Phonic Tics in a Rat Model of Tourette Syndrome Enable Research on Symptom-Based DBS

The lack of a rodent model for both motor and phonic tics hinders research on deep brain stimulation (DBS) for refractory Tourette syndrome (TS). Striatal disinhibition with a GABA-A antagonist (bicuculline) was previously shown to induce tic-like hyperkinesia in rats and monkeys, while tic-like vocalizations were studied and confirmed only in the latter. We, therefore, assessed whether vocalizations accompany hyperkinesia also in rats and whether they respond to thalamic DBS. Rats underwent surgical implantation of a unilateral guide cannula targeting the caudate putamen (CPu) or nucleus accumbens (NAc). Additionally, they were implanted with an ipsilateral stimulation electrode targeting the border between the central medial (CM) and ventrolateral (VL) thalamic nuclei. Motor changes and ultrasound vocalizations were recorded and characterized offline. Bicuculline in CPu led to the development of hyperkinesia in the form of arrhythmic, myocloniform shoulder jerks sporadically alternating with episodes of dystonic lordosis. Likewise, bicuculline in NAc resulted in hyperkinesia, but at a much smaller dose and in conjunction with nonsensical vocalizations. DBS of CM/VL, but not adjacent regions, attenuated hyperkinesia. Also, early results indicate that thalamic DBS attenuates vocalizations, yet the hotspot for stimulation remains to be determined. In conclusion, striatal disinhibition leads not only to the development of hyperkinesia but also vocalizations in rats. The resemblance of hyperkinesia to motor tics and vocalizations to phonic tics is evident in their appearance and susceptibility to DBS. Rats can, therefore, be used to study DBS for symptom-based TS therapy.