Histamine elicits the sensation of itch at the site of skin application as well as alloknesis (itch elicited by innocuous mechanical stimuli) in a surrounding area in humans and expansion of the low-threshold mechanosensitive receptive field area of spinal wide dynamic range (WDR)- type dorsal horn neurons in rats. We presently tested if the histamine- evoked expansion of neuronal receptive field area depends on a spinal N- methyl-D-aspartate (NMDA) receptor-mediated process. In pentobarbital sodium- anesthetized rats, mechanical receptive field areas of single WDR-type dorsal horn neurons were mapped with graded von Frey filaments before and 10 min after intracutaneous (ic) microinjection of histamine (1 μl; 1, 3, or 10%) at a low-threshold site within the receptive field. Intracutaneous microinjection of histamine evoked dose-related increases in firing rate, as well as a dose-dependent expansion in mean receptive field area 10 min after 3 and 10%, but not 1%, histamine doses. When a noncompetitive or competitive NMDA receptor antagonist dizocilpine [MK-801; D(-)-2-amino-5- phosphonovalerate (APV), respectively; 1 μM] was first applied topically to the surface of the spinal cord, there was no significant change in mean receptive field area after ic microinjection of 10% histamine. The mean neuronal response to histamine in the presence of spinal MK-801 or APV was not significantly different from the mean response to histamine in the absence of these drugs. These results suggest that spinal NMDA receptors are involved in histamine-induced expansion of mechanical receptive field area, a neural event possibly involved in the development of alloknesis.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Neurophysiology|
|State||Published - 1998|
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