Figure 4
Role of GABAergic and glycinergic neurotransmission in regions of the medulla containing cardiac vagal preganglionic neurons in cardio-vagal responses to 5-HT 1A receptor activation. Panel A illustrates the effects of intravenous injection of the 5-HT1A agonist 8-OH-DPAT (0.1 mg/kg, n = 9) on heart rate (HR) and baroreflex bradycardia. Panels B and C shows the intravenous injection of 8-OH-DPAT on HR and baroreflex bradycardia following prior microinjection of the GABAA antagonist picrotoxin (2 mM, n = 6) and glycine antagonist strychnine (3 mM, n = 4) into regions of the medulla containing cardiac vagal preganglionic neurons respectively. Panel D shows that an injection of 8-OH-DPAT alone evokes a small bradycardia which is not altered by prior microinjection of picrotoxin. Prior microinjection of strychnine prevents this bradycardia. Panel E shows that injections of 8-OH-DPAT alone increase baroreflex sensitivity (BRS). This increase in BRS is still seen following prior microinjection of picrotoxin but not strychnine. * P < 0.05, ** P < 0.01.