Unipolar brush cells form a glutamatergic projection system within the mouse cerebellar cortex.
Unipolar brush cells (UBCs) of the mammalian vestibulocerebellum receive mossy fiber projections primarily from the vestibular ganglion and vestibular nuclei. Recently, the axons of UBCs have been shown to generate an extensive system of cortex-intrinsic mossy fibers, which resemble traditional cerebellar mossy fiber afferents and synapse with granule cell dendrites and other UBCs. However, the neurotransmitter used by the UBC axon is still unknown. In this study, we used long-term organotypic slice cultures of the isolated nodulus (lobule X) from postnatal day 8 mouse cerebella to identify the neurotransmitter and receptors at synapses of the UBC axon terminals, relying on the notion that, in these cultures, all of the cortex-extrinsic fibers had degenerated during the first few days in vitro. Quantification of glutamate immunogold labeling showed that the UBC axon terminals have the same high gold-particle density as the glutamatergic parallel fiber varicosities. Furthermore, UBCs identified by calretinin immunoreactivity expressed the glutamate receptor subunits GluR2/3, NMDAR1, and mGluR2/3, like they do in the mature mouse cerebellum in situ. Evoked excitatory postsynaptic currents (EPSCs), spontaneous EPSCs, and burst discharges were demonstrated in UBCs and granule cells by patch-clamp recording. Both the evoked and spontaneous EPSCs were blocked by ionotropic glutamate receptor antagonists CNQX and D-AP5. We conclude that neurotransmission at the UBC axon terminals is glutamatergic. Thus, UBCs provide a powerful network of feedforward excitation within the granular layer, which may amplify vestibular signals and synchronize activity in clusters of functionally related granule cells which project vertically to patches of Purkinje cells.
Nunzi
M G
MG
Institute for Neuroscience, Northwestern University Medical School, Chicago, Illinois 60611, USA. MG-Nunzi@nortwestern.edu
Birnstiel
S
S
Bhattacharyya
B J
BJ
Slater
N T
NT
Mugnaini
E
E
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D064032:Calbindin 2; D048429:Cell Size; D002525:Cerebellar Cortex / Q000737:chemistry / Q000166:cytology* / Q000502:physiology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000502:physiology*; D007395:Interneurons / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D051379:Mice; D008810:Mice, Inbred C57BL / Q000033:anatomy & histology*; D016253:Microscopy, Immunoelectron; D009412:Nerve Fibers / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D009434:Neural Pathways; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D018091:Receptors, AMPA / Q000032:analysis; D016194:Receptors, N-Methyl-D-Aspartate / Q000032:analysis; D064030:S100 Calcium Binding Protein G / Q000032:analysis; D016610:Tissue Embedding
D015763:2-Amino-5-phosphonovalerate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D064032:Calbindin 2; D018691:Excitatory Amino Acid Antagonists; D018698:Glutamic Acid; D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; D064030:S100 Calcium Binding Protein G; C576511:Calb2 protein, mouse; C104723:glutamate receptor ionotropic, AMPA 3; C104722:glutamate receptor ionotropic, AMPA 2