Topographical organization of the projections from the reticular thalamic nucleus to the intralaminar and medial thalamic nuclei in the cat

Abstract

The topography of the projections from the reticular nucleus of the thalamus (RT) to the intralaminar and medial thalamic nuclei were studied in the cat by the method of retrograde transport of horseradish peroxidase (HRP). Single small injections of the enzyme were made in the different intralaminar nuclei--mediodorsal, ventromedial, midline, and habenular--and in anterior group nuclei. The location and density of the neuronal labeling in the different parts of the RT were studied in each case. Our results show that 1) after injections located in all the nuclei here studied, a consistent number of labeled neurons were found in the RT, except for the injections in the lateral habenula and the anterior thalamic nuclear complex, both of which did not label neurons in the RT. 2) Among the other thalamic nuclei here studied, the most medially situated receive less numerous RT projections than those most laterally located. 3) Injections in all the nuclei studied gave rise to a cellular labeling in the anterior sectors of the RT, except for the anterior nuclear group and the lateral habenula. The projections from the rostral pole of the RT were topographically mediolaterally organized. 4) The anterodorsal part of the pregeniculate sector of the RT projects upon the large-celled part of the lateral central nucleus and to a lesser extent upon the paracentral, centromedian, and ventromedial nuclei, the anterior part of the lateral central nucleus, and the lateral band of the mediodorsal nucleus. The posterodorsal part of the RT pregeniculate sector only projects to the large-celled part of the lateral central nucleus. The dorsal portion of the posteroventral part of the RT pregeniculate sector also projects upon the large-celled part of the lateral central nucleus; its ventral portion projects to the ventromedial nucleus, the posterior part of the paracentral nucleus, the lateral band of the mediodorsal nucleus, and the centromedian nucleus. 5) The infrageniculate sector of the RT projects to the posterior part of the ventromedial nucleus. A weaker projection to the large-celled part of the lateral central nucleus, the centromedian nucleus, and the lateral band of the mediodorsal nucleus was also observed. 6) The ventral lateral geniculate nucleus projects upon the large-celled part of the lateral central nucleus, the lateral band of the mediodorsal nucleus, and the ventromedial nucleus. All these findings suggest an important modulatory action of the RT on the activity of the thalamic nuclei considered here.

Organization of projections from the anterior pole of the nucleus reticularis thalami (NRT) to subdivisions of the motor thalamus: Light and electron microscopic studies in the Rhesus monkey

“…These findings are in good agreement with the results of studies in the rat and cat Velayos et al, 1989;Lozsadi, 1995;Gonzalo-Ruiz and Lieberman, 1995;Kolmac and Mitrofanis, 1997) that also described connections of the anterior pole with a variety of a,c,f), the symmetric nature of the synapse with some underlying dense substance is clearly seen. In b, e, and f note also Puncta aedherentia to the right from synaptic contacts.…”

“…However, it is not clear whether this concept can be extrapolated to all NRT sectors, specifically those related to the motor, limbic, association, and intralaminar nuclei connected with the frontal lobe. Based on retrograde tracing studies in cats and rats, it has been suggested that the rostral NRT sector or anterior pole as it is also known, is organized differently from the sensory sectors: it is connected with a large number of thalamic nuclei, including intralaminar, midline, and limbic without precise topography (Velayos et al, 1989;Gonzalo-Ruiz and Lieberman, 1995;Lozsadi, 1995;Kolmac and Mitrofanis, 1997;Lizier et al, 1997). Recent anterograde tracing studies (Yi et al, 1993;Kultas-Ilinsky et al, 1995;Tai et al, 1995) have further confirmed the connections of the anterior sector of the NRT with the same nuclei in the rhesus monkey as well.…”

Insular cortex and neighboring fields in the cat: A redefinition based on cortical microarchitecture and connections with the thalamus

“…Anterograde labeling is faint in VM-VL. Terminallike labeling is visible in the anterodorsal zone of the pregeniculate sector (Velayos et al, 1989) of the reticular thalamic nucleus. Thereon, labeled axons can be followed medially and caudally as they traverse the ventral thalamic complex en route to PoM and LM, arranged in conspicuous small bundles.…”

“…Interestingly, the bundle of axons directed to the thalamus and other subcortical structures follows a route ventral to the putamen into the sublenticular portion of the internal capsule, whereas after injections in the other areas of the orbitosylvian region these fibers always follow a dorsal route into the main, dorsal portion of the internal capsule. When passing through the most caudal part of the infrageniculate sector (Velayos et al, 1989) of the reticular thalamic nucleus, labeled axons leave terminal-like labeling. Thereon, axons travel within the acoustic radiation toward the caudal pole of the medial geniculate complex.…”

Regional Cerebral Blood Flow Changes as a Function of Delta and Spindle Activity during Slow Wave Sleep in Humans

“…As a result of this disfacilitation, thalamic neurons would become sufficiently hyperpolarized to change their firing mode from tonic to phasic, as occurs in the transition to SWS (Steriade et al, 1994). Moreover, the thalamic reticularis neurons, which contain GABA (Houser et al, 1980) and project onto thalamic relay neurons, including midline, medial, and intralaminar nuclei of the diffuse thalamocortical projection system Jones, 1985;Velayos et al, 1989), would begin to burst, hyperpolarizing the thalamocortical neurons and entraining them first in a spindle and then ␦ rhythmicity (von Krosigk et al, 1993;Steriade et al, 1994). Thalamic neurons also oscillate in a slower rhythm with long-lasting hyperpolarizations in association with the "slow oscillation" on the cortex (Ͻ1 Hz) (Contreras et al, 1996), a recently described sleep rhythm (Steriade et al, 1994) that was not measured in the present study.…”