A NOVEL SLOW EXCITATORY POSTSYNAPTIC CURRENT IN SUBSTANTIA-GELATINOSANEURONS OF THE RAT SPINAL-CORD IN-VITRO

Whole-cell patch-clamp recordings were made from neurons in the substa ntia gelatinosa of adult rat spinal cord slices with attached dorsal r oot to study a slow synaptic current evoked by focal or dorsal root st imulation. Repetitive focal stimulation with a monopolar electrode pos itioned within substantia gelatinosa elicited a slow excitatory postsy naptic current preceded by a Fast excitatory postsynaptic current in 7 3 of 83 neurons. A similar slow excitatory postsynaptic current was al so elicited by stimulation of AF afferent fibres. The amplitude of slo w excitatory postsynaptic currents was unchanged when the recording el ectrode contained guanosine-5'-O-(2-thiodiphosphate). The slow excitat ory postsynaptic current and current evoked by aspartate revealed simi lar reversal potentials and showed a marked outward rectification at h olding potentials more negative than -30 mV, while the glutamate-induc ed current exhibited a relatively linear voltage relationship. In addi tion, the slow excitatory postsynaptic currents were reversibly occlud ed during the aspartate-induced current but were not occluded during t he glutamate-induced current. The slow excitatory postsynaptic current s evoked by focal stimulation were depressed but not abolished by 6-cy ano-7-nitroquinoxaline-2,3-dione (10 mu M) or by 6-cyano-7-nitroquinox aline-2,3-dione together with DL-2-amino-5-phosphonopentanoic acid (10 0 mu M). Similarly, the aspartate- and glutamate-induced currents were also resistant to these antagonists. These observations suggest that a transmitter released from interneurons or descending fibres which ar e activated in part by A delta afferents, mediates a slow excitatory p ostsynaptic currents in substantia gelatinosa neurons and that an exci tatory amino acid is implicated in the generation of the slow excitato ry postsynaptic current, although the receptor appears to differ From the known ligand-gated channels. C afferents are unlikely to contribut e to the slow excitatory postsynaptic current. This slow synaptic resp onse may participate in the pain pathway and play an important role in the processing of nociceptive information in the spinal dorsal horn. Copyright (C) 1996 IBRO.