Ontogeny of isolation rearing-induced deficits in sensorimotor gating in rats

Presentation of a weak stimulus immediately before a startling stimulus decreases the magnitude of the resultant startle response. This phenomenon, termed prepulse inhibition (PPI), provides an operational measure of sensorimotor gating, and is deficient in schizophrenia patients. Clinically observed PPI deficits can be modeled in rodents by housing rats individually from weaning until adulthood. The developmental time course of isolation rearing-induced PPI deficits, however, is unknown. The present studies characterized the ontogeny of isolation-induced PPI deficits and hyperactivity. Separate groups of Sprague-Dawley and Lister hooded rats were either singly housed (ISO) or socially housed (SOC, groups of two to three per cage) upon weaning and then maintained in these housing conditions for different periods of time until assessment of PPI and locomotor activity; animals were tested at time points that roughly corresponded to before puberty (2 weeks postweaning), during puberty (4 weeks postweaning), or after puberty (6-7 weeks post weaning). PPI deficits were seen in Sprague-Dawley ISO rats at either the 4- or 6-, but not the 2-week time points. In contrast, hyperactivity was noted in these animals starting at the 2-week time point. Lister rats showed the same general pattern of ISO-induced effects, with ISO-induced hyperactivity (observed 4 weeks postweaning) preceding ISO-induced PPI deficits (observed 7 weeks postweaning). Therefore, ISO produces dissociable effects on PPI and locomotor activity, with PPI deficits emerging only during or after puberty. ISO might thus provide a useful noninvasive tool with which to study the neural substrates of delayed-onset sensorimotor gating abnormalities.