Comparative study of the neuronal plasticity along the neuraxis of the vibrissal sensory system of adult rat following unilateral infraorbital nerve damage and subsequent regeneration |
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Authors: | Zsolt Kis Tamás Farkas Katalin Rábl Edina Kis Katalin Kóródi László Simon Ildikó Marusin Imre Rojik József Toldi |
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Institution: | (1) Department of Comparative Physiology, József Attila University, Szeged, POB 533, H-6701 Szeged, Hungary e-mail: toldi@bio.u-szeged.hu Tel.: +36-62-454149, Fax: +36-62-432486, HU |
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Abstract: | The aim of the present study was to examine the physiological consequences of a unilateral infraorbital nerve lesion and
its regeneration at different levels of the somatosensory neuraxis. In animals whose right infraorbital nerve had been crushed,
a large unresponsive area was found in the main brainstem trigeminal nucleus (Pr5). Responses evoked by ipsilateral vibrissal
deflection in the middle of Pr5 reappeared only on days 22–35 after the nerve had been transected, whereas recovery from the
nerve crush took only 7–9 days. However, no sign of short-term neuronal plasticity was observed in Pr5 after peripheral nerve
injury. An enlargement of the receptive fields in two-thirds of the units and a lengthening in the delay of the evoked responses
were observed as long-term plastic changes in Pr5 neurons after peripheral-nerve regeneration. In the ventral posteromedial
nucleus of the thalamus (VPM) of partly denervated animals, however, only minutes or hours after the nerve crush, certain
units were found to respond in some cases not only to the vibrissae, but also to mechanical stimulation of the face over the
eye (two units), the nose (one unit), and the midline (one unit). Apart from the experiments involving incomplete denervation,
the vibrissal representation areas of the VPM were unresponsive to stimulation of both the vibrissae and other parts of the
face until nerve regeneration had occurred. In the somatosensory cortex, an infraorbital nerve crush immediately resulted
in a large cortical area being unresponsive to vibrissal deflection. It was noteworthy, however, that shortly after the nerve
crush, this large unresponsive whisker representation cortical area was invaded from the rostromedial direction by responses
evoked by stimulation of the forepaw digits. In spite of the reappearance of vibrissa-evoked responses 7–10 days after the
nerve crush, an expanded digital representation could still be observed 3 weeks after the nerve crush, resulting in an overlapping
area of digital and vibrissal representations. The withdrawal of the expanded representation of forepaw digits was completed
by 60 days after the nerve crush. The results obtained in Pr5, the VPM, and the cortex strongly suggest that the higher the
station in the neuraxis, the greater the degree of plasticity after infraorbital nerve injury.
Received: 28 May 1998 / Accepted: 5 January 1999 |
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Keywords: | Neuronal plasticity Trigeminal system Somatosensory cortex Nerve injury Nerve regeneration |
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