In vivo extracellular unitary recordings, in vitro 3H-5-hydroxy- tryptamine (5-HT) uptake, and 3H-paroxetine binding assays were used to assess the effect of acute and long-term administration of the 5-HT reuptake inhibitor paroxetine on the neuronal 5-HT transporter in the rat dorsal hippocampus. Recovery time of the firing activity of CA3 hippocampus pyramidal neurons following microiontophoretic application of 5-HT was used as an index of in vivo reuptake activity. In a first series of experiments, the acute intravenous administration of paroxetine and 5-HT denervation with the neurotoxin 5,7- dihydroxytryptamine produced a marked prolongation of the suppressant effect of 5-HT, indicating that reuptake into 5-HT terminals plays a significant role in terminating the action of microiontophoretically applied 5-HT. In a second series of experiments, rats were treated with paroxetine (10 mg/kg/d, s.c.) for 2 or 21 d. In both treatment groups, there was a marked prolongation of the effect of microiontophoretically applied 5-HT; however, in rats treated for 2 d, the prolongation was significantly greater than that observed in rats treated for 21 d. After the 21 d treatment with paroxetine and a 48 hr washout, the prolongation of the effect of microiontophoretically applied 5-HT by acute intravenous paroxetine was significantly reduced, suggesting a decrease in the number of 5-HT carriers. In keeping with this interpretation, following the same treatment regimen, there was a 50% and 60% reduction of the in vitro 3H-5-HT uptake in hippocampal and dorsal raphe slices, respectively, and a reduced effectiveness of paroxetine in blocking 3H-5-HT uptake in both regions. The determination of the binding parameters of 3H-paroxetine revealed that, in rats treated for 21 d with paroxetine (10 mg/kg/d, s.c.), following a 48 hr washout Kd values were unchanged but Bmax values were reduced by 70% and 60% in hippocampal and cortical membranes, respectively.

Norepinephrine, 3-methoxy 4-hydroxyphenylethyleneglycol and homovanillic acid levels were similar in the locus ceruleus of 13 controls and 8 parkinsonian patients with no intellectual deterioration, but were decreased in 7 demented patients. The concentration of dopamine was similarly diminished in non-demented and demented parkinsonians, and binding of 3H-desmethylimipramine and 3H-rauwolscine was not abnormal in parkinsonians. These data indicate that norepinephrine metabolism in the locus ceruleus is subnormal only in demented parkinsonians.

The topography and magnitude of increase in peripheral type benzodiazepine binding sites (omega 3 sites) was investigated autoradiographically in the brains of patients with ischemic cerebrovascular disease, with multiple sclerosis, and with malignant glioma. 3H-PK 11195, a selective omega 3 site ligand, was employed. A manyfold increase in omega 3 site density was observed in all these disease states; this increase reflects macrophage invasion or glial proliferation or both as demonstrated by neuropathological studies carried out in parallel. There was an excellent spatial correlation between increased omega 3 site densities and extent of the lesion histologically. Specifically, an elevated density of omega 3 sites was observed in the plaques of demyelination in multiple sclerosis patients, in the periphery of infarcted zones in stroke patients, and throughout tumor in patients with grade IV astrocytomas. As our approach is applicable to both tomographic (in vivo) and autoradiographic investigations, imaging of omega 3 sites may be considered for the detection and monitoring of the natural evolution of many disorders of the human central nervous system.

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