Hollis Lab

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Circuit Repair Laboratory

Edmund Hollis - Principle Investigators Interview

The Hollis lab has three main areas of focus. We are interested in 1) the general response of neural architecture to spinal cord injury; 2) the function of neuronal circuits underlying movement; and 3) the recovery of neuronal circuits after injury. Our studies use genetic, molecular, and behavioral tools along with optogenetic stimulation of, and optical recording from, neuronal networks in order to understand mechanisms of spinal cord injury and neural circuit remodeling.

Spinal cord injury results in the disruption of neuronal circuits in the spinal cord, neuronal and glial cell death, inflammation, secondary degeneration, scarring, and the disconnection of local circuits from supraspinal networks. After injury, a limited amount of endogenous recovery is possible, likely driven by the plasticity of neural circuits in close proximity to the lesion site or from compensatory function from supraspinal projections. The cortical mechanisms supporting this recovery are not well understood, nor is it known whether limitations on plasticity of cortical networks underlie the failure of current therapies to restore lost function.

Our goal is to develop novel therapeutic interventions that take advantage of circuit plasticity to promote recovery from neurological injury. To do so, we are investigating all levels of the circuits supporting movement. Within the spinal cord, we are studying developmental regulation of axon regeneration as well as mechanisms of the astrocyte response to injury, in order to limit secondary degeneration and maintain local circuit survival. In the periphery, we are targeting pro-regenerative pathways to improve surgical interventions that support the return of hand function in individuals living with chronic cervical spinal cord injury. Within the cortex, we are focused on recovery and plasticity of the sensory and motor networks required for interpreting and regulating skilled movement and motor learning.

Ongoing projects in the lab include:

  1. Determining the role of epithelial-to-mesenchymal transition mechanisms in the astroglial response to spinal cord injury.
  2. Measuring the ability of cortical motor networks to incorporate regenerated axons after injury.
  3. Determining the role of neuromodulation of motor circuits in coordinated motor learning and recovery after spinal cord injury.
  4. Measuring the changes in intracortical architecture that occur in response to rehabilitation from spinal cord injury.
  5. Testing the extent of circuit remodeling driven by nerve transfer surgery to treat chronic, cervical spinal cord injury (clinical and pre-clinical studies).
  6. Exploring the conserved molecular mechanisms underlying peripheral regeneration.
Figure 1

Genetic depletion of cholinergic neurons impairs coordinated motor learning. (A) Timeline of genetic ablation of cholinergic neurons. (B-C) Diphtheria toxin depletion of NBM/SI cholinergic neurons expressing tdTomato in ChAT-Cre mice injected with AAV-FLEX-DTR-EYFP compared to control (AAV-FLEX-EYFP) (scale bar 200 um). (D-E) Genetic ablation of NBM/SI cholinergic neurons severely impaired performance on rotarod training (repeated-measures ANOVA, P = 0.001, F (1, 14) = 17.30; post-hoc Sidak’s comparison test, **P < 0.01).

Figure 2

Sciatic nerve crush triggers macrophage response in the dorsal root ganglia. (A) Macrophages labeled with Iba1 antibody in iDisco cleared L4 DRGs from intact, 3 and 7 days post-injury (scale bar 200 um). (B-D) Morphological reconstruction of Iba1+ resident macrophages revealed a shift from amoeboid (cyan) and elongated (orange) morphologies to a greater population of stellate (yellow) macrophages after injury (scale bar 50 um).

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Edmund R. Hollis II, Ph.D.

Conditions & Recovery

Spinal Cord Injury icon
Around the world, between 300,000 and 500,000 people are living with a SCI.
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Write and walk again.
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Pain free, touch and smell like before.