Nucleus Of The Optic Tract Research Articles

Retinal slip neurons in the nucleus of the optic tract and dorsal terminal nucleus in cats with congenital strabismus.

1. Visual response properties of neurons in the nucleus of the optic tract (NOT) and dorsal terminal nucleus of the accessory optic tract (DTN) were electrophysiologically investigated in five congenitally strabismic cats and compared with normal adult cats and 3- to 4-wk-old kittens. 2. As in normal cats, NOT-DTN cells of strabismic cats preferred horizontal ipsiversive stimulus movement. However, NOT-DTN neurons in strabismic cats altered their activity to a lesser amount per degree change of stimulus direction than do normal adult cats. In addition, NOT-DTN cells in strabismic cats exhibited a broader directional tuning, i.e., they increase their activity to a broader range of directions than control NOT-DTN cells. 3. Spontaneous activity and activity difference between preferred and nonpreferred direction were significantly lower in NOT-DTN neurons of strabismic cats than in normal adult cats and resembled that found in 3-wk-old kittens. Maximal stimulus-related activity was lower than in normal adult cats but higher than in kittens. 4. Visual latencies to onset of movement in the preferred direction were indistinguishable in strabismic and in normal adult cats. Visual latencies to onset of movement in the nonpreferred direction, however, were shorter in strabismic cats than in normal adult cats. 5. The average velocity tuning curve of NOT-DTN cells in strabismic cats was very flat without a well-defined optimal stimulus velocity. Thus it closely resembled data from 3-wk-old kittens. 6. Binocular convergence was significantly altered to a stronger dominance of the contralateral eye in NOT-DTN of strabismic cats. This reduction of binocular neurons was less pronounced than in cats with artificially induced strabismus or in 3-wk-old kittens. 7. In conclusion, the data presented here for retinal slip neurons in the NOT-DTN of strabismic cats closely resemble those from 3-wk-old kittens where no functional cortical input to the NOT-DTN is present. However, the elevated stimulus-driven activity and the still relatively high degree of binocularity give a clear indication of a functional, albeit weak and abnormal, cortical input to the NOT-DTN in these naturally strabismic cats.

Localization of AT2 angiotensin II receptor gene expression in rat brain by in situ hybridization histochemistry.

To localize the gene expression of AT2 angiotensin II receptors in rat brain we performed in situ hybridization histochemistry using 35S-labeled antisense riboprobes. The AT2 receptor mRNA expression pattern was compared in consecutive brain sections, from 2 week old rats, with the receptor expression by means of [125I]Sar1-ANG II binding and displacement with AT2 selective ligands followed by autoradiography. Expression of AT2 receptor mRNA was found in several thalamic nuclei (ventral posterolateral, mediodorsal, central medial, paracentral, and paraventricular), the medial geniculate nuclei, the nucleus of the optic tract, the subthalamic nucleus, the interposed nucleus of the cerebellum, and in the inferior olive. In these areas the AT2 receptor gene expression corresponds well with [125I]Sar1-ANG II binding. In addition, AT2 receptor mRNA expression was found in the red nucleus where no [125I]Sar1-ANG II binding was present. No significant hybridization of the AT2 receptor antisense probe was found in septal nuclei, the locus coeruleus, the dorsolateral geniculate nucleus, or the cerebellar cortex, areas rich in [125I]Sar1-ANG II binding. Our results indicate that some brain regions may be involved in AT2 receptor formation, transporting the receptor protein to other brain areas. However, in most structures, both the formation and expression of receptors occur, suggesting the existence of local AT2 receptor circuits, or that of AT2 autoreceptors. Other structures express only the receptor protein, indicating that these AT2 receptors are produced elsewhere. Our present data are the basis for further studies on the clarification of AT2 receptor pathways in the brain.

Optokinetic nystagmus in cats with congenital strabismus.

1. Eye movements were recorded in seven innately esotropic cats during monocular and binocular horizontal optokinetic stimulation, using the search coil technique in five cats and electrooculography in two cats. 2. During closed loop measurements in these strabismic cats, slow phases of optokinetic nystagmus (OKN) were characterized by an overall reduced gain when compared with normal controls. In addition, response gain to monocular nasotemporal stimulation was even more reduced than that to temporonasal stimulation, resulting in an increased asymmetry of closed loop gain. 3. During open loop measurements, eye velocity in strabismic cats was very low at all velocities tested. 4. Differential analysis of the symmetry of OKN revealed that all our strabismic cats had a "good" or more symmetric and a "poor" or more asymmetric eye. In addition, when analyzed separately at individual velocities, the symmetry index of the good eye was fairly constant over the velocity range tested. By contrast, the symmetry index of the poor eye dropped dramatically at higher stimulus velocities. 5. To analyze the relationship of OKN symmetry and cortical physiology, we calculated the ratio between the percentage of neurons driven by one eye in the ipsilateral and the contralateral cortical hemisphere. We found a weak correlation between OKN symmetry and this cortical symmetry index (P < 0.05, analysis of variance). 6. In conclusion, slow eye movements in cats with congenital esotropia are characterized by extremely low gain, especially at higher stimulus velocities. In addition, OKN symmetry during monocular stimulation is decreased. Our data suggest that OKN symmetry is weakly correlated with the proportion of binocular neurons in the visual cortex ipsilateral to the stimulated eye. However, OKN characteristics seem to reflect to a higher degree the response properties of neurons in the pretectal nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system than properties of neurons in the visual cortex.

Pretectal projections to the oculomotor complex of the monkey and their role in eye movements.

The nucleus of the optic tract (NOT) is associated with the generation of optokinetic nystagmus (OKN), whereas the olivary pretectal nucleus (ol), which lies embedded in the primate NOT, is believed to be essential for the pupillary light reflex. In this anatomical study of the pretectum, projections from NOT and ol to structures around the oculomotor nucleus were traced in the monkey, to determine which cell groups they innervated. 1. 3[H]-leucine injections were placed into NOT and ol, and labelled terminals were observed just outside the classical oculomotor nucleus (nIII), in the "C-group' and midline cell clusters, both of which contain small motoneurons of the extraocular eye muscles. In addition, there were strong projections to the lateral visceral cell column of the Edinger-Westphal complex (lvc), but not to the Edinger-Westphal nucleus (EW) itself. All of these projections were mainly contralateral. 2. NOT efferents terminated over the ipsilateral medial accessory nucleus of Bechterew (nB), but not over the adjacent nucleus Darkschewitsch. 3. Injections of a retrograde tracer into the oculomotor complex showed that the pretectal afferents described above originated mainly from the dorsomedial part of NOT and from ol. 4. The use of a transsynaptic retrograde tracer, tetanus toxin fragment (BIIb), established the monosynaptic nature of the connection between dorsomedial NOT (contralaterally) and ol (bilaterally), to the small extraocular motoneurons outside classical nIII. The "C-group' motoneurons may play a role in vergence, and lvc in pupillary constriction and depth of focus. Our results imply that NOT and ol participate in the control of some aspects of the near-response, which may be important in the generation of some components of OKN in primates.

Impulse responses distinguish two classes of directional motion-sensitive neurons in the nucleus of the optic tract.

1. Recordings were made from direction-selective neurons in the nucleus of the optic tract (NOT) and dorsal terminal nucleus (DTN) of the wallaby, Macropus eugenii. Responses were elicited in the cells by brief displacements of a wide-field sine wave grating pattern in their preferred and antipreferred directions. The grating pattern was moved by a quarter cycle or less during the experiments. Once the stimulus duration was less than a certain value, referred to as the integration time, the magnitude of the responses depended on the size of the displacement, regardless of the velocity of the movement. The responses elicited by movements of the image in less than the integration times are referred to as velocity impulse responses. 2. The NOT-DTN contains two kinds of direction-selective neurons. The cells of the first type were maximally sensitive to patterns moving at low velocities (slow cells). These neurons had integration times of 40-80 ms. The cells of the second type were most sensitive to stimulus movements at high velocities (fast cells) and had integration times of 20-40 ms. 3. The velocity impulse responses of the slow cells were characterized by a rapid increase in firing rate followed by a slow exponential decline over a period of 1-4 s back to their resting activities. The impulse responses of the fast cells showed a rapid increase in firing rate followed by a short-lived inhibition of the background activity. 4. When the duration of the moving stimulus was longer than the integration times of the cells, they began to resolve the time course of the stimulus velocity. Under these conditions the slow cells showed a slow rise in firing rate during stimulation and a slow, exponential decay in firing after the stimulus came to rest. The fast cells showed a rapid increase in firing rate followed by a slow decay during the period of motion and then a short-lived inhibitory phase after the motion stopped. 5. The responses to rectangular pulses of stimulus velocity could be predicted for both cell types by convolving the velocity impulse responses of the cells with the velocity profile of the stimulus. Thus the cells responded linearly to image displacement in the sense that their responses to the velocity pulses could be described as the sum of a set of velocity impulse responses each weighted by the instantaneous stimulus strength, the latter being governed by the size of the image displacement. 6. Given the demonstration of linearity with respect to image displacement as the input, the Fourier transforms of the impulse responses were calculated to reveal the temporal filtering characteristics of the neurons. The slow cells had low-pass characteristics, the main power in the responses being at frequencies below 5-10 Hz. The fast cells had band-pass temporal filtering properties, the optimum pass band being at 6-12 Hz. 7. The filtering properties of the two cell types complement each other such that the optokinetic system as a whole is able to operate accurately over a wide frequency range.

視運動性眼振と関連する網膜神経細胞の分布について 系統発生学的検討

The nucleus of the optic tract (NOT) in the pretectum has been considered to be the interface between the retina and premotor nuclei in the pathway conveying signals responsible for horizontal optokinetic nystagmus (OKN). However, what parts of the retina and which kinds of retinal ganglion cells project their fibers into the NOT have not been conclusively determined.We injected horseradish peroxidase conjugated with wheatgerm agglutinin (WGAHRP) into the NOT of rats, cats, and monkeys, and identified the labeled cells in the retina. Labeled retinal ganglion cells were observed bilaterally in each of these animal systems as follows:1. In rats, labeled retinal ganglion cells were diffusely distributed in the contralateral side, whereas those labeled cells were situated only in the lower temporal crescent in the ipsilateral side.2. In cats, the highest concentration of labeled cells was found in the area centralis and the region adjacent to it in both retinae. These cells were situated only above the horizontal meridian through the optic disk and the area centralis, and they were situated mainly in the temporal crescent involved in the area of the area centralis on both sides. No labeled cells were observed in nasal region of the area centralis on the ipsilateral side. In rats and cats, most of the labeled cells were judged to be small cells, i.e., W cells. However, X-and Y-like cells were also definitely labeled, suggesting that these cells participate in OKN.In the monkey, few labeled retinal ganglion cells were observed above the temporal area of the foveae on both retinae. These were small P γ cells. According to the pattern of cortical development, the distribution of retinal ganglion cells responsible for OKN may be altered so that those in the ipsilateral side in rats are in the lower temporal crescent but those in the cat are in upper temporal crescent at the level of the horizontal meridian. Furthermore, the distribution pattern was changed, and the retinal ganglion cells concentrated in the area centralis.By the time of the appearance of the fovea in the monkey, there are no retinal ganglion cells in the fovea and few small cells above the temporal area in both retinae. Consequently, the pursuit system by the fovea might prevail.

Chapter 30 Visual inputs to cerebellar ventral paraflocculus during ocular following responses

The activity of cerebellar Purkinje cells was recorded in the ventral paraflocculus (VPFL) of alert monkeys during ocular following responses induced by brief movements of the visual scene. The mossy fiber input evoked 'simple-spikes' which increased their activity during either ipsiversive or downward motion of the visual scene. On the other hand, the 'complex-spikes' evoked by the climbing fiber input increased their activity during either contraversive or upward movement. To further define the sources of the visual input to the VPFL, we recorded single units in the dorsolateral pontine nucleus (DLPN), which is known to project to the VPFL as mossy fibers, and in the pretectal nucleus of the optic tract (NOT), which is known to project to the inferior olive whose neurons project to the cerebellum as climbing fibers. In both areas, most neurons were directionally selective, and responded to the moving visual scene with very short latencies (approximately 40-60 ms). These results suggest that both DLPN and NOT neurons deliver information concerning movements of the visual scene to the VPFL through different pathways.

Responses of Neurons of the Nucleus of the Optic Tract and the Dorsal Terminal Nucleus of the Accessory Optic Tract in the Awake Monkey

The nucleus of the optic tract (NOT) and the dorsal terminal nucleus of the accessory optic tract (DTN) are essential nuclei for the generation of slow-phase eye movements during horizontal optokinetic nystagmus. We recorded from 101 neurons (all directionally selective) in four NOT/DTN of three trained and behaving rhesus monkeys. Neuronal activity increased when stimuli moved ipsiversively with respect to the recording site and decreased below spontaneous activity when stimuli moved contraversively. While the monkey fixated a small spot, some NOT/DTN neurons did not respond at all to the retinal image slip of a whole-field random dot pattern; others showed a monotonic increase of activity to increasing velocities of that stimulus. The velocity range tested was up to 100 degrees/s. During the execution of optokinetic nystagmus, 39 of 73 cells tested showed a velocity-tuned response with an average optimum at 21 degrees/s retinal image slip. Following saccades during optokinetic nystagmus (quick phases), the NOT/DTN neuronal activity briefly attained the level of spontaneous activity, as predicted from the velocity selectivity during optokinetic nystagmus. Immediately upon cessation of optokinetic stimulation in the preferred direction, NOT/DTN activity returned to the spontaneous level and did not reflect the ongoing optokinetic afternystagmus in darkness. Most NOT/DTN neurons displayed direction selectivity also during smooth pursuit. Twenty-one of 50 cells tested (42%) always responded to the retinal slip of the target (target velocity cells), 16 cells (32%) responded to the retinal slip of the background (background velocity cells), and 13 cells (26%) did not respond at all during smooth pursuit. We conclude from our results that the NOT/DTN is an essential structure for the processing of the direction and speed of retinal image slip. This information is then used for the generation and maintenance of slow eye movements, preferentially during horizontal optokinetic nystagmus but also during pursuit eye movements.

Neuronal basis of optokinetic reflex pathology in naturally strabismic monkeys

The optokinetic reflex and neuronal response properties in the central visual pathway were studied in three macaque monkeys (Macaca nemestrina) with early childhood strabismus of various origin. Binocularity in the primary visual cortex (VI) measured electrophysiologically was reduced both in a monkey with resolved strabismus and in a monkey with accommodative strabismus when compared to normal controls. By contrast, binocularity in the nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system (NOT-DTN) was only reduced in the monkey with resolved strabismus ('resolved'), but appeared normal in animals with accommodative strabismus ('accom. 1 'and 'accom. 2'). Sub-threshold binocular interactions were normal in all animals. The velocity tuning curves of retinal slip neurons in the NOT-DTN of all strabismic monkeys were not different from normal controls. Horizontal optokinetic nystagmus was asymmetric in monkey 'accom. 2', and for the non-fixating eye in monkey 'resolved'. In monkey 'accom. 1' OKN was normal. Open loop eye velocity was lower in the monkey with resolved strabismus than in monkeys with accommodative strabismus. These data suggest that different causes of strabismus may affect neuronal response properties and behavior to different degrees. The effects on the optokinetic reflex of resolved, but early onset strabismus were more severe than those of accommodative strabismus. This corresponds to the wide variability of defects in the optokinetic system of strabismic humans.

The nucleus of the optic tract (NOT) and the dorsal terminal nucleus (DTN) of opossums (Didelphis marsupialis aurita).

Wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was injected unilaterally into the pretectocollicular region of opossums (Didelphis marsupialis aurita), primarily to investigate the existence of a commissural subcortical pathway but also to reveal afferents and efferents of the nucleus of the optic tract (NOT) and dorsal terminal nucleus (DTN) in this species. Labelled cells and terminals were observed in the contralateral NOT-DTN. Furthermore, HRP was injected bilaterally in the region of the inferior olive (IO) to verify if the distribution of labelled cells in the NOT-DTN overlapped the region of commissural labelled cells. The two subpopulations of retrogradely labelled cells coincided, being distributed within the retinal terminal field attributed to the NOT-DTN, as revealed by contralateral eye injections of HRP. The commissural cells were located slightly more ventral than the olivary cells in the optic tract. The pretectocollicular WGA-HRP injections also labelled cells and terminals bilaterally in the lateral terminal nucleus (LTN), interstitial nucleus of the superior fasciculus, posterior fibers (INSFp), ventral lateral geniculate nucleus (vLGN), and superior colliculus (SC) and ipsilaterally in the medial terminal nucleus (MTN). In addition, further caudally, labelled cells and terminals were observed bilaterally in the nuclei prepositus hypoglossi (PH) and in the medial (MVN) and lateral (LVN) vestibular nuclei. Labelled terminals were found in the ipsilateral nucleus reticularis tegmenti pontis (NRTP) and in the IO with ipsilateral predominance. This study allowed an anatomical delimitation of the NOT-DTN in this opossum species, as defined by the olivary and commissural subpopulations, as well as a hodological evaluation of this region. The existence of some common anatomical aspects with other mammalian species is discussed.

1644 Excitotoxic lesions of the unilateral pedunculopontine tegmental nucleus produce contralateral hemiparkinsonism in the japanese monkey

Accommodative responses were evoked by microstimulation of a circumscribed area in the lateral suprasylvian (LS) cortex of the cat. We studied anatomical connections of this area with WGA-HRP. We identified an accommodation-related area by systematic microstimulation of the LS cortex in each of nine cats. Accommodative and pupillary responses were monitored by an infrared optometer and a pupillometer, respectively. WGA-HRP was injected into the accommodation-related area where accommodative responses were elicited with low-intensity microstimulation, but pupillary responses were not evoked. Retrogradely labeled cells were found mainly in ipsilateral areas 17, 18 and 19, the pulvinar, the lateral posterior nucleus of the thalamus (LP) and the contralateral LS area. Fewer labeled cells were found in ipsilateral areas 20 and 21, the ventral lateral suprasylvian area (VLS), the splenial visual area (SVA) and the lateral geniculate nucleus (LGN). Anterogradely labeled terminals were located mainly in the ipsilateral LP, the rostral portion of the pontine nuclei and the superficial layers of the ipsilateral superior colliculus which corresponds to the representation of the central visual field. Less dense labeled terminals were also found in the ipsilateral nucleus of the optic tract (NOT) in two cats.

Projections from visual areas of the cerebral cortex to pretectal nuclear complex, terminal accessory optic nuclei, and superior colliculus in macaque monkey.

The purpose of this study was to analyze the projections from visually related areas of the cerebral cortex of rhesus monkey to subcortical nuclei involved in eye-movement control; i.e., the pretectal nuclear complex, the terminal nuclei of the accessory optic system (AOS), and the superior colliculus (SC). The anterograde tracer 3H-leucine was pressure injected bilaterally into the cortex of six monkeys (for a total of 12 cases) involving the primary visual cortex (area 17); the medial prestriate cortex (medial 18/19); dorsomedial area 19; the caudal portion of the cortex of the superior temporal sulcus, upper bank (cytoarchitectural area OAa) and lower bank (area PGa); the lower bank of the caudal lateral intraparietal sulcus (area POa); and the inferior parietal lobule (area 7). The results revealed that the pretectal nucleus of the optic tract received inputs from medial prestriate cortex, dorsomedial part of area 19, OAa, and PGa. The posterior pretectal nucleus received sparse projections from area 7 and the cortex lining the intraparietal sulcus (dorsomedial part of area 19 and POa). The pretectal olivary nucleus was targeted by neurons in cortex of dorsomedial area 19, and the anterior pretectal nucleus was targeted by neurons in both dorsomedial 19 and area 7. The nuclei of the AOS (dorsal terminal; lateral terminal; and interstitial nuclei of the superior fasciculus, posterior and medial fibers) received projections exclusively from areas OAa and PGa. Furthermore, in one case with PGa injection, the medial terminal nucleus, dorsal portion, was also labeled. The visual cortical areas studied projected differentially upon the SC laminae. The primary visual area 17 projected only to the superficial laminae, i.e., stratum zonale (SZ), stratum griseum superficiale (SGS), and stratum opticum (SO). On the other hand, the medial portion of the prestriate cortex and caudal OAa and PGa targeted the superficial and intermediate laminae, i.e., SZ, SGS, SO, and stratum griseum intermediale (SGI), whereas caudal area POa projected primarily to the intermediate layer SGI. Rostral area 7 (mainly 7b) neurons terminated in the stratum album intermediale (SAI); no SC terminals were found in a case in which caudal area 7 (mainly 7a) was injected.

Projection of individual axons from the pretectum to the dorsal lateral geniculate complex in the cat.

The dorsal lateral geniculate nucleus of the thalamus transmits visual signals from the retina to the cortex. Within the lateral geniculate nucleus, the ascending visual signals are modified by the actions of a number of afferent pathways. One such projection originates in the pretectum and appears to be active in association with oculomotor activity. Much remains unknown about the pretectal-geniculate projection. Our purpose was to examine for the first time individual axon arbors from the pretectum that project to the lateral geniculate nucleus, describing their topography and nuclear and laminar targets. We made injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin into the cat pretectum, targeting the nucleus of the optic tract. Serial 40 microns coronal sections were processed by using immunohistochemistry to reveal labeled axons that were then serially reconstructed using light microscopy. Pretectal-geniculate axons appeared morphologically heterogeneous in terms of swelling size, branching patterns, and laminar target. Most axons innervated the geniculate A laminae. A separate, smaller population innervated the C laminae. All axons exhibited substantially greater spread medial-laterally than rostral-caudally in the lateral geniculate nucleus, displaying a topographical organization for visual field elevation, but not azimuth. Many pretectal axons that projected to the LGN also innervated adjacent structures, including the medial interlaminar nucleus, the perigeniculate nucleus, and/or the pulvinar. These results indicate that the projection from the pretectum to the dorsal lateral geniculate nucleus is heterogeneous, is semitopographical, and may coordinate neural activity in the lateral geniculate nucleus and in neighboring visual thalamic structures in association with oculomotor events.

Pretectofugal fibers from the nucleus of the optic tract in monkeys

The nucleus of the optic tract (NOT) is the visuo-motor relay between the retina and preoculomotor structures in the pathway mediating optokinetic nystagmus (OKN). NOT lesions in monkeys produce no OKN toward the lesioned side. Then, efferent fibers from the NOT course through the brainstem and may reach the vestibular nucleus, which is proposed to be the final nucleus to the motor nucleus. In the present study, the tracer was injected through a micropipette in the NOT in four monkeys. Labeled terminals were observed ipsilaterally in the parabigeminal nucleus, superficial layers of the superior colliculus, dorsal and lateral terminal nuclei of the accessory optic system and pretectal nuclei and contralaterally in the NOT and superficial layers of the superior colliculus. Descending fibers from the NOT consisted of two major pathways: (1) fibers descended medially from the injection site through the reticularis pontis oralis to reach the lateral part of the ipsilateral nucleus reticularis tegmenti pontis; (2) fibers projecting into the dorsal cap of inferior olive, by far the greatest number of labeled fibers, descended ventrally along the lateral border of the reticularis pontis oralis and reached the medial lemniscus where they descended further and branched into the dorsolateral pontine nucleus, the lateral part of the nucleus reticularis tegmenti pontis, the peduncular pontine nucleus, the lateral pontine nucleus, the nucleus prepositus hypoglossi, the medial vestibular nucleus and finally the dorsal cap of the inferior olive. Consistent with the physiological data, the direct terminals to the medial vestibular nucleus could serve to drive the storage mechanisms and to produce OKN in the monkey.

Retrograde fluorescent microsphere tracing of retinal and central afferents to the nucleus of the optic tract in pigmented and albino rats

The pretectal nucleus of the optic tract is involved in optokinetic nystagmus. Albino animals suffer from inverse optokinetic nystagmus, possibly due to a smaller number of ipsilateral projections. Animals with laterally placed eyes have an asymmetric nystagmus, attributed to a presumed lack of binocular cortical input to the nucleus of the optic tract. Moreover, a direct input from the ipsilateral retina is controversial. We investigated the retinal and central afferents to the nucleus of the optic tract in the rat by retrograde tracing using fluorescent latex microspheres. Ipsilaterally projecting retinal ganglion cells were observed in pigmented and also in albino rats. Projections from the visual cortex and primary visual nuclei were demonstrated.

Demonstration of retinal afferents in the RCS rat, with reference to the retinohypothalamic projection and suprachiasmatic nucleus.

In the Royal College of Surgeons (RCS) rat, characterized by inherited retinal dystrophy, retinal projections to the brain were studied using anterograde neuronal transport of cholera toxin B subunit upon injection into one eye. The respective immunoreactivity was found predominantly contralateral to the injection site in the lateral geniculate nucleus, superior colliculus, nucleus of the optic tract, medial terminal nucleus of the accessory optic tract, and bilateral hypothalamic suprachiasmatic nuclei. Although terminal density was somewhat reduced in dystrophic rats, the projection patterns in these animals appeared similar to those seen in their congenic controls and were comparable to the visual pathways described for the rat previously. In dystrophic rats, the number of cell bodies exhibiting immunoreactivity to vasoactive intestinal polypeptide, viz. a population of suprachiasmatic neurons receiving major retinohypothalamic input, was reduced by one-third, and some differences were observed in the termination pattern of the geniculohypothalamic tract, as revealed by immunoreactivity to neuropeptide Y in the suprachiasmatic nucleus.

Independent efferent populations in the nucleus of the optic tract: an anatomical and physiological study in rat and cat.

The efferent projections of the nucleus of the optic tract (NOT) and dorsal terminal nucleus of the accessory optic system (DTN) to the contralateral NOT-DTN, ipsilateral inferior olive (IO), ipsilateral nucleus prepositus hypoglossi (NPH), and ipsilateral dorsal lateral geniculate nucleus (LGNd) were examined in pigmented rats and in cats by using anterograde and retrograde tract tracing, as well as extracellular recording and electrical stimulation. Anterograde tracing in the rat revealed a dense termination field of NOT-DTN efferents throughout the homologous contralateral territory. In both species three different cell populations, projecting to the contralateral NOT-DTN, ipsilateral IO, and ipsilateral LGNd, respectively, were distinguished by means of multiple retrograde tracing. No clear topographical segregation of the different NOT-DTN relay cell populations was observed. On the other hand, a large proportion (at least 60%) of NOT-DTN neurons projecting to the ipsilateral NPH were found to bifurcate upon the IO in the rat. Electrophysiologically, NOT-DTN neurons projecting to the IO were identified by their directionally selective responses. Such neurons were never activated by electrical stimulation of either the contralateral NOT-DTN or the ipsilateral LGNd. Neurons antidromically activated from the contralateral NOT-DTN could not be activated from the ipsilateral LGNd. Thus, in both cat and rat the NOT-DTN includes at least three independent relay cell populations. As a consequence, the NOT-DTN must serve functions additional to the generation of eye movements during optokinetic nystagnus, a function subserved by the directionally selective NOT-DTN cells.

Induction of c- fos protein by patterned visual stimulation in central visual pathways of the rat

Localized patterned visual stimulation was used in rats to investigate the feasibility of stimulus-dependent induction of the immediate early gene c- fos in neurons of cortical and subcortical visual centers of this mammal. Moving and stationary visual patterns, consisting of gratings and arrays of dark dots, induced Fos-like immunoreactivity in populations of neurons in retinotopically corresponding stimulated regions of the dorsal and ventral lateral geniculate nucleus (dLGN, vLGN), stratum griseum superficiale of the superior colliculus, nucleus of the optic tract, and primary (striate) visual cortex. Only moving stimuli induced Fos-like immunoreactive (FLI) neurons in extrastriate visual areas, particularly in the anterolateral (AL) visual area. This suggests that area AL is equivalent to the motion sensitive areas MT and PMLS of the monkey and cat. Stimulus-induced FLI neurons in the striate cortex were predominantly distributed in layers 4 and 6, while few labeled neurons were present in layers 2–3, and almost none in layer 5. The laminar distribution of stimulus-induced FLI cells in the extrastriate cortical area AL was similar to that of the striate cortex, with the exception that more FLI cells were present in layer 5. Statistical comparison of somata size of the stimulus-induced FLI neurons in dLGN with that of Cresyl violet stained neurons in the same sections revealed that the population of geniculate FLI neurons is composed of relay cells and interneurons.

Sources of subcortical afferents to the macaque's dorsal lateral geniculate nucleus.

The dorsal lateral geniculate nucleus (dLGN) is the thalamic region responsible for transmitting retina signals to cortex. Brainstem pathways to this nucleus have been described in several species and are believed to control the retinocortical pathway depending on the state of the animal (awake, asleep, drowsy, etc.). The purpose of this study was to determine all of the subcortical sources of afferents to the dLGN in a higher primate, the macaque monkey, whose visual system is similar to that of humans. Injections of horseradish peroxidase (HRP), with or without conjugation to wheat germ agglutinin, were made into the dLGNs of seven macaque monkeys, followed by perfusion, brain sectioning, and analyses of neurons in the brainstem, thalamus, and hypothalamus that contained the retrogradely transported marker. The reticular nucleus of the thalamus, pedunculopontine nucleus, parabigeminal nucleus, pretectal nucleus of the optic tract, superior colliculus, dorsal raphe nucleus, and tuberomammillary region of the hypothalamus contained many retrogradely labeled neurons ipsilateral to the injections. In the contralateral brainstem, HRP-labeled cells were found only in the pedunculopontine nucleus, nucleus of the optic tract, and dorsal raphe nucleus. The number of labeled neurons on the contralateral side was about one-half of that in corresponding ipsilateral nuclei. The locus coeruleus contained no labeled neurons in four of the macaques that had injections limited to the dLGN. There are seven subcortical regions that send afferents to the dLGNs of macaque monkeys. Except for the locus coeruleus, these are the same as observed for other species, such as the cat and rat, and indicate the possible sources of subcortical control over the dLGNs of humans.

Organization of permanent and transient neuropeptide Y-immunoreactive neuron groups and fiber systems in the developing hamster diencephalon.

The development of neuropeptide Y-immunoreactive (NPY-IR) cell and fiber systems in the hamster diencephalon was studied. Eight perinatal groups of NPY-IR neurons develop into 12 distinct sets in nuclei of the adult diencephalon and mesencephalon. NPY-IR neurons of the thalamic precommissural nucleus, nucleus of the optic tract, and olivary pretectal nucleus are derived from the superior group. Those in the adult magnocellular nucleus of the posterior commissure and deep mesencephalic nucleus are from the dorsal group. An arcuate group contributes neurons to the arcuate nucleus and median eminence and a mammillary group transiently exists in the mammillary region. A medial group gives rise to two sets of neurons, one that migrates to the intergeniculate leaflet and another that develops in the medial nucleus reuniens. A very large ventral group provides NPY-IR neurons to the adult medial zona incerta and caudal reticular thalamus. Groups of NPY-IR neurons also appear in the bed nucleus of the stria terminalis and centromedian thalamic nucleus. Superior group neurons may undergo apoptosis. In several groups, neurons become fewer during development, and NPY-IR may disappear. NPY-IR neurons of several groups initially migrate away from the neuroepithelial zone with later emergence of a distinct, persistent set of NPY-IR neurons in the same neuroepithelial region. The data show that neuropeptide content can be used to identify particular sets of neurons early in development, thereby allowing migration patterns to be followed and principles of brain development to be elucidated.