The Effects of Dsip on Pain Threshold During Light and Dark Periods in Rats are not Naloxone-Sensitive

Abstract
The effects of Delta-Sleep-Induced Peptide (DSIP) were examined in rats kept at 12:12 light:dark schedule. The peak of the circadian pain threshold of saline-treated rats occurred at 10:00. Rats treated with 0.1 mg/kg, i.p. DSIP exhibited a significantly higher pain threshold level (as measured by hot plate) both in the light and dark periods. Prior to the treatment the peak was at 10:00. With treatment the peak shifted to 18:00. A dose of 1.0 mg/kg DSIP increased the pain threshold level only during the dark period. The analgesia induced by DSIP is insensitive to naloxone pretreatment.