Low-affinity CCK-A receptors are coexpressed with leptin receptors in rat nodose ganglia: implications for leptin as a regulator of short-term satiety

The paradigm for the control of feeding behavior has changed significantly. Research has shown that leptin, in the presence of CCK, may mediate the control of short-term food intake. This interaction between CCK and leptin occurs at the vagus nerve. In the present study, we aimed to characterize the interaction between CCK and leptin in the vagal primary afferent neurons. Single neuronal discharges of vagal primary afferent neurons innervating the gastrointestinal tract were recorded from rat nodose ganglia. Three groups of nodose ganglia neurons were identified: group 1 responded to CCK-8 but not leptin; group 2 responded to leptin but not CCK-8; group 3 responded to high-dose CCK-8 and leptin. In fact, the neurons in group 3 showed CCK-8 and leptin potentiation, and they responded to gastric distention. To identify the CCK-A receptor (CCKAR) affinity states that colocalize with the leptin receptor OB-Rb, we used CCK-JMV-180, a high-affinity CCKAR agonist and low-affinity CCKAR antagonist. As expected, immunohistochemical studies showed that CCK-8 administration significantly potentiated the increase in the number of c-Fos-positive neurons stimulated by leptin in vagal nodose ganglia. Administration of CCK-JMV-180 eliminated the synergistic interaction between CCK-8 and leptin. We conclude that both low- and high-affinity CCKAR are expressed in nodose ganglia. Many nodose neurons bearing low-affinity CCKAR express OB-Rb. These neurons also respond to mechanical distention. An interaction between CCKAR and OB-Rb in these neurons likely facilitates leptin mediation of short-term satiety.