Neocortical hyperexcitability in a human case of tuberous sclerosis complex and mice lacking neuronal expression of TSC1.
OBJECTIVE
To identify brain regions, cell types, or both that generate abnormal electrical discharge in tuberous sclerosis complex (TSC). Here we examined excitatory and inhibitory synaptic currents in human tissue samples obtained from a TSC patient with no discernible cortical tubers and acute neocortical brain slices from a mouse featuring synapsin-driven conditional deletion of a TSC1 gene. These studies were designed to assess whether TSC gene inactivation alters excitability.


METHODS
We used visualized patch-clamp (human and mouse) and extracellular field (mouse) recordings. Additional mice were processed for immunohistochemistry or Western blot analysis.


RESULTS
Detailed anatomic studies in brain tissue sections from synapsin-TSC1 conditional knock-out mice failed to uncover gross anatomic defects, loss of lamination, or frank tuber formation. However, regions of abnormal and potentially activated neocortex were shown using antibodies to nonphosphorylated neurofilaments (SMI-311) and immediate early genes (c-Fos). Extracellular recordings from neocortical slices, examining synaptic activity in these regions, demonstrated clear differences in excitability between conditional knock-out and age-matched control mice. Whole-cell patch-clamp recordings demonstrated excitatory synaptic currents with strikingly long duration and epileptiform discharge patterns, similar to waveforms observed in our human tissue samples. These events were 1-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor mediated and were most prominent in neocortex. Normal-appearing inhibitory postsynaptic currents (human) and intrinsic neuronal firing patterns (mouse) were also recorded.


CONCLUSIONS
This combination of human and mouse tissue studies suggests, for the first time, that synaptic excitation is altered in a direction that favors seizure generation in TSC brain tissue regardless of cortical tubers.
Wang
Yanling
Y
Department of Neurological Surgery, University of California, San Francisco, San Francisco, CA 94143, USA.
Greenwood
Joel S F
JS
Calcagnotto
Maria Elisa
ME
Kirsch
Heidi E
HE
Barbaro
Nicholas M
NM
Baraban
Scott C
SC
D000328:Adult; D000818:Animals; D015153:Blotting, Western; D004558:Electric Stimulation; D004594:Electrophysiology; D004827:Epilepsy / Q000503:physiopathology; D019706:Excitatory Postsynaptic Potentials; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials; D051379:Mice; D018345:Mice, Knockout; D019579:Neocortex / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D009474:Neurons / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D018091:Receptors, AMPA / Q000378:metabolism; D013569:Synapses; D014402:Tuberous Sclerosis / Q000378:metabolism / Q000503:physiopathology*; D000077004:Tuberous Sclerosis Complex 1 Protein; D025521:Tumor Suppressor Proteins / Q000172:deficiency*
D016760:Proto-Oncogene Proteins c-fos; D018091:Receptors, AMPA; C000624650:TSC1 protein, human; C000624651:Tsc1 protein, mouse; D000077004:Tuberous Sclerosis Complex 1 Protein; D025521:Tumor Suppressor Proteins