Efferent projections of reuniens and rhomboid nuclei of the thalamus in the rat

Center for Complex Systems and Brain Sciences, Florida Atlantic University, Boca Raton, Florida 33431, USA.
The Journal of Comparative Neurology (Impact Factor: 3.51). 12/2006; 499(5):768-96. DOI: 10.1002/cne.21135
Source: PubMed

ABSTRACT The nucleus reuniens (RE) is the largest of the midline nuclei of the thalamus and exerts strong excitatory actions on the hippocampus and medial prefrontal cortex. Although RE projections to the hippocampus have been well documented, no study using modern tracers has examined the totality of RE projections. With the anterograde anatomical tracer Phaseolus vulgaris leuccoagglutinin, we examined the efferent projections of RE as well as those of the rhomboid nucleus (RH) located dorsal to RE. Control injections were made in the central medial nucleus (CEM) of the thalamus. We showed that the output of RE is almost entirely directed to the hippocampus and "limbic" cortical structures. Specifically, RE projects strongly to the medial frontal polar, anterior piriform, medial and ventral orbital, anterior cingulate, prelimbic, infralimbic, insular, perirhinal, and entorhinal cortices as well as to CA1, dorsal and ventral subiculum, and parasubiculum of the hippocampus. RH distributes more widely than RE, that is, to several RE targets but also significantly to regions of motor, somatosensory, posterior parietal, retrosplenial, temporal, and occipital cortices; to nucleus accumbens; and to the basolateral nucleus of amygdala. The ventral midline thalamus is positioned to exert significant control over fairly widespread regions of the cortex (limbic, sensory, motor), hippocampus, dorsal and ventral striatum, and basal nuclei of the amygdala, possibly to coordinate limbic and sensorimotor functions. We suggest that RE/RH may represent an important conduit in the exchange of information between subcortical-cortical and cortical-cortical limbic structures potentially involved in the selection of appropriate responses to specific and changing sets of environmental conditions.

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    • "dorsal nucleus , the suprageniculate nucleus and the parvicellular subparafascicular nucleus , all of which are known to project to elements of the cortical - hippocampal - amygdalar circuit that is involved in fear conditioning , as described above ( Van Groen and Wyss , 1992 ; Linke et al . , 2000 ; Vertes et al . , 2006 ) . An important concept emerges from the present analysis : subcortical regions that process elemental fear to predator threats , such as the PMd and the dorsal PAG , may work as critical nodes that serve to instruct prosencephalic sites to promote fear learning . Accordingly , the processing of primal emotional states related to preda"
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