Microdialysis is a method to study the extracellular space invivo, based on the principle
of diffusion. It can be used to measure various small molecules including the neuroregulator
adenosine. Baseline levels of the compounds measured with microdialysis vary over
studies. We systematically reviewed the literature to investigate the full range of
reported baseline concentrations of adenosine and adenosine monophosphate in microdialysates.
We performed a meta-regression analysis to study the influence of flow rate, probe
membrane surface area, species, brain area and anaesthesia versus freely behaving,
on the adenosine concentration. Baseline adenosine concentrations in microdialysates
ranged from 0.8 to 2100nM. There was limited evidence on baseline adenosine monophosphate
concentrations in microdialysates. Across studies, we found effects of flow rate and
anaesthesia versus freely behaving on dialysate adenosine concentrations (p0.001),
but not of probe membrane surface, species, or brain area (p0.14). With increasing
flow rate, adenosine concentrations decreased. With anaesthesia, adenosine concentrations
increased. The effect of other predictor variables on baseline adenosine concentrations,
for example, post-surgical recovery time, could not be analysed because of a lack
of reported data. This study shows that meta-regression can be used as an alternative
to new animal experiments to answer research questions in the field of neurochemistry.
However, current levels of reporting of primary studies are insufficient to reach
the full potential of this approach; 63 out of 133 studies could not be included in
the analysis because of insufficient reporting, and several potentially relevant factors
had to be excluded from the analyses. The level of reporting of experimental detail
needs to improve.