Article

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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    • "Nucleus reuniens (NRe), one of the largest midline thalamic nuclei, receives extensive limbic inputs and provides a bridge linking the hippocampus (especially area CA1) with medial prefrontal cortex (McKenna and Vertes, 2004; Vertes, 2006; Prasad and Chudasama, 2013). Its functions are not well-understood, but it has been suggested that, via these connections, NRe influences memory consolidation for spatial learning and generalisation of fear conditioning (Eleore et al., 2011; Loureiro et al., 2012; Xu and Sudhof, 2013). "
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    • "The Cg1 and Cg2 (also known as dorsal and ventral cingulate cortices) were grouped together to represent the dPFC. This parcellation was determined on the basis of previously published work demonstrating connectional similarities between the two cingulate areas (Vertes et al., 2006). However, we also quantified total neuron number in the Cg1 and Cg2 separately. "
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    • "In the hippocampus , RE terminals establish asymmetric synapses with both GABAergic and non-GABAergic dendrites (Dolleman-Van der Weel and Witter, 2000). The RE sends region specific glutamatergic fibers to the septal complex (Bokor et al., 2002), EC, subiculum and the amygdala (Dolleman-Van der Weel and Witter, 1996; Su and Bentivoglio, 1990; Vertes et al., 2006). The RPO, PH, SUM and PPT all innervate the RE (Hallanger et al., 1987; Newman and Ginsberg, 1994). "
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