Olivary Pretectal Nucleus


Oscillations with a mean period of approximately 140 s were identified in 127 recording sites in Olivary pretectal nucleus (OPT).  

Melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) innervate the hypothalamic suprachiasmatic nucleus (SCN) and the Olivary pretectal nucleus (OPN), providing irradiance information for entrainment of circadian rhythms and for stimulating the pupillary light reflex.  

Exp Eye Res 43:867-869) to quantitatively assess the effects of albinism on retinal projections to a number of subcortical visual nuclei including the ventral lateral hypothalamus (VLH), ventral lateral preoptic area (VLPO), Olivary pretectal nucleus (OPN), posterior limitans (PLi), commissural pretectal area (CPA), intergeniculate leaflet (IGL), ventral lateral geniculate nucleus (vLGN) and superior colliculus (SC).  

They send axons directly to the suprachiasmatic nucleus (SCN), intergeniculate leaflet (IGL), and Olivary pretectal nucleus (OPN), thereby contributing to photic synchronization of circadian rhythms and the pupillary light reflex.  

We have examined the cellular and subcellular distribution and the patterns of expression of brain-derived neurotrophic factor (BDNF), and of its high affinity receptor, tyrosine kinase B (TrkB), in retinorecipient regions of the brain, including the superior colliculus, the lateral geniculate nucleus and the Olivary pretectal nucleus.  

Fos-ir was compared in brains of control mice that did and did not receive oestradiol treatment prior to sacrifice, and cell numbers in the preoptic area (POA), ventromedial nucleus of the hypothalamus (VMH), area 2 of cingulate cortex (CG2), granular layer of accessory olfactory bulb (Gr-AOB), Olivary pretectal nucleus (OPT) and pyramidal layer of field CA3 of hippocampus (Py-CA3) were increased 90 min after oestradiol treatment.  

The Olivary pretectal nucleus was reduced but still retained its characteristic morphology, possibly indicating a role in light detection.  

3) Pretectal injections that included the nucleus of the optic tract (NOT), and the Olivary pretectal nucleus (OLN), labeled terminals only over nontwitch motoneurons, in the contralateral C group and in the S group.  

The nucleus of the optic tract, the Olivary pretectal nucleus, and the anterior and posterior pretectal nuclei were innervated by the retina.  

Our results show that the PACAP-containing nerve fibres not only constituted the major projections to the SCN and the intergeniculate leaflet of the thalamus but also had a large terminal field in the Olivary pretectal nucleus.  

Here, we use immunohistochemistry for calretinin (CR) to label retinal afferents in the superior colliculus (SC), lateral geniculate nucleus, and Olivary pretectal nucleus of RCS rats aged between 2 and 26 months of age. Loss of CR fibers was also observed in the lateral geniculate nucleus and Olivary pretectal nucleus.  

Most nuclei of the pretectum receive innervation largely, but not solely, from the contralateral retina, although the Olivary pretectal nucleus has very dense patches of innervation derived exclusively from one retina or the other.  

The results showed that retinal ganglion cells projecting to the SCN send collaterals to the IGL, Olivary pretectal nucleus, and superior colliculus, among other places. Melanopsin-immunoreactive (IR) ganglion cells are present in the hamster retina, and some of these cells project to the SCN, IGL, Olivary pretectal nucleus, or superior colliculus.  

Although only a small change of VGluT2 immunoreactivity was observed in the contra- and ipsilateral suprachiasmatic nuclei, Olivary pretectal nucleus, anterior pretectal nucleus, and posterior pretectal nucleus, moderate reduction of VGluT2 was found in these regions after bilateral enucleation.  

The photopigment melanopsin has recently been identified in intrinsically photosensitive retinal ganglion cells (RGCs) that project to the suprachiasmatic nucleus (SCN), intergeniculate leaflet (IGL), and Olivary pretectal nucleus, suggesting that melanopsin might influence a variety of irradiance-driven responses.  

We have focussed here on the pathway that is responsible for the pupillary light reflex, which is mediated through the Olivary pretectal nucleus (OPN).  

The results show that the probable destruction of the Olivary pretectal nucleus and the nucleus of the optic tract has little or no effect on pupil grating or pupil colour responses.  

We found three regions in the pretectum (the Olivary pretectal nucleus, posterior limitans, and a region homologous to the hamster commissural pretectal nucleus), and two regions in the lateral geniculate complex (the intergeniculate leaflet and ventral lateral geniculate nucleus) that demonstrated significant Fos activation in response to light. Furthermore, the Olivary pretectal nucleus, the posterior limitans, and the ventral lateral geniculate nucleus showed preferential Fos activation after acute light onset rather than following chronic exposure to light at midday, whereas at midnight these nuclei showed Fos activation following both chronic light exposure and acute light onset.  

Neurons in a subset of retinorecipient nuclei [ i.e., suprachiasmatic nucleus (SCN), intergeniculate leaflet, Olivary pretectal nucleus (OPN), and lateral terminal nucleus] and autonomic nuclei [ i.e., paraventricular hypothalamic nucleus and Edinger-Westphal nucleus (EW)] are labeled by late stages of infection.  

The Olivary pretectal nucleus possessed NPY fibres, too.  

The onset and distribution of calbindin (CB) and parvalbumin (PV) immunoreactivity were investigated in the lateral geniculate nuclear complex and the Olivary pretectal nucleus (OPT) in developing rats.  

Best results were obtained at 24 h postinjection, revealing a continuous pattern of anterograde labeling from the retina, optic nerve, and chiasm to the contralateral optic tract, the dorsal and ventral lateral geniculate nucleus, the superior colliculus and its brachium, the Olivary pretectal nucleus, the nucleus of the optic tract, and the suprachiasmatic nucleus.  

Caudal IGL axons also terminate in the Olivary pretectal nucleus, the superficial gray of the superior colliculus, and the lateral and dorsal terminal nuclei of the accessory optic system.  

The retinae and retino-recipient areas of non-stimulated animals remained unlabeled, but many of these structures showed strong c-Fos expression bilaterally [ retina, dorsal lateral geniculate body (DLG), Olivary pretectal nucleus, retrosplenial cortex, neocortex] in light-exposed animals. Interestingly, the Olivary pretectal nucleus, which in mammals is involved in light/dark discrimination, as well as the DLG as part of the image-forming visual system were consistently labeled by c-Fos after light stimulation, indicating that vision in Cryptomys possibly plays a more significant role than previously assumed..  

The Olivary pretectal nucleus (OPN) is the first central nucleus in the pupillary light reflex arc (PLR).  

Although axons followed different patterns of ingrowth depending on their site of entry to the brainstem, within the pretectum, they innervated preferentially the nucleus of the optic tract and the Olivary pretectal nucleus in which they formed two types of terminal arbors.  

In addition, Fkh5/Mf3 is expressed by the developing endopiriform nucleus and by the Olivary pretectal nucleus.  

The functional reinnervation of the Olivary pretectal nucleus (OPN) was studied in adult rats with peripheral nerve (PN) grafts bridging the interrupted retinopretectal pathway.  

The pupillary light reflex (PLR) is under the control of retinal ganglion cells projecting to the Olivary pretectal nucleus (OPN).  

It is well established that the pupillary light reflex (PLR) in rats is mediated by a direct retinal projection to the Olivary pretectal nucleus (OPN).  

After Fluoro-Gold injections into the SCN, retrogradely labeled neurons are present in a number of brain areas, including the infralimbic cortex, the lateral septum, the medial preoptic area, the subfornical organ, the paraventricular thalamus, the subparaventricular zone, the ventromedial hypothalamic nucleus, the posterior hypothalamic area, the intergeniculate leaflet, the Olivary pretectal nucleus, the ventral subiculum, and the median raphe nuclei.  

The integration occurs at the primary input nucleus, the Olivary pretectal nucleus, and at the output nucleus, the Edinger-Westphal nucleus. Restriction of the site of integration to one Olivary pretectal nucleus by ablating the contralateral nucleus causes a substantial enhancement of the transplant-mediated response and a major reduction in the host eye-mediated response.  

The pretectal area contained degenerated fibers which were widespread in (i) the nucleus of the optic tract, (ii) Olivary pretectal nucleus, (iii) anterior pretectal nucleus, and (iv) the posterior pretectal nucleus.  

The Olivary pretectal nucleus is a primary visual centre, involved in the pupillary light reflex. In the present study an ultrastructural analysis was made of the Olivary pretectal nucleus by means of separate, anterograde and retrograde tracing techniques and immunohistochemistry of gamma-aminobutyric acid. Large-projection neurons and two types of gamma-aminobutyric acid-immunoreactive (GABA-ir) neurons are observed in the Olivary pretectal nucleus. In the neuropil of the Olivary pretectal nucleus, retinal terminals are found that contain round clear vesicles and electron-lucent mitochondria. Terminals originating from the contralateral Olivary pretectal nucleus exhibit small, round clear vesicles, electron-dense mitochondria and make asymmetric synaptic contacts (Gray type I) mainly with dendritic profiles. Retinal terminals, terminals originating from the contralateral Olivary pretectal nucleus and GABA-ir terminals are organized in glomerulus-like structures, in which dendrites of the large projection neurons form the central elements. The complexity of the synaptic organization and the abundancy of inhibitory elements in the Olivary pretectal nucleus suggest that the Olivary pretectal nucleus is strongly involved in processing visual information in the pupillary light reflex arc..  

Pupilloconstriction was evoked by microstimulation of the posteromedial pretectum around the NPC and the anterior pretectum around the Olivary pretectal nucleus..  

Following the injection of biocytin, in the ascending projections, labeled terminals were seen mainly in the caudal portion of the nucleus of the optic tract, the nucleus of the posterior commissure, the posterior pretectal nucleus, the Olivary pretectal nucleus, the mesencephalic reticular formation at the level of the oculomotor nucleus, and the lateral posterior nucleus of the thalamus on the ipsilateral side. These findings suggest that the accommodation area in the superior colliculus projects to the oculomotor nucleus through the ipsilateral pretectal area, especially the nucleus of the optic tract, the nucleus of posterior commissure, and the posterior pretectal nucleus, and also projects to the pupilloconstriction area (the Olivary pretectal nucleus), the vergence-related area (the mesencephalic reticular formation), and the active visual fixation-related area (the nucleus raphe interpositus)..  

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.  

Other regions in which [ 3H]epibatidine binding was greater than that of [ 3H]cytisine included the medial habenula, fasciculus retroflexus, Olivary pretectal nucleus and superficial gray layer of the superior colliculus.  

Crossed and uncrossed retinal projections to the Olivary pretectal nucleus occupy non-overlapping regions of this bilaterally represented nucleus in normal rats, with a greater number of optic axons directed to the contralateral Olivary pretectal nucleus. Retinae transplanted to the midbrain of neonatal rats, from whom the contralateral eye had been removed, also project to the Olivary pretectal nucleus at maturity. In addition, the relative proportion of transplant axons directed to the ipsilateral and contralateral Olivary pretectal nucleus varied among animals.  

In albino rats the size of the uncrossed optic pathway to the pupilloconstrictor centre, the Olivary pretectal nucleus, is reduced three-fold and there is a concomitant but less dramatic reduction in the size of the consensual response. Unilateral lesions of the Olivary pretectal nucleus in pigmented rats restrict all optic input to the opposite pretectum. Stimulation of one or both eyes in these animals suggests that integration occurs not only at the level of the Olivary pretectal nucleus, but also downstream in the Edinger-Westphal nucleus.  

In this study an ultrastructural analysis was made of the efferent projections of the Olivary pretectal nucleus in the rat. The anterograde tracer Phaseolus vulgaris leucoagglutinin was injected iontophoretically into the Olivary pretectal nucleus. In the descending pathway special attention was paid to the fine structural features of the Olivary pretectal nucleus efferents projecting to the Edinger-Westphal nucleus, the interstitial nucleus of Cajal, the nucleus of Darkschewitsch and the periaqueductal gray.  

The Olivary pretectal nucleus is a primary visual centre sensitive to luminance changes. 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. 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. 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.  

NPY-IR neurons of the thalamic precommissural nucleus, nucleus of the optic tract, and Olivary pretectal nucleus are derived from the superior group.  

Although autoradiography studies indicate that the binding distribution of [ 3H]ABT-418 and (-)-[ 3H]cytisine are largely identical, there are some brain regions including the striatum, Olivary pretectal nucleus and the superior colliculus, in which [ 3H]ABT-418 demonstrates significantly (P < .05) less binding.  

Results show a first and largest LTN projection to the pretectal and AOS nuclei including the ipsilateral nucleus of the optic tract, dorsal terminal nucleus, and interstitial nucleus of the superior fasciculus (posterior fibers); smaller contralateral projections are to the Olivary pretectal nucleus, dorsal terminal nucleus, and LTN.  

In the rat, the RHT has two components, one which projects to the SCN and the intergeniculate leaflet of the thalamus and has no known peptide content and one which projects to the SCN and, perhaps, to the Olivary pretectal nucleus and contains substance P (SP).  

Injecting the retrograde fluorescent neuronal tracer fluoro-gold into the dorsal nucleus of the lateral geniculate body (dLGN), the Olivary pretectal nucleus (OPN), and the superior colliculus (SC) revealed the existence of some ganglion cells (RGCs) scattered outside the temporoventral crescent of the ipsilateral retina in the adult albino rats.  

While the Olivary pretectal nucleus has been shown to be central to the pupillary constriction response in rats, it is not at all clear at which level the consensual response is generated. To examine this we have investigated the efferent projections of this nucleus, as well as the effect of unilateral lesions of the Olivary pretectal nucleus, on the direct and consensual pupillary light reflexes. The results demonstrate that the Olivary pretectal nucleus projects bilaterally to the Edinger-Westphal nucleus, as well as to the nucleus of the posterior commissure, which itself projects bilaterally to the Edinger-Westphal nucleus. The Olivary pretectal nucleus also projects to the ipsilateral ventral lateral geniculate nucleus. Unilateral lesions of the Olivary pretectal nucleus decrease, but do not abolish, the direct and consensual pupillary light reflexes by as much as 66%. Since some degree of consensual response remains, this is likely to be due to the bilateral projection from the Olivary pretectal nucleus, either directly or indirectly through the nucleus of the posterior commissure, to the Edinger-Westphal nucleus. These results show that while the bilateral projection from the Olivary pretectal nucleus to the Edinger-Westphal nucleus contributes to the consensual pupillary light reflex, the bilateral retinal projection to the Olivary pretectal nucleus is the more determinant component of the pathway.  

Suprachiasmatic nucleus efferents comprise four major fiber groups: (i) an anterior projection to the ventral lateral septum, the bed nucleus of the stria terminalis and anterior paraventricular thalmus; (ii) a periventricular hypothalamic projection extending from the preoptic region to the premammillary area; (iii) a lateral thalamic projection to the intergeniculate leaflet and ventral lateral geniculate; and (iv) a posterior projection to the posterior paraventricular thalamus, precommissural nucleus and Olivary pretectal nucleus.  

Neocortical, cerebellar, and thalamic regions had low levels of binding, except lobules 9-10 of the cerebellum, the Olivary pretectal nucleus, zona incerta and lateral mammillary nucleus, in which moderate to high levels of binding were detected.  

We examined the effects of constant dark or constant light on substance P (SP) and/or neuropeptide Y (NPY) immunoreactive fibres in the rat suprachiasmatic nucleus (SCN) and Olivary pretectal nucleus (OPT) by immunohistochemistry.  

Changes of terminals were investigated in the Olivary pretectal nucleus, which contains a dense aggregation of retinal terminals in the core region. Within the core region of the Olivary pretectal nucleus, strong increases of immunoreactivity of NF-L and NF-M were detected beginning at 2 days postlesion and persisting at 8 days.  

Four nuclei of the pretectal complex, the Olivary pretectal nucleus, the medial pretectal nucleus, the nucleus of the optic tract and the posterior pretectal nucleus, all have a demonstrated role in visual function.  

Following monocular injection of either horseradish peroxidase or rhodamine-B-isothiocyanate, four pretectal nuclei, including the nucleus of the optic tract, posterior pretectal nucleus, anterior pretectal nucleus and the Olivary pretectal nucleus, could be identified to receive direct retinal input in both pigmented and albino strains.  

GAD65 mRNA is more abundant in several structures of the visual system, including the lateral geniculate nuclei, superior colliculi, and Olivary pretectal nucleus, as well as in several hypothalamic and pontine nuclei.  

In the pretectum, both the Olivary pretectal nucleus and the nucleus of the optic tract could be identified as receiving ipsilateral and contralateral retinal projections.  

Immunohistochemistry with monoclonal antibodies was used on vibratome sections through optic tract (OT), dorsal lateral geniculate nucleus (dLGN), Olivary pretectal nucleus (OPN), and superior colliculus (SC).  

These areas were the substantia gelatinosa of the spinal cord dorsal horn; the solitary tract; the nucleus of the solitary tract, visceral portion; the area postrema; the trigeminal nerve and spinal trigeminal nucleus; the medial nucleus of the inferior olive; the rostral, dorsomedial and dorsolateral interpeduncular subnuclei and overlying interfascicular nucleus; the supramammillary area; the lateral septal nucleus; the bed nucleus of the stria terminalis, anterior medial portion; the optic nerve and tract; the suprachiasmatic nucleus, ventroposterolateral portion; the magnocellular subnucleus of the ventrolateral geniculate nucleus; the intergeniculate leaf; the medial pretectal nucleus and the Olivary pretectal nucleus.  

Projections to the nucleus of the optic tract (first relay station of the optokinetic pathway) appear significantly more affected than those to the Olivary pretectal nucleus (involved in the pupillary light response).  

The ocular stump of the transected optic nerve of adult rats was connected by means of an autologous peripheral nerve graft with the pretectal region which contains the relay nucleus of pupillary constriction, the Olivary pretectal nucleus.  

Delicate PHA-L-immunoreactive nerve fibers were observed in the posterior paraventricular thalamic nucleus, precommissural nucleus, Olivary pretectal nucleus, anterior and posterior pretectal nuclei, and posterior commissure.  

The highest densities of these alpha BT-insensitive, nicotine-sensitive sites were found in the fasciculus retroflexus, the lateral geniculate nucleus, the medial terminal nucleus of the accessory optic tract, and the Olivary pretectal nucleus.  

In both types of injection we found labeled pretectal cells mainly in the nucleus of the optic tract but also found some cells labeled in the Olivary pretectal nucleus and the posterior pretectal nucleus.  

In all 7 co-processed groups, the best responders within each group showed the heaviest innervation of the Olivary pretectal nucleus.  

Some of these nuclei (superior colliculus, nucleus of the optic tract, dorsal terminal nucleus) usually receive extensive transplant projections, others are innervated partially (dorsal division of the lateral geniculate nucleus, Olivary pretectal nucleus, medial terminal nucleus), while a few (ventral division of the lateral geniculate nucleus, suprachiasmatic nucleus, intergeniculate leaflet) are not innervated at all.  

Nerve growth factor receptor-immunoreactive fibers and varicosities were seen in the olfactory bulb, piriform cortex, neocortex, amygdala, hippocampus, thalamus, Olivary pretectal nucleus and hypothalamus.  

The projection to the Olivary pretectal nucleus (OPN) from the contralateral eye is observed on the first day after birth and appears adult-like on postnatal day 5.  

Areas that contain only NGF-R immunoreactive fibers and terminals can be distinguished from the cellular sites of NGF-R biosynthesis and include the suprachiasmatic nucleus, the principal Olivary pretectal nucleus, the superior colliculus, the inferior olive, and the principal and spinal trigeminal nuclei.  

Illumination of the transplant caused pupilloconstriction of the host eye, a response abolished by removal of the transplant or damage to the Olivary pretectal nucleus which is the pupilloconstriction center of the brain stem. The density of label in the Olivary pretectal nucleus did not, however, correlate with the briskness of the graft-mediated pupillary reflex.  

NGFRI staining was seen in a variety of sensory pathways and related structures, such as olfactory tract and glomerular layer of olfactory bulb; retina, optic nerve and tract, lateral geniculate nucleus, medial terminal nucleus of the accessory optic tract, and Olivary pretectal nucleus; ventral cochlear nucleus and to a lesser degree in dorsal cochlear nucleus, superior olive, and nucleus of lateral lemniscus; solitary tract; cuneate nucleus, gracile nucleus, and ventroposterior thalamic nucleus.  

In addition, axon and terminal degeneration was observed in several discrete forebrain and hindbrain areas not previously associated with capsaicin-induced degeneration in either adult or neonatal rats: the inferior olive, the Olivary pretectal nucleus, the interpeduncular nucleus, the suprachiasmatic nucleus, and the lateral septum/medial accumbens region.  

These neurons are composed of fusiform cells and small-sized multipolar cells in the Olivary pretectal nucleus, superficial horizontal cells, fusiform cells, small-, medium- and large-sized multipolar cells in the optic tract nucleus, and small- and medium-sized multipolar cells in the posterior pretectal nucleus.  

In the pretectum, the projections to the rostral pretectal areas were greatly increased in area, especially in the region of the Olivary pretectal nucleus and posterior pretectal nucleus.  

There is no topographic organization in the retinal projection to the Olivary pretectal nucleus (NOL).  

In wild-type mice, strong contralateral retinal projections covered the entire nucleus of the optic tract, the anterior and posterior divisions of the Olivary pretectal nucleus, and the posterior pretectal nucleus.  

The medullary blink premotor area receives afferents especially from oculomotor control structures in the reticular formation of the brainstem while the pontine blink premotor area receives afferents from the Olivary pretectal nucleus and/or the nucleus of the optic tract and from the dorsal red nucleus and its dorsally adjoining area.  

The results indicated that these afferents were derived from the following brainstem areas: the dorsal red nucleus and the mesencephalic tegmentum dorsal to it; the Olivary pretectal nucleus and/or the nucleus of the optic tract; the dorsolateral pontine tegmentum (parabrachial nuclei and nucleus of K├Âlliker-Fuse) and principal trigeminal nucleus; the ventrolateral pontine tegmentum at the level of the motor trigeminal nucleus; the caudal medullary medial tegmentum; the lateral tegmentum at the level of the rostral pole of the hypoglossal nucleus and the ventral part of the trigeminal nucleus and the nucleus raphe pallidus and caudal raphe magnus including the adjoining medullary tegmentum.  

Afferents project bilaterally from the parabigeminal nuclei, the nucleus of the optic tract, the posterior pretectal region, the dorsal part of the lateral posterior-pulvinar complex and the ventral nucleus of the lateral lemniscus; and ipsilaterally from the substantia nigra pars reticulata, the pars lateralis of the ventral lateral geniculate nucleus, the intergeniculate leaflet, the zona incerta, the Olivary pretectal nucleus, the nucleus of the posterior commissure, the lateral thalamus, Forel's field H2, and the ventromedial hypothalamus.  

Very high concentrations of 5-HT1 receptors were localized in the choroid plexus, lateroseptal nucleus, globus pallidus and ventral pallidum, dentate gyrus, dorsal subiculum, Olivary pretectal nucleus, substantia nigra, reticular and external layer of the entorhinal cortex. From the areas strongly enriched in 5-HT1 sites, dentate gyrus and septal nucleus contained 5-HT1A sites, while globus pallidus, dorsal subiculum, substantia nigra and Olivary pretectal nucleus were enriched in 5-HT1B.  

The terminals of axons projecting to the Olivary pretectal nucleus have been identified by electron microscopy following injections of horseradish peroxidase into the superior colliculus of adult albino rats.  

The Olivary pretectal nucleus (PO) is characterized by distinctive neurons with a gnarled, tufted, richly branched dendritic arbor forming a dense neuropil within the nucleus.  

The luminance detectors in the Olivary pretectal nucleus, which are likely candidates mediating the pupillary light reflex, responded to all frequencies of sinusoidally modulated light up to 12-25 Hz.  

All luminance detectors were located in the Olivary pretectal nucleus, whereas darkness detectors were located in the posterior pretectal nucleus. The Olivary pretectal nucleus may therefore be involved in pupilloconstruction in the light, and the posterior pretectal nucleus, with pupillodilation in the dark..  

The nucleus of the optic tract and/or the Olivary pretectal nucleus.  

Pretectofacial fibers arise from the Olivary pretectal nucleus and end mainly in the dorsal division of the facial motor nucleus, bilaterally, with a contralateral predominance. It is known that the Olivary pretectal nucleus receives retinal fibers, and that the dorsal division of the facial motor nucleus contains orbicularis oculi motoneurons.  

(2) Monosynaptic projections from the superior colliculus and some of the pretectal nuclei (nucleus of the optic tract, Olivary pretectal nucleus) to the nucleus prepositus hypoglossi may constitute polysynaptic visual afferents to the VN, which would account for the residual visual sensitivity of the VN neurons after cerebellar or inferior olivary lesions..  

A second change in central retinal pathways was found in the Olivary pretectal nucleus where a significant loss of retinal input also occurred.  

The greatest concentration of radioactivity within each optic center was found in the visuotopic aspect subserving the superior visual field; particularly the medial aspects of the superior colliculus, Olivary pretectal nucleus, and posterior pretectal nucleus, and the anterior portion of the nucleus of the optic tract.  

The endings of retinal axons form three terminal fields in the pretectum in: 1, Olivary pretectal nucleus (PO), bilaterally; 2, posterior pretectal nucleus (PP), bilaterally; and 3, nucleus of the optic tract (NTO), contralaterally.  

The development of retinopretectal projections is assessed mostly from the analysis of the Olivary pretectal nucleus (PO).  


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