In the present study, we have investigated the potential neuroprotective effects of a novel peripheral benzodiazepine binding site (PBR) ligand,N,indole-1-acetamide (SSR180575), in models of central and peripheral neurodegeneration in vivo and its effect on steroid concentrations in plasma and nervous tissue. SSR180575 shows high affinity (IC 50 , 2.5-3.5 nM) and selectivity for the rat and human PBR and potently inhibits the in vivo binding of [ 3 H]alpidem to PBR in the rat brain and spleen after oral or i.p. administration (ID 50 , 0.1-0.3 mg/kg). In an experimental model of motoneuron degeneration induced by facial nerve axotomy in the immature rat, SSR180575 given i.p. or orally for 8 days rescued facial motoneurons, increasing their survival by 40 to 72% at 6 and 10 mg/kg p.o. b.i.d. Moreover, in this model, SSR180575 (10 mg/kg p.o. b.i.d.) increased by 87% the number of motoneurons immunoreactive to peripherin, a type III intermediate filament, whose expression is up-regulated during nerve regeneration. SSR180575 also improved functional recovery in acrylamide-induced neuropathy in the rat when given therapeutically at 2.5 to 10 mg/kg/day p.o. Furthermore, SSR180575 (3 mg/kg i.p. b.i.d.) accelerated functional recovery of the blink reflex after local injury of the facial nerve in the rat. SSR180575 increased pregnenolone accumulation in the brain and sciatic nerve (ϩ100% at 3 mg/kg i.p.), suggesting that its neuroprotective effects are steroid-mediated. These results indicate that PBR ligands (e.g., SSR180575) promote neuronal survival and repair in axotomy and neuropathy models and have potential for the treatment of neurodegenerative diseases (e.g., peripheral neuropathies or amyotrophic lateral sclerosis).

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Primary cultures of cortical neurons were employed to investigate the modulatory effects of neurotensin on glutamate excitotoxicity and the possible neuroprotective actions of the neurotensin receptor antagonist SR48692. NT(1-13) and its biologically active fragment NT(8-13) at 10 nM (30 min) increased endogenous glutamate levels. The inactive fragment NT(1-7) (10-100 nM; 30 min) was ineffective. SR48692, applied 20 min before NT and maintained in contact with cells during NT exposure as well as a low calcium medium (from the onset of the experiment) prevented the NT(1-13)-induced increase in extracellular glutamate levels. The addition of NMDA (0.01-10 micro M; 10 min) to the medium concentration-dependently increased extracellular glutamate levels. When 0.1 nM NT(1-13) was added in combination with 0.01 micro M NMDA, in concentrations by themselves ineffective, a significant increase in glutamate levels was observed. SR48692 at 100 nM counteracted the increase in glutamate levels induced by 0.1 nM NT(1-13) plus 0.01 micro M NMDA. The inhibitor of the protein kinase C (PKC) calphostin C (0.1 micro M; 10 min before NT) prevented the increase in glutamate levels induced by the combined treatments. The morphological analysis indicated that 10 nM NT(1-13) enhanced the glutamate (10 min)-induced apoptosis. The peptide was added 30 min prior to glutamate and maintained in contact with cells during the glutamate exposure. The presence of 100 nM SR48692 (20 min before NT) antagonized this effect of NT(1-13). These findings support the view of a pathophysiological role for NT in the cerebral cortex. Thus, under pathological conditions NT by enhancing glutamate outflow and by amplifying the NMDA-mediated glutamate signaling may be involved in increasing the degeneration of cortical neurons.

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