Efferent projections of reuniens and rhomboid nuclei of the thalamus in the rat
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). "
ABSTRACT: eLife digest Whether it is foraging for food or finding its way back to its nest, an animal often needs to know which direction it is heading in. Some neurons in a mammal’s brain have been shown to act like a compass, and send out nerve impulses whenever the animal points its head in a certain direction. For example, some of these neurons will fire when the animal faces northeast, but not when it faces northwest, and vice versa. Importantly these neurons, called ‘head direction’ cells, do not actually measure the Earth's magnetic field. Rather, they respond to information about landmarks in the environment and the animal's movements of its head or body to work out which way the animal is facing. Head direction cells are largely found in a closely-connected network of a few sites in the brain. However, Jankowski et al. have now discovered more of these cells in another region found deep within the centre of the brain. Measuring the nerve impulses from these neurons in rats that were moving freely around a test arena revealed that the neurons fired in exactly the same way as some other head direction cells in other regions of the brain. For example, they fired whenever the rat faced one direction, but stopped firing when it turned its head to face another. Jankowski et al. showed that the head direction cells in this region of the brain continued to work when the lights were turned off in the test arena, or when the shape of the arena was changed from a circle to a square. These neurons began sending information about head direction as soon as the rat entered the test arena, and many continued to fire when the rat faced the same direction even when they were retested on several different days. The head direction cells discovered by Jankowski et al. are connected to another region of the brain that is involved in remembering different locations in the environment and navigating between them. This suggests that these neurons might provide some of the information required to carry out these tasks. It also means that areas of the brain close to those that receive input from the outside world may perform more complex cognitive functions than previously thought. DOI: http://dx.doi.org/10.7554/eLife.03075.002eLife Sciences 07/2014; 3:e03075. DOI:10.7554/eLife.03075 · 8.52 Impact Factor
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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. "
ABSTRACT: For many years, aging was thought to be accompanied by significant decreases in total neuron number across multiple brain regions. However, this view was revised with the advent of modern quantification methods, and it is now widely accepted that the hippocampus and many regions of the cortex show substantially preserved numbers of neurons during normal aging. Nonetheless, age-related changes in neuron number do occur in focal regions of the primate prefrontal cortex (PFC), but the question of whether age-related neuron loss is an exclusive characteristic of the PFC in primates remains relatively unexplored. To investigate the loss of neurons with normal aging in rodents, we used unbiased stereological methods to quantify the number of principal neurons and interneurons in the PFC of young and aged rats. We observed a significant age-related decline in the number of principal neurons in the dorsal PFC. The number of interneurons positively stained with antibodies to glutamic acid decarboxylase 67 was also reduced in the dorsal PFC of aged rats. These observations indicate that the dorsal PFC is susceptible to neuron loss with aging in rodent brain and suggest some common basis for vulnerability in cortical circuits across species.The Journal of Comparative Neurology 04/2012; 520(6):1318-26. DOI:10.1002/cne.22790 · 3.51 Impact Factor
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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). "
ABSTRACT: Theta oscillations represent the neural network configuration underlying active awake behavior and paradoxical sleep. This major EEG pattern has been extensively studied, from physiological to anatomical levels, for more than half a century. Nevertheless the cellular and network mechanisms accountable for the theta generation are still not fully understood. This review synthesizes the current knowledge on the circuitry involved in the generation of theta oscillations, from the hippocampus to extra hippocampal structures such as septal complex, entorhinal cortex and pedunculopontine tegmentum, a main trigger of theta state through direct and indirect projections to the septal complex. We conclude with a short overview of the perspectives offered by technical advances for deciphering more precisely the different neural components underlying the emergence of theta oscillations.Journal of Physiology-Paris 09/2011; 106(3-4):81-92. DOI:10.1016/j.jphysparis.2011.09.007 · 2.35 Impact Factor