A: effect of injection of muscimol into caudal lateral/dorsolateral periaqueductal gray (l/dlPAG) on cardiovascular response to air jet stress. Mean values for heart rate (HR) and mean arterial pressure (MAP) over time (min) after microinjection of vehicle (VEH; 100 nl; •) or muscimol (MUS; 300 pmol/100 nl; ○) into caudal l/dlPAG at t = 5 min followed 5 min later by 20 min of air jet stress (n = 10). *Significant difference between muscimol and saline treatment in PAG by two-factor repeated-measures ANOVA [treatment and time as repeated factors) for interaction of treatment × time − HR: F (17, 153) = 3.82, P < 0.0001; MAP: F (17, 153) = 5.24, P < 0.0001] and Fisher's least significant difference (LSD) post hoc test, P < 0.05. B: schematic coronal sections of rat brain adapted from the atlas of Paxinos and Watson (35), illustrating approximate sites of injections of muscimol into caudal l/dlPAG for which data are reported at left. Numbers indicate distance from bregma in millimeters.