Effects of intrastriatal botulinum neurotoxin A on the behavior of Wistar rats

Central pathophysiological pathways of basal ganglia dysfunction imply a disturbed interaction of dopaminergic and cholinergic circuits. In Parkinson's disease imbalanced cholinergic hyperactivity prevails in the striatum. As recently shown intrastiatal botulinum neurotoxin A (BoNT-A) improves motor function in hemiparkinsonian rats. Before going further steps in using intracerebral BoNT-injections as possible treatment we here explore whether pure BoNT-injections into normal rats’ striata affect their cognitive and emotional properties. Wistar rats were injected bilaterally with 1 ng BoNT-A or vehicle (sham injection) into the striatum, whereas a naïve control group was left untreated. Locomotor activity, balance and coordination were assessed in open field and accelerod tests. Anxiety was evaluated in the open field and elevated plus maze. Spatial learning was assessed by radial and water maze tests. Intrastriatal BoNT-A, but also sham injections caused decreased motor activity and impaired balance and motor coordination of rats. Slight working memory deficits were observed in radial maze testing of both BoNT-A and sham injected animals arguing for a consequence of surgery rather than for a specific BoNT-A effect. In contrast, BoNT-A injected animals showed a reduced anxiety in open field and elevated plus maze compared to both sham-treated and naïve controls. As bilateral intrastriatal BoNT-A injections in normal rats do not cause cognitive impairments and reduce anxiety, and previous findings showed improvements of motor function in hemiparkinsonian rats following intrastriatal BoNT-A, it can be argued that intrastriatal BoNT-A could be a new therapeutic approach in Parkinson's disease.

► Intrastriatal botulinum neurotoxin application reduces anxiety.
► Spatial learning is not impaired by intrastriatal botulinum neurotoxin application.
► Working memory is slightly impaired by intrastriatal surgery.