Excitatory amino acids depress synaptic currents in neonate rat sympathetic preganglionic neurons

1. Whole-cell patch-clamp recordings were made from sympathetic preganglionic neurons (SPNs) in transverse thoracolumbar spinal cord slices of 10- to 16-day-old rats, and the effects of L-glutamate (L-Glu) and analogues on excitatory (EPSCs) and inhibitory (IPSCs) postsynaptic currents evoked by stimulation of lateral funiculus were studied. 2. L-Glu (10-300 microM), quisqualate (QA, 0.1-3 microM), kainate (KA, 0.3-10 microM), ibotenate (10-25 microM), and L-2-amino-4-phosphonobutyrate (L-AP4, 25-300 microM) depressed the EPSCs and IPSCs in a concentration-dependent manner, the rank order being QA > KA > ibotenate > L-AP4 > or = L-Glu. The metabotropic glutamate receptor agonist trans-1-amino-1,3-cyclopentane-dicarboxylic acid (trans-ACPD, 25-100 microM) reduced the synaptic currents as well. A similar effect was not observed with N-methyl-D-aspartate (NMDA). 3. The excitatory amino acid uptake inhibitor L-aspartic acid-beta-hydroxamate (AAH, 100 microM), although having little or no direct effect on EPSCs, unmasked the inhibitory effect of low (< or = 1 microM) concentrations of L-Glu. 4. The synaptic depression was not accompanied by a detectable change in holding currents or EPSC reversal potentials and decay constants in the majority of SPNs studied. At higher concentrations, L-Glu and analogues, but not L-AP4, induced an inward current in some SPNs. 5. Although strongly depressing the EPSCs, L-AP4 and trans-ACPD had no significant effect on the amplitude of inward current induced by exogenous L-Glu.(ABSTRACT TRUNCATED AT 250 WORDS)