Biomedical subjects
Publications and source records attributed to M DeSantis.
The western spotted skunk has a well-developed retinohypothalamic tract projecting to the middle and caudal parts of the suprachiasmatic nuclei. The nuclei have a complex 3-dimensional shape and contain small neuronal somas.
Cytological development in the ventricular zone of the chicken's lumbosacral spinal cord was studied by light and transmission electron microscopy before and after hatching. Two morphologically distinct types of cell were first noted by embryonic stage 41 and were present in the 2-day-old chick. From cell bodies located at the border of the ependymal layer, a lightly stained process extended among the more numerous and typical ependymal cells to reach the central canal. Synapses were observed only on the cell bodies of the lightly stained cells.
In starfish a neuropeptide responsible for the induction of ovulation and the reinitiation of meiotic maturation in fully grown oocytes appears to be released from the radial nerves at the time of spawning. The objectives of this investigation were to determine if the radial nerve would release this gonadotrophin when electrically stimulated in vitro and to locate other possible sources of this factor. Electrical stimulation of radial nerves isolated from the starfish, Pycnopodia helianthoides, resulted in the release of the gonadotrophin. Significant amounts of this neuropeptide were detected neither in other tissues of the starfish nor in mammalian nervous tissue.
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Sections through the soleus muscle of the rat were incubated with concanavalin A (Con A) or wheat germ agglutinin (WGA) conjugated to fluorescein isothiocyanate. Binding of these lectins to structures which comprise the muscle spindle was studied by fluorescence microscopy. The distribution of the lectins was heaviest in the outer capsule of the spindle and at the surface of intrafusal muscle fibres. The periaxial space in the equatorial region of spindles was unlabelled except in the immediate vicinity of the axial bundle. Binding by Con A was more extensive than by WGA, suggesting that more glucopyranoside units are accessible within the muscle spindle than are those of N-acetylglucosamine.
Muscle spindles in the tenuissimus muscle of the cat were studied between 12 and 168 h after cutting or freezing the nerve to this muscle. Degenerative changes in sensory and motor nerve terminals on intrafusal muscle fibres were observed using the electron microscope. Comparisons were made with spindles from unoperated or sham-operated cats. The earliest degenerative changes were seen in sensory and motor terminals at 20-24 h after the lesion. No nerve endings were seen by 114 h after denervation. The most consistent initial signs of degeneration were: (1) the presence of abnormal mitochondria and dense bodies in sensory terminals, and (2) a decrease in the number and clumping of synaptic vesicles combined with an increase in glycogen and neurofilaments in motor endings. Intrafusal fibres participate in the removal of degenerating sensory endings. Schwann cells phagocytose degenerating motor terminals. The disappearance of nerve terminals precedes the complete degeneration of preterminal myelinated fibres within the muscle spindle.
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The masseter muscle of Sprague-Dawley rats was injected with 10 mg of horseradish peroxidase. The electrical activity of the trigeminal motor nucleus was investigated 24-36 hours later using micropipettes filled with a 2.0 M NaCl-7% fast green FCF solution. A parallel series of penetrations at 200 micron intervals was made through the motor complex at known depths. The grid formed from these penetrations was reconstructed using the following techniques. Marks were made at known depths in one or more of the tracts by iontophoresing fast green from the microelectrode tip with a hyperpolarizing current of 10 muA for 10 minutes. To assure proper alignment of the tissue containing the green marks, two agar-India ink plugs were placed caudal and parallel to the recording sites. The frozen tissue was sectioned on a microtome, first through the agar plugs and then through the tissue containing the green marks. The tissue could be incubated for the peroxidase reaction product or stained for Nissl substance. These combined procedures offer a means to correlate the structure and function of brain stem nuclear groups.
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Sprague-Dawley rats were studied to learn whether gestation in the near-zero gravity, high radiation environment of space impacts selected mammalian postnatal events. Ten rats spent days nine to twenty of pregnancy aboard the space shuttle orbiter Atlantis (STS-66). Their movement was studied shortly after return to Earth; subsequently, several of their offspring were cross-fostered and examined through postnatal day 81 (P81) for whole body growth and somatic motor development. Values for the flight animals were compared to ground-based control groups. Relative to controls, the pregnant flight rats showed a marked paucity of locomotion during the first few hours after returning to Earth. There was greater likelihood of perinatal morbidity for the offspring of flight dams when compared to the control groups. Whole body weight of surviving offspring, averaged for each group separately, showed typical sigmoidal growth curves when plotted against postnatal age. The flight group for our study had a larger ratio of female to male pups, and that was sufficient to account for the lower average daily weight gained by the flight animals when compared to the control groups. Walking was universally achieved by P13 and preceded eye opening, which was complete in all pups by P17. Thus, both of these developmental horizons were attained on schedule in the flight as well as the control rats. Characteristic changes were observed in hind limb step length and gait width as the pups grew. These patterns occurred at the same time in each group of rats. Therefore, prenatal space flight from days nine to twenty of gestation did not interfere with the establishment of normal patterns for hind paw placement during walking.