Neuropeptides modulate rat chorda tympani responses

The neuropeptide leptin has been shown to selectively modulate rat chorda tympani (CT) responses to sweet tastants. To explore whether other neuropeptides can modulate such responses, rat whole nerve CT responses to NaCl, HCl, quinine HCl, and sucrose were measured while administering cholecystokinin-8 (CCK-8), substance P4-11 (SP4-11), or calcitonin gene-related peptide ( CGRP). To avoid possible confounding effects on CT responses that take long times to develop, such as those that arise from intraperitoneal injections, we investigated the effects of the above peptides injected into the ipsilateral lingual artery ( LA) on CT nerve responses during the initial seconds after a tastant was placed on the tongue. We found that CT responses to NaCl and HCl were increased by CCK-8 and decreased by CGRP. SP4-11 had no noticeable effect. Peptide-induced CT responses to quinine HCl or sucrose were too small to accurately detect. These data suggest that at short latencies, after local infusion via the LA, neuropeptides can alter CT responses in a peptide-specific manner.