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PubMed1993

Individual corticorubral neurons project bilaterally during postnatal development and following early contralateral cortical lesions.

The corticorubral projections in adult cats are primarily uncrossed. However, early in development and after early unilateral lesions of the sensorimotor cortex, crossed corticorubral projections are also observed. The present study was performed to disclose (1) whether the crossed projections originate from neuronal subpopulations different from those producing uncrossed ones and (2) how the neurons that give rise to the crossed projections in the lesioned animals are related to those occurring in normal development. We injected fluorescent latex microspheres into the red nucleus of two groups of animals: (1) intact kittens at postnatal week 3 and (2) kittens that had received unilateral ablation of the cerebral cortex at this stage and were then allowed to survive for at least 4 weeks. Red fluorescing microspheres were injected on one side and green ones on the other. In both normal and lesioned kittens, a number of cells in the cortex were labeled as a result of the contralateral as well as the ipsilateral injections, and no difference in size or distribution was found between the cells labeled from contralateral and ipsilateral injections. More than half of the cells labeled from contralateral injections were double-labeled in both groups of animals. These results indicate that individual corticorubral cells project bilaterally in normal development as well as following unilateral lesions of the cortex. With respect to the cells producing crossed projections, they were similar in both laminar and regional distributions between the intact and lesioned animal, suggesting that the crossed projections arise from the same neuronal subpopulation before and after cortical lesions. This view was supported by sequential injections of the tracers, which indicated that cells normally projecting contralaterally maintained the crossed projection after the lesions. Taking into account our previous observations that growth and proliferation of crossed corticorubral axons took place in the red nucleus (Murakami et al. 1991a), it is likely that growth and proliferation of the axons in denervated targets play a major role in lesion-induced establishment of aberrant projections.

Aging↗
PubMed1994

Retinal specificity in eye fragments: investigations on the retinotectal projections of different quarter-eyes in Xenopus laevis.

According to Sperry's chemoaffinity hypothesis, the projection of a small eye fragment with a reduced amount of optic fibres should be restricted to that position in the optic tectum corresponding to its own specificity. However, previous investigations on different types of quarter-eyes in Xenopus laevis have revealed that their retinal projection was always restricted to the rostral part of the tectum, no matter what the origin of the remaining retinal quadrant. To get an indication of the state of specificity in such eye fragments, we investigated by electrophysiological and histological methods several features of the retinal projections of tempo-roventral (TV), naso-ventral (NV) and ventral (V) quarter-eyes which referred to their positional identity. Irrespective of their different origins, the projections were always located in the rostral part of the tectum, the size of the innervated tectal area depending for all fragment types on the size of the quarter-eyes, i.e. number of optic fibres. However, quantitative analyses revealed that with increasing eye size the various fragments expand their projections preferentially into those tectal areas that match their original specificity: TV projection is more concentrated in the rostral tectum, NV eyes expand their projections mainly to the caudal tectum, and V eyes enlarge their projections equally into the medial and caudal tectum. In addition, fibre-tracing experiments with cobaltic lysine showed that, according to the different origins of the quarter-eyes, retinal fibres follow the appropriate branch of the optic tract selectively: fibres of NV and V eyes pass mainly through the medial tract, and most fibres of TV eyes innervate the rostral tectum directly from a central position between the two side branches. All these findings suggest that the different types of quarter-eyes retain their original positional identity. Thus, their rostrally located retinotectal projections are not in register with their retinal specificity. We conclude that in X. laevis local positional markers in the tectum, if present at all, do not influence the development of the retinotectal projection. Instead we suggest a concept of self-sorting of the optic fibres, which can account for the partial innervation of the rostral tectum in different types of quarter-eyes.

Animals↗
PubMed1992

Descending projections of Forel's field H neurones to the brain stem and the upper cervical spinal cord in the cat.

1. Descending projections from Forel's field H (FFH) to the brain stem and upper cervical spinal cord were studied in cats. 2. Following implantation of HRP pellets into the spinal gray matter (C1-C3) or in the ponto-medullary reticular formation, the nucleus reticularis pontis caudalis (NRPC) or in the nucleus reticularis gigantocellularis (NRG), numerous neurones were retrogradely labelled in FFH on the ipsilateral side. In the former cases, the sizes of labelled neurones were medium-large (20-40 microns in diameter) while both small and medium-large neurones were labelled in the latter cases. 3. The lowest levels of spinal projection of single FFH neurones (n = 70) were assessed by antidromic spikes elicited by stimulating electrodes placed in C1, C3 and C7. The majority (59%) projected to C1 (but not to C3), about 27% to C3 (but not to C7), and only 14% to C7. 4. Axonal trajectories of single FFH neurones in C1-C3 segments were investigated by antidromic threshold mapping methods. The stem axons of spinal-projecting FFH neurones descended in the ventral or in the ventrolateral funiculi and the collaterals were projected to neck motor nuclei (lamina IX, Rexed 1954) and laminae V-VIII. The conduction velocities were estimated as 8-37 m/s from the antidromic latencies. 5. Axonal trajectories of 7 FFH neurones were investigated in the ponto-medullary reticular formation. All were antidromically activated from C1. In six neurones, the stem axons were located in the ventral part of the central tegmental tract and collaterals were projected to the NRPC and/or the NRG. Some of them projected to the inferior olive and the nucleus prepositus hypoglossi as well. The stem axon, in the remaining cell, was in the most dorso-medial part of the medial longitudinal fasciculus and collaterals were projected mainly to the dorsal part of the NRPC and the NRG, and also to the medial vestibular nucleus. 6. Anterograde transport of WGA-HRP injected into FFH revealed that in the upper cervical spinal cord, stem axons were found in the ventral funiculus and ventral part of the lateral funiculus. Collateral projections and presumed bouton-like deposits were observed in the laminae VI-IX, especially in their medial part. In the brain stem, dense bundles of the descending fibres were found in the central and the medial tegmental tracts and in the medial longitudinal fasciculus. FFH neurones projected densely to the caudal half of the NRPC and to the rostral half of the NRG.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1976

Projections from the lateral reticular nucleus to the cerebellar cortex and nuclei in the cat.

The fiber projection from the lateral reticular nucleus (LRN) to the cerebellum was examined in the cat. Electrolytic lesions were placed in a confined area of the LRN using a parapharyngeal approach, and the ensuing degeneration was studied in sections stained by the Nauta and the Fink-Heimer methods. Fibers from the LRN ascend the ipsilateral restiform body, terminating bilaterally but chiefly in the ipsilateral cerebellum. In the ipsilateral cortex projections were found to lobules I to V, with denser terminations in sublobules IVb to Ve. The projections are stronger in the intermediate-lateral zones than in the vermis proper. There is also a dense projection to sublobules VId and VIf and to the medialmost part of the simple lobule (HVI). Scanty termination was seen in the medialmost part of crus I. There is a moderate projection to the caudalmost folium of sublobule VIIb and to the rostral folia of sublobule VIIIa and the paramedian lobule. The contralateral projection by fibers crossed within the cerebellum is far less dense but clearcut in the anterior lobe, the rostral folia of lobule VI and the medial part of the simple lobule. In the ipsilateral nuclei strong projections were found to rostral portions of the medial nucleus (M) and the caudal two thirds of the anterior interpositus nucleus (IA) with predominance in the lateral part of the latter. A focal projection was found to rostrodorsal portions of the posterior interpositus nucleus (IP). No projection was found to the lateral nucleus (L). Contralaterally there is a weak projection to the rostral part of M and the medial parts of IA and IP.

Afferent Pathways↗
PubMed1989

Projections from the rostral mesencephalic reticular formation to the spinal cord. An HRP and autoradiographical tracing study in the cat.

Eye and head movements are strongly interconnected, because they both play an important role in accurately determining the direction of the visual field. The rostral brainstem includes two areas which contain neurons that participate in the control of both movement and position of the head and eyes. These regions are the caudal third of Field H of Forel, including the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and the interstitial nucleus of Cajal with adjacent reticular formation (INC-RF). Lesions in the caudal Field H of Forel in monkey and man result in vertical gaze paralysis. Head tilt to the opposite side and inability to maintain vertical eye position follow lesions in the INC-RF in cat and monkey. Projections from these areas to extraocular motoneurons has previously been observed. We reported a study of the location of neurons in Field H of Forel and INC-RF that project to spinal cord in cat. The distribution of these fiber projections to the spinal cord are described. The results indicate that: 1. Unlike the neurons projecting to the extra-ocular muscle motoneurons, the major portion of the spinally projecting neurons are not located in the riMLF or INC proper but in adjacent areas, i.e. the ventral and lateral parts of the caudal third of the Field H of Forel and in the INC-RF. A few neurons were also found in the nucleus of the posterior commissure and ventrally adjoining reticular formation. 2. Neurons in caudal Field H of Forel project, via the ventral part of the ventral funiculus, to the lateral part of the upper cervical ventral horn. This area includes the laterally located motoneuronal cell groups, innervating cleidomastoid, clavotrapezius and splenius motoneurons. At lower cervical levels labeled fibers are distributed to the medial part of the ventral horn. Projections from the caudal Field H of Forel to thoracic or more caudal spinal levels are sparse. 3. Neurons in the INC-RF, together with a few neurons in the area of the nucleus of the posterior commissure, project bilaterally to the medial part of the upper cervical ventral horn, via the dorsal part of the ventral funiculus. This area includes motoneurons innervating prevertebral flexor muscles and some of the motoneurons of the biventer cervicis and complexus muscles. Further caudally, labeled fibers are distributed to the medial part of the ventral horn (laminae VIII and adjoining VII) similar to the projections of Field H of Forel. A few INC-RF projections were observed to low thoracic and lumbosacral levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1981

Development of projections between areas of the nervous system.

A theory of projections in the nervous system (such as the retino-tectal projection) is proposed. Components of axonal growth cones and target tissue interact and cooperate, within the area of contact, to generate a guiding parameter, in the simplest case a "guiding substance" of distribution p. The components which are involved in this production are assumed to have graded distributions with respect to position in the projecting and target area, respectively. The distribution p thus produced guides the growth cone in the direction of maximal slope until the minimal value of p is reached. In this way, each growth cone can be guided to a position on the target tissue which depends on the origin of the fiber in such a manner that a projection results. Adhesive forces could but need not be involved in the guiding mechanism. The slope of p may interfere with an intracellular pattern forming mechanism within the growth cone, determining the polarity of activation (as modelled previously on the basis of autocatalysis and lateral inhibition) and thus the direction of growth. For the generation of a distribution of p leading to a reliable projection, simple graded distributions in the projecting and target area suffice, involving one or two components in each dimension. Their effect on the generation of p may be activatory as well as inhibitory. Exponential gradients give rise to particularly simple mapping functions. The following is an example of this general type of model: Growth cones as well as target tissue contribute to the production of a guiding substance. For each dimension, there is, in the target tissue, an exponentially graded component exerting (directly or indirectly) two functions: it actively produces guiding substance p and it interacts, in an inhibitory fashion, with the production of p by a component of the growth cone (which is, in turn, graded with respect to position of origin in the projecting area). While the theory is proposed as a fair approximation of the primary events in neural projections, superimposed regulatory effects can also be incorporated. These include fiber-fiber interactions, mechanisms smoothing out unequal density distributions of axon terminals and effects of time of arrival of fibers on the projection, which have been proposed previously as primary mechanisms generating projections. A further extension of the model is to assume that crude and more refined positional specificity is determined in a combinatorial fashion, allowing the possibility of interchanges and transformations of parameters.

Animals↗
PubMed1985

Effects of projection and background correction method upon calculation of right ventricular ejection fraction using first-pass radionuclide angiography.

There is no consensus as to the best projection or correction method for first-pass radionuclide studies of the right ventricle. We assessed the effects of two commonly used projections, 30 degrees right anterior oblique and anterior-posterior, on the calculation of right ventricular ejection fraction. In addition two background correction methods, planar background correction to account for scatter, and right atrial correction to account for right atrio-ventricular overlap were assessed. Two first-pass radionuclide angiograms were performed in 19 subjects, one in each projection, using gold-195m (half-life 30.5 seconds), and each study was analysed using the two methods of correction. Right ventricular ejection fraction was highest using the right anterior oblique projection with right atrial correction 35.6 +/- 12.5% (mean +/- SD), and lowest when using the anterior posterior projection with planar background correction 26.2 +/- 11% (p less than 0.001). The study design allowed assessment of the effects of correction method and projection independently. Correction method appeared to have relatively little effect on right ventricular ejection fraction. Using right atrial correction correlation coefficient (r) between projections was 0.92, and for planar background correction r = 0.76, both p less than 0.001. However, right ventricular ejection fraction was far more dependent upon projection. When the anterior-posterior projection was used calculated right ventricular ejection fraction was much more dependent on correction method (r = 0.65, p = not significant), than using the right anterior oblique projection (r = 0.85, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2001

Postnatal development of biotinylated dextran amine-labeled corpus callosum axons projecting from the visual and auditory cortices to the visual cortex of the rat.

The distribution and morphology of developing corpus callosum (CC) axons in rat visual cortex was studied by unilateral application of the in vivo anterograde tracer biotinylated dextran amine (BDA) to the visual or auditory cortex of newborns through adults. Changes in the distribution and morphology of CC axons during development were observed. Following BDA placement only in visual cortex, nearly all CC projections were to visual cortex (homotopic CC projections). At postnatal day (PND) 5-8, labeled CC axons were found throughout the contralateral visual cortex, including area 17; these CC axons could be followed from the white matter to layer I. By PND 13, few CC axons were found in medial area 17, indicating the existence of transitory CC axons in area 17 at younger ages. Morphological changes were investigated at the area 17/18a border and showed that CC axon collaterals were not formed until PND 8, and terminal arbors were not visible until PND 13; by PND 17, the adult CC-axon terminal pattern was present. At all ages, only a few heterotopic CC projections from visual to auditory cortex were found in the gray matter, although many labeled CC axons extended laterally into the white matter underlying the auditory cortex. Following BDA placement only in auditory cortex, CC projections to both auditory (homotopic CC projections) and visual (heterotopic CC projections) cortex were observed. At all ages, the homotopic CC projections were present throughout the auditory cortex, but were not distributed homogeneously; densely labeled CC axons showed a distinct columnar organization. The heterotopic CC projections were present in all visual cortical areas, including medial area 17, in significant numbers until PND 24, but were mostly eliminated by PND 28, at which time a labeling pattern similar to the adult was found. Thus, most of the heterotopic CC projections were transitory. The present study confirms the existence of transitory CC axons projecting through all layers of the visual cortex, as revealed by DiI, and extends the DiI results by showing that these transitory CC axons arise from both homotopic and heterotopic origins. Furthermore, different sources of transitory CC axons have different timetables for elimination.

Age Factors↗
PubMed1998

Correlation of electrophysiology, morphology, and functions in corticotectal and corticopretectal projection neurons in rat visual cortex.

In most mammals the superior colliculus (SC) and the pretectal nucleus of the optic tract (NOT) receive direct input from the ipsilateral visual cortex via projection neurons from infragranular layer V. We examined whether these projection neurons belong to different populations and, if so, whether it is possible to correlate the electrophysiological features with the suggested function of these neurons. Projection cells were retrogradely labeled in vivo by rhodamine-coupled latex beads or fast blue injections into the SC or the NOT 2-5 days prior to the electrophysiological experiment. Intracellular recordings of prelabeled neurons were made from standard slice preparations and cells were filled with biocytin in order to reveal their morphology. Both cell populations consist of layer V pyramids with long apical dendrites that form terminal tufts in layer I. In electrophysiological terms, 12 of the corticotectal cells could be classified as intrinsically bursting (IB), while two neurons showed a doublet firing characteristic and one neuron was classified as regular-spiking (RS). Intracortical microstimulation of cortical layer II/III revealed that SC-projecting neurons responded optimally to stimulation sites up to a distance of 1000 microm from the recorded cell. The morphological features of the SC-projecting cells reveal an apical dendritic tuft in layer I with a lateral extension of 300 microm, a mean spine density of 65 spines per 40 microm on the apical dendrites located in layer II/III, and a bouton density of 13 boutons per 100 microm on the intracortical axons. Sixteen NOT-projecting neurons exhibited an IB and five cells an RS characteristic. Intracortical microstimulation of cortical layer II/III showed that NOT-projecting neurons responded optimally to stimulation sites up to a distance of 1500 microm. Their morphological features consist of an apical dendritic tuft with a lateral extension of 500 microm, a mean spine density of 25 spines per 40 microm on the apical dendrites located in layer II/III, and a bouton density of 6 boutons per 100 microm on the intracortical axons. When the passive membrane parameters, responses to intracortical microstimulation in layer V, the extension of the basal dendritic field, and spine densities in layers I or V were compared between SC- and NOT-projecting cells, no differences were revealed. Differences were only consistently found in the supragranular layers, either for morphological parameters or for intracortical microstimulation. The results suggest that NOT-projecting and SC-projecting neurons, although biophysically similar, could integrate and transmit different spatial aspects of cortical visual information to their target structures.

Action Potentials↗
PubMed2007

Spatial symmetries in vestibular projections to the uvula-nodulus.

The discharge of secondary vestibular neurons relays the activity of the vestibular endorgans, occasioned by movements in three-dimensional physical space. At a slightly higher level of analysis, the discharge of each secondary vestibular neuron participates in a multifiber projection or pathway from primary afferents via the secondary neurons to another neuronal population. The logical organization of this projection determines whether characteristics of physical space are retained or lost. The logical structure of physical space is standardly expressed in terms of the mathematics of group theory. The logical organization of a projection can be compared to that of physical space by evaluating its symmetry group. The direct projection from the semicircular canal nerves via the vestibular nuclei to neck motor neurons has a full three-dimensional symmetry group, allowing it to maintain a three-dimensional coordinate frame. However, a projection may embed only a subgroup of the symmetry group of physical space, which incompletely mirrors the properties of physical space. The major visual and vestibular projections in the rabbit via the inferior olive to the uvula-nodulus carry three degrees of freedom-rotations about one vertical and two horizontal axes-but do not have full three dimensional symmetry. Instead, the vestibulo-olivo-nodular projection has symmetries corresponding to a product of two-dimensional vestibular and one-dimensional optokinetic spaces. This combination of projection symmetries provides the foundation for distinguishing horizontal from vertical rotations within a three dimensional space. In this study, we evaluate the symmetry group given by the physiological organization of the vestibulo-olivo-nodular projection. Although it acts on the same sets of elements and mirrors the rotations that occur in physical space, the physiological transformation group is distinct from the spatial group. We identify symmetries as products of physiological and spatial transformations. The symmetry group shapes the information the projection conveys to the uvula-nodulus; this shaping may depend on a physiological choice of generators, in the same way that function depends on the physiological choice of coordinates. We discuss the implications of the symmetry group for uvula-nodulus function, evolution, and functions of the vestibular system in general.

Animals↗
PubMed1975

An autoradiographic study of the projections from the lateral geniculate body of the rat.

The projections from the lateral geniculate body of the rat were followed using the technique of autoradiography after injections of [3H] proline into the dorsal and/or ventral nuclei of this diencephalic structure. Autoradiographs were prepared from either frozen or paraffin coronal sections through the rat brain. The dorsal nucleus of the lateral geniculate projected via the optic radiation to area 17 of the cerebral cortex. There was also a slight extension of label into the zones of transition between areas 17, 18 and 18a. The distribution of silver grains in the various layers of the cerebral cortex was analyzed quantitatively and showed a major peak of labeling in layer IV with minor peaks in outer layer I and the upper half and lowest part of layer VI. The significance of these peaks is discussed in respect to the distribution of geniculocortical terminals in other mammalian species. The ventral nucleus of the lateral geniculate body had 5 major projections to brain stem structures both ipsilateral and contralateral to the injected nucleus. There were two dorsomedial projections: (1) a projection to the superior colliculus which terminated mainly in the medial third of the stratum opticum, and (2) a large projection via the superior thalamic radiation which terminated in the ipsilateral pretectal area; a continuation of this projection passed through the posterior commissure to attain the contralateral pretectal area. The three ventromedial projections involved: (1) a geniculopontine tract which coursed through the basis pedunculi and the lateral lemniscus to terminate in the dorsomedial and dorsolateral parts of the pons after giving terminals to the lateral terminal nucleus of the accessory optic tract, (2) a projection via Meynert's commissure to the suprachiasmatic nuclei of both sides of the brain stem as well as to the contralateral ventral lateral geniculate nucleus and lateral terminal nucleus of the accessory optic tract, and (3) a medial projection to the ipsilateral zona incerta. The results obtained in these experiments are contrasted with other data on the rat's central visual connections to illustrate the importance of these connections in many subcortical visual functions.

Animals↗
PubMed1976

Laminar patterns of geniculocortical projection in the cat.

The cortical afferents from individual laminae of the dorsal lateral geniculate nucleus (LGN) were studied using both light and electron microscope autoradiography. In area 17, the A geniculate laminae (A and A1) had two main bands of projection, one extending from the bottom of IVc to the deepest cells in layer III, and one in layer VI. The C geniculate laminae projected in two dense bands to the upper and lower borders of layer IV, thus bracketing the A laminae projection, though with some overlap. In addition, the C laminae projected to the superficial half of layer I, which the A laminae did not. Conversely, while the A laminae projected to layer VI, the C laminae did not. The two sets of laminae also showed differences in the areas to which they projected. The A geniculate laminae projected to areas 17 and 18, whereas the C geniculate laminae had a more extensive projection, including areas 17, 18, 19 and other areas on the suprasylvian gyrus. The laminar organization of the projection to area 18 was similar to that found in area 17. At the electron microscopic level the geniculate terminals were found to make Gray's type 1 synapses, for the most part onto dendritic spines. Labeled terminals were found in all the projection bands seen in the light microscope. The implications of these findings on the connectivity of cells in layer IV are discussed. The presence of labeled terminals in layer VI, which contains the cells of origin of the corticogeniculate pathway, suggests that the recurrent loop to the LGN is mediated monosynaptically. Finally, the afferents from each geniculate lamina were found to be segregated into patches, about 500 mum wide, which probably form the anatomical basis for ocular dominance columns.

Animals↗
PubMed1978

Topographic projections of substance P and GABA pathways in the striato- and pallido-nigral system: a biochemical and immunohistochemical study.

The topographical projections of substance P pathways from the caudateputamen and globus pallidus to the pars compacta and pars reticulata of the substantia nigra have been investigated in the rat using immunohistochemical and radioimmunoassay techniques and compared with the projections of GABA nergic striatal neurones. Unilateral vertical knife cuts through the anterior and posterior striatum have shown the majority of substance P-containing neurones which project to the substantia nigra to originate in the most rostral part of the caudate-putamen. This projection appears to innervate the pars reticulata and pars compacta of the substantia nigra to a similar extent. A separate projection of substance P-containing neurones to the substantia nigra appears to originate in the globus pallidus. Undercutting the cerebral cortex which overlies the corpus striatum did not affect the substance P content of the globus pallidus or substantia nigra. However, there appears to be an additional substance P projection from the basal ganglia to the entopeduncular nucleus. In contrast, GABA-containing neurones which project to the substantia nigra are mainly located in more caudal parts of the caudate-putamen and in the globus pallidus. There is a marked differentiation in the region of the substantia nigra innervated by GABA cells originating in the rostral and caudal parts of the corpus striatum. Rostrally situated neurones project almost exclusively to the pars reticulata, while neurones in the caudal part of the caudate-putamen and globus pallidus project to both the pars compacta and pars reticulata. These results suggest that there is a partial topographical separation of the sites of origin of substance P- and GABA-containing neurones which project to the substantia nigra.

Animals↗
PubMed1980

Differences in the collateralization of neuronal projections from the dorsal column nuclei and lateral cervical nucleus to the thalamus and tectum in the cat: an anatomical study using two different double-labeling techniques.

The dorsal column nuclei (DCN) and the lateral cervical nucleus (LCN) project to the diencephalon and tectum. In order to determine which neurons project to these targets and whether any of them have collateral projections, the double-retrograde labeling techniques developed by Hayes and Rustioni and Kuypers et al. were used. Both strategies produced similar results. Within DCN, neurons which projected to the diencephalon were located differently and had a different morphology than those which projected to the tectum. The diencephalic-projecting neurons, which were preferentially located within the middle part of the DCN complex were mainly large (> 15 micrometer diameter) and round. The tectal-projecting neurons, often located along the edges of the gracile and cuneate nuclei or between them, were most often found outside of the middle parts of the DCN complex (i.e. predominantly rostrally and frequently also caudally). These tectal-projecting neurons varied in size and were usually oval or fusiform in shape. In contrast to DCN, neurons in LCN which projected either to the tectum or diencephalon did not differ morphologically and in both groups were of various sizes and shapes. They were intermixed haphazardly, predominantly within the lateral two-thirds of the nucleus. In addition, another class of neurons, constituting more than 40% of the labeled population in some experiments, had collateral projections to both terminal targets. These double-labeled neurons were haphazardly mixed with other labeled neurons.

Animals↗
PubMed1983

Parabigeminal projections to the superior colliculus in the cat.

Small amounts of horseradish peroxidase were injected into the superior colliculus of the cat and the distribution of labeled neurons in the parabigeminal nuclei was mapped. After injections placed dorsal to the stratum opticum in the superior colliculus, the parabigeminal nucleus is the only mesencephalic and/or rhombencephalic structure in which labeled neurons are observed. The number of labeled neurons in the parabigeminal nucleus increases after injections that include both the superficial and the deep layers of the superior colliculus. Each part of the superior colliculus receives projections from wide areas of both parabigeminal nuclei, although it also receives more abundant projections from one or more restricted parts of these nuclei. The anterior third of the parabigeminal nuclei is the part which sends the fewest projections to the superior colliculus. These projections terminate principally in the central and intermediate part of the contralateral colliculus, while a smaller number of fibers terminate in the lateral and rostral part of the ipsilateral colliculus. The intermediate third of the parabigeminal nuclei sends projections to all parts of the ipsilateral colliculus, but the greatest number of these goes to the contralateral colliculus. These contralateral projections terminate principally in the lateral parts of the contralateral colliculus, and in lesser number in its central and rostral, and medial and rostral areas. The posterior third of the parabigeminal nucleus sends scant efferents to wide areas of the ipsilateral and contralateral colliculi, and a dense projection to the medial and intermediate, medial and caudal and central and intermediate parts of the ipsilateral colliculus. There are also consistent projections from the posterior third of the parabigeminal nucleus to the central and rostral and medial and rostral parts of this ipsilateral colliculus. These results demonstrate a topographical organization of the parabigemino-tectal projections in the cat, as a pathway that facilitates the integration in the colliculus of visual impulses of different origin in the retina. This organization permits the modulation of the superior colliculus in its participation in both the extrageniculate visual system and in the regulation of eye and head orientation movements through the parabigeminal projections to the superficial and deep layers of the colliculus, respectively.

Animals↗
PubMed1990

Topographical projections from the thalamus, subthalamic nucleus and pedunculopontine tegmental nucleus to the striatum in the Japanese monkey, Macaca fuscata.

Topographical projections from the thalamus, subthalamic nucleus (STN) and pedunculopontine tegmental nucleus (PPN) to the striatum were examined in the Japanese monkey (Macaca fuscata) by using the retrograde axonal transport technique of WGA-HRP (wheat germ agglutinin-conjugated horseradish peroxidase). After WGA-HRP injection in the head of the caudate nucleus (CN) or putamen (Put), labeled neuronal cell bodies in the thalamus were distributed mainly in the nucleus ventralis anterior (VA)-nucleus ventralis lateralis (VL) complex and the nucleus centrum medianum (CM)-nucleus parafascicularis (Pf) complex, and additionally in the paraventricular, parataenial, rhomboid, reuniens, centrodorsal, centrolateral, paracentral, and centromedial nuclei. The data indicated that the pars principalis of VA (VApc) projected mainly to CN and additionally to Put, and that the pars magnocellularis of VA (VAmc) or pars oralis of VL (VLo) projected selectively to CN or Put, respectively. It was also indicated that CM projected to the middle and caudal parts of Put, while Pf projected to CN and the rostral part of the Put. The data further indicated that the dorsomedial, ventromedial, or lateral part of CM projected respectively to the dorsolateral, ventromedial, or intermediate part of Put, and that the medial or lateral part of Pf projected respectively to the medial or lateral part of the head of CN. Direct projections from STN and PPN to the striatum were confirmed. The subthalamostriatal projections showed a mediolateral topography. The PPN was shown to project bilaterally to the striatum with an ipsilateral predominance.

Animals↗
PubMed1995

Efferent projections of the olivary pretectal nucleus in the albino rat subserving the pupillary light reflex and related reflexes. A light microscopic tracing study.

The olivary pretectal nucleus is a primary visual centre sensitive to luminance changes. It is involved in the pupillary light reflex, the consensual pupillary light reflex and related reflexes, such as the lid closure reflex whereby pupillary constriction takes place. Since the olivary pretectal nucleus is a small nucleus, previous studies using degeneration, horseradish peroxidase and radioactive amino acid tracing were limited regarding to the exclusiveness of the projections from the olivary pretectal nucleus. In the present study the position of the olivary pretectal nucleus in the rat was first localized by physiological recording of the neurons upon luminance stimulation. Subsequently, an anterograde tracer Phaseolus vulgaris leucoagglutinin was injected iontophoretically. This allows a much more precise localization of the olivary pretectal nucleus projections. Ascending and descending pathways originating from the olivary pretectal nucleus were observed. Ascending fibres project bilaterally to the intergeniculate leaflet, the ventral part of the lateral geniculate nucleus and ipsilaterally to the anterior pretectal nucleus. In addition, contralateral projections were observed to the zona incerta and the fields of Forel. Descending fibres project bilaterally to the periaqueductal gray, the nucleus of Darkschewitsch, the interstitial nucleus of Cajal, the Edinger-Westphal nucleus and the intermediate gray layer of the superior colliculus. Also a contralateral projection to the oculomotor nucleus and an ipsilateral projection to the pontine nucleus and the nucleus of the optic tract were found. Furthermore, the contralateral olivary pretectal nucleus received a small projection. Retrograde tracing experiments using two fluorescent dyes revealed that the fibres projecting to the contralateral olivary pretectal nucleus and to the contralateral interstitial nucleus of Cajal are collaterals. The projection from the olivary pretectal nucleus to the facial nucleus which has been described to receive an input in cats could not be confirmed for the rat. The fact that the Edinger-Westphal nucleus, the interstitial nucleus of Cajal and the superior colliculus receive an input from the olivary pretectal nucleus suggests that this primary visual centre is not only involved in the pupillary light reflex, but also in controlling eye and head position and saccadic eye movements. Although visual acuity largely depends on receptive field sizes of retinal ganglion cells and their central connections, the stronger sympathetic influence during the pupillary light reflex in animals with frontally placed eyes compared to animals with laterally placed eyes may also contribute to the higher visual acuity in animals with frontally placed eyes.

Afferent Pathways↗
PubMed1991

Ontogenesis of the cerebellofugal projection in the rat.

Ontogenesis of the cerebellofugal projection was studied in the rat by the tract-tracing method with WGA-HRP. The projection, forming a uniform front of compact fibre bundle tipped by growth cones, began entering the brainstem on embryonic day 17 (E17), grew rapidly and orderly with no random extension of fibers, and arrived at the most rostral part of the thalamus already by E18, distributing dense terminals to various brainstem and thalamic nuclei. The course and termination of this projection in prenatal animals was largely similar to normal adult projection although differences were found. Some projections increased postnatally, whereas some projections which were existent in embryos regressed with age and finally disappeared completely. The adult pattern of the projection was attained by 3 weeks of age. It is worth noting that the projections which appeared transiently are similar to those reported as aberrantly regenerated projections in kittens which are born in more mature state than rats and have no such projections at birth.

Aging↗