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PubMed2003

Anatomy of olivocochlear neurons in the hamster studied with FluoroGold.

The golden hamster (Mesocricetus auratus) is often used in auditory research, but little is known about the anatomical organization of its olivocochlear (OC) neurons, the source of the efferent innervation of the organ of Corti. Accordingly, we labeled the OC neurons projecting to one cochlea by means of retrograde axonal transport of FluoroGold. In four animals, all labeled OC neurons were counted and digital images of the labeling were captured and analyzed morphometrically. In one case, a 3D computer reconstruction of the bilateral distribution of OC neurons was made. The largest group of OC neurons was comprised by small, intrinsic lateral OC neurons within the ipsilateral lateral superior olivary nucleus (LSO), almost all of which (97%) were located ipsilaterally. The second largest group consisted of medial OC neurons in the ventral nucleus of the trapezoid body, 75% of which were located contralaterally. The smallest group consisted of shell neurons surrounding the LSO, 80% of which projected ipsilaterally. These three types of neurons are generally similar in morphology and distribution to those previously described in the rat and the chinchilla. However, there were several unique findings, including the fact that the hamster possesses the smallest total number of OC neurons (mean 341) of any rodent yet studied.

Animals↗
PubMed2003

A nitrergic projection from the superior olivary complex to the inferior colliculus of the rat.

The present study was conducted to test whether the ascending auditory projection from the superior olivary complex (SOC) of the brainstem to the inferior colliculus (IC) may use nitric oxide (NO) as a neuroactive compound. We identified olivo-collicular projection neurons in subnuclei of the SOC by retrograde neuronal tracing with Fluoro-Gold (FG) injected into the central nucleus of the IC. Sections containing retrograde labelled neurons were subjected to immunohistochemical incubation in an antiserum directed against the enzyme responsible for NO production in nerve cells, neuronal NO synthase (nNOS). The analysis showed that FG-containing neurons as well as nNOS-immunoreactive neurons were present in the lateral superior olive (LSO), superior paraolivary nucleus (SPO), ventral nucleus of the trapezoid body (VNTB), medial superior olive (MSO) and in dorsal and ventral periolivary regions to different amounts. However, only in the LSO, SPO and VNTB double-labelled neurons were found. They made up to less than 10% of all nNOS neurons in the SOC. Considering that only about 5% of the nNOS cells in the SOC are olivocochlear neurons [Riemann and Reuss, 1999], it is still open whether the majority of nitrergic neurons of the SOC project to other sites or whether they rather have intrinsic actions in providing NO to the SOC.

Afferent Pathways↗
PubMed2004

Dopaminergic olivocochlear neurons originate in the high frequency region of the lateral superior olive of guinea pigs.

Dopaminergic neurons are known to exist within the lateral superior olive (LSO). The LSO is the nucleus of origin of the lateral olivocochlear neurons, which project to the cochlea and synapse onto the primary afferents contacting the inner hair cells. We investigated whether the dopaminergic neurons in the LSO are part of the lateral olivocochlear neuron population. We combined intracochlear injections of a fluorescent retrograde tracer with immunofluorescent staining of tyrosine hydroxylase (TH). TH was used as a marker for dopaminergic neurons. After the injection with retrograde tracer most of the TH-labelled neurons in the LSO also contained the tracer, which directly demonstrates for the first time that the TH-labelled, dopaminergic neurons in the LSO are lateral olivocochlear neurons. TH-labelled neurons were not equally distributed over the LSO as is observed for the lateral olivocochlear neurons in general. TH-labelled neurons were almost exclusively seen in the medial, high frequency, limb of the LSO. Since the projection of the lateral olivocochlear neurons to the cochlea is known to be tonotopic, we investigated the TH-labelling in the cochlea as well. We found that the staining pattern of TH in the cochlea is in broad agreement with the distribution of TH-labelling in the LSO. Cochlear sections showed dense labelling in the basal and second, high frequency, turns and decreasing intensity of staining in the third turn, while the extreme apical, low frequency, turn was almost devoid of any positive TH-labelling. These observations imply that the dopaminergic neurons of the lateral olivocochlear system may play a role in the selective suppression of the high frequency fibers of the auditory system.

Animals↗
PubMed1998

Projections from the superior olive and lateral lemniscus to tonotopic regions of the rat's inferior colliculus.

The projections to physiologically defined tonotopic regions of the central nucleus of the inferior colliculus (ICC) from the adult rat's superior olivary complex (SOC) and lateral lemniscus were investigated using retrograde tract tracing methods. Iontophoretic injections of the retrograde tracers, Fluoro-Gold (FG) or horseradish peroxidase (HRP), were made into the ICC through a glass micropipette, which also served as a recording electrode to determine the frequency response at the injection site. Injections were made into frequency-specific regions based on the best responses of neurons to contralaterally presented tones between 2 25 kHz. In the dorsal nucleus of the lateral lemniscus (DNLL) neurons were labeled both ipsilaterally and contralaterally to the injection site with a larger proportion projecting to the contralateral side. The distribution of labeled cells was concentric, with high frequencies represented along the outer margin and low frequencies represented centrally within DNLL. The lateral superior olive (LSO) was labeled bilaterally, with high frequencies represented medially and low frequencies laterally along the nuclear axis. The projection from the medial superior olive (MSO) was ipsilateral, with high frequencies represented ventrally and low frequencies dorsally. The projection from the superior paraolivary nucleus (SPN) was also largely ipsilateral, with high frequencies represented medially and low frequencies laterally. The intermediate and ventral nuclei of the lateral lemniscus (INLL and VNLL) were also labeled ipsilaterally and exhibited a distribution of tracer that depended on the frequency of the injection site: the low frequency projection was banded but the high frequency projection was more evenly distributed.

Animals↗
PubMed1998

GABAergic projections from the lateral lemniscus to the inferior colliculus of the rat.

The objective of the present study was to provide direct evidence regarding GABAergic projections from the nuclei of the lateral lemniscus to the central nucleus of the inferior colliculus (ICC), and from the ICC to the opposite ICC. Projections of GABAergic neurons in the rat were investigated by a combination of fluorogold (FG) retrograde tracing and GABA immunocytochemistry. FG was first injected into a frequency-defined region (11-13 kHz) in the center of the ICC, and 1-2 weeks was allowed for retrograde transport. Vibratome sections were then cut through the brainstem and stained with GABA antibody. Double-labeling was taken as evidence of GABAergic neurons projecting to the ICC. The results from FG retrograde labeling alone showed that neurons in the dorsal nucleus of the lateral lemniscus (DNLL) bilaterally, in the intermediate and ventral nucleus of the lateral lemniscus (INLL and VNLL) ipsilaterally, and in the ICC contralaterally project to the ICC. GABA immunostaining alone showed substantial numbers of GABA positive neurons in the nuclei of the lateral lemniscus and the inferior colliculus. FG and GABA double-labeled neurons were present in all nuclei of the lateral lemniscus that project to the ICC. The greatest concentration of double-labeled neurons was found bilaterally in the DNLL, suggesting a prominent GABAergic projection from the DNLL to the ICC. The presence of many double-labeled neurons in the ipsilateral INLL and VNLL suggests that there are also GABAergic inputs from the INLL and VNLL to the ICC. No double-labeled neurons were found in the contralateral ICC, which suggests the possibility of a prominent non-GABAergic projection.

Animals↗
PubMed1998

Sources of input to the cochlear granule cell region in the guinea pig.

Anterograde and retrograde transport of fluorogold was used to trace input to the superficial granule cell layer of the ventral cochlear nucleus in the guinea pig. Infusion of fluorogold into the labyrinth resulted in heavy labeling of eighth nerve axons and their terminals in the ventral cochlear nucleus, but only a few labeled axons entered the granule cell layer. Injections of fluorogold restricted to the granule cell layer retrogradely labeled neurons in the ipsilateral lateral superior olivary nucleus, in the periolivary region predominantly contralaterally, and in the inferior colliculus predominantly ipsilaterally. Labeled neurons were also present in the ipsilateral ventral cochlear nucleus, but this may be due to interruption of axons of passage in the lateral ventrotubercular tract. Overall this study demonstrates very restricted direct cochlear input to the granule cell region, but provides evidence for projections from several brainstem auditory nuclei.

Animals↗
PubMed1999

Olivocochlear neurons in the chinchilla: a retrograde fluorescent labelling study.

Although the chinchilla is widely used as a model for auditory research, little is known about the distribution and morphology of its olivocochlear neurons. Here, we report on the olivocochlear neurons projecting to one cochlea, as determined by single and double retrograde fluorescent tracer techniques. 10 adult chinchillas were anesthetized and given either unilateral or bilateral injections of a fluorescent tracer (either Fluoro-Gold or Fast Blue) into scala tympani or as a control, a unilateral injection into the middle ear cavity. The results indicate that there are similarities as well as significant differences between the chinchilla and other species of rodents in the distributions of their olivocochlear neurons. Based on three well-labelled cases, there was a mean total of 1168 olivocochlear neurons in the chinchilla. Of these, the majority (mean 787) were small, lateral olivocochlear neurons found almost exclusively within the ipsilateral lateral superior olivary nucleus. The next largest group consisted of a mean of 280 medial olivocochlear neurons virtually all of which were located in the dorsomedial peri-olivary nucleus. Chinchilla medial olivocochlear neurons were more predominantly crossed in their projections (4:1) than in any known species. The smallest group of olivocochlear neurons (mean 101) consisted of larger lateral olivocochlear neurons (shell neurons) which were located on the margins of the superior olivary nucleus and which projected mainly (2.2:1) ipsilaterally. Double retrograde labelling was observed only in medial olivocochlear neurons and occurred in only 1-2% of these cells. The results confirm previous findings which indicated a relative paucity of fibers belonging to the uncrossed as compared to the crossed olivocochlear bundle. This, together with the strong apical bias of the uncrossed projection reported previously, offers possible explanations for the apparent absence of efferent-mediated suppressive effects of contralateral acoustic stimulation in this species. Regarding the lateral olivocochlear system, the chinchilla is shown to possess both intrinsic and shell neurons, as in the rat.

Amidines↗
PubMed1999

Nitric oxide synthase in identified olivocochlear projection neurons in rat and guinea pig.

Nitric oxide (NO) is thought to be involved in the effects of amino acids at the level of cochlear hair cell afferents. Recently, the isoform of the NO-producing enzyme, neuronal NO synthase (nNOS), has been demonstrated in neuronal structures of the cochlea in rats and guinea pigs histochemically and immunohistochemically. To investigate the sources of cochlear NO, we injected Fluoro-Gold (FG) into the cochlea of rats and guinea pigs. Upon terminal uptake of the tracer and neuronal transport we observed FG in terminals at the base of inner (IHC) and outer hair cells (OHC) and in neurons of the spiral ganglion. Ganglion cells and terminals at the IHC were clearly nNOS-positive, while terminals at the OHC exhibited nNOS-immunoreactivity to a minor degree. The immunohistochemical investigation of the auditory brainstem showed that about one-fourth of the neurons of the superior olivary complex contained nNOS. The comparison with retrogradely labeled neurons showed that perikarya in the lateral superior olivary nucleus and, in particular, the medial nucleus of the trapezoid body were double-labeled. These results were similar in both, rat and guinea pig. Our data reveal that neurons of the superior olivary complex are likely to be additional sources of neuronal NOS in the cochlea.

Animals↗
PubMed2001

Origin and pathway of sensory nerve fibers to the ventral and dorsal sides of the sacroiliac joint in rats.

The purpose of this study is to clarify sensory innervation in the ventral and dorsal sides of the sacroiliac joint. Fluoro-gold, a neural tracer, was injected into the left sacroiliac joint of adult rats from the dorsal side after denervation of the dorsal side, and the bilateral dorsal root ganglia (DRGs) from T13 to S4 were examined by fluorescence microscopy five days after injection. In another rat group, the DRGs were examined using the same methods after injection of fluoro-gold from the ventral side. In the case of dorsal denervation (ventral nerve supply), labeled neurons were mainly located in the ipsilateral DRGs from L1 to S2. On the other hand, in the case of ventral denervation (dorsal nerve supply), labeled neurons were noted in the ipsilateral DRGs from L4 to S2. The sacroiliac joint in rats is innervated differently on the ventral and dorsal sides: the sensory nerve fibers to the dorsal side of the sacroiliac joint were derived from the DRGs of lower lumbar and sacral levels (from L4 to S2); and those to the ventral side from the DRGs of upper lumbar, lower lumbar, and sacral levels (from L1 to S2).

Afferent Pathways↗
PubMed2001

Effects of increased intraocular pressure on rat retinal ganglion cells.

The effects of elevated intraocular pressure (IOP) on the morphology of rat retinal ganglion cells (RGCs) was analyzed in this study. After cauterizing two limbal derived episcleral veins, IOP in experimental eyes was elevated 1.5--1.8 times that of control. RGCs of experimental and control eyes were analyzed after: bilateral tectal injections of Fluoro-Gold, and application of fluorescent dye crystals, 4-Di-10-ASP to the proximal stump of the cut optic nerve, at different time intervals after IOP elevation. The RGCs in control and experimental eyes were evaluated at 4, 6, 8, and 10 weeks by counting, as well as by determining the soma diameter. The dendritic field of three types (I, II, III) of RGCs between control and experimental eyes were also studied at 4,6,10 weeks after IOP elevation. At every time point, the number of cells in experimental eyes were significantly less than those of the control eyes. The average retinal ganglion cell death was 3--4% per week in the eyes with elevated IOP. The soma and dendritic field diameter of the RGCs in the experimental eyes were significantly larger in all cell types. However, types I and III cells expanded their dendritic fields more rapidly than type II cells. Furthermore, dendritic fields of surviving RGCs in experimental eyes occupied about the same extent of the retina as the controls. The increase in soma diameter and expansion of dendritic fields in the remaining RGCs in eyes with elevated IOP suggests the existence of plasticity in adult retina.

Animals↗
PubMed2001

Origin of the noradrenergic innervation of the superior olivary complex in the rat.

In the rat, the superior olivary complex contains lateral and medial olivocochlear neurones, which respectively innervate two separate targets within the cochlea; the auditory afferents contacting the inner hair cells and the outer hair cells themselves. Previous double label immunohistochemical studies have shown that both lateral and medial olivocochlear neurones are contacted by noradrenergic nerve endings, and electrophysiological studies on in-vitro rat brain slices have demonstrated that noradrenaline exerts a direct, predominantly excitatory effect on medial olivocochlear neurones. In this paper, we have investigated the origin of the noradrenergic input to the superior olivary complex (SOC). A retrograde tracer, Fluorogold, was used to map the inputs to the SOC, and this was combined with immunofluorescent staining for dopamine-beta-hydroxylase (DbetaH) to identify which of the afferent inputs was noradrenergic. These experiments showed small numbers of neurones double-stained for both Fluorogold and DbetaH in the A6 cell group (the locus coeruleus). In the A7 cell group, within and medial to the lateral lemniscus, numerous Fluorogold labelled and DbetaH positive neurones were found, but no neurones were seen that were double-labelled. In none of the other major noradrenergic cell groups were labelled Fluorogold neurones ever detected. To confirm the results obtained by retrograde tracer injections, anterograde tracer injections with biotinylated dextran amine were made in the locus coeruleus. This resulted in labelled fibres within all subdivisions of the superior olivary complex. These experiments indicate that the noradrenergic input to the olivocochlear neurones originates solely from the locus coeruleus. The small numbers of double-labelled neurones found in the locus coeruleus indicate a very divergent non-selective noradrenergic input to the SOC.

Animals↗
PubMed2002

Cocaine- and amphetamine-regulated transcript peptide-immunoreactivity in adrenergic C1 neurons projecting to the intermediolateral cell column of the rat.

Cocaine- and amphetamine-regulated transcript (CART) peptide-immunoreactivity was detected in neurons of the rostral ventrolateral medulla (RVLM), but few in the caudal ventrolateral medulla (CVLM). Double-labeling the medullary sections with sheep polyclonal phenylethanolamine N-methyltransferase-antiserum (PNMT) or monoclonal tyrosine hydroxylase-antibody and rabbit polyclonal CART peptide-antiserum revealed that nearly all adrenergic cells in the C1 area were CART peptide-positive and vice versa; tyrosine hydroxylase-positive cells in the A1 area were not. In the thoracolumbar spinal cord, neurons in the intermediolateral cell column (IML) and other sympathetic autonomic nuclei were CART peptide-positive; some of these were contacted by immunoreactive fibers arising from the lateral funiculus. By immuno-electron microscopy, axon terminals containing closely packed agranular CART peptide-immunoreactive vesicles appeared to make synaptic contacts with immunoreactive dendrites and soma in the IML, albeit the incidence of such contacts was low. Microinjection of the retrograde tracer Fluorogold into the lateral horn area of the T1-T3 spinal segments labeled a population of neurons in the C1 area, many of which were also CART peptide-positive. The results indicate that CART peptide-immunoreactivity is expressed in C1 adrenergic neurons, some of which project to the thoracolumbar spinal cord. The presence of this novel peptide in C1 adrenergic neurons underscores the multiplicity of putative transmitters that may be involved in signaling between putative cardiovascular neurons in the medulla oblongata and sympathetic preganglionic neurons (SPNs) in the spinal cord.

Animals↗
PubMed1996

Nitric oxide synthase-containing magnocellular neurons of the rat hypothalamus synthesize oxytocin and vasopressin and express Fos following stress stimuli.

We investigated the chemical and anatomical features of nitric oxide synthase (NOS)-containing neurons in the paraventricular and supraoptic nuclei in the rat hypothalamus using combinations of enzyme histochemistry, in situ hybridization and immuno-histochemistry. Neurons expressing NOS mRNA completely overlapped with NADPH-diaphorase-positive neurons. Topographical distribution of NOS was segregated from that of CRF-containing parvicellular neurons in the posterior paraventricular nucleus but overlapped with that of magnocellular neurons. In the paraventricular nucleus, 70% of oxytocin neurons contained NOS, which corresponded to one half of NOS neurons. About one third of vasopressin-immunoreactive neurons were NADPH-diaphorase-positive and the same proportion of NADPH-diaphorase-positive neurons were vasopressin-immunoreactive. In the supraoptic nucleus, 50% of oxytocin neurons were NADPH-diaphorase-positive, which corresponded to 40% of NOS neurons. About 25% of vasopressin neurons were NADPH-diaphorase-positive, and 30% of NADPH-diaphorase-positive neurons were vasopressin-immunoreactive. When NADPH-diaphorase histochemistry was performed first, subsequent immunostaining was markedly perturbed. Using fluoro-gold as a retrograde tracer, 4% of NADPH-diaphorase-positive neurons were shown to contribute to the descending projection to the spinal cord. About 40%-50% of NADPH-diaphorase-positive neurons exhibited Fos immunoreactivity after injection of lipopolysaccharide or hypertonic saline, while only 10%-15% of these neurons expressed Fos in response to immobilization or pain. Endogenous NO may be involved in the regulation of magnocellular functions, especially when the internal environment is disturbed.

Animals↗
PubMed1997

Expression of galanin and nitric oxide synthase in subpopulations of serotonin neurons of the rat dorsal raphe nucleus.

The dorsal raphe nucleus (DR) of the rat was studied with triple labeling immunofluorescence histochemistry to evaluate the quantitative relationships between neurons expressing 5-hydroxytryptamine (5-HT), the neuropeptide galanin (GAL) and the nitric oxide (NO) synthesizing enzyme NO synthase (NOS). In addition retrograde tracing studies were performed. It could be established that a high percentage (between 40 and 60%) of the 5-HT neuron profiles in the ventromedial and dorsomedial subgroups of the DR contained both GAL and NOS after colchicine treatment. This triple coexistence was lower in the dorso-lateral subgroup and much lower in the lateral subgroup (down to 5%). All GAL neuron profiles contained 5-HT, and they constituted up to 80% of all labeled profiles in the rostral ventromedial and caudal dorsomedial subgroups, with the lowest percentage in the lateral subgroup (45%). The percentage of 5-HT-alone neuron profiles in these four subgroups varied between 15-40%. The proportion of 5-HT/NOS neurons was low (a few percent) at all levels, and this was the case also for NOS-alone neuron profiles except in the lateral subgroup, where 10-20% were of this type. It could be established that some 5-HT/GAL/NOS neurons project to the striatum. These retrogradely labeled cells were mainly found in the mid-line subgroups. In the striatum a moderately dense 5-HT fiber network and numerous NOS-positive cell bodies and fibers could be observed. However, only a few, weakly fluorescent GAL fibers were found and in a small number of cases it could be shown or was likely that 5-HT and GAL coexisted. No evidence for coexistence between 5-HT and NOS was obtained. The present findings strongly suggest that a large proportion of the DR 5-HT neurons can synthesize and release two additional messenger molecules, GAL and NO. Furthermore, even if the 5-HT/GAL/NOS neurons project to the striatum, the amounts of GAL and NOS transported to the terminal ramifications in this area are very low. This is in agreement with a very low GAL synthesis in the DR under normal circumstances, which is also indicated by the fact that colchicine treatment is needed to visualize GAL-like immunoreactivity in DR cell bodies. It is possible that NO, and perhaps GAL, in 5-HT neurons exert their main actions at the somatic and dendritic level in the DR.

Animals↗
PubMed1998

Separate populations of neurons within the paraventricular hypothalamic nucleus of the rat project to vagal and thoracic autonomic preganglionic levels and express c-Fos protein induced by lithium chloride.

The role of different hypothalamic nuclei, particularly the paraventricular nucleus (PVN), in the control of food intake and feeding behaviour is well known. It is also well established that lithium chloride (LiCl) causes various disorders in feeding behaviour. In this study, we analyzed the precise distribution of hypothalamic neurons activated by i.p. LiCl administration (LCA neurons) and compared it to that of hypothalamic neurons which project to autonomic preganglionic levels (HAP neurons). We also analysed the possibility that some neurons belong to both populations of nerve cells. To this end, a multiple-labelling technique, using two retrograde fluorescent tracers together with c-Fos-like immunohistochemistry, was performed. Fast Blue was injected in the dorsal motor nucleus of the vagus and Fluorogold (FG) in the thoracic intermedial-lateral cell column, to trace parasympathetic and sympathetic pathways, respectively. LiCl was used as stimulus for c-Fos-like immunohistochemistry. HAP neurons were located mainly in the dorsal, ventral and lateral regions of the parvocellular PVN, while LCA neurons were observed predominantly in the magnocellular region of the PVN rostrally to HAP neurons. A significant number of FG/Fos double-labelled neurons were located in the dorsal parvocellular subnucleus of the PVN (dp) in the LiCl-stimulated rats. We concluded that there is a clear segregation of LCA neurons from HAP neurons within the PVN. The presence of FG/Fos double-labelled neurons in the dp suggests that this nucleus could mediate a sympathetic response after LiCl administration.

Animals↗
PubMed1998

Anatomical interactions between the central amygdaloid nucleus and the hypothalamic paraventricular nucleus of the rat: a dual tract-tracing analysis.

Axonal connections between the amygdala and the hypothalamic paraventricular nucleus were examined by combined anterograde-retrograde tract tracing. Iontophoretic injections of the retrograde tracer Fluorogold were placed in the paraventricular nucleus, and the anterograde tracer PHA-L in the ipsilateral central or medial amygdaloid nuclei. Single and double-label immunohistochemistry were used to detect tracers. Single label anterograde and retrograde tracing suggest limited evidence for direct connections between the central or medial amygdala and the paraventricular nucleus. In general, scattered PHA-L-positive terminals were seen in autonomic subdivisions of the paraventricular nucleus (lateral parvocellular, dorsal parvocellular and ventral medial parvocellular subnuclei) following central or medial amygdaloid nucleus injection. Double-label studies indicate that central and medial amygdaloid nucleus efferents contact paraventricular nucleus-projecting cells in several forebrain nuclei. In the case of central nucleus injections, PHA-L positive fibers occasionally contacted Fluorogold-labeled neurons in the anteromedial, ventromedial and preoptic subnuclei of the bed nucleus of the stria terminalis. Overall, such contacts were quite rare, and did not occur in the bed nucleus of the stria terminalis regions showing greatest innervation by the central amygdaloid nucleus. In contrast, medial amygdala injections resulted in a significantly greater overlap of PHA-L labeling and Fluorogold-labeled neurons, with axosomatic appositions observed in medial divisions of the bed nucleus of the stria terminalis, anterior hypothalamic area and preoptic area. The results provide anatomical evidence that a substantial proportion of amygdaloid connections with hypophysiotrophic paraventricular nucleus neurons are likely multisynaptic, relaying in different subregions of the bed nucleus of the stria terminalis and hypothalamus.

Amygdala↗
PubMed1999

Afferents to the rostral olfactory bulb in sheep with special emphasis on the cholinergic, noradrenergic and serotonergic connections.

The olfactory bulb (OB) is involved in the processing of olfactory information particularly through the activation of its afferents. To localize their cell origin in sheep, a specific retrograde fluorescent tracer, Fluoro-Gold, was injected into the olfactory bulb of seven ewes. By using immunocytochemical techniques, retrogradely labeled neurons were colocalized with choline acetyltransferase, tyrosine hydroxylase, dopamine-beta-hydroxylase and serotonin to characterize cholinergic, noradrenergic and serotonergic Fluoro-Gold-labeled neurons. Most afferents originated from the ipsilateral side of the injection site. The OB received major inputs from the anterior olfactory nucleus (AON), the piriform cortex (PC), the olfactory tubercle, the diagonal band of Broca (DBB) and the amygdala. Other retrogradely labeled neurons were observed in the taenia tecta, the septum, the nucleus of the lateral olfactory tract, the preoptic area, the lateral hypothalamic area, the mediobasal hypothalamus, the lateral part of the premammillary nucleus, the paraventricular nucleus of the hypothalamus, the paraventricular thalamic nucleus, the central grey, the substantia nigra (SN), the ventral tegmental area (VTA), the lateral nucleus to the interpeduncular nucleus (IIP), the raphe and the locus coeruleus (LC). Contralateral labeling was also found in the AON, the PC, the SN compacta, the VTA, the IIP and the LC. Cholinergic Fluoro-Gold-labeled neurons belonged to the horizontal and vertical branch of the DBB. Noradrenergic afferents came from the LC and serotoninergic afferents came from the medial raphe nuclei and the 1IP. These data are discussed in relation with olfactory learning in the context of maternal behavior in sheep.

Animals↗
PubMed2000

Afferent connections of the caudal raphe pallidus nucleus in rats: a study using the fluorescent retrograde tracers fluorogold and true-blue.

Afferent connections to the caudal region of the nucleus raphe pallidus (RPa) in rats were studied using fluorogold and true-blue as tracers. Due to its ability to produce limited injection sites, true-blue proved to be more appropriate than fluorogold for studying long distance connections in a narrow structure such as the RPa. Fluorescent, retrogradely-labeled perikarya were found in the preoptic area (median, medial and lateral nuclei), hypothalamus (anterior, dorsal, lateral and posterior areas, and the peri- and paraventricular nuclei), zona incerta, central gray (dorsal, ventral and ventro-lateral), reticular formation of the brainstem, trigeminal spinal nuclei and in the spinal cord (laminae V-X at thoracic, lumbar and sacral levels). This connection pattern suggests the involvement of the RPa in autonomic, somatic and endocrine functions.

Afferent Pathways↗