The sigma receptor (σR), once considered a subtype of the opioid receptor, is now described as a distinct pharmacological entity. Modulation of N -methyl-D-aspartate receptor (NMDAR) functions by σR-1 ligands is well documented; however, its mechanism is not fully understood. Using patch-clamp whole-cell recordings in CA1 pyramidal cells of rat hippocampus and (+)pentazocine, a high-affinity σR-1 agonist, we found that σR-1 activation potentiates NMDAR responses and long-term potentiation (LTP) by preventing a small conductance Ca 2+ -activated K + current (SK channels), known to shunt NMDAR responses, to open. Therefore, the block of SK channels and the resulting increased Ca 2+ influx through the NMDAR enhances NMDAR responses and LTP. These results emphasize the importance of the σR-1 as postsynaptic regulator of synaptic transmission.

To investigate the effects of persistent elevation of synaptic glycine at Schaffer collateral-CA1 synapses of the hippocampus, we studied the glutamatergic synaptic transmission in acute brain slices from mice with reduced expression of glycine transporter type 1 (GlyT1+/−) as compared to wild type (WT) littermates using whole-cell patch-clamp recordings of CA1 pyramidal cells. We observed faster decay kinetics, reduced ifenprodil sensitivity and increased zinc-induced antagonism in N -methyl-D-aspartate receptor (NMDAR) currents of GlyT1+/− mice. Moreover, the ratio α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR)/NMDAR was decreased in mutants compared to WT. Surprisingly, this change was associated with a reduction in the number of AMPARs expressed at the CA1 synapses in the mutants compared to WT. Overall, these findings highlight the importance of GlyT1 in regulating glutamatergic neurotransmission.