Systemic administration of MPTP to experimental animals induces neurodegeneration of dopaminergic neurons in the central nervous system. MPTP crosses the blood-brain barrier where it is taken up by astrocytes and converted to MPP+ by monamine oxidase-B (MAO-B). Subsequently, MPP+ is selectively taken up by dopaminergic neurons upon which it exerts intracellular neurotoxic effects. Systemic administration of the selective MAO-B inhibitor deprenyl prevents the conversion of MPTP to MPP+ and by this mechanism is able to protect against MPTP neurotoxicity. Deprenyl has also been reported to exert neuroprotective effects that are independent of its MAO-B inhibitory properties, but since MPP+ itself does not cross the blood-brain barrier it is difficult to directly study the MAO-B independent in vivo effects of MPP+ itself. One approach is to use organotypic tissue cultures of the canine substantia nigra (CSN) which permit administration of precise concentrations of pharmacological agents directly to mature, well-developed and metabolically active dopaminergic neurons. These neurons as well as other components of the cultures exhibit morphological and biochemical characteristics identical to their in vivo counterparts. This study was undertaken to evaluate the neuroprotective effects of deprenyl in MPP(+)-treated cultures by measuring changes in the levels of HVA as an indicator of dopamine release and metabolism by dopaminergic neurons and to correlate this indication of dopaminergic function with morphological evidence of survival or loss of dopaminergic neurons in mature CSN cultures. Mature CSN cultures, at 44 days in vitro (DIV), were exposed to either MPP+ alone, deprenyl alone or simultaneously to both deprenyl and MPP+ or to MPP+ following 4 day pretreatment with deprenyl. Exposure to MPP+ alone caused significant reduction in HVA levels, evidence of widespread injury and ultimate disappearance of large neurons in the cultures. These effects were attenuated by simultaneous exposure to MPP+ and deprenyl and the destructive effects of MPP+ appeared to be prevented by pretreatment with deprenyl. Thus the neuroprotective effects of deprenyl on MPP(+)-induced reduction of HVA levels in living cultures appears similar to the effects of deprenyl on dopamine levels and tyrosine hydroxylase activity reported by others in cultures previously exposed to deprenyl and MPP+. These studies also confirm that the neuroprotective effects of deprenyl against MPP+ in dopaminergic neurons are, at least in part, independent of deprenyl's inhibition of MAO-B.

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SUMMARY (S)-(-)-N-[( l-ethyl-2-pyrrolidinyl)methyl]-5-[ 1231]iodo-2,3-dimethoxy-benzamide (TDP 517) (proposed generic name, [I23I]epidepride) is the iodine-123 substituted analogue of isoremoxipride (FLB 457). both of which are very potent dopamine D-2 antagonists (epidepnde KD 0.024 nM). [ 12311Epidepride was radioiodinated in 60-70% radiochemical yields i n 35 min from the corresponding 5-(mbutyltin) derivative using NaI23I with a specific radioactivity of 3000 Wmmol, and oxidized in situ with chloramine-T. The aryltin precursor was prepared from non-labelled epidepride by palladium-catalyzed stannylation using bis(m-n-butyltin) in tnethylamine. Alternatively, using no carrier-added Na 1251 as the radioisotope, [ 125Ilepidepride at 2000 Ci/mmol specific radioactivity was prepared in 86% radiochemical yield and 99% radiochemical purity after purification by reverse phase HPLC in ethanolic phosphate buffer.

Abstract— —A variety of monoamine oxidase substrates (tyramine, dopamine, serotonin, tryptamine) have been used with and without Iproniazid inhibition to evaluate further the extent to which enzyme multiplicity may exist in various regions of rat brain. Levels of monoamine oxidase activity, as measured by ammonia production, were found to vary as a function of both brain area and kind of substrate used, in the absence as well as in the presence of Iproniazid, in vivo and in vitro. Similarity of substrate metabolizing patterns among the different brain areas, however, strongly suggests that only one kind of monoamine oxidase exists in rat brain.

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