Association of adhesive macromolecules with terminal sprouts at the neuromuscular junction after botulinum treatment

Small quantities of botulinum toxin (BTX) are useful in the treatment of ce rtain movement disorders, such as laryngeal spasmodic dysphonia, blepharosp asm, and cervical dystonia, However, the corrective paralytic effects of BT X are only temporary, in part because of the formation of remodeled neuromu scular junctions. Here, we questioned whether various factors within and ne ar the neuromuscular junction could contribute to the remodeling seen after BTX treatment. BTX was injected subcutaneously in the region of the levato r auris longus muscle. At 1-week intervals, levator auris longus muscles we re removed and examined histochemically, As previously described, BTX treat ment results in a progressive elongation of end plates. The neural cell adh esion molecule was not associated with the elongated end plates but was ass ociated with the BTX-induced nerve sprouts after long intervals (3 to 4 wee ks). Similarly, after BTX, laminin-l (composed of alpha 1, beta 1, and gamm a 1 chains) reactivity was associated with the nerve sprouts, but not with the end plates, Laminin beta 2 reactivity at the end plate dispersed somewh at within 1 week but remained diffusely associated with the elongating end plates for up to 5 weeks. Together these results suggest that neural cell a dhesion molecule and laminins may participate in the sprouting observed aft er BTX treatment and that alterations in laminin beta 2 expression may part icipate in initial loss of contacts.