Effect of thyrotropin-releasing hormone on the neurologic impairment in rats with spinal cord injury: treatment starting 24 h and 7 days after injury

Abstract

The effect of treatment with thyrotropin-releasing hormone (TRH) or naloxone on the neurologic impairment after spinal cord injury was studied in rats with the severest neurologic impairment (complete paraplegia, no withdrawal response upon tail pinching, and urinary incontinence) 24 h and 7 days after injury. Subcutaneous treatment with TRH (2.5, 10 and 40 mg kg per day) once daily for 7 consecutive days starting 24 h or 7 days after injury improved the neurologic function in the rats with cord injury in a dose-related manner, with a minimum effective dose of less than 2.5 mg kg per day in both cases. However, subcutaneous treatment with naloxone (40 mg kg per day) once daily for 7 consecutive days starting 24 h after injury did not exert any beneficial effects on neurologic function. These results indicate that TRH but not naloxone treatment starting 24 h and as late as 7 days after injury is effective in rats with the severest neurologic impairment following spinal cord injury. Thus, it is suggested that the duration of the effectiveness of late treatment with TRH on the neurologic impairment in rats with spinal cord injury is more than 1 week, while the duration with naloxone is less than 24 h.