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PubMed1995

Development of ventral cochlear nucleus projections to the superior olivary complex in gerbil.

The postnatal development of the projection from the ventral cochlear nucleus to the principal nuclei in the superior olivary complex in gerbil (Meriones unguiculatus) was studied in an age-graded series of pups ranging from 0 to 18 days old. Small crystals of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) were inserted into the ventral cochlear nucleus of aldehyde-fixed brains, and the labeled projections were examined with epifluorescence microscopy. Selected sections were photooxidized in a solution of diaminobenzidine and subsequently processed for electron microscopy to examine the development of labeled synapses in the target nuclei. Horseradish peroxidase was injected into the ventral cochlear nucleus of adult gerbils to assess the form and persistence of projections observed in the neonatal animals. In addition, electrophysiological responses to acoustic stimuli of single units in the adult auditory brainstem were analyzed to confirm the functionality of the novel projection from the ventral cochlear nucleus to the contralateral lateral superior olive. By the day of birth (P0), developing axons from the ventral cochlear nucleus have already established highly ordered pathways to the three primary nuclei of the superior olivary complex: the ipsilateral lateral superior olive, the contralateral medial nucleus of the trapezoid body, and at the lateral and medial dendrites of the ipsilateral and contralateral medial superior olive, respectively. Developing axons from the ventral cochlear nucleus that innervated the contralateral medial nucleus of the trapezoid body lacked the terminal morphology characteristic of the calyx of Held, but began to adopt a more characteristic form on P5. The mature calyx appeared around P14-16. Exuberant developmental projections to topographically inappropriate areas of the superior olivary complex were not observed at the postnatal ages studied. In addition to the projections of the ventral cochlear nucleus to the superior olivary complex described in other species, we observed the development and maintenance of a major direct projection from the ventral cochlear nucleus to the contralateral lateral superior olive. On P0, ventral cochlear nucleus axons decussate in the dorsal trapezoid body, form a plexus at the dorsal edge of the contralateral medial superior olive, and enter the ventrolateral limb of the contralateral lateral superior olive. Over the next 2 weeks, fascicles of fibers form on the hilar and ventral aspects of the ventrolateral limb. Fibers arising from these fascicles form converging, but nonoverlapping, arborizations within the ventrolateral limb at right angles to the curvature of the nucleus. The medial region was devoid of labeled axons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Genetic control of retinal projections in inbred strains of albino mice.

Mutations in the tyrosinase gene are often associated with a misrouting of retinal ganglion cell axons at the optic chiasm. In albinos, tyrosinase activity is lost and some ganglion cell axons that would normally project into the ipsilateral optic tract instead cross midline and project into the contralateral tract. The developmental mechanisms that cause this modification in neuronal connectivity are unknown. In this study, we screened six diverse strains of albino mice (strains 129, A, AKR, BALB/c, C57BL/6-c/c, and CD-1) to discover genetically determined variations and possible gene loci that might affect the severity of the albino decussation abnormality. Ganglion cells were retrogradely labeled with horseradish peroxidase, and the ipsilaterally and contralaterally projecting cells were counted. The average number of ipsilaterally projecting ganglion cells in the six albino strains varies from 1,000 to 1,300. Despite this variation, 1.8-1.9% of the total population projects ipsilaterally in each strain. In comparison, 2.8% project ipsilaterally in the pigmented strain, C57BL/6(-)+/+. However, the percentage of displaced, ipsilaterally projecting cells varies substantially among albino strains--from a low of 4% in strain CD-1 to a high of nearly 10% in C57BL/6-c/c. We conclude that even with large differences in genetic background and in absolute numbers of ganglion cells, there is no appreciable variation in the magnitude of decussation error among albino mice. The consistent effect of null alleles at tyrosinase suggests a comparably tight linkage between the biochemical activity of this enzyme and the mechanisms that control decussation phenotype.

Alleles↗
PubMed1995

Direct projections from the dorsolateral pontine tegmentum to pudendal motoneurons innervating the external urethral sphincter muscle in the rat.

Direct projections from the dorsolateral pontine tegmentum to pudendal motoneurons innervating the external urethral sphincter and the external and sphincter muscles were examined in the rat by the tract-tracing methods utilizing retrograde transport of cholera toxin B subunit and anterograde transport of biotinylated dextran amine. The dorsolateral pontine tegmental region, corresponding to the micturition reflex center of Barrington, was confirmed to send bilaterally, with an ipsilateral dominance, projection fibers to the spinal parasympathetic nucleus (inferior intermediolateral nucleus). The micturition reflex center of Barrington, however, did not seem to send many projection fibers to the ventral horn of the lumbosacral cord segments, whereas the region immediately ventral to the micturition reflex center of Barrington was found to send bilaterally, with a contralateral dominance, projection fibers to the dorsolateral group of pudendal motoneurons in both the male and female rats. In the female rat, the dorsolateral group of pudendal motoneurons are comprised primarily of motoneurons that innervate the external urethral sphincter muscle. The dorsomedial group of pudendal motoneurons, which contain motoneurons that innervate the external and sphincter and the bulbocavernosus muscles, did not seem to receive major projections from the dorsolateral pontine tegmental regions. It was also observed that the locus coeruleus sent some projection fibers bilaterally to the spinal parasympathetic nucleus but only a few to the ventral horn of the lumbosacral cord segments. Thus, the present results indicate that the dorsolateral group of pudendal motoneurons containing those innervating the external urethral sphincter muscle receive pontospinal projection fibers mainly from the dorsolateral pontine tegmental region immediately ventral to the micturition reflex center of Barrington.

Anal Canal↗
PubMed1995

Morphology of thalamocortical neurons projecting to the primary somatosensory cortex and their relationship to spinothalamic terminals in the squirrel monkey.

This study examined the morphology of thalamocortical neurons projecting to the primary somatosensory cortex (SI; hand region of areas 3a, 3b, 1, and 2) and their relationship to the spinothalamic (STT) terminals in the squirrel monkey. Retrogradely labeled thalamocortical neurons were intracellularly filled with Lucifer yellow (LY), and the STT terminals were anterogradely labeled with biotinylated dextran. Both filled neurons and labeled terminals were differentially visualized in the same field by a dual immunocytochemical staining method. SI-projecting neurons appeared at the light level to be in contact with STT terminal boutons in the ventroposterior lateral (VPL), ventroposterior inferior (VPI), and centrolateral (CL) nuclei and the posterior complex (PO). The analyses of the neuronal morphology revealed that somatic and dendritic morphologies of SI-projecting neurons in these thalamic nuclei, as well as in the anterior pulvinlar (Pulo), centromedial (CM), and ventrolateral (VL) nuclei, were generally comparable with some exceptions: VL neurons had the largest soma sizes, the most primary dendrites, and the longest total dendritic length among all neurons studied; VPI neurons had the smallest soma sizes; VPL SI-projecting neurons were different from those in VPI in their soma sizes, shape factors, and orientations; in VPL the cells projecting to the superficial layers of SI were smaller than those projecting to the deeper layers, but in VPI the two groups of neurons were similar in soma sizes. In general, the SI-projecting neurons in VPL, VPI, and CL were similar in their dendritic morphologies and branching patterns, and varied from those in Pulo, PO, CM, and VL.

Animals↗
PubMed1995

Morphology and connections of neurons in area 17 projecting to the extrastriate areas MT and 19DM and to the superior colliculus in the monkey Callithrix jacchus.

Neurons of area 17, the primary visual cortex, project to various anatomically and physiologically different extrastriate areas and subcortical regions. In the present investigation, we addressed the question of whether the efferent neurons in area 17 can contribute to functional diversity between these regions. We approached this question by analyzing the dendritic morphology of neurons in area 17 projecting to area MT, area 19DM, and the superior colliculus in the new world simian primate Callithrix jacchus, because dendritic morphology is an important factor in determining physiological properties of nerve cells. Retrograde transport of fluorochromes injected into the target regions, and intracellular injections of Lucifer yellow in the prelabelled neurons, revealed the following. 1) Morphologically identical large pyramidal cells in layer VI of area 17 project to all three targets. Some of them possess axon collaterals to two or all three targets, suggesting that they provide common information to all three areas. 2) Pyramidal cells in layer IIIc projecting to area MT form a morphologically homogeneous population. 3) Three small to medium-sized pyramidal cell types in layers IIIa-c, spiny stellate cells in layer IIIc, and another large pyramidal cell type in layer VI project to area 19DM. 4) Pyramidal cells in the lower two-thirds of layer V in area 17 project to the superior colliculus. In conclusion, we have shown that in Callithrix one efferent pathway may originate from several cell types. However, with the exception of the large cells in layer VI, efferent cells projecting to area MT, area 19DM, and the superior colliculus were morphologically distinct. This suggests that functional differences between brain regions could arise in part from morphological heterogeneity between and within the efferent cell populations.

Animals↗
PubMed1988

Afferent projections of the trigeminal nerve in the goldfish, Carassius auratus.

The horseradish peroxidase (HRP) histochemical technique was used to examine the peripheral distribution and afferent projections of the trigeminal nerve in the goldfish, Carassius auratus. Sensory fibers of the trigeminal nerve distribute over the head via four branches. The ophthalmic branch distributes fibers to the region above the eye and naris. The maxillary and mandibular branches innervate the regions of the upper and lower lip, respectively. A fourth branch of the trigeminal nerve was demonstrated to be present in the hyomandibular trunk. Upon entering the medulla the trigeminal afferent fibers divide into a rostromedially directed bundle and a caudally directed bundle. The rostromedially directed bundle terminates in the sensory trigeminal nucleus (STN) located within the rostral medulla. The majority of fibers turn caudally, forming the descending trigeminal tract. Fibers of the descending trigeminal tract terminate within three medullary nuclei: the nucleus of the descending trigeminal tract (NDTV), the spinal trigeminal nucleus (Spv), and the medial funicular nucleus (MFn). All projections, except for those to the MFn, are ipsilateral. Contralateral projections were observed at the level of the MFn following the labeling of the ophthalmic and maxillomandibular branches. All branches of the trigeminal nerve project to all four of the trigeminal medullary nuclei. Projections to the STN and MFn were found to be topographically organized such that the afferents of the ophthalmic branch project onto the ventral portion of these nuclei, while the afferents of the maxillo- and hyomandibular branches project to the dorsal portion of these nuclei. Cells of the mesencephalic trigeminal nucleus were retrogradely labeled following HRP application to the ophthalmic, maxillary, and mandibular branches of the trigeminal nerve. In addition to demonstrating the ascending mesencephalic trigeminal root fibers, HRP application to the above-mentioned branches also revealed descending mesencephalic trigeminal fibers. The descending mesencephalic trigeminal fibers course caudally medial to the branchiomeric motor column and terminate in the ventromedial portion of the MFn.

Animals↗
PubMedDate not supplied

Papillary projections in ovarian neoplasms: appearance on MRI.

Papillary projections are distinctive pathologic features of epithelial ovarian neoplasms. We sought to determine whether these structures have recognizable features on MRI. A search of a database of 125 patients on whom MRI was performed with pelvic phased-array coil and abdominal surgical exploration was performed for suspected gynecologic disease identified 15 patients who had either MRI reports or pathology reports mentioning papillary projections in an adnexal mass. The MR images were reviewed to characterize the size, structure, and signal intensity of papillary projections. Pathologic correlation was performed on these and on four surgical specimens imaged with high resolution technique. Pathologic correlation showed that larger papillary projections had a distinctive structure of a fibrous stalk supporting clumps of edematous papillae with signal intensity similar to that of fluid on T2-weighted images. Smaller papillae showed nondescript intracystic projections of intermediate signal intensity on T2-weighted images. All papillary projections in vivo enhanced after injection of gadopentetate dimeglumine. Papillary projections have an appearance on MRI that reflects their histologic structure.

Adnexa Uteri↗
PubMedDate not supplied

Projection-neurons that send axons through the lumbar spinal cord of the chick embryo are not obviously distributed in a segmentally repetitive pattern.

Earlier studies have shown that the formation of the segmentally repetitive pattern of spinal nerves in avian embryos depends upon the segmental arrangement of the somites and does not reflect an intrinsic pattern of the spinal cord. These studies could not, however, rule out the possibility that some elements of the central nervous system are intrinsically segmented. The question remained, for instance, whether projection-neurons are distributed in a segmentally repetitive pattern within the spinal cord. To address this question, horseradish peroxidase was injected into one or two segments of the lumbar spinal cord of chick embryos, thereby labeling projection-neurons that had ascending or descending axons passing through the injection site. In all stages examined, the number of labeled projection-neurons in the anterior and posterior halves of each segment did not differ significantly. In addition, segmentally repetitive peaks or troughs in the numbers of labeled projection-neurons were not detected in the center of each segment. Three subpopulations of projection-neurons, defined by their position along the dorsal-ventral axis of the spinal cord, were also not segmentally distributed by these criteria. While these results do not rule out the possibility that subpopulations of projection-neurons defined by dendritic morphology, functional class, or some other parameter are segmentally arranged or that there is a basic modular repetition of neural populations from segment to segment, they do show that projection-neurons as a class and subpopulations of these neurons defined by their dorsal-ventral position are not obviously distributed in a repetitive segmental pattern.

Animals↗
PubMed1991

Fast Fourier projection for MR angiography.

We have developed a technique called fast Fourier projection which rapidly produces projections through images and is particularly useful for generating MR angiograms. Based on the projection-slice theorem of Fourier transform theory, this method extracts planes from three-dimensional spatial frequency space and computes projections at arbitrary viewing angles by two-dimensional inverse Fourier transformation. Typical computation times are on the order of 1 s per projection. This performance makes possible interactive selection of optimal projection directions for visualizing the desired vasculature in single or stereo-pair angiographic images and drastically reduces the time required to generate sequences of projections for display in movie loops compared to the conventional ray-casting approach. The method is easily implemented on off-line workstations or directly on MRI computer systems.

Angiography↗
PubMed1986

Control of the development of the ipsilateral retinothalamic projection in Xenopus laevis by thyroxine: results and speculation.

The ipsilateral retinothalamic projection of the frog Xenopus laevis is formed by the axons of a subset of retinal ganglion cells which are found throughout peripheral and non-nasodorsal retina. Unlike the crossed retinotectal and retinothalamic projections, which begin to form during early embryonic stages, the ipsilateral projection does not begin to develop until late in tadpole life, at stages when thyroxine first becomes detectable in the circulation. Blocking the production of thyroid hormone in tadpoles prevents the development of the ipsilateral projection, in a reversible manner. Intraocular injection of thyroxine can "rescue" the development of the projection in tadpoles which otherwise remain premetamorphic. In addition, the projection from one eye of a metamorphically-blocked tadpole can be induced to form by an intraocular injection of thyroxine at a dose which has no detectable effect on retinal development in the other, untreated eye. These results indicate that the development of the ipsilateral retinothalamic projection is dependent upon thyroxine, and strongly suggest that the hormone acts at the level of the eye, rather than at the optic chiasm or thalamic target, to bring about the development of a new pathway. A number of ways in which thyroxine might act in the system are discussed.

Animals↗
PubMed1996

Embryonic neurons transplanted to regions of targeted photolytic cell death in adult mouse somatosensory cortex re-form specific callosal projections.

In the neocortex, the effectiveness of potential transplantation therapy for diseases involving neuronal loss may depend upon whether donor neurons can reestablish the precise long-distance projections that form the basis of sensory, motor, and cognitive function. During corticogenesis, the formation of these connections is affected by tropic factors, extracellular matrix, structural pathways, and developmental cell death. Previous studies demonstrated that embryonic neurons and multipotent neural precursors transplanted into neocortex or mice undergoing photolytically induced, synchronous, apoptotic neuronal degeneration selectively migrate into these regions, where they differentiate into pyramidal neurons and accept afferent synaptic input. The experiments presented here assess whether embryonic neurons transplanted into regions of somatosensory cortex undergoing targeted cell death differentiate further and develop long-distance axons and whether this outgrowth is target specific. Neocortical neurons from Gestational Day 17 mouse embryos were dissociated, prelabeled with fluorescent nanospheres and a lipophilic dye (DiI or PKH), and transplanted into adult mouse primary somatosensory cortex (S1) undergoing apoptotic degeneration of callosal projection neurons. Donor neurons selectively migrated into and differentiated within regions of targeted neuronal death in lamina II/III over a 2-week period, in agreement with our prior studies. To detect possible projections made by donor neurons 2, 4, 6, 8, or 10 weeks following transplantation, the retrogradely transported dye fluorogold (FG) was stereotaxically injected into contralateral S1, ipsilateral secondary somatosensory cortex (S2), or ipsilateral thalamus. Ten weeks following transplantation, 21 +/- 5% of the labeled donor neurons were labeled by FG injections into contralateral S1, demonstrating that donor neurons sent projections to the distant area, the original target of host neurons undergoing photolytically induced cell death. No donor neurons were labeled with FG injections into ipsilateral S2 or thalamus, nearby targets of other subpopulations of neurons in S1. These data indicate that in the adult neocortex: (1) transplanted immature neurons are capable of extending long-distance projections between hemispheres through the mature white matter of the corpus callosum and (2) these projections are formed with specificity to replace projections by neurons undergoing synchronous degeneration. These experiments provide an experimental system with which to test factors affecting such outgrowth and connectivity. Taken together, these results suggest that the reconstruction and repair of cortical circuitry responsible for sensory, motor, or cognitive function may be possible in the mature neocortex, if donor neurons or precursor cells are provided with the correct combination of local and distant signals within an appropriately permissive host environment.

Age Factors↗
PubMed1999

Fast and accurate three-dimensional reconstruction from projections with random orientations via radon transforms

A new algorithm for three-dimensional reconstruction from randomly oriented projections has been developed. The algorithm recovers the 3D Radon transform from the 2D Radon transforms (sinograms) of the projections. The structure in direct space is obtained by an inversion of the 3D Radon transform. The mathematical properties of the Radon transform are exploited to design a special filter that can be used to correct inconsistencies in a data set and to fill the gaps in the Radon transform that originate from missing projections. Several versions of the algorithm have been implemented, with and without a filter and with different interpolation methods for merging the sinograms into the 3D Radon transform. The algorithms have been tested on analytical phantoms and experimental data and have been compared with a weighted back projection algorithm (WBP). A quantitative analysis of phantoms reconstructed from noise-free and noise-corrupted projections shows that the new algorithms are more accurate than WBP when the number of projections is small. Experimental structures obtained by the new methods are strictly comparable to those obtained by WBP. Moreover, the algorithm is more than 10 times faster than WPB when applied to a data set of 1000-5000 projections. Copyright 1999 Academic Press.

Journal Article↗
PubMed1990

Morphological evidence for callosally projecting nonpyramidal neurons in rat visual cortex.

This investigation shows that some of the callosally projecting neurons in rat visual cortex are nonpyramidal cells. Callosally projecting neurons were labeled by injections of horseradish peroxidase (HRP) into the area 17/18a border zone of the contralateral hemisphere. The retrogradely transported HRP was visualized with diaminobenzidine or with tetramethylbenzidine. In some of the labeled neurons the reaction product was diffuse, so that the neurons had a Golgi-like appearance, but in others the reaction product was granular, or punctate. The majority of neurons with a Golgi-like appearance were pyramidal cells, but one callosally projecting neuron from layer V area 18a was confirmed by electron microscopy to be a nonpyramidal neuron. This dearth of well-filled nonpyramidal cells suggested that callosally projecting nonpyramidal neurons may not transport sufficient HRP to show Golgi-like filling, and so punctately labeled neurons from areas 17, 18a and 18b were examined. Reacted sections from areas 17, 18a and 18b of control animals, into which no tracer had been injected, were also examined, but in these control preparations no granules similar to the HRP granules within the neuronal profiles of the experimental animals were encountered. In methylene blue-stained 1-microns sections, neuronal profiles from the control animals possessed only blue staining lysosomes, while neuronal profiles from the experimental animals exhibited both lysosomes and HRP granules. It was determined, from the counts of HRP granules in neurons from the experimental animals, that in selected regions of areas 17, 18a, and 18b similar percentages of the pyramidal and nonpyramidal neuronal populations (ranging from 100% to 34%) contained HRP granules, and so had callosally projecting axons. However, most callosally projecting nonpyramidal neurons had far fewer HRP granules than the pyramidal neurons, again indicating that they transport less HRP. This could account for the fact that callosally projecting nonpyramidal neurons only rarely show a Golgi-like filling, and this could be one reason why such cells have been overlooked in most previous studies.

Animals↗
PubMed1986

Ultrastructure of capitate projections in the optic neuropil of Diptera.

Photoreceptor axons in the first optic neuropil of the dipteran flies Musca domestica and Drosophila melanogaster was examined with electron microscopy. The objective was to determine ultrastructure, persistence and glial source of the capitate projections found within these neurons. Capitate projections are simple or compound processes of epithelial glial cells which profusely insert into form-fitting folds of axon terminals of the peripheral retinular cells (R1-6) in the synaptic plexus portion of the first optic neuropil. These neuro-glial junctions may be simple indentations, have a head with a single stalk, or possess a single, circular stalk from which 3 or 4 bulbous (glial) heads are elaborated. Using serial thick sections of Drosophila neuropil for HVEM we were able to observe that the stalks connecting nearly all capitate projections led directly to a glial cell. Thus no disembodied heads were found suspended in axoplasm. Capitate projections appeared to be persistent structures, present in young as well as senescent adults. No evolution of form was found; thus 3 distinct expressions of these glial processes (without transitional forms) are present. From freeze-fracture replicas and serial HVEM sections it was determined that there were approximately 3 capitate projections per micron 2 in Drosophila and Musca, respectively. About 800 capitate projections exist per Musca axon terminal or about 5 times the number of chemical synapses. Cp's were slightly larger in Drosophila than in Musca, although the Musca retinular axon has twice the diameter and length of that of the fruit fly. The evidence was reviewed in light of the likely supportive function of capitate projections on the R1-6 terminals.

Animals↗
PubMed1976

A critical evaluation of the relationship between the presynaptic network, synaptic vesicles and dense projections in central synapses.

Synapses of the oculomotor nucleus of Echidna have been examined ultrastructurally with the aim of integrating data obtained from osmicated and nonosmicated PTA stained material. Particular emphasis has been laid on the relationship between the synaptic vesicles of the osmicated material and the presynaptic network and vesicular grid of the PTA material. This relationship has been explored qualitatively by examining osmicated material of varying qualities of fixation. Such material contains dense projections in addition to synaptic vesicles, and various vesicular network appearances. A variety of measurement techniques have shown that the PTA network is characterised by reticular strands, spaces, and regular hexagonal units smaller than vesicles, these observations prompting the formulation of a "vesicle-network coincidence" model of the presynaptic terminal. This model has been tested by tracing the profiles of vesicles within the PTA network and comparing their size and shape frequency distributions with those of osmicated synaptic vesicles. The distributions have been found to be essentially similar, suggesting that vesicles can be located within the network, and that the hexagonal network units are formed only in the presence of an underlying vesicular matrix. Additionally, the following points have emerged: 1) the dense projections in the two types of material appear to be quivalent; 2) a loose correlation exists between dense projections and vesicles in osmicated terminals, increase in the area of the dense projections being associated with a decrease in the area of the vesicles; 3) network and dense projection units are similar. In view of the similarity between network and dense projection units, the demonstrated vesicular basis of the network raises the question of whether dense projections are entirely independent structures, or whether they depend in part for their existence on the nearby presence of synaptic vesicles.

Animals↗
PubMed1996

The projections of the retrorubral field A8 to the hippocampal formation in the rat.

The dopaminergic neurons in the midbrain of the rat are located in three groups: the ventral tegmental area (VTA-A10), substantia nigra (SN-A9), and retrorubral field (RRF-A8). We have recently examined the organization of the projections from the VTA and the SN to the hippocampal formation (HF) in the rat. In the present study we characterize the projections of the RRF to the HF by using anterograde tracing, retrograde tracers, and tyrosine hydroxylase (TH) immunohistochemistry. Following iontophoretical injections of Phaseolous vulgaris leucoagglutinin (PHA-L) into the RRF, anterograde labeling was observed primarily in the ipsilateral subiculum and adjacent CA1 cell field. Sparse labeling was also observed in the CA3 cell field and dentate gyrus. The distribution of RRF neurons projecting to the HF was examined by injecting retrograde fluorescent tracers (fluorogold, fast blue, and nuclear yellow) into several hippocampal areas. The retrograde tracer findings indicate that the medial aspects of the RRF project to the subiculum and adjacent CA1 cell field of both the septal and temporal HF. In order to evaluate the percentage of dopaminergic cells of the RRF projecting to the HF, the retrograde neuronal tracer fluorogold was used in combination with TH immunohistochemistry. The quantitative evaluation of retrograde labeled and TH-immunoreactive (IR) cells showed that RRF projections to the HF are partially (10-18%) dopaminergic. The findings suggest that the general pattern of distribution and organization of the RRF-A8 projections to the HF is similar to that observed in our previous studies examining hippocampal afferents from the VTA and SN. The data also suggest a crude topographical organization of RRF afferents to the HF and a more prominent input to the temporal than to the septal HF.

Amidines↗
PubMed1991

Nigrotectal projections in the primate Galago crassicaudatus.

The pattern of the nigrotectal projection in Galago crassicaudatus was determined using retrograde and anterograde transport methods. These experiments revealed that pars reticulata and pars lateralis of the substantia nigra project to all layers of the ipsilateral and contralateral superior colliculus, except to layer I. The nigrotectal projection is not homogeneous, but is concentrated in particular collicular layers and sublayers, and the intensity and laminar distribution of the projection varies along the rostral-caudal dimension of the superior colliculus. The ipsilateral and contralateral nigrotectal projections are generally similar, except that a tier of dense label which is prominent in the ventral part of much of the ipsilateral layer IV is not obvious contralaterally; moreover, the contralateral projection is much sparser than the ipsilateral. Deposits of tracers at different medial-lateral locations within the substantia nigra did not result in different laminar patterns of anterogradely transported label in the superior colliculus. Based on the known connections and functions of the collicular layers and sublayers, the pattern and distribution of the nigrotectal projection suggests that the substantia nigra may use this pathway to gain access to particular components of vision- and visuomotor-related networks.

Afferent Pathways↗
PubMed1984

An autoradiographic study of topographical relationships between pallidal and cerebellar projections to the cat thalamus.

Injections of 3H-leucine were made in the entopeduncular nucleus or dentate nucleus of the cerebellum in eight cats. The terminal projection zones of both pathways in the thalamus were studied using the sagittal plane and their relationships to one another as well as to cytoarchitectural boundaries of thalamic nuclei were compared. The data indicate that the territories controlled by the two projection systems are almost entirely segregated. The segregation is mainly along the antero-posterior axis as the main pallidal projection zone occupies the medio-ventral VA while the main dentate projection zone lies posterior to it in the VL. Furthermore, the dorsolateral part of the VA not occupied by pallidal projections receives dentate projections. In the VM, both afferent systems terminate in the lateral part of the nucleus with pallidal territory located anteriorly and dentate territory located posteriorly, again without overlap. As the delineations of nuclear subdivisions in the ventral thalamus of the cat have been a subject of some controversy, it is suggested that the boundaries of the VA, VL and VM in the cat thalamus be defined on the basis of basal ganglia and cerebellar projection zones.

Afferent Pathways↗