Efferent projections of 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: 3.23). 12/2006; 499(5):768-96. DOI: 10.1002/cne.21135
Source: PubMed


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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    ABSTRACT: Different types of predator odors engage elements of the hypothalamic predator-responsive circuit, which has been largely investigated in studies using cat odor exposure. Studies using cat odor have led to detailed mapping of the neural sites involved in innate and contextual fear responses. Here, we reviewed three lines of work examining the dynamics of the neural systems that organize innate and learned fear responses to cat odor. In the first section, we explored the neural systems involved in innate fear responses and in the acquisition and expression of fear conditioning to cat odor, with a particular emphasis on the role of the dorsal premammillary nucleus (PMd) and the dorsolateral periaqueductal gray (PAGdl), which are key sites that influence innate fear and contextual conditioning. In the second section, we reviewed how chemical stimulation of the PMd and PAGdl may serve as a useful unconditioned stimulus in an olfactory fear conditioning paradigm; these experiments provide an interesting perspective for the understanding of learned fear to predator odor. Finally, in the third section, we explored the fact that neutral odors that acquire an aversive valence in a shock-paired conditioning paradigm may mimic predator odor and mobilize elements of the hypothalamic predator-responsive circuit.
    Full-text · Article · Sep 2015 · Frontiers in Neuroscience
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    • "In addition to prefrontal cortex projections, the nucleus reuniens has dense projections directly to the CA1 region of the hippocampus, although most of the labeling seen in anatomical studies is within the ventral portion of the hippocampus (Hoover and Vertes, 2012; Varela et al., 2013; Vertes et al., 2006; but see Cassel et al., 2013), whereas the dorsal hippocampus is more known to be important for spatial learning and navigation (Fanselow and Dong, 2010). There is also evidence that the nucleus reuniens projects to both the medial and lateral entorhinal cortices (Dolleman-van der Weel and Witter, 1996; Vertes et al., 2006). What also remains unclear is how the HD signal is generated in the nucleus reuniens. "
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    ABSTRACT: Navigation is a complex cognitive process that is vital for survival. The rodent hippocampus has long been implicated in spatial memory and navigation. Following the discovery of place cells, found in the hippocampus, a variety of other spatially tuned neural correlates of navigation have been found in a widely distributed network that is both anatomically and functionally interconnected with the hippocampus. Angular head velocity, head direction, and grid cells are among some of the additional spatial neural correlates. The importance of these different cells and how they function interdependently to subserve navigation is reviewed below. © 2015 Elsevier B.V. All rights reserved.
    Full-text · Article · Jun 2015 · Progress in brain research
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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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    ABSTRACT: Discrete populations of brain cells signal heading direction, rather like a compass. These ‘head direction’ cells are largely confined to a closely-connected network of sites. We describe, for the first time, a population of head direction cells in nucleus reuniens of the thalamus in the freely-moving rat. This novel subcortical head direction signal potentially modulates the hippocampal CA fields directly and, thus, informs spatial processing and memory. DOI:
    Full-text · Article · Jul 2014 · eLife Sciences
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