Cat Nictitating Membrane DEMO

Introduction

What is the Nictitating Membrane?

The visible Nictitating Membrane (NM) consists of cartilage and is moved by two orbital smooth muscles, the inferior and medial. In the conscious, awake cat the NM receives a continuous flow of impulses from the CNS via the sympathetic innervation and is contracted. Relaxation of the smooth muscles produces a prolapse of the visible NM over the eye.

Why is this Experiment Useful?

The in vivo superior cervical ganglion-nictitating membrane preparation is used to investigate the action of drugs acting either at sympathetic ganglia or at the nictitating membrane (NM).

It has several advantages:

• Movements of the NM can be recorded easily and contractions can be elicited by electrical stimulation of preganglionic nerves;
• The NM has a relatively simple innervation - purely adrenergic fibres with their cell bodies in the easily accessible superior cervical ganglion (SCG);
• The blood supply is accessible for intra-arterial injections of drugs either to the SCG or to the NM;

It is a paired organ and both NMs are equi-sensitive to drugs (Trendelenburg & Haeusler, 1975). The contralateral NM thus acts as a control as it can only be affected if the action of a drug is systemic and causes stimulation of the adrenal medulla.

Reference

Trendelenburg, U. & Haeusler, G. (1975) Nerve-muscle preparation of the nictitating membrane. In "Methods in Pharmacology" (Edited by Daniel E.E. and Paton, D.M.) Vol. 3 pp 457-468. Plenum Press New York.

What the Program Covers

The program contains a Tutorial section which presents a brief introduction to the pharmacology of the sympathetic ganglionic synapse and the neuro-effector junction. The potential sites of action of drugs are also covered.

Methods outlines and illustrates: the preparation of the cat; nerve stimulation; recording the contractions of the nictitating membrane and administration of drugs to the superior cervical ganglion and the nictitating membrane.

The Experiments section presents simulated data for a range of drugs which may be administered by close arterial injection to either the ganglion or the nictitating membrane on one side (ipsilateral). Preganglionic nerves may also be stimulated electrically. Results are displayed on a chart-recorder like display which shows contractions of the ipsilateral and contralateral nictitating membranes. 'Experiments' also contains some suggested student tasks.