Effects of intrathecal nocistatin on the flexor reflex and its interactionwith orphanin FQ nociceptin

WE studied the effects of intrathecal (i.t.) nocistatin, a peptide identifi ed from the precursor of orphanin FQ/nociceptin (OFQ) on the spinal nocicep tive flexor reflex in decerebrate, spinalized, unanesthetized rats and its interaction with i.t. OFQ, Nocistatin induced a moderate, non-dose-dependen t facilitation of the flexor reflex without producing reflex depression whe reas i.t. OFQ induced a biphasic dose-dependent facilitatory and inhibitory effect. The facilitatory effect of low dose (0.55 pmol) OFQ was significan tly increased by nocistatin. On the other hand, the duration, but not magni tude, of reflex depression induced by a high (550 pmol) dose of OFQ was sig nificantly shortened by 5.5 nmol nocistatin. Thus, nocistatin interacts wit h OFQ in a complex fashion, increasing excitation and reducing inhibition. No evidence was obtained for an antinociceptive effect of nocistatin in rat spinal cord. (C) 1999 Lippincott Williams & Wilkins.