We combined a study of the subcellular distribution of the ␣1, ␣2, ␣4, ␤1, ␤2/3, ␥2, and ␦ subunits of the GABA A receptor with an electrophysiological analysis of GABA A receptor currents to determine the types of receptors expressed on cultured hippocampal pyramidal neurons. The immunocytochemistry study demonstrated that ␣1, ␣2, ␤2/3, and ␥2 subunits formed distinct clusters of various sizes, which were colocalized with clusters of glutamate decarboxylase (GAD) immunoreactivity at rates ranging from 22 to 58%. In contrast, ␣4, ␤1, and ␦ subunits were distributed diffusely over the cell soma and neuronal processes of cultured neurons and did not colocalize with the synaptic marker GAD. Whole-cell GABA A receptor currents were moderately sensitive to GABA and were modulated by diazepam. The whole-cell currents were also enhanced by the neurosteroid allopregnanolone (10 nM). Tonic currents, measured as changes in baseline current and noise, were sensitive to Zn 2ϩ , furosemide, and loreclezole; they were insensitive to diazepam. These studies suggest that two kinds of GABA A receptors are expressed on cultured hippocampal neurons. One kind of receptor formed clusters, which were present at GABAergic synapses and in the extrasynaptic membrane. The ␣1, ␣2, ␤2/3, and ␥2 subunits were contained in clustered receptors. The second kind was distributed diffusely in the extrasynaptic membrane. The ␣4, ␤1, and ␦ subunits were contained in these diffusely distributed receptors. The properties of tonic currents recorded from these neurons were similar to those from recombinant receptors containing ␣4, ␤1, and ␦ subunits.

No abstract

Event related desynchronization (ERD) allows evaluation of brain signals in multiple frequency dimensions. The purpose of this study was to determine left hemispheric non-primary motor cortex differences at varying frequencies of premovement ERD for similar movements by endeffectors of the upper and lower extremities. We recorded 32-channel electroencephalography (EEG) while subjects performed self-paced right ankle dorsiflexion and wrist extension. Electromyography (EMG) was recorded over the tibialis anterior and extensor carpi ulnaris. EEG was analyzed for premovement ERD within the alpha (8-12 Hz), low beta (13-18 Hz) and high beta (18-22 Hz) frequencies over the premotor, motor, and sensory areas of the left and mesial cortex from −1.5 to 0 s before movement. Within the alpha and high beta bands, wrist movements showed limited topography, but greater ERD over posterior premotor cortex areas. Alpha ERD was also significantly greater over the lateral motor cortex for wrist movements. In the low beta band, wrist movements provided extensive ERD differences to include the left motor and mesial/ lateral premotor areas, whereas ankle movements showed only limited ERD activity. Overall, alpha and high beta activity demonstrated distinctions that are consistent with mapping of wrist Correspondence to: Lewis A. Wheaton, lwheaton@grecc.umaryland.edu. and ankle representations over the sensorimotor strip, whereas the low beta representation demonstrated the clearest distinctions between the limbs over widespread brain areas, particularly the lateral premotor cortex. This suggests limited leg premovement activity at the dorsolateral premotor cortex. Low beta ERD may be reflect joint or limb specific preparatory activity in the premotor area. Further work is required to better evaluate the extent of this low beta activity for multiple comparative joints. NIH Public Access