The function of the adrenocortical axis in permanent middle cerebral artery occlusion: effect of glucocorticoids on the neurological outcome.

We characterized the effect of acute ischemic stroke on the activation of the hypothalamic-pituitary-adrenal (HPA) axis and evaluated the role of glucocorticoids (GC) in the clinical outcome following ischemic stroke. Male spontaneous hypertensive rats underwent permanent middle cerebral artery occlusion (PMCAO) and developed a cortical infarct. At 4h post-PMCAO or sham operation, serum levels of ACTH and corticosterone (CS) were elevated 5 and 4 fold respectively as compared to controls and then returned to basal levels at 24h post surgery. In these experimental groups we found also a significant depletion of median eminence (ME)-CRH(41). In adrenalectomized (Adx) rats that underwent PMCAO the degree of motor disability and infarct volume was similar to that of intact rats. Administration of dexamethasone (Dex) to Adx-PMCAO rats significantly improved the motor disability and decreased the infarct volume. However, in sham-Adx with PMCAO, Dex had no effect on these two parameters. In rats with PMCAO or sham-PMCAO, brain production of PGE(2) was significantly increased. This effect was further enhanced in Adx-PMCAO rats and significantly inhibited by Dex. In conclusion, activation of the HPA axis following PMCAO is due to stress induced by surgery. This activation is mediated by hypothalamic CRH(41). Absence of endogenous GC or administration of Dex in naïve rats does not alter motor and pathological parameters in the acute stage following PMCAO. In contrast, administration of Dex significantly improved the outcome following cerebral ischemia in Adx rats which may be due to increased glucocorticoid receptors. Brain production of PGE(2) does not play an important role in the pathophysiology of the acute phase of cerebral ischemia.

Diverse effects of stress and additional adrenocorticotropic hormone on digitalis-like compounds in normal and nude mice.

Digitalis-like compounds (DLC) are steroidal hormones that are synthesized in, and released from, the adrenal gland, whose regulation may be directed by the hypothalamic-pituitary-adrenal (HPA) axis. Increasing evidence points to antitumour properties of these compounds and we hypothesized that the establishment of tumours in athymic nude mice may be facilitated by an abnormal synthesis or secretion of DLC. To explore this hypothesis, DLC concentrations were determined in the plasma, and in adrenal and hypothalamic tissues of nude compared to normal mice under basal conditions, and 30 min after a stress stimulus (i.p. injection of 100 micro l saline) with or without additional adrenocorticotropic hormone (ACTH) 1 micro g/per animal. Simultaneously, plasma corticosterone and serum adrenocorticotropic hormone (ACTH) concentrations were analysed. The basal DLC concentrations were similar in the plasma and the hypothalamus of both strains, whereas the basal adrenal DLC concentration was significantly lower in the nude mice compared to normal mice. The stress stimulus induced in normal mice a significant increase in DLC concentrations in the adrenal gland, the plasma and the hypothalamus. However, in nude mice, it caused an increase only in the adrenal gland and the hypothalamus, whereas the plasma DLC concentration was not affected. In both strains, the administration of ACTH in addition to injection stress did not provoke a further increase in DLC concentrations while inducing a significant increase in plasma corticosterone concentration. Regardless of the applied stimulus, the nude mice expressed significant lower DLC concentrations in the adrenal gland and the plasma compared to normal mice. The low basal adrenal DLC concentration in nude mice and their impaired DLC response towards stress- and ACTH stimulation both support an involvement of DLC in tumorigenesis.

Electrical stimulation of the dorsal hippocampus caused a long lasting inhibition of ACTH and adrenocortical responses to photic stimuli in freely moving rats.

The effect of a single train of electrical hippocampal stimulation on ACTH and corticosterone (CS) responses to subsequent photic stimulation was studied in freely moving male rats. The hippocampal stimulation inhibited the stress-induced rise [corrected] in serum CS levels up to 150 h when compared to sham stimulated animals. This effect did not exist at 300 h following stimulation. This sustained hippocampal inhibitory effect on the adrenocortical response, which was not reported previously, was partially abolished by section of the dorsal fornix. The present data demonstrate that dorsal hippocampal stimulation has a long lasting inhibitory effect on pituitary adrenocortical secretion following neural stimuli and this is partially mediated by the dorsal fornix.

Cytokines inhibit sexual behavior in female rats: II. Prostaglandins mediate the suppressive effects of interleukin-1beta.

The proinflammatory cytokine interleukin-1 (IL-1) induces several behavioral alterations that are characteristic of illness, such as anorexia and reduced locomotor and social activity. We have recently demonstrated that IL-1 inhibits sexual activity, motivation and attractivity in female, but not in male rats following either central or peripheral administration. In the present study we examined the involvement of prostaglandin (PG) synthesis in mediating IL-1-induced suppression of female sexual behavior. Administration of the cyclooxygenase blockers indomethacin or ibuprofen completely prevented IL-1-induced suppression of female sexual behavior, including the reduction in proceptive behavior, the lordosis response to a male's mounts, and the preference for a sexually active partner. In a subsequent study, ex-vivo release of hypothalamic PGE2 and the secretion of corticosterone (CS) were measured in males and estrous females following IL-1 administration. At the same time and dose of IL-1 administration that significantly reduced sexual behavior in female but not male rats, IL-1 produced a significant increase in PGE2 release in female, but not in male rats. In contrast, IL-1 induced a significant elevation of serum CS levels in males but not in females. These findings suggest that PG synthesis is involved in mediating the effects of IL-1 on female sexual behavior. Furthermore, differential secretion of PGs and CS may underlie the gender difference in the effects of IL-1 on sexual behavior.

The excitatory effects of the amygdala on hypothalamo-pituitary-adrenocortical responses are mediated by hypothalamic norepinephrine, serotonin, and CRF-41.

The hypothalamic neural mechanisms that are involved in the facilitatory effects of the amygdala (AMG) on the hypothalamo-pituitary-adrenocortical (HPA) axis have been investigated in rats. Stimulation of the central AMG nucleus caused a depletion of hypothalamic CRF-41, presumably due to its release into the portal circulation, and a subsequent rise in plasma ACTH and corticosterone (CS) levels. These effects were inhibited in rats in which hypothalamic norepinephrine (NE) or serotonin (5-HT) was depleted by catecholamine or serotonin neurotoxins, respectively. Furthermore, the administration of prazosin, an alpha1, but not of atenolol, which is a beta-blocker, as well as administration of the 5-HT2 blocker ketanserin inhibited the ACTH and CS responses to AMG stimulation. These results indicate that the facilitatory effects of the AMG on the HPA axis are mediated by hypothalamic NE via alpha1 receptors and by 5-HT via 5-HT2 receptors, as well as by CRF-41 in the paraventricular nucleus.

Effects of bacterial endotoxin on the glucocorticoid feedback regulation of adrenocortical response to stress.

Previous studies have shown that LPS and cytokines modulate the binding of glucocorticoids (GCs) in the CNS, and therefore may affect the negative feedback exerted by GCs. In this study, we investigated the effect of lipopolysaccharide (LPS) on the inhibitory action of GCs upon the adrenocortical response to a neural stressful stimulus. Male rats were treated with either LPS (50 micrograms/kg) or saline for 5 consecutive days. Two days later, the LPS- and saline-treated rats were injected intraperitoneally with either dexamethasone (20 micrograms/kg) or saline and sacrificed 3.5 h later, after exposure to acute stressful photic stimulation. In saline-pretreated rats, photic stimulation caused a 5-fold increase in serum corticosterone levels compared to basal levels, and pretreatment with dexamethasone completely abolished this response. In LPS-pretreated rats, corticosterone levels following photic stimulation increased 20-fold, and dexamethasone was ineffective. Additional experiments were conducted to examine whether the impairment in the negative feedback was specific to the prolonged LPS treatment, rather than to LPS-induced hypersecretion of GCs. In groups of rats which were exposed to either daily acoustic stress or daily administration of corticosterone (5 mg, twice daily) for 5 days, the pattern of corticosterone secretion mimicked the corticosterone secretion induced by LPS. In these groups, the adrenocortical response to acute photic stimulation and the effect of dexamethasone were similar to saline-pretreated controls. These results suggest that LPS impairs the negative feedback of either endogenous or exogenous GC upon the adrenocortical response to stress. This finding may be relevant to the enhanced adrenocortical activity associated with sepsis and major depression.

Norepinephrine depletion in the amygdala inhibits CRF-41, ACTH, and corticosterone responses following photic simulation.

The effects of amygdaloid norepinephrine depletion by 6-hydroxydopamine on changes in corticotropin releasing factor-41 (CRF-41) and serum adrenocorticotropic hormone (ACTH) and corticosterone levels, following neural stimuli were investigated. In intact animals, photic or acoustic stimulation caused CRF-41 depletion from the median eminence and a rise in serum ACTH and corticosterone levels. In rats with amygdalar norepinephrine depletion there were no changes in basal CRF-41, ACTH, or corticosterone levels. However, the above responses of the hypothalamo-pituitary adrenocortical axis were blocked following photic, but not acoustic, stimulation. These results indicate that the facilitatory role of the amygdala on the above responses following photic stimulation depends on the presence of norepinephrine in this region.

Mycoplasma fermentans activates the hypothalamo-pituitary adrenal axis in the rat.

Intracerebroventricular administration in rats of heat inactivated Mycoplasma fermentans caused a dose- and time-dependent increase in serum adrenocorticotrophin (ACTH) and corticosterone (CS). In rats with complete deafferentation of the mediobasal hypothalamus, which markedly depleted the median eminence CRF-41, the ACTH and CS responses to M. fermentans were completely inhibited. Pretreatment with dexamethasone abolished the adrenocortical response to M. fermentans. In lipopolysaccharide (LPS) unresponsive C3H/HeJ mice LPS failed to induce the adrenocortical response while administration of M. fermentans elicited a normal CS response. These results suggest that: M. fermentans can activate the hypothalamo-pituitary-adrenal axis via a central mechanism which involves hypothalamic ACTH secretagogue(s), and this effect is sensitive to the negative feedback of glucocorticoids. It is possible that the elevated glucocorticoid levels resulting from mycoplasma infection may be involved in the pathogenesis of mycoplasma-associated diseases.

Limbic pathways and hypothalamic neurotransmitters mediating adrenocortical responses to neural stimuli.

One of the major phenomena related to the stress response is the activation of the hypothalamo-pituitary-adrenocortical (HPA) axis. This axis consists of corticotropin releasing factor-41 in the paraventricular nucleus of the hypothalamus (PVN), which in response to a variety of stimuli is released into the portal circulation and stimulates pituitary ACTH secretion and subsequently adrenocortical discharge. The mechanisms involved in the activation are not uniform and the responses to various stimuli are mediated by different neural pathways. Since extrahypothalamic limbic structures play a significant role in the HPA function, it is the purpose of this review to describe the neural pathways between the hippocampus, septum and amygdala and the hypothalamus in relation to adrenocortical activity and the differential role of the medial forebrain bundle as well as the effects of various hypothalamic deafferentation on the transmission of the neural impulses to the hypothalamus. Also, the importance of norepinephrine and serotonin in the activation of the HPA axis will be delineated.

Effect of the brain constituent anandamide, a cannabinoid receptor agonist, on the hypothalamo-pituitary-adrenal axis in the rat.

Anandamide (arachidonylethanolamide), an endogenous ligand of the cannabinoid receptor, was recently isolated from porcine brain. We report here for the first time on the effect of this ligand on the hypothalamo-pituitary adrenal (HPA) axis in comparison to that of the plant cannabinoid delta 9-tetrahydrocannabinol (THC). Intracerebroventricular injection of anandamide or THC (50 or 150 micrograms/rat) increased significantly the serum levels of ACTH and corticosterone in a dose-dependent manner and caused a pronounced depletion of CRF-41 in the median eminence. These data suggest that anandamide parallels THC in activating the HPA axis via mediation of a central mechanism which involves the secretion of CRF-41.

Hypothalamic norepinephrine depletion inhibits CRF-41 release following neural stimuli.

The effects of depletion of hypothalamic norepinephrine (NE) on median eminence (ME)-corticotropin-releasing factor (CRF-41) content, serum ACTH and corticosterone (CS) levels, following photic and acoustic stimulation, were investigated. While in intact rats these stimuli caused depletion in CRF-41 and a rise in ACTH and CS level, in rats pretreated with 6-hydroxydopamine (6-OHDA), these effects were prevented. This would suggest that the blockage in the release of ME CRF-41 into the portal plasma following neural stimuli in rats with hypothalamic NE depletion, is responsible for the inhibition of the pituitary-adrenocortical response.

Glucocorticoid feedback regulation of adrenocortical responses to neural stimuli: role of CRF-41 and corticosteroid type I and type II receptors.

In the present study we characterized the negative feedback effect of exogenous and endogenous glucocorticoids (GC) on the responses of the hypothalamo-pituitary-adrenal (HPA) axis to neural stimuli in male rats. Dexamethasone (Dex) was injected intraperitoneally at a dose of 0.5-4.0 micrograms/100 g BW and rats were exposed to photic or acoustic stress 3.5 h later. The serum ACTH and corticosterone (CS) responses to these stimuli were inhibited in a dose-dependent manner by Dex, such that the stress-induced response was completely abolished at a Dex dose of 4.0 micrograms/100 g BW. Injection of Dex (4.0 micrograms/100 g BW i.p.) did not affect the content of CRF-41 at the median eminence under basal conditions but prevented the depletion in CRF-41 content following acoustic and photic stimulation observed in vehicle-treated animals. Pretreatment with a subcutaneous injection of corticosteroid type I receptor antagonist RU-28318 (5 mg/100 g BW) did not affect the inhibition of the stress-induced adrenocortical response exerted by Dex; in contrast the type II receptor antagonist RU-38486 (5 mg/100 g BW) completely abolished the inhibitory effect of Dex following both types of neural stimuli. To investigate the role of type I and type II corticosteroid receptors in mediating the feedback effect of endogenous GC, the two receptor antagonists were injected intracerebroventricularly (100 ng/100 g BW). RU-28318 did not affect the response to photic stress at 10, 30 or 90 min following the stress, whereas RU-38486 caused a significant increase (approximately 40%) in serum ACTH and CS at all three time points tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of 6-hydroxydopamine and 5,7-dihydroxytryptamine on tissue uptake and cell nuclear retention of corticosterone in the rat hypothalamus.

Previous studies have shown that norepinephrine and serotonin can modulate the glucocorticoid (GC) binding capacity in the hippocampus. The aim of the present study was to evaluate the role of these neurotransmitters in regulating GC receptors in the hypothalamus. Injection of the neurotoxin 6-hydroxydopamine (6-OHDA) into the ventral noradrenergic bundle (VNAB) and 5,7-dihydroxytryptamine (5,7-DHT) into the raphe nuclei caused a marked depletion in norepinephrine and serotonin, respectively, in the paraventricular nucleus (PVN) and mediobasal hypothalamus (MBH). The injection of these neurotoxins did not change the basal levels of ACTH and corticosterone. Injection of 6-OHDA into the VNAB caused a significant reduction in the cell nuclear binding of corticosterone in the PVN but not in the MBH. Conversely, injection of 5,7-DHT into the raphe nuclei caused a significant reduction in cell nuclear binding of corticosterone in the MBH but did not affect binding in the PVN. These results demonstrate that at least part of the nuclear corticosteroid receptors in the PVN and MBH are differentially regulated by the noradrenergic and serotonergic systems.

Effect of hypothalamic norepinephrine depletion on median eminence CRF-41 content and serum ACTH in control and adrenalectomized rats.

In this study we examined the role of the noradrenergic innervation of the hypothalamus on the adrenalectomy-induced changes in median eminence (ME) CRF-41 and serum ACTH. 6-Hydroxydopamine (6-OHDA), the catecholaminergic neurotoxin, or vehicle was injected into the ventral noradrenergic bundle of male rats. One week later animals underwent adrenalectomy or sham operation and were sacrificed 18 or 120 h later. In sham-operated rats 6-OHDA did not affect ME CRF-41 content or serum ACTH. In vehicle-injected adrenalectomized rats ACTH was increased approximately 3-fold at 18 h and almost 6-fold at 120 h. At 18 h CRF-41 content was markedly depleted (reduced approximately 20-fold) but by 120 h CRF-41 content had partially recovered and was about 70% of control animals. In adrenalectomized animals, 6-OHDA lesions caused a complete inhibition of the increase in serum ACTH both at 18 h and at 120 h. Pretreatment with 6-OHDA partially attenuated the drastic reduction in ME CRF-41 content following adrenalectomy at 18 h. However, at 120 h, the neurotoxin prevented the recovery of CRF-41 following adrenalectomy. These results suggest that intact norepinephrine innervation to the hypothalamus is necessary for the increased production of ACTH following adrenalectomy and that its interruption interferes with both the adrenalectomy-induced ME CRF-41 reduction and subsequent recovery.

Depletion of hypothalamic norepinephrine and serotonin enhances the dexamethasone negative feedback effect on adrenocortical secretion.

The role of norepinephrine (NE) and serotonin (5-HT) in the negative feedback effect of dexamethasone (DEX) on the adrenocortical response to ether stress was investigated. Injection of the catecholamine neurotoxin, 6-hydroxydopamine, into the ventral noradrenergic bundle or the paraventricular nucleus of the hypothalamus (PVN) which produced a very significant depletion in hypothalamic NE content enhanced the negative feedback effect of DEX. Injection of the 5-HT neurotoxin, 5,7-dihydroxytryptamine, into the raphé nuclei or PVN, which caused a depletion of hypothalamic 5-HT, produced a similar effect on the adrenocortical response to DEX. The degree of negative feedback may be viewed as a balance of neural stimulatory and glucocorticoid influences of the hypothalamus. Thus the removal of the stimulatory effects of NE and 5-HT on adrenocortical secretion, by the neurotoxic lesions, enhanced the inhibitory influence of DEX.

Differential recovery of adrenocortical responses to neural stimuli following administration of 5,7-dihydroxytryptamine into the hypothalamus.

In view of the role of serotonin in adrenocortical regulation, the effects of depletion of hypothalamic serotonin, using localized injections of the neurotoxin 5,7-dihydroxytryptamine into the hypothalamic paraventricular nucleus, on the rise in plasma corticosterone following afferent neural stimulation, were studied. The neurotoxin caused a significant reduction (p less than 0.001) in hypothalamic serotonin content of about 50% during the first month and about 30% up to two months later. Basal and ether stress-induced rises in plasma corticosterone levels were unaffected at all times after this treatment, but responses to stimulation of the sciatic nerve were reduced for up to four weeks (p less than 0.01), recovering at later times. Responses to photic and acoustic stimuli were almost entirely prevented up to four weeks following the treatment (p less than 0.001) but showed a gradual recovery to full, or almost full, adrenocortical responses at eight weeks, following acoustic and photic stimulation respectively. These results demonstrate a differential recovery of the adrenocortical responses, following the neurotoxin injection and indicate that different neural modalities require different 5-HT concentrations in the PVN for the expression of a full adrenocortical response.

Evidence for the involvement of the central adrenergic system in the febrile response induced by interleukin-1 in rats.

We have studied the effect of noradrenaline- and serotonin-depleting agents on the febrile response induced by an intracerebroventricular (i.c.v.) injection of interleukin-1 (IL-1) in rats. Pretreatment with an injection into the lateral ventricle of the catecholamine-depleting agent, 6-hydroxydopamine (6-OHDA), abolished the febrile response induced by IL-1. Injection of 6-OHDA into the ventral noradrenergic ascending bundle (VNAB) did not affect the pyrogenic effect of IL-1. Pretreatment with the serotonin-depleting agent, 5,7-dihydroxytryptamine (5,7-DHT), did not inhibit the febrile response to IL-1. In addition, pretreatment with a beta-adrenergic blocker (propranolol) but not an alpha-adrenergic blocker (yohimbine) attenuated the fever induced by an i.c.v. injection of IL-1. These results suggest that the integrity of the central catecholaminergic system is important in mediating the IL-1-induced fever in rats. The central serotonergic system, as well as noradrenergic neurotransmission at the hypothalamus, do not appear to participate in this endogenous pyrogen-induced febrile response.

Effect of L-DOPA on glucose oxidation and incorporation into glycogen in discrete brain regions of the rat.

Previous reports in which the [14C]deoxyglucose mapping technique was used, have demonstrated that systemic administration of L-DOPA can either increase or decrease glucose utilization in various brain regions. However, in the striatum, which contains a high concentration of dopamine, no conclusive results were found using this technique. In the present study we attempted, by implicating a different technique, to evaluate the effect of L-DOPA on glucose metabolism in the striatum. This approach is based on in vitro measuring of glucose oxidation to CO2 and its incorporation to glycogen. Rats were injected with carbidopa (100 mg/kg) and 1 h later with L-DOPA (50 mg/kg). The rats were sacrificed by decapitation 1 h after L-DOPA injection and the following brain regions were assayed for glucose oxidation to CO2 and its incorporation to glycogen: striatum, hypothalamus, hippocampus and prefrontal cortex. A significant increase of glucose oxidation of 50% was found in the striatum and hippocampus, while no change was demonstrated in the hypothalamus and cortex. The incorporation of glucose to glycogen was markedly reduced in the striatum and hippocampus while no change was found in the hypothalamus or cortex. The present results demonstrate that L-DOPA treatment increases glucose metabolism in specific brain areas. The mechanism involved might be an increase in cellular uptake of glucose and/or activation of enzymes participating in glucose metabolic pathways.

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.

Effects of extrahypothalamic structures on the hypothalamic cell nuclear binding of corticosterone.

Hypothalamic or hippocampal slices were taken from adrenolectomized male rats either sham operated or with anterior (AHD) of posterior (PHD) hypothalamic deafferentations and from rats with dorsal hippocampectomy (DHIPP). The slices were incubated in Krebs-Ringer bicarbonate buffer in the presence of 10-60 nM 3H-corticosterone (CS) with or without 500 fold excess of unlabeled CS for 30 min. The cell nuclear binding in the hypothalami from either PHD of DHIPP rats were markedly reduced (by 50-70%) as compared to control or AHD rats. The binding of 3H-CS in hippocampi from AHD or PHD rats was not affected. These results suggest that extrahypothalamic structures can modulate the binding of CS in the hypothalamus by neural inputs entering the medio-basal hypothalamus from the caudal direction; such modulation may explain previously observed influences upon hypothalamic sensitivity to the feedback action of glucocorticoids by extrahypothalamic structures.