A: effect of injection of a combination of glutamate receptor antagonists (AP5 + NBQX) into caudal l/dlPAG on cardiovascular response to air jet stress (n = 6). Mean values for HR and MAP over time (min) after microinjection of VEH (100 nl; •) or glutamate receptor antagonist (AP5 300 pmol/100 nl + NBQX 100 pmol/00 nl; ○) into caudal l/dlPAG at t = 5 min followed 5 min later by 20 min of air jet stress. *Significant difference between antagonist and saline treatment in PAG by two-factor repeated-measures ANOVA (treatment and time as repeated factors) for interaction of treatment × time and Fisher's LSD post hoc test, P < 0.05, for HR but not MAP − HR: F (17, 85) = 2.48, P = 0.0032; MAP: F (17, 85) = 1.61, P = 0.08. B: schematic coronal sections of the rat brain adapted from the atlas of Paxinos and Watson (35), illustrating approximate sites of injections of muscimol into caudal l/dlPAG. Numbers indicate distance from bregma in millimeters.