Recent studies indicate that the extraneuronal concentrations of different neurotransmitters increase in the brain following anoxia (Zetterstr6m et al. 1982;Benveniste et al. 1984;Globus et al. 1988;Slivka et al. 1988). Accordingly, a massive release of dopamine (DA) has recently been measured by microdialysis in perfusates of the rat striatum (Phebus et al. 1986;Rollema et al. 1986) and nucleus accumbens (Vulto et al. 1988) within minutes of death. This effect might be attributed to the blockade of the energy-linked oxygen-dependent mechanisms for transport, storage and disposition of neurotransmitters as a consequence of the postmortem anoxia. However, the effect of death on the extraneuronal release of noradrenaline (NA) is not known. The present study was carried out to compare the postmortem changes in DA and NA release in rats, using a microdialysis technique.
Brain microdialysis was performed in male Sprague-Dawley CD 350-400 g rats (Charles River) essentially as described by Imperato and Di Chiara (1984), using bicarbonate Krebs-Ringer buffer, pH 7.4 as perfusing solution. Dialysis membranes (Vitafiber, Amicon Co.) were implanted transversally either through both striata (A: 7.4; V: 5.5, from temporal bone) or through the frontal cortex (A: 6.9; V: 2.5 from temporal bone) (K6nig and Klippel 1963) 24 h before the experiment. The perfusates (50 ~tl/20 min) were directly applied to an HPLC-EC system for the measurement of NA and DA by reverse-phase ion-pairing chromatography, using a computer-controlled, fully automated system. The mobile phase (citrate/acetate buffer, 50 mM, pH 5.00, containing EDTA, 1 mM) for the analysis of NA and DA differed in the content of the ion-pairing agent (sodium octylsulphate, 70 and 40 mg/1, respectively) and organic solvent (methanol, 3.5 and 10% v/v, respectively). The column was a 25 cm octadecyl silica, 5 gm particle size (Supelco), the flowrate 0.9 ml/min (Waters 510 pump) and the applied potential 0.7 V versus an Ag/AgC1 reference electrode (Bioanalytical Systems LC-4B detector with a glassy carbon electrode). An integrator (Waters 710 Data Module) was used to record the signal.
After obtaining a stable baseline for the release of the amines (basal release of DA and NA 12_+2.1 and 21 +3.3 fmol/min, respectively), the animals were killed by cervical dislocation and the perfusion was continued for 2 h thereafter. Figure 1 shows the dramatic difference in the release of the two amines as a consequence of death. As expected,