Gregory M. Shoukimas

Abstract 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 E15 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 at 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 at 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/s28 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 processes could not always be determined. Occasional asymmetric synapses have been found between unidentified axons and the horizontal cell soma or its processes. Autoradiographic studies show that horizontal cells have the earliest time of origin of any cortical cell type.

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.

Using a modification of the partial saturation (PS) pulse sequence, we developed an MR method that permits the acquisition of highly T1- and T2-weighted images of the head and body in as little as 10 sec. The PS images, which were acquired at 0.6 T in a series of six patients with acute and subacute hemorrhage, showed a striking reduction in the signal intensity of hemorrhagic lesions. This effect, which is related to bulk magnetic susceptibility variations, was either minimal or absent on conventional T1- and T2-weighted spin-echo (SE) images. Our results suggest that high-field systems are not needed in order to image acute and subacute hemorrhage.

A new technique is described that allows for the creation of pure pulsatile flow magnetic resonance (MR) images in a single acquisition. Five to 16 electrocardiographically gated images spanning the entire cardiac cycle are obtained with use of a gradient-echo pulse sequence. The section can be varied from 4 mm thick to full thickness projection. Taken singly, each image provides direct assessment of flow direction and velocity. Subtraction of image pairs eliminates signal detected from stationary protons, producing images of pulsatile flow. In this study the technique was used to image the flow of cerebrospinal fluid (CSF) in healthy subjects and in one patient with syringohydromyelia. The data suggest that multiphasic MR imaging provides a powerful means for the noninvasive assessment of CSF pulsatile flow dynamics and may have potential clinical application for the investigation of a variety of abnormalities such as normal pressure hydrocephalus, syrinx, and spinal block.

Twenty patients in whom CT had unequivocally demonstrated the presence of calcification in a diversity of lesions and who had undergone MR, performed at 0.6 T and with standard T1- and T2-weighted pulse sequences, were retrospectively studied to determine the MR signal-intensity characteristics of the calcifications and to assess the ability of MR to detect the presence of this abnormality. CT proved superior to MR in detecting and characterizing calcification. In seven of 20 cases, the apparent extent of calcification was equal by both imaging techniques, and in 13 of the 20 cases, CT showed more extensive abnormality. In five of the 20 cases, the calcifications were seen by MR as regions of profoundly reduced signal intensity, approximately equal to cortical bone, in all pulse sequences. In 12 of the 20 cases, the signal intensity was profoundly reduced in one or more, but not all, pulse sequences. T2-weighted pulse sequences were most sensitive in detecting calcification of signal void. Reviewed without knowledge of the CT findings, the MR images were interpreted as definitely indicative of the presence of calcification in three of the 20 cases. In seven of the 20 cases, the MR images raised the possibility of calcification but were less definitive than the CT findings. In 10 of the 20 cases, MR was judged indeterminate for the presence of calcification.