Organization in the somatosensory sector of the cat's thalamic reticular nucleus

Abstract

This study describes the organization of cells in the thalamic reticular nucleus (TRN) that project to the somatosensory part of the dorsal thalamus in the cat. Injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) and fluorescent dyes were made into the ventrobasal complex (VB) and the medial division of the posterior complex (POm) of the thalamus. The resultant retrograde labelling in TRN was analyzed. Large injections of a tracer in VB label many reticular cells that are restricted to a centroventral, or somatosensory, sector of TRN. Small injections of a tracer in VB produce narrow zones of labelled cells in this sector. In reconstructions these zones resemble thin "slabs," which lie parallel to the plane of TRN along its oblique rostrocaudal dimension and occupy only a fraction of its thickness. In comparisons of the zones of labelled cells in TRN resulting from tracer injections in different nuclei of VB, inner cells, intermediate cells, and outer cells across the thickness of TRN project to the ventral posteromedial, the medial division of the ventral posterolateral, and the lateral division of the ventral posterolateral nuclei, respectively. Furthermore, shifts in injected areas along the dorsoventral dimension of VB produce similar shifts in zones of labelled cells in TRN. Thus, reticular cells form an accurate map on the basis of their connections with VB. Large injections of a tracer in the ventral subdivision of POm label many reticular cells that are also restricted to the centroventral sector of TRN. Small injections of a tracer in ventral POm produce broad zones of labelled cells in this sector. In comparisons of the zones of labelled cells in TRN resulting from tracer injections in different regions of ventral POm, cells that project to these regions are scattered across the thickness of TRN and occupy overlapping territories. Large injections of a tracer in either VB or ventral POm also label cells in a restricted centroventral region of the perireticular nucleus. Double injections of different tracers in VB and ventral POm produce many cells in TRN that are labelled from both of these dorsal thalamic structures and fewer cells that are labelled from only one or the other of these structures. These results indicate that there is a dual organization in the projections of cells in the somatosensory sector of TRN to dorsal thalamus: Projections to VB are topographically organized whereas those to ventral POm lack a topographical organization. Furthermore, both of these mapped and nonmapped projections can arise from single reticular cells in the somatosensory sector.

The calcium-binding protein parvalbumin modulates the firing 1 properties of the reticular thalamic nucleus bursting neurons

“…Notice that the RTN is abundantly innervated by cholinergic fibers that may contribute to modulate the firing properties of its neurons in vivo (Jones 1991;Villa et al 1996). Spatial organization of the rostral and somatotopic sector of RTN was observed on the basis of its connectivity pattern and sensory-evoked activity in several species, namely in the rat (Shosaku et al 1984;Lozsádi 1994;Pinault et al 1995), rabbit (Crabtree 1992), and cat (Crabtree 1996).…”

Distinct Electrical and Chemical Connectivity Maps in the Thalamic Reticular Nucleus: Potential Roles in Synchronization and Sensation

“…5 A, B) and mostly restricted to the same mediolateral portion of nRt containing the soma. nRt is topographically organized along the mediolateral axis with three divisions (lateral, central, and medial tiers), each interconnected with a specific thalamic relay nucleus (Crabtree, 1996). This suggests that intra-nRt connections primarily mediate communication within functionally related tiers of nRt.…”

“…Topographic and sensory modality-specific organization exist in nRt both longitudinally (sectors), as well as within the mediolateral extent of the nucleus (tiers) (Jones, 1975;Shosaku et al, 1984;Crabtree, 1996;Crabtree et al, 1998;Lam and Sherman, 2005). For example, neurons located in the central tier of somatosensory nRt project to the ventral posterior nuclei, whereas medial tier neurons connect to the posterior complex (Crabtree, 1996). Thus, our results showing that synaptic connectivity is restricted to neurons located in the same nRt tier suggest that nRt cell interactions occur primarily between cells projecting to the same relay nucleus.…”

Different Topography of the Reticulothalmic Inputs to First- and Higher-Order Somatosensory Thalamic Relays Revealed Using Photostimulation

“…First, in agreement with our experience in rats , the reticulothalamic input to the ventral posterior nucleus is already highly topographic even at this age, suggesting an early development of the somatosensory system in rats and mice. Second, injection of retrograde tracers into the posterior nucleus has indicated that differences between the reticular inputs to the first-and higher-order relays are found in adults (Crabtree 1996;Crabtree et al 1998).…”

“…One difference is suggested by prior retrograde tracing studies in cats and rats: the higher-order posterior nucleus was reported to have a more diffusely organized reticulothalamic input compared with the first-order ventral posterior nucleus (Crabtree 1996;Crabtree et al 1998). Labeling of a large number (Ͼ100) of cells juxtacellularly in the somatosensory and other sections of the thalamic reticular nucleus of rats, however, has led to a somewhat different conclusion, namely, that the axonal arbors of reticular neurons are mostly circumscribed, quite topographically organized and usually contained within a single thalamic nucleus (Pinault and Deschênes 1998;Pinault et al 1995).…”