Ikuo Taniguchi

Optical imaging of spatiotemporal patterns of glutamatergic excitation and GABAergic inhibition in the guinea-pig auditory cortex in vivo.

1. Glutamatergic excitation and gamma‐aminobutyric acid (GABA)‐ergic inhibition in layers II and III of the auditory cortex of anaesthetized guinea‐pigs were recorded optically using a voltage‐sensitive dye RH795 and a 12 x 12 photodiode array. 2. After contralateral ear stimulation with pure tones, transient excitatory responses followed by inhibitory responses were observed in fields A (primary) and DC of the auditory cortex. The area of the excitatory responses was sandwiched or surrounded by the areas of the inhibitory responses. 3. Optically recorded excitatory responses to pure tones had two components: a component sensitive to 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX), a non‐N‐methyl‐D‐aspartate (non‐NMDA) receptor antagonist, and a component sensitive to 2‐amino‐5‐phosphono‐valerate (APV), an NMDA receptor antagonist. Application of CNQX (5 microM) to the auditory cortex suppressed an early, but not a late, phase of the excitation; application of APV (100 microM) had the opposite effect. Concomitant application of CNQX and bicuculline methiodide (BMI, 4 microM), a GABAA receptor antagonist, increased the amplitude of the late phase 4‐fold. This enhanced response was suppressed by APV. 4. These results indicate that (i) auditory cortical excitatory responses are mediated by both non‐NMDA and NMDA receptors, (ii) inhibition is mediated by GABAA receptors, (ii) the excitatory bands are sandwiched or surrounded by GABAA receptor‐mediated inhibitory areas and (iv) GABAA receptors effectively inhibit the NMDA, but not the non‐NMDA, receptor‐mediated excitation.

Optical imaging of neural activity in multiple auditory cortical fields of guinea pigs

Neural activity of multiple fields in the auditory cortex of anesthetized guinea pigs in response to pure tones was visualized by optical recording using a voltage-sensitive dye (RH795). Ten auditory fields were identified based on the tonotopic organization and response latency: the core fields consisting of the primary (AI) and secondary (AII) fields and surrounding belt areas consisting of dorso-anterior (DA), dorsal (D), dorso-posterior (DP), posterior (P), ventro-poster- ior (VP), ventro-medial (VM), ventro-anterior (VA) and ventral (V) fields. Tonotopic organization was observed in all the fields apart from DA, D, DP and V. Spatio-temporal displays suggest that the auditory information spreads from the core fields of AI and AII to belt fields via three distinct (dorsocaudal, caudal and ventrorostral) pathways.

The columnar and layer-specific response properties of neurons in the primary auditory cortex of Mongolian gerbils

The columnar and layer-specific response properties of neurons in the primary auditory cortex (AI) of Mongolian gerbils were studied using single-unit recordings of responses to tone-burst stimuli presented to the ear contralateral to the recording side. During near-radial microelectrode penetrations of the AI in 100-microm steps, the best frequency (BF), best threshold (BT), best amplitude (BA), latency, tuning curve and Q10dB were recorded. Neurons encountered during single penetrations showed similar BFs, indicating a columnar frequency organization, but their latencies and Q10dBs differed. The BAs and BTs recorded within single penetrations often showed a similar value in the middle cortical layers. The latencies and Q10dBs of these neurons exhibited a tendency toward a layer-specific distribution. The latencies of neurons located in layers I-V were longer than those located in layer VI. The Q10dBs of neurons located in layers III and IV were higher than those located in layers I and VI. These results are almost consistent with those of previous studies on frequency representation, and indicated the existence of an integrative mechanism of frequency processing in the AI. This is the first study in which a layer-specific, partially columnar organization for stimulus amplitude is described.

Spatio-temporal pattern of frequency representation in the auditory cortex of guinea pigs

The spatio-temporal pattern of sound-evoked neural activity in the guinea pig auditory cortex was studied by optical recording with the aid of voltage-sensitive dye. Changes in light intensity induced by sounds at various frequencies and pressure levels were recorded with a 12 x 12 array of photodiodes. The amplitudes of the responses were displayed as sequential two-dimensional images. Tonotopical organization was found in two subdivisions of the auditory cortex, the anterior field (field A) and the dorsocaudal field (field DC). The frequency gradients in fields A and DC had a mirror-image relationship. This agrees with results obtained by the microelectrode technique. However, the tonotopic response observed in our study was transient. The focal activity that began in field A propagated in two directions; dorsally along the iso-frequency bands in field A, and caudally toward field DC. This suggests that the sound information processing initiates at field A, and its outputs are transferred to field DC, which is probably a hierarchically higher center.

Correlation between the size of song control nuclei and plumage color change in orange bishop birds

Adult male orange bishop birds (Euplectes franciscanus) develop beautiful nuptial plumage during the breeding season, but have the same sober plumage as the female during the non-breeding season. The male conspecific song is highly stereotyped during nuptial plumage. Large volume differences were found in two song control nuclei in the cerebrum between the male and female during the breeding season, and in the same nuclei of the males during the breeding and non-breeding seasons. The seasonal changes in the size of cerebral song control nuclei were dominant in the male and may not correlate with the improvement or modification of the song repertories.

Optical imaging of dynamic horizontal spread of excitation in rat auditory cortex slices.

Optical recordings using a voltage-sensitive dye (RH482) were conducted in brain slice preparations to investigate spatiotemporal patterns of excitation in the rat auditory cortex. Electrical stimulation of the border between the white matter and layer VI evoked vertical as well as horizontal spreading responses. While velocities of vertical and horizontal propagation of excitation were similar to those reported in non-disinhibited preparations, the horizontal propagation was widespread and strong especially in layers II/III in auditory cortex slices. This horizontal spread was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) but not by D-2-amino-5-phosphonopentanoic acid (D-AP5). These results suggest that the horizontal responses, especially in layers II/III, are prominent and are mediated primarily by non-N-methyl-D-aspartic acid (NMDA) receptors in the auditory cortex.

Echolocation sounds and hearing of the greater Japanese horseshoe bat (Rhinolophus ferrumequinum nippon)

SummaryThe relationship between the orientation sounds and hearing sensitivity in the greater Japanese horseshoe bat,Rhinolophus ferrumequinum nippon was studied.An orientation pulse consisted of a constant frequency (CF) component followed by a short downward frequency-modulated (FM) component. Sometimes, an initial upward FM component preceded the CF component. Duration of pulses was about 30 ms and the CF of resting pulses (RF) averaged 65.5 kHz. The best frequency (BF) at the lowest threshold in audiograms as measured by the pinna reflex averaged 66.1 kHz. Audiograms showed remarkable sharp cut-offs on both sides near the BF. The frequency difference between the BF and the RF was about 0.6 kHz, and the RF was always below the BF. The values of RF and BF were characteristically different from those of the European subspecies,Rhinolophus ferrumequinum ferrumequinum.

Biomechanical Characteristics of Brain Edema: the Difference Between Vasogenic-Type and Cytotoxic-Type Edema

Some of the basic biomechanical properties of edematous brain tissue have yet to be clarified. Therefore we measured regional tissue compliance and swelling isotropy/anisotropy in cat brain during development of vasogenic-type and cytotoxic-type edema. In vasogenic-type edema induced by cryogenic injury, the edematous white matter showed an increase of regional tissue compliance (indentation method), which paralleled the increase in the regional tissue water content (gravimetry). Swelling of the white matter due to edema was anisotropic, in which expansion transverse to the neuronal fibers caused by their dissociation was 91.1%, whereas longitudinal expansion was 2.3%. In cytotoxic-type edema induced by cerebral ischemia for 3 h, regional tissue compliance was decreased in the area suffering energy failure, which was visualized as an area of reduced succinic dehydrogenase activity. The ischemic gray matter showed isotropic swelling, and morphologically, prominent swelling of neuroglial cells. These marked differences in basic biomechanical properties between vasogenic-type and cytotoxic-type edema should be taken into account when analyzing the mechanism of edema-mediated tissue injury.

Spatio-temporal representation of sound intensity in the guinea pig auditory cortex observed by optical recording

The spatio-temporal representation of sound intensity in the guinea pig auditory cortex was studied by optical recording with the aid of a voltage-sensitive dye. Changes in light intensity due to neural activity induced by sounds at various pressure levels were recorded with a 12 x 12 array of photodiodes. The amplitudes of the responses were displayed as sequential two-dimensional images. The iso-intensity bands revealed by neural activity were orthogonal to the isofrequency bands of tonotopical organization in the anterior field and dorsocaudal field. The frequency-intensity representation through the orthogonal organization varied with time. This mechanism may be adapted to the auditory cortex to sequentially process the three parameters of sound: frequency, intensity, and time. Furthermore, a new field was found in the ventrocaudal region of the auditory cortex. This field showed tonotopicity, but high thresholds.

Optical recording of responses to frequency-modulated sounds in the auditory cortex

USING an optical recording method with a voltage-sensitive dye, we recorded activities in the primary auditory cortex (AI) of anesthetized guinea pigs in response to frequency-modulated (FM) sounds and sounds with stepwise changes in frequency (SF). Responses to the FM sound showed a spatiotemporal pattern in which a localized active spot traversed the isofrequency bands in the AI, and they differed from the band-like responses to the SF sound. These results indicate that time-varying sounds are represented as spatiotemporal activation of tonotopic organization in the AI by spectral cues with interactions between frequency bands.