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Abstract

In the diencephalon of the weakly electric gymnotiform fish Apteronous leptorhynchus, part of the central posterior/prepacemaker nucleus innervates the preglomerular nucleus. A minor population of these neurons expresses immunoreactivity against somatostatin, as has been shown by combining peptide immunohistochemistry with an in vitro tract-tracing technique. In contrast to the expectation, however, this neuropeptide does not appear to be transported along the axons to the projection site, as somatostatin-like immunoreactivity could not be detected in the preglomerular nucleus. It is, therefore, likely that somatostatin expressed in these neurons exerts a non-synaptic function in the region of the central posterior/prepacemaker nucleus itself.