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CART Peptides Differently Regulate Firing Rates and GABAergic Synaptic Inputs of DMV Neurons Innervating the Stomach Antrum and Cecum of Adult Male Rats

Background/Aim: Central administration of cocaine- and amphetamine-regulated transcript peptides (CARTp) alters gastrointestinal motility and reduces food intake in rats. Since neurons in the dorsal motor nucleus of the vagus (DMV) receive GABAergic and glutamatergic inputs and innervate the smooth muscle of gastrointestinal organs, we hypothesized that CARTp acts on the DMV or presynaptic neurons. Methods: We used 3,3′-dioctadecyloxa-carbocyanine perchlorate (DiO) retrograde tracing with electrophysiological methods to record DMV neurons innervating the stomach antrum or cecum in brainstem slices from adult rats. Results: DiO application did not change the electrophysiological properties of DMV neurons. CART55–102 had no effect on the basal firing rates of neurons in either the stomach antrum-labeled group (SLG) or cecum-labeled group (CLG). When presynaptic inputs were blocked, CART55–102 further increased the firing rates of the SLG, suggesting a direct excitatory effect. Spontaneous inhibitory postsynaptic currents (sIPSCs) occurred at a higher frequency in SLG neurons than in CLG neurons. CART55–102 reduced the amplitude and the frequency of sIPSCs in SLG neurons dose-dependently, with higher doses also reducing spontaneous excitatory postsynaptic currents (sEPSCs). Higher doses of CART55–102 reduced sIPSC and sEPSC amplitudes in CLG neurons, suggesting a postsynaptic effect. In response to incremental current injections, the SLG neurons exhibited less increases in firing activity. Simultaneous applications of current injections and CART55–102 decreased the firing activity of the CLG. Therefore, stomach antrum-projecting DMV neurons possess a higher gating ability to stabilize firing activity. Conclusion: The mechanism by which CARTp mediates anorectic actions may be through a direct reduction in cecum-projecting DMV neuron excitability and, to a lesser extent, that of antrum-projecting DMV neurons, by acting on receptors of these neurons.