Stimulated Raman scattering microscopy reveals a unique and steady nature of brain water dynamics.

The biological activities of substances in the brain are shaped by their spatiotemporal dynamics in brain tissues, all of which are regulated by water dynamics. In contrast to solute dynamics, water dynamics have been poorly characterized, owing to the lack of appropriate analytical tools. To overcome this limitation, we apply stimulated Raman scattering multimodal multiphoton microscopy to live brain tissues. The microscopy system allows for the visualization of deuterated water, fluorescence-labeled solutes, and cellular structures at high spatiotemporal resolution, revealing that water moves faster than fluorescent molecules in brain tissues. Detailed analyses demonstrate that water, unlike solutes, diffuses homogeneously in brain tissues without differences between the intra- and the extracellular routes. Furthermore, we find that the water dynamics are steady during development and ischemia, when diffusions of solutes are severely affected. Thus, our approach reveals routes and uniquely robust properties of water diffusion in brain tissues.

Probing the Spatiotemporal Dynamics of Oxytocin in the Brain Tissue Using a Simple Peptide Alkyne-Tagging Approach.

The dynamics of oxytocin and its site of action in the brain are poorly understood due to the lack of appropriate tools, despite the interest in the central action of oxytocin signaling. Here, we develop and apply an oxytocin analogue probe by conjugating it with an alkyne via a widely applicable simple coupling reaction. Alkyne-tagged oxytocin behaves similarly to endogenous oxytocin while allowing specific and highly sensitive detection of extracellularly applied oxytocin. Using this probe, we find the existence of high-affinity specific binding sites of oxytocin in the hippocampus. Furthermore, characterization of oxytocin dynamics reveals the cellular basis of its volume transmission in the brain tissue. Finally, we show the wide applicability of this technique for other centrally acting peptides. Thus, the alkyne tagging strategy provides a unique opportunity to characterize the spatiotemporal dynamics of oxytocin and other small-sized peptides in the brain tissue.

Super-multiplex imaging of cellular dynamics and heterogeneity by integrated stimulated Raman and fluorescence microscopy.

Observing multiple molecular species simultaneously with high spatiotemporal resolution is crucial for comprehensive understanding of complex, dynamic, and heterogeneous biological systems. The recently reported super-multiplex optical imaging breaks the "color barrier" of fluorescence to achieve multiplexing number over six in living systems, while its temporal resolution is limited to several minutes mainly by slow color tuning. Herein, we report integrated stimulated Raman and fluorescence microscopy with simultaneous multimodal color tunability at high speed, enabling super-multiplex imaging covering diverse molecular contrasts with temporal resolution of seconds. We highlight this technique by demonstrating super-multiplex time-lapse imaging and image-based cytometry of live cells to investigate the dynamics and cellular heterogeneity of eight intracellular components simultaneously. Our technique provides a powerful tool to elucidate spatiotemporal organization and interactions in biological systems.

Alkyne-Tagged Dopamines as Versatile Analogue Probes for Dopaminergic System Analysis.

The dopaminergic system is essential for the function of the brain in health and disease. Therefore, detailed studies focused on unraveling the mechanisms involved in dopaminergic signaling are required. However, the lack of probes that mimic dopamine in living tissues, owing to the neurotransmitter's small size, has hampered analysis of the dopaminergic system. The current study aimed to overcome this limitation by developing alkyne-tagged dopamine compounds (ATDAs) that have a minimally invasive and uniquely identifiable alkyne group as a tag. ATDAs were established as chemically and functionally similar to dopamine and readily detectable by methods such as specific click chemistry and Raman scattering. The ATDAs developed here were verified as analogue probes that mimic dopamine in neurons and brain tissues, allowing the detailed characterization of dopamine dynamics. Therefore, ATDAs can act as safe and versatile tools with wide applicability in detailed studies of the dopaminergic system. Furthermore, our results suggest that the alkyne-tagging approach can also be applied to other small-sized neurotransmitters to facilitate characterization of their dynamics in the brain.

Deficiency of transcription factor Brn4 disrupts cochlear gap junction plaques in a model of DFN3 non-syndromic deafness.

Brn4, which encodes a POU transcription factor, is the gene responsible for DFN3, an X chromosome-linked, non-syndromic type of hearing loss. Brn4-deficient mice have a low endocochlear potential (EP), hearing loss, and ultrastructural alterations in spiral ligament fibrocytes, however the molecular pathology through which Brn4 deficiency causes low EP is still unclear. Mutations in the Gjb2 and Gjb6 genes encoding the gap junction proteins connexin26 (Cx26) and connexin30 (Cx30) genes, respectively, which encode gap junction proteins and are expressed in cochlear fibrocytes and non-sensory epithelial cells (i.e., cochlear supporting cells) to maintain the proper EP, are responsible for hereditary sensorineural deafness. It has been hypothesized that the gap junction in the cochlea provides an intercellular passage by which K+ is transported to maintain the EP at the high level necessary for sensory hair cell excitation. Here we analyzed the formation of gap junction plaques in cochlear supporting cells of Brn4-deficient mice at different stages by confocal microscopy and three-dimensional graphic reconstructions. Gap junctions from control mice, which are composed mainly of Cx26 and Cx30, formed linear plaques along the cell-cell junction sites with adjacent cells. These plaques formed pentagonal or hexagonal outlines of the normal inner sulcus cells and border cells. Gap junction plaques in Brn4-deficient mice did not, however, show the normal linear structure but instead formed small spots around the cell-cell junction sites. Gap junction lengths were significantly shorter, and the level of Cx26 and Cx30 was significantly reduced in Brn4-deficient mice compared with littermate controls. Thus the Brn4 mutation affected the assembly and localization of gap junction proteins at the cell borders of cochlear supporting cells, suggesting that Brn4 substantially contributes to cochlear gap junction properties to maintain the proper EP in cochleae, similar to connexin-related deafness.

Assembly of the cochlear gap junction macromolecular complex requires connexin 26.

Hereditary deafness affects approximately 1 in 2,000 children. Mutations in the gene encoding the cochlear gap junction protein connexin 26 (CX26) cause prelingual, nonsyndromic deafness and are responsible for as many as 50% of hereditary deafness cases in certain populations. Connexin-associated deafness is thought to be the result of defective development of auditory sensory epithelium due to connexion dysfunction. Surprisingly, CX26 deficiency is not compensated for by the closely related connexin CX30, which is abundantly expressed in the same cochlear cells. Here, using two mouse models of CX26-associated deafness, we demonstrate that disruption of the CX26-dependent gap junction plaque (GJP) is the earliest observable change during embryonic development of mice with connexin-associated deafness. Loss of CX26 resulted in a drastic reduction in the GJP area and protein level and was associated with excessive endocytosis with increased expression of caveolin 1 and caveolin 2. Furthermore, expression of deafness-associated CX26 and CX30 in cell culture resulted in visible disruption of GJPs and loss of function. Our results demonstrate that deafness-associated mutations in CX26 induce the macromolecular degradation of large gap junction complexes accompanied by an increase in caveolar structures.

Dominant negative connexin26 mutation R75W causing severe hearing loss influences normal programmed cell death in postnatal organ of Corti.

BACKGROUND: The greater epithelial ridge (GER) is a developmental structure in the maturation of the organ of Corti. Situated near the inner hair cells of neonatal mice, the GER undergoes a wave of apoptosis after postnatal day 8 (P8). We evaluated the GER from P8 to P12 in transgenic mice that carry the R75W + mutation, a dominant-negative mutation of human gap junction protein, beta 2, 26 kDa (GJB2) (also known as connexin 26 or CX26). Cx26 facilitate intercellular communication within the mammalian auditory organ. RESULTS: In both non-transgenic (non-Tg) and R75W + mice, some GER cells exhibited apoptotic characteristics at P8. In the GER of non-Tg mice, both the total number of cells and the number of apoptotic cells decreased from P8 to P12. In contrast, apoptotic cells were still clearly evident in the GER of R75W + mice at P12. In R75W + mice, therefore, apoptosis in the GER persisted until a later stage of cochlear development. In addition, the GER of R75W + mice exhibited morphological signs of retention, which may have resulted from diminished levels of apoptosis and/or promotion of cell proliferation during embryogenesis and early postnatal stages of development. CONCLUSIONS: Here we demonstrate that Cx26 dysfunction is associated with delayed apoptosis of GER cells and GER retention. This is the first demonstration that Cx26 may regulate cell proliferation and apoptosis during development of the cochlea.