Developmental profile of messenger RNA for the corticotropin-releasing hormone receptor in the rat limbic system

Abstract

The ontogeny of corticotropin-releasing hormone (CRH) receptor messenger ribonucleic acid (mRNA) in rat brain, using in situ hybridization, is the focus of this study. The developmental profile of CRH receptor using binding assays and receptor autoradiography has been reported, but may be confounded by the presence of a binding protein. The recent cloning of the rat CRH receptor gene has permitted the use of in situ hybridization histochemistry to map the distribution of cells expressing CRH receptor mRNA in the developing brain. We used antisense 35S-labeled oligodeoxynucleotide probes for the two reported splice-variants of the CRH receptor mRNA, which yielded essentially identical localization patterns. CRH receptor mRNA was clearly detectable in infant brain starting on the second postnatal day. Signal in hippocampal CA1, CA2 and CA3a increased to 300-600% of adult levels by postnatal day 6 with a subsequent gradual decline. In the amygdala, in contrast, CRH receptor mRNA abundance increased steadily between the second and the ninth postnatal days, to levels twice higher than those in the adult. In the cortex, CRH receptor mRNA levels were high on postnatal day 2 and decreased to adult levels by day 12. Transient signal over the hypothalamic paraventricular nucleus, observed on the second postnatal day, was not evident at older ages. These results demonstrate robust synthesis of CRH receptor as early as on the second postnatal day and unique region-specific developmental profiles for CRH receptor gene expression.

Fig. 1

Graph showing distinct developmental profiles of CRH receptor mRNA in three limbic structures, cortex, hippocampus and amygdala.

Fig. 2

Computer-generated pseudocolor image, showing CRH receptor mRNA distribution in the nine day old rat forebrain. Large arrow points to the CA3 pyramidal layer of the hippocampus, revealing high receptor mRNA density (yellow-pink). Small arrow shows the piriform cortex. Bar = 0.18 mm.

Fig. 3

Coronal section through adult forebrain after in situ hybridization for the CRH receptor mRNA. High receptor density is seen in hippocampal CA3 (small arrow), the inferior blade of the dentate gyrus (large arrow) and the piriform cortex (star). Bar = 0.20 mm.

Fig. 4

Coronal section of an adult rat forebrain. The section was subjected to in situ hybridization using an oligodeoxynucleotide probe complementary to that used for localization of CRH-receptor-mRNA (‘sense’ control). Little signal is visible. Bar = 0.2 mm.