Pro-Opiomelanocortin-Containing Neurons in Rat Median Eminence

Abstract

A significant number of pro-opiomelanocortin (POMC)-containing cells were detected in the rat median eminence (ME) by immunocytochemistry using an antibody raised against a synthetic peptide corresponding to the cleavage site between adrenocorticotropin and β-lipotropin moieties. Distribution of POMC-positive cells was restricted to the internal zone of the anterior parts of the ME. Such cells were observed as early as the 14th day of gestation in the area of the primitive ME, long before glial fibrillary acidic protein-positive cells appeared postnatally in this structure. Dissociated cell cultures obtained from the ME of 1-day-old rats produced cells immunoreactive for neurofilaments and the POMC moiety. Such cells displayed a neuronal morphology: the cell body was oval (13–18 µm) with long and fine beaded fibers. These findings clearly demonstrate the early appearance of POMC neurons in the developmental ME, a target organ of the hypothalamic infundibular neurons.

Mu, delta, and kappa opioid receptor mRNA expression in the rat CNS: An in situ hybridization study

“…Colocalization studies with glial-and neuronal-specific markers are necessary to characterize the K receptor-expressing cells in the median eminence and infundibular stem. A few scattered neurons expressing P-endorphin have been identified in the median eminence (Ishikawa et al, 1992), and it will be interesting to see if they also express K receptors.…”

Arcuate nucleus of the hypothalamus: Effects of age and sex

“…In fact, neurons in the ARN establish direct synaptic contacts with CRH neurons in the paraventricular nucleus (Sawchenko et al, 1982;Bai et al, 1985;Wahlestedt et al, 1987;Baker and Herkenham, 1995) and with LHRH neurons in the medial preoptic area (Mezey et al, 1985;Leranth et al, 1988); on the other hand, ARN neurons also project to the median eminence where they modulate the release of LHRH and CRH (Wiegand and Price, 1980;Mezey et al, 1985;Haas and George, 1989;Ishikawa et al, 1992). Although no complete picture has yet emerged concerning the type of influence exerted by the ARN on the production of these hormones, there is accumulating evidence that specific subsets of its neurons, those containing neuropeptide Y (NPY), proopiomelanocortin (POMC)-related peptides and somatostatin, modulate the synthesis and/or the release of LHRH and CRH (Mezey et al, 1985;Haas and George, 1989;Ishikawa et al, 1992;Cheung and Hammer, 1997). Should that be so, then we can hypothesize that changes in these peptides might underpin the age-related alterations in the production of CRH and LHRH, all the more because those peptides are altered in aged rats.…”