TISSUE DISTRIBUTION AND SUBCELLULAR-LOCALIZATION OF NA-RNA IN THE NERVOUS-SYSTEM OF THE SQUID, LOLIGO-OPALESCENS( CHANNEL MESSENGER)

Recent cloning of a putative Nat channel a subunit cDNA, GFLN1, from t he squid stellate ganglion has allowed us to study the expression of t his ion channel at a cellular level. In situ hybridizations with a pro be derived from and specific to 3' untranslated and coding sequence of GFLN1 were used to determine its tissue distribution as well as its s ubcellular localization. In sections of the stellate ganglion, the pro be labeled all of the cells in the giant fiber lobe (GFL) and most cel ls in the cellular layer of the main ganglion. In these non-GFL portio ns of the stellate ganglion, labeling was particularly intense in the ventral large cells and weak or absent in the dorsal small cells. In t he optic lobe, only a select group of cells, the second-order visual g iant neurons, were intensely labeled. These results are consistent wit h electrophysiological data that show GFL-like Na+ currents in rare la rge cells dissociated from the optic lobe and in most but not all cell s from the non-GFL part of the stellate ganglion. In sections of the s ubesophageal mass of the central nervous system, strong labeling for G FLN1 mRNA occurred in the fin lobe, posterior chromatophore lobe, cent ral and latero-ventral palliovisceral lobes, and posterior pedal lobe. In all cases, labeling was detected only in the cellular layer of the se tissues and never in nerves or neuropil. In situ hybridization with dissociated GFL neurons maintained in primary culture verified that N a+ channel mRNA is confined to the cell body. These results indicate t hat GFLN1 is expressed predominately in large cells with large or long axons, and that this mRNA is restricted to the cell bodies of these n eurons.