Technical note

New devices for recording the contractions of the nictitating membrane and skeletal muscles in experimental animals*

K e y w o r d s - - N i c t i t a t i n g membrane, Skeletal muscles, Tetanus, Twitch

Introduction Two techniques are often used for the study of neuro- blocking agents in experimental animals: (a) the measurement of the contractile force of the

nictitating membrane during pre- or postsympathetic stimulation (BURN, 1952)

(b) the measurement of the contractile force of the peroneus longus muscle during sciatic-nerve stimula- tion (WILKIE, 1956).

nected to the force-displacement transducer by means of a thread. A pre -tension of 5 to 7 g needs to be applied to the nictitating membrane and maintained during the whole experiment. This is difficult to achieve unless the transducer is securely fixed to the head of the animal.

Fig. 1 shows the assembled and exploded view of the new device for this recording. A brass rod (8 mm dia- meter) is bent on one side at an angle of 60 ~ . On the other side it is threaded (M 8 x 1) for about 50 mm and a

Fig. I

When force-displacement transducers are used for the measurement of these forces, difficulties may occur owing to the changes in the position of the transducer in relation to the membrane or the muscle; two new devices have been developed to overcome these difficulties.

Nictitating membrane In this technique, the nictitating membrane is con-

*First received 20th December 1975 and in final form 4th February 1976

groove (3 mm wide and 3 mm deep) is made in the rod along its length for about 70 mm. The holder for the transducer moves over the threaded part of the rod and a pin (3 ram diameter and 3 mm long) sliding in the groove prevents the holder from rotating. A stainless-steel spring and a nut allow adjustment of the holder's position along the rod. The bent part of the rod is securely fixed in the cat's mouth by placing it behind the canine teeth and binding the jaws together with a string.

The cervical sympathetic nerve is stimulated at fre- quencies of 4, 8 and 16 Hz, with square waves of 1 ms duration and 2-5 V in amplitude.

690 Medical and Biological Engineering November 1976

Fig. 2

Skeletal muscles

The contractions of a leg muscle (e.g. peroneus longus) in response to stimulation of the sciatic nerve are quite powerful, and the transducer should therefore be well attached to the bones of the hind leg of the animal. Fig. 2 shows the instrument made for this purpose. A 10 ram-thick perspex sheet is shaped and provided with a knee clamp and an ankle clamp. The transducer is held in an adjustable holder and rests against a bracket attached to the rear of the plastic plate. The leg muscle is firmly connected with a heavy thread to the transducer. Correct tension is obtained by moving the holder in the slit provided. The instrument allows free dissection of the

sciatic nerve in the thigh and is suitable for the recording of single twitches or tetanic responses of the muscle.

A. L. DELAUNOIS

J. F. and C. Heymans Institute University of Ghent Belgium

References

BURN, J. H. (1952) Practical pharmacology. Blackwel| Scientific Publications.

WILKIE, D. R. (1956) Brit. Med. Bull. 12, 177.

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