[3H]Imipramine Is Accumulated but Not Released from Slices of the Rabbit Caudate and Hypothalamus

Abstract: Slices of rabbit caudate and hypothalamus take up and accumulate ³H]imipramine. In superfused slices of both structures electrical stimulation or exposure to tyramine failed to release recently taken up ³H]imipramine. De-polarization by exposure to 30–60 mm-potassium caused only a small release of ³H]imipramine that was not concentration-dependent. The release of ³H]imipramine by high potassium was independent of the presence of calcium ions in the superfusion medium. These results contrasted with those obtained for the release of ³H]dopamine from the caudate and ³H]noradrenaline from the hypothalamus, where tyramine, electrical stimulation, and high potassium caused a significant release of the labeled neurotransmitters. The release of ³H]dopamine from the caudate and ³H]noradrenaline from the hypothalamus elicited by electrical stimulation or high potassium was entirely calcium-dependent. It is concluded that ³H]imipramine is taken up into the two brain regions and is accumulated in a nonvesicular site from which it is not released by calcium-dependent depolarizing stimuli.