EXPRESSION PATTERNS OF RAT SOMATOSTATIN RECEPTOR GENES IN PRENATAL AND POSTNATAL BRAIN AND PITUITARY

The relative abundances of mRNAs encoding four different somatostatin receptors were examined using PCR techniques during postnatal developm ent of the rat brain and hypophysis. In most tissues, somatostatin rec eptor 1 and 4 mRNAs are more abundant than those encoding somatostatin receptor 2 and 3. Transcript levels of somatostatin receptor subtype 4 are relatively high in the cortex, hippocampus, and striatum, those of subtype 1 in the cortex and brainstem, and those of subtype 3 in th e cerebellum. In situ hybridization revealed the presence of significa nt amounts of somatostatin receptor 1 mRNA, as early as prenatal day 1 4, in the trigeminal ganglion and in the neuroepithelial layers surrou nding the lateral, third, and fourth ventricles. In the developing cor tex a morphological change in the sites of somatostatin receptor 1 gen e expression occurs; mRNA is present superficially in the cortex at pr enatal stages, appears in all layers shortly after birth, and in adult rats is restricted to the deep cortical layers. In the cerebellum, so matostatin receptor 1 mRNA levels are highest around birth, declining thereafter. In contrast, cerebellar somatostatin receptor 3 transcript s are absent at birth, become detectable around postnatal day 7, and r each a maximal level during maturation.