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A S Feng

Publications and source records attributed to A S Feng.

At least 55 records · Page 3Linked to original sources
PubMed1990

Classification of the temporal discharge patterns of single auditory neurons in the dorsal medullary nucleus of the northern leopard frog.

1. The dorsal medullary nucleus (DMN) of frogs is the presumed homolog of the mammalian cochlear nucleus (CN). Like the CN, the DMN is the sole target of centrally projecting primary auditory-nerve fibers and the first central auditory-processing center. To study the transformation of acoustic information in the DMN, we have utilized relatively simple stimuli--tone bursts--to detail the temporal discharge patterns of DMN neurons that can be compared with those shown by auditory-nerve fibers. 2. Based on the shape of poststimulus time (PSTH) and interspike interval (ISIH) histograms, we observed six distinctive discharge patterns to tone bursts presented at the best excitatory frequency (BEF), 10 dB above threshold. Four of these (primary-like type 1-4) resembled discharge patterns seen at the level of the auditory nerve, whereas two (phasic and phasic burst) were only observed in the DMN. 3. At stimulus levels of 20-30 dB above BEF threshold several phasic neurons became tonic responders, whereas several primary-like type-2 cells gave "pauser" discharges. The response patterns of the remaining cells were intensity independent. 4. We further showed that many of the single-unit discharge patterns were related to other neuronal response properties; specifically, spontaneous firing rate, intensity-rate functions, threshold, latency, BEF, and sharpness of tuning (Q10). 5. The implications of our findings are discussed with respect to 1) the transformation of acoustic information as it is passed from the auditory nerve to the DMN, and 2) the functional organization of the DMN.

Acoustic Stimulation↗
PubMed1988

Influence of envelope rise time on neural responses in the auditory system of anurans.

The influence of envelope rise time on neural responses was investigated in the central auditory pathway of frogs. Single unit and evoked potential recordings were made from the dorsal medullary nucleus (DMN) and thalamus, respectively. It was found that phasic neurons (15% of the population) in the DMN responded preferentially to stimuli with rapid (less than 25 ms) rise times. Acoustically evoked potentials (AEPs) recorded from the thalamus, specifically the Nucleus of Bellonci, also showed more pronounced responses to stimuli with rapid, rather than slower, envelope rise times. Interestingly, the leopard frog mating call, which has a rapid onset, elicited strong neuronal discharge both within the DMN and thalamus. In contrast, the mating call of bullfrogs, a species sympatric with leopard frogs, has a characteristically slow (greater than 100 ms) envelope rise time and elicited little, if any, response. These findings indicate the presence of neural specializations within the frog's auditory pathway for the optimal detection of the conspecific mating call. The relevance of these findings for stimulus coding in the auditory pathway of other vertebrates is discussed.

Animals↗
PubMed1987

Evidence for parallel processing in the frog's auditory thalamus.

We have conducted anatomical and physiological experiments to investigate the functional organization of the dorsal thalamus in the northern leopard frog (Rana pipiens pipiens). Our studies provide evidence for parallel auditory processing at this level of the frog's brain. Acoustically evoked potentials were recorded from the posterior and central thalamic nuclei and several differences in sound-evoked activity were noted between them: the amplitude of acoustically evoked potentials (AEPs), in response to a standard search stimulus, was always greater in the central, as opposed to the posterior, nucleus; the posterior, but not central, nucleus exhibited the phenomenon of nonlinear summation when 350-Hz and 1,700-Hz tones were presented simultaneously rather than individually; and the central, but not posterior, nucleus showed selectivity for the repetition rate of pulsed sound signals. The posterior and central thalamic nuclei also possessed distinct innervation patterns as revealed by the HRP transport patterns arising from these structures. The central nucleus was reciprocally connected with the major auditory relay stations along the frog's central auditory pathway including the superior olive, nucleus of the lateral lemniscus, and the torus semicircularis. Major projections to the lateral thalamic nucleus, ventral hypothalamus, and the telencephalic striatal complex were also observed. The posterior nucleus, on the other hand, established reciprocal connections primarily with the medial reticular nucleus, ventral midbrain tegmentum, and structures constituting of the ventral thalamic nuclei, particularly the nucleus of Bellonci. Thus, time and frequency cues contained within the species mating call, and conveying information concerning species identity, appear to be processed independently within the frog's thalamus with separate neural channels for each.

Animals↗
PubMed1987

Autoradiographic study of descending pathways from the pontine reticular formation and the mesencephalic trigeminal nucleus in the rat.

Descending projections were studied in autoradiographically prepared material after injections of tritiated leucine in the pontine tegmentum of rats. Injections involving the medial pontine reticular formation resulted not only in labeling commissural fibers, the medial reticulospinal tract, and the dorsal cap of the inferior olive, but also, in two cases, in labeling a cerebellar projection that originated from a region near the midline and clearly dorsal to the nucleus reticularis tegmenti pontis. The labeled fibers passed ventral in the midline to the pontine gray, then laterally through the gray and into the middle cerebellar peduncle to terminate as mossy fibers primarily in the flocculus, lobulus simplex, and Crus I of the ansiform lobule. Injections involving the mesencephalic nucleus of the trigeminal nerve (Vmes), resulted in labeling of Probst's tract, which descends in the dorsolateral reticular formation. Probst's tract gave off extensive terminal branches to the lateral medullary reticular formation and weaker projections to restricted portions of the descending trigeminal nucleus, the solitary nucleus, and the hypoglossal nucleus. In one case, fibers could be traced into the dorsal horn of the upper cervical cord.

Abducens Nerve↗
PubMed1986

Afferent and efferent innervation patterns of the cochlear nucleus (dorsal medullary nucleus) of the leopard frog.

The afferent and efferent innervation patterns of the frog dorsal medullary nucleus (DMN; anuran homolog of the cochlear nucleus) were examined by studying the anterograde and retrograde transport patterns of horseradish peroxidase injected focally into the nucleus. It was found that this structure projected bilaterally to the superior olivary nuclei (SON) and dorsal midbrain tegmental nuclei, and contralaterally to the opposite DMN, the lateral lemniscus nucleus (LLN) and the torus semicircularis (TS). The termination sites in the TS were restricted to the laminar and principal nuclei. The DMN in turn received projections from these structures with the exception of the TS and dorsal tegmental nuclei. The projection to the ipsilateral LLN and TS was not pronounced. In addition to the above findings, the ascending projection to the DMN, SON and TS, as well as the centrifugal projection from the SON, were found to be organized tonotopically.

Animals↗
PubMed1986

Neural analysis of temporally patterned sounds in the frog's thalamus: processing of pulse duration and pulse repetition rate.

We conducted a single unit study of auditory neurons in the central thalamic nucleus of the northern leopard frog. These cells, unlike those of the posterior thalamic nucleus (J. Comp. Physiol., 150 (1983) 333-344), were broadly tuned and sensitive to one or more temporal features (pulse duration and repetition rate) of complex sound signals. When compared with previous studies, these results suggest that temporal and spectral information may be processed separately by distinct populations of neurons within the frog's thalamus.

Acoustic Stimulation↗
PubMed1986

Afferent and efferent innervation patterns of the superior olivary nucleus of the leopard frog.

An HRP study of the frog's superior olivary nucleus (SON) revealed that it (1) receives reciprocal tonotopic projections from dorsal medullary nuclei and principal nuclei of the torus semicircularis (TS) bilaterally; (2) receives bilateral projections from caudalis nuclei and brainstem reticular nuclei, and unilateral projections from the ipsilateral ventral tegmental nuclei and the contralateral SON; (3) is reciprocally connected with the ipsilateral laminar and magnocellular nuclei of the TS, dorsal tegmental nuclei and the posterior thalamic nucleus; (4) projects directly to the ipsilateral central thalamic nucleus.

Animals↗
PubMed1985

Functional organization of the cochlear nucleus of rufous horseshoe bats (Rhinolophus rouxi): frequencies and internal connections are arranged in slabs.

The functional organization of the cochlear nucleus (CN) was studied with physiological recording and anatomical tracing techniques. Recordings were made from single CN neurons to examine their temporal firing patterns to tone burst stimuli and their frequency tuning characteristics. Recording loci of individual neurons were carefully monitored in order to understand how the functional properties of a cell relate to its location within the CN. We found that tonal frequencies were systematically represented in each of the three CN divisions (anteroventral, AVCN; posteroventral, PVCN; dorsal, DCN). Eight temporal response patterns were observed in CN neurons when stimulated at units' best excitatory frequencies (BF). With a few exceptions, neurons in each CN division could generate all eight firing patterns with different distributions for the three division. A focal injection of horseradish peroxidase (HRP), at the end of the physiological study, to a group of neurons possessing a similar BF in one CN division resulted in anterograde labeling of nerve terminals in the other two divisions at precisely the areas where the same frequency band was processed in these divisions. Labeled terminals in each division were closely congregated in the form of a thin slab. The slab orientation was division specific whereas its location was frequency specific, which could be predicted on the basis of physiological data. HRP injections into the DCN also resulted in retrograde labeling of somata in the AVCN and PVCN. On the other hand, only DCN neurons were retrogradely labeled when HRP was injected into the AVCN or the PVCN. These data showed how the three CN divisions are internally connected. Furthermore, retrogradely labeled cells occupied the same slabs where we found anterogradely labeled nerve terminals. Additionally, in a group of bats, HRP was injected into various functionally (i.e., BF) identified regions of the central nucleus of the inferior coliculus (IC) to clarify the type and location of CN projecting neurons. Retrogradely labeled cells in individual CN divisions likewise were arranged in slabs whose locations in the CN nuclei depended on the BFs of neurons at the injection site in the IC. These results show that slabs represent units of functional organization (i.e., tonal frequency, local connection and central projection) in the CN.

Animals↗
PubMed1985

An HRP-study of the frequency-place map of the horseshoe bat cochlea: morphological correlates of the sharp tuning to a narrow frequency band.

The frequency-place map of the horseshoe bat cochlea was studied with the horseradish peroxidase (HRP) technique involving focal injections into various, physiologically defined regions of cochlear nucleus (CN). The locations of labeled spiral ganglion cells and their termination sites on inner hair cells of the organ of Corti from injections into CN-regions responsive to different frequencies were analyzed in three dimensional reconstructions of the cochlea. Horseshoe bats from different geographical populations were investigated. They emit orientation cells with constant frequency (CF) components around 77 kHz (Rhinolophus rouxi from Ceylon) and 84 kHz (Rhinolophus rouxi from India) and their auditory systems are sharply tuned to the respective CF-components. The HRP-map shows that in both populations: the frequency range around the CF-component of the echolocation signal is processed in the second half-turn of the cochlea, where basilar membrane (BM) is not thickened, secondary spiral lamina (LSS) is still present and innervation density is maximal; frequencies more than 5 kHz above the CF-component are processed in the first half-turn, where the thickened BM is accompanied by LSS and innervation density is low; frequencies below the spectral content of the orientation call are represented in apical turns showing no morphological specializations. The data demonstrate that the cochlea of horseshoe bats is normalized to the frequency of the individual specific CF-component of the echolocation call. The HRP-map can account for the overrepresentation of neurons sharply tuned to the CF-signal found in the central auditory system. A comparison of the HRP-map with a map derived with the 'swollen nuclei technique' following loud sound exposure (Bruns 1976b) reveals that the latter is shifted towards cochlear base by about 4 mm. This discrepancy warrants a new interpretation of the functional role of specialized morphological structures of the cochlea within the mechanisms giving rise to the exceptionally high frequency selectivity of the auditory system.

Animals↗
PubMed1984

Quantitative light and scanning electron microscopic study of the developing auditory organs in the bullfrog: implications on their functional characteristics.

During postmetamorphic development in the bullfrog, there is a downward shift in the distributions of best excitatory frequencies (BEFs) of the three populations of primary auditory fibers. This decrease in BEF distribution suggests that concurrent morphological changes occur in the peripheral auditory system during postmetamorphic growth. The postmetamorphic development of the auditory organs in the bullfrog was quantitatively investigated with light and scanning electron microscopy. In the basilar papilla, there are dramatic increases in the lumen volume, contact membrane area, and mass of the tectorial membrane (TM). The area of the sensory epithelium and the total number of hair cells also increase slightly. In the amphibian papilla, the mass of the TM is spatially graded in a step-wise fashion along the length of the organ in both juvenile and adult bullfrogs, but there is an increase in the absolute mass of the TM throughout the papilla with age. The height of the tallest stereocilia of the predominant hair cell type systematically decreases caudally in the juvenile amphibian papilla, but is uniform throughout the adult papilla. The increase in stereociliary height in the caudal end of the organ presumably results in a decrease in stereociliary stiffness with postmetamorphic age. The length of the amphibian papilla sensory epithelium and the number of hair cells also increase during postmetamorphic development. Theoretically, the observed morphological changes alter the micromechanical tuning properties of the auditory organs so that there is a decrease in the BEFs of the auditory fibers that innervate the two papillae.

Animals↗
PubMed1983

Morphology of neurons in the torus semicircularis of the northern leopard frog, Rana pipiens pipiens.

The neuronal morphology of the torus semicircularis of the northern leopard frog, Rana pipiens pipiens, was examined in Golgi-impregnated material. Neurons in each of the five subdivisions of the torus semicircularis (Potter, '65a) have distinct morphologies which are characteristic of the subdivision. Laminar nucleus neurons are mostly multipolar with spherical or ovoidal somata and smooth dendrites oriented primarily parallel and perpendicular to the cell laminae. Principal nucleus neurons have variable soma shapes with short dendrites (less than 100 micrometers) radiating in all directions. In the magnocellular nucleus, there are three major cell types: neurons characterized by small, spherical-shaped somata, with short, thin, radiating dendrites and many varicosities; bi- or tripolar neurons with ovoidal somata, and long (100-200 micrometers) and smooth dendrites orienting primarily dorsoventrally and mediolaterally; and multipolar neurons with triangular-shaped somata and very long (200-350 micrometers) dendrites, which are either smooth or highly spiny. Neurons in the commissural nucleus are mostly multipolar cells with ovoidal somata and beaded dendrites projecting mostly dorsally and ventrally. The subependymal midline nucleus contains mostly uni- or bipolar neurons with small ovoidal somata and straight, spiny dendrites. In addition to revealing the morphological features of neurons in the torus, the counterstained material shows further cytoarchitectural organization of the principal nucleus, i.e., the presence of a circular lamellar organization. The functional significance of these anatomical features is discussed.

Animals↗
PubMed1983

A quantitative light microscopic study of the bullfrog amphibian papilla tectorium: correlation with the tonotopic organization.

The height, width and cross-sectional area of the bullfrog amphibian papilla tectorial membrane were quantitatively analysed from frontal serial sections. The cross-sectional area (which is a measure of mass) of the tectorium does not appear to be linearly graded along the length of the papilla, but rather spatial gradations occur in more or less a step-wise manner. The spatially graded area (or mass) is well correlated with the width of the tectorium and their relationships with the tonotopic organization of the amphibian papilla are discussed.

Animals↗
PubMed1982

Neck muscles innervation patterns in the northern leopard frog (Rana P. pipiens).

The motor innervation patterns of neck and middle ear muscles were investigated in 24 northern leopard frogs (Rana p. pipiens) using the horseradish peroxidase retrograde tracing technique. The results show that various neck muscles were innervated by motoneurons in medial motor column of the ventral horn extending from the second to third spinal nerves, and positioned medially to the lateral motor column (LMC). Middle ear muscle, on the other hand, was innervated by motoneurons in LMC.

Animals↗
PubMed1982

Quantitative analysis of intensity--rate and intensity--latency functions in peripheral auditory nerve fibers of northern leopard frogs (Rana p. pipiens).

The intensity--rate and intensity--latency functions were analyzed quantitatively from single auditory fibers in the eighth nerve of northern leopard frogs (Rana p. pipiens). There was a firing rate change of as high as 15 impulses/s and a latency shift of as much as 1.4 ms per dB change in sound intensity. These rates of change were different for units with the same best excitatory frequency and greater for each unit studied at lower intensities than at high intensities. The significance of the latency function on central binaural time processing was discussed.

Acoustic Stimulation↗
PubMed1981

Binaural response characteristics of single neurons in the medial superior olivary nucleus of the albino rat.

Binaural response properties of single neurons in the medial superior olivary nucleus (MSO) were investigated in the anesthetized rat. Stimulus parameters studied included interaural time difference and interaural intensity difference. In the present study, of the two cell types observed in the rat MSO nucleus, EE and EI, variations in the binaural response properties of the MSO neurons permitted further subclassifications, which may be related to the dendritic dominance of the MSO neurons.

Acoustic Stimulation↗
PubMed1981

Normal postnatal development of medial superior olivary neurons in the albino rat: a Golgi and Nissl study.

Bipolar neurons in the medial superior olivary (MSO) nucleus of albino rats were studied at various ages (0-75 days) during development in order to elucidate normal neuronal growth patterns. Neurons, visualized in celloidin embedded Golgi/Nissl- and frozen Nissl-stained sections, were analyzed quantitatively for cell size and extent of dendritic arborization. These parameters, from both sets of data, showed a consistent developmental trend with the existence of two major stages in the ontogenetic process: a rapid developmental and a stabilization stage. The first stage, encompassing postnatal days 0 through approximately 14, was characterized by a rapidly increasing cell size, as observed in frozen sections. At the peak of this rapid growth, Golgi-stained neurons possessed thick dendrites with many appendages, growth cones, and filopodia. The peak in neuronal development coincided with the initiation of ear opening. Morphological features attained a more mature form in the second, stabilizing stage of development, which began at approximately postnatal day 14. This phase was distinguished by a decrement in cell size and dendritic branching. Also, dendrites possessed more regularly distributed varicosities and fewer appendages, growth cones, and filopodia in this period. It was observed that dendritic branching trends paralleled those of cell diameter growth.

Aging↗
PubMed1981

Peripheral basis of sound localization in anurans. Acoustic properties of the frog's ear.

Directional responses of single auditory fibers in the eighth nerve of northern leopard frogs (Rana pipiens) were studied in order to gain some insights into the acoustical properties of the frog's ear. In addition to the actual directional response of a fiber, a theoretical directional-response curve to the intensity-rate function of the unit. The difference in the two responses provided a measure of the directional characteristics of the frog's ear at the stimulating frequency which can be plotted in a polar diagram to show the directivity pattern of the frog's acoustic receiver. Directivity patterns were obtained from three groups of experimental animals under the following conditions: (I) mouth filled with moistened cotton; (II) contralateral ear coated with silicone rubber cement; (III) open mouth. Changes in the directivity patterns were observed with experimental manipulations and these were compared to those obtained from normal animals (Feng, A.S. (1980) J. Acoust. Soc. AM. 68, 1107-1114). The results suggest that the frog's ear behaves as a combination pressure-pressure gradient receiver.

Animals↗