Evidence for involvement of cholinoceptive cells of the parabrachial region in environmentally induced nociceptive suppression in the cat.

We have previously observed that activation of muscarinic receptors within the pontine parabrachial region (PBR) of cats produces potent analgesia. This study demonstrated that bilateral microinjections of the muscarinic antagonist atropine (each 4.0 micrograms in 1.0 microliter) into PBR attenuated nociceptive suppression elicited by exposure of cats to novel environmental changes without affecting general responsiveness to environmental stimulation. This observation suggests that muscarinic cholinoceptive cells in PBR function physiologically to modulate nociceptive responsiveness in response to certain environmental stimuli.