Isolation-induced locomotor hyperactivity and hypoalgesia in rats are prevented by handling and reversed by resocialization

Differences in locomotor activity in the open field were found between individually and group-housed rats (isol > soc). Daily handling, initiated at postnatal day 1, was without effect in group-housed rats but prevented the isolation-induced hyperactivity. For tail-flick latency, strikingly similar differences (isol > soc; prevention by handling) have been observed. The isolation-induced aberrations in both locomotor reactivity in a novel environment and in pain sensitivity could be reversed by subsequent resocialization. This indicates that the altered sensitivities to external stimuli are caused by the environmental manipulation.