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Tajika, Y.

Publications and source records attributed to Tajika, Y..

3 recordsLinked to original sources

Competing valence-related roles of dopamine in the tail of the striatum

Understanding how the brain evaluates aversion and appetition to guide behavior remains an open question. Here, we investigated the role of dopamine signaling in the tail of the striatum (TS) in regulating competing valence-based behaviors and learning. TS dopamine dynamics were monitored as mice performed a classical conditioning task in which an odor cue predicted either an aversive air puff or a water reward. Initially, mice exhibited anticipatory blinking, which diminished over time, while anticipatory licking emerged later, coinciding with adaptation to the air puff. Dopamine responses in the TS to the air puff and its associated odor were initially elevated but declined with repeated exposure. Optogenetic disruption of this decline suppressed adaptation and hindered appetitive learning. These findings demonstrate that TS dopamine dynamics are essential for behavioral adaptation to aversive stimuli, which indirectly facilitates appetitive learning, underscoring a regulatory mechanism for shifting between defensive and reward-seeking behaviors.

neuroscience↗

A simple immunohistochemical method for perinatal mammalian ovaries revealed different kinetics of oocyte apoptosis caused by DNA damage and asynapsis.

Oocytes having meiotic defects are assumed to be eliminated by apoptosis in perinatal period. However, the oocyte apoptosis caused by meiotic defects has not been well analyzed, partly due to the great technical demands for tissue sectioning of perinatal ovaries. In the present study, we applied a squash method for immunohistochemical analysis of perinatal mouse ovaries as a substitute for tissue sectioning. As a result, we could show different kinetics of apoptosis caused by DMC1- and SPO11-deficiencies, indicating that DNA damage-induced apoptosis precedes asynapsis-induced apoptosis in mouse oocytes. Double mutant analysis revealed that only asynapsis-induced apoptosis was significantly dependent on HORMAD2. The present method is simple, easy, and able to analyze a sufficient number of oocytes for detecting infrequent events in a single specimen, accelerating detailed immunohistochemical analyses of mammalian ovaries during the fetal and perinatal periods.

developmental biology↗

Membrane molecule bouncer enables follicle fertilization in a viviparous teleost: Poecilia reticulata (guppy)

Fertilization is a fundamental mechanism of sexual reproduction. Generally, oocytes are ovulated from the ovarian follicles and contact the sperm outside the ovarian medulla. Unlike this, follicle fertilization which means the egg contact with sperm in the ovarian medulla without ovulation is known in the viviparous teleost species belonging to the Poeciliidae. In this study, we focused on a viviparous teleost species, Poecilia reticulata (guppy). Our sperm tracking assay indicated that the sperm reached the immature oocytes with a germinal vesicle, and the fertilized immature oocytes were presumed to contribute to littermates. The binding between immature oocytes and sperm is a specific trait in the guppy, which was not observed in Danio rerio (zebrafish) or Oryzias latipes (medaka). The loss- and gain-of-function assays indicated that bouncer plays a critical role in immature oocyte-to-sperm binding. This fertilization trait in immature oocytes may provide certain advantages for females with respect to nutrition or other gestation costs. Our findings shed light on the unique reproductive strategies of guppy and contribute to our understanding of the diverse reproductive mechanisms in vertebrates. Summary statementUnlike general vertebrates, guppys oocyte fertilizes with sperm in the ovarian medulla at the immature stages. The distinctive trait depends on the Ly6/uPAR protein bouncer.

developmental biology↗