Morphological evidence for direct interaction between kisspeptin and gonadotropin-releasing hormone neurons at the median eminence of the male goat: an immunoelectron microscopic study.

Kisspeptin has been thought to play pivotal roles in the control of both pulse and surge modes of gonadotropin-releasing hormone (GnRH) secretion. To clarify loci of kisspeptin action on GnRH neurons, the present study examined the morphology of the kisspeptin system and the associations between kisspeptin and GnRH systems in gonadally intact and castrated male goats. Kisspeptin-immunoreactive (ir) and Kiss1-positive neurons were found in the medial preoptic area of intact but not castrated goats. Kisspeptin-ir cell bodies and fibers in the arcuate nucleus (ARC) and median eminence (ME) were fewer in intact male goats compared with castrated animals. Apposition of kisspeptin-ir fibers on GnRH-ir cell bodies was very rare in both intact and castrated goats, whereas the intimate association of kisspeptin-ir fibers with GnRH-ir nerve terminals was observed in the ME of castrated animals. Neurokinin B immunoreactivity colocalized not only in kisspeptin-ir cell bodies in the ARC but also in kisspeptin-ir fibers in the ME, suggesting that a majority of kisspeptin-ir fibers projecting to the ME originates from the ARC. A dual immunoelectron microscopic examination revealed that nerve terminals containing kisspeptin-ir vesicles made direct contact with GnRH-ir nerve terminals at the ME of castrated goats. There was no evidence for the existence of the typical synaptic structure between kisspeptin- and GnRH-ir fibers. The present results suggest that the ARC kisspeptin neurons act on GnRH neurons at the ME to control (possibly the pulse mode of) GnRH secretion in males.

Neurokinin B peptide-2 neurons project from the hypothalamus to the thoracolumbar spinal cord of the rat.

The presence and location of CNS neurokinin B peptide-2-like immunoreactive neurons that project to the spinal cord were studied by a combination of retrograde transport of fluorescent dye (FluoroGold) and fluorescence immunocytochemistry. After injections of FluoroGold into the thoracic or lumbar segments of the rat spinal cord, serial sections of brain were stained with antisera directed against neurokinin B peptide-2. The results of the study showed that neurokinin B peptide-2-like immunoreactive neurons were located in the nucleus arcuate, median eminence, ventral and external bed nuclei of the stria terminalis, dorsal hypothalamic area, and medial habenula. Neurokinin B peptide-2 neurons that give rise to the long descending projections from the hypothalamus to thoracolumbar spinal cord were found only in the dorsal hypothalamic area. Approximately 36% of the neurokinin B peptide-2 neurons in the dorsal hypothalamic area projected to the spinal cord, whereas about 28% of the spinal projecting neurons in the dorsal hypothalamic area contained neurokinin B peptide-2-like immunoreactivity. Most of the spinal projecting neurokinin B peptide-2 neurons in the dorsal hypothalamic area had a cell size of 15 x 25 microns. In the spinal cord, immunoreactive neurokinin B peptide-2 fibers and terminals were distributed mainly in the superficial dorsal horn and the central autonomic area, with the highest density in laminae II and X, with less density in laminae IV and V. A few neurokinin peptide-2 fibers and terminals were also found in the ventral horn of the spinal cord. The results of the present study show that hypothalamic neurokinin B peptide-2 neurons are the main source of the spinal neurokinin B peptide-2.

Distribution of neurokinin B in rat spinal cord and peripheral tissues: comparison with neurokinin A and substance P and effects of neonatal capsaicin treatment.

In the present study, highly specific radioimmunoassays were developed and used to measure neurokinin B, neurokinin A and substance P in the rat spinal cord and various peripheral tissues. The results are as follows. (1) Neurokinin B and neurokinin A were distributed all along the rostrocaudal axis of the spinal cord, as is substance P, and were more concentrated in the dorsal than in the ventral region. (2) Substance P was more abundant in the central and peripheral nervous tissues than neurokinin A, while in certain peripheral organs, neurokinin A was more abundant than substance P. In the spinal cord, neurokinin B concentrations were lower than those of the other two tachykinins. (3) In contrast to neurokinin A and substance P, neurokinin B was not detected in any of the peripheral tissues examined. (4) Capsaicin treatment reduced by half neurokinin A and substance P concentrations in the dorsal region of the spinal cord, the dorsal root ganglia and the sciatic nerve, but was without effect on neurokinin B concentrations in the spinal cord. Neurokinin A, like substance P, may therefore have an important function in the transmission of sensory information, particularly in nociceptive transmission from the periphery to the spinal cord and in peripheral neurogenic inflammation. In contrast, since neurokinin B was not found in the sensory neurons, it is not likely to have these functions, but may perhaps control them.

Hypothalamic regulatory peptides in obese and lean Zucker rats.

1. Hypothalamic concentrations of nine peptides with experimental effects on energy balance were compared in obese (fa/fa) and lean (Fa/?) male Zucker rats. To determine whether any peptide differences between obese and lean rats might be due to the overweight condition per se, separate groups of obese rats were food-restricted to reduce their body weight to lean values. 2. Concentrations of neuromedin B, a bombesin-like peptide, in the central hypothalamus were significantly higher in obese than in lean rats. This difference was not affected in food-restricted obese rats. 3. Hypothalamic levels of neuropeptide Y, an extremely potent central appetite stimulant, were similar in lean and freely fed obese rats but central hypothalamic levels of neuropeptide Y rose significantly in food-restricted obese rats. 4. These findings suggest that disturbances in hypothalamic neuromedin B concentrations may be involved in the obesity syndrome of the fa/fa Zucker rat. Increased central hypothalamic levels of neuropeptide Y in food-restricted rats suggest that this peptide may help to defend body weight by stimulating eating after weight loss.