University of Zagreb. School of Medicine. Department of Pharmacology.
Abstract
Botulinum neurotoksin se koristi za liječenje spasticiteta i hiperkinetičkih poremećaja pokreta. Nedavna istraživanja su pokazala da BoNT/A, osim dobro poznatim perifernim učincima na neuromuskularnoj spojnici, inducira antispastički efekt djelovanjem na centralni živčani sustav. U ovoj studiji ispitali smo ulogu perifernih mišićnih te centralnih spinalnih učinaka BoNT/A na redukciju abnormalno povećanog tonusa mišića u štakorskom modelu lokalnog spasticiteta izazvanog TeNT-om, tijekom produljenog vremenskog razdoblja. Injekcijom TeNT-a (1.5 ng) u m.gastrocnemius štakora izazvali smo reverzibilnu spastičnu paralizu u trajanju od 3 tjedna. Nakon indukcije mišićnog spazma, aplicirali smo BoNT/A (5 U/kg) u spastični mišić. Životinje su podijeljene u 3 grupe: kontrolna grupa s primljenim TeNT + fiziološka + konjski serum, grupa TeNT + BoNT/A + konjski serum i grupa TeNT + BoNT/A + i.t. botulinum antitoksin. Videoanalizom i bihevioralnim testovima motorike- mjerenjem otpora na pasivnu dorzifleksiju gležnja, DAS skorom te BBB (Basso Beattie Breshnan) skalom ocjenjene su motoričke sposobnosti štakora. Studija je provedena slijepo i randomizirano. Dugotrajni učinci BoNT/A ispitani su kroz dulji vremenski period, ponavljanim injekcijama TeNT-induciranog spasticiteta. Intramuskularna aplikacija BoNT/A uzrokovala je redukciju lokalnog spasticiteta mišića, kojeg obilježava rigidna ekstenzija stražnje noge štakora. Tijekom perioda mlohave paralize (do 14 dana poslije i.m. injekcije BoNT/A), centralni učinci nisu imala utjecaja na antispastičku aktivnostu BoNT/A. Ipak, sekundarnom indukcijom spasticiteta TeNT-om (35 dana poslije BoNT/A), životinje koje su primile antitoksin (čime su onemogućeni centralni učinci) su na bihevioralnim testovima motorike pokazale manju redukciju spasticiteta, za razliku od onih koje nisu primile antitoksin. Tercijarnom indukcijom spasticiteta TeNT-om, ista grupa životinja koja nije primila antitoksin je i dalje pokazivala lokalni spazam manjeg stupnja, radi očigledne mišićne atrofije. Zaključno, osim perifernih učinaka BoNT/A na razvoj mlohave paralize, centralni učinci neurotoksina dolaze do izražaja dva do tri tjedna nakon aplikacije i uzrokuju redukciju spasticiteta. Konačno, nakon nastupa obiju učinaka dolazi do razvoja mišićne atrofije.Botulinum neurotoxin is used for the treatment of spasticity and hyperkinetic movement disorders. Recent research showed that, besides well-known peripheral action of BoNT/A on neuromuscular junction, the toxin induces an antispastic effect by affecting the central nervous system. In this study we examined the peripheral muscular and central spinal effects of BoNT/A on reduction of abnormal muscle tone in rat model of local spasticity provoked by TeNT, over prolonged observation period. By injecting TeNT (1.5ng) in m.gastrocnemius of a rat we induced a reversible spastic paralysis lasting for 3 weeks. After induction of muscular spasm, we injected BoNT/A (5 U/kg) into the spastic muscle. Animals were divided in three groups: control group which received TeNT + saline solution + horse serum, group TeNT + BoNT/A + horse serum and group TeNT + BoNT/A + i.t. botulinum antitoxin. Videoanalysis and bihevioural motor tests- ressistance to passive dorsiflexion of the ankle, DAS score and BBB (Basso Beattie Breshnan) scale were used to evaluate motor capabilities of rats. The study was blinded and randomized. Longterm effects of BoNT/A were examined over prolonged period of time, by repeated injections of TeNT-induced spasticity. Intramuscular application of BoNT/A caused reduction of local muscle spasticity, which was characterized by rigid extension of the hind paw. During the period of flaccid paralysis (up to 14 days after i.m. BoNT/A), the central effects didn't influence the antispastic activity of BoNT/A. However, after secondary induction of spasticity by TeNT (up to 35 days post i.m.BoNT/A), animals which received antitoxin (thus disabling central effects) showed lower reduction of spasticity on behavioural motor tests, unlike the ones who didn't receive the antitoxin. After tertiary induction of spasticity by TeNT, same group of animals which didn't receive the antitoxin, still exhibited local spasm of lower degree, apparently due to lasting muscle atrophy. In conclusion, besides peripheral effects of BoNT/A in development of flaccid paralysis, central effects of this neurotoxin came to the fore 2-3 weeks after peripheral application and caused reduction of spasticity. Finally, after both effects wore off, lasting muscle atrophy remained
