The responses of the isolated anococcygeus muscle of the mouse to drugs and to field stimulation were investigated. 2. Fluorescence micrographs of transverse sections of the muscle revealed fluorescent nerve fibres in control tissues, but not in tissues from mice pretreated with 6-hydroxydopamine. 3. The isolated muscle displayed no spontaneous tone or rhythmic activity. Field stimulation produced frequency dependent contractions which were blocked by phentolamine and by low concentrations of guanethidine (500 nM). Higher concentrations of guanethidine (30 microM) raised muscle tone and, subsequently field stimulation produced frequency dependent relaxations. In muscles from 6-hydroxydopamine pretreated mice neither field stimulation nor guanethidine produced contractions, but when muscle tone was raised by carbachol inhibitory responses to field stimulation were still observed. 4. Contractions of the muscle were produced by noradrenaline (alpha-adrenoreceptors), acetylcholine (muscarinic receptors), 5-hydroxytryptamine, and prostaglandins E1, E2, and F2 alpha. 5. Adenosine 5'-triphosphate (ATP) normally produced muscle contraction, but following incubation of the tissue with indomethacin, ATP produced relaxations of carbachol-induced tone. 6. Vasoactive intestinal polypeptide, but not bradykinin, produced relaxations of tissues in which tone had been raised by carbachol. 7. The isolated anococcygeus muscle of the mouse provides a useful preparation for the study of various aspects of autonomic neurotransmission in smooth muscle.
