Effects of muscarinic receptor antagonism upon two forms of stress-induced analgesia.
The present study assessed in rats the effects of muscarinic receptor antagonism upon analgesia induced by cold-water swims (CWS: 2 degrees C for 3.5 min) and 2-deoxy-D-glucose (2DG: 600 mg/kg). First, CWS analgesia was significantly reduced 30 min after the swim by scopolamine (0.01 and 0.1 mg/kg) and methylscopolamine (10 mg/kg) pretreatment, and was eliminated 60 min after the swim by scopolamine (0.01-10 mg/kg) and methylscopolamine (1,10 mg/kg) pretreatment. In contrast, scopolamine potentiated CWS hypothermia. Second, while scopolamine (1 mg/kg) and methylscopolamine (1,10 mg/kg) pretreatment prolonged 2DG analgesia, both antagonists dose-dependently reduced 2DG hyperphagia. Third, the changes in analgesic and hypothermic stress responses were not due to baseline shifts in jump thresholds or body temperatures. However the dose-dependent reductions by scopolamine and methylscopolamine in baseline food intake and 2DG hyperphagia were significantly correlated. Fourth, the dose-dependent reduction by scopolamine and methylscopolamine of pilocarpine analgesia differed in pattern from the other analgesic effects, suggesting heterogeneity in muscarinic receptor modulation of different analgesic responses.
D000109:Acetylcholine; D000818:Animals; D001831:Body Temperature; D005247:Feeding Behavior / Q000502:physiology; D008297:Male; D019832:N-Methylscopolamine; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains; D011976:Receptors, Muscarinic / Q000502:physiology*; D012601:Scopolamine; D012602:Scopolamine Derivatives; D012684:Sensory Thresholds; D013312:Stress, Physiological / Q000503:physiopathology*
D011976:Receptors, Muscarinic; D012602:Scopolamine Derivatives; D012601:Scopolamine; D000109:Acetylcholine; D019832:N-Methylscopolamine