Full regeneration of descending corticotropin-releasing hormone axons after a complete spinal cord injury in lampreys

Spontaneous regeneration of cholecystokinergic reticulospinal axons after a complete spinal cord injury in sea lampreys

“…Based on these data, we decided to analyse the regenerative capacity of axotomized CCK-ir axons after a complete spinal cord transection. We choose the 10 wpl time point because previous work has shown that 10 wpl larvae present a high degree of swimming recovery [28] , [44] , [45] , [46] and axon regeneration [11] , [28] , [5] , [47] after a transection SCI at the level of the 5th gill. 10 wpl animals (n = 11) showed a mean value of 4.9 ± 0.24 in Ayer’s scale (minimum of 4 with 55% of the larvae between 5 and 6; these 10 wpl animals are the same animals in which we studied the regeneration of CRHergic axons in a previous study in a different set of spinal cord cryostat sections [28] ; Table 1 ].…”

“…We choose the 10 wpl time point because previous work has shown that 10 wpl larvae present a high degree of swimming recovery [28] , [44] , [45] , [46] and axon regeneration [11] , [28] , [5] , [47] after a transection SCI at the level of the 5th gill. 10 wpl animals (n = 11) showed a mean value of 4.9 ± 0.24 in Ayer’s scale (minimum of 4 with 55% of the larvae between 5 and 6; these 10 wpl animals are the same animals in which we studied the regeneration of CRHergic axons in a previous study in a different set of spinal cord cryostat sections [28] ; Table 1 ]. At level 4 in the Ayer’s scale, rostro-caudal undulatory movements become coordinated and propagating waves travel along the body, which is suggestive of the recovery of intersegmental coordination related to axon regeneration.…”

“…Fig. 1 a was taken from González-Llera et al [28] . Abbreviations: C: caudal, CC: central canal, DC: dorsal column, LAT: lateral region, R: rostral, VM: ventromedial region.…”

“…The anti-SV2 antibody was generated against purified synaptic vesicles of the electric ray [35] . The antibody recognizes the 3 SV2 isoforms (A to C) and labels synaptic vesicle clusters in all tested vertebrates, including lampreys [28] , [36] , [37] , [38] , [39] , [9] .…”

“…This allows to study the regeneration of small-caliber descending neuropeptidergic axons by using simple immunofluorescence methods. Indeed, by using an antibody against the sea lamprey CRH mature peptide we have recently showed that by 10 weeks after a complete SCI at the level of the 5th gill, descending CRHergic axons of lampreys fully regenerate to at least the level of the 6th gill opening [28] . However, because CRHergic axons originate from 3 different neuronal populations of the brainstem [27] , this neuropeptidergic system does not allow us to work with a single neurochemically distinct neuronal population as a model of spontaneous regeneration of small-caliber axons.…”