DISTRIBUTION OF OMEGA-CONOTOXIN GVIA BINDING-SITES IN TELEOST CEREBELLAR AND ELECTROSENSORY NEURONS

The distribution of omega-Conotoxin GVIA (CgTx) binding sites was used to localize putative N-type Ca2+ channels in an electrosensory cerebe llar lobule, the eminentia granularis pars posterior, and in the elect rosensory lateral line lobe of a gymnotiform teleost (Apteronotus lept orhynchus). The binding sites for CgTx revealed by an anti-CgTx antibo dy had a consistent distribution on somatic and dendritic membranes of specific cell types in both structures. The distribution of CgTx bind ing was unaffected by co-incubation with nifedipine or AgaToxin IVA, b locking agents for L- and P-type Ca2+ channels, respectively. Incubati on with CgTx in the presence of varying levels of extracellular Ca2+ a ltered the number but not the cell types exhibiting immunolabel. A pun ctate immunolabel was detected on somatic membranes of granule and ste llate cell interneurons in both the eminentia granularis pars posterio r and the electrosensory lateral line lobe. Punctate CgTx binding site s were also present on spherical cell somata and on the large presynap tic terminals of primary afferents that terminate on spherical cells i n the electrosensory lateral line lobe. No label was detected in assoc iation with distal dendritic membranes of any cell class, or with para llel fibers in the respective molecular layers. Binding sites for CgTx in the eminentia granularis are consistent with the established role for N-type Ca2+ channels in cell migrations, an activity which is know n to persist in this layer in adult Apteronotus. The distribution of l abeled stellate cells with respect to topographic maps in the electros ensory lateral line lobe further suggest that N-type Ca2+ channels are expressed in relation to functional activity across these sensory map s. (C) 1996 Wiley-Liss, Inc.