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Cortical Afferents (cortical + afferent)
Selected AbstractsCortical efferents of the perirhinal, postrhinal, and entorhinal cortices of the ratHIPPOCAMPUS, Issue 12 2009Kara L. Agster Abstract We investigated the cortical efferents of the parahippocampal region by placing injections of the anterograde tracers, Phaseolus vulgaris -leuccoagglutinin, and biotinylated dextran amine, throughout the perirhinal (PER), postrhinal (POR), and entorhinal cortices of the rat brain. The resulting density of labeled fibers was evaluated in 25 subregions of the piriform, frontal, insular, temporal, cingulate, parietal, and occipital areas. The locations of labeled terminal fibers differed substantially depending on whether the location of the injection site was in PER area 35, PER area 36, POR, or the lateral or the medial entorhinal (LEA and MEA). The differences were greater for sensory regions. For example, the POR efferents preferentially target visual and spatial regions, whereas the PER efferents target all sensory modalities. The cortical efferents of each region largely reciprocate the cortical afferents, though the degree of reciprocity varied across originating and target regions. The laminar pattern of terminal fibers was consistent with the notion that the efferents are feedback projections. The density and amount of labeled fibers also differed substantially depending on the regional location of injection sites. PER area 36 and POR give rise to a greater number of heavy projections, followed by PER area 35. LEA also gives rise to widespread cortical efferents, arising mainly from a narrow band of cortex adjacent to the PER. In contrast, the remainder of the LEA and the MEA provides only weak efferents to cortical regions. Prior work has shown that nonspatial and spatial information is transmitted to the hippocampus via the PER-LEA and POR-MEA pathways, respectively. Our findings suggest that the return projections follow the same pathways, though perhaps with less segregration. © 2009 Wiley-Liss, Inc. [source] Hierarchical model of the population dynamics of hippocampal dentate granule cellsHIPPOCAMPUS, Issue 5 2002G.A. Chauvet Abstract A hierarchical modeling approach is used as the basis for a mathematical representation of the population activity of hippocampal dentate granule cells. Using neural field equations, the variation in time and space of dentate granule cell activity is derived from the summed synaptic potential and summed action potential responses of a population of granule cells evoked by monosynaptic excitatory input from entorhinal cortical afferents. In this formulation of the problem, we have considered a two-level hierarchy: the synapses of entorhinal cortical axons define the first level of organization, and dentate granule cells, which include these synapses, define the second, higher level of organization. The model is specified by two state field variables, for membrane potential and for synaptic efficacy, respectively, with both evolving according to different time scales. The two state field variables introduce new parameters, physiological and anatomical, which characterize the dentate from the point of view of neuronal and synaptic populations: (1) a set of geometrical constraints corresponding to the morphological properties of granule cells and anatomical characteristics of entorhinal-dentate connections; and (2) a set of neuronal parameters corresponding to physiological mechanisms. Assuming no interaction between granule cells, i.e., neither ephaptic nor synaptic coupling, the model is shown to be mathematically tractable and allows solution of the field equations leading to the determination of activity. This treatment leads to the definition of two state variables, volume of stimulated synapses and firing time, which describe observed activity. Numerical simulations are used to investigate the populational characterization of the dentate by individual parameters: (1) the relationship between the conditions of stimulation of active perforant path fibers, e.g., stimulating intensity, and activity in the granule cell layer; and (2) the influence of geometry on the generation of activity, i.e., the influence of neuron density and synaptic density-connectivity. As an example application of the model, the granule cell population spike is reconstructed and compared with experimental data. Hippocampus 2002;12:698,712. © 2002 Wiley-Liss, Inc. [source] Frontal cortical afferents facilitate striatal nitric oxide transmission in vivo via a NMDA receptor and neuronal NOS-dependent mechanismJOURNAL OF NEUROCHEMISTRY, Issue 3 2007Stephen Sammut Abstract Striatal nitric oxide (NO) signaling plays a critical role in modulating neural processing and motor behavior. Nitrergic interneurons receive synaptic inputs from corticostriatal neurons and are activated via ionotropic glutamate receptor stimulation. However, the afferent regulation of NO signaling is poorly characterized. The role of frontal cortical afferents in regulating NO transmission was assessed in anesthetized rats using amperometric microsensor measurements of NO efflux and local field potential recordings. Low frequency (3 Hz) electrical stimulation of the ipsilateral cortex did not consistently evoke detectable changes in striatal NO efflux. In contrast, train stimulation (30 Hz) of frontal cortical afferents facilitated NO efflux in a stimulus intensity-dependent manner. Nitric oxide efflux evoked by train stimulation was transient, reproducible over time, and attenuated by systemic administration of either the NMDA receptor antagonist MK-801 or the neuronal NO synthase inhibitors 7-nitroindazole and NG -propyl- l -arginine. The interaction between NO efflux evoked via train stimulation and local striatal neuron activity was assessed using dual microsensor and local field potential recordings carried out concurrently in the contralateral and ipsilateral striatum, respectively. Systemic administration of the non-specific NO synthase inhibitor methylene blue attenuated both evoked NO efflux and the peak oscillation frequency (within the delta band) of local field potentials recorded immediately after train stimulation. Taken together, these observations indicate that feed-forward activation of neuronal NO signaling by phasic activation of frontal cortical afferents facilitates the synchronization of glutamate driven oscillations in striatal neurons. Thus, NO signaling may act to amplify coherent corticostriatal transmission and synchronize striatal output. [source] Motor thalamic circuits in primates with emphasis on the area targeted in treatment of movement disordersMOVEMENT DISORDERS, Issue S3 2002Igor A. Ilinsky MD Abstract The ventral region of the motor thalamus that receives cerebellar afferents has been and still is the target of stereotactic interventions for movement disorders. According to Hassler, this area includes ventro-oralis posterior (Vop) and ventral intermedius (Vim) nuclei, although some investigators believe that Vop is associated with the pallidothalamic pathway. We sought to correlate our experimental data on distribution of nigral, pallidal, and cerebellar afferents to the monkey thalamus with Hassler's motor thalamic parcelations. We concluded that Hassler's parcelations retained their value, although some adjustments were needed to relate them to the current neuroanatomic data; particularly, the cerebellothalamic zone that represents the monkey ventral lateral nucleus (VL) corresponds topographically to Hassler's Vop, Vim, and most of Voi. Electron microscopic tracing studies have shown very complex circuitry in this region of the monkey thalamus, as the cerebellar and cortical afferents innervating it are engaged in complex synapses with thalamocortical projection neurons, and this interaction is strongly modulated by local circuit neurons and the input from the reticular thalamic nucleus, which are both inhibitory and ,-aminobutyric acid (GABA)ergic. Spinothalamic afferents also reach the VL, but this input is less studied in the monkey. The circuitry subserving the activity of thalamocortical projection neurons in the VL should be considered while interpreting the functional data obtained in stereotactic surgery. © 2002 Movement Disorder Society [source] | ||||||||||