Dimethylsulfoxide (DMSO) eliminates the response of the sensory neurones of an insect mechanoreceptor, the femoral chordotonal organ of Locusta migratoria, but blocks conduction of their sensory axons at much higher concentrations: a possible mechanism of analgesia.

The analgesic effects of dimethylsulfoxide (DMSO) on the sensory neurones and the sensory axons of an insect mechanoreceptor, the femoral chordotonal organ of Locusta migratoria, were examined. The metathoracic femur was dissected, to expose the chordotonal organ and its sensory nerve, in a chamber containing oxygenated physiological solution where the DMSO was gradually added. The tibia movement was used for the mechanical stimulation of the chordotonal organ while neural activity was recorded and measured using standard electrophysiological methods. For the chordotonal organ, the blocking concentration of DMSO, the concentration which eliminates the response of the sensory neurones to mechanical stimulation by 50% in 18-20 min, was estimated to be 0.85 +/- 0.11% (n = 6) v/v. On the contrary, the blocking concentration of the DMSO for the sensory axons was 4.6 +/- 0.7% (n = 6) v/v, approximately five times higher than the concentration required to inactivate the sensory neurones. The implications of this difference in the physiological mechanisms involved for the DMSO-induced analgesia are discussed.