LONG-TERM POTENTIATION AND LONG-TERM DEPRESSION OF PRIMARY AFFERENT NEUROTRANSMISSION IN THE RAT SPINAL-CORD

Synaptic transmission between dorsal root afferents and neurons in the superficial laminae of the spinal dorsal horn (laminae I-III) was exa mined by intracellular recording in a transverse slice preparation of rat spinal cord. Brief high-frequency electrical stimulation (300 puls es at 100 Hz) of primary afferent fibers produced a long-term potentia tion (LTP) or a long-term depression (LTD) of fast (monosynaptic and p olysynaptic) EPSPs in a high proportion of dorsal horn neurons. Both t he AMPA and the NMDA receptor-mediated components of synaptic transmis sion at the primary afferent synapses with neurons in the dorsal horn can exhibit LTP and LTD of the synaptic responses. In normal and neona tally capsaicin-treated rats, the induction of LTP requires the activa tion of NMDA receptor-gated conductances. The induction of LTP or LTD, however, was not abolished in the presence of bicuculline, a GABA(A) receptor antagonist. The results demonstrate that distinct and long-la sting modulation in synaptic efficiency can be induced at primary affe rent synapses with neurons in the superficial laminae of spinal dorsal horn by high-frequency stimulation of dorsal root afferents and that these changes may be physiologically relevant for transmission and int egration of sensory information, including pain.