Terminal Nucleus Research Articles

Comparative topography of projections from the mesodiencephalic junction to the inferior olive, vestibular nuclei, and upper cervical cord in the cat.

Distributions of neurons located in the central rostral mesencephalon and caudal diencephalon that project to the upper cervical spinal cord, vestibular nuclei, or inferior olive were studied in the cat by using retrograde axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Afferent sources to all of these targets were observed in the interstitial nucleus of Cajal (INC), the region surrounding the fasciculus retroflexus (PF), and the nucleus of the fields of Forel (NFF). Three-dimensional reconstruction revealed differences in densities of cells projecting from these common areas. Spinal projecting cells were present in slightly greater numbers in the caudal two-thirds of the INC, whereas those projecting to the vestibular complex were more numerous in the rostral two-thirds of this nucleus. A relatively smaller number of olivary projecting cells were dispersed throughout the INC. Olivary afferent sources outnumber those with spinally directed or vestibularly directed axons in the PF region. In the fields of Forel, cells projecting to the vestibular nuclei or inferior olive were concentrated medially, whereas cells projecting to the spinal cord appeared both medially and laterally. Each type of afferent source was also seen in the nucleus of the posterior commissure and the posterior ventral lateral hypothalamic area. Unique sources of afferents to the inferior olive were observed in the parvicellular red nucleus (ipsilateral to the injections) and the anterior and posterior pretectal nuclei. A large number of labeled neurons was seen in the nucleus of Darkschewitsch after injections of tracer into the inferior olive, but this projection did not appear to be unique, as small numbers of labeled cells were also seen after injections into the cervical spinal cord. The Edinger-Westphal nucleus and the adjacent somatic oculomotor nucleus contained cells which projected separately to the spinal cord or the vestibular complex, and the superior colliculus contained cells which projected separately to the contralateral spinal cord or the contralateral inferior olive. In this study, it was also noted that neurons in the medial terminal nucleus of the accessory optic tract projected to the ipsilateral inferior olive or to the contralateral vestibular complex. These differences in locations and densities of cells projecting to the cervical spinal cord, vestibular complex, and inferior olive may underlie functional specializations in these areas in relation to vertical eye and head movement control and to neural systems controlling postural adjustments accompanying limb movements.

The accessory optic system of the rabbit, cat, dog and monkey: a whole-mount HRP study

The three-dimensional fiber pathways of the accessory optic system in the rabbit, cat, dog and monkey were studied in whole-mounted preparations of the diencephalon and the midbrain, without sectioning, by anterograde labeling of retinal axons with horseradish peroxidase (HRP). HRP histochemical studies on alternate serial coronal sections were also performed. The rabbit accessory optic system exhibited two fasciculi (the inferior fasciculus, and the superior fasciculus consisting of the anterior fibers and the posterior fibers) and three terminal nuclei (the medial terminal nucleus, and the anterior and posterior portions of the lateral terminal nucleus), but lacked the dorsal terminal nucleus. In the cat and dog, only the posterior fibers of the superior fasciculus were detected. The inferior fasciculus and the anterior fibers of the superior fasciculus were absent. The medial terminal nucleus and the posterior portion of the lateral terminal nucleus were commonly observed in the cat and dog. The cat accessory optic system possessed the dorsal terminal nucleus, and the dog accessory optic system possessed the anterior portion of the lateral terminal nucleus. The monkey (Macaca fuscata) accessory optic system consisted of the posterior fibers of the superior fasciculus, but blacked the inferior fasciculus and the anterior fibers of the superior fasciculus. Most of the posterior fibers terminated in the well-developed posterior portion of the lateral terminal nucleus located on the upper surface of the cerebral peduncle. A small number of posterior fibers projected to the poorly-developed medial terminal nucleus. Based on these findings, species differences in the mammalian accessory optic system were discussed.

Physiological and anatomical identification of the nucleus of the optic tract and dorsal terminal nucleus of the accessory optic tract in monkeys

Physiological and anatomical criteria were used to clearly establish the existence of a pretectal relay of visual information to the ipsilateral inferior olive in the macaque monkey. After injection of horseradish peroxidase into the inferior olivary nucleus, retrogradely labelled neurons were found in the nucleus of the optic tract (NOT) and the dorsal terminal nucleus of the accessory optic tract (DTN). The labelled cells were distributed in a sparse band arching below the margin of the brachium of the superior colliculus between the dorsal and lateral borders of the brainstem at the caudal edge of the pulvinar. Various types of cells could be distinguished. More superficially the cells were extremely spindle shaped, cells deeper within the midbrain had more compact somata. NOT-DTN neurons in the same region were also found to respond with short latencies to electrical stimulation of both the inferior olive and the optic chiasm. All neurons in the NOT-DTN which were antidromically activated from the inferior olive were also found to have direction specific binocular visual responses. Such neurons were excited by ipsiversive motion and suppressed by contraversive motion, regardless of whether large area random dot stimuli moved across the visual field or small single dots moved across the fovea. Direct retinal input to these neurons was via slowly conducting fibers (3-9 m/s) from the monkey's optic tract conduction velocity spectrum. As shown previously for non-primates, NOT-DTN cells may also in the monkey carry a signal representing the velocity error between stimulus and retina (retinal slip), and relay this signal into the circuitry mediating the optokinetic reflex.

Retinofugal projections in hedgehog-tenrecs (Echinops telfairi and Setifer setosus)

Using the autoradiographic tracing technique the retinal projections were studied in the tenrecs, Echinops telfairi and Setifer setosus (insectivora, tenrecidae). Bilateral projections were found to the n. suprachiasmaticus, the anterior hypothalamic area, the dorsal and ventral lateral geniculate bodies, the pretectal olivary nucleus and the superior colliculus. The contralateral projections were usually more intense than the ipsilateral ones except the retinohypothalamic connections. A partial segregation of the projection fields from both eyes was present in the dorsal and ventral lateral geniculate bodies. In the superior colliculus retinal fibers predominantly involved the stratum zonale and the upper portion of the stratum griseum superficiale on both sides. The projections to the deeper portion of the colliculi were rather faint, particularly on the ipsilateral side. Target areas receiving contralateral projections exclusively were the periamygdaloid area (labeled only in Setifer), the terminal accessory nuclei including the n. tractus optici and the inferior colliculus. The data are compared with other species. The most striking finding may concern the projection to the medial terminal nucleus being quite prominent in marsupials and most eutherian mammals (including the erinaceomorphous hedgehogs), but greatly reduced in tenrecs and primates.

Chapter 11: The role of the primate lateral terminal nucleus in visuomotor behavior

This chapter discusses the role of the primate lateral terminal nucleus in visuomotor behavior. The neural pathways subserving the optokinetic reflex and its interaction with the vestibulo-ocular reflex (VOR) are not fully understood, but they are thought to involve the accessory optic system (AOS). In the cat and rabbit, the AOS consists of three terminal nuclei (lateral, medial and dorsal; LTN, MTN, DTN) distributed along the mesencephalic brainstem and the nucleus of the optic tract (NOT) located in the pretectum. Although the anatomical organization of the monkey AOS has received some attention, relatively little is known about the signals it carries. Recently, it is shown that single NOT units encode the direction of visual movement and that electrical stimulation of the primate NOT elicits a horizontal optokinetic nystagmus (OKN) with most of the classic features present in visually induced OKN. In addition to responding to full-field visual motion, many of the LTN units discharged to movement of a small spot. This ability to respond to small visual stimuli has also been reported in the primate NOT.

Pathways for transmission of visual and auditory information to the cat caudate nucleus

Visual and auditory projections to the cat caudate nucleus were investigated using the horseradish peroxidase retrograde axonal transport technique in conjunction with that of experimental degeneration of retinal axons. It was found that visual information may reach the caudate nucleus not just through well-known polysynaptic pathways from the cerebral cortex but also following oligosynaptic (transpulvinar, lateroposterior nucleus, suprageniculate nucleus, and nucleus limitans of the thalamus) as well as bisynaptic pathways (via the medial and lateral terminal nuclei of the accessory optical tract, pulvinar, pretectum, intermediary layer of the superior colliculus, and the supraoptic nucleus); some of these pathways were identified for the first time. Direct retinal inputs were found in the suprageniculate nucleus. Additional structures were discovered through which auditory information may reach the caudate nucleus, i.e., the dorsal nucleus of the parvocellular portion of the lateral geniculate body, the deep-lying superior colliculus, and the dorsal and ventral nuclei of the lateral lemniscus. The physiological significance of the pathways described for possible transmission of visual and auditory impulses is discussed and a new principle underlining the organization of sensory inputs into the caudate nucleus is put forward.

Chapter 48 Multiple trophic influences which act on developing retinal ganglion cells: studies of retinal transplants

This chapter discusses and identifies molecules present in the pathway of growing retinal axons in the developing brain, which might serve as an adhesive substrate. The chapter focuses on the multiple trophic influences, which act on developing retinal ganglion cells. Transplants of retina placed over the superior colliculus of newborn rats form extensive axonal connections with the primary visual nuclei of the host brain. Significantly, different results are obtained, when retina is transplanted to the visual cortex of newborn rats. Collectively, the results make two important points: first, ganglion cells degenerate if unable to form connections in their proper terminal nuclei, and second, retinal axons whether in cortex or colliculus appear to select a very specific path to grow, based on local environmental cues. Transplantation studies offer evidence that laminin is a substrate for retinal axon growth, and fetal retina transplanted adjacent to the colliculus of adult host rats exhibits very limited axon growth into the host brain. Axons from cortical transplants run rostrally and caudally in rather tight tracts deep in the brainstem; however, it remains for future work to distinguish the substrate molecules followed by each axon population.

Retinal projection to the formatio reticularis tegmenti mesencephali in the Old World monkeys

We studied the retinal projections of Old World monkeys using the anterograde transport of tritiated amino acid and wheat germ agglutinin conjugated to horseradish peroxidase. In addition to well-known retinal connections, these methods revealed that a small number of labeled retinofugal fibers might terminate in a small area of the contralateral formatio reticularis tegmenti mesencephali between the red nucleus and the substantia nigra. In the autoradiographic cases, a few labeled retinal terminals were also found in the same area on the ipsilateral side. In order to reach their terminal field, these labeled fibers appeared to leave the accessory optic tract in the vicinity of the dorsal border of the lateral terminal nucleus and run medially through the substantia nigra.

Immunohistochemical localization of neuronal nicotinic receptors in the rodent central nervous system

The distribution of nicotinic acetylcholine receptors (AChR) in the rat and mouse central nervous system has been mapped in detail using monoclonal antibodies to receptors purified from chicken and rat brain. Initial studies in the chicken brain indicate that different neuronal AChRs are contained in axonal projections to the optic lobe in the midbrain from neurons in the lateral spiriform nucleus and from retinal ganglion cells. Monoclonal antibodies to the chicken and rat brain AChRs also label apparently identical regions in all major subdivisions of the central nervous system of rats and mice, and this pattern is very similar to previous reports of 3H-nicotine binding, but quite different from that of alpha-bungarotoxin binding. In several instances, the immunohistochemical evidence has strongly indicated that neuronal AChR undergoes axonal transport. The clearest example of this has been in the visual system, where labeling was observed in the retina, the optic nerve and tract, and in all of the major terminal fields of the optic nerve except the ventral suprachiasmatic nucleus. This was confirmed in unilateral enucleation experiments in the rat, where labeling was greatly reduced in the contralateral optic tract, ventral lateral geniculate nucleus, pretectal nuclei receiving direct visual input, superficial layers of the superior colliculus, and medical terminal nucleus, and was significantly reduced in the dorsal lateral geniculate nucleus. Clear neuronal labeling was also observed in dorsal root ganglion cells and in cranial nerve nuclei containing motoneurons that innervate branchial arch-derived muscles, although the possibility that neuronal AChR undergoes axonal transport in the latter cells was not tested experimentally.(ABSTRACT TRUNCATED AT 250 WORDS)

The pretectal necleus of the optic tract modulates the direction selectivity of accessory optic neurons in rats

Direction-selective singel units within the medical terminal nucleus of the rat were shown to prefer motion in upward-temporal or downward-nasal directions. Lesions of the optic tract nucleus practically abolished responses to the nasal direction of motion and increased the directional bias toward the temporal direction. Such results suggest a significant role of that pretectal nucleus in the determination of direction selectivity of accessory optic neurons.

Retinal ganglion cells projecting to the accessory optic system in the rat.

The present data identify the distribution and morphological features of a homogeneous group of rat retinal ganglion cells. These cells were labelled after injection of either horseradish peroxidase or a fluorescent tracer, Fast Blue, into the medial terminal nucleus (MTN) of the accessory optic system. After retrograde fluorescent labelling, MTN-projecting retinal ganglion cells were intracellularly injected with Lucifer Yellow to reveal their complete dendritic morphology. There were on average 1,750 MTN-projecting cells fairly evenly distributed over the entire retinal ganglion cell layer. Their density ranged from 40-49 cells/mm2 in superior retina to 10-19 cells/mm2 towards the peripheral regions of both inferior and superior retina. The area of highest density formed a nasal-temporal band suggestive of a visual streak. Soma diameters ranged from 8.7 to 14.5 micron centrally and from 9.9 to 17.1 microns peripherally. Maximal dendritic field diameter ranged from 431 to 644 micron and averaged 516 micron with no obvious eccentricity dependence. The majority of MTN-projecting cells were bistratified. Dendrites stratified predominantly in the inner sublamina of the inner plexiform layer (IPL) with a varying number of branches from the remaining dendrites contained within the outer IPL, both strata presumably corresponding to the electrophysiologically determined on-off dichotomy. Cells projecting to the MTN were characterised by higher-order dendritic branching patterns that resulted in a dense dendritic tree with minor dendritic overlap. The slender dendrites had a beaded appearance and displayed spiny protrusions. The dendritic coverage of 5-6, stratification pattern, and overall morphological appearance of rat MTN-projecting cells renders them suitable candidates for on-direction--selective cells shown electrophysiologically to be linked with the MTN of the accessory optic system.

Synaptic organization of the nucleus of the optic tract in the rabbit: a combined Golgi-electron microscopic study.

The organization of the nucleus of the optic tract was investigated with light and electron microscopy in combination with Golgi impregnation. In Golgi material, neurons ranged in size from 10 to 25 microns with three to seven principal dendrites extending predominantly parallel to the fibres of the optic tract, irrespective of their location within the nucleus. In some areas dendrites extended into the neuropil of the adjacent dorsal terminal nucleus of the accessory optic system and the posterior pretectal nucleus. Occasionally spines and appendages were observed. The fine structure of the nuclei, perikarya and the dendritic arborization did not allow a well-defined distinction between interneurons and projection neurons. The synaptic organization of the nucleus of the optic tract showed great resemblance to the neuropil of the lateral geniculate nucleus and the superior colliculus. Similar types of presynaptic terminals were noticed: (i) R-terminals were either large and scalloped or small and regular in outline with spherical vesicles and electron-lucent mitochondria, and showed asymmetric contact zones; (ii) F-terminals with flattened vesicles, opaque mitochondria and symmetric contact zones; (iii) RLD-terminals with spherical vesicles and electron-dense mitochondria and asymmetric contact zones; (iv) P-terminals with pleomorphic vesicles and electron-lucent or opaque mitochondria and asymmetric synaptic thickenings. These different types of terminal were found isolated in the neuropil or in clusters of synapses. The most striking differences between the nucleus of the optic tract and the lateral geniculate nucleus were the relative scarcity of F-terminals in the clusters, the paucity of triadic arrangements and the relatively small size of the R-terminals. The differences in ultrastructure may be related to retinal W-type ganglion cells, which form the main retinal input to the nucleus of the optic tract and could also be related to the physiologically identified direction-selective units within the nucleus of the optic tract.

Vertical and horizontal visual whole-field motion differently affect the metabolic activity of the rat medial terminal nucleus

The metabolic activity of the medial terminal nucleus (MTN) of the Accessory Optic System was studied by means of the [ 14C]2-deoxyglucose (2-DG) method in Long-Evans rats exposed to moving and stationary visual stimuli. In particular we explored the rate of local cerebral glucose utilization (LCGU) and the spatial distribution of 2-DG uptake within MTN related to visual stimuli capable of triggering optokinetic nystagmus. It was found that increases in MTN metabolism accompanied the retinal slip signals evoked by whole-field visual patterns moving in the vertical as well as in the horizontal direction. At the same level of luminous flux neither the same but stationary pattern, nor constant, diffuse illumination were able to elicit comparable changes in MTN metabolic rates. The effects of vertical and horizontal motions differed, however, from each other. In binocular testing LCGU rates resulted significantly higher after vertically moving patterns and upon the same stimulus condition the spatial distribution of 2-DG matched very closely the spatial distribution of the retinal afferents and the cellular density within MTN, in sharp contrast with the diffuse spreading out of the label across the nucleus following horizontal motion. In monocular testings only the vertically moving patterns were able to increase LCGU rates significantly and then in contralateral MTN alone. However, comparison between the levels of glucose consumption measured in binocular and in monocular vision also showed the involvement of the uncrossed retinal path in relaying the retinal slip signals to MTN. No difference in LCGU and in spatial distribution of the label were finally observed in relation to the upward or to the downward direction of the moving pattern.

Retinal projections in the hedgehog (Erinaceus europaeus). An autoradiographic and horseradish peroxidase study.

The retinal projections of the hedgehog were studied using tritiated leucine and horseradish peroxidase as orthograde tracers. In both series of experiments labeling was seen bilaterally in the suprachiasmatic nucleus, the dorsal and the ventral lateral geniculate nucleus, the superior colliculus, and the pretectal area and contralaterally in the terminal nuclei (dorsal, lateral and medial) of the accessory optic system. A retino-intergeniculate leaflet projection is described for the first time in this species, and its significance is discussed.

Uncrossed retinal projection to the medial terminal nucleus of the accessory optic system in the hereditary unilaterally microphthalmic rat

The uncrossed optic projection to the medial terminal nucleus of the accessory optic system was studied in adult rats with hereditary unilateral microphthalmia. The vestigial eye of the mutant completely lacks the optic nerve. After injection of HRP into the remaining eye the ipsilateral labeled fibers of the accessory optic system via the superior fasciculus distinctly covered the three terminal nuclei. No ipsilateral inferior fasciculus of the accessory optic system was labeled. Aberrant expansion of the uncrossed superior fasciculus fibers was observed in the medial terminal nucleus.

The accessory optic system of the monocularly deprived cat

Single-unit extracellular recordings were made in the lateral (LTN) and dorsal (DTN) terminal nuclei of the accessory optic system (AOS) of 10 monocularly deprived cats. The separate effects of monocular deprivation (MD) observed in each hemisphere are outlined below. Unlike many units in normal animals, LTN and DTN cells in the hemisphere contralateral to the non-deprived (open) eye, were no longer activated through visual stimulation of the ipsilateral (deprived) eye. In both nuclei, cells were driven effectively only by stimuli presented via the contralateral eye. The distribution of preferred directions was considerably altered in the LTN but not in the DTN. Almost every LTN unit encountered in MD cats preferred downward stimulus motion, in contrast to normal animals where equal numbers of LTN cells show preferences for upward and downward movement ( J. Neurophysiol., 51 (1984) 276–293). DTN units showed the usual preference for horizontal motion toward the recorded hemisphere. Velocity preferences were slower on average in the DTN, and unaffected in the LTN. In the hemisphere contralateral to the deprived eye, the ocular dominance distribution of LTN and DTN cells showed a distinct shift in favor of the contralateral (deprived) eye. This effect was not as complete as that observed in the other hemisphere. Cells in both nuclei displayed a small influence from the ipsilateral (exposed) eye in some animals, but this input was much less than that observed in normally reared cats. Average velocity preferences among DTN units were slower than normal, and slower relative to the DTN population in the opposite hemisphere. No pronounced changes were observed in LTN velocity tuning. The distributions of preferred directions for both nuclei were similar to those obtained in the other hemisphere: DTN cells were found to prefer horizontal motion, while most LTN units were activated best by stimuli moving vertically and down within their receptive fields.

Retinal Projections in the Northern Native Cat, Dasyurus-Hallucatus (Marsupialia, Dasyuridae)

The retinal projections of the northern native cat, Dasyurus hallucatus, were studied by the anterograde transport of tritiated proline and by autoradiography. Seven regions in the brain were found to receive direct retinal projections: (1) the suprachiasmatic nucleus; (2) the dorsal lateral geniculate nucleus; (3) the ventral lateral geniculate nucleus; (4) the lateral posterior nucleus; (5) the nuclei of the accessory optic tract; (6) the pretectal nuclei; (7) the superior colliculus. All nuclei studied received a bilateral retinal projection except the medial terminal nucleus of the accessory optic system, in which only a contralateral input was found. The contralateral eye had a greater input in all cases. As with the related species, Dasyurus viverrinus, there is extensive binocular overlap in the dorsal lateral geniculate nucleus (LGNd). In the LGNd contralateral to the injected eye, the autoradiographs show four contralateral terminal bands occupying most of the nucleus. The axonal terminations in the ipsilateral LGNd are more diffuse but show a faint lamination pattern of four bands. The ventral portion of the LGNd receives only contralateral retinal input, and therefore probably represents the monocular visual field. The other principal termination of the optic nerve, the superior colliculus, has a predominantly contralateral input to both sublayers of the stratum griseum superficiale. However, the ipsilateral fibres terminate only in patches in the more inferior sublayer.

Somatic labeling of the medial terminal nucleus of the accessory optic system with WGA-HRP injected into the rat occipital cortex

Neuronal cell bodies in the medial terminal nucleus of the accessory optic system (MTN) were labeled with WGA-HRP which was injected ipsilaterally into the occipital cortex in the rat. We suggest that the label was first transported anterogradely to the pretectal nucleus of the optic tract, then moved transneuronally from axon terminals of occipital cortical neurons to axon terminals of MTN neurons and finally transported retrogradely to reach cell bodies of MTN neurons.

A common mammalian plan of accessory optic system organization revealed in all primates

The accessory optic system (AOS), which was described as early as 1870 by Gudden, constitutes a distinct midbrain visual pathway in all classes of vertebrates. In non-primate mammals, retinal fibres of this system project to a set of three nuclei: the dorsal (DTN), the lateral (LTN) and the medial (MTN) terminal nuclei. Whereas all AOS cells respond to the slow motion of large visual stimuli, the neurons are tuned to complementary directions of movement: horizontal temporo-nasal direction for the DTN, vertical up and down for the LTN and vertical down for the MTN. It has thus been suggested that these nuclei establish a system of retinal coordinates for the detection of whole field motion. As the AOS provides direct and indirect pathways to both oculomotor and vestibular structures, each of these nuclei is thought to be an essential link in the co-ordination of eye and head movements in relation to movement within the visual-field. One problem for the generalization of this theory is that the medial terminal nucleus has never been found in primates. In this report we establish both the existence of this nucleus and its afferent input from the retina in all major groups of primates (prosimians, New and Old World monkeys and apes), indicating a common anatomical plan of organization of the AOS in mammals.

Morphology of rabbit retinal ganglion cells projecting to the medial terminal nucleus of the accessory optic system.

Rabbit retinal ganglion cells were retrogradely labeled following injection of rhodamine-labeled microspheres into the medial terminal nucleus. The small fraction of rhodamine-labeled neurons reached their peak concentration within the visual streak and then decreased with increasing eccentricity until none were encountered in the far periphery. The same rabbits also received injections of the fluorescent tracer Fast Blue into the superior colliculus. No double-labeled neurons were observed, i.e., ganglion cells projecting to the medial terminal nucleus (MTN) had no axon collaterals to the superior colliculus. In fixed retinae rhodamine-labeled ganglion cells were intracellularly injected with the fluorescent dye Lucifer Yellow to reveal their full dendritic arborization. MTN-projecting cells had medium-sized to large somata with thin and frequently branched dendrites. The large dendritic trees had a distinct morphology and were predominantly unistratified in a narrow band that presumably corresponded to the electrophysiologically determined on-sublamina of the inner plexiform layer. Dendritic field sizes were inversely related to ganglion cell density, thus providing an eccentricity-independent, constant dendritic coverage factor. Approximately five to six dendritic fields from neighboring cells cover every point of the retina. Published reports claim that the physiological class of on-direction-selective ganglion cells provides the sole retinal input to the MTN in the rabbit. In this context morphological features of MTN-projecting cells and their presumed functional correlation with on-direction-selective ganglion cells are discussed.