Chronic sustained stress increases levels of anterior pituitary prolactin mRNA

Our laboratory is investigating the effects of chronic stress on physiological, endocrine and behavioral measures, in order to elucidate the neuronal substrates for the pathophysiological consequences of stress in humans. In these studies, we have employed a rodent model of sustained stress in which rats are exposed to around-the-clock intermittent footshock that can be avoided or escaped by rats in the controllable stress group, but not by rats in the uncontrollable stress group. Each rat in the uncontrollable stress group is paired (yoked) to a rat in the controllable stress group such that the controllable stress group rat avoids or escapes shock for both rats. A third group of rats receives no shock (controls). We have previously reported that in male rats, plasma prolactin levels were elevated after 3 days of stress in both stress groups. In the present experiments we determined whether the increases in plasma prolactin were correlated with increases in anterior pituitary prolactin mRNA. In addition, we measured hormones and mRNA at three time points and we examined these responses in female as well as male rats. Adult male and female Sprague-Dawley rats were exposed to chronic stress for 1, 3 or 14 days. In unstressed control rats, levels of anterior pituitary prolactin mRNA were fivefold higher in female as compared to male rats. However, stress increased levels of anterior pituitary prolactin mRNA over baseline in both genders. After 1 day of stress, anterior pituitary prolactin mRNA levels increased in male and female rats belonging to both stress groups, with no significant difference seen between the uncontrollable vs. controllable stress groups. After 3 days of stress, anterior pituitary prolactin mRNA levels were even more elevated, and rats in the uncontrollable stress group had higher anterior pituitary prolactin mRNA levels than those in the controllable stress group. After 14 days of stress, there were no significant differences in control and stressed groups with respect to anterior pituitary prolactin mRNA. These data suggest that chronic sustained stress increases the synthesis of anterior pituitary prolactin mRNA during the first days of stress, and that levels return to prestress values sometime between 3 and 14 days of stress.

Treadmill exercise training blunts suppression of splenic natural killer cell cytolysis after footshock

This study extended to treadmill exercise training our prior report (Dishman RK, Warren JM, Youngstedt SD, Yoo H, Bunnell BN, Mougey EH, Meyerhoff JL, Jaso-Friedmann L, and Evans DL. J Appl Physiol 78: 1547-1554, 1995) that activity wheel running abolished the suppression of footshock-induced natural killer (NK) cell cytolysis. Twenty-four male Fischer 344 rats were assigned to one of three groups (n = 8, all groups): 1) a home-cage control group, 2) a sedentary treatment group, or 3) a treadmill-running group (0 degrees incline, 25 m/min, 35 min/day, 6 days/wk). After 6 wk, the treadmill and sedentary groups received 2 days of footshock. Splenic NK cytotoxicity was determined by standard 4-h (51)Cr release assay. Percentages of lymphocytes were determined by flow cytometry. Plasma levels of ACTH, corticosterone, and prolactin concentration were measured by radioimmunoassay. After footshock, percentage of lysis relative to home-cage controls was 40% and 80% for sedentary and treadmill-trained animals, respectively (P < 0.05). Our results indicate that the protective effect of chronic exercise on innate cellular immunity in the Fischer 344 male rat is not restricted to activity wheel running, nor is it explained by elevations in basal NK activity, increased percentages of splenic NK and cytotoxic T cells, or increased plasma levels of ACTH, corticosterone, and prolactin.

Activity wheel running blunts increased plasma adrenocorticotrophin (ACTH) after footshock and cage-switch stress

We examined whether chronic circadian physical activity attenuates hypothalamic-pituitary-adrenal hormone responses after footshock with or without cage-switch stress. Young (45 g) male Fischer 344 rats were randomly assigned to individual suspended home cages (HC) or cages with activity wheels (AW) (12 h:12 h light-dark photoperiod). After 6 weeks, each animal from a pair matched on mass (HC and AW) and average weekly running distance (AW) was randomly assigned to controllable or uncontrollable footshock on 2 days separated by 24 h. Half the animals were returned to the HC after the first day of shock, and half were switched to a new shoebox cage. One animal of each pair could end the shock for both rats by performing an FR-2 lever press. The yoked animal could not control the shock. After shock on Day 2, trunk blood was collected after decapitation. Plasma adrenocorticotrophin (ACTH), corticosterone, and prolactin were determined by radioimmunoassay. ANOVA for a 2 Group (AW vs. sedentary) x 2 Test (controllable vs. uncontrollable shock) x 2 Condition (HC vs. cage-switch) design indicated a Group x Test x Condition effect [F(1, 48) = 5.07, p = 0.03] and a Test main effect [F(1, 47) = 6.93, p = 0.01] for ACTH. ACTH was higher for sedentary animals after uncontrollable footshock under cage-switch conditions and higher after uncontrollable versus controllable footshock when averaged across groups and cage conditions. No effects were found for corticosterone or prolactin. Our results extend to activity wheel running prior findings of a cross-stressor attenuation in plasma [ACTH] in response to cage-switch after treadmill exercise training, though the cross-stressor effect was additive with footshock. Consistent with our prior reports, the cross-stressor effect of wheel running was not apparent after footshock administered under home-cage conditions.

Activity wheel running reduces escape latency and alters brain monoamine levels after footshock

We examined the effects of chronic activity wheel running on brain monoamines and latency to escape foot shock after prior exposure to uncontrollable, inescapable foot shock. Individually housed young (approximately 50 day) female Sprague-Dawley rats were randomly assigned to standard cages (sedentary) or cages with activity wheels. After 9-12 weeks, animals were matched in pairs on body mass. Activity wheel animals were also matched on running distance. An animal from each matched pair was randomly assigned to controllable or uncontrollable inescapable foot shock followed the next day by a foot shock escape test in a shuttle box. Brain concentrations of norepinephrine (NE), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), 5-hydroxytryptamine (5-HT), and 5-hydroxyindole acetic acid (5-HIAA) were assayed in the locus coeruleus (LC), dorsal raphe (DR), central amygdala (AC), hippocampus (CA1), arcuate nucleus, paraventricular nucleus (PVN), and midbrain central gray. After prior exposure to uncontrollable foot shock, escape latency was reduced by 34% for wheel runners compared with sedentary controls. The shortened escape latency for wheel runners was associated with 61% higher NE concentrations in LC and 44% higher NE concentrations in DR compared with sedentary controls. Sedentary controls, compared with wheel runners, had 31% higher 5-HIAA concentrations in CA1 and 30% higher 5-HIAA concentrations in AC after uncontrollable foot shock and had 28% higher 5-HT and 33% higher 5-HIAA concentrations in AC averaged across both foot shock conditions. There were no group differences in monoamines in the central gray or in plasma prolactin or ACTH concentrations, despite 52% higher DA concentrations in the arcuate nucleus after uncontrollable foot shock and 50% higher DOPAC/DA and 17% higher 5-HIAA/5-HT concentrations in the PVN averaged across both foot shock conditions for sedentary compared with activity wheel animals. The present results extend understanding of the escape-deficit by indicating an attenuating role for circadian physical activity. The altered monoamine levels suggest brain regions for more direct probes of neural activity after wheel running and foot shock.

Treadmill exercise training and estradiol increase plasma ACTH and prolactin after novel footshock

We examined whether rats that were treadmill exercise trained (Tr) or chronically immobilized (CI) had similar responses by the hypothalamic-pituitary-adrenal (HPA) cortical axis to acute stress and whether the HPA responses interacted with the hypothalamic-pituitary-gonadal (HPG) axis. After 6 wk (1 h/day, 6 days/wk) of Tr or CI, plasma concentrations of adrenocorticotropic hormone ([ACTH]), [prolactin], and [corticosterone] were measured after familiar (treadmill running or immobilization) or novel (footshock) stress. Ovariectomized Sprague-Dawley females (n = 72) were implanted with capsules containing estradiol benzoate (E2) and randomly assigned in a 2-group (E2 vs. no E2) x 3 treatment (Tr vs. CI vs. sedentary) x 4 acute stressor [footshock vs. treadmill running (Run) vs. immobilization (Im) vs. no stress] x 3 recovery time (1 vs. 15 vs. 30 min) mixed-model analysis of variance. E2 capsules were removed from one-half of the animals 48 h before the first stressor session. After 10 min of acute stress, blood was drawn from a jugular catheter at 1, 15, and 30 min of recovery. [ACTH] and [prolactin] after footshock were higher in Tr rats with E2 compared with CI and sedentary rats without E2; recovery levels for sedentary animals were higher after Run compared with Im. The elevation in [corticosterone] from minute 1 to 15 of recovery was higher after the familiar Run and Im conditions. Our findings are consistent with an increased responsiveness of the HPA axis to novel footshock after treadmill exercise training that is additionally modulated by the HPG axis.

Stressors, including social conflict, decrease plasma prolactin in male golden hamsters

Following exposure to a stressor, plasma prolactin (PRL) rises in most species. The purpose of the present study was to examine the effect of social conflict or of footshock stress on PRL responsiveness in male Syrian hamsters. Contrary to expectations, PRL was significantly lower in subordinate hamsters than in their dominant opponents or in controls following one, five, or nine exposures to social conflict. Similarly, PRL was reduced in hamsters subjected to a mild footshock stressor. By contrast, adrenocorticotropin, another stress-responsive hormone, was elevated following exposure to each of these stressors. We also demonstrate that PRL release is inhibited by dopamine as it is in other species by showing that there is a dose-dependent increase in PRL release following treatment with the dopamine receptor blocker, domperidone.

Activity-wheel running attenuates suppression of natural killer cell activity after footshock

We studied whether voluntary running in an activity wheel moderates splenic natural killer (NK) cell cytotoxicity after footshock. Young (50-day) male Fischer 344 rats were randomly assigned to 1) sedentary (n = 16) or 2) activity-wheel (n = 16) groups that each received controllable or uncontrollable footshock on 2 consecutive days or 3) a sedentary home-cage control group (n = 8). Spleens and trunk blood were collected 30 min after the second footshock session. Cytotoxicity was determined by a standard 4-h 51Cr release assay. Percentages of OX6+ (B), OX8+ [T suppressor/cytotoxic (Ts/c)], W3/25+ (T helper), Thy-1.1 (Pan T cell marker), and 5C6+ (NK) cells were determined by flow cytometry. Plasma adrenocorticotropic hormone, corticosterone, and prolactin concentrations were measured by radioimmunoassay as modulators of NK activity. Percentage of specific lysis after footshock was approximately 52% of control values for sedentary animals compared with approximately 96% of control values for activity-wheel animals. The groups did not differ in percentages of NK or Ts/c cells. We conclude that voluntary activity-wheel running protects against the suppression of splenic NK activity induced by footshock. This protective effect of wheel running is not explained by an elevation in baseline NK activity; increased percentages of splenic NK or Ts/c cells; or plasma levels of adrenocorticotropic hormone, corticosterone, and prolactin.

Whole-body irradiation transiently diminishes the adrenocorticotropin response to recombinant human interleukin-1 alpha

Recombinant human interleukin-1 alpha (rhIL-1 alpha) has significant potential as a radioprotector and/or treatment for radiation-induced hematopoietic injury. Both IL-1 and whole-body ionizing irradiation acutely stimulate the hypothalamic-pituitary-adrenal axis. We therefore assessed the interaction of whole-body irradiation and rhIL-1 alpha in altering the functioning of the axis in mice. Specifically, we determined the adrenocorticotropin (ACTH) and corticosterone responses to rhIL-1 alpha administered just before and hours to days after whole-body or sham irradiation. Our results indicate that whole-body irradiation does not potentiate the rhIL-1 alpha-induced increase in ACTH levels at the doses used. In fact, the rhIL-1 alpha-induced increase in plasma ACTH is transiently impaired when the cytokine is administered 5 h after, but not 1 h before, exposure to whole-body irradiation. The ACTH response may be inhibited by elevated corticosterone levels after whole-body irradiation, or by other radiation-induced effects on the pituitary gland and hypothalamus.

Treadmill exercise training and estradiol differentially modulate hypothalamic-pituitary-adrenal cortical responses to acute running and immobilization

It is generally believed that physical fitness promotes health by attenuating responsiveness to other stressors. The experimental evidence for this belief is limited and does not extend to interactions between the hypothalamic-pituitary-adrenal cortical (HPA) and hypothalamic-pituitary-gonadal (HPG) axes. We tested the hypothesis that treadmill exercise training would lead to an estrogen-dependent hyporesponsiveness of the HPA axis that would generalize to immobilization stress. Ovariectomized female Sprague-Dawley rats (N = 74) that had been treadmill trained (TT) or sedentary for 6 weeks received intramuscular injections of estradiol benzoate (Eb) or sesame oil on each of 3 days prior to 15 min of acute treadmill running or immobilization. Plasma (adrenocorticotrophin) (ACTH), (corticosterone) (B) and (prolactin) (PRL) were determined from trunk blood by radioimmunoassay and compared in a 2 group (TT vs. sedentary)-by-2 treatment (Eb vs. oil)-by-2 acute stressor (running vs. immobilization) design. Home-cage (HC) animals (N = 24) provided baseline hormone levels. ACTH and B levels were elevated after stressors in animals treated with either Eb or oil compared to HC, but increases in PRL after stressors were dependent on Eb. Treadmill exercise training led to an attenuation of ACTH and prolactin to running, but the attenuation did not generalize to immobilization. In contrast, treadmill exercise training led to a hyperresponsiveness of ACTH. Treadmill training did not modulate prolactin responses to immobilization. The modulating effects of the estradiol treatment are consistent with an interaction of the HPA and HPG axes in response to stress.(ABSTRACT TRUNCATED AT 250 WORDS)

Systemically administered histamine H1 and H2 receptor antagonists do not block the ACTH response to bacterial lipopolysaccharide and interleukin-1

The administration of lipopolysaccharide (LPS) results in the activation of the hypothalamic-pituitary-adrenal axis (HPAA). We recently reported that the participation and interaction of LPS-induced proinflammatory cytokines were obligatory for the stimulation of adrenocorticotropic hormone (ACTH) release by LPS. LPS and LPS-derived cytokines also stimulate the release of histamine (HA). HA is a known hypothalamic neurotransmitter and activates the HPAA. Therefore, to elucidate the role of HA in LPS- and cytokine-induced ACTH release, we evaluated the effects of several HA H1 and H2 receptor antagonists on the ACTH response to LPS, recombinant human interleukin-1 alpha (rhIL-1 alpha) and HA in mice. Although all 3 of the H1 receptor antagonists administered (mepyramine (MEP), diphenhydramine (DPH) or promethazine (PMZ) were able to block the 10-min ACTH response to HA, only PMZ (a less selective H1 receptor antagonist than MEP) was able to reduce the LPS- or rhIL-1 alpha-induced ACTH responses. Ranitidine, a powerful and selective H2 receptor antagonist, had little effect on the LPS- and rhIL-1 alpha-induced ACTH responses, while metiamide (MET), a much less potent first-generation H2 receptor antagonist, substantially diminished ACTH release. The greater effectiveness of PMZ, in contrast to MEP or DPH, probably relates to the ability of phenothiazine derivatives to inhibit non-HA-dependent pathways involved in the stimulation of the HPAA by cytokines; the same may be true of MET.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased vasopressin content in parvocellular CRH neurosecretory system of Lewis rats

Rats possess stress-responsive, vasopressin (VP)-expressing and stress-nonresponsive, VP-deficient subpopulations of parvocellular corticotropin-releasing hormone (CRH) neurosecretory cells. Both subpopulations are activated by bacterial lipopolysaccharide (LPS) and cytokines. Lewis rats exhibit hyporesponsive hypothalamo-pituitary-adrenocortical axes (HPAAs). The Lewis CRH neurosecretory system has been reported to be defective in females and normal in males. We used post-embedding electron microscopic (EM) immunocytochemistry to study baseline levels and LPS-stimulated depletion of neurosecretory vesicles. Male Lewis rats possessed normal numbers of CRH+/VP- varicosities and low numbers of CRH+/VP+ varicosities, indicating abnormally low release of VP into portal blood. This defect contrasts with the reported increase in VP content and release in magnocellular neurosecretory cells in Lewis rats.

Synergistic roles of interleukin-6, interleukin-1, and tumor necrosis factor in the adrenocorticotropin response to bacterial lipopolysaccharide in vivo

Administration of lipopolysaccharide (LPS) results in activation of the hypothalamic-pituitary-adrenal axis. LPS induces the release of a number of proinflammatory cytokines, i.e. interleukin-1 (IL-1), IL-6, and tumor necrosis factor (TNF), which activate the hypothalamic-pituitary-adrenal axis as well and may mediate the effects of LPS. Variations in the kinetics of appearance of IL-1, TNF, and IL-6 after LPS challenge suggested that these cytokines may play different roles at different times. To elucidate the mutual dependence and contribution of individual cytokines in the course of LPS-induced ACTH release, we used blocking antibodies to IL-6, TNF, and the IL-1 receptor. Our results demonstrate that anti-IL-6 antibody abrogated ACTH induction throughout the course of the response both 2 and 4 h after LPS challenge. In contrast, anti-IL-1 receptor and anti-TNF antibody, given individually, blocked ACTH production at 4 h, but not at 2 h. Only combined administration of these two antibodies diminished, but did not eliminate, ACTH release at 2 h. This is the first demonstration that all three inflammatory cytokines are obligatory for LPS-induced elevation of plasma ACTH. In addition, these results suggest that IL-1, IL-6, and TNF play different roles in LPS-induced ACTH release.

Effects of interleukin-1 on the stress-responsive and -nonresponsive subtypes of corticotropin-releasing hormone neurosecretory axons

Administration of interleukin-1 (IL-1) induces increases in plasma ACTH and glucocorticoids. Numerous experiments have implicated the hypothalamic CRH neurosecretory system in these responses, but have failed to provide evidence for involvement of the ACTH secretagogue vasopressin (VP). The rat CRH neurosecretory system contains two types of cells: VP expressing and VP deficient. Hence, the above findings suggested that IL-1 may selectively activate the VP-deficient subtype of CRH neurosecretory cells. In this study we employed postembedding electron microscopic immunocytochemistry to directly assay IL-1-induced depletion of secretory vesicles from identified VP-expressing and VP-deficient CRH neurosecretory axons. IL-1-induced depletion of secretory vesicles from these axons was correlated with increases in plasma ACTH and decreases in plasma PRL. No dose of IL-1 was found that could selectively activate one subtype of CRH neurosecretory axons; at doses of 0.67 microgram/100 g and above for both IL-1 alpha and IL-1 beta, equal depletion of vesicles from the two subtypes was observed. Similar results were previously found after the injection of bacterial lipopolysaccharide, which induces the release of IL-1 from macrophages. The findings unequivocally establish for the first time that IL-1 activates hypothalamic CRH neurosecretory cells in the absence of surgical stress, anesthesia, disruption of the infundibular area, or administration of toxic drugs. In addition, these data clearly demonstrate that IL-1 induces the release of VP from neurosecretory axons in the portal capillary zone of the external zone of the median eminence. Previous studies have shown that the VP-deficient subtype of CRH neurosecretory axons is not strongly activated by several types of stress; therefore, activation of the system by inflammatory mediators involves mechanisms different from those mediating the stress response.

Effects of controllable vs. uncontrollable chronic stress on stress-responsive plasma hormones

We have previously reported effects of chronic stress on circadian rhythms of temperature, eating, and locomotor activity. These studies were conducted using an around-the-clock signalled intermittent footshock paradigm in which some rats have control over shock termination while other rats are yoked to the rats with control. Although this paradigm is stressful, as suggested by decreases in food intake and disrupted circadian rhythms, rats tolerate the paradigm well, continuing to eat, drink, gain weight, and groom. In the present studies, rats were sacrificed following 3 or 14 days of stress, and plasma was collected for hormonal assays. After 3 days of stress, plasma corticosterone and prolactin levels were elevated in both stress groups compared to controls; yoked rats had higher levels of corticosterone than rats in the group with control over shock termination, while prolactin levels in both stressed groups were similar. ACTH levels were similar in stressed and control rats. After 14 days of stress, ACTH and corticosterone levels in both stress groups were similar to control levels. Prolactin levels were elevated in the yoked experimental group compared to levels in control or controllable stress groups. These data support previous studies suggesting that control over stressors attenuates the effects of stress on physiology and demonstrate that two hormones with diverse biological effects are elevated by chronic stress.

Hormonal responses to fighting in hamsters: separation of physical and psychological causes

Male Syrian hamsters were paired and allowed to interact with a conspecific for 15 min a day for 4 days. On the fifth day, the animals were again paired, but they were kept physically separated by a mesh partition that allowed visual, olfactory, and auditory contact between the animals. Controls were placed with conspecifics on each of the 5 testing days, but the partition between them was never removed. Hamsters that were submissive on days 1-4 exhibited elevated plasma adrenocorticotropin-like immunoreactivity (ACTH-LI), beta-endorphin-like immunoreactivity (B-EP-LI), and cortisol on day 5 even though no fighting occurred on that day. Dominant hamsters did not differ from controls. These data support the hypothesis that there is an important psychological component to the pituitary-adrenocortical response in defeated hamsters.

Acute and repeated exposure to social conflict in male golden hamsters: increases in plasma POMC-peptides and cortisol and decreases in plasma testosterone

The purpose of the present study was to characterize the hormonal response of dominant and submissive male hamsters to acute and repeated exposure to social conflict. We found that submissive, but not dominant, males exhibited elevated plasma levels of adrenocorticotropin (ACTH), cortisol, and beta-endorphin (beta-EP) following one exposure to an agonistic encounter. After five exposures to a dominant opponent, submissive males showed smaller, but still significant, elevations in these plasma hormones. After nine exposures, submissive hamsters showed significant elevations only in plasma ACTH and beta-EP. Plasma testosterone was significantly suppressed in submissive males that fought nine times. We conclude that hamsters are a useful species with which to study the neuroendocrine correlates of social behavior.

Interleukin-1 and interleukin-6 act synergistically to stimulate the release of adrenocorticotropic hormone in vivo

Interleukin-1 (IL-1) and interleukin-6 (IL-6) share a number of biological functions. Because IL-1 induces IL-6 in vivo, the extent to which IL-6 mediates the effects of IL-1 has come under investigation. The stimulation of the hypothalamic-pituitary-adrenal axis by IL-1 and IL-6 is a critical component of the inflammatory response. The present study was designed to compare the effects of recombinant human IL-1 alpha (rhIL-1 alpha) and recombinant human IL-6 (rhIL-6) administered in combination and alone on the release of adrenocorticotropic hormone (ACTH) in mice. We have demonstrated that the administration of rhIL-6 alone does not duplicate the stimulatory effect of rhIL-1 alpha on ACTH release. On the other hand, suboptimal amounts of rhIL-1 alpha and rhIL-6 synergize to induce an early (30-60 min) ACTH response and produce a later (2-3 h) response that is similar to the one observed after rhIL-1 alpha is administered alone. These results suggest that the 2-3 h response to rhIL-1 alpha may be dependent on synergy with the endogenous IL-6 it induces systemically and in the central nervous system (including the hypothalamus and the pituitary gland).

Effects of soman on neuroendocrine and immune function

We have previously reported that plasma growth hormone (GH) and prolactin levels were markedly decreased in rats two weeks following a single dose (100 micrograms/kg, SC) of soman. We have now conducted additional experiments to attempt to determine whether neuroendocrine responses to physiological or pharmacological challenge are altered in rat survivors of soman exposure, and whether immune function, which can be affected by circulating hormones, is altered in the soman-exposed rats. In the present study, basal prolactin levels were not significantly lower in the soman-treated rats although prolactin increases in response to physiological or pharmacological challenge were attenuated. Also, basal growth hormone levels in soman survivors were similar to control levels in 2 of 3 experiments in the present report. In the third experiment, growth hormone levels were lower in soman-treated animals. Endocrine abnormalities appeared to be related to the severity of soman insult as assessed by changes in body weight following exposure. Both ACTH and prolactin responses to stress were impaired in a severely affected subpopulation of soman survivors. The thymus, an important immune organ, was decreased in weight in severely affected soman survivors, but other tests of immune function did not show differences between control and soman-exposed rats.

Effects of social conflict on POMC-derived peptides and glucocorticoids in male golden hamsters

The effects of fighting and footshock on circulating adrenocorticotropin-like immunoreactivity (ACTH-LI), cortisol, corticosterone, beta-endorphin-like immunoreactivity (beta-EP-LI), and beta-lipotropin-like immunoreactivity (beta-LPH-LI) were examined. In the first experiment, catheterized males were paired with large, ovariectomized females for 15 min. Submissive males exhibited significant increases in plasma ACTH-LI, cortisol, corticosterone, and beta-EP-LI. In the second experiment, two males were paired to determine whether the hormonal response in submissive animals was different from that in dominant hamsters. The pattern and magnitude of the hormonal response was also compared to that following a commonly used stressor-footshock. Footshock was associated with large increases in each of the plasma hormones measured. Submission, but not dominance, was associated with smaller, but still significant, increases in ACTH-LI, cortisol, beta-EP-LI and beta-LPH-LI. The data indicate that fighting is not a generalized stressor. "Losing," in particular, appears to be an example of a biologically relevant stressor.

Hyperresponsiveness of the rat neuroendocrine system due to repeated exposure to stress

Sequential exposure to stressors may elicit a period of endocrine hyperresponsiveness during which plasma hormone concentrations reach higher levels after repeated exposure to a stressor compared to levels after initial exposure. The present study was designed to further characterize hyperresponsiveness to repeated stress and determine if hyperresponsiveness is dependent upon repeated exposure to the same stressful stimuli. In Experiment 1, rats were stressed by inescapable tailshock, immobilization or exposure to shock chamber without shock for one, two, three, four or five consecutive days (15 min/day). In rats exposed to tailshock, corticosterone (CS) levels in plasma collected on days 2, 3, 4 and 5 were higher than CS levels following acute tailshock on day 1, demonstrating hyperresponsiveness to repeated tailshock. Hyperresponsiveness of CS secretion also occurred in groups of rats restrained for four or five days. No changes occurred in the CS response of animals repeatedly exposed to immobilization. Prolactin (PRL) levels were not affected by repeated exposure to the stressors. However, PRL values were different between the stress conditions and indicated that the order of stressor severity was tailshock greater than immobilization greater than exposure to shock chamber without shock. In Experiment 2, rats were exposed to either one or two consecutive days of tailshock or immobilization. Other rats were exposed to either tailshock or immobilization on the first day, then switched to the other stressor on the next day. Hyperresponsiveness to repeated tailshock, but not immobilization, was reflected in plasma levels of CS and adrenocorticotropic hormone (ACTH), but not PRL. Hyperresponsiveness of CS and ACTH secretion also was found in rats first stressed by immobilization then switched to tailshock, demonstrating that hyperresponsiveness is not dependent upon reexposure to familiar stressful stimuli. However, hyperresponsiveness did not occur in rats first exposed to tailshock then switched to immobilization. The data suggest that both immobilization and tailshock primed the organism to hyperrespond, but only the more severe stressor (tailshock) elicited hyperresponsiveness of the neuroendocrine system.

The influence of fitness on neuroendocrine responses to exhaustive treadmill exercise

Neuroendocrine and sympathoadrenal responses to exhaustive graded treadmill exercise were examined in 17 male subjects of varying degrees of fitness. The mean duration of exercise to exhaustion was 15.2 +/- 0.7 (+/- SE) min. Exercise duration was inversely correlated with baseline heart rate (P less than 0.05). Compared to standing baseline values, mean plasma norepinephrine and epinephrine levels increased 339% and 301%, respectively, in an integrated 2-min blood sample collected immediately after completion of exercise. Mean adrenocorticotrophic hormone (ACTH), beta-endorphin (beta-EP), beta-lipotropin (beta-LPH), and prolactin levels increased 282%, 720%, 372%, and 211%, respectively, in an integrated 4-min blood sample beginning 2 min after completion of exercise. Cortisol levels increased 183% in the sample collected 17-21 min after exercise. The magnitude of these neuroendocrine responses to exercise was similar among individuals at the same relative intensity of exhaustive exercise, regardless of the duration of exercise. The exercise-induced increases of the pro-opiomelanocortin (POMC)-derived peptides, ACTH, beta-EP, and beta-LPH, were highly correlated with each other (P values less than 0.001), and were correlated with prolactin increases, (P values less than 0.05). During a 20-min recovery period after exercise, changes in heart rate, ACTH, and beta-LPH levels were correlated with duration of exercise, (P less than 0.01, P less than 0.03, and P less than 0.03, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroendocrine responses to emotional stress: possible interactions between circulating factors and anterior pituitary hormone release

We have shown that a psychological stressor can elicit increases in plasma AVP levels in normal human subjects. Since AVP can enhance the release of ACTH, and the pituitary gland is outside the blood-brain barrier, AVP present in the general circulation might extend the time course of stress-induced, CRF-mediated release of ACTH from the anterior lobe. Since PRA is involved in the synthesis of angiotensin I, the precursor of AII, and AII is known to enhance CRF-mediated release of ACTH from pituitary cells and to stimulate release of AVP, it is possible that the increase in PRA also contributed to the release of AVP and ACTH in this study. Reports differ as to whether circulating catecholamines can release ACTH in vivo by direct action on the pituitary. Finally, it has been reported that beta-EP enhances the release of PRL, and inhibits release of AVP. Since the increase in beta-EP in the present study was quite robust, it might have extended the PRL release, and truncated the AVP response.

ACTH, prolactin, corticosterone and pituitary cyclic AMP responses to repeated stress

The present experiment was conducted to determine whether the plasma hormonal and pituitary cyclic AMP responses observed following a single exposure to an acute stressor would diminish following reexposures to the same stressor. Fifteen-min stress exposures (forced running) were separated by 45-min recovery periods. Separate groups of control and stressed animals were sacrificed before and after each of four 15-min stress periods and after each recovery period. The first exposure to 15 min of forced running raised plasma ACTH, corticosterone and pituitary cyclic AMP levels approximately 6-fold and more than tripled levels of plasma prolactin. Plasma ACTH and pituitary cyclic AMP responses to the second, third and fourth stress exposures were very similar to the responses to the first stress exposure, and levels of these substances returned to prestress levels during each 45-min recovery period. Plasma prolactin responses to the four stress sessions were somewhat variable but no significant trend among the responses was seen. Plasma prolactin levels also returned to prestress levels between stress exposures. Corticosterone levels were similar following each of the four stress sessions but levels remained elevated compared to prestress levels between stress exposures. These data suggest that pituitary responses to acute stress are rapid, that return to prestress levels is also rapid, with the exception of corticosterone, and that repeated responses of the same magnitude may be evoked when stressors are separated by short recovery periods.

Dexamethasone suppresses ACTH release without attenuating pituitary cyclic AMP response to stress in vivo

Dexamethasone, a synthetic glucocorticoid, has been shown to decrease basal and stress-elevated levels of the pituitary hormone ACTH. Glucocorticoids are known to bind to multiple sites within the brain and pituitary and it is not known which site(s) is most important in mediating the observed inhibition of ACTH release. At the level of the corticotroph, there is contradictory data from in vitro studies regarding whether dexamethasone acts proximal or distal to the formation of the cyclic AMP second messenger that has been shown to be involved in CRF-stimulated ACTH release. In the present report, we have examined the effects of dexamethasone pretreatment on stress-induced elevations in pituitary cyclic AMP and the release of ACTH in vivo. Acute stress (15 min of intermittent footshock) elevated levels of pituitary cyclic AMP and plasma ACTH consistent with previous studies. Dexamethasone administration (0.4 mg/kg 24 hr prior to sacrifice plus 0.2 mg/kg 2 hr prior to sacrifice) inhibited stress-induced elevations in plasma ACTH but did not affect pituitary cyclic AMP response to acute stress. These findings suggest that dexamethasone inhibits the release of ACTH via an action distal to the generation of cyclic AMP.

Psychologic stress increases plasma levels of prolactin, cortisol, and POMC-derived peptides in man

Stressful social interactions have been shown to elicit increases in heart rate as well as in plasma levels of epinephrine, norepinephrine, and cortisol in humans. We sought to determine whether a competitive oral examination would affect plasma levels of the pituitary hormones ACTH, beta-endorphin, beta-lipotrophic hormone, and prolactin in a group of healthy young males. Seven min after beginning the examination, heart rate increased 27% and plasma levels of ACTH, beta-endorphin, beta-lipotropic hormone and prolactin rose 59%, 79%, 42%, and 46%, respectively, compared to values shortly before the examination. These hormone values returned to initial levels after the subjects returned to the waiting room. Plasma cortisol changes were similar in direction to those of ACTH but occurred about 15 min later. The present study demonstrates that a stressful social interaction can elicit rapid increases in plasma levels of the proopiomelanocortin derived peptide hormones and prolactin in man.

Neuroendocrine correlates of sustained stress: the activity-stress paradigm

Rats sacrificed after 4 days in the activity-stress paradigm or after 4 days of food restriction had significantly elevated levels of plasma corticosterone as compared to control rats. The approximately 5 fold increase in corticosterone in the stressed treatment groups was consistently found in all experiments. ACTH levels were elevated in activity-stress and food-restricted groups in some experiments but these increases were not statistically significant. Prolactin levels were significantly elevated in food-restricted group rats as compared to controls or activity-stress group animals in one experiment but this finding was not repeated in further experiments. In a second series of experiments, rats from activity-stressed and food-restricted treatment groups and controls were exposed to an acute stressor for 15 min prior to sacrifice to assess the effects of prior sustained stress on hormonal responses to an acute stressor. Exposure to 15 min of immobilization or intermittent footshock immediately prior to sacrifice increased plasma levels of corticosterone, ACTH and prolactin in control, food-restricted and activity-stressed rats. Generally, hormonal responses to the acute stress were similar in all treatment groups. However, in two experiments where the resting levels of corticosterone were especially elevated in the activity-stress group, the acute stress-induced rise in corticosterone was less than that seen for the other two treatment groups. In another experiment, administration of dexamethasone suppressed acute stress-evoked levels of ACTH and corticosterone in control, activity-stressed and food-restricted rats. Thus, rats exposed to 4 days of sustained stress were found to have consistently elevated resting levels of corticosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term sequelae of soman exposure: hormonal rhythms two weeks postexposure to a single dose

Two weeks following a single exposure to either soman (100 micrograms/kg, sc) or saline, rats were sacrificed at 2-hr intervals over a 26-hr period. Trunk blood was collected and plasma was stored until assayed for corticosterone, prolactin, growth hormone, adrenocorticotropin, beta-endorphin, and beta-lipotropin. Rats surviving for 2 weeks following soman appeared well groomed and were gaining weight at a rate similar to saline-treated rats at the time of termination. Thus, they appeared to have recovered from the initial physiological effects of soman exposure. However, substantial differences in plasma levels of most hormones were seen in comparing soman- vs saline-treated rats. Levels of prolactin were suppressed at all time points in soman-treated rats. Growth hormone secretion was also suppressed and the normal episodic peaks of growth hormone were missing in soman-treated rats. Both soman- and saline-treated rats displayed circadian rhythms in levels of plasma corticosterone, but the usual late afternoon rise in plasma corticosterone levels was shifted to earlier time points in the soman-treated rats. Levels of beta-endorphin and beta-LPH were slightly but significantly suppressed in soman-treated rats at almost all time points. Levels of adrenocorticotropin were similar in control and soman-treated rats. The results of this experiment demonstrate that a single exposure to soman may have long-lasting effects on neuroendocrine function.

Paraventricular lesions abolish the stress-induced rise in pituitary cyclic adenosine monophosphate and attenuate the increases in plasma levels of proopiomelanocortin-derived peptides and prolactin

Acute exposure to footshock stress increased the pituitary level of cyclic adenosine monophosphate (AMP) in vivo and sharply increased plasma levels of adrenocorticotropic hormone, beta-endorphin and beta-lipotrophic hormone, as well as prolactin. Seven days after bilateral lesions of the paraventricular nucleus of the hypothalamus, the pituitary cyclic AMP response to stress was totally eliminated and the increases in plasma levels of these pituitary hormones were blunted. We conclude that while the pituitary hormonal responses to stress might be mediated by several neurohumoral factors, the stress-induced increases in pituitary levels of cyclic AMP in vivo are mediated largely via corticotropin-releasing factor, released from neurons which project from the paraventricular nucleus to the median eminence.

Effects of chronic stress on plasma corticosterone, ACTH and prolactin

Rats were placed in a stressful environment for 24 hr per day and levels of plasma hormones were measured after varying numbers of days in the environment. Rats were habituated to operant chambers placed in sound-attenuated enclosures. Food pellets were available by lever press on a FR1 schedule. After 3 days of habituation, rats in the "stressed" group were trained to pull a ceiling chain to avoid or escape shock. Following training, stress trials, consisting of a consecutive sequence of 5 sec each of a warning light, warning tone and 0.16, 0.32, 0.65, 1.3 and 2.6 mA of footshock, occurred approximately once per 5 min around-the-clock. For the first day, the sequence was terminated when the ceiling chain was pulled. On subsequent days, 90% of all shock presentations could be avoided or escaped by chain pull; the remaining 10% of trials were inescapable and the entire sequence was presented. Control rats lived in identical chambers without presentation of shock. Rats were sacrificed after 1, 2, 3, 4, 7 or 14 days in this environment and levels of plasma corticosterone, ACTH and prolactin were determined. Levels of plasma corticosterone were elevated during the first 7 days in the stressful environment, but returned to control values by day 14. Levels of plasma ACTH and prolactin were similar in stressed and control rats at all time points measured. These data suggest that stress-induced changes in glucocorticoids but not in ACTH or prolactin might mediate some of the physiological changes that occur as the result of chronic stress.

Pituitary cyclic AMP and plasma hormone responses to epinephrine administration in vivo

The present study was conducted to characterize the in vivo effects of epinephrine administration on levels of pituitary cyclic AMP and plasma hormones. Rats were injected with saline or epinephrine bitartrate (1 mg/kg lP) and sacrificed by decapitation 1, 5, 15, 30 or 60 min post-injection. Levels of pituitary cyclic AMP and plasma ACTH, beta-endorphin, beta-LPH, corticosterone and prolactin were determined by radioimmunoassays. The injection procedure itself was somewhat stressful as demonstrated by increased levels of plasma prolactin and ACTH 5 min following either saline or epinephrine injection. This "stress" response was rapid and short-lasting for the pituitary hormones. The response of the adrenal hormone, corticosterone, to saline injection was slower in onset and longer in duration. Pituitary cyclic AMP levels did not increase following saline injection. Epinephrine-injected animals displayed markedly elevated plasma levels of ACTH, beta-endorphin and beta-LPH at 15, 30 and 60 min as compared to control or saline-injected rats. In addition, levels of pituitary cyclic AMP were increased over 10 fold at these times. Levels of plasma prolactin, a stress-responsive hormone, were not significantly increased in epinephrine-injected animals as compared to saline-injected rats indicating that these later responses seem to be specific to epinephrine rather than to stress.

Comparison of the effects of CRF and stress on levels of pituitary cyclic AMP and plasma ACTH in vivo

We have previously reported that acute stress increases levels of rat pituitary cyclic AMP in vivo. The present study was conducted to test the hypothesis that stress-induced increases in pituitary cyclic AMP in vivo were mediated via CRF. We compared the effects of various stressors with the effects of CRF or epinephrine administration on pituitary cyclic AMP and plasma ACTH responses in vivo. Stressors, epinephrine or CRF increased levels of pituitary cyclic AMP. Pituitary cyclic AMP response to either immobilization or CRF was much greater at light onset than at lights off in rats maintained on a 12 hr light:12 hr dark lighting regimen. In rats with pituitary stalk transections, footshock did not increase levels of pituitary cyclic AMP, suggesting that some factor of central origin was required for this stress response. Exogenous CRF administration did increase levels of pituitary cyclic AMP in stalk-transected rats, while epinephrine increased levels in sham-operated but not in stalk-transected rats. Antisera to CRF markedly decreased pituitary cyclic AMP response to exogenous CRF administered 6 min following antisera and partially attenuated pituitary cyclic AMP response to forced running. Taken as a whole these data support a major role for CRF in the pituitary cyclic AMP response to stress.

Hemorrhagic hypotension increases plasma beta-endorphin concentrations in the nonhuman primate

The role which beta-endorphin plays in the pathogenesis of hemorrhagic hypotension is controversial. In the present experiment, 20 ml/kg of blood was bled from ten healthy male baboons (Papio anubis) over 60 min and then retransfused over the next 30 min. We found that the mean plasma beta-endorphin level increased 109% above baseline (p less than .05) within 15 min after starting hemorrhage, and rapidly returned to a baseline concentration with retransfusion. We conclude that in a primate species, circulating endogenous opioid peptide concentrations increase rapidly in response to sublethal hemorrhagic hypotension and normalize with restoration of the baseline intravascular volume. These findings support the concept that endogenous opioid peptides may mediate the hypotension of shock states.

Diurnal variation in neuroendocrine response to stress in rats: plasma ACTH, beta-endorphin, beta-LPH, corticosterone, prolactin and pituitary cyclic AMP responses

The effects of restraint stress applied at different times of the day on levels of five stress-responsive plasma hormones (ACTH, beta-endorphin, beta-LPH, corticosterone and prolactin) and pituitary cyclic AMP levels were assessed. Different groups of rats were subjected to 15 min of restraint stress at 2-hour intervals over a 24-hour period. Rats were sacrificed immediately upon removal from their home cage (controls) or immediately following restraint (stressed). The time of day of stress exposure markedly affected the stress responses measured. Generally, responses to stress applied at the beginning of the dark cycle (18:00) were less than those seen following stress applied at the beginning of the light cycle (06:00). Stress at 06:00 increased levels of pituitary cyclic AMP 10-fold, while stress applied at 18:00 did not significantly increase pituitary cyclic AMP levels. In stressed rats, high correlations were seen among levels of hormones derived from the common precursor, proopiomelanocortin (ACTH, beta-endorphin, beta-LPH) and between these hormones and levels of pituitary cyclic AMP. These findings support the hypothesis that pituitary cyclic AMP is involved in the stress-induced release or synthesis of the pituitary hormones ACTH, beta-endorphin, and beta-LPH.

Subsensitive pituitary cyclic AMP response to stress following adrenalectomy is not caused by loss of adrenal epinephrine

We have previously reported that various stressors acutely elevate levels of pituitary cyclic AMP in vivo and that this stress response is not seen in animals tested 7 or 30 days post-adrenalectomy. In this report we present data that demonstrate that the loss of the pituitary cyclic AMP stress response following adrenalectomy is not the result of the loss of stress-induced adrenal epinephrine release. These data show that (1) although administration of epinephrine to intact rats does not elevate levels of pituitary cyclic AMP, administration of epinephrine to adrenalectomized animals does not elevate pituitary cyclic AMP levels in vivo; (2) splanchnic denervation prevents stress-induced adrenal epinephrine release but does not abolish stress-induced increases in pituitary cyclic AMP; and (3) the time course of the developing subsensitive pituitary cyclic AMP response to stress following adrenalectomy is much slower (2 to 3 days) than the loss of circulating epinephrine.

Effects of 72 hour sleep deprivation on urinary cortisol and indices of metabolism

Cortisol, urea, glucose, electrolytes, and other compounds were measured in five consecutive 24 h urine collections during a 72 h sleep deprivation study in six young men. Urine was collected during a 24 h predeprivation day, 3 days of sleep deprivation, and a recovery day. Whereas urinary cortisol decreased only slightly, marked changes in other urinary constituents were observed. During sleep deprivation, urinary urea rose markedly, glucose decreased, and urinary electrolytes decreased. These data indicate that sleep deprivation under ad lib food and water conditions can cause disturbances in normal metabolism.

Adrenalectomy abolishes the stress-induced increase in pituitary cyclic AMP

We have previously demonstrated that various stressors increase pituitary cyclic AMP in vivo in the rat. In the course of studying the mechanisms mediating this response, we examined the effect of bilateral adrenalectomy on footshock-induced increases in pituitary cyclic AMP. In unoperated rats, intermittent footshock markedly increased pituitary levels of cyclic AMP and plasma levels of corticosterone and prolactin. Adrenalectomy completely abolished the stress-induced increase in pituitary cyclic AMP. The marked increase in plasma prolactin following footshock was not affected by adrenalectomy. Our results indicate that adrenal factors are involved in the stress-induced increase in pituitary cyclic AMP.

Graded footshock stress elevates pituitary cyclic AMP and plasma beta-endorphin, beta-LPH corticosterone and prolactin

Male rats were subjected to 15 min of various intensities of footshock current (0.0, 0.2, 0.4, 0.8, 1.6, 2.4, 3.2m A) on a variable interval schedule with an average intershock interval of 30 sec (30 shocks/15 min session). Each shock lasted 5 sec. Animals were sacrificed immediately after being removed from the shock box. Two similar studies were conducted. In the first experiment, rats were sacrificed by microwave irradiation and pituitary cyclic AMP levels were determined. In the second study, rats were decapitated and plasma hormones (prolactin, corticosterone, beta-endorphin, beta-LPH) were measured by radioimmunoassay. Although all biochemical indices of stress measured increased as shock intensity increased, some differences among the substrates measured were observed with respect to threshold intensity, range of proportional response and maximal response.

Small groups in programmed environments. Behavioral and biological interactions

This paper reviews a research program undertaken within a laboratory environment that was designed and constructed to support behavior analyses of individual and group performance effectiveness viewed conceptually within the context of a small-scale human microsociety. Summarized are previous research emphases and findings in relationship to (1) conditions that sustain group cohesion and productivity and that prevent social fragmentation and performance deterioration, (2) motivational effects resulting from the programmed consequences of individual and group performance requirements, and (3) behavioral and biological effects resulting from a change in group size. A more detailed description is presented of the results of a recent series of experiments that were conducted to assess performance and hormonal effects of replacing an established group participant with a novitiate member. The significance of these investigative undertakings is to be understood in terms of emergent environmental, motivational, and behavioral-biological principles having practical relevance for the establishment and maintenance of small-scale human social systems.

Effects of repeated stress on pituitary cyclic AMP, and plasma prolactin, corticosterone and growth hormone in male rats

The effects of five putative stressors (saline injection, cold exposure, forced running, immobilization, and footshock) on levels of pituitary cyclic AMP, plasma prolactin, corticosterone and growth hormone were examined. In naive rats exposed to 15 min of these stressors for the first time, running, immobilization and footshock increased levels of pituitary cyclic AMP, plasma corticosterone and prolactin and decreased growth hormone, typical of stress response in the rat. Cold exposure only increased corticosterone and saline injection did not affect any measured parameter. In rats chronically exposed to the same stressor (once a day for 15 min) for 10 days immediately prior to the experiment, an attenuated pituitary cyclic AMP and plasma prolactin response was seen upon application of 15 min of that stressor on the day of the experiment, compared to the responses observed in the naive rats.

Comparison of stress response in male and female rats: pituitary cyclic AMP and plasma prolactin, growth hormone and corticosterone

Three potent stressors (forced running, immobilization, and footshock) were found to increase levels of cyclic AMP in the pituitaries of both female and male rats. The pituitary cyclic AMP response in females was generally similar to that observed in males. The tested stressors elevated both plasma corticosterone and prolactin and decreased plasma growth hormone. Plasma corticosterone rose more rapidly in females than in males following stress. Control growth hormone levels were higher in male rats. There was no clear cause and effect relationship between elevations of pituitary cyclic AMP and changes in plasma levels of prolactin, corticosterone, and growth hormone.

Specific hormonal and neurochemical responses to different stressors

The neuroendocrine and neurochemical responses of rats to 5 min of cold exposure versus 5 min of forced immobilization were determined and compared. We found that plasma hormones and brain neurochemical systems responded differently to the two different stressors. Plasma prolactin levels were elevated over 10-fold in the immolilized group, while rising only 2-fold in the cold stress group. Levels of corticosterone were significantly increased and growth hormone levels were decreased in both stressed groups as compared to controls. Levels of cyclic GMP were markedly elevated in 11 brain regions following cold exposure. Surprisingly, no elevation of cyclic GMP was found after forced immobilization. Cyclic AMP, norepinephrine, and dopamine levels throughout the 17 regions of brain examined showed no significant response to 5 min of either stressor. Lesions of the ventral medial tegmental area did not affect the cyclic GMP or neuroendocrine responses to cold stress. Lesion of the nucleus locus ceruleus did not affect the cyclic GMP response but significantly reduced growth hormone levels in the cold-stressed rats.

A prospective study of corticosteroid and catecholamine levels in relation to viral respiratory illness

Urinary 17-OHCS, epinephrine and norepinephrine levels were studied for one week before and one week after the onset of acute, severe Adenovirus 4 respiratory illness in 12 Army recruits during Basic Combat Training. During the pre-illness period, a tendency was frequently noted for all three hormone levels to show "spiking" elevations two to four days before illness onset. There was also a tendency for 17-OHCS levels to rise on the day before fever onset. The possible relationship of these pre-illness hormonal changes to stressful experiences and, in turn, to altered host resistance to infectious illness is discussed. Following onset of respiratory illness, 17-OHCS, epinephrine and norepinephrine levels all showed about 60 percent increases over the early pre-illness period baseline value. Elevations of these hormones persisted for about four to five days, roughly in correlation with fever duration, with only slight differences in configuration and timing of curves from one hormone to the next. The problem of evaluating which of several independent variables operating concurrently during infectious illness may be responsible for stimulating the final common neuroendocrine pathways is discussed.