Experiments on the physiological mechanism of noise-induced seizures in the albino rat. I. The action of parasympathetic drugs.

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Abstract
I. In the light of evidence (previously noted) of the participation of the autonomic n.s. in audio-genic seizures in rats, it was decided to investigate the effect upon susceptibility to these seizures of drugs known to exert depressing or exciting influence upon the parasympathetic system. Rats of both sexes from 3-5 mos. of age were confined in a wire cage and stimulated by an electric bell beneath. Animals injected with atropine sulphate (ca. 0.04 mg per 100 g body wt. in 0.01% soln.) were compared with 2 types of normal animals (un-injected, and control-injected with H2O). The 2 kinds of controls did not differ. 21 of 50 controls had seizures in the expt. situation, as against 4 of 50 atropine-injected animals. In a 2d expt. 22 animals were injected on alternate days (3 days of each) with 0.5 cc of 0.01% eserine sulphate and a similar quantity of saline soln. To check the results of this expt., other groups were similarly tested. Together these exps. yielded: in eserinized animals 76 stimulations yielded 33 attacks, as against 5 attacks in 85 control stimulations. An expt. with combinations of atropine and eserine yielded inconclusive results. There is a brief discussion of the relationship between these results and Cannon''s work on emotion.[long dash]II. It was thought that the action of atropine noted earlier (decreasing frequency of audiogenic seizures) might be due to its effect upon the smooth musculature of the gastro-intestinal tract. Hence several exps. were conducted with benzyl benzoate, which acts to relieve smooth muscle spasm. The results of these expts. led to the conclusion that this drug did not decrease the frequency of seizures. But a complementary experiment was performed under the theory that if atropine''s action was due to its influence on gastro-intestinal tract, then contraction of this musculature should increase the frequency of seizures,[long dash]this was attempted with pituitrin but with negative results. On the basis of the relationships between acetylcholine, nicotine, and muscarine, it was thought that if the atropine influence is by its action on the parasympathetic n.s., mecholyl should increase the frequency of attacks. No increase in frequency was noted. A similar expt. with nicotine tartrate indicated increased frequency of seizures. Expts. with combinations of nicotine and atropine indicate that the atropine in this situation does not counteract the effect of nicotine. The author concludes that the effects of eserine and atropine upon frequency of audiogenic seizures are not the result of their parasympathetic effects.

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