Elsevier

Neuroscience

Volume 100, Issue 4, 11 October 2000, Pages 829-834
Neuroscience

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

https://doi.org/10.1016/S0306-4522(00)00348-1Get rights and content

Abstract

Synaptic transmission evoked by focal stimulation in the ventrolateral periaqueductal gray was characterized using the whole-cell recording technique in rat brain slices. At resting membrane potential (−62±1 mV), focal stimulation (0.05–0.1 ms, 0.03 Hz) usually evoked a 6-cyano-7-nitroquinoxaline-2,3-dione-sensitive fast excitatory postsynaptic potential and a dl-2-amino-5-phosphonopentanoic acid-sensitive slow excitatory postsynaptic potential with a bicuculline-sensitive inhibitory postsynaptic potential in between. In the presence of kynurenic acid, bicuculline-sensitive inhibitory postsynaptic currents recorded in the voltage-clamp mode displayed a reversal potential of −68±3 mV, resembling GABAA receptor-mediated inhibitory postsynaptic currents. However, no GABAB receptor-mediated inhibitory postsynaptic current was evoked, even at stronger stimulating intensity. 6-Cyano-7-nitroquinoxaline-2,3-dione-sensitive fast excitatory postsynaptic currents were isolated by dl-2-amino-5-phosphonopentanoic acid plus bicuculline and dl-2-amino-5-phosphonopentanoic acid-sensitive slow fast excitatory postsynaptic currents by bicuculline plus 6-cyano-7-nitroquinoxaline-2,3-dione. Both types of excitatory postsynaptic current reversed at potentials near 0 mV. The IV curve of slow fast excitatory postsynaptic currents or N-methyl-d-aspartate currents displayed a negative slope at potentials more negative than −30 mV in an Mg2+-sensitive manner. The control postsynaptic currents reversed at potentials between −50 and −35 mV, inclined to the reversal potential of GABAA, but not glutamate, receptor channels.

It is concluded that, in the ventrolateral periaqueductal gray, focal stimulation elicits both inhibitory and excitatory transmission, while the former is dominant. The inhibitory transmission is mediated by GABAA but not GABAB receptors. The excitatory transmission is mediated by glutamate acting on α-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate as well as N-methyl-d-aspartate receptors.

Section snippets

Brain slice preparations

Brain slices of 400 μm containing the midbrain PAG were dissected coronally from Wistar rats of 12–18 days age, as reported previously.12 After equilibrium, slices were transferred to a submerged chamber and perfused with artificial cerebral spinal fluid (ACSF) at 2–3 ml/min. ACSF contained (mM) NaCl 117, KCl 4.5, CaCl2 2.5, MgCl2 1.2, NaH2PO4 1.2, NaHCO3 25 and dextrose 11.4, and was oxygenated with 95% O2 plus 5% CO2.

Electrophysiological recordings

Blind patch-clamp whole-cell recording8 was conducted in the ventrolateral

Results

Experiments were performed on 60 cells. The mean resting membrane potential was −62±1 mV. Input resistance varied from 90 MΩ to 1.6 GΩ and averaged 531±37 MΩ.

Discussion

The present study demonstrates that focal stimulation within the ventrolateral PAG elicited a dominant inhibitory neurotransmission as well as an excitatory one. The inhibitory synaptic transmission is mediated by GABAA, but not GABAB, receptors. The excitatory synaptic transmission is mediated by glutamate acting on AMPA/kainate and NMDA receptors. The NMDA receptor-mediated synaptic response is characterized by an Mg2+-sensitive voltage-dependent block, like those found in other brain areas.30

Acknowledgements

This work was supported by grant NSC 89-2320-B002-076 from the National Science Council, ROC (L.C.C.).

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