Hindquarters vasoconstriction through central GABA(B) receptors in conscious rats

The exogenous application of GABA into the cisterna magna of the freely moving rat decreases hindquarters vascular tone as well as arterial pressure. GABA could influence GABA receptor subtypes A, B or C. However, the hindquarters vascular response to the stimulation of each receptor subtype has not yet been investigated. The present study therefore characterized the response to the GABA(B) receptor agonist baclofen injected into the cisterna magna of the conscious rat. Intracisternally injected baclofen induced long-lasting increases in hindquarters vascular resistance and arterial pressure in a dose-dependent manner. Both actions induced by baclofen were completely blocked by a prior intracisternal injection with the GABA(B) receptor antagonist CGP 35348 (p-[3-aminopropyl]-p-diethoxymethylphosphinic acid), and systemically by ganglionic blockade. These actions of baclofen were also abolished centrally by sodium pentobarbital anaesthesia. The results suggest that GABA(B) receptor stimulation via the cisterna magna induced hindquarters vasoconstriction, probably due to central disinhibition of sympathetic activity.