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Biochemical Markers of Excitability in Human Neocortex

Published online by Cambridge University Press:  18 September 2015

A.L. Sherwin ,
O. Vernet ,
F. Dubeau  and
A. Olivier
A.L. Sherwin*
Affiliation:
Montreal Neurological Institute and the Department of Neurology and Neurosurgery, McGill University, Montreal
O. Vernet
Affiliation:
Montreal Neurological Institute and the Department of Neurology and Neurosurgery, McGill University, Montreal
F. Dubeau
Affiliation:
Montreal Neurological Institute and the Department of Neurology and Neurosurgery, McGill University, Montreal
A. Olivier
Affiliation:
Montreal Neurological Institute and the Department of Neurology and Neurosurgery, McGill University, Montreal
*
Montreal Neurological Institute, 3801 University Street, Montreal, Quebec, Canada H3A 2B4
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Abstract:

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We measured biochemical markers of excitability in brain excised for neurosurgical therapy of epilepsy. Intraoperative electrocorticography was used to identify and compare samples from regions of persistent interictal spike discharges and areas of the cerebral convexity which were free of interictal piking. We found that interictal spiking was associated with elevated tissue levels of the excitatory amino acids glutamic acid (26%, p < 0.001) and aspartic acid (25%, p < 0.05). There was also a significant increase in the activity of the enzymes glutamic acid dehydrogenase (20%, p < 0.01) and aspartate acid aminotransferase (18%, p < 0.01) which are involved in their formation. There was no change in the levels of the inhibitory neurotransmitters GABA or taurine. We also found a significant increase in the activity of tyrosine hydroxylase (52%, p < 0.001), the rate controlling enzyme in catecholamine biosynthesis. There was a reduction in the density (Bmax) of cortical alpha-1 adrenoceptors (26%, p < 0.01) and a concommitant diminution of receptor coupled phosphatidylinositide metabolism (21%, p < 0.01). This blunting of inhibitory noradrenergic transmembrane signaling may contribute to a relative imbalance between excitatory and inhibitory mechanisms in epileptogenic neocortex.

Information

Type
Research Article
Information
Canadian Journal of Neurological Sciences , Volume 18 , Issue S4 , November 1991 , pp. 640 - 644
Copyright
Copyright © Canadian Neurological Sciences Federation 1991

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