Action of drugs upon the central nervous system of insects

Abstract

Peculiarities revealed by study of the action of neurophil drugs in lepidopterous larvæ 1 , 2 led to an extension of the observations to include an imaginal insect. Effects following injection of solutions of drugs into the thorax of grasshoppers were compared with those attending the direct application of these substances to the thoracic ganglia (exposed by removal of the ventral thoracic sclerites). In all essentials, the two methods gave comparable results.

As in caterpillars, strychnine produces momentary general excitation, but only when present in very high concentration; it fails to induce “reversal of inhibition.” In the grasshopper, however, such “reversal” appears after administration of nicotine or of camphor. The legs are thrown outward and upward if (under nicotine) the abdomen or a femur be touched, and (under camphor) when the mouth-parts are stimulated tactically. The grasshopper normally clasps a stimulating object if, as in these tests, the animal be held by a clip fastened upon the wingcovers. Nicotine, and pilocarpine, stimulate especially movements of the two posterior pairs of legs, while under camphor all three pairs and the mouthparts undergo spasmodic movements.

Grasshoppers, caterpillars, and crayfish 3 agree in presenting definite evidence of neuronic excitation by these substances: strychnine, pilocarpine, picrotoxin, nicotine, veratrine, atropine, caffeine, camphor, phenol. To this general correspondence there may be added certain aspects of detailed agreement. These arthropods differ pronouncedly from the earthworm in the fact that, with the latter, 4 nicotine, caffeine and phenol fail to produce central nerevous stimumation. There is reasonable ground, therefore, for the opinion that the central nervous systems of arthropods possess certain common features, revealed through the actions of neurophie drugs; and that these features distinguish the arthropod central nervous system from that of an oligochaete.