Abstract
BackgroundBuprenorphine is an opioid receptor ligand whose mechanism of action is incompletely understood. MethodsUsing Ca2+ imaging, we assessed the effects of buprenorphine, β-endorphin, and morphine on cytosolic Ca2+ concentration [Ca2+]i, in rat striatal neurons. ResultsBuprenorphine (0.01–1μM) increased [Ca2+]i in a dose-dependent manner in a subpopulation of rat striatal neurons. The effect of buprenorphine was largely reduced by naloxone, a non-selective opioid receptor antagonist, but not by μ, κ, δ or NOP-selective antagonists. β-Endorphin (0.1μM) increased [Ca2+]i with a lower amplitude and slower time course than buprenorphine. Similar to buprenorphine, the effect of β-endorphin was markedly decreased by naloxone, but not by opioid-selective antagonists. Morphine (0.1–10μM), did not affect [Ca2+]i in striatal neurons. ConclusionsOur results suggest that buprenorphine and β-endorphin act on a distinct type/subtype of plasmalemmal opioid receptors or activate intracellular opioid-like receptor(s) in rat striatal neurons.
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