β-Endorphin-immunoreactive neurons in the hypothalamus and medulla of the rat brain: Effect of prenatal ethanol

Individual arcuate nucleus proopiomelanocortin neurons project to select target sites

Proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARH) are a diverse group of neurons that project widely to different brain regions. It is unknown how this small population of neurons organizes its efferent projections. In this study, we hypothesized that individual ARH POMC neurons exclusively innervate select target regions. To investigate this hypothesis, we first verified that only a fraction of ARH POMC neurons innervate the lateral hypothalamus (LH), the paraventricular nucleus of the hypothalamus (PVN), the periaqueductal gray (PAG), or the ventral tegmental area (VTA) using the retrograde tracer cholera toxin B (CTB). Next, two versions of CTB conjugated to distinct fluorophores were injected bilaterally into two of the regions such that PVN and VTA, PAG and VTA, or LH and PVN received tracers simultaneously. These pairs of target sites were chosen based on function and location. Few individual ARH POMC neurons projected to two brain regions at once, suggesting that there are ARH POMC neuron subpopulations organized by their efferent projections. We also investigated whether increasing the activity of POMC neurons could increase the number of ARH POMC neurons labeled with CTB, implying an increase in new synaptic connections to downstream regions. However, chemogenetic enhancement of POMC neuron activity did not increase retrograde tracing of CTB back to ARH POMC neurons from either the LH, PVN, or VTA. Overall, subpopulations of ARH POMC neurons with distinct efferent projections may serve as a way for the POMC population to organize its many functions.

Alcohol stimulates ACTH secretion in the rat: mechanisms of action and interactions with other stimuli

This review discusses some of the mechanisms through which alcohol (EtOH) alters the activity of the hypothalamic-pituitary-adrenal (HPA) axis. In adult rats, acute EtOH treatment increases plasma ACTH and corticosteroids levels primarily by stimulating the release of corticotropin-releasing factor (CRF) and possibly vasopressin (VP) from nerve terminals in the median eminence. Increased CRF gene transcription in the hypothalamus may also be important. The HPA axis remains activated during chronic EtOH exposure, although habituation may take place. Changes in the responsiveness of hypothalamic neurons, a phenomenon itself dependent in part on a number of intermediate secretagogues, as well as decreased pituitary responsiveness to VP, all play a role. Finally, the activity of the HPA axis is influenced by exposure to EtOH during embryonic development, with mature offspring showing hyporesponsiveness to many stimuli. These altered responses appear to be caused in part by changes in the synthesis/release CRF, possibly under the influence of nitric oxide. CRF, VP, ACTH, and corticosteroids are important regulators of the immune system, behavior, metabolic pathways, and reproductive parameters. Alcohol therefore may influence such functions through the pathological secretion of these hormones. A better understanding of the mechanisms through which the drug alters their release thus may permit the development of therapies designed to alleviate some of the consequences of alcoholism.

Arcuate nucleus neurons that project to the hypothalamic paraventricular nucleus: neuropeptidergic identity and consequences of adrenalectomy on mRNA levels in the rat

The possible role that the hypothalamic arcuate nucleus might play in mediating the increase in paraventricular nucleus corticotropin-releasing hormone mRNA levels following adrenalectomy was investigated in two series of experiments. In the first series in situ hybridization histochemistry was used to quantify levels of eight accurate nucleus neuropeptide and neurotransmitter mRNAs in neurons that potentially relay adrenal steroid feedback to the paraventricular nucleus. In the second series of experiments, arcuate neuropeptidergic projections to the hypothalamic paraventricular nucleus were characterized using retrograde tracing in combination with in situ hybridization histochemistry. Despite an increase in paraventricular nucleus corticotropin-releasing hormone (60%) and pituitary proopiomelanocortin mRNA levels (sixfold), arcuate mRNA levels for proopiomelanocortin, neuropeptide Y, somatostatin, galanin, dynorphin, tyrosine hydroxylase, glutamate decarboxylase, and the glucocorticoid receptor were unchanged 14 days following adrenalectomy. Neuropeptidergic characterization of arcuatoparaventricular projections was achieved by injection of the retrograde tracer fluorogold into the paraventricular nucleus; retrogradely labeled neurons were characterized with polyclonal antisera against fluorogold in combination with oligonucleotide probes directed against neuropeptide Y, proopiomelanocortin, or somatostatin. Out of these three arcuate neuropeptide Y mRNA was contained in 18% of the fluorogold-positive neurons in the arcuate, proopiomelanocortin mRNA was contained in 8%, and somatostatin mRNA was contained in 6%. Overall, the results from both experiments suggest that the arcuatoparaventricular neuropeptide Y, proopiomelanocortin, and somatostatin projections are not sensitive to a chronic (14 day) lack of adrenal steroids. These projections as well as the other arcuate neurotransmitter and neuropeptide systems appear not to contribute to the persistent elevations in paraventricular nucleus corticotropin-releasing hormone mRNA levels or pituitary proopiomelanocortin mRNA levels found in 14 day adrenalectomized rats.

Effect of prenatal ethanol and stress on levels of beta-endorphin in different brain regions of the rat

The combination of prenatal ethanol exposure and footshock stress was investigated for its effects on brain beta-endorphin levels. Subjects were offspring of rats that received 1 of 3 prenatal dietary treatments: an ethanol-containing liquid diet, a identical liquid diet with ethanol substituted isocalorically with maltose-dextrin (pair-fed group), and standard laboratory rat chow (chow-fed group). Two different stress paradigms were used: a short (30-sec) footshock stress paradigm and a prolonged (180-sec) footshock stress paradigm. Levels of beta-endorphin were measured with radioimmunoassay in eight brain regions of unstressed (baseline) rats, and of stressed rats at 3 and 30 min following termination of the stress. Seven brain regions containing high densities of beta-endorphin axons and terminals were chosen, as well as the arcuate region of the hypothalamus, the only brain region where both beta-endorphin perikarya and terminals are located. Following the short footshock stress paradigm, there were no changes in beta-endorphin levels, except for a trend toward increased levels in the pair-fed group. After the prolonged stress paradigm, levels of beta-endorphin in both the pair-fed and chow-fed groups tended to be decreased in several brain regions, including the arcuate region, at 3 min after termination of the stress. In contrast, for the prenatally ethanol-exposed group, beta-endorphin levels were increased significantly in the arcuate region, and moderately increased in the septal/preoptic region and medulla/pons at 3 min after the prolonged stress paradigm.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of alcohol, acetaldehyde, and salsolinol on beta-endorphin secretion from the hypothalamic neurons in primary cultures

The effect of ethanol, acetaldehyde, and salsolinol on hypothalamic beta-endorphin secreting neurons is studied by using rat fetal hypothalamic neurons in primary culture. Exposure of these neuronal cells to different concentrations of ethanol (12.5-50 mM) and acetaldehyde (12.5-50 microM) caused a concentration-dependent increase in the secretion of beta-endorphin. Salsolinol (12.5-50 microM) did not cause any significant change in the secretion of beta-endorphin. Ethanol's effect was short-lasting (2 hr). Acetaldehyde's effect on beta-endorphin secretion was greater and longer lasting, as compared with ethanol. Ethanol and salsolinol do not have any effect on cell viability, whereas higher concentrations of acetaldehyde appear to reduce the number of viable cells after 6 hr of treatment. None of the above treatments has any effect on cellular DNA content. These results suggest that ethanol is a potent stimulator of hypothalamic beta-endorphin. These results also show for the first time that ethanol's metabolite acetaldehyde is more potent in stimulating beta-endorphin secretion and may be significant in the ethanol regulated beta-endorphin secretion.

Endogenous opiates: 1992

This paper is the fifteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1992 involving the behavioral, non-analgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.