The techniques of reconstructions of cells from serial thin sections and autoradiography after tritiated thymidine injections have been employed to study the early histogenesis of the cerebral cortex in the embryonic day-15 (E15) mouse. The autoradiographic studies show that cells below the E l 5 cortical plate in the intermediate layer are destined to migrate through the preexisting cortical plate cells to take up a more superficial position. Having this information, it has been possible, through reconstructions of large numbers of cells (more than 150) throughout the thickness of the cerebral vesicle, to identify some of the important morphogenetic events of cortical histogenesis. The following scheme is proposed. The first step in neuronal differentiation involves the detachment of the ventricularly directed process of the ventricular cell from the junctional region next to the ventricle. In thin sections, these junctions have the appearance of zonulae adherentes, but freeze cleavage experiments performed in this study show that, in addition, some of them resemble small gap junctions while others appear to be remnants of tight junctions or possibly linear gap junctions. Detachment of the ventricular process accompanies the migration of the nucleus and perikaryon through the ventricular layer. Within the intermediate layer the migrating cells become rounded and sprout numerous processes. Some cells may undergo a mitotic division a t this stage. Eventually the differentiating cells sprout a longer lateral process which is oriented tangentially to the pial surface. This process originates from the anterior surface of the soma and a t its tip has the characteristics of an axonal growth cone. The cells migrate externally and radially with simultaneous elongation of the primitive axon. In the subcortical plate region of the intermediate layer all cells contain an anteriorly directed axon. Subsequently, the cells sprout an apical process which extends into the cortical plate, and the nucleus and perikaryon apparently migrate radially within this process. The result is that the primitive axon first descends into the intermediate layer proper before turning to run tangentially. Dendritic growth and further differentiation begins once the cells reach their definitive position in the cortical plate.One interesting finding is the presence of eight cells in the cortical plate without long anteriorly directed axons. Yet, autoradiographic data show that subcortical plate cells are the immediate precursors of cortical plate cells, and all 28/28 reconstructed subcortical plate cells have long anteriorly directed axons. Thus, it is possible that the long axon of some cells may be lost as the cells continue to differentiate in the cortical plate. In fact, one cell has been found which appears to be in the process of losing its anteriorly directed axon.A number of molecular layer cells have also been reconstructed. These cells have several processes oriented tangentially to the pial surface. The identity of these processe...

This brief case report describes the successful outcome after surgical excision of multiple adventitial cysts of the popliteal artery in a 75-year-old man with rapidly worsening claudication. It highlights several unsettled points concerning the diagnosis, cause, and management of cystic adventitial disease of the popliteal artery and compares duplex ultrasound, computed tomography, and magnetic resonance angiography in the noninvasive diagnosis and treatment of this condition.

A 42-year-old homosexual man without evidence of immune deficiency developed cerebral granulomatous angiitis in association with the isolation of human T-lymphotropic virus type III (HTLV-III) from brain tissue and cerebrospinal fluid. This syndrome may be an additional neurological sequela of HTLV-III infection.

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