bluuebunny/crossref_metadata_2025 huggingface dataset:
Dorsal hippocampus and classical fear conditioning to tone and context in rats: Effects of local NMDA‐receptor blockade and stimulation
Authors: Bast Tobias , Zhang Wei‐Ning , Feldon Joram
Published: August 2003

Consistent with the importance of the hippocampus in learning more complex stimulus relations, but not in simple associative learning, the dorsal hippocampus has commonly been implicated in classical fear conditioning to context, but not to discrete stimuli, such as a tone. In particular, a specific and central role in contextual fear conditioning has been attributed to mechanisms mediated by dorsal hippocampal N‐methyl‐D‐aspartate (NMDA)‐type glutamate receptors. The present study characterized the effects of blockade or tonic stimulation of dorsal hippocampal NMDA receptors by bilateral local infusion of the noncompetitive NMDA receptor antagonist MK‐801 (dizocilpine maleate; 6.25μg/side) or of NMDA (0.7μg/side), respectively, on classical fear conditioning to tone and context in Wistar rats. Freezing was used to measure conditioned fear. Regardless of whether conditioning was conducted with tone‐shock pairings or unsignaled footshocks (background or foreground contextual conditioning), both NMDA and MK‐801 infusion before conditioning resulted in reduced freezing during subsequent exposure to the conditioning context. Freezing during subsequent tone presentation in a new context, normally resulting from conditioning with tone‐shock pairings, was not impaired by MK‐801 but was strongly reduced by NMDA infusion before conditioning; this freezing was also reduced by NMDA infusion before tone presentation (in an experiment involving NMDA infusions before conditioning and subsequent tone presentation to assess the role of state‐dependent learning). It was assessed whether unspecific infusion effects (altered sensorimotor functions, state dependency) or infusion‐induced dorsal hippocampal damage contributed to the observed reductions in conditioned freezing. Our data suggest that formation of fear conditioning to context, but not tone, requires NMDA receptor‐mediated mechanisms in the dorsal hippocampus. As indicated by the effects of NMDA, some dorsal hippocampal processes may also contribute to fear conditioning to tone. The role of the dorsal hippocampus and local NMDA receptor‐mediated processes in fear conditioning to tone and context is discussed in comparison with ventral hippocampal processes. © 2003 Wiley‐Liss, Inc.
Dynamically detuned oscillations account for the coupled rate and temporal code of place cell firing
Authors: Lengyel Máté , Szatmáry Zoltán , Érdi Péter
Published: August 2003

Firing of place cells in the exploring rat conveys doubly coded spatial information: both the rate of spikes and their timing relative to the phase of the ongoing field theta oscillation are correlated with the location of the animal. Specifically, the firing rate of a place cell waxes and wanes, while the timing of spikes precesses monotonically as the animal traverses the portion of the environment preferred by the cell. We propose a mechanism for the generation of this firing pattern that can be applied for place cells in all three hippocampal subfields and that encodes spatial information in the output of the cell without relying on topographical connections or topographical input. A single pyramidal cell was modeled so that the cell received rhythmic inhibition in phase with theta field potential oscillation on the soma and was excited on the dendrite with input depending on the speed of the rat. The dendrite sustained an intrinsic membrane potential oscillation, frequency modulated by its input. Firing probability of the cell was determined jointly by somatic and dendritic oscillations. Results were obtained on different levels of abstraction: a purely analytical derivation was arrived at, corroborated by numerical simulations of rate neurons, and an extension of these simulations to spiking neurons was also performed. Realistic patterns of rate and temporal coding emerged and were found to be inseparable. These results may have implications on the robustness of information coding in place cell firing and on the ways information is processed in structures downstream to the hippocampus. © 2003 Wiley‐Liss, Inc.
Comparison of commissural sprouting in the mouse and rat fascia dentata after entorhinal cortex lesion
Authors: Del Turco Domenico , Woods Alisa G. , Gebhardt Carl , Phinney Amie L. , Jucker Mathias , Frotscher Michael , Deller Thomas
Published: August 2003

Reactive axonal sprouting occurs in the fascia dentata after entorhinal cortex lesion. This sprouting process has been described extensively in the rat, and plasticity‐associated molecules have been identified that might be involved in its regulation. To demonstrate causal relationships between these candidate molecules and the axonal reorganization process, it is reasonable to analyze knockout and transgenic animals after entorhinal cortex lesion, and because gene knockouts are primarily generated in mice, it is necessary to characterize the sprouting response after entorhinal cortex lesion in this species. In the present study, Phaseolus vulgaris‐leucoagglutinin (PHAL) tracing was used to analyze the commissural projection to the inner molecular layer in mice with longstanding entorhinal lesions. Because the commissural projection to the fascia dentata is neurochemically heterogeneous, PHAL tracing was combined with immunocytochemistry for calretinin, a marker for commissural/associational mossy cell axons. Using both techniques singly as well as in combination (double‐immunofluorescence) at the light or electron microscopic level, it could be shown that in response to entorhinal lesion mossy cell axons leave the main commissural fiber plexus, invade the denervated middle molecular layer, and form asymmetric synapses within the denervated zone. Thus, the commissural sprouting response in mice has a considerable translaminar component. This is in contrast to the layer‐specific commissural sprouting observed in rats, in which the overwhelming majority of mossy cell axons remain within their home territory. These data demonstrate an important species difference in the commissural/associational sprouting response between rats and mice that needs to be taken into account in future studies. © 2003 Wiley‐Liss, Inc.
Changes in hippocampal histamine receptors across the hibernation cycle in ground squirrels
Authors: Sallmen Tina , Lozada Adrian F. , Anichtchik Oleg V. , Beckman Alexander L. , Leurs Rob , Panula Pertti
Published: August 2003

Hibernation is a physiological state characterized by a dramatic reduction in various functions, such as body temperature, heart rate, and metabolism. The hippocampus is thought to be important for regulation of the hibernation bout because it remains electrophysiologically active throughout this extremely depressed state. The question arises as to what neuronal influences act within the hippocampus during hibernation to sustain its activity. We hypothesized that histaminergic input might be an important contributor. Brain histamine is involved in functions relevant to hibernation, such as the regulation of diurnal rhythms, body temperature, and energy metabolism. Furthermore, we have previously shown that the histaminergic system appears to be activated during the hibernating state. In this study, we used receptor binding autoradiography, in situ hybridization, and GTP‐γ‐S binding autoradiography to study changes in histamine receptors across the hibernation bout. We were able to demonstrate an increase in histamine H1 and H2 receptors in the hippocampus during hibernation, whereas the mRNA expression and receptor density of the inhibitory H3 receptor decreased. Histamine H3 receptors were shown to exhibit both histamine‐activated and constitutive GTP‐γ‐S‐binding activity in the ground squirrel hippocampus, both of which decreased during hibernation, indicating a decrease in H3 receptor G‐protein activation. Taken together, our results indicate that histamine may be involved in maintaining hibernation by sustaining hippocampal activity, possibly through H1 and H2 receptor activity and decreased inhibition by H3 receptors. The involvement of brain histamine, which is generally thought of as an arousal molecule, in maintaining a depressed state of the brain suggests a more general role for the amine in controlling arousal state. © 2003 Wiley‐Liss, Inc.
Electrophysiological and morphological diversity of neurons from the rat subicular complex in vitro
Authors: Menendez de la Prida L. , Suarez F. , Pozo M.A.
Published: August 2003

We combined whole‐cell recordings with Neurobiotin labeling to examine the electrophysiological and morphological properties of neurons from the ventral subicular complex in vitro (including the subicular, presubicular, and parasubicular areas). No a priori morphological sampling criteria were used to select cells. Cells were classified as bursting (IB), regular‐spiking (RS), and fast‐spiking (FS) according to their firing patterns in response to depolarizing current pulses. A number of cells remained unclassified. We found 54% RS, 26% IB, 11% FS, and 9% unclassified cells out of a total of 131 neurons examined. We also found cells showing intrinsic membrane potential oscillations (MPO) (6%), which represented a subgroup of the unclassified cells. We analyzed several electrophysiological parameters and found that RS and IB cells can be subclassified into two separate subgroups. RS cells were subclassified as tonic and adapting, according to the degree of firing adaptation. Both responded with single spikes to orthodromic stimulation. IB cells were subclassified in two subgroups according to their capacity to fire more than one burst, and showed different responses to orthodromic stimulation. We observed that bursting in these two subgroups appeared to involve both Ca2+ and persistent Na+ components. Both IB and RS cells, as well as MPO neurons, were projecting cells. FS cells were morphologically identified as local circuit interneurons. We also analyzed the spatial distribution of these cell types from the vicinity of CA1 to the parasubicular areas. We conclude that, in contrast to the commonly accepted idea of the subicular complex as a bursting structure, there is a wide electrophysiological variability even within a given cellular group. © 2003 Wiley‐Liss, Inc.
Reelin‐expressing neurons in the postnatal and adult human hippocampal formation
Authors: Abraham Hajnalka , Meyer Gundela
Published: August 2003

Reelin plays a major role in the development of laminated brain structures. In the developing neocortex and hippocampus, Reelin is secreted by Cajal‐Retzius cells in the marginal zone. In the present report, we characterize Reelin‐immunoreactive neurons in the perinatal and adult human hippocampal formation. Two main populations of cells are described: Cajal‐Retzius cells and interneurons. Cajal‐Retzius cells are defined as neurons that coexpress Reelin and p73, a nuclear protein of the p53 family. Colocalization experiments of p73 with calcium‐binding proteins indicate that most Cajal‐Retzius cells express calretinin, but not calbindin. Cajal‐Retzius cell density decreases dramatically during the postnatal period, although a few Reelin/p73‐positive neurons are still found in the adult. At birth, Reelin‐positive, p73‐negative neurons are present in all layers of the hippocampal formation. Their morphology and localization indicate that they belong to a heterogeneous population of interneurons. They are numerous in the strata lacunosum‐moleculare and radiatum of CA1‐CA3, in the hilus, and in the molecular layer of the dentate gyrus, but less common in stratum oriens and alveus, and rare in the principal cell layers. Subpopulations of Reelin‐positive interneurons express calretinin or calbindin. The packing density of Reelin‐positive cells decreases postnatally, which may be related to the disappearance of Cajal‐Retzius cells and to the growth of the hippocampal formation. The presence of Reelin‐immunoreactive cells in the adult hippocampal formation indicates that Reelin is not restricted to development but that it may have additional functions in adult life. © 2003 Wiley‐Liss, Inc.
Entorhinal inputs to dentate gyrus are activated mainly by conditioned events with long time intervals
Authors: Talnov Arkadiy N. , Quiroga Rodrigo Quian , Meier Martin , Matsumoto Gen , Brankačk Jurij
Published: August 2003

Brain mechanisms of mammalian learning and memory have long been associated with the hippocampus. Although the role of the hippocampus in spatial behavior is well established, there is no general consensus on the function of the hippocampus in nonspatial tasks. Task‐related changes in evoked potentials were first reported by Deadwyler and colleagues in the dentate gyrus, with a peak at 100 ms in rats trained in an auditory discrimination task (Deadwyler et al., Brain Res 161:211–225, 1979). Surprisingly, these results have not been confirmed by other investigators. In the present report, we set out to assess the task parameters that induce, modulate, and suppress this potential. Using multielectrode probes and current source density analysis, we monitored the entorhinal input to the dentate gyrus in behaving rats. Both differential and simple auditory conditioning led to the appearance of a large negative potential at 100 ms in the perforant path zone of the dentate gyrus. This negativity was found in averaged and in single‐trial, evoked potentials. Current source density analysis revealed sinks in the perforant path zone of the molecular layer of the dentate gyrus with corresponding sources in the hilus. Once trained for differential conditioning, decrements of target probability consistently increased the amplitude of this negativity. When using a single‐tone, stimulus‐response task, the negative potential occurred with long (70‐s), but not with short (10‐s) intertrial intervals. Appearance of the potential coincided with a switch in response strategy and disappeared under stereotypical behavior. These data are best explained under the assumption that long intertrial intervals lead to transitions in task‐related reference frames enabling a switch to more appropriate response strategies. Such transitions are not required during short interval stereotyped performance. © 2003 Wiley‐Liss, Inc.
Subsurface topography to enhance the prediction of the spatial distribution of soil wetness
Authors: Chaplot V. , Walter C.
Published: August 2003

The estimation of the spatial distribution of soil wetness within a catchment is one of the most important issues in hydrological and erosion modelling. So far, such models have been based on soil surface topographic information only. However, soil hydrology is also controlled by subsurface flow pathways that may not be explained only by surface terrain features. This study examined how the topography of the lower limit of the soil cover could improve quantitative modelling for the spatial prediction of soil wetness. The study was conducted in an agricultural catchment of the Armorican Massif (western France) characterized by impermeable granitic saprolites. Two digital elevation models (DEMs) with a 10‐m grid mesh and with a 0·3 m vertical resolution were generated from field investigations throughout the catchment. One DEM was a numerical representation of the soil surface and the other described the topography of the boundary between the soil cover and the underlying impermeable saprolite. Soil wetness (θ) was surveyed systematically from 1996 to 1997 along a hillslope. The sampling scheme consisted of 149 nodes of a 10‐m grid where θ at 0–10 cm was estimated using time‐domain reflectometry. The value of θ at depths of 20–30, 50–60 and 110–120 cm was estimated for a subset of 112 data points using a gravimetric method. For both surface and subsurface DEMs, soil wetness at all depths significantly correlated with the topographic attributes, namely the distance to the stream bank, the elevation above the stream bank (E), the downslope gradient, the revised compound topographic index (CTI), and the specific monodirectional and multidirectional catchment areas. The best correlations were observed between θ10 of winter 1996 and the physically based attributes E and CTI estimated by using the subsurface DEM (r = 0·83 and 0·86, respectively). Two multiple non‐linear regression models for θ10 spatial prediction were generated using non‐autocorrelated topographic attributes estimated from both surface and subsurface topography. Model validation using a new set of 41 data points showed root mean square errors (RMSE) lower than 10% of the θ10 range. The model based on subsurface topography decreased RMSE by 43%. Prediction errors were not spatially distributed. Finally, theses results are discussed in respect of processes involved in hillslope hydrology. Copyright © 2003 John Wiley & Sons, Ltd.
Ser217Leu polymorphism of the HPC2/ELAC2 gene associated with prostatic cancer risk in Japanese men
Authors: Takahashi Hiroyuki , Lu Wei , Watanabe Masatoshi , Katoh Takahiko , Furusato Masakuni , Tsukino Hiromasa , Nakao Hiroyuki , Sudo Akemi , Suzuki Hiroyoshi , Akakura Koichiro , Ikemoto Isao , Asano Kouji , Ito Takaaki , Wakui Shin , Muto Tomoko , Hano Hiroshi
Published: August 2003

The HPC2/ELAC2 gene may be associated with hereditary/familial prostate cancer (PCa). Two common missense variants (Ser217Leu and Ala541Thr) have been reported in the gene. We performed mutational, allelotyping and expression analyses and a molecular epidemiological study to clarify the relations between this gene and prostatic diseases, including PCa and benign prostatic hyperplasia (BPH) in Japanese men. We screened for mutations in 109 patients with PCa including 11 patients from 1 hereditary and 9 familial PCa. Loss of heterozygosity and expression were analyzed. An epidemiological study was done in sporadic PCa (n=98) and BPH (n=143) using 1 novel (Ser627Leu) and 2 previously described polymorphisms of the HPC2/ELAC2 gene. Somatic or germline mutations were not confirmed in any cases of PCa. Loss of heterozygosity at 2 microsatellites, D17S1289 and D17S520, was detected in 1 of 38 and 1 of 35 cases, respectively. Expression analysis revealed decreased or absent mRNA expression in 6 of 38 tumors. Epidemiologic analysis showed that a Leu allele at codon 217 was significantly more frequent in patients with PCa than in controls (10.2% vs. 3.5%, odds ratio = 3.11; 95% confidence interval, 1.22–7.90). At codon 541, all patients with PCa or BPH and all control subjects had the Ala/Ala genotype. At codon 627, the incidence of the Leu variant was slightly, but not significantly, higher in patients with BPH than in controls (7.0% vs. 2.8%, odds ratio = 2.59, 95% confidence interval, 0.94–7.13, not statistically significant). We concluded that germline/somatic mutations of HPC2/ELAC2 are uncommon in PCa. Similarly, allelic imbalances at the gene locus and changes in expression are rare. Although no difference in allele frequency at Ser217Leu between patients with PCa and controls has been reported in a Western population, this polymorphism is a potential indicator of PCa risk in Japanese men and it should be examined in other ethnic groups. © 2003 Wiley‐Liss, Inc.
Dietary factors protective against breast cancer in Japanese premenopausal and postmenopausal women
Authors: Hirose Kaoru , Takezaki Toshiro , Hamajima Nobuyuki , Miura Shigeto , Tajima Kazuo
Published: August 2003

Since components of the Japanese diet that might be responsible for the relatively low breast cancer incidence rates observed in Japan have not been clarified in detail, a case‐referent study with reference to menopausal status was conducted using data from the hospital‐based epidemiologic research program at Aichi Cancer Center (HERPACC). In total, 2,385 breast cancer cases were included, and 19,013 women, confirmed as free of cancer, were recruited as the reference group. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were determined by multiple logistic regression analysis. There were reductions in risk associated with high intake of milk and green–yellow vegetables (green leafy vegetables, carrots and pumpkins) among both pre‐ and postmenopausal women. The protective effects of the Japanese diet were more prominent among postmenopausal than premenopausal women. The adjusted OR of fish consumption (5 or more times per week vs. fewer than 3 times per month) was 0.75 (95% CI 0.57–0.98, ptrend = 0.01) for postmenopausal breast cancer. A significant decrease in postmenopausal breast cancer risk was also observed for increasing intake of fruit (OR = 0.61, 95% CI 0.41–0.91). Thus, traditional Japanese dietary factors may protect against breast cancer development, especially among postmenopausal women. © 2003 Wiley‐Liss, Inc.
Does pizza protect against cancer?
Authors: Gallus Silvano , Bosetti Cristina , Negri Eva , Talamini Renato , Montella Maurizio , Conti Ettore , Franceschi Silvia , La Vecchia Carlo
Published: August 2003

We analyzed the potential role of pizza on cancer risk, using data from an integrated network of case‐control studies conducted in Italy between 1991 and 2000. Cancer sites were: oral cavity and pharynx (598 cases), esophagus (304 cases), larynx (460 cases), colon (1,225 cases) and rectum (728 cases). Controls were 4,999 patients admitted for acute, non‐neoplastic conditions to the same hospital network as cases. Odds ratios for regular pizza consumers were 0.66 (95% confidence interval, CI = 0.47–0.93) for oral and pharyngeal cancer, 0.41 (95% CI = 0.25–0.69) for oesophageal, 0.82 (95% CI = 0.56–1.19) for laryngeal, 0.74 (95% CI = 0.61–0.89) for colon and 0.93 (95% CI = 0.75–1.17) for rectal cancer. Pizza appears therefore to be a favorable indicator of risk for digestive tract neoplasms in this population. © 2003 Wiley‐Liss, Inc.
Risk factors for multiple oral premalignant lesions
Authors: Thomas Gigi , Hashibe Mia , Jacob Binu J. , Ramadas Kunnambathu , Mathew Babu , Sankaranarayanan Rengaswamy , Zhang Zuo‐Feng
Published: August 2003

Oral leukoplakia, oral submucous fibrosis and erythroplakia are 3 major types of oral premalignant lesions. Multiple oral premalignant lesions may possibly develop due to field cancerization, where carcinogenic exposures can cause simultaneous genetic defects to the upper aerodigestive tract epithelium, putting the epithelium at high risk for development of premalignant lesions at different stages of carcinogenesis. There have been no epidemiological studies on risk or protective factors of the disease. A case‐control study was conducted with data from the baseline screening of a randomized oral cancer screening trial in Kerala, India. A total of 115 subjects with multiple oral premalignant lesions (8–10% of oral premalignant lesions in our case series) were included: 64 subjects with oral leukoplakia and oral submucous fibrosis, 19 subjects with oral leukoplakia and erythroplakia, 22 subjects with oral submucous fibrosis and erythroplakia and 10 subjects with all 3 lesions. Individuals without oral lesions were considered controls (n=47,773). The odds ratio (OR) for ever tobacco chewers was 37.8 (95% confidence interval (CI)=16.2–88.1) when adjusted for age, sex, education, BMI, smoking, drinking and fruit/vegetable intake. Dose‐response relationships were seen for the frequency (p<0.0001) and duration of tobacco chewing (p<0.0001) with the risk of multiple oral premalignant lesions. Whereas alcohol drinking may possibly be a risk factor for multiple oral premalignant lesions, smoking was not associated with the risk of multiple oral premalignant lesions (OR=0.9, 95%CI=0.5–1.7). The results suggest that tobacco chewing was the most important risk factor for multiple oral premalignant lesions and may be a major source of field cancerization on the oral epithelium in the Indian population. © 2003 Wiley‐Liss, Inc.
Autotrophic and Heterotrophic Picoplankton in Wetlands: Differences with Lake Patterns
Authors: Rodrigo María A. , Rojo Carmen , Álvarez‐Cobelas Miguel
Published: August 2003

This study describes the occurrence, importance and seasonal patterns of picoplankton in two wetlands (TDNP and La Safor), and compares them to a system of fifteen interconnected lakes (Ruidera). In TDNP we performed a six‐year monthly study in three sites of the wetland. Bacterial abundance increased throughout time and the autotrophic picoplankton (APP) range was wide (up to 33 × 106 cells/ml). The annual averaged APP contribution to total picoplankton and phytoplankton biovolumes was 0.5–22% and 0.03–6% respectively. There were large differences among sites in terms of APP absolute and relative abundance and seasonal patterns. In La Safor, the APP relative contribution to picoplankton and phytoplankton biovolumes was 0–25% and 0–40%, respectively, while in the Ruidera lakes was 0–47% and 0–5%, respectively. In the three systems there was a significant correlation between bacterial abundance and chlorophyll a but the slopes of the linear regressions were different. No significant relationships were found of APP abundance and trophic status in the wetlands, but were noted in the lake system. There was no clear relationship of APP contribution to total phytoplankton biomass to the trophic gradient in wetlands. In the lakes, the higher contribution of APP was found in those with higher trophic levels.
Photophysiology of Surface Phytoplankton Communities in a Transect from the Mouth of the Peene‐Strom to the Arkona Sea (Baltic)
Authors: Müller Anna Maria , Wasmund Norbert
Published: August 2003

The potential of surface phytoplankton to withstand photostress was investigated in August 1998 along a transect from the mouth of the Peene‐Strom (Pomeranian Bight) to the open Arkona Sea (Baltic). Photosynthetic efficiency, algal class composition and pigment pattern were determined. Algae were photoinhibited by artificial illumination and the kinetics of recovery were recorded. Under photoinhibitory treatment, algae from the estuary showed a low effective quantum yield but a high potential to recover their maximum photosynthetic efficiency. Contrary to this, the relatively high effective quantum yield of open sea algae under photoinhibitory treatment is accompanied by a low final recovery of maximum photosynthetic efficiency. These phenomena are discussed with respect to nutrient supply, algal class composition and to different strategies of algae to react to light stress. Literature data of summer primary productivity of open sea and coastal algae are compared with our data on electron transport rates. This revealed a low influence of photoinhibitory effects on productivity.
Chemical and Microbial Composition of Sediments in Reservoirs with Different Trophic State
Authors: Maassen Sebastian , Röske Isolde , Uhlmann Dietrich
Published: August 2003

For the assessment of the metabolic potential of a sediment, the upper 5 cm layer should preferentially be regarded, since this is the horizon with the highest biochemical activity in the entire reservoir. Sediment cores from four different reservoirs were examined. These represent a broad range of trophic conditions (Neunzehnhain – oligotrophic; Muldenberg – oligotrophic, acidic, dystrophic; Saidenbach – mesotrophic; Quitzdorf – highly eutrophic). The vertical concentration gradients in the interstitial water of the examined sediments showed the tendencies characteristic of the trophic state of the reservoirs. The gradients increased with the trophic state, which affected the release of dissolved substances. The internal P load was substantial in all cases, in Quitzdorf it even exceeded the external P load. The total cell numbers of the bacteria in the sediment were only slightly influenced by the trophic state, all being in the same order of magnitude. The reservoir Quitzdorf displayed very high P release rates from the sediment and mass growths of Microcystis with a high content of intracellular polyphosphate granules in the summer months.
Quantifying Burial, the Transport of Matter from the Lake Biosphere to the Geosphere
Authors: Håkanson Lars
Published: August 2003

Burial is one of the most fundamental processes in contexts of massbalance calculations for substances (such as nutrients, organics, metals and radionuclides) in lakes. Substances can leave a lake by two processes, outflow, i.e., the transport to a downstream system, and burial, i.e., the transport by sedimentation from the lake biosphere to the geosphere. This work gives for the first time, to there best of the author's knowledge, a review on the factors and processes regulating burial and presents a general model for burial. This approach accounts for bottom dynamic conditions (i.e., where areas of fine sediment erosion, transport and accumulation prevail), sedimentation, bioturbation, mineralisation, and the depth and age of the bioactive sediment layer. This approach has been critically tested with very good results for radiocesium, radiostrontium, many metals, calcium from liming and phosphorus, but it has not been presented before in a comprehensive way. This model for burial is meant to be used in massbalance models based on ordinary differential equations (i.e., box models) in contexts where burial is not a target y‐variable but a necessary model variable (an x‐variable). This means that there are also specific demands on this approach, e.g., it must be based on readily accessible driving variables so that it is not too difficult to use the model in practice within the context of an overall lake model. The factors influencing burial, e.g., the deposition of materials and the depth of the bioactive sediment layer, are also needed in calculations of sediment concentrations and to determine amounts of substances or pollutants in sediments. To carry out such calculations, one also needs information on sediment bulk density, water content and organic content. This paper also presents new empirical models for such calculations to be used in the new model for burial.
Predictive Length–Dry Mass Regressions for Freshwater Invertebrates in a Pre‐Alpine Lake Littoral
Authors: Baumgärtner Daniel , Rothhaupt Karl‐Otto
Published: August 2003

To date, no regressions for invertebrates from lentic environments are available to facilitate biomass estimation. Predictive length–dry mass regressions for 20 freshwater invertebrate taxa from a pre‐alpine lake littoral in Central Europe are presented here. Regressions were calculated by fitting a power function to body‐length parameters. For Gammarus roeseli, the head height, an easily measurable length parameter, was used. Differences between regressions of different taxa were confirmed by analyses of covariance. Equations for invertebrates grouped at a higher taxonomic level had lower coefficients of determination; therefore, the use of regression equations at the lowest possible taxonomic level is indicated. A comparison of regressions with those published for related taxa in streams revealed significant differences, supporting the opinion that equations should be applied carefully and their use restricted to waterbodies with similar abiotic conditions.
The Role of Fish Communities in Water Quality Management of a Large Shallow Lake
Authors: Tátrai István , Paulovits Gábor , Mátyás Kálmán , Korponai János
Published: August 2003

Management measures of Lake Balaton such as wetland reconstruction at the main inflow to the lake along with the “unplanned” commercial fishery led to great changes in the density and biomass of fish populations. There was no significant difference in CPUE data between the two, eastern and western, basins. Biomass of total fish stock in Lake Balaton has decreased substantially, 2–3 times between 1991–1999, and ranges between 120–194 kg ha−1. Bottom‐up effects are more important than the top‐down effects due to the impact of internal nutrient load. Changes in the biomass and thus the activity of omnivorous fish in the lake lowered the intensity of various indirect effects and feedback mechanisms causing changes in the nutrient metabolism of the lake. Intensified fishery effort in Lake Balaton did not result in an increased stock of piscivores. The ratio of piscivores and omnivores remained at 5% during the whole study period. Despite this low piscivores to omnivores ratio, the water quality has improved in all basins.
The Physical and Chemical Limnology of 24 Ponds and One Lake from Isachsen, Ellef Ringnes Island, Canadian High Arctic
Authors: Antoniades Dermot , Douglas Marianne S. V. , Smol John P.
Published: August 2003

The limnology of freshwaters surrounding Isachsen, Ellef Ringnes Island, Nunavut was examined to determine the baseline physical and chemical limnological conditions present in the region. Sites were found to be circumneutral to slightly acidic, and were oligotrophic. Concentrations of most measured chemical variables were highly variable, with broad ranges that greatly exceeded those found in previous surveys conducted in the High Arctic. Ratios of nitrogen to phosphorus suggest that nitrogen may be the limiting nutrient for algal growth at the majority of sites. Principal Components Analysis (PCA) indicated that the major controls on water chemistry variability between sites were conductivity and related variables, and nutrients, explaining 36.5% and 26.5% of the variation in the dataset, respec‐tively.
A Quantitative Food Web Model for the Macroinvertebrate Community of a Northern German Lowland Stream
Authors: Poepperl Rainer
Published: August 2003

Trophic interactions and cycling of organic carbon within the macroinvertebrate community of a Northern German lowland stream were analyzed based on a compartment model. The network model describes the structure of the food web quantifying biomass, production, and consumption of their elements, of the entire system and between trophic levels. System primary production is 153.7 g C m−2 yr−1 and invertebrate production 53.3 g C m−2 yr−1. Invertebrate consumption amounts to 702.6 g C m−2 yr−1. Main flows are identified between trophic level 1 and 2 and are connected with highly productive compartments. ‘Anodonta and Pseudanodonta’ and Dreissena polymorpha show the highest consumption of all groups with 269.9 g C m−2 yr−1 and 114.1 g C m−2 yr−1, respectively. System consumption is highest on the import from the upstream lake with 532.5 g C m−2 yr−1, sediment detritus with 135.5 g C m−2 yr−1, and primary producers with 25.7 g C m−2 yr−1. The lowest predation pressure is observed for Bivalvia with an ecotrophic efficiency of <10% and highest for Chironomidae with 91%. Approximately 20% of organic matter entering the detritus pool are recycled to the living groups of the system. Transfer efficiencies between discrete trophic levels are generally low except for transfer of detrital material between level I and II.
Evolutionary transformations of fetal membranes and reproductive strategies
Authors: Mess Andrea , Blackburn Daniel G. , Zeller Ulrich
Published: August 2003

Fetal membranes (such as the chorioallantois and yolk sac) are essential to embryonic development, and have contributed importantly to the evolutionary and ecological diversity of vertebrates. Since the mid ‐ 19th century, many scientific careers have been devoted to investigations of their structure, function, and development. However, significant gaps remain in our understanding of the diversity and evolution of fetal membranes. This symposium volume focuses on the use of cladistic principles and phylogenetic relationships to reconstruct the evolutionary morphology of fetal membranes. The main goal of the present paper is to introduce the application of such methods to the evolution of vertebrate fetal membranes, as well as to provide the reader with background information on relevant concepts and terminology. Contributions within this journal issue draw upon studies of metatherian and eutherian mammals, as well as sauropsid reptiles (notably squamates). Particular attention is given to historical transformations of fetal membranes associated with the evolution of such phenomena as placentation and matrotrophy, and reproductive strategies such as viviparity. What emerges from the contributed papers is a broad sampling of contemporary research on fetal membranes, and an overview of how these membranes have evolved to support embryonic life in diverse terrestrial and intra‐uterine environments. J. Exp. Zool. 299A:3–12 2003. © 2003 Wiley‐Liss, Inc.
Evolutionary transformations of the fetal membranes of viviparous reptiles: A case study of two lineages
Authors: Stewart James R. , Thompson Michael B.
Published: August 2003

The reptilian placenta is a composite structure formed by a functional interaction between extraembryonic membranes and the maternal uterus. Study of placental structure of squamate reptiles over the past century has established that each of the multiple independent origins of placentation, which characterize the reproductive diversity of squamates, has resulted from the evolutionary transformation of these homologous structures. Because each evolutionary transformation is an independent novel relationship between maternal and embryonic tissues, the resulting placentae are not homologous, even though the individual components may be. The evolution of reptilian placentation should reveal much about evolutionary patterns and mechanisms because similar structural—functional systems have been transformed along parallel trajectories on multiple occasions. We compared extraembryonic membrane and placental development and pattern of embryonic nutrition in thamnophiine snakes and Pseudemoia lizards in the context of recent hypotheses of phylogenetic relationships. Two primary types of placentation, chorioallantoic and yolk sac, evolved in each lineage. Smooth, highly vascular regions of chorioallantoic placentation are indistinguishable homoplasies that evolved in parallel, likely to facilitate respiratory exchange. The yolk sac placenta of each lineage is specialized for histotrophic nutrient transfer, yet composition of these structures differs because of variation in the ancestral snakes and lizards. In addition, the omphalopleure that contributes to yolk sac placentation persists to later embryonic stages compared to oviparous outgroups, but the two lineages have evolved different structures that prevent replacement of the omphalopleure by the allantois. Each lineage has also evolved unique structural specializations of the chorioallantoic placenta. J. Exp. Zool. 299A:13–32, 2003. © 2003 Wiley‐Liss, Inc.
Evolution of placental specializations in viviparous African and South American lizards
Authors: Flemming Alexander F. , Blackburn Daniel G.
Published: August 2003

Phylogenetic information offers an important resource in analyses of reproductive diversity, including interpretations of fetal membrane evolution. In this paper, we draw upon ongoing studies of South American and African lizards to consider the value of combining phylogenetic and reproductive evidence in the construction of evolutionary interpretations. South American lizards of the genusMabuyaexhibit several reproductive specializations that are convergent on those of eutherian mammals, including viviparity, long gestation periods, ovulation of tiny eggs, and placental supply of the nutrients for development. Studies of placental morphology and development indicate that New WorldMabuyashare several other derived features, including chorionic areolae and a “Type IV” epitheliochorial placenta with a villous, mesometrial placentome. Some characteristics of these lizards are shared by two African skinks,M. ivensiiandEumecia anchietae, including minuscule eggs, placentotrophy, an absorptive chorioallantois, and features of the yolk sac. Available evidence is consistent with two explanations: (1) placentotrophy originated in Africa, predating a trans‐Atlantic colonization byMabuyaof the New World; and (2) placentotrophy arose two or three separate times among these closely related skinks. As illustrated by analysis of these animals, not only can data on fetal membrane morphology yield phylogenetic information, but phylogenetic evidence in turn provides a valuable way to reconstruct the evolution of fetal membranes in a biogeographic context. When appropriately interpreted, morphological and phylogenetic evidence can be combined to yield robust evolutionary conclusions that avoid the pitfalls of circular reasoning.J. Exp. Zool. 299A:33–47, 2003.© 2003 Wiley‐Liss, Inc.
Histology of the extraembryonic membranes of an oviparous snake: Towards a reconstruction of basal squamate patterns
Authors: Blackburn Daniel G. , Johnson Amy R. , Petzold Jennifer L.
Published: August 2003

An understanding of the evolutionary morphology of extraembryonic membranes in reptiles requires information about oviparous as well as viviparous species. We are studying histology and ultrastructure of the extraembryonic membranes of snakes to clarify the evolutionary history of reptilian fetal membranes, including determination of basal (ancestral) ophidian and squamate patterns. Microscopic anatomy of the membranes of oviparous corn snakes (Elaphe guttata) was examined using light and electron microscopy. At mid – development the inner surface of the eggshell is lined by two extraembryonic membranes, the chorioallantois and the omphalallantoic membrane. The chorioallantois consists of a bilayered cuboidal epithelium that overlies the allantoic blood vessels. During development, allantoic capillaries become more abundant, and the chorionic epithelium thins, decreasing the diffusion distance for respiratory gas exchange. The abembryonic pole of the egg is delimited by a bilaminar omphalopleure and isolated yolk mass, the latter of which is lined on its inner face by the allantois. The isolated yolk mass regresses developmentally, and patches of yolk droplets become isolated and surrounded by allantoic blood vessels. By late development, the abembryonic hemisphere has been fully vascularized by allantoic vessels, forming a “secondary chorioallantois.” With regard to its extraembryonic membranes, Elaphe gutatta is similar to viviparous snakes. However, this species exhibits features that have not previously been reported among squamates, perhaps reflecting its oviparous reproductive habits. Morphological evidence for the uptake of eggshell material by epithelia of the chorion and omphalopleure suggests that the potential for absorption by extraembryonic membranes predates the origin of viviparity. J. Exp. Zool. 299A:48–58 2003. © 2003 Wiley‐Liss, Inc.
The marsupial placenta: A phylogenetic analysis
Authors: Freyer Claudia , Zeller Ulrich , Renfree Marilyn B.
Published: August 2003

The structure, physiology, and endocrinology of the yolk sac placenta of different marsupial groups is compared and phylogenetically analyzed to provide information on placental characters in the marsupial stem species. We conclude that the marsupial stem species possessed a functional yolk sac placenta. Histotrophic nutrition by uterine secretion decreased during late pregnancy and at least half of the yolk sac was vascularized at the time of shell coat rupture. Due to yolk sac fusion, the larger part of the avascular, bilaminar yolk sac could not serve as a placenta at late gestation in the polyovular marsupial stem species. The bilaminar yolk sac gained a relatively greater importance for nutrition in monovular australidelphians. In macropodids a greater proportion of the yolk sac remained bilaminar at the time of shell coat rupture than in the stem species. Another derived feature of macropodids is the sustained plasma progesterone synthesis that is in turn responsible for an extended secretory phase of the uterus and a lengthened gestation. The placenta of the marsupial stem species was probably capable of metabolising histo‐ and hemotrophes. Recognition of pregnancy during early stages of development is a derived character of macropodids that we suggest did not occur in the marsupial stem species. However, birth and birth behaviour were apparently induced by prostaglandins in the marsupial stem species. Although the yolk sac formed the definitive placenta, it is likely that the allantois provided a supplementary placental function in the marsupial stem species, but that the role of the allantois became progressively less important during the evolution of marsupial placentation. J. Exp. Zool. 299A:59–77 2003. © 2003 Wiley‐Liss, Inc.
Evolutionary transformations of chorioallantoic placental characters in rodentia with special reference to hystricognath species
Authors: Mess Andrea
Published: August 2003

The aim of this paper is to reconstruct the evolution of chorioallantoic placental characters in Rodentia. The analysis is based on pre‐existing hypotheses of rodent relationships and the tracing of character evolution. Data on 64 rodent species of 49 genera are derived from the literature. New results refer to the hystricognath species Petromus typicus A. Smith, 1831 and Octodon degus (Molina, 1782). This comprehensive analysis confirms that the stem species pattern of Rodentia is characterised by a haemochorial placenta which is divided horizontally. Inside the placental labyrinth, fetal vessels and their trophoblastic external border build up a network through which the maternal blood flows. The trophoblastic tissue is one‐layered, syncytial and possess a considerable surface extension. Within Rodentia, evolutionary transformations occurred on the macroscopic as well as the fine structural level. The results suggest that the stem species of Hystricognathi underwent transformations only on the macroscopic level, i.e., forming a ring‐shaped arrangement of placental regions with centrally situated maternal arteries and the acquisition of a subplacenta. By contrast, in Muridae the chorioallantoic placenta shows derived features only in regard to the fine structure of the labyrinth, i.e. the interhaemal membrane is modified in composition, and the fetal capillary endothelium is fenestrated. Geomyoidea underwent transformations on both levels. Macroscopically, their placenta is modified into a hillock shape. Microscopically, the interhaemal membrane is formed by the cytotrophoblast. In addition to the mentioned transformations, some aspects of other fetal membrane differentiation in Rodentia are briefly discussed. J. Exp. Zool. 299A:78–98, 2003. © 2003 Wiley‐Liss, Inc.
Development and evolution of the amniote integument: Current landscape and future horizon
Authors: Chuong Cheng‐Ming , Homberger Dominique G.
Published: August 2003

This special issue on the development and evolution of the amniote integument begins with a discussion of the adaptations to terrestrial conditions, the acquisition of water‐impermeability of the reptilian integument, and the initial formation of filamentous integumentary appendages that prepare the way towards avian flight. Recent feather fossils are reviewed, and a definition of feathers is developed. Hierarchical models are proposed for the formation of complex structures, such as feathers. Molecular signals that alter the phenotype of integumentary appendages at different levels of the hierarchy are presented. Tissue interactions and the roles of keratins in evolution are discussed and linked to their bio‐mechanical properties. The role of mechanical forces on patterning is explored. Elaborate extant feather variants are introduced. The regeneration/gene mis‐expression protocol for the chicken feather is established as a testable model for the study of biological structures. The adaptations of the mammalian distal limb end organs to terrestrial, arboreal and aquatic conditions are discussed. The development and cycling of hair are reviewed from a molecular perspective. These contributions reveal that the structure and function of diverse integumentary appendages are variations that are superimposed on a common theme, and that their formation is modular, hierarchical and cyclical. They further reveal that these mechanisms can be understood at the molecular level, and that an integrative and organismal approach to studying integumentary appendages is called for. We propose that future research should foster interdisciplinary approaches, pursue understanding at the cellular and molecular level, analyze interactions between the environment and genome, and recognize the contributions of variation in morphogenesis and evolution. J. Exp. Zool. (Mol. Dev. Evol.) 298B:1–11, 2003. © 2003 Wiley‐Liss, Inc.