Telencephalic projections in two teleost species

The efferent pathways of the telencephalon were investigated in the percomorph Eugerres and the berycomorph Holocentrus. One telencephalic hemisphere was resected by suction and the animals were perfused 7-35 days thereafter. The brains were processed according to a modification (Method 7 in Ebbesson, '70) of the Fink-Heimer ('67) technique for selective silver impregnation of degenerating axons and terminals. Some fibers emerging from the lesioned telencephalic hemisphere terminate upon the contralateral hemisphere. The large bulk of efferent fibers, however, descends into the ipsilateral diencephalon and gives off the so-called strio-tectal bundle (STB) as well as the medial forebrain bundle (MFB). The remaining contingent eventually splits into the so-called strio-lobar bundle (SLB) and the lateral forebrain (LFB), but, previous to splitting, it contributes most of the telencephalic projection to the optic tectum in Eugerres, and gives abundant terminals to the ipsilateral nucleus rotundus or prethalamicus in both Eugerres and Holocentrus. The STB conveys all telencephalo-tectal fibers in Holocentrus, and some of them in Eugerres. Telencephalic efferents teminate ipsilaterally in the middle level of the tectum's stratum griseum centrale; in Holocentrus there is also a small projection to the stratum opticum. The MFB terminates at the caudal hypothalamus and gives terminals all along its course. The LFB also gives terminals all along its course and terminates upon a nucleus located between the midline and the corpus glomerulosum. The SLB spreads out and terminates in the inferior lobe of the hypothalamus.