Kisspeptin and neurokinin B expression in the human hypothalamus: Relation to reproduction and gender identity

Neuropeptides in the hypothalamus

The hypothalamus is one of the most complex region in the central nervous system regarding neuroanatomy, neurochemical content, neuropeptide/classical neurotransmitter interactions, physiological actions, and pathophysiology. Hypothalamic neuropeptides have been involved in a large plethora of mechanisms related with obesity, anxiety, feeding, energy metabolism, defensive behavior, mood, and reproduction. The therapeutic potential of these findings is enormous but the physiological complexity occurring in the hypothalamus is huge due in part to the interactions between numerous neuropeptides as well as between neuropeptides and other neuroactive substances. Here, we review the development and neuroanatomy of the hypothalamus as well as the involvement of 31 neuropeptides in hypothalamic functions and pathologies. Alterations in the secretion, release, and/or concentrations of neuropeptides and/or their hypothalamic receptors can trigger different pathologies. Several therapeutic strategies that could be carried out by adjusting neuropeptide levels in the hypothalamus are suggested. The combination of imaging techniques with a detailed neurochemical knowledge of the hypothalamus would be an excellent diagnostic tool, allowing personalized treatment. Several approaches for future research that may contribute to improve or resolve these pathologies are also mentioned.

Optogenetics studies of kisspeptin neurons

Optical systems and genetic engineering technologies have made it possible to control neurons and unravel neuronal circuit behavior with high temporal and spatial resolution. The application of optogenetic strategies to understand the physiology of kisspeptin neuronal circuits has evolved in recent years among the neuroendocrine community. Kisspeptin neurons are fundamentally involved in controlling mammalian reproduction but also are implicated in numerous other physiological processes, including but not limited to feeding, energy expenditure, core body temperature and behavior. We conducted a review aiming to shed light on the novel findings obtained from in vitro and in vivo optogenetic studies interrogating kisspeptin neuronal circuits to date. Understanding the function of kisspeptin networks in the brain can greatly inform a wide range of clinical studies investigating infertility treatments, gender identity, metabolic disorders, hot flushes and psychosexual disorders.

Olfactory and neuropeptide inputs to appetite neurons in the arcuate nucleus

The sense of smell has potent effects on appetite, but the underlying neural mechanisms are largely a mystery. The hypothalamic arcuate nucleus contains two subsets of neurons linked to appetite: AgRP (agouti-related peptide) neurons, which enhance appetite, and POMC (pro-opiomelanocortin) neurons, which suppress appetite. Here, we find that AgRP and POMC neurons receive indirect inputs from partially overlapping areas of the olfactory cortex, thus identifying their sources of odor signals. We also find neurons directly upstream of AgRP or POMC neurons in numerous other areas, identifying potential relays between the olfactory cortex and AgRP or POMC neurons. Transcriptome profiling of individual AgRP neurons reveals differential expression of receptors for multiple neuromodulators. Notably, known ligands of the receptors define subsets of neurons directly upstream of AgRP neurons in specific brain areas. Together, these findings indicate that higher olfactory areas can differentially influence AgRP and POMC appetite neurons, that subsets of AgRP neurons can be regulated by different neuromodulators, and that subsets of neurons upstream of AgRP neurons in specific brain areas use different neuromodulators, together or in distinct combinations to modulate AgRP neurons and thus appetite.