ATTENUATION OF 1-METHYL-4-PHENYLPYRIDINIUM (MPP-NIGRA CULTURES() NEUROTOXICITY BY DEPRENYL IN ORGANOTYPIC CANINE SUBSTANTIA)

Systemic administration: of MPTP to experimental animals induces neuro degeneration of dopaminergic neurons in the central nervous system. MP TP 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 sele ctive 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+ its elf does not cross the blood-brain barrier it is difficult to directly study the MAO-B independent in vivo effects of MPP+ itself. One appro ach is to use organotypic tissue cultures of the canine substantia nig ra (CSN) which permit administration of precise concentrations of phar macological agents directly to mature, well-developed and metabolicall y active dopaminergic neurons. These neurons as well as other componen ts of the cultures exhibit morphological and biochemical characteristi cs identical to their in vivo counterparts. This study was undertaken to evaluate the neuroprotective effects of deprenyl in MPP+-treated cu ltures by measuring changes in the levels of HVA as an indicator of do pamine 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. Ma ture CSN cultures, at 44 days in vitro (DIV), were exposed to either M PP+ alone, deprenyl alone or simultaneously to both deprenyl and MPPor to MPP+ following 4 day pretreatment with deprenyl. Exposure to MPP + alone caused significant reduction in HVA levels, evidence of widesp read injury and ultimate disappearance of large neurons in the culture s. 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 dep renyl on MPP+-induced reduction of HVA levels in living cultures appea rs 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 neuroprotec tive effects of deprenyl against MPP+ in dopaminergic neurons are, at least in part, independent of deprenyl's inhibition of MAO-B.