Effect of Cerebellar Granule Cell Depletion on Learning of the Equilibrium Behaviour: Study in Postnatally X-irradiated Rats

• Published in: The European journal of neuroscience 1997-11, Vol.9 (11), p.2472-2478
• Main Authors: Le Marec, N., Stelz, T., Delhaye-Bouchaud, N., Mariani, J., Caston, J.
• Format: Article
• Language: English
• Subjects: Aging - physiology; Animals; Animals, Newborn; balance; Behavior, Animal - physiology; Behavior, Animal - radiation effects; cerebellum; Cerebellum - cytology; Cerebellum - physiology; Cerebellum - radiation effects; Cytoplasmic Granules - physiology; Cytoplasmic Granules - radiation effects; Learning - physiology; Learning - radiation effects; motor behaviour; Neural Pathways - cytology; Neural Pathways - physiology; Neural Pathways - radiation effects; ontogenesis; Postural Balance - physiology; Postural Balance - radiation effects; Rats; Rats, Inbred Strains; training; X-Rays
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/j.1460-9568.1997.tb01664.x

To assess the role of the mossy fibre‐granule cell pathway in learning, the cerebellum of young DA/HAN strain rats was irradiated to make the cortex completely or partially agranular. The X‐rays were delivered according to two different schedules, between 5–14 postnatal days (early group) and between 10–14 postnatal days (late group). Histological controls at 35 days showed a mean loss of granule cells of 96 ± 1% in the early group and of 61 ± 3% in the late group. The irradiated animals were subjected, from day 23 to day 35, to daily sensorimotor training on a rotorod. The scores and the strategy used (walking or hanging) by the rats were noted. The results demonstrate that a partial loss of granule cells due to a late X‐irradiation schedule induced mild motor disabilities but no learning deficit, the only problem being difficulty in elaborating rapidly an efficient strategy to solve a novel problem. A sub‐total loss of the granule cells, due to an early X‐irradiation schedule, induced gross motor disabilities and the animals used hanging >90% of the time. Due to the discrepancy between the learning abilities, which were preserved at least in part, and the gross motor impairments, the animals elaborated a novel strategy (jumping from the beam), allowing them to escape the experimental situation. This avoidance behaviour may be due to a decrease of anxiety, a lack of behavioural inhibition and/or attentional deficits that have been already observed in several other examples of cerebellar abnormalities.