Selective blockade of an excitatory synapse in rat cerebral cortex by the sigma opiate cyclazocine: an intracellular, in vitro study.

In isolated slices of rat cortex, intracellularly recorded responses of pyramidal neurones to N-methylaspartate (NMA) and glutamate and responses to stimulation of the underlying white matter were compared and challenged with the sigma opiate cyclazocine. Cyclazocine blocked responses to iontophoretically applied NMA and one component of the postsynaptic response to stimulation, but left other postsynaptic events and responses to glutamate intact. These results are consistent with the view that sigma opiates act as selective NMA antagonists and block synaptic events mediated by NMA receptors.