Alteration of GABAergic synapses and gephyrin clusters in the thalamic reticular nucleus of GABAA receptor alpha3 subunit-null mice.
Multiple GABAA-receptor subtypes are assembled from alpha, beta and gamma subunit variants. GABAA receptors containing the alpha3 subunit represent a minor population with a restricted distribution in the CNS. In addition, they predominate in monoaminergic neurons and in the nucleus reticularis thalami (nRT), suggesting a role in the regulation of cortical function and sleep. Mice with a targeted deletion of the alpha3 subunit gene (alpha3(0/0)) are viable and exhibit a subtle behavioural phenotype possibly related to dopaminergic hyperfunction. Here, we investigated immunohistochemically the consequences of the loss of alpha3 subunit for maturation of GABAA receptors and formation of GABAergic synapses in the nRT. Throughout postnatal development, the regional distribution of the alpha1, alpha2, or alpha5 subunit was unaltered in alpha3(0/0) mice and the prominent alpha3 subunit staining of nRT neurons in wildtype mice was not replaced. Subcellularly, as seen by double immunofluorescence, the alpha3 and gamma2 subunit were clustered at postsynaptic sites in the nRT of adult wildtype mice along with the scaffolding protein gephyrin. In alpha3(0/0) mice, gamma2 subunit clustering was disrupted and gephyrin formed large aggregates localized at the cell surface, but unrelated to postsynaptic sites, indicating that nRT neurons lack postsynaptic GABAA receptors in mutant mice. Furthermore, GABAergic terminals were enlarged and reduced in number, suggesting a partial deficit of GABAergic synapses. Therefore, GABAA receptors are required for gephyrin clustering and long-term synapse maintenance. The absence of GABAA-mediated transmission in the nRT may have a significant impact on the function of the thalamo-cortical loop of alpha3(0/0) mice.
Studer
Remo
R
Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
von Boehmer
Lotta
L
Haenggi
Tatjana
T
Schweizer
Claude
C
Benke
Dietmar
D
Rudolph
Uwe
U
Fritschy
Jean-Marc
JM
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D007150:Immunohistochemistry / Q000379:methods; D020646:Intralaminar Thalamic Nuclei / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D021122:Protein Subunits / Q000172:deficiency; D011963:Receptors, GABA-A / Q000172:deficiency*; D013569:Synapses / Q000502:physiology*; D050495:Vesicular Inhibitory Amino Acid Transport Proteins / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002352:Carrier Proteins; D008565:Membrane Proteins; D021122:Protein Subunits; D011963:Receptors, GABA-A; D050495:Vesicular Inhibitory Amino Acid Transport Proteins; C492244:Viaat protein, mouse; C073441:gephyrin; D005680:gamma-Aminobutyric Acid