Changes in brain catecholamine turnover and receptor sensitivity induced by social deprivation in rats

Catecholamine turnover was compared in two brain areas of rats housed under different social conditions. Rats reared in isolation for 6-8 weeks had a significantly lower noradrenaline turnover in the brainstem and lower noradrenaline and dopamine turnover in a brain segment comprising all other areas except the cerebellum, pineal gland, thalamus, and and subthalamus. In the open-field test, isolated rats were much more active than group-housed animals. Noradrenaline turnover increased in both brain areas of isolated rats but not in grouped animals after exposure to the open field. Hyperactivity was selectively reduced in isolated rats by chronic oral treatment with d-amphetamine, 5 mg/kg/24 h. It was also reduced 15 min after pretreatment with α-methyl-p-tyrosine 200 mg/kg. It is suggested that a prolonged period of reduced noradrenaline release may sensitise postsynaptic receptors in isolated rats. Hyperactivity appears to be associated with an increase in transmitter release onto sensitised receptors.