CHEMICAL STIMULUS DETERMINANTS OF CAT GENICULATE GANGLION CHEMORESPONSIVE GROUP II UNIT DISCHARGE

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Abstract
Geniculate ganglion chemoresponsive group II units were studied in anesthetized cats. A wide variety of chemical substances were applied to the surface of the tongue to test for their stimulating effectiveness. Distilled water extracts of animal tissues (beef, cod, eggs, etc.) proved to be strong stimuli. A survey of a variety of chemical subtances disclosed that the most effective excitatory stimuli were certain amino acids (L-proline, L-cysteine, L-lysine, L-histidine, etc.), di- and triphosphate nucleosides and certain other substances (usually containing nitrogen). In testing compounds related to proline and histidine it was discovered that the heterocyclic ring components pyrrolidine and imidazole were as stimulatory as the parent amino acids. To further specify the properties of excitatory stimuli many simple heterocyclic compounds were tested. Optimum heterocyclic stimuli were four to six member nonaromatic (except for imidazole), nitrogen compounds. Neural discharge to nitrogen heterocycles was related to two structural and chemical factors: (1) a steric factor (in particular, ring size); and (2) the relative basicity of the compounds as indicated by pKa values.

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