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The connections of the posterior part of the medial prefrontal cortex with the thalamic lateral posterior nucleus in rats were studied using anterograde and retrograde axonal transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) and tritiated leucine. After injections of WGA-HRP into the medial prefrontal cortex, an area confirmed to receive direct projections from the visual cortex, retrogradely labeled neurons were observed ipsilaterally in the lateral posterior nucleus of the thalamus, as well as in the mediodorsal, anteromedian ventromedial, ventrolateral, laterodorsal, centrolateral, paracentral, rhomboid, parafascicular and posterior nuclei. In the lateral posterior nucleus, the labeled cells were located mainly in the lateroventral portion of its anterior half. In contrast, the posterior half of this nucleus was free of label. Axons labeled by the anterograde transport of tritiated leucine were dispersed over the same region which contained retrogradely labeled cells. The functional significance of these connections is discussed with special reference to their possible role in visuomotor integration in rats.

Following injections of horseradish peroxidase-wheat germ agglutinin conjugate (HRP-WGA) and tritiated leucine into area 20 of the cat, terminal labeling was observed in visual areas 19, 21, the splenial visual area, the lateral suprasylvian area as well as in premotor, association and limbic related cerebral cortical regions. Labeled terminals in the subcortex were distributed in the caudate nucleus, the claustrum, the putamen, the anterior ventral nucleus, the intralaminar nuclei, the caudal division of the intermediate lateral nucleus, the lateralis posterior-pulvinar complex, the parvocellular C laminae of the dorsal lateral geniculate nucleus and the ventral lateral geniculate nucleus. In HRP-WGA preparations, retrogradely labeled somata were observed in these regions with the exception of certain subcortical structures. The projections are discussed with respect to the possible role area 20 plays in the cortical control of pupillary constriction.

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