Altered functions of ion channels, membrane receptors and neuronal networks associated with thalamocortical dysrhythmia syndrome.

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Thalamic abnormalities are common in neurological and psychiatric diseases (e. g., absence epilepsy, cocaine abuse). Based on the presence of slow delta and theta range bursting during wakefulness they are referred to as thalamocortical dysrhythmia syndromes. A hyperpolarized membrane potential of thalamocortical (TC) neurons is suggested to be the basis for aberrant burst activity. Neuronal hyperpolarization may occur by excess inhibition, deafferentation or block of NMDA receptors. However sensory deprivation and enhanced function of K+ channels, both potentially inducing membrane hyperpolarizations, have not been considered yet. Members of the K2P channel family crucially contribute to the generation of the hyperpolarized resting membrane potential in neurons. In order to be able to fully address the possible contribution of K2P channels to thalamocortical dysrhythmia, it is necessary to characterize the cellular signaling pathways modulating these channels in different thalamic cell types. Concerning this aspect, information is completely missing for GABAergic thalamic neurons (local interneurons; neurons of the reticular thalamic nucleus, NRT).The aims of the project are: (1) To determine the function of K2P channels in GABAergic thalamic neurons. (2) To determine the influence of psychostimulants and K2P channel activators / inhibitors on cellular and network activity. Since psychostimulants act via the increased availability of monoamines, especially dopamine, we will analyze dopaminergic pathways. (3) To determine the role of K2P channels in sensory deprivation as a new model of thalamocortical dysrhythmia based on deafferentation.The experimental approach will be: (1) PCR and immunohistochemical staining will be used to determine the expression and location of ion channels and membrane receptors. (2) Whole-cell patch-clamp recordings will be performed to determine electrophysiological and pharmacological properties of ion channels and membrane receptors in different thalamic cell types. GABAergic neurons will be directly targeted in knock-in mice expressing enhanced green fluorescent protein (EGFP) under the control of the glutamate decarboxylase 67 promotor (GAD67-EGFP). (3) Network activity will be addressed by performing local field potential (LFP) recordings in horizontal thalamic slices and thalamocortical slices of the somatosensory system (i.e., containing the ventrobasal thalamic complex; NRT; primary somatosensory cortex). (4) System function will be determined by combining LFP / single unit recordings in the somatosensory system and behavioral analysis in vivo. (5) As experimental animal models K2P channel knock out mice and unilateral sensory deprivation in mice by trimming of whiskers will be used.The results of the proposed study will help to determine new functional roles and possible pathological influences of K2P channels and their therapeutic potential in thalamocortical dysrhythmia syndromes.