Apoptosis in substantia nigra following developmental striatal excitotoxic injury.

Abstract

We have previously observed that an axon-sparing injury to the developing striatum induced by the excitotoxin quinolinate results in a decrease in dopaminergic neurons in the substantia nigra pars compacta (SNpc) of the adult. This decrease occurs in the absence of direct injury to the SNpc. As the striatum is a major target for the SNpc dopaminergic system, we have hypothesized that a decrease in the size of the striatal target during development may result in an induced regressive event in the SNpc, similar to what has been described for many developing neural systems with peripheral targets. We have examined by morphologic and biochemical means the time course and character of cell death in SN following a unilateral striatal lesion with quinolinate in immature rats. The striatal lesion is associated with an induced cell death event in the ipsilateral SN, observed first in SNpc and then in SN pars reticulata. The morphologic characteristics of the dying cells were typical of apoptosis. Immunostaining for tyrosine hydroxylase indicated that some of the apoptotic cells in the SNpc were dopaminergic. We conclude that developmental striatal excitotoxic injury is associated with induced apoptotic cell death in SN.

Early Developmental Destruction of Terminals in the Striatal Target Induces Apoptosis in Dopamine Neurons of the Substantia Nigra

“…3A). This appearance of chromatin clumps on silver stain has been shown to correspond to electron-dense chromatin clumps, characteristic of apoptosis, on ultrastructural study of apoptotic dopaminergic neurons of the SN (Macaya et al, 1994). The apoptotic nature of this morphological pattern of cell death was confirmed further by histochemical demonstration of abundant free 3Ј ends, in the nucleus of the nigral cells in association with basophilic chromatin clumps, again demonstrated by Nissl counterstain (Fig.…”

“…The demonstration of intensely basophilic, rounded, and well demarcated chromatin clumps using Nissl stains has been considered by many investigators to be highly suggestive of apoptosis at the light microscope level (Clarke and Oppenheim, 1995), and in many instances this has been confirmed by ultrastructure (Cunningham, 1982;Williams and Rakic, 1988;Ferrer et al, 1990;Sloviter et al, 1993;Macaya et al, 1994). The apoptotic nature of such clumps can be confirmed by silver impregnation techniques, which demonstrate intensely argyrophilic, rounded intranuclear clumps (Yamamoto et al, 1986;Janec and Burke, 1993;Macaya et al, 1994;Mitchell et al, 1994), and which have also been demonstrated by ultrastructure (Macaya et al, 1994) to conform to classic descriptions of apoptosis (Kerr et al, 1995). In addition, we have shown that apoptosis occurs by demonstrating a high concentration of free 3Ј ends within the nucleus in the presence of basophilic chromatin clumps, visualized with Nissl counterstain.…”

“…These neurons could be identified by a TH-immunostained cytoplasm encompassing a clear nuclear region that contained one or more intensely basophilic, rounded, sharply delineated chromatin clumps, as is characteristic of apoptosis identified by Nissl counterstain (Fig. 2) (Janec and Burke, 1993;Macaya et al, 1994;Clarke and Oppenheim, 1995). The apoptotic nature of this cell death was confirmed by the demonstration of intensely argyrophilic, rounded, and discrete chromatin clumps on silver stain in neurons of the SN, in sections adjacent to those demonstrating Nissl-positive chromatin clumps (Fig.…”

“…Positive controls were neonatal tissue sections of the SN in which apoptosis had been induced by intrastriatal quinolinic acid injection, as reported previously (Macaya et al, 1994). Quantitative morphological analysis.…”

“…This decrease occurs despite the axon-sparing nature of this injury (Schwarcz et al, 1983;Macaya and Burke, 1992) and in the absence of any direct injury to the SN. We have also shown that natural cell death occurs within the SN pars compacta (SNpc) (Janec and Burke, 1993), with the morphology of apoptosis (Kerr et al, 1972), and that this death event is augmented after excitotoxic (Macaya et al, 1994) injury to the striatum during development. These results support the hypothesis that the striatal target may regulate the magnitude of a developmental death event among dopaminergic neurons of the SN.…”