EVALUATION OF THE FUNCTION OF MICRODIALYSIS PROBES PERMANENTLY IMPLANTED INTO THE RAT CNS AND COUPLED TO AN ONLINE HPLC SYSTEM OF ANALYSIS

The aim of the microdialysis technique is to reflect as closely as pos sible the status and fluctuations of substances contained in the extra cellular space. Most often, microdialysis is performed with repetitive ly implanted probes. We have recently devised an experimental set-up w hich allows microdialysis to be performed in the spinal cord of unrest rained rats through chronically permanently implanted probes. In the p resent study, we have compared the in vitro recovery of a non-biogenic amine (DHBA) and of 5-HT, and the in vivo recovery of the former. Thu s, we could extrapolate the in vivo recovery of endogenous 5-HT releas ed. Moreover, we have found that the recovery does not vary irrespecti ve of whether the animal is at rest or performing sustained physical e xercise, and that it also remains stable with time, from 8 to 36 days after permanent implantation of the probe. We conclude that this simpl e method can be applied to standard experiments of microdialysis, and thus allow one to measure the actual rate of recovery for a given prob e. Moreover, it permits control of the stability of dialysis parameter s with time for long-term permanently implanted probes.