The parabigeminogeniculate projection: Connectional studies in eight mammals

Abstract

Anterograde and retrograde tracing methods have been used to analyze the origin and distribution of parabigeminogeniculate axons in the gray squirrel, the gopher, the rat, the opossum, the cat, the greater bushbaby, the squirrel monkey and the macaque monkey. Our findings reveal that parabigeminogeniculate axons most heavily innervate regions of the lateral geniculate that are also targeted by axons arising from the superior colliculus (tectogeniculate). These geniculate layers and zones of parabigeminal and tectal overlap contain small cells, and in several species are associated with the small W cell retino-geniculocortical pathway. In addition to the dense input to small-celled layers and zones, parabigeminal axons in several species also innervate regions of the lateral geniculate nucleus that are relatively free of tectogeniculate axons and that are associated with the medium (X) and large (Y) cell streams. Finally, our data reveal that the laterality of parabigeminogeniculate pathways varies across mammals, being primarily crossed in the gray squirrel, the gopher, the rat, and the opossum, bilateral in the cat, and primarily ipsilateral in the three primates.

Calcium binding proteins distinguish large and small cells of the ventral posterior and lateral geniculate nuclei of the prosimian galago and the tree shrew (Tupaia belangeri).

“…In tree shrew the tectal fibers terminating in GL send collaterals to other centers, notably the ventral lateral geniculate nucleus and the pretectum (19). In both species, the parabigeminal nucleus, which is a target of SC, projects to layers of GL that include 4 and 5 in galago and 3 and 6 in Tupaia (20). All of these connections taken together fit Bishop's view of a phylogenetic old path.…”

Morphology of retinal axons induced to arborize in a novel target, the medial geniculate nucleus. I. Comparison with arbors in normal targets

“…Our injections were far from the tectogeniculate pathway, the optic radiations, and the internal capsule. Other inputs to the colliculus and LGN (e.g., parabigeminal nucleus, ventral LGN, brainstem reticular formation) are present in the optic tract or near it but in a more ventral location than our injection sites (Graybiel, 1978;Huerta and Harting, 1984;Reese, 1987;Fitzpatrick et al, 1988Fitzpatrick et al, , 1989Harting et al, 1991). We did not note arbors in any nonretinorecipient target structure, nor did we find labelled cells in the parabigeminal nucleus of any of the animals.…”

Oscillatory Bursts in the Optic Tectum of Birds Represent Re-Entrant Signals from the Nucleus Isthmi Pars Parvocellularis

“…The bilateral retinotopic projection is in register and mainly targets the SC representation of the near central and peripheral visual field (Graybiel, 1978;Sherk, 1979b), a fact perhaps related to attending to novel stimuli. This anatomical evidence suggests that the Pbg has a heterogeneous cellular composition, which is also supported by the presence of different Pbg subdivisions in the rat (Tokunaga and Otani, 1978), larger neuronal size of neurons projecting to the contralateral SC (Sherk, 1979b;Baizer et al, 1991;Jiang et al, 1996), and prominent Pbg projections to the thalamus (Fitzpatrick et al, 1988;Harting et al, 1991). Also, two types of Pbg terminal profiles have been distinguished in the SC (Jeon et al, 1993).…”