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Hippocampal Projections (hippocampal + projection)
Selected AbstractsProjections from the hippocampal region to the mammillary bodies in macaque monkeysEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2005John P. Aggleton Abstract A combination of anterograde and retrograde tracers mapped the direct hippocampal and parahippocampal inputs to the mammillary bodies in two species of macaque monkey. Dense projections arose from pyramidal cells in layer III of the subiculum and prosubiculum, and terminated in the medial mammillary nucleus. While there was no evidence of an input from the dentate gyrus or fields CA1,3, a small contribution arose from the presubiculum and entorhinal cortices. All of the hippocampal and parahippocampal projections to the mammillary bodies appeared to use the fornix as a route. The caudal portions of the subiculum and prosubiculum contained the greatest numbers of cells projecting to the mammillary bodies. A light contralateral projection to the medial mammillary nucleus was also observed, although this appeared to arise primarily from the more rostral portions of the subiculum and prosubiculum. There was a crude topography within the medial mammillary nucleus, with the caudal subicular projections terminating in the mid and dorsal portions of the nucleus while the rostral subicular and entorhinal projections terminated in the ventral and lateral portions of the medial nucleus. Light ipsilateral projections throughout the lateral mammillary nucleus were sometimes observed. Comparisons with related studies of the macaque brain showed that the dense hippocampal projections to the mammillary bodies arise from a population of subicular cells separate from those that project to the anterior thalamic nuclei, even though the major output from the mammillary bodies is to the anterior thalamic nuclei. Other comparisons revealed underlying similarities with the corresponding projections in the rat brain. [source] Subicular and CA1 hippocampal projections to the accessory olfactory bulbHIPPOCAMPUS, Issue 2 2009C. de la Rosa-Prieto Abstract The hippocampal formation is anatomically and functionally related to the olfactory structures especially in rodents. The entorhinal cortex (EC) receives afferent projections from the main olfactory bulb; this constitutes an olfactory pathway to the hippocampus. In addition to the olfactory system, most mammals possess an accessory olfactory (or vomeronasal) system. The relationships between the hippocampal formation and the vomeronasal system are virtually unexplored. Recently, a centrifugal projection from CA1 to the accessory olfactory bulb has been identified using anterograde tracers. In the study reported herein, experiments using anterograde tracers confirm this projection, and injections of retrograde tracers show the distribution and morphology of a population of CA1 and ventral subicular neurons projecting to the accessory olfactory bulb of rats. These results extend previous descriptions of hippocampal projections to the accessory olfactory bulb by including the ventral subiculum and characterizing the morphology, neurochemistry (double labeling with somatostatin), and distribution of such neurons. These data suggest feedback hippocampal control of chemosensory stimuli in the accessory olfactory bulb. Whether this projection processes spatial information on conspecifics or is involved in learning and memory processes associated with chemical stimuli remains to be elucidated. © 2008 Wiley-Liss, Inc. [source] Parallel activation of field CA2 and dentate gyrus by synaptically elicited perforant path volleysHIPPOCAMPUS, Issue 8 2004Renata Bartesaghi Abstract Previous studies showed that dorsal psalterium (PSD) volleys to the entorhinal cortex (ENT) activated in layer II perforant path neurons projecting to the dentate gyrus. The discharge of layer II neurons was followed by the sequential activation of the dentate gyrus (DG), field CA3, field CA1. The aim of the present study was to ascertain whether in this experimental model field, CA2, a largely ignored sector, is activated either directly by perforant path volleys and/or indirectly by recurrent hippocampal projections. Field potentials evoked by single-shock PSD stimulation were recorded in anesthetized guinea pigs from ENT, DG, fields CA2, CA1, and CA3. Current source-density (CSD) analysis was used to localize the input/s to field CA2. The results showed the presence in field CA2 of an early population spike superimposed on a slow wave (early response) and of a late and smaller population spike, superimposed on a slow wave (late response). CSD analysis during the early CA2 response showed a current sink in stratum lacunosum-moleculare, followed by a sink moving from stratum radiatum to stratum pyramidale, suggesting that this response represented the activation and discharge of CA2 pyramidal neurons, mediated by perforant path fibers to this field. CSD analysis during the late response showed a current sink in middle stratum radiatum of CA2 followed by a sink moving from inner stratum radiatum to stratum pyramidale, suggesting that this response was mediated by Schaffer collaterals from field CA3. No early population spike was evoked in CA3. However, an early current sink of small magnitude was evoked in stratum lacunosum-moleculare of CA3, suggesting the presence of synaptic currents mediated by perforant path fibers to this field. The results provide novel information about the perforant path system, by showing that dorsal psalterium volleys to the entorhinal cortex activate perforant path neurons that evoke the parallel discharge of granule cells and CA2 pyramidal neurons and depolarization, but no discharge of CA3 pyramidal neurons. Consequently, field CA2 may mediate the direct transfer of ENT signals to hippocampal and extrahippocampal structures in parallel with the DG-CA3-CA1 system and may provide a security factor in situations in which the latter is disrupted. © 2004 Wiley-Liss, Inc. [source] Single neuron burst firing in the human hippocampus during sleepHIPPOCAMPUS, Issue 6 2002Richard J. Staba Abstract Although there are numerous non-primate studies of the single neuron correlates of sleep-related hippocampal EEG patterns, very limited hippocampal neuronal data are available for correlation with human sleep. We recorded human hippocampal single neuron activity in subjects implanted with depth electrodes required for medical diagnosis and quantitatively evaluated discharge activity from each neuron during episodes of wakefulness (Aw), combined stage 3 and 4 slow-wave sleep (SWS), and rapid eye movement (REM) sleep. The mean firing rate of the population of single neurons was significantly higher during SWS and Aw compared with REM sleep (p = 0.002; p < 0.0001). In addition, burst firing was significantly greater during SWS compared with Aw (p = 0.001) and REM sleep (p < 0.0001). The synchronized state of SWS and associated high-frequency burst discharge found in human hippocampus may subserve functions similar to those reported in non-primate hippocampus that require burst firing to induce synaptic modifications in hippocampal circuitry and in hippocampal projections to neocortical targets that participate in memory consolidation. Hippocampus 2002;12:724,734. © 2002 Wiley-Liss, Inc. [source] Cholinergic modulation of synaptic physiology in deep layer entorhinal cortex of the ratJOURNAL OF NEUROSCIENCE RESEARCH, Issue 1 2001Mi Young Cheong Abstract We have recently shown that cholinergic effects on synaptic transmission and plasticity in the superficial (II/III) layers of the rat medial entorhinal cortex (EC) are similar, but not identical, to those in the hippocampus (Yun et al. [2000] Neuroscience 97:671,676). Because the superficial and deep layers of the EC preferentially convey afferent and efferent hippocampal projections, respectively, it is of interest to compare cholinergic effects between the two regions. We therefore investigated the physiological effects of cholinergic agents in the layer V of medial EC slices under experimental conditions identical to those in the previous study. Bath application of carbachol (0.5 ,M) induced transient depression of field potential responses in all cases tested (30 of 30; 18.5% ± 2.3%) and rarely induced long-lasting potentiation (only 3 of 30; 20.4% ± 3.2% in successful cases). At 5 ,M, carbachol induced transient depression only (20 of 20, 48.9% ± 2.8%), which was blocked by atropine (10 ,M). Paired-pulse facilitation was enhanced during carbachol-induced depression, suggesting presynaptic action of carbachol. Long-term potentiation (LTP) could be induced in the presence of 10 ,M atropine by theta burst stimulation, but its magnitude was significantly lower (9.1% ± 4.7%, n = 15) compared to LTP in control slices (22.4% ± 3.9%, n = 20). These results, combined with our previous findings, demonstrate remarkably similar cholinergic modulation of synaptic transmission and plasticity across the superficial and deep layers of EC. J. Neurosci. Res. 66:117,121, 2001. © 2001 Wiley-Liss, Inc. [source] | ||||||||||