, 1998 and Van Bockstaele et al., 1989). Particulary, electrical stimulation of the dorsal PAG (dPAG) increases arterial pressure through a

sympathoexcitatory action (Kubo et al., 1999). However, electrical stimulation of the dorsal, dorsolateral or lateral PAG evokes hypertension, tachycardia and hindlimb vasodilatation in anesthetized rats (Hamalainen and Lovick, 1997 and Lovick, 1992a). Additionally, microinjection of DL-homocysteic acid into the dPAG of anesthetized rats has been reported to cause hypertension and tachycardia, whereas depressor and bradycardiac responses have been observed after its injection into the ventrolateral PAG of anesthetized rats (vlPAG) (Bandler et al., 1991, Huang et al., 2000, Lovick,

1985, Lovick, Dapagliflozin in vivo 1992a and Rossi et al., selleck 1994). Therefore, pressor responses are evoked by dorsal and lateral columns in PAG stimulation, whereas depressor and bradycardiac responses are evoked after stimulation of the ventrolateral PAG (Carrive and Bandler, 1991, Carrive et al., 1989, Lovick, 1992a and Rossi et al., 1994). Interestingly, Pelosi and Correa (2005) reported that the microinjection of noradrenaline (NA) into either the vlPAG or the dPAG evoked hypertensive and bradycardiac responses in unanesthetized rats (Pelosi et al., 2008). It has been described that cholinergic systems of several brain regions are involved in cardiovascular modulation, among them those in the lateral septal area (Scheucher et al., 1987), the posterior hypothalamus (Brezenoff and Xiao, 1989), the nucleus of the solitary tract (Sundaram et al., 1989) and the medial prefrontal cortex (Crippa et al., 1999). There are results showing the presence of both cholinergic synapses and muscarinic receptors in the PAG (Wamsley et al., 1981). Idoxuridine Because a cholinergic system is present in the PAG, and this brain area is involved in central cardiovascular modulation,

it is possible to suggest that such PAG cholinergic neurotransmission could also modulate the cardiovascular system. However, there are no reports on the cardiovascular effects of local injection of Ach into the PAG, and particularly into the dPAG or the vlPAG at different rostrocaudal coordinates, in the rat brain. Therefore, the present work examined the cardiovascular effects of local Ach microinjection into the vlPAG and dPAG columns of anesthetized rats and the subtype of cholinergic receptors that mediate these responses. The basal levels of both MAP and HR of the rats used to generate the dose–response curves were, respectively, 91 ± 3 mmHg and 390 ± 8 bpm (n = 20). Microinjections of Ach (9, 27, 45 and 81 nmol/50 nL) into the rostral, medial and caudal portions of the vlPAG of anesthetized rats caused dose-related MAP decreases (r2 = 0.92, *P < 0.05) ( Fig. 1).