RhoU forms homo-oligomers to regulate cellular responses

RhoU is an atypical member of the Rho family of small G-proteins, which has N- and C-terminal extensions compared to the classic Rho GTPases RhoA, Rac1 and Cdc42, and associates with membranes through C-terminal palmitoylation rather than prenylation. RhoU mRNA expression is upregulated in prostate cancer and is considered a marker for disease progression. Here, we show that RhoU overexpression in prostate cancer cells increases cell migration and invasion. To identify RhoU targets that contribute to its function, we found that RhoU homodimerizes in cells. We map the region involved in this interaction to the C-terminal extension and show that C-terminal palmitoylation is required for self-association. Expression of the isolated C-terminal extension reduces RhoU-induced activation of p21-activated kinases (PAKs), which are known downstream targets for RhoU, and induces cell morphological changes consistent with inhibiting RhoU function. Our results show for the first time that the activity of a Rho family member is stimulated by self-association, and this is important for its activity.

HDAC Inhibition Restores Response to HER2-Targeted Therapy in Breast Cancer via PHLDA1 Induction

The downregulation of Pleckstrin Homology-Like Domain family A member 1 (PHLDA1) expression mediates resistance to targeted therapies in receptor tyrosine kinase-driven cancers. The restoration and maintenance of PHLDA1 levels in cancer cells thus constitutes a potential strategy to circumvent resistance to inhibitors of receptor tyrosine kinases. Through a pharmacological approach, we identify the inhibition of MAPK signalling as a crucial step in PHLDA1 downregulation. Further ChIP-qPCR analysis revealed that MEK1/2 inhibition produces significant epigenetic changes at the PHLDA1 locus, specifically a decrease in the activatory marks H3Kme3 and H3K27ac. In line with this, we show that treatment with the clinically relevant class I histone deacetylase (HDAC) inhibitor 4SC-202 restores PHLDA1 expression in lapatinib-resistant human epidermal growth factor receptor-2 (HER2)+ breast cancer cells. Critically, we show that when given in combination, 4SC-202 and lapatinib exert synergistic effects on 2D cell proliferation and colony formation capacity. We therefore propose that co-treatment with 4SC-202 may prolong the clinical efficacy of lapatinib in HER2+ breast cancer patients.

Statins change the cytokine profile in Trypanosoma cruzi-infected U937 macrophages and murine cardiac tissue through Rho-associated kinases inhibition

Introduction

Chronic Chagasic cardiomyopathy (CCC), caused by the protozoan Trypanosoma cruzi, is the most severe manifestation of Chagas disease.CCC is characterized by cardiac inflammation and fibrosis caused by a persistent inflammatory response. Following infection, macrophages secrete inflammatory mediators such as IL-1β, IL-6, and TNF-α to control parasitemia. Although this response contains parasite infection, it causes damage to the heart tissue. Thus, the use of immunomodulators is a rational alternative to CCC. Rho-associated kinase (ROCK) 1 and 2 are RhoA-activated serine/threonine kinases that regulate the actomyosin cytoskeleton. Both ROCKs have been implicated in the polarization of macrophages towards an M1 (pro-inflammatory) phenotype. Statins are FDA-approved lipid-lowering drugs that reduce RhoA signaling by inhibiting geranylgeranyl pyrophosphate (GGPP) synthesis. This work aims to identify the effect of statins on U937 macrophage polarization and cardiac tissue inflammation and its relationship with ROCK activity during T. cruzi infection.

Methods

PMA-induced, wild-type, GFP-, CA-ROCK1- and CA-ROCK2-expressing U937 macrophages were incubated with atorvastatin, or the inhibitors Y-27632, JSH-23, TAK-242, or C3 exoenzyme incubated with or without T. cruzi trypomastigotes for 30 min to evaluate the activity of ROCK and the M1 and M2 cytokine expression and secretion profiling. Also, ROCK activity was determined in T. cruzi-infected, BALB/c mice hearts.

Results

In this study, we demonstrate for the first time in macrophages that incubation with T. cruzi leads to ROCK activation via the TLR4 pathway, which triggers NF-κB activation. Inhibition of ROCKs by Y-27632 prevents NF-κB activation and the expression and secretion of M1 markers, as does treatment with atorvastatin. Furthermore, we show that the effect of atorvastatin on the NF-kB pathway and cytokine secretion is mediated by ROCK. Finally, statin treatment decreased ROCK activation and expression, and the pro-inflammatory cytokine production, promoting anti-inflammatory cytokine expression in chronic chagasic mice hearts.

Conclusion

These results suggest that the statin modulation of the inflammatory response due to ROCK inhibition is a potential pharmacological strategy to prevent cardiac inflammation in CCC.

Assembly of nuclear dimers of PI3K regulatory subunits is regulated by the Cdc42-activated tyrosine kinase ACK

Activated Cdc42-associated kinase (ACK) is an oncogenic nonreceptor tyrosine kinase associated with poor prognosis in several human cancers. ACK promotes proliferation, in part by contributing to the activation of Akt, the major effector of class 1A phosphoinositide 3-kinases (PI3Ks), which transduce signals via membrane phosphoinositol lipids. We now show that ACK also interacts with other key components of class 1A PI3K signaling, the PI3K regulatory subunits. We demonstrate ACK binds to all five PI3K regulatory subunit isoforms and directly phosphorylates p85α, p85β, p50α, and p55α on Tyr607 (or analogous residues). We found that phosphorylation of p85β promotes cell proliferation in HEK293T cells. We demonstrate that ACK interacts with p85α exclusively in nuclear-enriched cell fractions, where p85α phosphorylated at Tyr607 (pTyr607) also resides, and identify an interaction between pTyr607 and the N-terminal SH2 domain that supports dimerization of the regulatory subunits. We infer from this that ACK targets p110-independent p85 and further postulate that these regulatory subunit dimers undertake novel nuclear functions underpinning ACK activity. We conclude that these dimers represent a previously undescribed mode of regulation for the class1A PI3K regulatory subunits and potentially reveal additional avenues for therapeutic intervention.

New Caledonian crows plan for specific future tool use

The ability to plan for future events is one of the defining features of human intelligence. Whether non-human animals can plan for specific future situations remains contentious: despite a sustained research effort over the last two decades, there is still no consensus on this question. Here, we show that New Caledonian crows can use tools to plan for specific future events. Crows learned a temporal sequence where they were (a) shown a baited apparatus, (b) 5 min later given a choice of five objects and (c) 10 min later given access to the apparatus. At test, these crows were presented with one of two tool-apparatus combinations. For each combination, the crows chose the right tool for the right future task, while ignoring previously useful tools and a low-value food item. This study establishes that planning for specific future tool use can evolve via convergent evolution, given that corvids and humans shared a common ancestor over 300 million years ago, and offers a route to mapping the planning capacities of animals.

Targeting Rho GTPase Signaling Networks in Cancer

As key regulators of cytoskeletal dynamics, Rho GTPases coordinate a wide range of cellular processes, including cell polarity, cell migration, and cell cycle progression. The adoption of a pro-migratory phenotype enables cancer cells to invade the stroma surrounding the primary tumor and move toward and enter blood or lymphatic vessels. Targeting these early events could reduce the progression to metastatic disease, the leading cause of cancer-related deaths. Rho GTPases play a key role in the formation of dynamic actin-rich membrane protrusions and the turnover of cell-cell and cell-extracellular matrix adhesions required for efficient cancer cell invasion. Here, we discuss the roles of Rho GTPases in cancer, their validation as therapeutic targets and the challenges of developing clinically viable Rho GTPase inhibitors. We review other therapeutic targets in the wider Rho GTPase signaling network and focus on the four best characterized effector families: p21-activated kinases (PAKs), Rho-associated protein kinases (ROCKs), atypical protein kinase Cs (aPKCs), and myotonic dystrophy kinase-related Cdc42-binding kinases (MRCKs).

Cuttlefish retrieve whether they smelt or saw a previously encountered item

According to the Source Monitoring Framework, the origin of a memory is remembered through the retrieval of specific features (e.g. perceptive, sensitive, affective signals). In two source discrimination tasks, we studied the ability of cuttlefish to remember the modality in which an item had been presented several hours ago. In Experiment 1, cuttlefish were able to retrieve the modality of presentation of a crab (visual vs olfactory) sensed before 1 h and 3 hrs delays. In Experiment 2, cuttlefish were trained to retrieve the modality of the presentation of fish, shrimp, and crabs. After training, cuttlefish performed the task with another item never encountered before (e.g. mussel). The cuttlefish successfully passed transfer tests with and without a delay of 3 hrs. This study is the first to show the ability to discriminate between two sensory modalities (i.e. see vs smell) in an animal. Taken together, these results suggest that cuttlefish can retrieve perceptual features of a previous event, namely whether they had seen or smelled an item.

Emerging Roles of Fibroblast Growth Factor 10 in Cancer

Whilst cross-talk between stroma and epithelium is critical for tissue development and homeostasis, aberrant paracrine stimulation can result in neoplastic transformation. Chronic stimulation of epithelial cells with paracrine Fibroblast Growth Factor 10 (FGF10) has been implicated in multiple cancers, including breast, prostate and pancreatic ductal adenocarcinoma. Here, we examine the mechanisms underlying FGF10-induced tumourigenesis and explore novel approaches to target FGF10 signaling in cancer.

PHLDA1 Mediates Drug Resistance in Receptor Tyrosine Kinase-Driven Cancer

Development of resistance causes failure of drugs targeting receptor tyrosine kinase (RTK) networks and represents a critical challenge for precision medicine. Here, we show that PHLDA1 downregulation is critical to acquisition and maintenance of drug resistance in RTK-driven cancer. Using fibroblast growth factor receptor (FGFR) inhibition in endometrial cancer cells, we identify an Akt-driven compensatory mechanism underpinned by downregulation of PHLDA1. We demonstrate broad clinical relevance of our findings, showing that PHLDA1 downregulation also occurs in response to RTK-targeted therapy in breast and renal cancer patients, as well as following trastuzumab treatment in HER2+ breast cancer cells. Crucially, knockdown of PHLDA1 alone was sufficient to confer de novo resistance to RTK inhibitors and induction of PHLDA1 expression re-sensitized drug-resistant cancer cells to targeted therapies, identifying PHLDA1 as a biomarker for drug response and highlighting the potential of PHLDA1 reactivation as a means of circumventing drug resistance.

Fibroblast growth factor-mediated crosstalk in cancer etiology and treatment

It is becoming increasingly evident that multiple cell types within the tumor work together to drive tumour progression and impact on both the response to therapy and the dissemination of tumour cells throughout the body. Fibroblast growth factor signalling (FGF) is perturbed in a number of tumors, serving to drive tumor cell proliferation and migration, but also has a central role in orchestrating the plethora of cells that comprise the tumor microenvironment. This review focuses on how this family of signalling molecules can influence the interactions between tumor cells and their surrounding environment. Unraveling the complexities of FGF signalling between the distinct cell types of a tumor may identify additional opportunities for FGF-targeted compounds in therapy and could help combat drug resistance. Developmental Dynamics 246:493-501, 2017. © 2017 Wiley Periodicals, Inc.

Western scrub-jays (Aphelocoma californica) solve multiple-string problems by the spatial relation of string and reward

String-pulling is a widely used paradigm in animal cognition research to assess what animals understand about the functionality of strings as a means to obtain an out-of-reach reward. This study aimed to systematically investigate what rules Western scrub-jays (Aphelocoma californica) use to solve different patterned string tasks, i.e. tasks in which subjects have to choose between two or more strings of which only one is connected to the reward, or where one is more efficient. Arranging strings in a parallel configuration showed that the jays were generally capable of solving multiple-string tasks and acted in a goal-directed manner. The slanted and crossed configurations revealed a reliance on a "proximity rule", that is, a tendency to choose the string-end closest to the reward. When confronted with strings of different lengths attached to rewards at different distances the birds chose according to the reward distance, preferring the reward closest to them, and were sensitive to the movement of the reward, but did not consistently prefer the shorter and therefore more efficient string. Generally, the scrub-jays were successful in tasks where the reward was closest to the string-ends they needed to pull or when string length and reward distance correlated, but the birds had problems when the wrong string-end was closest to the reward or when the food items were in close proximity to each other. These results show that scrub-jays had a partial understanding of the physical principles underlying string-pulling but relied on simpler strategies such as the proximity rule to solve the tasks.

Inhibition of Ral GTPases Using a Stapled Peptide Approach

Aberrant Ras signaling drives numerous cancers, and drugs to inhibit this are urgently required. This compelling clinical need combined with recent innovations in drug discovery including the advent of biologic therapeutic agents, has propelled Ras back to the forefront of targeting efforts. Activated Ras has proved extremely difficult to target directly, and the focus has moved to the main downstream Ras-signaling pathways. In particular, the Ras-Raf and Ras-PI3K pathways have provided conspicuous enzyme therapeutic targets that were more accessible to conventional drug-discovery strategies. The Ras-RalGEF-Ral pathway is a more difficult challenge for traditional medicinal development, and there have, therefore, been few inhibitors reported that disrupt this axis. We have used our structure of a Ral-effector complex as a basis for the design and characterization of α-helical-stapled peptides that bind selectively to active, GTP-bound Ral proteins and that compete with downstream effector proteins. The peptides have been thoroughly characterized biophysically. Crucially, the lead peptide enters cells and is biologically active, inhibiting isoform-specific RalB-driven cellular processes. This, therefore, provides a starting point for therapeutic inhibition of the Ras-RalGEF-Ral pathway.

Song, sex and sensitive phases in the behavioural devebpment of birds

A number of parallels can be drawn between song learning and sexual imprinting, but how do the two processes interact during development? In zebra finches, the only species for which there are data on both song learning and sexual imprinting, an important difference between the two processes is that song learning usually occurs after the birds have sexually imprinted. Does sexual imprinting influence subsequent song tutor choice? Recent work comparing the song and sexual preferences of individual males suggests that a male does not necessarily choose a song tutor who is of the same species as he has sexually imprinted on.

Planning for the future by western scrub-jays

Knowledge of and planning for the future is a complex skill that is considered by many to be uniquely human. We are not born with it; children develop a sense of the future at around the age of two and some planning ability by only the age of four to five. According to the Bischof-Köhler hypothesis, only humans can dissociate themselves from their current motivation and take action for future needs: other animals are incapable of anticipating future needs, and any future-oriented behaviours they exhibit are either fixed action patterns or cued by their current motivational state. The experiments described here test whether a member of the corvid family, the western scrub-jay (Aphelocoma californica), plans for the future. We show that the jays make provision for a future need, both by preferentially caching food in a place in which they have learned that they will be hungry the following morning and by differentially storing a particular food in a place in which that type of food will not be available the next morning. Previous studies have shown that, in accord with the Bischof-Köhler hypothesis, rats and pigeons may solve tasks by encoding the future but only over very short time scales. Although some primates and corvids take actions now that are based on their future consequences, these have not been shown to be selected with reference to future motivational states, or without extensive reinforcement of the anticipatory act. The results described here suggest that the jays can spontaneously plan for tomorrow without reference to their current motivational state, thereby challenging the idea that this is a uniquely human ability.

Changes in spatial memory mediated by experimental variation in food supply do not affect hippocampal anatomy in mountain chickadees (Poecile gambeli)

Earlier reports suggested that seasonal variation in food-caching behavior (caching intensity and cache retrieval accuracy) might correlate with morphological changes in the hippocampal formation, a brain structure thought to play a role in remembering cache locations. We demonstrated that changes in cache retrieval accuracy can also be triggered by experimental variation in food supply: captive mountain chickadees (Poecile gambeli) maintained on limited and unpredictable food supply were more accurate at recovering their caches and performed better on spatial memory tests than birds maintained on ad libitum food. In this study, we investigated whether these two treatment groups also differed in the volume and neuron number of the hippocampal formation. If variation in memory for food caches correlates with hippocampal size, then our birds with enhanced cache recovery and spatial memory performance should have larger hippocampal volumes and total neuron numbers. Contrary to this prediction we found no significant differences in volume or total neuron number of the hippocampal formation between the two treatment groups. Our results therefore indicate that changes in food-caching behavior and spatial memory performance, as mediated by experimental variations in food supply, are not necessarily accompanied by morphological changes in volume or neuron number of the hippocampal formation in fully developed, experienced food-caching birds.

Hippocampal growth and maintenance depend on food-caching experience in juvenile mountain chickadees (Poecile gambeli)

This experiment investigated the development of caching behavior and the hippocampus (HF) in postfledging mountain chickadees (Poecile gambeli). From Days 35 to 53, the number of seeds stored increased but the proportion recovered did not. Birds that stored and recovered during 3 or more trials had significantly enlarged HF but not telencephalon volumes (experienced) compared with those that stored but did not recover (store only) and those deprived of caching experience altogether (deprived). HF size did not increase linearly with the number of experience trials. Birds that received less than 3 experience trials did not differ from deprived birds in HF size, suggesting a threshold effect. Experienced birds prevented from caching for 1 month had significantly smaller HF volumes than those examined immediately after caching experience and did not differ from deprived birds. Experience of both storing and recovery is required to initiate growth and maintain HF size.

Effects of experience and social context on prospective caching strategies by scrub jays

Social life has costs associated with competition for resources such as food. Food storing may reduce this competition as the food can be collected quickly and hidden elsewhere; however, it is a risky strategy because caches can be pilfered by others. Scrub jays (Aphelocoma coerulescens) remember 'what', 'where' and 'when' they cached. Like other corvids, they remember where conspecifics have cached, pilfering them when given the opportunity, but may also adjust their own caching strategies to minimize potential pilfering. To test this, jays were allowed to cache either in private (when the other bird's view was obscured) or while a conspecific was watching, and then recover their caches in private. Here we show that jays with prior experience of pilfering another bird's caches subsequently re-cached food in new cache sites during recovery trials, but only when they had been observed caching. Jays without pilfering experience did not, even though they had observed other jays caching. Our results suggest that jays relate information about their previous experience as a pilferer to the possibility of future stealing by another bird, and modify their caching strategy accordingly.

Elements of episodic-like memory in animals

A number of psychologists have suggested that episodic memory is a uniquely human phenomenon and, until recently, there was little evidence that animals could recall a unique past experience and respond appropriately. Experiments on food-caching memory in scrub jays question this assumption. On the basis of a single caching episode, scrub jays can remember when and where they cached a variety of foods that differ in the rate at which they degrade, in a way that is inexplicable by relative familiarity. They can update their memory of the contents of a cache depending on whether or not they have emptied the cache site, and can also remember where another bird has hidden caches, suggesting that they encode rich representations of the caching event. They make temporal generalizations about when perishable items should degrade and also remember the relative time since caching when the same food is cached in distinct sites at different times. These results show that jays form integrated memories for the location, content and time of caching. This memory capability fulfils Tulving's behavioural criteria for episodic memory and is thus termed 'episodic-like'. We suggest that several features of episodic memory may not be unique to humans.

Long-term unpredictable foraging conditions and physiological stress response in mountain chickadees (Poecile gambeli)

Birds respond to short-term deterioration in foraging conditions by increasing their plasma level of corticosterone but the physiological effects of long-term deterioration in food supplies are not well known. In resident passerine birds that winter in temperate climates, such as the mountain chickadee (Poecile gambeli), the food supply may be limited and unpredictable over long periods of time. Whether the long-term limited and unpredictable food supply has an effect on (a) baseline levels of corticosterone and (b) the adrenocortical stress response to a standardized acute stress of handling and restraint in mountain chickadees was assessed. For a period of 94 days, one group of chickadees was maintained on limited and unpredictable food (food-restricted) and the other group was maintained on an ad libitum food supply. The food-restricted birds had significantly higher baseline levels of corticosterone than those maintained on ad libitum food. All birds responded to the acute stressor by an increasing secretion of corticosterone but there were no differences between the treatment groups in their stress response. There was a significant effect of sex on the stress response, with females reaching higher levels of corticosterone and responding at a faster rate than males. These results suggest that permanent resident birds wintering in harsh environments may have elevated levels of corticosterone on a long-term basis. Whereas other factors, such as day length and ambient temperature, may contribute to energetic hardship during the winter, the results showed that limited and unpredictable food alone can trigger significant changes in baseline levels of plasma corticosterone. The potential costs and benefits of long-term increased corticosterone levels in resident food-caching birds are discussed.

Testing episodic memory in animals: a new approach

Episodic memory involves the encoding and storage of memories concerned with unique personal experiences and their subsequent recall, and it has long been the subject of intensive investigation in humans. According to Tulving's classical definition, episodic memory "receives and stores information about temporally dated episodes or events and temporal-spatial relations among these events." Thus, episodic memory provides information about the 'what' and 'when' of events ('temporally dated experiences') and about 'where' they happened ('temporal-spatial relations'). The storage and subsequent recall of this episodic information was thought to be beyond the memory capabilities of nonhuman animals. Although there are many laboratory procedures for investigating memory for discrete past episodes, until recently there were no previous studies that fully satisfied the criteria of Tulving's definition: they can all be explained in much simpler terms than episodic memory. However, current studies of memory for cache sites in food-storing jays provide an ethologically valid model for testing episodic-like memory in animals, thereby bridging the gap between human and animal studies memory. There is now a pressing need to adapt these experimental tests of episodic memory for other animals. Given the potential power of transgenic and knock-out procedures for investigating the genetic and molecular bases of learning and memory in laboratory rodents, not to mention the wealth of knowledge about the neuroanatomy and neurophysiology of the rodent hippocampus (a brain area heavily implicated in episodic memory), an obvious next step is to develop a rodent model of episodic-like memory based on the food-storing bird paradigm. The development of a rodent model system could make an important contribution to our understanding of the neural, molecular, and behavioral mechanisms of mammalian episodic memory.

Hippocampal volume does not change seasonally in a non food-storing songbird

Seasonal differences in hippocampal morphology have been reported in food-storing birds. Non food-storing species have not been investigated however. It is therefore unclear whether seasonal changes in the hippocampus are specifically related to food-storing or reflect a more general seasonal mechanism that occurs in both food-storing and non food-storing birds alike. We determined the volumes of the hippocampal formation and remaining telencephalon in the non-storing male song sparrow (Melospiza melodies morphna) in two experiments comparing birds collected in the spring and fall of 1992-94 (Experiment 1) and 1997 (Experiment 2). Although pronounced seasonal changes in song control nuclei such as the HVC and RA were previously reported for the same brains used in Experiment 1, we found that hippocampal volume did not change with season in either Experiment 1 or 2 for these song sparrow brains. These results suggest that seasonal changes in the hippocampus do not occur in this non food-storing species and may be specific to food-storing birds.

Hippocampal growth and maintenance depend on food-caching experience in juvenile mountain chickadees (Poecile gambeli)

This experiment investigated the development of caching behavior and the hippocampus (HF) in postfledging mountain chickadees (Poecile gambeli). From Days 35 to 53, the number of seeds stored increased but the proportion recovered did not. Birds that stored and recovered during 3 or more trials had significantly enlarged HF but not telencephalon volumes (experienced) compared with those that stored but did not recover (store only) and those deprived of caching experience altogether (deprived). HF size did not increase linearly with the number of experience trials. Birds that received less than 3 experience trials did not differ from deprived birds in HF size, suggesting a threshold effect. Experienced birds prevented from caching for 1 month had significantly smaller HF volumes than those examined immediately after caching experience and did not differ from deprived birds. Experience of both storing and recovery is required to initiate growth and maintain HF size.

Effects of demanding foraging conditions on cache retrival accuracy in food-caching mountain chickadees (Poecile gambeli)

Birds rely, at least in part, on spatial memory for recovering previously hidden caches but accurate cache recovery may be more critical for birds that forage in harsh conditions where the food supply is limited and unpredictable. Failure to find caches in these conditions may potentially result in death from starvation. In order to test this hypothesis we compared the cache recovery behaviour of 24 wild-caught mountain chickadees (Poecile gambeli), half of which were maintained on a limited and unpredictable food supply while the rest were maintained on an ad libitum food supply for 60 days. We then tested their cache retrieval accuracy by allowing birds from both groups to cache seeds in the experimental room and recover them 5 hours later. Our results showed that birds maintained on a limited and unpredictable food supply made significantly fewer visits to non-cache sites when recovering their caches compared to birds maintained on ad libitum food. We found the same difference in performance in two versions of a one-trial associative learning task in which the birds had to rely on memory to find previously encountered hidden food. In a non-spatial memory version of the task, in which the baited feeder was clearly marked, there were no significant differences between the two groups. We therefore concluded that the two groups differed in their efficiency at cache retrieval. We suggest that this difference is more likely to be attributable to a difference in memory (encoding or recall) than to a difference in their motivation to search for hidden food, although the possibility of some motivational differences still exists. Overall, our results suggest that demanding foraging conditions favour more accurate cache retrieval in food-caching birds.

Scrub jays (Aphelocoma coerulescens) form integrated memories of the multiple features of caching episodes

Four experiments examined whether food-storing scrub jays remember when and where they cached different foods. The scrub jays cached and recovered perishable and nonperishable foods in visuospatially distinct and trial-unique cache sites. They rapidly learned to avoid searching for foods that had perished by the time of recovery, while continuing to search for the same foods after shorter retention intervals when the foods were still fresh. The temporal control of searching at recovery was also observed when the familiarity of cache sites did not provide any information about the time of caching and when the same food was cached in distinct sites at different times. The authors argue that the jays formed an integrated memory for the location and time of caching of particular foods.

The hippocampus and memory: a comparative and ethological perspective

During the past year, considerable progress has been made in our understanding of the wide-ranging functions of the hippocampus. Highlights include the development of new tasks with which to assess spatial/topographic memory in humans and monkeys, novel tests of relational memory in rats, and episodic-like memory tasks in birds. In addition, novel theories of hippocampal function have been developed that are notable for their applicability to both humans and animal models.

Rapid effects of corticosterone on cache recovery in mountain chickadees (Parus gambeli)

Environmental perturbations increase adrenal activity in several vertebrates. Increases in corticosterone may serve as a proximate trigger whereby organisms can rapidly adapt their behavior to survive environmental fluctuations. In food-caching songbirds, inclement weather may present the need to alter caching and/or retrieval behaviors to ensure food supplies. We hypothesized that corticosterone may increase the rate of caching and/or retrieval behaviors in the mountain chickadee, a food-storing songbird, and tested if these potential effects were mediated by alterations in appetite, activity, or memory for cache sites. Corticosterone or vehicle was administered to subjects 5 min prior to either caching or recovery in a naturalistic laboratory paradigm during which we recorded the number of caching events, sites visited, and seeds eaten (caching) or caches recovered, total sites visited, cache-related visits, and non-cache-related visits (recovery). Data were analyzed using nested ANOVA for treatment within sequential trial. There was no effect on any caching behaviors following treatment. However, birds treated with corticosterone during retrieval recovered more seeds and tended to visit more cache-related sites than did controls. Since groups did not differ in the number of seeds eaten or the total number of sites visited, it seems unlikely that corticosterone affected appetite or activity. Rapid surges in corticosterone may increase the efficacy of an underlying memory process for cache sites which is reflected in higher cache recovery in corticosterone-treated birds than in controls. Thus, rapid alterations in plasma corticosterone following environmental change may alter memory-reliant behaviors which promote survival in the food-caching mountain chickadee.

Scrub jays (Aphelocoma coerulescens) remember the relative time of caching as well as the location and content of their caches

Two experiments examined whether food-storing scrub jays (Aphelocoma coerulescens) could remember when they cached particular food items as well as what they cached and where. In Experiment 1, scrub jays cached and recovered perishable "wax worms" (wax moth larvae) and nonperishable peanuts in 2 visuospatially distinct and trial-unique trays. The birds searched preferentially for fresh wax worms if they had cached them 4 hr earlier but rapidly learned to search for peanuts and avoid decayed wax worms that had been cached 124 hr previously. This pattern also was observed when the food items were removed before recovery on test trials. These results were replicated in Experiment 2 using a procedure in which both types of food were cached in different sides of the same caching tray: On the basis of a single, trial-unique experience, scrub jays could remember the relative time of caching as well as what type of food was cached in each cache site.

Sexual dimorphism and species differences in HVC volumes of cowbirds

Cowbirds exhibit extensive variation in their social, territorial, and reproductive behaviors. Nissl-stained brain sections of specimens from a previous study (J. C. Reboreda, N. S. Clayton, & A. Kacelnik, 1996) were used to study the gross anatomy of a song control nucleus in 3 South American cowbirds (bay-winged, Molothrus badius; shiny, M. bonariensis; and screaming, M. rufoaxillaris). Cowbird high vocal center (HVC) volumes were consistently higher in males than in females in all 3 species. The largest HVC size of females found in bay-winged cowbirds is consistent with observations that females of this species, but not of the other 2 species, occasionally sing. The extent of the sexual dimorphism of relative HVC size was highest for the sexually dichromatic and promiscuous shiny cowbirds and smaller for the monochromatic and monogamous bay-winged and screaming cowbirds, suggesting that selection pressures associated with morphological traits and social systems are reflected in brain architecture.

Androgen metabolism in the juvenile oscine forebrain: a cross-species analysis at neural sites implicated in memory function

Juvenile songbirds are useful models for studying the neural bases of memory. Memory-reliant behaviors demonstrated at this stage include song learning (most songbirds) and food caching (food-storing songbirds). Sex steroids are implicated in the modulation of memory processes in several vertebrates. The songbird forebrain expresses aromatase, 5alpha-reductase and 5beta-reductase, enzymes which convert testosterone to estradiol, 5alpha-, and 5beta-dihydrotestosterone, respectively. To explore the role of local androgen metabolism on memory processes, we documented the activities of these enzymes in the anterior neostriatum (NAN), caudomedial neostriatum (NCM), and hippocampus (HP) of four species of juvenile songbird, two of which are food storers. Areas were dissected, homogenized, and provided with radiolabeled substrate; and formed estrogens, and 5alpha- and 5beta-reduced androgens were measured. In the NAN, 5beta-reductase was the predominant enzyme, suggesting that local inactivation of testosterone may preserve the sensitive period of song acquisition. In the NCM, estrogens were formed in abundance despite high 5beta-reductase, suggesting that locally high estrogen synthesis may play a role in processes of song perception. In the HP, both estrogens and 5alpha reduced androgens were formed, suggesting that HP function may be modulated by both estrogens and androgens. Finally, a derived measure of steroid-differential reveals that food-storing songbirds differ from nonstorers in the steroidal milleiu within the HP, but not in the NAN or NCM. Thus, distinct loci within the juvenile songbird forebrain are exposed to different patterns of androgen metabolites. This local conversion may play a role in the neuroendocrine modulation of memory in these birds.

Song behavior, NGF level and NPY distribution in the brain of adult male zebra finches

The aim of the present study was to investigate the role of nerve growth factor (NGF) and neuropeptide Y (NPY) in the higher vocal center (HVC) on singing behavior of adult male zebra finches. The results of our studies show: (a) that NGF is present in the brain of these birds and it is higher in the HVC than in the other neostriatal tissues; (b) that exogenous administration of NGF or NGF-antibody had no discernible effect on singing behavior; and (c) that NGF enhances the NPY immunoreactivity in neurons and fibers localized in HVC and other areas of the neostriatum and hippocampus whereas anti-NGF decreased NPY stained cells in the hippocampus. These studies indicate that NGF is produced in the brain of zebra finch and that it plays a role in the regulation of NPY.

Motivational control of caching behaviour in the scrub jay, Aphelocoma coerulescens

We investigated the motivational control of caching behaviour in scrub jays using a two-stage procedure to examine the effects of prefeeding and/or precaching (stage 1) on subsequent caching behaviour (stage 2). Experiment 1 demonstrated that both prefeeding and precaching reduced the subsequent caching of both edible (peanuts) and inedible (stones) items. The reduction in caching was greatest when the items available for storing were the same in the two stages. This item specificity was confirmed in experiment 2 using two food types, peanuts and dog food kibbles. The final experiment demonstrated that the effect of prefeeding on subsequent caching can also be food specific, in that birds that received food in a powdered form that they could eat, but not cache in stage 1, showed a reduction in subsequent caching in stage 2 only when the food type was the same in the two stages. These results suggest that caching behaviour is controlled by both the feeding system and an independent caching system, and that this control is mediated by the incentive value of the specific items rather than by a general motivational state. Copyright 1999 The Association for the Study of Animal Behaviour.

Analysing hippocampal function in transgenic mice: an ethological perspective

Advances in molecular genetics and technology have led to the dawn of a new era for neuroscience: manipulation of single genes now makes it possible to dissect the complexities of neurobiological phenotypes and to understand many of the intricacies of brain and behaviour, even in mammals. The phenotypical analysis of these mutant animals is complicated because the potential outcome of gene manipulation is difficult to predict. While behavioural analysis should form an integral part of any multidisciplinary research programme investigating the phenotypical effects of single genes on hippocampal function, it is crucial that the behavioural tests are designed and conducted appropriately. Approaches that take species-specific behavioural characteristics into account and use ethological methods could be the most useful for interpreting these behavioural findings and understanding the biological mechanisms of brain function.

Memory for the content of caches by scrub jays (Aphelocoma coerulescens)

To test whether scrub jays (Aphelocoma coerulescens) remember the contents of food caches, in Experiment 1 birds cached peanuts and kibbles in two distinct caching trays and recovered them 4 or 172 hr later. The relative incentive value of the foods was manipulated by prefeeding one of the foods immediately before cache recovery. Birds preferentially searched for non-prefed food caches even when the caches had been pilfered prior to the recovery test. In Experiment 2, birds cached both foods in different sites within each tray, recovering peanuts from one tray and kibbles from the other tray 3 hr later. After prefeeding with one food, birds preferentially searched tray sites in which they had cached but not retrieved the non-prefed food. Thus jays remember the specific foods they cache and recover by a mnemonic process that cannot be explained in terms of simple associations between the foods and their cache locations.

Episodic-like memory during cache recovery by scrub jays

The recollection of past experiences allows us to recall what a particular event was, and where and when it occurred, a form of memory that is thought to be unique to humans. It is known, however, that food-storing birds remember the spatial location and contents of their caches. Furthermore, food-storing animals adapt their caching and recovery strategies to the perishability of food stores, which suggests that they are sensitive to temporal factors. Here we show that scrub jays (Aphelocoma coerulescens) remember 'when' food items are stored by allowing them to recover perishable 'wax worms' (wax-moth larvae) and non-perishable peanuts which they had previously cached in visuospatially distinct sites. Jays searched preferentially for fresh wax worms, their favoured food, when allowed to recover them shortly after caching. However, they rapidly learned to avoid searching for worms after a longer interval during which the worms had decayed. The recovery preference of jays demonstrates memory of where and when particular food items were cached, thereby fulfilling the behavioural criteria for episodic-like memory in non-human animals.

Memory and the hippocampus in food-storing birds: a comparative approach

Comparative studies provide a unique source of evidence for the role of the hippocampus in learning and memory. Within birds and mammals, the hippocampal volume of scatter-hoarding species that cache food in many different locations is enlarged, relative to the remainder of the telencephalon, when compared with than that of species which cache food in one larder, or do not cache at all. Do food-storing species show enhanced memory function in association with the volumetric enlargement of the hippocampus? Comparative studies within the parids (titmice and chickadees) and corvids (jays, nutcrackers and magpies), two families of birds which show natural variation in food-storing behavior, suggest that there may be two kinds of memory specialization associated with scatter-hoarding. First, in terms of spatial memory, several scatter-hoarding species have a more accurate and enduring spatial memory, and a preference to rely more heavily upon spatial cues, than that of closely related species which store less food, or none at all. Second, some scatter-hoarding parids and corvids are also more resistant to memory interference. While the most critical component about a cache site may be its spatial location, there is mounting evidence that food-storing birds remember additional information about the contents and status of cache sites. What is the underlying neural mechanism by which the hippocampus learns and remembers cache sites? The current mammalian dogma is that the neural mechanisms of learning and memory are achieved primarily by variations in synaptic number and efficacy. Recent work on the concomitant development of food-storing, memory and the avian hippocampus illustrates that the avian hippocampus may swell or shrivel by as much as 30% in response to presence or absence of food-storing experience. Memory for food caches triggers a dramatic increase in the total number of number of neurons within the avian hippocampus by altering the rate at which these cells are born and die.

Spatial learning induces neurogenesis in the avian brain

It is known from previous work that neurones are born continuously in the ventricular zone of the bird brain. In this study, we show that the amount of cell proliferation in the ventricular zone of the hippocampus (HP) and the hyperstriatum ventrale (HV) is influenced by behavioural experience. Two groups of birds (marsh tits) were compared: those allowed to store and retrieve food once every 3 days between days 35 and 56, and age-matched controls treated in an identical way, except that they were not allowed to store and retrieve food. After three trials of storing and retrieval, between days 35 and 41 posthatch, experienced birds showed a significantly higher rate of cell proliferation than did controls. The experienced birds also showed a significant increase in total cell and neuronal number by day 56 posthatch, after eight trials of storing and retrieval. There were no significant differences in the amount of programmed cell death in the hippocampus in this study. In a novel analysis of the data we demonstrate that the effect of experience between days 35 and 41 was to increase the daily rate of neurogenesis in the ventricular zone from 3.9 to 10%, and that this change could account for the increase in total hippocampal neuronal number by day 56 in the experienced birds. Thus, the observed increase in hippocampal volume and neuronal number as a result of food storing and retrieval, may be caused by an increase in neurogenesis in the first few trials of food storing experience.

Hippocampal tissue transplants reverse lesion-induced spatial memory deficits in zebra finches (Taeniopygia guttata)

The avian hippocampal formation (Hf) plays an important role in spatial memory for food storing. Here we examined the effects of excitotoxic lesions of the Hf and subsequent neural transplantation on a one-trial associative memory task in zebra finches. The results showed (1) that small ibotenic acid lesions of the dorsal Hf of zebra finches produced significant spatial memory impairments compared with controls, sham-lesioned birds, and prelesion performance; and (2) that Hf-lesioned birds given transplants of embryonic hippocampal (H) tissue, but not those given transplants of embryonic anterior telencephalon (AT) tissue, showed a significant reversal of the performance deficits on the spatial memory task. Lesioned-only birds and lesioned birds given H or AT transplants that did not survive did not show behavioral improvement. Sham-lesioned and untreated control birds maintained good performance throughout the experiment. The H and AT transplants were found to be growing partially within the Hf and partially within the underlying ventricle. The transplants appeared healthy and contained neurons with beaded and unbeaded fibers (shown by immunohistochemistry with antibodies to parvalbumin, substance P, and a 200 kDa neurofilament protein). Blood vessels and erythrocytes were also present within the transplants. The results show that neural transplants can survive within the bird brain and that small lesions of the Hf produce significant spatial memory deficits that can only be reversed by surviving homologous H transplants, and not by heterologous telencephalon transplants.

Nerve growth factor effects on the song control system of zebra finches

The aim of this experiment was to test whether or not nerve growth factor (NGF) is involved in cholinergic processes in the avian brain, by injecting NGF into the higher vocal center (HVC) and examining its effects on adult male zebra finch song. Since NGF has been hypothesized to protect cells after injury, some birds received both NGF and ibotenic acid (IBO) lesions of HVC, while others received either NGF or IBO or neither (SHAM). Only the IBO-treated birds showed alterations in song. Although there was no evidence of cell preservation in the immunocytochemical and morphological analysis NGF appears to prevent the IBO induced impairment in song augmenting the activity of the remaining neurons and enhancing brain repair.

Species and sex differences in hippocampus size in parasitic and non-parasitic cowbirds

To test the hypothesis that selection for spatial abilities which require birds to locate and to return accurately to host nests has produced an enlarged hippocampus in brood parasites, three species of cowbird were compared. In shiny cowbirds, females search for host nests without the assistance of the male; in screaming cowbirds, males and females inspect hosts' nests together; in bay-winged cowbirds, neither sex searches because this species is not a brood parasite. As predicted, the two parasitic species had a relatively larger hippocampus than the non-parasitic species. There were no sex differences in relative hippocampus size in screaming or bay-winged cowbirds, but female shiny cowbirds had a larger hippocampus than the male.

Development of food-storing and the hippocampus in juvenile marsh tits (Parus palustris)

Food-storing birds, e.g., marsh tits, Parus palustris, use memory to retrieve stored food and have a larger hippocampus relative to the rest of the telencephalon than do species that store little or no food, e.g., blue tits, P. caeruleus. The difference in relative hippocampal volume arises after the young have fledged from the nest and recent work on the dual ontogeny of the hippocampus and memory in hand-raised marsh tits suggests that the hippocampal growth depends upon some aspect of the experience of storing and retrieving food. The aim of this experiment was to test whether hippocampal growth precedes or accompanies changes in food-storing behaviour. Hand-raised marsh tits were provided with the opportunity to store and retrieve food every third day from day 35 post-hatch and the volume of the hippocampus and remainder of the telencephalon was measured and compared with those of age-matched controls at three different stages (days 41, 47 and 56 post-hatch). Experience had no significant effect on telencephalon volume but experienced birds had larger absolute and relative hippocampal volumes than did controls at all stages of the experiment, even before the increase in food-storing intensity on day 44. The stage at which the birds were killed had a significant effect on the absolute volume of both the hippocampus and telencephalon but there was no significant interaction between experience and stage. The results suggest that both hippocampus and telencephalon continue to increase in volume between days 35 and 56 but that the hippocampus shows a additional increase in volume relative to telencephalon in the experienced groups. One interpretation of these results is that the one or two seeds stored before day 44 may have been sufficient to stimulate the growth of the hippocampus and that there is an increase in relative hippocampal volume in preparation for the increased memory demands associated with the sharp increase in food-storing.

The neuroethological development of food-storing memory: a case of use it, or lose it!

Some species of birds that scatter-hoard food e.g. marsh tits, Parus palustris, use memory to retrieve stored food. These scatter-hoarding species have a larger hippocampus relative to the rest of the telencephalon than do species that store little or no food e.g. blue tits, P. caeruleus. The difference in relative hippocampal volume arises after the young have fledged from the nest and recent work on the dual ontogeny of the hippocampus and memory in hand-raised marsh tits suggests that some aspect of memory for retrieving food (whether or not stored by the bird) can stimulate hippocampal growth in juveniles at a relatively late stage in their development.

Effects of photoperiod on food-storing and the hippocampus in birds

Birds that store food have a relatively large hippocampus compared to non-storing species. The hippocampus shows seasonal differences in neurogenesis and volume in black-capped chikadees (Parus atricapillus) taken from the wild at different times of year. We compared hippocampal volumes in black-capped chickadees captured at the same time but differing in food-storing behaviour because of manipulations of photoperiod in the laboratory. Differences in food-storing behaviour were not accompanied by differences in the volume of the hippocampus. Hippocampal volumes also did not differ between two groups of a non-food-storing control species, house sparrows (Passer domesticus), exposed to the same conditions as the chickadees.

Development of memory and the hippocampus: comparison of food-storing and nonstoring birds on a one-trial associative memory task

Food-storing birds, for example, marsh tits, Parus palustris, use memory to retrieve stored food and have a larger hippocampus relative to the rest of the telencephalon than do species that store little or no food such as the blue tit, P. caeruleus. The difference between food storers and nonstorers in relative hippocampal volume occurs after the young birds have fledged from the nest and is dependent upon some aspect of memory for retrieving caches of stored food. To test whether or not species differences in memory and volumetric changes in the hippocampus could be triggered by experience of memory tasks other than retrieval of stored food, groups of hand-raised marsh tits and blue tits were tested between days 35 and 192 posthatch on a one-trial associative memory task in which they were rewarded in phase II for returning to the feeder where they had eaten part of a peanut 20 min earlier. No species differences were found when the peanut was visible in phase I, but when the peanut was hidden in phase I, marsh tits performed better than blue tits, irrespective of whether or not they had had previous experience of storing and retrieving food. In dissociation trials (transformed array of feeders), marsh tits with food-storing experience responded preferentially to spatial cues, whereas blue tits responded equally to both spatial position and object-specific cues. These species differences are also found in wild-caught adults. However, marsh tits without food-storing experience responded equally to both spatial position and object-specific cues, which suggests that experience of storing and/or retrieving caches is required in order for marsh tits to develop the spatial preference seen in adult food storers. Both marsh tits with experience of the one-trial associative memory task and those that had also had food-storing experience had larger relative hippocampal volumes than did controls, independent of age. Of the marsh tits trained on the one-trial associative memory task, there was no difference between those that had had food-storing experience and those that had not. However, in blue tits, there was no effect of experience on relative hippocampal volume. No volumetric differences were observed in ectostriatum, which served as a control brain region. The results suggest that some aspect of memory for retrieving food (whether or not stored by the bird) directly influences growth of the hippocampal region in marsh tits, the food-storing species, but not in blue tits, the nonstoring species.

Memory in food-storing birds: from behaviour to brain

As a result of natural history studies, it has been hypothesized that food-storing birds may develop a special kind of memory to cope with the demand imposed by their food-storing behaviour (i.e. the ability to retrieve food from a wide variety of stores over varying amounts of time after storage). Recent studies on food-storing birds suggest that, at a relatively late stage in their development, the specific memories associated with food-storing behaviour can stimulate growth of the hippocampus, an area of the brain concerned with memory processing.

Comparative studies of food-storing, memory, and the hippocampal formation in parids

Birds which scatter-hoard large numbers of food items such as marsh tits, Parus palustris, use memory to retrieve their caches and have an enlarged hippocampal formation relative to the rest of the telencephalon compared with species that store little or no food. Preliminary observations suggested that captive blue tits, P. caeruleus, may store small quantities of food albeit in limited amounts. This experiment compared food-storing intensity, memory for cache sites, and relative hippocampal formation in marsh tits and blue tits. Comparisons were made both within species, by comparing wild-caught adults and hand-raised juvenile blue tits that store and those that do not, and between closely related species, by comparing food-storing adult wild-caught blue tits and juvenile hand-raised blue tits with adult wild-caught marsh tits. Food-storing blue tits stored fewer seeds than did marsh tits, and they had a less accurate memory for cache sites and a smaller absolute and relative hippocampal formation than did marsh tits. For further analysis, the hippocampal volume was divided into a rostral (front) portion and a caudal (rear) portion, separated by the first appearance of the anterior commissure. Marsh tits had both larger rostral and caudal portions than did blue tits, but the species difference in hippocampal volume was greater for the rostral than for the caudal portion. In blue tits, wild-caught adults had significantly larger absolute and relative hippocampal volumes than did hand-raised juveniles, but there was no difference in the proportion of rostral to caudal portions, irrespective of whether they had stored and retrieved food. Although food-storing blue tits did not differ from non-storing blue tits in total absolute or relative hippocampal volume, they had larger rostral portions of the hippocampal formation and small caudal portions. Possible reasons for this are discussed.

Hippocampal growth and attrition in birds affected by experience

Hand-raised marsh tits (Parus palustris) were exposed to experience of storing and retrieving food at three different ages (35-59, 60-83, 115-138 days posthatch). At equivalent ages, control birds were given identical experience except for storing and retrieving food. Volumetric analysis was carried out to measure the hippocampal region, ectostriatum, and telencephalon of experienced and control birds. Individuals with experience of storing and retrieving food had a larger hippocampal region relative to the rest of the telencephalon than did controls, independent of age. The hippocampal region of experienced birds also contained more neurons and fewer apoptotic cells than that of controls. No volumetric differences were observed in ectostriatum, which served as a control brain region. The results suggest that some aspect of food-storing and retrieval directly influences growth and attrition of the hippocampal region in food-storing birds.

Development of hippocampal specialisation in two species of tit (Parus spp.)

Food storing birds have been shown to have a larger hippocampus, relative to the rest of the telencephalon, than do non-storers. A previous study reported that this difference in relative hippocampal volume is not apparent in a comparison of nestling birds, but emerges after birds have fledged. This conclusion was based on a comparison of a storing and a non-storing species in the corvid family. The present study compared another storer/non-storer pair of species in order to test whether the results of the previous study can be replicated in another family of birds. The volumes of the hippocampal region and remainder of the telencephalon were measured and estimates of neuron size, density and total number in the hippocampal region were made for nestlings and adults of the food-storing marsh tit Parus palustris and non-storing blue tit Parus caeruleus. Relative hippocampal volume did not differ between nestlings of the two species, whilst the relative hippocampal volume of adult marsh tits was greater than that of blue tits. The difference between adults arose because in marsh tits but not blue tits, adults had a significantly larger relative hippocampal volume than did nestlings. Neuron density was significantly higher in both species in nestlings than in adults and adult blue tits had fewer neurons than did adult marsh tits. The results of this study are largely consistent with the earlier study comparing a storing and non-storing species of corvid, suggesting that the observed patterns may reflect a general difference between storers and non-storers in the development of the hippocampal region.