Role Of Serotonin And Its Receptors In Regulating Cortical Epileptiform Activity

Background:5-hydroxytryptamine (5-HT, serotonin) is a critical neurotransmitter or neuro modulator which has participated in the modulating of cortical network activities and animal behavioral states. Research conducted in Brain slices in vitro confirmed the prominent effect of serotonin on network excitability, furthermore, serotonin concentration as well as density of related receptors altered during the process of chronic repetitive seizure. Previous studies indicated that increasing the level of5-HT in the brain could elevate the threshold of seizure; In contrast, decreasing the level of5-HT accelerated experimentally evoked seizure in rodents. The above study suggested that serotonin has played a part in the modulation of epilepsy; however, the potential mechanism is not quite yetObjective:We made an in vitro epileptic model using cortical slices obtained from15-18d Sprague-Dawley (SD) rats, wild type Swiss-Webster mice and5-HT1A receptors knockout mice. By performing whole-cell and local field recording, we sought to investigate the modulation of5-HT and5-HT1a,5-HT2A receptors to epileptic activities in entorhinal-hippocampus cortexMethods:1. Preparation of entorhinal-hippocampal slices obtained from rats and mice.2. We investigated the influence of20μM serotonin on membrane potential of layer V pyramidal cells by means of whole-cell recording technology.3. In order to evoke epileptic activities in entorhinal-hippocampus cortex, we utilized picrotoxin and high potassium artificial cerebrospinal fluid (ACSF) to perfuse brain slices, and whole-cell and local field recording were used to record the traces. By adding5-HT,5-HT1A and5-HT2A receptors agonist and antagonists, we intended to observe the modulation effect of5-HT,5-HT1A and5-HT2A receptors to the epileptic activities in entorhinal-hippocampus cortex.Results:1.5-HT(20μM) had potent influence on membrane potential of layer V pyramidal cells in entorhinal cortex, which could be divided into the following3types:①Hyperpolarization(40%);②Hyperpolarization after transient depolarization (26.67%);③Depolarization(33%).2. Epileptic activities both in rats and mice brain slices could be steadily evoked when picrotoxin and high potassium existed in the ACSF. Whole-cell recording and local field recording were completely synchronous during the whole process.3. Bath application of5-HT (20μM) dramatically inhibited the epileptiform activity. This inhibition could be completely blocked by pretreatment of the5-HT1A receptor antagonist WAY-100635.4. Experiments in slices obtained from5-HT1A knockout mice revealed that5-HT (20μM) prolonged the duration of single epileptiform discharge, and this effect could be reversibly mimicked by5-HT2A receptor agonist TCB-2and blocked by the5-HT2A receptor antagonist ketanserin.Conclusion:1.5-HT could impact on the excitation of layer V pyramidal cells of Entorhinal cortex.2. Our results indicate that5-HT show an antiepileptic effect in entorhinal-hippocampus cortex, which was result from a combination of5-HT1A and5-HT2A receptors. But the inhibition mainly through the activation of5-HT1A receptors, which suggested that selectively activated5-HT1A receptor may play positive role in regulation of epilepsy.3. In contrast, activation of5-HT2Areceptor may aggravate the activities by increasing the duration of epileptiform discharges. This result indicated5-HT2A receptor participated in the origination of seizure and the transition of seizure to status epilepticus. Selectively activated5-HT2A receptor may play negative role in regulation of epilepsy.