No abstract

Certain psychiatric disorders are known to alter the body's biological rhythms. However, currently, very little information is known about the effect of chronic ethanol administration on the circadian clock or the rhythm of b-endorphin-containing neurons that participate in the control of the reward and reinforcement of alcohol drinking. Here, we report that administration of ethanol, via a liquid diet paradigm for a period of 2 weeks, abolishes the circadian rhythm of proopiomelanocortin mRNA expression of b-endorphin neurons in the arcuate nucleus of the hypothalamus. The circadian expression of the clock governing rat period genes (rPeriod1 mRNA and rPeriod2 mRNA) in the arcuate nucleus was significantly altered, suggesting that ethanol administration disrupted the internal clock. Moreover, ethanol consumption altered the circadian rhythms of rPeriod2 and rPeriod3 mRNA levels in the suprachiasmatic nucleus, suggesting that ethanol also affected the function of the central pacemaker. Our findings identified the vulnerability of the body's clock machinery and its opioidergic system to chronic alcohol drinking.

The role of β-endorphin (β-EP) in ethanol-altered NK cell cytolytic activity is studied using male Fischer-344 rats as an animal model. Ethanol was administered for 1, 2, 3, or 4 wk in a liquid diet containing 8.7% ethanol (v/v), which means that 37% of the total calories were derived from ethanol. Rats treated with ethanol for 1 wk showed an increase in hypothalamic and plasma levels of immunoreactive (IR)-β-EP, but displayed no significant effect on NK cell activity determined by 51Cr release assay, as compared with those in pair-fed and ad libitum-fed animals. However, animals treated with ethanol for 2, 3, or 4 wk showed decreased hypothalamic and plasma levels of IR-β-EP and decreased splenic NK cell activity. No significant decrease in the number of splenocytes and NK cells or in the percentage of NK cells was seen until after 3 and 4 wk of ethanol treatment. Exposure in vitro of splenic lymphocytes obtained from control animals to various concentrations of β-EP increased NK cell activity. The opiate antagonist naltrexone blocked the β-EP-stimulated effect. The in vitro NK cell response to β-EP was reduced in the splenocytes obtained from animals treated with ethanol for 2 wk, but not in those obtained from animals treated with ethanol for 1 wk as compared with those in control animals. Additionally, β-EP administration into the paraventricular nucleus of the hypothalamus stimulated NK cell cytolytic activity, whereas the opiate blocker administration reduced NK cell activity. The NK cell responses to paraventricular nucleus β-EP were reduced in the animals treated with ethanol for 2 wk. These data provide evidence for the first time that ethanol inhibits NK cell cytolytic activity, possibly by reducing β-EP-regulated splenic NK cell function.

Immunocytochemical labeling revealed that the arcuate nucleus (ARN) of the ewe's hypothalamus contains numerous tyrosine hydroxylase (TH)-positive neurons, that appear to lack dopamine-beta-hydroxylase (DBH)-like immunoreactivity. Axons of these presumed dopaminergic neurons converge in the median eminence (ME) with Luteinizing Hormone Releasing Hormone (LHRH)-containing axons originating mostly from neurons situated in the medial preoptic area. Electron microscopic double labeling revealed synaptic contacts between TH-positive presynaptic profiles and LHRH-containing postsynaptic elements. Samples of ME, ARN, paraarcuate and lateral hypothalamus were dissected and incubated to assess LHRH release and tissue content. Only ME-LHRH release was significantly reduced in the presence of dopamine (DA). All other regions released equal amounts with and without DA. Thus, a presynaptic dopaminergic inhibition of LHRH-containing axons at the level of the ME might contribute to the regulation of LHRH release into the portal vessels.

We tested the working hypothesis that Fos will identify the critical population of kisspeptin neurons that accompanies the LHRH surge using a synchronized follicular phase model in intact cycling ewes. The model generates an LH surge that starts within a defined 2-h window in a 20-d synchronized cycle. With a modified push-pull cannula in vivo LHRH release from the median eminence was sampled in luteal phase ewes, ewes undergoing an LH surge for 2-4 h, and postsurge animals whose LH surge peaked 10-12 h earlier. In vivo release of LHRH was lower in the luteal and follicular phases than in animals undergoing an LH surge (P < 0.01); it fell to presurge levels after the LH surge. Ewes killed 2-4 h after the surge started, expressed Fos in a large portion of preoptic area (POA) kisspeptin (53.90 ± 4.69%, P < 0.01) and LHRH neurons (48.20 ± 4.49%, P < 0.0001) compared with animals euthanized at any of the other times tested (under <5% of the cells activated). Little Fos activation (under 5%) was observed during any of the times sampled in arcuate (Arc) kisspeptin neurons. The relationship between the number of LHRH neurons and the POA kisspeptin neurons stimulated showed a striking positive correlation with r(2) = 0.68, P = 0.0003, reinforcing the evidence that POA kisspeptin neurons actively participate in the stimulation of LHRH surges.

No abstract

Sleep-wake disturbances and stress hyper-responsiveness have been observed in human neonates, children and adolescents who were exposed to alcohol during the prenatal period. Using the laboratory rat as an animal model, we investigated whether fetal ethanol exposure during gestational days 10-21 affects the circadian function of the stress-axis regulatory b-endorphin neurons in the hypothalamus. Fetal ethanol-exposed rats showed abnormality in the circadian expression of proopiomelanocortin (POMC) mRNA encoding the peptide b-endorphin in the arcuate nucleus of the hypothalamus during the adult period. These rats also showed altered circadian expression of the clock governing Period genes rPer1, rPer2 and rPer3, in the arcuate nucleus, and rPer1 and rPer 2 mRNA levels in the suprachiasmatic nucleus. Laser captured microdissection analysis identified constitutive expression of rPer1, rPer2 and rPer3 genes in b-endorphin-containing neurons. These data suggest for the first time that fetal exposure to ethanol significantly alters the clock mechanisms governing the circadian function of b-endorphin neurons.

Castration of male and female rats resulted in a marked rise in serum LH. The rise in serum LH was partially or completely prevented by injection of prolactin (Prl), by implantation of a small amount of Prl in the median eminence (ME), by grafting 2 anterior pituitaries (APs) underneath the kidney capsule, or by transplantation of a Prl-secreting pituitary tumor underneath the skin. The larger pituitary tumor transplants secreted more Prl and were more effective in reducing LH release than the smaller tumors which secreted less Prl. Suppression of LH release generally was greater during the earlier than in the later phases of the different treatments. The pituitary LH response to synthetic LH-RH was the same in ovariectomized rats with or without pituitary grafts, and the decrease in hypothalamic LH-RH after orchidectomy was prevented by pituitary grafts. These results indicate that Prl can depress LH release after castration and that these effects are mediated via the hypothalamus.