Normal formation of the postsynaptic elements of GABAergic synapses in the reeler cerebellum

Abstract

Synaptic transmission mediated by γ-amino butyric acid (GABA) plays an important role in inhibition of glutamatergic excitatory transmission and expression of higher brain functions, such as memory, learning and anxiety. To elucidate mechanisms underlying formation of the postsynaptic elements for GABAergic transmission, we employed the reeler mutant mice in this study. In the reeler cerebellum, abnormal cytoarchitecture and an aberrant environment affect the formation of neural networks and maturation of neurons. We examined the expression and localization of GABA A receptor α subunits in the reeler cerebellum and determined whether various abnormalities in the reeler mice affected formation of the postsynaptic elements. In situ hybridization analysis revealed that the specific expression of α subunit mRNAs in each neuronal type was preserved. Abnormal expression of α subunits was not detected, although GABAergic networks were altered and neuronal maturation was severely disturbed. Immunohistochemistry for the α1 and α6 subunits, which were expressed abundantly in the reeler cerebellum, revealed that both subunit-proteins accumulated at positions adjacent to GABAergic terminals. These results, taken together, suggested that expression of the GABA A receptor subunits in postsynaptic neurons might be genetically determined, but trafficking and accumulation of the subunit proteins at the GABAergic synapse may be induced by GABAergic innervation. Classification Terms

Transient expression of GABAA receptor α2 and α3 subunits in differentiating cerebellar neurons

“…In a previous study, we examined expression of the GABA A receptor α subunits under aberrant conditions of the reeler cerebellum [57]. Although neuronal maturation of malpositioned Purkinje cells was assumed to be arrested due to lack of excitatory input from parallel fibers and the presence of climbing fibers' multiple innervation, expression of the α3 subunit was almost as negative as that in the normal cerebellum, and malpositioned Purkinje cells abundantly expressed the α1 subunit [13,57]. These results indicated that formation of excitatory synapses with parallel fibers is independent of decreasing expression of the α3 subunits, and that formation of …”

“…In situ hybridization histochemistry was performed as described in a previous paper [57]. Under deep ether anesthesia, embryonic mice were taken from the uteri of the mother mice and brains were removed from the skulls of postnatal mice.…”

Morphological development and maturation of the GABAergic synapses in the mouse cerebellar granular layer

“…Moreover, the majority of both α1 and α6 subunit proteins accumulated adjacent to the Golgi cell axon terminals. These results demonstrated that (1) GAD-positive growth cones and varicosities probably undergo a change to GABAergic terminals [26,48], (2) GABAergic synapses were massively formed during the second postnatal week [2,28,31,37], and (3) GABAergic innervation might initiate the expression of the GABA A receptor α1 and α6 subunit genes, as well as trafficking and clustering of proteins to the synaptic site [1,8,12,13,16,17,20,24,46,48,61].…”

“…The specificity of these probes was verified in a previous report [61]. In situ hybridization histochemistry was performed as described in a previous paper [61].…”

“…Specificity of the antibodies against the α1 and α6 subunits and the procedure for the immunohistochemical staining were described in a previous report [61].…”