Ascending and descending projections to the inferior colliculus in the rat

The ascending and descending projections to the central nucleus of the inferior colliculus (IC) were studied with the aid of retrograde transport of horseradish peroxidase (HRP). HRP-labelled cells were found in contralateral cochlear nuclei, where the majority of different cell types was stained. Few labelled cells were observed in the ipsilateral cochlear nuclei. HRP-positive neurones were found in all nuclei of the superior olivary complex on the ipsilateral side with the exception of the medial nucleus of the trapezoid body, which was never labelled either ipsilaterally or contralaterally. The largest concentration of HRP-labelled cells was usually observed in the ipsilateral superior olivary nucleus. Smaller numbers of labelled cells were present in contralateral nuclei of the superior olivary complex. Massive projections to the inferior colliculus were found from the contralateral and ipsilateral dorsal nucleus of the lateral lemniscus and ipsilateral ventral nucleus of the lateral lemniscus. Many neurones of the central and external nuclei of the contralateral inferior colliculus were labelled with HRP. Topographic organisation of the pathways ascending to the colliculus was expressed in the cochlear nuclei, lateral superior olivary nucleus and in the dorsal nucleus of the lateral lemniscus. HRP--positive cells were found in layer V of the ipsilateral auditory cortex, however, the evidence for topographic organisation was lacking.     

The inferior colliculus of the mustached bat has the frequency-vs-latency coordinates

In the mustached bat, the central auditory system contains FM–FM (delay-tuned) neurons which are specialized for processing target-distance information carried by echo delays. Mechanisms for creating the FM–FM neurons involve delay lines, coincidence detection and amplification. A neural basis for delay lines can be a map representing response latencies. The aim of the present study is to explore whether the central nucleus of the inferior colliculus has a latency axis incorporated into iso-best frequency slabs. Responses of single or multiple neurons were recorded from the inferior colliculus of unanesthetized mustached bats with tungsten-wire electrodes, and their response latencies were measured with tone bursts at their best frequencies and best amplitudes or 65 dB SPL. In the dorsoventral electrode penetrations across the inferior colliculus, response latency systematically shortens from ˜12 to ˜4␣ms. Tonotopic representation in the inferior colliculus is somewhat complex. Iso-best frequency slabs are tilted and/or curved, but they orient more or less ventrodorsally. Nevertheless, the latency axis is evident in each iso-best frequency slab, regardless of best frequency. The inferior colliculus has the frequency-vs-latency coordinates. Accepted: 2 October 1996     

Arctiid moths and bat echolocation: broad-band clicks interfere with neural responses to auditory stimuli in the nuclei of the lateral lemniscus of the big brown bat

Clicks emitted by arctiid moths interfere with the ranging ability of echolocating bats. To identify possible neural correlates of this interference, we recorded responses of single units in the nuclei of the lateral lemniscus to combinations of a broad-band click and a test signal (pure tones or frequency-modulated sweeps). In 77% of 87 units tested, clicks interfered with neural responses to the test stimuli. The interference fell into two categories: latency ambiguity and suppression. Units showing latency ambiguity responded to both the click and the test signal. However, when the click occurred within a window of approximately 3 ms before the onset of the test signal, the latency of the response to the test signal was affected. Units that were suppressed did not respond to clicks. Nevertheless, when a click was presented immediately before or simultaneously with a test signal, the response to the test signal was eliminated. Both types of units were found throughout the lateral lemniscus except for the columnar division of the ventral nucleus, where all units tested exhibited latency ambiguity. There is a close match between the single unit data and previous studies of range difference discrimination in the presence of clicks. Accepted: 10 March 1997     

Dynamics of potentials evoked in the auditory pathway and reticular formation of the cat. Studies during waking and sleep stages

Averaged evoked potentials in the inferior colliculus (IC), medial geniculate nucleus (MG) and reticular formation (RF) of chronically implanted and freely moving cats were measured using auditory step functions in the form of tone bursts of 2000 Hz. The most prominent components of the AEP of the inferior colliculus were a positive wave of 13 msec and a negative wave of 40–55 msec latency. The AEP of the medial geniculate nucleus was characterized by a large negative wave peaking at 35–40 msec. During spindle sleep and slow wave sleep stages changes in the AEPs of both nuclei occured.Transient evoked responses of the inferior colliculus, medial geniculate nucleus and reticular formation were transformed to the frequency domain using the Laplace transform (one sided Fourier transform) in order to obtain frequency characteristics of the systems under study. The amplitude characteristics of IC, MG. and RF obtained in this way revealed maxima in alpha (8–13 Hz), beta (18–35 Hz) and higher frequency (50–80 Hz) ranges. During spindle sleep stage a maximum in the theta frequency range (3–8 Hz) and during slow wave sleep maximum in the delta (1–3 Hz) frequency range appeared in the amplitude characteristics of these nuclei.The amplitude characteristics of the inferior colliculus and medial geniculate nucleus were compared with the amplitude characteristics of other brain structures. The comparison of AEPs and amplitude frequency characteristics obtained using these AEPs reveals that the existence of a number of peaks (waves) with different latencies in the time course does not necessarily indicate the existence of different functional structures or neural groups giving rise to these waves. The entire time course of evoked potentials and not the number and latencies of the waves, carries, the whole information concerning different activities and frequency selectivities of brain structures.Supported by Turkish Scientific and Technical Research Council Grant TAG-266.Presented in Part at the VIIIth International Congress of Electroencephalography and Clinical Neurophysiology in Marseilles, September 1–7, 1973.     

Labile cochlear tuning in the mustached bat

Summary Acoustic stimuli near 60 kHz elicit pronounced resonance in the cochlea of the mustached bat (Pteronotus parnellii parnellii). The cochlear resonance frequency (CRF) is near the second harmonic, constant frequency (CF2) component of the bat's biosonar signals. Within narrow bands where CF2 and third harmonic (CF3) echoes are maintained, the cochlea has sharp tuning characteristics that are conserved throughout the central auditory system. The purpose of this study was to examine the effects of temperature-related shifts in the CRF on the tuning properties of neurons in the cochlear nucleus and inferior colliculus.Eighty-two single and multi-unit recordings were characterizedin 6 awake bats with chronically implanted cochlear microphonic electrodes. As the CRF changed with body temperature, the tuning curves of neurons sharply tuned to frequencies near the CF2 and CF3 shifted with the CRF in every case, yielding a change in the unit's best frequency. The results show that cochlear tuning is labile in the mustached bat, and that this lability produces tonotopic shifts in the frequency response of central auditory neurons. Furthermore, results provide evidence of shifts in the frequency-to-place code within the sharply tuned CF2 and CF3 regions of the cochlea. In conjunction with the finding that biosonar emission frequency and the CRF shift concomitantly with temperature and flight, it is concluded that the adjustment of biosonar signals accommodates the shifts in cochlear and neural tuning that occur with active echolocation.Abbreviations BF best frequency - CF characteristic frequency - CF2, CF3 second and third harmonic, constant frequency components of the biosonar signal - CM cochlear microphonic - CN cochlear nucleus - CRF cochlear resonance frequency - IC inferior colliculus - MT minimum threshold - OAE otoacoustic emission - Q_10dB BF (or CF) divided by the response bandwidth at 10 dB above MT     

Immunohistochemical mapping of perineuronal nets containing chondroitin unsulfate proteoglycan in the rat central nervous system

Subsets of neurons ensheathed by perineuronal nets containing chondroitin unsulfate proteoglycan have been immunohistochemically mapped throughout the rat central nervous system from the olfactory bulb to the spinal cord. A variable proportion of neurons were outlined by immunoreactivity for the monoclonal antibody (Mab 1B5), but only after chondroitinase ABC digestion. In forebrain cortical structures the only immunoreactive nets were around interneurons; in contrast, throughout the brainstem and spinal cord a large proportion of projection neurons were surrounded by intense immunoreactivity. Immunoreactivity was ordinarily found in the neuropil between neurons surrounded by an immunopositive net. By contrast, within the pyriform cortex the neuropil of the plexiform layer was intensely immunoreactive even though no perineuronal net could be found. The presence of perineuronal nets could not be correlated with any single class of neurons; however a few functionally related groups (e.g., motor and motor-related structures: motor neurons both in the spinal cord and in the efferent somatic nuclei of the brainstem, deep cerebellar nuclei, vestibular nuclei; red nucleus, reticular formation; central auditory pathway: ventral cochlear nucleus, trapezoid body, superior olive, nucleus of the lateral lemniscus, inferior colliculus, medial geniculate body) were the main components of the neuronal subpopulation displaying chondroitin unsulfate proteoglycans in the surrounding extracellular matrix. The immunodecorated neurons found in the present study and those shown by different monoclonal antibodies or by lectin cytochemisty, revealed consistent overlapping of their distribution patterns.     

Commissural connections mediate inhibition for the computation of interaural level difference in the barn owl

Summary In the barn owl (Tyto alba), the posterior nucleus of the ventral lateral lemniscus (VLVp) is the first site of binaural convergence in the pathway that processes interaural level difference (ILD), an important sound-localization cue. The neurons of VLVp are sensitive to ILD because of an excitatory input from the contralateral ear and an inhibitory input from the ipsilateral ear. A previously described projection from the contralateral cochlear nucleus, can account for the excitation. The present study addresses the source of the inhibitory input.We demonstrate with standard axonal transport methods that the left and right VLVps are interconnected via fibers of the commissure of Probst. We further show that the anesthetization of one VLVp renders ineffective the inhibition that is normally evoked by stimulation of the ipsilateral ear. Thus, one cochlear nucleus (driven by the ipsilateral ear) appears to provide inhibition to the ipsilateral VLVp by exciting commissurally-projecting inhibitory neurons in the contralateral VLVp.Abbreviations ABL average binaural level - CP commissure of Probst - DNLL dorsal nucleus of the lateral lemniscus - IC inferior colliculus - ILD interaural level difference - IPc nucleus isthmi, pars parvocellularis - ITD interaural time difference - LSO lateral superior olive - MNTB medial nucleus of the trapezoid body - NA nucleus angularis - SL nucleus semilunaris - VLVa nucleus ventralis lemnisci lateralis, pars anterior - VLVp nucleus ventralis lemnisci lateralis, pars posterior     

The functional role of GABA and glycine in monaural and binaural processing in the inferior colliculus of horseshoe bats

Summary The functional role of GABA and glycine in monaural and binaural signal analysis was studied in single unit recordings from the central nucleus of the inferior colliculus (IC) of horseshoe bats (Rhinolophus rouxi) employing microiontophoresis of the putative neurotransmitters and their antagonists bicuculline and strychnine.Most neurons were inhibited by GABA (98%; N=107) and glycine (92%; N=118). Both neurotransmitters appear involved in several functional contexts, but to different degrees.Bicuculline-induced increases of discharge activity (99% of cells; N=191) were accompanied by changes of temporal response patterns in 35% of neurons distributed throughout the IC. Strychnine enhanced activity in only 53% of neurons (N=147); cells exhibiting response pattern changes were rare (9%) and confined to greater recording depths. In individual cells, the effects of both antagonists could markedly differ, suggesting a differential supply by GABAergic and glycinergic networks.Bicuculline changed the shape of the excitatory tuning curve by antagonizing lateral inhibition at neighboring frequencies and/or inhibition at high stimulation levels. Such effects were rarely observed with strychnine.Binaural response properties of single units were influenced either by antagonization of inhibition mediated by ipsilateral stimulation (bicuculline) or by changing the strength of the main excitatory input (bicuculline and strychnine).Abbreviations BF best frequency - Bic bicuculline - C control - CF constant frequency - CN cochlear nucleus - DNLL dorsal nucleus of the lateral lemniscus - FM frequency modulation - GABA gamma amino butyric acid - IC inferior colliculus - LSO lateral superior olive - Str strychnine     

Sources of thalamic afferents projecting to the suprasylvian gyrus of the black sea porpoise

Neurons sending fibers to different loci of the suprasylvian gyrus (SSG) of the porpoise(Phocaena phocaena) cortex were located in the thalamus by retrograde horseradish peroxidase transport and fluorescent tracing techniques. Horseradish peroxidase injection into the anterior section of the suprasylvian gyrus led to retrograde labelling of neurons in the lateral portion of the ventrobasal complex of nuclei and the ventroposteroinferior nucleus. A group of labelled cells was found in the ventral section of the main medial geniculate nucleus. Injecting bisbenzimide into different loci of the medial suprasylvian gyrus also led to retrograde labelling of neurons belonging to the ventral division of the main medial geniculate nucleus. Somewhat lower numbers of labelled cells were found in the inferior nucleus of the pulvinar. Small groups of labelled neurons were also found in the lateral nucleus of the pulvinar, the medioventral nucleus of the medial geniculate body, and the posterior complex of nuclei. A similar distribution of labelled cells was also observed after injecting bisbenzimide into the more caudal portion of the gyrus, although the location of labelled cells in the ventral division of the main medial geniculate nucleus and the lower pulvinar nucleus were shifted in a lateral direction.A. N. Severtsov Institute of Animal Evolutionary Moprhology and Ecology, Academy of Sciences of the USSR, Moscow. National University, Singapore. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 529–539, July–August, 1989.     

The nuclei of the lateral lemniscus in the rufous horseshoe bat,Rhinolophus rouxi

In the rufous horseshoe bat, Rhinolophus rouxi, responses to pure tones and sinusoidally frequency modulated (SFM) signals were recorded from 289 single units and 241 multiunit clusters located in the nuclei of the lateral lemniscus (NLL). The distribution of best frequencies (BFs) of units in all three nuclei of the lateral lemniscus showed an overrepresentation in the range corresponding to the constant-frequency (CF) part of the echolocation signal ('filter frequency' range): in the ventral nucleus of the lateral lemniscus (VNLL) 'filter neurons' represented 43% of all units encountered, in the intermediate nucleus (INLL) 33%, and in dorsal nucleus (DNLL) 29% (Fig. 2a). Neurons with best frequencies in the filter frequency range had highest Q10dB-values (maxima up to 400, Fig. 2c) and only in low-frequency units were values comparable to those found in other mammals. On the average, filter neurons in ventral nucleus had higher Q10dB-values (about 220) than did those in intermediate and dorsal nucleus (both about 160, Fig 2d). Response patterns and tuning properties showed higher complexity in the dorsal and intermediate nucleus than in the ventral nucleus of the lateral lemniscus (Figs. 4 and 6). Multiple best frequencies were found in 12 neurons, nine of them with harmonically related excitation maxima (Fig. 5c, d). Best frequencies of six of these harmonically tuned units could not be correlated with any harmonic components of the echolocation signal. Half of all multiple tuned neurons were located in the caudal dorsal nucleus the other half in the caudal intermediate nucleus. Synchronization of responses to sinusoidally frequency modulated (SFM) signals occurred in VNLL-units in the average up to modulation frequencies of 515 Hz (maximum about 800 Hz) whereas in the intermediate and dorsal nucleus of the lateral lemniscus responses were synchronized in the average only up to modulation frequencies of about 300 Hz (maximum about 600 Hz) (Figs. 7 and 8). A tonotopic arrangement of units was found in the intermediate nucleus of the lateral lemniscus with units having high best frequencies located medially and those with low best frequencies laterally. In the dorsal nucleus the tonotopic distribution was found to be fairly similar to that in the intermediate nucleus but much less pronounced. In more rostral parts of the dorsal nucleus additionally higher best frequencies predominated whereas in caudal areas of that nucleus and also of the intermediate nucleus low BFs were found more regularly.(ABSTRACT TRUNCATED AT 400 WORDS)     

Pathways for transmission of visual and auditory information to the cat caudate nucleus

Visual and auditory projections to the cat caudate nucleus were investigated using the horseradish peroxidase retrograde axonal transport technique in conjunction with that of experimental degeneration of retinal axons. It was found that visual information may reach the caudate nucleus not just through well-known polysynaptic pathways from the cerebral cortex but also following oligosynaptic (transpulvinar, lateroposterior nucleus, suprageniculate nucleus, and nucleus limitans of the thalamus) as well as bisynaptic pathways (via the medial and lateral terminal nuclei of the accessory optical tract, pulvinar, pretectum, intermediary layer of the superior colliculus, and the supraoptic nucleus); some of these pathways were identified for the first time. Direct retinal inputs were found in the suprageniculate nucleus. Additional structures were discovered through which auditory information may reach the caudate nucleus, i.e., the dorsal nucleus of the parvocellular portion of the lateral geniculate body, the deep-lying superior colliculus, and the dorsal and ventral nuclei of the lateral lemniscus. The physiological significance of the pathways described for possible transmission of visual and auditory impulses is discussed and a new principle underlining the organization of sensory inputs into the caudate nucleus is put forward.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 512–520, July–August, 1987.     

Effects of stimulation of peripheral nerves,the lateral reticular nucleus,and the inferior olive on fastigial neurons of the cat cerebellum

Activity of fastigial neurons was investigated during stimulation of peripheral nerves of the fore- and hind limbs and also of brain-stem nuclei — the lateral reticular nucleus and inferior olive, transmitting indirect peripheral impulses to the cerebellum, in cats under superficial pentobarbital anesthesia. Stimulation of the nerves was accompanied by excitation of most neurons tested, reflected in repeated discharges to a single stimulus. Three main groups of responses latencies were distinguished: Those corresponding to conduction of peripheral impulses along slow and (partly) fast spinocerebellar tracts were predominant. Stimulation of the lateral reticular nucleus and inferior olive was accompanied by mono- and polysynaptic, and also by antidromic activation of fastigial neurons. Monosynaptic and antidromic activation of neurons are regarded as evidence of the presence of direct reticulo-and olivofastigial projections and of feedback in the system of these inputs into the nucleus fastigius respectively.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 168–178, March–April, 1981.     

Efferent connections of the centrum medianum of the cat thalamus revealed by autoradiography

Efferent connections of the centrum medianum and parafascicular nucleus of the thalamus (CM-Pf complex) in cats were studied by the method of anterograde axonal transport of tritiated amino acids followed by autoradiography. Projections from CM-Pf ascend to nuclei of the ventral group and nonspecific nuclei of the thalamus, preoptic, dorsal, lateral, and posterior areas of the hypothalamus, and also into the subthalamic region. Descending pathways are formed only by neurons of the caudomedial part of CM-Pf. They project into the pretectal region, superior colliculus, reticular formation, locus coeruleus, region of the ramus communicans, and substantia grisea centralis of the mesencephalon and pons, and also into the nuclei raphe, magnocellular reticular area, and inferior olivary nucleus of the medulla. In agreement with previous observations it was found that the caudomedial part of CM-Pf does not send direct projections into the cortex and striatum.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 224–230, March–April, 1984.     

Interval-specific event related potentials to omitted stimuli in the electrosensory pathway in elasmobranchs: an elementary form of expectation

Multiunit activity and slow local field potentials show Omitted Stimulus Potentials (OSP) in the electrosensory system in rays (Platyrhinoidis triseriata, Urolophus halleri) after a missing stimulus in a 3 to >20 Hz train of V pulses in the bath, at levels from the primary medullary nucleus to the telencephalon. A precursor can be seen in the afferent nerve. The OSP follows the due-time of the first omitted stimulus with a, usually, constant main peak latency, 30–50 ms in medullary dorsal nucleus, 60–100 ms in midbrain, 120–190 ms in telencephalon — as though the brain has an expectation specific to the interstimulus interval (ISI). The latency, form and components vary between nerve, medulla, mid-brain and forebrain. They include early fast waves, later slow waves and labile induced rhythms. Responsive loci are quite local. Besides ISI, which exerts a strong influence, many factors affect the OSP slightly, including train parameters and intensity, duration and polarity of the single stimulus pulses. Jitter of ISI does not reduce the OSP substantially, if the last interval equals the mean; the mean and the last interval have the main effect on both amplitude and latency.Taken together with our recent findings on visually evoked OSPs, we conclude that OSPs do not require higher brain levels or even the complexities of the retina. They appear in primary sensory nuclei and are then modified at midbrain and telencephalic levels. We propose that the initial processes are partly in the receptors and partly in the first central relay including a rapid increase of some depressing influence contributed by each stimulus. This influence comes to an ISI-specific equilibrium with the excitatory influence; withholding a stimulus and hence its depressing influence causes a rebound excitation with a specific latency.Abbreviations DN dorsal nucleus of medullary lateral line lobe - EEG electroencephalogram - EP evoked potential - ERP event related potential - IR induced rhythm - ISI interstimulus interval - OSP omitted stimulus potential - MLN mesencephalic lateral nucleus - P75 positive peak at 75 ms     

On the ability of neurons in the barn owl's inferior colliculus to sense brief appearances of interaural time difference

Summary This paper investigates the ability of neurons in the barn owl's (Tyto alba) inferior colliculus to sense brief appearances of interaural time difference (ITD), the main cue for azimuthal sound localization in this species. In the experiments, ITD-tuning was measured during presentation of a mask-probe-mask sequence. The probe consisted of a noise having a constant ITD, while the mask consisted of binaurally uncorrelated noise. Collicular neurons discriminated between the probe and masking noise by showing rapid changes from untuned to tuned and back to untuned responses.The curve describing the relation between probe duration and the degree of ITD-tuning resembled a leaky-integration process with a time constant of about 2 ms. Many neurons were ITD-tuned when probe duration was below 1 ms. These extremely short effective probe durations are interpreted as evidence for neuronal convergence within the pathway computing ITD. The minimal probe duration necessary for ITD-tuning was independent of the bandwidth of the neurons' frequency tuning and also of the best frequency of a neuron. Many narrowly tuned neurons having different best frequencies converge to form a broad-band neuron. To yield the short effective probe durations the convergence must occur in strong temporal synchronism.Abbreviations ICc central nucleus of the inferior colliculus; - ICx external nucleus of the inferior colliculus; - ITD interaural time difference - LP Likelihood parameter     

Ontogenesis of tonotopy in inferior colliculus of a hipposiderid bat reveals postnatal shift in frequency-place code

Summary The postnatal development of midbrain tonotopy was investigated in the inferior colliculus (IC) of the south Indian CF-FM batHipposideros speoris. The developmental progress of the three-dimensional frequency representation was determined by systematic stereotaxic recordings of multiunit clusters from the 1st up to the 7th postnatal week. Additional developmental measures included the tuning characteristics of single units (Figs. 3f; 4f; 5f), the analysis of the vocalised pulse repertoire (Figs. 3e, 4e, 5e), and morphometric reconstructions of the brains of all experimental animals (Fig. 1).The maturation of auditory processing could be divided into two distinct, possibly overlapping developmental periods: First, up to the 5th week, the orderly tonotopy in the IC developed, beginning with the low frequency representation and progressively adding the high frequency representation. With regard to the topology of isofrequency sheets within the IC, maturation progresses from dorsolateral to ventromedial (Figs. 3c, 4c). At the end of this phase the entire IC becomes specialised for narrowly tuned and sensitive frequency processing. This includes the establishment of the auditory fovea, i.e. the extensive spatial representation of a narrow band of behaviorally relevant frequencies in the ventromedial part of the IC. In the 5th postnatal week the auditory fovea is concerned with frequencies from 100–118 kHz (Fig. 4c, d). During subsequent development, the frequency tuning of the auditory fovea increases by 20–25 kHz and finally attains the adult range of ca. 125–140 kHz. During this process, neither the bandwidth of the auditory fovea (15–20 kHz) nor the absolute sensitivity of its units (ca. 50 dB SPL) were changed. Further maturation occurred at the single unit level : the sharpness of frequency tuning increased from the 5th to the 7th postnatal weeks (Q-₁₀-dB-values up to 30–60), and upper thresholds emerged (Figs. 4f, 5f).Although in the adult the frequency of the auditory fovea matches that of the vocalised pulses, none of the juvenile bats tested from the 5th to the 7th weeks showed such a frequency match between vocalisation and audition (Figs. 4e, 5e).The results show that postnatal maturation of audition in hipposiderid bats cannot be described by a model based on a single developmental parameter.Abbreviations BF best frequency - CF constant frequency - Cer cerebellum - CN cochlear nucleus - CO auditory cortex - CUF cuneiform nucleus - DAB days after birth - FAL forearm length - FM frequency modulation - IC inferior colliculus - NLL nucleus of the lateral lemniscus - PAG periaqueductal gray - SC superior colliculus     

Structural Changes and Lack of HCN1 Channels in the Binaural Auditory Brainstem of the Naked Mole-Rat (Heterocephalus glaber)

Naked mole-rats (Heterocephalus glaber) live in large eu-social, underground colonies in narrow burrows and are exposed to a large repertoire of communication signals but negligible binaural sound localization cues, such as interaural time and intensity differences. We therefore asked whether monaural and binaural auditory brainstem nuclei in the naked mole-rat are differentially adjusted to this acoustic environment. Using antibody stainings against excitatory and inhibitory presynaptic structures, namely the vesicular glutamate transporter VGluT1 and the glycine transporter GlyT2 we identified all major auditory brainstem nuclei except the superior paraolivary nucleus in these animals. Naked mole-rats possess a well structured medial superior olive, with a similar synaptic arrangement to interaural-time-difference encoding animals. The neighboring lateral superior olive, which analyzes interaural intensity differences, is large and elongated, whereas the medial nucleus of the trapezoid body, which provides the contralateral inhibitory input to these binaural nuclei, is reduced in size. In contrast, the cochlear nucleus, the nuclei of the lateral lemniscus and the inferior colliculus are not considerably different when compared to other rodent species. Most interestingly, binaural auditory brainstem nuclei lack the membrane-bound hyperpolarization-activated channel HCN1, a voltage-gated ion channel that greatly contributes to the fast integration times in binaural nuclei of the superior olivary complex in other species. This suggests substantially lengthened membrane time constants and thus prolonged temporal integration of inputs in binaural auditory brainstem neurons and might be linked to the severely degenerated sound localization abilities in these animals.     

Sensitivity to interaural time difference and representation of azimuth in central nucleus of inferior colliculus in the barn owl

Standard electrophysiology and virtual auditory stimuli were used to investigate the influence of interaural time difference on the azimuthal tuning of neurons in the core and the lateral shell of the central nucleus of the inferior colliculus of the barn owl. The responses of the neurons to virtual azimuthal stimuli depended in a periodic way on azimuth. Fixation of the interaural time difference, while leaving all other spatial cues unchanged, caused a loss of periodicity and a broadening of azimuthal tuning. This effect was studied in more detail in neurons of the core. The azimuthal range tested and the frequency selectivity of the neurons were additional parameters influencing the changes induced by fixating the interaural time difference. The addition of an interaural time difference to the virtual stimuli resulted in a shift of the tuning curves that correlated with the interaural time difference added. In this condition, tuning strength did not change. These results suggest that interaural time difference is an important determinant of azimuthal tuning in all neurons of the core and lateral shell of the central nucleus of the inferior colliculus, and is the only determinant in many of the neurons from the core.     

大鼠脑内代谢型谷氨酸受体5亚型(mGluR5)定位分布的免疫细胞化学研究

本研究用免疫细胞化学技术观察了大鼠脑内参与兴奋性突触传递的代谢型谷氨酸受体5亚型(mGluR5)的精确定位分布.mGluR5阳性浓染的神经元胞体和纤维密集地分布于大脑皮质浅层、嗅球、伏核、尾壳核、前脑基底部、隔区、苍白球、腹侧苍白球、海马CA1和CA2区、下丘中央核、被盖背侧核和三叉神经脊束核尾侧亚核浅层;淡染而稀疏的mGluR5阳性神经元胞体和纤维见于屏状核、终纹床核、杏仁中央核、丘脑部分核团、上丘浅灰质层、外侧丘系背侧核和延髓中央灰质.     

Oscillating neurons in the cochlear nucleus: I. Experimental basis of a simulation paradigm

Anatomical and physiological auditory data and pitch measurements are presented including some additional analysis. The data provide the basis for a new computer model of sustained chopper neurons in the ventral cochlear nucleus. New and old evidence indicating a preference for multiples of 0.4 ms in oscillations of chopper neurons in the cochlear nucleus of different species such as man, cats, and Guinea fowls, is summarized. Our hypothesis is that the time constant of 0.4 ms is due to the minimum synaptic delay of chopper neuron connections. Anatomical findings show that chopper neurons are indeed connected and can excite each other; a model of a circular network of neurons that are connected via synapses with a delay of 0.4 ms is thus plausible. Results concerning frequency tuning and dynamical properties of periodicity encoding of chopper neurons are reviewed. It is concluded that chopper neurons receive input both from auditory nerve fibres and onset neurons.