Figure 2.

Learning-induced enhancement of synaptic inhibition results from increased single-channel conductance. A, Spontaneous inhibitory events were peak scaled and used for the NSFA (only events with a rise time of <1.5 ms were used). Variance between these peak scaled events was calculated at different time points. The current–variance plot extracted from the peak scaled mIPSCs using the NSFA could be well fitted with the parabolic current–variance equation (see Materials and Methods), allowing the extraction of the average single-channel conductance and average number of active GABA_A channels. Examples from a pseudo-trained cell and from a trained cell are shown. As is evident from the differences in the initial slope of the parabola, the single-channel conductance of the pseudo-trained cell was markedly lower compared with the conductance of the trained cell. B, The average GABA_A single-channel conductance is enhanced after learning. Values represent the mean ± SE (*p < 0.05). Data taken from neurons in which R > 0.85; 22 cells from 17 naive rats, 36 cells from 22 trained rats, and 27 cells from 14 pseudo-trained rats. C, The number of active GABA_A channels per event does not differ between groups. D, The expression level of GABA β2, GABA β3, and GABA γ2 receptors in the piriform cortex of rats from the three groups (trained, pseudo-trained, and naïve rats) was analyzed 4–5 d after training using Western blot. The expression of the three GABA_A receptor protein levels is not modified by learning. Top, Representative immunoblots for the three subunits receptor proteins prepared from the piriform cortex of naive, trained, and pseudo-trained rats. Bottom, Protein expression level of the three GABA_A receptors is not modified by olfactory learning. For each channel type, the protein level is normalized to the value of GAPDH. Summarized data are presented as the mean OD ± SD, n = 5 for each group.