Studies on the responses of the isolated nictitating membrane of the cat

The contraction of the cat's nictitating membrane has long been used experimentally as a sign of activity of the cells of the superior cervical ganglion and for the study of the properties of smooth muscle. There are, however, two major difficulties attending the use of the nictitating membrane in the whole animal. It is influenced not only by its nerve supply, but also by substances released elsewhere and carried by the blood to the membrane; and it is anatomically connected to the external ocular muscles whose contractions may be transmitted to the membrane (Rosenblueth & Bard, 1932; Paton & Thompson, 1953). These difficulties can be overcome by suitable control experiments, but a really rigorous investigation of the smooth muscle retracting the membrane would be greatly helped by its study in isolation, free from humoral and -other influences. The first successful attempt to obtain contractions of the isolated nictitating membrane was made by Westcott & Christensen (1951) using the inferior smooth muscle bundle in the cat. Later, Cervoni & West (1955), Cervoni, West & Fink (1956), and Westcott, Christensen & Marrazzi (1956) used this preparation to study the specificity of the response to acetylcholine. These studies dealt only with the inferior muscle and were relatively restricted. The present paper describes the method whereby a preparation sensitive to appropriate drugs is obtained. The responses of both the medial and inferior muscle bundles of the normal membrane to stimulant drugs and some antagonists are described. The preparation was demonstrated to the Physiological Society in 1955 (Thompson, 1955).