Induction and Assessment of Levodopa-induced Dyskinesias in a Rat Model of Parkinson's Disease

Summary

This article describes methods to induce and evaluate levodopa-induced dyskinesias in a rat model of Parkinson's disease. The protocol offers detailed information regarding the intensity and frequency of a range of dyskinetic behaviors, both dystonic and hyperkinetic, providing a reliable tool to test treatments targeting this unmet medical need.

Abstract

Levodopa (L-DOPA) remains the gold-standard therapy used to treat Parkinson's disease (PD) motor symptoms. However, unwanted involuntary movements known as L-DOPA-induced dyskinesias (LIDs) develop with prolonged use of this dopamine precursor. It is estimated that the incidence of LIDs escalates to approximately 90% of individuals with PD within 10–15 years of treatment. Understanding the mechanisms of this malady and developing both novel and effective anti-dyskinesia treatments requires consistent and accurate modeling for pre-clinical testing of therapeutic interventions. A detailed method for reliable induction and comprehensive rating of LIDs following 6-OHDA-induced nigral lesioning in a rat model of PD is presented here. Dependable LID assessment in rats provides a powerful tool that can be readily utilized across laboratories to test emerging therapies focused on reducing or eliminating this common treatment-induced burden for individuals with PD.

Introduction

Although it has been more than 50 years since levodopa (L-DOPA) was first introduced as a treatment for individuals with PD^1,2, it remarkably remains the most effective therapy for parkinsonian motor symptoms. The clinical motor symptoms associated with PD stem from the loss of dopamine (DA) neurons in the substantia nigra (SN) pars compacta, resulting in the dramatic decrease in available dopamine in the striatum. L-DOPA effectively restores striatal DA levels, resulting in motor benefit early in the disease^3,4. Inopportunely, with long-term treatment....

Protocol

The animals presented here were maintained and handled in compliance with the institutional guidelines. All animal procedures were approved by the Michigan State University Institutional Animal Care and Use Committee (IACUC) in compliance with federal and state regulations.

1. Drug-free confirmation of 6-OHDA lesion status

1. Postural Tail hang test^11,12,13
   NOTE: Asses.......

Discussion

Presented here are details for the reproducible induction and rating of LIDs in a parkinsonian rat model following unilateral 6-OHDA lesioning of the nigrostriatal DA system. While it was once thought that rodents did not develop LID and that rotational asymmetry may be the analog of LID in rats³¹, rat and mouse models have been characterized over the past two decades and are a well-accepted tool for LID research^15,32,

Materials

Name	Company	Catalog Number	Comments
100 Minutes Digital Timer	Staples	1111764
Compass CX Compact Scale	Ohaus	30428202
5-(2-aminoethyl)-1,2,4-benzenetriol, monohydrobromide	Cayman Chemicals	25330	6-OHDA is a catecholaminergic neurotoxin that is used to induce dopaminergic lesions and parkinsonian symptoms in rodents.
Allentown cages	Allentown, LLC	Rat900	Allentown cages provide the ability to view the rats from all sides.
BD Allergist Trays with Permanently Attached Needle	BD	BD 305540	For subcutaneous L-DOPA injections
Benserazide hydrochloride	Sigma-Aldrich	B7283	Benserazide is a peripheral decarboxylase inhibitor used with L-DOPA to to induce dyskinesia in rodent models of PD.
Glass amber scintillation vials	Thermo Scientific	B7921	Used for storage of L-DOPA/benserazide at -20 °C until mixed with sterile saline.
L-3,4-Dihydroxyphenylalanine methyl ester hydrochloride	Sigma-Aldrich	D1507	L-3,4-Dihydroxyphenylalanine methyl ester is a precursor to L-DOPA that crosses the blood-brain barrierand use to treat parkinsonian symptoms in rodents.
Paper Mate Sharpwriter Mechanical Pencils	Staples	107250
Rodent nutritionally complete enrichment treats	Bio-Serv	F05478
Round Ice Bucket with Lid, 2.5 L	Corning	432129
Standard Plastic Clipboard	Staples	1227770
Steel wired 6' long movable shelving units	Uline	H9488	Width/Height can be adjusted to need/number of rats per experiment
Sterile Saline 0.9%	Covidien/Argyle	1020	For mixing with L-DOPA/benserazide prior to subcutaneous injections.