Fig. 2

TDP-43 pathology drives a reversible hyperexcitability of spinal motoneurones. A Cartoon of the experimental setup for the in vivo intracellular recording. Stimulation of the distal peripheral nerve initiates antidromic action potentials in motor axons towards the spinal cord. The antidromic action potentials in motoneurones (blue trace) are recorded intracellularly. B Representative voltage traces (see membrane potential) showing the spike discharge frequency in response to triangular intracellular injections of current in motoneurones. Examples are shown for each of the four different groups (Bigenic not-induced (grey), Bigenic induced (magenta), Bigenic resuppressed (green) and tTA control (blue)). C Representative current-frequency gain to illustrate the primary range and secondary range. Red arrow indicates the transition between the two ranges. D Scatter dot plot showing the recruitment currents (rheobase) for the four different groups displayed. This shows the rheobase decreased significantly in the induced mice and returned to control values upon resuppression. Plot shows medians and interquartile ranges and each dot shows the rheobase of a single neurone. Medians (and IQR), Not-induced: 4.635nA (4.584), Induced: 1.215nA (1.543), Resuppressed: 3.54nA (5.838), tTA control: 3.6nA (2.773). Kruskal Wallis, P <0.0001, Not- induced: n = 82 cells (6 mice, 3 female, 3 male), Induced: n= 42 (9 mice, 5 female, 4 male), Resuppressed: n= 62 cells (6 mice 3 female, 3 male) and tTA control: n=52 cells (5 mice, 3 female, 2 male). Dunn’s Multiple comparisons tests: Not-induced vs. Induced P <0.0001, Induced vs. resuppressed P <0.0001, Induced vs tTA P <0.0001. Other pairwise comparisons were not significant. E Scatter dot plot showing the current-frequency (I-f) gains measured in the primary range from the four different groups. This increased significantly in the induced mice and returned to control values upon resuppression. Plot shows medians and interquartile ranges and each dot shows the primary range I-f slope of a single neurone in the data set. Medians (and IQR), Not-induced: 13.12 Hz/nA (4.65), Induced: 34.22 Hz/nA (19.35), Resuppressed: 14.05 Hz/nA (6.30), tTA control: 15.12 Hz/nA (4.97). Kruskal Wallis, P <0.0001, Not-induced: n = 82 cells (6 mice, 3 female, 3 male), Induced: n= 42 (9 mice, 5 female, 4 male), Resuppressed: n= 62 cells (6 mice, 3 female, 3 male) and tTA control: n=58 cells (5 mice, 3 female, 2 male). Dunn’s Multiple comparisons tests: Not-induced vs. Induced P <0.0001, Induced vs. resuppressed P <0.0001, Induced vs tTA P <0.0001. Other pairwise comparisons were not significant. F Scatter dot plot showing the onset of the secondary range for the four different groups. This decreased significantly in the induced mice and returned to control values upon resuppression. Plot shows means and standard deviations and each dot shows the firing frequency at the onset of the secondary of a single neurone in the data set. Means (and SDs), Not-induced: 140.06 Hz (36.93), Induced: 104.00 Hz (21.91), Resuppressed: 149.00 Hz (29.99), tTA control: 134.20 Hz (31.34). Kruskal Wallis, P <0.0001, Not-induced: n = 28 cells (6 mice, 3 female, 3 male), Induced: n= 33 cells (8 mice, 5 female, 3 male), Resuppressed: n= 39 cells (6 mice, 3 female, 3 male) and tTA control: n=18 cells (5 mice, 3 female, 2 male). Tukey's multiple comparisons tests: Not-induced vs. Induced P <0.0001, Induced vs. resuppressed P <0.0001, Induced vs tTA P <0.0045). G Scatter dot plot showing the rheobase for motoneurones with AHP (2/3) durations less than 30 ms for induced and non-induced groups which is significantly lower in induced mice. Plot shows mean and standard deviations and each dot shows the rheobase of a single neurone. Means (and SD), Not-induced: 5.87 nA (1.32), Induced: 1.32 nA (0.99), Not- induced: n = 28 cells (6 mice, 3 female, 3 male), Induced: n= 17 (9 mice, 5 female, 4 male), T-test: P <0.0001. H Scatter dot plot showing the rheobase for motoneurones with AHP (2/3) durations more than 30 ms for induced and non-induced groups which is also significantly lower in induced mice. Plot shows mean and standard deviations and each dot shows the rheobase of a single neurone. Means (and SD), Not-induced: 4.36 nA (2.23), Induced: 1.61 nA (1.05), Not- induced: n = 26 cells (6 mice, 3 female, 3 male), Induced: n= 11 (9 mice, 5 female, 4 male), T-test: P=0.0004). I Scatter dot plot showing the current-frequency (I-f) gains measured in the primary range for motoneurones with AHP (2/3) durations less than 30 ms for induced and non-induced groups which is significantly higher in induced mice. Plot shows mean and standard deviations and each dot shows the gain of a single neurone. Means (and SD), Not-induced: 12.61 Hz/nA (3.74), Induced: 33.94 Hz/nA (13.77), Not- induced: n = 29 cells (6 mice, female, 3 male), Induced: n= 18 (9 mice, 5 female, 4 male), T-test: P <0.0001. J Scatter dot plot showing the current-frequency (I-f) gains for motoneurones with AHP (2/3) durations more than 30 ms for induced and non-induced groups which is also significantly higher in induced mice. Plot shows mean and standard deviations and each dot shows the gain of a single neurone. Means (and SD), Not-induced: 14.62 Hz/nA (4.91), Induced: 37.03 Hz/nA (16.53), Not- induced: n = 26 cells (6 mice, 3 female, 3 male), Induced: n= 15 (9 mice, 5 female, 4 male), T-test: P=0.0001). Other pairwise comparisons were not significant. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001