The FXG: a presynaptic fragile X granule expressed in a subset of developing brain circuits.

The loss of Fragile X mental retardation protein (FMRP) causes Fragile X syndrome, the most common inherited mental retardation and single gene cause of autism. Although postsynaptic functions for FMRP are well established, potential roles at the presynaptic apparatus remain largely unexplored. Here, we characterize the expression of FMRP and its homologs, FXR1P and FXR2P, in the developing, mature and regenerating rodent nervous system, with a focus on presynaptic expression.

Synaptic and nonsynaptic localization of GABAA receptors containing the alpha5 subunit in the rat brain.

The alpha5 subunit of the GABA(A) receptors (GABA(A)Rs) has a restricted expression in the brain. Maximum expression of this subunit occurs in the hippocampus, cerebral cortex, and olfactory bulb. Hippocampal pyramidal cells show high expression of alpha5 subunit-containing GABA(A)Rs (alpha5-GABA(A)Rs) both in culture and in the intact brain.

GABAergic and glutamatergic axons innervate the axon initial segment and organize GABA(A) receptor clusters of cultured hippocampal pyramidal cells.

We have studied gamma-aminobutyric acid (GABA)(A) receptor (GABA(A)R) clustering within the axon initial segment (AIS) in low-density cultures of hippocampal pyramidal cells following GABAergic and glutamatergic innervation of the AIS. Large, intensely fluorescent, and postsynaptic GABA(A)R clusters were present in the AIS. More than 95% of these clusters colocalized with presynaptic GABAergic or glutamatergic terminals, forming matched or mismatched synapses, respectively.

alpha5 Subunit-containing GABA(A) receptors form clusters at GABAergic synapses in hippocampal cultures.

We have used triple-label fluorescence immunocytochemistry to demonstrate that alpha5 subunit-containing GABA(A) receptors (GABA(A)Rs) form large clusters at GABAergic synapses in dendrites and axon initial segment of cultured hippocampal neurons. The large synaptic clusters of alpha5 subunit-containing GABA(A)Rs also contained alpha1, beta2/3, gamma2 GABA(A)R subunits and gephyrin. The alpha5 subunit-containing GABA(A)Rs also formed small clusters.

GABAergic innervation organizes synaptic and extrasynaptic GABAA receptor clustering in cultured hippocampal neurons.

We have studied the effects of GABAergic innervation on the clustering of GABA(A) receptors (GABA(A)Rs) in cultured hippocampal neurons. In the absence of GABAergic innervation, pyramidal cells form small (0.36 +/- 0.