Robert G. Nagele

Ultrastructure of a new microtubule-neurofilament coupler in nerves

A new structure associated with the surfaces of neuronal microtubules is described which connects microtubules to neurofilaments in the axonal processes of cultured chick sensory ganglia. These couplers consist of a spherical core particle (15 nm in diameter) from which radiate several thin filaments (4 nm in diameter). Connection of adjacent microtubules and neurofilaments is achieved by thin filaments radiating from core particles positioned between these cytoskeletal elements. Couplers are most conspicuous in regions of axonal processes containing widely separated microtubules and neurofilaments. The structure and distribution of these couplers suggests that they are directly involved in intra-axonal organelle movements, possibly by modulating the spatial separation of adjacent microtubules and neurofilaments, thereby allowing the passage of transported organelles.

Intrinsic forces alone are sufficient to cause closure of the neural tube in the chick

An isolated neural plate or a postnodal piece of early chick embryos, when cultured under appropriate experimental conditions, can undergo morphogenetic movements and form tubular structures closely resembling neural tubes of early chick embryos.

Examination of geniculate ganglion cells contributing sensory fibers to the rat facial ‘motor’ nerve

Using a method to visualize HRP-containing cells in the geniculate ganglion (GG) in situ after decalcifying surrounding bone, we found that about 30% of the total (about 1000) GG cells contributed sensory fibers to the posterior auricular branch of the facial motor nerve. These cells are relatively large for GG cells in general. The remaining facial motor nerve branches, including those involved in vibrissal movement, contained few sensory afferent fibers originating from GG cells.

Diazepam inhibits the spreading of chick embryo fibroblasts

Diazepam (Valium/Roche), a benzodiazepine derivative, reversibly inhibited the spreading of chick embryo fibroblasts in a dose-related manner. This inhibition was accompanied by: 1 Fewer and less organized microfilament bundles. 2 A reduction in myosin fluorescence along these structures. 3 A reduction in the total myosin content of cells compared to corresponding controls. Overall results suggest that myosin plays an active role in the spreading of chick embryo fibroblasts.

Possible involvement of calmodulin in apical constriction of neuroepithelial cells and elevation of neural folds in the chick

Chlorpromazine and trifluoperazine HCl, antipsychotic drugs known to bind to calmodulin, reversibly inhibited elevation of neural folds by interfering with the contractile activity of apical microfilament bundles in developing chick neuroepithelial cells.

Further studies on neural tube defects caused by concanavalin A in early chick embryos

Neural tube defects caused by concanavalin A in chick embryos are consequences of change in the cell surface of developing neuroepithelium.

A method for preparing and handling cross-sections from early chick embryos for scanning electron microscopy.

A method is described for processing multiple cross‐sections from early chick embryos for scanning electron microscopy. Embryos are cut through the desired regions. Sections are affixed to a coverslip with Duco cement and critical point dried by Freon 13 or liquid CO2. This method provides a reliable means for preparing multiple cross‐sections from single embryos and eliminates the need for direct handling of brittle tissues after drying.

Studies on the mechanisms of neurulation in the chick: The intracellular distribution of Ca++1

Coated vesicles were found to accumulate Ca++ in neuroepithelial cells and may play a role in regulating the contractile activities of apical microfilament bundles during uplifting of neural folds in the chick.

A transmission and scanning electron microscopic study of cytoplasmic threads of dividing neuroepithelial cells in early chick embryos

Cytoplasmic threads found on the luminal surface of the developing chick neuroepithelium contain a remnant of the spindle complex and an electron-dense midbody. Most threads become long and thin and eventually split at the midbody. This finding suggests that the midbody plays a role in the final separation of daughter cells.

A method for studying the three‐dimensional organization of cytoskeletal elements of cells: improvements in the polyethylene glycol technique

A method utilizing polyethylene glycol (PEG) as an extractable embedment for electron microscopy is described. Tissues are fixed according to conventional protocols, embedded in PEG, and sectioned. Sections (ranging from 100 to 500 nm in thickness) are mounted on grids, divested of their PEG matrix, critical‐point‐dried, and examined stereoscopically. This method greatly facilitates studies on the three‐dimensional organization of cytoskeletal and cytoplasmic contractile systems in both muscle and nonmuscle cells.