Silent NMDA Receptor-Mediated Synapses Are Developmentally Regulated In The Dorsal Horn Of The Rat Spinal Cord. Hiroshi Baba, Timothy P. Doubell, Kimberly A. Moore and Clifford J. Woolf. Neural Plasticity Research Group, Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, Boston 02129.
APStracts 6:0524N, 1999.
In vitro whole-cell patch clamp recording techniques were utilized to study silent pure-NMDA receptor-mediated synaptic responses in lamina II (substantia gelatinosa, SG) and lamina III of the spinal dorsal horn. To clarify whether these synapses are present in the adult and contribute to neuropathic pain, transverse lumbar spinal cord slices were prepared from neonatal, naive adult and adult sciatic nerve transected rats. In neonatal rats, pure-NMDA receptor mediated EPSCs were elicited in SG neurons either by focal intraspinal stimulation (n = 15 of 20 neurons) or focal stimulation of the dorsal root (n = 2 of 7 neurons). In contrast, in slices from naive adult rats, no silent pure-NMDA EPSCs were recorded in SG neurons following focal intraspinal stimulation (n = 27) and only one pure-NMDA EPSC was observed in lamina III (n = 23). Furthermore, in rats with chronic sciatic nerve transection, pure-NMDA EPSCs were elicited by focal intraspinal stimulation in only 2 of 45 SG neurons. Although a large increase in A( fiber evoked mixed AMPA and NMDA receptor mediated synapses was detected after sciatic nerve injury, A? fiber mediated pure-NMDA EPSCs were not evoked in SG neurons by dorsal root stimulation. Pure-NMDA receptor mediated EPSCs are, therefore, a transient, developmentally regulated phenomenon, and while they may have a role in synaptic refinement in the immature dorsal horn, they are unlikely to be involved in receptive field plasticity in the adult.
Received 7 July 1999; accepted in final form 14 October 1999.
APS Manuscript Number J552-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999