In vivo effects of psychotropic agents on the physical properties of cell membranes in the rat brain.

Marked changes in biophysical properties, including structural order, have been observed in the hydrophobic core of cell membranes exposed to phenothiazines in vitro. In this study, similar changes are reported in vivo in cell membranes from the brains of rats treated with phenothiazines at doses thought to yield tissue concentrations approximating those attained in the clinical treatment of psychiatric patients. The membrane structural order parameter was estimated ex vivo by steady-state fluorescence polarization determinations using 1,6-diphenyl 1,3,5-hexatriene (DPH), a fluorescent probe that localizes preferentially to the hydrocarbon region of cell membranes. In these preliminary studies, rats received chlorpromazine (20 mg/kg), fluphenazine (1 mg/kg), haloperidol (1 mg/kg), and imipramine (1 mg/kg) in single or multiple dose protocols. As in earlier in vitro studies, exposure to the phenothiazine antipsychotics led to an observed increase in DPH fluorescence polarization ex vivo and a presumed increase in structural order. As predicted from the in vitro experiments, the effect of chlorpromazine was greater than that of fluphenazine, probably because chlorpromazine was given at higher doses. The magnitude of the effects seen was great enough to imply that physiologically significant changes in cell membrane characteristics may be produced in patients receiving phenothiazines.