AbstractsBiology & Animal Science

The stimulation of nervous tissue leads first to excitation at the point of application, and from here the excitation is propagated to an effector organ which responds to the transmitter excitation. Prior to the first decade of 1900, there were only hypotheses which sought to suggest the intimate mechanism by which nervous excitation produces a functional change in an organ. Elliott, observing that the effect of stimulation of sympathetic nerves and of adrenaline was identical, proposed the hypothesis that stimulation of sympathetic nerves caused liberation of adrenaline and that it was the adrenaline which was responsible for the end effect of nervous stimulation. The question of whether nervous stimulation directly affected the organs involved was tested experimentally by Howell who indicated that stimulation of the vagus led to a liberation of potassium, this substance in turn causing the resulting phenomenon. Although Howell's assumption was not corroborated, he was the first to investigate experimentally the possible mechanism of the inhibitory function of a nerve. In the same year, Dixon cited evidence for the presence of a substance in heart tissue, "pro-inhibitin", which was converted to "inhibitin" on vagal stimulation. This substance, when combined with heart muscle, brought about cardiac arrest. [...]