Nucleus Of Lateral Lemniscus Research Articles

Neurons with perineuronal sulfated proteoglycans in the mouse brain and spinal cord: their distribution and reactions to lectin Vicia villosa agglutinin and Golgi's silver nitrate.

This study demonstrates that many neurons in the somatosensory cortex, cingulate cortex, retrosplenial cortex and hippocampal subiculum of the mouse brain are covered by sulfated proteoglycans which are intensely negative-charged and stained with cationic iron colloid, while being digested with hyaluronidase. Neurons with similar perineuronal proteoglycans are also recognized in the extrapyramidal system (superior colliculus, red nucleus, reticular formation, vestibular nuclei and cerebellar nuclei), in the secondary auditory system (cochlear nuclei, nucleus of trapezoid body, inferior colliculus and nucleus of lateral lemniscus), in the vestibulo-ocular reflex system (vestibular nuclei and extraocular motor nuclei), and in the pupillary reflex system. The neurons with perineuronal sulfated proteoglycans in the cerebral cortices and hippocampal subiculum are usually labeled with the lectin Vicia villosa agglutinin, though those in the cerebellar, vestibular and cochlear nuclei may not be reactive to this lectin. Double staining of the retrosplenial cortex, hippocampal subiculum and cerebellar nuclei with Golgi's silver nitrate and cationic iron colloid indicates that the perineuronal sulfated proteoglycans are identical with the Golgi's reticular coating or glial nets.

Responses of neurons in the auditory pathway of the barn owl to partially correlated binaural signals.

1. Extracellular single-unit recording in anesthetized barn owls was used to study neuronal response to dichotic stimuli of variable binaural correlation (BC). Recordings were made in the output fibers of nucleus laminaris (NL), the anterior division of the ventral lateral lemniscal nucleus (VLVa), the core of the central nucleus of the inferior colliculus (ICcC), the lateral shell of the central nucleus of the inferior colliculus (ICcLS), and the external nucleus of the inferior colliculus (ICx). 2. The response of all neurons sensitive to interaural time difference (ITD) varied with BC. The relationship between BC and impulse number fits a linear, a parabolic, or a ramp model. A linear or parabolic model fits most neurons in low-level nuclei. Higher order neurons in ICx did not respond to noise bursts with strong negative binaural correlation, creating a ramp-like response to BC. 3. A neuron's ability to detect ITD varied as a function of BC. Conversely, a neuron's response to BC changed with ITD. Neurons in NL, VLVa, and ICcC show almost periodic ITD response curves. In these neurons peaks and troughs of ITD response curves diminished as BC decreased, creating a flat ITD response when BC = 0. When BC was set to -1, the most favorable ITD became the least favorable one and vice versa. The ITD response curve of ICx neurons usually has a single dominant peak. The response of those neurons to a negatively correlated noise pair (BC = -1) showed two ITD peaks, flanking the position of the primary peak. 4. The parabolic BC response of NL neurons fits the prediction of the cross-correlation model, assuming half-wave rectification of the sound by the cochlea. Linear response is not predicted by the model. However, the parabolic and the linear neurons probably do not belong to two distinct groups as the difference between them is not statistically significant. Thus, the cross-correlation model provides a good description of the binaural response not only in NL but also in VLVa and ICcC. 5. Almost all ramp neurons occurred in either ICx or ICcLS where neurons are more broadly tuned to frequency than those in the lower nuclei. The synthesis of this response type requires, however, not only the convergence of different frequency channels but also inhibition between different ITD channels. We modeled the ramp response as a three-step process. First, different spectral channels converge to create broad frequency tuning. The response to variation in BC will be linear (or parabolic) because it is a sum of linear (parabolic) responses. Second, the activity in some adjacent ITD channels is subtracted by lateral inhibition. Finally, the result is rectified using a high threshold to avoid negative activity.

Distribution of acidic fibroblast growth factor mRNA-expressing neurons in the adult mouse central nervous system.

The distribution of acidic fibroblast growth factor (aFGF) mRNA-expressing neurons was studied throughout the adult mouse central nervous system (CNS) with in situ hybridization histochemistry using a radiolabelled synthetic oligodeoxynucleotide probe complementary to the mRNA of human aFGF. We report here a widespread distribution of aFGF mRNA in several defined functional systems of the adult mouse brain, whereby the highest levels of aFGF mRNA were found in large somatomotor neurons in the nuclei of the oculomotor, trochlear, abducens, and hypoglossal nerves; in the motoneurons of the ventral spinal cord and the special visceromotor neurons in the motor nucleus of the trigeminal nerve; and in the facial and ambiguus nuclei. Labelled perikarya were also detected in all central structures of the auditory pathway including the level of the inferior colliculus, i.e., the lateral and medial superior nuclei; the trapezoid, cochlear, and lateral lemniscal nuclei; and parts of the anterior colliculus. Furthermore, many aFGF-positive cell bodies were found in the vestibular system and other structures projecting to the cerebellum, in the deep cerebellar nuclei, in somatosensory structures of the medulla (i.e., in the gracile, cuneate, and external cuneate nuclei), as well as in the spinal nucleus of the trigeminal nerve. The findings that aFGF mRNA is expressed in all components of several well-defined systems (i.e., in sensory structures) as well as in central neurons that process sensory information and, finally, in some efferent projections point towards a concept of aFGF expression primarily within certain neuronal circuitries.

Central mechanism of neural activation with cold acclimation of rats using Fos immunohistochemistry

The expression of Fos protein in the rat diencephalon, brain stem, cerebellum, and spinal cord was investigated using immunohistochemistry during chronic cold exposure, in order to clarify the neural regions involved in the thermoregulatory responses and the central mechanism of neural activation with cold acclimation. Numerous Fos-positive cells were observed in many brain regions after cold exposure and changes in the number of Fos-positive cells were analyzed quantitatively. Fos-positive regions were classified into three groups on the basis of the expression period of Fos protein. The first group was where a significant number of Fos-positive cells were seen 3 h and 24 h after cold exposure, but not observed 14 days after exposure; the regions included the lateral septal nucleus (LS), parvocellular paraventricular hypothalamic nucleus (pPVN), posterior hypothalamic area (PH), supramammillary nucleus (SuM), locus coeruleus (LC), dorsal tegmental nucleus (DTg), vestibular nucleus (Ves), and nucleus of solitary tract (Sol). The second group was where a significant number of Fos-positive cells were found 3 h, 24 h and 14 days after cold exposure; the regions included the preoptic hypothalamic area (POA), paraventricular thalamic nucleus (PV), lateral preoptic area (LPO), zona incerta (ZI), subparafascicular thalamic nucleus (SPF), lateral dorsal central grey (CGLD), lateral ventral central grey (CGLV), microcellular tegmental nucleus (MiTg), lateral lemniscus nucleus (LL), dorsal parabrachial nucleus (DPB), and the cerebellum. The third group was where Fos-positive cells were more numerous 14 days after cold exposure than they were after 3 h and 24 h of exposure; these regions included the ventromedial hypothalamic nucleus (VMH) and the spinal cord. These results demonstrate that the numbers and regions of Fos-positive cells in the rat brains changed during chronic cold exposure, and such changes may reveal the cellular adaptation of the thermogenic responsive neurons in the rat brain to cold acclimation.

Frequency tuning and response latencies at three levels in the brainstem of the echolocating bat, Eptesicus fuscus.

To determine the level at which certain response characteristics originate, we compared monaural auditory responses of neurons in ventral cochlear nucleus, nuclei of lateral lemniscus and inferior colliculus. Characteristics examined were sharpness of frequency tuning, latency variability for individual neurons and range of latencies across neurons. Exceptionally broad tuning curves were found in the nuclei of the lateral lemniscus, while exceptionally narrow tuning curves were found in the inferior colliculus. Neither specialized tuning characteristic was found in the ventral cochlear nuclei. All neurons in the columnar division of the ventral nucleus of the lateral lemniscus maintained low variability of latency over a broad range of stimulus conditions. Some neurons in the cochlear nucleus (12%) and some in the inferior colliculus (15%) had low variability in latency but only at best frequency. Range of latencies across neurons was small in the ventral cochlear nucleus (1.3-5.7 ms), intermediate in the nuclei of the lateral lemniscus (1.7-19.8 ms) and greatest in the inferior colliculus (2.9-42.0 ms). We conclude that, in the nuclei of the lateral lemniscus and in the inferior colliculus, unique tuning and timing properties are built up from ascending inputs.

Immunohistochemical localization of hyaluronic acid in rat and human brain

The immunohistochemical localization of hyaluronic acid (HA) was studied in rat and human brain using the monoclonal antibody NDOG1, which specifically recognizes HA. In both rat and human brain, HA-like immunoreactivity formed characteristic coats around neurons in highly selective areas. The staining was abolished by pretreatment of sections with testicular and Streptomyces hyaluronidases, indicating that the staining was specific for HA. In rat brain, positive neurons were located in the cerebral cortex, subiculum, amygdala, thalamic reticular nucleus, nuclei of the inferior colliculus, nuclei of the trapezoid body, and vestibular nuclei. They were also scattered in the hypothalamus, substantia nigra pars reticularis, red nucleus, parabrachial nuclei, brainstem reticular nuclear group, ventral cochlear nucleus, nuclei of lateral lemniscus, and deep cerebellar nuclei. Double immunohistochemical studies showed that many neurons staining for HA were positive for parvalbumin, with minor exceptions in the amygdala and piriform cortex, where some HA-positive neurons were also positive for calbindin-D28k. In the areas studied in human brain, the distribution of HA-positive neurons was virtually identical to that in rat brain. HA-positive neurons were not significantly altered in Alzheimer disease (AD) brain, suggesting that these neurons are resistant to the pathological process of AD.

Connections of the auditory forebrain in the pigeon (Columba livia).

Ascending auditory efferents in birds terminate mainly within Field L2, a cytoarchitectonically distinct region of the caudomedial telencephalon. The organization of Field L2, and that of its flanking regions, L1 and L3, was investigated with 14C-2-deoxyglucose (14C-2-DG), cytochrome oxidase, and both retrograde and anterograde tracing techniques. Field L2 was found to contain a high concentration of cytochrome oxidase. Following auditory stimulation, 14C-2-DG autoradiography revealed that Field L2 consists of two adjacent but seemingly discontinuous zones, designated Field L2a, which lies ventromedially, and Field L2b, which lies dorsolaterally. Termination of thalamic efferents: The thalamic auditory nuclei ovoidalis (Ov) and semilunaris parovoidalis (SPO) project predominantly upon Field L2, and possibly sparsely upon L1, L3 and the overlying hyperstriatum ventrale (HV). Ov subnuclei project upon L2a and SPO projects predominantly upon L2b. The topography of the projections is inverted along the ventromedial-to-dorsolateral axis of L2, and is in accord with an inverted tonotopic representation of frequencies; high frequencies (< 3.5 kHz) being found in the more ventromedial parts of L2a, and low frequencies and broad band responses in L2b. Intra- and extratelencephalic connections: Field L2a also receives a substantial projection from HV, but the efferent projections of L2a appear confined to adjacent "neostriatal" regions. The subsequent projections of L2b were not identified in this study. L1 and L3 project predominantly to the dorsal neostriatum (Nd) caudolateral to Field L, and have fewer projections to the caudomedial paleostriatum and anterior hyperstriatum accessorium. Nd projects massively upon the ventromedial nucleus of the intermediate archistriatum (Aivm), which has bilateral projections upon the caudomedial telencephalon and is the origin of a major descending pathway having dense terminations surrounding the ovoidalis complex (Ov and SPO), MLd, the lateral lemniscal nuclei, and sparse terminations within SPO itself. It is suggested that within the telencephalon the major components of the auditory pathway consist of cell groups which collectively correspond to the populations of neurons found within the auditory cortex of mammals.

Localization of mRNA for c- kit receptor and its ligand in the brain of adult rats: an analysis using in situ hybridization histochemistry

Localization of mRNA for the c- kit receptor and its ligand ( Sl factor) in the brain of adult rats was studied using in situ hybridization histochemistry. The mRNA for the c- kit receptor was detected in the forebrain, the lower brain stem and the cerebellum. In the forebrain, the c- kit mRNA signals were detected in the olfactory bulb, the caudate-putamen, throughout the superficial cortex, the accumbens nucleus, the nucleus of vertical limb diagonal band, the bed nucleus of anterior commissure, Ammon's horn, the entopeduncular nucleus, the subthalamic nucleus, the dorsal raphe nucleus, the parasubiculum, the presubiculum, the ventricular nucleus of lateral lemniscus, and the entorhinal cortex. In the lower brain stem, the signals were detected in the inferior colliculus, the spinal vestibular nucleus, the spinal tract nucleus of trigeminal nerve, and the pyramidal tract. In the cerebellum, the signals were detected in the molecular layer of the cortex and cerebellar nuclei. By contrast, the signals of mRNA for Sl factor were detected in the forebrain and the cerebellum. In the forebrain, the signals were detected in the olfactory bulb, the endopiriform nucleus, the septohippocampal nucleus, the habenular nuclei, and most of the thalamic nuclei. In the cerebellum, the signals were detected in Purkinje cells. Several pairs of structures were found in which mRNA of either the c- kit receptor or the Sl factor was expressed and between which the synaptic connection had been reported, suggesting that the interaction between the c- kit receptor and the Sl factor may play some roles in the development of such synaptic connections.

Differential innervation patterns of three divisions of frog auditory midbrain (torus semicircularis)

The connectivity pattern of the laminar, principal, and magnocellular nuclei of the frog torus semicircularis (TS) was investigated. A small amount of horseradish peroxidase was injected focally into individual divisions of the TS and anterograde and retrograde transport patterns were observed. Results of our tracing study showed that these divisions of the TS possessed distinct innervation patterns. The principal nucleus appeared to be the primary input port of the TS receiving extensive inputs from all caudal brainstem auditory nuclei bilaterally, but especially from the contralateral dorsal medullary nucleus and the ipsilateral superior olivary and lateral lemniscus nuclei. Descending projection to this nucleus was limited to that from the posterior thalamic nucleus. In contrast, the laminar nucleus, but even more markedly the magnocellular nucleus, received extensive descending inputs from numerous structures in the dorsal thalamus and less pronounced ascending afferents from caudal brainstem auditory nuclei. Similar to the afferent connection patterns, the efferent projections originating from these three toral divisions differed substantially. The principal nucleus gave restricted ascending projections, limited mainly to the caudal region of the posterior thalamic nucleus, a region important in processing spectral information of complex sounds, and the pretectal gray. Its descending projection was also somewhat restricted, being limited to the superior olivary and lateral lemniscus nuclei. The laminar nucleus and especially the magnocellular nucleus gave robust descending as well as ascending projections; these nuclei serve as the main output paths for the TS and provide the main routes by which auditory input reaches the central thalamic nucleus, a structure previously shown to be involved in temporal information processing.

Effects on breathing of rostral pons glutamate injection during opossum development

To determine whether pathways from the rostral pons, capable of influencing breathing, were present in immature mammals, the excitatory amino acid glutamate (sodium salt) was pressure injected in very small volumes into the rostral pons of suckling and adult opossums. The youngest animals tested were approximately 3 wk old (1.5-2.9 g). Animals were anesthetized with the thiobarbituric acid derivative, Inactin, and the electromyogram of the diaphragm was used to assess changes in breathing rhythm and ventilatory output. Glutamate concentrations of 50, 150, and 1,000 mM were injected into the rostral pons. Active sites were generally located between parabrachial and either lateral lemniscal or trigeminal nuclei. Effects of glutamate in opossums of all ages included changes in diaphragm activity and respiratory timing over several breaths. In the youngest animals, a very high incidence of apnea occurred as an initial response (17 of 20 sites) at the 1,000 mM concentration. The high incidence of apneic response in the youngest animals suggests that strong activation of rostral pontine neurons can more easily disrupt respiratory output; a physiological circumstance of such activation might include a diving response stimulated by trigeminal afferents.

Transient expression of somatostatin mRNA in the auditory system of neonatal rat

Postnatal changes of preprosomatostatin mRNA expression in the rat auditory system were examined using in situ hybridization histochemical techniques. It was found that during postnatal days 1 and 2 most of the neurons in the dorsal and ventral cochlear nuclei, and large numbers of neurons in the inferior colliculus, paralemniscal nucleus, and lateral lemniscal nucleus, expressed somatostatin mRNA with a strong intensity. During postnatal development a marked decrease in the number and intensity of neurons expressing somatostatin mRNA was seen. These findings suggested that somatostatin was actively produced in the cochlear nuclei at a very early stage but that production later became reduced or ceased during postnatal ontogeny.

Zinc, selenium and lipid peroxides levels in hemodialysed patients

In order to test for the presence or absence of endogenous peroxidatic activities within the brains of normal squirrel monkeys, sections from the brain stems were incubated in buffered media of diaminobenzidine (DAB) and hydrogen peroxide, according to the methods of Graham and Karnovsky20 or Novikooff and Goldfischer39. It was found that neurons within certain regions were consistently stained both media. These reactive neurons belong to the extrapyramidal motor system (globus pallidus, substantia nigra (pars diffusa), red nucleus, pontine and mesencephalic reticular formation), to certain cranial nerve nuclei (oculomotor, trochlear, abducens, mesencephalic trigeminal, vestibular) and to relay nuclei of the auditory pathway (superior olivary nucleus and nucleus of the trapezoid body). Neurons within other regions of the brain stem, such as thalamus, hypothalamus and corpus striatum were not stained. On the other hand, the neuropil, excluding the neurons, in other motor areas (such as the subthalamic nucleus, inferior olivary nucleus and corpus striatum) and other auditory relay nuclei (inferior colliculus, nucleus of lateral lemniscus) were also significantly stained. Processes around the Purkinje cells of the cerebellum were particularly reactive.Under the electron microscope, reaction products were localized prominently along the cristae and limiting membranes of the mitochondria and within peroxisome-like bodies of the staiined neurons. Non-reactive neurons have little or no reaction products in their organelles.The staining was absent when DAB was withheld, and it was weak or absent if H2O2 was omitted from the media. The addition of inhibitors of catalase, 3-amino-1, 2,4-triazole and 2,6-dichlorophenolindophenol did not affect the staining intensity, whereas the addition of potassium cyanide, a strong inhibitor of metalloenzymes, especially heme-enzymes, almost completely abolished the reactions. In addition, a 3-day ‘bleaching treatment’ with 30% H2O2 did not affect the reactions. These results suggest that the reactivity in the above regions was due not to neuromelanin or other pigments, but rather to heme-enzymes and/or other hemoproteins.It was postulated that a higher concentration of the reactive agents was characteristic of certain neuronal types in the brain stem of the squirrel monkeys, and could be related to the cells' functional needs, energy requirements and perhaps to the metabolism of their specific neurotransmitters.

The neural coding of auditory space.

The barn owl's auditory system computes interaural differences in time and amplitude and derives from them the horizontal and vertical coordinates of the sound source, respectively. Within the external nucleus of its inferior colliculus are auditory neurones, called 'space-specific neurones', that have spatial receptive fields. To activate a space-specific neurone, a sound must originate from a circumscribed region of space, or, if the sounds are delivered to each ear separately, using earphones, the stimuli must have the combination of interaural time and amplitude difference that simulates a sound broadcast from their receptive field. The sound-localization cues are processed in parallel, non-overlapping pathways extending from the cochlear nuclei to the subdivision of the inferior colliculus that innervates the space-specific neurones. Processing in the time pathway involves the coding of monaural phase angle, the derivation of sensitivity for interaural phase difference, and the calculation of interaural time difference (ITD) from interaural phase difference. The last process involves groups of neurones in the inferior colliculus whose collective firing signals a unique ITD, even though the activity of each constituent neurone signals multiple ITDs. The projections of these ensembles to the space-specific neurone endow the latter with a selectivity for ITD. Processing in the amplitude channel, about which less is known, initially involves an inhibitory process that sharpens the directional sensitivity of neurones in a lateral lemniscal nucleus. The inhibition is mediated by a commissural projection from the same lemniscal nucleus of the opposite side. At higher levels of the auditory system, neurones that are tuned to a limited range of interaural amplitude differences are found. It is proposed that at these higher stages, interaural amplitude difference, like ITD, is coded amidst an ensemble of neurones.

Superior olivary and lateral lemniscal neurons projecting to the cochlea in the guinea pig

Efferent neurons to the cochlea in the guinea pig were observed in the superior olivary complex and ventral lateral lemniscal nuclei after injection of WGA-HRP into the cochlea via the round window. Of HRP-labeled nerve cells found in the brainstem, about 60% and 10% were located in the ipsilateral lateral superior olivary nucleus (LSO) and the contralateral ventral nucleus of the trapezoid body (VTB), respectively. A few labeled neurons were found in the ipsilateral VTB, contralateral LSO and the bilateral superior paraolivary nucleus (SPO). Seven percent and 5% of the labeled neurons were definitely observed in the ventrocaudal part of the contra- and ipsilateral ventral nucleus of the lateral lemniscus (VLL), respectively. A combination of acetylcholine esterase (AChE) histochemistry with the tracing of retrograde axonal transport of a fluorescent dye (DAPI) revealed that VLL neurons projecting to the cochlea, as well as about 85% of LSO neurons projecting to the ipsilateral cochlea, were AChE-positive.

An immunohistochemical study of the nerve growth factor receptor in developing rats

Nerve growth factor (NGF) receptor expression was studied in rats between embryonic day 11 (E11) to postnatal day 10 (PND10) by using a monoclonal antibody, 192-IgG, that specifically recognizes rat NGF receptor. Sympathetic ganglia were lightly stained by 192-IgG for NGF receptor immunoreactivity (NGFRI) (E11-PND10). Neural crest-derived sensory ganglia were moderately to densely stained (E11-PND10). Areas in CNS innervated by the central processes of these ganglia were also stained. Parasympathetic ciliary ganglion showed some detectable staining (E16-PND6). Placode-derived sensory ganglia were stained more densely than that of neural crest-derived sensory ganglia. The most densely stained tissue for NGFRI was found in all peripheral nerves. Basal forebrain cholinergic neurons were NGFRI positive from E15 throughout the period examined. Motoneurons in both spinal cord and brain stem were positive for NGFRI between E15 and PND10. NGFRI staining was seen in a variety of sensory pathways and related structures, such as olfactory tract and glomerular layer of olfactory bulb; retina, optic nerve and tract, lateral geniculate nucleus, medial terminal nucleus of the accessory optic tract, and olivary pretectal nucleus; ventral cochlear nucleus and to a lesser degree in dorsal cochlear nucleus, superior olive, and nucleus of lateral lemniscus; solitary tract; cuneate nucleus, gracile nucleus, and ventroposterior thalamic nucleus. The specific staining was also found in some other CNS structures, including brain-stem reticular formation; amygdala; medial nucleus of inferior olive but not the rest of inferior olive, external granule cell layer and Purkinje's cells of cerebellum, and deep cerebellar nuclei. Some non-neuronal tissues such as meninges and dental tissue showed very distinctive staining. Limb buds and somites were NGFRI positive starting at E11, and the staining on muscle tissue became very dense at E15-E18 and largely disappeared around PND10. Embryonic thymus was positive for NGFRI. The adventitia surrounding blood vessels was very densely stained. The changes in NGFRI staining seen in this study suggest that NGF may have broader effects during development than previously thought.

Projections of nucleus angularis and nucleus laminaris to the lateral lemniscal nuclear complex of the barn owl

Interaural phase and intensity are cues by which the barn owl determines, respectively, the azimuth and elevation of a sound source. Physiological studies indicate that phase and intensity are processed independently in the auditory brainstem of the barn owl. The phases of spectral components of a sound are encoded in nucleus magnocellularis (NM), one of the two cochlear nuclei. NM projects solely and bilaterally to nucleus laminaris (NL), wherein interaural phase difference is computed. The other cochlear nucleus, nucleus angularis (NA), encodes the amplitudes of spectral components of sounds. We report here the projections of NA and NL to the lateral lemniscal nuclei of the barn owl. The lateral lemniscal complex comprises nucleus olivaris superior (SO); nucleus lemnisci lateralis, pars ventralis (LLv); and nucleus ventralis lemnisci lateralis (VLV). At caudal levels, VLV may be divided into a posterior (VLVp) and an anterior (VLVa) subdivision on cytoarchitectonic grounds. At rostral levels, the cytoarchitectural differences diminish and the boundaries between the two subdivisions become obscured. Likewise, our data from anterograde tracing studies suggest that at caudal levels the terminal fields of NA and NL remain confined to VLVp and VLVa, respectively. They merge, however, at rostral levels. The data also suggest that NL projects to the medial portion of the ipsilateral SO and that NA projects bilaterally to all parts of SO and LLv. Studies with the retrograde transport of horseradish peroxidase confirm these projections.

Regional cerebral palmitate incorporation after unilateral auditory deprivation in immature and adult Fischer-344 rats

Regional cerebral incorporation of intravenously injected [U- 14C]palmitate was measured from 1 day to 13 weeks after left cochlear destruction in 11-day- and 3 month-old, awake Fischer-344 rats. In 11-day-old animals, statistically significant left-right differences in incorporation were absent 1 day after cochlear destruction and were found only in parts of the cochlear nucleus and inferior colliculus after 1 week. After 6 to 13 weeks, consistent with functional neuroanatomy of central auditory regions, incorporation was reduced by 6 to 9% in the left cochlear nucleus and left lateral superior olivary nucleus, compared with corresponding right-side regions. The right medial superior olivary nucleus, medial nucleus of the trapezoid body, lateral lemniscus nucleus, inferior colliculus, medial geniculate body, and auditory cortex had 5 to 9% less incorporation than did corresponding left-side regions. Fewer significant differences after chronic auditory deprivation occurred in 3-month-old rats than in 11-day-old rats following cochlear destruction. Reduced incorporation corresponded to reported changes in cell morphology, which also were greater in immature than mature rats following auditory deprivation. The results suggest that the palmitate method can be used to identify long-term regional changes in the turnover of brain lipids after sensory deprivation.

Nuclei of the lateral lemniscus project directly to the thalamic auditory nuclei in the pigeon

Non-mesencephalic origins of ascending afferents to the thalamic auditory nuclei, nuclei ovoidalis (Ov) and semilunaris parovoidalis (SPO), were identified in the pigeon in retrograde tracing experiments. These origins comprise dorsal and ventral lateral lemniscal nuclei. Injections of anterograde tracers into these nuclei produced terminal labelling in SPO in particular. These experiments show for the first time that the inferior colliculus is not an obligatory relay to the auditory thalamus.

Afferent and efferent innervation patterns of the cochlear nucleus (dorsal medullary nucleus) of the leopard frog

The afferent and efferent innervation patterns of the frog dorsal medullary nucleus (DMN; anuran homolog of the cochlear nucleus) were examined by studying the anterograde and retrograde transport patterns of horseradish peroxidase injected focally into the nucleus. It was found that this structure projected bilaterally to the superior olivary nuclei (SON) and dorsal midbrain tegmental nuclei, and contralaterally to the opposite DMN, the lateral lemniscus nucleus (LLN) and the torus semicircularis (TS). The termination sites in the TS were restricted to the laminar and principal nuclei. The DMN in turn received projections from these structures with the exception of the TS and dorsal tegmental nuclei. The projection to the ipsilateral LLN and TS was not pronounced. In addition to the above findings, the ascending projection to the DMN, SON and TS, as well as the centrifugal projection from the SON, were found to be organized tonotopically.

Brainstem location of efferent neurones projecting to the guinea pig cochlea

Retrograde transport of horseradish peroxidase using tetramethylbenzidine as a chromagen was used to map the cell bodies of origin of the efferent projection to the cochlea in the guinea pig. Large numbers of small labelled neurones were found within the body of the lateral superior olivary nucleus (LSO) ipsi-lateral to the injected cochlea. Labelled cells within the contra-lateral LSO were extremely rare (1% or less). Large labelled neurones were found both ipsi-laterally and contra-laterally in the dorsomedial periolivary region, including the medial nucleus of trapezoid body and in the ventral and lateral nuclei of the trapezoid body and the ventral nucleus of lateral lemniscus. It was concluded that some aspects of the distribution of these efferent neurones in the guinea pig are similar to the situation in the rat, whilst others resemble more closely the arrangement found in cat.