Identification and localization of somatostatin-like immunoreactivity in the cerebellum of gymnotiform fish, Apteronotus leptorhynchus.

Previous studies have shown major mismatches between the localization of the neuropeptide somatostatin of its mRNA and the distribution of somatostatin receptors in the cerebellum of gymnotiform fish. By employing highly sensitive immunohistochemical techniques, we re-examined these mismatches in the gymnotiform fish Apteronotus leptorhynchus. We found somatostatin-like immunoreactivity in the corpus cerebelli, valvula cerebelli, eminentia granularis anterior, eminentia granularis posterior, and transitional zone. While labelled somata were predominantly restricted to a region near the boundary between the granule cell layers and molecular layers, immunopositive processes were distributed throughout large areas within the respective molecular layer. These immunopositive cells appear to represent a novel cell type in the cerebellum of gymnotiform fish.