336 B. Szabo and E. Schlicker
Fig. 1A, B.Cannabinoids inhibit glutamatergic synaptic transmission in the substantia nigra pars reticulata
(SNR) of the rat via a presynaptic mechanism. The major glutamatergic afferent input of SNR neurons
originates in the subthalamic nucleus.ASNR neurons were patch-clamped and their glutamatergic afferent
axons electrically stimulated. The stimulation elicited excitatory postsynaptic currents (EPSCs) in SNR neurons.
EPSCs remained stable in solvent (SOL)-superfused slices. The synthetic cannabinoid agonists WIN55212-2
(WIN) and CP55940 (CP) inhibited the EPSCs.BSNR neurons were patched-clamped and glutamate (GLU)
was pressure-ejected from a pipette in their vicinity. Glutamate-evoked currents remained stable in SOL-
superfused slices. Superfusion of WIN also did not change the glutamate-evoked currents. This observation
indicates that cannabinoids do not interfere with the postsynaptic effect of glutamate; thus, the inhibition of
neurotransmission seen in panelAis due to presynaptic inhibition of glutamate release from axon terminals.
In both panels, a typical original recording obtained in a WIN experiment (inset) and the statistical analysis
are shown.PRE, initial reference period. See Szabo et al. (2000) for details of the experiments.*,Significant
difference from SOL (p<0.05)