Nucleus Of Lateral Lemniscus Research Articles

Comparison of the connectivity of the posterior intralaminar thalamic nucleus and peripeduncular nucleus in rats and mice.

The posterior intralaminar thalamic nucleus (PIL) and peripeduncular nucleus (PP) are two adjoining structures located medioventral to the medial geniculate nucleus. The PIL-PP region plays important roles in auditory fear conditioning and in social, maternal and sexual behaviors. Previous studies often lumped the PIL and PP into single entity, and therefore it is not known if they have common and/or different brain-wide connections. In this study, we investigate brain-wide efferent and afferent projections of the PIL and PP using reliable anterograde and retrograde tracing methods. Both PIL and PP project strongly to lateral, medial and anterior basomedial amygdaloid nuclei, posteroventral striatum (putamen and external globus pallidus), amygdalostriatal transition area, zona incerta, superior and inferior colliculi, and the ectorhinal cortex. However, the PP rather than the PIL send stronger projections to the hypothalamic regions such as preoptic area/nucleus, anterior hypothalamic nucleus, and ventromedial nucleus of hypothalamus. As for the afferent projections, both PIL and PP receive multimodal information from auditory (inferior colliculus, superior olivary nucleus, nucleus of lateral lemniscus, and association auditory cortex), visual (superior colliculus and ectorhinal cortex), somatosensory (gracile and cuneate nuclei), motor (external globus pallidus), and limbic (central amygdaloid nucleus, hypothalamus, and insular cortex) structures. However, the PP rather than PIL receives strong projections from the visual related structures parabigeminal nucleus and ventral lateral geniculate nucleus. Additional results from Cre-dependent viral tracing in mice have also confirmed the main results in rats. Together, the findings in this study would provide new insights into the neural circuits and functional correlation of the PIL and PP.

Molecular identity of the lateral lemniscus nuclei in the adult mouse brain.

The dorsal (DLL), intermediate (ILL), and ventral (VLL) lateral lemniscus nuclei are relay centers in the central auditory pathway of the brainstem, commonly referred to as the lateral lemniscus nuclei (LLN). The LLN are situated in the prepontine and pontine hindbrain, from rhombomeres 1 to 4, extending from the more rostral DLL to the caudal VLL, with the ILL lying in between. These nuclei can be distinguished morphologically and by topological and connectivity criteria, and here, we set out to further characterize the molecular nature of each LLN. We searched in situ hybridization studies in the Allen Mouse Brain Atlas for genes differentially expressed along the rostrocaudal axis of the brainstem, identifying 36 genes from diverse functional families expressed in the LLN. Available information in the databases indicated that 7 of these 36 genes are either associated with or potentially related to hearing disorders. In conclusion, the LLN are characterized by specific molecular profiles that reflect their rostrocaudal organization into the three constituent nuclei. This molecular regionalization may be involved in the etiology of some hearing disorders, in accordance with previous functional studies of these genes.

Non-motor connections of the pedunculopontine nucleus of the rat and human brain

IntroductionThe connections of the pedunculopontine nucleus (PPN) with motor areas of the central nervous system (CNS) are well described in the literature, in contrast relations with non-motor areas are lacking. Thus, the aim of the present study is to define the non-motor connections of the PPN in rats using the fluoro-gold (FG) tracer and compare the presence of these connections in healthy human adults using diffusion tensor tractography (DTI). Materials and MethodsWe injected FG into the PPN of 12 rats. The non-motor connections of the PPN with cortical, subcortical, and brainstem structures were documented. The non-motor connections of the rats were compared with the DTI obtained from 35 healthy adults. ResultsThe results of the tract-tracing study in the rat showed that the PPN was connected to non-motor cortical (cingulate, somatosensory, visual, auditory, medial frontal cortices), subcortical (amygdala, hypothalamus, thalamus, habenular, and bed nucleus of stria terminalis), and brainstem (medullary reticular, trigeminal spinal, external cuneate, pontine reticular, vestibular, superior and inferior colliculus, locus ceruleus, periaqueductal gray, parabrachial, dorsal raphe, pretectal, lateral lemniscus nuclei, and the contralateral PPN) structures. The DTI obtained from healthy adults showed similar PPN non-motor connections as in rats. ConclusionUnderstanding the connections of the PPN with non-motor cortical, subcortical, and brainstem areas of the CNS will enrich our knowledge of its contribution in various circuits and the areas that PPN activity can influence. Further, it will provide insight into the role of Parkinson's disease and related disorders and explain the non-motor complications which occur subsequent to deep brain stimulation (DBS) of the PPN.

Hearing loss is an early biomarker in APP/PS1 Alzheimer’s disease mice

Alzheimer's disease (AD) is a neurodegenerative disease characterized by a progressive loss of memory and cognitive decline. Over the last decade, it has been found that defects in sensory systems could be highly associated with AD. Hearing is an important neural sense. However, little is known about hearing functional changes in AD. In this study, APP/PS1 AD mice (Jackson Lab: Stack No. 004462) were used. Hearing function was assessed by auditory brainstem response (ABR), distortion product otoacoustic emission (DPOAE), and cochlear microphonics (CM) recordings. Wild-type (WT) littermates served as control. We found that APP/PS1 AD mice measured as ABR threshold had hearing loss. The hearing loss appeared at high frequency as early as 2 months old, prior to the reported occurrence of spatial learning deficit at 6–7 months of age in this AD mouse model. The hearing loss was progressive and extended from high frequency to low frequency. At 3–4 months old, the hearing loss appeared in the whole-frequency range. Moreover, the wave IV and V in the super-threshold ABR were eliminated, indicating substantial impairment in inferior colliculus, nuclei of lateral lemniscus, and medial geniculate body in the upper brainstem. DPOAE in APP/PS1 AD mice was also reduced. However, there was no reduction in CM in APP/PS1 mice. These data demonstrate that unlike age-related hearing loss APP/PS1 AD mice have early onset of hearing loss. These data also suggest that hearing function testing could provide a simple, sensitive, non-invasive screen-tool for early detecting AD and localizing lesion.

Neuronal specializations for the processing of interaural difference cues in the chick.

Sound information is encoded as a series of spikes of the auditory nerve fibers (ANFs), and then transmitted to the brainstem auditory nuclei. Features such as timing and level are extracted from ANFs activity and further processed as the interaural time difference (ITD) and the interaural level difference (ILD), respectively. These two interaural difference cues are used for sound source localization by behaving animals. Both cues depend on the head size of animals and are extremely small, requiring specialized neural properties in order to process these cues with precision. Moreover, the sound level and timing cues are not processed independently from one another. Neurons in the nucleus angularis (NA) are specialized for coding sound level information in birds and the ILD is processed in the posterior part of the dorsal lateral lemniscus nucleus (LLDp). Processing of ILD is affected by the phase difference of binaural sound. Temporal features of sound are encoded in the pathway starting in nucleus magnocellularis (NM), and ITD is processed in the nucleus laminaris (NL). In this pathway a variety of specializations are found in synapse morphology, neuronal excitability, distribution of ion channels and receptors along the tonotopic axis, which reduces spike timing fluctuation in the ANFs-NM synapse, and imparts precise and stable ITD processing to the NL. Moreover, the contrast of ITD processing in NL is enhanced over a wide range of sound level through the activity of GABAergic inhibitory systems from both the superior olivary nucleus (SON) and local inhibitory neurons that follow monosynaptic to NM activity.

Assembly of the Auditory Circuitry by a Hox Genetic Network in the Mouse Brainstem

Rhombomeres (r) contribute to brainstem auditory nuclei during development. Hox genes are determinants of rhombomere-derived fate and neuronal connectivity. Little is known about the contribution of individual rhombomeres and their associated Hox codes to auditory sensorimotor circuitry. Here, we show that r4 contributes to functionally linked sensory and motor components, including the ventral nucleus of lateral lemniscus, posterior ventral cochlear nuclei (VCN), and motor olivocochlear neurons. Assembly of the r4-derived auditory components is involved in sound perception and depends on regulatory interactions between Hoxb1 and Hoxb2. Indeed, in Hoxb1 and Hoxb2 mutant mice the transmission of low-level auditory stimuli is lost, resulting in hearing impairments. On the other hand, Hoxa2 regulates the Rig1 axon guidance receptor and controls contralateral projections from the anterior VCN to the medial nucleus of the trapezoid body, a circuit involved in sound localization. Thus, individual rhombomeres and their associated Hox codes control the assembly of distinct functionally segregated sub-circuits in the developing auditory brainstem.

Differences in parvalbumin and calbindin chemospecificity in the centers of the turtle ascending auditory pathway revealed by double immunofluorescence labeling

Using double immunofluorescence labeling, quantitative ratio between parvalbumin- and calbindin-containing neurons, neurons that co-localize both peptides, as well as the intensity of their immunoreactivities were studied in the brainstem, midbrain and forebrain auditory centers of two chelonian species, Testudo horsfieldi and Emys orbicularis. In the spiral ganglion and first-order cochlear nuclei, highly immunoreactive parvalbumin-containing neurons predominated, and almost all neurons in these nuclei also exhibited weak immunoreactivity to calbindin. The number of strongly calbindin-immunoreactive (-ir) cells increased in the second-order brainstem auditory centers (the laminar cochlear nucleus, superior olivary complex, lateral lemniscal nucleus), and co-localization with parvalbumin in some of them was observed. In the midbrain, a complementary distribution of parvalbumin and calbindin immunoreactivity was found: the central (core) region of the torus semicircularis showed strong parvalbumin immunoreactivity, while the laminar (belt) nucleus was strongly calbindin-ir. In the thalamic nucleus reuniens, almost complete topographic overlapping of the parvalbumin-ir and calbindin-ir neurons was shown in its dorsomedial region (core), with the intensity of immunoreactivity to calbindin being much higher than that to parvalbumin. The predominance of calbindin immunoreactivity in neurons of the dorsomedial region of the nucleus reuniens is correlated with the existence of the dense calbindin-ir terminal field in its projection area in the telencephalon. We conclude that the turtle auditory pathway is chemically heterogeneous with respect to calcium-binding proteins, the predominance of parvalbumin in the brainstem and midbrain centers giving way to that of calbindin in the forebrain centers; the portion of neurons co-localizing both peptides nonlinearly decreases from lower to higher order centers.

Changes in projections to the inferior colliculus following early hearing loss in rats

The purpose of this study was to investigate the effects of early hearing loss on the anatomy of the central auditory system, specifically, the ascending projections to the inferior colliculus (IC). We compared normal animals with animals deafened during early development by administration of amikacin, an ototoxic antibiotic that is known to destroy the hair cells in the inner ear. The amikacin was injected subcutaneously every day from postnatal days P7 to P16. A retrograde tract tracer, Fluoro-Gold (FG), was then injected unilaterally directly into the IC at either 4 weeks of age or 12 weeks of age. After axonal transport the animals were sacrificed and their brains were prepared for histology. The FG labeled neurons in the cochlear nucleus (CN) and the dorsal nucleus of lateral lemniscus (DNLL) were counted for each of the animals in the two age groups. For deaf animals sacrificed at 4 weeks of age there was a significant reduction in the number of FG labeled neurons that was limited to the ventral CN ipsilateral to the tracer injection. For deaf animals sacrificed at 12 weeks of age, however, there was a significant decrease in the number of labeled cells in both dorsal and ventral CN on both sides of the brain. In DNLL there was no change in the number or pattern of labeled neurons. The results show that neonatal deafness reduces the number of labeled neurons projecting from the CN to the IC with the effect being more evident during later stages of deafness. In contrast, there are no significant changes in the projections from DNLL to IC.

Mechanisms of spectral and temporal integration in the mustached bat inferior colliculus

This review describes mechanisms and circuitry underlying combination-sensitive response properties in the auditory brainstem and midbrain. Combination-sensitive neurons, performing a type of auditory spectro-temporal integration, respond to specific, properly timed combinations of spectral elements in vocal signals and other acoustic stimuli. While these neurons are known to occur in the auditory forebrain of many vertebrate species, the work described here establishes their origin in the auditory brainstem and midbrain. Focusing on the mustached bat, we review several major findings: (1) Combination-sensitive responses involve facilitatory interactions, inhibitory interactions, or both when activated by distinct spectral elements in complex sounds. (2) Combination-sensitive responses are created in distinct stages: inhibition arises mainly in lateral lemniscal nuclei of the auditory brainstem, while facilitation arises in the inferior colliculus (IC) of the midbrain. (3) Spectral integration underlying combination-sensitive responses requires a low-frequency input tuned well below a neuron's characteristic frequency (ChF). Low-ChF neurons in the auditory brainstem project to high-ChF regions in brainstem or IC to create combination sensitivity. (4) At their sites of origin, both facilitatory and inhibitory combination-sensitive interactions depend on glycinergic inputs and are eliminated by glycine receptor blockade. Surprisingly, facilitatory interactions in IC depend almost exclusively on glycinergic inputs and are largely independent of glutamatergic and GABAergic inputs. (5) The medial nucleus of the trapezoid body (MNTB), the lateral lemniscal nuclei, and the IC play critical roles in creating combination-sensitive responses. We propose that these mechanisms, based on work in the mustached bat, apply to a broad range of mammals and other vertebrates that depend on temporally sensitive integration of information across the audible spectrum.

Distribution of Satb1 in the central nervous system of adult mice

This study consists of a thorough immunohistochemical examination of the expression profile of the transcription factor Satb1 (special AT-rich sequence binding protein 1) in the adult mouse central nervous system (CNS). Satb1-positive neurons were abundant in the deep layers of the neocortex, subiculum, anterior olfactory nucleus, nucleus of diagonal band, anterior part of the basolateral amygdaloid nucleus, compact part of substantia nigra, ventral tegmental area, ventral and dorsal tegmental nuclei, laterodorsal tegmental nucleus, and medullary and spinal dorsal horns. Relatively smaller populations of Satb1-positive neurons were observed in the piriform cortex, hippocampus, other subnuclei of the amygdala, centrolateral thalamic nucleus, parafascicular thalamic nucleus, posterior hypothalamic area, ventral part of the premammillary nucleus, supramammillary nucleus, deep layers of the superior colliculus, dorsal raphe nucleus, nucleus of trapezoid body, superior periolivary nucleus and nucleus of lateral lemniscus, and parabrachial region. Double immunostaining showed that Satb1 was expressed in midbrain dopaminergic neurons, but not in cholinergic or serotonergic neurons. Satb1 expression was never observed in glial cells. This study presents a comprehensive overview of Satb1 expression in the CNS, and provides insights for investigating the role of Satb1 in the mature CNS.

Connections of the auditory brainstem in a songbird, Taeniopygia guttata. III. Projections of the superior olive and lateral lemniscal nuclei

Sequential to companion articles that report the projections of the cochlear nucleus angularis (NA) and the third-order nucleus laminaris (NL) to the central nucleus of the inferior colliculus (MLd) and to the superior olive (OS) and lateral lemniscal nuclei (LLV, LLI, and LLD) (Krützfeldt et al., J Comp Neurol, this issue), we here describe the projections of the latter group of nuclei using standard tract-tracing methods. OS projects on LLV and both have further ascending projections on LLI, LLD, and MLd. LLV also provides auditory input to the song system, via nucleus uvaeformis, and to the thalamo-telencephalic auditory system, via nucleus ovoidalis (Ov), thus bypassing MLd. The two divisions of LLD (LLDa and LLDp) project across the midline via the commissure of Probst each to innervate the homologous contralateral nucleus and MLd. Both, particularly LLDp, also project on Ov. Injections in LLD and LLV resulted in anterograde labeling of caudal nucleus basorostralis (Bas) in the frontal telencephalon, but retrograde tracing so far suggests that only LLI is a real source of this projection (Wild and Farabaugh [1996] J Comp Neurol 365:306-328). OS and LLV also have descending projections on the ipsilateral NA, NM, and NL, and LLV also projects on OS. The ascending inputs to MLd and more rostral nuclei may contribute importantly to mechanisms of auditory pattern (song) recognition. Consistent with previous studies, some of the descending projections may be inhibitory.

Origins of glutamatergic terminals in the inferior colliculus identified by retrograde transport and expression of VGLUT1 and VGLUT2 genes

Terminals containing vesicular glutamate transporter (VGLUT) 2 make dense axosomatic synapses on tectothalamic GABAergic neurons. These are one of the three types of glutamatergic synapses in the inferior colliculus (IC) identified by one of three combinations of transporter protein: VGLUT1 only, VGLUT2 only, or both VGLUT1 and 2. To identify the source(s) of these three classes of glutamatergic terminals, we employed the injection of Fluorogold (FG) into the IC and retrograde transport in combination with in situ hybridization for VGLUT1 and VGLUT2 mRNA. The distribution of FG-positive soma was consistent with previous reports. In the auditory cortex, all FG-positive cells expressed only VGLUT1. In the IC, the majority of FG-positive cells expressed only VGLUT2. In the intermediate nucleus of the lateral lemniscus, most FG-positive cells expressed VGLUT2, and a few FG-positive cells expressed both VGLUT1 and 2. In the superior olivary complex, the majority of FG-positive cells expressing VGLUT2 were in the lateral superior olive, medial superior olive, and some periolivary nuclei. Fewer FG-positive cells expressed VGLUT1&2. In the ventral cochlear nucleus, almost all FG-positive cells expressed VGLUT1&2. On the other hand in the dorsal cochlear nucleus, the vast majority of FG-positive cells expressed only VGLUT2.Our data suggest that (1) the most likely sources of VGLUT2 terminals in the IC are the intermediate nucleus of the lateral lemniscus, the dorsal cochlear nucleus, the medial and lateral superior olive, and the IC itself, (2) VGLUT1 terminals in the IC originate only in the ipsilateral auditory cortex, and (3) VGLUT1&2 terminals in IC originate mainly from the VCN with minor contributions from the SOC and the lateral lemniscal nuclei.

Origins of Glutamatergic Terminals in the Inferior Colliculus Identified by Retrograde Transport and Expression of VGLUT1 and VGLUT2 Genes

Terminals containing vesicular glutamate transporter (VGLUT) 2 make dense axosomatic synapses on tectothalamic GABAergic neurons. These are one of the three types of glutamatergic synapses in the inferior colliculus (IC) identified by one of three combinations of transporter protein: VGLUT1 only, VGLUT2 only, or both VGLUT1 and 2. To identify the source(s) of these three classes of glutamatergic terminals, we employed the injection of Fluorogold (FG) into the IC and retrograde transport in combination with in situ hybridization for VGLUT1 and VGLUT2 mRNA. The distribution of FG-positive soma was consistent with previous reports. In the auditory cortex, all FG-positive cells expressed only VGLUT1. In the IC, the majority of FG-positive cells expressed only VGLUT2. In the intermediate nucleus of the lateral lemniscus, most FG-positive cells expressed VGLUT2, and a few FG-positive cells expressed both VGLUT1 and 2. In the superior olivary complex (SOC), the majority of FG-positive cells expressing VGLUT2 were in the lateral superior olive, medial superior olive, and some periolivary nuclei. Fewer FG-positive cells expressed VGLUT1&2. In the ventral cochlear nucleus, almost all FG-positive cells expressed VGLUT1&2. On the other hand in the dorsal cochlear nucleus, the vast majority of FG-positive cells expressed only VGLUT2. Our data suggest that (1) the most likely sources of VGLUT2 terminals in the IC are the intermediate nucleus of the lateral lemniscus, the dorsal cochlear nucleus, the medial and lateral superior olive, and the IC itself, (2) VGLUT1 terminals in the IC originate only in the ipsilateral auditory cortex, and (3) VGLUT1&2 terminals in IC originate mainly from the VCN with minor contributions from the SOC and the lateral lemniscal nuclei.

Interaural phase difference modulates the neural activity in the nucleus angularis and improves the processing of level difference cue in the lateral lemniscal nucleus in the chicken

We investigated the chicken auditory system to understand how an interaural level difference (ILD) is processed. Sound intensity is extracted in the nucleus angularis (NA) and an ILD is processed in the dorsal lateral lemniscal nucleus (LLD). We found that the neural activity in these nuclei is affected by the interaural phase difference (IPD). Activity in the NA was suppressed by strong contralateral sound when binaural stimuli were presented in-phase, but the activity was enhanced by out-of-phase stimuli. These IPD dependent suppression or enhancement probably occurs through acoustic interference across the interaural canal connecting the middle ears of the two sides. The LLD neurons were excited by contralateral sound and inhibited by ipsilateral sound, reflecting excitation by the contralateral NA and inhibition from the ipsilateral NA, probably through the contralateral LLD as in the barn owl. The LLD unit activity encoded an ILD and was strongly modulated by the IPD. We propose a simple model to explain the interaural coupling effects and IPD modulation of LLD activity, and conclude that the modulation of neuronal activity by IPD may improve ILD processing and the direction sensitivity of LLD neurons to the contralateral ear, compensating for the small ILD cues.

Glycinergic Inhibition Creates a Form of Auditory Spectral Integration in Nuclei of the Lateral Lemniscus

For analyses of complex sounds, many neurons integrate information across different spectral elements via suppressive effects that are distant from the neurons' excitatory tuning. In the mustached bat, suppression evoked by sounds within the first sonar harmonic (23-30 kHz) or in the subsonar band (<23 kHz) alters responsiveness to the higher best frequencies of many neurons. This study examined features and mechanisms associated with low-frequency (LF) suppression among neurons of the lateral lemniscal nuclei (NLL). We obtained extracellular recordings from neurons in the intermediate and ventral nuclei of the lateral lemniscus, observing different forms of LF suppression related to the two above-cited frequency bands. To understand the mechanisms underlying this suppression in NLL neurons, we examined the roles of glycinergic and GABAergic input through local microiontophoretic application of strychnine, an antagonist to glycine receptors (GlyRs), or bicuculline, an antagonist to gamma-aminobutyric acid type A receptors (GABA(A)Rs). With blockade of GABA(A)Rs, neurons showed an increase in firing rate to best frequency (BF) and/or LF tones but retained LF suppression of BF sounds. For neurons that displayed LF suppression tuned to 23-30 kHz, the suppression was eliminated or nearly eliminated by GlyR blockade. In contrast, GABA(A)R blockade did not eliminate nor had any consistent effect on suppression tuned to these frequencies. We conclude that LF suppression tuned in the 23- to 30-kHz range results from neuronal inhibition within the NLL via glycinergic inputs. For neurons displaying suppression tuned <23 kHz, neither GlyR nor GABAR blockade altered LF suppression. We conclude that such suppression originates at a lower auditory level, perhaps a result of cochlear mechanisms. These findings demonstrate that neuronal interactions within NLL create a particular form of LF suppression that contributes to the analysis of complex acoustic signals.

Anatomical projections of the nuclei of the lateral lemniscus in the albino rat (rattus norvegicus)

The ascending projections to the lateral lemniscal nuclei and the inferior colliculus were investigated in the albino rat by using Fluoro-Gold, either alone or in combination with other retrograde tract tracers. Injections were made into the central nucleus of the inferior colliculus (ICC), the dorsal nucleus of the lateral lemniscus (DNLL), the intermediate nucleus of the lateral lemniscus (INLL), or the ventral nucleus of the lateral lemniscus (VNLL). The ICC receives both ipsilateral and contralateral projections from the DNLL and the lateral superior olive, major ipsilateral projections from the INLL, VNLL, medial superior olive, and superior paraolivary nucleus, and major contralateral projections from both dorsal and ventral cochlear nucleus. The DNLL receives a similar pattern of projections from the auditory lower brainstem nuclei. The INLL, in contrast, receives its major projections from the ipsilateral VNLL, lateral superior olive, medial superior olive, superior paraolivary nucleus, and medial nucleus of the trapezoid body, but does not receive a heavy projection from the contralateral lateral superior olive. It receives a major contralateral projection from the ventral cochlear nucleus, but a much lighter projection from the contralateral dorsal cochlear nucleus. The VNLL receives projections from the ipsilateral medial nucleus of the trapezoid body and the contralateral ventral cochlear nucleus, but does not receive projections from the medial or lateral superior olives, the superior paraolivary nucleus, or the dorsal cochlear nucleus. Thus, the three primary subdivisions of the rat's lateral lemniscus can be distinguished from each other on the basis of their distinctive projection patterns.

The medial paralemniscal nucleus and its afferent neuronal connections in rat.

Previously, we described a cell group expressing tuberoinfundibular peptide of 39 residues (TIP39) in the lateral pontomesencephalic tegmentum, and referred to it as the medial paralemniscal nucleus (MPL). To identify this nucleus further in rat, we have now characterized the MPL cytoarchitectonically on coronal, sagittal, and horizontal serial sections. Neurons in the MPL have a columnar arrangement distinct from adjacent areas. The MPL is bordered by the intermediate nucleus of the lateral lemniscus nucleus laterally, the oral pontine reticular formation medially, and the rubrospinal tract ventrally, whereas the A7 noradrenergic cell group is located immediately mediocaudal to the MPL. TIP39-immunoreactive neurons are distributed throughout the cytoarchitectonically defined MPL and constitute 75% of its neurons as assessed by double labeling of TIP39 with a fluorescent Nissl dye or NeuN. Furthermore, we investigated the neuronal inputs to the MPL by using the retrograde tracer cholera toxin B subunit. The MPL has afferent neuronal connections distinct from adjacent brain regions including major inputs from the auditory cortex, medial part of the medial geniculate body, superior colliculus, external and dorsal cortices of the inferior colliculus, periolivary area, lateral preoptic area, hypothalamic ventromedial nucleus, lateral and dorsal hypothalamic areas, subparafascicular and posterior intralaminar thalamic nuclei, periaqueductal gray, and cuneiform nucleus. In addition, injection of the anterograde tracer biotinylated dextran amine into the auditory cortex and the hypothalamic ventromedial nucleus confirmed projections from these areas to the distinct MPL. The afferent neuronal connections of the MPL suggest its involvement in auditory and reproductive functions.

Co-localization of nitric oxide synthase and choline acetyltransferase in the brain of the goldfish ( Carassius auratus)

This work investigates the nitrergic and cholinergic systems in the brain and spinal cord of the goldfish ( Carassius auratus). We studied the immunohistochemical localization of antibodies against the neuronal nitric oxide synthase (nNOS) and choline acetyltransferase (ChAT) by bright-field and confocal microscopy. Nitrergic and cholinergic cells were segregated within the telencephalon, in both dorsal and ventral areas, and co-distributed in some nuclei of the diencephalon, mesencephalon, rhombencephalon, and spinal cord. Double-labeling experiments revealed nNOS/ChAT-positive cells in (1) the diencephalon: the preoptic and suprachiasmatic nuclei, the habenula, the dorsal thalamus, and the nucleus of the medial longitudinal fasciculus; (2) the mesencephalon: the optic tectum, the mesencephalic portion of the trigeminal nucleus, the oculomotor and trochlear nuclei, and the Edinger-Westphal nucleus; and (3) the rhombencephalon: the secondary gustatory nucleus, the nucleus isthmi, the lateral lemniscus nucleus, the cerebellum, the reticular formation, different nuclei of the octaval column, the motor zone of the vagal lobe, and the trigeminal, facial, abducens, glosso-pharyngeal, vagal, and hypobranchial motor nuclei. Double-labeled cells were also observed in the spinal motor column. The percentage of double-labeled cells was different in each studied nucleus, indicating a selective distribution pattern. Because double-labeled cells were more abundant in those nuclei involved with sensory and motor physiological processes, we suggest the involvement of both nitric oxide and acetylcholine in these neural functions in fish.

Distribution of metabolic activity (cytochrome oxidase) and immunoreactivity to calcium-binding proteins in the turtle brainstem auditory nuclei

Using histochemical and immunohistochemical techniques, distribution of activity of oxidative mitochondrial enzyme cytochrome oxidase (CO) and of immunoreactivity to calcium-binding proteins has been studied in spiral ganglion and auditory nuclei of brainstem in two turtle species. It has been shown that immunoreactivity to calbindin, parvalbumin, and calretinin in neurons and neuropil of nuclei of cochlear and superior olivary complexes, in nucleus of lateral lemniscus, and in spiral ganglion neurons coincides topographically with the high CO activity. The similarity of the studied metabolic and neurochemical characteristics of these auditory centers in reptiles, birds, and mammals indicates the existence of some common principles of their organization in amniotes in spite of phylogenetic differences and peculiarities of specialization of the auditory system in different species.

Variability Reduction in Interaural Time Difference Tuning in the Barn Owl

The interaural time difference (ITD) is the primary auditory cue used by the barn owl for localization in the horizontal direction. ITD is initially computed by circuits consisting of axonal delay lines from one of the cochlear nuclei and coincidence detector neurons in the nucleus laminaris (NL). NL projects directly to the anterior part of the dorsal lateral lemniscal nucleus (LLDa), and this area projects to the core of the central nucleus of the inferior colliculus (ICcc) in the midbrain. To show the selectivity of an NL neuron for ITD requires averaging of responses over several stimulus presentations for each ITD. In contrast, ICcc neurons detect their preferred ITD in a single burst of stimulus. We recorded extracellularly the responses of LLDa neurons to ITD in anesthetized barn owls and show that this ability is already present in LLDa, raising the possibility that ICcc inherits its noise reduction property from LLDa.