NMDA Receptor Involvement in Neuroplastic Changes Induced By Neonatal Capsaicin Treatment in Trigeminal Nociceptive Neurons

Chen Yu Chiang, James W. Hu, Barry J. Sessle
1997 Journal of Neurophysiology  
NMDA nociceptive neurons in trigeminal (V) subnucleus caudalis receptor involvement in neuroplastic changes induced by neonatal (medullary dorsal horn) of adult rats and 2) that NMDA capsaicin treatment in trigeminal nociceptive neurons. J. Neuroreceptor mechanisms are involved in these neuroplastic physiol. 78: 2799-2803, 1997. This study examines whether 1) changes. Preliminary data have been presented in abstract the neonatal loss of C-fiber afferents results in neuroplastic changes form
more » ... ic changes form (Chiang et al. 1995; Sessle et al. 1995a). in the mechanoreceptive field (RF) properties and spontaneous activity of nociceptive neurons in trigeminal subnucleus caudalis (medullary dorsal horn) of adult rats, and that 2) N-methyl-D-M E T H O D S aspartic acid (NMDA) receptor mechanisms are involved in these This study was carried out in 52 male Sprague-Dawley rats. The neuroplastic changes. Compared with vehicle-treated (i.e., control, rats were injected subcutaneously after 36-48 h of birth either CON) rats, capsaicin-treated (CAP) rats showed a marked increase with capsaicin (50 mg/kg, Sigma, dissolved in saline containing in neuronal spontaneous activity and RF size per se, but these 10% Tween 80 and 10% ethyl alcohol, n Å 30) or with vehicle only neuroplastic changes could be significantly reduced by MK-801 (i.e., control, CON rats, n Å 22) (Gamse et al. 1980 ; Hammond (1 mg/kg, iv), a noncompetitive NMDA receptor antagonist; RF and Ruda 1991;; both groups were studied size and spontaneous activity remained unchanged in CON rats electrophysiologically 2-4 mo later. The effectiveness of neonatal after MK-801 administration and in CAP rats after vehicle (saline, capsaicin treatment in markedly reducing the number of C-fiber iv). Administration of 7-chlorokynurenic acid intrathecally (5 mg/ afferents was assessed by spectrophotometric analysis of the 10 ml), an antagonist of strychnine-insensitive glycine binding plasma extravasation of injected 1% Evan's blue dye (20 mg/kg, sites on the NMDA receptor, also significantly reduced neuronal iv). The Evan's blue was infused into the CAP or CON adult RF size and spontaneous activity in CAP rats, but not in CON rats. rat after termination of neuronal recording (see next paragraph). These data provide evidence that C-fiber afferents play a role in Extravasation was induced by cutaneous application of 20% musshaping the properties of nociceptive neurons and that the neutard oil (allyl-isothiocyanate, BDH, Toronto, Canada; diluted in roplastic changes involve NMDA receptor mechanisms. mineral oil; 0.02 ml) to the shaved skin of the left hindlimb. Then, 20 min later this hindlimb skin, as well as the analogous part of the contralateral hindlimb, was excised and the amount of extravasated 0022-3077/97 $5.00
doi:10.1152/jn.1997.78.5.2799 pmid:9356428 fatcat:goe2t5e74bbjlbqdwxso2oiwni