Medullary GABA Receptors and the Regulation of Blood Pressure in the Rat

by Robert N. Willette et al.

The purpose of this study was to determine the cardiovascular effect of a GABAergic agonist and antagonist upon vasopressor and vasodepressor motoneuron pools in the ventrolateral medulla. Rats underwent microinjection of muscimol (GABA receptor agonist) to vasopressor (VLDA) and vasodepressor (VLPA) sites in the ventrolateral medulla.

Muscimol injection to VLDA sites consistently caused an increase in BP, HR and pulse pressure. Pretreatment with alpha adrenergic blockers abolished the pressor effect of muscimol. It should be noted that increases in HR were resistant to this blockade. Muscimol injection to VLPA sites caused a fall in BP, HR and pulse pressure. Additionally, injection of biuculline (GABA receptor antagonist) reversed the effects of muscimol in both VLDA and VLPA sites.

These results indicate that VLPA and VLDA sites are tonically active in maintaining BP. The results also suggest that a GABAergic system may be involved with the modulation of neural activity in these areas.

-BH