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pubmed:abstractText |
Using whole cell patch clamp in thin brain stem slices, we tested the effects of cholecystokinin (CCK) on identified gastric-projecting neurons of the rat dorsal motor nucleus of the vagus (DMV). Perfusion with the sulfated form of CCK octapeptide (CCK8s, 30 pM-300 nM, EC50 approximately 4 nM) induced a concentration-dependent inward current in 35 and 41% of corpus- and antrum/pylorus-projecting DMV neurons, respectively. 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 +/- 4 mV, indicating that the excitatory effects of CCK8s were mediated by the closure of a potassium conductance. Pretreatment with the synaptic blocker TTX (0.3-1 microM) 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 (0.3-3 microM) attenuated the CCK8s-induced inward current in a concentration-dependent manner, with a maximum inhibition of 69 +/- 12% obtained with 3 microM lorglumide. Conversely, pretreatment with the selective CCK-B antagonist triglumide did not attenuate the CCK8s-induced inward current; pretreatment with triglumide (3 microM) and lorglumide (1 microM) attenuated the CCK8s-induced current to the same extent as pretreatment with lorglumide alone. Immunohistochemical experiments showed that CCK-A receptors were localized on the membrane of 34, 65, and 60% 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 that their activation leads to excitation of the DMV membrane.
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pubmed:affiliation |
Department of Neuroscience, Pennington Biomedical Research Center, Louisiana State University System, 6400 Perkins Rd., Baton Rouge, Louisiana 70808, USA.
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