Autoradiographic distribution of [3H]nicotine binding in human cortex: Relative abundance in subicular complex
ABSTRACT Distinct patterns of [3H]nicotine (3 nm) binding were apparent in various regions of adult human neo- and archicortex. Receptor binding was greatest in the subicular complex—particularly presubiculum—and entorhinal cortex, where it was prominent in the characteristic parvo- and magnocellular islands of these regions and in middle layers of entorhinal cortex. In somatosensory cortex (Brodmann areas 3, 1 and 2) and occipital (area 17) cortex binding was highest in the upper and lower layers, and relatively sparse in the sensory input, layer IV. In primary motor (area 4) and temporal (area 21) cortex, binding in the outer half of the cortical ribbon was denser than that in the inner half and a distinct band was apparent in temporal and cingulate (area 32) in the lower portion of layer III. In prefrontal association cortex the pattern of binding was less distinct although slightly higher in the lower architectonic layers. There was generally little binding in the hippocampus (areas CA1–4) and dentate gyrus with the exception of the stratum lacunosum moleculare in CA2–3 and, to a lesser extent, supra- and subgranule zones of the dentate. These patterns of reactivity, which are distinct from that of the major cortical cholinergic innervation, suggest that the nicotinic receptor, detected using nanomolar concentrations of [3H]nicotine, may primarily be associated with intracortical circuitry in the neocortex. The relatively high density in entorhinal and subicular regions may be related to the extensive phylogenetic development of these regions which has occurred in conjunction with the development of multimodal association circuitry in the human cortex.
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ABSTRACT: We present here in terms of a dyadic Green's function (DGF) a general description of optical phenomena in photonic crystal (PC) structures, described particularly by frequency-dependent components, assuming that PC structures are decomposed into their relatively simple constituent parts via conductivity tensors. We demonstrate this approach by explicitly calculating the DGFs for electromagnetic waves propagating in the one- and two-dimensional dispersive PCs consisting of a periodic array of identical metallic quantum wells and a periodic square array of identical metallic quantum wires, each embedded in a three-dimensional dispersive medium. By means of the explicit analytic dispersion relations, which result from the frequency poles of the corresponding DGFs, we also calculate the band structures of these dispersive PCs by simple numerical means. Our analysis shows that the band structures calculated from our DGF approach conform well with those calculated from the traditional computational methods.Journal of Quantitative Spectroscopy and Radiative Transfer 12/2011; 112(18):2814-2825. DOI:10.1016/j.jqsrt.2011.08.011 · 2.29 Impact Factor
Article: CNS Nicotinic Receptors[Show abstract] [Hide abstract]
ABSTRACT: CNS nicotinic acetylcholine receptors are a family of ligand-gated cation channels that allow the passage of calcium ions. They are structurally and functionally distinct from nicotinic receptors at the neuromuscular junction. CNS nicotinic receptors show a variation in distribution and pharmacology. The number of these receptors is reduced with normal aging, and a further reduction in number occurs in dementing conditions that are common in elderly individuals. A comparison of receptor loss in the substantia nigra of patients with Parkinson’s disease and Lewy body dementia indicates that this process may occur early in the disease and precede cell loss. In addition, nicotine binding sites in humans are concentrated in the entorhinal cortex and subicular formation, areas that are affected early in the course of Alzheimer-type disease. The number of nicotine binding sites is high in human neonatal brain, at which stage exposure to nicotine and tobacco smoke is deleterious. Conversely, epidemio-logical evidence suggests that later in life tobacco smoking may offer some protection against Parkinson’s and Alzheimer’s diseases. Exposure to nicotinic agonists and tobacco smoke increases the number of brain nicotinic receptors both in humans and experimental animals, although the functional significance of this and its precise relationship to receptor desensitisation is not completely understood. Acute exposure to nicotine and nicotinic antagonists has beneficial and adverse effects, respectively, on cognitive function. Subcutaneous administration of nicotine to patients with Alzheimer’s disease improves discriminative sensitivity and reaction times. Available nicotinic agonists appear to induce diverse functional responses, and models for the testing of such novel compounds are needed.CNS Drugs 09/1994; 2(3). DOI:10.2165/00023210-199402030-00006 · 4.38 Impact Factor