125I-labelled botulinum A neurotoxin: pharmacokinetics in cats after intramuscular injection

On unilateral injection of sublethal doses of 125I-botulinum A neurotoxin (BTA) into one gastrocnemius muscle of the cat we found after 48 h: a disto-proximal gradient of radioactivity (RA) hat developed in the sciatic nerve of the injected side. The ventral roots of the spinal cord half segments supplying the injected muscle showed a higher RA than the ventral roots of the contralateral control side. The spinal cord half segments innervating the injected muscle had a RA much higher than the corresponding segments of the contralateral side. However, a small rise of RA was also observed in the contralateral half segments. In histoautoradiographs of the (ligatured) ventral roots the RA was strictly confined to the intraaxonal space of a few nerve fibres. On injection of equal doses of 125I-BTA into either gastrocnemius muscle we found after 38 h: direct stimulation of only one of the injected muscles caused the RA to reach a higher level in the spinal cord half segments ipsilateral to the stimulated muscle than in the spinal cord half segments of the non-stimulated side. Unilateral stimulation of one gastrocnemius nerve under the influence of gallamine or unilateral antidromic stimulation of the dorsal roots L7, S1 failed to cause a difference in RA between stimulated and non-stimulated side. (orig.)