Two pathways from the superior colliculus (SC) to the tree shrew pulvinar nucleus have been described, one in which the axons terminate in dense (or specific) patches and one in which the axon arbors are more diffusely organized J. . As predicted by Lyon et al. ([2003] J. Comp. Neurol. 467:593-606), we found that anterograde labeling of the diffuse tectopulvinar pathway terminated in the acetylcholinesterase (AChE)-rich dorsal pulvinar (Pd), whereas the specific pathway terminated in the AChE-poor central pulvinar (Pc). Injections of retrograde tracers in Pd labeled non-γ-aminobutyric acid (GABA)-ergic wide-field vertical cells located in the lower stratum griseum superficiale and stratum opticum of the medial SC, whereas injections in Pc labeled similar cells in more lateral regions. At the ultrastructural level, we found that tectopulvinar terminals in both Pd and Pc contact primarily non-GABAergic dendrites. When present, however, synaptic contacts on GABAergic profiles were observed more frequently in Pc (31% of all contacts) compared with Pd (16%). Terminals stained for the type 2 vesicular glutamate transporter, a potential marker of tectopulvinar terminals, also contacted more GABAergic profiles in Pc (19%) compared with Pd (4%). These results provide strong evidence for the division of the tree shrew pulvinar into two distinct tectorecipient zones. The potential functions of these pathways are discussed. J. Comp. Neurol. 510:24 -46, 2008. Indexing termssynapse; ultrastructure; GABA; pulvinar nucleus; superior colliculus; vesicular glutamate transporter; Tupaia belangeri Parallel visual pathways from the retina to the cortex, relayed via the dorsal lateral geniculate nucleus (dLGN), or the superior colliculus (SC) and pulvinar nucleus, likely serve distinct functions in the coding of form, movement, and spatial location signals. In the dLGN, further segregations of anatomically and physiologically distinct visual pathways have been identified and extensively characterized (Sherman, 1985). Likewise, studies in a variety of species have provided evidence for the existence of multiple pathways from the SC to the thalamus (May, 2006), although these pathways are largely uncharacterized, and their functions are unclear. The tree shrew, with its expanded tectopulvinar system, is good choice for studies of how pathways from the SC influence cortical activity via their projections to the pulvinar nucleus.In 1988, Luppino et al. labeled tectothalamic terminals in the tree shrew by placing small injections of axonal tracers in the SC and discovered that the pulvinar nucleus receives input *Correspondence to: Martha E. Bickford, Department of Anatomical Sciences and Neurobiology, University of Louisville, School of Medicine, 500 S. Preston St., Louisville, KY 40292. E-mail: martha.bickford@louisville.edu. We recently examined the synaptic organization of two tectorecipient zones of the cat thalamus (Kelly et al., 2003). We found that tectal terminals in the medial subdivision of the lateral posterior (LPm) ...

Visually guided movement is possible in the absence of conscious visual perception, a phenomenon referred to as “blindsight.” Similarly, fearful images can elicit emotional responses in the absence of their conscious perception. Both capabilities are thought to be mediated by pathways from the retina through the superior colliculus (SC) and pulvinar nucleus. To define potential pathways that underlie behavioral responses to unperceived visual stimuli, we examined the projections from the pulvinar nucleus to the striatum and amygdala in the tree shrew (Tupaia belangeri), a species considered to be a prototypical primate. The tree shrew brain has a large pulvinar nucleus that contains two SC-recipient subdivisions; the dorsal (Pd) and central (Pc) pulvinar both receive topographic (“specific”) projections from SC, and Pd receives an additional non-topographic (“diffuse”) projection from SC (Chomsung et al., 2008). Anterograde and retrograde tract tracing revealed that both Pd and Pc project to the caudate and putamen, and Pd, but not Pc, additionally projects to the lateral amygdala. Using immunocytochemical staining for substance P (SP) and parvalbumin (PV) to reveal the patch/matrix organization of tree shrew striatum, we found that SP-rich/PV-poor patches interlock with a PV-rich/SP-poor matrix. Confocal microscopy revealed that tracer-labeled pulvino-striatal terminals preferentially innervate the matrix. Electron microscopy revealed that the postsynaptic targets of tracer-labeled pulvino-striatal and pulvino-amygdala terminals are spines, demonstrating that the pulvinar nucleus projects to the spiny output cells of the striatum matrix and the lateral amygdala, potentially relaying: (1) topographic visual information from SC to striatum to aid in guiding precise movements, and (2) non-topographic visual information from SC to the amygdala alerting the animal to potentially dangerous visual images.

An anatomical study of the formation of the sural nerve (SN) was carried out on 76 Thai cadavers. The results revealed that 67.1% of the SNs were formed by the union of the medial sural cutaneous nerve (MSCN) and the lateral sural cutaneous nerve (LSCN); the MSCN and LSCN are branches of the tibial and the common fibular (peroneal) nerves, respectively. The site of union was variable: 5.9% in the popliteal fossa, 1.9% in the middle third of the leg, 66.7% in the lower third of the leg, and 25.5% at or just below the ankle. One SN (0.7%) was formed by the union of the MSCN and a different branch of the common fibular nerve, running parallel and medial to but not connecting with the LSCN, which joined the MSCN in the lower third of the leg. The remaining 32.2% of the SNs were a direct continuation of the MSCN. The SNs ranged from 6-30 cm (mean = 14.41 cm) in length with a range in diameter of 3.5-3.8 mm (mean = 3.61 mm), and were easily located 1-1.5 cm posterior to the posterior border of the lateral malleolus. The LSCNs were 15-32 cm long (mean = 22.48 cm) with a diameter between 2.7-3.4 mm (mean = 3.22 mm); the MSCNs were 17-31 cm long (mean = 20.42 cm) with a diameter between 2.3-2.5 mm (mean = 2.41 mm). Clinically, the SN is widely used for both diagnostic (biopsy and nerve conduction velocity studies) and therapeutic purposes (nerve grafting) and the LSCN is used for a sensate free flap; thus, a detailed knowledge of the anatomy of the SN and its contributing nerves are important in carrying out these and other procedures.

We examined the synaptic organization of reciprocal connections between the temporal cortex and the dorsal (Pd) and central (Pc) subdivisions of the tree shrew pulvinar nucleus, regions innervated by the medial and lateral superior colliculus, respectively. Both Pd and Pc subdivisions project topographically to 2 separate regions of the temporal cortex; small injections of anterograde tracers placed in either Pd or Pc labeled 2 foci of terminals in the temporal cortex. Pulvinocortical pathways innervated layers I-IV, with beaded axons oriented perpendicular to the cortical surface, where they synapsed with spines that did not contain gamma amino butyric acid (GABA), likely located on the apical dendrites of pyramidal cells. Projections from the temporal cortex to the Pd and Pc originate from layer VI cells, and form small terminals that contact small caliber non-GABAergic dendrites. These results suggest that cortical terminals are located distal to tectopulvinar terminals on the dendritic arbors of Pd and Pc projection cells, which subsequently contact pyramidal cells in the temporal cortex. This circuitry could provide a mechanism for the pulvinar nucleus to activate subcortical visuomotor circuits and modulate the activity of other visual cortical areas. The potential relation to primate tecto-pulvino-cortical pathways is discussed.

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...