Fernandez-Lopez, B. | Search bioRxiv

bioRxiv2019

Taurine promotes axonal regeneration after a complete spinal cord injury in lampreys

Taurine is one of the most abundant free amino acids in the brain. It is well known that taurine protects the brain from further damage after a traumatic event. However, only a few ex vivo studies have looked at the possible role of taurine in the regulation of axon regeneration after injury. Here, we aimed to reveal the possible role for taurine in the modulation of axonal regeneration following a complete spinal cord injury (SCI) using lampreys as an animal model. The brainstem of lampreys contains several individually identifiable descending neurons that differ greatly in their capacity for axonal regeneration after SCI. This offers a convenient model to promote or inhibit axonal regrowth in the same in vivo preparation. First, we carried out high performance liquid chromatography experiments to measure taurine levels in the spinal cord following SCI. Our results revealed a statistically significant increase in taurine levels 4 weeks post lesion, which suggested that taurine might have a positive effect on axonal regrowth. Based on these results, we decided to apply an acute taurine treatment at the site of injury to study its effect on axon regeneration. Results from these experiments show that an acute taurine treatment enhances axonal regeneration following SCI in lampreys. This offers a novel way to try to promote axon regeneration after nervous system injuries in mammalian models.

neuroscience↗

bioRxiv2018

GABA promotes survival and axonal regeneration in identifiable descending neurons after spinal cord injury in larval lampreys

In mammals, spinal cord injury (SCI) causes permanent disability. The poor regenerative capacity of descending neurons is one of the main causes of the lack of recovery after SCI. In addition, the prevention of retrograde degeneration leading to the atrophy or death of descending neurons is an obvious prerequisite for the activation of axonal regeneration. Lampreys show an amazing regenerative capacity after SCI. Recent histological work in lampreys suggested that GABA, which is massively released after a SCI, could promote the survival of descending neurons. Here, we aimed to study if GABA, acting through GABAB receptors, promotes the survival and axonal regeneration of descending neurons of larval sea lampreys after a complete SCI. First, we used in situ hybridization to confirm that identifiable descending neurons of late stage larvae express the gabab1 subunit of the sea lamprey GABAB receptor. We also observed an acute increase in the expression of this subunit in descending neurons after a complete SCI, which further supported the possible role of GABA and GABAB receptors in promoting the survival and regeneration of these neurons. So, we performed gain and loss of function experiments to confirm this hypothesis. Treatments with GABA and baclofen (GABAB agonist) significantly reduced caspase activation in descending neurons 2 weeks after a complete SCI. Long-term treatments with GABOB (a GABA analogue) and baclofen significantly promoted axonal regeneration of descending neurons after SCI. These data indicate that GABAergic signalling through GABAB receptors promotes the survival and regeneration of descending neurons after SCI. Finally, we used morpholinos against the gabab1 subunit to specifically knockdown the expression of the GABAB receptor in descending neurons. Long-term morpholino treatments caused a significant inhibition of axonal regeneration, which shows that endogenous GABA promotes axonal regeneration after a complete SCI in lampreys by activating GABAB receptors expressed in descending neurons. These data implicate GABAB receptors in spinal cord regeneration in lampreys and further provide a new target of interest for SCI.

neuroscience↗