Role of GABAB Receptor of the Pedunculopontine Tegmental (PPT) Nucleus on Cardiovascular Responses in Normotensive Rats

The Pedunculopontine Tegmental (PPT) is a mesencephalic nucleus that involved in numerous functions including movements, sleep, pain andalso respiratory and cardiovascular regulation. This nucleus has many neurotransmitters including gamma aminobutyric acid (GABA). In our previous study, the effect of GABAA receptor of the PPT on cardiovascular function was determined. In this study the role of theGABAB receptor of this nucleus on cardiovascular response has been studied. Materials and Methods: In this study animals were randomly divided in following groups: 1) Control and 2-4) Baclofen (as a GABAB agonist with 3 doses; 0.5, 1 and 2.5 nm), 5-7) Phaclofen (as a GABAB antagonist with 3 doses; 0.5, 1 and 2.5 nm). To measure the cardiovascular parameters, the femoral artery was cannulated and connected to pressure transducer and by means of a power lab device the mean arterial pressure (MAP), systolic blood pressure (SBP) and heart rate (HR) were recorded. The drugs were microinjected into the PPT nucleus using stereotactic device. Changes of SBP, MAP and HR before andafter injection of drugs were calculated and compared with the control group (one-way ANOVA with post hoc tukey’s). Results: Microinjection of baclofen and phaclofen at 0.5 and 1 nm doses did not significantly change the MAP, SBP and HR. However, dose 2.5 baclofen (GABAB agonist), significantly reduced HR (P<0.05) and had not significant effect on SBP and MAP. The dose 2.5 phaclofen (GABAB antagonist) alsosignificantly increased SBP (P<0.05) and HR (P<0.01) but had not significant effect on MAP. Conclusions: The results show that the GABAB receptor agonist in higher dose has inhibitory effects on cardiovascular parameters, especially on HR.