Subjects were male Sprague Dawley rats derived from 21 timed pregnant female Sprague Dawley rats (Charles River Laboratories, INC, Wilmington, MA) received from the supplier at 14 days gestation. A third of the selected dams were used for neuroanatomical and biochemical experiments and the remainder were used for behavioral experiments. Dams were monitored daily to determine the date of parturition. All dams selected for use in the present experiments gave birth to a litter containing up to five male pups. Pups remained undisturbed and co-housed with their dam and siblings from birth until weaning. A total of 80 rats were used in behavioral experiments and 32 rats were used in neuroanatomical and biochemical experiments. All experimental groups consisted of pups derived from a minimum of two separate litters. Rats used in the same experiment were held in a shared holding room maintained under a 12:12 light:dark cycle and temperature of 23 ± 1 °C to ensure similar sensory experience (i.e., shared visual, auditory, and some olfactory cues). Rats were given ad libitum access to food and water. All procedures were
