Biomedical subjects

Vladimir V Pravosudov

Publications and source records attributed to Vladimir V Pravosudov.

11 recordsLinked to original sources

PubMed2006

The relationship between migratory behaviour, memory and the hippocampus: an intraspecific comparison.

It has been hypothesized that memory-demanding ecological conditions might result in enhanced memory and an enlarged hippocampus, an area of the brain involved in memory processing, either via extensive memory experience or through evolutionary changes. Avian migration appears to represent one of such memory-demanding ecological conditions. We compared two subspecies of the white-crowned sparrow: migratory Zonotrichia leucophrys gambelii and non-migratory Z. l. nuttalli. Compared to non-migratory Z. l. nuttalli, migratory Z. l. gambelii showed better memory performance on spatial one-trial associative learning tasks and had more hippocampal neurons. Migratory subspecies also had larger hippocampi relative to the remainder of the telencephalon but not relative to body mass. In adults, the differences between migratory and non-migratory sparrows were especially pronounced in the right hippocampus. Juvenile migratory Z. l. gambelii had relatively larger hippocampal volume compared to juvenile non-migratory Z. l. nuttalli. Adult migratory Z. l. gambelii had more neurons in their right hippocampus compared to juveniles but such differences were not found in non-migratory Z. l. nuttalli. Our results suggest that migratory behaviour might be related to enhanced spatial memory and an enlarged hippocampus with more neurons, and that differences in the hippocampus between migratory and non-migratory sparrows might be experience-dependent. Furthermore, for the first time our results suggest that the right hippocampus, which encodes global spatial information, might be involved in migratory behaviour.

Analysis of Variance↗

PubMed2005

Is the western scrub-jay (Aphelocoma californica) really an underdog among food-caching corvids when it comes to hippocampal volume and food caching propensity?

Food caching has been linked to better performance on spatial memory tasks and enlarged hippocampal volume in both birds and mammals. Within food-caching birds, it has also been predicted that species less reliant on stored food should have inferior spatial memory and a smaller hippocampus compared to species that depend heavily on food caches. Several comparisons suggest that North American corvids have a significantly smaller hippocampus and overall brain volume compared to the Eurasian corvid species and that western scrub-jays (Aphelocoma californica) have a smaller hippocampus compared to the more specialized Clark's nutcracker. Here we present the largest data set of scrub-jay brains and, in contrast to previous reports, show that relative to body mass western scrub-jays have a brain size similar to the largest brain size of Eurasian corvids. The relative hippocampal volume of scrub-jays is also among the largest of all investigated corvids. These findings may not be surprising considering that scrub-jays have been reported to have remarkable cognitive capacities such as episodic-like memory and experience projection. Our data suggest that many previously made assumptions about western scrub-jays as less specialized food hoarders might be an oversimplification and that simple categorization of species into specialized and non-specialized hoarders might not provide useful insights into the evolution of memory and the hippocampus.

Animals↗

PubMed2005

Effects of nutritional restrictions during post-hatching development on adrenocortical function in western scrub-jays (Aphelocoma californica).

Altricial birds grow rapidly during post-hatching period and are developmentally sensitive to variations in food supply. Limited food results in elevated corticosterone levels in chicks of semi-precocial birds but it is not clear whether altricial songbirds show similar adrenocortical stress response to nutritional restrictions during early development. It is also unknown how nutritional stress during early development affects the adrenocortical function later in life in altricial birds which show tremendous variation in the magnitude of adrenocortical stress response. Using western scrub-jays (Aphelocoma californica), we experimentally demonstrated that moderate food restrictions (65% of ad libitum) during post-hatching development caused significant elevation of baseline corticosterone levels in nest-bound chicks. Compared to controls, 1-year-old scrub-jays that experienced nutritional deficits during post-hatching development also showed a marginally significant trend to have stronger adrenocortical stress response and significantly greater degree of fluctuating asymmetry in bone and feather measurements. Thus, our results demonstrated that developing altricial birds show adrenocortical response to nutritional deficits, which might produce long-term changes in responsiveness of the adrenal system. Our study suggests that baseline corticosterone levels are a good indicator of physiological conditions of developing birds and that individual variance in adrenocortical stress response commonly observed in many species might, at least in part, be explained by environmental conditions during early development. Considering that nutritional restrictions during early development are linked to many permanent changes including impaired cognitive abilities, corticosterone levels in developing young might be a reliable predictor of their future fitness.

Adrenal Cortex↗

PubMed2005

Dominance-related changes in spatial memory are associated with changes in hippocampal cell proliferation rates in mountain chickadees.

It is well established that spatial memory is dependent on the hippocampus in both mammals and birds. As memory capacity can fluctuate on a temporal basis, it is important to understand the mechanisms mediating such changes. It is known that early memory-dependent experiences in young animals result in hippocampal enlargement and in increased neurogenesis, including cell proliferation and neuron survival. It is less clear, however, whether temporal changes in spatial memory are also associated with changes in hippocampal anatomy and cell proliferation in fully grown and experienced adult animals. In a previous study, we experimentally demonstrated that socially subordinate mountain chickadees (Poecile gambeli) showed inferior spatial memory performance compared to their dominant group mates, in the absence of significant differences in baseline corticosterone levels. Here we investigated whether these differences in memory between dominant and subordinate birds were associated with changes in the hippocampus. Following memory tests, chickadees were injected with 5-bromo-2'-deoxyuridine to label dividing cells and sacrificed 2 days after the injections. We found no significant differences in volume or the total number of neurons in the hippocampal formation between dominant and subordinate chickadees, but subordinate birds had significantly lower cell proliferation rates in the ventricular zone adjacent to both the hippocampus and mesopallium compared to the dominants. Individuals, which performed better on spatial memory tests tended to have higher levels of cell proliferation. These results suggest that social status can affect cell proliferation rates in the ventricular zone and support the hypothesis that neurogenesis might be involved in memory function in adult animals.

Animals↗

PubMed2005

Prolonged moderate elevation of corticosterone does not affect hippocampal anatomy or cell proliferation rates in mountain chickadees (Poecile gambeli).

Chronic stress and corresponding chronic elevations of glucocorticoid hormones have been widely assumed to have deleterious effects on brain anatomy and functions such as learning and memory. In particular, it has been suggested that chronic elevations of glucocorticoid hormones result in death of hippocampal neurons and in reduced rates of hippocampal neurogenesis. It is not clear, however, if any increase in glucocorticoid levels has negative effects on hippocampal anatomy as many animals regularly maintain moderately elevated levels of glucocrticoids over long periods of time under natural energetically demanding conditions. We used unbiased stereological methods to investigate whether mountain chickadees (Poecile gambeli) implanted for 49 days with continuous time-release corticosterone pellets, designed to approximately double the baseline corticosterone levels, differed from placebo-implanted chickadees in their hippocampal anatomy and cell proliferation rates. We found no significant differences between corticosterone and placebo-implanted birds in either telencephalon volume, volume of the hippocampal formation, or the total number of hippocampal neurons. Cell proliferation rates, measured as the total number of BrdU-labeled cells in the ventricular zone adjacent either to the hippocampus or to the mesopallium, were also not significantly different between corticosterone and placebo-implanted chickadees. Our results suggest that prolonged moderate elevation of corticosterone might not provide the suggested deleterious effects on hippocampal anatomy and neurogenesis in food-caching birds and, as we have shown previously, it actually enhances spatial memory.

Bromodeoxyuridine↗

PubMed2005

Nutritional deficits during early development affect hippocampal structure and spatial memory later in life.

Development rates vary among individuals, often as a result of direct competition for food. Survival of young might depend on their learning abilities, but it remains unclear whether learning abilities are affected by nutrition during development. The authors demonstrated that compared with controls, 1-year-old Western scrub jays (Aphelocoma californica) that experienced nutritional deficits during early posthatching development had smaller hippocampi with fewer neurons and performed worse in a cache recovery task and in a spatial version of an associative learning task. In contrast, performance of nutritionally deprived birds was similar to that of controls in 2 color versions of an associative learning task. These findings suggest that nutritional deficits during early development have long-term consequences for hippocampal structure and spatial memory, which, in turn, are likely to have a strong impact on animals' future fitness.

Age Factors↗

PubMed2004

No latitudinal differences in adrenocortical stress response in wintering black-capped chickadees (Poecile atricapilla).

Birds respond to deterioration in environmental conditions by elevating their corticosterone levels, which can enhance their survival. It is less clear if animals constantly living in energetically challenging environment show similar increases in adrenocortical function. Previous work has demonstrated that under controlled conditions black-capped chickadees (Poecile atricapilla) from northern latitudes cache more food and perform better on spatial memory tasks than their southern conspecifics. As elevated levels of corticosterone have been shown previously to correlate with spatial memory performance in chickadees, this study aimed to investigate whether black-capped chickadees from northern latitudes have elevated baseline levels of corticosterone and/or a stronger adrenocortical stress response than their southern conspecifics, irrespective of their immediate environment. We found no differences between Alaskan and Colorado chickadees maintained under identical conditions for 3 months in either baseline levels of corticosterone or maximum levels of corticosterone achieved during the stress response. Baseline corticosterone levels were negatively correlated with relative body mass across both groups of birds. Our results suggest that the population differences in food catching behavior and spatial memory were not related to differences in corticosterone levels. We conclude that many reported population differences in baseline levels and in strength of adrenocortical stress response may often reflect differences in local environmental conditions rather than population-specific physiological traits.

Adrenal Cortex↗

PubMed2003

Long-term moderate elevation of corticosterone facilitates avian food-caching behaviour and enhances spatial memory.

It is widely assumed that chronic stress and corresponding chronic elevations of glucocorticoid levels have deleterious effects on animals' brain functions such as learning and memory. Some animals, however, appear to maintain moderately elevated levels of glucocorticoids over long periods of time under natural energetically demanding conditions, and it is not clear whether such chronic but moderate elevations may be adaptive. I implanted wild-caught food-caching mountain chickadees (Poecile gambeli), which rely at least in part on spatial memory to find their caches, with 90-day continuous time-release corticosterone pellets designed to approximately double the baseline corticosterone levels. Corticosterone-implanted birds cached and consumed significantly more food and showed more efficient cache recovery and superior spatial memory performance compared with placebo-implanted birds. Thus, contrary to prevailing assumptions, long-term moderate elevations of corticosterone appear to enhance spatial memory in food-caching mountain chickadees. These results suggest that moderate chronic elevation of corticosterone may serve as an adaptation to unpredictable environments by facilitating feeding and food-caching behaviour and by improving cache-retrieval efficiency in food-caching birds.

Adaptation, Physiological↗

PubMed2003

The relationship between dominance, corticosterone, memory, and food caching in mountain chickadees (Poecile gambeli).

It has been hypothesized that in avian social groups subordinate individuals should maintain more energy reserves than dominants, as an insurance against increased perceived risk of starvation. Subordinates might also have elevated baseline corticosterone levels because corticosterone is known to facilitate fattening in birds. Recent experiments showed that moderately elevated corticosterone levels resulting from unpredictable food supply are correlated with enhanced cache retrieval efficiency and more accurate performance on a spatial memory task. Given the correlation between corticosterone and memory, a further prediction is that subordinates might be more efficient at cache retrieval and show more accurate performance on spatial memory tasks. We tested these predictions in dominant-subordinate pairs of mountain chickadees (Poecile gambeli). Each pair was housed in the same cage but caching behavior was tested individually in an adjacent aviary to avoid the confounding effects of small spaces in which birds could unnaturally and directly influence each other's behavior. In sharp contrast to our hypothesis, we found that subordinate chickadees cached less food, showed less efficient cache retrieval, and performed significantly worse on the spatial memory task than dominants. Although the behavioral differences could have resulted from social stress of subordination, and dominant birds reached significantly higher levels of corticosterone during their response to acute stress compared to subordinates, there were no significant differences between dominants and subordinates in baseline levels or in the pattern of adrenocortical stress response. We find no evidence, therefore, to support the hypothesis that subordinate mountain chickadees maintain elevated baseline corticosterone levels whereas lower caching rates and inferior cache retrieval efficiency might contribute to reduced survival of subordinates commonly found in food-caching parids.

Analysis of Variance↗

PubMed2002

The effect of photoperiod on adrenocortical stress response in mountain chickadees (Poecile gambeli).

Birds respond to environmental changes by modulating their levels of plasma corticosterone, a stress hormone produced by the adrenal glands. Baseline levels of corticosterone and the magnitude of adrenocortical response to acute stress are known to vary seasonally. Photoperiod is one of several potential factors which could affect the seasonal modulation of corticosterone secretion. In this study, we examined the effects of photoperiod on baseline and acute-stress-induced levels of corticosterone in adult mountain chickadees (Poecile gambeli). We exposed 20 mountain chickadees to short days (8L:16D h) for 60 days, after which half of the chickadees were switched to long days (14L:10D h). We collected blood samples from both groups 33 days after the switching. Our results showed that photoperiod had no significant effect either on baseline levels of corticosterone or on the maximum levels reached during the adrenocortical response to acute stress. However, photoperiod had a significant effect on the way that chickadees responded to acute stress: birds maintained on long days reached significantly higher levels of corticosterone between 5 and 20 min after capture than birds maintained on short days, which reached their maximum levels of corticosterone between 20 and 50 min. Females reached significantly higher levels of corticosterone than males in response to acute stress. Our results suggest that factors other than photoperiod are responsible for the observed seasonal changes in baseline levels of corticosterone, whereas photoperiod is directly involved in regulation of adrenocortical stress response.

Adrenal Cortex↗

PubMed2002

A test of the adaptive specialization hypothesis: population differences in caching, memory, and the hippocampus in black-capped chickadees (Poecile atricapilla).

To test the hypothesis that accurate cache recovery is more critical for birds that live in harsh conditions where the food supply is limited and unpredictable, the authors compared food caching, memory, and the hippocampus of black-capped chickadees (Poecile atricapilla) from Alaska and Colorado. Under identical laboratory conditions, Alaska chickadees (a) cached significantly more food; (b) were more efficient at cache recovery: (c) performed more accurately on one-trial associative learning tasks in which birds had to rely on spatial memory, but did not differ when tested on a nonspatial version of this task; and (d) had significantly larger hippocampal volumes containing more neurons compared with Colorado chickadees. The results support the hypothesis that these population differences may reflect adaptations to a harsh environment.

Adaptation, Physiological↗