Physiological effects produced by ingestion of the drug of abuse phencyclidine (PCP) are mediated by PCP acting through several receptors, ion channels, and neurotransmitter reuptake transporters. Among the receptors activated by PCP is the sigma receptor, located in motor and limbic areas of rodent, non-human primate, and human brains. In rodent striatum, nucleus accumbens, prefrontal cortex, hippocampus and cerebellum, we have shown that one role of the sigma receptors is regulation of catecholamine release. The catecholamine dopamine is critical to reinforcement, movement, and psychosis; the catecholamine norepinephrine is involved in mood stability, attention, and cognition. Interference with these neurotransmitter systems by PCP acting through the sigma receptor might be expected to contribute to the psychosis and dysphoria resulting from PCP abuse. Several second messengers involved in the stimulation of catecholamine release from brain tissue and cells have been identified, but nothing is known about the signal transduction pathways mediating sigma receptor inhibition of catecholamine release. In this project, the relationships among sigma receptor agonist binding, activation or inhibition of second messengers, and release of catecholamines will be established in cell models, including the human neuroblastoma cells SK-N-SH and SH-SY5Y for studies on regulation of norepinephrine release, and in rat pheochromocytoma (PC12) cells for regulation of dopamine release. These cell lines have proved valuable in understanding catecholamine release mechanisms in the past, and many second messenger systems have been studied in them. In some experiments not involving catecholamine release, we will use rat neonatal cerebellar granule cells in culture. We have used this cell type extensively to study sigma-1 receptor inhibition of arachidonic acid release. Sigma receptors of the sigma-1 subtype are thought to be coupled to their transducers via a G protein. By using antisense oligonucleotides to the alpha subunits of various inhibitory G proteins, we have begun to identify G protein(s) involved in sigma-1-mediated responses. The physiological relevance of the identified second messengers coupling sigma receptors to catecholamine release in cell models will be determined in brain slices using our established superfusion methodologies. Our findings should be helpful in designing appropriate therapies for abuse of PCP, and related psychotic syndromes.
