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Results for “Inferior Colliculi”

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PubMed1999

Intracellular chloride and calcium transients evoked by gamma-aminobutyric acid and glycine in neurons of the rat inferior colliculus.

Microfluorometric recordings showed that the inhibitory neurotransmitters gamma-aminobutyric acid (GABA) and glycine activated transient increases in the intracellular Cl- concentration in neurons of the inferior colliculus (IC) from acutely isolated slices of the rat auditory midbrain. Current recordings in gramicidin-perforated patch mode disclosed that GABA and glycine mainly evoked inward or biphasic currents. These currents were dependent on HCO3- and characterized by a continuous shift of their reversal potential (E(GABA/gly)) in the positive direction. In HCO3- -buffered saline, GABA and glycine could also evoke an increase in the intracellular Ca2+ concentration. Ca2+ transients occurred only with large depolarizations and were blocked by Cd2+, suggesting an activation of voltage-gated Ca2+ channels. However, in the absence of HCO3-, only a small rise, if any, in the intracellular Ca2+ concentration could be evoked by GABA or glycine. We suggest that the activation of GABAA or glycine receptors results in an acute accumulation of Cl- that is enhanced by the depolarization owing to HCO3- efflux, thus shifting E(GABA/gly) to more positive values. A subsequent activation of these receptors would result in a strenghtened depolarization and an enlarged Ca2+ influx that might play a role in the stabilization of inhibitory synapses in the auditory pathway.

Animals↗
PubMed1998

Fetal hearing.

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Autoradiography↗
PubMed2000

An extralemniscal component of the mustached bat inferior colliculus selective for direction and rate of linear frequency modulations.

Frequency modulations (FMs) are prevalent in human speech, and are important acoustic cues for the categorical discrimination of phonetic contrasts. For bats, FM sweeps are also important for communication and are often the only component in echolocation calls. Auditory neurons tuned to the direction and rate of FM might underlie the encoding of rapid frequency transitions. In the mustached bat, we have discovered a population of such FM selective cells in an area interposed between the central nucleus of the inferior colliculus (ICC) and the nuclei of the lateral lemniscus (NLL). We believe this area to be the ventral extent of the external nucleus of the inferior colliculus (ICXv). To describe FM selectivity of neurons in the ICXv and to compare it to other midbrain nuclei, up- and down-sweeping linear FM stimuli were presented at different modulation rates. Extracellular recordings were made from 171 single units in the ICC, ICXv, and NLL of 10 mustached bats. In the ICXv, there was a much higher degree of FM selectivity than in ICC or NLL and a consistent preference for upward over downward FM sweeps. Anterograde and retrograde transport was examined following focal injections of wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) into ICXv. The main targets of anterograde transport were the deep layers of the superior colliculus and the suprageniculate division of the medial geniculate body. The primary site of retrograde transport was the nucleus of the central acoustic tract in the brainstem. Thus, the ICXv appears to be a part of the central acoustic tract, an extralemniscal pathway linking the auditory brainstem directly to a multimodal nucleus of the thalamus.

Acoustic Stimulation↗
PubMed2001

Expression of AMPA receptor subunit flip/flop splice variants in the rat auditory brainstem and inferior colliculus.

The expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunit mRNAs and their flip/flop splice variants was evaluated in the rat auditory brainstem and inferior colliculus employing in situ hybridization with radiolabeled oligonucleotide probes. A differential expression of AMPA receptor subunits in auditory nuclei was observed. In general, neurons in all nuclei of the auditory brainstem express high levels of GluR-C flop and GluR-D flop mRNA, but low to very low levels of GluR-A and GluR-B mRNA. The strongest GluR-C and -D flop expression is found in the ventral and medial part of the anteroventral cochlear nucleus, the posteroventral cochlear nucleus, and the medial and the lateral superior olive. These nuclei are part of the binaural auditory pathway which is important for sound localization in space. In contrast, neurons in the central nucleus of the inferior colliculus express high levels of GluR-B flip but only low levels of the other AMPA receptor subunits. From our data, we conclude that neurons of nuclei involved in binaural processing exhibit a specific "auditory AMPA receptor" which consists primarily of GluR-C flop and -D flop and often lacks GluR-B subunits; this indicates fast kinetics and high Ca(2+) permeability of AMPA receptor currents. In contrast, neurons in the central nucleus of the inferior colliculus contain large amounts of GluR-B flip subunits resulting in Ca(2+) impermeable AMPA receptors with slow kinetics.

Animals↗
PubMed2000

Ascending efferent projections of the superior olivary complex.

The superior olivary complex conveys information about binaural time and intensity to higher centers in the auditory pathway. This information is sent primarily to the subdivisions of the inferior colliculus and to the nuclei of the lateral lemniscus. Olivary projections are the predominant afferents to the central nucleus of the inferior colliculus. Electron microscopic observations of axonal endings in the central nucleus suggest that the ipsilateral medial superior olive and contralateral lateral superior olive make excitatory synapses. In contrast, the axons from the ipsilateral lateral superior olive to the central nucleus contain glycine and have a morphology consistent with inhibitory synapses. Little is known about the transmitter types used by olivary projections to the nuclei of the lateral lemniscus, but they are presumed to be similar to the collicular projections. Olivary ascending efferents are tonotopically organized and terminate in laminae in the inferior colliculus. They combine with other laminar afferents and postsynaptic neurons to create fibro-dendritic laminae in the colliculus. The key to the functional organization of the olivary efferents is the possible segregation of excitatory olivary efferents from each other in "synaptic domains" located on the laminae. This segregation may be the major determinant of response properties in the colliculus. Olivary efferents may converge with other non-olivary afferents on the same postsynaptic neurons in the colliculus. Inhibitory efferents from the lateral superior olive are essential in shaping the response properties of neurons in the colliculus. Olivary efferents to the nuclei of the lateral lemniscus are also key components of ascending pathways that inhibit neurons in the midbrain.

Animals↗
PubMed1989

Postnatal development of vascularity in the inferior colliculus of the young rat.

The inferior colliculus in the rat midbrain is an auditory relay center whose functional maturation occurs postnatally. We examined by morphometry the vascularity and the nuclear profile density of the inferior colliculus in normal young rats at different ages (before and after the onset of auditory input). We also compared this region with a frontal region of the cerebral cortex in 24-day-old rats. The inferior colliculus from aldehyde-perfused Sprague-Dawley rats aged 5, 9, 14, and 24 days was analyzed by light microscopy of semithin plastic sections. The central region (mostly the central nucleus) was sampled at 5 levels representing its entire rostrocaudal extent. Patent-blood-vessel profiles were counted and classified according to their size and profile orientation. Counts of nuclear profiles in the same sections were also made. In the inferior colliculus of rats between 5 and 24 days of age, the small (less than 10-microns diameter) cross-sectioned vessel profiles increased over 6-fold in number per unit area. Correspondingly the vascular volume density, estimated by differential point counting, increased between these ages. However, there was a decrease in the number of neuronal and glial nuclear profiles per unit area, probably because of growth in the volume of the neuronal perikarya and processes, along with cell emigration reported to occur at early postnatal ages. This study has shown that an increase in vascularity in the central region of the rat inferior colliculus continues for up to 2 weeks after the onset of hearing.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1986

Auditory processing deficit in a patient with Rett syndrome.

Because of the consistent and prominent language failure in Rett syndrome, a patient with the characteristic phenotype was tested for subtle auditory processing deficits by visual reinforcement audiometry. In spite of excellent detection threshold and frequency discrimination, frequency sweep discrimination was at a chance level. This discrimination is normally performed by 5-8 month old infants. This observation suggests a defect in the specialized units of the inferior colliculus or higher auditory centers which subserve frequency sweep discrimination.

Audiometry↗
PubMed2002

Immunolocalization of PICK1 in the ascending auditory pathways of the adult rat.

Protein that interacts with C-kinase alpha (PICK1) is a PDZ domain protein that interacts with many binding partners in the central nervous system (CNS), including activated protein kinase Calpha and subunits of the AMPA subtype of glutamate receptor. Almost nothing is known about the anatomic distribution of PICK1 in the intact adult CNS. By using PICK1 antisera and peroxidase immunocytochemistry, we report on the distribution of PICK1 in the ascending pathways of the central auditory system of the adult rat. PICK1-immunoreactivity (ir) was observed in many component nuclei of the central auditory system, including the dorsal cochlear nucleus, anteroventral cochlear nucleus, posteroventral cochlear nucleus, some divisions of the superior olivary complex, inferior colliculus, medial geniculate body, and primary auditory cortex. The general staining pattern for PICK1-immunoreactivity was somatodendritic with scattered puncta in neuropil and somatodendritic regions. The distribution of PICK1 partially overlaps with PKCalpha and glutamate receptor subunits such as GluR2. These data suggest that PICK1 may function in the regulation of PKCalpha and GluR2 localization in components of the rat auditory system, which may be a fundamental mechanism of synaptic transmission and/or plasticity. J. Comp. Neurol.

Animals↗