Figure 5.

Individual and average effects of combined prazosin and methysergide microinjections into the XII nucleus on the carbachol-induced depression of XII nerve activity (A) and slowing of the respiratory rate (B). (A) Individual (top graph) and average (bottom graph) responses of the XII nerve to pontine carbachol. Each data triplet shows the level of XII nerve activity just before, at the peak of, and just after the response to carbachol. XII nerve activity is normalized relative to the activity level at the beginning of each experiment. The three data sets illustrate the effects of carbachol before and during two periods after antagonist administration, as indicated at the bottom. XII nerve activity was significantly depressed by pontine carbachol under the control conditions and when tested 135 to 199 min after the antagonists. However, during the tests with carbachol conducted 32 to 81 min after antagonist administration, XII nerve activity was on average not altered, and only minimally increased or decreased in individual animals (middle data set, top graph). Thus, during this period, the combined antagonism of adrenergic and serotonergic receptors reversibly eliminated the depressant effect of pontine carbachol on XII nerve activity. (B) Average changes in respiratory rate elicited by carbachol at successive stages of these experiments, shown using the same format as in the bottom graph in A. The baseline respiratory rate and its carbachol-induced decreases were well maintained at all times after antagonist administration. * Significantly different from the precarbachol level at p < 0.05.