Dorsolateral pontine inhibition of dorsal horn cell responses to cutaneous stimulation: lack of dependence on catecholaminergic systems in cat.

The effect of stimulating the dorsolateral pons (DLP) in the region of locus ceruleus (LC) on lumbar dorsal horn cell responses to innocuous and noxious cutaneous stimuli was assessed and the dependence of these effects on intact pontospinal catecholaminergic systems was tested in chloralose-anesthetized cats. DLP stimulation inhibited the responses of dorsal horn cells to both noxious and innocuous skin stimuli. The inhibitory effect was most prominent when the responses to noxious stimuli were tested. The thresholds for eliciting DLP-spinal inhibition were lowest (less than 30 microA) in the region of LC. The inhibitory effect was found in both ipsilateral and contralateral dorsal horns. The DLP-spinal inhibition was unaltered by depletion of spinal catecholamines brought about by repeated lumbar intrathecal administration of 6-hydroxydopamine or systemic administration of reserpine. We conclude that the DLP-dorsal horn inhibition is not related to a catecholaminergic ceruleospinal system in the cat and that the dependence of pain modulation by catecholamine systems is a reflection of other descending pathways.