Developmental Origin of Diencephalic Sensory Relay Nuclei in Teleosts

We propose here a novel interpretation of the embryonic origin of cells of diencephalic sensory relay nuclei in teleosts based on our recent studies of gene expression patterns in the medaka (Oryzias latipes) embryonic brain and comparative hodological studies. It has been proposed that the diencephalic sensory relay system in teleosts is unique among vertebrates. Teleost relay nuclei, the preglomerular complex (PG), have been assumed to originate from the basal plate (the posterior tuberculum) of the diencephalon, whereas relay nuclei in mammals are derived from the alar plate (dorsal thalamus) of the diencephalon. Our results using in situ hybridization show, however, that many pax6- or dlx2-positive cells migrate laterally and ventrocaudally from the diencephalic alar plate to the basal plate during development. Massive clusters of the migrated alar cells become localized in the mantle layer lateral to the posterior tubercular neuroepithelium, from which main nuclei of the PG appear to differentiate. We therefore consider most if not all neurons in the PG to be of alar, not basal, origin. Thus, the teleost PG, at least in part, can be regarded as migrated alar nuclei. Developmental and hodological data strongly suggest that the teleost PG is homologous to a part of the mammalian dorsal thalamus. The organization and origin of the diencephalic sensory relay system might have been conserved across vertebrates.

Experience with intradermal injection and intradermal-plus-deep injection in the radioguided sentinel node biopsy of early breast cancer patients

AIMS

Methods of administering (99m)Tc-phytate during sentinel node biopsy of early breast cancer patients were compared to improve the sensitivity of the technique.

METHODS

Two injection methods, intradermal vs. intradermal-plus-deep injection, were compared in 648 early breast cancer patients. Intradermal injection was done in 323 consecutive patients (325 breasts), and intradermal-plus-deep injection was done in 325 consecutive patients (329 breasts). The following items were compared: (1) The number of axillary nodes detected scintigraphically and removed surgically, and the breast number of micrometastasis to axillary nodes; (2) The number of internal mammary nodes detected scintigraphically and removed surgically; and (3) The sensitivity of axillary SNB.

RESULTS

The number of axillary nodes scintigraphically detected was 1.63+/-0.80 (mean+/-SD) in patients given intradermal injection, and was 1.82+/-0.94 in patients given intradermal-plus-deep injection. The number of axillary nodes surgically removed was 1.78+/-0.93 in patients given intradermal injection, and was 1.95+/-0.99 in patients given intradermal-plus-deep injection. The visualization of internal mammary nodes was superior with intradermal-plus-deep injection (5/325 for intradermal, and 51/329 for intradermal-plus-deep). The putative sensitivity was 71/72 (98.6%) for the intradermal-plus-deep method and 56/62 (90.3%) for the intradermal method. The frequency of detection of micrometastasis was 24 in 71 true positive (38.8%) for the intradermal-plus-deep method and 13 in 56 true positive (23.2%) for the intradermal method.

CONCLUSIONS

The SNB procedure with the intradermal-plus-deep injection method detected more axillary and internal mammary nodes, more (not statistically significant) micrometastasis and improved the putative sensitivity more than the SNB procedure with the intradermal injection method.

Formation of a nanogroove-striped NiO surface using atomic steps

A nanogroove-striped pattern was formed on a NiO film surface. The periodic nanopattern was successfully obtained over the entire surface via high-temperature annealing of the epitaxial NiO thin film, which was grown on an atomically stepped sapphire substrate at low temperature. The depth, width and interval of straight nanogrooves were about 3 nm, 35 nm and about 100 nm, respectively. The periodicity of the stripe agrees well with that of the atomic steps of the substrate.

Detection of novel variant TMPRSS2 /ERG fusion transcripts suggests independent genomic alterations may underlie origin of multi-centric prostate cancer

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Background: Most of the early successes in identifying chromosomal translocations in neoplasias came from the study of hematological malignancies and sarcomas, with limited evidence that consistent genomic rearrangements were present in epithelial malignancies. Recently it was reported that ∼75% of prostate cancers carry a genomic rearrangement leading to fusion of the TMPRSS2 locus to either the ERG or ETV1 genes (both ETS transcription factors). In the fusion gene, the androgen-sensitive promoter elements of TMPRSS2 are thought to mediate over-expression of these ETS transcription factors. Over-activity of the ETS family of transcription factors has been suggested to be involved in the transition from pre-neoplasia to carcinoma as they regulate genes involved in processes such as adhesion, motility, invasion and angiogenesis. Methods: Using both RT-PCR and FISH with published primers and BACs respectively we analyzed 15 samples of prostatic carcinoma from radical prostatectomies and sequenced a subset of the TMPRSS2/ERG fusions. Results: We have found ERG-TMPRSS2 fusion transcripts in 6 samples and no ETV1-TMPRSS2 fusions. Of the 6 fusion tumours, 5 were Gleason 7 and 1 was Gleason 9. Tumour stages ranged from T2a-T3b. One sample with multi-centric carcinoma exhibited 2 distinct in-frame rearrangements generating novel TMPRSS2 /ERG fusion transcripts. Variant I TMPRSS2/ERG transcript was 430 bp and it led to fusion of exons 1 and 2 of the TMPRSS2 gene with exons 5 and 6 of the ERG gene. Variant II TMPRSS2/ERG fusion transcript was slightly smaller at 350 bp and it led to fusion of exon 1 of the TMPRSS2 gene to exons 5 and 6 of the ERG gene. These novel transcripts appear to be smaller than the published fusion proteins but preliminary analysis suggests that all known regulatory and functional protein domains are maintained. Conclusions: The demonstration of two new TMPRSS2/ERG variant fusion transcripts in prostate cancer deserves further study to evaluate their functional impact and prognostic and pathological importance. Moreover the presence of two distinct transcripts within a single multi-centric tumor provides genomic evidence that independent clonal neoplasms can arise synchronously in prostate cancer.

No significant financial relationships to disclose.

Radioactivity thresholds for sentinel node biopsy in breast cancer

AIMS

The aim of the present study is to clarify the level of radioactive lymph node should be biopsied after the most radioactive SN is removed.

METHODS

SNB using radionuclide was performed in our hospital for 1179 primary breast cancers between April 2000 and October 2005; most (1177/1179) were performed successfully. Our criterion for harvesting SNs is to remove tissue until no radioactive site is present. The level of radioactivity and the order of removal of each lymph node were compared with pathologic results.

RESULTS

More than 2 (overall average 1.9) radioactive SNs were biopsied in 686 of 1177 breasts. Cancer positive results were recorded for 142 breasts with multiple SNs. In 142 breasts, 64 showed metastasis to the most radioactive node only, 39 showed metastasis other than the most radioactive node only, and 39 showed the most radioactive node and other radioactive nodes. Moreover, if several other criteria were applied, false-positive cases were increased significantly.

CONCLUSIONS

It is necessary to harvest radioactive lymph nodes other than the most radioactive. Moreover, efforts to remove every radioactive lymph node will minimize false-negative results.

The medial branch of the lateral branch of the posterior ramus of the spinal nerve

In the needle insertion of epidural anesthesia with the paramedian approach, the needle can pass through the longissimus muscle in the dorsum of the patients. When the needle touches a nerve in the muscles, the patients may experience pain in the back. Obviously, the needle should avoid the nerve tract. To provide better anesthetic service, analysis of the structure and where the concerned nerves lie in that region is inevitable.

MATERIAL AND METHOD

We studied five cadavers in this study. Two cadavers were fixed with Thiel's method. With these cadavers, we studied the nerve running of the posterior rami of the spinal nerve from the nerve root to the distal portion. Three of them were used for the study of transparent specimen, with which we studied the course and size of the nerve inside the longissimus muscle.

RESULTS

We observed there were three branches at the stem of the posterior rami of the spinal nerves between the body segment T3 and L5, i.e. medial branch, medial branch of the lateral branch and lateral branch of the lateral branch. The medial branch of the lateral branch supplied to the longissimus muscle. With the transparent specimen, we found that there were different nerve layouts between the upper thoracic, lower thoracic, upper lumbar, and lower lumbar segments in the medial branch of the lateral branch in the longissimus muscle. In the lower thoracic and upper lumbar segments, the medial branch of the lateral branch of the upper lumbar segments produced layers nerve network in the longissimus muscle. L1 and L2 nerves were large in size in the muscle.

CONCLUSION

In the upper lumbar segments the medial branch of the lateral branch of the posterior rami of the spinal nerve produced dense network in the longissimus muscle, where the epidural needle has high possibility to touch the nerve. Anesthetists have to consider the existence of the medial branch of the lateral branch of the posterior rami of the spinal nerve when they insert the needle in the paramedical approach to the spinal column.

Three cases of retroesophageal right subclavian artery

We have experienced three cases of retroesophageal right subclavian artery. Two cases were cadavers, and one case was a live human. In the two cadavers of a 68-year-old and a 76-year-old, respectively Japanese and European males, the right subclavian artery originated from the aorta after the aorta branched the right carotid artery, the left carotid artery and the left subclavian artery. The right carotid artery immerged solely from the aorta. Where the right subclavian artery originated from the aorta, the artery took a dorsal direction. It passed between the esophagus and the vertebral column. The esophagus was compressed from the dorsal side by the right subclavian artery. The structural anomaly of the right subclavian artery accompanied the cephalad recurrence of the branch from the right vagal nerve toward the larynx. In the live human case, we obtained CT views. The patient was a 41-year-old Japanese, who complained of dysphagia lusoria. We found that the right subclavian artery was anomalous and originated from the aorta as the last cardinal branch in the thorax.

Projections of the sensory trigeminal nucleus in a percomorph teleost, tilapia (Oreochromis niloticus)

The sensory trigeminal nucleus of teleosts is the rostralmost nucleus among the trigeminal sensory nuclear group in the rhombencephalon. The sensory trigeminal nucleus is known to receive the somatosensory afferents of the ophthalmic, maxillar, and mandibular nerves. However, the central connections of the sensory trigeminal nucleus remain unclear. Efferents of the sensory trigeminal nucleus were examined by means of tract-tracing methods, in a percomorph teleost, tilapia. After tracer injections to the sensory trigeminal nucleus, labeled terminals were seen bilaterally in the ventromedial thalamic nucleus, periventricular pretectal nucleus, medial part of preglomerular nucleus, stratum album centrale of the optic tectum, ventrolateral nucleus of the semicircular torus, lateral valvular nucleus, prethalamic nucleus, tegmentoterminal nucleus, and superior and inferior reticular formation, with preference for the contralateral side. Labeled terminals were also found bilaterally in the oculomotor nucleus, trochlear nucleus, trigeminal motor nucleus, facial motor nucleus, facial lobe, descending trigeminal nucleus, medial funicular nucleus, and contralateral sensory trigeminal nucleus and inferior olive. Labeled terminals in the oculomotor nucleus and trochlear nucleus showed similar densities on both sides of the brain. However, labelings in the trigeminal motor nucleus, facial motor nucleus, facial lobe, descending trigeminal nucleus, and medial funicular nucleus showed a clear ipsilateral dominance. Reciprocal tracer injection experiments to the ventromedial thalamic nucleus, optic tectum, and semicircular torus resulted in labeled cell bodies in the sensory trigeminal nucleus, with a few also in the descending trigeminal nucleus.

The effect of an old surgical scar on sentinel node mapping in patients with breast cancer: a report of five cases

AIMS

To study the significance of lymphatic drainage disruption due to a surgical scar in sentinel node mapping (SNM) in breast cancer patients.

METHODS

We reviewed patients with stage I breast cancer who had undergone SNM and had an old surgical scar in the ipsilateral breast.

RESULTS

Of 534 breast cancer patients who had undergone SNM, five patients had an old scar in the ipsilateral breast. Inter-pectoral nodes, internal nodes, intramammary nodes, and contralateral axillary nodes were identified as sentinel nodes in three cases. In the remaining two cases, no sentinel lymph nodes were identified.

CONCLUSIONS

An old surgical scar in the breast may cause lymphatic drainage disruption, resulting in abnormal radioactive colloid uptake during SNM.

Modification of lipases with poly(ethylene glycol) and poly(oxyethylene) detergents and their catalytic activities in organic solvents

The alpha-chymotrypsin-poly(ethylene glycol) complex, which was prepared by lyophilizing an aqueous solution, was found to have high catalytic activity in organic media even when the molar ratio of polymer/enzyme in its preparation stage is unity. In this study, we obtained freeze-dried complexes of lipases and poly(ethylene glycol) or poly(oxyethylene) detergents including newly synthesized gemini-type detergents, and their transesterification activity in organic solvents was evaluated. The freeze-dried lipase from Pseudomonas cepacia prepared by using each modifier showed enhanced transesterification activity, exhibiting a similar dependence on the concentration of the modifier in the preparation stage to that of the alpha-chymotrypsin-poly(ethylene glycol) complex; in contrasts, the one from Candida rugosa did not do so.

Central Connection of the Optic, Oculomotor, Trochlear and Abducens Nerves in Medaka, Oryzias latipes

Medaka (Oryzias latipes) is one of the few vertebrate experimental animals in which inbred lines have been established. It is also a species that has advanced in genetic studies in a manner comparable to zebrafish. This fish is therefore a good model for studying functional organization of the nervous system, but anatomical analysis of its nervous system has been limited to embryonic stages. In the present study, we investigated anatomy of cranial nerves in adult fish focusing on the visual function, using an inbred strain of medaka. Cranial nerves of medaka were labeled using biocytin, revealing a central distribution of retinofugal terminals, retinopetal neurons, and oculomotor, trochlear and abducens motor neurons. The optic nerve of the adult medaka was of a complete decussation type. Retinofugal terminals were located in 8 brain nuclei, the suprachiasmatic nucleus, nucleus pretectalis superficialis, nucleus dorsolateralis thalami, area pretectalis pars dorsalis (APd), area pretectalis pars ventralis (APv), nucleus of the posterior commissure (NPC), accessory optic nucleus, and the tectum opticum. Retinopetal neurons were identified in 6 brain nuclei, the ganglion of the terminal nerve, preoptic retinopetal nucleus, nucleus dorsolateralis thalami, APd, APv, and NPC. The oculomotor neurons were mostly labeled ipsilaterally and were located dorsomedially, abutting the fasciculus longitudinalis medialis in the mesencephalon. The trochlear nucleus was located contralaterally and dorsolaterally adjacent to the fasciculus longitudinalis medialis in the mesencephalon. The abducens nucleus was located ipsilaterally in a ventrolateral part of the rhombencephalic reticular formation. These results, generally similar to those in other teleosts, provide the basis for future behavioral and genetic studies in medaka.

Somatotopic Organization of the Trigeminal Ganglion Cells in a Cichlid Fish, Oreochromis (Tilapia) niloticus

Somatotopic organization of the trigeminal ganglion is known in some vertebrates. The precise pattern of somatotopy, however, seems to vary in different vertebrate groups. Furthermore, the somatotopic organization remains to be studied in teleosts. From an evolutionary point of view, the morphology and somatotopic organization of the trigeminal ganglion of a percomorph teleost, Tilapia, were investigated by means of the tract-tracing method using biocytin and three-dimensional reconstruction models with a computer. The trigeminal ganglion was one cell aggregate elongated in the dorsoventral direction, which was separate from the facial and anterior lateral line ganglia. Biocytin applications to the trigeminal nerve root labeled ordinary ganglion cells in the trigeminal ganglion and a few displaced trigeminal ganglion cells in the facial ganglion. Biocytin applications to three primary branches (the ophthalmic, maxillary, and mandibular nerves) revealed that trigeminal ganglion cells were somatotopically distributed in the ganglion reflecting the dorsoventral order of the three branches. Ganglion cells of the ophthalmic nerve were distributed in the dorsal part of the trigeminal ganglion, those of the mandibular nerve in the ventral part, and those of the maxillary nerve in the intermediate part. Some of maxillary and mandibular ganglion cells appear to overlap in their boundary region, whereas ophthalmic ganglion cells did not intermingle with ganglion cells of other branches. Labeled-primary fibers terminated in the sensory trigeminal nucleus, descending trigeminal nucleus, medial funicular nucleus, a ventral part of the facial lobe, reticular formation, and trigeminal motor nucleus. Labeled cells were observed in the mesencephalic trigeminal nucleus and the trigeminal motor nucleus. The results suggest that the morphology and somatotopic organization of the trigeminal ganglion of tilapia are similar to those of mammals, except that the axis of the somatotopic organization of the ganglion in mammals is a mediolateral direction reflecting the mediolateral order of the ophthalmic, maxillary, and mandibular nerves.

A quantitative investigation of neuronal cytoplasmic and intranuclear inclusions in the pontine and inferior olivary nuclei in multiple system atrophy

Multiple system atrophy (MSA) is a sporadic neurodegenerative disease characterized by the presence of neuronal and oligodendroglial alpha-synuclein aggregates. To investigate the relationship between the occurrence of neuronal cytoplasmic and intranuclear inclusions (NCIs and NNIs, respectively) and the progression of neuronal degeneration, we performed a quantitative analysis of the pontine and inferior olivary nuclei based on 14 cases of MSA. alpha-Synuclein immunohistochemistry revealed that NCIs and NNIs were present in both brain nuclei in all the cases. The average incidence of NCIs in the pontine and inferior olivary nuclei was 9.1% and 25.8%, respectively, and that of NNIs was 9.2% and 9.0%, respectively. The number of NNIs was strongly correlated with that of neurones in the pontine and inferior olivary nuclei. Although the number of NCIs was not correlated with the neuronal population in both nuclei, the NCI count in patients with moderate MSA was higher than in patients with mild MSA. The NNI count was much higher than the NCI count in the pontine nucleus in four patients, and was the same in the olivary nucleus in three of the four patients. Moreover, the neuronal population in the NNI-predominant cases was significantly higher than in the NCI-predominant cases. These findings suggest that NCI formation is accelerated by the progression of the disease process, and that in MSA, NNI formation is an earlier phenomenon than NCI formation.

Comparison of two-year and five-year tamoxifen use in Japanese post-menopausal women

AIM

Large multicenter, randomized trials have revealed the advantages of using tamoxifen for 5 years vs 2 years in breast cancer patients. The aim of this report is to confirm the optimal duration of tamoxifen administration in a study of Japanese breast cancer patients.

METHODS

Japanese post-menopausal estrogen receptor-positive breast cancer patients treated with mastectomy were randomly assigned to either a 5-year or 2-year course of tamoxifen. The primary endpoint was disease-free survival, with secondary endpoints of overall survival and a reduction in the development of metachronous contra-lateral breast cancer.

RESULTS

A total of 256 breast cancer patients were randomized to a 5-year or 2-year tamoxifen administration group. After a median follow-up time of 81 months, there were no significant differences seen in terms of disease-free or overall survival (p=0.65 and 0.56, respectively). Furthermore, the impact of the 5-year use of tamoxifen on the development of contra-lateral breast cancer did not reach statistical significance (p=0.0511). However, 5-year tamoxifen use was closely associated with gynaecological complications (p=0.0081).

CONCLUSION

We could not show a beneficial effect of using tamoxifen for 5 years over 2 years in Japanese estrogen receptor-positive patients. This is likely due to the small number of patients enrolled in our study; however, racial disparity may influence this result. A reevaluation is necessary to study the advantages of the 5-year use of tamoxifen in the Japanese racial subgroup.

Axonogenesis in the medaka embryonic brain

In order to know the general pattern of axonogenesis in vertebrates, we examined axonogenesis in the embryonic brain of a teleost fish, medaka (Oryzias latipes), and the results were compared with previous studies in zebrafish and mouse. The axons and somata were stained immunocytochemically using antibodies to a cell surface marker (HNK-1) and acetylated tubulin and visualized by retrograde and anterograde labeling with a lipophilic dye. The fiber systems developed correlating with the organization of the longitudinal and transverse subdivisions of the embryonic brain. The first axons extended from the synencephalic tegmentum, forming the first fiber tract (fasciculus longitudinalis medialis) in the ventral longitudinal zone of the neural rod, 38 hours after fertilization. In the neural tube, throughout the entire brain two pairs of longitudinal fiber systems, one ventral series and one dorsal or intermediate series, and four pairs of transverse fiber tracts in the rostral brain were formed sequentially during the first 16 hours of axon production. In one of the dorsal longitudinal tracts, its branch retracted and disappeared at later stages. One of the transverse tracts was found to course in the telencephalon and hypothalamus. The overall pattern of the longitudinal fiber systems in medaka brain is similar to that in mouse, but apparently different from that in zebrafish. We propose that a ventral tract reported in zebrafish partially belongs to the dorsal fiber system, and that the longitudinal fiber systems in all vertebrate brains pass through a common layout defined by conserved genetic and developmental programs.

Fiber connections of the lateral valvular nucleus in a percomorph teleost, tilapia (Oreochromis niloticus)

Fiber connections of the lateral valvular nucleus were investigated in a percomorph teleost, the tilapia (Oreochromis niloticus), by tract-tracing methods. Following tracer injections into the lateral valvular nucleus, neurons were labeled in the ipsilateral dorsal part of dorsal telencephalic area, corpus glomerulosum pars anterior, dorsomedial thalamic nucleus, central nucleus of the inferior lobe, mammillary body, semicircular torus, valvular and cerebellar corpus, in the bilateral rostral regions of the central part of dorsal telencephalic area, dorsal region of the medial part of dorsal telencephalic area, habenula, anterior tuberal nucleus, posterior tuberal nucleus, and spinal cord, and in the contralateral lateral funicular nucleus. Labeled fibers and terminals were found in the ipsilateral cerebellar corpus and bilateral valvula of the cerebellum. Tracers were injected into portions of the telencephalon, pretectum, inferior lobe, and cerebellum to confirm reciprocally connections with the lateral valvular nucleus and to determine afferent terminal morphology in the lateral valvular nucleus. Telencephalic fibers terminated mainly in a dorsolateral portion of the lateral valvular nucleus. Terminals from the corpus glomerulosum pars anterior, central nucleus of the inferior lobe, and mammillary body showed more diffuse distributions and were not confined to particular portions of the lateral valvular nucleus. Labeled terminals in the lateral valvular nucleus were cup-shaped or of beaded morphology. These results indicate that the lateral valvular nucleus receives projections from various sources including the telencephalon, pretectum, and inferior lobe to relay information to the valvular and cerebellar corpus. In addition, the corpus glomerulosum pars anterior in tilapia is considered to be homologous to the magnocellular part of superficial pretectal nucleus in cyprinids.

Characterization of Acylated Anthocyanins in Callus Induced From Storage Root of Purple-Fleshed Sweet Potato, Ipomoea batatas L

Four anthocyanins were isolated from a highly pigmented callus induced from the storage root of purple-fleshed sweet potato (Ipomoea batatas L) cultivar Ayamurasaki. The anthocyanins were respectively identified as cyanidin 3- $O$ -(2- $O$ -(6- $O$ -( $E$ )-caffeoyl- $\beta$ -D-glucopyranosyl)- $\beta$ -D-glucopyranoside)-5- $O$ - $\beta$ -D-glucopyranoside, cyanidin 3- $O$ -(2- $O$ -(6- $O$ -( $E$ )- $p$ -coumaroyl- $\beta$ -D-glucopyranosyl)-6- $O$ -( $E$ )-caffeoyl- $\beta$ -D-glucopyranoside)-5- $O$ - $\beta$ -D-glucopyranoside, cyanidin 3- $O$ -(2- $O$ -(6- $O$ -( $E$ )- $p$ -coumaroyl- $\beta$ -D-glucopyranosyl)-6- $O$ -( $E$ )- $p$ -coumaroyl- $\beta$ -D-glucopyranoside)-5- $O$ - $\beta$ -D-glucopyranoside, and peonidin 3- $O$ -(2- $O$ -(6- $O$ -( $E$ )- $p$ -coumaroyl- $\beta$ -D-glucopyranosyl)-6- $O$ -( $E$ )- $p$ -coumaroyl- $\beta$ -D-glucopyranoside)-5- $O$ - $\beta$ -D-glucopyranoside by chemical and spectroscopic analyses. These anthocyanins were examined with respect to the stability in neutral aqueous solution as well as the radical scavenging activity against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. These acylated anthocyanins exhibited both higher stability and higher DPPH radical scavenging activity than corresponding nonacylated cyanidin and peonidin 3- $O$ -sophoroside-5- $O$ -glucosides.

Morphogenesis and regionalization of the medaka embryonic brain

We examined the morphogenesis and regionalization of the embryonic brain of an acanthopterygian teleost, medaka (Oryzias latipes), by in situ hybridization using 14 gene probes. We compared our results with previous studies in other vertebrates, particularly zebrafish, an ostariophysan teleost. During the early development of the medaka neural rod, three initial brain vesicles arose: the anterior brain vesicle, which later developed into the telencephalon and rostral diencephalon; the intermediate brain vesicle, which later developed into the caudal diencephalon, mesencephalon, and metencephalon; and the posterior brain vesicle, which later developed into the myelencephalon. In the late neural rod, the rostral brain bent ventrally and the axis of the brain had a marked curvature at the diencephalon. In the final stage of the neural rod, ventricles began to develop, transforming the neural rod into the neural tube. In situ hybridization revealed that the brain can be divided into three longitudinal zones (dorsal, intermediate, and ventral) and many transverse subdivisions, on the basis of molecular expression patterns. The telencephalon was subdivided into two transverse domains. Our results support the basic concept of neuromeric models, including the prosomeric model, which suggests the existence of a conserved organization of all vertebrate neural tubes. Our results also show that brain development in medaka differs from that reported in other vertebrates, including zebrafish, in gene-expression patterns in the telencephalon, in brain vesicle formation, and in developmental speed. Developmental and genetic programs for brain development may be somewhat different even among teleosts.