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PubMed1991

Topography of projections from the auditory cortex to the inferior colliculus in the rat.

We examined the organization of descending projections from auditory and adjacent cortical areas to the inferior colliculus (IC) in the rat by using the retrograde and anterograde transport of wheat germ agglutinin-horseradish peroxidase. Small tracer injections were placed into cytologically defined subnuclei of the IC. On the basis of the resulting pattern of retrogradely labeled neurons in the cortex, different cortical areas and fields were defined. Two secondary areas located ventrocaudally (Te2) and ventrally (Te3) to the primary auditory area (Te1) were delineated. The primary auditory area was subdivided into a posterior (Te1.p), a medial (Te1.m), and an anterior (Te1.a) auditory field. In addition, we outlined an area located rostrally to the auditory areas comprising a part of the secondary somatosensory cortex, as well as a dorsal belt surrounding dorsally the auditory areas. The following basic patterns of corticocollicular projections are revealed: 1) layers 2 and 3 of the dorsal cortex of the IC (DC2, DC3) are differentially innervated by the primary auditory fields (Te1.p and Te1.a project bilaterally to DC2, while Te1.m projects bilaterally and in topographical order to DC3); cells in Te1.m, arranged in caudal to rostral sequence, project to corresponding loci in DC3 arranged from dorsolateral to ventromedial; 2) the fibrocellular capsule of the IC, comprising layer 1 of the dorsal and external cortex of the IC, receives input from the secondary auditory area Te2; 3) layers 2 and 3 of the external cortex of the IC are only weakly innervated by the primary and secondary auditory cortex; 4) the intercollicular zone receives its major input from the secondary auditory area Te3, the secondary somatosensory cortex, and the dorsal belt; and 5) finally, the central nucleus of the IC receives no input from the temporal cortex at all. Our results demonstrate that the corticocollicular projections are highly organized. These pathways may modulate auditory processing in different functional circuits of the inferior colliculus.

Animals↗
PubMed1991

Origin of spinal projections to the anterior and posterior lobes of the rat cerebellum.

The present study was carried out to analyze the topography of spinal projections to the anterior and posterior lobes of the cerebellum and to investigate whether projections to the two lobes come from different spinocerebellar neurons or from branching axons of the same cells. We used orthograde transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) to identify the cerebellar areas where spinocerebellar axons terminate and retrograde double-labeling techniques to estimate the incidence of spinocerebellar neurons projecting to both anterior and posterior lobes via axon collaterals. Orthograde labeling confirmed that the rat, like other mammalian species, has spinocerebellar projections to two different regions of cerebellar cortex, i.e., lobules I-V of the anterior lobe and lobule VIII of the posterior lobe, with the highest incidence in lobules II, III, and VIII. We did not observe a clear difference in the distribution of afferents coming from different spinal segments to either of the two lobes. The double-labeled cells were located primarily in the lower thoracic and upper lumbar segments, almost exclusively in Clarke's column and in the dorso-lateral part of lamina 7 (in the region of the spinal border cells). It is likely that most or all of the spinocerebellar neurons in these structures project to both anterior and posterior lobes. Therefore, the two lobes of the cerebellum are likely to receive common information from these cells, but different information from the separate populations of spinocerebellar neurons that project only to one lobe or the other.

Afferent Pathways↗
PubMed1991

Inventory and distribution of synapses of identified uniglomerular projection neurons in the antennal lobe of Periplaneta americana.

Uniglomerular projection neurons in the antennal lobe of Periplaneta americana, the axons of which connect the lobe to the protocerebrum, were labeled by intracellular injection of Lucifer Yellow or biocytin. The fine structure of individual neurons within the antennal lobe was examined after the injected substances had been converted (by immunohistochemical or histochemical treatment) to electron microscopically visible reaction products. Seven projection neurons were investigated, including attractant neurons, with dendritic arbors in the macroglomerulus, and projection neurons of normal-sized glomeruli. From reconstructions of thin serial sections and examination of additional processes present at various places in the arborization regions, the distribution of synapses within the glomeruli was inferred. Although the projection neurons differ from one another in their glomerular arborization patterns, they are very similar in the spatial segregation of their input and output synapses within the arborization. Output synapses are found on the thick part of the fiber near its site of entry into the glomerulus, as well as in regions within the glomerulus where the neuron has begun to ramify into thinner fibers. In the latter regions, the many output synapses are accompanied by occasional input synapses; hence these are regarded as transitional regions. At the terminal arbors only input synapses were found. This suggests that neurons with dense terminal arborizations receive particularly numerous inputs in these regions. The large number of input synapses reflects the high degree of convergence of afferents onto projection neurons previously demonstrated physiologically. However, the presence of numerous output synapses indicates that projection neurons not only transport sensory information into the protocerebrum but are also a major component of the neuronal circuitry within the antennal lobe.

Animals↗
PubMed1991

Projections from the posteroventral cochlear nucleus to the superior olivary complex in guinea pig: light and EM observations with the PHA-L method.

The efferent neural projections from posteroventral cochlear nucleus to the superior olivary complex in guinea pig were examined with the Phaseolus vulgaris-leucoagglutinin anterograde tract-tracing method. Light microscopic analysis demonstrated that the posteroventral cochlear nucleus of guinea pig bilaterally projects to the superior para-olivary nucleus and the rostral, medioventral, and lateroventral peri-olivary regions. Ipsilaterally, the posteroventral cochlear nucleus projects to the lateral superior olive, the caudal peri-olivary region, and areas immediately surrounding the capsule of the lateral superior olive. Contralaterally, the posteroventral cochlear nucleus projects to the medial nucleus of the trapezoid body. All of these projection axons travel in the trapezoid body and their terminals make, primarily, en passant endings upon their targets. Exclusively within the contralateral medial nucleus of the trapezoid body, some neurons terminate also in calyceal endings. The assumption that immunolabeled structures observed with light microscopy made actual synaptic contact in their respective target areas was confirmed with electron microscopy. With postembedding immunocytochemical procedures applied to thin sections, the electron microscope revealed labeled synaptic vesicles and pre- and postsynaptic membrane specializations. The projection pattern from posteroventral cochlear nucleus was found to be topographically organized in three distinct regions. The more dorsally located neurons of the posteroventral cochlear nucleus terminated dorsomedially in the ipsilateral lateral superior olive, ventromedially in the contralateral superior para-olivary nucleus, and medially in the contralateral medioventral peri-olivary region. The more ventrally located neurons of the posteroventral cochlear nucleus terminated dorsolaterally in the ipsilateral lateral superior olive, dorsolaterally in the contralateral superior para-olivary nucleus, and laterally in the contralateral medioventral peri-olivary region.

Animals↗
PubMed1991

Patterns of connectivity in the cat sensory-motor cortex: a light and electron microscope analysis of the projection arising from area 3a.

Through its complex network of interconnections, each of the functionally specialized subdivisions in the cat primary somatosensory cortex may provide the motor cortex with different input and thus play a unique role in motor behavior. Areas 2 and 3a receive separate peripheral information. Cells in both regions project directly to the cat motor cortex but are thought to target different populations of neurons. In this study the morphology and distribution patterns of the area 3a projection to the motor cortex were compared to previous findings on the projection from area 2. Also, details of the projection from area 3a to area 2 were studied. Injections of Phaseolus vulgaris leucoagglutinin were made into area 3a and fixed brain tissue was processed for immunohistochemical staining of this anterograde tracer. Tissue was examined with the light microscope to determine the patterns of the 3a projections to area 2 and motor cortex, area 4. Axons arising from cells in area 3a terminated in multiple column-like clusters in both motor cortex and area 2. The small number of cells labeled at the injection sites suggested that multiple foci of the 3a fibers are formed by collateral axonal branches of the same neurons. The topography of the projection from area 3a to the motor cortex was more clearly defined than that from area 3a to area 2. Electron microscope analysis determined the laminar distribution and types of synapses formed between area 3a efferents and their target neurons. A high proportion of synapses was found in layer III in both target regions. However, unlike in area 4, labeled terminals were sparse in laminae I and II of area 2. Axospinous synapses were slightly more numerous than axodendritic synapses, but both were distributed similarly throughout the thickness of the cortex. In area 2 the axospinous synapses accounted for 63% of synapses and in area 4 for 57% of synapses. No axosomatic synapses were detected.

Animals↗
PubMed1992

Area 3a in the cat. II. Projections to the motor cortex and their relations to other corticocortical connections.

It is well known that area 3a in the cat may monosynaptically influence the activity of neurons in the motor cortex. Much less information is available, however, on the anatomy of these connections. By using single or combined injections of different retrograde axonal tracers, we investigated the topography (horizontal and laminar) of area 3a neurons projecting to the motor cortex, and the anatomical relationships between these neurons and those projecting to other areas (2, 5, and SII) which, in turn, project to the motor cortex. Area 3a projects to all parts of area 4 gamma, to area 4 delta, and to the agranular area 6 in the lateral bank of the presylvian sulcus (area 6 alpha gamma), but not to other parts of areas 4 and 6. This projection exhibits a loose topographic organization along the mediolateral dimension of area 3a, and, in many cases, arises predominantly from the rostral half of this area. Although single small injections in the motor cortex produced two or more separate patches of retrograde labeling in 3a, after simultaneous injections of fluorochromes in two separate loci there often appeared in area 3a overlapping populations of neurons which were labeled retrogradely by each of the dyes, but with very few double-labeled neurons. In horseradish peroxidase (HRP) cases, 72% of area 3a neurons projecting to area 4 gamma were distributed in supragranular layers (mainly layer III), although the proportion of labeling in infragranular layers was larger when using fluorescent dyes. Double-labeled cells predominated in infragranular layers. These results have a bearing upon the functional roles that have been attributed to area 3a, as a cortical locus involved in muscle sensation, and a cortical relay to the motor cortex of rapid feedback information from muscle activity during movement.

Amidines↗
PubMed1993

Location, morphology, and central projections of mesencephalic trigeminal neurons innervating rat masticatory muscles studied by axonal transport of choleragenoid-horseradish peroxidase.

Retrograde and transganglionic transport of horseradish peroxidase conjugated to the B-fragment of cholera toxin (B-HRP) was used to study the location, morphology, and central projections of mesencephalic trigeminal (Me5) neurons innervating rat masticatory muscles. Labeled Me5 cell bodies were found throughout the Me5 nucleus from a level slightly caudal to the trigeminal motor nucleus to the level of the superior colliculus 5 mm further rostrally. Occasionally, labeled Me5 cells were observed in the anterior medullary velum, in the cerebellum, and in the brainstem contralateral to the B-HRP injection. The vast majority of the labeled Me5 cells were pseudounipolar, but multipolar cells were also found. Extensive central projections from labeled Me5 cells could be seen extending from the nucleus of Darkschewitsch rostrally to the C2 segment caudally. Small but consistent projections from Me5 neurons were observed in nuclear islands among the incoming Me5 root fibers. Trigeminal and hypoglossal motor nuclei received direct projections from Me5 cells, but not the facial motor nucleus. The most prominent Me5 projections appeared in the brainstem reticular formation, including the supratrigeminal nucleus. Smaller projections also extended into the main sensory trigeminal nucleus, trigeminal subnucleus oralis, and the nucleus of the solitary tract.

Animals↗
PubMed1993

Distribution of cerebellothalamic and nigrothalamic projections in the dog: a double anterograde tracing study.

The distribution of nigrothalamic and cerebellothalamic projections was investigated in the dog by a double labeling strategy combining the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) and tritiated amino acids. Following tritiated amino acid injections into the substantia nigra pars reticulata (SNr) and WGA-HRP injections into the contralateral cerebellar nuclei, we found that the nigrothalamic and cerebellothalamic afferents distribute to three main targets: the central portion of the ventral anterior nucleus (VA) and the ventral lateral nucleus (VL), the internal medullary lamina (IML) region, which includes the paralaminar VA, the mediodorsal nucleus (MD) and the central lateral nucleus (CL), and finally the ventromedial nucleus (VM). We observed three distribution patterns of labeled fibers: a) Dense single label was observed in the central portion of VA following the SNr injections and in VL following the cerebellar nuclei injections. b) A complementary pattern consisting of alternating foci of nigral and cerebellar label was found in the IML region. This pattern was also observed in the caudal intralaminar nuclei where cerebellar label predominated in the centrum medianum (CM), while the parafascicular nucleus (Pf) primarily contained nigral label. c) An overlapping pattern of autoradiographic and WGA-HRP label was found in the lateral half of the VM. Overall, the distribution of nigrothalamic and cerebellothalamic projections was widespread throughout much of rostrocaudal thalamus. However, the pattern of projections varied along a continuum from lateral to medial thalamus. In lateral thalamus, nigral and cerebellar projections distributed to separate nuclei while in medial thalamus, the projection pattern changed to focal and complementary in the IML and overlapping in VM. Taken together, these thalamic projections may constitute crucial links in different functional channels involved in alerting and orienting mechanisms associated with motor behavior. Our findings also suggest that the organization of motor thalamic afferents in the dog shares similarities with the segregated and parallel circuitry characteristic of primates as well as with the overlapping and converging circuits of rodents and other carnivores.

Amino Acids↗
PubMed1993

Cytoarchitecture of spinal-projecting neurons in the brain of the larval sea lamprey.

The descending spinal projecting system of the lamprey is of interest because it includes axons that activate swimming pattern generators and because regeneration of this system is involved in the behavioral recovery of lampreys following spinal transection. However, little is known about the true size of this projection and of the distribution of its terminations along the spinal cord. Brain neurons with spinal projections were studied in larval sea lampreys by using wholemount preparations labeled retrogradely with horseradish peroxidase (HRP) from spinal injections at 10%, 15%, 25%, 50%, 70%, and 75% of body length from the anterior end. Neurons projecting to different levels of the spinal cord were mapped. A large number of descending axons terminated within nine segments caudal to the last gill. The spinal projection system was divided into 10 bilateral groups based on cytoarchitectural landmarks. All of the lateral nuclear groups had contralateral spinal projections. In addition to the 12 pairs of Müller cells, the pair of Mauthner cells, and the pair of auxiliary Mauthner cells described by previous authors, the study revealed four pairs of smaller neurons that were individually identifiable.

Animals↗
PubMed1993

The organization of projections from the mediodorsal nucleus of the thalamus to orbital and medial prefrontal cortex in macaque monkeys.

The organization of interconnections between the mediodorsal nucleus of the thalamus (MD) and the orbital and medial prefrontal cortex and the agranular insular cortex in the monkey was studied by retrograde and anterograde tracing techniques. In addition to the magnocellular and parvicellular divisions of MD, three other subdivisions can be recognized on the basis of myeloarchitecture, cytoarchitecture, and connections. The first two of these represent a parcellation of the magnocellular division into a lateral, fiber-rich MD pars fibrosa and a medial, poorly myelinated MD pars paramediana adjacent to the midline. The third is a small, poorly myelinated area located at the caudomedial and dorsal edges of MD; it is referred to as MD pars caudodorsalis. MD pars fibrosa is reciprocally interconnected primarily with areas 11, 12 and 13 in the central and lateral part of the orbital cortex. There is a general organization within this projection, with the rostrocaudal axis of the cortex represented from dorsal to ventral in the pars fibrosa, and the mediolateral cortical axis represented from medial to lateral. Cells that project to area 12 also extend laterally into the adjacent pars parvicellularis. MD pars paramediana is more heavily interconnected with the caudal and medial portions of the orbital region, particularly the agranular insular areas and the caudal parts of areas 13 and 14. Cells that project to two caudal areas, 13a and Iad, do not fit with the general organization, in that they are located in the dorsomedial parts of the pars fibrosa and pars paramediana, where they overlap with cells that project to area 14. The pars fibrosa and pars paramediana receive inputs from areas of the ventral forebrain such as the amygdala, piriform (olfactory) cortex, and entorhinal cortex, which project directly to the orbital and agranular insular cortex, as well as from the ventral pallidum. MD pars caudodorsalis is reciprocally interconnected with areas 14, 24, and 32 on the medial surface of the prefrontal cortex. In this part of the nucleus the dorsoventral axis of the medial prefrontal cortex is represented from caudal to rostral in the thalamus. The amygdala and other ventral forebrain structures do not send fibers into the pars caudodorsalis, even though some of these structures project directly to the medial prefrontal cortex. Ventral to MD, and separated from it by the internal medullary lamina, a small region was recognized that appears to be comparable to the anteroventral part of the submedial nucleus previously defined in the rat and cat.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Survey of the morphology of macaque retinal ganglion cells that project to the pretectum, superior colliculus, and parvicellular laminae of the lateral geniculate nucleus.

In common with other vertebrates, the primate retina contains a number of different ganglion cell types that project to different regions in the brain. We wanted to determine how the different ganglion cell types, distinguished morphologically, mapped to these regions of the brain. We injected a fluorescent dye into one of three regions of a macaque brain: the superior colliculus (SC), the pretectal region, and the parvicellular laminae of the lateral geniculate nucleus. By means of an in vitro preparation, the retrogradely labelled ganglion cells were intracellularly injected with horseradish peroxidase, so as to reveal their dendritic morphology. When the dendritic-field diameters of the injected cells were plotted against retinal eccentricity, each of the three regions was found to receive input from a distinctive population of cells. The pretectal projection was dominated by cells with large dendritic fields. The SC projection was composed of a number of distinct types, with smaller dendritic fields. Parasol cells project to SC but are extremely rare. In addition to midget ganglion cells, the parvicellular laminae receive inputs from at least two additional groups. Parvicellular bistratified (PB) cells have bistratified dendritic fields, slightly larger than those of parasol cells. Parvicellular giant (PG) cells have dendritic-field diameters larger than that of any parasol cell, ranging from 250 microns to greater than 850 microns--the largest of any primate ganglion cells. In contrast to the retinal projections of the cat, in which a specific ganglion cell type can project to different regions of the brain, each of the regions in this survey appears to receive inputs from its own distinct group of ganglion cells.

Animals↗
PubMed1994

Projections of the dorsal raphe nucleus to the brainstem: PHA-L analysis in the rat.

Early studies that used older tracing techniques reported exceedingly few projections from the dorsal raphe nucleus (DR) to the brainstem. The present report examined DR projections to the brainstem by use of the anterograde anatomical tracer Phaseolus vulgaris leucoagglutinin (PHA-L). DR fibers were found to terminate relatively substantially in several structures of the midbrain, pons, and medulla. The following pontine and midbrain nuclei receive moderate to dense projections from the DR: pontomesencephalic central gray, mesencephalic reticular formation, pedunculopontine tegmental nucleus, medial and lateral parabrachial nuclei, nucleus pontis oralis, nucleus pontis caudalis, locus coeruleus, laterodorsal tegmental nucleus, and raphe nuclei, including the central linear nucleus, median raphe nucleus, and raphe pontis. The following nuclei of the medulla receive moderately dense projections from the DR: nucleus gigantocellularis, nucleus raphe magnus, nucleus raphe obscurus, facial nucleus, nucleus gigantocellularis-pars alpha, and the rostral ventrolateral medullary area. DR fibers project lightly to nucleus cuneiformis, nucleus prepositus hypoglossi, nucleus paragigantocellularis, nucleus reticularis ventralis, and hypoglossal nucleus. Some differences were observed in projections from rostral and caudal parts of the DR. The major difference was that fibers from the rostral DR distribute more widely and heavily than do those from the caudal DR to structures of the medulla, including raphe magnus and obscurus, nucleus gigantocellularis-pars alpha, nucleus paragigantocellularis, facial nucleus, and the rostral ventrolateral medullary area. A role for the dorsal raphe nucleus in several brainstem controlled functions is discussed, including REM sleep and its events, nociception, and sensory motor control.

Animals↗
PubMed1994

Direct projections from the non-laminated divisions of the medial geniculate nucleus to the temporal polar cortex and amygdala in the cat.

The medial geniculate nucleus (MG) is well known to send projection fibers not only to the auditory cortex, but also to the limbic structures of the forebrain including the perirhinal cortex and amygdala. In the cat, the non-laminated portions of the MG are also known to project to the amygdala, as well as to the auditory cortical areas surrounding the primary auditory area. On the other hand, projections from the non-laminated MG to the limbic cortical areas have not so far been studied systematically. Thus, in the present study, direct projections from the non-laminated portions of the medial geniculate nucleus to the temporal polar cortex and amygdala were examined in the cat by retrograde and anterograde tract-tracing techniques. The temporal polar cortex is the ventral polar region of the posterior sylvian and posterior ectosylvian gyri, which is located dorsal to the posterior rhinal sulcus and includes the ectorhinal area. After injection of cholera toxin B subunit into the temporal polar cortex, retrogradely labeled neurons were seen in the caudal two-thirds of the medial geniculate nucleus ipsilateral to the injection; they were distributed in the non-laminated portions of the MG (the dorsal and medial divisions and the ventromedial part of the ventral division), but not in the laminated portion (the principal part of the ventral division). These findings were confirmed by injecting Phaseolus vulgaris leucoagglutinin into each division of the MG. After the injection into each non-laminated division, terminal labeling was observed in the temporal polar cortex. Terminal labeling was further found in the lateral amygdaloid nucleus ipsilateral to the injection. Then, cholera toxin B subunit was injected into the lateral amygdaloid nucleus; retrogradely labeled neurons were observed ipsilaterally in the non-laminated portions of the MG, as well as in the temporal polar cortex. The results indicate that the non-laminated portions of the MG send projection fibers to the temporal polar cortex and lateral amygdaloid nucleus, and that the non-laminated portions of the MG and temporal polar cortex give rise to overlapping projections to the lateral amygdaloid nucleus. These connections appear to constitute neuronal links in "emotional" and/or "motivational" circuitry in the forebrain.

Amygdala↗
PubMed1994

Direct projections from the ventrolateral medulla oblongata to the limbic forebrain: anterograde and retrograde tract-tracing studies in the rat.

Neurons in the ventrolateral medulla oblongata, a brain region implicated in central vasomotor regulation, have previously been reported to project to some forebrain limbic structures. The aim of the present study was (1) to describe the termination pattern of ventral medullary afferents in forebrain limbic areas using anterograde tract tracing, and (2) to determine the location and some morphological characteristics of the projection neurons using retrograde tract tracing from selected forebrain sites. Following ionophoretic microinjections of the anterograde tract tracer Phaseolus vulgaris leucoagglutinin into the rostral ventrolateral medulla, labelled afferents were observed in the hippocampus, entorhinal and retrosplenial cortices, dorsal septum, nucleus accumbens, and the medial prefrontal cortex. Anterogradely labelled axons, ascending from the caudal ventrolateral medulla, could be traced only to the rostral aspects of the investigated forebrain limbic structures. Here, the main target of the ascending projection was in the ventral septum. However, labelled terminals were also present in the nucleus accumbens, the dorsolateral septum, and in the infralimbic cortex. The density of the ventrolateral medullary projections into all examined forebrain areas was low. The location of the cells in the ventral medulla oblongata which give rise to direct forebrain projections was examined using retrograde tract tracing with wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP). Following WGA-HRP injections into the septo-accumbens region, retrogradely labelled cells were present in both the rostral and caudal ventrolateral medulla. When the tract tracer injection was restricted to the ventral region of the septal complex, the labelled cells were concentrated in the caudal aspects of the ventrolateral medulla (and the nucleus of the solitary tract). Following tracer injections into the anterior cingulate cortex or the hippocampus or the entorhinal cortex, retrogradely labelled cells in the medulla oblongata were predominantly in the rostral ventrolateral medulla. As a first attempt to reveal the chemical nature of the projection cells, the contribution of tyrosine hydroxylase-immunoreactive cells to the innervation of the septo-accumbens area was also investigated: tyrosine hydroxylase-immunoreactive cells of both the caudal ventrolateral medulla and the nucleus of the solitary tract were found to contribute to the innervation of the septo-accumbens area. The distribution of retrogradely labelled cells as well as the termination pattern of the anterogradely labelled terminals indicated that the innervation of the various forebrain limbic areas arises from cells, diffusely distributed in the rostral and/or the caudal ventrolateral medulla oblongata.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Projections of physiologically defined subdivisions of the inferior colliculus in the mustached bat: targets in the medial geniculate body and extrathalamic nuclei.

This study examined the output of the central nucleus of the inferior colliculus to the medial geniculate body and other parts of the nervous system in the mustached bat (Pteronotus parnellii). Small deposits of anterograde tracers (horseradish peroxidase, [3H]leucine, Phaseolus vulgaris leucoagglutinin, wheat germ agglutinin conjugated to horseradish peroxidase, or biocytin) were made at physiologically defined sites in the central nucleus representing major components of the bat's echolocation signal. The topography, frequency specificity, and axonal morphology of these outputs were studied. The medial geniculate body was a major target of inferior collicular neurons, with three distinct input patterns. The projection to the ventral division was tonotopically organized, but had a relatively sparse contribution from neurons representing frequency modulated components of the biosonar pulse. The second input was to the rostral medial geniculate body, in which projections from inferior collicular neurons representing constant frequency sonar components were separated from those representing frequency modulated components. A third input was to the suprageniculate nucleus, which received strong, topographically arranged projections. Inputs to the dorsal nucleus and medial division were also observed. Extrathalamic regions receiving input included the pontine gray, external nucleus of the inferior colliculus, pericollicular tegmentum, nucleus of the brachium of the inferior colliculus, and pretectum. These central nucleus projections differed in organization and the structure of axon terminals, suggesting different physiological influences on their target nuclei. These results demonstrate that the central nucleus has divergent projections to various sensory and premotor nuclei, besides its well-established projection to the medial geniculate body.

Acoustic Stimulation↗
PubMed1994

Projections of individual Purkinje cells of identified zones in the ventral nodulus to the vestibular and cerebellar nuclei in the rabbit.

The projections of Purkinje cells from zones in the ventral nodulus of pigmented rabbits were studied with the use of extracellularly injected biocytin as an anterograde tracer. The zones were physiologically identified according to the complex spike modulation of Purkinje cells in response to optokinetic stimulation. Purkinje cells in the most medial zone do not respond to optokinetic stimulation; they project to the fastigial nucleus, the perifastigial white matter, the periinterposed white matter, and the medial vestibular nucleus. In the adjacent zone, Purkinje cells respond best to optokinetic stimulation about the vertical axis; they project to the periinterposed white matter and the medial vestibular nucleus. Purkinje cells in the next zone respond best to optokinetic stimulation about an axis approximately perpendicular to the ipsilateral anterior canal; they project to the periinterposed white matter, dorsal group y, the superior vestibular nucleus, and the medial vestibular nucleus. In the most lateral zone, Purkinje cells respond best to optokinetic stimulation about the vertical axis; they project to the periinterposed white matter, dorsal group y, and the medial vestibular nucleus. The majority of axons gave off collaterals and innervated more than one nucleus. Often, three or four different areas received terminals from a single Purkinje cell axon. The zonal projection pattern of the ventral nodulus is compared to that of the flocculus, which, with respect to the visual climbing fiber afferents, has similar zones.

Animals↗
PubMed1994

Serotoninergic and nonserotoninergic neurons in the medullary raphe system have axon collateral projections to autonomic and somatic cell groups in the medulla and spinal cord.

Fluorescent double retrograde-tracing studies combined with fluorescent immunostaining for serotonin were carried out to determine the potential patterns of divergence in axonal projections to autonomic and somatic motor sites from medullary raphe and parapyramidal neurons. Injections (20-60 nl) of combinations of fluorescent retrograde tracers (Fast Blue, fluoro-gold, green latex microspheres, Diamidino Yellow) were made into the intermediolateral cell column (IML) of the spinal cord and the brainstem lateral tegmental field or ventral horn of the lumbar spinal cord of male Wistar rats. The animals were perfused after a 7-10-day survival period, and the brains were removed, sectioned (50 microns), and immunostained for serotonin. Following injections of different retrograde-tracer substances into the IML of the thoracic cord and the ventral horn of the lumbar cord, 36% of the neurons with axon collateral projections to the IML and the lumbar ventral horn were serotoninergic. Following injections of different retrograde-tracer substances into the IML and the lateral tegmental field, 26% of the neurons with axon collateral projections to the IML and the lateral tegmental field were serotoninergic. Many of the medullary neurons with projections to the lateral tegmental field and the lumbar cord were located dorsal and lateral to those neurons with projections to the IML. The results indicate that serotoninergic and nonserotoninergic neurons of the midline raphe system and parapyramidal region have axon collateral branches to the IML and the lateral tegmental field or the IML and the lumbar ventral horn. These projection neurons may form the anatomical substrate for the integration of autonomic and somatic motor activity.

Amidines↗
PubMed1995

Intrinsic connections of the rat amygdaloid complex: projections originating in the lateral nucleus.

The amygdaloid complex receives sensory information from a variety of sources. A widely held view is that the amygdaloid complex utilizes this information to orchestrate appropriate species-specific behaviors to ongoing experiences. Relatively little is known, however, about the circuitry through which information is processed within the amygdaloid complex. The lateral nucleus is the major recipient of extrinsic sensory information and is the origin of many intra-amygdaloid projections. In this study, we reinvestigated the organization of intra-amygdaloid projections originating from the lateral nucleus using the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). The lateral nucleus has highly organized intranuclear connections. Dense projections interconnect rostral and caudal levels of the lateral and the medial divisions of the nucleus, and the lateral and medial divisions of the lateral nucleus are also interconnected. The major extranuclear projections of the lateral nucleus are (in descending order of magnitude) to the accessory basal nucleus, the basal nucleus, the periamygdaloid cortex, the dorsal portion of the central division of the medial nucleus, the posterior cortical nucleus, the capsular division of the central nucleus, and the lateral division of the amygdalohippocampal area. The pattern of extranuclear projections varied depending on the rostrocaudal or mediolateral location of the injection site within the lateral nucleus. These findings indicate that intra-amygdaloid projections originating in the lateral nucleus are both more widespread and more topographically organized than was previously appreciated.

Amygdala↗