Functional role of mGluR1 and mGluR4 in pilocarpine-induced temporal lobe epilepsy.
Altered expression and distribution of neurotransmitter receptors, including metabotropic glutamate receptors (mGluRs), constitute key aspects in epileptogenesis, impaired hippocampal excitability and neuronal degeneration. mGluR1 mediates predominantly excitatory effects, whereas mGluR4 acts as inhibitory presynaptic receptor. Increased hippocampal expression of mGluR1 and mGluR4 has been observed in human temporal lobe epilepsy (TLE). In this study, we address whether genetic mGluR1 upregulation and mGluR4 knock-down influence seizure susceptibility and/or vulnerability of hippocampal neurons by analyzing transgenic animals in the pilocarpine TLE model. Therefore, we generated transgenic mice expressing mGluR1-enhanced green fluorescent protein (EGFP) fusion protein under control of the human cytomegalovirus (CMV) immediate early promoter. Status epilepticus (SE) was induced in (a) mice overexpressing mGluR1-EGFP and (b) mice deficient for mGluR4 (mGluR4 KO) as well as littermate controls. In the acute epileptic stage after pilocarpine application, mGluR4 KO mice showed a significant increase of severe seizure activity, in contrast to mGluR1 transgenics. Analysis of both transgenic mouse lines in the chronic epileptic phase, using a telemetric EEG-/video-monitoring system, revealed a significant increase in seizure frequency only in mGluR1-EGFP mice. In contrast, enhanced neuronal cell loss was only present in the hippocampus of epileptic mGluR4 KO mice. Our results suggest a role for mGluR1 in promoting seizure susceptibility as well as for mGluR4 to counteract excitatory activity and seizure-associated vulnerability of hippocampal neurons. Therefore, our data strongly recommend both mGluRs as potential drug targets to interfere with the development of hippocampal damage and seizure activity in TLE.
Pitsch
J
J
Department of Neuropathology, University of Bonn Medical Center, Sigmund-Freud Str. 25, D-53105 Bonn, Germany.
Schoch
S
S
Gueler
N
N
Flor
P J
PJ
van der Putten
H
H
Becker
A J
AJ
D000818:Animals; D003292:Convulsants; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000502:physiology; D004827:Epilepsy / Q000378:metabolism / Q000503:physiopathology; D004833:Epilepsy, Temporal Lobe / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D005786:Gene Expression Regulation / Q000235:genetics; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D018698:Glutamic Acid / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics; D006624:Hippocampus / Q000378:metabolism* / Q000503:physiopathology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009410:Nerve Degeneration / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D010862:Pilocarpine; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics; D015854:Up-Regulation / Q000502:physiology
D003292:Convulsants; D018094:Receptors, Metabotropic Glutamate; D011993:Recombinant Fusion Proteins; C485184:enhanced green fluorescent protein; C104077:metabotropic glutamate receptor type 1; D010862:Pilocarpine; D049452:Green Fluorescent Proteins; D018698:Glutamic Acid; C108823:metabotropic glutamate receptor 4