Botulinum toxin blocks neurotransmitter release from somata of rat neuropathic trigeminal ganglion neurons

Abstract

Many patients with trigeminal neuropathies suffer severe chronic pain which is inadequately alleviated with centrally acting drugs that possess severe side effects. One strategy is to develop new treatments by targeting peripheral sensory neurons whose excitability and neurotransmitter release is increased in chronic pain states. Such treatment may include newly developed Botulinum toxin type A 150 kDa (BoNT), which reportedly blocks vesicular neurotransmitter release. Recently, an experimental animal model of trigeminal neuropathy (TN) has been developed. We set out to determine whether neurotransmitter release from somata of sensory neurons increases in the TN model and if it can be attenuated by BoNT. Thus, we monitored the secretory activity of acutely dissociated trigeminal ganglion (TRG) neurons from TN and naive rats by measuring the fluorescence intensity of the membrane-uptake marker FM4-64. FM4-64 staining showed that neurons possess a pool of recycled vesicles which could be released by high KCl (75 mM) application. TRG neurons (n=15) from TN rats exhibited significantly greater FM4-64 dye release than naive rat neurons (n=32). BoNT significantly reduced FM4-64 dye release after KCl-stimulation. These results indicate that the exaggerated neurotransmitter release from neuropathic TRG neurons may be attenuated by BoNT. Supported by NIH DE014573, Ministry of Education, Science and Culture in Japan 18390512 and Ryobi Teien Memorial Foundation.