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PubMed1995

Tinnitus and hearing loss in pineal region tumours.

The authors report an underestimated symptom and sign arising in pineal region tumours: tinnitus and hearing loss. It has been observed in 13 out of 72 pineal region tumours (18%). Three illustrative cases are reported in this paper. The inferior colliculi, the structure more dense in fibres than any other auditory brain stem site and at which majority of the acoustic pathways relay, is closely adjacent to the pineal body. Displacement of this structure may be responsible for acoustic symptoms together with common visual symptoms.

Adult↗
PubMed1984

Quantitative light microscopic autoradiographic localization of cholinergic muscarinic receptors in the human brain: brainstem.

We have investigated the localization of muscarinic cholinergic receptors in the brainstem of eight patients free of neurological disease following quantitative autoradiography of microtome sections of postmortem tissue labeled in vitro with N-[3H]methyl scopolamine as a ligand. Receptor densities were quantified by microdensitometry with the aid of a computer assisted image analysis system. Our results reveal a heterogeneous distribution of receptor sites. High concentrations of muscarinic cholinergic receptor sites were associated with many nuclei and areas of the brainstem including the nucleus facialis (VII), hypoglossus (XII), ambiguus, the motor trigeminal nucleus (V), the nucleus solitarius, the nucleus of the lateral lemniscus, the superior and inferior colliculi, the sensory trigeminal nucleus (substantia gelatinosa), the pontine nuclei, the parabrachial nuclei, some tegmental nuclei and the periaqueductal gray matter. Very high concentrations of N-[3H]methyl scopolamine binding sites were also localized in the ventral tegmental area, the nucleus paranigralis and the nucleus ovalis. Receptor densities varied between individual brains although the relative distribution of the densities in the different nuclei was the same for all of the brains examined. Most of the brainstem nuclei containing muscarinic cholinergic receptors were enriched in high affinity agonist binding sites as shown by characteristic displacement of the ligand with carbachol. Exceptions were the substantia nigra, the nucleus olivaris inferior and the substantia gelatinosa of the fifth nerve. Receptor density values and pharmacological characteristics obtained in the cortex and basal ganglia in our cases are in good agreement with previously reported values in humans, using conventional biochemical methods. This indicates that procedures used in the autoradiographic technique are not detrimental to the pharmacological characteristics and densities of muscarinic cholinergic receptors. Our results thus clearly show the feasibility of using these techniques for the localization and quantification of muscarinic cholinergic receptors in human brain postmortem material. Furthermore, our findings indicate the potential involvement of the muscarinic cholinergic effect of acetylcholine in the normal function of many brainstem centers, including motor and sensory nuclei, visual and auditory relay nuclei and cardiovascular and respiratory-related nuclei.

Brain Stem↗
PubMed2004

A periodic network of neurochemical modules in the inferior colliculus.

A new organization has been found in shell nuclei of rat inferior colliculus. Chemically specific modules with a periodic distribution fill about half of layer 2 of external cortex and dorsal cortex. Modules contain clusters of small glutamic acid decarboxylase-positive neurons and large boutons at higher density than in other inferior colliculus subdivisions. The modules are also present in tissue stained for parvalbumin, cytochrome oxidase, nicotinamide adenine dinucleotide phosphate-diaphorase, and acetylcholinesterase. Six to seven bilaterally symmetrical modules extend from the caudal extremity of the external cortex of the inferior colliculus to its rostral pole. Modules are from approximately 800 to 2200 microm long and have areas between 5000 and 40,000 microm2. Modules alternate with immunonegative regions. Similar modules are found in inbred and outbred strains of rat, and in both males and females. They are absent in mouse, squirrel, cat, bat, macaque monkey, and barn owl. Modules are immunonegative for glycine, calbindin, serotonin, and choline acetyltransferase. The auditory cortex and ipsi- and contralateral inferior colliculi project to the external cortex. Somatic sensory influences from the dorsal column nuclei and spinal trigeminal nucleus are the primary ascending sensory input to the external cortex; ascending auditory input to layer 2 is sparse. If the immunopositive modular neurons receive this input, the external cortex could participate in spatial orientation and somatic motor control through its intrinsic and extrinsic projections.

Animals↗
PubMedDate not supplied

[Auditory afference of the central gray tissue in the rat midbrain (morphofunctional and electrophysiological research)].

Afferent connections between the central gray substance of the midbrain and central nuclei of the inferior colliculi have been revealed by horseradish peroxidase axonal transport technique in albino rats. Functional properties of neurones in the central gray substance of the midbrain were investigated by extracellular recording of their spike activity in response to continuous and amplitude-modulated tones. The results obtained are discussed in relation to integrity of structural and functional organization of the acoustico-vocalizational system of the brain.

Acoustic Stimulation↗
PubMed1983

Upper visual space neglect and motor deficits after section of the midbrain commissures in the cat.

The neurological deficits following section of the midbrain commissures were studied in the cat. After a lesion of the commissures between the superior and inferior colliculi, with or without involvement of the posterior commissure, the animals showed a long lasting inattention for stimuli in the upper visual space, lack of exploratory head movements towards the neglected space, head ventroflexion and vertical paralysis of gaze. After a lesion of the commissure between the superior colliculi or of its rostral part only, the same symptomatology appeared, but it was short lasting. After a lesion of the posterior commissure, the head was kept dorsiflexed, the exploratory head movements towards the lower visual space were reduced and the stimuli presented in this space were often neglected. There was a paralysis of vertical eye movements. The findings are discussed in the frame of a premotor theory of neglect.

Animals↗
PubMed1991

Deafness after bilateral midbrain contusion: a correlation of magnetic resonance imaging with auditory brain stem evoked responses.

A 46-year-old woman became deaf after a closed head injury. When a computed tomographic scan failed to disclose the cause, conversion disorder was suspected. Magnetic resonance imaging, however, showed bilateral contusions of the inferior colliculi, providing objective evidence for an organic cause of hearing loss. Auditory brain stem evoked responses and stapedial reflexes also provided objective evidence of brain stem injury. This case illustrates the phenomenon of dorsal midbrain injury after head trauma. It indicates the sensitivity of magnetic resonance imaging for small focal lesions after head trauma, and it demonstrates some difficulties in the diagnosis of "hysterical" deafness.

Brain Concussion↗
PubMed1998

Imaging subcortical auditory activity in humans.

There is a lack of physiological data pertaining to how listening humans process auditory information. Functional magnetic resonance imaging (fMRI) has provided some data for the auditory cortex in awake humans, but there is still a paucity of comparable data for subcortical auditory areas where the early stages of processing take place, as amply demonstrated by single-unit studies in animals. It is unclear why fMRI has been unsuccessful in imaging auditory brain-stem activity, but one problem may be cardiac-related, pulsatile brain-stem motion. To examine this, a method eliminating such motion (using cardiac gating) was applied to map sound-related activity in the auditory cortices and inferior colliculi in the brain stem. Activation in both the colliculi and cortex became more discernible when gating was used. In contrast with the cortex, the improvement in the colliculi resulted from a reduction in signal variability, rather than from an increase in percent signal change. This reduction is consistent with the hypothesis that motion or pulsatile flow is a major factor in brain-stem imaging. The way now seems clear to studying activity throughout the human auditory pathway in listening humans.

Auditory Cortex↗
PubMed1987

Auditory science tutorial. III: The role of the ascending pathways.

This paper attempts a thumbnail sketch of what is currently known about processing in the early parts of the auditory pathway. The paper briefly reviews the morphology and physiology of the auditory nuclei up to the inferior colliculi of the midbrain and discusses their function in processing sound information. Particular attention is paid to the role of these nuclei in sound localization and in analysing complex signals such as speech. One aim of the tutorial is to dispel any ideas that the peripheral auditory pathways are mere relays to the thalamus and cortex and to emphasize their fundamentally important role in auditory processing. The review is not comprehensive (indeed it can only touch upon some aspects of auditory processing) but key references are provided for those with more than just a passing interest.

Animals↗
PubMed1982

Noise-induced hearing loss can alter neural coding and increase excitability in the central nervous system.

Responses of auditory neurons in the inferior colliculi of mice were studied longitudinally before and shortly after each animal was exposed to intense noise. Noise exposure caused expected losses in auditory sensitivity, but in 31 percent of the neurons studied, unexpected alterations of temporal patterns of action potentials were observed: certain suprathreshold stimuli that had evoked only transient "onset" responses or inhibition of spontaneous discharges prior to noise exposure came to elicit sustained excitation after exposure. Thus, noise-induced hearing loss can be associated with increases in neural responsivity and alterations of normal neural coding processes.

Acoustic Stimulation↗
PubMed1983

Single-unit responses to cholinergic agents in the rat inferior colliculus.

Single units were recorded from the inferior colliculi of adult male rats anesthetized with urethane. Units were driven with tonal stimuli, and changes in unit responses to the tones were monitored during iontophoretic application of cholinergic drugs. The cholinergic agonists acetylcholine and carbamylcholine potentiated responses in about 50% and suppressed responses in about 35% of units tested. Cholinergic antagonists typically produced effects when delivered alone. Both d-tubocurarine and atropine methyl nitrate excited over 80% of units tested, while mecamylamine and scopolamine inhibited the majority of tested units. Dihydro-beta-erythroidine was generally ineffective. Alpha-bungarotoxin was generally ineffective when delivered alone, but blocked agonist effects. Post-stimulus time histogram (PSTH) patterns, response-intensity functions and response areas were examined for changes during drug delivery. Cholinergic agents did not differentially affect either time periods within the PSTH or frequency bands of response areas, but were especially effective for those intensities producing larger response rates. Taken together with evidence from biochemical studies, our results suggest the presence of a functional cholinergic input into the inferior colliculus which acts to modulate acoustic processing.

Animals↗
PubMed2005

Adaptation of brain regions to habitat complexity: a comparative analysis in bats (Chiroptera).

Vertebrate brains are organized in modules which process information from sensory inputs selectively. Therefore they are probably under different evolutionary pressures. We investigated the impact of environmental influences on specific brain centres in bats. We showed in a phylogenetically independent contrast analysis that the wing area of a species corrected for body size correlated with estimates of habitat complexity. We subsequently compared wing area, as an indirect measure of habitat complexity, with the size of regions associated with hearing, olfaction and spatial memory, while controlling for phylogeny and body mass. The inferior colliculi, the largest sub-cortical auditory centre, showed a strong positive correlation with wing area in echolocating bats. The size of the main olfactory bulb did not increase with wing area, suggesting that the need for olfaction may not increase during the localization of food and orientation in denser habitat. As expected, a larger wing area was linked to a larger hippocampus in all bats. Our results suggest that morphological adaptations related to flight and neuronal capabilities as reflected by the sizes of brain regions coevolved under similar ecological pressures. Thus, habitat complexity presumably influenced and shaped sensory abilities in this mammalian order independently of each other.

Adaptation, Physiological↗
PubMed1999

Degeneration and gliosis in rat retina and central nervous system following 3,3'-iminodipropionitrile exposure.

3,3'-Iminodipropionitrile (IDPN) exposure causes a neurofilamentous axonopathy and olfactory, audiovestibular and visual toxicity. Many events relevant to these effects and the neurotoxic properties of nitriles as a class remain to be elucidated. We characterized the gliosis associated with the IDPN-induced retinal degeneration in comparison to other effects on the visual and central nervous systems. Gliosis was quantified using an ELISA for the intermediate filament protein, glial fibrillary acidic protein (GFAP). IDPN (0-400 mg kg-1 day-1x3 days, i.p.) caused corneal opacity and dose- and time-dependent increases in retinal GFAP, up to 26-28 fold of control values at 4 weeks post-exposure; a second peak occurred at 16 weeks. In contrast, GFAP peaked at 1 week in olfactory bulbs (OB), cingulate cortex and hippocampus. Cerebellum and striatum showed no gliosis. Retinal dopamine decreased within 2 weeks. Delayed GFAP increases occurred in superior and inferior colliculi. Retina and superior colliculi also showed increased [3H]PK-11195 binding. Histological analysis demonstrated progressive degeneration and gliosis in retina and colliculi. Taken together, the data indicate that primary and secondary degenerative events occur in the retina, and that this retinal degeneration induces GFAP increases in retina and superior colliculus. In addition, GFAP assays demonstrated that the retinal toxicity of IDPN is enhanced by CCl4 hepatotoxicity and blocked by methimazole inhibition of flavin-mono-oxygenases, similarly to its ototoxicity. GFAP assays also indicated that neither vestibulotoxic doses of crotononitrile nor olfatotoxic doses of dichlobenil damage the retina. The data support the use of GFAP assays for assessing the retinal toxicity of IDPN and other nitriles.

Animals↗
PubMed1997

Detectability index measures of binaural masking level difference across populations of inferior colliculus neurons.

In everyday life we continually need to detect signals against a background of interfering noise (the "cocktail party effect"): a task that is much easier to accomplish using two ears. The binaural masking level difference (BMLD) measures the ability of listeners to use a difference in binaural attributes to segregate sound sources and thus improve their discriminability against interfering noises. By computing the detectability of tones from rate-versus-level functions in the presence of a suprathreshold noise, we previously demonstrated that individual low-frequency delay-sensitive neurons in the inferior colliculus are able to show BMLDs. Here we consider the responses of a population of such neurons when the noise level is held constant (as conventionally in psychophysical paradigms). We have sampled the responses of 121 units in the inferior colliculi of five guinea pigs to identical noise and 500 Hz tones at both ears (NoSo) and to identical noise but with the 500 Hz tone at one ear inverted (NoSpi). The result suggests that the neurons subserving detection of So tones in No (identical noise at the two ears) noise are those neurons with best frequencies (BFs) close to 500 Hz that respond to So tones with an increase in their discharge rate from that attributable to the noise. The detection of the inverted (Spi) signal is also attributable to neurons with BFs close to 500 Hz. However, among these neurons, the presence of the Spi tone was indicated by an increased discharge rate in some neurons and by a decreased discharge rate in others.

Animals↗
PubMed1982

DNA content and enzymic activities in the auditory regions of seizure-susceptible and non-susceptible strains of mice.

The developmental profiles of four glycosidase enzymes (beta-D-glucosidase, beta-D-glucuronidase, beta-D-N-acetylglucosaminidase and beta-D-galactosidase) in the cochleas, cochlear nuclei and inferior colliculi of four strains of mice were investigated. The strains used were an audiogenically seizure-susceptible strain (DBA/2) and three non-susceptible strains (BALB/c, C3H/He and Swiss/A2G). The enzymic activities fell to varying degrees from 7 to 28 days of age. Two significant observations were made--beta-D-glucuronidase was low in the regions of the C3H/He strain, and beta-D-galactosidase was particularly low in the regions of the DBA/2 strain. The very low activity of beta-D-galactosidase in the DBA/2 mice is discussed in relation to the ganglioside patterns known to be present in these seizure-susceptible mice. Studies on the DNA contents of these auditory regions in the four strains showed no correlation with seizure sensitivity.

Acetylglucosaminidase↗
PubMed1999

The long-term effect of bilateral inferior colliculus ablation on auditory brainstem response in awake cats.

In this study auditory brainstem responses (ABRs) were recorded repeatedly in three awake cats before and after bilateral aspiration of the inferior colliculi (ICs). All surgical procedures were performed under anaesthesia with Nembutal. Postoperative recordings were obtained 1 week, 3 months, 8 months and 13 months after bilateral aspiration of the ICs in order to study the long-term changes in ABRs. The P5 amplitude was markedly reduced only at 1 week after aspiration. P1 and P2 amplitudes were affected slightly at 3 months and 1 year, but those of P3 and P4 decreased significantly. After perfusion of these cats, histological examination of the brainstem revealed complete ablation of both ICs, neuronal loss in the nucleus of the lateral lemniscus and the superior olivary complex and preservation of the cochlear nucleus. Our results suggest that retrograde degeneration of neuronal cells of the brainstem, which project to the IC from the nucleus of the lateral lemniscus and superior olivary complex except the cochlear nucleus, affect the peak amplitudes of the ABR over the long-term.

Animals↗
PubMed1993

High-frequency neurons in the inferior colliculus that are sensitive to interaural delays of amplitude-modulated tones: evidence for dual binaural influences.

1. Localization of sounds has traditionally been considered to be performed by a duplex mechanism utilizing interaural temporal differences (ITDs) at low frequencies and interaural intensity differences at higher frequencies. More recently, it has been found that listeners can detect ITDs at high frequencies if the amplitude of the sound varies and an ITD is present in the envelope. Here we report the responses of neurons in the inferior colliculi of unanesthetized rabbits to ITDs of the envelopes of sinusoidally amplitude-modulated (SAM) tones. 2. Neurons were studied extracellularly with glass-coated Pt-Ir or Pt-W microelectrodes. Their sensitivity to ITDs in the envelopes of high-frequency sounds (> or = 2 kHz) was assessed using SAM tones that were presented binaurally. The tones at the two ears had the same carrier frequency but modulation frequencies that differed by 1 Hz. This caused a cyclic variation in the ITD produced by the envelope. In this "binaural SAM" stimulus, the carriers caused no ITD because they were in phase. In addition to the binaural SAM stimulus, pure tones were used to investigate responses to ipsilateral and contralateral stimulation and the nature of the interaction during binaural stimulation. 3. Neurons tended to display one of two kinds of sensitivity to ITDs. Some neurons discharged maximally at the same ITD at all modulation frequencies > 250 Hz (peak-type neurons), whereas others were maximally suppressed at the same ITD (trough-type neurons). 4. At these higher modulation frequencies (> 250 Hz), the characteristic delays that neurons exhibited tended to lie within the range that a rabbit might normally encounter (+/- 300 microseconds). The peak-type neurons favored ipsilateral delays, which correspond to sounds in the contralateral sound field. The trough-type neurons showed no such preference. 5. The preference of peak-type neurons for a particular delay was sharper than that of trough-type neurons and was comparable to that observed in neurons of the inferior colliculus that are sensitive to delays of low-frequency pure tones. 6. At lower modulation frequencies (< 150 Hz) characteristic delays often lay beyond +/- 300 microseconds. 7. Increasing the ipsilateral intensity tended to shift the preferred delay ipsilaterally at lower (< 250 Hz), but not at higher, modulation frequencies. 8. When tested with pure tones, a substantial number of peak-type neurons were found to be excited by contralateral stimulation but inhibited by ipsilateral stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1989

Anatomical bases of binaural interaction in auditory brain-stem responses from guinea pig.

There is a non-linear interaction of binaural stimulation on auditory brain-stem potentials in both human and animals. The interaction takes the form of the binaurally evoked ABR being of smaller amplitude than the sum of the monaurally evoked ABRs. In the guinea pig this interaction occurs at the time of components P4, N4 and P5. In order to investigate the generator sites of binaural interaction in the ABR, various lesions were made in the brain-stem auditory system in 29 guinea pigs. The effects of those lesions on binaural interaction were as follows: (1) unilateral lesion of lateral lemniscus or bilateral lesions of the inferior colliculi had no significant effect on binaural interaction; (2) transection of the lateral lemnisci bilaterally was associated with a loss of the component of binaural interaction associated in time with N4; (3) a lesion just lateral to the lateral superior olivary complex resulted in an attenuation of the component of binaural interaction associated in time with P4; (4) complete section of the decussating fibers of the trapezoid body or a complete unilateral lesion of the superior olivary complex led to a loss of all components of binaural interaction. These results suggest that binaural interaction in the guinea pig ABR requires the integrity of several distinct portions of the brain-stem auditory pathway, i.e., both lateral lemnisci are required for the interaction occurring at the time of N4; the brain-stem just lateral to the lateral superior olive participates in the interaction at the time of P4. The trapezoid body and superior olivary nucleus are required for binaural interaction at P4, N4 and P5.

Animals↗
PubMed1999

Intracochlear infusion of buthionine sulfoximine potentiates carboplatin ototoxicity in the chinchilla.

The aim of this experiment was to determine if buthionine sulfoximine (BSO), an inhibitor of glutathione (GSH) synthesis, enhances the ototoxicity of carboplatin. Osmotic pumps were used to infuse BSO into the right cochleas of 12 adult chinchillas for 14 days. The left cochleas served as controls. Animals were assigned to three groups: a drug control group that did not receive carboplatin, a group that received a single dose of carboplatin (25 mg/kg i.p.), and a group that received a double dose of carboplatin (25 mg/kg i.p. x 2), with 4 days between injections. Carboplatin was administered after three days of BSO pre-treatment. Ototoxicity was assessed with evoked potentials recorded from electrodes implanted in the inferior colliculi (ICPs), distortion product otoacoustic emissions (DPOAEs), and cochleograms. BSO infusion itself caused no long-term functional or morphological changes. One of four animals treated with it single dose of carboplatin showed a significant loss of inner hair cells (IHCs), with greater loss in the BSO-treated ear. All animals in the double-dose carboplatin group showed marked differences between BSO-treated and control ears. Average IHC losses were 59% in BSO-treated ears vs. 18% in control ears. Moreover, BSO-treated ears sustained significantly greater outer hair cell (OHC) losses than control ears (37% vs. 2%, respectively). ICP and DPOAE response amplitudes were reduced slightly in BSO-treated ears relative to control ears, consistent with their greater hair cell loss. The results clearly show that BSO can enhance carboplatin ototoxicity in the chinchilla, supporting a role of GSH and reactive oxygen species in platinum ototoxicity.

Animals↗