NEUROPROTECTIVE SIGMA-LIGANDS INTERFERE WITH THE GLUTAMATE-ACTIVATED NOS PATHWAY IN HIPPOCAMPAL CELL-CULTURE

We studied neuroprotective properties of 12 structurally different sig ma site ligands in primary rat hippocampal cell cultures and analyzed whether they interfere with glutamate-induced activation of the nitric oxide synthase (NOS) pathway. Neurotoxicity was triggered with 1 mM g lutamate on day 8 of culture. Cells were treated with various concentr ations of the compounds for 7 days before glutamate exposure (prolonge d pretreatment), or during glutamate exposure (acute treatment). Prote ction was seen after prolonged pretreatment (long-term protection) wit h sabeluzole, opipramole, haloperidol, ifenprodil, fenpropimorph, carb etapentane, and tiospirone, with pIC(50)s of 7.30, 7.15, 6.87, 6.68, 6 .66, 6.39, and 6.34, respectively. There was no protection with PD 128 298, 1,3-ortho-di-tolylguanidine, BMY-14802, (+)3-(3-hydroxyphenyl)-N- 1(propyl) piperidine, or dextromethorphan. Upon acute treatment, only ifenprodil was protective. Interference of the drugs with glutamate ac tivation of the NOS pathway was determined by measuring glutamate-acti vated cGMP formation and citrulline levels. Glutamate-activated cGMP f ormation was reduced by all neuroprotective sigma ligands after prolon ged pretreatment but not after acute treatment. Sigma ligands added to cell culture lysate did not reduce citrulline formation, evidence tha t there was no direct effect on the NOS enzyme. We conclude that some but not all sigma ligands exert long-term protective properties agains t glutamate-induced neurotoxicity in primary hippocampal cultures, and that this protection is accompanied by attenuation of cGMP formation in the NOS pathway. However, inhibition of cGMP formation by itself ap peared not sufficient for obtaining neuroprotective effects, as inhibi tion of glutamate-activated cGMP formation by N-omega-nitro-L-arginine , haemoglobin, or PD128298 did not provide neuroprotection. (C) 1995 W iley-Liss, Inc.