Tolerance to morphine-induced calcium depletion in regional brain areas: characterization with reserpine and protein synthesis inhibitors.

1 Administration of a single dose of morphine sulphate (25 mg/kg) induces tolerance to calcium depletion lasting seven days. 2 There are no apparent changes in calcium content in any of eight discrete brain regions throughout this seven day period. 3 Pretreatment with reserpine (5 mg/kg) did not alter the ability of morphine to induce tolerance. Reserpine alone produced no tolerance to its own calcium depleting action. 4 Cycloheximide (500 mug/kg) but not chloramphenicol (200 mg/kg) effectively prevented development of tolerance. 5 It is concluded that the induction of tolerance to calcium depletion seen after morphine may involve changes in various proteins in membranes of synaptic origin.