Systemic amitriptyline administration does not prevent the increased thermal response induced by paradoxical sleep deprivation

Sleep deprivation has been associated with hyperalgesia in humans and in animal models. The tricyclic antidepressant amitriptyline is used as an analgesic drug in patients and in animal models of chronic pain, including that associated with spinal nerve injury. Pain hypersensitivity following paradoxical sleep deprivation (PSD) and that following peripheral nerve injury seem to share common spinal mechanisms. Accordingly, we evaluated the effects of amitriptyline (acutely and chronically administered) on the increased thermal response observed in PSD rats (72 or 96 h). Rats were evaluated for thermal sensitivity using a hot plate (52 °C or 46 °C) at 1 or 24 h after the last administration of the drug. Following the hot plate test, motor behavior was analyzed in an open field arena for a period of 5 min. Paw withdrawal latency response to temperatures of 46 °C and 52 °C was significantly lower in PSD and in 24-hour post-PSD rats than in controls and it was not modified by amitriptyline (3, 10 and 30 mg/kg). Analgesic effects and reduced motor behavior were only observed in control groups. Overall, these findings indicate that a period of PSD can influence pain modulatory mechanisms, and that amitriptyline action is insufficient to reduce PSD-enhanced thermal sensitivity.