The role of neuronal activity in sensory axon regeneration following sciatic nerve transection. Open Access

Sanders, Kristen Elizabeth (2016)

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Peripheral nerve injuries (PNIs) are common, and although spontaneous, axon regeneration is slow and inefficient. Increasing activity in injured neurons via exercise has been proposed to drive neuronal BDNF expression, required for enhanced axon regeneration (Gomez-Pinilla et al., 2001; Wilhelm et al., 2012). I attempted to support this hypothesis through inhibition of neuronal activity with an inhibitory DREADD (Designer Receptor Exclusively Activated by Designer Drug). Once I was unable to achieve DREADD expression in sciatic motoneurons following intramuscular injections of AAV-DREADD vectors, I turned to an optogenetic approach to study sensory neurons, often ignored in PNI literature. I first characterized the proportion of sciatic dorsal root ganglion neurons (DRGs) which expressed YFP in an Advillin-Cre::YFPf reporter mouse. YFP+ visualizes expression of Cre-recombinase under the regulatory element Advillin, a sensory-neuron specific gene highly expressed in PNS ganglia (Zurborg et al., 2011). I found that a low percentage of sciatic DRGs (L4: 8.57% ± 1.92%; L5: 7.71% ± 2.35%) expressed YFP (were Cre+). However, Cre+ cells were biased towards larger sciatic DRGs in this strain. When exercised, the lengths of regenerating axons of the sensory neurons in Advillin-Cre::YFPf mice was increased in a manner similar to what has been observed in all (sensory and motor) axons after exercise. However, whether the activity of axotomized sensory neurons increases during exercise remains unknown. Additionally, factors other than activity could explain any enhancement of sensory axon regeneration with exercise. Repeating experimental results reported here will be an important first step in formulating further testable hypotheses.

Table of Contents

Overall Introduction. 8

Chapter I: Attempted use of AAV9-hm4Di vectors to target spinal motoneurons

Introduction. 10

Materials and Methods. 11

Table 1.1. 14

Results and Discussion. 15

Chapter II: Characterization of Advillin-cre:Thy1-YFP reporter mice

Introduction. 18

Materials and Methods. 19

Figure 2.1. 22

Results and Discussion. 22

Figure 2.2. 23

Figure 2.3. 24

Chapter III: The role of exercise in sensory neuron regeneration

Introduction. 25

Materials and Methods. 25

Figure 3.1. 27

Results and Discussion. 28

Figure 3.2. 30

References. 31

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