Doctor of Philosophy (PhD)
A chemotopic map of biologically relevant odorants (that include amino acids, bile salts and nucleotides) exists in the olfactory bulb (OB) and forebrain (FB) of channel catfish, Ictalurus punctatus (Chapter one). Neurons processing bile salt odorant information lie medially within these bilaterally symmetric structures; however, information as to how single neurons discriminate and process this odorant information is lacking. Chapters two and three of the dissertation identify the range of odorant bile salt molecules that excite these neurons [i.e. the excitatory molecular receptive range (EMRR)] within the bile salt chemotopic zones of the OB and FB. The results of the investigations of single bile salt responsive neurons within the OB indicate that these neurons are selectively excited by combinations of molecular features found on the side-chain and the steroid nucleus of bile salt molecules. Further, the results of the investigations of single bile salt responsive neurons within the FB indicate that their EMRRs are virtually identical to that of OB neurons suggesting that little modification of the neural olfactory quality code for these molecules occurred between the OB and the FB. Bile salts are known olfactory stimuli to teleosts, but only a single report (Yamashita et al. 2006) indicated that the taste system of a fish was sensitive to this class of stimuli. Chapter four investigates the gustatory sensitivity of the facial taste system to bile salts in the channel catfish. Bile salts were shown to be highly effective facial taste stimuli with estimated electrophysiological thresholds of approximately 10-11M-10-10M. Multiunit cross-adaptation experiments indicate that bile salts and amino acids bind to relatively independent receptor sites; however, nerve twig data and a few single fiber recordings suggest that both independent and shared neural pathways exist for the transmission of bile salt and amino acid information to the primary gustatory nucleus of the medulla. The findings of the present report aid in understanding how bile salt molecules are detected and initially processed by the olfactory and gustatory systems in catfish and further suggest that bile salt odorant information is not greatly transformed by central olfactory neurons (Chapter five).
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Rolen, Shane Howell, "Bile salts as olfactory and gustatory stimuli in the channel catfish" (2008). LSU Doctoral Dissertations. 2918.