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Biomedical subjects

M V Smith

Publications and source records attributed to M V Smith.

At least 37 records · Page 2Linked to original sources
PubMed1992

Response properties of upper cervical spinothalamic neurons in cats. A possible explanation for the unusual sensory symptoms associated with upper cervical lesions in humans.

Lesions in the foramen magnum and upper cervical spinal cord often cause an unusual array of sensory changes and atrophic weakness, primarily involving the ipsilateral forelimb. Furthermore, small midline myelotomies performed at C1 often lead to widespread analgesia covering most of the body in patients with chronic pain. These observations challenge physicians' understanding of anatomy and physiology in the upper cervical region. Using single cell recording techniques the authors have shown that spinothalamic neurons in the second cervical segment of cats have complex response properties, often responding to stimuli throughout the body. These findings together with a review of clinical and basic science literature are used to provide explanations for the unusual signs and symptoms observed in patients with upper cervical and foramen magnum lesions.

Animals↗
PubMed1991

Thalamically projecting cells of the lateral cervical nucleus in monkey.

The number, location, and morphology of thalamically projecting lateral cervical nucleus (LCN) cells were determined in monkey using retrograde transport of wheatgerm agglutinin-conjugated horseradish peroxidase. These data were compared to the total population of LCN neurons as determined by Nissl stain. In 4 Macaca fascicularis and one Saimiri sciureus the average size of the thalamic projection from LCN was found to be 506 +/- 94 cells contralateral to the injections. Thalamically projecting LCN neurons were located between the lower medulla and the third cervical segment; approximately 90% of these cells were in the first two cervical segments. Morphologic analysis of thalamically projecting LCN cells showed that they were smaller in size, and more oblong in shape in caudal regions of the nucleus. In 3 macaques, the average total number of LCN cells was determined to be 1617 +/- 908 on one side, in Nissl material. In these Nissl-stained preparations LCN neurons were found as far caudal as the fourth cervical segment; 68% were located in the first two cervical segments. Hence, thalamically projecting LCN neurons in the monkey are located in the rostral portion of the nucleus and comprise about one-third of the total population. Comparison of these data with reports in the literature imply that, unlike the cat, the major projection from LCN in monkeys is to the mesencephalon rather than to the thalamus.

Animals↗
PubMed1991

Somatosensory response properties of contralaterally projecting spinothalamic and nonspinothalamic neurons in the second cervical segment of the cat.

1. The upper cervical spinal cord contains over one-third of the cells of the spinothalamic tract (STT). This study investigated response properties of contralaterally projecting STT neurons in C2 of the cat by the use of single-unit, microelectrode recordings. Standard antidromic stimulation and collision techniques were used to identify STT units projecting to the contralateral thalamus. Once an STT unit was found, its receptive field (RF) and responses to cutaneous stimuli such as touch, pressure, deep muscle squeeze, tap, noxious pinch, and heat were characterized. C2 units that were not activated from the contralateral thalamus (non-STT units) were also characterized. The locations of thalamic stimulation electrodes and spinal recording sites were reconstructed from electrolytic lesions. 2. A total of 48 STT and 68 non-STT units were well characterized. RF sizes were classified as small, intermediate, large, or whole body. Each unit was also classified as having one of two possible response types: simple units were those with homogeneous responses within the RF and were classified as low threshold (LT), high threshold (HT), wide dynamic range (WDR), deep, or tap. Complex units were those that responded differently in different regions of the RF. 3. The average depth of non-STT units subdivided by RF size was 2.1 +/- 0.6 (SD) mm for cells with small RFs, 2.4 +/- 0.8 mm for cells with intermediate RFs, 2.8 +/- 0.3 mm for cells with large RFs, and 2.7 +/- 0.5 mm for cells with whole-body RFs. The average depth of non-STT units based on response type was 2.0 +/- 0.5 mm for LT, 2.3 +/- 0.7 mm for HT, 2.1 +/- 0.7 mm for WDR, 2.6 +/- 0.9 mm for deep, 2.6 +/- 0.5 mm for tap, and 2.4 +/- 0.2 mm for complex. 4. A somatotopic organization along the rostrocaudal length of C2 and upper C3 was observed for non-STT units with small- and intermediate-size RFs. The average distance of the recording sites from the rostralmost dorsal rootlet of C2 was 3.8 +/- 2.1 mm for units with RFs on the face, 7.1 +/- 4.3 mm for units with RFs on the neck, and 11.9 +/- 5.1 mm for units with RFs on the forelimb. 5. The average threshold for antidromic activation of STT units was 175 +/- 120 microA. Most C2 STT units were activated from the ventroposterior region of the thalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Comparing solutions to the linear and nonlinear CFK equations for predicting COHb formation.

The Coburn, Forster, Kane model of COHb formation as a result of exposure to CO exists in two forms: the linear CFK equation that assumes a constant level of oxyhemoglobin; and the nonlinear CFK equation that allows the oxyhemoglobin level to vary with the carboxyhemoglobin level. Although both equations are currently used, no rigorous analysis exists to show under what conditions the two models determine substantially different solutions. This paper provides such an analysis and shows that the linear model may be used as a reasonable approximation over a much wider range of carboxyhemoglobin levels than had been supposed on physiological grounds.

Carbon Monoxide↗
PubMed1989

The role of spatial filtering in sensitivity regulation.

The role of spatial filtering in controlling sensitivity to increments is hard to evaluate under normal viewing conditions because eye movements lead to a confounding of spatial and temporal transients. We measured sensitivity to increments on different sized backgrounds in photopic and scotopic vision when the backgrounds were stabilized on the retina, thus eliminating temporal transients. The saturating effect of small fields on photopic thresholds was preserved under these conditions indicating that spatial filtering by retinal cells is critical in maintaining photopic sensitivity. Some effect of spatial pattern on sensitivity in stabilized vision was also observed in scotopic vision, although it was much smaller than was observed in photopic vision. The interaction effects between rod and cone systems that are observed with small backgrounds were also preserved in stabilized vision, implicating a very peripheral site for the generation of these interactions.

Adaptation, Ocular↗
PubMed1988

Development of a quick reference guide to accommodate vegetarianism in diet therapy for multiple disease conditions.

With more Americans adopting vegetarian lifestyles, health-care professionals will encounter more patients whose vegetarian dietary practices must be reconciled with the therapeutic diets required by a variety of disease conditions. The development of a quick reference guide was undertaken to address several areas of concern unique to vegetarian patients and provide an expandable clinical resource. For the disease conditions examined, nutrition care goals were found to be met without compromising vegetarian practices.

Chronic Disease↗
PubMed1985

Essentiality of a specific cellular terrain for growth of axons into a spinal cord lesion.

To date, there are no reports of growth of significant numbers of axons into or across a lesion of the mammalian spinal cord. However, recent studies showing that CNS axons will grow into PNS environments indicate that comparable growth into spinal cord lesions could be achieved if ischemic necrosis could be prevented and the lesion site repopulated by astrocytes and ependymal cells rather than by the macrophages, lymphocytes, and fibroblasts that generally accumulate at sites of CNS injury. To examine this possibility, we made a laminectomy at T5 in rats and crushed the spinal cord for 2 s with a smooth forceps (leaving the dura mater intact to prevent ingrowth of connective tissue). At 1 week, the lesion was filled with mononuclear cells, degenerating nerve fibers, and capillaries that were oriented parallel to the long axis of the spinal cord. By 2 weeks, longitudinally oriented cords of ependymal cells and astrocytes had migrated into the lesion from the adjacent spinal cord, and similarly oriented nerve fibers had begun to grow into the lesion along these capillaries and cellular cordons. The mononuclear cells had now assumed phagocytic activity and were engorged with myelin and other cellular debris. After 3 weeks, the astrocytes had elaborated thick cell processes. The nerve fibers in the lesion were still oriented longitudinally but had increased in number and were often arranged in small fascicles. These observations provide the first histological evidence of growth of nerve fibers into a lesion of the rat spinal cord. We conclude that the intrinsic regenerative capacity of the spinal cord can be expressed if ischemic necrosis and collagenous scarring are prevented and the spinal cord parenchyma is first reconstructed by its nonneuronal constituents.

Animals↗
PubMed1985

Enhancement of axonal growth into a spinal lesion by topical application of triethanolamine and cytosine arabinoside.

We have demonstrated that a brief compression lesion of the rat spinal cord produces axotomy with minimal necrosis or scarring and that axons grow into such a lesion along longitudinally oriented capillaries and similarly oriented cordons of ependymal cells and astrocytes. Inasmuch as extensive, oriented growth of axons into a spinal lesion is never seen after transection, concussion, or other models of spinal cord injury, this new surgical procedure appeared to be applicable to the in vivo testing of pharmacological agents designed to promote neuritic outgrowth. The spinal cord of anesthetized rats was crushed extradurally for 1 s with a smooth jeweler's forceps. After 2 days when edema had subsided, the animals were reoperated. The dura mater was opened, and a polyethylene tube was implanted so that one end was fastened over the injury site and the other end was exteriorized at the back of the neck. The lesion site was superfused with 0.1 ml of control or test solutions four times daily for 2 weeks and then the animals were anesthetized and killed by vascular perfusion with fixative. After decalcification, the vertebral column and spinal cord were embedded in paraffin and stained by several histologic procedures including the protargol silver impregnation method for nerve fibers. Treatment with triethanolamine and cytosine arabinoside, substances which promote neuritogenesis in cultured spinal ganglia of chick embryos, markedly stimulated the growth of axons into the lesion of the rat spinal cord. We conclude (i) that it is possible to pharmacologically enhance the intrinsic growth capacity of CNS neurons and (ii) that brief compression provides a type of injury that is well suited to the evaluation of treatments aimed at promoting axonal regeneration.

Animals↗
PubMed1979

Effect of reducing agents on oxidation-reduction potential and the outgrowth of Clostridium botulinum type E spores.

Oxidation-reduction potential (Eh) levels were measured and standardized to pH (Eh7) for Trypticase soy broth containing various concentrations of reducing agents. Prereduced Trypticase soy broth with no added reducing agents exhibited a potential of -141 mV. Ascorbic acid at 0.2 to 0.005% and sodium thioglycolate at concentrations below 0.05% produced an Eh7 higher than the prereduced Trypticase soy broth containing no added reducing agents. The addition of cysteine hydrochloride,2-mercaptoethanol, and sodium formaldehyde sulfoxylate to prereduced Trypticase soy broth resulted in a reduction of Eh7 compared to the system without added reducing agents. The order of relative reducing intensity (from highest to lowest) for the reducing agents when comparing molar concentration was: sodium formaldehyde sulfoxylate,2-mercaptoethanol, cysteine hydrochloride, sodium thioglycolate, and ascorbic acid. Optimal growth of the test organism occurred at low Eh7 and low concentration of the reducing agents. A direct correlation existed between growth of the test organism and -Eh7 x -log concentration of the reducing agent.

Anaerobiosis↗