Phenotyping of nNOS neurons in the postnatal and adult female mouse hypothalamus

Abstract

Neurons expressing nitric oxide (NO) synthase (nNOS) and thus capable of synthesizing NO play major roles in many aspects of brain function. While the heterogeneity of nNOS-expressing neurons has been studied in various brain regions, their phenotype in the hypothalamus remains largely unknown. Here we examined the distribution of cells expressing nNOS in the postnatal and adult female mouse hypothalamus using immunohistochemistry. In both adults and neonates, nNOS was largely restricted to regions of the hypothalamus involved in the control of bodily functions, such as energy balance and reproduction. Labeled cells were found in the paraventricular, ventromedial, and dorsomedial nuclei as well as in the lateral area of the hypothalamus. Intriguingly, nNOS was seen only after the second week of life in the arcuate nucleus of the hypothalamus (ARH). The most dense and heavily labeled population of cells was found in the organum vasculosum laminae terminalis (OV) and the median preoptic nucleus (MEPO), where most of the somata of the neuroendocrine neurons releasing GnRH and controlling reproduction are located. A great proportion of nNOS-immunoreactive neurons in the OV/MEPO and ARH were seen to express estrogen receptor (ER) a. Notably, almost all ERa-immunoreactive cells of the OV/MEPO also expressed nNOS. Moreover, the use of EYFPVglut2, EYFPVgat, and GFPGad67 transgenic mouse lines revealed that, like GnRH neurons, most hypothalamic nNOS neurons have a glutamatergic phenotype, except for nNOS neurons of the ARH, which are GABAergic. Altogether, these observations are consistent with the proposed role of nNOS neurons in physiological processes.

Female sexual behavior in mice is controlled by kisspeptin neurons

“…Furthermore, progestin receptors are also present in the lateral part of the VMH and its expression is highly dependent on estrogens 49 – 52 . Finally, a recent study 53 showed that close to 100% of neurons expressing estradiol receptors in the VMHvl are actually nNOS-expressing neurons. Taken together, these findings reveal that kisspeptin neurons communicate with nNOS neurons in the VMHvl, a central hub driving female sexual behavior.…”

Female sexual behavior in mice is controlled by kisspeptin neurons

“…Furthermore, progestin receptors are also present in the lateral part of the VMH and its expression is highly dependent on estrogens [49][50][51][52] . Finally, a recent study 53 showed that close to 100% of neurons expressing estradiol receptors in the VMHvl are actually nNOS-expressing neurons. Taken together, these findings reveal that kisspeptin neurons communicate with nNOS neurons in the VMHvl, a central hub driving female sexual behavior.…”

The Role of Kisspeptin in Sexual Behavior

“…It is interesting to note that close to 100% of neurons expressing estradiol receptors in the VMHvl are actually nNOS expressing neurons. 55 However, it cannot be ruled out that other nNOS populations are also involved, for instance, in the OVLT, where nNOS neurons are part of a neural circuit regulating ovarian cyclicity and ovulation. 56 It is interesting to note that mating stimulation induced an activation of nNOS neurons in the OVLT as measured by the number of phosphorylated nNOS (pnNOS) neurons (►Fig.…”