ANTINOCICEPTIVE ACTION OF INTRATHECALLY ADMINISTERED IGF-I AND THE EXPRESSION OF ITS RECEPTOR IN RAT SPINAL-CORD

mRNA transcripts for insulin-like growth factor I (IGF-I) and its rece ptor are expressed in the lumbar region of the spinal cord. Accordingl y, we examined the involvement of IGF-I in nociceptive transmission. A n intrathecal injection of IGF-I (200-1000 ng) produced a dose-depende nt elevation in nociceptive threshold as indicated by tail flick/withd rawal latency. In contrast, comparable doses of insulin had no signifi cant effect. The time-response curve (15-75 min) revealed that the pea k for IGF-I's antinociceptive effect is attained at 30 min. Our data p rovide evidence that the IGF-I system within the spinal cord may serve as a target for novel analgesics.