Table 2.
Electrical properties of each subgroup of GABAergic interneurons.
| Property | FS (n = 32) | SOM (n = 11) | Non-FS/non-SOM (n = 7) |
|---|---|---|---|
| PROPERTIES DEFINING FS | |||
| Spike width at half amplitude (ms) | 0.54 ± 0.10a | 0.99 ± 0.21*** | 0.85 ± 0.45** |
| Spike rise rate (mV/ms) | 249.7 ± 71.4 | 142.4 ± 40.4*** | 160.1 ± 63.6** |
| Spike fall rate (mV/ms) | −178.4 ± 56.3 | −91.0 ± 25.6*** | −108.6 ± 41.7** |
| Fast AHPb (mV) | −10.8 ± 5.7 | −5.25 ± 7.8** | −7.4 ± 3.4 |
| Medium-range AHPb (mV) | −2.5 ± 1.8 | −2.4 ± 2.9 | −3.7 ± 3.7 |
| Maximal frequencyc (Hz) | 110.9 ± 34.7 (60–180) | 56.3 ± 30.0*** (30–104) | 66.7 ± 34.9* (14–100) |
| Adaptationd | 0/32 | 11/11*** | 5/7*** |
| OTHER PROPERTIES | |||
| Resting potential (mV)e | −72.6 ± 2.7 | −72.9 ± 2.0 | −73.6 ± 4.5 |
| Input resistance (MΩ) | 224.1 ± 117.7 | 289.9 ± 147.1 | 347.6 ± 169.3 |
| Membrane time constant τm (ms)f | 11.6 ± 5.8 | 19.5 ± 8.5** | 14.5 ± 5.9 |
| First time constant τ1 (ms)f | 0.71 ± 0.35 | 0.74 ± 0.29 | 0.74 ± 0.25 |
| Electrotonic lengthg | 0.81 ± 0.14 | 0.65 ± 0.12** | 0.74 ± 0.10 |
| Spike amplitude (mV) | 82.4 ± 9.4 | 83.3 ± 7.6 | 82.5 ± 5.8 |
aMean ± SD.
bThe sizes of fast and medium-range AHPs were measured at 3.5 and 27 ms, respectively, after the spike onsets (Kawaguchi, 1993).
cThe maximal frequency was measured only in neurons showing tonic responses to 500-ms-long current injection: all FS neurons, seven SOM neurons and six non-FS/non-SOM. Frequency range was indicated in the parentheses.
dAdaptation was examined by the ratio of the ninth to the third inter-spike intervals in a representative record containing more than 20 Hz (Gottlieb and Keller, 1997; Cho et al., 2004a). When the adaptation ratio was more than 1.1, the neuron was judged to be adapting or accommodating. Two non-FS/non-SOM neurons were irregular spiking as reported frequently in VIP-immunopositive neurons (Cauli et al., 1997).
eJunction potential was compensated.
fTime constants were measured by injecting 0.2 ms depolarizing pulses of 1 nA. Potential decay from 0.4 to 50 ms after the current injection was mostly well fitted with a double exponential curve.
gElectrotonic length of an equivalent sealed-end cylinder was estimated by expression
*p < 0.05, **p < 0.01, ***p < 0.001 compared with FS neurons by Tukey’s post hoc test following one-way ANOVA or chi-square test with Bonferroni correction.