Table 1.

Intrinsic electrophysiological properties of layer 4 interneurons and excitatory L4 spiny neurons

Parameters	Spiny neurons mean ± SD	P (spiny neurons vs. L4 IN)	Barrel inhibitor	Noncluster 3		P (cluster 3 vs. noncluster 3)	P (cluster 3 vs. 2)	P (cluster 3 vs. 1)
			Cluster 3 mean ± SD	Cluster 2 mean ± SD	Cluster 1 mean ± SD
Morphology
Total axon length (mm)	n/a	n/a	16.0 ± 6.0	19.6 ± 7.0	25.5 ± 11.4	ns	ns	<0.05
Axon barrel ratio	n/a	n/a	0.89 ± 0.05	0.66 ± 0.06	0.28 ± 0.11	<0.001	<0.01	<0.001
Static EP
AP half width (ms)	1.10 ± 0.13	<0.001	0.32 ± 0.08	0.39 ± 0.11	0.34 ± 0.10	0.1	ns	ns
AHP amplitude (mV)	−11.8 ± 1.7	<0.01	−16.0 ± 3.5	−13.7 ± 3.8	−15.7 ± 3.7	0.21	ns	ns
AP threshold (mV)	−40.8 ± 9.8	0.02	−34.4 ± 7.6	−33.3 ± 6.0	−35.0 ± 5.4	0.99	ns	ns
Dynamic EP
Fmax (Hz)	60 ± 9	<0.001	279 ± 51	293 ± 88	280 ± 56	0.69	ns	ns
Adaptation ratio	0.18 ± 0.10	<0.001	0.67 ± 0.11	0.68 ± 0.14	0.75 ± 0.20	0.29	ns	ns
AHP difference (mV)	−7.6 ± 1.6	<0.001	1.1 ± 1.1	1.8 ± 1.1	1.2 ± 0.6	0.25	ns	ns
Passive EP
Baseline Vm (mV)	−70.1 ± 8.2	0.10	−67.2 ± 4.9	−67.2 ± 4.8	64.2 ± 7.7	0.35	ns	ns
Membrane resistance (MΩ)	138.9 ± 26.8	<0.001	85 ± 19.8	91.2 ± 21.9	96.2 ± 19.8	0.14	ns	ns

Different morphological subtypes as defined by cluster analysis are represented by “barrel inhibitor” neurons (cluster 3) and 2 noncluster 3 subgroups (pooled data of cluster 1 and 2 interneurons). There was no difference in any physiological parameter between the 3 different morphological clusters of layer 4 interneurons (ANOVA with Dunn's post-test analysis; ns, nonsignificant). When compared with L4 interneurons (L4 IN), L4 spiny neurons showed differences in all physiological parameters except baseline membrane voltage (n/a, nonapplicable).