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PubMed1981

Discharge characteristics of neuronal pairs in the rabbit inferior colliculus.

Activity of neuronal pairs in the inferior colliculus of the rabbit was recorded with a single stainless-steel microelectrode. Seventy pairs were investigated with monaural and binaural tonal stimuli. The most common parameter of the response in neuronal pairs was the best frequency, which was similar in 100% of the pairs (n = 45). Q10 values were identical in 44% of pairs and threshold tuning curves in 27% of pairs. Units with a smaller spike amplitude usually had a shorter latency to both binaural and monaural stimuli, when measured 10-20 dB above the best frequency threshold. Most units discharged during the entire period of the 100 ms tone stimulation at their best frequency; large differences, however, were found in their firing pattern, when peristimulus histograms were compared. High correlation was found in pairs where both neurones exhibited the same type of binaural interaction. The following types of binaural interaction were found: binaural excitatory drive with occlusion, binaural excitatory drive with facilitation; monaural excitatory drive with inhibition from the other ear and pure monaural excitatory drive. In a significant number of neuronal pairs the influence of binaural stimulation was similar for both neurones. The results suggest that: (a) many adjacent neurones in the inferior colliculus convey parallel information concerning features of the auditory stimulus; (b) units with a similar type of binaural interaction may be organized in clusters within isofrequency layers.

Acoustic Stimulation↗
PubMed1983

Retrograde labeling of ascending and descending neurons in the inferior colliculus. A fluorescent double labelling study in the cat.

By means of retrograde axonal transport of fluorescent substances, e.g., Propidium Iodide, Fast Blue, and Nuclear Yellow, the present study was made to determine whether or not single neurons in the cat inferior colliculus share ascending and descending projections to the following two pairs of structures, i.e. (1) to the medial geniculate body and cochlear nuclei, and (2) to the superior colliculus and pontine nuclei. Our findings indicate that extremely few neurons, if any, in the inferior colliculus harbor such divergent axon collaterals, although most of the different types of projection neurons are located in the same subdivisions of the colliculus.

Animals↗
PubMed1981

Development of responses to acoustic interaural intensity differences in the car inferior colliculus.

Responses of single neurones in the inferior colliculus of anesthetized adult cats and kittens were studied using best-frequency stimuli of varying interaural intensity differences (IID). Two broad classes of neurone, distinguished by the predominant type of input from each ear, were examined. One class of cells received predominantly excitatory input from each er (EE cells). The other class were excited by monaural stimulation of the contralateral ear and showed no response to monaural stimulation of the ipsilateral ear, but inhibition of the excitatory response by simultaneous ipsilateral stimulation (EI cells). Fourteen of the 18 adult EI cells showed marked changes in discharge rate with variation in IID. Adult EI cells showed low response variability and were insensitive to changes in average binaural intensity. In all cases of IID sensitivity, the onset component of the response was less sensitive to IID than the sustained component. Eight out of ten EE cells were insensitive to IID over the range tested. Cells of high best-frequency in kittens younger than 28 days showed irregular changes in discharge rate with variation in IID and wide response variability. Some low-frequency EI cells in young kittens showed sensitivity to IID, but it is unlikely that these could be involved in sound localization as their frequency response was inappropriate. Many cells in kittens aged 31-40 days showed monotonic, adult-like IID functions, but the response variability of these cells remained higher than that of adult cat neurones. These data provide evidence for a developmental change of binaural interaction in the cat.

Aging↗
PubMed1982

Functional ontogeny in the central auditory pathway of the Mongolian gerbil. A 2-deoxyglucose study.

The 2-deoxyglucose (2-DG) autoradiographic technique was used to map functional activity in the central auditory system of the mongolian gerbil, throughout the period of functional onset. Uptake of 2-DG during exposure to 105 dB SPL wide band noise (WBN) was compared to silence in adults and in neonates at 12, 14, 16 and 18 days after birth (DAB). At 12 DAB, WBN exposure increased 2-DG uptake relative to silence only in the ventral cochlear nucleus. At 14 DAB, 2-DG uptake increased during WBN in the entire cochlear nuclear complex, superior olivary complex, and ventral nucleus of the lateral lemniscus. These stimulus-evoked increases in 2-DG uptake were at adult levels. However, little or no stimulus-evoked increase was seen in higher auditory nuclei at 14 DAB. By 16 DAB, 2-DG uptake also increased during WBN exposure in the dorsal nucleus of the lateral lemniscus, inferior colliculus and medial geniculate nucleus. By 18 DAB, WBN exposure produced increases in 2-DG uptake of medullary and pontine auditory nuclei which exceeded those seen in adults. At higher levels of the pathway, increases were comparable to those seen in adults. WBN-induced increases in 2-DG uptake observed in the cochlear nuclear and superior olivary complexes of neonates were comparable in all regions at all ages, even at 12 DAB. However, the 2-DG uptake increases observed at 16 and 18 DAB were appreciably greater in those regions of the inferior colliculus and medial geniculate nucleus which respond to high frequencies.

Aging↗
PubMed1988

Distribution of cochlear efferents and olivo-collicular neurons in the brainstem of rat and guinea pig. A double labeling study with fluorescent tracers.

In rat and guinea pig, cochlear efferents to the two ears were labeled simultaneously with different fluorescent tracers. It was found that in both species only few (1-3%) olivo-cochlear neurons were double-labeled and project to both cochleae. In most periolivary regions large olivocochlear neurons (OCN) projecting to the ipsilateral and contralateral side are intermingled and form a continuous cell column between the facial nucleus and lateral lemniscus. In a second series of experiments in rat, cochlear efferents and ascending olivo-collicular neurons were labeled. Olivo-cochlear and olivo-collicular neurons are intermingled in the lateral superior olive (LSO) and in the ventromedial periolivary region. No double-labeled neurons were found that project to the cochlea and the inferior colliculus.

Amidines↗
PubMed1987

Processing of interaural time and intensity differences in the cat inferior colliculus.

1. Binaural neurones were recorded in the central nucleus of the cat inferior colliculus and were stimulated with tone and noise bursts. Closed field sound systems were used to produce independent interaural time (ITD) and intensity (IID) differences. Particular attention was paid to high frequency (above 2 kHz) cells. 2. Three main types of binaural neurone were found: High frequency excitatory-inhibitory neurones (EI cells), excited by input from the contralateral ear and inhibited by ipsilateral input, high frequency excitatory-excitatory cells (EE cells), excited by inputs from either ear and low frequency cells sensitive to interaural phase differences (IPD cells). 3. The EI cells had characteristics similar to those of IE cells in the contralateral lateral superior olive. They were sensitive to envelope ITDs (most cells) and IIDs (all cells) favouring the contralateral ear. The response of these cells increased with increasing contra lead ITDs or contra loud IIDs up to values well outside the physiological range. 4. Low frequency binaural cells were sensitive to interaural phase differences (IPDs). The peak response was often in the contralateral physiological range and the response was unaffected by IIDs. 5. Many high frequency EE cells were sensitive to envelope ITDs. These units were relatively unaffected by IID. Although the ITD sensitivity of these cells was generally less than that of the IPD cells, the peak response of the ITD curve was also often in the contralateral physiological range. 6. Some of the high frequency EI and EE cells were sensitive to ongoing time differences (OTDs) in white noise signals, i.e. they showed ITD response curves to carrier only shifted noise bursts. 7. The EI cells often showed recovery from inhibition at large ipsilateral lead. This tendency was increased as the sound pressure level on the inhibitory side was lowered and by the use of click stimuli. Similarly, cycles of suppression could be seen to follow excitation in some EE cells. The time course of these effects was in the order of hundreds of microseconds. 8. Binaural characteristics (degree of ITD, IID or OTD sensitivity) showed considerable interunit variation within each cell type. These variations were also affected by signal type (tone or noise bursts) and did not appear to be correlated with best frequency, nature of the tuning curve or PSTH type. We suggest that the time course of the inhibitory and excitatory effects at each unit (and its interaction with the signal type) determines the type of ITD response and that this time course varies from cell to cell.

Acoustic Stimulation↗
PubMed1995

Somatostatin and leu-enkephalin in the rat auditory brainstem during fetal and postnatal development.

A transient expression of the neuropeptide somatostatin has been described in several brain areas during early ontogeny and several opioid peptides, such as leu-enkephalin, have also been found in the brain at this stage in development. It is therefore believed that somatostatin and leu-enkephalin may play a role in neural maturation. The aim of the present study was to describe the spatiotemporal pattern of somatostatin and leu-enkephalin immunoreactivity in the auditory brainstem nuclei of the developing rat and to correlate it with other developmental events. In order to achieve this goal, we applied peroxidase-antiperoxidase immunocytochemistry to rat brains between embryonic day (E) 17 and adulthood. Somatostatin immunoreactivity (SIR) was found in all nuclei of the auditory brainstem, yet it was temporally restricted in most nuclei. SIR appeared prenatally and reached maximum levels around postnatal day (P) 7, when great numbers of immunoreactive neurons were present in the ventral cochlear nucleus (VCN) and in the lateral lemniscus. At that time relatively low numbers of cells were labeled in the dorsal cochlear nucleus, the lateral superior olive (LSO), and the inferior colliculus (IC). During the same period, when somata in the VCN were somatostatin-immunoreactive (SIR), a dense network of labeled fibers was also present in the LSO, the medial superior olive (MSO), and the medial nucleus of the trapezoid body (MNTB). As these nuclei receive direct input from VCN neurons, and as the distribution and morphology of the somatostatinergic fibers in the superior olivary complex (SOC) was like that of axons from VCN neurons, these findings suggest a transient somatostatinergic connection within the auditory system. Aside from the LSO, MSO, and MNTB, labeled fibers were found to a smaller extent in all other auditory brainstem nuclei. After P7, the SIR decreased and only a few immunoreactive elements were found in the adult auditory brainstem nuclei, indicating that somatostatin is transiently expressed in the rat auditory brainstem. Leu-enkephalin immunoreactivity showed a lower number and weaker intensity of labeled structures as compared to SIR, with E18 being the earliest day at which labeled fibers appeared in the SOC. At birth, immunoreactive fibers were also present in the cochlear nuclear complex and in the IC. Leu-enkephalin immunoreactive somata were found only after P12 in the CN and after P16 in the IC. Leu-enkephalin immunoreactivity was not transient, but increased progressively with age until about P21, when the adult levels were reached.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Distribution of parvalbumin immunoreactivity in the human brain.

The cellular distribution of parvalbumin-like immunoreactivity (PA-LI) in the human brain was investigated by peroxidase-antiperoxidase methods using antiserum to rat skeletal muscle parvalbumin. PA-LI was present in non-pyramidal neurons of the cerebral cortices, stellate cells, basket cells and Purkinje cells in cerebellar cortices, and neurons of some nuclei in human brain stem; the distribution of PA-LI in human brain was very similar to that in rat brain. These results indicate that PA-LI is widely distributed in a specific subpopulation of neurons of the human brain.

Aged↗
PubMed1986

Projection from the inferior colliculus to the superior olivary complex in the albino rat.

The origin and termination of the fibers projecting from the inferior colliculus to the superior olivary complex have been studied in rat by means of the Fink and Heimer and horseradish peroxidase techniques (anterograde and retrograde transport of free horseradish peroxidase and peroxidase conjugated to wheat germ agglutinin). The colliculoolivary fibers originate in layer 3 of the external cortex and the adjacent part of the central nucleus, particularly in the former. Via the lateral lemniscus the fibers reach the ipsilateral periolivary region where they terminate in the rostral and medioventral zones. The terminal field contains at least two types of cells which could constitute the next link in the descending projection to the cochlea and/or the cochlear nuclei. One of these is the large olivocochlear neuron, and the other a smaller neuron projecting to the cochlear nuclei. Judged by their topographic relationship in the inferior colliculus and in the superior olive, the colliculoolivary neurons may form a link in a oligosynaptic projection from the auditory cortex to the cochlea and/or the cochlear nuclei. The observations are based on light microscopy, however, and do not allow conclusions concerning synaptic contacts.

Animals↗
PubMed1984

The termination of spinomesencephalic fibers in cat. An experimental anatomical study.

The projections to the midbrain from the spinal cord have been investigated in the cat with the degeneration technique and by using horseradish peroxidase (HRP) as an anterograde tracer. Two types of spinal cord lesions were performed: 1) Cordotomies at cervical or thoracic levels transecting the ventral and lateral funiculi. 2) Transections of the ventral, ventrolateral, dorsolateral or dorsal funiculus, respectively, at cervical levels. In the anterograde tracing experiments HRP was injected into the spinal cord at cervical, lumbar or sacral levels. The results show large projections to the lateral and ventrolateral parts of the periaqueductal gray (PAG1), the posterior pretectal nucleus (PP) and the nucleus of Darkschewitsch (D). More moderate projections go to the medial division of the periaqueductal gray (PAGm), the cuneiform nucleus (CF), the mesencephalic reticular formation (MRF), lateral part of the deep layer of the superior colliculus (SP) and magnocellular medial geniculate nucleus (GMmc), while scattered spinal fibers are present in the dorsal part of the periaqueductal gray (PAGd), the external inferior collicular nucleus (IX), the intermediate layer of the superior colliculus (SI), the lateral part of the red nucleus (NR) and in the Edinger-Westphal portion of the oculomotor nucleus (3). In addition a few fibers are present in the interstitial nucleus of Cajal (CA) and anterior pretectal nucleus (PAc). The results indicate that at midcervical levels most of the spinomesencephalic fibers ascend in the ventral funiculus, with only a moderate fraction ascending in the ventral half of the lateral funiculus. Almost no fibers ascend in the dorso-lateral funiculus and none appear to pass in the dorsal funiculus. No distinct somatotopic pattern was found in the spinomesencephalic projections, but more fibers from cervicobrachial segments terminate in the rostral than in the caudal parts of the terminal fields in PAG, CF, SP and IX, while the lumbar fibers were more numberous in the caudal parts. PP seems to receive spinal fibers mainly from the caudal half of the cord.

Animals↗
PubMed1985

Anatomy of the inferior colliculus in rat.

This paper defines the pattern of subdivision of the inferior colliculus in rat. It is based on serial sections of brains of albino and hooded rats cut in the frontal, sagittal and horizontal planes using Golgi, Nissl and a combined cell-myelin method. In rat, like in other mammals, the inferior colliculus consists of a central nucleus, an external cortex, and a dorsal cortex. The central nucleus is flattened in the frontal plane and confined to the caudomedial part of the inferior colliculus. It is characterized by a lamellar organization of disc-shaped neurons interspersed with multipolar cells. The cells are small to medium-sized. Although there is a dorsoventral gradient in size and packing density of cells within the nucleus, the overall size is smaller and the packing density larger than in adjacent subdivisions. The two cortices each consists of three layers. The outer-most layer is common to the two cortices, forming a fibrocellular capsule continuous along most of the circumference of the inferior colliculus. The external cortex is located lateral, rostral, ventral and ventrocaudal to the central nucleus. Its second layer, deep to the superficial capsule, is characterized by clusters of many small and a few medium-sized neurons in a myelin-dense neuropil. Layer 3, which constitutes the major portion of the subdivision, consists of relatively scattered, small, medium and large cells, the most characteristic element being large multipolar neurons with coarse Nissl granules. The dorsal cortex is located dorsocaudal and dorsomedial to the central nucleus. Its second layer is composed of small neurons, while the third, deep layer in addition contains medium-sized neurons. The cell density is intermediate to that of the central nucleus and the deep part of the external cortex. We have tried to facilitate the parcellation by reference to easily recognizable, nearby structures and to standard stereotaxic coordinates.

Animals↗
PubMed1984

An anatomical study of the projections from the dorsal column nuclei to the midbrain in cat.

The termination of the fibers from the dorsal column nuclei (DCN) to the midbrain has been investigated in the cat with the degeneration method, the anterograde horseradish peroxidase (HRP) method and autoradiography after 3H-leucine injections. The results show that the DCN project to several midbrain regions. The external nucleus of the inferior colliculus (IX) receives the heaviest projection from both the gracile and cuneate nuclei. The DCN fibers form three joint terminal zones in IX. Each terminal zone contains clusters with dense aggregations of DCN fibers. Fairly dense terminal networks are found in the posterior pretectal nucleus (PP) and the compact part of the anterior pretectal nucleus (PAc) as well. More scattered DCN fibers are present in the cuneiform nucleus (CF), the lateral part of the periaqueductal gray (PAG1), the red nucleus (NR), the nucleus of the brachium of the inferior colliculus (B), the mesencephalic reticular formation (MRF) and the intermediate and deep layers of the superior colliculus (SI, SP). The projections to all regions are mainly contralateral. Most of the few ipsilateral fibers terminate in IX. A somatotopic organization was seen in IX and NR. The gracile fibers terminate preferentially in the caudal and lateral part of IX and the cuneate ones preferentially in its rostral and medial part. In the red nucleus the gracile fibers terminate ventral to the cuneate ones. In the pretectal region there was a predominance for gracile fibers. There also appeared to be quantitative differences in the projections from various levels of the gracile nucleus, with more midbrain projecting fibers originating in the rostral than in the middle and caudal parts of the nucleus.

Animals↗
PubMed1979

Combined dynamics of EEG and evoked potentials. I. Studies of simultaneously recorded EEG-EPograms in the auditory pathway, reticular formation, and hippocampus of the cat brain during the waking stage.

This study is carried out on single (not averaged) recordings combining the spontaneous activity preceding the stimulus onset and the EP recorded upon acoustical stimulation. These recordings, which we call EEG-EPograms, are measured simultaneously from different subdural brain structures, such as the auditory cortex, medial geniculate nucleus, inferior colliculus, reticular formation and the hippocampus of awake cats. Using a combined analysis procedure (C.A.P.), the relevant frequency components of spontaneous EEG and EPs, recorded simultaneously from these brain nuclei, are analyzed according to the consistent selectivity bands depicted by the determined amplitude-frequency characteristics. These analyses provide us the following information: (1) there is an important congruency in the time courses of simultaneous response components in common frequency bands, especially in the alpha and beta frequency ranges; (2) there exist significant coupling and synchrony between the evoked amplitude enhancements in the simultaneously recorded single response components; (3) the inter-nuclei coherency in the brain's electrical activity is enormously increased upon stimulation; (4) the evoked response magnitude can be predicted, with reasonable accuracy, from the spontaneous activity preceding the stimulation. The strong dependence of the response magnitude on the stimulus-preceding EEG is explained by means of a model network consisting of a population of relaxation oscillators, which can be brought to different states of synchrony and asynchrony. Some suggestions and comments are also made for investigators working toward theories of signal transmission in the brain.

Animals↗
PubMed1979

Combined dynamics of EEG and evoked potentials. II. Studies of simultaneously recorded EEG-EPograms in the auditory pathway, reticular formation, and hippocampus of the cat brain during sleep.

This study is carried out on single (not averaged) recordings combining the spontaneous activity preceding the stimulus onset and the EP recorded upon acoustical stimulation. These recordings, which we call EEG-EPograms, are measured simultaneously from different subdural structures, such as the auditory cortex, medial geniculate nucleus, inferior colliculus, reticular formation and the hippocampus of the cat brain during the slow wave sleep stage. Using a combined analysis procedure (C.A.P.), the relevant frequency components of spontaneous EEG and EPs, recorded simultaneously from these brain nuclei, are analyzed according to the consistent selectivity bands depicted by the determined amplitude-frequency characteristics for the SWS-stage. In parallel with the results which we obtained for the waking stage, these analyses provide also the following information: (1) there is an important congruency in the time courses of simultaneous response components in common frequency bands, especially in the alpha and beta frequency ranges; (2) there exist significant coupling and synchrony between the evoked amplitude enhancements in the simultaneously recorded single response components; (3) the inter-nuclei coherency in the brain's electrical activity is enormously increased upon stimulation;(4) the evoked response magnitude can be predicted, with reasonable accuracy, from the spontaneous activity preceding the stimulus. All these findings are discussed with reference to those obtained for the waking stage.

Animals↗