Stress-induced changes in cholecystokinin and substance P concentrations in discrete regions of the rat hypothalamus.

The effects of acute stress exposure upon cholecystokinin (CCK) and substance P (SP) concentrations in discrete hypothalamic regions of the adult male rat brain were studied. Animals were exposed to foot shock stress for periods of 2, 4, 10, 30 or 60 min duration; immediately afterwards they were decapitated; brains were frozen and subsequently microdissected. CCK and SP concentrations were assayed by a specific RIA, as were serum levels of ACTH, corticosterone, PRL, GH, LH and testosterone. Stress had no effect upon SP concentrations in the anterior or posterior parts of the arcuate nucleus (ARC), but led to elevated CCK levels in the posterior ARC following 60 min of exposure. In both the ventromedial and dorsomedial hypothalamic areas, stress induced depletions of both neuropeptides. In the anterior (but not the posterior) portions of the lateral hypothalamic area, CCK and SP concentrations were reduced by stress exposure. These studies demonstrate that discrete hypothalamic CCK and SP neuronal systems are responsive to stress. This suggests that endogenous hypothalamic CCK and SP participate, along with other neurotransmitters/neuromodulators, in the integrated hypothalamic stress response, and mediate stress-neuroendocrine interactions.

Cholecystokinin and substance P concentrations in discrete areas of the rat brain: sex differences.

Cholecystokinin (CCK) and substance P (SP) concentrations were measured in discrete brain areas of adult male and diestrous female rats. Significant sex differences in CCK concentration were found in the ventromedial hypothalamic area, medial and lateral preoptic area, nucleus of the diagonal band of Broca, ventral tegmental area, entorhinal and in several cortical areas. No sex differences in SP concentrations were observed in any of these areas. However, significant sex differences in SP concentration were found in the amygdala. These data indicate that the CCK and to some extent the SP systems are sexually differentiated in certain brain areas.

Acute continuous exposure to cigarette smoke produces discrete changes in cholecystokinin and substance P levels in the hypothalamus and preoptic area of the male rat.

By means of a Walton Horizontal Smoking Machine, male rats were exposed to the smoke from I-4 cigarettes burned in a continuous fashion. Cholecystokinin (CCK) and substance P levels (determined by means of radio-immunoassay) were measured in discrete hypothalamic and preoptic regions. Acute continuous exposure to cigarette smoke induced increases in CCK levels in the paraventricular hypothalamic region as well as decreases in CCK levels in the median eminence. Furthermore, this treatment resulted in decreased CCK and substance P levels in the medial preoptic region. The results have been interpreted to indicate that CCK and substance P containing neuronal systems can be regulated by cholinergic nicotine-like receptors.

The effect of delta 1tetrahydrocannabinol on luteinizing hormone release in castrated and hypothalamic deafferented male rats.

delta 1Tetrahydrocannabinol (THC) acutely suppresses tonic serum luteinizing hormone (LH) and prolactin levels in adult male rats. The exact site of its action has not been identified. We have performed complete hypothalamic deafferentation (CHD), which disrupts the medial basal hypothalamus (MBH) from the rest of the CNS, but did not abolish the ability of THC to suppress hypothalamic-pituitary responses in gonadectomized male rats. This was shown by the equal reduction in serum levels of LH and prolactin in non-deafferented (ND) and CHD animals. These results indicate that THC is able to act inside the MBH and that the MBH-pituitary axis remains responsive to its inhibitory effect despite interruption of the neural connections between the MBH and extrahypothalamic areas. However, the corticotropin releasing factor neurons in the MBH appear functionally impaired as a result of the transection and become unresponsive to the normally produced THC stimulation. Different patterns of action seem to govern the various hypophyseal hormones controlled by the hypothalamus, suggesting that the release of LH releasing hormone and prolactin inhibiting factor might be maintained by the activity of neurons surviving inside the island.

Rapid and discrete changes in hypothalamic catecholamine nerve terminal systems induced by audiogenic stress, and their modulation by nicotine-relationship to neuroendocrine function.

The effects of acute audiogenic stress, with or without simultaneous nicotine treatment (0.3 mg/kg i.v.), on catecholamine levels in discrete dopamine and noradrenaline nerve terminal systems of the hypothalamus, and on the secretion of adenohypophyseal hormones and of corticosterone, were studied using quantitative microfluorometric evaluations of catecholamine stores and radioimmunoassays for the determination of serum hormone levels. Audiogenic stress and nicotine induced very rapid and discrete decreases in noradrenaline levels in the subependymal layer (SEL), in the parvocellular part of nuc. paraventricularis hypothalamic (PA FP) and in the posterior periventricular hypothalamic systems, (PV II); the decreases were apparent 2 min following the onset of treatment. Increases of arterial blood pressure were observed after nicotine treatment but could not have been a major factor in producing the changes in catecholamine levels. These changes in NA levels may be related to the nicotine- and stress-induced increases of ACTH (SEL and PA FP) and prolactin secretion (PV II) found in the present experiments. Stress enhanced the rapid but variable increase in vasopressin secretion induced by nicotine, suggesting one possible mechanism by which stress combined with smoking can contribute to the development of increased arterial blood pressure and finally to sustained hypertension.

Immobilization stress-induced changes in discrete hypothalamic catecholamine levels and turnover, their modulation by nicotine and relationship to neuroendocrine function.

Immobilization stress (1 h) induced discrete reductions in noradrenaline (NA) levels in the posterior periventricular hypothalamic region and in the paraventricular hypothalamic nucleus, and a decrease in dopamine (DA) turnover in the medial palisade zone (MPZ) of the median eminence, but failed to induce regional increases of hypothalamic NA turnover. Stress also stimulated the secretion of ACTH, corticosterone and prolactin, while vasopressin, LH and FSH serum levels were unaffected. The stress induced reduction of DA turnover in MPZ may mediate the stress induced increase of prolactin secretion. Nicotine (0.3 mg/kg, s.c., 1 h) did not by itself significantly influence catecholamine (CA) turnover in the various CA nerve terminal systems analyzed in the hypothalamus, but reduced NA levels in the subependymal layer (SEL) of the median eminence. Nicotine administration did not affect the serum levels of any of the hormones evaluated. Nicotine counteracted to a minor degree the immobilization stress-induced reduction in NA levels, and also the stress-induced secretion of ACTH, but not of prolactin suggesting the involvement of noradrenergic mechanisms possibly in the paraventricular nucleus in the nicotine modulation of stress induced increases of ACTH secretion. The nicotine-induced reduction of NA levels in SEL was blocked by stress as well as the tendency for nicotine induced increases of dopamine (DA) turnover in the medial and lateral palisade zones of the median eminence indicating opposing influences of immobilization stress and nicotine on at least some hypothalamic CA systems.

Effects of naloxone on basal and stress-induced prolactin secretion, in intact, hypothalamic deafferentated, adrenalectomized, and dexamethasone-pretreated male rats.

The effects of naloxone (Na1) on basal and stress-induced PRL secretion were investigated in intact (N) adult male rats, as were its effects in rats with complete hypothalamic deafferentation (CHD), in adrenalectomized (adrenX) rats, and in rats pretreated with dexamethasone (dex). Forty-five minutes subsequent to Na1 administration (5 mg/kg, BW, IP) basal serum levels of PRL were reduced by approximately 25% (p less than 0.05), in both N and CHD groups. PRL secretory responses to acute exposure to both photic and acoustic stress wee markedly attenuated in Na1-injected, as compared to vehicle-injected animals. Basal serum PRL concentrations were elevated by 40% in adrenX rats (p less than 0.05), as reduced by 25% (p less than 0.05) in dex-treated rats, as compared to controls. In both these experimental groups, Na1 administration caused significant reductions in serum PRL. This study demonstrates that stress-induced, as well as basal PRL secretion, is attenuated by Na1, and points to a hypothalamic site of action in this regard. Furthermore, these Na1 effects are independent of glucocorticoid interactions with the CNS.

Adrenocortical responses following limbic stimulation in rats with hypothalamic deafferentations.

In view of the involvement of limbic structures in adrenocortical regulation, their afferent projections to the mediobasal hypothalamus were investigated. Electrical stimulation via chronically implanted electrodes in the dorsal hippocampus, the medial septal nuclei, the basolateral amygdala or the mesencephalic reticular formation all elicited a significant increment in plasma corticosterone levels in adult male rats under pentobarbital anesthesia. Complete or anterior hypothalamic deafferentation blocked these adrenocortical responses completely, and posterior hypothalamic deafferentation attenuated them to a marked extent. In animals with bilateral medial forebrain bundle lesions, hippocampal stimulation had no effect upon plasma corticosterone levels. These studies demonstrate that extrahypothalamic effects upon adrenocortical secretion are neurally mediated, and that the integrity of neural pathways impinging upon the mediobasal hypothalamus from both the rostral and the caudal directions is essential to these effects.

ACTH and corticosterone secretion following insulin in intact and in variously hypothalamic deafferented male rats.

Adult male rats, intact (N) or with posterior (PHD), anterior (AHD) or complete (CHD) hypothalamic deafferentations, were injected with either 0.04 or 0.2 mu/100 g b.wt. of insulin. Forty-five minutes later they were decapitated and trunk blood was collected for serum glucose, adrenocorticotropic hormone (ACTH) and corticosterone (CS) determinations. The high insulin dose reduced serum glucose by approximately 50% and elicited a marked increase in serum ACTH and CS levels in all groups of animals as compared to the vehicle-treated group. In contrast, the low insulin dose which reduced serum glucose approximately 30% elicited a significant adrenocortical response only in the intact or PHD groups but failed to stimulate this response in animals with CHD or AHD. These results demonstrate that (1) CNS sites, outside the medial basal hypothalamus (MBH), mediate the adrenocortical response during the initial stages of hypoglycemia by a neural pathway impinging upon the CRF neurons from the rostral direction, and (2) the adrenocortical response during the more enhanced hypoglycemia stages is mediated by a systemic mechanism which acts directly on the MBH.

Corticotrophin and corticosterone secretion following delta 1-Tetrahydrocannabinol, in intact and in hypothalamic deafferentated male rats.

Adult male rats, either intact (N) or bearing complete hypothalamic deafferentations (CHD), were injected with delta 1-tetrahydrocannabinol (THC: 5 mg/kg BW, IP). Forty-five minutes later, they were decapitated and trunk blood was collected for serum ACTH and corticosterone (CS) determinations. In the N animals, serum levels of both ACTH and CS were markedly elevated in the drug-treated, as compared to the vehicle-treated group (approximately 8-fold and 10-fold, respectively). In CHD rats, on the contrary, THC administration did not significantly alter serum concentrations of either ACTH or CS. These results demonstrate (1) that acute treatment with THC stimulates the secretion of ACTH as well as of CS; and (2) that extrahypothalamic sites and/or neural pathways mediate this effect.

Site and mode of action of indomethacin on the hypothalamo-hypophyseal-adrenal axis: a temporal study in intact, hypothalamic-deafferentated, and hypothalamic-lesioned male rats.

Adult male rats were given single sc injections of indomethacin (IM; 5 mg/100 g BW) and sacrificed 2-24 h later. IM effects upon serum ACTH and corticosterone (CS) levels, rectal temperature, and hypothalamic and adenohypophyseal prostaglandin E2 (PGE2) and cAMP contents were observed. Rectal temperature was normal for 5-10 h post injection and later decreased by approximately 2.5 C. Both hypothalamic and adenohypophyseal PGE2 concentrations were reduced from 2-24 h after IM administration; no changes in cAMP content were observed. Serum ACTH and CS levels were elevated 4- and 6-fold, respectively, over the entire period observed. In animals with complete hypothalamic deafferentations, the ACTH and CS responses to IM were as marked as they were in intact rats. In rats with hypothalamic lesions in which the ACTH and CS responses to ether stress were attenuated, marked ACTH and CS secretory responses to IM were seen. It is concluded: 1) that the main site of action of systemically administered IM on the hypothalamohypophyseal-adrenal axis, is within the adenohypophysis; 2) that this effect is mediated by PGE2, and cAMP is not involved; and 3) that central nervous system PGs may be involved in the maintenance of basal body temperature in the rat.

Neural pathways mediating basal and stress-induced secretion of luteinizing hormone, follicle-stimulating hormone, and testosterone in the rat.

Adult male rats, intact or bearing complete, anterior, or posterior hypothalamic deafferentations (CHD, AHD, or PHD, respectively) or bilateral medial forebrain bundle (MFB) lesions, were acutely exposed to visual, audiogenic, or thermal stress. Two to 30 min after stress onset, the rats were decapitated, and trunk blood was collected from serum LH, FSH, and testosterone (T) determinations. While basal serum LH levels were found to be normal in all experimental groups, FSH levels were reduced in CHD and AHD rats, and serum T concentrations were found to be 3-fold greater than control values in the AHD group. In intact animals, exposure to all modalities caused significant elevations in serum levels of both LH and T, with no effect on FSH secretion. In the CHD and AHD groups, the LH and T responses were eliminated, with the exception of the T response to heat exposure, which persisted in CHD animals. In the PHD group, the LH and T responses persisted and were, in fact, potentiated. Bilateral medial forebrain bundle lesions inhibited the LH and T responses to audiogenic and thermal, but not to visual, stimulation. These data demonstrate that 1) basal FHS, but not LH, secretion is dependent upon extrahypothalamic afferents to the medial basal hypothalamus; 2) acute neurogenic stress stimulates LH and T, but not FSH, secretion; and 3) central nervous system sites, rostral to the medial basal hypothalamus, mediate the stress-induced elevations in LH release.

Effects of sciatic nerve stimulation on ACTH secretion, in intact and in variously hypothalamic deafferentated male rats.

Serum ACTH levels were determined by RIA following sciatic nerve stimulation, in intact rats and in rats bearing anterior (AHD), posterior (PHD) or complete (CHD) hypothalamic deafferentations. In both N and PHD groups, serum ACTH concentrations were markedly elevated following stimulation. In CHD animals this response was completely eliminated, and in the AHD group only a very slight and marginally significant increase in serum ACTH occurred, upon stimulation. These results demonstrate that the increased corticosterone secretion which occurs following sciatic nerve stimulation is due to elevated blood levels of ACTH, and confirm that this somatosensory stimulation impinges upon the hypothalamus from the rostral directions.

Neural pathways mediating the prolactin secretory response to acute neurogenic stress in the male rat.

Adult male rats, intact (N) or bearing complete, anterior or posterior hypothalamic deafferentations (CHD, AHD or PHD, respectively), or bilateral medial forebrain bundle (MFB) lesions, were acutely exposed to visual or audiogenic stimulation. At 2, 4, 10 or 30 min following stress onset the animals were decapitated and trunk blood was collected for prolactin (PRL) determinations. Basal serum PRL levels were found to be similar in all groups. In N animals, exposure to both modalities resulted in rapid and marked PRL secretory responses. These responses were totally abolished in the CDH group. In AHD rats, no significant elevation in serum PRL concentration was found upon stress exposure. In PHD animals, the PRL secretory responses were only slightly attenuated when compared with the N group. In MFB-lesioned rats, a marked elevation in serum PRL concentrations was recorded following visual stimulation; contrary thereto, the PRL secretory response following audiogenic stress was markedly attenuated. These data (1) describe the temporal aspects of the PRL secretory response to acute exposure to neurogenic stresses in the male rat, and (2) demonstrate that these PRL responses are elicited via a neural pathway impinging upon the medial basal hypothalamus from the rostral direction.

Effects of systemically administered indomethacin on basal and stress-induced ACTH and corticosterone secretion in the male rat.

The effects of the prostaglandin (PG) synthetase inhibitor indomethacin (IM) on basal and stress-induced activity of the hypothalamo-hypophyseal-adrenal (HHA) axis were investigated. IM was systemically administered to adult male rats in a single injection (5 mg/100 g BW s.c.). The animals were sacrificed 24 h later, either under basal conditions, or following 30 min exposure to environmental temperature of 36 degrees C. Serum ACTH and corticosterone (CS) were determined by RIA and CBG, respectively, and hypothalamic and adenohypophyseal PGE2 and total PGE concentrations were estimated by RIA. IM treatment resulted in elevated basal levels of both hormones. Heat exposure led to elevated serum ACTH and CS concentrations in both vehicle- and IM-treated groups, with the ACTH heat response in IM-treated animals being greater than that observed in controls. PGE2, and PGE1 plus PGE2 concentrations were markedly reduced in both hypothalamic and adenohypophyseal tissues, following IM treatment. This study demonstrates that simultaneous reductions in hypothalamic and adenohypophyseal PG concentrations are compatible with hyperactivity of the HHA axis.

PRL and ACTH secretion following acute heat exposure, in intact and in hypothalamic deafferentated male rats.

Adult male rats, intact or bearing complete, anterior or posterior hypothalamic deafferentiations (CHD, AHD AND PHD, respectively) were acutely exposed to environmental temperature of 36 degrees C, and serum PRL and ACTH concentrations were determined by RIA. In intact animals, heat exposure resulted in elevated serum PRL and ACTH levels. None of the deafferentations affected basal serum PRL concentrations, whereas those of ACTH were elevated in both CHD and AHD, but not in PHD groups, as compared to intact controls. The PRL heat response was completely absent in CHD, attenuated in AHD, and delayed in PHD animals, and the ACTH heat response was absent in all three groups. These results demonstrate (1) that acute exposure to elevated environmental temperature stimulates secretion of PRL and of ACTH; (2) that this stimulation is carried out by diverse neural pathways; and, (3) that hypothalamic modulation of the secretion of PRL and ACTH is effected by independent mechanisms.

TSH secretion following acute heat exposure, in intact and in hypothalamic deafferentated male rats.

Male rats, intact (N) or with complete, anterior, or posterior hypothalamic deafferentations (CHD, AHD, or PHD, respectively), were acutely exposed to an environmental temperature of 36 degrees C, and serum TSH concentrations were determined by RIA. In intact animals, 30 min of exposure to elevated environmental temperature resulted in decreased serum TSH levels. In both CHD and AHD animals, basal serum TSH concentrations were reduced, and heat exposure produced further decreases. In the PHD group, no significant difference in resting serum TSH concentrations was observed, as compared to intacts. Exposure of these animals to 36 degrees C was followed by a reduction in this parameter, similar to that in intact rats. Exposure of intact animals to 3 nonthermal stress modalities produced no changes in serum TSH concentrations. These experiments demonstrate (1) that the hypothalamo-hypophyseal-thyroid axis responds specifically to heat exposure; (2) that extrahypothalamic centers which innervate the medial basal hypothalamus from the rostral direction maintain basal activity of the axis; and (3) that humoral factors, possibly extrahypothalamic thyrotrophin-releasing hormone carried to the median eminence via the CSF, may also mediate both basal and heat-induced secretory activity of the thyrotrophs.

cAMP in temperature- and ADH-regulating centers after thermal stress.

cAMP concentrations in temperature-regulating sites of the brain and plasma osmolality were measured after exposure of male rats to 36 degrees C and 37-42% rh. for 10, 20, or 30 min. Plasma osmolality was affected by none of the heat exposures. In both the preoptic area and the posterior medial hypothalamus, cAMP concentrations were increased compared to controls, after 10, 20 and 30 min of heat exposure. In the supraoptic-paraventricular nuclei, neither 10 nor 20 min of exposure resulted in augmented cAMP concentrations; but after 30 min of heat exposure, cAMP levels in these nuclei were significantly greater than in controls. Neurohypophysial cAMP concentrations were increased after both 10 and 30 min of exposure. Cerebral cortical cAMP concentrations were not affected by thermal stress. It is concluded that cAMP is involved in the neural mechanisms which are brought into play to regulate body temperature during acute heat exposure. The significance of this involvement and its relation to the overall temperature-regulating mechanisms of the body are discussed.