In Vivo Patch-Clamp Analysis of Dopaminergic Antinociceptive Actions in the Spinal Cord

INTRODUCTIONS: It is well understood that dopamine (DA) has an action in the brain as a neurotransmitter and neuromodulator. However, little is known about the roles of DA in the spinal cord. The periventricular, posterior region (A11) of the hypothalamus is the principle source of descending dopaminergic pathways. Focal electrical stimulation in the region of the A11 area suppresses the nociceptive responses of neurons in the spinal dorsal horn. In addition, behavioral studies demonstrate that intrathecal administration of DA induced thermal antinociceptive effects through D2-like receptors when assessed by the tail flick test. These findings strongly suggest that the descending dopaminergic pathway plays an important role in the process of antinociception in the spinal cord. In the present study, to elucidate the mechanisms of antinociception mediated by the dopaminergic descending pathway in the spinal cord, we investigated actions of DA on spinal dorsal horn (DH) neurons by in vivo whole-cell patch-clamp technique.