Figure 1.
CCI of sciatic nerve increased small diameter neuron excitabilities, but had no effect on large diameter neurons.
A. Current clamp recordings of the membrane potential (upper traces) and injected current (lower traces) from small diameter DRG neurons of naïve and CCI animals, showing a lowered rheobase after CCI. B. Following CCI, small diameter neurons also exhibited a lowered membrane threshold (upper trace) during a ramp stimulus (lower trace). The dashed lines indicate a membrane threshold of −11.9 mV for the naïve neurons and −21.1 mV for CCI neurons. Statistical analysis showed that CCI significantly reduced rheobase (C) and membrane threshold (D) compared to naïve animals. No difference was found in resting membrane potential between naïve and CCI animals (E). Large diameter neurons showed no difference in rheobase (F) or membrane threshold (G) between naïve and CCI animals, but the CCI group had a lower resting membrane potential (RMP) compared with the naïve group (H). Numbers in each column represents recorded neurons. MT: membrane threshold. Mean ± SEM, ** p<0.01, *** p<0.001.
Figure 2.
CCI of sciatic nerve increased responses to glutamate and AMPA in small diameter neurons.
A1. Example of glutamate-induced (1 mM, 200 ms) increases in inward currents in small diameter neurons after CCI compared to naïve. Bar indicates the duration of drug application. A2. Statistical analysis showed that glutamate induced significantly larger inward currents in the CCI group compared with naïve. A3. Population analysis showed that CCI increased the proportion of the neurons responsive to glutamate. B1. Example of AMPA-induced (100 µM, 200 ms) increases in inward current in small diameter neurons after CCI compared to naïve. Bar indicates the duration of drug application. B2. Statistical analysis showed that AMPA induced significantly larger inward currents in the CCI group compared with naïve. B3. Population analysis showed that CCI increased the proportion AMPA-responsive neurons. C. Western blot analysis showed increased GluA1 expression (normalized membrane/normalized total protein) in naïve and CCI DRGs. D. Western blot analysis showing decreased GluA2 expression in naïve and CCI DRGs. Numbers in each column represents recorded neurons. Mean ± SEM, * p<0.05, ** p<0.01.
Figure 3.
CCI of sciatic nerve increased responses to NMDA and KA in small diameter neurons.
A. Upper panel: Puff application of NMDA (100 µM, 200 ms) had no effect on inward currents in small DRG neurons from naïve or CCI rats. Bar indicates the duration of drug application. Lower panel: Statistical analysis showed no differences in inward currents induced by NMDA between CCI and naïve rats. B. Population analysis showed that the percentage of the NMDA-responsive neurons increased after CCI. C. Upper panel: Example of KA-induced (100 µM, 200 ms) increases in inward currents in CCI DRGs. Bar indicates the duration of drug application. Lower panel: Statistical analysis showed that KA induced a significantly larger response in CCI group compared with naïve. D. Population analysis showed that the percentage of the KA-responsive neurons did not change significantly after CCI. Numbers in each column represents recorded neurons. Mean ± SEM, * p<0.05.
Figure 4.
CCI of sciatic nerve increased responses to DHPG in small diameter neurons.
A. Upper panel: Example of DHPG-induced (100 µM, 200 ms) increases in currents in CCI vs. naïve DRGs. Bar indicates the duration of drug application. Lower panel: Statistical analysis showed that DHPG induced a much bigger response in CCI group compared with naïve. B. Population analysis showed that the percentage of DHPG-responsive neurons increased after CCI. C. Western blot analysis showed increased mGluR1 expression (normalized membrane/normalized total protein) in naïve and CCI DRGs. D. Western blot analysis showing that the expression of mGluR5 subunit in the membrane did not change significantly after CCI, compared to the naïve group. Numbers in each column represents recorded neurons. Mean ± SEM, * p<0.05, **p<0.01.
Figure 5.
The effect of DHPG incubation on responses to AMPA, NMDA and KA in small diameter neurons.
A. Incubation with 50 µM DHPG for 2 hours reduced AMPA-induced (100 µM) inward currents in small diameter neurons in both naïve and CCI groups. B. Incubation with 50 µM DHPG for 2 hours reduced NMDA-induced (100 µM) inward currents in small diameter neurons in both naïve and CCI groups. C. Incubation with 50 µM DHPG for 2 hours increased KA-induced (100 µM) inward currents in small diameter neurons in the naïve group, but had no effect on KA-induced currents in the CCI group. Numbers in each column represents recorded neurons. Mean ± SEM, * p<0.05, **p<0.01.