Efferents from the optic tectum to the brain stem in the Japanese quail (Coturnix japonica). Anterogradely biocytin method.

Abstract

Efferents from the optic tectum to the brain stem in the Japanese quail (Coturnix japonica) were studied with the anterogradely biocytin method. After injection of biocytin into the ipsilateral optic tectum, labeled terminals were seen in the rotund nucleus (Rt), neuropil part of the ventral lateral geniculate nucleus (GLnv), principal part of the dorsal lateral geniculate nucleus, lateral part of the dorsolateral thalamic nucleus, triangular nucleus (T), superficial parvocellular nucleus (SPC), pretectal nucleus, pretectal area (PA), subpretectal nucleus, central gray matter (GC), isthimo optic nucleus (ION), magnocellular and parvocellular parts of the isthimo nuclei (Imc and Ipc), semilunar nucleus (SLu), lateral and medial pontine nuclei and reticular formation (FRM) of the medulla, ipsilaterally. Labeled fibers were seen in the septomesencephalic tract nucleus, FRM, interstitio-paraetecto-subpraetectal nucleus, and the dorsal and ventral tectoreticular tracts (TRd and TRv). In the contralateral brain stem, labeled terminals were seen in the Rt, T. FRM, PA and paramedian nucleus. The contralateral terminals were remarkably fewer than those of the ipsilateral side. The present findings of the labeled terminals of the SPC and the GC at the level of the mesencephalic nucleus of the trigeminal nerve (MnT), and the topographic projection from optic tectum to the Rt in the thalamus, were original observations in the avian. The labeled terminals in the GLnv, Ipc, Imc and ION showed topographical projections from the optic tectum. Pathways to the contralateral brain stem were via the commissure posterior, ventral supraoptic decussation, and the predorsal bundle. The present results suggest that tectofugal impulses in the quail relate to various functions with special relation to the function of the GC at the level of the MnT as well as a visual function.