The role of the vagal pathway and gastric dopamine in the gastroparesis of rats after a 6‐hydroxydopamine microinjection in the substantia nigra

Abstract

Gastroparesis is a common non-motor system symptom of Parkinson's disease (PD). However, the mechanism responsible for the gastric motor abnormality is not clear. We previously reported on the impaired gastric motility in 6-hydroxydopamine (6-OHDA) rats, which were treated with a bilateral microinjection of 6-OHDA in the substantia nigra (SN). We hypothesize that the enhanced dopamine system and reduced acetylcholine (Ach) in gastric tissues might contribute to the delayed gastric emptying observed in PD. A strain gauge force transducer, digital X-ray imaging system, Western blot, immunofluorescence and Radio Immunoassay were used in this study. Dopaminergic neurones in the SN were greatly reduced following the bilateral microinjection of 6-OHDA. 6-OHDA rats exhibited impaired gastric motility and delayed gastric emptying, accompanied by increased dopamine content and the overexpression of D2 receptors in the stomach. The administration of the D2 receptor antagonist domperidone relieved gastric dysmotility in 6-OHDA rats, but the D1 receptor antagonist SCH23390 failed to do so. Subdiaphragmatic vagotomy prevented the increase in the gastric dopamine content and D2 receptor expression and improved gastric dysmotility in 6-OHDA rats. Dopaminergic deficiency in the SN results in impaired gastric motility, possibly as a result of the enhanced activity of dopamine system and reduced Ach in gastric tissue. The vagus nerve plays an important role in peripheral gastric motility disorder.