Afferent projections to nucleus reuniens of the thalamus

Abstract

The nucleus reuniens (RE) is the largest of the midline nuclei of the thalamus and the major source of thalamic afferents to the hippocampus and parahippocampal structures. Nucleus reuniens has recently been shown to exert powerful excitatory actions on CA1 of the hippocampus. Few reports on any species have examined afferent projections to nucleus reuniens. By using the retrograde anatomical tracer Fluorogold, we examined patterns of afferent projections to RE in the rat. We showed that RE receives a diverse and widely distributed set of afferents projections. The main sources of input to nucleus reuniens were from the orbitomedial, insular, ectorhinal, perirhinal, and retrosplenial cortices; CA1/subiculum of hippocampus; claustrum, tania tecta, lateral septum, substantia innominata, and medial and lateral preoptic nuclei of the basal forebrain; medial nucleus of amygdala; paraventricular and lateral geniculate nuclei of the thalamus; zona incerta; anterior, ventromedial, lateral, posterior, supramammillary, and dorsal premammillary nuclei of the hypothalamus; and ventral tegmental area, periaqueductal gray, medial and posterior pretectal nuclei, superior colliculus, precommissural/commissural nuclei, nucleus of the posterior commissure, parabrachial nucleus, laterodorsal and pedunculopontine tegmental nuclei, nucleus incertus, and dorsal and median raphe nuclei of the brainstem. The present findings of widespread projections to RE, mainly from limbic/limbic-associated structures, suggest that nucleus reuniens represents a critical relay in the transfer of limbic information (emotional/cognitive) from RE to its major targets, namely, to the hippocampus and orbitomedial prefrontal cortex. RE appears to be a major link in the two-way exchange of information between the hippocampus and the medial prefrontal cortex.

The rat perirhinal cortex: A review of anatomy, physiology, plasticity, and function

“…The projection from the perirhinal cortex to the thalamus mainly originates in layers V and VI and terminates in the reuniens, posterior and ventral posteromedial nuclei (Cornwall and Phillipson, 1988;McIntyre et al, 1996). Projections from the deep layers of the perirhinal cortex to the rostral, caudomedial and rostrolateral regions of the nucleus reuniens have also been described (McKenna and Vertes, 2004). McKenna and Vertes (2004) also describe a light projection to rhomboid nucleus from the deep layers of the perirhinal cortex.…”

“…Projections from the deep layers of the perirhinal cortex to the rostral, caudomedial and rostrolateral regions of the nucleus reuniens have also been described (McKenna and Vertes, 2004). McKenna and Vertes (2004) also describe a light projection to rhomboid nucleus from the deep layers of the perirhinal cortex. As with the projections from the thalamus to the perirhinal cortex, there have been no electrophysiological studies done either on synaptic plasticity or epileptiform activity.…”

Decoding signal processing in thalamo-hippocampal circuitry: implications for theories of memory and spatial processing

“…The nucleus reuniens head-direction cells are similar to the head-direction cells of the anterodorsal and anteroventral thalamic nuclei, lateral mammillary nucleus (Taube, 2007), and some parahippocampal regions. Nucleus reuniens receives widespread cortical and subcortical afferent inputs (McKenna and Vertes, 2004). Nucleus reuniens is not part of the more usual head direction circuit, which is regarded as deriving principally from the dorsal tegmental nucleus of Gudden and the lateral mammillary nucleus (Cassel et al, 2013;Taube, 2007)(see Fig.…”

Hippocampal-Prefrontal Cortical Circuit Mediates Inhibitory Response Control in the Rat

“…Interestingly, the hippocampal-prefrontal projections are not reciprocal; direct projections from the prefrontal cortex to the hippocampus have not been reported. Nonetheless, there is likely to be indirect transmission of prefrontal signals to the hippocampus through relays in the midline thalamus (Wouterlood et al, 1990;McKenna and Vertes, 2004;Vertes et al, 2006;Prasad et al, 2012). Furthermore, both the vHC and vPFC provide direct input to the nucleus accumbens Totterdell, 2002, 2003).…”