We have used time-lapse multiphoton microscopy to map the migration and settling pattern of GABAergic interneurons that originate in the ganglionic eminence of the ventral forebrain and incorporate into the neocortex of the cerebral hemispheres. Imaging of the surface of the cerebral hemispheres in both explant cultures and brains of living mouse embryos revealed that GABAergic interneurons migrating within the marginal zone originate from three different sources and migrate via distinct and independent streams. After reaching their areal destination, interneurons descend into the underlying cortex to assume positions with isochronically generated, radially derived neurons. The dynamics and pattern of cell migration in the marginal zone (see movies, available at www.jneurosci.org) suggest that the three populations of interneurons respond selectively to distinct local cues for directing their migration to the appropriate areas and layers of the neocortex. This approach opens a new avenue for study of normal and abnormal neuronal migration in their native environment and indicate that interneurons have specific programs for their areal and laminar deployment.

Neurons of the cerebral neocortex in mammals, including humans, are generated during fetal life in the proliferative zones and then migrate to their final destinations by following an inside-tooutside sequence. The present study examined the effect of ultrasound waves (USW) on neuronal position within the embryonic cerebral cortex in mice. We used a single BrdU injection to label neurons generated at embryonic day 16 and destined for the superficial cortical layers. Our analysis of over 335 animals reveals that, when exposed to USW for a total of 30 min or longer during the period of their migration, a small but statistically significant number of neurons fail to acquire their proper position and remain scattered within inappropriate cortical layers and͞or in the subjacent white matter. The magnitude of dispersion of labeled neurons was variable but systematically increased with duration of exposure to USW. These results call for a further investigation in larger and slower-developing brains of non-human primates and continued scrutiny of unnecessarily long prenatal ultrasound exposure.brain malformations ͉ cerebral cortex ͉ embryonic development A fundamental feature of cerebral cortical organization is that positions of its neuronal constituents into horizontal (laminar) and vertical (radial) arrays ultimately define their connectivity and function (1). Cortical neurons acquire appropriate positions by migration from the site of their origin in the proliferative zones lining the cerebral ventricle, according to a precise schedule (2, 3) and along well defined pathways (4-6). When the rate of neuronal migration and the sequence of arrival are altered because of genetic and͞or environmental factors, various consequences, including abnormal behavior, have been observed (7-13). In terms of orientation and directionality of movement, neuronal migration to the cerebral cortex can be classified into radial (proceeding radially from the ventricular to the pial surface) (5, 14) and tangential (running parallel to the brain surface) (15)(16)(17). Contact interaction between migrating neurons and the surfaces of neighboring cells plays a decisive role in selecting the migratory pathway and determining their final position (18,19). Neuronal migration involves translocation of the nucleus and the surrounding cytoplasm with the leading process, which requires rearrangement of the cytoskeleton (20, 21). As a consequence of these complex cellular and molecular interactions, the process of neuronal migration is highly sensitive to a variety of biological, physical, and chemical agents, as well as to specific genetic mutations (7-13). For example, repeated exposure of the rodent and primate fetal brain to environmental agents, such as alcohol (9), drugs (22), neurotrophic viruses (23), and ionizing irradiation (24, 25), causes misplacement of neurons and behavioral deficits.To our knowledge, the effect of ultrasound waves (USW) on the rate of migration in the cerebral cortex has never been tested, although it has been reported ...

Although the serotonergic system plays an important role in various neurological disorders, the role of early serotonergic projections to the developing cerebral cortex is not well understood. Because serotonergic fibers enter the marginal zone (MZ) before birth, it has been suggested that they may influence cortical development through synaptic contacts with Cajal-Retzius (CR) cells. We used immunohistochemistry combined with confocal and electron microscopy to show that the earliest serotonergic projections to the MZ form synaptic contacts with the somata and proximal dendrites of CR cells as early as embryonic day 17. To elucidate the functional significance of these early serotonergic contacts with CR cells, we perturbed their normal development by injecting pregnant mice with 5-methoxytryptamine. Lower reelin levels were detected in the brains of newborn pups from the exposed animals. Because reelin plays an important role in the cortical laminar and columnar organization during development, we killed some pups from the same litters on postnatal day 7 and analyzed their presubicular cortex. We found that the supragranular layers of the presubicular cortex (which normally display a visible columnar deployment of neurons) were altered in the treated animals. Our results suggest a mechanism of how serotonergic abnormalities during cortical development may disturb the normal cortical organization; and, therefore, may be relevant for understanding neurological disorders in which abnormalities of the serotonergic system are accompanied by cortical pathology (such as autism).

Citation and quotation errors are common in medical journals. We assessed the prevalence of those errors in gross anatomy journals, where articles often cite old anatomical studies. The study included 199 randomly selected references from articles published in the first 2001 issue of three major gross anatomy journals: Annals of Anatomy, Clinical Anatomy, and Surgical and Radiologic Anatomy. The selected references were checked for accuracy against the original articles. Citation errors were classified as major, intermediate, and minor. Quotation errors were classified as major and minor. Citations errors were found in 27% (54/199) of the references and 38% of them were major errors. Errors occurred in 19% (52/272) of quotations and nearly all (94%) were major. Furthermore, 24% of the quotations were indirect references to a secondary, instead of original, source. There was no statistically significant difference in the rates of citation or quotation errors between the references published before or after the introduction of MEDLINE (chi2 test, P > 0.05) in 1963, and the prevalence of these errors in gross anatomy journals was similar to that found in other medical fields. A high proportion of major citation errors, a very high proportion of major quotation errors, and the substantial number of indirect quotations call for serious editorial action in anatomy journals.

We present a rare case of combined high bifurcation of the common carotid artery, anomalous origin of the ascending pharyngeal artery and unusual branching pattern of the external carotid artery. The right common carotid artery bifurcated at the level between the second and the third cervical vertebrae, giving rise to the ascending pharyngeal artery just below the bifurcation. The right external carotid artery branched directly at its origin into the superior thyroid, lingual and occipital arteries and the distal part of the external carotid artery. The latter gave rise to the right facial artery and finally bifurcated into the maxillary and superficial temporal arteries. The right posterior auricular artery arose from the right occipital artery. The finding was unilateral and other vascular anomalies were not observed. The embryogenesis of such a combination of anomalies is not clear, but the anatomic consequences may have important clinical implications.