ESTIMATING EXTRACELLULAR CONCENTRATIONS OF DOPAMINE AND 3,4-DIHYDROXYPHENYLACETIC ACID IN NUCLEUS-ACCUMBENS AND STRIATUM USING MICRODIALYSIS - RELATIONSHIPS BETWEEN IN-VITRO AND IN-VIVO RECOVERIES
Sd. Glick et al., ESTIMATING EXTRACELLULAR CONCENTRATIONS OF DOPAMINE AND 3,4-DIHYDROXYPHENYLACETIC ACID IN NUCLEUS-ACCUMBENS AND STRIATUM USING MICRODIALYSIS - RELATIONSHIPS BETWEEN IN-VITRO AND IN-VIVO RECOVERIES, Journal of neurochemistry, 62(5), 1994, pp. 2017-2021
It is common practice in microdialysis studies for probes to be ''cali
brated'' in artificial CSF and in vitro recoveries determined for all
substances to be measured in vivo. Dialysate concentrations of such su
bstances are then ''corrected'' for in vitro recoveries to provide ''e
stimates'' of extracellular concentrations. At least for dopamine, in
vitro and in vivo recoveries are significantly different and, therefor
e, an estimate of extracellular dopamine based on correction for in vi
tro recovery is likely to be erroneous. Generally, however, the relati
ve relationships of such estimates among animals are of interest rathe
r than the ''true'' extracellular values. Such relationships would be
valid to the extent that estimated values are correlated with or predi
ctive of true values. Using the ''no net flux'' procedure, the present
study sought to determine, for both dopamine and its metabolite 3,4-d
ihydroxyphenylacetic acid (DOPAC), whether in vitro and in vivo recove
ries would correlate with each other as well as whether respective est
imated and true (no net flux) values of these substances would correla
te with each other. Probes (3 mm; BAS/CMed MF-5393), previously calibr
ated, were lowered into both the nucleus accumbens and striatum of fre
ely moving rats the day before sample collection was begun. In vitro a
nd in vivo recoveries were not significantly correlated (r = 0.1-0.3),
for either dopamine or DOPAC. For both dopamine and DOPAC, however, t
here were significant correlations (r = 0.7-0.8) between estimated and
true values. Surprisingly, when using these commercial probes, absolu
te dialysate levels for both substances were even better correlated (r
= 0.9-0.95) with true values. This suggests that, with these probes,
a direct comparison of dialysate concentrations can be used to determi
ne relative changes in basal extracellular levels of dopamine and DOPA
C when it is not practical to do no net flux studies (e.g., because of
the time required to characterize a drug effect). The use of in vitro
calibrations adjusts the values closer to the true values but also ad
ds noise to each value and therefore should be avoided.