CHANGES IN REFLEX RESPONSE, AND ELECTRICAL EXCITATION OF PERIPHERAL MOTOR NERVES IN EXPERIMENTAL HYPO- AND HYPERTHYROIDISM

Abstract

The skin reflex (cutaneous maximus) is present in all normal rabbits. This reflex is elicited by applying light tactile stimuli to the skin of the back of the rabbit. A response to the stimulus is manifest by a vigorous pulling forward of the skin due to the reflex contraction of the M. cutaneous maximus. The skin reflex completely disappears in absolute cretins, experimentally induced, approximately 4 mos. after extirpation of the thyroid. This reflex persists in semi-cretins and serves as a reliable guide in differentiating between partial and complete thyroid insufficiency. Ingestion of thyroid substance by a complete cretin causes a return of the skin reflex after about 20 days. After discontinuing the thyroid substance the reflex persists 2-4 mos. The contralateral knee jerk disappears in untreated cretin rabbits with loss of skin reflex. In experimental hyperthyroidism in rabbits the knee jerk may be accompanied by foot clonus. Electrical excitability of peripheral motor nerves (N. thoracalis ant.) is not appreciably altered by experimental hypo- or hyperthyroidism in rabbits.