Significance of the interstimulus time interval in repeating combined presentations of L-glutamate and acetylcholine for change in the reactivity of cortical neurons.

A comparative study of the probability, directionally, and intensity of the changes in the baseline and L-glutamate (Gl)- and acetylcholine(ACh)-induced average frequency of the impulse activity (BIA, GlIA, and AChIA, respectively) of individual neurons of the sensorimotor cortex of unanesthetized rats in the course of repeated isolated and combined presentations of Gl and ACh showed that the process of reduction in reactivity to Gl is slowed in the population of cells which experienced the combined action of Gl and ACh with a 1.5 second postponement of applications of ACh in comparison with the situation of its isolated and combined presentation with a 3 second postponement of ACh. The AChIA decreases to a greater degree in the case of a 3 second postponement of ACh, and the probability of an increase in BIA is less than with the isolated application of ACh. It is concluded that the character of the dynamics of the reactivity of neurons is determine by the temporal relationships of local neurochemical stimuli.