, 16 and placed to another cage lined with cotton wool at controlled temperature 37 øC. Body weight was estimated repeatedly from postnatal day 9 to 97. At 14 weeks of life the behavioral activity was measured in an open field on 2 occasions, 2 days apart. One week later the rats were exposed to 15 min novelty stress or to 3 min handling and decapitated 15 min after the initiation of both. Trunk blood was collected and plasma prolactin (PRL) was measured by radioimmunoassay. RESULTS: On postnatal day 15 the eye opening was found in 75 % of control pups and 73 % of pups with RMD. In the rats after RMD the body weight gain was significantly decreased from day 21 until the day 97. Vertical behavioral activity (rearing) was enhanced in RMD rats when measured on the first occasion. Horizontal behavioral activity did not significantly differ from the control group. Stress of novel environment elicited the activation of PRL secretion in untreated animals (19.3 1+4.6 ng/ml vs. 7.17+1.03 ng/ml, P<0.05), while no change was found in the rats after RMD (8.15+2.0 ng/ml vs. 4.35+0.48 ng/ml). CONCLUSIONS: In the rats exposed to neonatal mother deprivation the lower emotionality was found. Significantly decreased body weight gain in these animals was probably due to the nutritional deprivation during the postnatal separation from the mother. The nonresponsiveness of lactotrophs to mild stressor in adult rats after RMD may have a negative impact on defense mechanisms to immune challenges.

[Changes in the level of catecholamines in norepinephrine-producing structures of the brain of rats subjected to immobilization]. / Izmeneniia urovnia katekholaminov v noradrenalinsinteziruiushchikh strukturakh mozga krys posle immobilizatsii.

Radioenzymatic assay was used to determine the catecholamine content in locus ceruleus and n. subceruleus in Wistar rats after 6.5-hour immobilization. During immobilization the arterial blood pressure was measured, whereas the state of the gastric mucosa was assessed after the decapitation. Locus ceruleus showed definite correlations of changes in the catecholamine content to the time course of the arterial pressure in the course of immobilization. Upon arterial pressure deviations towards one or another side there was an increase in the content of noradrenaline and dopamine, with this increase being more abrupt during blood pressure elevation. In relatively stable arterial pressure, the level of catecholamines in locus ceruleus does not virtually differ from the control one.

[Catecholamines in the brain structures of rats responding differently to the "open field" test]. / Katekholaminy v strukturakh mozga krys, razlichaiushchikhsia po testu "otkrytogo polia".

Wistar rats divided into groups according to the open-field test showed essential differences in the catecholamine level in 3 out of eight principal catecholamine-synthesizing brain nuclei. In rats with a sharp decrease in crossing and rearing seen throughout the experiment, the adrenaline and dopamine levels in A1 area were significantly higher and the dopamine level in locus ceruleus and n. arcuatus was lower as compared with rats which were not so emotional. It is suggested that the open-field behavior of Wistar rats correlates with the brain catecholamine interplay, the main part being played by adrenaline-synthesizing neurons of A1 area, noradrenaline-synthesizing neurons of locus ceruleus and dopamine-synthesizing neurons of n. arcuatus.

Do the circulating neurohypophysial hormones affect basal or stress induced prolactin (PRL) release in male rats?

The action of acute administration of oxytocin (OXY), vasopressin (AVP) or its analog 1-deamino-8-D-arginine-vasopressin (dDAVP) on basal and stress induced PRL release in normal male rats and the effect of chronic injection of AVP on PRL stress response in AVP deficient rats were studied. The hormones (OXY, 600 ng min-1 per rat; AVP 6, 12 or 24 ng min-1 per rat and dDAVP 24 ng min-1 per rat) were infused to conscious rats via the jugular vein for 10 min and then the rats were immobilized under continuing the infusion for further 20 min. In parallel experiments arterial blood pressure (BP) was measured. OXY and 24 ng min-1 AVP caused high BP elevation of the same magnitude, yet the effect of 12 ng min-1 AVP was significantly lower. Neither OXY, dDAVP, nor 6 and 12 ng min-1 of AVP affected basal or stress stimulated PRL values when compared with saline treated animals. 24 ng min-1 of AVP highly stimulated nonstressed PRL levels and no additional stress effect was observed. Intramuscular injection of 2 micrograms (1 U) of AVP daily for 7 days did not influence the basal values or stress induced PRL response in Brattleboro homogygous rats as compared with vehicle treated controls or heterozygous rats treated with AVP or vehicle. These results show that the infusion of 24 ng min-1 per rat of AVP stimulated PRL release which cannot be explained by the nonspecific effect of high BP. Repeated AVP administration did not modulate either the basal or IMO stress stimulated PRL secretion in rats with or without genetic vasopressin deficiency.

Prior immobilization stress alters adrenal hormone responses to hemorrhage in rats.

The effect of prior immobilization stress (IMO) on the plasma epinephrine (EPI), norepinephrine (NE), adrenocorticotropic hormone (ACTH), and corticosterone (CS) responses to acute hemorrhage was studied in conscious male rats with chronic catheters in tail artery, using two combinations of IMO and hemorrhage. IMO per se led to significant increases of EPI, NE, ACTH, and CS in all animals. Hemorrhage of 25% of estimated blood volume (EBV) performed immediately after 150 min IMO caused exaggerated release of EPI and NE, whereas CS remained unchanged at the level previously elevated by IMO. ACTH response to initial blood loss of 12.5% was diminished in previously immobilized rats. Hemorrhage of 35% EBV after 60 min IMO and a 10-min recovery period also resulted in potentiated increases in EPI and NE, suppressed ACTH secretion, and no further change in stress-elevated CS concentration. No differences between groups were observed in relative mean arterial blood pressure, plasma protein, and lactate responses to 35% hemorrhage. Posthemorrhagic increase of plasma concentration of several tissue enzyme activities was significantly higher in prestressed rats. Furthermore, 24-h mortality rate increased by 49%. In summary, our results indicate that prior IMO potentiated activation of the sympathoadrenomedullary system and suppressed ACTH response to subsequent hemorrhage. Altered neuroendocrine responsiveness and stress-induced prehemorrhagic tissue damage may play roles in the increased susceptibility of the organism to blood loss.

[Open-field behavior of rats following bilateral coagulation of the locus coeruleus]. / Povedenie krys v otkrytom pole posle bilateral'noi koaguliatsii sinego piatna.

A modified open-field test was used in the experiments on rats. It was shown that animals 6 days after bilateral coagulation of locus coeruleus displayed weight changes and some behavioural parameters distinct from those of sham-operated and control animals. The most pronounced differences observed in animals after locus coeruleus coagulation, as compared to the control, were inversion and adaptive responses to a sudden brief stimulus, locomotor dysfunction and absence of response to handling.

Hypertension induced by repeated stress: possible participation of sympathetic-adrenomedullary catecholamines.

Several groups of male Wistar rats weighing 250-300 g were subjected to immobilization stress (IMO) for various intervals (2.5 h to 19 h daily omitting weekends for a total of 2 to 15 weeks). Blood pressure (BP) was measured with the aid of indirect cuff pressure method under routine conditions once weekly during the whole period of immobilization and in some groups also for 10 weeks after the end of this period. It was found that BP significantly increased after 2 weeks of 2.5 h IMO daily and progressively increased later on. There was an indirect relationship between the duration on individual intervals of IMO and the period which was necessary to develop a significant increase of BP. Adrenal medullectomized animals showed a significantly less increase of BP than normal ones during 16 weeks course of IMO. The level of adrenaline and noradrenaline was significantly increased in animals having 24-hour rest after 39th IMO compared to controls, the blood being taken by chronically implanted cannula in a tail artery.

Sympathoadrenal activity facilitates beta-endorphin and alpha-MSH secretion but does not potentiate ACTH secretion during immobilization stress.

The potential involvement of the sympathoadrenal system in stress-induced secretion of peptides from the intermediate lobe of the pituitary gland and the activation of the pituitary-adrenal axis was studied. Male Wistar rats were subjected to control procedures, to sympathectomy by chronic administration (8 weeks) of guanethidine and/or to medullectomy by adrenal enucleation 9 weeks prior to exposure to forced immobilization stress for various periods of time. In intact or sham-operated rats, immobilization caused a prompt increase of circulating norepinephrine, epinephrine (EPI), corticosterone and of immunoreactive adrenocorticotropic hormone (ACTHi), alpha-melanocyte-stimulating hormone (alpha-MSHi) and beta-endorphin (beta-ENDi). Peak levels of pituitary hormones were found after 10 min of stress exposure, but fell to less than 30% of these levels after 2.5 h of immobilization. Adrenal medullectomy, which abolished the stress-induced release of EPI, reduced the acute increase of plasma alpha-MSHi and beta-ENDi, but did not influence the acute increase of plasma ACTHi during immobilization stress. Also in medullectomized plus sympathectomized rats, the initial stress response of circulating ACTHi was not different from that of controls. Adrenal medullectomy with or without additional sympathectomy caused a marked increase in plasma ACTHi concentrations after prolonged stress exposure. We conclude that: catecholamines originating from the adrenalmedulla facilitate the stress-induced secretion of intermediate lobe peptides (alpha-MSHi, beta-ENDi); catecholamines from the sympathoadrenomedullary system do not contribute to the acute release of ACTH during immobilization stress; the sympathoadrenomedullary system is involved in the secondary reduction of circulating ACTHi levels seen during prolonged stress.

[Immobilization stress-induced changes in catecholamine levels in the individual cerebral nuclei in rats of different zoosocial ranks]. / Vyzvannye immobilizatsionnym stressom izmeneniia urovnia katekhola- minov otdel'nykh iader mozga krys, razlichaiushchikhsia po zoo- sotsial'nomu rangu.

Immobilization stress induced catecholamines level changes were studied in brain nuclei, taking part in blood pressure central regulation in rats with different zoosocial position. The significant differences in catecholamines level between the zoosocial groups of rats were shown in dopamine synthesized hypothalamic nuclei-n. arcuatus, n. periventricularis and noradrenaline synthesized-n. subcoeruleus++. The dominant rats were characterized by the highest catecholamines level.