Proceedings of The Physiological Society
University College Dublin (2009) Proc Physiol Soc 15, PC205
Gut peptide hormones ghrelin and obestatin differentially effect structure and synaptic function of rat hippocampal neurones in vitro
R. P. Murphy1, K. J. Murphy1, M. Pickering1
1. School of Biomolecular and Biomedical Sciences, University College Dublin, Dublin 4, Ireland.
Ghrelin and obestatin, both products of the ghrelin gene which have been implicated in regulating appetite, have also been shown to have pro-cognitive effects in vivo. However, it is not clear if cognitive effects result from direct effects on relevant brain structures (e.g. hippocampus), or what, if any, interaction exists between both peptides. We examined the effect of both peptides, alone and in combination, on neuronal structure and synaptic function in-vitro, by exposing primary hippocampal neuronal cultures to a range of doses of ghrelin (0.05, 0.5, 1.25, 5, 50 µM), obestatin or both in the medium for 48 hours prior to testing. Results of all experiments are shown in table 1. Neuronal structure was analysed by calculating the area under curve (AUC) of the Sholl plots (Sholl 1953). No dose of ghrelin or obestatin had an effect on AUC, but a significant increase was seen at 5 µM dose when both peptides were co-applied. Additionally, while no ghrelin doses increased the length of the longest neurite, obestatin caused an increase at the 0.5 and 5 µM doses, and no increases were seen when both peptides were co-applied. Synaptic release rate was calculated from the half life of FM 1-43 destaining with 65 mM KCl stimulation. Ghrelin at a dose of 5µM decreased synaptic release rate, as did obestatin at 0.05, 0.5 and 50 µM doses. No effect on synaptic release was seen when both peptides were co-administered. While both peptides were found to have effects on hippocampal neurones, no simple dose response relationship or interaction was found, suggesting an underlying complexity in the signalling of these peptides which has yet to be elucidated. In particular, the complex dose response to obestatin raises the possibility of more than one receptor for obestatin, which may have different affinities and which may function through interacting signalling pathways. Elucidating these pathways is likely to be key to understanding the pro-cognitive effects of both peptides.
Where applicable, experiments conform with Society ethical requirements