We examined whether neurons in the midbrain ventral tegmental area (VTA) play a role in generating central command responsible for autonomic control of the cardiovascular system in anesthetized rats and unanesthetized, decerebrated rats with muscle paralysis. Small volumes (60 nl) of an N-methyl-D-aspartate receptor agonist (L-homocysteic acid) and a GABAergic receptor antagonist (bicuculline) were injected into the VTA and the substantia nigra (SN). In anesthetized rats, L-homocysteic acid into the VTA induced short-lasting increases in renal sympathetic nerve activity (RSNA) 66 ± 21%, mean arterial pressure (MAP) 5 ± 2 mmHg, and heart rate (HR) 7 ± 2 beats/min, while bicuculline into the VTA produced long-lasting increases in RSNA 130 ± 45%, MAP 26 ± 2 mmHg, and HR 66 ± 6 beats/min. Bicuculline into the VTA increased blood flow and vascular conductance of the hindlimb triceps surae muscle, suggesting skeletal muscle vasodilatation. However, neither drug injected into the SN affected all variables. The renal sympathetic nerve and cardiovascular responses to chemical stimulation of the VTA were not essentially affected by decerebration at the premammillary-precollicular level, indicating that the ascending projection to the forebrain from the VTA was not responsible for evoking the sympathetic and cardiovascular responses. Furthermore, bicuculline into the VTA in decerebrate rats produced long-lasting rhythmic bursts of RSNA and tibial motor nerve discharge, which occurred in good synchrony. It is likely that activation of neurons in the VTA is capable of eliciting synchronized stimulation of the renal sympathetic and tibial motor nerves without any muscular feedback signal.
- Voluntary exercise
- Central command
- Motor-sympathetic synchronization
- Substantia nigra
- Copyright © 2010, Journal of Applied Physiology