Sensitivity to spectral interaural intensity difference cues in space-specific neurons of the barn owl

Barn owls use interaural intensity differences to localize sounds in the vertical plane. At a given elevation the magnitude of the interaural intensity difference cue varies with frequency, creating an interaural intensity difference spectrum of cues which is characteristic of that direction. To test whether space-specific cells are sensitive to spectral interaural intensity difference cues, pure-tone interaural intensity difference tuning curves were taken at multiple different frequencies for single neurons in the external nucleus of the inferior colliculus. For a given neuron, the interaural intensity differences eliciting the maximum response (the best interaural intensity differences) changed with the frequency of the stimulus by an average maximal difference of 9.4±6.2 dB. The resulting spectral patterns of these neurally preferred interaural intensity differences exhibited a high degree of similarity to the acoustic interaural intensity difference spectra characteristic of restricted regions in space. Compared to stimuli whose interaural intensity difference spectra matched the preferred spectra, stimuli with inverted spectra elicited a smaller response, showing that space-specific neurons are sensitive to the shape of the spectrum. The underlying mechanism is an inhibition for frequency-specific interaural intensity differences which differ from the preferred spectral pattern. Collectively, these data show that space-specific neurons are sensitive to spectral interaural intensity difference cues and support the idea that behaving barn owls use such cues to precisely localize sounds.Abbreviations ABI average binaural intensity - HRTF head-related transfer function - ICx external nucleus of the inferior colliculus - IID interaural intensity difference - ITD interaural time difference - OT optic tectum - RMS root mean square - VLVp nucleus ventralis lemnisci laterale, pars posterior     

Pattern of afferents to the lateral septum in the guinea pig

Summary The septal region represents an important telencephalic center integrating neuronal activity of cortical areas with autonomous processes. To support the functional analysis of this brain area in the guinea pig, the afferent connections to the lateral septal nucleus were investigated by the use of iontophoretically applied horseradish peroxidase (HRP). Retrogradely labeled perikarya were located in telencephalic, diencephalic, mesencephalic and metencephalic sites. The subnuclei of the lateral septum (pars dorsalis, intermedia, ventralis, posterior) receive afferents from the (i) medial septal nucleus, diagonal band of Broca (pars horizontalis and pars ventralis), and the principal nucleus of the stria terminalis, the hippocampus, and amygdala (nucleus medialis); (ii) the medial habenular nucleus, and the para- (peri-) ventricular, parataenial and reuniens nuclei of the thalamus; the anterior, lateral and posterior hypothalamic areas in particular, the medial and lateral preoptic, suprachiasmatic, periventricular, paraventricular, arcuate, premammillary, and supramammillary nuclei; (iii) the periaquaeductal grey, ventral tegmental area, nucleus interfascicularis, nucleus reticularis linearis, central linear nucleus, interpeduncular nucleus; (iv) dorsal and medial raphe complex, and locus coeruleus. Each subnucleus of the lateral septum displays an individual, differing pattern of afferents from the above-described regions. Based on a double-labeling method, the vasopressinergic and serotonergic afferents to the lateral septum were found to originate in the nucleus paraventricularis hypothalami and the raphe nuclei, respectively.Abbreviations ARC arcuate nucleus - BNST bed nucleus of the stria terminalis - CL central linear nucleus - DBBh diagonal band of Broca (pars horizontalis) - DBBv diagonal band of Broca (pars ventralis) - DR dorsal raphe nucleus - HC hippocampus - IF interfascicular nucleus - IP interpeduncular nucleus - LC locus coeruleus - LDT laterodorsal tegmental nucleus - LHA lateral hypothalamic area - LPO lateral preoptic area - LSN lateral septal nucleus - MA medial amygdaloid nucleus - MH medial habenular nucleus - MPO medial preoptic region - MR medial raphe nucleus - MSN medial septal nucleus - PAG periaquaeductal grey - PEN periventricular nucleus - PHA posterior hypothalamic area - PMd premammillary region (pars dorsalis) - PMv premammillary region (pars ventralis) - PT parataenial nucleus - PVN paraventricular hypothalamic nucleus - PVT paraventricular thalamic nucleus - RE nucl. reuniens - RL nucl. reticularis linearis - SCN suprachiasmatic nucleus - SMl supramammillary region (pars lateralis) - SMm supramammillary region (pars medialis) - SUB subiculum - TS triangular septal nucleus - VTA ventral tegmental area - ac anterior commissure - bc brachium conjunctivum - bp brachium pontis - cc corpus callosum - fr fasciculus retroflexus - fx fornix - ml medial lemniscus - mlf fasciculus longitudinalis medialis - mp mammillary peduncle - mt mammillary tract - oc optic chiasm - on optic nerve - pc posterior commissure - pt pyramidal tract - sm stria medullaris - st stria terminalis - vhc ventral hippocampal commissure Supported by the Deutsche Forschungsgemeinschaft (Nu 36/2-1)     

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.     

1例雄性朱鹮脑内脑啡肽的免疫组织化学分布

用免疫组织化学方法研究脑啡肽(ENK)在极危物种朱(Nipponia nippon)脑内的分布,结合计算机图像分析仪检测免疫阳性细胞和末梢的灰度值。ENK阳性细胞、纤维和终末分布如下:发声核团有原纹状体中间区腹部、丘脑背内侧核外侧部、中脑丘间核、中脑背内侧核、延髓舌下神经核。听觉中枢有丘脑卵圆核壳区、中脑背外侧核壳区、脑桥外侧丘系腹核、上橄榄核、耳蜗核等。内分泌核团有视前区前核、旧纹状体增加部、下丘脑外侧核、下丘脑腹内侧核等。结果表明,朱脑内ENK可能对发声、听觉和下丘脑内分泌的生理活动有一定的调制作用。     

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.     

蜡嘴,锡嘴雀和法国鹌鹑耳蜗—中脑听觉中枢的比较观察

用辣根过氧化物酶HRP顺行标记方法表明蜡嘴(Eophona migratoria)、锡嘴(Coccothra-ustes coccothraustes)和鹌鹑(France Coturnix coturnix)脑干内听觉中枢的初级神经元位于耳蜗核(nCO,Cochlear unclei)内。较高级神经元位于中脑背外侧核(MLD,Nucleus mesen-cephalicus lateralis,pars dorsalis)。脑干内听觉传入通路始于nCO,经外侧丘系(LL,Lemni-scus lateralis)可直接投射于MLD。鸣禽鸟蜡嘴、锡嘴是对侧投射,同侧仅有个别纤维被标记,非鸣禽鹌鹑仅是对侧性投射。     

Noninvasive fMRI Investigation of Interaural Level Difference Processing in the Rat Auditory Subcortex

Objective

Interaural level difference (ILD) is the difference in sound pressure level (SPL) between the two ears and is one of the key physical cues used by the auditory system in sound localization. Our current understanding of ILD encoding has come primarily from invasive studies of individual structures, which have implicated subcortical structures such as the cochlear nucleus (CN), superior olivary complex (SOC), lateral lemniscus (LL), and inferior colliculus (IC). Noninvasive brain imaging enables studying ILD processing in multiple structures simultaneously.

Methods

In this study, blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) is used for the first time to measure changes in the hemodynamic responses in the adult Sprague-Dawley rat subcortex during binaural stimulation with different ILDs.

Results and Significance

Consistent responses are observed in the CN, SOC, LL, and IC in both hemispheres. Voxel-by-voxel analysis of the change of the response amplitude with ILD indicates statistically significant ILD dependence in dorsal LL, IC, and a region containing parts of the SOC and LL. For all three regions, the larger amplitude response is located in the hemisphere contralateral from the higher SPL stimulus. These findings are supported by region of interest analysis. fMRI shows that ILD dependence occurs in both hemispheres and multiple subcortical levels of the auditory system. This study is the first step towards future studies examining subcortical binaural processing and sound localization in animal models of hearing.     

Afferent connections of the optic tectum in channel catfish Ictalurus punctatus

Summary Horseradish peroxidase was injected unilaterally into the optic tectum of the channel catfish, Ictalurus punctatus. The sources of tectal afferents were thereby revealed by retrogradely labeled neurons in various brain centers. Retrogradely labeled cells were seen in both the ipsilateral and contralateral telencephalon. The superficial pretectal area was labeled on both sides of the brain. Ipsilateral projections were also observed coming from the entopeduncular nucleus. Both the anterior thalamic nucleus and the ventro-medial thalamic nucleus projected to the ipsilateral optic tectum. Cells in the ipsilateral nucleus of the posterior commissure were seen to project to the tectum. Labeled fibers were visualized in the lateral geniculate nucleus ipsilateral to the injected tectum, however, no labeled cell bodies were observed. Therefore, tectal cells project to the lateral geniculate nucleus, but this projection is not reciprocal. No labeled cells were found in the cerebellum. Labeled cells occurred in both the ipsilateral and contralateral medial reticular formation; they were also observed in the ipsilateral nucleus isthmi. A projection was seen coming from the dorsal funicular nucleus. Furthermore, labeled cells were shown in the inferior raphe nucleus.Abbreviations AP Area pretectalis - C Cerebellum - DPTN Dorsal posterior tegmental nucleus - H Habenula - IRF Inferior reticular formation - LI Inferior lobe - LGN Lateral geniculate nucleus - LR Lateral recess - MB Mammillary body - MRF Medial reticular formation - MZ Medial zone of the telencephalon - NC Nucleus corticalis - NDL-M Nucleus opticus dorsolateralis/pars medialis - NI Nucleus isthmi - NPC Nucleus of the posterior commissure - OPT Optic tectum - OT Optic tract - PC Posterior commissure - PN Pineal organ - PrOP Preoptic nucleus - PT Pretectum - TBt Tectobulbar tract - TEL Telencephalon - TL Torus longitudinalis - TS Torus semicircularis - VC Valvula cerebelli - VLTN Ventrolateral thalamic nucleus - VMTN Ventromedial thalamic nucleus     

The directionality of the ear of the pigeon (Columba livia)

Summary The directionality of cochlear microphonic potentials in the azimuthal plane was investigated in the pigeon (Columba livia), using acoustic free-field stimulation (pure tones of 0.25–6 kHz).At high frequencies in the pigeon's hearing range (4–6 kHz), changing azimuth resulted in a maximum change of the cochlear microphonic amplitude by about 20 dB (SPL). The directionality decreased clearly with decreasing frequency.Acoustic blocking of the contralateral ear canal could reduce the directional sensitivity of the ipsilateral ear by maximally 8 dB. This indicates a significant sound transmission through the bird's interaural pathways. However, the magnitude of these effects compared to those obtained by sound diffraction (maximum > 15 dB) suggests that pressure gradients at the tympanic membrane are only of subordinate importance for the generation of directional cues.The comparison of interaural intensity differences with previous behavioral results confirms the hypothesis that interaural intensity difference is the primary directional cue of azimuthal sound localization in the high-frequency range (2–6 kHz).Abbreviations CM cochlear microphonic potential - IID interaural intensity difference - IID-MRA minimum resolvable angle calculated from interaural intensity difference - MRA minimum resolvable angle - OTD interaural ongoing time difference - RMS root mean square - SPL sound pressure level     

Coding of sound location and frequency in the auditory midbrain of diurnal birds of prey,families accipitridae and falconidae

Summary The coding of sound frequency and location in the avian auditory midbrain nucleus (nMLD) was examined in three diurnal raptors: the brown falcon (Falco berigora), the swamp harrier (Circus aeruginosus) and the brown goshawk (Accipiter fasciatus). Previously this nucleus has been studied with free field stimuli in only one other species, the barn owl (Tyto alba).We found some parallels between the organisation of nMLD in the diurnal raptors and that reported in the barn owl in that the central region of nMLD was tonotopically organised and contained cells that did not encode location, and the lateral region (nMLDl) contained cells which were sensitive to stimulus position. However, unlike the barn owl, which has units with circumscribed receptive fields, cells sensitive to stimulus location had large receptive fields which were restricted in azimuth but not in elevation (hemifield units). Such cells could not provide an acoustic space map in which both azimuthal and elevational dimensions were represented, but there was a tendency for units with contralateral borders to be found superficially, and those with ipsilateral borders to be found deep, in nMLDl. Hemifield units displayed receptive field properties consistent with the directional properties of the tympana in the presence of sound transmission through the interaural canal, if there is a central mechanism which is sensitive to interaural intensity differences.Abbreviations nMLD nucleus mesencephalicus lateralis pars dorsalis - SPL sound pressure level re 20 Pa - nMLDl lateral region of nMLD - ICC central nucleus of the inferior colliculus - ICX external nucleus of the inferior colliculus - IID interaural intensity difference - EI excitatory inhibitory     

Sensory inputs to the nucleus basalis prosencephali,a feeding-pecking centre in the pigeon

Summary Evoked potentials were recorded from the nucleus basalis prosencephali (Bas) of the pigeon through chronically implanted electrodes. The auditory sensitivity of the Bas was assessed by the amplitude of the potentials. Audiograms thus obtained were comparable to those similarly measured from stations of the orthodox auditory pathway and resembled those obtained by others with behavioural techniques from the same species. The sensitivity to vibration applied to the beak was also measured. The vibrogram revealed two separate optima, one located in the lower frequency and another in the higher frequency region. These were shown to be due to trigeminal mechanoreceptive sensitivity and to bone/cochlea mediated sound sensitivity, respectively. Evoked potentials of the Bas in response to vestibular stimulation are described for the first time. The possibility that they were artefacts was excluded with several control procedures. These findings confirm recent anatomical evidence of a direct pathway from the vestibular nucleus to the nucleus basalis prosencephali. All afferents to the Bas are discussed in conjunction with the probable function of the nucleus as a sensorimotor coordinator of the pigeon's pecking/feeding behaviour.Abbreviations A archistriatum - aL area L of the medial neostriatum caudale - Bas nucleus basalis prosencephali - Cb cerebellum - FA tractus fronto-archistriatalis - HA hyperstriatum accessorium - Hp hippocampus - HRP horseradish peroxidase - HV hyperstriatum ventrale - LLv nucleus lemnisci lateralis, pars ventralis - LPO lobus parolfactorius - MV nucleus motorius nervi trigemini - MLd nucleus mesencephalicus lateralis, pars dorsalis - nVI nucleus nervi facialis - nVIII nervus vestibulocochlearis - N neostriatum - NFL neostriatum frontolaterale - OM tractus occipitomesencephalicus - Ov nucleus ovoidalis - PrV nucleus sensorius principalis nervi trigemini - QF tractus quintofrontalis - Rpv nucleus reticularis parvocellularis, pars lateralis - TrO tractus opticus - VS nucleus vestibularis superior     

Effects of binaural decorrelation on neural and behavioral processing of interaural level differences in the barn owl (Tyto alba)

The effect of binaural decorrelation on the processing of interaural level difference cues in the barn owl (Tyto alba) was examined behaviorally and electrophysiologically. The electrophysiology experiment measured the effect of variations in binaural correlation on the first stage of interaural level difference encoding in the central nervous system. The responses of single neurons in the posterior part of the ventral nucleus of the lateral lemniscus were recorded to stimulation with binaurally correlated and binaurally uncorrelated noise. No significant differences in interaural level difference sensitivity were found between conditions. Neurons in the posterior part of the ventral nucleus of the lateral lemniscus encode the interaural level difference of binaurally correlated and binaurally uncorrelated noise with equal accuracy and precision. This nucleus therefore supplies higher auditory centers with an undegraded interaural level difference signal for sound stimuli that lack a coherent interaural time difference. The behavioral experiment measured auditory saccades in response to interaural level differences presented in binaurally correlated and binaurally uncorrelated noise. The precision and accuracy of sound localization based on interaural level difference was reduced but not eliminated for binaurally uncorrelated signals. The observation that barn owls continue to vary auditory saccades with the interaural level difference of binaurally uncorrelated stimuli suggests that neurons that drive head saccades can be activated by incomplete auditory spatial information.     

Localization of neuropeptide Y-immunoreactive cells and fibres in the brain of the Japanese quail

Summary In the present study, we have demonstrated, by means of the biotin-avidin method, the widespread distribution of neuropeptide Y (NPY)-immunoreactive structures throughout the whole brain of the Japanese quail (Coturnix coturnix japonica). The prosencephalic region contained the highest concentration of both NPY-containing fibres and perikarya. Immunoreactive fibres were observed throughout, particularly within the paraolfactory lobe, the lateral septum, the nucleus taeniae, the preoptic area, the periventricular hypothalamic regions, the tuberal complex, and the ventrolateral thalamus. NPY-immunoreactive cells were represented by: a) small scattered perikarya in the telencephalic portion (i.e. archistriatal, neostriatal and hyperstriatal regions, hippocampus, piriform cortex); b) medium-sized cell bodies located around the nucleus rotundus, ventrolateral, and lateral anterior thalamic nuclei; c) small clustered cells within the periventricular and medial preoptic nuclei. The brainstem showed a less diffuse innervation, although a dense network of immunopositive fibres was observed within the optic tectum, the periaqueductal region, and the Edinger-Westphal, linearis caudalis and raphes nuclei. Two populations of large NPY-containing perikarya were detected: one located in the isthmic region, the other at the boundaries of the pons with the medulla. The wide distribution of NPY-immunoreactive structures within regions that have been demonstrated to play a role in the control of vegetative, endocrine and sensory activities suggests that, in birds, this neuropeptide is involved in the regulation of several aspects of cerebral functions.Abbreviations AA archistriatum anterius - AC nucleus accumbens - AM nucleus anterior medialis - APP avian pancreatic polypeptide - CNS centrai nervous system - CO chiasma opticum - CP commissura posterior - CPi cortex piriformis - DIC differential interferential contrast - DLAl nucleus dorsolateralis anterior thalami, pars lateralis - DLAm nucleus dorsolateralis anterior thalami, pars medialis - E ectostriatum - EW nucleus of Edinger-Westphal - FLM fasciculus longitudinalis medialis - GCt substantia grisea centralis - GLv nucleus geniculatus lateralis, pars ventralis - HA hyperstriatum accessorium - Hp hippocampus - HPLC high performance liquid chromatography - HV hyperstriatum ventrale - IF nucleus infundibularis - IO nucleus isthmo-opticus - IP nucleus interpeduncularis - IR immunoreactive - LA nucleus lateralis anterior thalami - LC nucleus linearis caudalis - LFS lamina frontalis superior - LH lamina hyperstriatica - LHRH luteinizing hormone-releasing hormone - LoC locus coeruleus - LPO lobus paraolfactorius - ME eminentia mediana - N neostriatum - NC neostriatum caudale - NPY neuropeptide Y - NIII nervus oculomotorius - NV nervus trigeminus - NVI nervus facialis - NVIIIc nervus octavus, pars cochlearis - nIV nucleus nervi oculomotorii - nIX nucleus nervi glossopharyngei - nBOR nucleus opticus basalis (ectomamilaris) - nCPa nucleus commissurae pallii - nST nucleus striae terminalis - OM tractus occipitomesencephalicus - OS nucleus olivaris superior - PA palaeostriatum augmentatum - PBS phosphate-buffered saline - POA nucleus praeopticus anterior - POM nucleus praeopticus medialis - POP nucleus praeopticus periventricularis - PP pancreatic polypeptide - PYY polypeptide YY - PVN nucleus paraventricularis magnocellularis - PVO organum paraventriculare - R nucleus raphes - ROT nucleus rotundus - RP nucleus reticularis pontis caudalis - Rpc nucleus reticularis parvocellularis - RPgc nucleus reticularis pontis caudalis, pars gigantocellularis - RPO nucleus reticularis pontis oralis - SCd nucleus subcoeruleus dorsalis - SCv nucleus subcoeruleus ventralis - SCNm nucleus suprachiasmaticus, pars medialis - SCNl nucleus suprachiasmaticus, pars lateralis - SL nucleus septalis lateralis - SM nucleus septalis medialis - Ta nucleus tangentialis - TeO tectum opticum - Tn nucleus taeniae - TPc nucleus tegmenti pedunculo-pontinus, pars compacta - TSM tractus septo-mesencephalicus - TV nueleus tegmenti ventralis - VeL nucleus vestibularis lateralis - VLT nucleus ventrolateralis thalami - VMN nucleus ventromedialis hypothalami A preliminary report of this study was presented at the 15th Conference of European Comparative Endocrinologists, Leuven, Belgium, September 1990     

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     

Retinal projections in the catfish,Mystus vittatus (Bloch) as revealed by tracer studies with horseradish peroxidase

Summary The retinal efferents of the catfish, Mystus vittatus, were investigated with the use of the horseradish peroxidase (HRP) technique. Most retinal fibres extended contralateral to the eye that had received HRP label, while a few fascicles projected to the ipsilateral side without decussation in the optic chiasma. The contralateral fibres projected to the suprachiasmatic nucleus, the nucleus opticus dorsolateralis, the nucleus of the posterior commissure, the nucleus geniculatus lateralis, pretectal nuclear complex, and to two layers of the optic tectum, i.e., stratum fibrosum et griseum superficiale and stratum griseum centrale. The accessory optic tract arose from the inner area of the optic tract and extended ventromedially to the accessory optic nucleus. The ipsilateral fascicles projected to almost all the above mentioned nuclei, but these projections were comparatively sparse. The ipsilateral retinal projection was restricted to the rostral tectum.     

Spatial tuning of neurons in the inferior colliculus of the big brown bat: effects of sound level, stimulus type and multiple sound sources

We examined factors that affect spatial receptive fields of single units in the central nucleus of the inferior colliculus of Eptesicus fuscus. Pure tones, frequency- or amplitude-modulated sounds, or noise bursts were presented in the free-field, and responses were recorded extracellularly. For 58 neurons that were tested over a 30 dB range of sound levels, 7 (12%) exhibited a change of less than 10° in the center point and medial border of their receptive field. For 28 neurons that were tested with more than one stimulus type, 5 (18%) exhibited a change of less than 10° in the center point and medial border of their receptive field.The azimuthal response ranges of 19 neurons were measured in the presence of a continuous broadband noise presented from a second loudspeaker set at different fixed azimuthal positions. For 3 neurons driven by a contralateral stimulus only, the effect of the noise was simple masking. For 11 neurons driven by sound at either side, 8 were unaffected by the noise and 1 showed a simple masking effect. For the remaining 2, as well as for 5 neurons that were excited by contralateral sound and inhibited by ipsilateral sound, the peak of the azimuthal response range shifted toward the direction of the noise.Abbreviations E/E excitation at either ear - I/E inhibition at the ipsilateral ear, excitation at the contralateral ear - O/E no effect from the ipsilateral ear, excitation at the contralateral ear - FM downward frequency modulation - FM upward frequency modulation - IC inferior colliculus - ICC central nucleus of the inferior colliculus - ILD interaural level difference - ITD interaural time difference - PT pure tone - SAM sinusoidally amplitude modulated sounds - SFM sinusoidally frequency modulated sounds     

Pheromone detection and olfactory pathways in the brain of the female African catfish,Clarias gariepinus

Summary The olfactory tract of the African catfish, Clarias gariepinus, consists of two tracts, the medial and lateral olfactory tract. Ovulated female catfish are attracted by male steroidal pheromones. Attraction tests with catfish in which the medial and lateral olfactory tract have been selectively lesioned show that the effects of these pheromones are mediated by the medial olfactory tract. The central connections of the medial and lateral olfactory tract have been studied by retro- and anterograde transport techniques using horseradish peroxidase as a tracer. Upon entering the forebrain, the medial olfactory tract innervates the posterior pars ventralis and pars supracommissuralis of the area ventralis telencephali and the nucleus preopticus periventricularis, the nucleus preopticus and the nucleus recessus posterioris. Application of horseradish peroxidase to the olfactory epithelium shows that part of the innervation of the area ventralis telencephali and the nucleus preopticus periventricularis can be attributed to the nervus terminalis, which appears to be embedded in the medial olfactory tract. The lateral olfactory tract sends projections to the same brain areas but also innervates the nucleus habenularis and a large terminal field in the area dorsalis telencephali pars lateralis ventralis. Furthermore, the medial olfactory tract carries numerous axons from groups of perikarya localized in the area dorsalis telencephali. Contralateral connections have been observed in the olfactory bulb, telencephalon, diencephalon and mesencephalon. It is suggested that processes of the medial olfactory tract innervating the preoptic region may influence the gonadotropin-releasing hormone system and in doing so may lead to behavioral and physiological changes related to spawning.     

Corticofugal modulation of initial neural processing of sound information from the ipsilateral ear in the mouse

Background

Cortical neurons implement a high frequency-specific modulation of subcortical nuclei that includes the cochlear nucleus. Anatomical studies show that corticofugal fibers terminating in the auditory thalamus and midbrain are mostly ipsilateral. Differently, corticofugal fibers terminating in the cochlear nucleus are bilateral, which fits to the needs of binaural hearing that improves hearing quality. This leads to our hypothesis that corticofugal modulation of initial neural processing of sound information from the contralateral and ipsilateral ears could be equivalent or coordinated at the first sound processing level.

Methodology/Principal Findings

With the focal electrical stimulation of the auditory cortex and single unit recording, this study examined corticofugal modulation of the ipsilateral cochlear nucleus. The same methods and procedures as described in our previous study of corticofugal modulation of contralateral cochlear nucleus were employed simply for comparison. We found that focal electrical stimulation of cortical neurons induced substantial changes in the response magnitude, response latency and receptive field of ipsilateral cochlear nucleus neurons. Cortical stimulation facilitated auditory response and shortened the response latency of physiologically matched neurons whereas it inhibited auditory response and lengthened the response latency of unmatched neurons. Finally, cortical stimulation shifted the best frequencies of cochlear neurons towards those of stimulated cortical neurons.

Conclusion

Our data suggest that cortical neurons enable a high frequency-specific remodelling of sound information processing in the ipsilateral cochlear nucleus in the same manner as that in the contralateral cochlear nucleus.     

Anterograde labelling from the optic nerve reveals multiple central targets in the teleost,Lethrinus chrysostomus (Perciformes)

Summary Cobaltous-lysine is transported anterogradely from the optic nerve of the teleost, Lethrinus chrysostomus (Lethrinidae, Perciformes). The marginal optic tract is labelled in longtitudinal bands of light and dark staining fibres which persists caudally within the ventral division but not in the dorsal division. This species possesses multiple central targets in the contralateral preoptic, diencephalic, pretectal, periventricular and tectal regions of the brain. In addition, a greater subdivision of the marginal optic tract is found to project to various nuclei. Ipsilateral projections are found in the suprachiasmatic nucleus and in the region of the horizontal commissure. Projections are also found in the telencephalic region of the nucleus olfactoretinalis and the thalamic region of the nucleus thalamoretinalis. The retinotopicity of some of these nuclei, found in previous studies, is discussed in relation to the possibility of specific sub-populations of retinal ganglion cells having different central targets.Abbreviations used in the Text and Figures A nucleus anteriorthalami - AO accessory optic nucleus - AOT accessory optic tract - AxOT axial optic tract - BO nucleus of the basal optic root - C cerebellum - HCv ventral division of horizontal commissure - I nucleus intermedius thalami - IL inferior lobe - MdOT medial optic tract - MO medulla oblongata - MOTd dorsal division of the marginal optic tract - MOTi intermediate division of the marginal optic tract - MOtv ventral division of the marginal optic tract - O olfactory bulb - OT optic tract - PC nucleus pretectalis centralis - PCo posterior commissure - Pd nucleus pretectalis dorsalis - PG preglomerular complex - PPd nucleus pretectalis periventricularis, pars dorsalis - PPv nucleus pretectalis periventricularis, pars ventralis - PSm nucleus pretectalis superficial pars magnocellularis - PSp nucleus pretectalis superficialis, pars parvocellularis - Sn suprachiasmatic nucleus - TEL telencephalon - TeO optic tectum - TL torus longtitudinalis - TrOlfR tractus olfactoretinalis - VCg granular layer of the valvula cerebelli - VCm molecular layer of the valvula cerebelli - VM nucleus medialis thalami - VL nucleus ventrolateralis thalami - VMdOT ventro-medial optic tract     

Sensory projections to the nucleus basalis prosencephali of the pigeon

Summary The afferent pathways to the nucleus basalis prosencephali of the pigeon were studied by use of the horseradish peroxidase (HRP) technique. It was confirmed that this nucleus receives a direct pathway from the nucleus sensorius principalis nervi trigemini and that, as in the starling, it receives a direct input from the nucleus lemnisci lateralis, pars ventralis, an auditory relay. Totally novel is the finding that the nucleus basalis prosencephali is the target of a direct pathway originating in the medullary nucleus vestibularis superior. All three pathways bypass the thalamus. From within the telencephalon the nucleus basalis prosencephali also receives fibres from the tuberculum olfactorium and the peri-ectostriatal belt, suggestive of olfactory and visual input. Marked cell bodies were also found in the neostriatum frontolaterale. It is assumed that these arose from HRP uptake by axons of the tractus fronto-archistriatalis that course through the nucleus basalis prosencephali to the anterodorsal archistriatum. Marked fibres and bouton-like formations were observed in the latter structure. The afferents to the nucleus basalis prosencephali are discussed in conjunction with the probable role of the nucleus as a sensorimotor coordinator of the pecking/feeding behaviour of the pigeon.