Distribution of ?-Conotoxin GVIA binding sites in teleost cerebellar and electrosensory neurons

Abstract

The distribution of omega-Conotoxin GVIA (CgTx) binding sites was used to localize putative N-type Ca2+ channels in an electrosensory cerebellar lobule, the eminentia granularis pars posterior, and in the electrosensory lateral line lobe of a gymnotiform teleost (Apteronotus leptorhynchus). The binding sites for CgTx revealed by an anti-CgTx antibody had a consistent distribution on somatic and dendritic membranes of specific cell types in both structures. The distribution of CgTx binding was unaffected by co-incubation with nifedipine or AgaToxin IVA, blocking agents for L- and P-type Ca2+ channels, respectively. Incubation with CgTx in the presence of varying levels of extracellular Ca2+ altered the number but not the cell types exhibiting immunolabel. A punctate immunolabel was detected on somatic membranes of granule and stellate cell interneurons in both the eminentia granularis pars posterior and the electrosensory lateral line lobe. Punctate CgTx binding sites were also present on spherical cell somata and on the large presynaptic terminals of primary afferents that terminate on spherical cells in the electrosensory lateral line lobe. No label was detected in association with distal dendritic membranes of any cell class, or with parallel 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 known to persist in this layer in adult Apteronotus. The distribution of labeled stellate cells with respect to topographic maps in the electrosensory lateral line lobe further suggest that N-type Ca2+ channels are expressed in relation to functional activity across these sensory maps.

A prominent soma‐dendritic distribution of Kv3.3 K+ channels in electrosensory and cerebellar neurons

“…The medial segment (MS) receives input from ampullary receptors, whereas the centromedial (MS), centrolateral (CLS), and lateral (LS) segments receive a common input from tuberous electroreceptors. The cell types and neural circuitry of each map are believed to be equivalent, although differences in the cytochemistry and physiology of cells between segments are apparent (Shumway, 1989; Metzner and Heiligenberg, 1991; Turner and Moroz, 1995; Tharani et al, 1996; Turner et al, 1996; Metzner and Juranek, 1997).…”

“…The EGp differs from the CCb in representing a cerebellar lobule specific to electroreceptive teleosts that provides electrosensory feedback to the ELL via parallel fiber projections (Bastian, 1999). In addition, several aspects of EGp structure (i.e., a dorsal position of granule cells), granule cells in the stage of migration, and cytochemical properties (NADPH‐diaphorase, ω‐conotoxin GVIA binding) are very closely aligned with those of developing mammalian cerebellum (Turner and Moroz, 1995; Tharani et al, 1996; Zupanc, 1999). It is interesting that Kv3.3b is expressed in mouse cerebellar Purkinje cells only after postnatal day 10 and coincident with the migration of cerebellar granule cells and maturation of Purkinje cell morphology (Goldman‐Wohl et al, 1994).…”