Abstract
Galanin message associated peptide (GMAP), the C-terminal flanking peptide in the precursor protein of galanin, has been studied to established whether this peptide has its own biological action. With some exceptions, GMAP is generally co-localized with 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 identification of endogenously occurring fragments of GMAP. Nerve injury is one incident which regulates the expression of the precursor protein of galanin/GMAP. Two weeks after axotomy of the sciatic nerve in rat the effect of intrathecal GMAP on the flexor reflex becomes altered in comparison to animals with intact sciatic nerves.
The effect of GMAP on baseline flexor reflex was not changed, but the effect on the facilitation induced by conditioning stimuli (CS) was strongly decreased and GMAP could only weakly antagonise the facilitation. This was in contrast to the dose dependent manner GMAP antagonised the effect of CS in animals with intact sciatic nerves. Interactions with substance P (SP) and vasoactive intestinal peptide (VIP) effects in the flexor reflex were also changed after axotomy. SP-induced excitation of the flexor reflex was not inhibited by GMAP following axotomy as it was in normal rats. In contrast, the effect of VIP was antagonised in axotomized animals by GMAP. Modulation by putative synthetic fragments of GMAP of the flexor reflex were investigated. At least two of the fragments exert significant pharmacological activity.
In degradation studies of GMAP in vitro, five degradation products were isolated with high performance liquid chromatography. Their amino acids composition were analysed. The pharmacological effects of the fragments were studied in the flexor reflex and were shown to partially mimic the effects of 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 was synthesized by solid phase method in the beginning of this project, which created a lot of problem with very low yield of the peptide. Recently we successfully expressed recombinant GMAP with the QIAGEN expression system which will open possibilities to further studies of GMAP in the future.
