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Biomedical subjects

H Pratt

Publications and source records attributed to H Pratt.

At least 181 records · Page 10Linked to original sources
PubMed1973

A study of the thermal stability of ribosomes and biologically active subribosomal particles.

1. The ability of Escherichia coli ribosomes to function in poly(U)-directed protein synthesis was measured at elevated temperatures by using thermostable supernatant factors from Bacillus stearothermophilus. The amount of polyphenylalanine synthesized at 55 degrees C was about the same as at 37 degrees C, but the rate of synthesis was increased approximately fivefold. At 60 degrees C the activity of the ribosomes was halved. 2. E. coli ribosomes can sustain the loss of approx. 10% of the double-helical secondary structure of RNA without losing activity. 3. Within the active ribosome the double-helical secondary structure of the rRNA moiety is stabilized compared with isolated rRNA, as judged by enzymic hydrolysis and by measurements of E(260). 4. The main products, over the range 0-55 degrees C, of ribonuclease T(1) digestion of the smaller subribosomal particle of E. coli were two fragments (s(0) (20,w) 15S and 25.3S) of approximately one-quarter and three-quarters of the size of the intact molecule, revealing the presence of a ;weak spot' where intramolecular bonds appear insufficient to hold the fragments together. 5. Subribosomal particles of B. stearothermophilus were more stable to heating, by approx. 10 degrees C, than those of E. coli, and the stabilization of double-helical secondary structure of the RNA moiety was more striking. 6. Rabbit reticulocyte ribosomes were active in poly(U)-directed protein synthesis at 45 degrees C, and half the activity was lost after heating to 53 degrees C. Active subribosomal particles of rabbit reticulocytes and of oocytes of Xenopus laevis, like the bacterial subribosomal particles, underwent a conformational change to a slower-sedimenting form on heating. The temperature range of the transition depended on the species. 7. Slower-sedimenting particles, whether produced by EDTA treatment or by heating, had different ;melting' profiles compared with active subribosomal particles, providing another indication of conformational differences. 8. Comparison of the properties of the various subribosomal particles revealed greater variation in the secondary structure of the protein moieties (judged by measurement of circular dichroism) than in the secondary structure of the RNA moieties, which appeared to have features in common.

Animals↗
PubMed1971

Dissociation of ribosomes from oocytes of Xenopus laevis into active subparticles.

Ribosomes from oocytes of Xenopus laevis possess low endogenous activity in vivo and in vitro, yet are readily stimulated by poly(U). The ease with which these ribosomes dissociate into active subparticles under conditions where polyribosomes and active monoribosomes are stable supports the view that the majority are unprogrammed.

Animals↗
PubMed1970

Ribosomes from Xenopus laevis ovaries and the polyuridylic acid-directed biosynthesis of polyphenylalanine.

Single ribosomes account for 90% or more of the ribosome fraction of Xenopus laevis ovaries. These ribosomes have low endogenous activity in a cell-free protein-synthesizing system but synthesize polyphenylalanine in the presence of poly U under conditions comparable with those reported for mammalian or bacterial systems. These observations agree with the view that the ribosome is deficient in mRNA.

Animals↗
PubMedDate not supplied

Biphasic plasma aldosterone responses to four single-dose ACTH regimens.

Adrenocorticotropic hormone (ACTH) administration increases cortisol synthesis but produces a biphasic aldosterone response. Some investigators believe that the hypercortisolism from prolonged ACTH administration is responsible for this aldosterone response. The present study evaluated the plasma aldosterone response to four acute single-dose ACTH regimens that produced only a transient increase in plasma cortisol. Fourteen normal adult men received (1) 1-18 ACTH intravenous bolus (IV), (2) 1-18 ACTH intramuscular (IM), (3) 1-39 ACTH (IM), and (4) 1-24 ACTH (IV). The plasma aldosterone increased within one hour and tended to parallel the cortisol increment with all four ACTH regimens. With all of these ACTH regimens, the plasma aldosterone level decreased below placebo with 1-24 ACTH (IV) (24 hours), 1-39 ACTH (IM) (24 hours), and 1-18 ACTH (IV) and (IM) (48 hours) at a time when the cortisol had returned to normal. These results suggest that the delayed ACTH-induced aldosterone inhibition production are not directly related to cortisol production and do not require prolonged ACTH administration. These observations are consistent with ACTH induction of a nonaldosterone mineralocorticoid, which is independently suppressing aldosterone production.

Adrenocorticotropic Hormone↗
PubMedDate not supplied

Three-channel Lissajous' trajectories of auditory event-related potentials to target stimuli.

Three orthogonal recordings ('X,' 'Y' and 'Z') of event-related potentials (ERPs) evoked by auditory target stimuli were represented in 3-dimensional voltage-space, to produce 3-channel Lissajous' trajectories (3-CLTs). Stimuli were verbal or non-verbal and were differentiated by their pitch, phonemic or phonetic attributes. Visual inspection and quantitative evaluations unexpectedly revealed that the 3-CLT of these ERPs strongly resembles a 'hair-pin' trajectory. This trajectory titled in space at characteristic angles with each of the analysis axes: 133 degrees with the 'X' axis, 87 degrees with the 'Y' axis, and 54 degrees with the 'Z' axis. The relatively small inter-subject variability observed in the geometrical measures, particularly in orientation, may be attributed to the slight variation in the underlying generators. 3-CLT analysis could be useful in future clinical as well as source studies of ERP generators.

Acoustic Stimulation↗
PubMedDate not supplied

The effects of digital filtering on feline auditory brain-stem evoked potentials.

The power spectrum of the feline auditory brain-stem evoked potentials (ABEPs) consists of 3 frequency bands, similar to the human wave form, but differing in range. The frequency bands in the feline spectra were separated by notches at 326 Hz and 732 Hz. Click-evoked ABEP from 15 cats were digitally filtered in 3 passbands: (1) below 326 Hz ('slow filter'), (2) between 326 and 732 Hz ('medium filter'); and (3) between 732 and 1790 Hz ('fast filter'). Filtering in each of these bands differentially affected the ABEP components. The vertex positive components are labeled by their order of appearance, i.e., 1, 2, ... 5. Peak 1 is subdivided into 2 subcomponents labeled 1a and 1b. The slow filter was associated with the loss of all components leaving a slow potential shift, i.e., the 'pedestal' peaking at the latency of peak 4. The medium filter was associated with the loss of components 1a, 1b and 2, sparing 3 and 4. The fast filter was associated with the loss of 1b and a diminution of 2. Comparing cat and human ABEP, feline components 2, 3 and 4 behaved precisely the same as the human II, III and V. In contrast to the human I, the feline first component (1a) was not detected with the medium filter. No feline component, following peak 1 in the unfiltered wave form, disappeared with the slow and medium filters, and reemerged with the fast filter (as human IV does).(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMedDate not supplied

Temporal correspondence of intracranial, cochlear and scalp-recorded human auditory nerve action potentials.

Conventional, vertex-ipsilateral ear records ('A'), as well as 3-channel Lissajous' trajectories (3-CLTs) of auditory brain-stem evoked potentials (ABEPs) were recorded from the scalp simultaneously with tympanic membrane electrocochleograms ('TME') and auditory nerve compound action potentials ('8-AP') recorded intracranially using a wick electrode on the auditory nerve between the internal auditory meatus and the brain-stem. The recordings were made during surgical procedures exposing the auditory nerve. The peak latency recorded from 'TME' corresponded to trajectory amplitude peak 'a' of 3-CLT and to peak 'I' of the 'A' channel ABEP. Peak latency of '8-AP' was slightly longer than the latency of peak 'II' of 'A' when '8-AP' was recorded from the root entry zone and the same or shorter when recorded from the nerve trunk. '8-AP' peak latency was shorter than trajectory amplitude peak 'b' of 3-CLT regardless of where the wick electrode was along the nerve. Peak latencies from all recording sites clustered into two distinct groups--those that included N1 from 'TME,' peak 'I' of the 'A' record and trajectory amplitude peak 'a' of 3-CLT, and those that included the negative peak of '8-AP' and trajectory amplitude peak 'b' of 3-CLT, as well as peak 'II' of the 'A' record, when present. In one case, the latency of peak 'II' and trajectory amplitude peak 'b' was manipulated by changing the conductive properties of the medium surrounding the auditory nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMedDate not supplied

Surface-recorded cochlear microphonic potentials during temporary threshold shifts in man.

Cochlear microphonic potentials (CM) were recorded, by means of surface electrodes, before, during and after white-noise-induced temporary threshold shifts (TTS) in human volunteers. The behavioural threshold shift was not accompanied by a change in amplitude of CM. These findings indicate that in humans, the site affected by the noise exposure and which probably gives rise to the TTS is central to the site of generation of CM. In a previous study, the compound action potential generated in the auditory nerve was found to be of lower amplitude and longer latency during TTS, and it is thus proposed that the site affected is peripheral to the generation of conducted action potentials. The synapse between hair cells and the auditory nerve fibres is the most likely candidate to be the affected site.

Acoustic Stimulation↗
PubMedDate not supplied

Auditory brainstem evoked potentials in insulin-dependent diabetics with and without peripheral neuropathy.

Auditory Brainstem Evoked Potentials (ABEP) were recorded from 33 insulin-dependent diabetes mellitus (IDDM) patients (17 with diabetic peripheral neuropathy and 16 without) as well as from 20 normals. Pure-tone audiometry, speech reception threshold and discrimination were also evaluated. Sub-clinical pure-tone threshold elevation was observed for IDDM patients with neuropathy. Pure-tone thresholds of IDDM patients without neuropathy were not significantly different from those of normals. ABEP abnormality (at 10/sec click rate) was observed in 31% of IDDM patients with neuropathy, rising to 44% when 55/sec click rate measures were included. Abnormalities included bilateral and symmetrical peak-latency prolongations for all waves, greater for the later waves, and prolongation of V-I and V-III interpeak latency differences, all at 10/sec, and only prolonged peak latency for I at increased rate. Abnormalities coincided with microangiopathy and peripheral neuropathy. The incidence of ABEP abnormality for IDDM patients without neuropathy was only 12%, unilateral and sporadic in nature. As a group, IDDM patients with neuropathy had significantly prolonged IV and V peak-latencies, compared with the normals, or with the IDDM patients without peripheral neuropathy. In contrast, IDDM patients without neuropathy resembled the normals in all respects. ABEP have proven useful in understanding the variety of pathologies underlying the clinical manifestation of diabetes.

Adolescent↗
PubMedDate not supplied

Electrocochleography during noise-induced temporary threshold shifts.

The responses of the auditory nerve and brain stem auditory nuclei were recorded non-traumatically in human subjects by means of electrocochleography before, during and after exposure to white noise intensities which produced temporary threshold shifts. The largest decrement (amplitude decrease and latency increase) was seen in the response of the auditory nerve. Large intersubject variability was seen in the effects of the noise exposure on response amplitude, latency and recovery rates.

Acoustic Stimulation↗
PubMedDate not supplied

Comparison of hearing threshold determined by auditory pathway electric responses and by behavioural responses.

In order to evaluate their reliability for determing the hearing threshold, the cochlear microphonic potentials, the auditory nerve and brain stem neural evoked responses as well as the cortical evoked responses were compared with the behavioural hearing thresholds of the same subjects in the same session. The threshold for recording the cochlear microphonic potnetial was found to be appreciably higher than the behavioral threshold. The threshold for recording the auditory nerve and brain stem responses was within a few decibels of the behavioural threshold. The thresold of the cortical evoked response was several decibels higher. It is concluded that (1) the auditory nerve and brain stem neural evoked responses are the best indicators of hearing threshold; (2) the cortical evoked responses are usually comparable, and (3) all types of evoked responses are indispensable aids in the evaluation of hearing and the determination of site of lesion in the auditory system.

Audiometry↗
PubMedDate not supplied

Effects of click polarity on the binaural interaction components of human auditory brainstem-evoked potentials: a three-channel Lissajous trajectory study.

Three-channel Lissajous trajectories (3-CLTs) of the binaural interaction components of the auditory brainstem-evoked potentials were recorded from 17 adult subjects in response to rarefaction, condensation and alternating polarity clicks. All 3-CLTs included 3 planar segments (named Bd, Be and Bf) whose latencies, amplitudes, orientations, sizes and shapes were not affected by click polarity. A significant increase was found in the duration of planar segment Be to alternating polarity clicks. This effect may be explained by limitations of spatiotemporal resolution of the method, which did not allow distinction of contributions from temporally overlapping generators participating in binaural processing.

Acoustic Stimulation↗
PubMedDate not supplied

The effect of broad-band noise on the binaural interaction components of human auditory brainstem-evoked potentials.

Three-channel Lissajous trajectories (3-CLTs) of binaural interaction components (BI) of auditory brainstem potentials (ABEPs) were derived from 13 normally hearing adults by subtracting the response to binaural clicks from the algebraic sum of monaurally evoked responses to clicks. ABEPs were recorded in response to 65 dB nHL, alternating-polarity clicks, presented at a rate of 11/s. The procedure was repeated with clicks alone as well as with clicks with broad-band masking noise. Noise was presented at 25 and 45 dB nHL, producing a signal-to-noise ratio of +40 and +20 dB, respectively. All BI 3-CLTs included 6 planar segments (labeled BdI, BdII, BdIII, BeI, BeII and Bf) whose apex latencies, except Bf, increased with increasing noise level above 25 dB nHL, and whose durations, sizes, shapes and orientations did not change across noise levels. There were also significant increases in peak latencies of the BI from single channels vertex-mastoid and vertex-neck with increasing noise level. No significant change was found in the trajectory amplitude of apices, with the exception of apices BdIII and Bf whose amplitudes increased with increasing noise level. We suggest that the paradoxical increase in BI amplitude with masking noise may reflect a binaural enhancement of the effect of noise. The effects observed indicate that, whereas the response to clicks displays occlusion, the response to noise displays spatial facilitation at the brainstem level.

Adolescent↗
PubMedDate not supplied

Detailed analysis of auditory brainstem responses in patients with noise-induced tinnitus.

The role of the auditory brainstem in tinnitus is questionable. This study aimed comprehensively to assess auditory brainstem responses (ABRs) in patients suffering from noise-induced tinnitus (NIT). ABRs were recorded from 13 chronic NIT patients (21 ears) and 11 (21 ears) age and hearing matched control subjects without tinnitus. ABRs were recorded with scalp electrodes placed ipsilateral and contralateral to the stimulated ear, and in three orthonormal differential configurations. The ABRs were analyzed as a function of time, frequency and voltage space. A significantly enhanced ipsilaterally recorded, time domain wave III amplitude was observed for the tinnitus patients. This finding was not confirmed by any of the other ABR measures, which were indistinguishable between subject groups. Although this may be a spurious result, it nonetheless may point to an alteration in the functioning of the putative wave III auditory brainstem generator, which deserves further study.

Adult↗
PubMedDate not supplied

The effect of binaural masking noise disparity on human auditory brainstem binaural interaction components.

The binaural interaction components (BIC) of the human auditory brainstem responses have been associated with sound lateralization which involves analyzing correlated inputs from the two ears. To test the hypothesis that BIC generators are specifically sensitive to binaural, correlated sounds, the effects of monaural and binaural correlated and uncorrelated masking on BIC to clicks were compared. Analysis included peak-to-prestimulus baseline amplitudes and latencies of BIC peaks from the vertex-mastoid ('A') and vertex-neck ('Z') channels, as well as the three-channel Lissajous trajectory (3-CLT) measures. Trajectory amplitudes of BIC BdIII, BeI and BeII were significantly suppressed by correlated (but not by uncorrelated) binaural noise, when compared with the unmasked condition. Moreover, component BdIII was more affected by masking with correlated than with uncorrelated binaural noise. Overall, binaural noise was more effective in suppressing BIC then monaural noise, and interaurally correlated binaural noise was more effective than uncorrelated binaural noise. These results are compatible with BIC generation by a binaurally activated subset of central auditory neurones which is sensitive to interaurally correlated sounds. Such a subset has been associated with the superior olivary complex and is assumed to be involved in sound lateralization.

Adolescent↗