Biology subjects

Tostivint, H.

Publications and source records attributed to Tostivint, H..

6 recordsLinked to original sources

bioRxiv2026

Differential maturation in vestibular neuronal groups related to developmental motor reorganization in amphibians

Vestibular neurons are core elements of the pathways involved in vestibulo-motor functions, such as vestibulo-spinal and vestibulo-ocular reflexes. To meet behavioral needs, electrophysiological neuronal properties are adequately adapted to the sensory-motor computation sustaining these distinct vestibular reflexes. During frog metamorphosis, there is a complete reorganization of the posturo-locomotor system while the oculomotor system remains minimally changed, probably associated to so far unknown changes in vestibular neuronal properties. We used this unique model to investigate the central developmental mechanisms underlying such a reconfiguration of vestibular-associated behaviors. Central vestibular neurons exhibit two types of electrophysiological phenotypes: tonic neurons with a continuous discharge and phasic neurons with a transitory discharge mainly due to the activation of Kv1.1 channel. Electrophysiological recordings and Kv1.1 immunolabeling of vestibulospinal (VS) and vestibulo-ocular (VO) neurons at both larval and juvenile stages revealed that the majority of VS neurons exhibited a tonic discharge in larvae but a phasic discharge in juvenile, while VO neurons remained mainly tonic throughout development. Changes in phasic and tonic neurons proportions in VS population are partly explained by neurogenesis. But we provide evidences that an electrophysiological phenotype switch is a concomitant developmental mechanism participating in the maturation of these central vestibular neurons. All together our results showed that the maturation process in central vestibular neuronal groups is highly related to the metamorphosis-induced remodeling of vestibulo-motor functions they are involved in, with the ultimate purpose of ensuring an adequate adaptation of neuronal elements properties to the developmental changes of behavioral constrains.

neuroscience↗

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↗

bioRxiv2025

Hormonal gene expression changes in the zebrafish caudal neurosecretory system under acute environmental challenges

The caudal neurosecretory system (CNSS) is a neuroendocrine complex, found only in fishes, suggested to be involved in osmoregulation and thermo-adaptation. Although being discovered 70 years ago, the CNSS has been understudied and its physiological significance remains poorly understood. The zebrafish (Danio rerio) is a well-established model organism for functional studies, yet, so far, the role of the CNSS has not really been investigated in this species. In the present study, we attempted to identify environmental factors whose variations induce changes in CNSS activity. Juvenile zebrafish were submitted to acute (2 h, 8 h, and 24 h) pH, salinity, and temperature challenges, and CNSS activity was quantified by measuring the expression levels of peptide hormone-encoding genes using quantitative PCR. Our findings revealed that temperature challenge affected the expression of the largest number of gene, followed by salinity and pH challenges. This suggested that, in the zebrafish, the CNSS is involved in thermo-adaptation and osmoregulation, which is consistent with what has been reported in other species, and showed that the zebrafish is a relevant model to study the function of the CNSS.

physiology↗

bioRxiv2022

Urp1 and Urp2 act redundantly to maintain spine shape in zebrafish larvae.

Urp1 and Urp2 are two neuropeptides, members of the Urotensin 2 family, that have been recently involved in the control of body axis morphogenesis in zebrafish. They are produced by a population of sensory spinal neurons, called cerebrospinal fluid contacting neurons (CSF-cNs), under the control of signals relying on the Reissner fiber, an extracellular thread bathing in the CSF. Here, we have investigated further the function of Urp1 and Urp2 (Urp1/2) in body axis formation and maintenance. We showed that urp1;urp2 double mutants develop strong body axis defects during larval growth, revealing the redundancy between the two neuropeptides. These defects were similar to those previously reported in uts2r3 mutants. We observed that this phenotype is not associated with bone formation defects nor with increased inflammation status but, by using specific inhibitors, we found that the action of Urp1/2 depends on myosin II contraction. Finally, we provide evidence that while the Urp1/2 signaling is functioning during larval growth but is dispensable for embryonic development. Taken together, our results show that Urp1/2 signaling is required in larvae to promote correct vertebral body axis, most likely by regulating muscle tone.

developmental biology↗

bioRxiv2019

Differential expression of five prosomatostatin genes in the central nervous system of the catshark Scyliorhinus canicula

Five prosomatostatin genes (PSST1, PSST2, PSST3, PSST5 and PSST6) have been recently identified in elasmobranchs (Tostivint, Gaillard, Mazan, & Pezeron, 2019). In order to gain insight into the contribution of each somatostatin to specific nervous systems circuits and behaviors in this important jawed vertebrate group, we studied the distribution of neurons expressing PSST mRNAs in the catshark Scyliorhinus canicula using in situ hybridization with specific probes for the five PSSTs transcripts. Additionally, we combined in situ hybridization with tyrosine hydroxylase (TH) immunochemistry for better localization of some PSSTs-positive populations. The five PSST genes showed expression in the brain, although with important differences in distribution. PSST1 and PSST6 were widely expressed in different brain regions. Instead, PSST2 and PSST3 were expressed only in the ventral hypothalamus and in some hindbrain lateral reticular neurons, whereas PSST5 was only expressed in the region of the entopeduncular nucleus. PSST1 and PSST6 were expressed by numerous pallial neurons, although in different populations judging from the colocalization of tyrosine hydroxylase (TH) immunoreactivity and PSST6 expression in pallial neurons and the absence of colocalization between TH and PSST1 expression. Differential expression of PSST1 and PSST6 was also observed in the subpallium, hypothalamus, diencephalon, optic tectum, midbrain tegmentum and rhombencephalon. Expression of PSST1 was observed in numerous cerebrospinal fluid-contacting (CSF-c) neurons of the paraventricular organ of the hypothalamus and the central canal of the spinal cord. These wide differences in expression of PSST genes together with the numerous brain nuclei expressing PSSTs, indicate that catshark somatostatinergic neurons are implicated differentially in a number of neural circuits.

neuroscience↗

bioRxiv2017

Functional limb muscle innervation prior to cholinergic transmitter specification during early metamorphosis in Xenopus

In vertebrates, functional motoneurons are defined as differentiated neurons that are connected to a central premotor network and activate peripheral muscle using acetylcholine. Generally, motoneurons and muscles develop simultaneously during embryogenesis. However, during Xenopus metamorphosis, developing limb motoneurons must reach their target muscles through the already established larval cholinergic axial neuromuscular system. Here, we demonstrate that at metamorphosis onset, spinal neurons retrogradely labeled from the emerging hindlimbs initially express neither choline acetyltransferase nor vesicular acetylcholine transporter. Nevertheless, they are positive for the motoneuronal transcription factor Islet1/2 and exhibit intrinsic and axial locomotor-driven electrophysiological activity. Moreover, the early appendicular motoneurons activate developing limb muscles via nicotinic antagonist-resistant, glutamate antagonist-sensitive, neuromuscular synapses. Coincidently, the hindlimb muscles transiently express glutamate, but not nicotinic receptors. Subsequently, both pre- and postsynaptic neuromuscular partners switch definitively to typical cholinergic transmitter signaling. Thus, our results demonstrate a novel context-dependent re-specification of neurotransmitter phenotype during neuromuscular system development.

neuroscience↗