Neonatal treatment with L-name (NG-nitro-L-arginine methyl ester) attenuates stereotyped behavior induced by acute methamphetamine but not development of behavioral sensitization to methamphetamine

Effects of selective calcium-permeable AMPA receptor blockade by IEM 1460 on psychotomimetic-induced hyperactivity in the mouse

Diminished glutamate neurotransmission via the N-methyl-D-aspartate type glutamate receptor (NMDAR) has been considered to be involved in the pathophysiology of schizophrenia based upon the observation that the antagonists and autoantibodies of NMDAR cause positive, negative and cognitive symptomatologies similar to those of schizophrenia. The possible reduced extracellular levels of D-serine by overstimulation of the calcium-permeable α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate glutamate receptor (CP-AMPAR) following the NMDAR hypofunction-induced compensatory increase in the glutamate release could aggravate the NMDAR hypofunction in the brain of the drug- or antibody-associated psychoses and schizophrenia, because D-serine is an intrinsic coagonist for the NMDAR. To obtain an insight into the therapeutic approach to such a glutamate-linked psychotic state, we have studied the effects of the systemic administration of the CP-AMPAR-selective antagonist, IEM 1460 (N,N,N-trimethyl-5- [(tricyclo[3.3.1.1^3,7]dec-1-ylmethyl)amino]-1-pentanaminium bromide hydrobromide), on the hyperactivity following an injection of a schizophrenomimetic NMDAR antagonist, phencyclidine, in the mouse. The subcutaneous IEM 1460 application produced a dose-dependent inhibition of the increased movement counts after the subcutaneous injection of phencyclidine. This inhibiting influence was also seen on the hyperactivity elicited by another NMDAR antagonist, dizocilpine. Moreover, the IEM 1460 administration attenuated the ability of a schizophrenomimetic dopamine agonist, methamphetamine, to increase spontaneous movements. These findings indicate that dysregulation of the CP-AMPAR could, at least in part, be implicated in the glutamate pathology of schizophrenia and/or related psychotic symptoms and be a potential target for the development of their novel treatment.

Phencyclidine-induced dysregulation of primary cilia in the rodent brain

Significant roles of the primary cilia in the central nervous system have been reported in neural generation and cognitive functions. However, little is known about the possible pathological changes in brain primary cilia in neuropsychiatric disorders. To obtain an insight into the relationship between cilial dysregulation and schizophrenia, we presently investigated the effects of psychotomimetics, phencyclidine, MK-801 (dizocilpine), and methamphetamine, on morphological and molecular indices in the rodent brain. Using an immunohistochemical technique, we found that a subcutaneous injection of phencyclidine, an NMDA type glutamate receptor (NMDAR) antagonist, caused a reduction in the long axis length of a primary cilium in the CA1 region of the hippocampus without affecting that in the dentate gyrus and medial prefrontal cortex of rats and mice. The region-selective modulation of primary cilia was mimicked by another NMDAR antagonist, MK-801, but not by the indirect dopamine agonist methamphetamine. Furthermore, systemic administration of phencyclidine, but not methamphetamine, down-regulated mRNA expression of primary cilium morphology-related genes, including kif3a, 5-HTR6, RPGRIP1L, and TMEM67, and of genes composing the cilial Wnt/β-catenin signaling pathway, β-catenin, syn2 and Bcl-2, in the hippocampus, but not in the cerebral cortex of rats. These findings suggest that NMDAR hypofunction-induced dysregulation of CA1 primary cilia could be involved in the pathophysiology of dopamine transmission-independent symptoms of schizophrenia.

Impact of neonatal NOS-1 inhibitor exposure on neurobehavioural measures and prefrontal-temporolimbic integration in the rat nucleus accumbens

Nitric oxide (NO) is a gaseous neurotransmitter that plays a significant role in the establishment and refinement of functional neural circuits. Genetic and post-mortem studies have suggested that neuronal NO synthase (NOS-1) activity may be compromised in frontal and temporal lobes, and related structures, in schizophrenia. The goal of this study was to determine if there is a link between neonatal disruptions in NO signalling and disturbances in the development and function of prefrontal-temporolimbic circuits. Neonatal rats were injected on postnatal days PD3-5 with the selective NOS-1 inhibitor Nω-propyl-L-arginine (NPA) and tested in adulthood (≥PD60) or as juveniles (PD30). Adult rats treated with NPA as neonates exhibited increased amphetamine-induced locomotion compared to animals receiving vehicle as neonates, whereas this was not observed in juvenile rats treated with NPA as neonates. Adult rats exposed to NPA as neonates also exhibited deficits in social interaction and short-term recognition memory, as well as reduced brain weight, compared to vehicle-treated controls. Finally, neonatal NPA exposure increased the responsiveness of nucleus accumbens neurons to prefrontal cortical input and disrupted the modulation of cortico-accumbens circuits by hippocampal afferents that is normally observed in adult animals. These results show for the first time that neonatal inhibition of NOS-1 during a critical neurodevelopmental period leads to aberrant behaviours that manifest in adulthood, as well as electrophysiological abnormalities in prefrontal-temporolimbic circuits. Greater understanding of the role of NOS-1 in the development of these circuits will shed light on how developmental insults translate to pathophysiology associated with schizophrenia.

Neonatal nitric oxide synthase inhibition: social interaction deficits in adulthood and reversal by antipsychotic drugs

Nitric oxide synthase (NOS) is thought to migrate improperly during development in the brains of schizophrenic patients. Also it is known that nitric oxide (NO) effects synaptogenesis during development of the CNS. Previously we have shown that neonatal treatment with a NOS inhibitor effects an animal's sensitivity to amphetamine and PCP. In the present study, neonatal rats were challenged with a NOS inhibitor (L-nitroarginine, 10mg/kg, s.c.) daily on post-natal days (PD) three, four and five. L-Nitroarginine (L-NoArg) treated male rats at adulthood (PD56 and older) had a deficit in social interaction (SI) when placed in an environment with another foreign male rat and this deficit was reproducible on a weekly basis for at least five weeks. Haloperidol failed to significantly reverse this deficit before pronounced secondary effects on general behavior were seen at high doses. However, the atypical antipsychotics, clozapine and olanzapine, were able to significantly reverse this deficit at doses which did not effect baseline SI values. In a separate cohort of animals the effect of DOI was investigated, this was done to ascertain if there was a differential sensitivity of serotonergic pathways in this model. There was no difference in the behavioral score elicited from control or NoArg-treated rats. It is suggested that the SI deficits seen here may be more sensitive to atypical antipsychotics rather than haloperidol.