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

Abstract

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. 247:191–209, '85). The mutants used were (1) pearl, which exhibits an inverted OKN in response to stimulation of only the temporal retina, and (2) 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 auto‐radiography or HRP histochemistry. In wild‐type mice, strong contra lateral 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. As with the wild‐type mice, ipsilateral projections to the terminal accessory optic nuclei were rarely found in the mutant mice. The reduced inferior fasciculus of the accessory optic tract of the beige and beige‐J mutants suggests that the optic inputs that reach the medial terminal nucleus may be reduced or abnormal. These mutants also show an abnormal vertical component of eye movements in response to horizontally moving stimuli. Thus, abnormal responses mediated by neurons of the medial terminal nucleus may be involved in these misdirected eye movements.