Impairment of AMPA receptor function in cerebellar granule cells of ataxic mutant mouse stargazer.
The spontaneous recessive mutant mouse stargazer (stg) begins to show ataxia around postnatal day 14 and display a severe impairment in the acquisition of classical eyeblink conditioning in adulthood. These abnormalities have been attributed to the specific reduction in brain-derived neurotrophic factor (BDNF) and the subsequent defect in TrkB receptor signaling in cerebellar granule cells (GCs). In the stg mutant cerebellum, we found that EPSCs at mossy fiber (MF) to GC synapses are devoid of the fast component mediated by AMPA-type glutamate receptors despite the normal slow component mediated by NMDA receptors. The sensitivity of stg mutant GCs to exogenously applied AMPA was greatly reduced, whereas that to NMDA was unchanged. Glutamate release from MF terminals during synaptic transmission to GCs appeared normal. By contrast, AMPA receptor-mediated EPSCs were normal in CA1 pyramidal cells of the stg mutant hippocampus. Thus, postsynaptic AMPA receptor function was selectively impaired in stg mutant GCs, although the transcription of four AMPA receptor subunit genes in the stg GC was comparable to the wild-type GC. We also examined the cerebellum of BDNF knockout mice and found that their MF-GC synapses had a normal AMPA receptor-mediated EPSC component. Thus, the impaired AMPA receptor function in the stg mutant GC is not likely to result from the reduced BDNF-TrkB signaling. These results suggest that the defect in MF to GC synaptic transmission is a major factor that causes the cerebellar dysfunction in the stg mutant mouse.
Department of Physiology, Jichi Medical School, Minamikawachi-machi, Tochigi-ken 329-0498, Japan.
K
K
Hashimoto
M
M
Fukaya
X
X
Qiao
K
K
Sakimura
M
M
Watanabe
M
M
Kano
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D002524:Cerebellar Ataxia / Q000235:genetics / Q000503:physiopathology*; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D008818:Mice, Neurologic Mutants; D009412:Nerve Fibers / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology; D020801:Receptor, Ciliary Neurotrophic Factor; D018091:Receptors, AMPA / Q000235:genetics / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology; D017475:Receptors, Nerve Growth Factor / Q000502:physiology; D015398:Signal Transduction; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014158:Transcription, Genetic; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D019208:Brain-Derived Neurotrophic Factor; D046911:Macromolecular Substances; D020801:Receptor, Ciliary Neurotrophic Factor; D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; D017475:Receptors, Nerve Growth Factor; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D020794:Receptor Protein-Tyrosine Kinases