A Selective Inhibitory Effect of the Posterior Cerebellar Vermis on 10‐Hz Sympathetic Nerve Discharge

Abstract

We compared the changes in inferior cardiac sympathetic nerve discharge (SND) and mean arterial pressure (MAP) produced by aspiration of portions of lobule IX and in some cases lobule X of the posterior cerebellar vermis with those produced by chemical inactivation (muscimol microinjection) or electrical stimulation of the same regions. The experiments were performed on 13 baroreceptor‐denervated and vagotomized cats anesthetized with urethane. Autospectral analysis was used to decompose SND into its frequency components. Special attention was paid to the question of whether the experimental procedures differentially affected the rhythmic and aperiodic components of SND. Aspiration or chemical inactivation with muscimol of lobule IX produced an approximately three‐fold increase in the 10‐Hz rhythmic component of SND (P = 0.05). In contrast, wideband SND at lower frequencies (= 6 Hz) was either slightly reduced or unaffected. Total power (0‐ to 20‐Hz band) was unchanged. Despite this, there was a statistically significant increase in MAP. High frequency (50‐Hz) electrical stimulation of depressor sites in lobule IX of the posterior vermis selectively and significantly reduced 10‐Hz power in SND. The lower frequency components of SND were unchanged. These results demonstrate for the first time a role of cerebellar cortical neurons of the posterior vermis in regulating the frequency composition of naturally occurring SND. The functional implications of these findings are discussed.(Supported by NIH HL33266.)