Distribution, Innervation, and Cellular Organization of Taste Buds in the Sea Catfish, Plotosus japonicus.

The gustatory system of the sea catfish Plotosus japonicus, like that of other catfishes, is highly developed. To clarify the details of the morphology of the peripheral gustatory system of Plotosus, we used whole-mount immunohistochemistry to investigate the distribution and innervation of the taste buds within multiple organs including the barbels, oropharyngeal cavity, fins (pectoral, dorsal, and caudal), and trunk. Labeled taste buds could be observed in all the organs examined. The density of the taste buds was higher along the leading edges of the barbels and fins; this likely increases the chance of detecting food. In all the fins, the taste buds were distributed in linear arrays parallel to the fin rays. Labeling of nerve fibers by anti-acetylated tubulin antibody showed that the taste buds within each sensory field are innervated in different ways. In the barbels, large nerve bundles run along the length of the organ, with fascicles branching off to innervate polygonally organized groups of taste buds. In the fins, nerve bundles run along the axis of fin rays to innervate taste buds lying in a line. In each case, small fascicles of fibers branch from large bundles and terminate within the basal portions of the taste buds. Serotonin immunohistochemistry demonstrated that most of the taste buds in all the organs examined contained disk-shaped serotonin-immunopositive cells in their basal region. This indicates a similar organization of the taste buds, in terms of the existence of serotonin-immunopositive basal cells, across the different sensory fields in this species.

Food- and light-entrainable oscillators control feeding and locomotor activity rhythms, respectively, in the Japanese catfish, Plotosus japonicus.

Feeding and locomotor activities of the Japanese catfish Plotosus japonicus under solitary condition were recorded to identify mechanisms controlling these behaviours. In the absence of food, the catfish showed nocturnal locomotor activity, but no feeding activity. Under ad libitum food conditions, both feeding and locomotor activities occurred during the dark period and were synchronized with light/dark (LD) cycles. Feeding activity lasted for 11-24 days when food was stopped after ad libitum food availability. Restricted food during the light phase produced both food-anticipatory and light-entrainable feeding activity. Furthermore, this condition produced weak food-anticipatory and light-entrainable locomotor activity. Under the light/light (LL) condition, restricted food produced food-anticipatory feeding and locomotor activities, suggesting that a food-entrainable oscillator controls both feeding and locomotor activities. However, under the LL condition, light-entrainable feeding and locomotor activities were not observed, suggesting that a light-entrainable oscillator controls both feeding and locomotor activities. During a restricted food schedule, LD cycle shifts resulted in disrupted synchronization of feeding activity onset in three of the four fish, but one fish showed synchronized feeding activity. These results suggest that the food- and the light-entrainable oscillator may control feeding and locomotor activities, respectively.

Imaging mass spectrometry of gold nanoparticles in a tissue section as an immunohistochemical staining mass probe.

For analysis of low abundance peptides in a tissue section, immunohistochemical staining through antibody-antigen interaction is a usual technique. The antibody is conjugated with a probe moiety that aids in highly sensitive detection. Gold nanoparticles, which show excellent chemical stability and variation of surface modifications, are expected to act as a sensitive mass probe to desorb gold ions (Au+ , Au2 + , Au3 + ) that are distinguishable from fragment ions from organic molecules. Here, green fluorescent proteins (GFP) in a tissue section of a transgenic zebrafish were detected by the gold mass probe conjugated with antibodies. Due to the efficient ionization and desorption of gold ions, imaging mass spectrometry of Au2 + ions indicated the distribution of gold nanoparticles stained in a tissue section, and the mass signal distribution was consistent with the area where the GFP-expressing cells were distributed. Conventional immunofluorescence techniques showed intense autofluorescence that come from intrinsic fluorophores in the tissue section. In contrast, the gold nanoparticles acted as an immunostaining mass probe that displayed significantly lower background signals.

The enhancement effect of estradiol on contextual fear conditioning in female mice.

Several studies have reported regulatory effects of estrogens on fear conditioning in female rodents. However, these studies used different doses, durations, and/or administration methods, and reported inconsistent results. To clarify the effect of estrogen on fear conditioning, we investigated the effects of different doses and durations of estradiol administration on freezing behavior during contextual fear conditioning in ovariectomized (OVX) mice. In Experiment 1, OVX ICR mice received a single subcutaneous (s.c.) injection of either oil vehicle (control, 0.1 ml sesame oil) or varied doses (0.5 µg/0.1 ml, 5 µg/0.1 ml, or 50 µg/0.1 ml) of 17ß-estradiol-3-benzoate (EB). Fear conditioning was conducted two days post-EB treatment, and the mice were tested for the learned fear response the following day. In Experiment 2, OVX female mice received an s.c. implantation of a Silastic capsule (I.D. 1.98 × 20.0 mm) containing either vehicle or varied doses (0.05 µg/0.1 ml, 0.5 µg/0.1 ml, 5 µg/0.1 ml, 50 µg/0.1 ml) of EB. Two weeks after implantation, fear conditioning was conducted. During the tests conducted 24 h after conditioning, the high dose EB group showed longer freezing times in both experiments, and lower locomotor activity compared to the control or lower dose groups. In Experiment 3, serum estradiol concentrations of the mice that were treated like those in Experiment 2, were measured; the serum levels of estradiol increased linearly according to the dose of EB administered. The results suggest that mice treated with a high dose of EB exhibit enhanced fear learning, regardless of treatment duration. As a woman's vulnerability to emotional disorders increases in the peripregnancy period, during which estrogen levels are high, the results from the high-dose EB groups may be important for understanding the hormonal mechanisms involved in these disorders.

Thermal properties of acid-induced depolarization in cultured rat small primary afferent neurons.

Tissue ischemia and inflammation result in localized acidosis, and acidic pH can trigger a sensation of pain. Pain is known to be often modified by the tissue temperature. The purpose of this study is to clarify the thermal behavior of nociceptors in response to acidification using intracellular recordings from cultured rat primary afferent neurons. Extracellular acidification induced depolarization of two types, transient and sustained responses. The former (to pH 6.3 and 5.2) was augmented at lower temperature (26, 16 degrees C) and amiloride blocked the response to pH 6.3 at 26 degrees C. On the other hand, the sustained depolarization, which often followed the transient one, in response to pH 6.3 was greater at 36 degrees C and significantly blocked by capsazepine at 36 degrees C, but not at 26 degrees C. The sustained response to pH 5.2 was blocked even at 26 degrees C. These results suggest that the low pH evoked depolarization is temperature-dependent, and the contribution of transient receptor potential V1 (vanilloid receptor 1) to proton-induced response is greater in the physiological body temperature range, while that of the acid-sensing-ion-channel family is greater at room temperature or lower.

Reexamination of the difference in susceptibility to adjuvant-induced arthritis among LEW/Crj, Slc/Wistar/ST and Slc/SD rats.

The present investigations were performed to assess the differences among rat colonies commonly used for neurophysiological research regarding the development of complete Freund's adjuvant (CFA)-induced arthritis. Inflammatory signs including edema in the paw fluctuated remarkably among individual Wistar (Slc/Wistar/ST) and Sprague-Dawley (Slc/SD) rats, while the inflammatory signs of Lewis (LEW/Crj) rats appeared earlier and was severer and more consistent than Slc/Wistar/ST and Slc/SD rats. Edema in the hind paw developed in 100% of LEW/Crj rats with the lowest dose of CFA (0.6 mg/rat) used as compared with 64% of Slc/Wistar/ST (CFA 1 mg/rat) and 38% of Slc/SD rats (CFA 1.2 mg/rat). Retardation of weight gain was observed in Slc/Wistar/ST and Slc/SD rats in contrast to a severe weight decrease in inflamed LEW/Crj rats after the development of arthritis.

Improving charge/discharge properties of radical polymer electrodes influenced strongly by current collector/carbon fiber interface.

Charge/discharge processes of organic radical batteries based on the radical polymer's redox reaction are largely influenced by carbon fibers consisting in the composite electrodes to help electron transfer. To find the optimal structure of the composite electrodes, the dominant electron transfer processes were determined by ac impedance measurement of the composite electrodes. A strong correlation between the overall electron transfer resistance of the composite electrodes and the materials of the current collector suggests that the electric conduction to the current collector through the contact resistance should be crucial. It was also confirmed that the charge/discharge performance of the composite electrode was related to the overall electron transfer resistance of the composite electrode. These results indicated that the charge/discharge performance of the radical battery was dominated by the interfacial electron transfer processes at the current collector/carbon fiber interface and that the rate performance would be much improved by suitably designing the interfacial structure.