Seasonal variations of the beta-endorphin neuronal system in the mediobasal hypothalamus of the jerboa (Jaculus orientalis).

The distribution of neurons expressing beta-endorphin immunoreactivity was explored in the brain of adult jerboa during two distinct periods characterizing its reproductive cycle. A large presence of cell bodies displaying beta-endorphin immunoreactivity occured within different parts of the mediobasal hypothalamus along its rostrocaudal extent, from the retrochiasmatic area to the posterior arcuate nucleus. Quantitatively, the highest density of immunoreactive beta-endorphin neurons was noted at the medial level of the arcuate nucleus. Furthermore, a seasonal study showed that the number of IR-beta-endorphin neurons was highest in the anterior portion of the arcuate nucleus of jerboas sacrificed in autumn as compared to those sacrificed during spring-summer. Quantitatively, the number of beta-endorphin containing neurons in autumn was 200% in comparison to that found in spring-summer. These results suggest that beta-endorphin containing neuronal population especially localized in the anterior part of arcuate nucleus, exerts an inhibitory influence on the GnRH neurosecretory system in the jerboa, notably in autumn, probably via an increasing expression of its products. The results provide morphofunctional arguments in favour of inhibitory opioid control of GnRH neurons activity and hence the neuroendocrine events regulating reproduction in jerboa.

Immunocytochemical distribution of Met-enkephalin-Arg6-Gly7-Leu8 (Met-8) in the auditory system of the rat.

Methionine-enkephalin-Arg(6)-Gly(7)-Leu(8) (Met(8)) is known to act as a neurotransmitter or neuromodulator and it has been implicated in pain, cardiovascular and motor mechanisms, but its role in audition is currently unknown. In the present study we have applied an immunocytochemical technique and describe the distribution of cell bodies and fibers containing Met(8) in the auditory pathway of the rat. The main finding is that we found either Met(8)-immunoreactive fibers or cell bodies or both in virtually all nuclei of the rat auditory system except for the medial superior olive and the ventral division of the medial geniculate body in which we did not find any immunoreactivity for Met(8). This suggests that the neuropeptide Met(8) is widely distributed throughout the auditory system of the rat. Our results suggest that Met(8) could play at least two roles in hearing. It seems to be involved in the processing of the descending auditory pathway, and it may be implicated in the multisensory integration of auditory information that takes place in the non-lemniscal auditory pathway.

A confocal microscopic study of gonadotropin-releasing hormone (GnRH) neuron inputs to dopaminergic neurons containing estrogen receptor alpha in the arcuate nucleus of GnRH-green fluorescent protein transgenic mice.

The purpose of the present study was to determine whether the septo-preoptico-tuberoinfundibular gonadotropin-releasing hormone (GnRH) pathway comes in close juxtaposition with tyrosine hydroxylase immunoreactive (TH-IR) neurons in the arcuate nucleus of female mice. Immunohistochemical staining with a TH monoclonal antibody coupled with confocal microscopy was employed on vibratome-cut brain sections of female GnRH-green fluorescent protein (GFP) transgenic mice to evaluate possible appositions between GnRH and tuberoinfundibular dopaminergic (TIDA) neurons. TH-IR neurons of the arcuate nucleus received GnRH neuronal appositions in adult female mice at proestrus and estrus stages. In contrast, no GnRH appositions were observed in adult females at diestrus. Subsequently, double immunohistochemical staining for TH and estrogen receptor-alpha (ERalpha) was performed to examine the role of estradiol on this relationship. We found that most TH-IR neurons contacted by GnRH fibers were immunoreactive for ERalpha. Our observations suggest that GnRH neurons communicate directly with TIDA neurons in the adult female. Furthermore, ERalpha activation in TIDA neurons may be involved in the formation of connections between GnRH neurons and TIDA neurons.

GABAA receptor epsilon subunit expression in identified peptidergic neurons of the rat hypothalamus.

Dual-labeling immunohistochemical or in situ hybridization studies for the recently cloned epsilon-subunit and several neuropeptides were performed in the rat hypothalamus. We revealed an extensive co-expression (>90%) with hypocretin (Hcrt), oxytocin (OT), the gonadotropin-releasing hormone (GnRH), and the melanin-concentrating hormone (MCH) peptides, whereas occasional co-expression (<10%) with cocaine-amphetamine-regulated transcript (CART) was found. Our results suggest that novel GABA(A) receptor subtypes comprising epsilon-subunit are important for metabolic and neuroendocrine functions.