L-Dopa treatment and abnormal involuntary movement rating
Seventy-eight (78) rats that successfully passed the threshold values in the bar and drag test were treated for 21 days with L-Dopa (6 mg kg-1 + benserazide 15 mg kg-1, s.c., once daily) to induce abnormal involuntary movements (AIMs), a correlate of LID (Cenci et al. , 1998; Cenci et al. , 2007), as previously described (Brugnoli et al. , 2020; Marti et al. , 2012; Paolone et al. , 2015). Rats were observed for 1 min, every 20 min, during the 3 h that followed L-DOPA injection or until dyskinetic movements ceased. Dyskinetic movements were classified based on their topographical distribution into three subtypes: (i) axial AIM, that is, twisted posture or turning of the neck and upper body toward the side contralateral to the lesion; (ii) forelimb AIM, that is, jerky and dystonic movements and/or purposeless grabbing of the forelimb contralateral to the lesion; and (iii) orolingual AIM, that is, orofacial muscle twitching, purposeless masticatory movements and contralateral tongue protrusion. Each AIM subtype was rated on a frequency scale from 0 to 4 (1, occasional; 2, frequent; 3, continuous but interrupted by an external distraction; 4, continuous and not interrupted by an external distraction). In addition, the amplitude of these AIMs was measured on a scale from 0 to 4 based on a previously validated scale (Cenciet al. , 2007). Axial, Limb and Orolingual (ALO) AIMs total value were obtained as the sum of the product between amplitude and frequency of each observation (Cenci et al. , 2007), and fully dyskinetic rats scored ≥100.