A functional analysis of the components of the mesencephalic nucleus of the fifth nerve in the cat

1. The mesencephalic nucleus of the trigeminal nerve has been studied using extracellular micro-electrode recording and the constituent cell types identified.2. Two types of unit were found, namely, muscle spindle first order afferents of ipsilateral jaw-closing muscles and mechanoreceptor afferents of ipsilateral maxillary and mandibular teeth.3. No evidence was found for representation of extra-ocular muscle stretch receptors, of temporo-mandibular joint receptors or of tendon organs of jaw muscles.4. Spindle units of each of the jaw-closing muscles were recorded in all parts of the nucleus and there was no evidence of their segregation according to muscle of origin.5. Attempts to classify spindle units by their dynamic response to ramp stretches, their following of high frequency vibration and their interspike interval variability at constant length gave no indication of two populations when fusimotor activity was suppressed.6. Following the injection of suxamethonium, however, units fell into two groups according to their dynamic index. Their behaviour resembled that described for primary and secondary spindle afferents. In data pooled from all of the jaw-closing muscles there were approximately equal numbers of units in each group.     

Electron microscopic observations of the nucleus,glial dome,and meninges of the rat acoustic nerve

The rat acoustic nerve is separated into central and peripheral portions by an astrocytic glial dome which is convex peripheralward. The long central portion is of typical central nervous system structure with narrow extracellular space (100–200 Å in width), oligodendrocytes and astrocytes. The glial dome is penetrated by acoustic nerve fibers at a node of Ranvier; the basal lamina of the astrocytes is reflected back over the peripheral Schwann cells at this site. Centrally, the myelin is thinner than peripherally. Acoustic nerve neurons, ranging in size from 25–60 μ, occur in the central portion of the nerve and may be divided into two groups based upon size and density of organelles: large and medium-sized. All the neurons possess an eccentric nucleus and a peripheral clear zone in the perikaryon beneath which Nissl substance is aggregated, but the medium-sized neurons have fewer organelles than the large cells. Dendrites and axons are similar in ultrastructure. While collagenous fibrils, fibroblasts, Schwann cells and extensive extracellular space occur in the peripheral portion of the nerve, no structure corresponding to perineurium or epineurium exists. Instead, dura mater surrounds the acoustic nerve within the modiolus and the pia mater encloses bundles of nerve fibers up to the modiolar foramina where it is reflected back as arachnoid mater. Nerve fibers traversing the modiolar foramina are devoid of a meningeal or perineurial covering; this condition also prevails in the osseous spiral lamina, although wisps of pia-like cells enclose groups of ganglion cells and nerve fibers in the spiral tract. These findings may help to explain acoustic nerve involvement in pathological processes such as meningitis and encephalitis.     

Induced hypothermia in peripheral nerve: Electron microscopic and electrophysiological observations

Summary Localized cooling of the cat sciatic nerve was achieved by application of a thermoelectric device to the exposed nerve at mid-thigh. The temperature of the nerve was maintained at 5°C for 2 h. Before, during, and after cooling, the response of the nerve to electrical stimulation was monitored, and compared with responses obtained in normothermic control preparations. In all cases, dropping the temperature of the nerve to 5°C resulted in total nerve block, and in all cases, function was restored when cooling stopped. Light and electron microscopic analysis of the cooled nerves revealed that despite functional recovery, a lesion affecting large myelinated axons developed over the course of 7 days. Both Waherian degeneration and segmental demyelination occurred. Unmyelinated fibres were not affected.     

Remodelling of internodes in regenerated rat sciatic nerve: Electron microscopic observations

Summary Twelve adult rats received a crush lesion of the left sciatic nerve in the upper thigh. Following survival times of 2 weeks to 6 months, the animals were perfused with glutaraldehyde. Longitudinal thin sections from regenerated nerve segments were examined by electron microscopy. At survival periods of 2 weeks to 1 month, exceptionally short internodes composed of a Schwann cell lacking myelin, a more or less wrinkled Schwann cell-myelin sheath unit, or Schwann cell cytoplasm containing lamellated bodies and lipid droplets, were found intercalated between conventional regenerated myelin sheaths. Such intercalated sheaths were always bordered by sites with a nodal differentiation. Although much less frequent, short distorted myelin sheaths were also found at regeneration times of 2 and 3 months, but they have not been found in sections from 6-month specimens. In the long-term regenerated nerves many paranodes were distorted by prominent myelin folds and some nodes of Ranvier exhibited abnormal axon-Schwann cell networks and adaxonal Schwann cell protrusions. These observations show that internodes in regenerated rat sciatic nerves are subject to extensive remodelling. This includes internodal shortening and nodal migration, myelin sheath breakdown and demyelination, elimination of redundant Schwann cells and nodal fusion. These morphological changes may have important physiological implications.     

Electron microscopic observations of Pseudomonas aeruginosa

Preparative techniques were developed for the purpose of visualizing, by negative contrast, some of the cytological characteristics of unsectioned cells of Pseudomonas aeruginosa. Concentrated fimbriae free from cells had a length of approximately 1.5 μm and a diameter of 6 nm. Pyocin-like structures ranging in length from 32-64 nm with a width of 8.6 nm were “attached” to the terminal ends of a small percentage of these fimbriae. Microtubules and ringlets having a diameter of 10-20 nm were also visualized in the bacteria. Budding or evagination of cell wall material in multiple units up to 135 nm in length was frequently observed in older cultures grown on agar media.     

The trigeminal mesencephalic nucleus. II. Electron microscopy

The fine structure of cells in the trigeminal mesencephalic nucleus was examined in adult mouse and cat. Cell surfaces were studed with small spinous processes which were free of synaptic contacts. Some cells in soma-soma and axosomatic contact were joined by maculae and membrane fusions resembling in cross section the zonula adherens and macula occludens of epithelial cells. Synapses containing three distinct morphological types of vesicles contacted the cell soma. The possible functions of synapses and membrane fusions were discussed.     

Electron microscopic observations of the kidney in the generalized Shwartzman reaction

Summary Sequential changes in the kidney during the generalized Shwartzman reaction were studied electron microscopically. The first anatomical change was infiltration of neutrophils into the glomerular capillaries. Endothelial damage was not noticeable until the capillaries were filled with fibrin deposits. Fibrin appeared in the mesangium at almost the same time as in the capillary lumina, traversing through the endothelial fenestrae. Endothelial damage was more common in the mesangial portion than in the peripheral portion of the capillaries. Severe mesangiolysis developed after loss of endothelial cells had been followed by massive penetration of intracapillary contents. Later, signs of repair were evident in some parts of the damaged endothelium. The development of cortical necrosis coincided with the appearance of mesangiolysis and arteriolar thrombotic lesions.Supported in part by grants from the Japanese Ministry of Education