Tetrahydropapaveroline and salsolinol alter 45Ca2+ efflux within perfused hippocampus of unrestrained rats

The kinetics of 45Ca2+ efflux were examined at circumscribed sites in the perfused hippocampus of the freely moving rat with either one of two tetrahydroisoquinoline (TIQ) products, tetrahydropapaveroline (THP) or salsolinol. Guide tubes for unilateral push-pull perfusion were implanted stereotaxically to rest just above sites within the dorsal hippocampus. Upon recovery from surgery, a tissue site in the hippocampus was prelabeled with 1.0 microliter of 45Ca2+ (2.0 microCi) injected through the indwelling guide tube. After 16-20 hr had elapsed, successive push-pull perfusions of the site were carried out with an artificial cerebrospinal fluid (CSF), at 5.0 min intervals and at a rate of 20 microliters/min, in order to obtain a control washout curve of declining radioactivity. On the fifth of a series of 5.0 min perfusions, either THP or salsolinol was added to the perfusion medium in a concentration of 10 or 100 ng/microliters. Then the hippocampal site was perfused again with control CSF for the collection of an additional three samples. Although THP in both of the test concentrations generally augmented the efflux of 45Ca2+, the temporal course and magnitude of the enhancement depended on the anatomical site of the perfusion. In the more rostral hippocampal planes of AP 3.0 and AP 4.0, THP caused a delayed efflux of the cation, after the perfusion of THP had been discontinued, in nearly half of the loci reactive to the TIQ. Similarly, salsolinol enhanced significantly the efflux of 45Ca2+ in a concentration-dependent manner during the interval of its perfusion within the hippocampal plane of AP 3.0.(ABSTRACT TRUNCATED AT 250 WORDS)