Axonal transport in embryonic visual system in zebrafish.
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Responses of single units in the inferior colliculus of the mouse (Mus musculus) as a function of tone intensity.
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Acoustic Stimulation↗
Ascending projections from the nucleus of the brachium of the inferior colliculus in the cat.
Ascending projections from the nucleus of the brachium of the inferior colliculus (NBIC) in the cat were studied by the autoradiographic tracing method. Many fibers from the NBIC ascend ipsilaterally in the lateral tegmentum along the medial border of the brachium of the inferior colliculus. At midbrain levels, fibers from the NBIC end in the superior colliculus, the pretectum, the central gray and the peripeduncular tegmental region bilaterally with ipsilateral predominance. NBIC fibers to the superior colliculus are distributed densely to laminae VI and III throughout the whole rostrocaudal extent of the colliculus. In the pretectum, NBIC fibers terminate in the anterior and medial nuclei and the nucleus of the posterior commissure. NBIC fibers to the dorsal thalamus are distributed largely ipsilaterally. Many NBIC fibers end in the dorsal and medial divisions of the medial geniculate body, but few in the ventral division. The NBIC also sends fibers to the suprageniculate, limitans and lateralis posterior nuclei and the lateral portion of the posterior nuclear complex; these regions of termination of NBIC fibers constitute, as a whole, a single NBIC recipient sector. Additionally, the NBIC sends fibers to the centralis lateralis, medialis dorsalis, paraventricular and subparafascicular nuclei of the thalamus.
Afferent Pathways↗
Physiology of pathway from dorsal cochlear nucleus to inferior colliculus revealed by electrical and auditory stimulation.
The dorsal cochlear nucleus (DCN) projects axons to the contralateral central nucleus of the inferior colliculus (ICC) via the dorsal acoustic stria (DAS). In the anaesthetised cat, when brief electrical stimuli are applied to the caudal surface of DCN, single unit and field activity is evoked preferentially in the ventro-lateral region of ICC. Most single ICC units judged by electrical stimulation to have received a direct input from DCN are excited by contralateral tonal stimulation and inhibited or uninfluenced by ipsilateral tones. The sharp non-monotonic intensity functions of most of these units are similar to those of units in the dorsal cochlear nucleus, but ipsilateral inhibition is likely to be provided by a source other than DCN. Thus, although it is suggested that axons of DAS terminate preferentially in the ventro-lateral aspect of the contralateral ICC, it is likely that at least some neurones in this latter region receive additional input from another source - possibly the lateral superior olivary nucleus.
Acoustic Stimulation↗
Effects of lesioning the dorsal and intermediate acoustic striae on binaural interaction at the inferior colliculus.
Contralateral clicks normally activate units in the inferior colliculus of rats. Ipsilateral clicks usually inhibit this activity when their intensity just exceeds the contralateral intensity. When the contralateral dorsal and intermediate acoustic striae are lesioned as they pass over the restiform body, ipsilateral clicks inhibit even if they are substantially less intense than contralateral clicks. Contralateral click thresholds for unit activation are elevated by about 10 dB, but this shift in sensitivity cannot account for the marked advantage gained by the ipsilateral inhibitory input. These findings suggest that one or both of these pathways contributes heavily to binaural interaction at the inferior colliculus.
Animals↗
Ascending and intrinsic projections of the superior olivary complex in the cat.
The ascending and intrinsic projections of the superior olivary complex (SO) in the cat were investigated by injection of 3H-leucine and horseradish peroxidase (HRP) in SO and the inferior colliculus (IC), respectively. A topically arranged projection was demonstrated from the nucleus of the trapezoid body (NTB) to the ipsilateral lateral superior olivary nucleus (LSO) wiht a lesser connection in the opposite direction. The medial superior olivary nucleus (MSO) has a strictly ipsilateral projection, whilst LSO projects symmetrically through the lateral lemniscus (LL) of both sides, to end with topically arranged terminals in the ventrolateral part of the central nucleus of the inferior colliculus (CNIC). Terminal labelling found in the ventral and dorsal nuclei of LL (VNLL and DNLL) probably represents collaterals from bypassing fibres originating in MSO and LSO, respectively. These results were demonstrated by both techniques, whilst in addition the HRP method revealed an ipsilateral and contralateral projection to IC from VNLL and DNLL, respectively.
Animals↗
Time of origin of neurons of the rat inferior colliculus and the relations between cytogenesis and tonotopic order in the auditory pathway.
Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational day 12 and 13 (E12+13) until the day before parturition (E21+22) in order to label in their embryos the proliferating precursors of neurons. At 60 days of age the proportion of neurons generated (or no longer labelled) on specific embryonic days was determined quantitatively in six vertical strips of the inferior colliculus. It was established that the neurons of the inferior colliculus are produced between days E14 and the perinatal period in an orderly sequence: the earliest generated cells are situated rostrally, laterally and ventrally in the principal nucleus, the latest generated cells are situated caudally, medially and dorsally in the pericentral nucleus. This cytogenetic gradient suggested that the cells are produced dorsally in the caudal recess of the embryonic aqueduct and are deployed in an "outside-in" pattern. This study has brought to a conclusion our datings of neuron production in the central auditory pathway of the rat. The results revealed that in those structures in which a cytogenetic gradient could be recognized, the orientation of this gradient and the regional tonotopic order (demonstrated mostly in species other than the rat) tended to be aligned. Moreover, with the exception of the medial trapezoid nucleus and the dorsal nucleus of the lateral lemniscus (which receive contralateral input from the cochlear nuclei), sites with early-produced neurons correlated with units responding preferentially to high frequency tones and vice versa. This suggested that the orderly production of neurons within different components of the auditory system is a factor in their subsequent topographic organization. A comparison of the temporal order of neuron production in different components of the auditory pathway suggested that the establishment of orderly topographic relations between some of the structures (e.g., the medial geniculate body and the primary auditory cortex) takes place before this spatial relationship could be specified as a cochleotopic order.
Animals↗
Tonotopic organization in the inferior colliculus of the rat demonstrated with the 2-deoxyglucose method.
We studied the tonotopic organization in the inferior colliculus of the rat with the 2-deoxyglucose method. Isofrequency bands were observed in the central nucleus of the inferior colliculus. In coronal sections, higher sound frequencies elicited bands that were located more ventrally. At caudal levels of the inferior colliculus, isofrequency bands were relatively short and tilted slightly downward toward the midsagittal plane. As the plane of section moved more rostrally, isofrequency bands gradually lengthened, their orientation first turned horizontally and continued with a downward tilt toward the lateral aspect of the brainstem. At rostral levels, high-frequency (greater than 8000 Hz) bands showed more significant increases in length than low-frequency (less than 4000 Hz) bands. Thus, the amount of tissue in the inferior colliculus devoted to higher frequencies was significantly more than that for lower frequencies. In sagittal sections, the isofrequency band moved from a dorsoposterior position to a ventroanterior one as the plane of section moved more laterally. A three-dimensional model of isofrequency planes was reconstructed from the above data.
Acoustic Stimulation↗
The auditory corticopontocerebellar projection in the rat: inputs to the paraflocculus and midvermis. An anatomical and physiological study.
This study investigated afferent projections to the cerebellum, in particular those from the auditory cerebral cortex. The parafloccular lobule of the rat cerebellum is shown to be a primary target for the auditory cortical information with the midvermal region being a receiving area from the inferior colliculus. The method of anterograde transport of tritiated amino acids was employed to determine projections of the auditory cortex to the pons. Autoradiography showed that the site of termination of efferents from the auditory cortex corresponds to the location of neurons that project to the paraflocculus. Histogram analysis of neuronal activity in halothane anesthetized rats was employed to determine the response characteristics of neurons in paraflocculus and midvermis following cortical and tectal electrical stimulation. In addition, unit recordings of parafloccular neurons in immobilized, locally anesthetized animals demonstrated general characteristics of the responses of these neurons to auditory field stimulation. Electrical stimulation of the auditory cortex evoked mixed, excitatory-inhibitory and pure inhibitory mossy fiber responses in 33% of neurons in the paraflocculus, with no responses evident in the midvermis. Following inferior collicular stimulation, 12.6% of the neurons in the midvermis elicited a response. Recordings from parafloccular neurons in unanesthetized, immobilized rats showed evidence for excitatory and inhibitory mossy fiber responses, following auditory field stimulation. This spectrum of basic studies establishes the existence of a pathway in which the paraflocculus is revealed as an integrating target for cortical auditory information.
Animals↗
Development of inferior colliculus response properties in C57BL/6J mouse pups.
Response properties of inferior colliculus (IC) neurons were studied in traquilized C57BL/6J mice during a period of rapid auditory system development between 12 and 17 days of age. In IC units of the youngest mice, spontaneous activity was absent, a disproportionate number of onset responses was observed, and many units were not securely driven by sound. Frequency response ranges were restricted to relatively low frequencies, sharpness of tuning was poor, and thresholds at best frequencies (BFs) were quite high. Dynamic intensity ranges were restricted, but nonmonotonic functions were observed. By 15--17 days of age, spontaneous activity was appreciable, incidences of response patterns were near adult proportions, and most units in the ventrolateral nucleus were securely driven by tones. Response ranges had expanded markedly to include high frequencies, sharpness of tuning increased, and thresholds had decreased. Dynamic intensity ranges and intensity functions were similar to those observed in adult mice.
Acoustic Stimulation↗
Coding of spatial location by single units in the inferior colliculus of the alert cat.
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Acoustic Stimulation↗
Development of binaural input, response patterns, and discharge rate in single units of the cat inferior colliculus.
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Aging↗
Iso-frequency 2-DG contours in the inferior colliculus of the awake monkey.
Tone bursts produced bands of selective 2-[14C]-deoxyglucose labelling in the inferior colliculus (IC) of the awake monkey. Low tone frequencies produced labelling in dorsal regions and high tone frequencies produced labelling in ventral regions. The position of the bands coincided with the position of a single unit with a characteristic frequency, which was the same as the frequency producing the labelling. These findings indicate that the bands of labelling represent iso-frequency contours in IC. The iso-frequency contours extended across most of the nucleus and were oriented from dorsomedially to ventro-laterally at 20-30 degrees from the horizontal and became more vertical anteriorly. The width of the contours was as narrow as 200 micron, suggesting that the contours might represent 2 or 3 overlapping cellular laminae.
Animals↗
Inhibitory contours in the inferior colliculus as revealed by the 2-deoxyglucose method.
2-Deoxyglucose experiments were carried out during which tone bursts were presented to one ear of cats, while white noise bursts were presented to the other ear. Autoradiography revealed that the tones had produced clear bands of reduced labelling in the ipsilateral inferior colliculus, in addition to the expected band of increased labelling in the contralateral inferior colliculus. The positions of the bands or contours appeared to be organized tonotopically into iso-frequency inhibitory contours.
Animals↗
Neuron morphology and synaptic architecture in the medial superior olivary nucleus. Light- and electron microscope studies in the cat.
Dendritic arborization pattern, spatial and synaptic relations of various neuron types and the terminal distribution of afferent axons of various origin were studied in the medial superior olivary nucleus of the cat using Golgi, degeneration, electron microscope and horseradish peroxidase techniques. Three types of neurons clearly different in morphological features, distribution, neighbourhood relations, input and output characteristics were distinguished: (1) fusiform cells having specific dendritic orientations and arborization patterns and synaptic relations to various types of terminal axon arborizations (2) multipolar neurons with wavy dendrites bearing spine-like appendages, receiving relatively few synaptic contacts and having a locally arborizing axon, and (3) elongated marginal cells, largely restricted to the fibrous capsule of the nucleus. The fusiform and marginal neurons were identified by retrograde peroxidase labeling as the olivo-collicular projection cells. Ultrastructural analysis of normal and experimental material revealed the presence of four distinct kinds of axon terminals differing in size, synaptic vesicles type, relation to postsynaptic targets and in origin: (i) large terminals with multiple extended asymmetric synaptic membrane specializations and containing round, clear vesicles arise from the spherical cells of the ipsilateral anteroventral cochlear nucleus, (ii) most of the small axon terminal profiles - engaged in asymmetric synaptic contacts - originated from the trapezoid nucleus, (iii) terminal boutons containing pleomorphic vesicles belong to fibers descending from the ipsilateral multipolar neurons in the central nucleus of the inferior colliculus and from the nuclei of the lateral lemniscus while (iv) boutons containing exclusively ovoid vesicles and remaining intact after complete deafferentation of the nucleus were considered to be of local origin.
Animals↗
Coding of small sinusoidal frequency and amplitude modulations in the inferior colliculus of 'CF-FM' bat, Rhinolophus ferrumequinum.
Single neurons in the inferior colliculus of the Greater Horseshoe bat, Rhinolophus ferrumequinum, showed two broad categories of response patterns to sinusoidally frequency (SFM) or amplitude (SAM) modulated stimuli. Tonic responding cells (best excitatory frequency (BEF) between 10 and 90 kHz) showed a rough sinusoidal modulation of the discharge pattern to SFM. Transient responding neurons generally showing on- or off-responses to pure tones, (BEF between 65 and 88 kHz), displayed highly synchronized discharge patterns to SFM-cycles (Fig. 1). Modulation rates between 20 and 100 Hz were most effective and some neurons encoded modulation rates up to 350 Hz (Figs. 2 and 3). The SFM responses were best synchronized to the modulation envelope for center frequencies in the upper portion of the tuning curve (Figs. 4 and 5). Sharply tuned neurons with BEF around 80 kHz had the lowest threshold for modulation depth (+/- 10 Hz or 0.025%) (Fig. 6). In general, SAMs evoked the same type of response patterns and were encoded down to modulation index of 3% (Fig. 7). The fine frequency and amplitude discriminations for periodical modulations by collicular neurons is discussed as related to the detection and discrimination performance of bats, when preying on flying insects in clustered surroundings.
Acoustic Stimulation↗
The central cervical nucleus in the cat. II. The cerebellar connections studied with retrograde transport of horseradish peroxidase.
After HRP injections in kittens and adult cats into parts of the cerebellum known to receive spinal afferents, retrogradely labelled neurones were found in the C1--C4 segments of the spinal cord, primarily in the central cervical nucleus (CCN). A few labelled neurones were also found in laminae IV and VI--IX of Rexed. The results obtained in kittens and adult cats were similar. Control HRP injections were made into the vestibular nuclei and the inferior colliculus. After injections mainly involving the vestibular nuclei a few faintly labelled neurones were found in the C1--C4 segments in, and occasionally also outside the CCN, in laminae VI--VIII. After injections into the inferior colliculus, however, no labelled neurones were observed in these segments. After spinal cord hemisections at C1 and bilateral HRP injections into the anterior lobe, nearly all labelled CCN neurones were found ipsilateral to the hemisections. Labelled axons of such CCN neurones could be traced across the midline to the lateral funiculus. A few neurones were found outside the CCN in laminae VII--IX. Contralaterally labelled neurones were found mainly in lamina VI.
Afferent Pathways↗
Single unit responses in the inferior colliculus of the awake and performing rhesus monkey.
1. The activity of single units in the inferior colliculus of unanesthetized monkeys was recorded during performance in an auditory reaction time task. Stimulus intensity and frequency were varied. 2. Spontaneous rate of unit discharge varied from 0 to 78.2 discharges per second, with a mean of 14.7 discharges/sec. 3. Both broadly and narrowly tuned units were encountered in the central nucleus of the inferior colliculus. The temporal discharge pattern of most units varied with changes in stimulus frequency; onset bursts and/or sustained discharge suppression dominated the unit discharge at the edges of receptive fields. 4. Half of the units examined at several intensity levels displayed nonmonotonic relationships between evoked discharge rate and stimulus intensity, with most nonmonotonic units showing a distinct "best intensity". The temporal response pattern of almost all units varied with changes in stimulus intensity, with onset bursts and discharge suppression increasing in occurrence with increasing intensity. 5. Units recorded in the external nucleus of the inferior colliculus displayed spontaneous rates which were similar to those of central nucleus units, and were affected by variation in stimulus intensity in the same fashion. However, the average initial latency of such units to intense stimuli was no longer than the latency of central nucleus units. 6. Variations in unit discharge with changes in stimulus frequency and intensity are consistent with an interaction of excitatory and inhibitory inputs with different initial latencies, dynamic ranges and receptive fields. In particular, our data suggest that inhibitory inputs have longer initial latencies and higher thresholds. Inhibition is stronger at the edges of a unit's receptive field, and dominates at high frequencies in units with low characteristic frequency. 7. Our data are not consistent with previous reports that single units in the unanesthetized animal display uniformly monotonic intensity functions and uniformly broad frequency responses.
Acoustic Stimulation↗