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

Norepinephrine depletion of antimicrobial peptides from the skin glands of Xenopus laevis

The dermal granular glands of the South African clawed frog, Xenopus laevis, contain antimicrobial peptides (AMPs) that are secreted following local nerve stimulation. These natural antibiotics are active against bacteria and fungi including Batrachochytrium dendrobatidis, a fungal pathogen that causes the skin disease chytridiomycosis. Granular gland secretion can be stimulated in the laboratory by norepinephrine injection. We found that two injections of 80nmol/g norepinephrine were necessary to fully deplete the AMP stores. One injection resulted in the secretion of most of the stored peptides. A second injection, 2 days later, released a small amount of additional AMPs that are not compositionally different from those released by the first injection. A third injection, 4 days after the first, did not result in further AMP release. Mass spectrometry and histology confirmed that glands are depleted after two injections. Periodic acid-Schiff staining indicated that mucus gland secretion was also induced by norepinephrine.

Changes in HPA reactivity and noradrenergic functions regulate spatial memory impairments at delayed time intervals following cerebral ischemia

This study investigates the association of ischemia-induced spatial memory impairment to alterations of the HPA axis and noradrenergic activation post insult. Experiment 1 characterized the effects of 10 min forebrain ischemia on corticosterone (CORT) secretion following ischemia and in response to spatial memory assessment in the Barnes maze, as well as the impact of pre-ischemia treatment with the glucocorticoid inhibitor metyrapone (175 mg/kg; s.c.). The results showed that cerebral ischemia represents a significant physiological stressor that upregulated CORT secretion 1, 24 and 72 h post-ischemia but not at 7 days. In response to testing in the Barnes maze ischemic animals showed elevated CORT secretion simultaneously with spatial memory deficits. The single dose of metyrapone attenuated the ischemia-induced adrenocortical hyper-responsiveness and subsequent memory deficits despite not providing neuroprotection in the hippocampal CA1 pyramidal cells. To complement these findings, we examined whether norepinephrine which provides positive feedback to the HPA axis and is upregulated following brain ischemia could influence memory performance at delayed intervals after ischemia. Experiment 2 demonstrated that pre-testing administration of the alpha2-adrenoceptor agonist clonidine (.04 mg/kg, s.c.) attenuated ischemia-induced working memory impairments in a radial maze while opposite effects were obtained with the antagonist yohimbine (.3 mg/kg, s.c.). Post-testing administration of clonidine produced spatial reference memory impairments in ischemic rats. The findings from the current study demonstrate increased sensitization and responsiveness of systems regulating stress hormones at long intervals post ischemia. Importantly, we demonstrate that these effects contribute to post ischemic cognitive impairments which can be attenuated pharmacologically even in the presence of hippocampal degeneration at time of testing.

Acupuncture Attenuates Anxiety-Like Behavior by Normalizing Amygdaloid Catecholamines during Ethanol Withdrawal in Rats

Previously, we demonstrated acupuncture at acupoint HT7 (Shen-Men) attenuated ethanol withdrawal syndrome by normalizing the dopamine release in nucleus accumbens shell. In the present study, we investigated the effect of acupuncture on anxiety-like behavior in rats and its relevant mechanism by studying neuro-endocrine parameters during ethanol withdrawal. Rats were treated with 3 g kg(-1)day(-1) of ethanol (20%, w/v) or saline by intraperitoneal injections for 28 days. The rats undergoing ethanol withdrawal exhibited anxiety-like behavior 72 h after the last dose of ethanol characterized by the decrease of time spent in the open arms of the elevated plus maze compared with the saline-treated rats (P < .05). Radioimmunoassay exhibited there were notably increased concentrations of plasma corticosterone in ethanol-withdrawn rats compared with saline-treated rats (P < .05). Additionally, high performance liquid chromatography analysis also showed the levels of norepinephrine and 3-methoxy-4-hydroxy-phenylglycol were markedly increased while the levels of dopamine and 3,4-dihydroxyphenylacetic acid were significantly decreased in the central nucleus of the amygdala of ethanol-withdrawn rats compared with saline-treated rats (P < .01). Acupuncture groups were treated with acupuncture at acupoint HT7 or PC6 (Nei-Guan). Acupuncture at HT7 but not PC6 greatly attenuated the anxiety-like behavior during ethanol withdrawal as evidenced by significant increases in the percentage of time spent in open arms (P < .05). In the meantime, acupuncture at HT7 also markedly inhibited the alterations of neuro-endocrine parameters induced by ethanol withdrawal (P < .05). These results suggest that acupuncture may attenuate anxiety-like behavior during ethanol withdrawal through regulation of neuro-endocrine system.

Effects of adrenergic and serotonergic agonists in the amygdala on the hypothalamo-pituitary-adrenocortical axis

The effect of direct administration of adrenergic and serotonergic (5-HT) agonists into the central nucleus of the amygdala (AMG) on the hypothalamo-pituitary-adrenal (HPA) axis have been studied in intact male rats and in animals with 6-hydroxydopamine (6-OHDA) or 5, 7-dihydroxytryptamine (5,7-DHT) neurotoxic lesions in the paraventricular nucleus of the hypothalamus (PVN). In intact animals, the administration of phenylephrine, an alpha1 adrenergic agonist or 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) a 5-HT(1A) agonist caused depletion of median eminence corticotropin releasing hormone and a rise in serum adrenocorticotrophic hormone (ACTH) and corticosterone (CS) levels. Isoproterenol a beta agonist was more effective than phenylephrine and a 5-HT(1B) agonist CP-93, 129 was less effective than 8-OH-DPAT on the adrenocortical activity. The 6-OHDA or 5,7-DHT hypothalamic lesions prevented the stimulatory effects of phenylephrine and 8-OH-DPAT, respectively, which where injected into the AMG, on serum ACTH and CS levels. In view of our previous studies on the effects of the adrenergic and 5-HT antagonists in the AMG and the present data, it is suggested that norepinephrine and 5-HT play an important role in the stimulatory effect of the AMG on the HPA axis. These effects depend on the presence of these excitatory neurotransmitters in the PVN.

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.

Effect of glucocorticoids on the adrenocortical axis responses to electrical stimulation of the amygdala and the ventral noradrenergic bundle

In the present study we examined the negative feedback effect of exogenous and endogenous glucocorticoids (GC) on the responses of the hypothalamo-pituitary-adrenocortical (HPA) axis to electrical stimulation of the central amygdaloid nucleus (AMG) and the ventral noradrenergic bundle (VNAB). Injection of dexamethasone (DEX 5-50 microg/kg BW) 3.5 h prior to the electrical stimuli inhibited the serum ACTH and corticosterone (CS) responses in a dose dependent manner. At a dose of 50 microg/kg BW DEX, the stress induced responses was completely abolished. Pretreatment with a subcutaneous injection of corticosteroid type II receptor antagonist (RU-38486) 30 mg/kg BW, enhanced the ACTH and CS responses to both stimuli. In contrast, the type I receptor antagonist (RU-28381) did not affect neither the responses to both stimuli nor the inhibitory effect exerted by DEX. Electrical stimulation of both the AMG and VNAB caused a significant depletion of CRF-41 content of the median eminence (ME). Pretreatment with DEX (50 microg/kg BW) inhibited the electrical stimuli-induced depletion of ME CRH-41. These results suggest that: (1) the HPA axis responses to electrical stimuli of the AMG and the VNAB are sensitive to the negative feedback of GC; (2) the feedback effect exerted by GC is mediated by type II GC receptors; (3) CRH-41 released from the ME plays a dynamic role in mediating pituitary-adrenocortical responses to the electrical stimuli; (4) the inhibitory effect of exogenous DEX is mediated by a reduction of CRF-41 release from the ME.