What to expect from MRI in the investigation of the central nervous system?

Functional magnetic resonance imaging (fMRI) has appeared as a new tool that is very powerful for cognitive neuroscience, offering the potential to look at the dynamics of cerebral processes underlying cognition, non-invasively and on an individual basis. Work remains to be done to optimize the technique and to better understand its basic mechanisms, but one may expect to build in a foreseeable future a functional list of the main brain cortical networks implicated in sensory-motor or cognitive processes. Still, the real understanding of brain function requires direct access to the functional unit consisting of the neuron, so that one may look at the transient temporal relationships that exist between largely distributed groups of hundreds or thousands of neurons. Furthermore, communication pathways between networks, which are carried by brain white matter, must be identified to establish connectivity maps at the individual scale, taking into account individual variability resulting from genetic factors and cerebral plasticity. In this respect, MRI of molecular diffusion is very sensitive to water molecular motion and, thus, to tissue dynamic microstructure, such as cell size and geometry. Preliminary data suggest that diffusion MRI visualizes dynamic tissue changes associated with large neuronal activation and space orientation of large bundles of myelinated axons in the white matter.     

Brief communication: Is variation in the cranial capacity of the Dmanisi sample too high to be from a single species?

This study uses data resampling to test the null hypothesis that the degree of variation in the cranial capacity of the Dmanisi hominid sample is within the range variation of a single species. The statistical significance of the variation in the Dmanisi sample is examined using simulated distributions based on comparative samples of modern humans, chimpanzees, and gorillas. Results show that it is unlikely to find the maximum difference observed in the Dmanisi sample in distributions of female-female pairs from comparative single-species samples. Given that two sexes are represented, the difference in the Dmanisi sample is not enough to reject the null hypothesis of a single species. Results of this study suggest no compelling reason to invoke multiple taxa to explain variation in the cranial capacity of the Dmanisi hominids.     

Palm distribution patterns in Amazonian rainforests: What is the role of topographic variation?

Question: Are soil properties and topographic variation related with palm (Arecaceae) species composition and distribution patterns? If so, are species distribution patterns consistent across sites? Location: 100–200 m a.s.l, non‐inundated Amazonian rainforest, NE Peru. Methods: One 0.65‐ha line transect divided into 5 m by 5 m subunits was inventoried for all palm individuals at each site. Soil samples were collected, and topography was measured. Results: A total of 56 palm taxa were recorded. Floristic similarity among transects clearly corresponded with similarity in soil cation content when species abundances were taken into account, but less so when only presence‐absence data were used. Taxon‐wise distribution analyses were done for the 37 most abundant palm taxa. Quite a few of these taxa proved not to be randomly distributed along the transects, but instead were clearly more abundant in some topographic positions than in others. However, the consistency of the distribution patterns across study sites proved to be rather low, and many of the palm taxa showed different distribution patterns at different sites. Conclusions: The ambiguity in distribution patterns across study sites may partly be due to the complexity of topography as a measure of ecological conditions, and the probability that it is related to the variation in different environmental variables at different sites.     

Therapeutic effects of metformin in breast cancer: involvement of the immune system?

Breast cancer and associated diabetes mellitus have gained raising interest as an elevated risk of breast cancer prognosis resulting in increased mortality in diabetic patients. In this context, the long-acting insulin analog glargine and other antidiabetics have been discussed to promote tumorigenesis. In contrast, the biguanide class oral antidiabetic metformin has been shown capable of enhancing cell cycle arrest and inducing apoptosis as well as reducing growth factor signaling. Consequently, several studies are underway to evaluate a possible role of metformin in breast cancer treatment. Although mechanisms involved are not definitely clear yet, here, we discuss metformin’s anticancer effects including the potential impact of the immune system.     

Consequences of reduced nutrient loading on a lake system in a lowland catchment: deviations from the norm?

1. Lake restoration from eutrophication often rests on a simple paradigm that restriction of phosphorus sources will result in recovery of former relatively clear‐water states. This view has apparently arisen from early successful restorations of deep lakes in catchments of poorly weathered rocks. Lakes in the lowlands, however, particularly shallow ones, have proved less tractable to restoration. This study of three lowland lakes provides insights that illuminate a more complex picture. 2. The lakes lie in a sequence along a single stream in a mixed urban and rural landscape. Severely deoxygenating effluent from an overloaded sewage treatment works was diverted from the catchment in 1991. Effects on two lakes, Little Mere (z_max <2 m) and Rostherne Mere (z_max 31 m) were followed until 2002. Mere Mere (z_max = 8 m), upstream of the former works, acted as a comparison for changes in water chemistry. Mere Mere showed no change in total phosphorus (TP), total inorganic nitrogen, or planktonic chlorophyll a concentrations. Increased winter rainfall was associated with higher winter soluble reactive phosphorus (SRP) and ammonium concentrations in its water. 3. Little Mere changed from a deoxygenated, highly enriched, fishless system, with large populations of Daphnia magna Straus, clear water and about 40% aquatic plant cover, to a slightly less clear system following diversion. Daphnia magna was replaced by D. hyalina Leydig as fish recolonised. Spring peaks of chlorophyll a declined but summer concentrations increased significantly. Annual mean chlorophyll a concentrations thus showed no change. Submerged plants became more abundant (up to 100% cover), with fluctuating community composition from year to year. Summer release of SRP from the sediment was substantial and has not decreased since 1993. The summer phytoplankton was apparently controlled by nitrogen availability perhaps with some influence of zooplankton grazing. SRP was always very abundant. The lake appeared to have reached a quasi‐stable state by 2002. 5. Rostherne Mere showed a steady decline in TP and SRP concentrations following effluent diversion apparently as a result of steady dilution by water with lower phosphorus concentration. Decline in phosphorus concentrations was much less rapid than expected because of internal remobilisation from the hypolimnion and sediments. There have been no changes in chlorophyll a concentration or of nitrogen availability and by 2002 the phytoplankton probably remained limited by a combination of mixing, grazing and nitrogen. 6. A seeming paradox is, thus, that immense changes in phosphorus budgets have shown no consequences for phytoplankton chlorophyll concentrations in either of the lakes, although the seasonal distribution has altered in Little Mere. Although these case studies deviate from others, for both shallow and deep lakes, they represent distinctive situations rather than undermining conventional models.     

Activation of command fibres to the stomatogastric ganglion by input from a gastric mill proprioceptor in the crab,Cancer pagurus †

In semi‐intact preparations of the crab Cancer pagurus the normal output from the stomatogastric ganglion (StG) was a regular pyloric cycle (Figure 4). Repeated stimulation of the posterior stomach nerve (psn) of the posterior gastric mill proprioceptor (PSR) often induced series of spontaneous gastric cycles. We were therefore able to describe the normal gastric cycle as recorded in the output nerves from StG and to identify most of the relevant motor neurones by reference to the muscles that they innervate (Figure 10). The gastric cycle output was variable (Figures 5, 6), although in many preparations one complex type of output predominated (Figure 7). The basic feature of the gastric cycle was an alternation of activity between the single cardio‐pyloric neurone (CP) and a complex variable burst in the lateral cardiac (LC), the gastro‐pyloric (GP), the gastric (GM), and other associated neurones. During this normally occurring complex gastric burst significant changes occurred in the pyloric cycle, notably an increase in activity of the pacemaker pyloric dilator (PD) group and an inhibition of the lateral pyloric (LP), inferior cardiac (IC) and ventricular dilator (VD) neurones (Figures 6, 7, 8, 9). These changes are probably associated with an opening of the cardio‐pyloric valve and food passage into the pyloric filter. The gastric output was related to the normally observed movements of the dorsal ossicles of the gastric mill and thus to the operation of the teeth of the mill (Figure 11). Increased input from the PSR is associated with the grinding action of the teeth which is caused by the complex gastric burst (Figure 12).

Stimulation of the psn during an ongoing regular pyloric output caused changes in the cycle which mimicked those occurring during the spontaneous gastric cycle (Figure 13; Table 1). Stimulation of the psn during ongoing gastric activity also affected the gastric units (Figure 14). The input pathway from the PSR is shown to be through the stomatogastric nerve (sgn), the connection between the commissural ganglia and the stomatogastric ganglion (Figure 15). The commissural ganglia are known to receive most of the sensory input from the foregut and PSR input is probably processed there. Recordings from the sgn show that psn stimulation activates a small number of centrally originating units, and that the activity of these units coincides with the pyloric output changes (Figures 15, 16). We therefore label the units command interneurones. Their effects could be mediated by direct connections to only the PD pacemaker neurones of the pyloric cycle. Control experiments showed that PSR input is not necessary for the pyloric output changes to occur during gastric output but that similar output changes can be evoked by input resulting from induced gastric movements (Figure 15(E)). We think that the pyloric cycle output changes are normally controlled by a number of mechanisms at different levels (Figure 17). We cannot easily explain the effects of PSR input on the gastric cycle neurones.

These findings are important because they allow us to study a specific input to the StG without disrupting its normal input‐output pathways to the central nervous system. Further experiments on the system designed to test the assumption that the sgn units are in fact responsible for the pyloric output changes, and to investigate the processing of the PSR input are outlined.     

Hypothesis: could the signalling function of membrane microdomains involve a localized transition of lipids from liquid to solid state?

Background  

Over the past decade, it has become apparent that specialised membrane microdomains, commonly called rafts, where lipids like sphingolipids and cholesterol are arranged compactly in a liquid ordered phase are involved in cell signalling.     

Can environmental variation generate positive indirect effects in a model of shared predation?

Classic models of apparent competition predict negative indirect effects between prey with a shared enemy. If predator per capita growth rates are nonlinear, then endogenously generated periodic cycles are predicted to generate less negative or even positive indirect effects between prey. Here I determine how exogenous mechanisms such as environmental variation could modify indirect effects. I find that exogenous variation can have a broader range of effects on indirect interactions than endogenously generated cycles. Indirect effects are altered by environmental variation even in simple models for which the per capita growth rate of the predator species is a linear function of population densities. Temporal variation that affects the predator attack rate or the conversion efficiency can lead to large increases or decreases in the indirect effects between prey, dependent on how prey populations co-vary with the environmental variation. Positive indirect effects can occur when the period of environmental variation is close to the natural period of the biological system and shifts in subharmonic resonance occur with the addition of the second prey. Models that include nonlinear numerical responses generally lead to indirect effects that are sensitive to environmental variation in more parameters and across a wider range of frequencies.     

Dynamic social system in Nubian ibex: can a second mating season develop in response to arid climate?

We studied a population of Nubian ibex Capra ibex nubiana in the eastern extreme of its range, the hyper-arid central desert of the Sultanate of Oman. Long-term data were collected from January 1983 to December 1997 by direct observation, as well as VHF telemetry on 12 animals (eight from 1987 to 1990; four from 1994 to 1996). We recorded 884 sightings: 40.4% of single animals and 59.6% of groups. Although no significant monthly variation of group size (Jarman's Typical Group Size) was found, there were distinct peaks in March (4.0 ind. group⁻¹) and September (5.1 ind. group⁻¹). Groups of males and females formed especially in March and November, and female–kid groups in February and July–August. Our data may suggest two mating periods: the first one in autumn (similar to the rut of ibex in temperate mountain areas), with kids born in spring/early summer, after winter–spring rainfall, and the second one in spring, with kids born in late summer/autumn, before winter–spring rainfalls. We suggest that the second rutting period may have evolved as a micro-evolutionary process, with the local population adapting to hyper-arid environment constraints. The spring mating season may favour only females in prime conditions, who can afford a pregnancy in the local severe summers and will deliver kids when plant greening begins, in the autumn, whereas the autumn (original) mating season may be afforded by any female, but kids will be born in an unfavourable period, before the summer drought.     

Time-dependent regimes of a tourism-based social–ecological system: Period-doubling route to chaos

The period-doubling route to chaos has occupied a prominent position and it is still object of great interest among the different complex phenomena observed in nonlinear dynamical systems. The reason of such interest is that such route to chaos has been observed in many physical, chemical and ecological models when they change over from simple periodic to complex aperiodic motion. In interlinked social–ecological systems (SESs) there might be an apparent great ability to cope with change and adapt if analysed only in their social dimension. However, such an adaptation may be at the expense of changes in the capacity of ecosystems to sustain the adaptation and it could affect the quality of ecosystem goods and services since it could degrade natural renewable and non-renewable resources and generate traps and breakpoints in the whole SES eventually leading to chaotic behaviour. This paper is rooted in previous results on modelling tourism-based SESs, only recently object of theoretical investigations, focusing on the dynamics of the coexistence between mass-tourists and eco-tourists. Here we describe a finer scale analysis of time-dependent regimes in the ranges of the degradation coefficient (bifurcation parameter), for which the system can exhibit coexistence. This bifurcation parameter is determined by objective changes in the real world in the quality of ecosystem goods and services together with whether and how such changes are perceived by different tourist typologies. Varying the bifurcation parameter, the dynamical system may in fact evolve toward an aperiodical dynamical state in many ways, showing that there could be different scenarios for the transition to chaos. This paper provides a further evidence for the period-doubling route to chaos with reference to tourism-based socio-ecological models, and for a period locking behaviour, where a small variation in the bifurcation parameter can lead to alternating regular and chaotic dynamics. Moreover, for many models undergoing chaos via period-doubling, it has been showed that structural perturbations with real ecological justification, may break and reverse the expected period-doublings, hence inhibiting chaos. This feature may be of a certain relevance also in the context of adaptive management of tourism-based SESs: these period-doubling reversals might in fact be used to control chaos, since they potentially act in way to suppress possibly dangerous fluctuations.     

A willow drawing from 1786: the earliest depiction of intraspecific trait variation in plants?

Background and AimsThe study of intraspecific trait variation (ITV) in plants has a long history, dating back to the fourth century BC. Its existence was widely acknowledged by the end of the 18th century, although systematic and experimental studies commenced only a century later. However, the historiography of ITV has many gaps, especially with regard to early observations and visual documents. This note identifies an early depiction of plant ITV.MethodsThe botanical works of Johann Wolfgang von Goethe (1749–1832), a German writer and naturalist, were subjected to close reading. This included all publications and unpublished sources related to botany between 1785 and 1832 (e.g. notes, drafts, diaries, letters, drawings). This material is accessible in the multi-volume historical-critical edition of Goethe’s studies in natural science (Leopoldina-Ausgabe).Key ResultsA diary entry from 9 September 1786 described changes in leaf morphology along an elevation gradient in the Bavarian Alps. The leaves of an unidentified species of willow (Spix sp.) and gentian (Gentiana sp.) were said to become narrower with increasing elevation; leaves also stood further apart on twigs, and the latter became thinner. A crude drawing of two willow twigs illustrated the differences. Goethe conjectured that the differences were due to environmental conditions.ConclusionsGoethe’s notes were anecdotal, and it is unclear whether the observed plant individuals actually belonged to the same species. Nevertheless, the notes represent an early and clear articulation of the hypothesis that changes in environmental conditions can cause ITV in a natural plant population. The drawing may be the earliest visual record of environmentally caused plant ITV in the wild.