Involvement of cocaine- and amphetamine-regulated transcript neurons in glucoprivic suppression of pulsatile luteinizing hormone secretion in female rats

抄録

Malnutrition often suppresses reproductive function by inhibiting the pulsatile secretion of gonadotropin-releasing hormone (GnRH)/gonadotropins in mammals. This study aimed to determine whether cocaine- and amphetamine-regulated transcript (CART) neurons mediate the suppression of GnRH/gonadotropin pulses under malnutrition, since CART neurons have been reported to project to kisspeptin/neurokinin B/dynorphin A neurons (also known as the GnRH pulse generator) and GnRH neurons in rats. Wistar-Imamichi female rats were ovariectomized (OVX), and some of these rats were immediately implanted with subcutaneous Silastic tubing containing estradiol-17β (OVX + low E2) to maintain a diestrous level of estrogen. Free-moving conscious OVX and OVX + low E2 rats were subjected to 1-h frequent blood sampling followed by brain sampling to examine whether acute glucoprivation by peripheral administration of 2-deoxy-D-glucose (2DG), a glucose utilization inhibitor, suppressed the secretion of luteinizing hormone (LH) and activated hypothalamic CART neurons. The other cohort of animals was subjected to 3-h frequent blood sampling to examine whether central CART administration suppresses pulsatile LH secretion. Peripheral 2DG administration suppressed LH secretion and activated CART neurons in the hypothalamic supraoptic nucleus (SON) and parvocellular paraventricular nucleus (PVN), but not in the magnocellular PVN-zona incerta-dorsomedial nucleus continuum and arcuate nucleus, in OVX and OVX + low E2 rats. In addition, central CART administration suppressed pulsatile LH secretion in OVX and OVX + low E2 rats. These results suggest the possible involvement of CART neurons in the SON and parvocellular PVN in malnutrition-induced suppression of pulsatile LH secretion in female rats.