Behavioural and neurochemical effects of early social deprivation in the rat.

The behavioural and neurochemical sequelae of rearing in early social isolation are reviewed. Rats isolated from their peers at ~ 20 days of age are hyperactive, exhibit ambivalent responses to novelty, altered response to stressors, and cognitive impairments when tested as adults. They also overrespond to stimuli predictive of reinforcement, as shown by their elevated levels of conditioned activity when the presentation of food reliably follows daily activity tests in photocell cages. The dose-effect curve for D-amphetamine is shifted to the left in this situation, confirming the enhanced locomotor and stereotyped behaviours seen following systemic treatment with a variety of other psychomotor stimulant drugs. In vivo measurement of amine activity in isolates using microdialysis shows elevations in dopamine concentration in both the nucleus accumbens (ventral striatum) and the caudate-putamen. There are also changes in central 5-HT metabolism. These results are considered in the light of recent studies in isolates using the latent inhibition or pre-pulse inhibition procedures, two putative models of the attentional dysfunction in schizophrenia. Finally, the implications of these findings are considered and future problems requiring resolution are raised.