Untersuchungen zur Rolle ionotroper Glutamatrezeptoren bei der Neuritogenese neocorticaler Neuronen
Zusammenfassung der Projektergebnisse
We completed a study on the role of eight naturally occuring AMPA receptor editing and splice variants in dendritic elongation, branching, and spine building in neocortical pyramidal cells and multipolar interneurons. The study employed organotypic slice cultures and biolistic transfection of GluA-encoding plasmids, thus overexpressing GluA subunits during the period of initial dendritic growth at postnatal days 5-10. The endogenous glutamate signaling elicited the observed effects on the cultured slice without any pharmacological treatment. We can show the following: 1. In multipolar interneurons, only the GluA1(Q)-flip subunit promotes dendritic growth, but failed to concurrently increase the spine density. 2. In multipolar interneurons, both GluA2(Q) subunits increase the spine density. 3. In ontogenetically younger and older pyramidal cells of supra- and infragranular layers, GluA2(Q)-flip and (Q)-flop promotes apical dendrite growth; we expected this to occur because of the calcium permeability of these subunits. 4. In pyramidal cells, GluA3(Q)-flip, but not GluA3(Q)-flop promotes dendritic growth indicating the importance of the flip variants. 5. In pyramidal cells, the calcium-impermeable GluA2(R)-flip strongly promotes dendritic growth. Comparing calcium signals in GluA2(R)flip- and (R)-floptransfected pyramidal neurons (two-photon imaging) reveals substantially higher calcium signals in the flip transfectants. We confirmed with this method that AMPA receptor-mediated glutamatergic transmission is present between days 5-10 in the slice cultures. 6. Spine density along proximal oblique branches of the apical dendrites remains at control level in GluA2(Q) transfectants, suggesting that spines become constantly added with ongoing growth. In contrast, spine density decreases in GluA2(R)-flip and GluA3(Q)-flip transfectants, suggesting that these subunits, albeit promoting dendrite growth, do not promote spine building. 7. Spine density along basal dendrites is similar for all subunits; in fact, none of them elicits basal dendritic growth. 8. The functionality of the overexpressed subunits was quantitatively confirmed with AMPA-mediated induction of dendritic injury; further, coexpression efficiency and presence of overexpressed GluA receptor proteins and the GABAergic nature of nonpyramidal transfectants was confirmed with histochemisty. Qur study shows several novel findings. The most unexpected was the strikingly selective effects of the GluA variants. They act in a cell class-specific manner: for dendritic growth the two neuron classes employ the subunits they naturally express at high levels. Unexpectedly, spines are induced by GluA2(Q) signalling in pyramidal cells naturally high in GluA2, but surprisingly also in GABA-ergic neurons, which in nature are low in GluA2. Also unexpectedly, the flip variants with longer channel open times turned out to be as effective as the calcium-permeable Q variants. In the age window investigated GluA subunits act exclusively in the apical but not the basal dendritic compartment.
Projektbezogene Publikationen (Auswahl)
- (2006) Calciumpermeable ionotropic glutamate receptor subunits promote dendritogenesis of early postnatal neocortical pyramidal cells. 5th FENS Meeting Vienna, Austria
Veitinger T, Habijan T, Grabert J, Wirth MJ, Hollmann M & Wahle P
- (2007) Calcium-permeable ionotropic glutamate receptor subunits overexpression promote dendritogenesis but not spinogenesis of early postnatal neocortical pyramidal cells. Second Westerburg Symposium on Molecular Dynamics of the Chemical Synapses. Westerburg, Germany
Hamad M, T Veitinger, T Habijan, J Grabert, MJ Wirth, ZL Ma, M Hollmann and P Wahle
- (2007) Calcium-permeable ionotropic glutamate receptor subunits overexpression promote dendritogenesis but not spinogenesis of early postnatal neocortical pyramidal cells. Symposium “Neuronal Mechanisms of Vision” October 11-13 2007, Ruhr-Universität Bochum, Germany
Hamad M, T Veitinger, T Habijan, J Grabert, MJ Wirth, ZL Ma, M Hollmann and P Wahle
- (2007) Calcium-permeable ionotropic glutamate receptor subunits promote dendritogenesis of early postnatal neocortical pyramidal cells. Göttingen Neurobiology Conference - German Neuroscience Society
Hamad, M, Veitinger T, Habijan T , Grabert J , Ma ZL, Wirth MJ ,Hollmann M, and P Wahle
- (2007) Quantitative analysis of cotransfection efficiencies in studies of ionotropic glutamate receptor complexes. J Neurosci Res. 85:99-115
Ma ZL, Werner M, Körber C, Joshi I, Hamad M, Wahle P and M Hollmann
- (2007) The transmembrane AMPA receptor regulatory protein gamma 4 is a more effective modulator of AMPA receptor function than stargazin (gamma 2). J Neurosci. 27:8442-8447
Körber C, Werner M, Kott S, Ma ZL and M Hollmann
- (2007) Dendritic growth of postnatal cortical pyramidal cells is promoted b Calciumpermeable ionotropic glutamate receptor subunits. Abstract presented for the Society of Neuroscience. SFN Meeting, San Diego, CA, USA
Hamad M, Veitinger T, Habijan T, Grabert J, Ma, ZL, Hollmann M and P Wahle
- (2008) Ionotropic glutamate receptor subunits control dendritic growth of pyramidal cells and interneurons in postnatal rat visual cortex. 6th FENS Meeting, Genève, Switzerland
Hamad M, Schulz JN, Ma ZL, Hollmann M & Wahle P
- (2009) A novel technique for loading calcium indicators in organotypic cultures and acute brain slices. 6th Neurovision Symposium, Ruhr-Universität Bochum, Germany
Hamad MIK, Krause M, Hoffmann KP, Hollmann M and Wahle P
- (2009).Functional complementation of Glra1spd-ot, a glycine receptor subunit mutant, by independently expressed C-terminal domains. Journal of Neuroscience 29:2440-2452
C. Villmann, J. Oertel, Z.-L. Ma-Högemeier, M. Hollmann, R. Sprengel, K. Becker, H.- G. Breitinger, and C.-M. Becker
- (2010) AMPA receptor subunits differentially control dendritic growth in early postnatal neocortical pyramidal cells and interneurons. 7th FENS Meeting, Amsterdam, Netherlands
Hamad MI, Schulz JN, Ma-Högemeier ZL, Krause M, Hollmann M & Wahle P
- (2010) Oligomerization in the endoplasmic reticulum and intracellular trafficking of kainate receptors are subunit-dependent but not editing-dependent. J Neurochem. 113:1403-1415
Ma-Högemeier ZL, Körber C, Werner M, Racine D, Muth-Köhne E, Tapken D and M Hollmann
