In situ hybridization of putative somatostatin mRNA in the brain of electric gymnotiform fish.

The distribution of somatostatin mRNA in the brain of Apteronotus leptorhynchus, a weakly electric gymnotiform fish, has been mapped by employing in situ hybridization with an oligodeoxynucleotide probe corresponding to nucleotides 1-26 of catfish somatostatin mRNA; this probe was end-labelled with digoxigenin. Most labelled cell groups were found in the telencephalon, followed by the diencephalon. This distribution is in good agreement with previous immunohistochemical investigations. In the complex of the diencephalic central-posterior/prepacemaker nucleus, a cluster of neurons controlling electrocommunicatory behavior, somatostatin mRNA could be detected only in lateral aspects, although many medial cells also stain positively with immunohistochemical techniques. This difference may be related to the growth of these neurons during adulthood.