Synaptic Organization of Connections between the Temporal Cortex and Pulvinar Nucleus of the Tree Shrew

Abstract

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.

Synapses, spines, zinc and pathology of Alzheimer's disease.

“…We compared the data collected in the present study to that collected in a previous study of pulvinocortical connections (Chomsung et al, 2010 We also found that the synapses formed by pulvinocortical terminals are more complex (perforated or multiple) than those formed by geniculocortical terminals, and whereas pulvinocortical terminals do not contact any GABAergic profiles, approximately 9% of geniculocortical terminals contact GABAergic profiles. Finally, we found that the horizontal orientation of layer IV geniculocortical terminals is quiet distinct from the more vertically oriented pulvinocortical terminals.…”

“…We compared the features of the 311 geniculocortical synapses examined in this study to 444 pulvinocortical synapses examined in the previous study from our laboratory (Chomsung et al, 2010). The size of geniculocortical terminals (mean area 1.06 ± 0.58 µm 2 ) was significantly (p < .001) larger than the size of pulvinocortical terminals (0.51 ± 0.28 µm 2 ).…”

“…areas. Our previous study of the projections from the pulvinar nucleus to the temporal cortex in the tree shrew (Tupaia) revealed that pulvinocortical terminals innervate layers I-IV, where they all contact dendritic spines (Chomsung et al, 2010). The goal of the current study was to examine the ultrastructure of geniculocortical terminals in the tree shrew so that we could directly compare the characteristics of thalamocortical terminals in the striate and extrastriate cortex of the same species.…”

Circuits for active vision : parallel tectothalamocortical visual pathways in the mouse.

“…In general, the tectorecipient pulvinar subdivisions receive afferent projections that originate exclusively from layer VI of the extrastriate cortex (Kawamura and Diamond, 1978;Chomsung et al, 2010).…”

Morphological comparison of visual pathway projections to the temporal lobe from cortical area VI and the tectorecipient zone of the pulvinar nucleus in the tree shrew (Tupaia belangeri).

“…Lyon et al (2003b) subsequently used retrograde tracing techniques to uncover pathways from PO to temporal cortical areas TP and TPI, from PC to temporal cortical area TD and from PP to temporal cortical areas TA, TI and TAL. Most recently, Chomsung et al (2010) used anterograde tracing techniques to establish that projections from the PO and PC define two areas within the temporal cortex ventrorostral to the V2 border, one caudal and one rostral. That study did not differentiate the architectonic temporal lobe areas along that border.…”