Gene Expression Profiling during Pregnancy in Rat Brain Tissue

The neurophysiological changes that occur during pregnancy in the female mammal have led to the coining of the phrases “expectant brain” and “maternal brain”. Although much is known of the hormonal changes during pregnancy, alterations in neurotransmitter gene expression have not been well-studied. We examined gene expression in the ventromedial nucleus of the hypothalamus (VMH) during pregnancy based on the fact that this nucleus not only modulates the physiological changes that occur during pregnancy but is also involved in the development of maternal behavior. This study was designed to identify genes that are differentially expressed between mid- and late-pregnancy in order to determine which genes may be associated with the onset and display of maternal behavior and the development of the maternal brain. A commercially available PCR array containing 84 neurotransmitter receptor and regulator genes (RT(2) Profiler PCR array) was used. Brains were harvested from rats on days 12 and 21 of gestation, frozen, and micropunched to obtain the VMH. Total RNA was extracted, cDNA prepared, and SYBR Green qPCR was performed. In the VMH, expression of five genes were reduced on day 21 of gestation compared to day 12 (Chrna6, Drd5, Gabrr2, Prokr2, and Ppyr1) whereas Chat, Chrm5, Drd4, Gabra5, Gabrg2, LOC289606, Nmu5r2, and Npy5r expression was elevated. Five genes were chosen to be validated in an additional experiment based on their known involvement in maternal behavior onset. This experiment confirmed that gene expression for both the CCK-A receptor and the GABA(A)R γ2 receptor increases at the end of pregnancy. In general, these results identify genes possibly involved in the establishment of the maternal brain in rats and indicate possible new genes to be investigated.