Bareyre Lab – Neuronal Repair

Our Aim

Traumatic, ischemic and inflammatory lesions to the spinal cord lead to the transection of descending and ascending axonal tract systems. If these lesions are complete – i.e. if all axons in the spinal cord are transected – severe and persistent functional deficits ensue. If however the lesions are incomplete and some axonal tracts are spared, some recovery of function can be observed. We are studying the anatomical, functional and molecular mechanisms underlying the recovery process in an attempt to develop new therapeutic strategies that can support spinal cord repair in neurological disease caused by trauma, ischemia or inflammation.

Our Approach

Over the recent years we have used various axonal tracts – ascending and descending pathways – to study how axonal connections remodel in response to injury. We could identify the de novo formation of intraspinal detour circuits as a key remodelling process that mediates recovery of function. We are currently using (i) anterograde, retrograde and trans-synaptic tracing techniques in combination with confocal microscopy to reveal the anatomy of spinal detour circuits, (ii) genetic and pharmacological manipulations to dissect the molecular interactions that regulate detour circuit formation and (iii) electrophysiological recordings and behavioural testing to assess effects on functional recovery.

Some of our current projects

Regulation of synapse formation and elimination following spinal cord injury

The incidence of Spinal Cord Injury (SCI) in Germany is estimated at about 36 cases per million of the population, which translates to about 3000 new spinal cord injured patients per year. Most of these patients are young adults injured at work or during traffic accidents who will have to live the rest of their life disabled due to the limited repair capacity of severed central axons. Recently, therapeutic options have emerged that can promote some level of axonal outgrowth after SCI. However, our work emphasizes that axonal outgrowth is in itself insufficient and that regrowing axons have to be integrated into reorganized intraspinal networks to promote functional recovery. To achieve this aim we address the following questions: (i) How do regrowing axons find the correct path to their targets and how do they make appropriate synaptic connections? (ii) how are newly formed intraspinal circuits refined over time to foster functional recovery and which cells contribute to the shaping of circuits? (iii) Which therapeutic strategies can support appropriate synapse formation/elimination?

Activity-dependent regulation of axonal plasticity following spinal cord injury

The transection of axonal connections leads to motor and sensory deficits in many traumatic, ischemic and inflammatory conditions of the central nervous system (CNS). Despite the fact that axonal regeneration generally fails in the CNS, dramatic functional recovery can be observed in particular after incomplete lesions to brain and spinal cord. Our recent work indicates that spontaneous recovery of motor function can be mediated by the formation of intraspinal detour circuits. Detour circuits are formed in the following steps: First, a subpopulation of transected projection neurones forms new collaterals that contact intraspinal relay neurones. Initially these collaterals contact relay neurones irrespective of their projection pattern. However over the following weeks only those sprouts which contact neurones that connect to the original target area are maintained while other sprouts are eliminated. Electrophysiological and behavioural experiments confirm that intraspinal detour circuits are key anatomical substrates of functional recovery. To understand when and where detour circuits can be formed and which regulatory principles guide their formation we study: (i) how neuronal activity guides the formation and stabilization of newly formed connections and (ii) whether we can design therapies based on enhanced activity paradigms to promote the formation of detour circuits and thereby improve functional recovery after CNS injury.

Acute and long term effects of mild repetitive traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity worldwide, particularly among younger adults. In Germany, traumatic brain injury occurs with a frequency of 323 per 100,000 inhabitants annually. Among all brain injuries, it is now recognized that repeated concussions, a mild form of brain injury, are by far the most frequent forms of brain injury. They often occur in the context of sport and have the potential for long-term neurological impairments. A comprehensive understanding of the underlying neurobiological mechanisms associated with repeated concussive and sub-concussive head impacts is essential to identify points of intervention and potential drug targets. Hence in this project we address the following questions: (i) which neuronal, glial and immune responses follow mild repeated brain injury? (ii) which potential therapies can alleviate the structural and functional consequences of synapse loss following mild repetitive brain injury?