Chemogenetic Enhancement of Axon Regeneration Following Peripheral Nerve Injury in the SLICK-A Mouse

Abstract

The effects of chemogenetics on axon regeneration following peripheral nerve transection and repair were studied in mice expressing a Cre-dependent excitatory designer receptor exclusively activated by designer drugs (DREADD) and Cre-recombinase/yellow fluorescent protein (YFP) in a subset of motor and sensory neurons and cortical motoneurons (SLICK-A). Sciatic nerves were cut and repaired and mice were treated either once, at the time of injury, or five days per week for two weeks with clozapine N-oxide (CNO) (1 mg/kg, i.p.), or were untreated controls. Two weeks after injury, the lengths of YFP+ axon profiles were measured in nerves harvested from euthanized animals. Compared to untreated controls, regenerating axon lengths were not significantly longer in mice treated only once with CNO, but they were more than three times longer in mice receiving CNO repeatedly. Based on results of retrograde labeling experiments, axons of more sensory and motor neurons had regenerated successfully in mice receiving multiple CNO treatments than animals receiving only one treatment or no treatments. The increase in numbers of labeled sensory, but not motor neurons could be accounted for by increases in the proportion of retrogradely labeled neurons also expressing the DREADD. Chemogenetic increases in neuronal excitability represent a potent and innovative treatment to promote peripheral nerve regeneration.

Chronic neuronal activation increases dynamic microtubules to enhance functional axon regeneration after dorsal root crush injury

“…2 weeks) following sciatic nerve injury resulted in greater axon regeneration than a single activation 67 . However, continuous electrical stimulation for 2 weeks does not 68 .…”

Optical Stimulation and Electrophysiological Analysis of Regenerating Peripheral Axons

“…By comparing EMG response amplitudes in the same latency windows over a range of stimulus intensities (optical or electrical), a full motor recruitment curve can be generated (Figure 5B) and the stimulus threshold for activation and maximal evoked responses can be determined. If a change in neuronal excitability is expected, such as when using an inhibitory opsin (Jaiswal et al , 2018), such an effect can be evaluated as changes in stimulus threshold. Using recording electrodes placed on the nerve, optical nerve stimulation can be used to collect an evoked electroneurogram (Ward et al , 2018) and similar quantitative measurements can be made.…”

“…Future advances in excitatory and inhibitory opsins, bioluminescence, luminopsins and chemogenetics will continue to facilitate the development of neuromodulation and novel gene therapy approaches. Via chemogenetic manipulation using DREADDs (Cre-dependent excitatory designer receptor exclusively activated by designer drugs), we have shown that subthreshold excitation of motoneurons and sensory neurons is sufficient to enhance their regeneration (Jaiswal et al , 2018). The application of these new optogenetic tools will expand our ability to further define the activity requirements of highly specific neuronal populations.…”

The Role of BDNF in Peripheral Nerve Regeneration: Activity-Dependent Treatments and Val66Met

“…Enhancement of regeneration of axons of many more motoneurons than are likely to be brought into full activity is found after treatments with exercise at a slow treadmill speed (Gordon and English, 2016). Simply increasing the excitability of injured neurons using chemogenetics could be sufficient to enhance regeneration (Jaiswal et al, 2018).…”