Peripheral nerve transaction (distal axotomy) is often used to study motoneuronal degeneration in immature animals, but it causes little or no loss of motoneurones in the adult. This makes it difficult to adduce data based on studies of the immature motor system to conditions where motoneuronal degeneration occurs in adulthood or later life. We have used facial nerve avulsion, which produces a proximal axotomy, to cause motoneuronal degeneration across the lifespan of the rat and have used this model to compare the magnitude and time course of motoneuronal loss at different ages. The facial nerve of groups of anaesthetised Sprague Dawley rats aged 7d (young), 3m (adult) or 24m (ageing) was avulsed unilaterally at the stylomastoid foramen and the intracranial portion of the nerve delivered from the facial canal. After 2d to 3m anaesthetised rats were perfused with fixative and serial Vibratome sections cut through the facial nucleus. On sections selected systematically and randomly, numbers of motoneurones were estimated bilaterally using an optical disector method modified for use in the confocal microscope. In young rats, 64% of motoneurones had been lost by 2d and 85% by 7d (p<0.001). In contrast, only 35% of adult rat motoneurones were lost by 7d (p<0.01) and no significant loss of ageing motoneurones was found at this time. By 14d, 71% of motoneurones in adult rats had been lost (p<0.001), with no significant loss in ageing rats. Little further loss of motoneurones was seen in adult rats at 1m (75%) and 3m (80%). Moderate (41%) motoneurone loss was seen by 1m in ageing rats (p<0.05). We show that a similar loss of motoneurones occurs after facial nerve avulsion of both young and adult rats, but this takes longer in adult rats. Ageing rats lose least motoneurones and this takes longest to develop. Whether these age-related differences reflect changes in the time-course- or the absolute nature- of the degenerative response of motoneurones to injury is unknown. Such information might help explain the failure in adult and ageing individuals of neuroprotective strategies developed in neonates.
|Number of pages
|Published - 2011
|Society for Neuroscience Meeting - Washington, United States
Duration: 12 Nov 2011 → 16 Nov 2011
|Society for Neuroscience Meeting
|12/11/11 → 16/11/11