Characteristics of the NMDA receptor modulating hypoxia/hypoglycaemia-induced rat striatal dopamine release in vitro

Abstract

We investigated the functional characteristics of the NMDA receptor that modulates hypoxia/hypoglycaemia-induced striatal dopamine release. Dopamine release was detected by fast cyclic voltammetry in rat neostriatal slices. Four variables were measured: T on — time from initiation of hypoxia/hypoglycaemia to the onset of dopamine release, T pk — time from onset to maximum, δDA/ δ t — rate of dopamine release and DA max — maximum extracellular dopamine concentration. In controls, T on=164.9±1.7 s, T pk=20.9±0.9 s, δDA/ δ t=5.31±0.44 μM/s and DA max=79.1±2.5 μM (means±S.E.M., n=203). Cis-4-(phosphonomethyl)piperidine-2-carboxylic acid (CGS 19755, 20 μM) lengthened, while N-methyl- d-aspartate (NMDA) (100 μM) shortened T on. (5 R,10 S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK 801, 1 and 10 μM) and dextromethorphan (10 and 100 μM) increased T pk and decreased DA max. Neither glycine (100 μM), 7-chlorokynurenic acid (50 μM) nor 5-nitro-6,7-dichloro-1,4-dihydroquinoxaline-2,3-dione (ACEA 1021, 100 μM) had any effect although 7-chlorokynurenic acid blocked the effect of NMDA. Increasing [Mg 2+] from 1.3 to 3.7 mM, increased T pk and decreased δDA/ δt. Dithiothreitol (1 mM) accelerated T on while 5,5-dithio-bis-(2-nitrobenzoic acid) (1 mM) delayed T on. Neither drug affected T pk, DA max or δDA/ δt. Neither spermidine (100 μM) nor arcaine (100 μM) affected T on, T pk or δDA/ δt although arcaine decreased DA max. In conclusion, hypoxia/hypoglycaemia-induced dopamine release was influenced by an NMDA receptor although modulation of the glycine recognition site of the receptor was ineffective, as were agents acting at polyamine modulatory zones. These findings highlight differences between recombinant and native NMDA receptors and suggest caution in extrapolating molecular biology to functional studies.