The effect of galanin message-associated peptide in spinal sensory processing

The effect of Galanin Message-Associated Peptide in spinal sensoryprocessing Galanin message associated peptide (GMAP), the C-terminal flanking peptide inthe precursor protein of galanin, has been studied to established whether this peptidehas its own biological action. With some exceptions, GMAP is generally colocalizedwith galanin in the central nervous system as well as the peripheral nervous system.This study was focused on the effect of GMAP in spinal sensory processing and identificationof endogenously occurring fragments of GMAP. Nerve injury is one incident which regulatesthe expression of the precursor protein of galanin/GMAP. Two weeks after axotomyof the sciatic nerve in rat the effect of intrathecal GMAP on the flexor reflex becomesaltered in comparison to animals with intact sciatic nerves. The effect of GMAP onbaseline flexor reflex was not changed, but the effect on the facilitation inducedby conditioning stimuli (CS) was strongly decreased and GMAP could only weakly antagonisethe facilitation. This was incontrast to the dose dependent manner GMAP antagonisedthe effect of CS in animals with intact sciatic nerves. Interactions with substanceP (SP) and vasoactive intestinal peptide (VIP) effects in the flexor reflex werealso changed after axotomy. SP-induced excitation of the flexor reflex was not inhibitedby GMAP following axotomy as it was in normal rats. In contrast, the effect of VIPwas antagonised in axotomized animals by GMAP. Modulation by putative synthetic fragmentsof GMAP of the flexor reflex were investigated. At least two of the fragments exertsignificant pharmacological activity. In degradation studies of GMAP in vitro, fivedegradation products were isolated with high performance liquid chromatography. Theiramino acids composition were analysed. The pharmacological effects of the fragmentswere studied in the flexor reflex and were shown to partially mimick the effectsof the whole GMAP sequence. GMAP mediated effect on adenylate cyclase and guanylatecyclase were examined to evaluate the coupling to G-protein connected receptors.GMAP had poor affinity to the galanin receptor with a ICso value on 104 M. GMAP wassynthesized by solid phase method in the beginning of this project, which createda lot of problem with very low yield of the peptide. Recently we successfully expressedrecombinant GMAP with the QIAGEN expression system which will open possibilitiesto further studies of GMAP in the future. Key words: galanin, galanin message-associated peptide, spinal cord, flexor reflex,nociception ISBN 91-628-2656-