The mechanism of action of botulinum toxin is:
Ans: a (Inhibits synthesis of Acetyl choline)Ref: Tripathi 6th ed. Pg. 93Botulinum toxin acts by inhibiting the release of acetyl choline from synaptic vesicles to the synaptic junction. So it indirectly inhibits its synthesis. This is the best option.Synthesis of Acetyl cholineAcetyl choline is actively transported into synaptic vesicles and is then stored there. It is then released to the synaptic junction by exocytosis.Here the Ach is immediately hydrolyzed by the enzyme cholinesterase and choline is recycledNote: Hemicholinium- blocks choline uptakeVesamicol- blocks active transport of Ach into synaptic vesicle where it is storedBotulinum toxin- inhibits the release of Ach from synaptic vesiclesBlack widow spider- it induces massive release of Ach and depletionClostridium botulinum* gram +ve bacillus, anaerobic with subterminal oval bulging spores* spores are heat and radiation resistant! but botulinum toxin is heat labile)* depending upon the toxin it has 8 types(A. B, C1, C2, D. E, F, G), all are neurotoxin except C2 which is a cytotoxin* Clostridium toxin is the most toxic substance known;(lethal dose 1 -2 ug) a type of exotoxin liberated by the autolysis of the cell* MOA: blocks the release of acetyl choline at peripheral cholinergic neurons irreversibly ( but CNS is not involved (AI2007)* Characteristic pattern is symmetrical descending paralysisBotulismFood borne botulismWound botulismInfant botulismDue to ingestion of preformed toxinToxin produced at the site of woundToxico infectionSpores ingested in food get established in the gut & produce toxinToxin A B & EToxin AInfants < 6 mSource- preserved meat products, canned vegetables Symp; vomiting thirst, constipation, dysphagia, dysarthria, diplopia, resp. failureSymp: same as food botulism except GIT symptomsConstipation, poorfeeding, lethargy, weak/ altered cry, floppiness, loss of head controlRx: trivalentantitoxin, laxatives, respiratory effort, penicillin (least important) Rx: supportive careAssisted feedingAntitoxin, antibiotics are not indicated.Botulism toxin is used for therapeutic uses also:TOXIN ATOXIN BStrabismusCervical dystoniablepharospasm Cervical dystonia, glabellar lines
Inhibits synthesis of acetyl choline
Inhibits nicotic receptors at the myoneuronal junction
Increases synthesis of Ach
Inhibits reuptake of Ach
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