Differences in the temperature dependencies of uptake of botulinum and tetanus toxins in Aplysia neurons

Assessment, goal setting, and botulinum neurotoxin a therapy in the management of post-stroke spastic movement disorder: updated perspectives on best practice

INTRODUCTION

Post-stroke spastic movement disorder (PS-SMD) appears up to 20% in the first week following stroke and 40% in the chronic phase. It may create major hurdles to overcome in early stroke rehabilitation and as one relevant factor that reduces quality of life to a major degree in the chronic phase.

AREAS COVERED

In this review, we discuss predictors,early identification, clinical assessments, goal setting, and management in multiprofessional team, including Botulinum neurotoxin A (BoNT-A) injection for early and chronic management of PS-SMD.

EXPERT OPINION

The earlier PS-SMD is recognized and managed, the better the outcome will be. The comprehensive management in the subacute or chronic phase of PS-SMD with BoNT-A injections requires detailed assessment, patient-centered goal setting, technical-guided injection, effective dosing of BoNT-A per site, muscle, and session and timed adjunctive treatment, delivered in a multi-professional team approach in conjunction with physical treatment. Evidence-based data showed BoNT-A injections are safe and effective in managing focal, multifocal, segmental PS-SMD and its complications. If indicated, BoNT-A therapy should be accompanied with adjunctive treatment in adequate time slots. BoNT-A could be added to oral, intrathecal, and surgical treatment in severe multisegmental or generalized PS-SMD to reach patient/caregiver's goals, especially in chronic PS-SMD.

Explanation of timing of botulinum neurotoxin effects, onset and duration, and clinical ways of influencing them

While the steps in the action of botulinum neurotoxin (BoNT) are well known, the factors underlying the timing of these steps are not fully understood. After toxin is injected into a muscle, it resides in the extracellular space and must be taken up into the nerve terminals. More toxin will be taken up if near the endplate. Toxin is distributed mainly by convection and there is likely little diffusion. Toxin that is not taken up will go into the general circulation where it may have a slight systemic effect. The uptake is activity and temperature dependent. Encouraging the unwanted muscle contractions after injection should be helpful. Cooling will decrease the uptake. The times for washout from the extracellular space and uptake of the toxin are not well established, but are likely measured in minutes. Toxin in the general circulation has a long half time. The time from injection to weakness is determined by how long it takes to get sufficient damage of the SNARE proteins to interfere with synaptic release. Toxins are zinc dependent proteases, and supplemental zinc may produce a greater effect. There will be weakness as long as there is residual toxin in the nerve ending.

Differences in the multiple step process of inhibition of neurotransmitter release induced by tetanus toxin and botulinum neurotoxins type A and B at Aplysia synapses

In order to gain insights into the steps (binding, uptake, intracellular effect) which differ in the inhibitory actions of tetanus toxin and botulinum neurotoxins types A or B, their temperature dependencies were investigated at identified cholinergic and non-cholinergic synapses in Aplysia. Upon lowering the temperature from 22 degrees C to 10 degrees C, extracellularly applied botulinum neurotoxin type A and B appeared unable to inhibit transmitter release whilst tetanus toxin exhibited a residual activity. Binding of each toxin to the neuronal membrane appeared virtually unaltered following this temperature change. By contrast, the intracellular effects of botulinum neurotoxin type B and tetanus toxin were strongly attenuated by temperature reduction whereas the inhibitory action of botulinum neurotoxin type A was only moderately reduced. Importantly, this discrepancy relates to the known proteolytic cleavage of different synaptic proteins by these two toxin groups. Since both the binding and intracellular activity of botulinum neurotoxin type A are minimally affected at 10 degrees C, its inability to inhibit neurotransmission at this low temperature when applied extracellularly indicated attenuation of its uptake. Due to the strict temperature dependence of the intracellular action of tetanus toxin and botulinum neurotoxin type B, but not A, an examination of the effects of changes in temperature on the internalization step was facilitated by the use of heterologous mixtures of the toxins' heavy and light chains. At 10 degrees C, heavy chain from tetanus toxin but not from botulinum neurotoxin type B mediated uptake of botulinum neurotoxin type A light chain. Collectively, these results provide evidence that, at least in Aplysia, the uptake mechanism for botulinum neurotoxin types A and B differs from that of tetanus toxin.

Tetanus toxin mechanism of action in Torpedo electromotor system: a study on different steps in the intoxication process

The mechanism of action of tetanus toxin was characterized in the electromotor system of Torpedo marmorata either at peripheral and central nervous system. The consecutive steps of the intoxication pathway were observed: (i) [125I]tetanus toxin specifically bound to neuronal plasma membranes isolated both from electric organ and electric lobe of Torpedo, exhibiting one and two binding sites respectively; (ii) [125I]tetanus toxin was internalized into nerve terminals and retrogradely transported to the electric lobe after its injection in the electric organ; (iii) finally, intracellular effect of tetanus toxin was studied either at electric organ and electric lobe membrane fractions. In both preparations tetanus toxin cleaved synaptobrevin, as detected by immunoblotting methods. In conclusion, our findings exhibit the presence of two different populations of acceptors for tetanus toxin in central and peripheral nervous system and show that synaptobrevin cleavage may account for intracellular toxicity in Torpedo.