The thalamic reticular nucleus of the adult rat: experimental anatomical studies

Abstract

The thalamic reticular nucleus (TRN) is a sheet-like nucleus partially enclosing the dorsolateral and anterior aspects of the thalamus and traversed by the thalamo-cortical and cortico-thalamic fibre systems. This paper describes the cellular and synaptic organization of the TRN in adult albino rats on the basis of LM and EM studies of normal animals and experimental animals with injections of horseradish peroxidase (HRP) and/or lesions in various parts of the brain. Particular attention was paid to the dorso-caudal part of the TRN, which establishes connections with visual centres. LM-HRP preparations show that the neurons of TRN project only to ipsilateral dorsal thalamus; no labelled cell bodies were found in TRN after injections into the cortex or any part of the brain stem caudal to the thalamus. Small injections into dorsal thalamus result in a small cluster of labelled neurons and an associated patch of terminal label in TRN. The dorso-caudal part of the nucleus projects to the dorsal lateral geniculate nucleus, the ventro-caudal part to the medial geniculate nucleus and a large part of the nucleus anterior to the areas associated with the geniculate nuclei projects to the ventrobasal nucleus. No evidence was found for a widespread distribution of reticulo-thalamic axons and the connections between TRN and the dorsal lateral geniculate nucleus and between TRN and the ventrobasal nucleus show a fine-grain topographical organization with more rostral and dorsal parts of TRN projecting to more rostral and dorsal parts of the dorsal lateral geniculate and ventrobasal nuclei. The neurons of TRN are variable in size (range of somal diameters c. 10-20 micron), shape (cell bodies are most commonly ellipsoidal) and dendritic morphology (bitufted and bipolar arrangements most common), but no basis for subdividing them into more than one class was found with any of the techniques used. The cell body and dendrites are commonly aligned parallel to the surface of TRN and at right angles to the traversing fibre bundles. The dendrites do not branch extensively and are only moderately spinous. Long, hair-like spines corresponding to those described by Scheibel & Scheibel (1966) were not found: nor were dendritic bundles found to be as prominent in EM material as reported by these authors in LM-Golgi material. Plasma membranes of dendrites in small bundles and of contiguous somata were commonly in direct contact over large areas, but gap junctions between them were not seen.(ABSTRACT TRUNCATED AT 400 WORDS)

Noradrenergic Activation Amplifies Bottom-Up and Top-Down Signal-to-Noise Ratios in Sensory Thalamus

“…Corticothalamic fibers originating in layer VI of barrel cortex (Bourassa et al, 1995) provide top-down influences. Fibers from nucleus reticularis thalamic (nRt) cells (Ohara and Lieberman, 1985) provide the main inhibitory control in VPM. Finally, a variety of neuromodulator fibers originate mainly in several brainstem nuclei.…”

Attentional Modulation of Thalamic Reticular Neurons

“…TRN can be divided into five modality-specific sectors. Each sector is defined by the specific relays in thalamus to which they project, the origin of the cortical and thalamic collaterals they receive, and their physiology (Carman et al, 1964;Jones, 1975;Ohara and Lieberman, 1985) (for review, see Guillery et al, 1998;Crabtree, 1999;Pinault, 2004). Visual TRN in the primate receives input from the visual thalamic relay [the lateral geniculate nucleus (LGN)] via LGN axon collaterals projecting to primary visual cortex (V1).…”

Cerebellar connections to the rostral reticular nucleus of the thalamus in the rat

“…The majority of the inputs to the RNT are from collaterals of thalamocortical and corticothalamic axons and most of the outputs of the RNT are to the dorsal thalamus (Jones, 1975;Ohara & Lieberman, 1985;Yen et al 1985;De Biasi et al 1986). In addition to thalamic and cortical afferents, thalamic reticular cells also receive afferents from various brainstem centres and from the basal forebrain (Steriade et al 1984a;Cornwall et al 1990; Reardon & Mitrofanis, 2000).…”