Experimental neurology
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Experimental neurology · Feb 2005
Functional and electrophysiological changes after graded traumatic spinal cord injury in adult rat.
A graded contusion spinal cord injury (SCI) was created in the adult rat spinal cord using the Infinite Horizons (IH) impactor to study the correlation between injury severity and anatomical, behavioral, and electrophysiological outcomes. Adult Fisher rats were equally divided into five groups and received contusion injuries at the ninth thoracic level (T9) with 100, 125, 150, 175, or 200 kdyn impact forces, respectively. Transcranial magnetic motor-evoked potentials (tcMMEPs) and BBB open-field locomotor analyses were performed weekly for 4 weeks postinjury. ⋯ Comparison of tcMMEP responses with areas of WM loss or demyelination identified the medial ventrolateral funiculus (VLF) as the location of the tcMMEP pathway. Immunohistochemical and electromicroscopic (EM) analyses showed the presence of demyelinated axons in WM tracts surrounding the lesion cavities at 28 days postinjury. These data support the notion that widespread WM damage in the ventral and lateral funiculi may be a major cause for locomotor deficits and lack of tcMMEP responses after SCI.
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Experimental neurology · Feb 2005
Nerve growth factor injection into semispinal neck muscle evokes sustained facilitation of the jaw-opening reflex in anesthetized mice -- possible implications for tension-type headache.
Nociceptive input from neck muscles probably plays a role in the pathophysiology of tension-type headache. In order to elaborate an animal model, the impact of noxious input from neck muscles on orofacial sensorimotor processing was investigated by electrophysiological means in anesthetized mice. Group IV muscle afferents of the semispinal neck muscle were excited by local injection of nerve growth factor (NGF, 0.8 microM, 20 microl). ⋯ After intramuscular injection of isotonic saline into the right semispinal neck muscle (20 microl), the JOR remained unchanged (n = 10). Local NGF injection into neck muscles evoked noxious input to the brainstem that induced a sustained central facilitation of the JOR for more than 1 h. This long-term facilitation of orofacial sensorimotor processing by a singular NGF injection possibly reflects plastic changes of nociceptive synaptic processing that may be involved in the pathophysiology of headache.
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Experimental neurology · Feb 2005
Intrinsic neural circuits between dorsal midbrain neurons that control fear-induced responses and seizure activity and nuclei of the pain inhibitory system elaborating postictal antinociceptive processes: a functional neuroanatomical and neuropharmacological study.
The blockade of GABA-mediated Cl(-) influx with pentylenetetrazol (PTZ) was used in the present work to induce seizures in Rattus norvegicus. The aim of this work was to study the involvement of monoamines in the antinociception induced by convulsions elicited by peripheral administration of PTZ (64 mg/kg). The analgesia was measured by the tail-flick test in seven or eight Wistar rats per group. ⋯ The functional neuroanatomical study of the neural link between the mesencephalic tectum and nuclei of the central pain inhibitory system showed evidence for the interconnection between superior colliculus, both dorsal and ventral periaqueductal gray matter (PAG), and inferior colliculus. Defensive substrates of the inferior colliculus, also involved with wild running and epilepsy, send inputs toward dorsal raphe nucleus and locus coeruleus. Since these nuclei are rich in monoamines and send neural connections toward other monoaminergic nuclei of the brainstem involved with the control of the nociceptive inputs in the dorsal horn of the spinal cord, the present results offer a neuroanatomical and psychopharmacological basis for the antinociceptive processes following tonic-clonic seizures.
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Experimental neurology · Feb 2005
Stepwise motor and all-or-none sensory recovery is associated with nonlinear sparing after incremental spinal cord injury in rats.
Spinal cord injury (SCI) causes motor and sensory deficits that impair functional performance. While more functional recovery occurs with greater white matter sparing (WMS), it is unclear which locomotor features are more vulnerable to SCI than others, if recovery of certain features depends on specific amounts of WMS, and whether motor recovery patterns differ from sensory recovery. Locomotor and sensory recovery after graded contusive SCI with cord displacements of 0.3, 0.5, 0.7, 0.9, 1.1, 1.25, and 1.3 mm was examined for 6 weeks in 80 female Sprague-Dawley rats. ⋯ Mechanical allodynia developed only after injuries resulting in < or =10% WMS. Nonlinear motor and sensory recovery patterns suggest that small reparative changes may substantially improve function in individuals with SCI. A hierarchical locomotor recovery based on simple segmental versus complex supraspinal motor control is proposed.