Antipsychotic-like effects of the N-methyl-D-aspartate receptor modulator neboglamine: an immunohistochemical and behavioural study in the rat

Neboglamine is a functional modulator of the glycine site on the N-methyl-d-aspartate (NMDA) receptor. Dysfunction of this receptor has been associated with negative and cognitive symptoms in schizophrenia. Thus, we tested the hypothesis that neboglamine behaves as a potential antipsychotic. We compared the effects of neboglamine, D-serine, clozapine, and haloperidol on the expression of Fos-like immunoreactivity (FLI), a marker of neuronal activation, in rat forebrain. We also studied the effects of these agents on phencyclidine (PCP)-induced behaviour in rats, a model predictive of potential antipsychotic activity. Neboglamine, like haloperidol and clozapine, significantly increased the number of FLI-positive cells in the prefrontal cortex, nucleus accumbens, and lateral septal nucleus (3.2-, 4.8-, and 4.5-fold over control, respectively). Haloperidol dramatically increased FLI (390-fold over control) in the dorsolateral striatum, a brain region in which neboglamine and clozapine had no effect. The pattern of FLI induced by neboglamine closely matched that of d-serine, an endogenous agonist at the glycine site of NMDA receptors. Consistent with this finding, neboglamine restored NMDA-mediated neurotransmitter release in frontal cortex punches exposed to the NMDA antagonist PCP. In the behavioural model, all test compounds significantly inhibited PCP-induced hyperlocomotion. Unlike haloperidol and clozapine, neither neboglamine nor D-serine affected the basal levels of locomotor activity. Moreover, oral neboglamine dose-dependently inhibited both the hyperlocomotion and the frequency of rearing behaviour induced by PCP. These results, while confirming that the NMDA glycine site is a feasible target for activating the frontostriatal system, support the clinical evaluation of neboglamine as a treatment for schizophrenia.