Long-term effects of a single 24-hour maternal separation on three different latent inhibition paradigms

Abstract

Basing animal models for psychiatric diseases on purely environmental manipulations would be a great asset in biological research, such as in the screening of antipsychotic drugs, since they preclude possible interference from pharmacologically induced deficits. Recent investigations have yielded evidence that a single 24-h maternal separation (MS) in rats during the stress hyporesponsive period (SHRP) alters hypothalamic-adrenal-pituitary (HPA) axis response in adult rats and produces long-term behavioral effects, such as deficits in sensorimotor gating (prepulse inhibition) and selective attention (latent inhibition [LI]), which have been related to schizophrenia. Since there are implications that the age of the pups at the time of separation may be a crucial parameter for the neuroendocrine and behavioral effects on adult animals, we investigated the effects of a single 24-h MS on postnatal day (PND) 4, 9, or 18 in unrelated adult male and female Wistar rats on three paradigms of LI: conditioned taste aversion (CTA), active avoidance (AA), and conditioned emotional response (CER). Whereas there was no effect of MS on CER, MS on PND 9 enhanced LI in the CTA paradigm, and MS on PND 18 disrupted LI in the AA paradigm in males only. Within subjects separated on PND 4, males displayed a severe learning deficit in the AA paradigm, and consequently LI was not observed. The results suggest that a single 24-h MS, irrespective of the developmental stage of the pups when separated, does not provide a robust animal model for adult disruption of selective attention similar to that observed in schizophrenia.