Functional deficits following neonatal dopamine depletion and Isolation housing: Circular water maze acquisition under pre-exposure conditions and motor activity

Seven experiments and several behavioural tests were performed to study the effects of housing condition and experimental test conditions upon the behavioural responses and performance of adult rats neonatally treated with 6-hydroxydopamine (6-OHDA, 100 ug intracisternally, i.c.) or with vehicle. Postnatal 6-OHDA induced locomotor and total activity hyperactivity and deficits in navigational learning in a circular swim maze that were blocked by pre-treatment with a dopamine (DA) reuptake inhibitor but not a noradrenaline (NA) reuptake inhibitor. Isolation-housing induced deficits in maze learning performance. Grouped housing improved the maze learning performance of 6-OHDA treated rats whereas vehicle treated rats that were isolation housed performed better following latent learning (LL) pre-exposure trials. 6-OHDA treated rats that received both Grouped housing and latent learning trials performed better on the spatial navigation task than those that received Grouped housing but no latent learning or Isolation housing and latent learning. Analysis of habituation quotients indicated marked deficits by 6-OHDA-treated rats suggesting inability to acquire this simple, nonassociative form of learning. Methylphenidate increased all three parameters of motor activity: locomotion, rearing and total activity, in both Isolation-housed and Group-housed rats from 60- to 90- or 120-min post-injection. NDO 008 induced variable and parameter-dependent effects: locomotion was elevated initially in both Isolated and Grouped rats by the compound and then reduced in the Isolated rats only whereas total activity was only elevated initially in the Isolated rats and unaffected in the Grouped rats. Rearing behaviour was reduced markedly, directly post-injection, in the Isolation-housed rats. DA, DOPAC and HVA concentrations in the striatum, nucleus accumbens, olfactory tubercle and midbrain were reduced but most markedly in the striatum. 5-Hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) concentrations were elevated in the striatum, nucleus accumbens (not 5-HIAA) and olfactory tubercle.