EFFECT OF ACUTE COCAINE INJECTION ON THE EXTRACELLULAR LEVEL OF DOPAMINE, BLOOD-FLOW, AND OXYGEN-PRESSURE IN BRAIN OF NEWBORN PIGLETS

The present study examined the effects of acute cocaine administration on oxygen pressure in the vasculature of the cortex as well as on blo od dow and extracellular levels of dopamine in the striatum of newborn piglets. The oxygen dependent quenching of phosphorescence was used t o continuously monitor oxygen pressure in the vasculature of the corte x. Following acute cocaine injection (1.5 mg/kg iv) the cortical oxyge n pressure rapidly decreased from 36.3 +/- 1.2 to 32.9 +/- 1.4 Torr an d remained at the lower level during the 120 min of postinjection peri od during which measurements were made. Blood dow in striatum, as dete rmined by laser Doppler, was decreased by 8-10% at 5 min after injecti on of cocaine. This decrease in blood flow was statistically significa nt up to 40 min postinjection. Extracellular dopamine, measured using in vivo micro dialysis, showed a large increase after cocaine injectio n. The dopamine level increased from 14 +/- 7 to 88 +/- 21 pmol/ml by 15 min after drug administration, then decreased to 45 +/- 11 pmol/ml and remained stable for the 120 min post-injection period. The mechani sm(s) by which the increase in the extracellular level of dopamine occ urred may include a direct effect of cocaine on the dopamine transport er and/or an indirect effect due to the decrease in cerebral oxygenati on and blood flow. The increase in extracellular dopamine can be respo nsible for several alterations in neuronal metabolism with potentially deleterious effects on neuronal function. (C) 1994 Academic Press, In c.