The immunocytochemical localization of glutamate in the electrosensory system of the gymnotiform fish, Apteronotus leptorhynchus.

The first processing station of the electrosensory system is the medullary electrosensory lateral line lobe. The electrosensory lateral line lobe of gymnotiform fish is a laminated structure with three anatomically distinct excitatory inputs: primary afferents from electroreceptors, the direct feedback from n. praeminentialis and indirect feedback from n. praeminentialis via a cerebellar lobe--the eminentia granularis posterior. We utilized immunocytochemistry on L-R White-embedded semithin sections, and immunogold on thin sections to localize glutamate and aspartate in the electrosensory lateral line lobe, its afferent inputs and efferent targets. The excitatory inputs and the electrosensory lateral line lobe projection neurons are immunopositive for glutamate only, suggesting that glutamate rather than aspartate is the excitatory transmitter of the electrosensory system.