ALTERNATIVE APPROACHES TO ANALGESIA: BACLOFEN AS A MODEL COMPOUND

Abstract

It is suggested that analgesia could be produced by drug action at the spinal level through (a) interference with neurotransmission at primary afferent terminals; (b) enhancement of the ‘gate control’ of the sensory input to the spinal cord mediated through descending spinal tracts; or (c) increased presynaptic inhibition of primary afferents by a direct action. Baclofen (9.4–70.3 μmol/kg, i.p.), which may mimic spinal presynaptic inhibition, produced a dose‐dependent increase in the response times of mice in a hot‐plate test, but high doses also impaired motor function. Morphine hydrochloride (5.3–40 μmol/kg, i.p.) increased the response time of mice in the hot‐plate test and had little effect on motor function. Combination of baclofen (9.4 or 23.4 μmol/kg) with morphine (13.3 μmol/kg) produced greater increases in response time than either drug administered alone but with little concurrent effect on motor function. The possibility that baclofen may have some analgesic action and a potentiating effect on other analgesics is discussed. 1975 British Pharmacological Society