C. Bugnon

Corticoliberin in rat brain: Immunocytochemical identification and localization of a novel neuroglandular system

Abstract A new hypothalamo-infundibular neuroglandular system was revealed in the rat brain using an antiserum raised against synthetic corticoliberin. In non-treated rats, a dense aggregation of corticoliberin-like immunoreactivity (CLI)-positive fibres and terminals was observed in all regions of the zona exterma of the median eminence and in the pituitary stalk. In animals treated with colchicine 72 h prior to sacrifice, CLI-positive cell bodies were found mainly in the paraventricular uncleus. These perikarya differ from those stained with vasopressin or oxytocin antisera.

Comparative study of the neuronal populations containing β-endorphin, corticotropin and dopamine in the arcuate nucleus of the rat hypothalamus

Neurons simultaneously immunoreactive with anti-beta-endorphin and anti-(17-39) corticotropin (anti(17-39) ACTH) have been detected in the arcuate and ventromedial nuclei of the hypothalamus of colchicine-treated rats. These neurons are different from those fluorescent with the Falck and Hillarp technique. These results show that in the arcuate nucleus, immunoreactive ACTH and beta-endorphine are stored in the same neurons which are different from dopamine-containing neurons.

Unrelated peptide immunoreactivities coexist in neurons of the rat lateral dorsal hypothalamus: Human growth hormone-releasing factor1–37−, salmon melanin-concentrating hormone- and α-melanotropin-like substances

Antisera raised against 3 unrelated synthetic neuropeptides - salmon melanin-concentrating hormone, human growth hormone-releasing factor1-37, and alpha-melanotropin - stained the same extensive neuron population in lateral and dorsal areas of the posterior hypothalamus. Controls for specificity have shown that these 3 antisera bind 3 different epitopes. Differences in intracellular staining patterns suggest that these epitopes could be borne by distinct peptides.

Immunoreactivities for antisera to three putative neuropeptides of the rat melanin-concentrating hormone precursor are coexpressed in neurons of the rat lateral dorsal hypothalamus

Antisera (AS) raised against rat melanin-concentrating hormone (rMCH) and against two additional peptides sequences derived from the rat MCH precursor (neuropeptide glutamic acid-isoleucineamide (NEI), and neuropeptide glycine-glutamic acid (NGE)) exclusively stained the hypothalamic neurons previously described using AS to salmon MCH, human somatocrinin 1-37 (GRF37) and alpha-MSH. Liquid phase and dot-blot controls for specificity indicated that rMCH-, NEI- and NGE-AS bound epitopes recognized by sMCH-, alpha-MSH- and GRF-37-AS, respectively. The distinct intracellular patterns of immunoreactivity obtained in control animals with rMCH-, NGE- and NEI-AS, as well as the changes observed after intracerebroventricular injection of colchicine matched previous findings using sMCH-, GRF37- and alpha-MSH-AS.

Colocalization of prolactin- and dynorphin-like substances in a neuronal population of the rat lateral hypothalamus

Using an antiserum (AS) raised against dynorphin B (DYN B), we revealed immunoreactive neurons in different nuclei of the rat hypothalamus as well as a population of neurons scattered in the lateral areas of the posterior hypothalamus. This population corresponds to that previously shown to be specifically recognized by an ovine prolactin (PRL) AS. Our results suggest that in these neurons, DYN B and PRL AS reacted with different epitopes and that these epitopes could be carried by distinct unidentified peptides.

Induction of Fos-immunoreactivity in prolactin-like containing neurons of the rat lateral hypothalamus after insulin treatment

The role of the lateral hypothalamus (LHT) in the regulation of feeding behavior has long been established. The major contribution of LHT glucose-sensitive neurons, activated by low glucose concentration, is well accepted. Two peptidergic neuron populations, whose perikarya are exclusively located within this area, have been recently described. They respectively produce peptides derived from the melanin-concentrating hormone (MCH) precursor and prolactin-like immunoreactive peptide (PLI). In the present study, hypoglycemia-induced neuron stimulation was assessed in the rat LHT, by using Fos immunocytochemistry 1 to 5 h after a single insulin injection. In control animals, very scarce Fos-like immunoreactivity (FLI)-containing nuclei were observed in LHT. Insulin treatment induced an important and progressive increase in the number and staining intensity of neuron nuclei detected by Fos antiserum. Five hours after injection, few MCH neurons exhibited FLI, but about 80% of PLI-containing neurons expressed FLI and more than 50% of the FLI-containing nuclei belonged to PLI neurons. It was thus concluded that PLI-expressing neurons, which dramatically responded to insulin treatment, might correspond to a subpopulation of the glucose-sensitive LHT neurons.

Human hypothalamic neuronal system revealed with a salmon melanin-concentrating hormone (MCH) antiserum

An antiserum raised against synthetic salmon melanin-concentrating hormone (MCH) reveals an extensive neuronal system in the posterior lateral areas of the human hypothalamus. These neurons correspond to those previously described in the rat, which are characterized by expression of MCH-like, alpha-melanotropin-like and human growth hormone-releasing factor (1-37)-like immunoreactivities.

Immunocytochemical demonstration of corticoliberin-like immunoreactivity (CLI) in neurones of the rat amygdala central nucleus (ACN)

Anti-corticotropin-releasing factor (CRF) antibodies revealed numerous perikarya in the amygdala central nucleus (ACN) of colchicine-injected rats. Most of the immunoreactive processes emerging from these neurone bodies seemed to project to the lateral hypothalamus by the ventral amygdalo-hypothalamic pathway. As well as parvocellular areas of the hypothalamic paraventricular nucleus where numerous neurones containing corticoliberin-like immunoreactivity (CLI) were demonstrated, ACN is densely innervated by beta-endorphin fibres originating from pro-opiomelanocortin neurones of the hypothalamic arcuate nucleus. The facilitatory influences of the amygdala on the corticotropic axis are most probably mediated by the ACN CLI neurones, the possible infundibular projections of which remain to be demonstrated.

Insulin treatment stimulates the rat melanin-concentrating hormone-producing neurons

Melanin-concentrating hormone (MCH) is involved in the regulation of body colour in teleost fish. A peptide highly homologous to salmon MCH has been found in the rat brain, but its physiological functions have not yet been precisely defined. The location of MCH neurons in the lateral hypothalamus (LHT) of the rat suggests possible implication in feeding behaviour. In the present study, immunohistochemical and in situ hybridization methods were used to investigate MCH gene expression following insulin injections. Five hours after insulin injection, a significant increase in the abundance and staining intensity of MCH immunoreactive perikarya and fibres was observed. Concurrently the level of MCH mRNA significantly increased (50%). Insulin-treatment also induced a marked and progressive increase in the number and staining intensity of nuclei detected by a Fos antiserum in LHT and other brain areas. Double labelling technique demonstrated that very few if any MCH neurons exhibited Fos-like immunoreactivity. These results demonstrate that an insulin-treatment stimulates MCH neuron activity without the mediation of the proto-oncogene c-fos. The mechanisms triggering this activation remain to be elucidated.

Changes in corticoliberin and vasopressin-like immunoreactivities in the zona externa of the median eminence in adrenalectomized rats. Immunocytochemical study ☆

The zona externa of the median eminence was found completely depleted of corticoliberin-like immunoreactivity (CLI) and of vasopressin-like immunoreactivity (VLI) 12-14 h and 22-24 h after bilateral adrenalectomy. Amount of CLI increased to the level of untreated rats 5 days after this operation while amount of VLI rose higher than in control animals. The same was found 20 days after surgery. These results emphasize the involvement of two infundibular neurosecretory systems--CLI and VLI--in the regulation of the pituitary--adrenal axis.