Figure 3. Analysis of evoked EPSCs indicates that GABA_B heteroreceptors are expressed on excitatory inputs to layer 2/3 pyramidal neurons, but are not subject to tonic activation in either young or aged neurons.

A) Raw data traces representative of the population mean are illustrated from a young neuron (top) and an aged neuron (bottom) in baseline conditions, after application of 10 μM baclofen, and in the presence of both baclofen and 10 μM CGP. Each trace is an average of 15–30 consecutive sweeps (generated at 0.1 Hz) in the stated conditions. Baclofen reduced evoked IPSC amplitude in both cells, but amplitude in the presence of baclofen and CGP did not exceed baseline values in either cell. The top dashed line in each set of traces illustrates a common baseline, while the bottom dashed line represents the evoked IPSC amplitude in baseline conditions. B) Population data illustrate that the same effects are apparent across cells when evoked EPSC amplitude is normalized to the baseline mean (young: n=5, 2, aged: n= 5, 2, in neurons, animals respectively). See text for specific values. PTX (50 μM) was present in the bath solution throughout the experiment.