Electrophysiological studies on benzodiazepine antagonists

Krespan, Barbara; Springfield, Sanya A.; Haas, Helmut L.; Geller, Herbert M.

doi:10.1016/0006-8993(84)90975-2

Cited by 32 publications

(10 citation statements)

References 36 publications

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“…This is not unexpected as flumazenil is known to act as a competitive antagonist with the benzodiazepine/GABA receptor complex 5,13 but was interesting to confirm as some workers have cast doubt on the commonly accepted GABAergic mechanism of action for midazolam and flumazenil. 14 This observation concurs with the findings of other studies 15,16 reporting very little or no effect seen in isolated tissues at even relatively high concentrations of flumazenil and suggests an absence of agonist activity.…”

Section: Discussionsupporting

confidence: 86%

The effects of midazolam and flumazenil on psychomotor function and alertness in human volunteers

Coulthard¹,

Sano²,

Thomson³

et al. 2000

Br Dent J

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Section: Discussionsupporting

confidence: 86%

The effects of midazolam and flumazenil on psychomotor function and alertness in human volunteers

Coulthard¹,

Sano²,

Thomson³

et al. 2000

Br Dent J

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“…DMCM decreased the current amplitude by half and its decay time by 20%. Since it has been shown that this compound reduces the response to direct application of GABA (13,20) (22,23), reduction of spontaneous and evoked inhibitory postsynaptic potential has been reported using a concentration of Ro 15-1788 lower by a factor of 10 than we used; however, with such concentrations we failed to detect any modification of IPSCs.…”

Section: Discussionmentioning

confidence: 57%

Modulation of gamma-aminobutyric acid-mediated inhibitory synaptic currents in dissociated cortical cell cultures.

Vicini¹,

Alho²,

Costa³

et al. 1986

Proc. Natl. Acad. Sci. U.S.A.

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Inhibitory y-aminobutyric acid-mediated synaptic currents were studied in dissociated primary cultures of neonatal rat cortex with the whole-cell patch-clamp technique. Immunocytochemical staining of the cultures showed the presence of a large number of glutamic acid decarboxylasecontaining neurons, and electrical stimulation of randomly selected neurons produced in many cases chloride-mediated and bicuculline-sensitive inhibitory synaptic currents in postsynaptic cells. The amplitude and decay time of the inhibitory synaptic currents were increased by flunitrazepam and decreased by the /3-carboline derivative methyl 6,7-dimethoxy-4-ethyl-)3-carboline-3-carboxylate, two high-affimity ligands for the allosteric regulatory sites of r-aminobutyric acid receptors. The imidazobenzodiazepine Ro 15-1788, another high-affinity ligand of the y-aminobutyric acid receptor regulatory sites that has negligible intrinsic activity, blocked the action of flunitrazepam and /3-carboline. However, Ro 15-1788 also increased the decay rate of the inhibitory synaptic currents. This might suggest that an endogenous ligand for the benzodiazepine-f8-carboline binding site is operative in Yaminobutyric acid-mediated synaptic transmission.The development of the patch-clamp technique (1) has greatly facilitated the study of receptor function in terms of specific ion currents. The intracellular perfusion characteristic of this technique (2) allows manipulation of the ionic environment that is useful for distinguishing and characterizing different ion currents.Among the functional synaptic connections that have been described in primary neuronal cultures from fetal rat cortex (3) are those mediated by y-aminobutyric acid (GABA), an inhibitory neurotransmitter that is synthesized, released, and taken up by these cells (4, 5). Voltage-clamp analysis of GABA-mediated inhibitory postsynaptic currents (IPSCs) has been reported on various synapses. The best characterized is the neuromuscular junction of the crayfish and locust (6-10). IPSCs were also recorded in hippocampal slices (11) and in primary cultures of hippocampal neurons in which diazepam, a ligand for the allosteric modulatory site of GABA receptors, potentiated the IPSCs (12).Another anxiolytic benzodiazepine, flunitrazepam, and an anxiogenic /3-carboline derivative, methyl 6,7-dimethoxy-4-ethyl-,8-carboline-3-carboxylate (DMCM), potentiate and reduce, respectively, the increase in chloride conductance induced by direct application of GABA on the cell bodies of spinal cord neurons (13). We studied the action of these drugs and of the imidazobenzodiazepine MATERIALS AND METHODS Primary Culture. Primary neuronal cultures were obtained from 1-day-old rat cerebral cortices by the dissociation procedure described (15) for neonatal rat cerebellar cultures. Cells were plated (2 x 106 cells per dish) on 35-mm Nunc dishes coated with poly (L-lysine) (10 ,Ag/ml; Mr, 70-150 X 103) and were cultured in basal Eagle's medium/10% (vol/vol) fetal bovine serum (both from GIBCO)/25 mM KC1/2 mM ...

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“…However, most electrophysiological studies have focused on the low-affinity site (micromolar range) (Anthony et al, 1993;Hevers and Lüddens, 1998). Because micromolar concentrations of GABA are generally required for the activation of receptor-gated chloride conductances in electrophysiological experiments (Krespan et al, 1984;Maconochie et al, 1994), it is reasonable to suppose that the lower-affinity agonist binding sites are physiologically relevant (Anthony et al, 1993). The EC 50 value for the GABA receptor determined here corresponds to the low-affinity binding site.…”

Section: Discussionmentioning

confidence: 84%

Expression and Functional Characterization of GABA Transporters in Crayfish Neurosecretory Cells

et al. 2002

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The effect of GABA on membrane potential and ionic currents of X-organ neurons isolated from the crayfish eyestalk was investigated. Under voltage-clamp conditions, GABA elicited an inward Na ϩ current followed by a sustained outward chloride current. Sodium current was partially blocked in a dose-dependent manner by antagonists of GABA plasma membrane transporters such as ␤-alanine, nipecotic acid, 1-[2([(diphenylmethylene)imino]oxy)ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride (NO 711), and SKF89976-A at concentrations between 1 and 100 M. This current was totally blocked by the combined application of NO 711 (5 M) and ␤-alanine (50 M). We obtained an EC 50 of 5 M and a Hill coefficient of 0.97 for the GABA transport mediated response. These results together with studies of immunolocalization using antibodies against neuronal vertebrate GABA transporters (GATs) indicate the presence of GAT-1-and GAT-3-like proteins in X-organ neurons. To isolate the sustained outward Cl Ϫ current, extracellular free sodium solution was used to minimize the contribution of GAT activity. We concluded that this current was caused by the activation of GABA A -like receptors with an EC 50 of 10 M and a Hill number of 1.7.To assign a functional role to the GATs in the X-organ sinus gland system, we determine the GABA concentration (0.46-0.15 M) in hemolymph samples using HPLC.In summary, our results suggest that a sodium-dependent electrogenic GABA uptake mechanism has a direct influence on the excitability of the X-organ neurons, maintaining an excitatory tone that is dependent on the circulating GABA level.

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Electrophysiological studies on benzodiazepine antagonists

Cited by 32 publications

References 36 publications

The effects of midazolam and flumazenil on psychomotor function and alertness in human volunteers

The effects of midazolam and flumazenil on psychomotor function and alertness in human volunteers

Modulation of gamma-aminobutyric acid-mediated inhibitory synaptic currents in dissociated cortical cell cultures.

Expression and Functional Characterization of GABA Transporters in Crayfish Neurosecretory Cells

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