Involvement of NMDA and non-NMDA receptors in transmission of spinal visceral nociception in cat

AIM: To study the role of N-methyl-D-aspartic acid (NMDA) and non-NMDA rece ptors in processing nociceptive visceral information in the spinal cord. ME THODS: The firing of:spinal dorsal horn neurons to colorectal distension (3 -15 kPa, 20 s) by inflation with air of latex balloon was recorded in 25 an esthetized cats. RESULTS: 1) According to the patterns of responses to colo rectal distension, the neurons with increase and decrease in firing were cl assified as excitatory and inhibitory, respectively. The former consisted o f 17 short-latency abrupt (SLA) neurons, 11 short-latency sustained (SLS) n eurons, 9 long-latency (LL) neurons. The 15 inhibited (Inh) neurons were re corded. 2) Microelectrophoretic administration of NMDA, quisqualic acid (QA ), and kainic acid (KA) activated 67.6 %, 78.4 %, and 59.5 % of the colorec tal distension-excited neurons tested. Also, 60 %, 86.7 %, and 53.3 % of In h neurons were activated by these 3 aminoacids. 3) Colorectal distension-in duced excitatory responses were reduced by 35 % +/- 10 % and 65 % +/- 14 % by a selective NMDA receptor antagonist d,l-2-amino-5-phosphonovalerate (AP V) and a selective non-NMDA receptor antagonist 6,7-dinitro-quinoxaline-2,3 -dione (DNQX), respectively. Such DNQX-induced inhibition was significantly more potent than that by APV (P < 0.05). Colorectal distension-induced inh ibitory responses were partially relieved by 30 %-50 % in 3/7 Inh neurons b y DNQX, but not APV. CONCLUSION: Both NMDA and non-NMDA receptors are invol ved in transmission and/or modulation of spinal visceral nociceptive inform ation and non-NMDA receptors may play more important role than NMDA recepto rs.