Kazuo Itoh

Brain-Derived Neurotrophic Factor Participates in Determination of Neuronal Laminar Fate in the Developing Mouse Cerebral Cortex

Lamina formation in the developing cerebral cortex requires precisely regulated generation and migration of the cortical progenitor cells. To test the possible involvement of brain-derived neurotrophic factor (BDNF) in the formation of the cortical lamina, we investigated the effects of BDNF protein and anti-BDNF antibody separately administered into the telencephalic ventricular space of 13.5-d-old mouse embryos. BDNF altered the position, gene-expression properties, and projections of neurons otherwise destined for layer IV to those of neurons for the deeper layers, V and VI, of the cerebral cortex, whereas anti-BDNF antibody changed some of those of neurons of upper layers II/III. Additional analysis revealed that BDNF altered the laminar fate of neurons only if their parent progenitor cells were exposed to it at approximately S-phase and that it hastened the timing of the withdrawal of their daughter neurons from the ventricular proliferating pool by accelerating the completion of S-phase, downregulation of the Pax6 (paired box gene 6) expression, an essential transcription factor for generation of the upper layer neurons, and interkinetic nuclear migration of cortical progenitors in the ventricular zone. These observations suggest that BDNF participates in the processes forming the neuronal laminas in the developing cerebral cortex. BDNF can therefore be counted as one of the key extrinsic factors that regulate the laminar fate of cortical neurons.

Cytoarchitectonic and connectional organization of the ventral lateral geniculate nucleus in the cat

The ventral lateral geniculate nucleus is a small extrageniculate visual structure that has a complex cytoarchitecture and diverse connections. In addition to small‐celled medial and lateral divisions, we cytoarchitectonically defined a small‐celled dorsal division. A large‐celled intermediate division intercalated between the three small‐celled divisions, which we divided into medial and lateral intermediate subdivisions. In WGA‐HRP injection experiments, the different cytoarchitectonic divisions were shown to have connections with different nuclei. The medial division was reciprocally connected to the pretectum and projected to the superficial layers of the superior colliculus and the intralaminar nuclei. The medial intermediate division received projections from the intermediate layer of the superior colliculus and the lateral and interpositus posterior cerebellar nuclei, and projected to the intermediate layer of the superior colliculus, the periaqueductal gray of midbrain, and the intralaminar nuclei. The lateral intermediate divisions received projections from the pretectum, the intermediate layer of the superior colliculus, and the lateral and interpositus posterior cerebellar nuclei, and projected to the pretectum, superficial layers of the superior colliculus, and the pulvinar. The lateral division received projections from superficial layers of the superior colliculus and had reciprocal connections with the pretectum. The dorsal division received projections from the pretectum and had reciprocal connections with the periaqueductal gray of midbrain. The different cytoarchitectonic divisions of the ventral lateral geniculate nucleus are thus suggested to play different functional roles related to vision, eye and head movements, attention, and defensive reactions. J. Comp. Neurol. 473:439–462, 2004.

Immunohistochemical localization of tyrosine hydroxylase, substance P, neuropeptide-Y and leucine-enkephalin in developing human retinal amacrine cells

Prenatal changes in the neurotransmitter/neuromodulator profiles of tyrosine hydroxylase (for dopamine), substance P, neuropeptide Y, and leucine-enkephalin were studied in developing human retinal amacrine cells by the use of immunohistochemical techniques. Tyrosine hydroxylase was localized between 10 and 12 weeks of gestation, substance P and neuropeptide Y appeared little later around 14 weeks, and leucine-enkephalin-like immunoreactivity was observed at 16 weeks.

Projections from the cytochrome oxidase modules of visual area V2 to the ventral posterior area in the macaque

The ventral part of the third visual cortical complex, the ventral posterior area (VP) or V3v, is located between the ventral half of visual areas V2 and V4. Because of its location and the physiological properties of its neurons, VP has been considered to be involved in the ventral stream visual areas. The ventral stream visual areas such as V4 and TEO receive projections from the cytochrome oxidase (CO)-rich thin stripes and CO-poor interstripe regions of V2; however, which CO-modules project to VP remains unclear. Moreover, it is not clear whether V1 projects to VP. We injected retrograde tracers into VP and found that VP receives projections from V2 neurons not only in the CO-rich thin stripes and CO-poor interstripe regions but also in the CO-rich thick stripes. We also confirmed the virtual absence of inputs from V1 to VP. These results support the hypothesis that VP constitutes a distinct extrastriate visual area and also suggest that, in addition to color and shape information, VP may also process visual information related to space and disparity.

The locus coeruleus projects to the mesencephalic trigeminal nucleus in rats.

The ganglion-cells in the mesencephalic trigeminal nucleus (Me5) process proprioceptive signals from the masticatory muscles and the periodontal ligaments, and are considered to regulate the rhythm of biting and bite strength. The locus coeruleus (LC) is the major source of noradrenergic projections in the brain and plays an important role in stressful situations and aggressive behavior. The two nuclei are adjacently located to each other in the lateral part of the periaqueductal gray matter of the fourth ventricle. In the present study, a small number of neurons were labeled in the LC with a neuronal tracer biotinylated dextran amine. The labeled single axons were traced from the labeled LC neuronal somata to the ipsilateral Me5 region where they produced terminal-like swellings. Some of the swellings appeared to make contact with the ganglion-cells of the Me5. These results suggest that the LC regulates the bite strength by modifying the ganglion-cell activity in the Me5. Additionally, these findings shed light on the enigma of why the main part of the Me5 at the level of pons is located at the lateral end of the gray matter ventral to the fourth ventricle, instead of at the trigeminal ganglion.

Direct projections from the central amygdaloid nucleus to the mesencephalic trigeminal nucleus in rats

The amygdala is activated by fear and plays an important role in the emotional response to life-threatening situations. When rats feel threatened, they respond by biting fiercely. Bite strength is regulated by the trigeminal motor nucleus and the mesencephalic trigeminal nucleus (Me5). The Me5 relays proprioceptive signals from the masticatory muscles and the periodontal ligaments to the trigeminal motor and premotor nuclei. The amygdala projects to the trigeminal motor nucleus and the premotor reticular formation. However, it is unknown whether the amygdala projects directly to the Me5. In the present study, neurons of the central amygdaloid nucleus (ACe) were labeled following injection of a retrograde tracer, Fast Blue, into the caudal Me5, and fibers and terminal buttons from the ACe to the Me5 were examined after injections of an anterograde neuronal tracer, biotinylated dextran amine into the ACe. Furthermore, wheat germ agglutinin-conjugated to horseradish peroxidase was injected into the ACe, and labeled fibers and terminal buttons in the Me5 were examined by electron microscopy. Labeled terminal buttons on Me5 somata were more abundant in the caudal than the rostral Me5. Electron microscopic observation revealed that a part of these terminal buttons formed axo-somatic synapses. These results indicate that the ACe sends direct projections to the Me5, and suggest that the amygdala regulates bite strength by modifying neuronal activity in the Me5.

NADPH-diaphorase and cytosolic urea cycle enzymes in the rat accessory olfactory bulb

The nitric oxide cycle consists of nitric oxide synthase, argininosuccinate synthetase and argininosuccinate lyase to form nitric oxide. We have examined the colocalization of nitric oxide synthase and the cytosolic urea cycle enzymes (argininosuccinate synthetase, argininosuccinate lyase and arginase) in the accessory olfactory bulb of the rat by using a double labeling procedure combining reduced-nicotinamide-adenine-dinucleotide-phosphate-diaphorase (NADPH-d) reaction with fluorescent immunocytochemistry. Each glomerulus showed a different NADPH-d activity, and those with the strongest NADPH-d activities were assembled in the caudomedial part of the accessory olfactory bulb. Argininosuccinate synthetase-like immunoreactive glomeruli were distributed in the caudomedial part of the accessory olfactory bulb, and most of them were also strongly NADPH-d positive. The mitral or tufted cells were argininosuccinate synthetase-, argininosuccinate lyase- and arginase-like immunoreactive, but were not NADPH-d positive. The granule cells were NADPH-d positive or argininosuccinate lyase-like immunoreactive, but were not argininosuccinate synthetase- or arginase-like immunoreactive. Some granule cells were both NADPH-d positive and argininosuccinate lyase-like immunoreactive. The results indicate the heterogeneity of glomeruli of the accessory olfactory bulb with respect to the distribution of these enzymes. The granule cells have nitric oxide synthase and argininosuccinate lyase, and thus may efficiently produce nitric oxide.

Projections of glutamate decarboxylase positive and negative cerebellar neurons to the pretectum in the cat

The pretectum is one of the primary visual centers, and plays an important role in the visuomotor reflexes. It also receives projections from the cerebellar nuclei that are considered to regulate these reflexes. Gamma aminobutylic acid (GABA) and glutamate are supposed to be two major neurotransmitters of the projection neurons of the cerebellar nuclei. We double labeled the projecting neurons with a tracer, biotinylated dextran amine (BDA), and with an antiserum to glutamate decarboxylase (GAD), the enzyme that synthesizes GABA. The results indicated that about 40% of the pretectal-projecting neurons of the cerebellar nuclei were GAD immunoreactive. The GAD positive pretectal-projecting neurons were significantly smaller than the GAD negative projecting neurons. Our findings thus suggest the existence of two distinct cerebello-pretectal projection systems: one is mediated by GABAergic inhibitory projections, while the other is mediated by non-GABAergic, probably glutamatergic excitatory ones.

Amygdala projection to the primary sensory nucleus

Vesicular neurotransmitter transporters (VNTs) are synaptic vesicle proteins that play an essential role in chemical transmission through vesicular storage of classical neurotransmitters. VNTs include vesicular monoamine transporter, vesicular acetylcholine transporter, vesicular inhibitory amino acid transporter (VIAAT), vesicular glutamate transporter (VGLUT), vesicular nucleotide transporter (VNUT) and vesicular excitatory amino acid transporter (VEAT) (refs. 1,2). Constitutive biochemical approach, which involves highly expression, purification and reconstitution of VNTs into proteoliposomes, is a powerful procedure to study their structure and function. In this symposium, I will update our VNTs study by the constitutive biochemistry and discuss the mode of action of VNTs with special reference to Cltransport. I will argue about the recent paper reported VGLUT as an either Cl-/glutamate co-transporter or Cl-/glutamate antiporter, whose transport mode was proposed to change dependent on the circumstances (3). 1,2, PNAS 105, 5683, 11720 (2008);3,Schenck S et al. Nature Neurosci 12, 156 (2009)