L-trans-2,3-Pyrrolidine Dicarboxylate: Characterization of a Novel Excitotoxin

Abstract

This study investigated the in vitro and in vivo excitotoxic properties of a novel conformationally constrained analogue of L- trans-2,3-pyrrolidine dicarboxylate ( L- trans-2,3-PDC). When tested for excitotoxic activity in rat cortical cultures, L- trans-2,3-PDC mimicked the action of NMDA in both acute (30 min) and chronic (24 hr) exposure paradigms. This neurotoxicity was attenuated by co-addition of MK-801 (10 μM). Microinjections of L- trans-2,3-PDC into the dorsal hippocampus of male rats also induced a selective pattern of pathology indicative of an NMDA receptor excitotoxin. In contrast to the equipotency observed in vitro, 100 nmol of L- trans-2,3-PDC were needed to produce cellular damage comparable to that induced by 25 nmol of NMDA. Consistent with an action at NMDA receptors, L- trans-2,3-PDC-induced damage could be significantly reduced by co-administration of MK-801 (3 mg/kg i.p.), but not by NBQX (25 nmol). In radioligand binding assays L- trans-2,3-PDC inhibited the binding of 3H- L-glutamate to NMDA receptors (IC 50 1 μM), although it also exhibited some cross reactivity with KA and AMPA receptors. L- trans-2,3-PDC was also identified as a competitive inhibitor ( K i = 33 μM) of 3H- D-aspartate uptake into rat forebrain synaptosomes. In contrast to the action of a transporter substrate, such as L-glutamate, L- trans-2,3-PDC did not exchange with 3H- D-aspartate that had been previously loaded into the synaptosomes. Copyright © 1996 Elsevier Science Ltd.