The effect of immunosympathectomy and of 6-hydroxydopamine on the responses of the rat anococcygeus to nerve stimulation and to some drugs.

1. The rat anococcygeus muscle possesses a dense motor adrenergic innervation and also a powerful inhibitory innervation whose transmitter is unknown. The possibility that the adrenergic nerves released both noradrenaline and the unknown inhibitory transmitter was investigated by destroying the adrenergic nerves either by immunosympathectomy or by 6-hydroxydopamine.2. Immunosympathectomy was only partially effective in destroying the adrenergic neurones to the anococcygeus. 6-Hydroxydopamine destroyed the terminal adrenergic varicosities abolishing almost completely the motor response. Neither treatment affected the inhibitory response.3. 6-Hydroxydopamine induced a specific hypersensitivity of the muscle to noradrenaline which was not shared with carbachol.4. The maximum tension response of the anococcygeus muscle was greater in the male than in the female probably because the muscle is bigger.