Biomedical subjects

K V Gopal

Publications and source records attributed to K V Gopal.

10 recordsLinked to original sources

PubMed2001

The I' potential of the human auditory brainstem response to paired click stimuli.

When stimulated with an appropriate stimulus, the hair cells of the organ of Corti depolarize, causing the release of a neurotransmitter substance, which excites afferent VIIIth nerve dendrites. It is reasonable to hypothesize that excitatory postsynaptic potentials (EPSPs) generated by the dendrites of the auditory nerve in turn initiate a compound action potential (CAP). The EPSP is thought to be the generator potential for the CAP, and may be recorded in auditory brainstem responses (ABRs) as the I' potential. Determining the anatomical origin of I' may enhance the sensitivity of the ABR technique in hair cell/dendrite/auditory nerve evaluations. Whether I' is of sensory or of neural origin is equivocal, and therefore I' is not well understood. To investigate this dilemma, ABRs were recorded from human subjects using standard and paired-click stimuli, and using subtraction methods to generate a derived ABR. Two early peaks, designated as I degree and I', occurred before wave I in the derived ABR. It was hypothesized that peaks I degrees and I' represent the summating potential and the generator potential, generated by the cochlea and VIIIth nerve dendrites, respectively.

Acoustic Stimulation↗

PubMed2000

Effects of selective serotonin reuptake inhibitors on auditory processing: case study.

Auditory sensitivity and processing ability were evaluated in a patient who suffered from hyperacusis, difficulty understanding speech, withdrawn depression, lethargy, and hypersensitivity to touch, pressure, and light. Treatment with fluvoxamine and fluoxetine (selective serotonin reuptake inhibitors) reversibly alleviated complaints. Testing while medicated and unmedicated (after voluntary withdrawal from medication for several weeks) revealed no difference in pure-tone thresholds, speech thresholds, word recognition scores, tympanograms, or acoustic reflex thresholds. Medicated SCAN-A (a screening test for central auditory processing disorders) results were normal, and unmedicated results were abnormal. Unmedicated transient otoacoustic emissions and auditory brainstem response waves I, III, and V were significantly larger bilaterally. Uncomfortable loudness levels indicated greater tolerance during the medicated condition. Central processing and vigilance were evaluated with analog-synthesized three-formant consonant-vowel syllables. While medicated, responses to stimuli at each ear revealed well-defined, labeling crossovers of about 90 msec. Vowel identification matched normal subject responses; labeling of /gE/jE/ and /bE/wE/ continua was well defined but all crossover points differed from normals (p < .0001). During unmedicated testing, responses to /gE/jE/ began at medicated levels but approached chance levels for the entire continuum within 10 min; labeling of /bE/wE/ was consistent with medicated responses throughout with earlier than normal crossover points.

Adult↗

PubMed1999

Binaural interaction component in children at risk for central auditory processing disorders.

The binaural interaction component (BIC) occurring in the latency range of peak V of the auditory brainstem responses (ABR) was investigated in nine normal children, comprising the control group, and nine children at risk for central auditory processing disorders (CAPD), comprising the CAPD group. All children tested had normal hearing, normal intelligence and normal ABR thresholds. Averaged BIC obtained from the difference between the summed and binaural ABR waveforms was compared between the two groups for amplitude and latency measures. Results indicated a significant reduction in the amplitude of the BIC occurring in the latency domain of ABR peak V, in the CAPD group.

Adolescent↗

PubMed1999

Slope analysis of Auditory Brainstem Responses in children at risk of central auditory processing disorders.

The method of slope vectors was used to quantify Auditory Brainstem Responses (ABR) obtained from nine normal children and nine children at risk for central auditory processing disorders (CAPD) with language impairment, for monaural and binaural stimulation conditions. Slopes thus obtained were subjected to K-Means Cluster Analysis. Distinction between the two groups was obtained only for binaural stimulation conditions, wherein all normal children were grouped under cluster 1 with higher slope values and 6 out of 9 CAPD children were grouped under cluster 2 with lower slopes. The results suggest that there may be several subcategories among children who are found to be at risk for CAPD. One of the subcategories may comprise children who exhibit poor ABR morphology, especially during binaural stimulation conditions, which could be due to binaural interference.

Adolescent↗

PubMed1999

Hypercalcemia associated with infection by Cryptococcus neoformans and Coccidioides immitis.

BACKGROUND: Of the 13 reported cases of hypercalcemia associated with fungal infection, 1 was caused by Cryptococcus neoformans and probably mediated by increased levels of 1,25-dihydroxyvitamin D [1,25(OH)2D]. Eight others were associated with Coccidioides immitis, of which only 2 had measured 1,25(OH)2D levels; in both, they were diminished. We report a patient with human immunodeficiency virus infection and simultaneous C. immitis and C. neoformans pneumonia and C. immitis fungemia associated with hypercalcemia. METHODS: Consecutive measurements of serum total and ionized calcium, phosphorous, blood urea nitrogen, creatinine, 25(OH)D, 1,25(OH)2D, parathyroid hormone (PTH), parathyroid hormone-related protein (PTHrp) and albumin were performed over a period of 46 months. RESULTS: While the patient was hypercalcemic, intact serum PTH and PTHrp were undetectable, serum 25(OH)D levels were normal, and serum 1,25(OH)2D levels were in the high normal range. Successful treatment of the C. immitis and C. neoformans infections resulted in resolution of the hypercalcemia and increase of PTH and PTHrp to the normal range. CONCLUSION: In some patients with HIV infection, coincident hypercalcemia, and severe fungal infection, the responsible factor may be 1,25(OH)2D. Although total serum levels of this compound may not be frankly elevated, they are inappropriately high for the circumstances. Free 1,25(OH)2D levels should be determined in this situation.

AIDS-Related Opportunistic Infections↗

PubMed1999

Auditory brainstem responses in Golden Syrian hamsters (Mesocricetus auratus) affected with the Wh gene.

BACKGROUND AND PURPOSE: The anophthalmic white (Wh) gene in Golden Syrian hamsters (Mesocricetus auratus) is autosomal semi-dominant and causes several developmental defects, including hearing loss. The Wh mutation is thought to be homologous to Waardenburg syndrome in humans, apparently affecting similar developmental processes. The purpose of this study was to assess the hearing of hamsters in the AN/As-Wh strain. METHODS: Using auditory brainstem responses, electrophysiologic activity was determined in 20 hamsters of the AN/As-Wh strain, with the aim of elucidating hearing status. Hamsters were classified into five genotypes and were evaluated by use of click stimuli. RESULTS AND CONCLUSION: Hamsters assigned to the genotypes differed in their hearing sensitivity and could be classified into categories of normal hearing, moderate hearing loss, and profound hearing loss.

Animals↗

PubMed1996

Auditory cortical neurons in vitro: cell culture and multichannel extracellular recording.

Self organization, pattern generation, and pattern processing in local cortical circuits are difficult to study in vivo. The complexities of cortical circuits require simplified systems for study. We have developed a simplified model of auditory cortical neurons growing as monolayer networks in culture. Neurons dissociated from auditory cortex of 14-day mouse embryos were grown on photoetched microelectrode array containing 64 transparent indium-tin oxide electrodes. Cultures were maintained in incubators for up to 113 days. Neurons developed processes and made synaptic connections. All cultures were spontaneously active and exhibited complex temporal burst patterns. In a data set of 12 cultures, the number of active channels varied from culture to culture and ranged from 6-17. Signal/noise ratios ranged from 3:1 to a maximum of 16:1. No significant correlations were found between age of the culture and number of active channels, or signal/noise ratios. Spontaneous firing patterns recorded from various channels showed complex bursting patterns in all cultures. Within a culture, coordinated synchronous bursting were found among some channels, and independent bursting on others. Preliminary histological analysis of cultures using the Loots-modified Bodian stain showed neurons with axonal and dendritic profiles growing extensively on top of the glial carpet. Neuronal processes crossing the electrodes singly or in small groups were also observed. Pyramidal and non-pyramidal cells could be identified. In a pool of 2,093 neurons in a 49-day-old culture, the average size of the somata was found to be 16 microns, with a mode of 12 microns.

Animals↗

PubMed1996

Auditory cortical neurons in vitro: initial pharmacological studies.

Dissociated embryonic tissue from murine auditory cortex formed spontaneously active monolayer networks in culture that were maintained for up to 113 days in vitro (div). As a first step in determining whether neurons retain histiotypic properties, we subjected a set of 10 cultures to a sequence of 4 synaptically active substances. The test sequence consisted of 50 microM bicuculline, 10 microM strychnine, 5 microM NMDA, and 20 microM GABA. Recordings were made for 5-30 min under each condition followed by complete medium changes. Six to 14 channels with the best signal-to-noise ratios were selected for analysis that consisted of continual chart recordings of integrated burst data and further analysis of short data segments after digitizing and processing. All networks showed spontaneous activity, but had greatly varying native activity ranging from organized, quasi-periodic bursting on all channels to more complex spatio-temporal patterns with less coordination among channels. Bicuculline triggered oscillatory activity, simplified bursting, increased burst amplitude, and enhanced burst regularity among electrodes. Strychnine also changed the burst activity to a simpler pattern and enhanced the burst amplitude, indicating presence of glycine receptors in cortical tissue. Application of NMDA increased burst frequencies, but reduced burst regularity and coordination among channels. 20 microM of GABA inhibited all bursting activity in the networks. These results suggest that monolayer networks cultured on multi-electrode arrays retain some basic histiotypic pharmacological responses and may provide useful platforms for the study of network dynamics in the auditory cortex.

Animals↗

PubMed1994

Dot blot hybridization assay for the detection of duck hepatitis B virus DNA among healthy Indian country ducks.

A DNA molecular hybridization technique employing Duck Hepatitis B Virus (DHBV) DNA of 3.0 kilobase pairs as a probe was used to screen for the presence of DHBV DNA in blood samples, collected from 90 apparently healthy Indian country ducks. Six out of 90 ducks showed positivity for DHBV DNA in serum (5.4%) and only 4 out of 6 DHBV DNA positive ducks answered in Counter Immuno Electrophoresis (CIEP) using specific antibody against DHBV surface antigen raised in Guinea pig. The results indicate the pilot observation that (a) DHBV carrier status exists to a tune of 5.4% among apparently healthy Indian country ducks also and (b) DHBV probe can be employed as a sensitive and reliable assay for DHBV DNA detection in DHBV infected ducks.

Animals↗

PubMed1993

Duck hepatitis B virus (DHBV) infection in Indian domestic ducks: a pilot study.

One hundred and two apparently healthy Indian domestic ducks from the Poultry Research Station, Madras were screened for duck hepatitis B virus (DHBV) infection by; 1. screening for the duck hepatitis B virus surface antigen (DHBsAg) in their sera using hepatitis B virus (HBV) reagents, 2. screening for DHBsAg using specific duck hepatitis B virus (DHBV) reagents and 3. demonstration of DHBV DNA using DHBV DNA probe by dot blot hybridisation. While 5 ducks (4.9%) were consistently positive with HBV reagents, use of DHBV reagents showed a total of 4 ducks (including 3 of the above 5) to be positive for DHBsAg. DNA hybridisation showed 6 ducks to be positive for DHBV DNA. On clinical examination, 5 out of these 6 ducks did not reveal abnormalities, the other one showed hepatomegaly and ascites. Post-mortem studies showed the presence of nodules on the surface of the liver in all 5 which were positive with HBV reagents including the one with hepatomegaly. On histopathological evaluation, they were found to be hepatocellular carcinoma with or without bile duct carcinoma. The present study is a pilot report on the occurrence of DHBV infection in Indian domestic ducks and the possibility of antigenic cross reactivity between human HBV and duck hepatitis B virus antigens.

Animals↗