Age-related changes in the target dependence of motoneurones are well-documented for the early neonatal period. However, the extent to which this applies to adult and aged animals is unclear. Here we have used a facial nerve avulsion model to compare axotomy-induced motoneuronal death with age-related changes in the peripheral target across the lifespan of the rat. The right facial nerve was avulsed as it emerged from the stylomastoid foramen in groups of 4-6 anaesthetised Sprague-Dawley rats aged 7 days (young), 3 months (adults) and 24 months (ageing). Anaesthetised rats were perfused with fixative 0 to 30 days later and numbers of motoneurones were determined stereologically using an optical disector method adapted for the confocal microscope. Mean numbers and areas of muscle fibres, and extent of immunohistochemical staining of intramuscular axons using PGP9.5 were also determined. An 85% loss of motoneurones was seen in young rats by 7d following nerve avulsion (p<0.001, vs non-op), 71% were lost in adults rats by 14 days (p>0.0001,vs non-op) and 75% by 30 days (p<0.05, vs non-op). Only 41% of motoneurones were lost in ageing rats by 30 days (p<0.05). Compared to young rats, mean muscle fibre area was larger in both adult- (1,193%, p<0.001) and ageing- rats (882%, p<0.01), whereas mean muscle fibre number per unit area was smaller in adult- (12%, p<0.05) and ageing- (16%, p<0.05) rats. Compared to young rats, PGP9.5 immunostaining was reduced to 46% in adult-(p<0.0001) and 54% in ageing- (p<0.01) rats. Our result show that avulsed facial motoneurones die more slowly and in reduced amounts as rats age. This is paralleled by marked changes in muscle between young and adult rats. In contrast, muscle in both adult- and ageing- rats is similar, yet far fewer ageing motoneurones are lost after avulsion. This may reflect a further reduction of motoneuronal target-dependence between adulthood and old age.
|Number of pages||1|
|Publication status||Published - 2014|
|Event||Society for Neuroscience Meeeting - Washington, United States|
Duration: 15 Nov 2014 → 19 Nov 2014
|Conference||Society for Neuroscience Meeeting|
|Period||15/11/14 → 19/11/14|