In vitro and in vivo evaluation of neuropeptide microdialysis in the brain of freely moving rats

Neuropeptides are subject of increased interest for their alleged role in various central nervous system processes. However, in vivo assessment of these compounds is complicated because of the generally low concentrations in the brain and the neuropeptides susceptibility to proteolytic degradation. This explains why so few microdialysis studies on neuropeptides have been published in the past. An additional problem is insufficient in vivo recovery of the neuropeptides when using microdialysis membranes. In this study we determined the recovery and dynamic behavior of several microdialysis membranes in vitro for three neuropeptides. For this purpose existing radio immuno assays (RIA) were optimized for Substance P (SP), vasopressin and corticotrophin releasing factor quantification in microdialysates. Finally, local potassium stimulation in freely moving rats was used to induce neurotransmitter release in order to assess the dynamic behavior of the membranes in vivo. Our results show that recovery of neuropeptides depends on the cut-off, pore-size and physico-chemical properties of the membrane, but the individual physicochemical properties of neuropeptides also play a role. Polyethersulfon (PES) membranes appeared to be most effective membranes for use in vitro and in vivo.