Protective effects of neurotrophin-4/5 and transforming growth factor-alpha on striatal neuronal phenotypic degeneration after excitotoxic lesioning with quinolinic acid.

Lesioning of the mammalian striatum with the excitotoxin quinolinic acid results in a pattern of neuropathology that resembles that of post mortem Huntington's disease brain. Certain neurotrophic factors can rescue degenerating cells in a variety of lesion types, including those produced by neurotoxins. Several neurotrophic factors promote the survival of striatal neurons and/or are localized within the striatum. Of these factors, neurotrophin-4/5 and transforming growth factor-alpha were chosen for administration to rats lesioned with quinolinic acid. Adult rats received a single unilateral intrastriatal injection of quinolinic acid (120 nmol) and either trophic factors or the control protein cytochrome c for seven days thereafter. The pattern of phenotypic degeneration was assessed by immunocytochemical labeling of various striatal neuronal populations at five rostrocaudal levels. Quinolinic acid produced a preferential loss in the number of cells immunoreactive for glutamate decarboxylase, with a relative sparing of the number of choline acetyltransferase-immunoreactive cells and, to a lesser degree, calretinin-immunoreactive cells. None of these phenotypic populations was protected by either neurotrophin-4/5 or transforming growth factor-alpha. In contrast, when glutamate decarboxylase cells were alternatively identified by calbindin immunolabeling, both factors were found to have partially reversed the loss in the number of calbindin-positive cells induced by excitolesioning. In addition, the loss in the number of parvalbumin-immunopositive cells due to quinolinic acid was partially reversed by neurotrophin-4/5, while the loss in the number of NADPH-diaphorase-stained cells was partially reversed by transforming growth factor-alpha. These findings reveal a new population of striatal cells, calretinin neurons, that are relatively resistant to quinolinic acid toxicity and that neurotrophin-4/5 and transforming growth factor-alpha partially protect against the phenotypic degeneration of striatal cell populations in an in vivo animal model of Huntington's disease.