Transmission of afferent information from urinary bladder, urethra and perineum to periaqueductal gray of cat

The micturition reflex pathway is a supraspinal pathway. Anatomical tracing evidence is compatible with an involvement of the periaqueductal gray (PAG ) in the ascending limb of this reflex. We tested the involvement of the FA G in receiving urinary tract- or perineum-related information and attempted to characterize this ascending path in terms of what type of information i s being conveyed. Electrical stimulation of the pelvic nerves, which carry afferent information from the urinary bladder, evoked maximum field potenti als in the caudal third of the FAG, primarily in the dorsal part of the lat eral FAG and in the ventrolateral FAG. Since the regions activated by pelvi c nerve stimulation differed from those activated by stimulation of the sen sory pudendal or superficial perineal nerves, it is possible that specific pathways for different nerve inputs to the FAG exist. Sacral spinal cord ne urons ascending to the FAG were identified by antidromic activation and the n tested for inputs from pelvic, sensory pudendal or superficial perineal n erves. Of 18 units identified, only five received inputs from any of the pe ripheral nerves tested and only two projecting neurons received a pelvic ne rve input. Thus the FAG may receive inputs from bladder and perineum, but t he small proportion of cells with direct projections to the FAG receiving i nputs from our test nerves implies that the major part of this pathway is n ot directly related to lower urinary tract function. (C) 1999 Elsevier Scie nce B.V. All rights reserved.