Expression of long-term potentiation in single wide dynamic range neurons in the rat is sensitive to blockade of glutamate receptors

Plasticity in pain control systems may play an important role in clinical p ain and some mechanisms of plasticity may be similar to those involved in l earning. In this study we investigate the importance of alpha-amino-3-hydro xy-5-methylisoxazole-4-proprionic acid (AMPA) and N-methyl-D-aspartate (NMD A) receptors for the maintenance of long-term potentiation (LTP) in wide dy namic range (WDR) neurons. Doses of 6-nitro-7-sulphomoylbenzoylquinoxaline- 2 disodium (NBQX) and D-Q-amino-5-phosphonopentanoic acid (D-AP5) equipoten t in reducing C-fiber mediated responses in controls, reduced the establish ed LTP by about 50 and 80%, respectively. The drug effect lasted less than 1 h in controls. After induction of LTP, NBQX caused a reversible reduction of the potentiation. D-AP5, however, caused a stronger attenuation of the LTP, outlasting the effect of the drug in controls. We suggest that both pr e-emptive analgesia preventing LIP induction and an early reduction of the excitation of neurons is important for the inhibition of LTP and central se nsitization. Thus, it is possible that an early antinociceptive treatment p reventing an excessive excitation of neurons in the dorsal horn may be of i mportance in preventing long-lasting and pathological pain states. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.