This project delineates biochemical and pharmacological properties of sigma-1 receptors (Sig-1R). Sig-1R are one-transmembrane proteins that are highly expressed in the brain as well as in several peripheral organs including liver, lungs, heart, spleen, pancrease, and adrenal gland. Over the past 20 years, Sig-1R have been implicated in many diseases including cocaine/methamphetamine craving, Alzeimer's disease, cancer, depression, amnesia, and Parkinsonism. However the exact molecular mechanism of action of sig-1R remains elusive. The overall goal of this project is to elucidate the molecular action of Sig-1R in order to unveil a mechanistic foundation for a novel therapeutic opportunity for treating many human diseases. ? In this fiscal year, we have been focusing on examining the effect of cocaine and methamphetamine treatment on the concentrations of Sig-1R in the brain and attempting to elucidate the underlying mechanism thereof. We previously found that rats that are actively self-administering methamphetamine have higher levels of Sig-1R in the brain whereas rats that passively received equal amount of methampehtamine exhibit no increases of Sig-1R. These results implicate that the motivational or the incentive """"""""drive"""""""" per se during drug use can elevate the level of Sig-1R. These results also suggest that the """"""""use"""""""" of cocaine or methamphetamine, and not the drugs per se, may cause an increase of Sig-1R. As Sig-1R were shown by us to increase neuronal differentiation, we hypothesize here that the motivational drive to use a drug, and not the drug's direct molecular action, can increase Sig-1R which in turn formulate an addictive state by causing structureal alterations of neurons. In this fiscal year thus we use a cellular model (B-104 cells) that has no receptors for cocaine or methamphetamine but has key intracellular pathways that are known to be important for drug addiction. Those key pathways are the cAMP-PKA pathway and the cAMP-ERK pathway. ? Here, we employed a neuroblastoma cell line B-104, devoid of dopamine receptors and transporter, and examined the effects of psychostimulants as well as cAMP on the expression of Sig-1Rs in this cell line, with a specific goal to identify signal transduction pathway(s) that may regulate Sig-1R expression. Chronic treatments of B-104 cells with physiological concentrations of cocaine or methamphetamine failed to alter the expression of Sig-1Rs. Dibutyryl cAMP (dB-cAMP), when used at 0.5 mM, caused a downregulation of Sig-1Rs that could be blocked by a protein kinase A (PKA) inhibitor H-89. However, dB-cAMP, when used at 2 mM, caused an upregulation of Sig-1Rs that was insensitive to the H-89 blockade but was partially blocked by an extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK) inhibitor PD98059. Further, 2 mM of dB-cAMP induced an ERK phosphorylation lasting at least 90 min, at which time the phosphorylation caused by 0.5 mM of dB-cAMP had already diminished. PD98059, applied 90 min after addition of 2 mM of dB-cAMP, attenuated the Sig-1R upregulation.? Our results therefore indicate that cAMP is bimodal in regulating Sig-1R expression: a downregulation via PKA and an upregulation via ERK. Results also suggest that psychostimulants may manipulate the cAMP-PKA-Sig-1R and/or the cAMP-ERK-Sig-1R pathways to achieve a neuroplasticity that favors addictive behaviors.
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