Biomedical subjects

P H Jen

Publications and source records attributed to P H Jen.

At least 19 recordsLinked to original sources

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↗

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↗

PubMed1998

Corticofugal regulation of auditory sensitivity in the bat inferior colliculus.

Under free-field stimulation conditions, corticofugal regulation of auditory sensitivity of neurons in the central nucleus of the inferior colliculus of the big brown bat, Eptesicus fuscus, was studied by blocking activities of auditory cortical neurons with Lidocaine or by electrical stimulation in auditory cortical neuron recording sites. The corticocollicular pathway regulated the number of impulses, the auditory spatial response areas and the frequency-tuning curves of inferior colliculus neurons through facilitation or inhibition. Corticofugal regulation was most effective at low sound intensity and was dependent upon the time interval between acoustic and electrical stimuli. At optimal inter-stimulus intervals, inferior colliculus neurons had the smallest number of impulses and the longest response latency during corticofugal inhibition. The opposite effects were observed during corticofugal facilitation. Corticofugal inhibitory latency was longer than corticofugal facilitatory latency. Iontophoretic application of gamma-aminobutyric acid and bicuculline to inferior colliculus recording sites produced effects similar to what were observed during corticofugal inhibition and facilitation. We suggest that corticofugal regulation of central auditory sensitivity can provide an animal with a mechanism to regulate acoustic signal processing in the ascending auditory pathway.

Animals↗

PubMed1998

GABAergic disinhibition affects responses of bat inferior collicular neurons to temporally patterned sound pulses.

Using the big brown bat, Eptesicus fuscus, as a model mammalian auditory system, we studied the effect of GABAergic disinhibition by bicuculline on the responses of inferior collicular (IC) neurons to temporally patterned trains of sound pulses delivered at different pulse repetition rates (PRRs) under free-field stimulation conditions. All 66 neurons isolated from eight bats either discharged one to two impulses (phasic on responders, n = 41, 62%), three to eight impulses (phasic bursters, n = 19, 29%), or many impulses throughout the entire duration of the stimulus (tonic responders, n = 6, 9%). Whereas 50 neurons responded vigorously to frequency-modulated (FM) pulses, 16 responded poorly or not at all to FM pulses. Bicuculline application increased the number of impulses of all 66 neurons in response to 4 ms pulses by 15-1,425%. The application also changed most phasic on responders into phasic bursters or tonic responders, resulting in 12 (18%) phasic on responders, 34 (52%) phasic bursters, and 20 (30%) tonic responders. Response latencies of these neurons were either shortened (n = 25, 38%) by 0.5-6.0 ms, lengthened (n = 9, 14%) by 0. 5-2.5 ms or not changed (n = 32, 48%) on bicuculline application. Each neuron had a highest response repetition rate beyond which the neuron failed to respond. Bicuculline application increased the highest response repetition rates of 62 (94%) neurons studied. The application also increased the highest 100% pulse-locking repetition rates of 21 (32%) neurons and facilitated 27 (41%) neurons in response to more pulses at the same PRR than predrug conditions. According to average rate-based modulation transfer functions (average rate MTFs), all 66 neurons had low-pass filtering characteristics both before and after bicuculline application. According to total discharge rate-based modulation transfer functions (total rate MTFs), filtering characteristics of these neurons can be described as band-pass (n = 52, 79%), low-pass (n = 12, 18%), or high-pass (n = 2, 3%) before bicuculline application. Bicuculline application changed the filtering characteristics of 14 (21%) neurons. According to synchronization coefficient-based modulation transfer functions, filtering characteristics of these neurons can be described as low-pass (n = 41, 62%), all-pass (n = 11, 17%), band-suppression (n = 7, 10.5%), and band-suppression-band-pass filters (n = 7, 10.5%). Bicuculline application changed filtering characteristics of 19 (29%) neurons.

Acoustic Stimulation↗

PubMed1998

Recovery cycles of neurons in the inferior colliculus, the pontine nuclei and the auditory cortex of the big brown bat, Eptesicus fuscus.

This study examines the recovery cycles of neurons in the inferior colliculus (IC), the pontine nuclei (PN) and the auditory cortex (AC) of the big brown bat, Eptesicus fuscus, using a pair of identical pulses at different interpulse intervals. Although the recovery cycle varies among neurons, on average, AC neurons have the longest recovery cycle and PN neurons have the shortest one. The recovery cycle of IC neurons is slightly longer than PN neurons. Neurons tend to have longer recovery cycles when determined with long pulse duration than short one. The minimum threshold of these neurons to the second pulse increases with decreasing interpulse interval. The difference in the recovery cycles of these neurons supports previous findings that IC and PN neurons can follow sound pulses at higher rates than AC neurons do.

Acoustic Stimulation↗

PubMed1997

GABAergic disinhibition changes the recovery cycle of bat inferior collicular neurons.

This study examines the contribution of GABAergic inhibition to the discharge pattern and recovery properties of 110 bat inferior collicular neurons by means of bicuculline application to their recording sites. When stimulated with single pulses, 74 (67%) neurons discharged one or two impulses (phasic responders), 19 (17%) discharged three to ten impulses (phasic bursters) and 17 (16%) discharged impulses throughout the entire stimulus duration (tonic responders). Bicuculline application changed phasic responders into phasic bursters or tonic responders, increased the number of impulses by 10-2000% and shortened the response latency of most neurons. When stimulated with pairs of sound pulses, the recovery cycles of these neurons can be described as: (1) long inhibition (n = 49, 45%); (2) short inhibition (n = 41, 37%); and (3) fast recovery (n = 20, 18%) based upon the 50% recovery time that was either longer than 20 ms, between 10 and 20 ms or shorter than 10 ms. Bicuculline application shortened the 50% recovery time of most neurons by 11-2350% allowing them to respond to pairs of sound pulses at very short interpulse intervals. These data demonstrate that GABAergic inhibition contributes significantly to auditory temporal processing.

Animals↗

PubMed1997

Binaural and frequency representation in the primary auditory cortex of the big brown bat, Eptesicus fuscus.

This study examines the binaural and frequency representation in the primary auditory cortex (AC) of the big brown bat, Eptesicus fuscus, by using an ear-phone stimulation system. All 306 cortical neurons studied were excited by contralateral sound stimulation but they were either excited, inhibited or not affected by ipsilateral sound stimulation. These cortical neurons were columnarly organized according to their binaural and frequency-tuning properties. The excitation-excitation columns which occupy about 15% of the AC are mainly aggregated within an oval-shaped area of the central AC. The excitation-inhibition neurons and binaural neurons with mixed properties are distributed in the remaining 85% of the surrounding primary AC. Although the best frequency (BF) of these neurons shows a tendency to decrease from high to low along the anteroposterior axis of the primary AC, systematic variation in BF is not always consistent across the entire mapping area. In particular, BFs of cortical neurons isolated in the anterior AC vary quite unsystematically such that neurons with similar BFs are aggregated in isolated patches. Isofrequency and binaural columns are segregated into bands that intersect each other.

Acoustic Stimulation↗

PubMed1997

Cytoarchitecture and sound activated responses in the auditory cortex of the big brown bat, Eptesicus fuscus.

Under free field and closed-system stimulation conditions, we studied the frequency threshold curves, auditory spatial sensitivity and binaurality of neurons in the primary auditory cortex (AC) of the big brown bat, Eptesicus fuscus. All 298 recorded AC neurons discharged phasically. They were recorded at depths less than 1,000 microns with response latencies of 7-25 ms, best frequencies (BFs) of 28-97 kHz and minimum thresholds (MTs) of 8-90 dB SPL. They received excitatory inputs from the contralateral ear and either excitatory (EE) or inhibitory (EI) inputs from the ipsilateral ear. These cortical neurons were tonotopically organized along the anteroposterior axis of the AC. High best frequency neurons were located anteriorly and low best frequency neurons posteriorly. They were most sensitive to sounds delivered from a restricted region of the contralateral frontal auditory space (0 degree-50 degrees in azimuth and 2 degrees up, 15 degrees down in elevation). Frontal auditory space representation appears to be systematically arranged according to the tonotopic axis such that the lateral space is represented posteriorly and the middle space anteriorly. Cortical neurons sequentially isolated from an orthogonally penetrated electrode had similar frequency threshold curves, BFs, MTs, points of maximal auditory spatial sensitivity and binaurality. The EE and EI columns are organized concentrically such that the small number of centrally located EE columns were surrounded by an overwhelming number of EI columns. Using Nissl and Golgi stains as well as c-fos immunocytochemistry, we studied the cytoarchitecture, cell types and sound elicited Fos-like immunoreactivity in the primary AC of this bat species. The primary AC of this bat species can be described into molecular (137 microns), external granular (55 microns), external pyramidal (95 microns), internal granular (102 microns), internal pyramidal (191 microns) and multiform (120 microns) layers. The main type of cells distributed among these six layers are the small, medium and large pyramidal cells. Others include the stellate, horizontal, granular, fusiform, basket, and Martinotii cells. When stimulated with 30 kHz and 79 dB SPL sounds under natural conditions, bilaterally and symmetrically distributed Fos-like immunoreactive neurons were observed in about 20% of neurons in each AC. When stimulated under monaurally plugged conditions, 39-48% more of Fos-like immunoreactive neurons were observed in the ipsilateral AC. This finding supports the fact that the primary AC receives auditory inputs mainly from the contralateral ear.

Acoustic Stimulation↗

PubMed1997

Responses of bat inferior collicular neurons to recorded echolocation pulse trains.

Under free field stimulation conditions, we studied the responses of inferior collicular neurons of the big brown bat, Eptesicus fuscus, to echolocation pulse trains which were recorded during the entire process of hunting. The entire series of recorded echolocation pulse trains was edited in different sequences according to echolocation pulses of different hunting phases. When stimulated with all edited sequences of echolocation pulse trains, the temporal characteristics and the relative position of the echolocation pulses of a specific hunting phase affect the number of impulses of each inferior collicular neuron studied. When stimulated with two different intensities, more than 59% of inferior collicular neurons studied discharged selectively to the echolocation pulses of a specific hunting phase such that the number of impulses discharged to the echolocation pulses of the most and least preferred hunting phases differed by at least 50%. Passible mechanisms for this selective response are discussed.

Animals↗

PubMed1997

Sound pressure transformation at the pinna of Mus domesticus.

Sound pressure transformation properties at the pinna of laboratory mice. Mus domesticus, were studied by measuring the sound pressure level of continuous tone at a series of frequencies at the tympanic membrane as a function of the position of a sound source under free-field stimulation conditions. Sound pressure transformation functions showed some prominent spectral notches throughout the frequency range of 10-80 kHz tested. When delivered from some angles within the ipsilateral frontal hemisphere, the sound pressure at the tympanic membrane of certain frequencies may be lower than that determined at the corresponding contralateral angles. For each sound frequency tested, there was an angle (the acoustic axis) within the ipsilateral frontal hemisphere from which the delivered sound reached a maximal pressure level at the tympanic membrane. However, sound delivered from the acoustic axis did not always generate a maximal pressure transformation. The isopressure contours determined within 2-5 dB of the maximal pressure were circumscribed, and their contained angular areas were found to decrease with increasing sound frequency. The 2 dB maximal pressure area may appear at more than one angular area for some test frequencies. Removal of the ipsilateral pinna or modification of pinna posture expanded isopressure contours irregularly and split the 2 dB maximal pressure area into several parts.

Animals↗

PubMed1996

Tracing the auditory pathways to electrophysiologically characterized neurons with HRP and Fos double-labeling technique.

By combining HRP histochemistry with Fos immunocytochemistry, we demonstrate in this study that electrophysiologically characterized auditory neurons can be double-labeled with HRP and Fos after iontophoretic injection of HRP into the recording site. Neurons which projected fibers to the recording site were labeled with HRP and were Fos-like immunoreactive. This double-labeling technique in combination with electrophysiological recording offers the possibility to determine the fiber projections between sound-activated neurons which are identified either electrophysiologically and/or immunocytochemically.

Animals↗

PubMed1996

Corticofugal control of central auditory sensitivity in the big brown bat, Eptesicus fuscus.

Using bats as a model auditory system, we studied corticofugal control of auditory sensitivity of neurons in the inferior colliculus. We demonstrate for the first time that the corticocollicular pathway continuously regulates acoustic signal processing in the inferior colliculus by increasing the threshold, reducing the auditory spatial response area, and sharpening the frequency tuning curve of recorded inferior collicular neurons. Regulation of auditory sensitivity of recorded inferior collicular neurons was observed when the corticocollicular pathway was activated by electrical stimulation in the auditory cortex. The effect of this corticofugal regulation of auditory sensitivity in inferior collicular neurons can also be produced by ionophoretical application of GABA to the collicular recording site. This regulation of ascending acoustic information by commands originating from higher brain centers may provide the bat with a mechanism to actively control acoustic signal processing and thus optimize acoustic signal analysis.

Animals↗

PubMed1996

Temporally patterned pulse trains affect directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus.

The directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, was studied under free field stimulation conditions with 3 temporally patterned trains of sound pulses which differed in pulse repetition rate and duration. The directional sensitivity curves of 92 neurons studied can be described as hemifield, directionally-selective, or non-directional according to the variation in the number of impulses with pulse train direction. When these neurons were stimulated with all 3 pulse trains, the directional sensitivity curves of 50 neurons was unchanged but that of the other 42 neurons changed from one type into another. When these pulse trains were delivered at high pulse repetition rate and short pulse duration, they significantly sharpened the directional sensitivity of two thirds of the neurons examined by reducing the angular range and increasing the slope of their impulse directional sensitivity curves. These pulse trains also sharpened the slope of the threshold directional sensitivity curves of 25 neurons studied. However, when directional sensitivity of collicular neurons was determined with pulse trains that differed only in pulse repetition rate or in pulse duration, significant sharpening of directional sensitivity was rarely observed in all experimental conditions tested. Possible mechanisms underlying these findings are discussed.

Animals↗

PubMed1996

Responses of bat inferior collicular and auditory cortical neurons to pulsatile amplitude modulated sound pulses.

Under free field stimulation conditions, this study examined the responses of inferior collicular and cortical neurons of the big brown bat, Eptesicus fuscus, to pulsatile amplitude modulated sound pulses by means of temporally patterned pulse trains. When the pulse trains were delivered at different pulse repetition rates between 1 and 100 pps, inferior collicular neurons can follow pulse repetition at a higher rate than can auditory cortical neurons. 85% of 40 inferior collicular neurons studied always discharged impulses to each presented pulse delivered at repetition rates of up to 40 pps and 20% of these neurons could follow the repetition rate throughout the entire range of repetition rates tested. In contrast, only 60% of 56 auditory cortical neurons could follow a repetition rate up to 10 pps. At higher repetition rates, they only discharged impulses to the first pulse of each pulse train. According to variation in number of impulses, filtering properties of responses of inferior collicular and auditory cortical neurons to pulse repetition rate can be described as low-pass, high-pass, or band-pass. Most (63%) inferior collicular neurons behaved like band-pass filters to pulse repetition rate while most auditory cortical neurons behaved like all-pass (52%) or low-pass (37%) filters. Possible mechanisms underlying the different filtering properties between the inferior collicular and auditory cortical neurons are discussed.

Acoustic Stimulation↗

PubMed1995

Responses of pontine neurons of the big brown bat, Eptesicus fuscus, to temporally patterned sound pulses.

Under free field stimulation conditions, this study examined the responses of pontine neurons of Eptesicus fucus to temporally patterned sound pulses by means of repetitive single pulses and pulse trains. Among 93 pontine neurons isolated, 90 always discharged less than 5 impulses to sound pulses presented during this study and 3 discharged impulses throughout the whole duration of each presented pulse. Responses to sound pulses at different repetition rates were examined in 65 neurons. The number of impulses of individual neurons discharged to each pulse varied within a given repetition rate and among different repetition rates. Although these pontine neurons showed different degrees of habituation to high repetition rates, more than 25% could follow the highest repetition rate tested (100 pps). However, they did not always discharge maximal number of impulses to this repetition rate. The total number of impulses discharged by a neuron was also affected by pulse duration. Thus, each pontine neuron discharged maximally to a specific combination of pulse repetition rate and duration. Using a 50% difference between the maximal and minimal responses as a criterion, the function with respect to repetition rate and duration can be described as band-pass, high-pass, all-pass and irregular. These response properties reflect more those of inferior collicular neurons than auditory cortical neurons. This study also showed that response latencies of pontine neurons examined were lengthened by increasing pulse repetition rate and duration. In addition, whereas minimum thresholds of pontine neurons were elevated by increasing repetition rate, they were lowered by increasing pulse duration.

Acoustic Stimulation↗

PubMed1995

Sound pressure transformation at the pinna of Mus domesticus.

Sound pressure transformation properties at the pinna of laboratory mice Mus domesticus were studied by measuring the sound pressure level of a continuous tone at a series of frequencies at the tympanic membrane as a function of the position of a sound source under free-field stimulation conditions. The spectral transformation, the interaural spectral difference, the isopressure contours and the interaural pressure difference contours were plotted. Sound pressure transformation functions showed some prominent spectral notches throughout the frequency range tested (10-80 kHz). However, the notch frequency did not appear to be systematically related to sound direction. The study of interaural pressure difference demonstrated that, when delivered from some angles within the ipsilateral frontal hemisphere, the sound pressure at the tympanic membrane of certain frequencies may be lower than that determined at the corresponding contralateral angles. For each sound frequency tested, there was an angle (the acoustic axis) within the ipsilateral frontal hemisphere from which the delivered sound reached a maximal pressure level at the tympanic membrane. However, the acoustic axis often changed to a new angle after removal of the ipsilateral pinna. In addition, sound delivered from the acoustic axis did not always generate a maximal pressure transformation. The isopressure contours determined within 2-5 dB of the maximal pressure were circumscribed, and their contained angular areas were found to decrease with increasing sound frequency. The 2 dB maximal pressure area may appear at more than one angular area for some test frequencies. Removal of the ipsilateral pinna or modification of pinna posture expanded isopressure contours irregularly and split the 2 dB maximal pressure area into several parts. The sound pressure difference determined between the angles of maximal and minimal sound pressure (the maximal directionality) increased with sound frequency regardless of pinna posture. Acoustic gain of the pinna at the acoustic axis reached 6-12 dB, depending upon sound frequency. However, the pinna gain was not always maximal at the acoustic axis for a given frequency.

Animals↗

PubMed1994

Fos-like immunoreactivity elicited by sound stimulation in the auditory neurons of the big brown bat Eptesicus fuscus.

C-fos immunocytochemistry was used as a rapid and sensitive technique for identification of sound activated neurons in the cerebral cortex, the cerebellum and subcortical nuclei of the big brown bat, Eptesicus fuscus. When bats were stimulated with sounds under the both-ears opened conditions, Fos-like immunoreactive neurons were bilaterally and symmetrically distributed in all subcortical auditory nuclei, the auditory cortex, the superior colliculus, the pontine nuclei and the cerebellar deep nuclei. Interestingly, when bats were stimulated with sounds under the monaurally plugged conditions, a larger (31-74% more) number of Fos-like immunoreactive neurons were observed. They were predominantly distributed in all contralateral auditory nuclei from the level of the nucleus of the lateral lemniscus down and in all ipsilateral auditory nuclei from the level of inferior colliculus up as well as in the contralateral superior colliculus, pontine nuclei and cerebellar deep nuclei. Implications of these observations in relation to known mammalian auditory pathways and electrophysiological studies are discussed.

Acoustic Stimulation↗

PubMed1994

Pulse repetition rate increases the minimum threshold and latency of auditory neurons.

The effect of pulse repetition rate on auditory sensitivity of the big brown bat, Eptesicus fuscus, was studied by determining the minimum threshold, response latency and recovery cycle of inferior collicular neurons at different repetition rates under free field stimulation conditions. In general, collicular neurons shortened the response latency and increased the number of impulses monotonically or non-monotonically with stimulus intensity. They recovered at least 50% when the interpulse interval was 10-57 ms. In addition, they increased the minimum threshold, lengthened the response latency, and reduced the number of impulses discharged to each pulse with increasing repetition rate. The increase in minimum threshold with repetition rate is partly because the neuron can not recover from previous stimulation when the interpulse interval is shortened. This increase reduces a neuron's response sensitivity and thus diminishes its number of impulses to each presented pulse. This increase also reduces the effectiveness of a given stimulus intensity which contributes to the lengthening of the neuron's response latency. Data obtained from single neuron recordings are used to highlight these observations. Implications of present findings regarding the bat's echolocation are also discussed.

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