Abstract:
The Damaraland mole-rat (Fukomys damarensis) is a eusocial, subterranean rodent, in which
breeding is limited to a single reproductive pair within each colony. Non-reproductive
females, while in the confines of the colony, exhibit socially-induced infertility. Anovulation
is thought to be caused by a disruption in the normal gonadotropin-releasing hormone
(GnRH) secretion from the hypothalamus. In order to assess whether social suppression is
associated with altered GnRH mRNA expression in the brain we investigated the distribution
and gene expression levels by means of in situ hybridization in female breeders and nonbreeders
from field captured colonies of the Damaraland mole-rat. We found expression of
GnRH mRNA as a loose network in several forebrain areas of female Damaraland mole-rats
with the majority of labelling in the preoptic and anterior hypothalamus. The distribution
matched previous findings using immunocytochemistry in this and other social mole-rat
species. Quantification of the hybridisation signal revealed no difference between breeding
and non-breeding females in the average optical density of the hybridization signal and the
size of the total area covered by GnRH mRNA. However, analysis along the rostro-caudal
axis revealed significantly elevated GnRH mRNA expression in the rostral preoptic region of
breeders compared to non-breeders, while the latter had increased GnRH mRNA expression
at the caudal level of the anterior hypothalamus. This study indicates that social suppression
affects the expression of GnRH mRNA in female Damaraland mole-rats. Furthermore,
differential regulation occurs within different neuron subpopulations.
