Masaki Kato

Molecular characterization of the song control nucleus HVC in Bengalese finch brain.

Songbirds have a specialized neural substrate for learned vocalization, called the song circuit, which consists of several song nuclei in the brain. The song control nucleus HVC (a letter-based name) is the intersection point of the song learning and vocal motor pathways. Knowledge of the types of genes expressed in the HVC is essential in understanding the molecular aspects of the HVC. Gene expression in the HVC under silent conditions shows the competence necessary for singing. To investigate this, we compared the HVC with its adjacent tissues in searching for the molecular specificities of the song nucleus HVC using an in-house cDNA microarray of the Bengalese finch (Lonchura striata var. domestica). Our microarray analysis revealed that 70 genes were differentially expressed in the HVC compared with the adjacent tissue. We investigated 27 of the microarray-selected genes that were enriched or repressed in the HVC by in situ hybridization. We found that multiple calcium-binding proteins (e.g., CAPS2, parvalbumin and ATH) were enriched in the HVC. Meanwhile, the adult HVC showed low expression levels of plasticity-related genes (e.g., CAMK2A and MAP2K1) compared with the juvenile HVC. The HVC plays an important role during song learning, but our results suggest that the plasticity of this nucleus may be suppressed during adulthood. Our findings provide new information about the molecular features that characterize the HVC.

Human speech- and reading-related genes display partially overlapping expression patterns in the marmoset brain.

Language is a characteristic feature of human communication. Several familial language impairments have been identified, and candidate genes for language impairments already isolated. Studies comparing expression patterns of these genes in human brain are necessary to further understanding of these genes. However, it is difficult to examine gene expression in human brain. In this study, we used a non-human primate (common marmoset; Callithrix jacchus) as a biological model of the human brain to investigate expression patterns of human speech- and reading-related genes. Expression patterns of speech disorder- (FoxP2, FoxP1, CNTNAP2, and CMIP) and dyslexia- (ROBO1, DCDC2, and KIAA0319) related genes were analyzed. We found the genes displayed overlapping expression patterns in the ocular, auditory, and motor systems. Our results enhance understanding of the molecular mechanisms underlying language impairments.

A multiplex PCR assay for molecular sexing of the naked mole‐rat (Heterocephalus glaber)

For molecular sexing of the naked mole‐rat (Heterocephalus glaber), we designed a PCR primer set to amplify part of the Y‐linked DBY gene. When this primer set was applied to the samples of known sex with the 16S rRNA gene (16S rDNA) primers as control, PCR products were successfully obtained as two DNA bands in males, a male‐specific 163 bp DBY band and a 446 bp band of 16S rDNA shared with females, whereas females showed only the common band. This result shows that this multiplex PCR assay is useful for sex identification of H. glaber.

Song memory in female birds: neuronal activation suggests phonological coding.

Male Bengalese finches sing complex song sequences during courtship. To examine the female perception of sequence complexity, we tested female auditory processing with respect to sequential differences in the caudomedial nidopallium and caudomedial mesopallium. Repeated song presentations caused lower expression of the immediate early gene ZENK; however, consecutive presentation of a new song reinduced full ZENK expression. We presented a sequence-shuffled version of the fathers song after repeated presentation of the original (unmodified) fathers song. The shuffled songs caused lower ZENK expression in both the caudomedial nidopallium and caudomedial mesopallium. Although phonological differences caused full ZENK expression, sequential differences in song elements did not induce ZENK expression. Thus, it appears that female song perception is based on phonological, rather than sequential, information.

Sequential information of self-produced song is represented in the auditory areas in male Bengalese finches

Male Bengalese finches have a complex song-sequence pattern containing multiple elements. Learning and producing songs require memorization of the phonology and the sequence of elements. We tested the auditory memory of male finches for their own songs to determine whether the auditory memory included the sequence of elements. An immediate early gene ZENK is induced by auditory processing in the secondary auditory area of the caudomedial nidopallium (NCM) and the caudomedial mesopallium (CMM) in response to song presentations. Repeated presentations of the same song result in a decrease in ZENK expression in these areas, reflecting habituation to auditory processing. We examined sequential differences in auditory processing using the habituation–dishabituation method. After repeatedly presenting the male finches’ own song stimulus, we changed the stimulus to a shuffled sequence of songs. If the shuffled songs induced ZENK expression, it indicated that the auditory areas had been dishabituated by the sequential differences. The shuffled songs caused intermediate ZENK expression in the NCM when compared with the expression by a conspecific new song and that by the same song. The tendency toward intermediate expression was similar in the CMM; however, a significant difference was observed between the conspecific song and shuffled songs. These results suggest that the sequential difference caused a partial dishabituation in the NCM. Thus, the auditory areas processed not only the phonology but also the sequence of songs.

Auditory processing of the element orders in self-produced songs by male Bengalese finches

tion in the brain, in vivo whole-cell recordings were made at the hindbrain Mauthner (M) cells, a pair of giant reticulospinal neurons, which receive statoacoustic inputs directly and initiate fast escape. In intact fish, postsynaptic potentials are obtained in the M-cell in response to the sound. The M-cell responses were still obtained after removing utricular, but not saccular, otolith. Correspondingly, fast escapes initiated by the M-cell in response to sound/vibratory stimuli were depressed after removing saccular otolith, whereas the body balance still remained. After removing utricular otoliths, in contrast, larvae showed fast escapes despite balance defects. These results suggest that acoustic signals are primarily received by saccule, whereas maintaining balance profoundly depends on utricle. In addition, it should be noted that the functional differentiation of otolith organs is already achieved at 5 dpf.