Change of Extracellular Glutamate Level in Striatum during Deep Brain Stimulation of the Entopeduncular Nucleus in Rats

Abstract

Objective: Globus pallidus interna (GPi) is acknowledged as an essential treatment for advanced Parkinson's disease (PD). Nonetheless, the neurotransmitter study about its results is undiscovered. The goal of this research was to examine influences of entopeduncular nucleus (EPN) stimulation, identical to human GPi, in no-lesioned (NL) rat and 6-hydroxydopamine (6-HD)-lesioned rat on glutamate change in the striatum.

Methods: Extracellular glutamate level changes in striatum of NL category, NL with deep brain stimulation (DBS) category, 6-HD category, and 6-HD with DBS category were examined using microdialysis and high-pressure liquid chromatography. Tyrosine hydroxylase (TH) immunoreactivities in substantia nigra and striatum of the four categories were also analyzed.

Results: Extracellular glutamate levels in the striatum of NL with DBS category and 6-HD with DBS category were significantly increased by EPN stimulation compared to those in the NL category and 6-HD category. EPN stimulation had no significant effect on the expression of TH in NL or 6-HD category.

Conclusion: Clinical results of GPi DBS are not only limited to direct inhibitory outflow to thalamus. They also include extensive alteration within basal ganglia.

Keywords: Deep brain stimulation; Entopeduncular nucleus; Glutamates; Parkinson disease.

Fig. 1.

Influence of EPN stimulation on striatal glutamate levels in no-lesioned rats. Each point represents the mean±standard error from six rats per category : no-lesioned rats without deep brain stimulation (NL category) and no-lesioned rats with deep brain stimulation (NL with DBS category). DBS : deep brain stimulation, NL : no-lesioned, EPN : entopeduncular nucleus.

Fig. 2.

Influence of EPN stimulation on striatal glutamate levels in 6-HD lesioned rats. Each point represents the mean±standard error from six rats per category : 6-HD lesioned rats without DBS (6-HD category) and 6-HD lesioned rats with deep brain stimulation (6-HD with DBS category). DBS : deep brain stimulation, 6-HD : 6-hydroxydopamine, EPN : entopeduncular nucleus.

Fig. 3.

TH-immunoreactivity in the Striatum. Representative images showed TH-immunoreactivity in the striatum of the ipsilateral (A, C, E, G) and contralateral (B, D, F, H) sides. Scale bar=200 μm. A and B : NL category. C and D : NL with DBS category. E and F : 6-HD category. G and H : 6-HD with DBS category. Mean (±standard error of mean) quantification (I) of TH expression showed significant decrease in both 6-HD and 6-HD with DBS categories compared to NL categories (n=5–6 per groups). *p<0.001 versus NL category. † p<0.001 versus NL with DBS category, ANOVA. n.s. : no significance, 6-HD : 6-hydroxydopamine, DBS : deep brain stimulation, TH : tyrosine hydroxylase, NL : no-lesioned, ANOVA : analysis of variance.

Fig. 4.

TH-immunoreactivity in the SN. Representative images showed TH-immunoreactivity in the SN. Left side is ipsilateral part and right side is contralateral part of the SN. Scale bar=200 μm. A : NL category. B : NL with DBS category. C : 6-HD category. D : 6-HD with DBS category. Mean (±standard error of mean) quantification (E) of TH expression showed significant decrease in both 6-HD category and 6-HD with DBS category compared to NL categories (n=4–6 per groups). *p<0.01 and † p <0.001 versus NL category. ‡ p<0.001 versus NL with DBS category, ANOVA. n.s. : no significance, 6-HD : 6-hydroxydopamine, DBS : deep brain stimulation, SN : substantia nigra, TH : tyrosine hydroxylase, NL : no-lesioned, ANOVA : analysis of variance.

Fig. 5.

Histological verification. The stereotaxic atlas from Paxinos [23] shows the location of MFB (B), dorsal striatum (D) and EPN (F). Representation of coronal sections verifies injection site of 6-hydroxydopamine in the MFB (A), position of the probe in the striatum (C) and the electrode in the EPN (E). Scale bars=200 μm. MFB : medial forebrain bundle, EPN : entopeduncular nucleus.