Do neurons in the vertebrate CNS migrate on laminin?

In adult rat brain the extracellular matrix glycoprotein, laminin, is found only in basement membranes, but is transiently expressed by astrocytes after brain injury. Here, I show that laminin also appears in immature brain cells during CNS development, and that its presence coincides with phases of neuronal migration. In early embryos, laminin is seen throughout the whole thickness of the forming brain, and is apparently synthesized by the cells, as judged by its intracytoplasmic localization. As development proceeds, intracellular laminin becomes restricted to the periventricular regions while punctate deposits of laminin follow the course of vimentin-positive radial glial fibers. In most brain regions, the adult pattern of laminin expression is achieved by birth. In the post-natal rat cerebellum, however, laminin is detected in external granule cells, in Purkinje cells, and in punctate deposits along the radial Bergmann glial fibers. By day 24 after birth, when the migration of external granule cells is complete, all laminin immunoreactivity disappears from these structures. The transient expression of laminin in regions where neurons are migrating raises the possibility that laminin plays a role in neuronal migration during CNS development.     

The road to ERK activation: Do neurons take alternate routes?

The ERK cascade is a central signaling pathway that regulates a wide variety of cellular processes including proliferation, differentiation, learning and memory, development, and synaptic plasticity. A wide range of inputs travel from the membrane through different signaling pathway routes to reach activation of one set of output kinases, ERK1&2. The classical ERK activation pathway beings with growth factor activation of receptor tyrosine kinases. Numerous G-protein coupled receptors and ionotropic receptors also lead to ERK through increases in the second messengers calcium and cAMP. Though both types of pathways are present in diverse cell types, a key difference is that most stimuli to neurons, e.g. synaptic inputs, are transient, on the order of milliseconds to seconds, whereas many stimuli acting on non-neural tissue, e.g. growth factors, are longer duration. The ability to consolidate these inputs to regulate the activation of ERK in response to diverse signals raises the question of which factors influence the difference in ERK activation pathways. This review presents both experimental studies and computational models aimed at understanding the control of ERK activation and whether there are fundamental differences between neurons and other cells. Our main conclusion is that differences between cell types are quite subtle, often related to differences in expression pattern and quantity of some molecules such as Raf isoforms. In addition, the spatial location of ERK is critical, with regulation by scaffolding proteins producing differences due to colocalization of upstream molecules that may differ between neurons and other cells.     

Do arthropod assemblages display globally consistent responses to intensified agricultural land use and management?

Aim To determine whether arthropod richness and abundance for combined taxa, feeding guilds and broad taxonomic groups respond in a globally consistent manner to a range of agricultural land‐use and management intensification scenarios. Location Mixed land‐use agricultural landscapes, globally. Methods We performed a series of meta‐analyses using arthropod richness and abundance data derived from the published literature. Richness and abundance were compared among land uses that commonly occur in agricultural landscapes and that represent a gradient of increasing intensification. These included land‐use comparisons, such as wooded native vegetation compared with improved pasture, and a management comparison, reduced‐input cropping compared with conventional cropping. Data were analysed using three different meta‐analytical techniques, including a simple vote counting method and a formal fixed‐effects/random‐effects meta‐analysis. Results Arthropod richness was significantly higher in areas of less intensive land use. The decline in arthropod richness was greater between native vegetation and agricultural land uses than among different agricultural land uses. These patterns were evident for all taxa combined, predators and decomposers, but not herbivorous taxa. Overall, arthropod abundance was greater in native vegetation than in agricultural lands and under reduced‐input cropping compared with conventional cropping. Again, this trend was largely mirrored by predators and decomposers, but not herbivores. Main conclusions The greater arthropod richness found in native vegetation relative to agricultural land types indicates that in production landscapes still containing considerable native vegetation, retention of that vegetation may well be the most effective method of conserving arthropod biodiversity. Conversely, in highly intensified agricultural landscapes with little remaining native vegetation, the employment of reduced‐input crop management and the provision of relatively low‐intensity agricultural land uses, such as pasture, may prove effective in maintaining arthropod diversity, and potentially in promoting functionally important groups such as predators and decomposers.     

Do neurons have a voltage or a current threshold for action potential initiation?

The majority of neural network models consider the output of single neurons to be a continuous, positive, and saturating firing ratef(t), while a minority treat neuronal output as a series of delta pulses (t — t _i ). We here argue that the issue of the proper output representation relates to the biophysics of the cells in question and, in particular, to whether initiation of somatic action potentials occurs when a certain thresholdvoltage or a thresholdcurrent is exceeded. We approach this issue using numerical simulations of the electrical behavior of a layer 5 pyramidal cell from cat visual cortex. The dendritic tree is passive while the cell body includes eight voltage- and calcium-dependent membrane conductances.We compute both the steady-state (I ^static (V _m )) and the instantaneous (I _o (V_m)) I–V relationships and argue that the amplitude of the local maximum inI ^static (V _m ) corresponds to the current thresholdI _th for sustained inputs, while the location of the middle zero-crossing ofI _o corresponds to a fixed voltage thresholdV _th for rapid inputs. We confirm this using numerical simulations: for rapid synaptic inputs, spikes are initiated if the somatic potential exceedsV _th, while for slowly varying inputI _th must be exceeded. Due to the presence of the large dendritic tree, no charge thresholdQ _th exists for physiological input.Introducing the temporal average of the somatic membrane potential (V _m) while the cell is spiking repetitively, allows us to define a dynamic I-V relationship ^dynamic ((V _m)). We find an exponential relationship between (V _m) and the net current sunk by the somatic membrane during spiking (diode-like behavior). The slope ofI/dynamic((V _m)) allows us to define a dynamic input conductance and a time constant that characterizes how rapidly the cell changes its output firing frequency in response to a change in its input.     

Outsourcing in the brain: Do neurons depend on cholesterol delivery by astrocytes?

Brain function depends on the cooperation between highly specialized cells. Neurons generate electrical signals and glial cells provide structural and metabolic support. Here, I propose a new kind of job-sharing between neurons and astrocytes. Recent studies on primary cultures of highly purified neurons from the rodent central nervous system (CNS) suggest that, during development, neurons reduce or even abandon cholesterol synthesis to save energy and import cholesterol from astrocytes via lipoproteins. The cholesterol shuttle may be restricted to compartments distant from the soma including synapses and may be regulated by electrical activity. Testing these hypotheses will help to improve our still insufficient understanding of brain cholesterol metabolism and its role in neurodegeneration.     

Noise improves transfer of near-threshold, phase-locked activity of the cochlear nerve: evidence for stochastic resonance?

 Stochastic resonance can be described as improved detection of weak periodic stimuli by a dynamic nonlinear system, resulting from the simultaneous presentation of a restricted dynamic range of low-intensity noise. This property has been reported in simple physical and biological activities. The present study describes data consistent with the interpretation that stochastic resonance can be observed in the response of cochlear neurons. These experiments utilized low levels (−5 to 25 dB SPL) of stimuli and noise (5 to 30 dB SPL). Stimuli consisted of simultaneously presented 8 kHz (F ₁) and 8.8 kHz (F ₂) tone bursts, which generated an 800 Hz F ₂–F ₁ cochlear nerve envelope ensemble response in the gerbil. The mean response threshold was approximately −3 dB SPL. Simultaneous presentation of a low-intensity wideband noise increased the amplitude of this response. This was observed with tonal stimuli having intensities of 0–5 dB SPL; responses to stimulus levels >10 dB were attenuated by noise. Response amplitude was increased by noise levels of 10–15 dB; the amplitude was unaffected by lower levels of noise, and decreased in the presence of higher noise levels. These properties are compatible with those of stochastic resonance. Accepted: 11 March 1999     

Do local conspecific density and floral display size influence fruit set via pollinator visitation in Orchis militaris?

Plant density varies naturally, from isolated plants to clumped individuals, and this can influence pollinator foraging behaviour and plant reproductive success. In addition, the effect of conspecific density on reproduction may depend on the pollination system, and deceptive species differ from rewarding ones in this regard, a high density being often associated with low fruit set in deceptive plants. In our study, we aimed to determine how local conspecific density and floral display size (i.e. number of flowers per plant) affect fruit set in a deceptive orchid (Orchis militaris) through changes in pollinator visitation. We measured fruit set in a natural population and recorded pollinator abundance and foraging behaviour within plots of different O. militaris densities. Detailed data were recorded for the most abundant potential pollinators of O. militaris, i.e. solitary bees. Floral display size was negatively correlated to fruit set in medium‐density plots, but uncorrelated in low‐ and high‐density plots. Plot density had no effect on solitary bee abundance and visitation, which may be due to low pollinator abundance within the study site. The proportion of visited flowers per inflorescence was negatively influenced by floral display size, which is in line with previous studies. In addition, solitary bees spent decreasing time in successive flowers within an inflorescence, and the time spent per flower was negatively affected by ambient temperature. Our results suggest that pollinator behaviour during visitation is poorly linked to pollen deposition and reproductive success in O. militaris.     

Different effects of α- and γ-glycine on the aberrant activity of pyramidal neurons of hippocampal slices

Experiments in vitro on hippocampal slices of mouse have shown that solutions prepared from polymorphic modifications α- and γ-glycine have different effect on the aberrant activity of neurons. In the presence of α-glycine the excitability of these neurons decreased more slowly, prolonging its modulating effect on NMDA type glutamate receptors. This effect agrees with higher biological activity of α-polymorphic modifications (as compared with that of the α-form) that previously observed with respect to behavior of mice from the line with genetic diathesis to catalepsy, which were used as a biological model for investigation of some pathological behavior forms.     

Do cells in a reproductive state exhibit a fermi-pasta-ulam-fröhlich resonance and emit electromagnetic radiation?

Cells in the reproductive state seem to act like small signal generators and emit radiation which is detectable by small polarizable particles nearby in a medium of suitable osmolarity, but very low conductivity. Evidence for this was seen upon using mouse sarcoma (ascites) cells, and by comparing rapidly dividing mouse "L" fibroblasts with confluent ones. Reproducing cells attracted many more highly polarizable BaTiO₃ particles than they did of the much less polarizable BaSO₄ (dielectric constants 4000 and 11, respectively).This preferential attraction of certain cells for highly polarizable small particles is interpreted as due in large measure to the action of dielectrophoresis on a very small scale.evoked by the presence of nonuniform electric fields of cellular origin acting upon the nearby neutral, polarizable particles.a process called microdielectrophoresis. Consideration of the conductive nature of the surrounding medium forces the conclusion that the cell-generated fields must be oscillatory in nature and have a frequency in the order of a megaherz. These observations recall predictions made earlier by Szent-Györgyi on cellular electronic processes, and by Fröhlich on the possibility of Bose-Einstein condensations to a single quantum state of oscillatory ferroelectric character, due to cooperative long-range interactions among dipolar features of cells. The persistence of oscillatory energy in the lower modes is reminiscent of the Fermi-Pasta-Ulam problem.     

Do female broiler breeder fowl display a preference for broiler breeder or laying strain males in a Y-maze test?

In recent years, the commercial broiler breeder industry has reported problems of male aggression towards females [Millman, S.T., 1999. An investigation into extreme aggressiveness of broiler breeder males. Unpublished PhD Thesis, University of Guelph]. Although this aggression is shown by the males and is apparently a defect in their behaviour [Millman, S.T., Duncan, I.J.H., 2000. Strain differences in aggressiveness of male domestic fowl in response to a male model. Appl. Anim. Behav. Sci. 66, pp. 217-233], it is also possible that it stems in some way from the females. For example, broiler breeder females may not be receptive to male courtship advances, and may avoid males, thus causing frustration in otherwise normal males. The objective of this study was to examine mate preference by broiler breeder females and the effects of sexual experience on preference. A total of 24 mature, broiler breeder females were individually tested in a Y-maze, with females choosing between a broiler breeder male and a laying strain male. Females were tested using male models and tethered live males, both when the females were sexually inexperienced and after they had been housed with broiler breeder or laying strain males for 6 weeks.Females did not display a male-strain preference when tested with models, but sexually experienced females displayed some evidence of a preference for laying strain males in tests with live males, which did not reach statistical significance (P<0.10). Live males were a stronger attractant for sexually experienced females than were models (P<0.005). Individual females tested with the same pair of males showed different preferences, suggesting females used male behaviour as a basis for their choices, and not male morphology.In conclusion, we found no evidence that broiler breeder females inherently discriminate against broiler breeder males.