Elsevier

Neuroscience

Volume 117, Issue 1, 17 March 2003, Pages 97-104
Neuroscience

Research paper
Age, diet and injury affect the survival of facial motoneurons

https://doi.org/10.1016/S0306-4522(02)00762-5Get rights and content

Abstract

Using the model of facial nerve avulsion, we have compared the effects of injury, age and diet on motoneuronal survival. One to four weeks after nerve avulsion, 50–75% motoneuron loss was quantified in ad libitum-fed rats aged 7 days (neonate), 6 months (adult) and 24 months (aging) at the time of injury. Evidence of apoptosis was found for neonatal rats at 3 days post-injury, but not for neonates examined 7 days or adult or aging rats examined 1 month after injury. Non-operated, ad libitum-fed rats showed no significant loss of facial motoneurons by 24 months. Surprisingly, non-operated rats whose food intake was restricted to 15 g standard rat chow per day from the age of 6 months lost 50% of their motoneurons by 24 months. Facial nerve avulsion of 24-month-old rats raised on this restricted diet did not result in any additional loss of motoneurons one month after injury. These results challenge the common view that aging results in neuronal loss and that dietary restriction is universally beneficial.

Section snippets

Animals and surgery

Sprague–Dawley rats aged 7 days (neonate), 6 months (adult) or 24 months (aging) were used. Male rats were used for all adult and aging groups. Whole litters, comprising male and female rats, were used for all the neonatal groups. All animals were housed and maintained in the Royal Free and University College Medical School Comparative Biology Unit. All experimental procedures were carried out in accordance with Home Office and local ethical committee approval and appropriate steps were taken

Age-related loss of facial motoneurons in DR animals

Stereological analysis of the facial nuclei of ad libitum-fed rats (Table 1) revealed no significant motoneuron loss between 1 week (mean 3322 motoneurons), 6 months (mean 3099 motoneurons) and 24 months of age (mean 2531 motoneurons) when data for left and right nuclei were combined. In contrast, 24-month-old DR rats had only 1400–1600 motoneurons in each nucleus (Table 1). This represented a loss of approximately 50% of motoneurons (P=0.05) from the onset of DR at 6 months of age.

Retrograde response

In all

Discussion

We report that DR of rats is associated with the loss of facial motoneurons by 24 months of age, whereas ad libitum-fed rats aged 24 months showed no significant loss. In addition, those motoneurons remaining at 24 months of age in DR rats are resistant to nerve avulsion-induced death, whilst this type of nerve injury provokes motoneuronal loss in ad libitum-fed rats aged 7 days, 6 months and 24 months. These results are surprising, as DR increases longevity in rodents and reduces the

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