title: Time course for the reappearance of vibrissal motor representation following botulinum toxin injection into the vibrissal pad of the adult rat.
abstract: The present study investigates the time course and pattern of movement representation recovery in the motor cortex during the recovery after a peripheral paralysis. To this end a transitory flaccid paralysis of the vibrissae muscle was induced in adult rats that underwent two unilateral injections of 8 U of botulinum toxin (BTX) into a vibrissal pad, at a duration of 12 days from one another. The compound muscle action potential (MAP) of the vibrissae muscle began to reappear 4 weeks after the first BTX injection. Intracortical microstimulation (ICMS) was used to map rat motor cortices 4, 5, 6, 7 and 8 weeks after the first BTX injection. Findings demonstrated that: (i) contralateral vibrissae movement reappears in the medial part of its normal cortical territory when the MAP is almost 10% of the control value; in the remaining part, ICMS elicits eye, ipsilateral vibrissae, neck and forelimb movements; (ii) the contralateral vibrissae movement reappears in sites where ipsilateral vibrissae and/or neck movement are co-represented; (iii) as MAP recovers, the vibrissae representation expands until it recovers the 90.8% of its territory after 7 weeks, when the MAP was almost 43.4% of the control value; (iv) from 4 to 7 weeks, the ICMS-evoked contralateral vibrissae movement shows a significantly higher electrical threshold vs. the control group; (v) recovery of the baseline excitability uniformly involves the vibrissae representation 1 week later, after its cortical territory has recovered 93.1% of the control value and the MAP has returned to 78.8% of the baseline value.
authors.affiliation: Centro di Neuroscienze and Dipartimento di Scienze Biomediche e Terapie Avanzate, Sezione di Fisiologia umana, Università di Ferrara, 44100 Ferrara, Italy. fhg@dns.unife.it
authors.forename: G
authors.initials: G
authors.lastname: Franchi
authors.forename: C
authors.initials: C
authors.lastname: Veronesi
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001905:Botulinum Toxins / Q000008:administration & dosage / Q000633:toxicity*; D001931:Brain Mapping; D005071:Evoked Potentials / Q000502:physiology*; D005552:Forelimb; D005625:Frontal Lobe / Q000473:pathology / Q000503:physiopathology*; D023421:Models, Animal; D009044:Motor Cortex / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values; D013997:Time Factors; D014738:Vibrissae / Q000187:drug effects / Q000502:physiology*
chemical_list: D001905:Botulinum Toxins