Reorganization and movement of microtubules in axonal growth cones and developing interstitial branches.

Local changes in microtubule organization and distribution are required for the axon to grow and navigate appropriately; however, little is known about how microtubules (MTs) reorganize during directed axon outgrowth. We have used time-lapse digital imaging of developing cortical neurons microinjected with fluorescently labeled tubulin to follow the movements of individual MTs in two regions of the axon where directed growth occurs: the terminal growth cone and the developing interstitial branch. In both regions, transitions from quiescent to growth states were accompanied by reorganization of MTs from looped or bundled arrays to dispersed arrays and fragmentation of long MTs into short MTs. We also found that long-term redistribution of MTs accompanied the withdrawal of some axonal processes and the growth and stabilization of others. Individual MTs moved independently in both anterograde and retrograde directions to explore developing processes. Their velocities were inversely proportional to their lengths. Our results demonstrate directly that MTs move within axonal growth cones and developing interstitial branches. Our findings also provide the first direct evidence that similar reorganization and movement of individual MTs occur in the two regions of the axon where directed outgrowth occurs. These results suggest a model whereby short exploratory MTs could direct axonal growth cones and interstitial branches toward appropriate locations.

Fibroblast growth factor-2 promotes axon branching of cortical neurons by influencing morphology and behavior of the primary growth cone.

Interstitial branching is an important mechanism for target innervation in the developing CNS. A previous study of cortical neurons in vitro showed that the terminal growth cone pauses and enlarges in regions from which interstitial axon branches later develop (Szebenyi et al., 1998). In the present study, we investigated how target-derived signals affect the morphology and behaviors of growth cones leading to development of axon branches. We used bath and local application of a target-derived growth factor, FGF-2, on embryonic pyramidal neurons from the sensorimotor cortex and used time-lapse digital imaging to monitor effects of FGF-2 on axon branching. Observations of developing neurons over periods of several days showed that bath-applied FGF-2 significantly increased growth cone size and slowed growth cone advance, leading to a threefold increase in axon branching. FGF-2 also had acute effects on growth cone morphology, promoting rapid growth of filopodia within minutes. Application of FGF-2-coated beads promoted local axon branching in close proximity to the beads. Branching was more likely to occur when the FGF-2 bead was on or near the growth cone, suggesting that distal regions of the axon are more responsive to FGF-2 than other regions of the axon shaft. Together, these results show that interstitial axon branches can be induced locally through the action of a target-derived growth factor that preferentially exerts effects on the growth cone. We suggest that, in target regions, growth factors such as FGF-2 and other branching factors may induce formation of collateral axon branches by enhancing the pausing and enlargement of primary growth cones that determine future branch points.

Catecholaminergic neurons in the ventrolateral medulla and nucleus of the solitary tract in the human.

Catecholaminergic neurons in the ventrolateral medulla (VLM) and nucleus of the solitary tract (NTS) are important because of their presumed roles in autonomic regulation, including the tonic and reflex control of arterial pressure, neuroendocrine functions, and the chemosensitivity associated with the ventral medullary surface. However, little is known about the connections of these neurons in the human brain. As a first step in analyzing the functional biochemical anatomy of catecholamine neurons in the human, we used antisera against tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) to localize medullary catecholamine-containing neurons and processes in the VLM and the NTS. Cells staining for TH were located throughout the VLM. Most cells staining for TH and PNMT, which are therefore adrenergic, occurred in an area of the VLM probably corresponding to the rostroventrolateral reticular nucleus. Axons of TH-immunoreactive neurons in the VLM projected (1) dorsally, in a series of parallel transtegmental trajectories, toward the dorsomedial reticular formation, the NTS, and vagal motor nucleus, (2) longitudinally, through the central tegmental field, as fascicles running parallel to the neuraxis, (3) ventrolaterally toward the ventral surface (VS) of the rostral VLM where they appeared to terminate, and (4) medially into the raphe, where they arborized. Similar systems of fibers were labeled for PNMT; the longitudinal bundles of PNMT-labeled axons were limited to the principal tegmental bundle and concentrated dorsally. Fibers containing PNMT were also identified in the medullary raphe, on the medullary ventral surface, and contacting intraparenchymal blood vessels. In the NTS, neurons exhibited immunoreactivity to both TH and PNMT: Four principal subgroups of TH-immunoreactive neurons were seen: a ventral, an intermediate, a medial, and a dorsal group. Perikarya containing PNMT were restricted to the dorsolateral aspect of the NTS. Processes containing TH and PNMT immunoreactivity were identified in the medial and dorsolateral NTS; others appeared to project between the NTS and the VLM and within the solitary tract. The presence of catecholaminergic fibers of the VLM interconnecting with the NTS, raphe, intraparenchymal microvessels, VS, and possibly the spinal cord suggests that the autonomic and chemoreceptor functions attributed to these neurons also may apply to the human.

Double labelling of neuronal somata by [3H]uridine and horseradish peroxidase: a technique to demonstrate two-stage connections with the light microscope.

A new technique is described that may demonstrate two-stage connection at the light microscopic level. Anterograde transneuronal transport of [3H]uridine is used in conjunction with retrograde transport of horseradish peroxidase (HRP). The two compounds are injected separately into different brain regions. Under conditions of proper controls, neuron somata that are double labelled are interpreted as receiving an afferent projection from the region injected with [3H]uridine and sending an efferent projection to the region injected with HRP. Thus, the technique can demonstrate two-stage connections in the nervous system.

Fatal injuries and alcohol.

We reviewed fatal injuries in Fulton County, Georgia, in collaboration with the medical examiner's office. This county encompasses most of the city of Atlanta and has a population of approximately 600,000 persons. Information collected for 1981 and 1982 was analyzed; and the results of blood alcohol content (BAC) testing and toxic screens were reviewed for all victims of homicide, suicide, and unintentional fatal injuries who died within six hours of being injured. Seventy-one percent of 271 homicide victims had been drinking, and 51 percent had BACs greater than or equal to 0.1 mg/dL. Of 153 suicide victims, 37 percent had been drinking and 20 percent had BACs greater than or equal to 0.1 mg/dL. Of 54 drivers who died in single-vehicle collisions, 78 percent had been drinking; 54 percent of 162 victims of nonvehicular unintentional fatal injuries had positive blood alcohol levels. There was little evidence of the use of psychotropic drugs among victims of fatal injury. Most of the victims of homicide and unintentional fatal injuries who had positive toxic screens also had a positive blood alcohol tests.

Angioendothelioma: report of an unusual case in an American black.

Angioendothelioma is a rare malignant vascular tumor occurring on the face or scalp in an elderly individual or in an area of antecedent radiotherapy or chronic lymphedema. We are reporting the second fully documented case of angioendothelioma occurring in a black patient. The case is also of interest because initially the tumor mimicked kerion, both clinically and histopathologically.