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Corticotropin-releasing hormone (CRH) is a neuropeptide thought to play a role in appetite regulation. In this report, we used a serial cerebrospinal fluid (CSF) sampling technique to examine the relationship between CSF CRH, plasma ACTH and cortisol and perceptions of hunger and satiety in fasting and sated volunteers. CSF was withdrawn continuously from 11:00 AM to 5:00 PM via an indwelling subarachnoid catheter. Blood was withdrawn every 10 min via an antecubital vein catheter. Fed subjects received a meal at 1:00 PM. Subjects who were fed had lower post-prandial ratings on hunger scales and higher ratings on satiety scales. Fed subjects also had slightly lower levels of CSF CRH after feeding. Furthermore, fed subjects had higher ACTH and cortisol concentrations in the first 3 h; by the fourth h the opposite was true. Our findings do not support the hypothesis that CNS CRH is a central satiety factor in the human. Instead our findings of slightly diminished CSF CRH levels after feeding may be accounted for by the rises in glucocorticoids and their associated negative feedback effects on CNS CRH. Alternatively, our findings could also reflect changes in CRH levels associated with feeding in multiple brain areas and in the spinal cord with the net effect being in the negative direction.

Neurotensin (NT) is an endogenous brain tridecapeptide for which high affinity binding sites exist in the central nervous system. We have investigated the effects of NT incubation with rat neotriatal slices on calcium/calmodulin (Ca/CaM)-dependent protein phosphorylation. Slices were incubated with NT (5 or 50 nM) for 3, 10, 16, or 30 min followed by in vitro phosphorylation, electrophoresis and autoradiography. NT significantly altered the phosphorylation of a 62 kDa protein which is likely the β subunit of the Ca/CaM dependent protein kinase. These changes may reflect the ability of NT to influence calcium mediated signal transduction.

Levels of hypophysial portal arginine-vasopressin (AVP), plasma ACTH and plasma corticosterone (B) were measured in four and 24 month old Fischer 344 rats. Portal levels of AVP were lower in older rats whereas plasma ACTH levels were elevated. Older rats given adrenalectomies with physiologic replacement doses of B exhibited levels of AVP, but not ACTH, which were comparable to that observable in younger rats. The findings suggest that altered AVP, but not ACTH, can be accounted for by higher B levels which are commonly demonstrable in aging rats.

Adaptation in aging may become impaired from abnormal expression of corticotropin-releasing factor (CRF) and altered CRF receptor function. In this study, we measured CRF mRNA levels in Fischer 344 rats at various ages. The brains of these rats were processed for in situ hybridization. Relative to 3-month-old rats, levels of CRF mRNA were significantly decreased in the following brain areas at the following ages: at 24 months in the paraventricular hypothalamus, at 11, 17, and 24 months in the amygdala and at 17 and 24 months in the bed nucleus of the stria terminalis. These changes may contribute to impaired adaptations to stress, cognitive decline and other pathophysiological processes during aging.

Corticotropin-releasing factor (CRF) coordinates the mammalian response to stress. In the amygdala, the CRF system appears to be responsible, at least in part, for the behavioral responses resulting from stress. Associated with amygdalar CRF is a 37 kDa binding protein (CRF-BP) which may also play a role in regulating stressful stimuli. Aging has been shown to be associated with abnormal neuroendocrine stress systems and little is known with regards to how amygdalar stress systems change with aging. In our study, we have assessed levels of amygdalar CRF and CRF-BP mRNA in Fischer 344 rats of 4, 12 or 24 months of age following 14 days of hourly restraint. Prior to sacrifice, rats were also tested for anxiety-like behaviors on the elevated plus maze. After behavioral testing, rats were perfused with 4% paraformaldehyde and the brains were processed for in situ hybridization. Twenty micron sections were hybridized with a CRF as well as a CRF-BP riboprobe. Following hybridization, tissue sections were oppossed to X-ray film and relative amounts of mRNA in the amygdala were quantitated. Levels of CRF mRNA in the amygdala of 12 and 24 month-old rats following chronic restraint were significantly lower relative to rats which were handled for 14 days. There were no significant differences in amygdalar CRF gene expression between stressed and handled 4 month-old rats. At 12 and 24 months of age but not 4 months, there were also significant effects of restraint associated with decreases in amygdalar CRF-BP gene expression. Furthermore, there were reciprocal decreases in anxiety-like behaviors in the 12 and 24 month-old rats which were significant; the changes in anxiety-like behaviors between restrained vs. handled 4 month-old rats were not significantly different. The decreased gene expression of CRF in the amygdala in concert with decreased anxiety-like behaviors following restraint is consistent with the known behavioral effects of exogenously applied intra-amygdalar CRF. The changes in amygdalar CRF-BP observed may be secondary to the known regulatory effects that CRF exhibits on its binding-protein. These studies have relevance to better understanding the molecular basis of aging related changes in neuroendocrine stress systems.

The present study examined the actions of the putative gaseous neurotransmitter carbon monoxide (CO) on secretion of corticotropin-releasing factor (CRF) from cultured primary rat hypothalamic cells. 6 h treatment of cells with 100% gaseous CO, or with the heme analog, hematin (100 microM) which produces CO as a by-product of its metabolism, increased basal secretion of CRF to 207 +/- 8% and 200 +/- 65% of control respectively. Zinc protoporphyrin IX (ZnPPIX) (0.3-100 microM), a selective inhibitor of CO formation, decreased CRF secretion in a dose-dependent manner. The changes in CRF secretion observed with hematin were attenuated during concurrent treatment with ZnPPIX. These studies suggest that basal secretion of CRF in the rat hypothalamus may be regulated by CO.

The effects of exogenously added phospholipase A2 (PLA2) and its hydrolytic products in isolated bullfrog sciatic nerve were investigated. Nerves were pretreated for 3 h with a dose of trypsin which did not affect conduction in order to enhance penetration of the added agents. Treatment of nerves with beta-glucosidase, neuraminidase or chymotrypsin had no effect on conduction. Whereas incubation of the nerves with normal Ringers for 2 h had no significant effect on conduction, incubation with PLA2 in Ringers caused decrements in the height of the compound action potential in a dose-related manner. In addition, incubation of the nerves with 10 mg/ml lysolecithin, arachidonic acid, or docosahexaenoic acid caused marked decrements in the height of the compound action potential. Electron microscopic analysis of nerves after each treatment which caused conduction block revealed varying levels of myelin damage. Although myelin was damaged at the paranodal and/or internodal region, depending on the agents used, the axonal membrane appeared to be intact at the ultrastructural level. It was concluded that the block in conduction resulting from PLA2 was due to the formation of lysolecithin and long chain polyunsaturated fatty acids.

The biochemical changes associated with conduction block following exogenous application of purified phospholipase A 2 to bullfrog sciatic nerves were investigated. Nerves were treated with concentrations of phospholipase A 2 needed to produce at least a 50% decrease in the compound action potential after a 2–21/2 h incubation. This phospholipase A 2 -induced conduction block was associated with lipid hydrolysis, depletion of high energy phosphates and decreases in [ 3 H]saxitoxin binding. Forty-two percent of the nerve phosphatidylcholine and 45% of the nerve phosphatidylethanolamine were hydrolyzed. [ 3 H]Saxitoxin binding was decreased by 85% in association with conduction block attained with phospholipase A 2 incubation. There were significant decrements in adenosine triphosphate levels (−58%) and in phosphocreatine levels (−78%), but no difference in the specific activities of these phosphate compounds. It is concluded that a number of mechanisms can account for the conduction failure resulting from phospholipase A 2 , including disruption of sodium channels needed for propagation of regenerative nerve impulses and the depletion of high energy phosphates needed to maintain ionic gradients.