Glutamate metabotropic receptor agonist 1S,3R-ACPD induces internucleosomal DNA fragmentation and cell death in rat...

Glutamate metabotropic receptor mediated mechanisms have been implicated in both neuroprotection and neurotoxicity. To characterize these mechanisms further in vivo, the effects of an intrastriatally injected metabotropic receptor agonist, trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid (1S,3R-ACPD), were studied alone and together with N-methyl-D-aspartate (NMDA) or kainic acid (KA) receptor agonists on DNA fragmentation and nerve cell death. 1S,3R-ACPD induced internucleosomal DNA fragmentation of striatal cells in a dose-dependent manner. TUNEL and propidium iodide staining showed DNA fragmentation and profound nuclear condensation around the injection site. Fragmented nuclei were occasionally seen under light microscopy. Internucleosomal DNA fragmentation induced by 1S,3R-ACPD was attenuated by the protein synthesis inhibitor cycloheximide as well as by the non-selective and selective metabotropic receptor antagonists L-(+)-2-amino-3-phosphonopionic acid (L-AP3), (RS)-aminoindan-1,5-dicarboxylic acid and (RS)-alpha-methylserine-o-phosphate monophenyl ester, respectively. The 1S,3R-ACPD (100-900 nmol) induced death of striatal neurons was suggested by the reduction in NMDA and D1 dopamine receptors by up to 13% (P < 0.05) and 20% (P < 0.05) as well as by the decline in GAD67 mRNA (25%, P < 0.01) and proenkephalin mRNA levels (35%, P < 0.01). Interestingly, 1S,3R-ACPD attenuated internucleosomal DNA fragmentation induced by NMDA, but potentiated that induced by KA. These results suggest that metabotropic receptor stimulation leads to the death of striatal neurons by a mechanism having the biochemical stigmata of apoptosis. Moreover, metabotropic receptor stimulation evidently exerts opposite effects on pre- or postsynaptic mechanisms contributing to the NMDA and KA-induced apoptotic-like death of these neurons.