Chemical characterization of leptin-activated neurons in the rat brain

Abstract

Leptin has profound effects on food intake, body weight, and neuroendocrine status. The lack of leptin results in hormonal and metabolic alterations and a dramatic increase in body weight. Leptin acts in the brain, especially in the hypothalamus; however, the central nervous system sites that respond to leptin have not been examined comprehensively. In this study, we explored systematically the distribution of leptin-activated neurons throughout the rat brain. Furthermore, we investigated the chemical identity of subsets of these leptin-activated cells. Fos-like immunoreactivity (Fos-IR) was investigated in the rat brain after two different doses of leptin (1.0 mg/kg and 5.0 mg/kg) at 2 hours and 6 hours after injections. The induction of Fos-IR was observed in hypothalamic nuclei, including the paraventricular nucleus (PVH), the retrochiasmatic area (RCA), the ventromedial nucleus (VMH), the dorsomedial nucleus (DMH), the arcuate nucleus (Arc), and the ventral premammillary nucleus (PMV). In addition, leptin-induced Fos-IR was found in several nuclei of the brainstem, including the superior lateral and external lateral subdivisions of the parabrachial nucleus (slPB and elPB, respectively), the supragenual nucleus, and the nucleus of the solitary tract (NTS). By using double-labeling immunohistochemistry or immunohistochemistry coupled with in situ hybridization, leptin-activated neurons were found that contained cocaine- and amphetamine-regulated transcript mRNA in several hypothalamic nuclei, including the RCA, Arc, DMH, and PMV. In the Arc and DMH, leptin-induced Fos-IR was observed in neurons that expressed neurotensin mRNA. Dynorphin neurons in the VMH and in the Arc also expressed Fos-IR. In the brainstem, we found that cholecystokinin neurons in the slPB and glucagon-like peptide-1 neurons in the NTS were activated by leptin. We also investigated the coexpression of Fos-IR and the long form of the leptin receptor (OBRb) mRNA. We found double-labeled neurons surrounding the median eminence and in the RCA, Arc, VMH, DMH, and PMV. However, in brainstem sites, very little OBRb mRNA was found; thus, there were very few double-labeled cells. These results suggest that leptin stimulates brain pathways containing neuropeptides that are involved in the regulation of energy balance, autonomic homeostasis, and neuroendocrine status.

Organization of the Hypothalamus

“…Integration of leptin signals with other systems mediating a variety of homeostatic mechanisms, such as reproduction (Mantzoros, 2000;Schneider et al, 2000) may take place at the level of the arcuate nucleus by virtue of common populations of peptidergic neurons with divergent connections. For example, injections of leptin activate both NPY and POMC neurons in the arcuate nucleus, which project to regions such as the paraventricular and dorsomedial nuclei and appear to convey leptin based signals (Elias et al, 2000), but arcuate neurons also project to GnRH cells in the preoptic region (Chen et al, 1989;Li et al, 1999). Thus, different physiological functions may be coordinated by interactions between neurons located in the arcuate nucleus through common activation by leptin, or possibly through communication organized by local circuits in the arcuate nucleus.…”

Central leptin and ghrelin signalling: Comparing and contrasting their mechanisms of action in the brain

“…ObRb neurons are certainly expressed in the VMN and peripheral leptin administration induces c-Fos and pSTAT3 in VMN neurons [70,71]. Additionally, ewes with a lesioned ARC show a similar extent of c-Fos activation in response to iv leptin treatment as control ewes [65], arguing for direct action of leptin on populations of VMN neurons.…”

“…Interestingly, although peripheral leptin treatment in mice induce increased pSTAT3-immunoreactivity in the NTS [104] and induce c-Fos in several nuclei of the brainstem including the NTS [70], Elias and colleagues observed that very few leptin induced c-Fos positive neurons in the brainstem actually express ObRb mRNA. The NTS is the only brain region in addition to the ARC that contain POMC neurons, however there is controversy over their characteristics.…”

The role of leptin in the regulation of neuroendocrine function and CNS development

“…PMv neurons project to the POA and other nearby regions, where elements of the reproductive axis reside, and the PMv regulates reproductive behavior in males and coordinates GnRH release and ovulation in response to seasonal and other inputs in females [89][90][91][92][93][94][95][96][97][98][99]. PMv LRb neurons represent a major population of LRb-expressing/ leptin-responsive neurons in the brain [88].…”