Involvement of GABA systems in feedback regulation of glutamate‐and GABA‐mediated synaptic potentials in rat neostriatum.

Abstract

SUMMARY1. Neostriatal neurones were recorded intracellularly from a rat corticostriatal slice preparation. Depolarizing postsynaptic potentials (DPSPs) were evoked by either cortical or intrastriatal stimulation.2. Kynurenic acid (600 /tM), an antagonist of excitatory amino acids, reduced the cortically-evoked DPSPs by 88 % while the intrastriatally evoked potentials were reduced by 48 %. Bicuculline (100,tM) produced only a slight inhibition of the cortically evoked DPSPs (12 %), but clearly depressed intrastriatal potentials (52 %).3. The effects of (-)-baclofen, a y-aminobutyric acid (GABA)B receptor agonist, were studied on the cortically evoked DPSPs. In all the tested neurones (-)-baclofen, added to the superfusion medium, caused a concentration-dependent decrease of these potentials (half-maximal effect (EC50) = 800 nM). This effect was not affected by bicuculline. (-)-Baclofen did not change the membrane potential, the input resistance, current-evoked firing frequency, or postsynaptic responses to exogenously applied glutamate.4. The effects of (-)-baclofen on the DPSPs were compared to those produced by application of GABA and muscimol. GABA and muscimol decreased the DPSPs and caused a membrane depolarization coupled with a decrease of the membrane resistance. Bicuculline (100 JtM) blocked the GABA-induced changes of the membrane potential and of the resistance, but not the decrease of the synaptic potentials. All the effects produced by muscimol were blocked by bicuculline.5. Following intrastriatal stimulation a residual kynurenate-insensitive potential persisted; this potential was blocked by bicuculline (100 ,tM). (-)-Baclofen produced a dose-dependent decrease of this potential (EC50 = 800 nM). The postsynaptic responses to exogenously applied GABA were unchanged by (-)-baclofen.6. The amplitude of kynurenate and bicuculline-sensitive DPSPs were stable at a frequency of 0 1 Hz. At frequencies between 0 3 and 3 Hz both these potentials were attenuated with the second stimulus and after about five stimuli a steady state was reached. Membrane potential and input resistance were not affected by these frequencies of stimulation.* To whom correspondence should be addressed. MS 8751P. CALABRESI AND OTHERS 7. Application of the GABA uptake inhibitor nipecotic acid (100-300 1uM) clearly reduced the amplitude of both kynurenate-and bicuculline-sensitive DPSPs evoked at low frequencies of stimulation (0-01-0{3 Hz), but had lower effects at higher stimulation rates (1-3 Hz). Application of nipecotic acid increased the duration of membrane responses to exogenously applied GABA.8. Applications of either 2-hydroxy-saclofen (100 JM) or phaclofen (0-7-1 mm), antagonists of the GABAB receptors, produced a parallel shift to the right of the dose-response curve of the effect of (-)-baclofen on the bicuculline-sensitive DPSPs, but did not significantly antagonize the effect of this agonist on the kynurenatesensitive DPSPs. 2-Hydroxy-saclofen produced an increase in the amplitude of bicuculline-sensitive DPSPs, while i...

Opposite Membrane Potential Changes Induced by Glucose Deprivation in Striatal Spiny Neurons and in Large Aspiny Interneurons

“…When the currents were evoked by hyperpolarizing command steps, there was no detectable time-dependent component. Some of these properties have been described previously both in vivo (Preston et al, 1979;Wilson and Groves, 1980;Calabresi et al, 1990c;Onn et al, 1994a;Xu, 1995) and in vitro (Kita et al, 1984;Calabresi et al, 1990bCalabresi et al, , 1991Calabresi et al, , 1995bJiang and North, 1991;Cepeda et al, 1994) and resemble those reported for intracellularly stained spiny striatal neurons (Preston et al, 1979;Cepeda et al, 1994;Onn et al, 1994b;Calabresi et al, 1995a).…”

Coactivation of GABA A and GABA B Receptor Results in Neuroprotection During In Vitro Ischemia

“…It has been reported that endogenous GABA controls its own release via GABA B autoreceptors. 25 Thus, high levels of GABAmimetic drugs reduce the release of endogenous GABA. Alternatively, it can be speculated that excessive activation of GABA A receptor may cause an overload of chloride ions into the neurons, leading to cell swelling.…”

Voluntary Exercise and Sucrose Consumption Enhance Cannabinoid CB1 Receptor Sensitivity in the Striatum

“…Many receptors participate in the presynaptic modulation of GABA transmission in the striatum, including the GABAB receptors (Calabresi et al, 1991). Thus, we investigated whether the abnormal control of GABA synapses observed in rewarded mice was specific only for CB1 receptors or also involved other presynaptic receptors.…”