PERIPHERAL AXOTOMY INCREASES THE EXPRESSION OF GALANIN MESSAGE-ASSOCIATED PEPTIDE (GMAP) IN DORSAL-ROOT GANGLION-CELLS AND ALTERS THE EFFECTS OF INTRATHECAL GMAP ON THE FLEXOR REFLEX IN THE RAT

We have previously reported that galanin message-associated peptide (G MAP), a fragment of galanin precursor protein, occurs in a limited num ber of dorsal root ganglion (DRG) cells in rats with intact sciatic ne rves. In the present study, the localization of GMAP in dorsal root ga nglia, dorsal roots and dorsal horn was analyzed immunohistochemically and compared between rats with intact and sectioned sciatic nerves. F urthermore, the effects of intrathecal (i.t.) GMAP on the flexor refle x in rats with intact and sectioned nerves were examined. In rats with intact sciatic nerves, i.t. GMAP elicited a moderate facilitation of the flexor reflex. The facilitation of the flexor reflex induced by co nditioning stimulation (CS) of cutaneous C-fibers was strongly blocked by GMAP. GMAP also selectively antagonized the reflex facilitatory ef fect of i.t. substance P (SP), but not i.t. vasoactive intestinal pept ide (VIP). Unilateral sciatic nerve section induced an upregulation of GMAP in the ipsilateral dorsal root ganglia 2 weeks after axotomy. Th e effect of GMAP on the baseline reflex was similar in normal and axot omized rats, but the blocking effect of GMAP on C-fiber CS-induced fac ilitation was significantly reduced after axotomy. GMAP did not antago nize the reflex facilitatory effect of SP after axotomy, whereas an an tagonism on VIP-induced facilitation was observed. The possible role o f GMAP in spinal transmission and comparison with the effects of galan in are discussed.