Fasting Reduces KiSS-1 Expression in the Anteroventral Periventricular Nucleus (AVPV): Effects of Fasting on the Expression of KiSS-1 and Neuropeptide Y in the AVPV or Arcuate Nucleus of Female Rats

Changes in metabolic state, such as those induced by fasting, have profound effects on reproduction. In rats, the time‐course over which fasting inhibits luteinising hormone (LH) release is reduced to 48 h by the presence of oestradiol‐17β (E2). Hypothalamic kisspeptin plays a key role in mediating the actions of E2 on gonadotrophin‐releasing hormone (GnRH) neurones, and thereby promotes LH release. KiSS‐1‐expressing neurones are found in the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC). Extensive evidence implicates the AVPV in GnRH release and the ARC in energy balance. The latter nucleus also contains neurones that express neuropeptide Y (NPY), an orexigenic peptide implicated in GnRH control. To elucidate the involvement of kisspeptin and/or NPY in hypothalamic responses to fasting, their expression was quantified by in situ hybridisation histochemistry in ovariectomised rats, with or without E2 replacement, before and after 48 h of fasting. In the presence of E2, but not in its absence, the fasting suppressed plasma LH. In the AVPV, the low level of KiSS‐1 expression found in the absence of E2 was unaffected by fasting. By contrast, the elevated level found in the presence of E2 was suppressed by fasting. Independent of E2, fasting had no effect on KiSS‐1 expression in the ARC, but increased NPY expression at that site. The present study has identified the AVPV as a site at which KiSS‐1 expression can be influenced by fasting. The results suggest that inhibition of KiSS‐1 expression in the AVPV may be a significant factor in restraining the gonadotrophic axis in response to negative energy balance in the presence of oestrogen. The extent to which the concurrent rise in NPY expression in the ARC may contribute to the suppression of LH release by influencing AVPV kisspeptin neurones, directly or indirectly, or by actions independent of kisspeptin, remains to be established.