The estimated ED50 was approximately 45 nmol/50 nL for the depressor response. The depressor response (ΔMAP = −17 ± 2.5 mmHg, n = 6) evoked by microinjection of Ach

(45 nmol/50 nL) into the vlPAG was significantly different from those effects observed by injection of 50 nL of ACSF (n = 5; t = 9, P < 0.05). In addition, the microinjection of Ach (45 nmol/50 nL) into the dorsal raphe nucleus and laterodorsal tegmental nucleus (outside the vlPAG) did not cause significant changes in either MAP (before: 93 ± 2.7 mmHg and after: 92.5 ± 3.mmHg; n = 5, P > 0.05, t = 0.7) or HR (before: 391 ± 5.4 bpm and after: 394 ± 5 bpm; n = 5, t = 0.9, P > 0.05). The basal levels this website of both MAP and HR of the rats used to generate the dose–response curves were respectively 93 ± 3 mmHg and 394 ± 7 bpm (n = 12). Microinjection of Ach (9, 27, 45 or 81 nmol/50 nL) into the rostral, medial or caudal portions of the dPAG did not affect either MAP (r2 = 0.3, P > 0.05) or HR (r2 = 0.4, P > 0.05). Pretreatment of the vlPAG with 50 nL of ACSF (n = 5) did not affect basal levels of either MAP (before: 92 ± 4.4 mmHg and after: 94 ± 1.2 mmHg, t = 0.64, P > 0.05) or HR (before: 405 ± 9.2 bpm and after: 403 ± 6.8 bpm, t = 0.45, P > 0.05).

Moreover, the pretreatment with ACSF did not affect the hypotensive response Akt inhibitor evoked by Ach (45 nmol/50 nL) into the vlPAG (ΔMAP before ACSF = −17.3 ± 2 mmHg ADP ribosylation factor and ΔMAP after ACSF = −16.9 ± 2.3 mmHg; n = 5, t = 0.8, P > 0.05). Inhibition of MAP responses by the microinjection of Ach (45 nmol/50 nL) into the vlPAG after local pretreatment with different doses of the nonselective muscarinic receptor antagonist atropine (1, 3 and 9 nmol, n = 4 for each dose). Pretreatment of the vlPAG with

1 nmol/50 nL did not affect basal levels of either MAP (MAP before atropine: 90 ± 1.7 mmHg and after: 91 ± 2.1 mmHg; n = 12, t = 1.1, P > 0.05) or HR (before atropine: 398 ± 9 bpm and after: 399 ± 6 bpm; n = 12, t = 0.9, P > 0.05). Pretreatment of the vlPAG with 3 nmol/50 nL did not affect basal levels of either MAP (MAP before atropine: 90 ± 2.5 mmHg and after: 93 ± 3 mmHg; n = 12, t = 1.1, P > 0.05) or HR (before atropine: 402 ± 7.2 bpm and after: 399 ± 6.5 bpm; n = 12, t = 0.9, P > 0.05). Pretreatment of the vlPAG with 9 nmol/50 nL did not affect basal levels of either MAP (MAP before atropine: 92 ± 2.3 mmHg and after: 93 ± 2 mmHg; n = 12, t = 1.1, P > 0.05) or HR (before atropine: 391 ± 5.7 bpm and after: 387 ± 6.8 bpm; n = 12, t = 0.9, P > 0.05). Local pretreatment with atropine (1, 3 and 9 nmol/50 nL) caused a dose-related inhibition (r2 = 0.9) of depressor responses to Ach microinjection into the vlPAG ( Fig. 2).