Mice lacking brain/kidney phosphate-activated glutaminase have impaired glutamatergic synaptic transmission, altered breathing, disorganized goal-directed behavior and die shortly after birth.
Neurotransmitter glutamate has been thought to derive mainly from glutamine via the action of glutaminase type 1 (GLS1). To address the importance of this pathway in glutamatergic transmission, we knocked out GLS1 in mice. The insertion of a STOP cassette by homologous recombination produced a null allele that blocked transcription, encoded no immunoreactive protein, and abolished GLS1 enzymatic activity. Null mutants were slightly smaller, were deficient in goal-directed behavior, hypoventilated, and died in the first postnatal day. No gross or microscopic defects were detected in peripheral organs or in the CNS. In cultured neurons from the null mutants, miniature EPSC amplitude and duration were normal; however, the amplitude of evoked EPSCs decayed more rapidly with sustained 10 Hz stimulation, consistent with an observed reduction in depolarization-evoked glutamate release. Because of this activity-dependent impairment in glutamatergic transmission, we surmised that respiratory networks, which require temporal summation of synaptic input, would be particularly affected. We found that the amplitude of inspirations was decreased in vivo, chemosensitivity to CO2 was severely altered, and the frequency of pacemaker activity recorded in the respiratory generator in the pre-Bötzinger complex, a glutamatergic brainstem network that can be isolated in vitro, was increased. Our results show that although alternate pathways to GLS1 glutamate synthesis support baseline glutamatergic transmission, the GLS1 pathway is essential for maintaining the function of active synapses, and thus the mutation is associated with impaired respiratory function, abnormal goal-directed behavior, and neonatal demise.
Masson
Justine
J
Unité Mixte de Recherche U677, NeuroPsychoPharmacologie, Faculté de Médecine Pitié-Salpêtrière, 75634 Paris Cedex 13, France. jumasson@ext.jussieu.fr
Darmon
Michèle
M
Conjard
Agnès
A
Chuhma
Nao
N
Ropert
Nicole
N
Thoby-Brisson
Muriel
M
Foutz
Arthur S
AS
Parrot
Sandrine
S
Miller
Gretchen M
GM
Jorisch
Renée
R
Polan
Jonathan
J
Hamon
Michel
M
Hen
René
R
Rayport
Stephen
S
D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000201:enzymology*; D018698:Glutamic Acid / Q000378:metabolism*; D005972:Glutaminase / Q000172:deficiency*; D006040:Goals; D007040:Hypoventilation / Q000503:physiopathology*; D007668:Kidney / Q000201:enzymology*; D001523:Mental Disorders / Q000503:physiopathology*; D051379:Mice; D018345:Mice, Knockout; D009434:Neural Pathways / Q000378:metabolism; D012120:Respiration Disorders; D015656:Respiratory Mechanics; D015996:Survival Rate; D009435:Synaptic Transmission
D018698:Glutamic Acid; D005972:Glutaminase