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S C Rao

Publications and source records attributed to S C Rao.

At least 19 recordsLinked to original sources
PubMed1999

Prospective coding for objects in primate prefrontal cortex.

We examined neural activity in prefrontal (PF) cortex of monkeys performing a delayed paired associate task. Monkeys were cued with a sample object. Then, after a delay, a test object was presented. If the test object was the object associated with the sample during training (i.e., its target), they had to release a lever. Monkeys could bridge the delay by remembering the sample (a sensory-related code) and/or thinking ahead to the expected target (a prospective code). Examination of the monkeys' behavior suggested that they were relying on a prospective code. During and shortly after sample presentation, neural activity in the lateral PF cortex primarily reflected the sample. Toward the end of the delay, however, PF activity began to reflect the anticipated target, which indicated a prospective code. These results provide further confirmation that PF cortex does not simply buffer incoming visual inputs, but instead selectively processes information relevant to current behavioral demands, even when this information must be recalled from long-term memory.

Action Potentials↗
PubMed1999

The optimal radiologic method for assessing spinal canal compromise and cord compression in patients with cervical spinal cord injury. Part I: An evidence-based analysis of the published literature.

STUDY DESIGN: An evidence-based analysis of published radiologic criteria for assessing spinal canal compromise and cord compression in patients with acute cervical spinal cord injury. OBJECTIVES: This study was conducted to determine whether literature-based guidelines could be established for accurate and objective assessment of spinal canal compromise and spinal cord compression after cervical spinal cord injury. SUMMARY OF BACKGROUND DATA: Before conducting multicenter trials to determine the efficacy of surgical decompression in cervical spinal cord injury, reliable and objective radiographic criteria to define and quantify spinal cord compression must be established. METHODS: A computer-based search of the published English, German, and French language literature from 1966 through 1997 was performed using MEDLINE (U.S. National Library of Medicine database) to identify studies in which cervical spinal canal and cord size were radiographically assessed in a quantitative manner. Thirty-seven references were included for critical analysis. RESULTS: Most studies dealt with degenerative disease, spondylosis, and stenosis; only 13 included patients with acute cervical spinal cord injury. Standard lateral radiographs were the most frequent imaging method used (23 studies). T1- and T2-weighted magnetic resonance imaging were used to assess spinal cord compression in only 7 and 4 studies, respectively. Spinal cord size or compression were not precisely measured in any of the cervical trauma studies. Interobserver or intraobserver reliability of the radiologic measurements was assessed in only 7 (19%) of the 37 studies. CONCLUSIONS: To date, there are few quantitative, reliable radiologic outcome measures for assessing spinal canal compromise or cord compression in patients with acute cervical spinal cord injury.

Cervical Vertebrae↗
PubMed1999

The optimal radiologic method for assessing spinal canal compromise and cord compression in patients with cervical spinal cord injury. Part II: Results of a multicenter study.

STUDY DESIGN: A multicenter, retrospective study using computed tomographic and magnetic resonance imaging data to establish quantitative, reliable criteria of canal compromise and cord compression in patients with cervical spinal cord injury. OBJECTIVES: To develop and validate a radiologic assessment tool of spinal canal compromise and cord compression in cervical spinal cord injury for use in clinical trials. SUMMARY OF BACKGROUND DATA: There are few quantitative, reliable criteria for radiologic measurement of cervical spinal canal compromise or cord compression after acute spinal cord injury. METHODS: The study included 71 patients (55 men, 16 women; mean age, 39.7 +/- 18.7 years) with acute cervical spinal cord injury. Causes of spinal cord injury included motor vehicle accidents (n = 36), falls (n = 20), water-related injuries (n = 8), sports (n = 5), assault (n = 1), and farm accidents (n = 1). Canal compromise was measured on computed tomographic scan and T1- and T2-weighted magnetic resonance imaging, and cord compression at the level of maximum injury was measured on T1- and T2-weighted magnetic resonance imaging. All films were assessed by two independent observers. RESULTS: There was a strong correlation of canal compromise and/or cord compression measurements between axial and midsagittal computed tomography, and between axial and midsagittal T2-weighted magnetic resonance imaging. Spinal canal compromise assessed by computed tomography showed a significant although moderate correlation with spinal cord compression assessed by T1- and T2-weighted magnetic resonance imaging. Virtually all patients with canal compromise of 25% or more on computed tomographic scan had evidence of some degree of cord compression on magnetic resonance imaging, but a large number of patients with less than 25% canal compromise on computed tomographic scan also had evidence on magnetic resonance imaging of cord compression. CONCLUSIONS: In patients with cervical spinal cord injury, the midsagittal T1- and T2-weighted magnetic resonance imaging provides an objective, quantifiable, and reliable assessment of spinal cord compression that cannot be adequately assessed by computed tomography alone.

Adolescent↗
PubMed1998

Modulation of calcium by inhibitory systems in the developing auditory midbrain.

Inhibitory synaptic transmission is of fundamental importance during the maturation of central auditory circuits, and their subsequent ability to process acoustic information. The present study investigated the manner in which inhibitory transmission regulates intracellular free calcium levels in the gerbil inferior colliculus using a brain slice preparation. Inhibitory and excitatory postsynaptic potentials were evoked by electrical stimulation of the ascending afferents at the level of the dorsal nucleus of the lateral lemniscus. Pharmacologically isolated inhibitory synaptic potentials were able to attenuate a calcium rise in collicular neurons that was generated by depolarizing current injection. In addition, GABA(A) and glycine receptor antagonists typically led to an increase of calcium in collicular neurons during electrical stimulation of the ascending afferent pathway at the level of the dorsal nucleus of the lateral lemniscus. Bath application of GABA or muscimol, a GABA(A) receptor agonist, evoked a brief hyperpolarization followed by a long-lasting depolarization in inferior colliculus neurons. This treatment also induced a transient calcium increase that correlated with the membrane depolarization phase. Baclofen, a GABA(B) receptor agonist, had no effect on either membrane potential or calcium levels. Ratiometric measures indicated that the muscimol-evoked rise in calcium was approximately 150 nM above basal levels. The muscimol-evoked responses were completely antagonized by bicuculline and attenuated by picrotoxin. Together, these results suggest that inhibitory synaptic transmission participates in the regulation of postsynaptic calcium during the developmental period. Inhibitory transmission may attenuate a calcium influx that is evoked by excitatory synapses, but it can also produce a modest influx of calcium when activated alone. These mechanisms may help to explain the influence of inhibitory transmission on the development of postsynaptic properties.

2-Amino-5-phosphonovalerate↗
PubMed1997

Optically imaged maps of orientation preference in primary visual cortex of cats and ferrets.

Feature maps in the cerebral cortex constitute orderly representations of response features created within the cortex; an example is the mapping of orientation-selective neurons in visual cortex. We have compared the properties of orientation maps in area 17 of cats and ferrets, obtained by optical imaging of intrinsic signals. Orientation maps in both species contain a quasi-periodic distribution of iso-orientation domains that are organized into a lattice of pinwheels. However, the spatial density of orientation domains and of pinwheels in ferret area 17 is nearly twice that in cat area 17. The ferret map also contains more discontinuities, or fractures, where orientation changes abruptly. The size of orientation domains scales with interdomain spacing, so that the ratio of the two is approximately the same in both species. Consistent with this finding, the orientation tuning width of individual pixels is similar in the two. The magnitude of orientation preference, however, is much lower in ferret compared to cat. The greater incidence of fractures in ferret appears to be due to proportionately greater overlap between domains of different orientations, particularly along fracture lines that link pinwheel centers. We hypothesize that a key determinant of orientation maps, the relationship between orientation domain size and spacing, expresses an anatomical link between sizes of thalamocortical arbors and horizontal intracortical connections in area 17.

Animals↗
PubMed1997

Integration of what and where in the primate prefrontal cortex.

The visual system separates processing of an object's form and color ("what") from its spatial location ("where"). In order to direct action to objects, the identity and location of those objects must somehow be integrated. To examine whether this process occurs within the prefrontal (PF) cortex, the activity of 195 PF neurons was recorded during a task that engaged both what and where working memory. Some neurons showed either object-tuned (what) or location-tuned (where) delay activity. However, over half (52 percent, or 64/123) of the PF neurons with delay activity showed both what and where tuning. These neurons may contribute to the linking of object information with the spatial information needed to guide behavior.

Animals↗
PubMed1997

Integration of local inputs in visual cortex.

In mammalian visual cortex, local connections are ubiquitous, extensively linking adjacent neurons of all types. In this study, optical maps of intrinsic signals and responses from single neurons were obtained from the same region of cat visual cortex while the effectiveness of the local cortical circuitry was altered by focally disinhibiting neurons within a column of known orientation preference. Maps of intrinsic signals indicated that local connections provide strong and functional subthreshold inputs to neighboring columns of other orientation preferences, altering the observed orientation preference to that of the disinhibited column. However, measuring the suprathreshold response using single-cell recordings revealed only mild changes of preferred orientation over the affected region. Because strongly tuned subthreshold inputs from cortex only marginally affect the tuning of a cortical cell's output, it is concluded that local cortical inputs are integrated weakly compared to geniculate inputs. Such circuitry potentially allows for the normalization of responses across a wide range of input activity through local averaging.

Animals↗
PubMed1996

Orientation maps of subjective contours in visual cortex.

Responses to subjective contours in visual cortical areas V1 and V2 in adult cats were investigated by optical imaging of intrinsic signals and single-unit recording. Both V1 and V2 contain maps of the orientation of subjective gratings that have their basis in specific kinds of neuronal responses to subjective orientations. A greater proportion of neurons in V2 than in V1 show a robust response to subjective edges. Through the use of subjective stimuli in which the orientation of the luminance component is invariant, an unmasked V1 response to subjective edges alone can be demonstrated. The data indicate that the processing of subjective contours begins as early as V1 and continues progressively in higher cortical areas.

Animals↗
PubMed1996

Subthreshold facilitation and suppression in primary visual cortex revealed by intrinsic signal imaging.

Neurons in primary visual cortex (area 17) respond vigorously to oriented stimuli within their receptive fields; however, stimuli presented outside the suprathreshold receptive field can also influence their responses. Here we describe a fundamental feature of the spatial interaction between suprathreshold center and subthreshold surround. By optical imaging of intrinsic signals in area 17 in response to a stimulus border, we show that a given stimulus generates activity primarily in iso-orientation domains, which extend for several millimeters across the cortical surface in a manner consistent with the architecture of long-range horizontal connections in area 17. By mapping the receptive fields of single neurons and imaging responses from the same cortex to stimuli that include or exclude the aggregate suprathreshold receptive field, we show that intrinsic signals strongly reveal the subthreshold surround contribution. Optical imaging and single-unit recording both demonstrate that the relative contrast of center and surround stimuli regulates whether surround interactions are facilitative or suppressive: the same surround stimulus facilitates responses when center contrast is low, but suppresses responses when center contrast is high. Such spatial interactions in area 17 are ideally suited to contribute to phenomena commonly regarded as part of "higher-level" visual processing, such as perceptual "popout" and "filling-in."

Animals↗
PubMed1994

Red edge excitation shifts of crystallins and intact lenses. A study of segmental mobility and inter-protein interactions.

The shift that occurs in the fluorescence emission wavelength upon changing the excitation wavelength towards the red edge of the absorption band is termed red edge excitation shift (REES). We have monitored the REES of intrinsic protein fluorescence of freshly isolated intact lenses, of individual crystallins in their native, denatured and photodamaged states and also of crystallin mixtures. The observed REES values for the lenses from different species are different suggesting that the mobilities and packing of the crystallins may vary with the species. Lens photodamage in all the cases resulted in an increase of REES. Denaturation of crystallins in solution reduces REES and renaturation restores it. Mixtures of alpha- and beta-crystallins prepared either by directly mixing equimolar solutions or mixing them in 4 M urea followed by dialysis (reconstituting) gave similar REES values indicating the absence of any specific interactions in dilute solutions. Possible existence of induced alterations facilitating inter-crystallin interactions at high protein concentration is suggested.

Animals↗
PubMed1991

The IVBF dual-blade plate and its applications.

A recently developed simple device, the intervertebral body fixation dual-blade plate, was used in 88 cases of different spinal disorders. This patients in the first series were operated on from 1984 to 1986. The device is biomechanically simple and its application safe and easy. Using a proper bone grafting technique, it is a reliable device to establish spinal stability in spine surgery through an anterior approach. Its application in cases of fractures and fracture-dislocations of the thoracolumbar spine with paraplegia, tuberculous spondylitis, and primary tumors of vertebral bodies is presented. The midterm results, covering a follow-up period of 24-49 months (mean, 32 months) were satisfactory; there were no serious complications directly related to the device. There were four cases of pseudarthrosis due to insufficient bone graft technique. Of these, there were three cases of failure of the dual-blade plate.

Adult↗
PubMed1990

The conformational status of a protein influences the aerobic photolysis of its tryptophan residues: melittin, beta-lactoglobulin and the crystallins.

We have studied the aerobic photolysis of the tryptophan residues of the proteins melittin and beta-lactoglobulin when the proteins are in ordered conformations and when they are in randomly coiled states. The results suggest that the conformational status of the protein is a factor that influences the photolysis of the constituent tryptophan residues. This point appears to be of relevance to the photo-oxidation of the tryptophan residues of the eye lens proteins crystallins.

Aerobiosis↗
PubMed1989

Binding site conformation dictates the color of the dye stains-all. A study of the binding of this dye to the eye lens proteins crystallins.

The interaction of the cationic carbocyanine dye Stains-all (1-ethyl-2-[3-(1-ethyl-naphthol[1,2-d]thiazolin-2-ylidene)-2- methylpropenyl]naphthol[1,2-d]thiazolium bromide) with the eye lens proteins crystallins has been studied. alpha- and gamma-crystallins do not bind the dye, while beta- and delta-crystallins do, consistent with the fact that the latter two proteins bind the calcium ion. beta-Crystallin resembles parvalbumin in that it induces only the J-band of the bound dye. delta-crystallin, on the other hand, induces only the gamma-band. Analysis of the metachromasia induced in the dye by these and other proteins suggests that Stains-all is responsive to the conformational status of the region to which it binds in a protein. The J-band of the dye is activated when it binds to a globular domain, and the gamma-band is activated when it binds to a helical stretch of the protein.

Animals↗
PubMed1989

Calcium ion binding to delta- and to beta-crystallins. The presence of the "EF-hand" motif in delta-crystallin that aids in calcium ion binding.

Abnormal levels of endogenous calcium ions are known to induce eye lens opacity, and a variety of causative factors has been proposed, including calcium-mediated aggregation and precipitation of the lens proteins crystallins. We have specifically looked in some detail at the interaction of Ca2+ with various crystallins and its consequences. Lenses incubated in solutions containing 10 mM Ca2+ or 5 mM Tb3+ opacified. Fluorescence titration of crystallins with TbCl3 revealed that this ion binds to delta- and beta-crystallins in solution. Equilibrium dialysis showed that four Ca2+ ions bind to one delta-crystallin tetramer with an affinity of 4.3 x 10(3) M-1. Analysis of the amino acid sequence of delta-crystallin reveals the presence of a calmodulin-type "helix-loop-helix" or "EF-hand" calcium ion binding conformational motif in the region comprising residues 300-350. This is a novel feature of the molecule not reported so far. No other crystallins appear to have this motif. beta-Crystallin also binds four Ca2+ ions/aggregate unit of mass 160 kDa, with an affinity of 2.6 x 10(3) M-1, presumably in the midregion of the molecule that is rich in anionic and polar residues. Circular dichroism spectroscopy shows that the binding of calcium ion leads to subtle conformational changes in the molecules, notably in the tertiary structure.

Amino Acid Sequence↗
PubMed1989

Red edge excitation effect in intact eye lens.

Shift in the wavelength of emission upon shift in the excitation wavelength towards the red edge of the absorption band is termed Red Edge Excitation Shift (REES). This effect is observed only in situation where the fluorophore mobility with respect to the surrounding matrix is considerably reduced. We have observed such red edge excitation effect in the intact eye lens. The REES observed for a normal lens is different from that seen in a photodamaged lens and hence appears to be a potential tool to monitor the changes in the state of the lens. Photodamage experiments with tryptophan in polyethylene glycol (PEG) and intact eye lens indicate that the red edge photon can also cause photodamage.

Animals↗
PubMed1988

Is vidian neurectomy worthwhile?

Vasomotor rhinitis is a frustrating experience both for the consultant and for the patient. The purpose of vidian neurectomy is to destroy the secretomotor nerve supply to the nasal mucosa, the main indication being severe intractable non-atopic vasomotor rhinitis. A review of 208 cases which have undergone transnasal vidian neurectomy by diathermy coagulation in the last five years is presented. The operation has proved worthwhile, the patients remaining symptom-free in 92 per cent of cases (longest follow-up 5 years). There have been no complications.

Adolescent↗
PubMed1988

Processed oat hulls as potential dietary fiber sources in rats.

Processed oat hull products were evaluated as potential dietary fiber sources. Three levels, 5, 10 and 15%, of processed oat hulls, bleached oat hulls or oat hulls coated with starch, were added to purified diets and fed to groups of rats for 6 wk. Control diets consisted of 5, 10 or 15% alpha-cellulose or commercial nonpurified diet. None of the oat hull products at the three levels tested had any negative effect on rat growth. Fresh and dry fecal weights increased linearly as the concentration of dietary fiber increased and were highly correlated with fiber intake (r = 0.95). Apparent digestibility of neutral detergent fiber in all diets was low and apparent calcium absorption was not consistently affected by any diet. None of the oat hull test diets lowered plasma or hepatic cholesterol levels, a finding consistent with the failure to detect mixed-linkage beta-glucans in any of the processed oat hull products. Detailed analysis of the processed oat hull fibers also indicated that they were greater than 95% insoluble fiber and high in cellulose and xylans. Light-microscopy histology of kidney, spleen, pancreas, stomach, duodenum, ileum and colon was normal. The extent of hepatocellular destruction produced by the cholesterol (1%) and cholic acid (0.2%) added to the diet to induce hypocholesterolemia was independent of the kind and amount of dietary fiber.

Absorption↗