The Journal of Neuroscience, May 15, 1999, 19(10):3731-3738
Mapping Quantitative Trait Loci for Seizure Response to a
GABAA Receptor Inverse Agonist in Mice
Howard K.
Gershenfeld1,
Paul E.
Neumann2,
Xiaohua
Li1,
Pamela L.
St.
Jean3, and
Steven M.
Paul4, 5
1 Department of Psychiatry, University of Texas
Southwestern Medical Center, Dallas, Texas 75235-8898, 2 Department of Anatomy and Neurobiology, Dalhousie
University, Halifax, Nova Scotia, Canada B3H 4H7, 3 Glaxo
Wellcome Research, Inc., Research Triangle Park, North Carolina 27514, 4 Lilly Research Laboratory, Indianapolis, Indiana 46285, and 5 Departments of Psychiatry, Pharmacology and
Toxicology, Indiana University School of Medicine, Indianapolis,
Indiana 46202
To define the genetic contributions affecting individual
differences in seizure threshold, a
carboline
[methyl-
-carboline-3-carboxylate (
-CCM)]-induced model of
generalized seizures was genetically dissected in mice.
-CCM is a
GABAA receptor inverse agonist and convulsant. By measuring
the latency to generalized seizures after
-CCM administration to A/J
and C57BL6/J mice and their progeny, we estimated a heritability of
0.28 ± 0.10. A genome wide screen in an F2 population of these
parental strains (n = 273) mapped quantitative
trait loci (QTLs) on proximal chromosome 7 [logarithm of the
likelihood for linkage (LOD) = 3.71] and distal chromosome 10 (LOD = 4.29) for seizure susceptibility, explaining ~22 and 25%, respectively, of the genetic variance for this seizure trait. The
best fitting logistic regression model suggests that the A/J allele at
each locus increases the likelihood of seizures approximately threefold. In a subsequent backcross population (n = 223), we mapped QTLs on distal chromosome 4 (LOD = 2.88) and
confirmed the distal chromosome 10 QTLs (LOD = 4.36). In the
backcross, the C57BL/6J allele of the chromosome 10 QTL decreases the
risk of seizures approximately twofold. These QTLs may ultimately lead to the identification of genes influencing individual differences in
seizure threshold in mice and the discovery of novel anticonvulsant agents. The colocalization on distal chromosome 10 of a
-CCM susceptibility QTL and a QTL for open field ambulation and vertical movement suggests the existence of a single, pleiotropic locus, which
we have named Exq1.
Key words:
quantitative trait locus (QTL); epilepsy; seizure;
-carboline; open field; individual differences
Copyright © 1999 Society for Neuroscience 0270-6474/99/19103731-08$05.00/0