Bicuculline Methochloride as a GABA Antagonist

All experiments were performed on rat isolated desheathed superior cervical ganglia maintained in Krebs solution containing amino‐oxyacetic acid (10 μm) at 25°C. Influx rates of γ‐amino‐n‐butyric acid (GABA) were measured by incubating ganglia in 0.5 μm [3H]‐GABA for 30 minutes. Influx was inhibited by 50% on adding 14.3 μm unlabelled GABA, 59.2 μm β‐alanine (BALA) or 424 μm β‐amino‐n‐butyric acid (BABA). Efflux of [3H]‐GABA into non‐radioactive solution superfused over ganglia previously incubated for 60 min in 1 μm [3H]‐GABA was measured. The mean resting efflux rate coefficient (k) was 0.64 ±0.05 × 10−3 min−1. Addition of high concentrations of unlabelled GABA, BABA or BALA to the superfusing solution increased k by (maximally) 3.6–4.3 times; half‐maximal increases occurred at the following concentrations: GABA, 16 μm; BALA, 85 μm; BABA, 606 μm. Replacement of external Na+ with Li+ or TRIS increased the resting value of k and inhibited acceleration by external amino acids. Prior incubation in 1 μm [3H]‐GABA with 1 mm unlabelled GABA increased resting k 1.5 times;, but did not alter the peak rate coefficient produced by external amino acids. Neuronal depolarization produced by the amino acids was measured with surface electrodes. Preincubation in 1 mm GABA for 60 min potentiated low‐amplitude responses to BALA or BABA but not those to GABA or 3‐aminopropanesulphonic acid (a potent agonist with low affinity for the GABA carrier). Omission of external Na+ reduced responses to BABA but increased those to GABA. Incubation in 1 mm GABA for 60 min (as required to potentiate BABA or BALA actions) increased the amount of GABA in the tissue from 0.21 to 0.73 mmol/kg wet weight. Autoradiographs in which labelled GABA was used indicated that uptake into neuroglial cells was responsible for this accumulation. It is suggested that: (i) BALA and BABA are substrates for the inward GABA carrier responsible for GABA entry into ganglionic glial cells; (ii) they accelerate efflux by inhibiting carrier‐mediated re‐accumulation of effluent GABA by the glial cells; (iii) interstitial GABA concentrations are thereby increased to a level capable of depolarizing adjacent neurones; and (iv) this, rather than direct GABA‐receptor activation, accounts for the depolarization produced by low concentrations of BALA and BABA. Potentiation of their depolarizing action after pre‐incubation in 1 mm GABA is suggested to result from the increased amount of intracellular GABA available for release, and is quantitatively compatible with this increase; inhibition in Na+‐free solution is due to their inability to inhibit re‐accumulation of GABA under these conditions. A model for the action of carrier substrates is described in an Appendix. Calculations based thereon yield increments in interstitial GABA concentration in the presence of carrier substrates compatible with those determined experimentally (up to 1 μm at rest or 3.4 μm after pre‐incubation in GABA).

show abstract

“…Methylbicuculline was synthesized by J.F. Collins according to the method of Johnston, Beart, Curtis, Game, McCulloch & MacLachlan (1972).…”

Section: Compoundsmentioning

confidence: 99%

Indirect Effects of Amino‐acids on Sympathetic Ganglion Cells Mediated Through the Release of Γ‐aminobutyric Acid From Glial Cells

Bowery

Brown

Collins

et al. 1976

British J Pharmacology

View full text Add to dashboard Cite

show abstract

“…Galindo, 1969;Bruggencate & Engberg, 1971; Duggan, Felix, Johnston & McLennan, 1971a;Curtis, Duggan & Johnston, 197 1b). (+)-Bicuculline methochloride and (+)-tubocurarine are two more recently introduced antagonists of GABA (Johnston, Beart, Curtis, Game, McCulloch & MacLachlan, 1972;Hill et al, 1973a;Coflins & Hill, 1974) and we have also used three other convulsants, penicillin, leptazol and bemegride, whose mechanisms of action are less well elucidated.…”

Section: Introductionmentioning

confidence: 99%

Antagonism of Γ‐aminobutyric Acid and Glycine by Convulsants in the Cuneate Nucleus of Cat

Hill

Simmonds

Straughan

1976

British J Pharmacology

View full text Add to dashboard Cite

1Some convulsant substances have been applied-to single neurones in the cat cuneate nucleus by microiontophoresis. Numerical values were derived for the effectiveness and selectivity of the substances as antagonists of y-aminobutyric acid (GABA) and glycine. 2 (+)-Bicuculline methochloride was the most effective GABA antagonist and it also excited many neurones. It antagonized GABA in 93% of experiments but also antagonized glycine in 41% of experiments. In most experiments the antagonism of GABA was greater than the antagonism of glycine resulting in an overall selective antagonism of GABA that was statistically significant. Nevertheless, in only about one quarter of the individual experiments was the GABA antagonism substantial and the selectivity clearcut. 3 (+)-Bicuculline and picrotoxin were less easily applied to neurones by microiontophoresis and were found to antagonize GABA in 30% and 35% of experiments, respectively. They also antagonized glycine in 25% and 30% of experiments, respectively. Overall, neither substance could be shown to be selective, statistically, although in the few individual experiments where the GABA antagonism was substantial the antagonism was clearly selective. 4 (+)Tubocurarine antagonized GABA in 59% and glycine in 32% of experiments and it also excited many neurones. Penicillin antagonized GABA in 33% of experiments without antagonizing glycine. Neither antagonist caused any substantial antagonisms of GABA and neither showed significant selectivity overall. (-)-Bicuculline methochloride, leptazol and bemegride antagonized GABA or glycine in less than 10% of experiments, although (-)-bicuculline methochloride excited most neurones. SStrychnine antagonized glycine in every experiment while antagonizing GABA in only 5% of experiments. In each individual experiment the antagonism of glycine was substantial and clearly selective, resulting in a statistically significant selectivity overall. 6 It is concluded that the selective glycine antagonist strychnine is considerably better than the presently available GABA antagonists for distinguishing between responses to GABA and glycine, when the antagonists are applied by microiontophoresis.

show abstract

“…Bicuculline is widely considered to be a relatively specific antagonist of the neuronal depressant effects of GABA (Curtis et al, 1970;Johnston, Beart, Curtis, Game, McCulloch & Maclachlan, 1972). The reversible blockade of EDA-evoked inhibitions in parallel with GABA by bicuculline, while responses to glycine were not affected, could suggest a direct agonist action of EDA on the GABA receptor.…”

Section: Discussionmentioning

confidence: 99%

Comparison of the Effects of Ethylenediamine Analogues and Γ‐aminobutyric Acid on Cortical and Pallidal Neurones

Perkins

Stone

1982

British J Pharmacology

View full text Add to dashboard Cite

1 The actions of ethylenediamine (EDA) and structurally related compounds were investigated by microiontophoresis in Wistar rats. 2 EDA inhibited, via a bicuculline-sensitive mechanism, the spontaneous firing rate of all cortical and pallidal cells tested. 3 The results with the analogues suggest that two amine groups are required for this neuronal depressant action whereas a carboxyl grouping is not. N-substitution reduces the depressant effect. The length of the molecule is also critical, more than 3 methylene components seriously reducing its effectiveness. A rigid analogue of EDA, piperazine, was also active. In addition the apparent transport numbers of EDA and y-aminobutyric acid (GABA) were calculated, showing a close similarity between the two. 4 The results are discussed with respect to the possibility that EDA may represent a new class of GABA-mimetics, or may indicate the existence of a novel diamine receptor mediating bicucullinesensitive inhibition in the rat CNS.

show abstract

Bicuculline Methochloride as a GABA Antagonist

Cited by 123 publications

References 6 publications

Indirect Effects of Amino‐acids on Sympathetic Ganglion Cells Mediated Through the Release of Γ‐aminobutyric Acid From Glial Cells

Indirect Effects of Amino‐acids on Sympathetic Ganglion Cells Mediated Through the Release of Γ‐aminobutyric Acid From Glial Cells

Antagonism of Γ‐aminobutyric Acid and Glycine by Convulsants in the Cuneate Nucleus of Cat

Comparison of the Effects of Ethylenediamine Analogues and Γ‐aminobutyric Acid on Cortical and Pallidal Neurones

Contact Info

Product

Resources

About