CCK-ergic mechanisms in sensory systems

The histochemical analysis of cholecystokinin (CCK) systems in sensory syst ems has revealed involvement of CCK-ergic mechanisms both at the spinal lev el and in the viscero-sensory vagal pathway, with distinct differences betw een these two systems as well as between species. Thus, the CCK1 receptor i s particularly abundant in rat nodose ganglion neurons which express the fo od intake-suppressing cocaine- and amphetamine-regulated transcript (CART) peptide(s), representing a likely link between gastrointestinal CCK and cen tral feeding-regulatory centers. In contrast, rat dorsal root ganglions hav e lower numbers of CCK receptor mRNA-positive neurons, and CART is only exp ressed sparingly in this system. The CCK2 receptor is normally almost absen t from both systems but is strongly upregulated after peripheral nerve inju ry, suggesting a role in regenerative and trophic phenomena as well as, at the spinal level, in nerve injury-induced pain. In man and monkey the CCK1 receptor seems important in the dorsal hom under normal conditions, indicat ing distinct species differences.