Somatostatin mRNA: regional variation in hybridization densities in individual neurons.

Somatostatin mRNA is detected by in situ hybridization of 35S-labeled single-stranded cDNA probes to coronal sections of the rat brain that include the periventricular nucleus of the hypothalamus. Features supporting hybridization specificity include its anatomic distribution, the results of studies using multiple cDNA probes, RNAase experiments, competition studies, and correlations with patterns of somatostatin peptide immunostaining in adjacent sections. The hybridization densities vary strikingly from region to region, with highest densities in the periventricular nucleus and more modest levels in areas such as the cerebral cortex and the striatum. On the basis of the results of in situ and immunohistochemical approaches, we suggest that this variation is due to regional differences in the density of hybridization per positive cell, as well as to regional variation in the densities of somatostatinergic perikarya.