The Limited Effects of Estradiol Administration Immediately after Spinal Cord Injury.

OBJECTIVE: We aimed to investigate estradiol (E2) as a therapeutic drug for spinal cord injury (SCI) and elucidate the disagreement in the field about the use of this hormone after an injury. METHODS: Eleven animals underwent surgery (laminectomy at the T9-T10 levels) followed by an intravenous injection (100 µg) of an E2 bolus and the implantation of 0.5cm of Silastic tubing containing 3 mg of E2 (sham E2 + E2 bolus) immediately after the laminectomy. The SCI control animals received a moderate contusion using the Multicenter Animal SCI Study impactor device over the exposed spinal cord followed by an intravenous bolus injection of sesame oil and were implanted with empty Silastic tubing (injury SE + vehicle); treated rats received a bolus of E2 and a Silastic implant with 3 mg of E2 (injury E2 + E2 bolus). Functional locomotor recovery and fine motor coordination were assessed by the Basso, Beattie, and Bresnahan (BBB) open field test and grid-walking tests, respectively, from the acute (7 days post-injury [DPI]) to the chronic stages (35 DPI). Anatomical studies of the cord were performed using Luxol fast blue staining followed by densitometric analysis. RESULTS: As observed in the BBB open field and the grid-walking tests, E2 post-SCI did not improve locomotor function but instead increased spared white matter tissue, in the rostral region. CONCLUSION: Estradiol post-SCI, at the dose and route of administration used in this study, failed to promote locomotor recovery but partially restored spared white matter tissue.

Cnr2 Is Important for Ribbon Synapse Maturation and Function in Hair Cells and Photoreceptors.

The role of the cannabinoid receptor 2 (CNR2) is still poorly described in sensory epithelia. We found strong cnr2 expression in hair cells (HCs) of the inner ear and the lateral line (LL), a superficial sensory structure in fish. Next, we demonstrated that sensory synapses in HCs were severely perturbed in larvae lacking cnr2. Appearance and distribution of presynaptic ribbons and calcium channels (Cav1.3) were profoundly altered in mutant animals. Clustering of membrane-associated guanylate kinase (MAGUK) in post-synaptic densities (PSDs) was also heavily affected, suggesting a role for cnr2 for maintaining the sensory synapse. Furthermore, vesicular trafficking in HCs was strongly perturbed suggesting a retrograde action of the endocannabinoid system (ECs) via cnr2 that was modulating HC mechanotransduction. We found similar perturbations in retinal ribbon synapses. Finally, we showed that larval swimming behaviors after sound and light stimulations were significantly different in mutant animals. Thus, we propose that cnr2 is critical for the processing of sensory information in the developing larva.

Expression patterns of activating transcription factor 5 (atf5a and atf5b) in zebrafish.

The Activating Transcription Factor 5 (ATF5) is a basic leucine-zipper (bZIP) transcription factor (TF) with proposed stress-protective, anti-apoptotic and oncogenic roles which were all established in cell systems. In whole animals, Atf5 function seems highly context dependent. Atf5 is strongly expressed in the rodent nose and mice knockout (KO) pups have defective olfactory sensory neurons (OSNs), smaller olfactory bulbs (OB), while adults are smell deficient. It was therefore proposed that Atf5 plays an important role in maturation and maintenance of OSNs. Atf5 expression was also described in murine liver and bones where it appears to promote differentiation of progenitor cells. By contrast in the rodent brain, Atf5 was first described as uniquely expressed in neuroprogenitors and thus, proposed to drive their proliferation and inhibit their differentiation. However, it was later also found in mature neurons stressing the need for additional work in whole animals. ATF5 is well conserved with two paralogs, atf5a and atf5b in zebrafish. Here, we present the expression patterns for both from 6 h (hpf) to 5day post-fertilization (dpf). We found early expression for both genes, and from 1dpf onwards overlapping expression patterns in the inner ear and the developing liver. In the brain, at 24hpf both atf5a and atf5b were expressed in the forebrain, midbrain, and hindbrain. However, from 2dpf and onwards we only detected atf5a expression namely in the olfactory bulbs, the mesencephalon, and the metencephalon. We further evidenced additional differential expression for atf5a in the sensory neurons of the olfactory organs, and for atf5b in the neuromasts, that form the superficial sensory organ called the lateral line (LL). Our results establish the basis for future functional analyses in this lower vertebrate.