Takashi Kihara

Pup odor and ultrasonic vocalizations synergistically stimulate maternal attention in mice

Pup ultrasonic vocalizations (USVs), which are emitted by hypothermic pups, and pup odor are thought to be triggers of maternal behavior in mice. We investigated whether pup odor stimulated maternal responses to pup USVs in mother C57BL/6 mice. Two-choice tests were conducted by introducing mothers into a test cage in which a tube was attached on each long wall, and the duration spent in each tube was compared. Pup USVs were reproduced by an ultrasonic speaker at the tube end. In some cases, cotton with pup odor was also presented at the end of the tube. Compared to no stimuli, mothers did not specifically approach the sole presentation of either reproduced pup USVs or pup odor. However, compared to the sole presentation of pup odor, the simultaneous presentation of pup USVs and odor induced a specific approach response. These results suggested that pup USVs and odor synergistically stimulated maternal behavior. In addition, it was confirmed that mothers approached hypothermic pups emitting pup USVs for longer than anesthetized silent pups. To investigate the underlying neural mechanisms, we observed neural responses to various stimuli with the immunohistochemistry of c-fos expression. In the bed nucleus of the stria terminalis, the medial preoptic area, the central nucleus of the amygdala, and the basolateral amygdala, the numbers of c-fos-positive cells were significantly increased following the simultaneous presentation of pup USVs and odor compared to the presentation of each alone, suggesting that these nuclei were involved in multimodal processing related to maternal behavior.

The Effects of Social Experience and Gonadal Hormones on Retrieving Behavior of Mice and their Responses to Pup Ultrasonic Vocalizations

Pup ultrasonic vocalizations (USVs) are emitted from maternally separated pups and are thought to be a trigger for eliciting maternal behavior in mice. We investigated the effects of social experience and gonadectomy on the retrieving behavior of mice and their responses to pup USVs produced by a nanocrystalline silicon thermo-acoustic emitter. In each experiment, virgin, gonadectomized, sham-operated, sexually experienced, and parenting mice of both sexes were used, and the effects of these manipulations were compared in each sex. The retrieving behavior of both sexes increased with social experience or gonadectomy. In particular, mothers showed the highest retrieving activity among female groups, while castrated male mice showed the highest retrieving activity among male groups. All groups of female mice responded to pup USVs, with the responsiveness of sexually experienced female mice being the most enhanced. Unlike the females, virgin male mice did not respond to pup USVs, although socially experienced or castrated males showed this response; fathers exhibited the highest responsiveness. These results suggest that not only parenting experience, but also mating experience, may enhance retrieving activity and response to pup USVs in mice of both sexes. Nevertheless, the degree to which parenting experience contributed to the enhancement of both activities differed between the sexes. Furthermore, gonadectomy enhanced both activities in both sexes, although its effect was more prominent in males. Overall, our findings suggest that alteration in responsiveness of mice to pup USVs might be one of the changes in parental behavior caused by social experiences or gonadal hormones.

Reproduction of mouse-pup ultrasonic vocalizations by nanocrystalline silicon thermoacoustic emitter

As one of the functional properties of ultrasound generator based on efficient thermal transfer at the nanocrystalline silicon (nc-Si) layer surface, its potential as an ultrasonic simulator of vocalization signals is demonstrated by using the acoustic data of mouse-pup calls. The device composed of a surface-heating thin-film electrode, an nc-Si layer, and a single-crystalline silicon (c-Si) wafer, exhibits an almost completely flat frequency response over a wide range without any mechanical surface vibration systems. It is shown that the fabricated emitter can reproduce digitally recorded ultrasonic mouse-pups vocalizations very accurately in terms of the call duration, frequency dispersion, and sound pressure level. The thermoacoustic nc-Si device provides a powerful physical means for the understanding of ultrasonic communication mechanisms in various living animals.

Precise Thermal Characterization of Confined Nanocrystalline Silicon by a 3ω Method

Due to a strong quantum confinement effect, the thermal conductivity and heat capacity per unit volume of a nanocrystalline silicon (nc-Si) layer prepared by electrochemical anodization are extremely lowered in comparison to those of single crystal silicon (c-Si). Based on this high contrast between the thermal properties of nc-Si and c-Si, we have developed novel thermally induced ultrasound emitter devices. The thermal insulating properties of the nc-Si layer play a key role in this case. This paper concerns precise measurements of the thermal conductivity and heat capacity per unit volume of the nc-Si layer using a dynamic approach called the 3ω method. The measured thermal conductivity is 1.08±0.2 W/(mK) in good agreement with that reported previously as measured by conventional techniques. The obtained heat capacity per unit volume of the nc-Si layer is, on the other hand, considerably smaller than that estimated from the porosity of the sample. These results provide useful information for designing an efficient ultrasound emitter.

Ultrasound Emisson Characteristics of a Thermally Induced Sound Emitter Employing a Nanocrystalline Silicon Layer

Due to a strong quantum confinement effect, the thermal conductivity and heat capacity per unit volume of a nanocrystalline silicon (nc-Si) layer prepared by electrochemical anodization are extremely low when compared to those of single crystal silicon (c-Si). These large differences in the thermal properties between nc-Si and c-Si make it possible to produce an efficient ultrasound emitter device based on thermo-acoustic conversion without any mechanical vibration. In this paper, the fundamental ultrasound characteristics of a fabricated thermally induced nc-Si ultrasound emitter are explained with regard to an application as an ultrasound speaker. Ultrasound generated at the same frequency as the input signal exhibits a flat frequency response over a wide range and is non-directional. This behavior is totally different from that of conventional airborne ultrasound devices such as piezoceramic transducers.

Study on generation mechanisms of second-order nonlinear signals in surface acoustic wave devices and their suppression

In this study, we examine the generation mechanisms of the second-order nonlinear signals in surface acoustic wave resonators/duplexers fabricated on a 42°YX-LiTaO3 substrate. It is shown that the crystal asymmetry of the substrate can generate the second-order nonlinear signals. The following two mechanisms mainly contribute to their generation: (a) self-mixing of the electrostatic field and (b) mixing of the electrostatic field with the strain field associated with laterally propagating modes. Both of them occur at the gaps between the electrode tip and the dummy electrode. In addition, an interdigital transducer design that cancels this asymmetry is proposed. The design is applied to a one-port resonator and a duplexer, and the effectiveness of this technique is demonstrated.

Effective suppression method for 2 nd nonlinear signals of SAW devices

Linearity performances are getting one of the most important characteristics of surface acoustic wave (SAW) duplexers because nonlinear signals generated in RF front-end of cellar phone handsets deteriorate the receiver sensitivities significantly. In this paper, the generation mechanisms of the 2nd order nonlinear signals of SAW resonators/duplexers on a 42°Y-X LiTaO3 substrate and an effective suppression method for them are discussed. The crystalline asymmetry properties of substrates are focused on as the one possibility of the occurrence factor of the 2nd order nonlinear signals. Additionally, based on this hypothesis, an interdigital transducer (IDT) design which realizes the cancellation of the crystalline asymmetry effect is proposed to improve the linearity. As the result, the 2nd order harmonics level of the one-port SAWresonators and the 2nd order intermodulation distortion (IMD2) levels of the SAW duplexers have been improved up to about 25dBm and 20dBm, respectively.