Assessing the role of dopamine in limb and cranial-oromotor control in a rat model of Parkinson's disease

Abstract

Parkinson's disease (PD) is a neurodegenerative disorder primarily characterized by sensorimotor dysfunction. The neuropathology of PD includes a loss of dopamine (DA) neurons of the nigrostriatal pathway. Classic signs of the disease include rigidity, bradykinesia, and postural instability. However, as many as 90% of patients also experience significant deficits in speech, swallowing (including mastication), and respiratory control. Oromotor deficits such as these are underappreciated, frequently emerging during the early, often hemi-Parkinson, stage of the disease. In this paper, we review tests commonly used in our labs to model early and hemi-Parkinson deficits in rodents. We have recently expanded our tests to include sensitive models of oromotor deficits. This paper discusses the most commonly used tests in our lab to model both limb and oromotor deficits, including tests of forelimb-use asymmetry, postural instability, vibrissae-evoked forelimb placing, single limb akinesia, dry pasta handling, sunflower seed shelling, and acoustic analyses of ultrasonic vocalizations and pasta biting strength. In particular, we lay new groundwork for developing methods for measuring abnormalities in the acoustic patterns during eating that indicate decreased biting strength and irregular intervals between bites in the hemi-Parkinson rat. Similar to limb motor deficits, oromotor deficits, at least to some degree, appear to be modulated by nigrostriatal DA. Finally, we briefly review the literature on targeted motor rehabilitation effects in PD models. Learning outcomes: Readers will: (a) understand how a unilateral lesion to the nigrostriatal pathway affects limb use, (b) understand how a unilateral lesion to the nigrostriatal pathway affects oromotor function, and (c) gain an understanding of how limb motor deficits and oromotor deficits appear to involve dopamine and are modulated by training.