A Golgi analysis of the accessory optic fibers terminating in the medial terminal nucleus of the mouse accessory optic system

Identification of retinal ganglion cells and their projections involved in central transmission of information about upward and downward image motion

The direction of image motion is coded by direction-selective (DS) ganglion cells in the retina. Particularly, the ON DS ganglion cells project their axons specifically to terminal nuclei of the accessory optic system (AOS) responsible for optokinetic reflex (OKR). We recently generated a knock-in mouse in which SPIG1 (SPARC-related protein containing immunoglobulin domains 1)-expressing cells are visualized with GFP, and found that retinal ganglion cells projecting to the medial terminal nucleus (MTN), the principal nucleus of the AOS, are comprised of SPIG1⁺ and SPIG1⁻ ganglion cells distributed in distinct mosaic patterns in the retina. Here we examined light responses of these two subtypes of MTN-projecting cells by targeted electrophysiological recordings. SPIG1⁺ and SPIG1⁻ ganglion cells respond preferentially to upward motion and downward motion, respectively, in the visual field. The direction selectivity of SPIG1⁺ ganglion cells develops normally in dark-reared mice. The MTN neurons are activated by optokinetic stimuli only of the vertical motion as shown by Fos expression analysis. Combination of genetic labeling and conventional retrograde labeling revealed that axons of SPIG1⁺ and SPIG1⁻ ganglion cells project to the MTN via different pathways. The axon terminals of the two subtypes are organized into discrete clusters in the MTN. These results suggest that information about upward and downward image motion transmitted by distinct ON DS cells is separately processed in the MTN, if not independently. Our findings provide insights into the neural mechanisms of OKR, how information about the direction of image motion is deciphered by the AOS.

Pattern of retinal projections in the California ground squirrel (Spermophilus beecheyi): anterograde tracing study using cholera toxin

The retinofugal pathways in the California ground squirrel, Spermophilus beecheyi, were mapped after intravitreal injections of cholera toxin B-subunit. The results of the current study are consistent with work in other mammals and provide new details relevant to the organization and evolution of the visual system. All retinorecipient nuclei received bilateral input, with a contralateral predominance. The suprachiasmatic nucleus is heavily innervated, and sparse terminals were noted in other hypothalamic areas. In addition to the interstitial, medial, lateral, and dorsal terminal nuclei, a few fibers of the accessory optic tract may enter the ventral lateral geniculate and the nucleus of the optic tract, though this innervation may not derive from the same ganglion cells innervating the accessory optic nuclei. Retinal terminals are found in the intergeniculate leaflet and the "dorsal cap" of the ventral lateral geniculate. Retinal fibers pass rostrally from the dorsal cap toward the anterodorsal thalamus, confirming a projection described in the tree shrew and monkeys. Retinal termination patterns in the dorsal lateral geniculate reveal a hexilaminate organization of alternating ipsilateral and contralateral input. Variations in terminal morphology suggest that sublayers receive input from distinct ganglion cell types and that laminar comparisons can be made with primates. Finally, terminal patterns in the superior colliculus reveal a dense, highly ordered columnar organization supporting functional properties of tectal receptive fields. All the visual structures in the ground squirrel are large and well differentiated, making the sciurid visual system an accessible rodent model for comparing visual processing with that in other diurnal vertebrates.

Presynaptic localization of mu-opioid receptor-like immunoreactivity in retinal axon terminals within the terminal nuclei of the accessory optic tract: a light and electron microscope study in the rat

Neuropil within the terminal nuclei of the accessory optic tract of the rat showed intense to moderate mu-opioid receptor-like immunoreactivity (MOR-LI). After unilateral enucleation, MOR-LI within the terminal nuclei almost disappeared or was markedly reduced on the side contralateral to the operation. Electron microscopy revealed that MOR-LI axon terminals within the terminal nuclei were filled with round synaptic vesicles and in asymmetric synaptic contact mainly with dendritic profiles, and occasionally with somatic profiles.

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)

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

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