Glutamine induces epileptiform discharges in superficial layers of the medial entorhinal cortex from pilocarpine-treated chronic epileptic rats in vitro.
OBJECTIVE
Glutamine (GLN) is a precursor for synthesis of glutamate and gamma-aminobutyric acid (GABA) and has been found in the cerebrospinal fluid (CSF) at mean concentrations of 0.6 mM. Experiments on slices are usually performed in artificial CSF (aCSF) kept free of amino acids. Therefore, the role of glutamine, particularly in tissue of epileptic animals, remains elusive.


METHODS
Using extracellular recordings we studied effects of GLN on field potentials and stimulus-evoked field responses in the medial entorhinal cortex (MEC) of combined entorhinal cortex hippocampal slices from pilocarpine-treated chronic epileptic rats and age-matched saline-injected control rats.


RESULTS
In presence of GLN (0.5 and 2 mM) recurrent epileptiform discharges (REDs) were observed in slices from epileptic rats (64% and 80%, respectively), but not in slices from control rats. REDs were restricted to the superficial MEC, suppressed by the alpha-Amino-3-hydroxy-5-methyl-4-isoxazol-propionate (AMPA)/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (30 microM), attenuated by the inhibitor of neuronal glutamine transporters methylamino-isobutyric acid (10 mM), and apparently augmented and prolonged by the GABA(A) receptor antagonist bicuculline-methiodide (5 microM). In contrast, amplitudes of stimulus evoked nonsynaptic and synaptic field responses increased in slices from control rats (+23% and +12% of the reference values) and insignificantly less or not in those of epileptic rats (+6.5% and -0.25%, respectively). Notably, stimulus-evoked slow negative transients confined to slices of epileptic animals were reduced in amplitude (-18%).


CONCLUSIONS
In combined entorhinal hippocampal slices from chronic epileptic animals, GLN induces glutamatergic REDs via neuronal uptake in superficial layers of the MEC where inhibitory function seemed to be partially preserved.
Sandow
Nora
N
Institute of Neurophysiology, Charité Universitätsmedizin Berlin, Berlin, Germany.
Zahn
Robert K
RK
Gabriel
Siegrun
S
Heinemann
Uwe
U
Lehmann
Thomas-Nicolas
TN
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000621:Aminoisobutyric Acids / Q000494:pharmacology; D000818:Animals; D001640:Bicuculline / Q000031:analogs & derivatives / Q000494:pharmacology; D004195:Disease Models, Animal; D018728:Entorhinal Cortex / Q000187:drug effects* / Q000503:physiopathology*; D005071:Evoked Potentials / Q000187:drug effects*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D005973:Glutamine / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D010862:Pilocarpine; D051381:Rats; D017208:Rats, Wistar; D013226:Status Epilepticus / Q000139:chemically induced / Q000473:pathology*
D000621:Aminoisobutyric Acids; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D010862:Pilocarpine; D005973:Glutamine; C017911:2-(methylamino)isobutyric acid; C017069:bicuculline methiodide; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D001640:Bicuculline