Projections of nucleus accumbens adenosine A2A receptor neurons in the mouse brain and their implications in mediating sleep-wake regulation

Jian-Ping Zhang,Rui-Xi Li,Yoan Cherasse,Alban De Kerchove D'Exaerde,Yoshihiro Urade,Qi Xu,Xiang-Shan Yuan,Wei-Min Qu,Zhi-Li Huang,Michael Lazarus,Serge N Schiffmann

doi:10.3389/fnana.2013.00043

Abstract

Adenosine A2A receptors (A2ARs) in the nucleus accumbens (Acb) have been demonstrated to play an important role in the arousal effect of adenosine receptor antagonist caffeine, and may be involved in physiological sleep. To better understand the functions of these receptors in sleep, projections of A2AR neurons were mapped utilizing adeno-associated virus (AAV) encoding humanized Renilla green fluorescent protein (hrGFP) as a tracer for long axonal pathways. The Cre-dependent AAV was injected into the core (AcbC) and shell (AcbSh) of the Acb in A2AR-Cre mice. Immunohistochemistry was then used to visualize hrGFP, highlighting the perikarya of the A2AR neurons in the injection sites, and their axons in projection regions. The data revealed that A2AR neurons exhibit medium-sized and either round or elliptic perikarya with their processes within the Acb. Moreover, the projections from the Acb distributed to nuclei in the forebrain, diencephalon, and brainstem. In the forebrain, A2AR neurons from all Acb sub-regions jointly projected to the ventral pallidum, the nucleus of the diagonal band, and the substantia innominata. Heavy projections from the AcbC and the ventral AcbSh, and weaker projections from the medial AcbSh, were observed in the lateral hypothalamus and lateral preoptic area. In the brainstem, the Acb projections were found in the ventral tegmental area, while AcbC and ventral AcbSh also projected to the median raphe nucleus, the dorsal raphe nucleus, and the ventrolateral periaqueductal gray. The results supply a solid base for understanding the roles of the A2AR and A2AR neurons in the Acb, especially in the regulation of sleep.

Highlights

Three cases showed that humanized Renilla green fluorescent protein (hrGFP) was almost exclusively confined to the accumbens nucleus (AcbC), mAcbSh, and vAcbSh, respectively, except for the case (M-7) showed few expressiones outside the AcbC in neurons located in the caudate putamen (Figure 1A) and the dorsal part of accumbens nucleus (AcbSh) (Figures 1A–D)
Consistent with the present data, Usuda et al (1998) depicted ventral AcbSh projections to the ventral tegmental area (VP), the substantia innominata (SI), the lateral pre-optic area (LPO), the lateral hypothalamus (LH), the ventral tegmental area (VTA), the PAG, the PB, and the locus coeruleus (LC). Furthering these observations, we detected numerous axons projecting to the HDB and the MnR, and to a lesser extent to the dorsal raphe nucleus (DR), and dorsal raphe nucleus (DRI). The reason for this discrepancy could be explained by the different techniques used, or by differences in species of the animals used in each study, we suggest other important considerations in the following aspects: (1) specific injection site results in the different projections, which is not an exception for this method
In summary, the present study demonstrated the projections of Acb A2AR neurons by means of an injection of hrGFP-expressing associated virus (AAV) as a tracer in A2AR-Cre transgenic mouse

Summary

Introduction

The adenosine A2Areceptors (A2ARs) in the nucleus accumbens (Acb), that consists of the core and shell sub-regions, play a critical role in many important physiological and pathological processes, including sleep, feeding, locomotion, motivation, and addiction (Barraco et al, 1993, 1994; Nagel et al, 2003; Kelley, 2004; Huang et al, 2007, 2011; Mingote et al, 2008; Lazarus et al, 2011, 2012, 2013; O’Neill et al, 2012). Because of limitations in tracing techniques, little data are available describing the efferent projections of A2AR neurons in the Acb. Because of limitations in tracing techniques, little data are available describing the efferent projections of A2AR neurons in the Acb Those data that are available have been obtained using conventional tracers, such as autoradiographic fiber-tracing (Nauta et al, 1978), wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP; Heimer et al, 1991), phaseolus vulgarisleucoagglutinin (PHA-L; Zahm and Heimer, 1993), and biotinylated dextran amine (BDA; Usuda et al, 1998). The efferent regions of Acb neurons do not stand for projection sites of A2AR neurons in Acb

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Discussion

Conclusion