Biomedical subjects
Publications and source records attributed to A R Tunturi.
A transverse section of the dorso-lateral white column and the white matter ventrally to the tip of the anterior horn at T-8 completely eliminated the hindlimb flexion response of the dog to an auditory command for a period of 2-5 years. The severed white matter was believed to contain the corticospinal, rubrospinal, lateral reticulospinal, and propriospinal tracts.
Longitudinal viscoelastic behavior of dog spinal cord was investigated by means of the stress-relaxation curve for various conditions. A 40-mm formalin-fixed piece showed little relaxation or relatively high elasticity. A freshly removed piece of cord displayed slightly longer relaxation at 5-20 degrees C than at 39-50 degrees C. The stress-relaxation curve for a 20-g load could be replicated several times with return to original length (viscous behavior). A 20-g load repeatedly applied before relaxation was complete or a 60-g load rapidly applied caused the 40-mm piece to elongate to twice its original length with no return to that length (plastic flow). The viscous coefficient was calculated for an average 20-g load at 39 degrees C from eta = epsilon tau = 3.54 x 10(7) poise. Histological examination of the tissue after rupture suggested that much of the viscoelasticity was due to glycosaminoglycans rather than axons.
The postural adjustments were studied in 3 unoperated dogs and 2 dogs with transection of the right lateral column of the spinal cord at T-9 for (1) quiet stance and (2) during right hindlimb (RH) flexion for an auditory command signal. The displacements of the center of gravity were measured with 4 force plates on which the dogs stood. For both groups of dogs, the center of gravity was concentrated in a small area (2 cm on a side). During hindlimb flexion, the unoperated dogs either slowly flexed the RH limb, shifting the center of gravity to the left, or forcefully extended the RH limb first to shift the weight across the RF-LH limb couple. The operated dogs failed to flex the RH limb but shifted the center of gravity to the left and slowly adducted the limb until it slid from the force plate. It was concluded that the lesion of the lateral column did not affect the postural adjustment.
The longitudinal elasticities of the dog spinal cord, pia, and denticulate ligaments were obtained by measuring the load-elongation curves. Both pia and denticulate ligaments were moderately elastic, but the spinal cord substance showed an upward curve, which indicated a predominantly viscous character. In situ, the spinal cord and pia were moderately strained. A 40-mm segment of the cord with dorsal and ventral roots severed and denticulate ligaments removed became 1 mm shorter when the cord and pia were transected at both ends. It was estimated that the cord and pia in situ were stressed by a force of 2 to 3 gm, the denticulate ligaments with 3 to 5 gm, and the dura with 50 to 70 gm. The elastic moduli of the spinal cord substance were 1.68 X 10(5) dynes/sq cm for loading between 5 and 10 gm and 1.19 X 10(5) dynes/sq cm between 30 and 35 gm.
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A new method has been developed for silver impregnation of neurons and myelinated axons in the cerebral cortex of the adult dog. By this method principal types of neurons including pyramidal, stellate, fusiform, horizontal neurons of Layer I, and special auditory neurons are colored black with a clear background, while myelinated fibers in the same piece of tissue are colored yellow. The yellow hue appears limited to the myelin sheath. Meyelinated axons of all sizes in the molecular layer, radial bundles, and deep tangential strata accept the stain. Comparison with data from other experiments indicates that osmium tetroxide inhibits the yellow staining of the myelinated axons, and that formaldehyde promotes such staining in conjunction with ammonium ions and sucrose.
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