Effect of ventrolateral thalamic nucleus lesions in the unilateral 6-hydroxydopamine rat model

Whilst dysfunction of basal ganglia-thalamic circuitry is implicated in the genesis of parkinsonian symptomatology, few studies have examined the effects of lesioning the motor thalamus in the context of parkinsonism. Forty rats were therefore subdivided into four lesion groups each of 10 rats with lesions or sham surgery targeting (1) the medial forebrain bundle and/or (2) motor thalamus, resulting in: Sham/Sham, 6-OHDA/Sham, Sham/NMDA and 6-OHDA/NMDA groups. Behavioural testing was performed prior to any surgery and after each surgery including analysis of posture, drug-induced rotation, sensorimotor and autonomic deficits. As expected 6-OHDA lesions induced abnormalities in posture, locomotion, sensorimotor and pilomotor function, ipsilateral and contralateral rotational asymmetries after amphetamine and apomorphine, respectively. These behavioural changes reflect parkinsonism in this model. Additional thalamic lesions virtually abolished apomorphine-induced rotational asymmetry and improved sensorimotor response latency to tactile stimulation on the contralateral side. These data support the contribution of dysfunctional motor thalamic circuitry in rotational asymmetry and abnormal sensorimotor function in parkinsonian rats.