THE INTERPRETATION OF SOME PHENOMENA OF SALIVARY SECRETION CAUSED BY DIRECT ELECTRICAL STIMULATION OF THE EFFECTOR NERVE, IN TERMS OF THE PRESENT KNOWLEDGE OF THE NERVOUS IMPULSE AND OF ITS CHEMICAL TRANSMISSION
Authors: Beznák M. , Farkas E. 
Published: December 2014

1. It has been found that when acetylcholine is given intra‐arterially in different concentrations and the amount of salivary secretion is plotted against the concentration of acetylcholine, the curve obtained may be expressed by an exponential formula. It also has been found that cats show individual variations as regards the just effective acetylcholine concentration given intra‐arterially needed to induce salivary secretion. The individual variation as regards dosage ranges from 0·003–0·1 γ. When the gland is eserinised the just effective minimal concentration is greatly decreased although the individual variations still remain. Under the influence of eserine, a given dosage of acetylcholine produces a greater volume of salivary secretion than it does without eserine. This is due, at least partly, to the fact that physostigmine inhibits the destruction of acetylcholine by the acetylcholine esterase.

2. The changes in the rate of salivary secretion at maximal strength of stimuli with different frequencies have been described. It has been found that as the frequency increases, the amount of saliva secreted in the unit of time increases asymptotically. If the amount of saliva secreted per single stimulus is plotted at different frequencies against the frequencies, the curve rises towards a maximum point as the frequency increases. After this maximum point is reached, the amount of saliva corresponding to a single stimulus decreases rapidly as the frequency of the stimulus is increased. The analysis of the two curves, the unit time and the single stimulus‐salivary secretion curve, shows that the acetylcholine liberated by the nervous impulse does not merely start saliva secretion, but also causes an increased sensitivity of the gland cell to the drug. Even 10 min. after the effective stimulus, the salivary gland is still more sensitive than normal. This same conclusion is reached from the observation of the behaviour of the “latent period.” It has been found that the “latent period” shortens as the interval between two consecutive sets of stimuli shortens. That the increase of the sensitivity of the gland cell to acetylcholine is due to a lasting effect of acetylcholine itself and not to any other effect of the nerve was proved by direct experiments with intra‐arterial injections of acetylcholine.

The effect of physostigmine on the frequency‐salivary secretion curve has been described. Physostigmine does not alter the shape of, the curve, the maximum point is shifted left, i.e. to a lower frequency point, and greater amounts of acetylcholine correspond to the same frequencies. All these effects may be explained by the supposition that physostigmine inhibits the destruction of acetylcholine during the period of time which elapses between the liberation of acetylcholine and its action on the sensitive points.

3. The salivary secretion rate at different strengths of stimulus and at different frequencies has also been described.

4. All the observed peculiarities of the salivary secretion, produced by direct stimulation of the chorda tympani can be interpreted on the theory of chemical transmission of the nervous impulse.

The authors have pleasure in expressing their gratitude to Professor A. B. L. Beznák for his constant help in the course of this work.