NEUROPROTECTIVE ROLE OF ENDOCANNABINOIDS IN A MODEL OF AXONAL DAMAGE AND REGENERATION

Endocannabinoids are lipid signaling mediators with neuromodulatory and neuroprotective roles in several types of brain injury. Unlike mammalian, the nervous system of low vertebrates is promptly able to regenerate neurons and spinal nerves after unjury. In the lizards, tail loss transects spinal nerves and the cut axons elongate in the regrowing tail, providing a natural paradigm of robust regenerative response of injured spinal motoneurons. On this basis we have investigated the possible involvement of the endocannabinoid system in the survival of motoneurons committed to axonal elongation. By our previous studies, a typical chromatolytic reaction to axotomy appears by 10-14 days of caudotomy in the so called “reactive” which is followed by “regenerative phase” up to the complete regrowing of tail. In the present work, we compared the endocannabinoid system of regenerating motoneurons, at 10 days (reactive phase) and at 4 months after caudotomy (regenerative phase), to those of intact motoneurons. Single and multiple immunohystochemistry were performed for CB1 and CB2 receptors, 2-AG endocannabinoid synthesizing (DAGL alpha) and degrading (MAGL) enzymes, glutamate and GABA vescicular transmitter transportes (VGluT1 and VGAT, respectively), glial marker GFAP and the activated microglial marker Iba-1. Our data suggest a general decrease of endocannabinoid system activity during the reactive phase. In the regenerative phase we observed a strong CB1-ir on both glutamatergic and GABAergic axon terminals surrounding motoneurons expressing DAGL-. CB-2-ir and Iba-1-ir came back to normal levels. These results support a neuroprotective role of 2-AG via inhibition of glutamate-mediated neuronal excitotoxicity.