Biology subjects

Pain, M.

Publications and source records attributed to Pain, M..

3 recordsLinked to original sources

bioRxiv2026

Functional maturation in abducens motoneurons populations during angular VOR larval development

Extraocular motoneurons are the final neuronal relay implicated in gaze motor control and are known to be subdivided in functional subgroups, differently implicated in ocular motion dynamics. However, the maturation of these functional populations of extraocular motoneurons, in relation with the development of gaze-stabilizing reflexes remains largely unexplored. In amphibian tadpoles, the angular vestibulo-ocular reflex (VOR) appears later than other visuo-vestibular ocular reflexes and matures until the metamorphosis climax. Two types of Abducens motoneurons have been described to participate to the angular VOR in larval frog: spontaneous motor units, exhibiting a robust resting activity and silent motor units recruited only during head motion. The aim of this study was to investigate the maturation of these two types of Abducens motor units in relation with the development of the angular VOR by evaluating their discharge dynamic in response to head rotation in semi-intact preparations of larval Xenopus laevis. During larval life, the discharge modulation during sinusoidal head rotations increases significantly for silent units only, demonstrating a better sensitivity of this Abducens motoneuron sub-population to horizontal semicircular canal activation. In addition, this functional maturation was accompanied by an increase of the myelination in the lateral rectus motor nerve, promoting a faster conductivity in late larval stages than in early one. These findings showed that the development of the angular VOR is supported by a selective maturation of extraocular motoneurons subpopulations, specifically implicated in the improvement of the ocular kinematic during the reflex.

neuroscience↗

bioRxiv2026

The retinal pigment epithelium undergoes anisotropic stretching and nuclear size scaling during optic cup morphogenesis in a fish model.

The morphogenesis of the optic cup provides a robust system for studying how two apposed epithelial monolayers with distinct properties fold and stretch in a coordinated manner to form the primordial eye. While much research has been conducted on the temporal dynamics of retinal neuroepithelium invagination, the spatial organization and stretching of the retinal pigment epithelium has received less attention. The fish species Astyanax mexicanus offers a unique model to examine the mechanisms of optic tissue morphogenesis through a comparative lens, as it exhibits natural variation in eye development between its river-dwelling and cave-adapted morphs. Using quantitative 3D imaging of optic cups from both morphs, we found that RPE morphogenesis involves transient, graded, and anisotropic cell stretching that patterns the epithelium during optic cup shaping. Analyses of RPE nuclear spacing and cell morphology showed that tissue stretching gradually increases along the proximo-distal axis, suggesting maximal tension in the elongated distal RPE cells aligned along the optic cup meridians. Furthermore, nuclear volumes and apical surface areas of RPE cells scaled spatially along the same axis, independently of endoreplication. In the cavefish natural mutant, RPE expansion was delayed by over six hours and proximal stretching exhibited altered isotropy, indicative of disrupted temporal coordination and suggesting modified mechanical constraints. These results demonstrate that RPE morphogenesis is a highly heterogeneous process from a spatiotemporal perspective, offering new insights into the study of the biomechanical principles of eye development in vertebrates. Summary statementThis study reveals the emergence of cell morphology gradients within the retinal pigment epithelium during morphogenesis of the eye in two distinct populations of the same species of fish.

developmental biology↗

bioRxiv2025

Deciphering the role of brainstem vestibular-related inhibitory networks in shaping postural reflexes in the Xenopus tadpole

Brainstem vestibulospinal (VS) nuclei generate excitatory commands in response to multi-modality sensory integration, to activate specific spinal networks in order to generate adapted postural reflexes. Comparably organized in bilateral nuclei with both ipsi- and contralateral pathways in all species, excitatory VS projections alone fail to explain the mostly unilateral reflex responses typically observed. In the Xenopus laevis tadpole, we describe secondary vestibular neurons of inhibitory nature, and the synaptic contacts they make on VS neurons. Then, using a brainstem/spinal cord in vitro preparation we show that the spinal responses evoked by galvanic vestibular stimulation are shaped by both commissural and local inhibitory brainstem networks. We further show that a complex interaction between GABAergic and glycinergic inhibitory networks regulate VS neuron excitability and, consequently, the expression of the spinal response. Our data reveal that while excitatory VS neurons execute the neural score, inhibitory neurons in the central vestibular system coordinate and modulate the overall performance.

neuroscience↗