Previous studies have shown that central administration of GABA (gamma
-aminobutyric acid), an inhibitory neurotransmitter, preferentially reduces
hindquarters and carotid vascular resistances but not renal and coeliac vascular
resistances in conscious rats. This study tested the hypothesis that these preferential
actions of central GABA receptors are related to differences between vessels in
resting autonomic vascular tone in freely moving rats. Rats were chronically
implanted with intracisternal cannulas and/or electromagnetic probes to measure
regional blood flows. In response to GABA administration, the changes in vascular
resistance (arterial blood pressure/regional blood flow) of the hindquarters (n = 23)
and carotid (n = 12) vascular beds were significantly and negatively correlated with
basal vascular resistance. No such relationship was found for the renal (n = 21),
coeliac (n = 13) and superior mesenteric (n = 23) vascular beds. This finding indicates
that the responsiveness to GABA of brainstem pathways controlling the hindquarters
and carotid vascular beds co-varies with resting resistance in hindquarters and
carotid vessels. A similar analysis was performed, correlating the ongoing vascular
resistance of each vessel with its response to ganglionic blockade by chlorisondamine.
In this case, a significant negative correlation was also found for the hindquarters (n
= 26) and carotid (n = 15) vascular beds, but not for the coeliac (n = 17) or superior
mesenteric (n = 19) vessels. Together, these findings suggest that central GABA
receptors accessible from the cisterna magna preferentially affect two vascular beds
which, in the freely moving rat, show resting autonomic vascular tone. Experimental
Physiology (2000) 85.5, 479-485.