AN ELECTRON MICROSCOPE STUDY OF THE ENDOPLASMIC RETICULUM IN NEWT NOTOCHORD CELLS AFTER DISTURBANCE WITH ULTRASONIC TREATMENT AND SUBSEQUENT REGENERATION

Ultrasonic treatment of the tails of Triturus alpestris tadpoles, at intensities of 8 to 15 watts/cm², at 1 megacycle/sec., for 5 minutes, disrupted the epidermis and caused pycnosis in individual cells of the muscle and neural tube, but caused no damage to the notochord that could be detected by light microscopy. Electron microscopy showed that this ultrasonic treatment disordered nearly all the endoplasmic reticulum (ER) of the notochord cells into irregularly rounded vesicles, but within 3 hours after treatment some parallel arrays of normal endoplasmic reticulum were seen near, and continuous with, the outer nuclear membrane. In addition, a re-ordering of the previously disordered ER took place throughout the cytoplasm, in some cases. A classification was made of the state of the ER as shown in electron micrographs of material fixed immediately, 3, and 24 hours after treatment. This showed that more than half the total endoplasmic reticulum in notochord cells was normal again by 24 hours after treatment.

ACUTE ASPHYXIATION OF THE SPINAL CORD AND OF OTHER SECTIONS OF THE NERVOUS SYSTEM

Oxygen lack causes an impedance increase of the spinal cord coinciding in time with an asphyxial potential which can be led off from the spinal gray matter against an indifferent electrode. After circulatory arrest the latency of these changes is of the order of 10 sec; after ventilation of the preparation with nitrogen the latency is 20–25 sec. An asphyxial transport of chloride was demonstrated into dendrites of dorsal horn neurons accompanied by a volume increase of these structures. The electrolyte movement can account for the impedance increase by a loss of extracellular ions which are the main carriers of the measuring current. The observed ion movement, taken as an indication of depolarization, suggests that the asphyxial potential is due to dendritic depolarization, the somas (and axons) acting as source. This explanation was supported by the much slower decline of the spinal asphyxial potential as compared with that of a similar potential which can be led off from the cerebral cortex. The difference in the rate of decline reflects the much slower asphyxial depolarization of the somas of spinal neurons as compared with that of cerebral nerve cell bodies which has been observed previously.

THE PATHOGENESIS OF HERPES VIRUS ENCEPHALITIS. I. VIRUS PATHWAYS TO THE NERVOUS SYSTEM OF SUCKLING MICE DEMONSTRATED BY FLUORESCENT ANTIBODY STAINING

The pathogenesis of herpes simplex virus encephalitis and myelitis was studied in suckling mice using routine titration procedures and fluorescent antibody staining for the identification of infected cells. After intracerebral inoculation virus was shown to disperse rapidly in the cerebrospinal fluid (CSF), multiply in meninges and ependyma, and then invade the underlying parenchyma infecting both neurons and glia. Following extraneural inoculation virus gained access to the central nervous system (CNS) by both hematogenous and neural pathways. After intraperitoneal and intranasal inoculation virus was found to multiply in viscera and produce viremia; foci of CNS infection then developed around small cerebral vessels. After subcutaneous and intranasal inoculation neural spread of virus was demonstrated along corresponding peripheral and cranial nerves. This spread resulted from the centripetal infection of endoneural cells (Schwann cells and fibroblasts). Antigen was not found in axons even after infection of the corresponding ganglion cell perikaryon. Subsequent spread within the CNS was unrelated to neural tracts, and there was no evidence of axonal spread of virus in the host-virus system studied. These findings are discussed in relation to previous and current theories of the viral "blood-brain barrier" and neural pathways of infection.

THE EXTRUSION OF SODIUM FROM CAT SPINAL MOTONEURONS

Sodium ions were injected into cat spinal motoneurons electrophoretically through an intracellular NaCl-filled microelectrode. Following an injection there were characteristic changes in the resting and spike potentials, the after-potential and the inhibitory postsynaptic potential, all of which recovered within about 7 min. The maximum rising slope of the spike recovered exponentially, suggesting the exponential decrease of the intracellular sodium concentration by the operation of the sodium pump in actively extruding excess sodium. The time course of the recovery of the maximum falling slope of the spike paralleled that of the rising slope, indicating a reciprocal change in the intracellular sodium and potassium concentrations. There was a good parallelism in the time courses of the recovery of the amplitude of the after-potential and the maximum falling slope of the spike, as would be expected from their postulated dependence on the same internal potassium concentration. The inhibitory postsynaptic potential recovered from its displacement in the depolarizing direction with the same time course as did the other potentials, which indicates parallel decreases of the intracellular sodium and chloride concentrations. From the exponential recovery curves obtained for these potentials, the rate constant of active sodium extrusion was estimated as 40 h -1 . The fast rate of sodium extrusion in cat motoneurons is related to the dynamic ionic balance in neurons of the central nervous system, and is explained by the geometry and by the membrane properties of motoneurons.