Evidence for effects of phoenixin on neurons of the paraventricular nucleus
The paraventricular nucleus (PVN) of the hypothalamus has been implicated in autonomic regulation. Through projections to the pituitary gland, median eminence and hindbrain, the PVN plays a role in stress response and other autonomic functions. Recent findings have indicated that both phoenixin (PNX), a peptide involved in such responses, and its receptor, GPR173, are expressed throughout the PVN. PNX is thought to sensitize the pituitary gland to releasing hormones, as well as contribute to regulation of reproductive and stress hormone release. Recently, specific stress-related effects of this peptide in the nucleus of the solitary tract (NTS) have been demonstrated. In this study we investigated the effects of PNX on PVN neuronal activity using in vitro extracellular recordings. Recordings from a total of 824 neurons showed that 16% (n= 130) of these cells were activated by bath administration of PNX, while 14% (n= 117) were inhibited. Remaining cells tested showed no obvious changes in spike frequency. Furthermore, we observed that both these excitatory and inhibitory effects are still observed when recordings are obtained in low-Ca2+/ high-Mg2+ artificial cerebral spinal fluid (to block synaptic release of neurotransmitters and thus synaptic transmission). A total of 187 neurons showed that 5% (n= 7) are excited and 22% (n= 43) are inhibited in the low calcium condition, supporting the conclusion that the effects of PNX on PVN neurons are both direct and indirect as both response types are observed in both conditions. These results implicate PNX in autonomic function, specifically in the central regulation of stress response, fluid and electrolyte balance, food intake, and reproductive function.