Purpose: To assess if neurturin (NTN) injection leads to accelerated recovery from Botulinum toxin type A (BTxA) injections in mice. Although diffusion outside the intended area of effect is a known complication of BTxA injection, there is no agent currently available to reverse or accelerate recovery from BTxA spread.
Methods: 38 mice underwent muscle force testing. Five control mice received no injections, while a further 18 received injections of 5pg of BTxA into the left and right gastrocnemius at t= -7days. At t=0, they received injections of 100pg of NTN into the left gastrocnemius, and vehicle solution (0.1% BSA) in the right. Three animals were randomly selected to undergo muscle force testing at each of 6 time points (t=0, 7, 14, 21, 28, 35d). Another group of 15 animals was repeated using 100ng of NTN for rescue of the left gastrocnemius. In addition, in vivo and confocal imaging were conducted using thy1-YFP(16) transgenic mice with constitutively fluorescing axons to determine the effect of NTN rescue on BTxA injections in mouse levator auris longus muscles.
Results: Animals were grouped according to days post-NTN rescue (t=0 to t=35days). NTN treated muscles had statistically significant increased peak tetanic forces in comparison to the non-NTN treated muscles by t = 21d (p-value 0.045, Student’s t-test) in the 100pg group. In the later time points, increased percent return of function in comparison to the untreated controls was also seen. Significant differences in the 100ng group were seen as early as t=7 d (p-value 0.0009). Live imaging and confocal microscopy in thy1-YFP(16) transgenic mice showed increased nerve sprouting and motor endplate density in NTN injected muscles vs. controls.
Conclusions: NTN, a neurotrophic factor, accelerates recovery from BTxA poisoning of mouse gastrocnemius muscles as early as 7 days post-NTN rescue when 100ng is used, and as early as 21 days post-NTN rescue when using 100pg. While our initial data does not demonstrate statistically significant different muscle force production between the 100pg and 100ng groups, it does demonstrate an earlier onset of recovery when using 100ng of NTN.
Pilot imaging studies suggest NTN augments neuronal sprouting and the number of motor endplates in mouse levator auris longus muscles that have been injected with BTxA. Our study suggests NTN may serve as a novel therapy for reversal of unintended BTxA spread, and could significantly reduce muscle paralysis time. The ease of delivery (injection) of NTN makes it an ideal therapy that is both effective and simple to employ.