The intergeniculate leaflet (IGL) of the thalamus constitutes a small but important part of the neural network controlling circadian activity in rodents. It appears that IGL integrates photic cues from retina with non-photic information originating from different nonspecific brain systems. Subsequently, this integrated signal is passed to the master biological clock - the suprachiasmatic nuclei (SCN). The common neurotransmitter of biological clock neural structures, the y-amino-butyric acid (GABA) is expressed in many, if not all, IGL and SCN neurons. Whole-cell patch clamp in vitro electrophysiological experiments were performed in order to evaluate GABA's influence on single IGL neurons in rat. Most neurons were hyperpolarized by GABA application and this effect was caused by activation of GABAa as well as GABAb receptors. The presence of GABAB receptors in rat's IGL has been suggested for the first time.
Patch clamp data of PETP track-etched membranes have been analysed by the crowd model based on three i.e. regular, exponential and delayed maps of the logistic family. The same data were worked out for all equations, indicating expressive difference between theoretical predictions of the models with constant coefficients and experimental data. The differences disappeared for suitably chosen time dependent coefficients. Some possibilities of relating the functional forms of the logistic coefficients to the "dynamical structure" of a membrane as well as "the memory" of a system have also been discussed.
The mammalian intergeniculate leaflet (IGL) of the thalamus is a neuronal element of the circadian timing system, which receives direct photic input from the retina. The purpose of this study was to analyze responses of rat IGL neurons in vitro to optic tract stimulation and to identify neurotransmitters released from the terminals of retinal ganglion cells in this structure. Following optic tract stimulation, most of the responding IGL cells were excited and only a minority of them were inhibited. Neurons showing the excitatory response were tested in the presence of AP-5, a selective antagonist of NMDA receptors. In most cases the responses were only partially inhibited by the presence of AP-5. Complete disappearance of excitatory responses was achieved by adding CNQX, an AMPA/kainate receptor-selective antagonist, to the standard incubation fluid. Inhibitory responses were blocked or considerably attenuated in the presence of bicuculline, a GABAA receptor antagonist, in the ACSF. This study demonstrated that glutamate is the main neurotransmitter mediating optic tract input to the IGL, acting mainly via non-NMDA ionotropic receptors. It was also shown that NMDA and GABAA receptors are involved in passing photic input to the IGL, albeit to a much lesser extent.
The present study was designed to investigate the influence of acute ethanol intake and its withdrawal on the anticonvulsant effect of alpha-tocopherol in penicillin-induced epileptiform activity. Ethanol-treated rats received a daily dose of 3 g/kg or 9.0 g/kg of 30% ethanol solution for 3 days. Thirty minutes after penicillin injection (500 units, i.c.), the most effective dose of alpha-tocopherol (500 mg/kg) was administered intramuscularly (i.m.). Acute administration of ethanol, in a dose of 3 g/kg, did not change either frequency or amplitude of penicillin-induced epileptiform activity, while dose of 9 g/kg ethanol significantly decreased the mean frequency of penicillin-induced epileptiform ECoG activity in the ethanol-treated group. Ethanol (9 g/kg) withdrawal also caused an increase in the amplitude of epileptiform ECoG activity in the withdrawal group. The results suggest that acute administration of high dose ethanol (9 g/kg) and alpha-tocopherol have some limited anticonvulsive effects in penicillin-induced epileptiform activity in rats.
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There is a great variety of techniques for complete neurone visualization currently available. Each of them has some advantages and disadvantages. The selection one of them depends upon the requirements of the situation. One of the most useful techniques for observing individual neurones has been the Golgi method with its variations. This method has been extended from the light microscopic to the ultrastructural level. The correlation of neural structure and function was advanced with the technique of intracellular injection of the fluorescent dyes. Investigations of the cross-correlations between morphology, electrophysiology and immunohistochemistry of neurones have significantly advanced current knowledge of the complex organization of at least some parts of the nervous system. Some crucial parameters including the selection of the dyes, the injection technique and tissue processing as well as the appropriate immunohistochemical fluorescent markers are discussed. Cell reconstruction techniques also are mentioned.
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The intergeniculate leaflet (IGL) has been shown to be a functional constituent of the circadian timing system. The IGL receives a monosynaptic input from the retina and is known to mediate some of the effects of light on the circadian clock. In the majority of retinal ganglion cells, glutamate functions as an excitatory neurotransmitter. The effect of monosodium glutamate and N-methyl-D-aspartate (NMDA), on the extracellularly recorded discharge activity of IGL neurons was studied in vitro. The application of monosodium glutamate induced either an excitatory, a biphasic or an inhibitory response. Application of NMDA induced an excitatory response in the majority of tested neurons. To determine the role of NMDA receptors in the response to glutamate application, the selective antagonist of NMDA receptors- AP-5, was applied to the incubation medium. The presence of AP-5 reduced the response of the IGL cells to focal application of glutamate and completely blocked their responsiveness to NMDA. To clarify whether GABAergic interneurons are involved in mediation of the inhibitory effects of glutamate, we repeated our experiments in the presence of bicuculline in the incubation medium. Since bicuculline did not influence the observed inhibitory effects, the involvement of GABAA receptors was excluded. The present study provides the first electrophysiological evidence that neurons in the rat IGL, respond to glutamate probably through NMDA receptors. However, our results also suggest that other types of glutamate receptors may play an additional role in mediating the action of this excitatory amino acid on the IGL neurons.