Critical involvement of the orbitofrontal cortex in hyperlocomotion induced by NMDA receptor blockade in mice

https://doi.org/10.1016/j.bbrc.2016.10.089Get rights and content

Highlights

  • MK-801 induced neuronal activation in the OFC revealed by Arc::dVenus expression.

  • OFC lesions suppressed the early phase of MK-801-induced hyperlocomotion.

  • Clozapine attenuated the MK-801-induced OFC activation and hyperlocomotion.

  • The OFC may play a critical role in NMDA receptor-mediated psychotic-like behavior.

Abstract

Glutamatergic N-methyl-d-aspartate (NMDA) receptors play critical roles in several neurological and psychiatric diseases. Blockade by noncompetitive NMDA receptor antagonist leads to psychotomimetic effects; however, the brain regions responsible for the effects are not well understood. Here, we determined the specific brain regions responsive to MK-801, a noncompetitive NMDA receptor antagonist, by mapping Arc expression as an indicator of neuronal activity using Arc::dVenus reporter mice. MK-801 increased dVenus expression predominantly in the orbitofrontal cortex (OFC) and, as expected, induced a marked hyperlocomotion. Local OFC lesions selectively attenuated the early phase (0–30 min) of MK-801-induced hyperlocomotion. Further, clozapine, an atypical antipsychotic, effectively attenuated both the MK-801-induced dVenus expression in the OFC and hyperlocomotion. These results suggest that the OFC may be critically involved in NMDA receptor-mediated psychotic-like behavioral abnormalities.

Introduction

N-methyl-d-aspartate (NMDA) receptors play a critical role in excitatory neurotransmission in the central nervous system and are involved in learning, memory and synaptic development [1]. Alterations of NMDA receptor functions have been reported in several brain disorders such as schizophrenia and autism spectrum disorder [1], [2]. Noncompetitive NMDA receptor antagonists, such as phencyclidine, MK-801 and ketamine, produce psychotic symptoms similar to a clinical syndrome of schizophrenia, which has led researchers to propose a glutamate hypofunction model of schizophrenia [2], [3], [4]. In rodents, models of schizophrenia-like behaviors, such as hyperlocomotion, impaired social interaction and novel object recognition, induced by NMDA receptor antagonists are widely used to study the pathophysiology of schizophrenia, the mechanism of action of antipsychotic drugs, and the identification of novel treatments [5]. These behavioral abnormalities are more effectively ameliorated by atypical antipsychotics, such as clozapine, than typical antipsychotics [3], [5], [6]. Because NMDA receptors are widely expressed throughout the central nervous system and play a wide array of functions, it is important to understand the brain regions responsible for the effects of NMDA receptor antagonists and the role of each region. Previous studies have suggested the importance of several brain regions in NMDA receptor antagonist-induced psychotic behavior, including the medial prefrontal cortex [7], [8], [9]. However, the precise function of different regions remains to be fully elucidated.

A growing number of studies have investigated the mechanisms underlying brain dysfunction in animal models of psychiatric disorders [10], [11], [12]. For this purpose, we previously generated mice lacking pituitary adenylate cyclase-activating polypeptide [13], [14]. The mutant mice exhibited remarkable behavioral abnormalities related to psychiatric disorders [15], [16], [17] that were amenable to atypical antipsychotics [18], [19] and the selective metabotropic glutamate 2/3 receptor agonist [20]. We also revealed that prostaglandin D2 signaling mediated by the type 2 receptor DP2/CRTH2 is involved in MK-801-induced cognitive impairments, proposing a novel therapeutic mechanism for cognitive disorders [21]. More recently, we developed cell imaging tools to examine neuronal processes, such as a mouse embryonic stem cell line that expresses green fluorescent protein driven by the enhancer of Pet-1/Fev to assess serotonergic differentiation [22], and a lentiviral system for simultaneous neuron- and astrocyte-specific fluorescent labeling in vivo [23]. These studies aimed to address brain region-based mechanisms to help understand pathological processes implicating alterations of major neurotransmitters, including glutamate.

In line with these studies, here we examined the brain regions responsible for MK-801 action using Arc::dVenus reporter mice, in which the expression of dVenus, a destabilized form of the fluorescence protein Venus, is driven by the promoter of the immediate early gene Arc to detect neuronal activation [24]. In the present study, we identified the layer 2/3 of the medial part of the orbitofrontal cortex (OFC) as the brain region predominantly activated by MK-801 and examined its role in MK-801-induced hyperlocomotion.

Section snippets

Animals and drugs

The generation of Arc::dVenus transgenic mice was previously reported [24]. Wild-type C57BL/6J mice were purchased from SLC (Hamamatsu, Japan). Mice were maintained on a 12-h light–dark cycle (lights on at 8:00 a.m.) at a controlled room temperature (22 ± 1 °C). Water and food (CMF, Oriental Yeast, Osaka, Japan) were available ad libitum. Male mice were used at 8–11 weeks of age. All animal care and handling procedures were approved by the Animal Care and Use Committee of Osaka University. All

MK-801 induces dVenus expression predominantly in the OFC in Arc::dVenus mice

The brain regions whose activities are modulated by the NMDA receptor antagonist MK-801 were examined in sagittal sections of Arc::dVenus mice treated with MK-801 (0.5 mg/kg body weight). MK-801-dependent dVenus expression was predominantly observed in the OFC, located in the ventral part of the prefrontal cortex (Fig. 1). Other regions, including the retrosplenial cortex, also showed dVenus expression but they were not dependent on MK-801.

A detailed analysis in coronal sections revealed that

Discussion

The importance of the medial prefrontal cortex in NMDA receptor antagonist-induced psychotic behavior has been suggested by studies using lesion, local administration and electrophysiological experiments [7], [8], [9]. The medial prefrontal cortex can be divided into the following subregions: the anterior cingulate cortex, prelimbic cortex, infralimbic cortex and the medial part of the OFC, which can be differentiated based on efferent and afferent projection patterns [29]. Although studies

Conflict of interest

None.

Acknowledgments

We are grateful to Dr. Megumi Eguchi (Gifu University) for her support with the Arc::dVenus reporter mice. This work was supported in part by JSPS KAKENHI Grant Numbers JP26293020 (H.H.), JP26670122 (H.H.), JP15H01288 (H.H.), JP14J01466 (K.S.), JP15K14964 (A.K.); the JSPS Program for Advancing Strategic International Networks to Accelerate the Circulation of Talented Researchers, Grant No. S2603 (H.H.); the JSPS Research Fellowships for Young Scientists (K.S.); the SRPBS from AMED (H.H.); and

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