Central neurotransmitters and mechanism of antinociceptive effect of botulinum toxin type A

Novi dokazi ukazuju da je antinociceptivno djelovanje botulinum toksina tipa A (BT-A) središnjeg porijekla. U ovom doktorskom radu smo provjerili ovu pretpostavku u ranije nedovoljno istraženim oblicima boli, istraživali interakciju sa središnjim neurotransmitorima kao mogući mehanizam djelovanja te pokušali pobliže utvrditi mjesto djelovanja toksina u središnjem živčanom sustavu (SŽS). Ispitivanja su izvedena na mužjacima Wistar štakora. U upalnoj, neuropatskoj i bilateralnoj mišićnoj boli ispitan je učinak selektivnih i neselektivnih antagonista opioidnih i GABAA receptora, primijenjenih sistemski, spinalno ili supraspinalno, na antinociceptivno djelovanje periferno (supkutano u šapu) primijenjenog BT-A. U tkivu kralješnične moždine ispitana je aktivacija neuronalnih i glija stanica, ekspresija mRNA proupalnih citokina i μ-opioidnih receptora te ekspresija Leu/Met-enkefalina metodama imunofluorescencije i lančane reakcije polimerazom s reverznom transkripcijom. Istraživano je antinociceptivno djelovanje BT-A nakon periferne, spinalne i supraspinalne primjene te je imunofluorescencijom ispitana enzimska aktivnost BT-A u tkivu SŽS-a. Opioidni i GABAA antagonisti su ovisno o dozi, sistemski i intratekalno, ali ne i supraspinalno, poništili antinociceptivno djelovanje BT-A u svim ispitanim modelima. Učinak antagonista bio je kratkotrajan. BT-A je smanjio neuronalnu aktivaciju u dorzalnom rogu kralješnične moždine, što su antagonisti blokirali. BT-A je smanjio bol u dosad neistraženim modelima visceralne boli (peritonitis, kolitis). Bilateralno antinociceptivno djelovanje BT-A posljedica je prisutnosti toksina samo na ipsilateralnoj strani. BT-A je smanjio bol nakon periferne i intratekalne primjene, dok primijenjen supraspinalno (cisterna magna, moždane komore) nije djelovao, unatoč nalazu njegove enzimske aktivnosti u pojedinim regijama mozga uključenima u nocicepciju. BT-A ima segmentalno antinociceptivno djelovanje spinalnoj razini, uz neizravnu aktivaciju endogenog opioidnog i GABA-ergičkog sustava. Ovi bi nalazi mogli biti važni za klinička ispitivanja potencijalno korisnih sinergističkih interakcija s konvencionalnim analgeticima i drugim lijekovima te usmjeriti klinička ispitivanja na nove indikacije i nove načine primjene, poput intratekalne.Novel evidence suggests that the antinociceptive effect of botulinum toxin type A (BT-A) is of central origin. In this doctoral thesis, we verified this assumption in previously insufficiently investigated types of pain, investigated the interaction with central neurotransmitters as the possible mechanism of action and tried to determine the site of the toxin’s action within the central nervous system (CNS). Male Wistar rats were used in experiments. We examined the effect of selective and nonselective opioid and GABAA antagonists, applied systemically, spinally and supraspinally, on antinociceptive effect of peripherally (subcutaneously into hind paw) applied BT-A in inflammatory, neuropathic, and bilateral pain. Neuronal and glial cells’ activation, proinflammatory cytokines’ and μ-opioid receptors mRNA expression, and Leu/Met-enkephalin protein expression were analyzed using immunofluorescence and quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) in lumbar spinal cord tissue. Further, we investigated the antinociceptive effect of BT-A following peripheral, spinal and supraspinal application. In parallel, enzymatic activity of BT-A in CNS tissue was examined using immunofluorescence. Opioid and GABAA antagonists, applied systemically and intrathecally, dose-dependently abolished the antinociceptive effect of peripheral BT-A in all tested models, while no effect was observed following their supraspinal application. The effect of antagonists was short-lasting. BT-A reduced neuronal activation in dorsal horn, which was abolished by both, opioid and GABAA antagonist. BT-A diminished pain in, yet uninvestigated, models of visceral pain (peritonitis and colitis). BT-A’s bilateral antinociceptive action occurs after toxin’s presence on ipsilateral side only. BT-A reduced pain after peripheral and intrathecal application, but not after application in cisterna magna or cerebral ventricles, despite of its enzymatic activity in brain regions involved in nociception. BT-A has segmental antinociceptive effect at the spinal level, which involves an indirect activation of endogenous opioid and GABA-ergic systems. These findings might guide clinical investigations of potentially useful additive or synergistic effects with conventional analgesics and direct clinical trials for novel indications and the routes of application, like intrathecal

Antinociceptive action of botulinum toxin type A in carrageenan-induced mirror pain

"Mirror pain" or mirror-image pain (MP) is pain opposite to the side of injury. Mechanism and frequency in humans are not known. There is no consent on therapy. Here we report that unilaterally injected botulinum toxin type A (BT-A) has bilateral effect in experimental MP, thus deserves to be investigated as therapy for this condition. We examined the localization of BT-A's bilateral antinociceptive action in MP induced by 3 % carrageenan intramuscular injection in Wistar rats. BT-A was applied peripherally (5 U/kg), into ipsilateral or contralateral hind paw pad (i.pl.) and centrally (1 U/kg), at spinal (intrathecally, i.t.) or supraspinal (intracisternally, i.c.) level. Additionally, we examined the involvement of central opioid and GABAergic systems, as well as the contribution of peripheral capsaicin-sensitive neurons to BT-A's bilateral antinociceptive effect. Ipsilateral i.pl. and i.t. BT-A reduced the bilateral mechanical sensitivity to von Frey filaments, while contralateral i.pl. and i.c. treatments had no effect on either tested side. Bilateral antinociceptive effect of ipsilateral i.pl. BT-A was prevented by μ-opioid antagonist naloxonazine (1.5 μg/10 μl) and GABAA antagonist bicuculline (1 μg/10 μl) if applied at the spinal level, in contrast to supraspinal application of the same doses. Local treatment of sciatic nerve with 2 % capsaicin 5 days following BT-A i.pl. injection caused desensitization of sciatic capsaicin-sensitive fibers, but did not affect bilateral antinociceptive effect of BT-A and the presence of cleaved SNAP-25 at the spinal cord slices. Present experiments suggest segmental actions of peripheral BT-A at spinal level, which are probably not solely dependent on capsaicin-sensitive neurons