Figure 1
A, B show contrasting forms of LTP expressed in distinct groups of spinal lamina I projection neurons in vitro. Time courses of mean amplitudes (± SEM) of C-fibre-evoked EPSCs in lamina I neurons with a projection to the parabrachial area (PB, n = 8) or the periaqueductal grey (PAG, n = 7). Conditioning HFS induced LTP in all spino-PB neurons tested (A) but was ineffective in spino-PAG neurons (data not shown). Conditioning LFS induced LTP in all 18 spino-PAG neurons tested (B) but was never effective in seven spino-PB neurons (data not shown). C-E LTP can be induced by natural, low frequency afferent barrage evoked by inflammation of peripheral tissue in vivo. Mean time courses of C-fibre-evoked field potentials recorded extracellulary in superficial spinal dorsal horn in response to electrical stimulation of left sciatic nerve of deeply anaesthetized adult rats with spinal cords and afferent nerves intact. Subcutaneous injections of transient receptor potential vanilloid 1 channel agonist capsaicin (1%, 100 μl, n = 5, C) or formalin (5%, 100 μl, n = 6, D) into the glabrous skin at the ipsilateral hind paw, within the innervation territory of the sciatic nerve at time zero (arrows) induced LTP (closed circles), while injections of the respective solvents (open circles) had no effects (n = 3 in each group). Conditioning electrical LFS (2 Hz, 2 min at C-fibre intensity) of sciatic nerve at time zero (arrow) induced LTP (n = 28, E) which was prevented by NMDA receptor antagonist MK-801 (3 mg kg-1, i.v.-infusion over 30 min, data not shown). Modified from [12].