Influence of small cardioactive peptide (b) on the efficiency of synaptic transmission and the excitability of command neurons of the defensive behavior of the edible snail.

The application of a small cardioactive peptide (SCPb) (mCPb) in a concentration of 5 x 10(-8) mole/l to a physiological solution washing the isolated central nervous system of the edible snail leads to an increase in the amplitude of the summated EPSP evoked by rhythmic stimulation of the intestinal nerve in the command neurons of defensive behavior by 55 +/- 20%. In addition to the change in the magnitude of the synaptic input, SCPb induces an increase in the excitability of the same neurons by 92 +/- 57%, tested intracellularly. These influences may lead to a total decrease in the threshold of the reaction of the neuronal network of the defensive behavior in response to stimulation. The possibility of the integration of integral behavior with the aid of peptides which are effective in very small concentrations is discussed.