Abnormal expression of connexin 36 plays a role in the pathogenesis of levodopa induced dyskinesia in rat model of Parkinson’ s disease

Abstract

Objective To explore whether gap junction disturbances are involved in the pathogenesis of levodopa-induced dyskinesia (LID). Methods The hemi-parkinsonian (PD) rat was treated intraperitoneally with L-dopa methylester (20 mg/kg) and benserazid (10 mg/kg) for 21 days and abnormal involuntary movement was evaluated to establish LID rat model. The experimental animals were divided into three groups: LID group, PD group and normal control group，respectively．The behavior responses of intraperitoneal injection of different doses of carbenoxolon and intracerebroventricular injection of quinine were observed to estimate the effects of gap junctional blockade on the abnormal involuntary movement (AIM) in the rat model of LID. Double immunofluorescence labeling was used to analyze the expression of connexin 36 (Cx36) in enkephalin positive medium spiny neurons and parvalbumin (PV) positive interneurons in the striatum. Western blottings was used to observe the expression of Cx36 in the striatum and moter cortex. Results Behavioral characteristics indicated that high dose of carbenoxolone (>60 mg/kg) intraperitoneal injection and intracerebroventricular injection of quinine (0.5，1.0，2.0 μmol/L, >2.5 μmol/L) could decrease the AIM score of LID rats. Western blotting indicated that expression of Cx36 in lesioned striatum and motor cortex of LID rat model was 219.56%±18.12% and 226.03%±16.33%, respectively, which induced a significant upregulation in comparison with the normal control group (104.05%±3.82%, t=15.389, P<0.01; 105.27%±2.82%，t=8.074, P<0.01) and untreated PD group (119.31%±8.92%, t=13.356, P<0.01; 138.20%±17.88%, t=5.872, P<0.01). Double immunofluorescence labeling staining revealed that Cx36 expression was increased in Enk-positive striatum neurons in LID model (57.59%±5.36%) compared with that in normal control group (32.67%±4.22%) and PD group (37.24%±0.86%, F=78.060, P<0.01). The expression of Cx36 in PV-positive interneurons was also elevated in LID group (68.49%±11.60%) in comparison with normal control group (40.43%±2.30%) and PD group (31.92%±5.68%, F=39.567, P<0.01). Conclusions The Cx36 expression is generally increased in lesioned striatum and motor cortex of LID rat model. In the striatum, the up-regulation of Cx36 is specifically observed in Enk-positive striatum neurons and in PV-positive interneurons. The dyskinesia behavior of LID rats can be significantly reduced by treatment with gap junction blockade. All these results suggest that gap junction dysfunction may play an important role in the pathogenesis of LID. Key words: Parkinson disease; Dyskinesias; Connexins; Gap junctions; Disease models, animal