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.