NMDA Receptors and Memory of Pain

NMDA is a receptor for the excitatory neurotransmitter glutamate, which is released with noxious peripheral stimuli. They are critical for the development of the central nervous system (CNS), generation of rhythms for breathing and locomotion, and the processes underlying learning, memory, and neuroplasticity. The activation of NMDA receptors has been associated with hyperalgesia, neuropathic pain, and reduced functionality of opioid receptors. Therefore, NMDA antagonists have a role in modulating pain. Ketamine is a strong NMDA antagonist. By blocking the receptors through antagonist ketamine given preemptively and postoperatively via epidural route in patients of lower limb amputation, its role in suppression of memory of pain is studied.

This study was conducted at Civil Hospital Ahmedabad during the year 2012–2015 with the permission of ethical committee of hospital and after written informed consent of 60 adult patients of age group 18–60 years of either sex and ASA grade 1 or 2 posted for lower limb amputation. Patients were divided into three groups where one was administered epidural opioid and ketamine, the second group was epidural opioid only and in the third group epidural saline only. Pain scores of all the groups were compared.

Requirement of first dose of analgesia in group 1 is after 12.5±1.03hrs, in group 2 after7.6± 0.98 hrs and in group3 after 3.4± 0.8hrs and average duration between consecutive analgesic doses were 11.5hrs in group 1, 7.6hrs in group 2 and 4.5hrs in group 3 respectively.

NMDA receptor antagonist is effective in management of acute post-operative pain compared to opioid analgesics alone as the time to first dose of analgesia is much larger in group 1 than 2 and 3. Ketamine has definitive role in opioid sparing effect as suppression of memory of pain. [Lamoria M NJIRM 2015; 7(1): 1]