The cerebellar dorsal granular ridge in an elasmobranch has proprioceptive and electroreceptive representations and projects homotopically to the medullary electrosensory nucleus.
1. Response properties of neurons in the dorsal granular ridge (DGR) of the little skate, Raja erinacea, were studied in decerebrate, curarized fish. Sensory responses included proprioceptive (426 of 952; 45%) and electroreceptive units (526 of 952; 55%). Electroreceptive units responded to weak electric fields with a higher threshold than lower-order units and had large ipsilateral receptive fields, whose exact boundaries were often unclear but contained smaller, identifiable best areas. Proprioceptive units responded to displacement of the ipsilateral fin and were either position- or movement-sensitive. 2. Both proprioceptive and electroreceptive units showed a progression of receptive fields from anterior to posterior body in the rostral to caudal direction along the length of DGR. Sensory maps in DGR projected homotopically to the electrosensory somatotopy in the dorsal nucleus. Peak evoked potentials and units responding to local DGR stimulation occurred only in areas of the dorsal nucleus with receptive fields located within the composite receptive field at the DGR stimulation site. 3. Single shocks to DGR produced a short spike train followed by a prolonged suppression period in the medullary dorsal nucleus. These results have implications for the role of the parallel fiber system in medullary electrosensory processing.
Department of Biology, Wesleyan University, Middletown, CT 06459-0170.
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D000818:Animals; D002531:Cerebellum / Q000502:physiology*; D004594:Electrophysiology; D008526:Medulla Oblongata / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D011434:Proprioception / Q000502:physiology*; D011984:Sensory Receptor Cells / Q000502:physiology*; D012860:Skates, Fish / Q000502:physiology*