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1 Department of Neuroscience, Louisiana State University System, Pennington Biomedical Research Center, Baton Rouge, LA, USA
* To whom correspondence should be addressed. E-mail: alberto.travagli{at}pbrc.edu.
Using whole cell patch clamp in thin brainstem slices we tested the effects of cholecystokinin on identified gastric-projecting neurons of the rat dorsal motor nucleus of the vagus (DMV). Perfusion with the sulfated form of cholecystokinin (CCK8s; 30pM-300nM; EC50~ 4nM) induced a concentration-dependent inward current in 35% of corpus- and 41% of antrum/pylorus-projecting DMV neurons. Conversely, none of the fundus-projecting DMV neurons responded to perfusion with CCK8s. The CCK8s-induced inward current was accompanied by a 65±17% increase in membrane input resistance and reversed at 90±4mV, indicating that the excitatory effects of CCK8s were mediated by the closure of a potassium conductance. Pretreatment with the synaptic blocker tetrodotoxin (0.3-1µM; TTX) reduced the CCK8s-induced current, suggesting that a portion of the CCK8s-induced current was mediated indirectly via an action on presynaptic neurons apposing the DMV membrane. Pretreatment with the selective CCK-A receptor antagonist lorglumide (0.3-3µM) attenuated the CCK8s-induced inward current in a concentration dependent manner, with a maximum inhibition of 69±12% obtained with lorglumide 3µM. Conversely, pretreatment with the selective CCK-B antagonist triglumide did not attenuate the CCK8s-induced inward current; pretreatment with both triglumide (3µM) and lorglumide (1µM) attenuated the CCK8s-induced current to the same extent as with lorglumide alone. Immunohistochemical experiments showed that CCK-A receptors were localized on the membrane of 35, 55 and 54% of fundus-, corpus- and antrum/pylorus-projecting DMV neurons, respectively. Our data indicate that CCK-A receptors are present on a subpopulation of gastric-projecting neurons and their activation leads to excitation of the DMV membrane.
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