Septum volume and food‐storing behavior are related in parids

The hippocampal formation (HF) of food‐storing birds is larger than non‐storing species, and the size of the HF in food‐storing Black‐Capped Chickadees (Poecile atricapillus) varies seasonally. We examined whether the volume of the septum, a medial forebrain structure that shares reciprocal connections with the HF, demonstrates the same species and seasonal variation as has been shown in the HF. We compared septum volume in three parid species; non‐storing Blue Tits (Parus caeruleus) and Great Tits (Parus major), and food‐storing Black‐Capped Chickadees. We found the relative septum volume to be larger in chickadees than in the non‐storing species. We also compared septum and nucleus of the diagonal band (NDB) volume of Black‐Capped Chickadees at different times of the year. We found that the relative septum volume varies seasonally in food‐storing birds. The volume of the NDB does not vary seasonally. Due to the observed species and seasonal variation, the septum, like the hippocampal formation of food‐storing birds, may be specialized for some aspects of food‐storing and spatial memory. © 2002 Wiley Periodicals, Inc. J Neurobiol 51: 215–222, 2002     

Seasonal variation in hippocampal volume in a food-storing bird,the black-capped chickadee

Black-capped chickadees (Parus atricapillus) in upstate New York show a peak in food-hoarding intensity in October. We caught chickadees at six different times of the year and measured the volume of several brain structures. We found that the hippocampal formation, which is involved in spatial memory for cached food items, has a larger volume, relative to the rest of the brain, in October than at any other time of the year. We conclude that there is an association between the intensity of food hoarding and the volume of the hippocampal formation and suggest that the enhanced anatomy might be caused by the increased use of spatial memory. © 1995 John Wiley & Sons, Inc.     

Seasonal changes in neuron numbers in the hippocampal formation of a food‐hoarding bird: The black‐capped chickadee

The volume of the hippocampal formation (HF) in black‐capped chickadees (Poecile atricapillus) varies across the seasons, in parallel with the seasonal cycle in food hoarding. In this study, we estimate cell density and total cell number in the HF across seasons in both juveniles and adults. We find that the seasonal variation in volume is due to an increase in the number of small and large cells (principally neurons) in the fall. Adults also have lower neuron densities than juveniles. Both juveniles and adults show an increase in cell density in the rostral part of the HF in August and a subsequent decrease toward October. This suggests that the net cell addition to the HF may already start in August. We discuss the implications of this early start with respect to the possibility that the seasonal change in HF volume is driven by the experience of food hoarding. We also speculate on the functional significance of the addition of neurons to the HF in the fall. © 2000 John Wiley & Sons, Inc. J Neurobiol 44: 414–422, 2000     

α8‐Integrins are required for hippocampal long‐term potentiation but not for hippocampal‐dependent learning

Integrins are heterodimeric transmembrane cell adhesion receptors that are essential for a wide range of biological functions via cell–matrix and cell–cell interactions. Recent studies have provided evidence that some of the subunits in the integrin family are involved in synaptic and behavioral plasticity. To further understand the role of integrins in the mammalian central nervous system, we generated a postnatal forebrain and excitatory neuron‐specific knockout of α8‐integrin in the mouse. Behavioral studies showed that the mutant mice are normal in multiple hippocampal‐dependent learning tasks, including a T‐maze, non‐match‐to‐place working memory task for which other integrin subunits like α3‐ and β1‐integrin are required. In contrast, mice mutant for α8‐integrin exhibited a specific impairment of long‐term potentiation (LTP) at Schaffer collateral–CA1 synapses, whereas basal synaptic transmission, paired‐pulse facilitation and long‐term depression (LTD) remained unaffected. Because LTP is also impaired in the absence of α3‐integrin, our results indicate that multiple integrin molecules are required for the normal expression of LTP, and different integrins display distinct roles in behavioral and neurophysiological processes like synaptic plasticity.     

Hippocampal neurogenesis in food‐storing red squirrels: the impact of age and spatial behavior

The adaptive significance of adult hippocampal neurogenesis remains unknown. In the laboratory, it is influenced by a variety of environmental and physiological stimuli. In the wild, it may be influenced by the reliance on spatial memory and by environmental stressors. The one common denominator in both settings is that neurogenesis declines markedly with age. Red squirrels are long‐lived rodents that store food (thousands of tree cones) to permit survival under harsh winter conditions. We compared a population from the eastern North America that stores its cones singly or in small clusters with one from the west that stores its cones in large stockpiles. The reliance on spatial memory should be much greater in the east than the west, and should not decline with age, as cone storage and recovery is a yearly necessity. We found no difference between the populations in the density of young neurons and both populations showed the same decline with age. Thus, we reject the spatial memory hypothesis for adult neurogenesis in mammals in its original form. Instead, our evidence is consistent with the neurogenic reserve hypothesis in which neuronal cell production early in life leads to enhanced hippocampal function later in life according to environmental demand but without requirement for ongoing cell production as a function of site‐ and species‐specific needs. A more general interpretation of the data leads us to consider a possible role of neurogenesis in novel, flexible episodic memories.     

Inhibition of cell proliferation in black‐capped chickadees suggests a role for neurogenesis in spatial learning

Following development, the avian brain continues to produce neurons throughout adulthood, which functionally integrate throughout the telencephalon, including the hippocampus. In food‐storing birds like the black‐capped chickadee (Poecile atricapillus), new neurons incorporated into the hippocampus are hypothesized to play a role in spatial learning. Previous results on the relation between hippocampal neurogenesis and spatial learning, however, are correlational. In this study, we experimentally suppressed hippocampal neuronal recruitment and tested for subsequent effects on spatial learning in adult chickadees. After chickadees exhibited significant learning, we treated birds with daily injections of either saline or methylazoxymethanol (MAM), a toxin that suppresses cell proliferation in the brain and monitored subsequent spatial learning. MAM treatment significantly reduced cell proliferation around the lateral ventricles and neuronal recruitment in the hippocampus, measured using the cell birth marker bromodeoxyuridine. MAM‐treated birds performed significantly worse than controls on the spatial learning task 12 days following the initiation of MAM treatment, a time when new neurons would begin functionally integrating into the hippocampus. This difference in learning, however, was limited to a single trial. MAM treatment did not affect any measure of body condition, suggesting learning impairments were not a product of non‐specific adverse effects of MAM. This is the first evidence of a potential causal link between hippocampal neurogenesis and spatial learning in birds. © 2014 Wiley Periodicals, Inc. Develop Neurobiol 74: 1002–1010, 2014     

Testosterone and dihydrotestosterone, but not estradiol, enhance survival of new hippocampal neurons in adult male rats

Past research suggested that androgens may play a role in the regulation of adult neurogenesis within the dentate gyrus. We tested this hypothesis by manipulating androgen levels in male rats. Castrated or sham castrated male rats were injected with 5-Bromo-2'deoxyuridine (BrdU). BrdU-labeled cells in the dentate gryus were visualized and phenotyped (neural or glial) using immunohistochemistry. Castrated males showed a significant decrease in 30-day cell survival within the dentate gyrus but there was no significant change in cell proliferation relative to control males, indicating that androgens positively affect cell survival, but not cell proliferation. To examine the role of testosterone on hippocampal cell survival, males were injected with testosterone s.c. for 30 days starting the day after BrdU injection. Higher doses (0.5 and 1.0 mg/kg) but not a lower dose (0.25 mg/kg) of testosterone resulted in a significant increase in neurogenesis relative to controls. We next tested the role of testosterone's two major metabolites, dihydrotestosterone (DHT), and estradiol, upon neurogenesis. Thirty days of injections of DHT (0.25 and 0.50 mg/kg) but not estradiol (0.010 and 0.020 mg/kg) resulted in a significant increase in hippocampal neurogenesis. These results suggest that testosterone enhances hippocampal neurogenesis via increased cell survival in the dentate gyrus through an androgen-dependent mechanism.     

Equal nonbreeding period survival in adults and juveniles of a long‐distant migrant bird

In migrant birds, survival estimates for the different life‐history stages between fledging and first breeding are scarce. First‐year survival is shown to be strongly reduced compared with annual survival of adult birds. However, it remains unclear whether the main bottleneck in juvenile long‐distant migrants occurs in the postfledging period within the breeding ranges or en route. Quantifying survival rates during different life‐history stages and during different periods of the migration cycle is crucial to understand forces driving the evolution of optimal life histories in migrant birds. Here, we estimate survival rates of adult and juvenile barn swallows (Hirundo rustica L.) in the breeding and nonbreeding areas using a population model integrating survival estimates in the breeding ranges based on a large radio‐telemetry data set and published estimates of demographic parameters from large‐scale population‐monitoring projects across Switzerland. Input parameters included the country‐wide population trend, annual productivity estimates of the double‐brooded species, and year‐to‐year survival corrected for breeding dispersal. Juvenile survival in the 3‐week postfledging period was low (S = 0.32; SE = 0.05), whereas in the rest of the annual cycle survival estimates of adults and juveniles were similarly high (S > 0.957). Thus, the postfledging period was the main survival bottleneck, revealing the striking result that nonbreeding period mortality (including migration) is not higher for juveniles than for adult birds. Therefore, focusing future research on sources of variation in postfledging mortality can provide new insights into determinants of population dynamics and life‐history evolution of migrant birds.     

Evidence for senescence in survival but not in reproduction in a short‐lived passerine

Senescence has been studied since a long time by theoreticians in ecology and evolution, but empirical support in natural population has only recently been accumulating. One of the current challenges is the investigation of senescence of multiple fitness components and the study of differences between sexes. Until now, studies have been more frequently conducted on females than on males and rather in long‐lived than in short‐lived species. To reach a more fundamental understanding of the evolution of senescence, it is critical to investigate age‐specific survival and reproduction performance in both sexes and in a large range of species with contrasting life histories. In this study, we present results on patterns of age‐specific and sex‐specific variation in survival and reproduction in the whinchat Saxicola rubetra, a short‐lived passerine. We compiled individual‐based long‐term datasets from seven populations that were jointly analyzed within a Bayesian modeling framework. We found evidence for senescence in survival with a continuous decline after the age of 1 year, but no evidence of reproductive senescence. Furthermore, we found no clear evidence for sex effects on these patterns. We discuss these results in light of previous studies documenting senescence in short‐lived birds. We note that most of them have been conducted in populations breeding in nest boxes, and we question the potential effect of the nest boxes on the shape of age‐reproductive trajectories.     

High within‐winter and annual survival rates in a declining Afro‐Palaearctic migratory bird suggest that wintering conditions do not limit populations

For migratory birds, it is necessary to estimate annual and overwinter survival rates, identify factors that influence survival, and assess whether survival varies with age and sex if we are to understand population dynamics and thus inform conservation. This study is one of the first to document overwinter and annual survival from the wintering grounds of a declining Afro‐Palaearctic migrant bird, the Whinchat Saxicola rubetra. We monitored a population of marked individuals for which dispersal was low and detectability was high, allowing accurate estimates of survival. Annual survival was at least 52% and did not differ significantly across demographic groups or with habitat characteristics or residency time in the previous winter. Overwinter survival was very high and monthly survival at least 98% at some sites. Although winter residency varied spatially and with age, lower residency did not correlate with reduced annual survival, suggesting occupancy of multiple wintering sites rather than higher winter mortality of individuals with shorter residency. Our results suggest that mortality occurs primarily outside the wintering period, probably during migration, and that wintering conditions have minimal influence on survival. The similarity between survival rates for all age and sex classes when measured on the wintering grounds implies that any difference in survival with age or sex occurs only during the first migration or during the post‐fledging stage, and that selection of wintering habitat, or territory quality, makes little difference to survival in Whinchats. Our findings suggest that the wintering grounds do not limit populations as much as the migratory and breeding stages, with implications for the conservation of declining Afro‐Palaearctic migrants more widely.     

From food‐dependent statistics to metabolic parameters,a practical guide to the use of dynamic energy budget theory

The standard model of the dynamic energy budget theory for metabolic organisation has variables and parameters that can be quantified using indirect methods only. We present new methods (and software) to extract food‐independent parameter values of the energy budget from food‐dependent quantities that are easy to observe, and so facilitate the practical application of the theory to enhance predictability and extrapolation. A natural sequence of 10 steps is discussed to obtain some compound parameters first, then the primary parameters, then the composition parameters and finally the thermodynamic parameters; this sequence matches a sequence of required data of increasing complexity which is discussed in detail. Many applications do not require knowledge of all parameters, and we discuss methods to extrapolate parameters from one species to another. The conversion of mass, volume and energy measures of biomass is discussed; these conversions are not trivial because biomass can change in chemical composition in particular ways thanks to different forms of homeostasis. We solve problems like “What would be the ultimate reproduction rate and the von Bertalanffy growth rate at a specific food level, given that we have measured these statistics at abundant food?” and “What would be the maximum incubation time, given the parameters of the von Bertalanffy growth curve?”. We propose a new non‐destructive method for quantifying the chemical potential and entropy of living reserve and structure, that can potentially change our ideas on the thermodynamic properties of life. We illustrate the methods using data on daphnids and molluscs.     

Improved spatial learning is associated with increased hippocampal but not prefrontal long‐term potentiation in mGluR4 knockout mice

Although much information about metabotropic glutamate receptors (mGluRs) and their role in normal and pathologic brain function has been accumulated during the last decades, the role of group III mGluRs is still scarcely documented. Here, we examined mGluR4 knockout mice for types of behavior and synaptic plasticity that depend on either the hippocampus or the prefrontal cortex (PFC). We found improved spatial short‐ and long‐term memory in the radial arm maze, which was accompanied by enhanced long‐term potentiation (LTP) in hippocampal CA1 region. In contrast, LTP in the PFC was unchanged when compared with wild‐type controls. Changes in paired‐pulse facilitation that became overt in the presence of the GABA_A antagonist picrotoxin indicated a function of mGluR4 in maintaining the excitation/inhibition balance, which is of crucial importance for information processing in the brain and the deterioration of these processes in neuropsychological disorders such as autism, epilepsy and schizophrenia .     

Effects of food‐web structure on periphyton stoichiometry in eutrophic lakes: a mesocosm study

1. Aquatic herbivores typically have much higher concentrations of nutrients (e.g. N and P) in their tissues than there is in the food they eat. These stoichiometric differences can cause herbivores to be limited by the elemental quality of their food, which could affect, in turn, the structure of consumer communities and even alter key ecosystem processes. 2. In streams and in the littoral zone of shallow lakes, periphyton is an important food resource for benthic animals. Studying the elemental composition of periphyton may help us to understand food‐web structure, and any reciprocal effect of this structure on periphyton stoichiometry. 3. To understand how alterations in the food‐web structure affect the elemental composition of periphyton in a eutrophic lake, we carried out a long‐term experiment (14 months) in large‐scale mesocosms (40 m³), in which we manipulated food‐web structure, and which were dominated either by planktivorous fish (Rutilus rutilus) or herbivorous invertebrates (without fish). Periphyton was sampled monthly at three depths (0.5, 1.5 and 2.5 m) to determine its biomass and elemental composition (C/N/P ratio). Food‐web structure, physical and chemical parameters were monitored throughout the experiment. 4. Fish had indirect positive effect on periphyton biomass, leading to twofold higher levels than in herbivore‐dominated mesocosms. This result was probably due to control of benthic consumers by fish, suggesting a strong top–down control on periphyton by their consumers in fishless enclosures. 5. The elemental ratios C/P and C/N were lower in deep water in both treatments, mainly mediated by light availability, in accordance with the light/nutrient ratio hypothesis. These ratios were also lower in fishless treatments, probably due to increases in inorganic nutrient availability and grazing pressure in herbivore‐dominated systems. During winter, periphyton elemental composition was similar in both treatments, and was unrelated to inorganic nutrient availability. 6. These results indicate that any alteration of food‐web structure in lakes, such as in biomanipulation experiments, is likely to modify both the biomass and elemental quality of periphyton. Resultant effects on the consumers of periphyton and macrophytes could play a key role in the success of biomanipulations and should be taken into account in further studies.     

Addition of docosahexaenoic acid,but not arachidonic acid,activates glutathione and thioredoxin antioxidant systems in murine hippocampal HT22 cells: potential implications in neuroprotection

Docosahexaenoic acid (DHA, 22:6n‐3) is a major constituent of nerve cell membrane phospholipids. Besides a role in membrane architecture, DHA is a pleiotropic molecule involved in multiple facets of neuronal biology and also in neuroprotection. We show here that supplementation with DHA (but not arachidonic acid) to mouse hippocampal HT22 cells modulates the expression of genes encoding for antioxidant proteins associated with thioredoxin/peroxiredoxin and glutathione/glutaredoxin systems. Thus, within the thioredoxin system, DHA increased Txn1‐2, Trxrd1‐2, Prdx3, and Srxn1 gene expression. Paralleling these changes, DHA increased thioredoxin reductase activity, the main enzyme involved in thioredoxin regeneration. For the glutathione system, the most important change triggered by DHA was the upregulation of Gpx4 gene, encoding for the nuclear, cytosolic and mitochondrial isoforms of phospholipid‐hydroperoxide glutathione peroxidase (PH‐GPx/GPx4, the main enzyme protecting cell membranes against lipid peroxidation), which was followed by a significant increase in total glutathione peroxidase and GPx4 activities. Noticeably, DHA also upregulated a new Gpx4 splicing variant that retained part of the first intronic region. Finally, we demonstrate that DHA treatment, under the same time course, protects HT22 cells from the oxitoxic exposure to amyloid beta (Aβ_25–35) peptide. Altogether, our data pinpoint to a role of DHA as Indirect Antioxidant that modulates neuronal defences in neuroprotection.

     

The function of GluR1 and GluR2 in cerebellar and hippocampal LTP and LTD is regulated by interplay of phosphorylation and O‐GlcNAc modification

Long‐term potentiation (LTP) and long‐term depression (LTD) are the current models of synaptic plasticity and widely believed to explain how different kinds of memory are stored in different brain regions. Induction of LTP and LTD in different regions of brain undoubtedly involve trafficking of AMPA receptor to and from synapses. Hippocampal LTP involves phosphorylation of GluR1 subunit of AMPA receptor and its delivery to synapse whereas; LTD is the result of dephosphorylation and endocytosis of GluR1 containing AMPA receptor. Conversely the cerebellar LTD is maintained by the phosphorylation of GluR2 which promotes receptor endocytosis while dephosphorylation of GluR2 triggers receptor expression at the cell surface and results in LTP. The interplay of phosphorylation and O‐GlcNAc modification is known as functional switch in many neuronal proteins. In this study it is hypothesized that a same phenomenon underlies as LTD and LTP switching, by predicting the potential of different Ser/Thr residues for phosphorylation, O‐GlcNAc modification and their possible interplay. We suggest the involvement of O‐GlcNAc modification of dephosphorylated GluR1 in maintaining the hippocampal LTD and that of dephosphorylated GluR2 in cerebral LTP. J. Cell. Biochem. 109: 585–597, 2010. © 2010 Wiley‐Liss, Inc.     

A new semisynthetic derivative of sauroine induces LTP in hippocampal slices and improves learning performance in the Morris Water Maze

Two semisynthetic acetyl derivatives of the alkaloid sauroine from Huperzia saururus, monoacetyl sauroine, and diacetyl sauroine (DAS) were obtained and their chemical structures were analyzed by NMR. While monoacetyl sauroine is the typical product of acetylation, DAS is an unexpected derivative related to the keto‐enol formation of sauroine. Recordings of field excitatory post‐synaptic potentials from the CA1 region of rat hippocampal slices showed that only DAS acutely applied induced chemical long‐term potentiation (LTP) in a dose‐dependent manner with an EC₅₀ of 1.15 ± 0.09 μM. This effect was blocked by 10 μM D(‐)‐2‐amino‐5‐phosphonopentanoic acid (AP5), suggesting dependence on the NMDA receptor. DAS significantly increased NMDA receptor‐dependent excitatory post‐synaptic currents without affecting α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate receptor‐dependent currents. Repetitive administration of DAS improved visuo‐spatial learning in the Morris Water Maze. In slices from rats tested in the Morris Water Maze, LTP resulting from electrical synaptic stimulation was 2.5 times larger than in controls. Concentration of DAS measured in the brain after repetitive administration was 29.5 μM. We conclude that slices perfused with DAS display a robust NMDA receptor‐dependent chemical LTP. During chronic treatment, DAS enhances learning abilities through a metaplastic mechanism as revealed by the augmentation of LTP in slices. DAS, therefore, may be a promising compound as a nootropic therapeutic drug.

     

Castration reduces motoneuron soma size but not dendritic length in the spinal nucleus of the bulbocavernosus of wild‐type and BCL‐2 overexpressing mice

Motoneurons in the spinal nucleus of the bulbocavernosus (SNB) and their target muscles, bulbocavernosus and levator ani (BC/LA), constitute an androgen‐sensitive neuromuscular system. Testosterone regulates SNB soma size, SNB dendritic length, and BC/LA muscle mass in adult male rats. Recent evidence indicates that the cell death‐regulatory protein, Bcl‐2, may also play a role in adult neural plasticity. The present study examined whether gonadal hormones and/or the Bcl‐2 protein influence the morphology of the SNB neuromuscular system in adult B6D2F1 mice. In Experiment 1, adult wild‐type and Bcl‐2 overexpressing males were castrated and implanted with silastic capsules containing testosterone or left blank. Six weeks after castration, cholera toxin‐horseradish peroxidase was injected into the BC muscle to label SNB dendrites. Animals were killed 48 h later, and BC/LA muscle mass, SNB soma size, and SNB dendritic arbors were examined. In Experiment 2, wild‐type and Bcl‐2 overexpressing males were castrated or sham castrated, implanted with testosterone‐filled or blank capsules, and examined 12 weeks later. In both experiments, BC/LA muscle mass and SNB soma size were significantly reduced in castrates receiving blank capsules. Surprisingly, however, there was no effect of hormone manipulation on any of several measures of dendritic length. Thus, the dendritic morphology of SNB motoneurons appears to be relatively insensitive to circulating androgen levels in B6D2F1 mice. Bcl‐2 overexpression did not influence BC/LA muscle mass, SNB soma size, or SNB dendritic length, indicating that the morphology of this neuromuscular system and the response to castration are not altered by forced expression of the Bcl‐2 protein. © 2002 Wiley Periodicals, Inc. J Neurobiol 53: 403–412, 2002