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Botulinum toxin type A (BoNT/A) injections into hyperactive muscles provide effective treatment for spasticity and dystonias, presumably due to its local effects on extrafusal and intrafusal motor fibres. A recent discovery of toxin's retrograde axonal transport to CNS might suggest additional action sites. However, in comparison to cholinergic peripheral terminals, functional consequences of BoNT/A direct central action on abnormally increased muscle tone are presently unknown. To address this question, the central effects of BoNT/A were assessed in experimental local spastic paralysis.

Local spastic paralysis was induced by injection of tetanus toxin (1.5 ng) into rat gastrocnemius. Subsequently, BoNT/A (5 U·kg⁻¹) was applied i.m. into the spastic muscle or intraneurally (i.n.) into the sciatic nerve to mimic the action of axonally transported toxin. Functional role of …