Parabrachial area and nucleus raphe magnus inhibition of corneal units in rostral and caudal portions of trigeminal subnucleus caudalis in the rat.

Abstract The cornea has been used extensively as a means to selectively stimulate trigeminal nociceptive neurons. The aim of this study was to determine the effects of descending modulatory control pathways on corneal unit activity by comparing the effects of conditioning stimulation of the pontine parabrachial area (PBA CS) and nucleus raphe magnus (NRM CS). Electrical stimulation of the cornea at A- and C-fiber intensities was used to activate neurons in two regions of the trigeminal spinal nucleus, the subnucleus interpolaris/caudalis transition (Vi/Vc, ‘rostral units’) and laminae I–II at the subnucleus caudalis/cervical cord transition (Vc/C1, ‘caudal units’), in chloralose-anesthetized rats. Corneal units were further classified according to convergent cutaneous receptive field properties and PBA projection status. None of 48 rostral and 23/28 caudal units projected to the ipsilateral or contralateral PBA. PBA CS inhibited the cornea-evoked responses ( P