RESUMEN

In vitro and in vivo electrophysiological studies were done to investigate the neuronal function of the hippocampus and prefrontal cortex in the amyloid precursor protein (APP) 23 transgenic mouse model for amyloidosis developed by Sturchler-Pierrat et al. [Proc Natl Acad Sci USA 94 (1997) 13287]. Brain slices were taken from 3, 6, 9, 12, 18 and 24 month old wildtype and hemizygous type APP23 mice. Extracellular field potentials were recorded from the CA1 region of the hippocampus while stimulating the Schaffer collaterals. In addition, extracellular field potentials were elicited from areas within layer V/VI of the prefrontal cortex by stimulating the same layer V/VI. Basic synaptic function in the hippocampus was reduced in hemizygous APP23 mice compared with their wildtype littermates at 12 and 18 months of age, whereas, it was unaltered within the prefrontal cortex. Long-term potentiation in the hippocampus and the prefrontal cortex of hemizygous APP23 mice was similar compared with their wildtype littermates. In vivo electrophysiological experiments were done in 3, 9, 18 and 24 month old wildtype and hemizygous APP23 mice. No differences were observed in the number of single spontaneously active units recorded within the prefrontal cortex of hemizygous APP23 mice compared with their wildtype littermates. Field potentials elicited during stimulation of cortico-cortical pathways to assess synaptic transmission and short-term synaptic plasticity were also unchanged in hemizygous APP23 mice. Furthermore, presumable antidromic field potentials recorded in the prefrontal cortex during stimulation of the striatum were similar between the hemizygous APP23 and wildtype mice at each age. The present study shows that amyloidosis impairs basic synaptic function but not long-term potentiation in the hippocampus, however, does not alter any of the neurophysiological functions measured within the prefrontal cortex. These findings suggest that amyloidosis may be involved in altering some neurophysiological functions within only certain brain structures. Although APP23 mice have impaired cognitive performance, long-term plasticity, a cellular model for memory, is not affected, raising the question on the relationship between these processes.

Asunto(s)

Enfermedad de Alzheimer/fisiopatología , Precursor de Proteína beta-Amiloide , Amiloidosis/fisiopatología , Hipocampo/fisiopatología , Potenciación a Largo Plazo , Corteza Prefrontal/fisiopatología , Transmisión Sináptica , Potenciales de Acción , Factores de Edad , Precursor de Proteína beta-Amiloide/genética , Animales , Modelos Animales de Enfermedad , Electrofisiología , Potenciales Postsinápticos Excitadores , Ratones , Ratones Transgénicos , Plasticidad Neuronal , Neuronas

RESUMEN

The mode of action of the antipsychotic drugs clozapine, haloperidol and iloperidone was investigated in layer V of prefrontal cortex slices using extracellular field potential, intracellular sharp-electrode as well as whole-cell voltage clamp recording techniques. Intracellular investigations on a broad range of concentrations revealed that the typical neuroleptic haloperidol at higher concentrations significantly depressed the excitatory postsynaptic component induced by electrical stimulation of layer II. This was not seen with the atypical neuroleptics clozapine and iloperidone. None of the three compounds had any effect on the resting membrane potential, spike amplitude or input resistance at relevant concentrations. Synaptic plasticity was assessed by means of extracellular field potential recordings. Clozapine significantly facilitated the potentiation of synaptic transmission, whereas haloperidol and iloperidone showed no effects. In line with its facilitating effect on synaptic plasticity, it could be demonstrated by whole-cell voltage clamp recordings that clozapine increased N-methyl-D-aspartic acid receptor-mediated excitatory postsynaptic currents in the majority of prefrontal cortical neurones. These investigations were made with neuroleptic drugs applied to the bath in the micromolar concentration range in order to approach clinical brain concentrations that are reached after administration of therapeutic doses. The drug concentrations reached in the slices after the experiments were assessed by means of high-pressure liquid chromatography coupled with mass-spectrometric detection. Surprisingly, drug accumulation in the in vitro preparation was of similar degree as reported in vivo. In conclusion, the typical neuroleptic haloperidol significantly depressed excitatory synaptic transmission in layer V neurones of the prefrontal cortex. In contrast, the two atypical neuroleptics iloperidone and clozapine revealed no depressing effects. This feature of the atypical neuroleptics might be beneficial since a hypofunctionality of this brain area is thought to be linked with the pathophysiology of schizophrenia. Additionally, clozapine facilitated long-term potentiation, which might be linked with the clinically observed beneficial effects on certain cognitive parameters. The clozapine-induced increase of N-methyl-D-aspartic acid receptor-mediated currents suggests that clozapine facilitates the induction of long-term potentiation. Furthermore, the present study points to the importance of considering the significant accumulation of neuroleptic drugs in in vitro studies.

Asunto(s)

2-Amino-5-fosfonovalerato/análogos & derivados , Antipsicóticos/farmacología , Química Encefálica/efectos de los fármacos , Plasticidad Neuronal/efectos de los fármacos , Corteza Prefrontal/efectos de los fármacos , Transmisión Sináptica/efectos de los fármacos , 2-Amino-5-fosfonovalerato/farmacología , 6-Ciano 7-nitroquinoxalina 2,3-diona/farmacología , Potenciales de Acción/efectos de los fármacos , Animales , Química Encefálica/fisiología , Clozapina/farmacología , Relación Dosis-Respuesta a Droga , Estimulación Eléctrica , Antagonistas de Aminoácidos Excitadores/farmacología , Haloperidol/farmacología , Técnicas In Vitro , Isoxazoles/farmacología , Magnesio/farmacología , Masculino , Técnicas de Placa-Clamp/métodos , Piperidinas/farmacología , Corteza Prefrontal/anatomía & histología , Corteza Prefrontal/citología , Corteza Prefrontal/fisiología , Células Piramidales/efectos de los fármacos , Células Piramidales/fisiología , Ratas , Ratas Sprague-Dawley , Receptores de N-Metil-D-Aspartato/fisiología , Factores de Tiempo

RESUMEN

1. Electrophysiological experiments were performed in vitro and in vivo. Voltage clamp recordings were done in Xenopus oocytes. Extracellular recordings were done in vitro in the neocortical slice and in the CA1 region of the hippocampal slice and in vivo in the CA1 region of the hippocampus of the anaesthetized rat. 2. In oocytes expressing either the human NMDAR1A/2A or 1A/2B subunit combinations, CGP68730A [sodium (-)-9-bromo-2,3,6,7-tetrahydro-5,6-dioxo-5H-pyrazino[1,2,3-de]-1,4-benzo thiazine-3-acetic acid] antagonized L-glutamate / glycine induced currents with calculated IC50s of 20.5 and 81.6 nM, respectively. 3. In vitro, CGP68730A was tested on NMDA induced depolarizations in the neocortical slice preparation and on epileptiform activity in hippocampal slices bathed in Mg2+-free-medium, which is known to be NMDA mediated. In both in vitro models CGP68730A exhibited antagonistic effects on the NMDA receptor mediated responses. 4. In vivo CGP68730A was tested on NMDA induced excitations in the CA1 region. CGP68730A abolished NMDA induced excitations when applied microiontophoretically. However, only weak effects on NMDA induced excitation were observed after systemic administration at 100 mg/kg i.v.. These results indicate that CGP68730A has poor central nervous system bioavailability. 5. In oocytes, an increase in the glycine concentration from the EC80 to the EC95.99 shifted the inhibition curves for CGP68730A to the right. Furthermore, in neocortical slices and in anaesthetized rats CGP68730A inhibited NMDA mediated depolarizations, and this effect could be reversed by the addition of the glycine mimetic D-serine. This indicates that these effects of CGP68730A are mediated by an action on the strychnine-insensitive glycine site. 6. Selectivity tests in oocytes and in the neocortical slice preparation, using NMDA, kainate and AMPA showed that CGP68730A was selective in antagonizing NMDA receptor mediated responses. In oocytes, the compound was about 1000 times less potent on the rat GluR3 and the human GluR6 receptors than on the human NMDAR1A/2A subunit combination. In the neocortical slice preparationCGP68730A had no effects on AMPA or kainate induced depolarizations at concentrations of 3 and 10 microM. At 30 microM CGP68730A reduced the effects of each of the three agonists tested. 7. Thus, CGP68730A seems to be a selective antagonist at the strychnine-insensitive glycine coagonist site of the NMDA receptor. However, the compound showed no obvious central NMDA antagonistic effects following intravenous application.

Asunto(s)

Hipocampo/fisiología , N-Metilaspartato/antagonistas & inhibidores , Receptores de N-Metil-D-Aspartato/fisiología , Animales , Sitios de Unión/fisiología , Electrofisiología , Hipocampo/efectos de los fármacos , N-Metilaspartato/farmacología , Neocórtex/efectos de los fármacos , Neocórtex/fisiología , Oocitos/efectos de los fármacos , Oocitos/fisiología , Técnicas de Placa-Clamp , Receptores de N-Metil-D-Aspartato/efectos de los fármacos , Estricnina/farmacología , Xenopus

Asunto(s)

Proteínas de Unión al GTP/metabolismo , Receptores de GABA-B/metabolismo , Animales , Línea Celular , Clonación Molecular , Proteínas Fluorescentes Verdes , Humanos , Inmunohistoquímica , Proteínas Luminiscentes , Canales de Potasio/metabolismo , Ratas , Receptores de GABA-B/genética , Proteínas Recombinantes de Fusión

RESUMEN

Synaptic activation of gamma-aminobutyric acid (GABA)B receptors at GABA synapses causes (a) postsynaptic hyperpolarization mediating a slow inhibitory postsynaptic potential/current (IPSP/C) and (b) presynaptic inhibition of GABA release which depresses IPSPs and leads to paired-pulse widening of excitatory postsynaptic potentials (EPSPs). To address whether these effects are mediated by pharmacologically identical receptors the effects of six GABA(B) receptor antagonists of widely ranging potencies were tested against each response. Monosynaptic IPSP(B)s were recorded in the presence of GABA(A), AMPA/kainate and NMDA receptor antagonists. All GABA(B) receptor antagonists tested depressed the IPSP(B) with an IC50 based rank order of potency of CGP55679> or =CGP56433 = CGP55845A = CGP52432>CGP51176>CGP36742. Paired-pulse EPSP widening was recorded as an index of paired-pulse depression of GABA-mediated IPSP/Cs. A similar rank order of potency of antagonism of paired-pulse widening was observed to that for IPSP(B) inhibition. Comparison of the IC50 values for IPSP(B) inhibition and paired-pulse EPSP widening revealed a close correlation between the two effects in that their IC50s lay within the 95% confidence limits of a correlation line that described IC50 values for inhibition of paired-pulse EPSP widening that were 7.3 times higher than those for IPSP(B) inhibition. Using the compounds tested here it is not possible to assign different subtypes of GABA(B) receptor to pre- and post-synaptic loci at GABAergic synapses. However, 5-10 fold higher concentrations of antagonist are required to block presynaptic as opposed to postsynaptic receptors when these are activated by synaptically released GABA.

Asunto(s)

Antagonistas de Receptores de GABA-B , Hipocampo/fisiología , Receptores Presinapticos/antagonistas & inhibidores , Sinapsis/fisiología , Ácido gamma-Aminobutírico/fisiología , Animales , Autorreceptores/antagonistas & inhibidores , Electrofisiología , Potenciales Postsinápticos Excitadores/fisiología , Antagonistas del GABA/farmacología , Hipocampo/efectos de los fármacos , Técnicas In Vitro , Microelectrodos , Ratas , Ratas Wistar , Receptores AMPA/antagonistas & inhibidores , Receptores de Ácido Kaínico/antagonistas & inhibidores

RESUMEN

Activation of NMDA receptors requires the presence of glycine as a coagonist which binds to a site that is allosterically linked to the glutamate binding site. To identify the protein constituents of the glycine binding site in situ the photoaffinity label [3H]CGP 61594 was synthesized. In reversible binding assays using crude rat brain membranes, [3H]CGP 61594 labeled with high affinity (K(D) = 23 nM) the glycine site of the NMDA receptor. This was evident from the Scatchard analysis, the displacing potencies of various glycine site ligands and the allosteric modulation of [3H]CGP 61594 binding by ligands of the glutamate and polyamine sites. Electrophysiological experiments in a neocortical slice preparation identified CGP 61594 as a glycine antagonist. Upon UV-irradiation, a protein band of 115 kDa was specifically photolabeled by [3H]CGP 61594 in brain membrane preparations. The photolabeled protein was identified as the NR1 subunit of the NMDA receptor by NR1 subunit-specific immunoaffinity chromatography. Thus, [3H]CGP 61594 is the first photoaffinity label for the glycine site of NMDA receptors. It will serve as a tool for the identification of structural elements that are involved in the formation of the glycine binding domain of NMDA receptors in situ and will thereby complement the mutational analysis of recombinant receptors.

Asunto(s)

Azidas/farmacología , Azidas/farmacocinética , Encéfalo/fisiología , Agonistas de Aminoácidos Excitadores/farmacocinética , Glicina/metabolismo , Quinolinas/farmacología , Quinolinas/farmacocinética , Receptores de N-Metil-D-Aspartato/metabolismo , Marcadores de Afinidad , Animales , Azidas/síntesis química , Sitios de Unión , Unión Competitiva , Encéfalo/efectos de los fármacos , Membrana Celular/metabolismo , Corteza Cerebral/fisiología , Electrofisiología , Potenciales Evocados/efectos de los fármacos , Agonistas de Aminoácidos Excitadores/farmacología , Hipocampo/fisiología , Técnicas In Vitro , Cinética , Ligandos , Masculino , N-Metilaspartato/farmacología , Neocórtex/fisiología , Quinolinas/síntesis química , Ratas , Ratas Sprague-Dawley , Serina/farmacología , Tritio

RESUMEN

Electrophysiological experiments were performed in vitro and in vivo to characterize the inhibitory effects of 6,7-dichloro-5-nitro-1,4-dihydro-2,3-quinoxalinedione (ACEA 1021; licostinel) on rat brain glutamate receptors. In vitro, ACEA 1021 was tested on N-methyl-D-aspartate (NMDA)-induced depolarizations in the neocortical slice preparation and on epileptiform activity in Mg2+-free hippocampal slices, which is known to be NMDA receptor mediated. In both in vitro models, ACEA 1021 exhibited antagonistic effects on the NMDA receptor-mediated responses. Selectivity tests in the neocortical slice preparation, using NMDA, kainate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) showed that 10 microM ACEA 1021 reduced NMDA and kainate responses to 27.9 and 79.9% of the control value, respectively, whereas responses to AMPA were increased by 2.4% above the control value, thus showing that at this concentration ACEA 1021 acts preferentially at NMDA receptors. However, at 30 microM, all the NMDA-, AMPA- and kainate-induced responses were reduced. In vivo, ACEA 1021 was tested on NMDA-induced excitation in the CA1 region. After systemic administration of ACEA 1021, central effects were observed at 10 mg/kg i.v. in the CA1 region. These results indicate that ACEA 1021 is centrally active and inhibits NMDA receptor-mediated responses. Interestingly, selectivity tests in the CA1 region did not show clear differences in the action of ACEA 1021 on NMDA- and AMPA-induced excitations. Furthermore, ACh-induced excitations were also reduced. Thus, at low concentrations, ACEA 1021 seems to be a selective antagonist at the strychnine-insensitive glycine site of the NMDA receptor. However, at 30 microM in vitro and at 10 mg/kg in vivo, non-NMDA receptor-mediated actions of ACEA 1021 are observed. Our results suggest that these additional effects of ACEA 1021 may contribute to its anticonvulsive properties in mice as well as to its neuroprotective properties in animal models of cerebral ischemia.

Asunto(s)

Antagonistas de Aminoácidos Excitadores/farmacología , Hipocampo/efectos de los fármacos , Neocórtex/efectos de los fármacos , Quinoxalinas/farmacología , Receptores de N-Metil-D-Aspartato/antagonistas & inhibidores , Acetilcolina/farmacología , Animales , Electrofisiología , Hipocampo/fisiología , Masculino , N-Metilaspartato/farmacología , Neocórtex/fisiología , Ratas , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/farmacología

RESUMEN

The novel tachykinin receptor antagonist CGP49823 ((2R,4S)-2-benzyl-1-(3,5-dimethylbenzoyl)-4-(quinolin-4-y lmethylamino)piperidine) has been compared with three other selective non-peptide tachykinin NK1 receptor antagonists. The drugs were tested as antagonists of the depolarization of spinal motoneurones induced by bath application of the selective tachykinin NK1 receptor agonist septide-(6-11) (300 nM) for 120 s at 15 min intervals. The antagonists were bath applied and the depolarizations were recorded from lumbar ventral roots of 7 to 12 day old rat and gerbil hemisected spinal cords in vitro. The gerbil preparation is considered to model the human species variant of the tachykinin NK1 receptor. With the exception of SR140333 ((S)-1-[2-[3-(3,4-dichlorophenyl)-1-[[3-(1-methylethoxy)phenyl]ace tyl]-3-piperidinyl]ethyl]-4-phenyl-1-azoniabicyclo[2.2.2]octane chloride), the antagonists were approximately thirty-fold more potent on gerbil preparations. The respective mean IC50 values from gerbil preparations produced by CP96345 ((2S-cis)-2-(diphenylmethyl)-N-[(2-methoxyphenyl)methyl]-1-azabicy clo[2.2.2]octan-3-amine), CGP49823, SR140333 and CP99994 ((2S-cis)-N-[(2-methoxyphenyl)methyl]-2-phenyl-3-piperidinamine) were, in microM +/- S.E. (n) 0.10 +/- 0.02 (6), 0.22 +/- 0.03 (6), 0.30 +/- 0.10 (5) and 0.38 +/- 0.02 (5) and the corresponding values from the rat preparations were 3.7 +/- 0.4 (5), 7.8 + 1.3 (5), 1.06 +/- 0.16 (6) and 10.5 +/- 2.2 (7). Dominance of tachykinin NK1 receptor activity in the measured responses was confirmed by low potency of the tachykinin NK2-selective antagonist SR48968 ((S)-N-methyl-N[4-(4-acetylamino-4-phenyl piperidino)-2-(3,4-dichlorophenyl)butyl] benzamide) which yielded an IC50 value of 12.0 +/- 2.8 (5) on gerbil preparations and produced less than 50% depression of septide-induced depolarization of rat motoneurones at the highest concentration (100 microM) tested.

Asunto(s)

Ansiolíticos/farmacología , Neuronas Motoras/efectos de los fármacos , Piperidinas/farmacología , Receptores de Taquicininas/antagonistas & inhibidores , Animales , Gerbillinae , Técnicas In Vitro , Antagonistas del Receptor de Neuroquinina-1 , Fármacos Neuromusculares Despolarizantes/farmacología , Fragmentos de Péptidos/farmacología , Ácido Pirrolidona Carboxílico/análogos & derivados , Quinolinas/farmacología , Ratas , Ratas Endogámicas , Receptores de Neuroquinina-2/antagonistas & inhibidores , Sustancia P/análogos & derivados , Sustancia P/farmacología

RESUMEN

This study sought to investigate the influence of GABAB receptor activation on acoustically induced excitation within the rat inferior colliculus. To this end, the GABAB receptor antagonist, CGP 35348, was applied systemically and iontophoretically. Single and multibarrel electrodes were used for extracellular recordings within the central nucleus of the inferior colliculus. The experimental model, a paired-pulse stimulus paradigm, applied two identical acoustic stimuli, 200 msec apart, evoking corresponding responses characterized by the second being consistently weaker than the first. Abolishment of the acoustically evoked response, following iontophoretic application of the GABAB receptor agonist, L-baclofen, verified the existence of GABAB receptors in all inferior colliculus cells tested. Intravenous application of CGP 35348 (200 mg/kg) evoked a 24% overall increase in stimulus responses. Likewise, a 13% increase in total evoked excitation was observed, following iontophoretic application. There was no significant reduction of inhibition on the second evoked response in the paired-pulse model, following either systemic or iontophoretic application of CGP 35348. This result implies that the decreased magnitude of the second response, with an interpulse interval of 200 msec, is not influenced by GABAB receptor mediated inhibition. These findings do indicate, however, that GABAB receptors play a small, but significant role during the processing of acoustic information, within the inferior colliculus.

Asunto(s)

Estimulación Acústica , Antagonistas del GABA/farmacología , Colículos Inferiores/fisiología , Neuronas/fisiología , Compuestos Organofosforados/farmacología , Receptores de GABA-B/fisiología , Potenciales de Acción/efectos de los fármacos , Animales , Baclofeno/farmacología , Antagonistas de Receptores de GABA-B , Colículos Inferiores/efectos de los fármacos , Iontoforesis , Masculino , Neuronas/efectos de los fármacos , Compuestos Organofosforados/administración & dosificación , Ratas , Ratas Endogámicas , Factores de Tiempo

RESUMEN

The synaptic release of gamma-aminobutyric acid (GABA) is thought to be regulated by presynaptic GABA receptors of the B-type. It was the goal of this study to validate this concept electrophysiologically using four selective antagonists of GABA-B receptors. Experiments were performed in hippocampal slices exposed to 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX 30 microM) and D-2-amino-5-phosphonopentanoate (AP5 40 microM) in order to block excitatory transmission. Consequently, electrical stimulation of the Schaffer collateral/commissural fibers evoked monosynaptic inhibitory potentials (IPSP) recorded intracellularly from CA 1 pyramidal neurons. In a test called paired-pulse paradigm two identical stimuli were applied at intervals ranging from 350 to 4000 ms. The IPSP evoked by the second stimulation was smaller in its amplitude over the entire interval range. This reduction of the second GABA-response is thought to result from the activation of presynaptic GABA receptors. The GABA-uptake inhibitor SKF 89976 (100 microM) increased the amplitude of the IPSP's and increased the ratio of the first to the second IPSP amplitude. These findings indicate that the drug increases the GABA content in the synaptic cleft leading to a facilitation of paired-pulse depression. The actions of four bath-applied GABA-B receptor antagonists were examined in the paired-pulse paradigm. None of these compounds abolished paired-pulse inhibition completely even at concentrations higher than those required to block postsynaptic GABA-B responses. The potent GABA-B antagonists CGP 55845 and CGP 52432 reduced paired-pulse depression by 80% at 10 microM (maximal effect).(ABSTRACT TRUNCATED AT 250 WORDS)

Asunto(s)

Hipocampo/efectos de los fármacos , Receptores de GABA-B/efectos de los fármacos , Receptores Presinapticos/efectos de los fármacos , Animales , Bencilaminas/farmacología , Interacciones Farmacológicas , Estimulación Eléctrica , Electrofisiología , Antagonistas de Receptores de GABA-B , Hipocampo/fisiología , Masculino , Compuestos Organofosforados/farmacología , Ácidos Fosfínicos/farmacología , Propanolaminas/farmacología , Ratas , Receptores de GABA-B/fisiología , Receptores Presinapticos/fisiología

RESUMEN

The new GABAB receptor antagonist CGP 55845A was tested on pre- and post-synaptic GABAB receptors in the hippocampus. CGP 55845A (1 microM) blocked (-)-baclofen (5-10 microM)-induced postsynaptic hyperpolarization and depression of evoked IPSPs and EPSPs. It also blocked three physiological consequences of GABAB receptor activation: the late IPSP, paired-pulse depression of IPSCs, and heterosynaptic depression of EPSPs. Therefore, CGP 55845A is an antagonist at pre- and post-synaptic GABAB receptors in the hippocampus and is approximately three orders of magnitude more potent than previously described GABAB receptor antagonists.

Asunto(s)

Hipocampo/metabolismo , Ácidos Fosfínicos/farmacología , Propanolaminas/farmacología , Receptores de GABA-B , Animales , Baclofeno/antagonistas & inhibidores , Baclofeno/farmacología , Potenciales Evocados/efectos de los fármacos , Antagonistas de Receptores de GABA-B , Hipocampo/efectos de los fármacos , Técnicas In Vitro , Ratas , Sinapsis/efectos de los fármacos , Sinapsis/metabolismo , Ácido gamma-Aminobutírico/metabolismo

RESUMEN

The goal of this report is to present the results obtained with three new GABAB receptor antagonists. CGP 54062 has an IC50 in a GABAB binding test of 0.013 microM which is roughly 2500-fold lower than one of the most potent blockers known so far, CGP 35348 (IC50 = 34 microM). CGP 46381 and CGP 36742 have IC50s of 4.9 and 36 microM respectively. The latter two compounds are the first orally active GABAB receptor antagonists. All three compounds bind to the GABAB receptor selectively, and are inactive in a number of binding tests assessing the compounds' affinity to various other receptor sites. The effect of these blockers on GABAergic transmission was investigated in the CA1 area of hippocampal slices. The Schaffer collateral/commissural fibers were stimulated and the evoked postsynaptic potentials were recorded intracellularly in pyramidal neurons. The three antagonists blocked the late inhibitory postsynaptic potential with the following rank order of potency CGP 54062 > 46381 > 36742 approximately 35348. These findings support the hypothesis that these potentials are mediated by GABAB receptors. Orally administered CGP 36742 and CGP 46381 block the neuronal depression induced by iontophoretically applied baclofen in anaesthetised rats. Up to a dose of 10 mg/kg i.v. CGP 54062 was inactive and thus does not appear to cross the blood-brain barrier at this dose. In anaesthetised rats the effects of the three new GABAB antagonists and of CGP 35348 were investigated on the paired-pulse inhibition of the population spikes evoked in the CA1 area of the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

Asunto(s)

Encéfalo/efectos de los fármacos , Antagonistas de Receptores de GABA-A , Ácido gamma-Aminobutírico/metabolismo , Administración Oral , Animales , Encéfalo/metabolismo , Masculino , Ratas , Receptores de GABA-A/metabolismo

RESUMEN

Understanding the mechanisms involved in long-term potentiation (LTP) should provide insights into the cellular and molecular basis of learning and memory in vertebrates. It has been established that in the CA1 region of the hippocampus the induction of LTP requires the transient activation of the N-methyl-D-aspartate (NMDA) receptor system. During low-frequency transmission, significant activation of this system is prevented by gamma-aminobutyric acid (GABA) mediated synaptic inhibition which hyperpolarizes neurons into a region where NMDA receptor-operated channels are substantially blocked by Mg2+ (refs. 5, 6). But during high-frequency transmission, mechanisms are evoked that provide sufficient depolarization of the postsynaptic membrane to reduce this block and thereby permit the induction of LTP. We now report that this critical depolarization is enabled because during high-frequency transmission GABA depresses its own release by an action on GABAB autoreceptors, which permits sufficient NMDA receptor activation for the induction of LTP. These findings demonstrate a role for GABAB receptors in synaptic plasticity.

Asunto(s)

Hipocampo/fisiología , Plasticidad Neuronal , Compuestos Organofosforados/farmacología , Receptores de GABA-A/fisiología , Receptores de N-Metil-D-Aspartato/fisiología , 2-Cloroadenosina/farmacología , Animales , Baclofeno/farmacología , Carbacol/farmacología , Técnicas In Vitro , Potenciales de la Membrana/efectos de los fármacos , Ratas

RESUMEN

We present a comparative study of the modulation of the N-methyl-D-aspartate (NMDA) receptor at the strychnine-insensitive glycine site in the spinal cord and in the cortex. The excitatory effect of NMDA was potentiated by D-serine (a glycine mimetic) in the hemisected rat spinal cord. The non-competitive NMDA antagonists 7-chlorokynurenic acid (7-Cl KYNA; 10 microM) and 3-amino-1-hydroxypyrrolid-2-one (HA-966; 100 or 200 microM) antagonized the effect of NMDA in the spinal cord and cortical wedge preparation. The antagonism was reversed by the addition of D-serine. This effect was strychnine-insensitive and hence not related to the inhibitory glycine receptor known to be present in the spinal cord. Our results suggest strongly that glycine positively modulates the NMDA system not only at a supraspinal level but also at the spinal level. As the positive modulation of NMDA responses by D-serine was also seen in the presence of tetrodotoxin, we conclude that the NMDA/glycine complex is (also) located on motoneurones in addition to the known glycine-mediated inhibitory system.

Asunto(s)

Corteza Cerebral/efectos de los fármacos , Receptores de N-Metil-D-Aspartato/efectos de los fármacos , Serina/farmacología , Médula Espinal/efectos de los fármacos , Animales , Corteza Cerebral/fisiología , Potenciales Evocados/efectos de los fármacos , Técnicas In Vitro , Ácido Quinurénico/análogos & derivados , Ácido Quinurénico/farmacología , Masculino , Pirrolidinonas/farmacología , Ratas , Receptores de N-Metil-D-Aspartato/antagonistas & inhibidores , Receptores de N-Metil-D-Aspartato/fisiología , Médula Espinal/fisiología , Estricnina/farmacología , Tetrodotoxina/farmacología

RESUMEN

The biochemical, electrophysiological and pharmacological properties of the new GABAB receptor blocker CGP 35348 are described. In a variety of receptor binding assays CGP 35348 showed affinity for the GABAB receptor only. CGP 35348 had an IC50 of 34 microM at the GABAB receptor. The compound antagonized (100, 300, 1000 microM) the potentiating effect of L-baclofen on noradrenaline-induced stimulation of adenylate cyclase in rat cortex slices. In electrophysiological studies CGP 35348 (10, 100 microM) antagonized the effect of L-baclofen in the isolated rat spinal cord. In the hippocampal slice preparation CGP 35348 (10, 30, 100 microM) blocked the membrane hyperpolarization induced by D/L-baclofen (10 microM) and the late inhibitory postsynaptic potential. CGP 35348 appeared to be 10-30 times more potent than the GABAB receptor blocker phaclofen. Ionophoretic and behavioural experiments showed that GABAB receptors in the brain were blocked after i.p. administration of CGP 35348. This compound may be of considerable value in elucidating the roles of brain GABAB receptors.

Asunto(s)

Anticonvulsivantes/farmacología , Compuestos Organofosforados/farmacología , Receptores de GABA-A/efectos de los fármacos , Inhibidores de Adenilato Ciclasa , Animales , Animales Recién Nacidos/metabolismo , Baclofeno/análogos & derivados , Baclofeno/farmacología , Conducta Animal/efectos de los fármacos , Química Encefálica/efectos de los fármacos , AMP Cíclico/metabolismo , Electrofisiología , Hipocampo/efectos de los fármacos , Técnicas In Vitro , Iontoforesis , Equilibrio Postural/efectos de los fármacos , Ensayo de Unión Radioligante , Ratas , Ratas Endogámicas , Médula Espinal/efectos de los fármacos , Médula Espinal/metabolismo

RESUMEN

The selectivity and potency of the novel competitive N-methyl-D-aspartate (NMDA) receptor antagonists, CGP 37849 and CGP 39551, were investigated in vitro and in vivo using electrophysiological approaches. Like the reference blocker DL-AP5, both compounds acted in vitro (hippocampus, substantia nigra, spinal cord) to antagonize the excitatory actions of exogenously administered NMDA as well as the synaptically elicited, physiological NMDA receptor responses in hippocampus and spinal cord. In all isolated preparations CGP 37849 was more potent than CGP 39551, and 5- to 10-fold more potent than DL-AP5. Neither compound showed any marked effect on responses evoked by quisqualate and kainate. NMDA excited dopaminergic cells in the pars compacta region of the substantia nigra in a concentration-dependent manner. This effect also could be selectively antagonized by CGP 37849 and CGP 39551. In the anaesthetized rat, excitatory responses of hippocampal pyramidal cells evoked by iontophoretic application of NMDA were antagonized by CGP 37849 and CGP 39551 following their oral administration without reducing quisqualate or kainate responses. In contrast to the in vitro situation, CGP 39551 was more potent than CGP 37849 in vivo. Effective doses were 30 mg/kg p.o. for CGP 39551 and 100 mg/kg p.o. for CGP 37849. In conclusion, it is demonstrated that CGP 37849 and CGP 39551 selectively antagonize NMDA evoked neuronal responses in vivo and in vitro and that the drugs are centrally active following their oral administration.

Asunto(s)

2-Amino-5-fosfonovalerato/análogos & derivados , Receptores de Neurotransmisores/antagonistas & inhibidores , 2-Amino-5-fosfonovalerato/farmacología , Animales , Conducta Animal/efectos de los fármacos , Electrofisiología , Hipocampo/efectos de los fármacos , Hipocampo/fisiología , Iontoforesis , Masculino , Oxadiazoles/farmacología , Piperazinas/farmacología , Ácido Quiscuálico , Ratas , Ratas Endogámicas , Receptores de N-Metil-D-Aspartato , Médula Espinal/efectos de los fármacos , Médula Espinal/fisiología , Sustancia Negra/efectos de los fármacos , Sustancia Negra/fisiología , Valina/análogos & derivados , Valina/farmacología

RESUMEN

1. The pharmacological properties of CGP 37849 (DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid; 4-methyl-APPA) and its carboxyethylester, CGP 39551, novel unsaturated analogues of the N-methyl-D-aspartate (NMDA) receptor antagonist, 2-amino-5-phosphonopentanoate (AP5), were evaluated in rodent brain in vitro and in vivo. 2. Radioligand binding experiments demonstrated that CGP 37849 potently (Ki 220 nM) and competitively inhibited NMDA-sensitive L-[3H]-glutamate binding to postsynaptic density (PSD) fractions from rat brain. It inhibited the binding of the selective NMDA receptor antagonist, [3H]-((+/-)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP), with a Ki of 35 nM, and was 4, 5 and 7 fold more potent than the antagonists [+/-)-cis-4-phosphonomethylpiperidine-2-carboxylic acid) (CGS 19755), CPP and D-AP5, respectively. Inhibitory activity was associated exclusively with the trans configuration of the APPA molecule and with the D-stereoisomer. CGP 39551 showed weaker activity at NMDA receptor recognition sites and both compounds were weak or inactive at 18 other receptor binding sites. 3. CGP 37849 and CGP 39551 were inactive as inhibitors of L-[3H]-glutamate uptake into rat brain synaptosomes and had no effect on the release of endogenous glutamate from rat hippocampal slices evoked by electrical field stimulation. 4. In the hippocampal slice in vitro, CGP 37849 selectively and reversibly antagonized NMDA-evoked increases in CA1 pyramidal cell firing rate. In slices bathed in medium containing low Mg2+ levels, concentrations of CGP 37849 up to 10 microM suppressed burst firing evoked in CAl neurones by stimulation of Schaffer collateral-commissural fibres without affecting the magnitude of the initial population spike; CGP 39551 exerted the same effect but was weaker. In vivo, oral administration to rats of either CGP 37849 or CGP 39551 selectively blocked firing in hippocampal neurones induced by ionophoreticallyapplied NMDA, without affecting the responses to quisqualate or kainate. 5. CGP 37849 and CGP 39551 suppressed maximal electroshock-induced seizures in mice with ED50 s of 21 and 4 mg kg'- p.o., respectively. 6. CGP 37849 and CGP 39551 are potent and competitive NMDA receptor antagonists which show significant central effects following oral administration to animals. As such, they may find value as tools to elucidate the roles of NMDA receptors in brain function, and potentially as therapeutic agents for the treatment of neurological disorders such as epilepsy and ischaemic brain damage in man.

Asunto(s)

2-Amino-5-fosfonovalerato/análogos & derivados , Receptores de Neurotransmisores/antagonistas & inhibidores , 2-Amino-5-fosfonovalerato/farmacología , Animales , Anticonvulsivantes , Unión Competitiva/efectos de los fármacos , Electrofisiología , Electrochoque , Glutamatos/metabolismo , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Técnicas In Vitro , Cinética , Masculino , Neurotransmisores/metabolismo , Ensayo de Unión Radioligante , Ratas , Ratas Endogámicas , Receptores de N-Metil-D-Aspartato , Receptores de Neurotransmisores/metabolismo , Sodio/metabolismo , Valina/análogos & derivados , Valina/farmacología

Asunto(s)

2-Amino-5-fosfonovalerato/análogos & derivados , Anticonvulsivantes/farmacología , Receptores de N-Metil-D-Aspartato/antagonistas & inhibidores , 2-Amino-5-fosfonovalerato/administración & dosificación , 2-Amino-5-fosfonovalerato/metabolismo , 2-Amino-5-fosfonovalerato/farmacología , Administración Oral , Animales , Anticonvulsivantes/administración & dosificación , Unión Competitiva , Cinética , Ratas , Receptores de N-Metil-D-Aspartato/metabolismo

RESUMEN

The goal of this study was to investigate whether locus coeruleus neurons of the rat are sensitive to agonists of the different excitatory amino acid receptors. All experiments were performed on a midpontine rat slice preparation. Bath-applied L-glutamate, kainate, N-methyl-D-aspartate (NMDA) and quisqualate induced concentration-dependent activations of all neurons which were reflected in an increase of the neurons' mean discharge rate. The rank order of cell activation was kainate approximately quisqualate greater than NMDA greater than L-glutamate. None of the agonists induced a bursting-type of discharge. The NMDA-receptor blocker DL-2-amino-5-phosphonovaleric acid (APV, 30 microM) selectively antagonized the NMDA-induced increase in cell firing. Kynurenic acid (100 microM) non-selectively attenuated the response to NMDA, kainate and quisqualate. Neither APV nor kynurenic acid per se had any effect on the spontaneous firing rate. If the Mg2+ concentration in the superfusion medium was lowered from 2 mM to nominally zero the response to NMDA was selectively increased. In conclusion, locus coeruleus neurons share with other neurons their sensitivity to agonists of all three types of excitatory amino acid receptors. However, in contrast to other neurons, they do not respond with a bursting type of discharge.

Asunto(s)

Locus Coeruleus/metabolismo , Receptores de Superficie Celular/metabolismo , 2-Amino-5-fosfonovalerato , Animales , Anticonvulsivantes/farmacología , Ácido Aspártico/análogos & derivados , Ácido Aspártico/farmacología , Glutamatos/farmacología , Técnicas In Vitro , Ácido Kaínico/farmacología , Magnesio/fisiología , Masculino , N-Metilaspartato , Neuronas/metabolismo , Oxadiazoles/farmacología , Ácido Quiscuálico , Ratas , Ratas Endogámicas , Receptores de Aminoácidos , Valina/análogos & derivados , Valina/farmacología

RESUMEN

The minor branch of the tritocerebral commissure of the locust, Locusta migratoria, contains only two axons which are from interneurons in the brain descending to the ventral cord ganglia. The smaller of these two neurons, the tritocerebral commissure dwarf (TCD), is immunoreactive to GABA, suggesting that it may be an inhibitory interneuron. We have exploited the accessibility of its axon in the commissure, first, to fill it with cobalt to define its morphology, and second, to record its input characteristics. It has a cell body and arborization of fine branches in the deutocerebrum of the brain, its axon passes contralateral through the tritocerebral commissure and it forms bilateral arborizations in the suboesophageal and three thoracic ganglia. It receives mechanosensory input from many regions of the ipsilateral body and head, and it is sensitive to illumination levels, generally showing greater spontaneous activity in the dark. It is one of the largest GABA-immunoreactive descending interneurons in the locust, suggesting it plays a prominent role in behaviour. Since it is easily accessible for physiological recording, its roles in circuits for particular components of behaviour should be amenable to investigation.

Asunto(s)

Encéfalo/citología , Saltamontes/anatomía & histología , Interneuronas/citología , Neuronas Aferentes/citología , Ácido gamma-Aminobutírico/metabolismo , Potenciales de Acción , Animales , Encéfalo/metabolismo , Encéfalo/fisiología , Mapeo Encefálico , Cobalto , Vías Eferentes/anatomía & histología , Ganglios/citología , Saltamontes/fisiología , Inmunohistoquímica , Interneuronas/metabolismo , Interneuronas/fisiología , Neuronas Aferentes/metabolismo , Neuronas Aferentes/fisiología , Estimulación Luminosa , Estimulación Física