Characterization of synaptic transmission in the ventrolateral periaqueductal gray of rat brain slices

Synaptic transmission evoked by focal stimulation in the ventrolateral peri aqueductal gray was characterized using the whole-cell recording technique in rat brain slices. At resting membrane potential (-62 +/- 1 mV), focal st imulation (0.05-0.1 ms, 0.03 Hz) usually evoked a 6-cyano-7-nitroquinoxalin e-2,3-dione-sensitive fast excitatory postsynaptic potential and a DL-2-ami no-5-phosphonopentanoic acid-sensitive slow excitatory postsynaptic potenti al with a bicuculline-sensitive inhibitory postsynaptic potential in betwee n. In the presence of kynurenic acid, bicuculline-sensitive inhibitory post synaptic currents recorded in the voltage-clamp mode displayed a reversal p otential of -68 +/- 3 mV, resembling GABA(A) receptor-mediated inhibitory p ostsynaptic currents. However. no GABA(B) receptor-mediated inhibitory post synaptic current was evoked, even at stronger stimulating intensity. 6-Cyan o-7-nitroquinoxaline-2,3-dione-sensitive fast excitatory postsynaptic curre nts were isolated by DL-2-amino-5-phosphonopentanoic acid plus bicuculline and DL-2-amino-5-phosphonopentanoic acid-sensitive slow fast excitatory pos tsynaptic currents by bicuculline plus 6-cyano-7-nitroquinoxaline-2,3-dione . Both types of excitatory postsynaptic current reversed at potentials near 0 mV. The I-V curve of slow fast excitatory postsynaptic currents or N-met hyl-D-aspartate currents displayed a negative slope at potentials more nega tive than -30 mV in an Mg2+-sensitive manner. The control postsynaptic curr ents reversed at potentials between -50 and -35 mV, inclined to the reversa l potential of GABA(A), but not glutamate, receptor channels. It is concluded that, in the ventrolateral periaqueductal gray, focal stimu lation elicits both inhibitory and excitatory transmission, while the forme r is dominant. The inhibitory transmission is mediated by GABA(A) but not G ABA(B) receptors. The excitatory transmission is mediated by glutamate acti ng on alpha -amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate as well as N-methyl- D-aspartate receptors. (C) 2000 IBRO. Published by Elsevier S cience Ltd. All rights reserved.