bicuculline-methobromide and gaboxadol

Epileptiform discharges recorded in the 4-aminopyridine (4-AP) in vitro epilepsy model are mediated by glutamatergic and GABAergic signaling. Using a 60-channel perforated multi-electrode array (pMEA) on corticohippocampal slices from 2 to 3 week old mice we recorded interictal- and ictal-like events. When glutamatergic transmission was blocked, interictal-like events no longer initiated in the hilus or CA3/CA1 pyramidal layers but originated from the dentate gyrus granule and molecular layers. Furthermore, frequencies of interictal-like events were reduced and durations were increased in these regions while cortical discharges were completely blocked. Following GABA(A) receptor blockade interictal-like events no longer propagated to the dentate gyrus while their frequency in CA3 increased; in addition, ictal-like cortical events became shorter while increasing in frequency. Lastly, drugs that affect tonic and synaptic GABAergic conductance modulated the frequency, duration, initiation and propagation of interictal-like events. These findings confirm and expand on previous studies indicating that multiple synaptic mechanisms contribute to synchronize neuronal network activity in forebrain structures. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

Topics: 4-Aminopyridine; Animals; Anticonvulsants; Bicuculline; CA3 Region, Hippocampal; Disease Models, Animal; Electrodes; Epilepsy; GABA-A Receptor Antagonists; gamma-Aminobutyric Acid; Hippocampus; In Vitro Techniques; Isoxazoles; Mice; Mice, Inbred C57BL; Microarray Analysis; Motion Pictures; Piperazines; Potassium Channel Blockers; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Software; Somatosensory Cortex

Based on an unexpected high maximum response to piperidine-4-sulphonic acid (P4S) at human alpha1alpha6beta2gamma2 GABA(A) receptors expressed in Xenopus oocytes attempts to correlate this finding with the pharmacological profile of P4S and other GABA(A) receptor ligands in neuronal cultures from rat cerebellar granule cells and rat cerebral cortex were carried out. GABA and isoguvacine acted as full and piperidine-4-sulphonic acid (P4S) as partial agonists, respectively, at alpha1beta2gamma2, alpha6beta2gamma2 and alpha1alpha6beta2gamma2 GABA receptors expressed in Xenopus oocytes with differences in potency. Whole-cell patch-clamp recordings were used to investigate the pharmacological profile of the partial GABA(A) receptor agonists 4,5,6,7-tetrahydroisoxazolo-(5,4-c)pyridin-3-ol (THIP), P4S, 5-(4-piperidyl)isoxazol-3-ol (4-PIOL), and 3-(4-piperidyl)isoxazol-5-ol (iso-4-PIOL), and the competitive GABA(A) receptor antagonists Bicuculline Methbromide (BMB) and 2-(3-carboxypropyl)-3-amino-6-methoxyphenyl-pyridazinium bromide (SR95531) on cerebral cortical and cerebellar granule neurons. In agreement with findings in oocytes, GABA, isoguvacine and P4S showed similar pharmacological profiles in cultured cortical and cerebellar neurones, which are known to express mainly alpha1, alpha2, alpha3, and alpha5 containing receptors and alpha1, alpha6 and alpha1alpha6 containing receptors, respectively. 4-PIOL and iso-4-PIOL, which at GABA(A) receptors expressed in oocytes were weak antagonists, showed cell type dependent potency as inhibitors of GABA mediated responses. Thus, 4-PIOL was slightly more potent at cortical neurones than at granule neurones and iso-4-PIOL was more potent in inhibiting isoguvacine-evoked currents at cortical than at granule neurons. Furthermore the maximum response to 4-PIOL corresponded to that of a partial agonist, whereas that of iso-4-PIOL gave a maximum response close to zero. It is concluded that the pharmacological profile of partial agonists is highly dependent on the receptor composition, and that small structural changes of a ligand can alter the selectivity towards different subunit compositions. Moreover, this study shows that pharmacological actions determined in oocytes are generally in agreement with data obtained from cultured neurons.

Topics: Animals; Bicuculline; Cells, Cultured; Cerebellum; Cerebral Cortex; Electrophysiology; GABA Agonists; GABA-A Receptor Agonists; Isonicotinic Acids; Isoxazoles; Mice; Neurons; Oocytes; Patch-Clamp Techniques; Piperidines; Pyridazines; Receptors, GABA-A; Xenopus laevis

Basal and vasoactive intestinal peptide (VIP)-stimulated accumulations of cyclic AMP were measured in slices of rat cerebral cortex. Neither gamma-aminobutyric acid (GABA) nor the selective GABAB receptor agonist (-)-baclofen stimulated basal cyclic AMP accumulation, whereas VIP caused a large dose-dependent increase in cyclic AMP levels. However, in the presence of 100 microM (-)-baclofen, the effects of VIP on cyclic AMP accumulation were significantly enhanced, with the responses to 1 microM and 10 microM VIP being approximately doubled. The enhancing effects of (-)-baclofen was dose related (1-1,000 microM), but an enhancing effect was not observed with 100 microM (+)-baclofen. In the presence of the GABA uptake inhibitor nipecotic acid (1 mM), GABA caused a similar dose-related enhancement of the VIP response. The ability of either GABA or (-)-baclofen to augment VIP-stimulated production of cyclic AMP was not mimicked by the GABAA, agonists isoguvacine and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) and was not antagonized by the GABAA antagonist bicuculline. The putative GABAB antagonist 5-aminovaleric acid (1 mM) significantly reduced the effect of (-)-baclofen. The ability of (-)-baclofen to enhance VIP-stimulated accumulation of cyclic AMP was observed in slices of rat cerebral cortex, hippocampus, and hypothalamus. These results indicate that GABA and (-)-baclofen can enhance VIP-stimulated accumulation of cyclic AMP in rat brain slices via an interaction with specific GABAB receptors.

Topics: Amino Acids; Amino Acids, Neutral; Animals; Baclofen; Bicuculline; Cerebral Cortex; Cyclic AMP; Dose-Response Relationship, Drug; Drug Synergism; gamma-Aminobutyric Acid; Isoxazoles; Male; Rats; Rats, Inbred Strains; Receptors, GABA-A; Vasoactive Intestinal Peptide

GABAA receptor agonists modulate [3H]diazepam binding in rat cortical membranes with different efficacies. At 23 degrees C, the relative potencies for enhancement of [3H]diazepam binding by agonists parallel their potencies in inhibiting [3H]gamma-aminobutyric acid [( 3H]GABA) binding. The agonist concentrations needed for enhancement of [3H]diazepam binding are up to 35 times higher than for [3H]GABA binding and correspond closely to the concentrations required for displacement of [3H]bicuculline methochloride (BMC) binding. The maximum enhancement of [3H]diazepam varied among agonists: muscimol = GABA greater than isoguvacine greater than 3-aminopropane sulphonic acid (3APS) = imidazoleacetic acid (IAA) greater than 4,5,6,7-tetrahydroisoxazolo (4,5,6)-pyridin-3-ol (THIP) = taurine greater than piperidine 4-sulphonic acid (P4S). At 37 degrees C, the potencies of agonists remained unchanged, but isoguvacine, 3 APS, and THIP acquired efficacies similar to GABA, whereas IAA, taurine, and P4S maintained their partial agonist profiles. At both temperatures the agonist-induced enhancement of [3H]diazepam binding was reversible by bicuculline methobromide and by the steroid GABA antagonist RU 5135. These results stress the importance of studying receptor-receptor interaction under near-physiological conditions and offer an in vitro assay that may predict the agonist status of putative GABA receptor ligands.

Topics: Androstanes; Animals; Azasteroids; Bicuculline; Cell Membrane; Cerebral Cortex; Diazepam; GABA Antagonists; gamma-Aminobutyric Acid; Imidazoles; Isonicotinic Acids; Isoxazoles; Muscimol; Piperidines; Rats; Receptors, GABA-A; Taurine

Sprague-Dawley rats were used to further characterize the anorexic action of orally-administered THIP, a GABA-analogue. The anorexic action of THIP (5 or 10 mg/kg) was antagonized by prior subcutaneous injection of bicuculline (1 mg/kg), but not by prior subcutaneous injection of bicuculline-methobromide (1.5 mg/kg), strychnine-SO4 (0.75 mg/kg), pentylenetetrazol (25 mg/kg), or picrotoxin (1 mg/kg). Orally-administered GABA (50-300 mg/kg), bicuculline (1-10 mg/kg) or picrotoxin (1-10 mg/kg) generally did not inhibit food intake. These results indicate that the anorexic action of THIP is mediated by central GABA-receptors.

Topics: Administration, Oral; Animals; Bicuculline; Eating; gamma-Aminobutyric Acid; Isoxazoles; Male; Oxazoles; Pentylenetetrazole; Picrotoxin; Rats; Rats, Inbred Strains; Receptors, Cell Surface; Receptors, GABA-A; Strychnine