Differential dependence of axo-dendritic and axo-somatic GABAergic synapses on GABAA receptors containing the alpha1 subunit in Purkinje cells.
Synapse formation and maintenance require extensive transsynaptic interactions involving multiple signal transduction pathways. In the cerebellum, Purkinje cells (PCs) receive GABAergic, axo-dendritic synapses from stellate cells and axo-somatic synapses from basket cells, both with GABAA receptors containing the alpha1 subunit. Here, we investigated the effects of a targeted deletion of the alpha1 subunit gene on GABAergic synaptogenesis in PCs, using electrophysiology and immunoelectron microscopy. Whole-cell patch-clamp recordings in acute slices revealed that PCs from alpha1(0/0) mice lack spontaneous and evoked IPSCs, demonstrating that assembly of functional GABAA receptors requires the alpha1 subunit. Ultrastructurally, stellate cell synapses on PC dendrites were reduced by 75%, whereas basket cell synapses on the soma were not affected, despite the lack of GABAA-mediated synaptic transmission. Most strikingly, GABAergic terminals were retained in the molecular layer of adult alpha1(0/0) mice and formed heterologous synapses with PC spines characterized by a well differentiated asymmetric postsynaptic density. These synapses lacked presynaptic glutamatergic markers and postsynaptic AMPA-type glutamate receptors but contained delta2-glutamate receptors. During postnatal development, initial steps of GABAergic synapse formation were qualitatively normal, and heterologous synapses appeared in parallel with maturation of dendritic spines. These results suggest that synapse formation in the cerebellum is governed by neurotransmitter-independent mechanisms. However, in the absence of GABAA-mediated transmission, GABAergic terminals in the molecular layer apparently become responsive to synaptogenic signals from PC spines and form stable heterologous synapses. In contrast, maintenance of axo-somatic GABAergic synapses does not depend on functional GABAA receptors, suggesting differential regulation in distinct subcellular compartments.
Institute of Pharmacology and Toxicology, University of Zurich, CH-8057 Zurich, Switzerland. fritschy@pharma.unizh.ch
Jean-Marc
JM
Fritschy
Patrizia
P
Panzanelli
Jason E
JE
Kralic
Kaspar E
KE
Vogt
Marco
M
Sassoè-Pognetto
D000818:Animals; D002451:Cell Compartmentation / Q000187:drug effects / Q000235:genetics; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D002525:Cerebellar Cortex / Q000002:abnormalities* / Q000378:metabolism / Q000648:ultrastructure; D003712:Dendrites / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D005455:Fluorescent Antibody Technique; D018756:GABA Antagonists / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D009433:Neural Inhibition / Q000187:drug effects / Q000235:genetics; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D011689:Purkinje Cells / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D011963:Receptors, GABA-A / Q000235:genetics*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D013570:Synaptic Membranes / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000235:genetics; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; C546241:Gabra1 protein, mouse; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid