AN EXTENSION OF THE "LAW OF DENERVATION" TO AFFERENT NEURONES

Abstract

To ascertain whether in accordance with Cannon''s "Law of Denervation" an increase of irritability occurs only after section of efferent connections, or whether deafferenta-tion too leads to a greater irritability of corresponding spinal neurones, the left hind limb of 12 cats was deafferented by aseptic intradural section of L2 to S2 dorsal roots, and after various periods of time the brain was pithed and the contractions of both quadriceps muscles recorded. Beginning 18 hrs. after deafferentation (longest time 3 months), intraaortic injns. of acetylcholine, adrenaline, strychnine, metrazol and camphor evoked greater responses on the deafferented side[long dash]the contractions appeared after smaller quantities of the drugs, started earlier, were more powerful and lasted longer than those on the intact side. Acute unilateral deafferentation, carried out immediately preceding the recording, reduced the effectiveness of the chemical agents on the corresponding side. In another series of expts. on 6 chronic cats in which deafferentation of the forelimb was carried out by section of C3 to T2 dorsal roots, intraven. injns. of the same drugs lead to asymmetrical contractions of the forelimbs[long dash]the deafferented limb responding first, swinging higher towards the head, and becoming more rigid during the contraction, the effects resembling somewhat those described in the case of frontallobecto-mized and semidecerebrated animals (see B. A. 18(8): entry 15979).