Abstract
The purpose of the studies reported in this paper is twofold: 1. To extend the systematic observations of Gellhorn 1 and collaborators on the effect of oxygen deficiency on the central nervous system to the autonomic nervous system. 2. To choose a reaction which is determined exclusively or to a large extent by a central inhibitory process in order to study the influence of oxygen deficiency on such processes.
Although the literature on the problem of reflex dilatation is still controversial a number of authors have shown that this reaction is largely due to an inhibition of the parasympathetic tonus of the Edinger-Westphal nucleus. This is particularly clear from the work of Bain, Irving and McSwiney, 2 who find that the stimulation of the central end of the splanchnic fails to elicit pupillary dilatation after sectioning of the third nerve, although “section of the cervical sympathetic nerves has not been found to alter either the rate or the degree of the reaction to stimulation of somatic or visceral afferent fibers.”
The experiments were carried out repeatedly on 12 rabbits, half of which had the cervical sympathetic cut on one side. The sciatic was exposed under light urethane anesthesia and 2-3 hours later the experiment was begun. The threshold reaction for pupillary dilatation was determined with faradic stimulation (Harvard inductorium, shielded electrode) while the animals inhaled air or a known O2-N2-mixture from Douglas bags.
Very weak currents (coil distance 11-12 cm. or at an angle) were used for 1-3 seconds and the pupillary reaction was measured with a telescope.
The results were uniform and showed that under the influence of 643% O2 the threshold for pupillary dilatation was raised.
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