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PubMed1998

Distribution of 5-hydroxytryptamine-immunoreactive boutons on alpha-motoneurons in the lumbar spinal cord of adult cats.

Recent studies have shown that at least some of the functional effects of serotonin (5-HT) on motoneuron excitability are direct and are mediated via postsynaptic 5-HT receptors on motoneurons. To determine the spatial distribution of direct inputs from the serotonin system on the proximal and distal dendrites of individual motoneurons, we examined identified motoneurons in vivo with a combination of immunohistochemical localization of 5-HT-immunoreactive boutons and intracellular staining with horseradish peroxidase. Seventeen intracellularly stained motoneurons from 12 adult cats were analyzed with light microscopy. Quantitative analysis of 5-HT boutons apposed to dendrites of five representative motoneurons that were entirely reconstructed in three dimensions (each from the lumbosacral spinal cord of a different animal) revealed a total of 7,848 contacts (1,570+/-487 contacts/postsynaptic neuron; mean +/- SD) over the dendrites of these cells. Analysis of contacts on the soma of two of these cells, and on the somas of an additional 12 intracellularly stained motoneurons, revealed a wide range of somatic contacts (11-211 contacts/cell) on motoneuron cell bodies, with an average of 52 contacts/cell. These results indicate that the vast majority of 5-HT-immunoreactive boutons are apposed to dendritic branches rather than to the somatic surface of motoneurons. The spatial distribution of contacts essentially matched the distribution of surface membrane area of the postsynaptic neuron, resulting in a relatively uniform density of contacts (<1/100 microm2) on proximal and distal dendrites. Consequently, the frequency of contacts was higher on the proximal dendritic compartments where available membrane area is greater. There was no preferential distribution of contacts to particular dendrites. Light/electron microscopic correlations were performed on 21 boutons that contacted dendrites (n = 7) of three motoneurons from different animals. At the electron microscope level, most appositions (18/21; 85.7%) selected by our light microscopic criteria were confirmed as direct contacts when the 5-HT boutons were examined through serial sections. Synaptic junctions, generally small and symmetric, were positively identified in only a subset of these cases (n = 6; 28.6%), in part due to the obscuring effects of the peroxidase histochemical precipitate present in both pre- and postsynaptic profiles. A few 5-HT boutons (3/21; 14.3%) selected as contacts by our light microscopic criteria were in fact separated from the adjacent labeled dendrites; in two of these three cases, the separation was due to intrusion of very thin glial lamellae (<0.3 microm in cross section). These results indicate that the bulbospinal serotonergic system(s) provide a significant, direct synaptic input to spinal motoneurons that innervate hindlimb muscles. The nature of the modulatory actions exerted by such widespread synaptic inputs will affect all regions of the somatodendritic membrane and will ultimately depend on the nature of the 5-HT receptors present over different parts of the postsynaptic neuron's dendritic tree.

Animals↗
PubMed2003

Distribution of acidic and neutral drugs in surface waters near sewage treatment plants in the lower Great Lakes, Canada.

Prescription and nonprescription drugs have been detected in rivers and streams in Europe and the United States. Sewage treatment plants (STPs) are an important source of these contaminants, but few data exist on the spatial distribution of drugs in surface waters near STPs. Samples of surface water were collected in the summer and fall of 2000 at open-water sites in the lower Great Lakes (Lake Ontario and Lake Erie), at sites near the two STPs for the city of Windsor (ON, Canada), and at sites in Hamilton Harbour (ON, Canada), an embayment of western Lake Ontario that receives discharges from several STPs. In a follow-up study in the summer of 2002, samples of surface water and final effluent from adjacent STPs were collected from sites in Hamilton Harbour and Windsor. In addition, surface water and STP effluent samples were collected in Peterborough (ON, Canada). All samples of surface water and STP effluents were analyzed for selected acidic and neutral drugs. In the survey of Hamilton Harbour and Windsor conducted in 2000, acidic drugs and the antiepileptic drug carbamazepine were detected at ng/L concentrations at sites that were up to 500 m away from the STP, but the hydrological conditions of the receiving waters strongly influenced the spatial distribution of these compounds. Drugs were not detected at open-water locations in western Lake Erie or in the Niagara River near the municipality of Niagara-on-the-Lake (ON, Canada). However, clofibric acid, ketoprofen, fenoprofen, and carbamazepine were detected in samples collected in the summer of 2000 at sites in Lake Ontario and at a site in the Niagara River (Fort Erie, ON, Canada) that were relatively remote from STP discharges. Follow-up studies in the summer of 2002 indicated that concentrations of acidic and neutral drugs in surface waters near the point of sewage discharge into the Little River (ON, Canada) STP were approximately equal to the concentrations in the final effluent from the STP. Caffeine and cotinine, a metabolite of nicotine, were generally present in STP effluents and surface waters contaminated by drugs. The antidepressant fluoxetine and the antibiotic trimethoprom were also detected in most STP effluents and some surface water samples. For the first time, the lipid regulating drug atorvastatin was detected in samples of STP effluent and surface water.

Acids↗
PubMed2005

Spatially complex distribution of dissolved manganese in a fjord as revealed by high-resolution in situ sensing using the autonomous underwater vehicle Autosub.

Loch Etive is a fjordic system on the west coast of Scotland. The deep waters of the upper basin are periodically isolated, and during these periods oxygen is lost through benthic respiration and concentrations of dissolved manganese increase. In April 2000 the autonomous underwater vehicle (AUV) Autosub was fitted with an in situ dissolved manganese analyzer and was used to study the spatial variability of this element together with oxygen, salinity, and temperature throughout the basin. Six along-loch transects were completed at either constant height above the seafloor or at constant depth below the surface. The ca. 4000 in situ 10-s-average dissolved Mn (Mnd) data points obtained provide a new quasi-synoptic and highly detailed view of the distribution of manganese in this fjordic environment not possible using conventional (water bottle) sampling. There is substantial variability in concentrations (<25 to >600 nM) and distributions of Mnd. Surface waters are characteristically low in Mnd reflecting mixing of riverine and marine end-member waters, both of which are low in Mnd. The deeper waters are enriched in Mnd, and as the water column always contains some oxygen, this must reflect primarily benthic inputs of reduced dissolved Mn. However, this enrichment of Mnd is spatially very variable, presumably as a result of variability in release of Mn coupled with mixing of water in the loch and removal processes. This work demonstrates how AUVs coupled with chemical sensors can reveal substantial small-scale variability of distributions of chemical species in coastal environments that would not be resolved by conventional sampling approaches. Such information is essential if we are to improve our understanding of the nature and significance of the underlying processes leading to this variability.

Environmental Monitoring↗
PubMed2005

Immunohistochemical localization of IAA and ABP1 in strawberry shoot apexes during floral induction.

By using an anti-indole-acetic acid (anti-IAA) monoclonal antibody and an anti-auxin-binding protein 1 (anti-ABP1) polyclonal antibody, IAA and ABP1 were immunohistochemically localized in strawberry (Fragaria ananassa Duch.) shoot apexes during floral induction. The spatial distribution patterns of endogenous IAA and ABP1 and their dynamic changes during floral induction were investigated. In addition, the affect of 1-N-naphthylphtalamic acid (NPA) on IAA distribution during floral induction was also analyzed. The results showed that IAA was present in the shoot apexes throughout the floral induction process, gradually concentrating in the shoot apical meristem (SAM). The distribution of ABP1 and its dynamic changes were similar to those of IAA. In addition, the ABP1 immune signal in SAM gradually increased as floral induction developed. On a morphological level, these results indicate both the spatial distribution and dynamic changes in endogenous IAA and ABP1 during the floral induction process. The close correlation found between IAA and ABP1 indicates that a cooperation occurs during the regulation of floral induction. The results also suggest that IAA was the significant agent for floral induction, and that SAM might be the place of the main action. Treatment with NPA during floral induction prevented the accumulation of IAA in the SAM, delayed the process of floral differentiation and induced an abnormal flower development. It is likely that IAA in the shoot apex is produced in young leaves and transported through the vascular tissues to the SAM and other places of function. Finally, an appropriate amount of IAA in the SAM and normal polar auxin transport are essential for floral induction and differentiation in strawberries.

Cell Differentiation↗
PubMed2004

Ecotoxicity assessment of natural attenuation effects at a historical dumping site in the western Baltic Sea.

During the late 1950s and early 1960s of the past century, industrial waste material highly enriched in various contaminants (heavy metals, PAHs) was dumped in the inner Mecklenburg Bay, western Baltic Sea. Large-scale shifts in the spatial distribution of heavy metals in surface sediments were mapped by geochemical monitoring in the mid-1980s and 12 years later in 1997. A further study in 2001 was designed to investigate the small-scale spatial distribution of contaminants inside, on top of, and around the historical dumping ground and to examine possible effects to benthic organisms (Arctica islandica, microbiological toxicity tests). The site is located within an area characterized by a discontinuous deposition of fine sediments, but net sedimentation rate of about 3mm/y led ultimately to a gradual coverage of the dumped material. During the first decades after the dumping, about half of the originally dumped material was already spread over the surrounding area as a result of sediment dynamics and re-suspension processes. Recent sediments of the historical dump site are still significantly enriched in heavy metals and PAHs. Microbiological toxicity test results were positive, though uptake of contaminants in mussels was found to deviate only slightly from that of a non-contaminated reference station due to a gradual dilution and decrease in bioavailability of the contaminants.

Animals↗
PubMed1997

Energy deposition pattern from tritium and different energy photons--a comparative study.

Energy deposition patterns of beta particles from tritium decay have been analyzed in comparison with photon radiation in the energy range from 12 to 1250 keV. Energy deposition was modeled by Monte Carlo means using electron tracks in water vapor with a complete follow up of delta electrons. Ionizations have been used as representative of track structure. Frequencies of clusters on a nanometer scale and their spatial distribution in spherical targets representing cell nuclei have been derived. Cluster analysis has been carried out by implementing a k-means method. Frequencies of ionization clusters from tritium are similar to 60-100 keV photons. Spatial distribution of clusters from tritium closely match approximately 70 keV photons up to 2 microm separation.

Monte Carlo Method↗
PubMed1996

Distribution of GABAA, GABAB, and glycine receptors in the central auditory system of the big brown bat, Eptesicus fuscus.

Quantitative autoradiographic techniques were used to compare the distribution of GABAA, GABAB, and glycine receptors in the subcortical auditory pathway of the big brown bat, Eptesicus fuscus. For GABAA receptors, the ligand used was 35S-t-butylbicyclophosphorothionate (TBPS) for GABAB receptors, 3H-GABA was used as a ligand in the presence of isoguvacine to block binding to GABAA sites; for glycine, the ligand used was 3H-strychnine. In the subcortical auditory nuclei there appears to be at least a partial complementarity in the distribution of GABAA receptors labeled with 35S-TBPS and glycine receptors labeled with 3H-strychnine, GABAA receptors were concentrated mainly in the inferior colliculus (IC) and medial geniculate nucleus, whereas glycine receptors were concentrated mainly in nuclei below the level of the IC. Within the IC, there was a graded spatial distribution of 35S-TBPS binding; the most dense labeling was in the dorsomedial region, but very sparse labeling was observed in the ventrolateral region. There was also a graded spatial distribution of 3H-strychnine binding. The most dense labeling was in the ventral and lateral regions and the weakest labeling was in the dorsomedial region. Thus, in the IC, the distribution of 35S-TBPS was complementary to that of 3H-strychnine. GABAB receptors were distributed at a low level throughout the subcortical auditory nuclei, but were most prominent in the dorsomedial part of the IC.

Animals↗
PubMed2005

Distribution patterns of mercury in lakes and rivers of northeastern North America.

We assembled 831 data points for total mercury (Hg(t)) and 277 overlapping points for methyl mercury (CH3Hg+) in surface waters from Massachussetts, USA to the Island of Newfoundland, Canada from State, Provincial, and Federal government databases. These geographically indexed values were used to determine: (a) if large-scale spatial distribution patterns existed and (b) whether there were significant relationships between the two main forms of aquatic Hg as well as with total organic carbon (TOC), a well know complexer of metals. We analyzed the catchments where samples were collected using a Geographical Information System (GIS) approach, calculating catchment sizes, mean slope, and mean wetness index. Our results show two main spatial distribution patterns. We detected loci of high Hg(t) values near urbanized regions of Boston MA and Portland ME. However, except for one unexplained exception, the highest Hg(t) and CH3Hg+ concentrations were located in regions far from obvious point sources. These correlated to topographically flat (and thus wet) areas that we relate to wetland abundances. We show that aquatic Hg(t) and CH3Hg+ concentrations are generally well correlated with TOC and with each other. Over the region, CH3Hg+ concentrations are typically approximately 15% of Hg(t). There is an exception in the Boston region where CH3Hg+ is low compared to the high Hg(t) values. This is probably due to the proximity of point sources of inorganic Hg and a lack of wetlands. We also attempted to predict Hg concentrations in water with statistical models using catchment features as variables. We were only able to produce statistically significant predictive models in some parts of regions due to the lack of suitable digital information, and because data ranges in some regions were too narrow for meaningful regression analyses.

Cities↗
PubMed2000

Lek mating systems: a case study in the Little Bustard Tetrax tetrax.

Leks have recently been defined as male display aggregations that females attend primarily for the purpose of mating. This is an extended version of previous definitions, as a clear-cut definition of leks is difficult to obtain. Four criteria should be verified to identify a lekking species: (i) there is no male parental investment beyond the sperm; (ii) males aggregate at specific sites for display; (iii) the only resource females find on the lek is the male, i.e. the male genes; (iv) females can select her mate(s), although the necessity of this latter condition for lekking species has been highly debated. We applied these criteria to the endangered little bustard Tetrax tetrax, a species that is claimed to show an exploded lek mating system, but for which this has never been fully investigated. We monitored a population of little bustards in western France during 2 years to investigate the two central criteria in the assessment of their mating system: male aggregation in arenas and lack of consistent resources in male territories. We analysed the spatial distribution of little bustard male territories, the individual variation in size, and the land use characteristics of male territories, with particular attention to the habitats that may be considered as defensible resources. Displaying males showed an aggregated spatial distribution over the study area during the 2 years of survey. Male territories were rather large (19+/-16 ha), but a large among-male variability in territory size was observed. Land use within the territories included mainly permanent and semi-permanent crops. The variability in land use among territories suggests also that resources found within male territories were selected according to male needs (food and display) rather than to female needs (permanent crops that are more appropriate for reproduction). The mating system of the little bustard seems to match the general (and extended) definition of leks, at least in some populations. However, limits between resource defence polygyny and extreme exploded or resource-based leks are thin and unclear, and the little bustard is a good example of how lek definitions may be difficult to apply in non clear-cut empirical situations.

Journal Article↗
PubMed2006

Macular pigment shows ringlike structures.

PURPOSE: The spatial distribution of macular pigment is generally assumed to monotonously decrease to very low values in the periphery. However, there are indications that this picture may be too simple. The purpose of this study was to examine the spatial distribution of the macular pigment optical density. METHODS: Fundus reflectance and autofluorescence maps at 488 and 514 nm Argon laser wavelengths were acquired in 53 healthy subjects with a custom-built scanning laser ophthalmoscope. Because the lens and the macular pigment are the only absorbers in this wavelength region, digital subtraction of log reflectance and log autofluorescence at the two wavelengths provides density maps of the sum of both absorbers. RESULTS: In approximately half of the subjects, we observed a distinct ring pattern at a mean distance of 0.7 degrees of the fovea. In a few subjects, the ring had an even larger optical density than did the central peak. A simple model with an exponentially decaying density as a function of eccentricity, in combination with a Gaussian-distributed ring pattern, yielded a good description of the data for both methods. The widths of the central peak and the Gaussian ring, and also the eccentricity at which the ring peaks, were similar for both methods. The prominence of the ring did not depend on age and gender. CONCLUSIONS: Both reflectance and autofluorescence maps showed ring patterns in the distribution of the macular pigment, which probably follow the inner plexiform layer.

Adult↗
PubMed2002

[Application of turning band method in conditional simulation of soil heavy metals].

Geostatistical simulation techniques are widely used in studying spatial phenomena. The purpose of this study is to make an experimental study in applying this technique to understand the spatial distribution of copper and lead in wastewater irrigated agricultural soil in the eastern suburb of Beijing. The results showed that the simulation is efficient, because it fits to the main characteristics of the revealed reality of the spatial distribution of these elements. Geostatistical simulation could play an important role in regional environmental and ecological studies.

Copper↗
PubMed2007

Identification of proteins directly from tissue: in situ tryptic digestions coupled with imaging mass spectrometry.

A novel method for on-tissue identification of proteins in spatially discrete regions is described using tryptic digestion followed by matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) with MS/MS analysis. IMS is first used to reveal the protein and peptide spatial distribution in a tissue section and then a serial section is robotically spotted with small volumes of trypsin solution to carry out in situ protease digestion. After hydrolysis, 2,5-Dihydroxybenzoic acid (DHB) matrix solution is applied to the digested spots, with subsequent analysis by IMS to reveal the spatial distribution of the various tryptic fragments. Sequence determination of the tryptic fragments is performed using on-tissue MALDI MS/MS analysis directly from the individual digest spots. This protocol enables protein identification directly from tissue while preserving the spatial integrity of the tissue sample. The procedure is demonstrated with the identification of several proteins in the coronal sections of a rat brain.

Amino Acid Sequence↗
PubMed1992

Photon field quantities and units for kernel based radiation therapy planning and treatment optimization.

The problem of choosing radiation quantities and units for energy deposition kernels and their associated kernel densities is treated with the aim of making them consistent with related classical radiation quantities and units such as restricted mass stopping powers and mass attenuation coefficients. It is shown that it is very useful to define the kernels h(r), in terms of the quotient of the mean specific energy imparted to the medium by the radiant energy incident on a volume element centred at the origin of the kernel. The basic building block used to generate these kernels is the point energy deposition kernel, h(p), describing the spatial distribution of the energy imparted by a photon interacting at a point in a medium. This will allow the kernels to be regarded as generalizations of the traditional mass stopping and attenuation coefficients, which in detail describe the spatial distribution of the mean energy deposition around an interaction site. As a consequence, the irradiation or kernel density, f(r) should be expressed in terms of the radiant energy incident per unit volume of the medium. It is shown that the kernel density is equal to minus the divergence of the incident unattenuated vectorial energy fluence, and it therefore acts as an irradiation density for the incident vectorial energy fluence. The microscopic kernels or the irradiation density may thus be viewed as a perfect 'sink' distribution to the required incident photon energy fluence which is totally absorbed at f(r), and instead replaced by the kernels which describe the detailed energy deposition in the medium in coordinates centred at the sinks. From these definitions the required incident energy fluence from an external radiation source used for treatment realization can be determined directly by projecting the irradiation density on the relevant positions of the radiation source. This procedure has the valuable property that maximal calculational accuracy is achieved in the tumour because the irradiation density has non-zero values only in the tumour, and the accuracy of the kernel is highest at its origin.

Humans↗
PubMed2000

Nuclear magnetic resonance in inhomogeneous magnetic fields

The response of the spin system has been investigated by numerical simulations in the case of a nuclear magnetic resonance (NMR) experiment performed in inhomogeneous static and radiofrequency fields. The particular case of the NMR-MOUSE was considered. The static field and the component of the radiofrequency field perpendicular to the static field were evaluated as well as the spatial distribution of the maximum NMR signal detected by the surface coil. The NMR response to various pulse sequences was evaluated numerically for the case of an ensemble of isolated spins (1/2). The behavior of the echo train in Carr-Purcell-like pulse sequences used for measurements of transverse relaxation and self-diffusion was simulated and compared with the experiment. The echo train is shown to behave qualitatively differently depending on the particular phase schemes used in these pulse sequences. Different echo trains are obtained, because of the different superposition of Hahn and stimulated echoes forming mixed echoes as a result of the spatial distribution of pulse flip angles. The superposition of Hahn and stimulated echoes originating from different spatial regions leads to distortions of the mixed echoes in intensity, shape, and phase. The volume selection produced by Carr-Purcell-like pulse sequences is also investigated for the NMR-MOUSE. The developed numerical simulation procedure is useful for understanding a variety of experiments performed with the NMR-MOUSE and for improving its performance. Copyright 2000 Academic Press.

Journal Article↗
PubMedDate not supplied

[Optimization model of spatial population structure: example of poplar moth laying eggs on leaves].

The authors analyze spatial distribution and survival of populations of poplar moth Litchcolletis populifoliella Tr. on its feeding plant--balsam poplar Populus balsamifera. Imago of the moth glue its eggs on the leaves thus determining the future location of their offspring on the host plant. Spatial distribution of eggs on leaf surface and distribution of leaves according egg numbers are not random. On the short distance from each egg the average number of eggs is less, than it should be in case of random distribution. While this distance increases up to some particular value the occurrence of eggs is higher than random. Thus, the eggs of moth are located by groups on the leaf surface. Within each group eggs are situated not very close to each other, this allowing larvae to lower competition for common resource. It is suggested that on the same feeding plant individuals have different interactions: competition, caused by limited quantity of resource and cooperation that is necessary to resist leaf defensive (antibiosis) reaction.

Animals↗
PubMed2004

Multiple promoters direct expression of three AKAP12 isoforms with distinct subcellular and tissue distribution profiles.

A Kinase Anchoring Protein 12 (AKAP12; also known as src-suppressed C kinase substrate (SSeCKS) and Gravin) is a multivalent anchoring protein with tumor suppressor activity. Although expression of AKAP12 has been examined in a number of contexts, its expression control remains to be elucidated. Herein, we characterize the genomic organization of the AKAP12 locus, its regulatory regions, and the spatial distribution of the proteins encoded by the AKAP12 gene. Using comparative genomics and various wet-lab assays, we show that the AKAP12 locus is organized as three separate transcription units that are governed by non-redundant promoters coordinating distinct tissue expression profiles. The proteins encoded by the three AKAP12 isoforms (designated alpha, beta, and gamma) share >95% amino acid sequence identity but differ at their N termini. Analysis of the targeting of each isoform reveals distinct spatial distribution profiles. An N-terminal myristoylation motif present in AKAP12alpha is shown to be necessary and sufficient for targeted expression of this AKAP12 isoform to the endoplasmic reticulum, a novel subcellular compartment for AKAP12. Our results demonstrate heretofore unrecognized complexity within the AKAP12 locus and suggest a mechanism for genetic control of signaling specificity through distinct regulation of alternately targeted anchoring protein isoforms.

3T3 Cells↗
PubMed1977

[K+]o clearance in cortex: a new analytical model.

1. It has been suggested that passive diffusion is the principal mechanism of the clearance of locally elevated extracellular potassium, K+o, in the cerebral cortex. This concept was based on the assumption that elevated K+ could be modeled as a point source. In the present study, the functional role of passive diffusion was reevaluated in the anesthetized cat cortex following local electrical stimulation. 2. The initial spatial distribution of extracellular potassium activity, [K+]o, elevated by monopolar stimulation, could be modeled by a two-dimensional Gaussian function at and below the 500-micron cortical depth. Azimuthal symmetry around the stimulating electrode was assumed and cylindrical spatial coordinates were used. 3. The observed clearance of transiently elevated [K+]o as a function of space and time was much more rapid than that predicted by an analytical model consisting of the homogeneous diffusion equation whose initial condition was the Gaussian spatial distribution of [K+]o at the onset of the clearance process. 4. It is concluded that passive diffusion does not significantly contribute to the rapid clearance of locally elevated extracellular potassium in the cortex. Active uptake of potassium by cortical cells should be more seriously considered as being primarily responsible for the potassium clearance.

Adenosine Triphosphatases↗
PubMed1993

Synaptic integration in an excitable dendritic tree.

1. Compartmental modeling experiments were carried out in an anatomically characterized neocortical pyramidal cell to study the integrative behavior of a complex dendritic tree containing active membrane mechanisms. Building on a previously presented hypothesis, this work provides further support for a novel principle of dendritic information processing that could underlie a capacity for nonlinear pattern discrimination and/or sensory processing within the dendritic trees of individual nerve cells. 2. It was previously demonstrated that when excitatory synaptic input to a pyramidal cell is dominated by voltage-dependent N-methyl-D-aspartate (NMDA)-type channels, the cell responds more strongly when synaptic drive is concentrated within several dendritic regions than when it is delivered diffusely across the dendritic arbor. This effect, called dendritic "cluster sensitivity," persisted under wide-ranging parameter variations and directly implicated the spatial ordering of afferent synaptic connections onto the dendritic tree as an important determinant of neuronal response selectivity. 3. In this work, the sensitivity of neocortical dendrites to spatially clustered synaptic drive has been further studied with fast sodium and slow calcium spiking mechanisms present in the dendritic membrane. Several spatial distributions of the dendritic spiking mechanisms were tested with and without NMDA synapses. Results of numerous simulations reveal that dendritic cluster sensitivity is a highly robust phenomenon in dendrites containing a sufficiency of excitatory membrane mechanisms and is only weakly dependent on their detailed spatial distribution, peak conductances, or kinetics. Factors that either work against or make irrelevant the dendritic cluster sensitivity effect include 1) very high-resistance spine necks, 2) very large synaptic conductances, 3) very high baseline levels of synaptic activity, and 4) large fluctuations in level of synaptic activity on short time scales. 4. The functional significance of dendritic cluster sensitivity has been previously discussed in the context of associative learning and memory. Here it is demonstrated that the dendritic tree of a cluster-sensitive neuron implements an approximative spatial correlation, or sum of products operation, such as that which could underlie nonlinear disparity tuning in binocular visual neurons.

Animals↗