PATCH-CLAMP CHARACTERIZATION OF NICOTINIC RECEPTORS IN A SUBPOPULATION OF LAMINA-X NEURONS IN RAT SPINAL-CORD SLICES

1. Nicotinic acetylcholine receptors (nAChRs) on lamina X neurones in neonate (P1-P12) rat transverse thoracolumbar spinal cord slices were studied using the whole-cell patch-clamp technique. These visually sel ected neurones are located dorsal to the central canal, mainly in the ventral half of the dorsal commissure. 2. Pressure application of the nicotinic agonist 1,1-dimethyl-4-phenyl-piperazinium (DMPP) (1 mM) ind uced a rapid depolarization on which action potentials are superimpose d. 3. At -50 mV, DMPP (1 mM), pressure ejected for 100 ms, induced a f ast inward current with a mean amplitude of -280 pA (n = 28) in 90% of the neurones recorded. Superfusion of tetrodotoxin (TTX), a solution containing 0 Ca2+-high Mg2+, CdCl2 or 6-cyano-7-nitroquinoxaline-2,3-d ione (CNQX) did not abolish the DMPP-induced current, which confirmed a direct postsynaptic effect of DMPP on recorded neurones. 3. The curr ent-voltage (I-V) relationship for DMPP-induced current exhibited a re versal potential of 0 mV (NaCl outside, potassium gluconate inside) an d a strong inward rectification. 4. The DMPP-induced responses were bl ocked by mecamylamine, hexamethonium and d-tubocurarine (dTC) but were insensitive to alpha-bungarotoxin and methyllycaconitine (MLA). 5. We conclude that lamina X neurones located dorsally to the central canal possess nicotinic acetylcholine receptors. Activation of these nicoti nic receptors results in depolarization and generation of action poten tials. These receptors may be involved in the modulation of the somato - and viscerosensory transmission.