RESUMEN
Ethylenediamine (EDA) activates GABA(A) receptors via both direct and indirect mechanisms. EDA has been shown to reduce seizures caused by systemic injection of proconvulsants in an animal model of generalized tonic-clonic seizures. However, there does not appear to have been any report on the effects of EDA in other seizure models. Hence, we used male Sprague-Dawley rats to test the effects of EDA on topically applied bicuculline (a model of simple partial seizures) and on maximal electroshock (MES, a model of generalized tonic-clonic seizures). We also examined the effects of EDA on motor coordination using a rotarod treadmill, and its potential anxiolytic properties using an elevated plus maze (EPM). EDA at concentrations of 50 µM and above reduced the frequency of epileptiform spikes on an electrocorticogram in a concentration-dependent manner. EDA at 100 and 1000 mg/kg i.p. increased the threshold for inducing limb extension on the MES. EDA did not affect the time spent by rats on the rotarod at 10 or 100mg/kg, but significantly reduced the time spent at doses of 1000 mg/kg. In the EPM, EDA at 10 or 100mg/kg significantly increased the frequency of entries and time spent in the open arms. We conclude that EDA has antiepileptic and anxiolytic activity at doses that do not affect motor coordination.
Asunto(s)
Anticonvulsivantes/farmacología , Ansiedad/tratamiento farmacológico , Etilenodiaminas/farmacología , Pentilenotetrazol/toxicidad , Desempeño Psicomotor/efectos de los fármacos , Convulsiones/tratamiento farmacológico , Animales , Ansiolíticos/farmacología , Ansiedad/inducido químicamente , Convulsivantes/toxicidad , Modelos Animales de Enfermedad , Electrochoque , Masculino , Ratas , Ratas Sprague-Dawley , Convulsiones/inducido químicamenteRESUMEN
The simple diamine diaminoethane (ethylenediamine, EDA) has been shown to activate GABA receptors in the central and peripheral nervous systems, partly by a direct action and partly by releasing endogenous GABA. These effects have been shown to be produced by the complexation of EDA with bicarbonate to form a carbamate. The present work has compared EDA, GABA and β-alanine responses in rat CA1 neurons using extracellular and intracellular recordings, as well as neocortical evoked potentials in vivo. Superfusion of GABA onto hippocampal slices produced depolarisation and a decrease of field epsps, both effects fading rapidly, but showing sensitivity to blockade by bicuculline. EDA produced an initial hyperpolarisation and increase of extracellular field epsp size with no fade and only partial sensitivity to bicuculline, with subsequent depolarisation, while β-alanine produces a much larger underlying hyperpolarisation and increase in fepsps, followed by depolarisation and inhibition of fepsps. The responses to β-alanine, but not GABA or EDA, were blocked by strychnine. In vivo experiments, recording somatosensory evoked potentials, confirmed that EDA produced an initial increase followed by depression, and that this effect was not fully blocked by bicuculline. Overall the results indicate that EDA has actions in addition to the activation of GABA receptors. These actions are not attributable to activation of β-alanine-sensitive glycine receptors, but may involve the activation of sites sensitive to adipic acid, which is structurally equivalent to the dicarbamate of EDA. The results emphasise the complex pharmacology of simple amines in bicarbonate-containing solutions.
Asunto(s)
Ratas , Animales , Humanos , Ácido gamma-Aminobutírico , Etilenodiaminas , Bicuculina , Ácido Quinurénico , HipocampoRESUMEN
In hippocampal slices, inhibition of AMPA receptors unmasks synaptic transmission via NMDA receptors, suggesting that AMPA receptor activation normally inhibits synaptic transmission via NMDA receptors. Activation of NMDA receptors is involved in the pathogenesis of cortical spreading depression (CSD) which has been implicated in the pathogenesis of migraine aura and neuronal damage from peri-infarct depolarizations. In this study we examined whether NMDA receptor transmission could be unmasked in the neocortex in vivo by AMPA receptor blockage and whether AMPA receptors could affect CSD induced by 200 mM KCl. We further compared the effects of AMPA to those of the NMDA receptor antagonist, 2-amino-5-phosphono-pentanoic acid (2AP5), and the GABA-mimetic drug clomethiazole. The NMDA receptor antagonist MK-801 did not affect the baseline somatosensory evoked potentials (SEPs). In a medium with no Mg(2+), the AMPA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) caused marked reduction in the SEP size which subsequently recovered partially; MK-801 blocked these partially recovered SEPs. AMPA (50 µM but not at 5 µM or 250 µM) and 2AP5 (10 µM) significantly reduced the number of CSD cycles. The effect of AMPA was not changed by co-applying it with cyclothiazide, which blocks AMPA receptor desensitization. Clomethiazole (100 mg/kg i.p.) did not significantly affect the number of CSD cycles. Only 2AP5 significantly reduced the potentiation that follows CSD. We conclude that activation of AMPA receptors can suppress the actions of NMDA receptors in the neocortex; this could be an intrinsic protective mechanism against CSD and also provide a possible therapeutic strategy against CSD-related neurological conditions.
Asunto(s)
Clormetiazol/farmacología , Depresión de Propagación Cortical/efectos de los fármacos , Receptores AMPA/efectos de los fármacos , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/farmacología , Animales , Maleato de Dizocilpina/farmacología , Relación Dosis-Respuesta a Droga , Potenciales Evocados Somatosensoriales/efectos de los fármacos , Agonistas de Aminoácidos Excitadores/administración & dosificación , Agonistas de Aminoácidos Excitadores/farmacología , Moduladores del GABA/farmacología , Masculino , Neocórtex/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Receptores AMPA/metabolismo , Receptores de N-Metil-D-Aspartato/efectos de los fármacos , Receptores de N-Metil-D-Aspartato/metabolismo , Transmisión Sináptica/efectos de los fármacos , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/administración & dosificaciónRESUMEN
Since the serine protease subtilisin has been reported to generate a novel form of long-term depression (LTD) in rat hippocampal slices, the present work was designed to determine whether it has any effect on learning and memory processes. Rats were used to examine the effects of subtilisin, injected directly into the dorsal hippocampus, on task performance in a step-through inhibitory avoidance of a mild footshock. The administration of 100 ng of subtilisin into each hippocampus, immediately after training, was sufficient to induce a detectable learning deficit with a footshock stimulus of 0.5 mA. Higher doses produced dose-related impairments in memory consolidation. These effects were not the result of irreversible toxicity, since rats trained with a higher amplitude footshock (0.75 mA) were able to perform as control animals; therefore, the amnesic effect was not further evident. Furthermore, the administration of subtilisin before avoidance training did not produce any detectable effect on performance during the training or test sessions, indicating that neither acquisition nor consolidation was affected. It is concluded that the post-training administration of a serine protease inhibitor is able to produce robust deficits of memory consolidation consistent with its ability to generate LTD, raising the possibility that related molecules could play physiological or pathological roles in the modulation of learning and memory.
Asunto(s)
Hipocampo/fisiología , Trastornos de la Memoria/inducido químicamente , Trastornos de la Memoria/psicología , Inhibidores de Serina Proteinasa/farmacología , Subtilisina/farmacología , Animales , Reacción de Prevención/efectos de los fármacos , Hemorragia Cerebral/inducido químicamente , Hemorragia Cerebral/patología , Relación Dosis-Respuesta a Droga , Electrochoque , Conducta Exploratoria/efectos de los fármacos , Inyecciones , Masculino , Memoria/efectos de los fármacos , Actividad Motora/efectos de los fármacos , Ratas , Ratas Wistar , Inhibidores de Serina Proteinasa/administración & dosificación , Inhibidores de Serina Proteinasa/efectos adversos , Subtilisina/administración & dosificación , Subtilisina/efectos adversosRESUMEN
We have previously reported that topical application of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) to the rat neocortex prevents the effects of a subsequent application of N-methyl-d-aspartic acid (NMDA). Activation of NMDA receptors is involved in the pathogenesis of epileptic activity. Therefore, we examined if topically applied AMPA could affect changes in the somatosensory evoked potentials (SEPs) and electrocorticogram (ECoG) epileptic spikes caused by bicuculline. AMPA (50 microM) prevented the epileptiform activity to a level that was comparable to that caused by diazepam (3 mg/kg i.p.) or clomethiazole (100 mg/kg i.p.). Also, the epileptiform activity was suppressed by the AMPAR antagonist, CNQX, or the blocker of AMPAR desensitization, cyclothiazide. In the hippocampal slice, bicuculline-induced changes in the population spike potentials recorded from the CA1 cells were not affected by AMPA. We conclude that in the complex neuronal network of the rat neocortex, epileptiform activity can be suppressed in a variety of strategies that target the AMPA receptors: (1) blocking AMPA receptors, (2) promoting an apparent desensitization of AMPA receptors (possibly on the pyramidal neurons) or (3) reducing an apparent desensitization of AMPA receptors (possibly on the inhibitory GABA-ergic interneurons).
Asunto(s)
Epilepsia/fisiopatología , Neocórtex/fisiopatología , Receptores AMPA/fisiología , 6-Ciano 7-nitroquinoxalina 2,3-diona/farmacología , Animales , Anticonvulsivantes/farmacología , Anticonvulsivantes/uso terapéutico , Benzotiadiazinas/farmacología , Bicuculina , Clormetiazol/farmacología , Clormetiazol/uso terapéutico , Diazepam/farmacología , Diazepam/uso terapéutico , Electroencefalografía/métodos , Epilepsia/inducido químicamente , Epilepsia/prevención & control , Potenciales Evocados Somatosensoriales/efectos de los fármacos , Potenciales Evocados Somatosensoriales/fisiología , Agonistas de Aminoácidos Excitadores/farmacología , Agonistas de Aminoácidos Excitadores/uso terapéutico , Antagonistas de Aminoácidos Excitadores/farmacología , Hipocampo/citología , Técnicas In Vitro , Masculino , Neocórtex/efectos de los fármacos , Neuronas/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/farmacología , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/uso terapéuticoRESUMEN
It was recently demonstrated that glutamate could precondition hippocampal slices against the damaging effects of hypoxia, and we have now extended this observation by investigating (i) the ability of glutamate receptor agonists to act as preconditioning agents and (ii) the effects of preconditioning on synaptic plasticity. Using rat hippocampal slices, 15 microM NMDA applied for 10 min (chemical insult) caused abolition of the population spike potentials (PS) followed by approximately 33% recovery at 60 min post-insult. In comparison, a 5 min preconditioning exposure of 10 microM NMDA given 30 min prior to the insult significantly improved the recovery to 69%. Preconditioning did not alter paired pulse facilitation; however, it significantly enhanced paired pulse depression and reduced population spike long-term potentiation (PS-LTP) and LTP in field recordings. This effect on PS-LTP appeared to be NMDA receptor dependent and was blocked by the nitric oxide synthase inhibitors nitro-L-arginine methyl ester (L-NAME) and 7-nitro indazole (7-NI) but not by the adenosine receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). We conclude that preconditioning by NMDA can improve recovery following acute insults but may have deleterious effects on neuronal plasticity.
Asunto(s)
Agonistas de Aminoácidos Excitadores/farmacología , Hipocampo/citología , N-Metilaspartato/farmacología , Plasticidad Neuronal/efectos de los fármacos , Neuronas/efectos de los fármacos , Potenciales de Acción/efectos de los fármacos , Antagonistas del Receptor de Adenosina A1 , Animales , Relación Dosis-Respuesta a Droga , Interacciones Farmacológicas , Estimulación Eléctrica/métodos , Inhibidores Enzimáticos/farmacología , Potenciales Postsinápticos Excitadores/efectos de los fármacos , Potenciales Postsinápticos Excitadores/fisiología , Potenciales Postsinápticos Excitadores/efectos de la radiación , Técnicas In Vitro , Potenciación a Largo Plazo/efectos de los fármacos , Potenciación a Largo Plazo/efectos de la radiación , Masculino , NG-Nitroarginina Metil Éster/farmacología , Inhibición Neural/efectos de los fármacos , Inhibición Neural/fisiología , Inhibición Neural/efectos de la radiación , Neuronas/fisiología , Ratas , Ratas Sprague-Dawley , Valina/análogos & derivados , Valina/farmacología , Xantinas/farmacologíaRESUMEN
Previous work has shown that long-term potentiation (LTP) can reduce the effects of hypoxia in depressing population spikes in rat hippocampal slices. We have now investigated the role of adenosine in this phenomenon. There is no mutual inhibition between the depressant effects of hypoxia and adenosine, but LTP reduces responses to both hypoxia and adenosine, as does application of an A1 receptor antagonist. The effect of LTP is not due to a change in the balance of activation of A1 and A2A adenosine receptors since a selective A2A receptor antagonist did not prevent the interaction. We suggest that LTP may reduce the response to hypoxia by attenuating neuronal sensitivity to adenosine A1 receptors.
Asunto(s)
Hipocampo/fisiopatología , Hipoxia/fisiopatología , Potenciación a Largo Plazo/fisiología , Receptores Purinérgicos P1/metabolismo , Adenosina/farmacología , Animales , Estimulación Eléctrica , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Técnicas In Vitro , Potenciación a Largo Plazo/efectos de los fármacos , Masculino , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Agonistas del Receptor Purinérgico P1 , Ratas , Ratas Sprague-Dawley , Triazinas/farmacología , Triazoles/farmacologíaRESUMEN
The overactivation of glutamate receptors is a major cause of Ca2+ overload in cells, potentially leading to cell damage and death. There is an abundance of agents and mechanisms by which glutamate receptor activation can be prevented or modulated in order to control these effects. They include the well-established, competitive and non-competitive antagonists at the N-methyl-D-aspartate (NMDA) receptors and modulators of desensitisation of the -amino-3-hydroxy-5-mmethyl-4-isoxazole-propionic acid (AMP) receptors. More recently, it has emerged that some compounds can acrt selectively at different subnuits of glutamate receptors,allowing a different blockade of subtypes. It is also becoming clear that a number of endogenous compounds, including purines, can modify glutamate receptor senistivity. The kynurenine pathway is an alternative but distinct pathway to the generation glutamate receptor ligands. The products of tryptophan metablism via kynurenine pathway include both quinolinic acid, a selective agonist at several glutamate receptor subtypes. The levels of these metabolites change as a result of the activation of inflammatory processes and immune-competent cells, and may have a significant impact on Ca2+ fluxes and neuronal damage. Drugs which target some of these various sites and processes, or which change the balance between the excitotoxin quinolinic acid and the neuroprotective kynurenic acid, could also have potential as neuroprotective drugs (AU)
Asunto(s)
Humanos , Quinurenina , Ácido Quinolínico , Ácido Quinurénico , Receptores de Glutamato/análisis , Receptores de Glutamato/efectos de los fármacos , Enfermedades Neurodegenerativas/diagnóstico , Fármacos Neuroprotectores/análisisRESUMEN
The ¢ ligand 1, 3-di-o-tolylguanidine (DTG) has been applied by microiontophoresis to neurones in the rat hippocampal slice and to neurones in the neocortex and hippocampus of rats anaesthetised with urethane. DTG depressed the excitatory responses of cells to both N-methyl-D-aspartate (NMDA) and quisqualate on a majority of the units tested, in no case causing an enhancement. Haloperidol had no consistent effect of its own and did not prevent the depressant effects of DTG. It is concluded that in the preparations used, DTG did not selectively modify neuronal sensitivity to NMDA (AU)