Abstract
The periaqueductal grey (PAG) of the brainstem is a central site for the various physiological functions including cardiovascular control, defensive behavior and pain. Since the cholinergic modulation on PAG activity is still unknown, we used infrared-videomicroscopy in conjunction with whole-cell recordings to elucidate the effects of acetylcholine on PAG neurons in midbrain slices of juvenile rats. In current clamp mode, 40% of all PAG neurons examined showed depolarization of their membrane potential during the application of carbachol (CCh). On the other hand, 20% of all PAG neurons examined were hyperpolarized by CCh. The remaining PAG neurons (40%) were insensitive to CCh. Both the depolarizing and the hyperpolarizing action of CCh were atropine-sensitive, indicating that they were mediated by muscarinic receptors. The depolarizing response to CCh was abrogated by M1 antagonist, pirenzepine, while the hyperpolarizing response was abolished by M2 antagonist, gallamine. These results suggest that rat PAG neurons have functional muscarinic receptors. [J Physiol Sci. 2006;56 Suppl:S162]
