Figure 2
Role of ionotropic GABA A and strychnine sensitive glycine receptors in areas of the medulla containing cardiac vagal preganglionic neurons in the tonic and baroreflex control of HR. Panel A and B show the effects of bilateral microinjection of the GABAA antagonists bicuculline (0.4 mM, n = 4) and picrotoxin (2 mM, n = 6) respectively on resting heart rate (HR) and baroreflex evoked bradycardia induced using phenylephrine (PE). Both bicuculline and picrotoxin evoked large and similar decreases in resting HR. Bicuculline, however, evoked arrhythmia and the effects on baroreflex bradycardia could not be quantified. Panel C shows the effects of bilateral microinjection of strychnine (3 mM, n = 4) on resting HR and baroreflex bradycardia. Group data (panels D and E) shows that picrotoxin evoked a large decrease in resting HR whereas strychnine had no effect (panel D). Neither picrotoxin nor strychnine affected baroreflex bradycardia or baroreflex sensitivity (BRS, panel E). *** P < 0.001.