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.

Phenobarbital-induced brain growth retardation in artificially reared rat pups

Phenobarbital was administered daily to rat pups during the period of their brain growth spurt. A new technique for artificially rearing rat pups, using chronic intragastric feeding cannulas, was used to prevent drug-induced undernutrition. Rats, receiving neonatal phenobarbital, experienced a marked interruption of early brain growth, although their body weights reflected normal growth.

Exaggerated avoidance of novel stimulation in rats partially recovered from central norepinephrine damage

Rats in which central norepinephrine lesions are made with 6-OHDA and a recovery period allowed show a behavioral syndrome distinct from controls, from rats with more extensive norepinephrine damage (lesioned with 6-OHDA, allowed to recover, and relesioned), and from rats with general depletion of serotonin (chronic PCPA). These rats administered central 6-OHDA injections and then allowed a recovery period rear less in open field than all other groups and are characterized by an exaggerated avoidance of novel visual stimulation in light onset and light escape tests. It is proposed that this reflects the hyperresponsivity of partially repaired, supersensitive norepinephrine circuitry to novel or intense stimulation.