Central injection of botulinum neurotoxins: behavioural effects in mice

Strains of Clostridium botulinum produce seven antigenically distinct botulinum neurotoxins (BoNTs) designated as serotypes A-G. All serotypes interfere with neural transmission by blocking the release of acetylcholine in cholinergic neurons. They cleave specific sites on proteins of the SNARE [soluble n-ethylmaleimide-sensitive factor (NSF) attachment protein receptor] complex, which play a key role in neuroexocytosis. This study assessed the behavioural effects due to central administration of BoNTs in mice. CD1 mice were injected intracerebroventricularly (icv) with sub-lethal doses of BoNT/A or /B and their behavioural responses in conditioning of active avoidance, object recognition test and pharmacologically induced locomotor activity were tested. Compared to control mice, BoNT-treated mice showed: (1) a reduced capacity to discriminate a novel object within a familiar environment; (2) an enhanced stimulant effect by scopolamine and a depressant effect by oxotremorine on locomotor activity. In contrast, central injection of BoNTs did not alter active avoidance acquisition. These results suggest an in vivo functional alteration due to the action of BoNTs directly administered into the central nervous system. The present data demonstrate that BoNTs may represent an analytical tool for studying the functional role of cholinergic neurons.