Body temperature dependency in baclofen-induced gastric acid secretion in rats relation to capsaicin-sensitive afferent neurons

Body temperature dependency in gastric functional responses to baclofen, a GABA(B) agonist, such as acid secretion, mucosal blood flow (GMBF) and motor activity, was examined in urethane-anesthetized rats under normal (37+/-1 degrees C) and hypothermic (31+/-1 degrees C) conditions. A rat stomach was mounted in an ex-vivo chamber, perfused with saline, and the acid secretion was measured using a pH-stat method, simultaneously with GMBF by a laser Doppler flowmeter. Gastric motility was measured using a miniature balloon as intraluminal pressure recordings. Intravenous administration of baclofen significantly increased acid secretion at the doses > 0.3 mg/kg under hypothermic conditions, yet it caused a significant stimulation only at doses > 10 mg/kg under normothermic conditions. The increases in gastric motility and GMBF were similarly induced by baclofen, irrespective of whether the animals were subjected to normothermic or hypothermic conditions. These functional responses to baclofen under hypothermic conditions were totally attenuated by either bilateral vagotomy or atropine (3 mg/kg, s.c.). Baclofen at a lower dose (1 mg/kg i.v.) significantly increased the acid secretion even under normothermic conditions when the animals were subjected to chemical deafferenation of capsaicin-sensitive neurons or pretreatment with intracisternal injection of CGRP8-37 (30 ng/rat). These results suggest that 1) gastric effects of baclofen are dependent on body temperature in stimulating acid secretion but not GMBF or motor activity, 2) the acid stimulatory action of baclofen is enhanced under hypothermic conditions, and 3) the suppression of baclofen-induced acid response under normothermic conditions may be related to capsaicin-sensitive afferent neuronal activity, probably mediated by central release