Acute cold exposure induces vagally mediated Fos expression in gastric myenteric neurons in conscious rats

Acute cold exposure-induced activation of gastric myenteric neurons in cons cious rats was examined on longitudinal muscle-myenteric plexus whole mount preparations. Few Fos-immunoreactive (IR) cells (<1/ganglion) were observe d in 24-h fasted rats semirestrained at room temperature. Cold exposure (4< degrees>C) for 1-3 h induced a time-related increase of Fos- IR cells in co rpus and antral myenteric ganglia with a maximal plateau response (17 +/- 3 and 18 +/- 3 cells/ganglion, respectively) occurring at 2 h. Gastric vagot omy partly prevented, whereas bilateral cervical vagotomy completely abolis hed, Fos expression in the myenteric cells induced by cold exposure (2 h). Hexamethonium (20 mg/kg) also prevented 3-h cold exposure-induced myenteric Fos expression by 76-80%, whereas atropine or bretylium had no effect. Dou ble labeling revealed that cold (3 h)-induced Fos- IR myenteric cells were mainly neurons, including a substantial number of choline acetyltransferase -containing neurons and most NADPH-diaphorase-positive neurons. These resul ts indicate that acute cold exposure activates cholinergic as well as nitre rgic neurons in the gastric myenteric ganglia through vagal nicotinic pathw ays in conscious rats.