Effects of localized pontine lesions on auditory brain-stem evoked potentials and binaural processing in humans

Potassium channels are involved in the control of neuronal excitability by fixing the membrane potential, shaping the action potential, and setting firing rates. Recently, attention has been focused on identifying the factors influencing excitability in second-order auditory and vestibular neurons. Located in the brainstem, second-order auditory and vestibular neurons are sites for convergence of inputs from first-order auditory or vestibular ganglionic cells with other sensory systems and also motor areas. Typically, second-order auditory neurons exhibit two distinct firing patterns in response to depolarization: tonic, with a repetitive firing of action potentials, and phasic, characterized by only one or a few action potentials. In contrast, all mature vestibular second-order neurons fire tonically on depolarization. Already, certain fundamental roles have emerged for potassium currents in these neurons. In mature auditory and vestibular neurons, I(K), the delayed rectifier, is required for the fast repolarization of action potentials. In tonically firing auditory neurons, I(A), the transient outward rectifier, defines the discharge pattern. I(DS), a delayed rectifier-like current distinguished by its low threshold of activation, is found in phasically firing auditory and some developing vestibular neurons where it limits firing to one or a few spikes, and also may contribute to forming short-duration excitatory postsynaptic potential (EPSPs). Also, I(DS) sets the threshold for action potential generation rather high, which may prevent spontaneous discharge in phasically firing cells. During development, there is a gradual acquisition and loss of some potassium conductances, suggesting developmental regulation. As there are similarities in membrane properties of second-order auditory and vestibular neurons, investigations on firing pattern and its underlying mechanisms in one system should help to uncover fundamental properties of the other.     

Effects of postinatal stress on visual and auditory evoked potentials

Maturation of visual and auditory evoked potentials (mainly the P3 wave) of 10 controls and of 10 infants exposed to recurrent postnatal stressful events (crying spells lacking organic basis) have been compared. The sourse of maturation of P3 waves may serve as indicator of growth and nature of cognitive processes (including perception). Recurrent srying spells seemed to delay appearance of visual P3 wave, prolonged its latency, and delayed appearance of visible differences in the shape of visual P3 wave upon exposure of the subjects to different visual experiences. A compensatory increase of maturation of the auditory P3 wave appeared. The results suggest that recurrent exposure to stressful events during the early postnatal period may delay the ability of the memory banks of auditory engrams with unusual contents (including memory traces of stresses), a potential basis for future auditory hallucinations.     

Adaptive denoising and multiscale detection of the V wave in brainstem auditory evoked potentials

This paper describes a wavelet-transform-based system for the V wave identification in brainstem auditory evoked potentials (BAEP). The system combines signal denoising and rule-based localization modules. The signal denoising module has the potential of effective noise reduction after signal averaging. It analyses adaptively the evolution of the wavelet transform maxima across scales. The singularities of the signal create wavelet maxima with different properties from those of the induced noise. A non-linear filtering process implemented with a neural network extracts out the noise-induced maxima. The filtered wavelet details are subsequently analysed by the rule-based localization module for the automatic identification of the V wave. In the first phase, it implements a set of statistical observations as well as heuristic criteria used by human experts in order to classify the IV-V complex. At the second phase, using a multiscale focusing algorithm, the IV and V waves are positioned on the BAEP signal. Our experiments revealed that the system provides accurate results even for signals exhibiting unclear IV-V complexes.     

Effects of tobacco smoking and abstinence on middle latency auditory evoked potentials

OBJECTIVE: To evaluate the effects of tobacco cigarette smoking and overnight abstinence on middle latency auditory evoked potentials among smokers and nonsmokers. METHODS: Groups of 9 to 10 adult male and female nonsmokers and smokers participated in the study. Each person volunteered for two laboratory sessions conducted in the early afternoon on 2 separate days. Smokers abstained from tobacco products 6 to 15 hours before the abstinent session and maintained their usual smoking behavior before the smoking session. The nonsmokers had a similar laboratory experience but sham smoked by means of inhaling air. Middle latency auditory evoked potentials were recorded from Cz to both ears as reference. RESULT: The latencies of the Na and Pa potentials during the smoking session were significantly (p < 0.01) shorter than those in abstinent smokers and nonsmokers. After smoking, peak-to-trough amplitudes for the V-Na, Na-Pa, and Pa-Nb potentials were larger than those after abstinence and significantly larger than those among nonsmokers. CONCLUSIONS: The shorter latencies of the middle latency brain wave components in the smoking session suggest faster processing of sensory information after cigarette smoking. Larger Pa amplitudes after cigarette smoking suggest a higher arousal level than that among partially abstinent smokers and nonsmokers.     

Effects of appetitive drive on auditory evoked potentials: A replication.

Reexamined click-evoked potentials in 6 female cats during periods of increased food deprivation under 3 experimental procedures. The amplitudes of click-evoked potentials recorded from the round window, cochlear nucleus, and auditory cortex remained constant as deprivation time increased from 0 to 24 hr regardless of the experimental procedures used. Increased food-deprivation time had no systematic effect on EEG activity recorded from the auditory cortex under the 3 procedures. It is suggested that since increased food-deprivation time under the experimental procedures did not produce a state of heightened EEG arousal, the lack of effect on auditory evoked potentials is related to the amount of environmental stimulation an animal receives during food deprivation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of noise burst rise time and level on the human brainstem auditory evoked response

An experiment was conducted to examine the effects of noise burst rise time and level on the human BAER. Noise burst levels included 15, 30, 45 and 60 dB nHL, with linear rise times of 0, 0.5, 1.25 and 2.5 ms. With increasing noise burst level, there is a decrease in wave V latency and an increase in peak amplitude. With increasing noise burst rise time, there is an increase in wave V latency and a decrease in wave V amplitude. The slope of the latency/intensity function increases with increasing rise time. The slope of the latency/rise time function increases with decreasing noise burst level. The change in wave V latency associated with changing rise time is less than the change in rise time for all experimental conditions.     

Contribution of initial median-nerve somatosensory evoked potentials and brainstem auditory evoked potentials to prediction of clinical outcome in cerebrovascular critical care patients: a statistical evaluation

OBJECTIVE: To analyze the pathological and clinical features of a variant of renal carcinoma: sarcomatoid renal carcinoma. METHODS: Of 316 patients diagnosed as having a renal tumor from 1975 to 1995, 11 (3.5%) with a pathological diagnosis of sarcomatoid renal carcinoma were analyzed. The clinical history, biological data and diagnostic imaging findings of these patients were reviewed. All patients had undergone surgical exploration. RESULTS: All the tumors showed a double cellular population, with a fusiform component. Histological analysis showed a high grade and stage tumor. Ten patients died from the disease, the mean survival rate was 9 months (range 2-48) following diagnosis. CONCLUSIONS: Sarcomatoid carcinoma of the kidney is uncommon and can be occasionally difficult to distinguish from sarcoma. It has a worse prognosis than other variants of renal carcinoma.     

Effects of styrene exposure on middle latency auditory evoked potentials and glial cells in rat

The demand for health care and social welfare services for the elderly has increased and in Japan, there is a need in the social system to improve the quality of life, especially for those who are disabled. This article directs attention to bed-ridden elderly persons from the standpoint of social problems attending economic development and population changes based on data from Japan, the United States, Sweden, and OECD countries. Compared to the United States, there are more bed-ridden elderly in Japan, and inadequate public resources for caring. Physicians, nurses, care workers, and rehabilitation specialists such as physiotherapist and occupational therapist per 1000 aged sixty-five or over are 89.5 in Japan while 237.4 in Sweden. Japan has the fewest such health and welfare personnel among developed countries. Even with increases in such personnel through the New Gold Plan, future increase in aged population would off-set the effect and the problem of providing care for the elderly remains.     

Effect of frontal and temporal seizure foci on P50 auditory evoked potentials

The aim of the investigation was to test the reproducibility and accuracy of a new method to measure temporomandibular joint (TMJ) fluid concentrations of various substances by saline washing, using exogenous B12 as a marker. An in vitro test was first performed with glucose as a test substance. The difference between a B12-calculated and known standard concentration of glucose was very small. Saline washing of the TMJ was performed on 13 patients having signs of TMJ arthritis, and the aspirates obtained were analyzed for neuropeptide Y-like immunoreactivity (NPY-LI) and interleukin-1 beta (IL-1 beta). Vitamin B12 was mixed with the saline immediately before injection, and a sample of the aspirate was later compared photometrically with the injection solution. There were positive correlations between saline aspirate and joint fluid concentrations for NPY-LI and IL-1 beta, and the correlations were stronger for saline aspirates with high joint fluid content. This study shows that the method is reliable for measurement of joint fluid concentrations of various substances, such as NPY-LI and IL-1 beta.     

Low-level steady-state auditory evoked potentials: effects of rate and sedation on detectability

Steady-state auditory evoked potentials (SSAEPs) in alert adults are most detectable at stimulus or modulation rates of about 40 Hz. Sedation reduces the detectability of 40-Hz SSAEPs and increases it for higher rate SSAEPs. This study examined whether rates higher than 40 Hz would be preferable for detecting responses to low-intensity tones in sedated adults. Fourteen normal adults listened to 640-Hz tones at modulation rates (and toneburst rates) of 20-160 Hz, in 10-Hz steps, at levels of 38 and 58 dB peak equivalent sound-pressure level (peSPL) (20 and 40 dB normal hearing level (nHL) for amplitude-modulated (AM) tones), both alert and sedated (1-2 g chloral hydrate). Sedation reduced both signal (SSAEP) power and noise power at all rates, but noise power reduction was greater for higher rates. Detectability in the alert condition was always greatest at 40 Hz. Under sedation, a second detectability peak was present at 90 Hz for 58-dB peSPL tones, approximately equal to that seen at 40 Hz. At 38 dB peSPL (sedated), peak detectability moved from 40 to 50 Hz. These results suggest that presentation/modulation rates around 40 Hz may be optimal for SSAEP detectability at low levels in adults, whether alert or sedated.     

Effects of click intensity and frequency on the brain-stem auditory evoked potentials in the common marmoset (Callithrix jacchus)

Brain-stem auditory evoked potentials (BAEPs) were recorded in 20 common marmosets (Callithrix jacchus) to investigate the effects of click frequency up to 99 kHz, in consideration of the higher hearing range of the marmoset, and intensity on wave forms and peak latencies. According to the results of BAEP recordings at frequencies of 4, 32, and 99 kHz, the number of components recorded was affected by the stimulus intensity and the clicks at an intensity of 80 dB peak equivalent sound pressure level (pe SPL) had the maximum number of clear components. Therefore, it was indicated that click stimulations at an intensity of 80 dB pe SPL over a broad range of frequencies appears to be useful for recording the maximum number of components in marmosets and may increase the information obtainable from BAEPs. BAEP latencies were prolonged as the stimulus intensity decreased from 100 to 50 dB pe SPL. The effects of stimulus frequency on the wave latencies and amplitudes in response to 80 dB pe SPL at frequencies between 0.5 and 99 kHz revealed various changes: the amplitude of wave I increased at 16 and 32 kHz, but that of waves III and V increased at 4-8 and 64-99 kHz. These increases in amplitudes of the waves may correlate with higher synchronous activity of the peripheral or central auditory pathways.     

Expression of myosin heavy chain and of myogenic regulatory factor genes in fast or slow rabbit muscle satellite cell cultures

We investigated the myogenic properties of rabbit fast or slow muscle satellite cells during their differentiation in culture, with a particular attention to the expression of myosin heavy chain and myogenic regulatory factor genes. Satellite cells were isolated from Semimembranosus proprius (slow-twitch muscle; 100% type I fibres) and Semimembranosus accessorius (fast-twitch muscle; almost 100% type II fibres) muscles of 3-month-old rabbits. Satellite cells in culture possess different behaviours according to their origin. Cells isolated from slow muscle proliferate faster, fuse earlier into more numerous myotubes and mature more rapidly into striated contractile fibres than do cells isolated from fast muscle. This pattern of proliferation and differentiation is also seen in the expression of myogenic regulatory factor genes. Myf5 is detected in both fast or slow 6-day-old cell cultures, when satellite cells are in the exponential stage of proliferation. MyoD and myogenin are subsequently detected in slow satellite cell cultures, but their expression in fast cell cultures is delayed by 2 and 4 days respectively. MRF4 is detected in both types of cultures when they contain striated and contractile myofibres. Muscle-specific myosin heavy chains are expressed earlier in slow satellite cell cultures. No adult myosin heavy chain isoforms are detected in fast cell cultures for 13 days, whereas cultures from slow cells express neonatal, adult slow and adult fast myosin heavy chain isoforms at that time. In both fast and slow satellite cell cultures containing striated contractile fibres, neonatal and adult myosin heavy chain isoforms are coexpressed. However, cultures made from satellite cells derived from slow muscles express the slow myosin heavy chain isoform, in addition to the neonatal and the fast isoforms. These results are further supported by the expression of the mRNA encoding the adult myosin heavy chain isoforms. These data provide further evidence for the existence of satellite cell diversity between two rabbit muscles of different fibre-type composition, and also suggest the existence of differently preprogrammed satellite cells.     

Effects of noise on inferior colliculus evoked potentials and cochlear anatomy in young and aged chinchillas

Site-specific modification of the chromosomal immunoglobulin locus by gene targeting is a powerful tool in studying the molecular requirements for immunoglobulin gene structure and function and in the production of engineered antibodies. Here, we describe a two step- integration then excision-gene targeting procedure for introducing planned genetic alterations into the chromosomal immunoglobulin locus. The efficiency of gene targeting with an enhancer-trap vector in which an enhancerless neo and HSV-tk gene were inserted into the vector backbone was compared to that of the corresponding enhancer-positive vector. Both insertion vectors also contained homology to the chromosomal immunoglobulin target locus along with the desired genetic alteration. The first step involved insertion of the transferred vector into the target locus by homologous recombination. An approximately 15-fold enrichment in the frequency of vector insertion was obtained with the enhancer-trap compared to the enhancer-positive vector. The majority of targeted cells (75%) contained a single copy of the vector integrated into the chromosomal immunoglobulin locus. The second step involved excision of the integrated vector by intrachromosomal homologous recombination between the duplicated region of homology that removed the integrated vector, neo and tk genes along with one copy of homologous DNA. Vector excision was very efficient generating G418S, FIAU(R) secondary recombinants at the high rate of approximately 10(-3)/cell generation. In the secondary recombinants, the overall structure of the chromosomal immunoglobulin locus was restored with the desired genetic alteration being present in an expected proportion of the cells.     

Effect of intrathecal nimodipine on spinal cord blood flow and evoked potentials in the normal or injured cord

A method was developed for administering intrathecal pharmacotherapy in a rat model of spinal cord injury. The effects of intrathecal administration of nimodipine on spinal cord blood flow (SCBF) and evoked potentials (EPs) were measured in the normal and injured spinal cord. It had previously been shown that systemic nimodipine caused severe hypotension after spinal cord injury. After baseline SCBF and EPs, 15 uninjured rats were blindly allocated to one of three groups: one placebo group (n = 5); and two groups with intrathecal nimodipine, 0.05 mg/kg (n = 5), or 0.2 mg/kg (n = 5). Ten other rats received a 35 g acute clip compression injury of the spinal cord for 1 minute and, were allocated to one of two groups: placebo (n = 5); and intrathecal nimodipine 0.05 mg/kg (n = 5) given 60 min after injury. In the uninjured groups, neither 0.05 nor 0.2 mg/kg of nimodipine increased SCBF during, or 30 min after, intrathecal infusion. However, the mean arterial blood pressure (MABP) decreased significantly to 69.73.1% after the infusion of 0.2 mg/kg nimodipine and did not recover by 98 min. In all three groups of uninjured rats, the amplitude of the cerebellar EP was decreased 30 min after infusion. After spinal cord injury, there were significant decreases in MABP, SCBF and EP amplitude in both placebo and treatment groups, but there was no therapeutic benefit from nimodipine. Thus, intrathecal infusion of nimodipine did not prevent the hypotension encountered with systemic administration and exerted no beneficial effect on SCBF or EPs after acute spinal cord injury.     

Effects of anesthetics and septal lesions and stimulation on 3H-acetylcholine formation in rat hippocampus

The rate of 3H-acetylcholine (ACh) formation from i.v. injected 3H-choline was studied in the rat hippocampus after various treatments which alter the activity of cholinergic septal hippocampal neurons. Administration of pentobarbital and placement of acute septal lesion reduced the formation of 3H-ACh but did not change 3H-choline content. Chloral hydrate administration reduced the formation of 3H-ACh and also increased 3H-choline content. The chloral hydrate induced increase in 3H-choline occurred also in animals with chronic septal lesions. Electrical stimulation of the septum caused an increase in both 3H-ACh and 3/-choline. Chronic septal lesion caused a reduction in both radioactive and endogenous ACh, but did not affect radioactive or endogenous choline. These findings suggest that there are multiple pools of choline in the brain and that the precursor pool for ACh synthesis is difficult to measure. Overall, the parameter that best correlated with cholinergic activity was the level of 3H-ACh. Possible mechanisms, for this finding are discussed.     

Effects of inner hair cell loss on inferior colliculus evoked potential thresholds, amplitudes and forward masking functions in chinchillas

The effects of outer hair cell (OHC) loss on evoked potential (EVP) thresholds, amplitudes and forward masking (FWM) functions have been fairly well characterized. In contrast, the effects of inner hair cell (IHC) losses are largely unknown, primarily due to the difficulty of producing selective IHC lesions. Recent studies have shown that IHCs of the chinchilla are preferentially damaged by the anticancer drug, carboplatin. In this study, we administered a single 100 mg/kg dose of carboplatin to four chinchillas, to examine the effects of IHC lesions on EVPs measured from the inferior colliculus (IC-EVPs). Thresholds and amplitude functions were measured for 0.25-16 kHz tone bursts, and FWM functions were measured at 1, 2 and 4 kHz, using masker probe intervals of 2, 5, 10, 20, 40 and 80 ms, before and 1-2 months after carboplatin treatment. Histology revealed IHC lesions ranging from approximately 15 to 90%, with virtually no loss of OHCs. Surprisingly, even massive IHC lesions were not associated with elevations of IC-EVP thresholds. IC-EVP amplitudes at suprathreshold levels were sometimes depressed, sometimes enhanced, and in some cases unchanged. IHC lesions increased susceptibility to FWM, particularly at intermediate (10-20 ms) masker-probe intervals, without significantly changing the overall time course of FWM. The results provide new perspectives on the contribution of IHCs to FWM, and on the ability of the central auditory system to adapt to a significant reduction of neural input from the cochlea.