Effects of maternal separation on brain nociceptin/orphanin FQ peptide levels in male Wistar rats.

Environmental manipulation early in life may induce persistent alterations in adult behaviour and physiology. In this study, we investigated the long-term effects of daily maternal separation, Days 1-21, on brain immunoreactive nociceptin/orphanin FQ (ir-N/OFQ) levels in male Wistar rats. The rat pups were separated in litters for 360 min (MS360) or 15 min (H15). Control rats were left undisturbed until weaning. Peptide levels were measured at 10 weeks of age. In the hypothalamus and periaqueductal gray, MS360 induced an increase in ir-N/OFQ levels in comparison with control rats. H15 rats had increased ir-N/OFQ levels in the hypothalamus and the medial prefrontal cortex compared with control animals. The rats were also tested at two occasions in an elevated plus-maze. An increased anxiety-like behaviour was shown in MS360 rats at weaning, whereas a decreased anxiety response was found at 9 weeks of age compared with control rats. The study shows that early life experiences induce long-term effects on behaviour, as well as brain N/OFQ levels.