Biomedical subjects

P H Jen

Publications and source records attributed to P H Jen.

At least 19 recordsLinked to original sources

PubMed2001

The effect of monaural middle ear destruction on postnatal development of mouse inferior colliculus.

This study examined the effect of monaural middle ear destruction on postnatal development of inferior collicular (IC) neurons of the laboratory mouse, Mus musculus. Monaural middle ear destruction was performed on juvenile mice and the density, number and size of IC neurons were determined at different postoperative ages. For electrophysiological study, collicular auditory response properties were always examined four weeks after operation. Monaural middle ear destruction produced larger neurons in the ipsilateral IC (relative to the operated ear) and smaller neurons in the contralateral IC of experimental mice in comparison with IC neurons of control mice. IC neurons of control mice typically had lower minimum thresholds and greater Q10 values than IC neurons of experimental mice. In experimental mice, neurons in the contralateral IC typically had longer latencies and higher minimum thresholds than neurons in the ipsilateral IC. Clear tonotopic organization was only observed for IC neurons of control mice. Possible mechanisms for these different observations are discussed.

Acoustic Stimulation↗

PubMed2001

The effect of bicuculline application on auditory response properties of inferior collicular neurons of mice with or without monaural middle ear destruction in early age.

Previous studies have demonstrated that abnormal auditory stimulation during early postnatal development can be manifested through physiological changes that occur in the inferior colliculus (IC) of mammals. To determine the contribution of the GABAergic transmitter systems to the development of response properties of IC neurons, we examined the effect of application of bicuculline (which is an antagonist for the GABA(A) receptors) on response properties of IC neurons of the laboratory mice, Mus musculus, with or without early monaural middle ear destruction. Monaural middle ear destruction was performed at 12-14 days after birth. At adulthood, the auditory response properties of IC neurons were examined in both experimental conditions. All IC neurons determined before and during bicuculline application can be described as (1) phasic responders which discharged 1-2 impulses; (2) phasic bursters which discharged 3-7 impulse; and (3) tonic responders which discharged impulses throughout the duration of presented sound pulses. Early monaural middle ear destruction only affected the percent distribution but not the type of discharge pattern, rate-intensity function and frequency tuning curve of IC neurons in the control and experimental mice. Neurons in the contralateral IC of experimental mice typically had longer latencies, higher minimum thresholds, broader frequency tuning curves and smaller dynamic ranges than neurons in the ipsilateral IC and in control mice. Bicuculline application produced differential effects in decreasing the latencies and minimum thresholds as well as broadening frequency tuning curves and dynamic ranges of IC neurons in these two groups of mice. All these data suggest that early monaural middle ear destruction did not affect the shaping of auditory response properties of IC neurons by GABAergic transmitter system.

Age Factors↗

PubMed2001

An electrophysiological study of neural pathways for corticofugally inhibited neurons in the central nucleus of the inferior colliculus of the big brown bat, Eptesicus fuscus.

This electrophysiological study tests the hypothesis that one possible neural pathway for corticofugally inhibited neurons in the central nucleus of the inferior colliculus (ICc) of the big brown bat, Eptesicus fuscus, is mediated through excitatory projections from the auditory cortex (AC) to the external nucleus of the IC (ICx), which then sends inhibitory inputs to the ICc. This study shows that all neurons in the ICx are broadly tuned to stimulus frequency. Electrical stimulation in the AC typically increases the number of impulses, expands the auditory spatial response areas, and broadens the frequency tuning curves (FTCs) of neurons in the ICx. This corticofugal facilitation is mediated at least in part through NMDA receptors, since application of DL-2-amino-5-phosphonovaleric acid (APV), an antagonist for NMDA, decreases these response properties of neurons in the ICx. Electrical stimulation in the ICx typically decreases the number of impulses, reduces the auditory spatial response areas, and narrows the FTCs of neurons in the ICc. This inhibition is mediated at least in part through GABAA receptors, since application of bicuculline, an antagonist for GABA, increases these response properties of neurons in the ICc. These data suggest that corticofugal facilitation of the ICx and the inhibition of the ICx to the ICc may be one of the polysynaptic pathways for corticofugal inhibition of neurons in the ICc. Possible functions of this polysynaptic pathway in acoustic orientation and signal processing are discussed.

Animals↗

PubMed2001

GABAergic and glycinergic neural inhibition in excitatory frequency tuning of bat inferior collicular neurons.

This study examined the effect of GABAergic and glycinergic inhibition on excitatory frequency tuning curves (FTCs) of inferior collicular (IC) neurons of the big brown bat, Eptesicus fuscus. The excitatory FTCs of 70 IC neurons were either V-shaped (57, 81%), closed (11, 16%), or double-peaked (2, 3%). By means of a two-tone stimulation paradigm, inhibitory FTCs were obtained at one frequency flank only (low-frequency flank: 11, 16%; high-frequency flank: 7, 10%), at both frequency flanks (36, 51%) of excitatory FTCs, or between two excitatory FTCs (2, 3%). IC neurons that had inhibitory FTCs typically had larger Q(10) and Q(30) values (i.e., sharper excitatory FTCs) than neurons that did not have inhibitory FTCs. Neurons with inhibitory FTCs at both frequency flanks had larger Q(10) and Q(30) values than neurons with inhibitory FTCs at one frequency flank only. IC neurons with a small difference between excitatory and inhibitory best frequencies typically had sharper excitatory frequency tuning. Bicuculline (an antagonist for GABAA) application produced a greater degree of abolishing inhibitory FTCs than strychnine (an antagonist for glycine) application. Application of both drugs was most effective in abolishing the inhibitory FTCs of IC neurons. The implications of these findings for bat echolocation are discussed.

Acoustic Stimulation↗

PubMed2001

The effect of sound intensity on duration-tuning characteristics of bat inferior collicular neurons.

Previous studies have shown that inferior collicular neurons of the big brown bat, Eptesicus fuscus, serve as short-, band-, long- and all-pass filters for sound durations. Neurons with band-, short- and long-pass filtering characteristics discharged maximally to a specific sound duration or a range of sound durations. In contrast, neurons with all-pass filtering characteristics do not have duration selectivity. To determine if duration-tuning characteristics of collicular neurons were tolerant to changes in sound intensity, we examined the duration-tuning characteristics of collicular neurons using a wide range of sound intensities. Duration-tuning characteristics examined included the type, bandwidth and slope of duration-tuning curves. Sound intensity delivered within 20 dB of minimum threshold did not affect duration-tuning characteristics of all collicular neurons studied. Sound intensities at still higher levels did not affect the tuning characteristics of two-thirds of collicular neurons but decreased the duration selectivity and changed the duration-tuning curves of the remaining one-third of neurons from one type to another. However, these two groups of duration-tuning collicular neurons were not separately organized inside the inferior colliculus. The biological relevance of these findings to bat echolocation is discussed.

Acoustic Stimulation↗

PubMed2001

Temporally patterned sound pulse trains affect intensity and frequency sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus.

This study examined the effect of temporally patterned pulse trains on intensity and frequency sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus. Intensity sensitivity of inferior collicular neurons was expressed by the dynamic range and slope of rate-intensity functions. Inferior collicular neurons with non-monotonic rate-intensity functions have smaller dynamic ranges and larger slopes than neurons with monotonic or saturated rate-intensity functions. Intensity sensitivity of all inferior collicular neurons improved by increasing the number of non-monotonic rate-intensity functions when the pulse repetition rate of pulse trains increased from 10 to 30 pulses per second. Intensity sensitivity of 43% inferior collicular neurons further improved when the pulse repetition rate of pulse trains increased still from 30 to 90 pulses per second. Frequency sensitivity of inferior collicular neurons was expressed by the Q10, Q20, and Q30 values of threshold frequency tuning curves and bandwidths of isointensity frequency tuning curves. Threshold frequency tuning curves of all inferior collicular neurons were V-shape and mirror-images of their counterpart isointensity frequency tuning curves. The Q10, Q20, and Q30 values of threshold frequency tuning curves of all inferior collicular neurons progressively increased and bandwidths of isointensity frequency tuning curves decreased with increasing pulse repetition rate in temporally patterned pulse trains. Biological relevance of these findings to bat echolocation is discussed.

Animals↗

PubMed2001

The effect of monaural middle ear destruction on postnatal development of auditory response properties of mouse inferior collicular neurons.

This study examined the effect of monaural middle ear destruction on postnatal development of auditory response properties of inferior collicular (IC) neurons of the laboratory mouse, Mus musculus. Monaural middle ear destruction was performed on juvenile and adult mice and the auditory response properties of neurons in both ICs were examined 4 weeks thereafter. IC neurons of control mice typically had lower minimum thresholds, larger dynamic ranges and greater Q(10) values than IC neurons of experimental juvenile and adult mice. In experimental mice, neurons in the ipsilateral IC (relative to the intact ear) typically had longer latencies, higher minimum thresholds, and smaller dynamic ranges than neurons in the contralateral IC. In experimental adult mice, neurons in the ipsilateral IC had sharper frequency tuning curves than neurons in the contralateral IC. Clear tonotopic organization was only observed in the IC of control mice and experimental adult mice. However, the correlation of increasing minimum threshold with best frequency was observed for IC neurons in control mice but not in experimental juvenile and adult mice. Possible mechanisms for these different response properties are discussed.

Acoustic Stimulation↗

PubMed2000

Corticofugal inhibition compresses all types of rate-intensity functions of inferior collicular neurons in the big brown bat.

Recent studies have shown that the auditory corticofugal system modulates and improves signal processing in the frequency, time and spatial domains. In this study, we examine corticofugal modulation of rate-intensity functions of inferior collicular (IC) neurons of the big brown bat, Eptesicus fuscus, by electrical stimulation in the primary auditory cortex (AC). Cortical electrical stimulation compressed all types of rate-intensity functions so as to increase the slope but decrease the dynamic range of IC neurons. Cortical electrical stimulation also shifts the responsive intensity of IC neurons to higher levels. These data indicate that corticofugal modulation also improves subcortical signal processing in intensity domain. The implication of these findings to bat echolocation is discussed.

Acoustic Stimulation↗

PubMed2000

The role of GABAergic inhibition on direction-dependent sharpening of frequency tuning in bat inferior collicular neurons.

This study examined the role of GABAergic inhibition on direction-dependent sharpening of frequency tuning curves (FTCs) in bat inferior collicular (IC) neurons under free field stimulation conditions. The minimum threshold (MT) at the neurons best frequency (BF) and the sharpness (Q(10), Q(20), Q(30)) of FTCs of most IC neurons increased as the sound direction changed from contralateral azimuths to ipsilateral azimuths. The application of GABA(A) antagonist, bicuculline, lowered all MTs but the application did not abolish direction-dependent variation in MT. MTs determined during bicuculline application at 40 ipsilateral were still significantly higher than those determined at 40 degrees contralateral (two-tailed paired t-test, P<0.0001). In contrast, although application of bicuculline essentially had no effect on the BFs of IC neurons, it differentially broadened neurons FTCs at different azimuths abolishing the direction-dependent sharpening of frequency tuning (i. e. Q(n) values, two-tailed paired t-test, P<0.01). These data indicate that GABAergic inhibition makes an important contribution to the direction-dependent frequency tuning of most IC neurons.

Animals↗

PubMed2000

Direction-dependent corticofugal modulation of frequency-tuning curves of inferior collicular neurons in the big brown bat, Eptesicus fuscus.

This study examined if corticofugal modulation of subcortical frequency-tuning curves varied with sound direction. Both excitatory and inhibitory frequency tuning curves of inferior collicular neurons of the big brown bat, Eptesicus fuscus were plotted before and during electrical stimulation in the auditory cortex at two sound directions (contra-40 degrees and ipsi-40 degrees). Most collicular neurons had broader excitatory frequency-tuning curves at contra-40 degrees but had broader inhibitory frequency-tuning curves at ipsi-40 degrees. Cortical electrical stimulation changed the excitatory minimum thresholds of most collicular neurons at a greater degree at ipsi-40 degrees than at contra-40 degrees. However, cortical electrical stimulation produced a greater increase in the sharpness of excitatory frequency-tuning curves of most corticofugally inhibited collicular neurons at contra-40 degrees but produced a greater decrease in the sharpness of excitatory frequency-tuning curves of most corticofugally facilitated collicular neurons at ipsi-40 degrees. Cortical electrical stimulation also produced a greater change in the sharpness of inhibitory frequency-tuning curves of most corticofugally inhibited collicular neurons at contra-40 degrees than at ipsi-40 degrees. Possible mechanisms for this direction-dependent corticofugal modulation of frequency-tuning curves of collicular neurons are discussed.

Animals↗

PubMed2000

Neural inhibition sharpens auditory spatial selectivity of bat inferior collicular neurons.

This study examines the role of neural inhibition in auditory spatial selectivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, using a two-tone inhibition paradigm. Two-tone inhibition decreases auditory spatial response areas but increases the slopes of directional sensitivity curves of inferior collicular neurons. Inferior collicular neurons have either directionally-selective or hemifield directional sensitivity curves. A directionally-selective curve always has a peak which is at least 50% larger than the minimum. A hemifield directional sensitivity curve rises from an ipsilateral angle by more than 50% and either reaches a plateau or declines by less than 50% over a range of contralateral angles. Two-tone inhibition does not change directionally-selective curves but changes most hemifield directional sensitivity curves into directionally-selective curves. Auditory spatial selectivity determined both with and without two-tone inhibition increases with increasing best-excitatory frequency. Sharpening of auditory spatial selectivity by two-tone inhibition is larger for neurons with smaller differences between excitatory and inhibitory best frequencies. The effect of two-tone inhibition on auditory spatial selectivity increases with increasing inhibitory tone intensity but decreases with increasing intertone interval. The implications of these findings in bat echolocation are discussed.

Animals↗

PubMed2000

Bicuculline application affects discharge patterns, rate-intensity functions, and frequency tuning characteristics of bat auditory cortical neurons.

This study examined the effect of bicuculline application on the auditory response properties in the auditory cortex of the big brown bat, Eptesicus fuscus. All auditory cortical neurons studied discharged either 1-2 or 3-7 impulses to 4 ms sound stimuli. Cortical neurons with high best frequencies tended to have high minimum thresholds. Bicuculline application increased the number of impulses and shortened the response latencies of all cortical neurons as well as changing the discharge patterns of half of the cortical neurons studied. Bicuculline application raised the rate-intensity functions but lowered the latency-intensity functions to varying degrees. Threshold-frequency tuning curves (FTCs) were either V-shaped, upper threshold or double-peaked. Threshold-FTCs and impulse-FTCs were mirror-images of each other. Bicuculline application expanded and raised the impulse-FTCs but lowered the threshold-FTCs, resulting in significantly decreased Q(n) values. Threshold-FTCs of cortical neurons determined within an orthogonally inserted electrode were very similar and expanded FTCs during bicuculline application were also very similar. Possible mechanisms for the contribution of GABAergic inhibition to shaping these response properties of cortical neurons are discussed.

Acoustic Stimulation↗

PubMed2000

Brief and short-term corticofugal modulation of subcortical auditory responses in the big brown bat, Eptesicus fuscus.

Recent studies show that the auditory corticofugal system modulates and improves ongoing signal processing and reorganizes frequency map according to auditory experience in the central nucleus of bat inferior colliculus. However, whether all corticofugally affected collicular neurons are involved in both types of modulation has not been determined. In this study, we demonstrate that one group (51%) of collicular neurons participates only in corticofugal modulation of ongoing signal processing, while a second group (49%) of collicular neurons participates in both modulation of ongoing signal processing and in reorganization of the auditory system.

Acoustic Stimulation↗

PubMed1999

corticofugal regulation of excitatory and inhibitory frequency tuning curves of bat inferior collicular neurons.

Corticofugal regulation of excitatory and inhibitory frequency tuning curves (FTCs) of neurons in the central nucleus of bat inferior colliculus (ICc) was studied by electrical stimulation of the primary auditory cortex (AC stimulation) under free field stimulation conditions using a two-tone inhibition paradigm. AC stimulation narrowed the excitatory FTCs and asymmetrically expanded the lateral inhibitory FTCs of corticofugally inhibited ICc neurons. The opposite results were observed for excitatory and inhibitory FTCs of corticofugally facilitated ICc neurons. These data support previous reports that corticofugal systems work together with widespread lateral inhibition to regulate subcortical frequency processing.

Acoustic Stimulation↗

PubMed1999

The effect of sound direction on frequency tuning in mouse inferior collicular neurons.

This study examined the effect of sound direction on frequency tuning of inferior collicular (IC) neurons of mice under free field stimulation conditions. Fewer than 20% of IC neurons studied were spontaneously active. Discharge patterns can be described as phasic on responders, phasic on-off responders, off responders, choppers and tonic responders. The frequency tuning curves (FTCs) of IC neurons can be described as narrow, intermediate or broad. Although sound direction typically had little effect on most best frequencies (BFs), sharpness of FTCs increased as sound direction changed from contralateral angles to ipsilateral angles. Sound delivered from the upper and lower portions of the frontal auditory space also appeared to produce sharper frequency tuning than from the front. Possible mechanisms underlying this direction dependent frequency tuning are discussed.

Action Potentials↗

PubMed1999

Bicuculline application affects discharge pattern and pulse-duration tuning characteristics of bat inferior collicular neurons.

This study examines the contribution of GABAergic inhibition to the discharge pattern and pulse duration tuning characteristics of 101 bat inferior collicular neurons by means of bicuculline application to their recording sites. When stimulated with single pulses 56 (55%) neurons discharged 1 or 2 impulses (phasic responders), 42 (42%) discharged 3-10 impulses (phasic bursters) and 3 (3%) discharged impulses throughout the stimulus duration (tonic responders). Bicuculline application increased the number of impulses and changed the discharge patterns of 66 neurons. Using 50% difference between maximal and minimal responses as a criterion, the duration tuning characteristics of these neurons can be described as band-pass (20, 20%), long-pass (17, 17%), short-pass (33, 32%), and all-pass (31, 31%). Each band-pass neuron discharged maximally to a specific duration (the best duration) which was at least 50% larger than the neuron's responses to a long-duration pulse and a short-duration pulse. In contrast, each long- or short-pass neuron discharged maximally to a range of long or short duration pulses. Bicuculline application changed the duration tuning characteristics of 65 neurons. Possible mechanisms underlying duration tuning characteristics and the behavioral relevance to bat echolocation are discussed.

Acoustic Stimulation↗

PubMed1999

Temporally patterned pulse trains affect duration tuning characteristics of bat inferior collicular neurons.

This study examines the effect of temporally patterned pulse trains on duration tuning characteristics of inferior collicular neurons of the big brown bat. Eptesicus fuscus, under free-field stimulation conditions. Using a 50% difference between maximal and minimal responses as a criterion, the duration tuning characteristics of inferior collicular neurons determined with pulse trains of different pulse durations are described as band-pass, long-pass, short-pass, and all-pass. Each band-pass neuron discharged maximally to a specific pulse duration that was at least 50% larger than the neuron's responses to a long- and a short-duration pulse. In contrast, each long- or short-pass neuron discharged maximally to a range of long- or short-duration pulses that were at least 50% larger than the minimal responses. The number of impulses of an all-pass neuron never differed by more than 50%. When pulse trains were delivered at different pulse repetition rates, the number of short-pass and band-pass neurons progressively increased with increasing pulse repetition rates. The slope of the duration tuning curves also became sharper when determined with pulse trains at high pulse repetition rates. Possible mechanisms underlying these findings are discussed.

Acoustic Stimulation↗

PubMed1998

The effect of pulse repetition rate, pulse intensity, and bicuculline on the minimum threshold and latency of bat inferior collicular neurons.

This study examines the effect of pulse repetition rate (PRR), pulse intensity, and bicuculline on the minimum threshold (MT) and latency of inferior collicular neurons of the big brown bat, Eptesicus fuscus, under free-field stimulation conditions. It tests the hypothesis that changes in MT and latency of collicular neurons are co-dependent on PRR. The number of impulses in inferior collicular neurons (n = 245) increased either monotonically (25%) or non-monotonically (75%) with pulse intensity. Latencies either decreased to a plateau (72%), fluctuated unpredictably within 3 ms (21%) or changed very little (7%) with increasing pulse intensity. Latencies and MTs of most collicular neurons increased by 1.5-24 ms (mean +/- SD = 4.8 +/- 3.3 ms) and 4-75 dB (mean +/- SD = 22.1 +/- 16.2 dB) with increasing PRR. In most neurons (94%), the latency increase was completely (42%) or partially (52%) eliminated when pulse intensity was compensated for the MT increase with PRR. Complete elimination of latency was achieved by bicuculline application. In a few neurons (6%), the latency increase with PRR was not affected by compensated pulse intensity or bicuculline application.

Animals↗