Epilepsy & Behavior 31 (2014) 114–116

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Epilepsy & Behavior

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Letter to the Editor

Stimulation of the dorsal portion ofsubthalamic nucleus may be a viable

therapeutic approach in pharmacoresistantepilepsy: A virally mediated transsynaptictracing study in transgenic mouse model

To the Editor

During the last decade, the neural bases of deep brain stimulationhave been widely investigated. The ability to insert electronic stimula-tion systems into precise locations of brain tissues provides powerful ca-pabilities to activate/deactivate critical cellular signaling and neuralsystems. In such cases, determining neuronal phenotype and biochem-ically anatomical identity of the exact targets for deep brain stimulationis essential to avoid adverse effects of stimulation on normal physiolog-ical processes. It is well known that accurate localization of the subtha-lamic nucleus (STN) is critical to the success of deep brain stimulationsurgery for pharmacoresistant epilepsy [1–3]. Though recent develop-ments in high-field-strength magnetic resonance imaging (MRI) hadmade it possible to visualize the STN in greater detail [4], the importantdifferences of the neuroanatomical and neurochemical structure be-tween STN subregions have not been observed.

Accumulating clinic reports highlight the functionally heteroge-neous nature of the STN region, and STN exhibits a wide heterogeneityin terms of neurochemical properties (cholinergic and noncholinergicneurons) and connectivity [5,6]. The regions of STN reported by Parentand Hazrati were collective structures consisting of a dorsal sensorimo-tor region, a ventral associative region, and a medial limbic region [7],and the regions defined by Eitan et al. as the dorsolateral part, corre-sponding to the anatomically defined sensorimotor STN, and the moremedial, more anterior, andmore ventral parts, corresponding to the an-atomically defined limbic and associative territories of the STN [8],whereas McNeely et al. reported that STN contains the dorsal part,which is involved in motor function, and the ventral part, which regu-lates cognitive function [9], based on anatomical connectivity. Little isknown about different parts of the subthalamic nucleus from a virallymediated transsynaptic tracing study.

As a marker for synaptic connectivity in CNS by propagatingretrogradely through chains of functionally connected neurons, theneurotropic pseudorabies virus (PRV) has provided new insight intoneuronal communication and complex brain function [10–18]. Wehad characterized projections from the kidney to the STN of the basalganglia system in adult male MC4R-green fluorescent protein (GFP)transgenic mice by using retrograde tracing techniques of pseudorabiesvirus (PRV)-614, expressing a novel monomeric red fluorescent protein(mRFP1) under control of the cytomegalovirus immediate early pro-moter for direct visualization under fluorescence microscope [19–24].We found that injections of PRV-614 into the kidney preferentially re-sulted in retrograde infection of neurons in the ventral STN, whichwas in agreement with a previous immunohistochemical study [25],suggesting direct neuronal circuit from the ventral STN to the kidney

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via the sympathetic pathways. Otherwise, we did not detect PRV-614-positive neurons in the dorsal STN (Fig. 1), suggesting that the dorsalSTN may not play a major role in the regulation of central sympatheticpathways.

Our results also showed that MC4R-GFP-positive neurons weremost heavily concentrated in the dorsal STN and rarely distributedin the ventral STN, suggesting that the dorsal STN may play a majorrole in the regulation of central MC4R signaling. These data werealso in line with previous studies in which the distinct subpopula-tions of neurons were detected in the subdivision of the STN region,suggesting that the STN should not be considered as a homogeneousstructure [5,6,26,27]. Therefore, it was presumed that deep brainstimulation of the ventral portions of STN involved in sympatheticfunction whereas stimulation of the dorsal portions of STN involvedin nonsympathetic signaling

Based on all these findings, we speculate that the dorsal portion ofSTN may play a major role in the regulation of central MC4R signalingand motor pathway, suggesting that stimulation for the dorsal, not theventral, portion of the subthalamic nucleus may be a viable therapeuticapproach in pharmacoresistant epilepsy.

Acknowledgments

The authors would like to gratefully acknowledge Dr. Lynn Enquistfor kindly providing us with PRV-614 and Dr. Joel Elmquist (UT South-western Medical Center) for providing the MC4R-GFP transgenic mice.

Funding

This work was supported by grants from the National Natural Sci-ence Foundation of PR China (No. 81271766 to H.X.), the National Nat-ural Science Foundation of Hubei Province (No. 2013CFB121 to H.X.),Special Fund of Fundamental Scientific Research Business Expense forHigher School of Central Government (2012 TS060 to H.X.), and a2010 Clinical Key Disciplines Construction Grant from the Ministry ofHealth of PR China.

Conflict of interest

The authors declare that they have no competing interests.

References

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Fig. 1. Sympathetic andmelanocortinergic neurons in the STN. The kidney has become amodel system inwhich to study sympathetic function. Because there is no evidence that connec-tions of themotor nerve and the parasympathetic nervous system innervate the kidneys, the neurotropic pseudorabies virus (PRV)-614was injected into the left kidney.We seek tomapthemelanocortin-sympathetic pathway between the kidney and subthalamic region inMC4R-GFP transgenicmice by using retrograde tracing techniques of PRV-614. A shows anatomicalplates taken from Franklin and Paxinos [28]; images B–D were taken from an animal that survived 5 d after injections of PRV-614. B shows overlaid images of B plus C; C shows neuronsinfectedwith PRV-614, which send transsynaptic projections to the kidney; D showsMC4R-GFP-positive neurons in the STN. LH, lateral hypothalamic area; dSTN, dorsal STN; dlSTN, dor-solateral STN; vSTN, ventral STN. Scale bar, 200 μm.

115Letter to the Editor

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116 Letter to the Editor

Li FengTao-Tao Liu

Department of Anesthesiology and Pain Medicine,Tongji Hospital of Tongji Medical College,

Huazhong University of Science and Technology, Wuhan,Hubei 430030, PR China

Da-Wei YeCancer Center, Tongji Hospital of Tongji Medical College,Huazhong University of Science and Technology, Wuhan,

Hubei 430030, PR China

Qiu QiuDepartment of Anesthesiology and Pain Medicine,

Tongji Hospital of Tongji Medical College,Huazhong University of Science and Technology, Wuhan,

Hubei 430030, PR ChinaDepartment of Anaesthesiology, The University of Hong Kong,

Queen Mary Hospital, Hong Kong, China

Hong-Bing XiangDepartment of Anesthesiology and Pain Medicine,

Tongji Hospital of Tongji Medical College,Huazhong University of Science and Technology, Wuhan,

Hubei 430030, PR ChinaCorresponding author. Fax: +86 27 83662853.E-mail address: xianghongbing0204@163.com.

Chi-Wai CheungDepartment of Anaesthesiology, The University of Hong Kong,

Queen Mary Hospital, Hong Kong, ChinaCorresponding author. Fax: +852 22553384.

E-mail address: cheucw@hku.hk.

16 November 2013