UI - 000212

AU - Dennis SG

AU - Melzack R

TI - Effects of cholinergic and dopaminergic agents on pain and morphine analgesia measured by three pain

tests

AB - AB - The effects of several cholinergic and dopaminergic agents on pain and morphine analgesia were

assessed using three pain tests. These tests--tail-flick, hot-plate, and Formalin--allow comparison of the

effects of different noxious stimuli and different motor responses. Each pain test yielded a unique

constellation of cholinergic and dopaminergic influences, suggesting that variation of stimulus and response

parameters can change the functional expression of cholinergic and dopaminergic systems related to pain

processing. Significant analgesia was observed in the Formalin test, compared with the saline control, after

administration of choline (30 or 60 mg/kg), atropine (2 mg/kg), mecamylamine (2 mg/kg or 10 mg/kg), or

apomorphine (0.3 or 8 mg/kg). No analgesic effects in this test were observed after atropine (10 mg/kg) or

pimozide (0.125 or 0.5 mg/kg). In contrast, there was no evidence of analgesia produced by any of these

drugs, in the doses given, in the hot-plate test, and only apomorphine (8 mg/kg) produced analgesia in the

tail-flick test. When these cholinergic and dopaminergic agents were administered to rats after an injection of

2.5 mg/kg morphine, which by itself has been shown not to produce analgesia in any of the tests, a general

pattern of facilitation was observed in the Formalin test but not in the tail- flick or hot-plate tests. Facilitation

was produced by choline, atropine, mecamylamine, apomorphine, and pimozide (at 0.5 mg/kg but not 0.125

mg/kg). The data suggest that differences in the type of noxious stimulation and in the motor responses

required in various pain tests are crucial in determining the observed pharmacologic profile of pain and

opiate analgesia UI - 83234877

SO - Exp Neurol 1983;81:167-176