Decades of mind study have identified various parallel loops linking the hippocampus with neocortical areas, enabling the acquisition of spatial and episodic remembrances. Here, we review data with particular reference to whole network-level methods, illustrating how activity propagation can take place within the trisynaptic circuit to drive formation of CA1 LTP. and studies using local field potential or single-cell recording in area CA1, excluding the detection of neuronal activity in upstream areas (Andersen et al., 1966; Herreras et al., 1987; Bliss and Collingridge, 1993; Whitlock et al., 2006). Yet, the well-defined regular structure and, at some locations, unidirectional circuitry (Amaral and Witter, 1989) makes the hippocampal formation an ideal candidate for network-level investigations. The entorhinal cortex (EC) represents the main input/output partner of the hippocampus (Witter et al., 2000), thus creating entorhinal-hippocampal loops, perfectly suited for high-speed imaging studies examining the Rocilinostat inhibitor database mechanisms of polysynaptic activity flow and induction of long-term synaptic plasticity (Andersen et al., 1966; Herreras et al., 1987; Buzski, 1988; Iijima et al., 1996; Nakagami et al., 1997; Stepan et al., 2012). Here, we review anatomical and functional characteristics of the hippocampal trisynaptic circuit and parallel pathways (e.g., temporoammonic pathway), which constitute the foundation for complex neuronal network dynamics during information processing. Including previous work and our recent findings (Stepan et al., 2012), we describe properties of local circuits in the DG and area CA3 and their interaction to enable activity propagation across several synapses for induction of CA1 LTP. We also discuss how our experimental findings can be integrated in the existing literature and how extensions of VSDI toward an all optical approach (e.g., by a combination with optogenetic tools) might prove useful for resolving the neuronal network dynamics underlying higher order brain functions. Structural architecture of the hippocampal trisynaptic circuit and parallel pathways The well-established role of the hippocampus in cognitive processes like memory formation relies, among other things, on remarkable anatomical features. In contrast to the reciprocal connectivity of most other cortical structures, the hippocampus is characterized by a unidirectional passing of information through its circuitry mainly. Nevertheless, before polymodal sensory info enters the hippocampus, it must move a organized neocortical network hierarchically. Upon sensory receptor excitement, major sensory cortices will be the first to be activated, accompanied by supplemental sensory Goat polyclonal to IgG (H+L)(FITC) areas and high-order association cortices. Appropriately, ready-made sensory info can be given in to the EC, with a specific concentrate on superficial levels II and III (Andersen et al., 2007; Rudy and Teyler, 2007). The EC can be often thought to be the first train station of info digesting in the hippocampal formation. This idea hails from the observation that its superficial levels provide the primary cortical insight towards the hippocampus, while its deep levels represent the primary target of info that returns back again from region CA1 as well as the subiculum. EC layer V and IV neurons subsequently task to superficial layers or high-order association cortices. In particular, coating Rocilinostat inhibitor database II neurons send their axons via the perforant way to the areas and DG CA3 and CA2. The second main insight emerges from coating III neurons, which task via the temporoammonic pathway towards the CA1 subfield as well as the subiculum (Witter et al., 2000; vehicle Strien et al., 2009; Kohara et al., 2014). Furthermore, some hippocampal areas are linked to subcortical constructions, like the amygdala, the hypothalamus, the medial septum, the raphe nucleus, as well as the locus coeruleus, finished with a pronounced commissural insight through the contralateral hippocampus and an ipsilateral associational loop (Nicoll and Schmitz, 2005; Andersen et al., 2007). Oddly enough, activation from the locus coeruleus can induce -adrenergic receptor-dependent LTP at perforant path-DG synapses (Walling and Harley, 2004). The popular neuroanatomists Ramn y Cajal and Lorente de No had been already attracted from the incredibly dense division from the perforant route connecting EC coating II cells using the DG (Lorente de No, 1934; Ramn con Cajal, 1995). These axons offer Rocilinostat inhibitor database excitatory synaptic insight (in the next abbreviated EC/DG-input) on apical dendrites of DG granule cells, which bring about mossy fibers, probably the most prominent non-commissural/associational excitatory innervation of CA3 pyramidal neurons. These cells subsequently synapse via Rocilinostat inhibitor database the glutamatergic Schaffer collaterals.