Ontogeny of the conus papillaris of the lizard Gallotia galloti and cellular response following transection of the optic nerve: an immunohistochemical and ultrastructural study

Abstract

Spontaneous regrowth of the axons of retinal ganglion cells (RGC) occurs after unilateral optic nerve transection (ONT) in the lizard Gallotia galloti. We have performed an immunohistochemical and ultrastructural study of the conus papillaris (CP) of this lizard during ontogeny and after ONT in order to characterize its cell subpopulations, innervation and putative blood-brain barrier (BBB) and to evaluate changes occurring throughout regeneration. Proliferating PCNA(+) cells were abundant between embryonic stage 33 (E33) and hatching. From E33, we observed Pax2(+)/GS(+) glial cells in the primitive CP, which became increasingly pigmented and vascularised from E35. Conal astrocytes coexpressing Pax2 with vimentin and/or GFAP were identified from E37-E38. GluT-1(+)/LEA(+)/Pax2(-) endothelial cells (ECs) formed a continuous endothelium with tight junctions and luminal and abluminal microfolds. In adults, the peripheral blood vessels showed a thinner calibre, stronger GluT-1 staining and more abundant microfolds than those of the central CP indicating the higher specialization involved during transport within the former. Occasional pericytes, abundant Pax2(+) pigment cells, LEA(+) microglia/macrophages, unmyelinated Tuj1(+) nerve fibres and SV2(+) synaptic vesicles were also observed in the perivascular zone. After ONT, the expression of GluT-1 and p75(NTR) persisted in ECs, suggesting the preservation/early recovery of the BBB. Relevant ultrastructural alterations were observed at 0.5 months postlesion, although, by 3 months, the CP had recovered the ultrastructure of controls indicating tissue recovery. Abnormal newly formed blood vessels had developed in the CP-optic nerve junction. Thus, the CP is a central nervous system structure whose regenerating capacity might be key for the nutritional support of regenerating RGCs in G. galloti.

Development of astroglia heterogeneously expressing Pax2, vimentin and GFAP during the ontogeny of the optic pathway of the lizard (Gallotia galloti): an immunohistochemical and ultrastructural study

“…We have also observed astrocyte processes extending towards blood vessels along the ON-OTr; these might participate in the blood brain barrier like those reported in the conus papillaris (Alfayate et al 2011). Vim + /GFAP + astrocytes arranged in rows in the lizard MN contain more organelles in their cytoplasm, at the expense of gliofilaments, than those of the CPONJ.…”

“…Unlike in mammals, the persistent astroglial scar, which, in lizard, expresses glial fibrillary acidic protein (GFAP; Lang et al 2002Lang et al , 2008 and neurotrophin-3 (NT-3; Santos et al 2008), is permissive to axon regrowth. The astroglial lineage of the optic tectum of G. galloti has been studied in detail during ontogeny (Monzón-Mayor et al 1990a, b, c, 1998Romero-Alemán et al 2003), whereas in the rest of the optic pathway, these cells are still poorly characterised (Alfayate et al 2011;Romero-Alemán et al 2003, 2010. We consider that the further characterisation of the astroglial lineage during development would be helpful for understanding RGC axon growth and regrowth, since both might require similar astroglial environments.…”

Form and Function of the Vertebrate and Invertebrate Blood-Brain Barriers

“…While the regeneration of gross structures (e.g., limbs, tail) have been studied in reptiles [136], there appears to have been little focus specifically on neural regeneration, and especially of the NVU. In the lizard Gallotia galloti, studies of cellular performance following transection of the optic nerve indicate rapid restoration of key components of the neurovascular barrier within a few weeks [137].…”

Adaptation of Eye of the Egyptian Agama "Trapelus Mutabilis" According to Its Activity Pattern

“…Braekevelt [21] studied ultrastructure of the conus papillaris in the bobtail goanna, Tiliqua rugosa. Alfayate et al [22] studied ontogeny of the conus papillaris cellular response after optic nerve transection in the lizard Gallotia galloti: an immunohistochemical and ultrastructural study. The current study presents description of anatomical, scanning electron microscopy, and histological investigations of lens, cornea, retina, and conus papillaris of the Egyptian agama, Trapelus mutabilis, related to the diurnal activity.…”