The mammalian pulvinar nucleus (PUL) establishes heavy interconnections with the parietal lobe, but the precise nature of these connections is only partially understood. To examine the distribution of corticopulvinar cells in the cat, we injected the PUL with retrograde tracers. Corticopulvinar cells were located in layers V and VI of a wide variety of cortical areas, with a major concentration of cells in area 7. To examine the morphology and distribution of corticopulvinar terminals, we injected cortical areas 5 or 7 with anterograde tracers. The majority of corticopulvinar axons were thin fibers (type I) with numerous diffuse small boutons. Thicker (type II) axons with fewer, larger boutons were also present. Boutons of type II axons formed clusters within restricted regions of the PUL. We examined corticopulvinar terminals labeled from area 7 at the ultrastructural level in tissue stained for γ-aminobutyric acid (GABA). By correlating the size of the presynaptic and postsynaptic profiles, we were able to quantitatively divide the labeled terminals into two categories: small and large (RS and RL, respectively). The RS terminals predominantly innervated small-caliber non-GABAergic (thalamocortical cell) dendrites, whereas the RL terminals established complex synaptic arrangements with dendrites of both GABAergic interneurons and non-GABAergic cells. Interpretation of these results using Sherman and Guillery's recent theories of thalamic organization (Sherman and Guillery [1998] Proc Natl Acad Sci U S A 95:7121-7126) suggests that area 7 may both drive and modulate PUL activity. Indexing termscortex; thalamus; visual system; sensorimotor; ultrastructure The feline pulvinar nucleus (PUL) receives input from a wide array of cortical areas (Raczkowski and Rosenquist, 1983) as well as the pretectum (PT;Berman, 1977;Berson and Graybiel, 1978;Schmidt et al., 2001;Baldauf et al., 2005). However, the contribution of these inputs to the response properties of PUL neurons is unknown. The cells of the PUL have large visual receptive fields that often lack clear boundaries; they respond more robustly to diffuse illumination than to small visual cues (Godfraind et al., 1972;Mason, 1981 by saccadic eye movements. Sudkamp and Schmidt (2000) identified three general classes of neurons in the feline PUL: "S" neurons are active during saccadic eye movements, "V" neurons are responsive to visual stimuli and unresponsive to eye movements, and "SV" neurons respond to both stationary ON and OFF stimuli and to sudden stimulus shifts.These response properties are similar in many respects to those of neurons in the parietal cortex, an area that establishes extensive reciprocal connections with the PUL (de V Clüver and Campos-Ortega, 1969;Heath and Jones, 1971;Robertson and Cunningham, 1981;Niimi et al., 1983;Raczkowski and Rosenquist, 1983;Avendaño et al., 1985;Olson and Lawler, 1987). In the cat, these cortical areas are primarily located within the middle suprasylvian gyrus (MSg) or cytoarchitectonically in areas 5 and 7 (Gu...

Both the pretectum (PT) and the superior colliculus (SC) play an important role in directing eye movements and in sensorimotor coupling. A reciprocal connection between the PT and the SC has been described, which suggests a strong interplay between these two structures. We injected the cat SC with retrograde tracers and examined the labeled pretectotectal (PTT) cells at the light and electron microscopic level. PTT cells were distributed mostly in the nucleus of the optic tract and 93.1% contained gamma amino butyric acid (GABA). We also observed that PTT cells are located outside of pretectal regions distinguished by dense retinal terminals and clusters of cells that contain calbindin. This suggests that the GABAergic PTT cells are distinct from the GABAergic pretectogeniculate cells that have been previously described as being distributed within these regions. Finally, to determine the synaptic targets of PTT terminals, we injected the PT with anterograde tracers and examined terminals labeled in the SC at the ultrastructural level. The labeled PTT terminals were beaded fibers that were distributed mainly within the stratum griseum superficiale (SGS) of the SC. Using postembedding immunocytochemistry, 94.5% were found to be GABAergic. The PTT terminals were mostly small in size and primarily contacted GABA-negative dendrites (88.1%) and in some cases somata (4.7%). The remainder terminated on GABAergic dendrites (7.2%). Our results suggest that the PTT cells constitute a separate population of GABAergic efferent cells in the PT, which may function to inhibit the activity of non-GABAergic SC efferent cells in the SGS.

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The pretectum (PT) can supply the pulvinar nucleus (PUL), and concomitantly the cortex, with visual motion information through its dense projections to the PUL. We examined the morphology and synaptic targets of pretecto-pulvinar (PT-PUL) terminals labeled by anterograde transport in the cat. By using postembedding immunocytochemical staining for γ-aminobutyric acid (GABA), we additionally determined whether PT-PUL terminals or their postsynaptic targets were GABAergic. We found that the main projection from the PT to the PUL is an ipsilateral, non-GABAergic projection (72.4%) that primarily contacts thalamocortical cell dendrites (87.6%), and also the dendritic terminals of interneurons (F2 profiles; 12.4%). The PT additionally provides GABAergic innervation to the PUL (27.6% of the ipsilateral projection), which chiefly contacts relay cell dendrites (84.6%) but also GABAergic profiles (15.4%). These GABAergic pretectal terminals are smaller, beaded fibers that likely branch to bilaterally innervate the PUL and dLGN, and possibly other targets. We also examined the neurochemical nature of PT-PUL cells labeled by retrograde transport and found that most are non-GABAergic cells (79%) and devoid of calbindin. Taking existing physiological and our present morphological data into account, we suggest that, in addition to the parietal cortex, the non-GABAergic PT-PUL projection may also strongly influence PUL activity. The GABAergic pretectal fibers, however, may provide a more widespread influence on thalamic activity. Indexing termsthalamus; visual system; jerk neurons; eye movements; GABA The feline pulvinar nucleus (PUL) receives input from the pretectum (PT; Graybiel, 1972;Berman, 1977;Itoh, 1977;Berson and Graybiel, 1978;Graybiel and Berson, 1980;Weber et al., 1986;Schmidt et al., 2001), as well as a wide array of visual cortical areas (Raczkowski and Rosenquist, 1983;Baldauf et al., 2005). The PUL contains neurons that respond to movements in the visual field and also during saccadic eye movements (for review, see Chalupa, 1991;Casanova, 2003). Likewise, the feline PT contains a variety of cell types that are active during saccadic eye movements or in response to the movement of visual stimuli *Correspondence to: Martha E. Bickford, Department of Anatomical Sciences and Neurobiology, University of Louisville, School of Medicine, 500 S. Preston Street, Louisville, KY 40292. E-mail: martha.bickford@louisville.edu. Dr. Zsolt B. Baldauf's present address is Université de Montréal, School of Optometry, Laboratory of Visual Neuroscience CP 6128 succ. centre ville, Montréal, QC H3C-3J7, Canada. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript (Hoffmann and Schoppmann, 1975;Schoppmann and Hoffmann, 1979;Ballas and Hoffmann, 1985;Hoffmann and Distler, 1989;Schmidt and Hoffmann, 1992;Sudkamp and Schmidt, 1995;Schmidt, 1996;Missal et al., 2002). Specifically, pretecto-pulvinar (PT-PUL) cells have large receptive fields, are not directionally selective, and-have been show...