Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

John Caprio

Abstract

Gustatory nuclei in the isthmic region of the metencephalon and in the posterior diencephalon of the channel catfish, Ictalurus punctatus, were examined anatomically and electrophysiologically. Neurons in the superior secondary gustatory nucleus (nGS) responded to taste and tactile stimulation of large peripheral receptive fields (RFs) that often included the epithelia of the oropharyngeal cavity and whole extraoral body surface. Taste responses to amino acids and nucleotides were dose-dependent, with detected thresholds from micromolar to millimolar concentrations. The RF organization within the nGS did not display the somatotopy present in the medullary gustatory nuclei. Anatomical labeling of secondary gustatory fibers showed that the distribution of fibers from different portions of both the facial (FL) and vagal (VL) lobes of the medulla overlapped within the nGS. Efferents from the nGS ascend in the tertiary gustatory tract to the caudal inferior lobe, where they terminate caudally in the nucleus lobobulbaris (nLB) and nucleus centralis (nCLI), and rostrolaterally in the nucleus diffusus (nDLI). Secondary projections from the FL also terminate in the nLB and in the nucleus subglomerulosus (nSG). The nLB forms three cell groups (caudal - nLB, rostrolateral - rl nLB, parvicellular - nLBp) which project to the FL, VL, and telencephalon, respectively. Cells from the nCLI project throughout the caudal inferior lobe and to the acousticolateral torus semicircularis and telencephalon, while the nDLI and nSG have intrinsic connections within the inferior lobe. The lateral thalamic nucleus (nLT) projects from this region back to the nGS. Taste responses similar to those from nGS units were recorded from units in the nCLI, nLB, rl nLB, nLBp, and nLT, supporting the proposed gustatory role for these nuclei. Tactile responsiveness was different between nuclei in the caudal inferior lobe. Units from the nCLI and nLB had lower spontaneous activity than those from other nuclei and typically had RFs including the whole ipsilateral extraoral body surface. Units from the rl nLB and nLBp had RFs that often included both oral and extraoral surfaces, bilaterally, but rl nLB RFs typically included the whole body while nLBp RFs were often restricted to the head or mouth.

Pages

160

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