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Central effects of botulinum toxin type A: Evidence and supposition

Authors

  • Antonio Currà MD,

    1. Dipartimento di Scienze Neurologiche and Istituto Neurologico Mediterraneo Neuromed IRCCS, Università degli Studi di Roma “La Sapienza,” Italia
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  • Carlo Trompetto MD,

    1. Dipartimento di Neuroscienze, Oftalmologia e Genetica, Università di Genova, Italia
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  • Giovanni Abbruzzese MD,

    1. Dipartimento di Neuroscienze, Oftalmologia e Genetica, Università di Genova, Italia
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  • Alfredo Berardelli MD

    Corresponding author
    1. Dipartimento di Scienze Neurologiche and Istituto Neurologico Mediterraneo Neuromed IRCCS, Università degli Studi di Roma “La Sapienza,” Italia
    • Dipartimento di Scienze Neurologiche, Università degli Studi di Roma “La Sapienza,” Viale dell'Università 30, 00185 Rome, Italy
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Abstract

No convincing evidence exists that botulinum toxin type A (BT-A) injected intramuscularly at therapeutic doses in humans acts directly on central nervous system (CNS) structures. Nevertheless, several studies, using various approaches, strongly suggest that BT-A affects the functional organization of the CNS indirectly through peripheral mechanisms. By acting at alpha as well as gamma motor endings, BT-A could alter spindle afferent inflow directed to spinal motoneurons or to the various cortical areas, thereby altering spinal as well as cortical mechanisms. Muscle afferent input is tightly coupled to motor cortical output, so that the afferents from a stretched muscle go to cortical areas where they can excite neurons capable of contracting the same muscle. The BT-A–induced reduction in spindle signals could, therefore, alter the balance between afferent input and motor output, thereby changing cortical excitability. © 2004 Movement Disorder Society

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