Preloading In Vivo: A Rapid and Reliable Method for Measuring γ‐Aminobutyric Acid and Glutamate Fluxes by Microdialysis

Abstract

In vivo microdialysis was used in conjunction with a novel dual-label preloading method, to monitor changes in extracellular levels of gamma-aminobutyric acid (GABA) and glutamate in the striatum of conscious, unrestrained rats. [3H]GABA and [14C]glutamate were applied in the dialysis stream for a preloading period of 30 min, after which dialysis perfusion was continued for up to 6 h, and dialysate samples were collected for scintillation counting. Veratridine (Vtd: 100 microM in the dialysate) caused significant rises in both 3H and 14C content measured in the dialysates, the majority of which remained associated with the preload GABA and glutamate, respectively. The Vtd-stimulated release of GABA and glutamate measured in this way was blocked by tetrodotoxin and was Ca2+ dependent. Thus, by reproducing results obtained using other techniques, we have shown that the preloading method provides a quick and reliable method for measuring the effects of drugs on the release of neurotransmitter GABA and glutamate in vivo by dyalisis. It should enable sample times as low as 1 min to be used, thus allowing resolution of transient stimulated responses taking place over a time course of minutes.

Effect of acute and subchronic nicotine treatment on cortical efflux of [3H]‐d‐aspartate and endogenous GABA in freely moving guinea‐pigs

“…Since GABA metabolism was inhibited by ethanolamine-0sulphate pretreatment, no attempt was made to ascertain to what extent the effluent tritium remained associated with GABA. In fact, under similar experimental conditions about 80%-90% of tritium proved to be represented by [3H]-GABA (Young et al, 1990). The samples were then measured for their tritium content as for [3H]-D-aspartate (see above).…”

“…Since (Young et al, 1990 Other animals were submitted to chronic nicotine treatment. The drug was injected s.c., twice daily for 16 days, at 3.6mgkg-1 per day, i.e.…”

Brain microdialysis of GABA and glutamate: What does it signify?

“…Veratridine opens TTX-sensitive sodium channels (Narahashi, 1974), resulting in stimulated release of amino acids as measured by microdialysis (Jacobsen and Hamberger, 1984;Young et al, 1990;Lu et al, 1991;Bourdelais and Kalivas, 1992;Renno et al, 1992;Hashimoto et al, 1995). The evoked release of amino acids is not calciumdependent.…”

Evidence for Neuronal Origin and Metabotropic Receptor‐Mediated Regulation of Extracellular Glutamate and Aspartate in Rat Striatum In Vivo Following Electrical Stimulation of the Prefrontal Cortex

“…Similar, albeit more variable, results have been reported for studies in which chemical stimuli have been used to facilitate neuronal Glu release in vivo. Although agents such as veratridine and potassium chloride markedly increase extracellular Glu concentration, the stimulated rise in Glu levels is reduced only partially by local Ca2~depletion or TTX treatment (Young et al, 1990;Yamamoto and Cooperman, 1994;Hashimoto et al, 1995;Semba et al, 1995), and the effectiveness of such treatments varies considerably among different investigators (see Herrera-Marschitz et al, 1996). Measurements of Asp have had similar atypical results (Herrera-Marschitz et al, 1996).…”