Search PubMed⌕ Search

Biomedical subjects

V Sahai

Publications and source records attributed to V Sahai.

At least 19 recordsLinked to original sources
PubMed2005

Vibrotactile frequency discrimination in human hairy skin.

The human capacity for vibrotactile frequency discrimination has been compared directly for glabrous and hairy skin regions by means of a two-alternative, forced-choice psychophysical procedure in five subjects. Sinusoidal vibratory stimuli, delivered by means of a 4-mm-diam probe, were first used to obtain detection threshold values for the two skin sites, the finger tip and the dorsal forearm, at four standard frequencies, 20, 50, 100, and 200 Hz. Values confirmed previous results showing detection thresholds were markedly higher on hairy skin than on glabrous skin. For the discrimination task, each standard frequency, at an amplitude four times detection threshold, was paired with a series of comparison frequencies, and discrimination capacity then was quantified by deriving from psychometric function curves, measures of the discriminable frequency increment (Deltaf) and the Weber Fraction (Deltaf/f), which, when plotted as a function of the four standard frequencies, revealed similar capacities for frequency discrimination at the two skin sites at the standard frequencies of 20, 100, and 200 Hz but an equivocal difference at 50 Hz. Cutaneous local anesthesia produced a marked impairment in vibrotactile detection and discrimination at the low standard frequencies of 20 and 50 Hz but little effect at higher frequencies. In summary, the results reveal, first, a striking similarity in vibrotactile discriminative performance in hairy and glabrous skin despite marked differences in detection thresholds for the two sites, and, second, the results confirm that vibrotactile detection and discrimination in hairy skin depend on superficial receptors at low frequencies but depend on deep, probably Pacinian corpuscle, receptors for high frequencies.

Discrimination Learning↗
PubMed2005

Vibrotactile coding capacities of spinocervical tract neurons in the cat.

The response characteristics and tactile coding capacities of individual dorsal horn neurons, in particular, those of the spinocervical tract (SCT), have been examined in the anesthetized cat. Twenty one of 38 neurons studied were confirmed SCT neurons based on antidromic activation procedures. All had tactile receptive fields on the hairy skin of the hindlimb. Most (29/38) could also be activated transynaptically by electrical stimulation of the cervical dorsal columns, suggesting that a common set of tactile primary afferent fibers may provide the input for both the dorsal column-lemniscal pathway and for parallel ascending pathways, such as the SCT. All but 3 of the 38 neurons studied displayed a pure dynamic sensitivity to controlled tactile stimuli but were unable to sustain their responsiveness throughout 1s trains of vibration at vibration frequencies exceeding 5-10 Hz. Stimulus-response relations revealed a very limited capacity of individual SCT neurons to signal, in a graded way, the intensity parameter of the vibrotactile stimulus. Furthermore, because of their inability to respond on a cycle-by-cycle pattern at vibration frequencies >5-10 Hz, these neurons were unable to provide any useful signal of vibration frequency beyond the very narrow bandwidth of approximately 5-10 Hz. Similar limitations were observed in the responsiveness of these neurons to repetitive forms of antidromic and transynaptic inputs generated by electrical stimulation of the spinal cord. In summary, the observed limitations on the vibrotactile bandwidth of SCT neurons and on the precision and fidelity of their temporal signaling, suggest that SCT neurons could serve as little more than coarse event detectors in tactile sensibility, in contrast to DCN neurons the bandwidth of vibrotactile responsiveness of which may extend beyond 400 Hz and is therefore broader by approximately 40-50 times than that of SCT neurons.

Action Potentials↗
PubMed2005

Processing of vibrotactile inputs from hairy skin by neurons of the dorsal column nuclei in the cat.

The capacity of single neurons of the dorsal column nuclei (DCN) for coding vibrotactile information from the hairy skin has been investigated in anesthetized cats to permit quantitative comparison first with the capacities of DCN neurons responding to glabrous skin vibrotactile inputs and second with those of spinocervical tract neurons responding to vibrotactile inputs from hairy skin. Dynamically sensitive tactile neurons of the DCN the input of which came from hairy skin could be divided into two classes, one associated with hair follicle afferent (HFA) input, the other with Pacinian corpuscle (PC) input. The HFA-related class was most sensitive to low-frequency (<50 Hz) vibration and had a graded response output as a function of vibrotactile intensity changes. PC-related neurons had a broader vibrotactile sensitivity, extending to > or =300 Hz and appeared to derive their input from the margins of hairy skin, near the footpads, or from deeper PC sources such as the interosseous membranes or joints. HFA-related neurons had phaselocked responses to vibration frequencies up to approximately 75 Hz, whereas PC neurons retained this capacity up to frequencies of approximately 300 Hz with tightest phaselocking between 50 and 200 Hz. Quantitative measures of phaselocking revealed that the HFA-related neurons provide the better signal of vibrotactile frequency up to approximately 50 Hz with a switch-over to the PC-related neurons above that value. In conclusion, the functional capacities of these two classes of cuneate neuron appear to account for behavioral vibrotactile frequency discriminative performance in hairy skin, in contrast to the limited capacities of vibrotactile-sensitive neurons within the spinocervical tract system.

Action Potentials↗
PubMed2004

Compactin-a review.

Compactin, a hypocholesterolemic molecule, is a competitive inhibitor of 3-hydroxy-3-methyl-glutaryl (HMG)-CoA reductase, which is a regulatory enzyme for cholesterol biosynthesis. The structural similarity and high affinity of the acid form of compactin and HMG, the natural substrate of enzyme, results in specific and effective inhibition of this enzyme. Inhibition results in reduced levels of mevalonic acid in the body, leading to pleiotropic effects. Various fungi have been used for the commercial production of compactin. Using different strategies for improving production levels, yields have been increased to around 900 times of the amount originally produced. Recently, the gene sequence responsible for compactin production has been cloned and sequenced. This review deals with the chemistry, mode of action, pharmacology, biosynthesis, and production of compactin. A comparative study of various reports dealing with the production of compactin is also included.

Anticholesteremic Agents↗
PubMed2003

Tactile neural mechanisms in monotremes.

Monotremes, perhaps more than any other order of mammals, display an enormous behavioural reliance upon the tactile senses. In the platypus, Ornithorhynchus anatinus, this is manifest most strikingly in the special importance of the bill as a peripheral sensory organ, an importance confirmed by electrophysiological mapping that reveals a vast area of the cerebral cortex allocated to the processing of tactile inputs from the bill. Although behavioural evidence in the echidna, Tachyglossus aculeatus, suggests a similar prominence for tactile inputs from the snout, there is also a great reliance upon the distal limbs for digging and burrowing activity, pointing to the importance of tactile information from these regions for the echidna. In recent studies, we have investigated the peripheral tactile neural mechanisms in the forepaw of the echidna to establish the extent of correspondence or divergence that has emerged over the widely different evolutionary paths taken by monotreme and placental mammals. Electrophysiological recordings were made from single tactile sensory nerve fibres isolated in fine strands of the median or ulnar nerves of the forearm. Controlled tactile stimuli applied to the forepaw glabrous skin permitted an initial classification of tactile sensory fibres into two broad divisions, according to their responses to static skin displacement. One displayed slowly adapting (SA) response properties, while the other showed a selective sensitivity to the dynamic components of the skin displacement. These purely dynamically-sensitive tactile fibres could be subdivided according to vibrotactile sensitivity and receptive field characteristics into a rapidly adapting (RA) class, sensitive to low frequency (</=50 Hz) vibration and another class, sensitive to a broader range of vibrotactile frequencies (approx. 50-300 Hz). The differential tactile sensitivity of the three principal fibre classes and their individual coding characteristics, determined by quantitative stimulus-response analysis, indicate first, that this triad of fibre classes can subserve high-acuity tactile signalling from the echidna footpad and second, that peripheral tactile sensory mechanisms are highly conserved across evolutionarily-divergent mammalian orders.

Animals↗
PubMed2002

Statistical medium optimization and production of a hyperthermostable lipase from Burkholderia cepacia in a bioreactor.

AIM: Statistical medium optimization for maximum production of a hyperthermostable lipase from Burkholderia cepacia and its validation in a bioreactor. METHODS AND RESULTS: Burkholderia cepacia was grown in shake flasks containing 1% glucose, 0.1% KH2PO4, 0.5% NH4Cl, 0.24% (NH4)2HPO4, 0.01% MgSO4.7H2O and 1% emulsified palm oil, at 45 degrees C and pH 7.0, agitated at 250 rev min(-1) with 6-h-old inoculum (2% v/v) for 20 h. A fourfold enhancement in lipase production (50 U ml(-1)) and an approximately three fold increase in specific activity (160 U mg(-1)) by B. cepacia was obtained in a 14 litre bioreactor within 15 h after statistical optimization following shake flask culture. The statistical model was obtained using face centred central composite design (FCCCD) with five variables: glucose, palm oil, incubation time, inoculum density and agitation. The model suggested no interactive effect of the five factors, although incubation period, inoculum and carbon concentration were the important variables. CONCLUSIONS: The maximum lipase production was 50 U ml(-1), with specific activity 160 U mg(-1) protein, in a 14 litre bioreactor after 15 h in a medium obtained after statistical optimization in shake flasks. Further, the model predicted reduction in time for lipase production with reduction in total carbon supply. SIGNIFICANCE AND IMPACT OF THE STUDY: Statistical optimization allows quick optimization of a large number of variables. It also provides a deep insight into the regulatory role of various parameters involved in enzyme production.

Bacterial Proteins↗
PubMed2001

Enhanced expression of the recombinant lethal factor of Bacillus anthracis by Fed-Batch culture.

High cell density cultivation has been one of the most effective ways to increase cell as well as the product yields. The structural gene for the 90-kDa lethal factor (LF) isolated from Bacillus anthracis was expressed as fusion protein with 6x histidine residues under the transcriptional regulation of the T5 promoter in Escherichia coli. Various strategies were tried to scale up the expression of the recombinant lethal factor by bioprocess optimization using fed batch culture technique in a 14 litre fermentor. The media, a defined mixture of salts, trace elements, vitamins, etc. along with a specified carbon source was used for the growth. The pH of the media was maintained at 6.8 while the temperature was changed from 37 to 28 degrees C during the cultivation. During the growth and induction phases, the DO was maintained above 20% by automatic control of agitation. The specific growth rate was controlled by utilizing an exponential feeding profile determined from mass balance equations. As a result of control of specific growth rate at two different levels, there was about twenty five fold increase in biomass compared to the biomass in the shake flask. E. coli cells yielded a soluble cytosolic protein with an apparent molecular mass of 90 kDa. The protein was purified to homogeneity using metal chelate affinity chromatography, followed by anion exchange on FPLC using Mono-Q column. In solution, trypsin cleaved protective antigen bound to native and recombinant LF with comparable affinity. The recombinant LF resembled the LF purified from B. anthracis in the macrophage lysis assay, using a murine macrophage cell line J774A.1 sensitive to anthrax toxin. It was possible to achieve a yield of 50 mg of the purified protein from 1 litre culture broth.

Antigens, Bacterial↗
PubMed2001

Optimization of xylanase production by Melanocarpus albomyces IIS68 in solid state fermentation using response surface methodology.

Xylanase production by the thermophilic fungus, Melanocarpus albomyces IIS68, during solid state fermentation of wheat straw was studied and the effects of various variables were observed. Using the response surface methodology and the multivariant statistical approach, the optimum levels of the variables affecting xylanase production were determined. The optimum levels of the variables were 600-850 microm particle size, 43 h inoculum age, 1.37% Tween 80, 86% initial moisture content, 5.1% urea, 0.74% yeast extract and a harvest time of 96 h. Under these optimized conditions, xylanase activity of 7760 U/g initial dry substrate was obtained which was in very good agreement with the value predicted by the quadratic model (7890 U/g initial dry substrate).

Journal Article↗
PubMed2000

Task related changes in ERP auditory vs visual tasks.

P3 component of event related potentials have been studied in relaxed state of mind. Changes in P3 latency and amplitude are expected if measured after a rigorous mental exercise. The event related potentials (ERP) were measured in 20 normal male subjects aged between 18 and 22 years. ERP was recorded twice in each subject before and after the administration of a mental task. The auditory mental task comprised of repeating in reverse order string of random digits read out to the subject at a uniform speed of 1 per second. The visual task comprised reading laterally inverted type written text. Each subject had to undergo 2 sessions in separate sittings. The latency and amplitude of P300 recorded before and after the task were compared statistically using Students' unpaired t-test. There was significant increase in P3 latency following both visual and auditory tasks (auditory task: before 330 +/- 24.43 msec and after 342.9 +/- 27.66 msec, similarly visual task: before 333.2 +/- 26.66 msec and after 345.65 +/- 26.56 msec). All other ERP waves latency and amplitude changes were insignificant.

Acoustic Stimulation↗
PubMed2000

Task related changes in contingent negative variation (CNV) response of endogenous evoked potentials.

Contingent negative variation (CNV) is a slow negative cortical potential shift, which occurs during a warned foreperiod reaction time paradigm. Most studies of evoked potentials have concentrated on components occurring during the first 300 msec, although there are important and recordable aspects of signal processing occurring well beyond 300 msec e.g. late negative slow wave. CNV has proven sensitive to a number of psychological variables, none of which can yet be singled out as a definitive or exclusive correlate. Changes are expected if measured after a rigorous mental exercise. CNV was measured in 20 normal male subjects aged between 18 and 20 years. CNV was recorded twice in each subject before and after the administration of a mental task. The auditory mental task comprised repeating in reverse order string of random digits read out to the subject at a uniform speed of 1 per second. The visual mental task comprised reading laterally inverted type written text. Each subject had to undergo 2 sessions in separate sittings. The latency and amplitude of waves N1, P3, orientation (O), expectancy (E), CNV, reaction time (RT) were recorded. These values recorded before and after the task were compared statistically using student's unpaired t-test. The significant latencies recorded before and after the auditory task were, N1: 88.00 +/- 11.96 and 100.00 +/- 21.52 msec, P3: 289.00 +/- 54.85 and 299.00 +/- 52.91 msec, reaction time (RT): 102 +/- 17.05 msec and 123 +/- 17.5 msec, and in case of visual task, N1: 88 +/- 13.16 msec and 99.00 +/- 16.51 msec, reaction time (RT): 107 +/- 11.74 msec and 127 +/- 13.42 msec respectively. All other CNV wave latencies and amplitude changes were insignificant. Hence task effects sensory perception as reflected by increased latency of the long latency response N1 and the cortical integrative processes resulting in increased reaction time.

Adolescent↗
PubMed1994

Evaluation of biomass.

Evaluation of biomass concentration is an important problem encountered in many microbial and other bioprocesses. It determines the catalytic activity of the microbial cell in a given time. Various direct and indirect methods for the estimation of biomass have been developed using physical and biochemical techniques. Despite many promising classical methods available, the evaluation of microbial growth in bioprocesses may sometimes become laborious, impracticable and give erroneous values. Various methods for enumeration of organisms and determination of biomass, including recent developments in monitoring biomass concentration for the control of biotechnological processes, are discussed taking into the consideration their practical importance, usefulness and constraints in application.

Biotechnology↗
PubMed1979

Production of cellulases by Trichoderma reesei QM 9414 in fed-batch and continuous-flow culture with cell recycle.

The scope in improving enzyme productivities from the cellulose fermentation process is examined in laboratory-scale fermentors. The maximum productivity (30 IU/liter hr) is attained in a continuous-culture process with cell recycle using modified medium containing 0.5% cellulose. Optimum dilution rate and recycle ratio are determined as 0.025 hr-1 and 1.2, respectively, for the process. The system is analyzed and steady-state equations for predicting enzyme protein concentrations in the fermentor are developed. In fed-batch cultures, slow addition of cellulose at high concentrations can improve enzyme productivity by as much as 33% over a batch process. The scope and results of using modified medium for cellulase production are also presented.

Cellulase↗
PubMedDate not supplied

Mechanosensory perception: are there contributions from bone-associated receptors?

1. The identity of the receptors and afferent nerve fibres that mediate the sense of touch varies somewhat with body location. Those that have been most intensively characterized are associated with the distal glabrous skin of the limbs and, in primates, mediate the sense of touch in the fingertips and palms. In this glabrous skin region, there appear to be three or four principal classes of tactile sensory nerves that fall into two broad groups. One group, the so-called slowly adapting (SA) receptors and afferent fibres, is responsive to static mechanical displacement of skin tissues and is made up of two classes, the type I (SAI) fibres that innervate Merkel receptors and the type II (SAII) fibres that innervate Ruffini endings. The second broad group displays a pure dynamic sensitivity to tactile stimuli and also falls into two principal classes, the rapidly adapting (RA) tactile fibres that are associated with Meissner corpuscle receptors and the Pacinian corpuscle (PC)-associated class of tactile afferent fibres. 2. In other regions of the skin, such as the hairy skin of the arms, legs and trunk, there are similar functional classes of tactile sensory nerves, although the receptor endings differ somewhat from those of the glabrous skin. 3. Receptors in close association with the long bones of the limbs include groups of Pacinian corpuscles distributed along the interosseous membranes. These are highly sensitive to dynamic forms of mechanical stimuli, in particular vibrotactile disturbances. However, despite their close association with bone, these receptors probably cannot be legitimately considered 'osseoreceptors'. 4. Both the periosteum and the bone marrow are richly supplied by nerve fibres. However, much evidence indicates that these are largely or entirely in the fine-diameter category of nerve fibres, whose roles may be confined to either nociception or to the efferent autonomic regulation of bone-associated blood vessels. 5. In conclusion, it remains uncertain whether any aspects of our innocuous touch or kinaesthetic senses, in either the limbs or in orofacial regions, can be ascribed to 'osseoreceptors' located in the periosteum or within the bone marrow itself.

Animals↗