Retinopretectal and accessory optic projections of normal mice and the OKN-defective mutant mice beige, beige-J, and pearl

Retinal projections to the pretectal and terminal accessory optic nuclei were studied in normal wild-type mice and mutant mice with abnormal optokinetic nystagmus (OKN, Mangini, Vanable, Williams, and Pinto: J. Comp. Neurol. 241:191-209, '85). The mutants used were pearl, which exhibits an inverted OKN in response to stimulation of only the temporal retina, and beige and beige-J, which show inverted OKN in response to stimulation of only the temporal retina and, in addition, exhibit eye movements with a vertical component in response to horizontally moving, full-field stimuli. These projections were studied following intraocular injections of 3H-proline or horseradish peroxidase (HRP) with, respectively, light microscopic autoradiography or HRP histochemistry. 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. Similar heavy contralateral projections were distributed over the dorsal and medial terminal nuclei of the accessory optic system. Also, terminals sparsely covered the entire neuropil of the contralateral lateral terminal nucleus in some but not all wild-type mice. The most prominent accessory optic input was to the medial terminal nucleus and was provided by the inferior fasciculus of the accessory optic tract. A typical mammalian superior fasciculus of the accessory optic system with anterior, middle, and posterior components was present. Ipsilateral label was found in anterior and posterior olivary pretectal nuclei in all of the wild-type animals, but was found inconsistently in the ipsilateral terminal accessory optic nuclei. The pattern of contralateral retinal projection to the nucleus of the optic tract and posterior pretectal nucleus in mutants was indistinguishable from that seen in the normal wild-type mice. However, retinal inputs to the ipsilateral anterior and posterior olivary pretectal nuclei were significantly reduced in pearl mutants and were exceedingly sparse in the beige and beige-J mutant mice, while the contralateral inputs to these nuclei were increased in a complementary fashion in the mutants. The labeling of the accessory optic input to the contralateral dorsal terminal nucleus appeared to be substantially reduced in all of the mutant mice. The size of the principal accessory optic fascicle, the inferior fasciculus, was significantly smaller in beige, beige-J, and pearl mice; this reduction was greater in the beige and beige-J than in the pearl mice.(ABSTRACT TRUNCATED AT 400 WORDS)     

Developmental changes in the pattern of retinal projections in pigmented and albino rabbits

The distribution of retinal axons and/or terminals in the retino-recipient nuclei of pigmented and albino rabbits varying in age from the 24th postconceptional day (24PCD) to adulthood was examined following unilateral intraocular injections of the enzyme horseradish peroxidase. Both in pigmented and albino rabbits contralateral retinal axons and/or terminals in the dorsal and ventral lateral geniculate nuclei (DLG and VLG), superior colliculi (SC), pretecta (PT) and accessory optic tract nuclei (AON) were already present on 24PCD. In the period 26-30PCD the contralateral projection occupied the entire volume of the DLG, VLG and SC. Although 32PCD (the day of birth) the proportions of the volumes of DLG and VLG occupied by the contralateral projections were slightly reduced, their volume continued to increase in absolute terms up to adulthood. In pigmented rabbits the ipsilateral projections to all retino-recipient nuclei were most dense and extensive on 26PCD. From 26PCD, the relative extent of the ipsilateral projections was gradually reduced, but a reduction in their absolute extent did not become evident until 32PCD. By 32PCD the ipsilateral projection to the AON had disappeared completely. The distribution of ipsilateral axons and/or terminals and the relative proportion of the nuclei occupied by the ipsilateral projection in all other retino-recipient nuclei had become adult-like by 34PCD. In albino rabbits only a sparse ipsilateral projection to the presumptive superficial collicular layers was present on 24PCD. In the remaining retino-recipient nuclei an ipsilateral projection was present on 26PCD. From 26PCD the relative extent and from 30PCD the absolute extent of ipsilateral retinal axons and/or terminals was gradually reduced. The relative extent of the ipsilateral projection had become almost adult-like by 34PCD. Throughout development ipsilateral projections in albinos were consistently less dense and less extensive than those in pigmented rabbits, and unlike in pigmented rabbits, the ipsilateral projections to the VLG and PT were only transient. The differences between the two strains in the pattern of retinofugal projections were further enhanced during the period of segregation of the ipsilateral and contralateral projections. Considering the fact that in both strains there is a partial correspondence between the period in which the spatial extent of the ipsilateral projections is reduced and the period of retinal ganglion cell (RGC) death, it is likely that RGC death plays a role in the process of segregation of the retinal afferents into ocular domains. However, our data suggest that other mechanism(s) also play an important role in the process.     

Visual projections to the pontine nuclei in the rabbit: orthograde and retrograde tracing studies with WGA-HRP

Visual projections to the pontine nuclei in the rabbit were examined by means of both orthograde and retrograde tracing of WGA-HRP. The tecto-pontine projection was examined following microinjections of WGA-HRP in the right superior colliculus. The projection to the pontine nuclei is strictly ipsilateral and terminates at middle and caudal levels of the pons. The projection is absent in rostral pontine nuclei. The strongest projection is to the dorsal border of the dorsolateral pontine nuclei and is the only projection seen when the primary injection site is confined to superficial laminae. When the primary injection site also includes intermediate and deep laminae, patches of labelled terminals are also seen within dorsolateral, lateral, peduncular, paramedian, and ventral pontine nuclei as well as in the contralateral nucleus reticularis tegmenti pontis. The striate corticopontine projection was also examined with orthograde tracing of WGA-HRP. The striate corticopontine projection is ipsilateral. Most labelled terminals were seen in dorsolateral and lateral pontine nuclei throughout the rostral half of pons with some additional terminal labelling in paramedian and peduncular nuclei. Labelled terminals were also seen in ventral pontine nuclei throughout the middle and caudal levels of the pons. In a retrograde tracing study, visual projections to the pontine nuclei were examined following microinjections of WGA-HRP into the pontine nuclei. Labelled cells were seen ipsilaterally in superficial and deep laminae of the superior colliculus and in layer V of striate and surrounding occipital cortex. The pontine nuclei also receive ipsilateral projections from the ventral lateral geniculate, the nucleus of the optic tract, anterior and posterior pretectal nuclei, and the dorsal and medial terminal nuclei of the accessory optic system. These pathways are potential sources of visual input to the cerebellum.     

Retinopretectal projections in albino and pigmented rabbits: an autoradiographic study

The ipsilateral and contralateral retinal projection was studied in pigmented rabbits and in 3 strains of albino rabbits by anterograde transport of [3H]proline and [3H]fucose combined with autoradiographic techniques. Special attention was paid to the terminals in the pretectal area of both the pigmented and albino strains. On the contralateral side terminal labeling was found in both pigmented and albino rabbits in the nucleus of the optic tract (NOT), the anterior pretectal nucleus (PA), the posterior pretectal nucleus (PP) and the pretectal olivary nucleus (PO). Ipsilaterally labeling was found only in the pigmented strain in small patches in the PP. Ipsilateral projection was not found in the albinos in the pretectal area. The results are in agreement with the findings of Scalia in pigmented rabbits. The absence of ipsilateral labeling in the pretectal region in albinos is in contrast with earlier findings of Giolli and Takahashi et al., in pigmented rabbits but is in agreement with the observations of Takahashi and Oyster. Since no radioactively labeled fibers were found to project to the NOT in either pigmented or albino rabbits, these results do not support the hypothesis of Collewijn that the inverted optokinetic nystagmus in albinos is due to misrouting of the ipsilateral retinal fibers to the NOT.     

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

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

The organization of the pretectal nuclei in the trout: a revision based on experimental holodogical studies

The neuronal tracer DiI was applied to different brain centers of the rainbow trout in order to study the connections of pretectal nuclei. Our results showed that some pretectal nuclei receive a direct projection from the contralateral retina: the parvocellular superficial pretectal nucleus, the central pretectal nucleus, the intermediate pretectal nucleus and the ventral accessory optic nucleus. In turn, the central pretectal, the intermediate pretectal and the ventral accessory optic nuclei, together with the paracommissural nucleus, project to the cerebellum and the torus longitudinalis. The magnocellular superficial pretectal nucleus does not receive retinal projections, but receives ipsilateral projections from the optic tectum and the mesencephalic tegmentum. In turn, it projects to the ipsilateral oculomotor nucleus and lateral nucleus of the valvula. The posterior pretectal nucleus and the parvocellular superficial pretectal nucleus receive afferents from the ipsilateral nucleus isthmi. The posterior pretectal nucleus projects to the inferior hypothalamic lobe. Our results reveal a conspicuous projection from the ipsilateral parvocellular superficial pretectal nucleus to the contralateral one and also to the contralateral posterior prectectal nucleus, not reported in previous experimental studies of teleosts. Pretectal centers appear to integrate visual/optic-related centers mainly with the hypothalamus and the cerebellum. The organization of the trout pretectum was compared with the pretectal organization patterns proposed in various teleosts.     

Retinal projections in the native cat, Dasyurus viverrinus.

Retinal projections were examined in the native cat, Dasyurus viverrinus using Fink-Heimer material and autoradiography. We found six regions in the brain which receive retinal projections. These are (1) the dorsal lateral geniculate nucleus (2) the ventral lateral geniculate nucleus (3) the lateral posterior nucleus (4) the pretectum (5) the superior colliculus, and (6) the accessory optic system. We did not examine the hypothalamus. The accessory optic system and the lateral posterior nucleus receive a contralateral retinal projection only and the other four regions receive a bilateral retinal projection. There is extensive binocular overlap in the dorsal lateral geniculate nucleus. On the side contralateral to an eye injection of 3H leucine our autoradiographs show four contralateral layers which fill most of the nucleus. Three of these layers, 3, 4 and 5, also receive input from the opsilateral eye. Layer 1 which lies adjacent to the optic tract receives only contralateral retinal input. Layer 2 receives a direct retinal input only from the ipsilateral eye. The ipsilateral projection to the dorsal lateral geniculate nucleus forms a fairly continuous patch which is not divided into separate layers. The ipsilateral retinal input is located in the dorsal part of the lateral geniculate nucleus. The ventral quarter of the nucleus only receives a contralateral retinal input and therefore represents the monocular part of the visual field.     

An autoradiographic study of the efferent connections of the ventral lateral geniculate nucleus in the albino rat and the cat

The efferent connections of the ventral lateral geniculate nucleus (LGN_v) of the albino rat and the cat have been studied using the autoradiographic method for tracing axonal pathways. Following the injection of ³H-proline or ³H-leucine into the LGN_v of the rat, label transported in the rapid phase of axonal flow was found bilaterally in the olivary pretectal nuclei, the lateral terminal nuclei of the accessory optic system, and the ventral portion of the suprachiasmatic nuclei of the hypothalamus, and ipsilaterally in the rostrolateral portion of the superior colliculus. Since these regions are known to receive a direct projection from the retina, comparisons have been made of the distribution of silver grains in autoradiographs of each region following injections of ³H-proline into the eye and into the LGN_v; in every nuclear region except the superior colliculus the grain distributions were found to overlap precisely and, in the suprachiasmatic nuclei there also appears to be a similarity in the relative intensity of the input to the nuclei on the two sides. In the superior colliculus, the retinal fibers end mainly within the more superficial laminae, whereas those from the LGN_v are distributed mainly to the deeper layers where they overlap the projection from the striate and peristriate cortex. The LGN_v has also been found to project to the zona incerta on the same side and to the contralateral LGN_v, In the cat a similar set of projections to the lateral terminal nuclei of the accessory optic tract, the suprachiasmatic nuclei, and the pretectal areas of both sides has been found, together with a projection to the ipsilateral superior colliculus and the zona incerta of both sides. No evidence could be found in either species for a projection from the LGN_v to the visual cortex.     

An autoradiographic investigation of the subcortical visual system in chimpanzee.

Based on one adult chimpanzee monocularly injected with radioactive proline, retinofugal fibers were found to terminate bilaterally in the suprachiasmatic, pregeniculate, lateral geniculate, olivary, pretectal and lateral terminal nuclei, and the superior colliculi; the existence of a dorsal terminal nucleus of the accessory optic system is in doubt. In the ipsilateral geniculate nucleus, the fibers terminate in layers 2, 3 and 5; in the contralateral nucleus, they end in layers 1, 4 and 6. Midway through the geniculate nucleus, layers 3 and 4 split medially into two daughter layers each. In the superior colliculi, most of the retinal terminals are aggregated superficially in a band located in the stratum griseum superficiale. The contralateral band is interrupted by gaps; the ipsilateral band has fewer gaps, is slightly thicker and located more deeply. There is a limited second tier of terminals in the contralateral superficial gray.     

Retinal projections in the ringtailed possum Pseudocheirus peregrinus.

The retinal projections in the ringtailed possum, Pseudocheirus peregrinus were determined using Fink-Heimer material and autoradiography. At least seven regions in the brain receive retinal projections. These are (1) the suprachiasmatic nucleus of the hypothalamus (2) the dorsal lateral geniculate nucleus (3) the ventral lateral geniculate nucleus (4) the lateral posterior nucleus (5) the pretectum (6) the superior colliculus, and (7) the accessory optic system. The accessory optic system and lateral posterior nucleus receive a contralateral retinal projection only and the other five regions receive a bilateral retinal projection. The dorsal lateral geniculate nucleus consists of two parts: an outer alpha division of closely packed cells and an inner beta division containing loosely scattered cells. There are no cell layers apparent within the alpha division in Nissl sections. The autoradiographs and Fink-Heimer material reveal four concealed laminae within the alpha division. Lamina 1, which is adjacent to the optic tract and lamina 3 receive a predominantly contralateral input. Laminae 2 and 4 receive a predominantly ipsilateral input. The beta segment contains a fifth lamina which receives contralateral retinal input.     

The primary optic projections in the rabbit. An experimental degeneration study

The brains of ten rabbits (4 pigmented and 6 albino) sacrificed 6–21 days after unilateral ocular enucleation were prepared by Nauta and Nissl methods and used to study the projection and terminal destribution of degenerating optic axons. The retina is bilaterally represented in the alpha sectors of both ventral and dorsal lateral geniculate nuclei (LGv and LGd), in n. tractus opticus (NTO), in the dorsolateral portions of nn. praetectalis anterior (NPA) and posterior (NPP), and in the superior colliculus (SC). The retina is unilaterally represented in the contralateral terminal accessory optic nuclei. The mode of termination of crossed and uncrossed retinal projections endows the LGd with a concealed laminar organization. Four laminae are recognized and numbered consecutively from lateral to medial. Lamina one is extensive and formed entirely of crossed retinal input. The remaining three laminae occupy the medial zone of the LGd. Of these, laminae two and four are innervated predommantly by the ipsilateral retina while lamina three is supplied mainly by the contralateral retina. Uncrossed retinal innervations of LGv, NTO, NPA, NPP and SC are scant and overlapped entirely by crossed retinal inputs. Chiasmal decussation of the optic nerve is 90–95% complete with the uncrossed component, and specifically the uncrossed retino-LGd and -SC projections, being larger in pigmented as compared with albino rabbits.     

Projection from the accommodation-related area in the superior colliculus of the cat

Our previous study has indicated that accommodative responses can be evoked with weak currents applied to a circumscribed area of the superior colliculus in the cat. We investigated efferent projections from this area with biocytin in the present study. The accommodation area in the superior colliculus was identified by systematic microstimulation in each of five anesthetized cats. Accommodative responses were detected by an infrared optometer. After mapping the superior colliculus, biocytin was injected through a glass micropipette into the accommodation area, where accommodative responses were elicited with low-intensity microstimulation. In addition, accommodative responses to stimulation of the superior colliculus were compared before and after an injection of muscimol, an agonist of inhibitory neurotransmitter, into the pretectum. 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. Less dense terminals were seen in the anterior pretectal nucleus, the zona incerta, and the centromedian nucleus of the thalamus. In the descending projections, labeled terminals were observed mainly in the paramedian pontine reticular formation, the nucleus raphe interpositus, and the dorsomedial portion of the nucleus reticularis tegmenti pontis on the contralateral side. Less dense terminals were also seen in the nucleus of the brachium of the inferior colliculus, the cuneiform nucleus, the medial part of the paralemniscal tegmental field, and the dorsolateral division of the pontine nuclei on the ipsilateral side. Following the injection of muscimol into the pretectum, including the nucleus of the optic tract, the posterior pretectal nucleus, and the nucleus of the posterior commissure, accommodative responses evoked by microstimulation of the superior colliculus were reduced to 33–55% of the value before the injections. 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). © 1996 Wiley-Liss, Inc.     

Retinal projections in the house musk shrew, Suncus murinus, as determined by anterograde transport of WGA-HRP.

Retinal projections in the house musk shrew (Suncus murinus) were determined by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Unilateral injection of WGA-HRP into the vitreous body resulted in the terminal labeling of the optic projections in the suprachiasmatic nucleus (SCH), the ventral (CGLv) and dorsal (CGLd) lateral geniculate nuclei, the intergeniculate leaflet (IGL), the pretectum, the superficial layers of the superior colliculus (CS), and the dorsal terminal nucleus (DTN) of the accessory optic system (AOS). Labeling of the SCH was bilateral, with ipsilateral predominance, and covered the whole dorsoventral extent of the nucleus. Immunohistochemical studies revealed that VIP-like immunoreactive neurons and fibers were present in almost all parts of the SCH. No hypothalamic regions other than the SCH received the optic fibers. The ipsilateral projections to the CGLv, CGLd, and IGL were sparse, and a considerable number of uncrossed retinal fibers were found in the pretectal olivary nucleus. No retinal projections to the lateral posterior thalamic nucleus (LP) were found. Ipsilateral optic fibers projected sparsely to the medial part of the CS. The AOS consisted of a small DTN with a very few crossed retinal projections but no lateral and medial terminal nuclei. In addition, the AOS had no inferior fascicle.     

Projections of the lateral terminal accessory optic nucleus of the common marmoset (Callithrix jacchus)

The connections of the lateral terminal nucleus (LTN) of the accessory optic system (AOS) of the marmoset monkey were studied with anterograde ³H-amino acid light autoradiography and horseradish peroxidase retrograde labeling techniques. 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. A second, mejor bundle produces moderate-to-heavy labeling in all ipsilateral, accessory oculornotor nuclei (nucleus of posterior commissure, interstitial nucleus of Cajal, nucleus of Darkschewitsch) and nucleus of Bechterew; some of the fibers are distributed above the caudal oculomotor complex within the supraoculornotor periaqueductal gray. A third projection is ipsilateral to the pontine and mesencephalic reticular formations, nucleus reticularis tegmenti pontis and basilar pontine complex (dorsolateral nucleus only), dorsal parts of the medial terminal accessory optic nucleus, ventral tegmental area of Tsai, and rostral interstitial nucleus of the medial longitudinal fasciculus. Lastly, there are two long descending bundles: (1) one travels within the medial longitudinal fasciculus to terminate in the dorsal cap (ipsilateral > > contralateral) and medial accessory olive (ipsilateral only) of the inferior olivary complex. (2) The second soon splits, sending axons within the ipsilateral and contralateral brachium conjunctivum and is distributed to the superior and medial vestibular nuclei. The present findings are in general agreement with the documented connections of LTN with brainstem oculomotor centers in other species. In addition, there are unique connections in marmoset monkey that may have developed to serve the more complex oculomotor behavior of nonhuman primates. © 1995 Wiley-Liss, Inc.     

Efferent pathways of the nucleus of the optic tract in monkey and their role in eye movements

To clarify the role of the pretectal nucleus of the optic tract (NOT) in ocular following, we traced NOT efferents with tritiated leucine in the monkey and identified the cell groups they targeted. Strong local projections from the NOT were demonstrated to the superior colliculus and the dorsal terminal nucleus bilaterally and to the contralateral NOT. The contralateral oculomotor complex, including motoneurons (C-group) and subdivisions of the Edinger-Westphal complex, also received inputs. NOT efferents terminated in all accessory optic nuclei (AON) ipsilaterally; contralateral AON projections arose from the pretectal olivary nucleus embedded in the NOT. Descending pathways contacted precerebellar nuclei: the dorsolateral and dorsomedial pontine nuclei, the nucleus reticularis tegmenti pontis, and the inferior olive. Direct projections from NOT to the ipsilateral nucleus prepositus hypoglossi (ppH) appeared to be weak, but retrograde tracer injections into rostral ppH verified this projection; furthermore, the injections demonstrated that AON efferents also enter this area. Efferents from the NOT also targeted ascending reticular networks from the pedunculopontine tegmental nucleus and the locus coeruleus. Rostrally, NOT projections included the magnocellular layers of the lateral geniculate nucleus (lgn); the pregeniculate, peripeduncular, and thalamic reticular nuclei; and the pulvinar, the zona incerta, the mesencephalic reticular formation, the intralaminar thalamic nuclei, and the hypothalamus. The NOT could generate optokinetic nystagmus through projections to the AON, the ppH, and the precerebellar nuclei. However, NOT also projects to structures controlling saccades, ocular pursuit, the near response, lgn motion sensitivity, visual attention, vigilance, and gain modification of the vestibulo-ocular reflex. Any hypothesis on the function of NOT must take into account its connectivity to all of these visuomotor structures. © 1996 Wiley-Liss, Inc.     

Retinal projections in adult and newborn grey squirrels

Retinal projections in newborn squirrels were compared to those in adults by using horseradish peroxidase (HRP) as a highly sensitive anterograde tracer. In both newborn and adult squirrels, the HRP reaction product was found in the dorsal lateral geniculate nucleus, the superior colliculus, the pretectal nuclei, and the nuclei of the accessory optic tract. Thus, newborn squirrels have retinal input to most or all structures normally innervated in the adult. However, the pattern of terminations differed in the newborn from that in the adult, and this was especially apparent in the dorsal lateral geniculate nucleus and the superior colliculus. In the dorsal lateral geniculate nucleus, the regions of ipsilateral and contralateral retinal inputs were clearly less segregated than in adults, although the adult laminar pattern of retinal terminations was partially apparent, even though there was yet no cytoarchitectural evidence of the adult lamination pattern. In the superior colliculus, a marked difference was seen in the pattern of ipsilateral retinal terminations. In the adult, ipsilateral retinotectal input was restricted to a narrow, dense, patchy, mediolateral band in stratum opticum in the rostral colliculus. In the newborn, the ipsilateral retinotectal input was less dense, free of patches, spread in thickness to include much of the stratum opticum and the superficial grey, and spread in extent to include all but the caudal pole of the colliculus. These observations are consistent with the prevailing view that visual connections are initially widespread and become restricted during the course of development.     

Autoradiographic study of the retinal projections in the Chinese pangolin, Manis pentadactyla

Autoradiography was used to investigate the optic system of the Chinese pangolin, Manis pentadactyla. The pattern of retinal projections in the Chinese pangolin is similar to that described in other mammals. Each retina projects bilaterally to the suprachiasmatic nucleus, dorsal and ventral lateral geniculate nuclei, pretectal area, and superior colliculus (SC). Only contralateral projections are found to the medial, lateral, and dorsal accessory optic nuclei. The large lateral nucleus receives a dense projection from the retina and forms a compact mass on the dorsolateral area of the cerebral peduncle. The lamination of the SC could not be clearly demonstrated in the brain of the Chinese pangolin.     

The pretectal complex in the opossum: projections from the striate cortex and correlation with retinal terminal fields

Two terminal fields were revealed in the pretectal complex of the opossum by the Fink-Heimer method after striate cortical lesions. A rostral field is located within a rostrolateral strip of the compact part of the anterior pretectal nucleus, where a partial topographic arrangement of this projection is present. A caudal field is located within the sub-brachial nucleus of the optic tract, located between the brachium of the superior colliculus and the posterior pretectal nucleus. The corticotopic projection to this field is mirror-symmetric to that found in the superior colliculus and overlaps a bilateral projection from the retina. Based on hodological evidence, it is concluded that the nucleus of the optic tract in the opossum can be subdivided in (a) an intrabrachial nucleus receiving a direct projection from the contralateral retina and (b) a sub-brachial nucleus receiving projections from both retinae and from the striate cortex. The pretectal complex, as the superior colliculus, can be anatomically subdivided in a superficial region receiving visual input (theoptic pretectum) and a deep region only remotely connected to the visual system. The optic pretectum, however, differs from the superior colliculus in displaying a multiple-map arrangement within its constituent nuclei, instead of a single continuous representation of the visual field.     

Subcortical visual system of the African mole‐rat Cryptomys anselli: to see or not to see?

Abstract We studied the retinal projections, the distribution of cytochrome oxidase activity and the cyto- and myeloarchitecture of the subcortical visual system in the subterranean Ansell's mole-rat Cryptomys anselli. The optic nerve contained 1500 myelinated and a similar number of unmyelinated fibres. The retina projected to all the visual structures described in surface-dwelling sighted rodents. The suprachiasmatic nucleus was large and received bilateral retinal input. All other visual nuclei were reduced in size, were cytoarchitecturally poorly developed and received almost exclusively contralateral retinal projections. The dorsal and ventral lateral geniculate nuclei were moderately reduced and heavily innervated. The intergeniculate leaflet could be identified between these two nuclei. Pretectal nuclei were also relatively well-developed. The nucleus of the optic tract, the olivary pretectal nucleus, and the anterior and posterior pretectal nuclei were innervated by the retina. By contrast, the superficial, retinorecipient layers of the superior colliculus showed extreme reduction. The strata zonale, griseum superficiale and opticum were collapsed to a single layer 40 micro m thick. The accessory optic system was vestigial. These findings indicate that the functional subsystems involved in photoperiod perception, form and brightness discrimination, and movement analysis are anatomically rather well developed, whereas those involved in coordination of visuomotor reflexes are severely reduced. Thus, the visual system of C. anselli is much better developed than that of the blind mole-rat Spalax ehrenbergi. We suggest that Cryptomys anselli has retained basic visual capabilities.