Elsevier

Neurobiology of Disease

Volume 50, February 2013, Pages 142-150
Neurobiology of Disease

Comparison of rating scales used to evaluate l-DOPA-induced dyskinesia in the 6-OHDA lesioned rat

https://doi.org/10.1016/j.nbd.2012.10.013Get rights and content

Abstract

Abnormal involuntary movement (AIM) rating scales are frequently used to study the mechanisms underlying l-DOPA-induced dyskinesia (LID) in 6-OHDA lesioned rodents and the propensity of novel treatments for Parkinson's disease to induce or alleviate similar abnormal behaviours. Despite the existence of at least one well validated method, other AIM scales are also in use. Moreover, there have been developments and variations in the original scales and their methods of use, without re-validation. In this study, 6-OHDA medial forebrain bundle lesioned Sprague–Dawley rats were treated with chronic l-DOPA 6 mg/kg/day for 5 weeks followed by 12 mg/kg/day for another 5 weeks. Rats were assessed weekly by simultaneous ratings on four published AIM and stereotypy scales with concurrent recording of rotation, over 3 hours following l-DOPA injection. Three contemporary AIM scales have then been validated pharmacologically using agents that are known to reduce LID clinically and in primates (amantadine) or to interfere with the activity of l-DOPA (the D1 and D2 dopamine receptor antagonists, SCH-23390 and raclopride) respectively. We also demonstrate that AIM, stereotypic and rotational behaviour are distinct motor dysfunctions induced by chronic and acute treatment of l-DOPA, and should be assessed separately. The undertaking of assessments at multiple time points is essential especially when testing the efficacy of new potential anti-dyskinetic treatments. Importantly critical to all AIM and rotation testing is the internal validation of both the scale being used and the environment being used.

Highlights

► Dyskinesia, stereotypy and rotation are distinct l-DOPA-induced behaviours. ► Published AIM rating methods vary in sensitivity to AIM development and pharmacological agents. ► The shape of the testing environment did not affect any behavioural measure.

Introduction

l-DOPA remains the most effective therapy in the management of the motor symptoms of Parkinson's disease (PD). However, its long-term utility is curtailed by the development of disabling side effects termed l-DOPA-induced dyskinesia (LID). These are choreic and dystonic abnormal and involuntary movements (AIM) affecting mainly the upper body, face and extremities (Barbeau, 1969). The appearance of LID affects up to 90% of patients within 10 years of chronic exposure to l-DOPA and is progressive and irreversible (Ahlskog and Muenter, 2001). Given that l-DOPA is still a necessity in the treatment of advanced PD, reducing or avoiding LID is a key objective in the management of PD motor symptoms. In clinical practice, LIDs are assessed using observational rating scales based on clinical examination, patient historical self-evaluation or both and to this end, over 15 different scales have been used since the 1970s. However, recent limited success of new anti-dyskinesiogenic agents in the clinic has highlighted the variability in evaluation techniques. The opinion has emerged that a general consensus is required to identify and use a single reliable, well validated dyskinesia rating scale, to permit greater comparability between clinical trials, and to increase the validity of their findings (Colosimo et al., 2010, Goetz et al., 2011).

The same issues of reliability and validation are encountered in preclinical research, a factor, which may also contribute to the lack of success in translational studies. Thus, in the MPTP-treated primate model of PD, LIDs are typically evaluated using rating scales adapted from the human yardstick, and there is a similar debate over both the validity of the various scales and the need for greater consistency between laboratories (Fox et al., 2012, Jenner, 2003, Jolkkonen et al., 1995, Pearce et al., 1995, Petzinger et al., 2001).

More recently, similar developments have taken place with the unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rodent (Cenci et al., 1998, Lundblad et al., 2002, Lundblad et al., 2005, Maries et al., 2006, Smith et al., 2012b, Steece-Collier et al., 2003, Winkler et al., 2002). The initial studies created intense debate (for detail see Cenci et al., 2002), in part stemming from early studies, which showed a causal link between over-stimulation of dopaminergic system and stereotypic behaviours in rodents (Fog, 1969, Randrup et al., 1963). Motor effects induced by l-DOPA in dopamine-denervated rats were therefore first simply described as stereotypies (Ervin et al., 1977). However, in 1998, Cenci and colleagues demonstrated that the animals also exhibit distinct abnormal dystonic and choreic movements comparable to the abnormal movements observed in PD patients or non-human primates when repeatedly exposed to l-DOPA. The first AIM scale for rodents described forelimb movements, orolingual and jaw movements, axial contortion and rotational locomotion; each rated based on the duration each was present during an observation phase (Cenci et al., 1998). In a later adaptation, a second parameter was added to each movement type, an amplitude score, which considers the extent of the movement, differentiating, for example, between small but clearly present movements of the forelimb and wrist and larger, more dystonic-like movements involving the whole shoulder (Winkler et al., 2002). In parallel, Steece-Collier and colleagues developed a similar scoring scale, which distinguished between a greater number of movement elements (Maries et al., 2006, Steece-Collier et al., 2003). Thus far, all three rating scales have been used to follow the development of AIM and explore the underlying mechanisms whilst also evaluating the propensity of new agents to reduce LID both by the authors and adapted by other groups (Lundblad et al., 2002, Monville et al., 2005, Munoz et al., 2009, Rylander et al., 2010, Taylor et al., 2005). Importantly, the first AIM scale is the only one that has ever been extensively validated with pharmacological agents known to reduce LID in primate models and in the clinic (Lundblad et al., 2002). Furthermore, no studies comparing these different scoring methodologies have been carried out, nor their direct comparison with classical rating measures of stereotypy (Creese and Iversen, 1973).

This paper evaluates the reliability of the 3 AIM behavioural rating scales and their associated methodologies in the assessment of the effects of repeated l-DOPA administration, and compares them to the most commonly used classical stereotypy scale (Creese and Iversen, 1973). Furthermore, we examine how these scales reflect the effects of dopamine receptor antagonists and the only anti-dyskinesia agent available in the clinic, amantadine.

Section snippets

6-Hydroxydopamine lesion

28 female Sprague–Dawley rats (Harlan UK), weighing 220–250 g at the start of the experiment were housed 2–4 per cage with ad libitum access to food and water. The experiment was approved by local ethical review at Cardiff University and conducted in accordance with the UK Animal (Scientific Procedure) Act 1996. 6-OHDA HBr was delivered directly into the right median forebrain bundle, as described in detail by Torres et al. (2011). Briefly, the rats were anaesthetised with 2–3% Isoflurane (IVAK,

Rotational behaviour

On the first day of l-DOPA administration the rats rotated at very low levels, with only a slight contralateral preference. Over the course of chronic administration the rotational response to 6 mg/kg l-DOPA remained relatively stable but maintained an overall contralateral bias. When the l-DOPA dose was increased to 12 mg/kg at week 6 the net rotations significantly increased in the contralateral direction (Fig. 1F; F9,243 = 40.52, p < 0.0001, Bonferroni post-hoc: p < 0.001) and continued to increase

Discussion

The disability caused by the development of abnormal movements in response to l-DOPA has stimulated significant research into novel therapeutics that can either alleviate the behaviours or replace l-DOPA and avoid their inception and into their pathology, in both patients and animal models. Despite this extensive research program, rating the movements is still heavily dependent upon subjective rating scales based on direct visual observation, be it in the clinic, primate or rodent models (Fahn

Conclusion

To ensure that AIM scoring in the rodent 6-OHDA lesioned models becomes a highly standardised tool, fully validated scales to produce robust and comparable data are a must. In the present experiment, we found that all published rodent scales do reflect the effects of l-DOPA and pharmacological reductions in LID. Nevertheless, it remains a fundamental of behavioural experimentation that individual assessment protocols revalidate scales in their own hands before any modifications are made and

Acknowledgments

The authors declare no conflicts of interest. We acknowledge funding from the Medical Research Council and the European Union (EC contract number 222918 REPLACES FP7 — Thematic priority HEALTH)

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