Interaction of GABAA-receptor function and network activity in the developing hippocampus
Synchronized oscillatory network activity represents a characteristic feature of the developing telencephalon and is believed to be essential for the morphological and functional maturation of immature neuronal circuits. In the hippocampus, the main representatives of synchronized network activity during early brain development are giant depolarizing potentials (GDPs) in vitro and sharp waves as their most probable in vivo counterparts. The generation of these activity patterns is strongly promoted by GABAAR activation which, at this time, is mainly depolarizing and mediates postsynaptic excitation. We hypothesize a reciprocal interaction of GABAA-receptor (GABAAR) function and this form of early network activity. We suggest that I) the proper maturation of synaptic and extrasynaptic GABAAR function is highly activity-dependent and, at the same time, II) GABAAR-mediated postsynaptic currents are governing early network activity.
To elucidate the interactions between GABAAR-mediated transmission and network activity we will manipulate GABAergic transmission both pre- and postsynaptically. Firstly, we will use a transgenic mouse line with a cell-type specific disruption of the chloride co-transporter NKCC1 to attenuate GABAergic depolarization in excitatory neurons, leaving presynaptic GABAergic cells unaffected. Secondly, we intend to disrupt GABA release by deleting the vesicular GABA transporter in a cell-type specific manner using cre-loxP technology. We will apply fast confocal and 3-dimensional 2-photon calcium imaging to record hippocampal neuronal network activity during the first postnatal week in acute slices in vitro and the intact hippocampus in vivo at single-cell resolution.
To achieve a cell-type specific readout of neuronal activity, calcium imaging with a synthetic indicator dye will be performed in mice expressing the fluorescent reporter tdTomato under the Emx1 promoter which allows differentiation between glutamatergic and GABAergic neurons. Alternatively, cell-type specific cre-driver lines will be used to induce expression of the genetically-encoded calcium indicator GCaMP3. All animal models with manipulations of early network activity will be analyzed for changes in GABAAR function using electrophysiological means, including analysis of pre- and postsynaptic parameters of synaptic strength, postsynaptic GABAAR properties as well as tonic GABAAR conductances. Recording from both genetically manipulated and unaffected cells in the same preparation will allow us to dissect cell-autonomous from network-driven mechanisms.
Knut Holthoff will coordinate and supervise the project together with other members of the team.
Knut Kirmse will coordinate and supervise the project together with other members of the team.
|GABAergic Transmission during Brain Development: Multiple Effects at Multiple Stages||2017||Kirmse, K., Hubner, C. A., Isbrandt, D., Witte, O. W., and Holthoff, K.||Neuroscientist||More|
|Functions of GABAergic transmission in the immature brain||2017||Kirmse, K., and Holthoff, K.||Neuroforum||More|
|Column-like Ca2+ clusters in the mouse neonatal neocortex revealed by three-dimensional two-photon Ca2+ imaging in vivo||2016||Kummer, M., Kirmse, K., Zhang, C., Haueisen, J., Witte, O.W., Holthoff, K.||Neuroimage||More|
|Inferring neuronal dynamics from calcium imaging data using biophysical models and Bayesian inference||2016||Rahmati, V., Kirmse, K., Markovic, D., Holthoff, K., Kiebel, S.J.||PLoS Comput Biol||More|
|GABA depolarizes immature neurons and inhibits network activity in the neonatal neocortex in vivo||2015||Kirmse, K., Kummer, M., Kovalchuk, Y., Witte, O.W., Garaschuk, O., Holthoff, K.||Nat Commun||More|
|Method to quantify accuracy of position feedback signals of a three-dimensional two-photon laser-scanning microscope||2015||Kummer, M., Kirmse, K., Witte, O.W., Haueisen, J., Holthoff, K.||Biomed Opt Express||More|
|Reliable in vivo identification of both GABAergic and glutamatergic neurons using Emx1-Cre driven fluorescent reporter expression||2012||Kummer, M., Kirmse, K., Witte, O. W., and Holthoff, K.||Cell Calcium||More|
|GABAergic depolarization during early cortical development and implications for anticonvulsive therapy in neonates||2011||Kirmse, K., Witte, O. W., and Holthoff, K.||Epilepsia||More|
|Rapid time course of action potentials in spines and remote dendrites of mouse visual cortex neurons||2010||Holthoff, K., Zecevic, D., and Konnerth, A.||J Physiol||More|
|GABA Depolarizes Immature Neocortical Neurons in the Presence of the Ketone Body β-Hydroxybutyrate||2010||Kirmse, K., Witte, O. W., and Holthoff, K.||J Neurosci||More|
|Developmental downregulation of excitatory GABAergic transmission in neocortical layer I via presynaptic adenosine A(1) receptors||2008||Kirmse, K., Dvorzhak, A., Grantyn, R., and Kirischuk, S.||Cereb Cortex||More|
|Ambient GABA constrains the strength of GABAergic synapses at Cajal-Retzius cells in the developing visual cortex||2006||Kirmse, K., and Kirischuk, S.||J Neurosci||More|
|In vivo two-photon calcium imaging of neuronal networks||2003||Stosiek, C., Garaschuk, O., Holthoff, K., and Konnerth, A.||Proc Natl Acad Sci USA||More|
|Calcium dynamics of spines depend on their dendritic location||2002||Holthoff, K., Tsay, D., and Yuste, R.||Neuron||More|