Relations between social status and the gonadotrophin-releasing hormone system in females of two cooperatively breeding species of African mole-rats, Cryptomys hottentotus hottentotus and Cryptomys hottentotus pretoriae: neuroanatomical and neuroendocrinological studies.

In common (Cryptomys hottentotus hottentotus) and highveld (Cryptomys hottentotus pretoriae) mole-rats, reproduction is subject to two forms of regulation in addition to incest avoidance. These are the only social bathyergids known to restrict breeding to a particular season; furthermore, subordinate members of their colonies show suppressed reproduction throughout the year. Females from both species were assessed and compared for social and seasonal effects on the gonadotrophin-releasing hormone (GnRH) system. GnRH-immunoreactive (ir) structures were visualized immunohistochemically; GnRH content was determined by radioimmunoassay. In both species, GnRH-ir cell bodies and processes are loosely distributed along the septopreopticoinfundibular continuum, with dense fiber aggregations in the region of the organum vasculosum of the lamina terminalis and median eminence. The two species differ in the rostrocaudal distribution of their GnRH-ir cell bodies. In highveld mole-rats, most of these cells are in the septal/preoptic area; in common mole-rats, more than half of them are in the mediobasal hypothalamus. Compared with common mole-rats, highveld mole-rats have a greater total number of GnRH-ir cell bodies, higher GnRH content, and more intense GnRH immunoreactivity in the median eminence. Within highveld colonies, the nonreproductive females have larger GnRH-ir cell bodies, more intense GnRH immunoreactivity in the median eminence, and higher GnRH content than the reproductive females; these findings suggest inhibited release of GnRH in the nonreproductive, subordinate females. In contrast, in common mole-rat females, neither status nor season appears to affect the investigated parameters of the GnRH system; this suggests a predominantly behavioral basis to their suppressed reproduction.