Cholecystokinin activates both A- and C-type vagal afferent neurons

Patch-clamp electrophysiological methods were used on dissociated rat nodose neurons maintained in culture to determine whether responses to cholecystokinin (CCK) were associated with capsaicin-resistant ( A type) or capsaicin-sensitive ( C type) neurons. Nodose neurons were classified as A or C type on the basis of the characteristics of the Na+ current, a hyperpolarization-activated current, and sensitivity to a low concentration of capsaicin to ascertain the presence of vanilloid receptor 1 that has been associated with C-type neurons in sensory ganglia. It was expected that only capsaicin-sensitive C-type neurons would respond to CCK, because most vagally mediated actions of CCK are blocked by capsaicin treatment. However, we found that subpopulations of both A- and C-type neurons responded to CCK ( 24 and 38%, respectively). Thus some vagally mediated actions of CCK may be mediated by capsaicin insensitive A- type neurons.