Basic mechanisms of MCD in animal models - PubMed (original) (raw)
Review
Basic mechanisms of MCD in animal models
Giorgio Battaglia et al. Epileptic Disord. 2009 Sep.
Abstract
Epilepsy-associated glioneuronal malformations (malformations of cortical development [MCD]) include focal cortical dysplasias (FCD) and highly differentiated glioneuronal tumors, most frequently gangliogliomas. The neuropathological findings are variable but suggest aberrant proliferation, migration, and differentiation of neural precursor cells as essential pathogenetic elements. Recent advances in animal models for MCDs allow new insights in the molecular pathogenesis of these epilepsy-associated lesions. Novel approaches, presented here, comprise RNA interference strategies to generate and study experimental models of subcortical band heterotopia and study functional aspects of aberrantly shaped and positioned neurons. Exciting analyses address impaired NMDA receptor expression in FCD animal models compared to human FCDs and excitatory imbalances in MCD animal models such as lissencephaly gene ablated mice as well as in utero irradiated rats. An improved understanding of relevant pathomechanisms will advance the development of targeted treatment strategies for epilepsy-associated malformations.
Figures
Figure 1
Temporal control of Dcx expression in misplaced neurons by conditional re-expression of the Dcx gene (from Manent et al., 2009). A) A schematic diagram of the experimental approach to verify the hypothesis that re-expression of Dcx can re-start migration in the early postnatal rat brain, reduce the size of SBH and restore neuronal patterning. B) A 4-hydrotamoxifen (4-OHT)–activatable Cre recombinase composed of two estrogen receptor (ER) binding domains is expressed under the control of the CAG promoter. In the presence of 4-OHT, recombination occurs and DCX-eGFP is expressed. C) Confocal images showing transfected neurons in neocortex of P15 rats that have received 4-OHT or vehicle injection at birth. Rats were electroporated at E14 with four plasmids. In 4-OHT–treated rats (left), DCX-GFP is expressed and Dcx is detectable with antibodies in transfected misplaced neurons. In vehicle-treated rats (right), no signal is detected in the green channel or with Dcx antibodies. D) Summary of the transfection conditions. E) Schematic diagram of experiments. Scale bar, 50 µm.
Figure 2
Experimental L2/3 neurons display high synaptic glutamatergic drive (modified from Ackman et al., 2009): A) Example traces of ongoing spontaneous activity recorded at − 70 mV (_E_Cl−) and − 40 mV in a pyramidal cell of control L2/3 (left traces), experimental L2/3 (middle traces), and white matter heterotopia (right traces). Schemes on the top indicate the field analyzed in each case. Note the large increase of glutamate PSCs in the pyramidal cell from experimental L2/3 compared with control. Note in the ectopic cell the low level of activity and the absence of GABA PSCs. B) Mean GABA (left) and glutamate (right) PSC frequencies in L2/3 pyramidal neurons from slices transfected with control mismatch (Mism) constructs or shDCX (experimental layers 2/3 and heterotopia). Note that the ongoing spontaneous activity in pyramidal cells from experimental L2/3 is largely dominated by glutamate. Most of the ectopic neurons (73%) lack GABA events. * Significantly different as compared to Mism.L2/3.
Figure 3
NMDA receptor expression and composition are altered in type IA FCD patients (from Finardi et al., 2006). A–F) NR1 (A–C) and NR2B signals (D–F) are more evident in cortical pyramidal neurons from FCD patients (B–C and E–F) in comparison with controls (A and D). G–I) Confocal immunofluorescence confirmed the increased NR2B signal in coarse granules within the cell body and apical dendrites of FCD IA pyramidal neurons. J) Western blot analysis of homogenate (left) and TIF (right) fractions from cortical specimens of FCD patients (Dys) and controls (Ctr). Note that NR2B expression levels are increased in all FCD patients, whereas NR2A (patient 8, aged 7 yrs) or GluR1 (patient 7, aged 10 yrs) expression levels are increased in some but not all patients. Statistical analysis reveals that NR2B was significantly increased in dysplastic versus control cortical areas (** p < 0.01 for the homogenate; * p < 0.05 for post-synaptic membranes). Scale bars: 20 µm (A–C); 50 µm (D–F; 20 µm in inserts); 20 µm (G–I).
Figure 4
An increase in excitatory drive onto GABAergic interneurons underlies enhanced activity of inhibitory systems in the hippocampus of Lis1 ± mice (from Jones and Baraban, 2007). A) Top: whole cell voltage-clamp recording of sEPSCs on a WT interneuron. Bottom: same cell recorded in current-clamp mode. B) Top: sEPSC recording from a Lis1 ± interneuron. Bottom: same cell recorded in current-clamp mode. C) Mean sEPSC frequency is increased in Lis1 ± interneurons (p < 0.05, Student’s t-test). D) Mean sEPSC amplitude is similar between WT and mutant mice. E) Mean sEPSC decay time is similar between WT and mutant mice.
Figure 5
In utero irradiated rat model of cortical dysplasia. Pyramidal cells from the dysplastic cortex (CD) are spatially disorganized and dysplay a regular spiking pattern to suprathreshold current pulses. A) Low power photomicrographs of coronal sections of control (left) and dysplastic (right) cortex with cresyl violet staining. B) Photomicrographs (upper) show two biocytin-stained pyramidal cells from dysplastic cortex. Arrows point to pia. Traces (lower) show spike patterns of these two cells to depolarizing current injection (300 ms, 300 pA).
References
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