Stages of recovery from central norepinephrine lesions in enriched and impoverished environments: a behavioral and biochemical study.

Adult rats were injected intraventricularly with 6-OHDA and allowed to recover for varying time periods in either an enriched colony environment or in isolation cages. When tested behaviorally in a novel environment, isolated animals showed a cyclical recovery pattern, with behavioral changes at 14 days after lesioning which were different from those seen at 2 and 45 days after lesioning. In contrast, animals housed in a colony environment showed progressive improvement and better recovery than isolates. Biochemical studies of uptake of H3NE and histofluorescence indicated that colony housed animals had enrichment effects (higher cortical NE uptake), but they were also more susceptible to 6-OHDA and did not recover well from the lesions. Isolated animals showed somewhat better recovery of NE uptake following 6-OHDA injections, especially in cortex. Because behavioral recovery from 6-OHDA was dissociated from biochemical indicators of recovery in NE circuitry, these results imply that brain systems other than NE were primarily responsible for the enhanced behavioral recovery which occurs in enriched environments.