Endogenous opioid peptides and opiates , like morphine , transmit their pharmacological effects through membrane bound opioid receptors. Pharmacological studies and molecular cloning have led to the identification of three different types of opioid receptor , mu-type , delta-type and kappa-type , also designated MOR-1 , DOR-1 and KOR-1 , respectively. MOR-1 is a receptor for beta-endorphin , DOR-1 is a receptor for enkephalins , and KOR-1 is a receptor for dynorphins.The three opioid receptor types are highly homologous and belong to the superfamily of G-protein-coupled receptors. Opioid receptors have been shown to modulate a range of brain functions , including instinctive behavior and emotions. This regulation is thought to involve the inhibition of neurotransmitter release by reducing calcium ion currents and increasing potassium ion conductance.
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