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A Hanazawa

Publications and source records attributed to A Hanazawa.

5 recordsLinked to original sources
PubMed2001

Electroretinogram analysis of relative spectral sensitivity in genetically identified dichromatic macaques.

The retinas of macaque monkeys usually contain three types of photopigment, providing them with trichromatic color vision homologous to that of humans. However, we recently used molecular genetic analysis to identify several macaques with a dichromatic genotype. The affected X chromosome of these animals contains a hybrid gene of long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) photopigments instead of separate genes encoding L and M photopigments. The product of the hybrid gene exhibits a spectral sensitivity close to that of M photopigment; consequently, male monkeys carrying the hybrid gene are genetic protanopes, effectively lacking L photopigment. In the present study, we assessed retinal expression of L photopigment in monkeys carrying the hybrid gene. The relative sensitivities to middle-wavelength (green) and long-wavelength (red) light were measured by electroretinogram flicker photometry. We found the sensitivity to red light to be extremely low in protanopic male monkeys compared with monkeys with the normal genotype. In female heterozygotes, sensitivity to red light was intermediate between the genetic protanopes and normal monkeys. Decreased sensitivity to long wavelengths was thus consistent with genetic loss of L photopigment.

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PubMed2001

Influence of the direction of elemental luminance gradients on the responses of V4 cells to textured surfaces.

The texture of an object provides important cues for its recognition; however, little is known about the neural representation of texture. To investigate the representation of texture in the visual cortex, we recorded single-cell activities in area V4 of macaque monkeys. To distinguish the sensitivity of the cells to texture parameters such as density and element size from that to spatial frequency, we used texture stimuli mimicking shaded granular surfaces. We varied the size and density of the texture elements and the direction of elemental luminance gradients (apparent shadings) as stimulus parameters. Most macaque V4 cells (151 of 170; 89%) exhibited sensitivity to the texture parameters. Interestingly, 21 of these cells were tuned to single shading directions (unidirectional tuning). This unidirectional tuning cannot be explained by complex-cell-like tuning for spectral power of spatial frequency, because texture stimuli with a shading direction and its opposite have almost the same spectral power. Unidirectional tunings of these cells were invariant for the position of the texture elements. Thus, this tuning cannot be explained by simple-cell-like phase-dependent spatial frequency tuning or selectivity to a particular arrangement of the elements. Moreover, the unidirectional tuning had a bias toward vertical directions, consistent with an anisotropy in the perception of three-dimensional shape from shading. This novel spatial property suggests that V4 cells are involved in extracting texture features from objects, including their three-dimensionality.

Action Potentials↗
PubMed2000

Neural selectivity for hue and saturation of colour in the primary visual cortex of the monkey.

In the inferior temporal (IT) cortex of monkeys, which has been shown to play a critical role in colour discrimination, there are neurons sensitive to a narrow range of hues and saturation. By contrast, neurons in the retina and the parvocellular layer of the lateral geniculate nucleus (pLGN) encode colours in a way that does not provide explicit representation of hue or saturation, and the process by which hue- and saturation-selectivity is elaborated remains unknown. We therefore tested the colour-selectivity of neurons in the primary visual cortex (V1) and compared it with those of pLGN and IT neurons. Quantitative analysis was performed using a standard set of colours, systematically distributed within the CIE (Commission Internationale de l'Eclairage)-xy chromaticity diagram. Selectivity for hue and saturation was characterized by analysing response contours reflecting the overall distribution of responses across the chromaticity diagram. We found that the response contours of almost all pLGN neurons were linear and broadly tuned for hue. Many V1 neurons behaved similarly; nonetheless, a considerable number of V1 neurons had clearly curved response contours and were selective for a narrow range of hues or saturation. The relative frequencies of neurons exhibiting various selectivities for hue and saturation were remarkably similar in the V1 and IT cortex, but were clearly different in the pLGN. Thus, V1 apparently plays a very important role in the conversion of colour signals necessary for generating the elaborate colour selectivity observed in the IT cortex.

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PubMed1992

Enhancement of glutaminase-like immunoreactivity in rat brain by an irreversible inhibitor of the enzyme.

Changes of glutaminase immunoreactivity in rat brain were examined after intracranial injection of 6-diazo-5-oxo-L-norleucine (DON), an irreversible inhibitor of glutaminase. When 1 M DON was injected into the lateral ventricle, a half-lethal dose was 7.5-10 mumol. After intraventricular injection of 2-7.5 mumol DON, glutaminase immunoreactivity was dose dependently enhanced with the maximum enhancement 3-5 days after the injection. The enhanced glutaminase immunoreactivity was recognized by enlarged granular immunodeposits in both perikarya and neuropil in many regions, such as the hippocampus, thalamus, hypothalamus, periaqueductal gray, and some brain stem, cerebellar, and spinal cord regions. Intrathalamic injection of 0.2 mumol DON enhanced glutaminase immunoreactivity in many neuronal perikarya in the thalamus and in some perikarya in layer VI of the cerebral cortex. Intrastriatal injection of the same dose of DON enhanced glutaminase immunoreactivity in neuropil of the caudoputamen and in many neuronal perikarya of the intralaminar thalamic nuclei. These results suggested that DON induced a new massive synthesis of glutaminase in the affected neurons.

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