ABSTRACT
INTRODUCTION: We examined the possibility that tetanus toxin can prevent muscle atrophy associated with limb immobility in rats. METHODS: While the knee and ankle joints were immobilized unilaterally, the tibialis anterior (TA) muscle on the immobilized side was injected with 1 µl saline or with 1 ng tetanus toxin. After 2 weeks, TA wet weights, contractile forces, and myofiber sizes from the immobilized sides were compared with those from body weight-matched normal animals. RESULTS: Saline group wet weights decreased and produced less absolute twitch and tetanic force and normalized tetanic force compared with the toxin or normal groups. Cross-sectional areas of saline group type I, IIa, and IId myofibers, and the masses of saline group IIa, IId, IIb, and toxin group IIb myofibers, were smaller compared with the normal group. CONCLUSIONS: Tetanus toxin prevented common signs of muscle atrophy and may become a useful adjunct to current rehabilitation strategies.
Subject(s)
Immobilization/adverse effects , Muscle Contraction/drug effects , Muscle, Skeletal/physiopathology , Muscular Atrophy/prevention & control , Neurotoxins/therapeutic use , Tetanus Toxin/therapeutic use , Adenosine Triphosphatases/metabolism , Animals , Body Weight/drug effects , Disease Models, Animal , Dose-Response Relationship, Drug , Electric Stimulation , Extremities/physiopathology , Female , Functional Laterality/drug effects , Muscle, Skeletal/drug effects , Muscular Atrophy/etiology , Muscular Atrophy/pathology , Neurotoxins/pharmacology , Organ Size/drug effects , Rats , Rats, Sprague-Dawley , Tetanus Toxin/pharmacologyABSTRACT
Although the majority of agents with antiexcitotoxic action act as glutamate receptor antagonists, enzymatic degradation of glutamate can also be neuroprotective. The very low specific activity of the mammalian form of glutamate decarboxylase (GAD), the enzyme that catalyzes the formation of gamma-aminobutyric acid (GABA) from glutamate in neurons, is likely to limit its utility as an antiglutamate neuroprotectant. In contrast, the bacterial form of GAD can be isolated with relatively high specific activity and is most active in acidic environments. We have expressed and purified GAD from Escherichia coli (bGAD) and tested the ability of the enzyme to protect against glutamate excitotoxicity. Incubation of rat hipppocampal slices with the potassium channel antagonist tetraethyl ammonium (TEA) resulted in widespread excitotoxic death of pyramidal and granule cell neurons. bGAD alone showed no significant neurotoxicity and significantly reduced excitotoxicity induced by TEA. We hypothesize that bGAD may be internalized into the synaptic vesicle compartment by nonspecific endocytosis, where both the appropriate pH and high glutamate concentrations are present. Targeting of this enzyme to the interior of synaptic vesicles may enhance its potency as a neuroprotectant against excitotoxicity.