Neural cytoskeleton capabilities for learning and memory

This paper proposes a physical model involving the key structures within the neural cytoskeleton as major players in molecular-level processing of information required for learning and memory storage. In particular, actin filaments and microtubules are macromolecules having highly charged surfaces that enable them to conduct electric signals. The biophysical properties of these filaments relevant to the conduction of ionic current include a condensation of counterions on the filament surface and a nonlinear complex physical structure conducive to the generation of modulated waves. Cytoskeletal filaments are often directly connected with both ionotropic and metabotropic types of membrane-embedded receptors, thereby linking synaptic inputs to intracellular functions. Possible roles for cable-like, conductive filaments in neurons include intracellular information processing, regulating developmental plasticity, and mediating transport. The cytoskeletal proteins form a complex network capable of emergent information processing, and they stand to intervene between inputs to and outputs from neurons. In this manner, the cytoskeletal matrix is proposed to work with neuronal membrane and its intrinsic components (e.g., ion channels, scaffolding proteins, and adaptor proteins), especially at sites of synaptic contacts and spines. An information processing model based on cytoskeletal networks is proposed that may underlie certain types of learning and memory.     

Evolutionary ecology of learning: insights from fruit flies

Ecologically and evolutionarily oriented research on learning has traditionally been carried out on vertebrates and bees. While less sophisticated than those animals, fruit flies (Drosophila) are capable of several forms of learning, and have the advantage of a short generation time, which makes them an ideal system for experimental evolution studies. This review summarizes the insights into evolutionary questions about learning gained in the last decade from evolutionary experiments on Drosophila. These experiments demonstrate that Drosophila has the genetic potential to evolve a substantially improved learning performance in ecologically relevant learning tasks. In at least one set of selected populations, the improved learning generalized to a task other than that used to impose selection, involving a different behavior, different stimuli, and a different sensory channel for the aversive reinforcement. This improvement in learning ability was associated with reductions in other fitness-related traits, such as larval competitive ability and lifespan, pointing to evolutionary trade-offs for improved learning. These trade-offs were confirmed by other evolutionary experiments where a reduction in learning performance was observed as a correlated response to selection for tolerance to larval nutritional stress or for delayed aging. Such trade-offs could be one reason why fruit flies have not fully used up their evolutionary potential for learning. Finally, another evolutionary experiment with Drosophila provided the first direct evidence for the long-standing idea that learning can under some circumstances accelerate and in others slow down genetically based evolutionary change. These results demonstrate the usefulness of fruit flies as a model system to address evolutionary questions about learning.     

胚胎期光照和皮质酮处理对日龄小鸡记忆的作用

该实验对胚胎发育后期的鸡胚进行光孵化,暗孵化以及药物注射处理后,采用一次性味觉被动回避行为模式观察它们对出生后小鸡记忆保持的影响并对其作用机制进行了初步探讨,结果表明胚胎期光照可增强小鸡记忆的保持,使用糖皮质激素受体拮抗剂可阻断光照对小鸡记忆的增强作用,对暗孵化鸡胚注射皮质酮可以促进出生后小鸡记忆的保持,因此皮质酮可能能与光照对小鸡记忆的增强过程,蛋白合成抑制剂在一定程度上阻断皮质醇对小鸡记忆的增     

Differential role of the hippocampus, amygdala, and dorsal raphe nucleus in regulating feeding, memory, and anxiety-like behavioral responses to ghrelin

Ghrelin is a peptide hormone produced and secreted from the stomach. Hypothalamic injection of the peptide increases food intake but it is not known if the peptide affects other brain regions. We measured several behavioral parameters such as anxiety (elevated plus maze), memory retention (step down test), and food intake after injections of different doses of the peptide in the hippocampus, amygdala, and dorsal raphe nucleus (DRN). The injection of ghrelin in the hippocampus and DRN significantly and dose dependently increased food intake in relation to controls rats, while injections into the amygdala did not affect the food intake. We also show for the first time that ghrelin clearly and dose dependently increases memory retention in the hippocampus, amygdala, and DRN. Moreover, ghrelin at different potencies induced anxiogenesis in these brain structures while the highest dose of 3 nmol/microl was effective in all of them. The comparison of sensitivity of each brain structure indicates a specific role of them for each of the behaviors studied. The results provide new insight in to the anatomical substrate and the functional role of extrahypothalamic ghrelin targets in the CNS.     

Memory and effector T cells modulate subsequently primed immune responses to unrelated antigens

Memory and effector T cells modulate subsequently primed T cell responses to the same antigen. However, little is known about the impact of pre-existing memory and effector T cell immunity on subsequently primed immune responses to unrelated antigens. Here, we show that an antigen-primed first wave of Th1 and Th2 immunity enhanced or inhibited the subsequently primed T cell immunity to an unrelated antigen, depending on whether the second antigen was administered in the same or opposite type of adjuvant. The regulatory effects of the first wave of T cell immunity on the subsequent T cell responses to an unrelated antigen attenuated over time. Notably, following challenge with the second antigen, there was a mutual cross-regulation between the first and second wave of humoral responses to unrelated antigens. Thus, immunization with one antigen not only primes immune responses to that antigen, but also influences subsequently primed immune responses to unrelated antigens.     

Prior exposure to a single stress session facilitates subsequent contextual fear conditioning in rats. Evidence for a role of corticosterone

Previous studies showed that exposure of rats to chronic restraint stress for 21 days enhances subsequent contextual fear conditioning. Since recent evidence suggest that this effect is not dependent on stress-induced neurodegenerative processes, but to elevated training-elicited glucocorticoid release in chronically stressed animals, we aimed to explore here whether a single exposure to restraint stress, which is not expected to induce neuronal damage, would also affect contextual fear conditioning. We also questioned whether post-training corticosterone levels might be associated with any potential effect of stress on fear conditioning. Adult male Wistar rats were exposed to acute restraint stress for 2 h and, two days later, trained in the contextual fear conditioning task, under training conditions involving either moderate (0.4 mA shock) or high (1 mA shock) stress levels. The results showed that acute stress enhanced conditioned freezing at both training conditions, although data from the 1 mA shock intensity experiment only approached significance. Stressed animals were shown to display higher post-training corticosterone levels. Furthermore, the facilitating effect of prior stress was not evident when animals were trained in the hippocampal-independent auditory-cued conditioning task. Therefore, these findings support the idea that stress experiences preceding exposure to new types of stressors facilitate the development of contextual fear conditioning. They also indicate that not only repeated, but also a single exposure to aversive stimulation is sufficient to facilitate context-dependent fear conditioning, and suggest that increased glucocorticoid release at training might be implicated in the mechanisms mediating the memory facilitating effects induced by prior stress experiences.     

Models of distributed associative memory networks in the brain

Summary Although experimental evidence for distributed cell assemblies is growing, theories of cell assemblies are still marginalized in theoretical neuroscience. We argue that this has to do with shortcomings of the currently best understood assembly theories, the ones based on formal associative memory models. These only insufficiently reflect anatomical and physiological properties of nervous tissue, and their functionality is too restricted to provide a framework for cognitive modeling. We describe cell assembly models that integrate more neurobiological constraints and review results from simulations of a simple nonlocal associative network formed by a reciprocal topographic projection. Impacts of nonlocal associative projections in the brain are discussed with respect to the functionality they can explain.     

Vaccinology for control of apicomplexan parasites: a simplified language of immune programming and its use in vaccine design

Most mammalian immune systems and parasites have co-evolved over the millennia, interacting within a common environment and communicating through a common language. This language is comprised of copious dialects in which a variety of host innate and acquired immune pathways actively interact with a multitude of parasite-specific survival strategies. Nonetheless, a simplified language is likely present since the same basic molecular and cellular mechanisms are associated with resistance or susceptibility to parasite infection. Protective immunity against protozoa within the phylum Apicomplexa (e.g. Cryptosporidia, Eimeria, Neospora, Plasmodia and Toxoplasma) is generally CD4+ T cell-dependent and elicited along the IL-12/IFN-gamma/iNOS effector axis. This simplified language can be decoded in part by significant advances in understanding na?ve T cell activation, differentiation and generation of immunologic memory. Vaccine adjuvants and new immunisation strategies for generation of more potent immunity can also be viewed through this common language lens. The aim of this paper is to summarise recently published fundamental immunology studies, their relevance through examples in specific coccidian-host immune dialects, and how this simplified language can be used for the more rationale design of parasite vaccine control strategies.     

海马记忆功能的神经网络模型

综合神经心理学,神经生理学、解剖学与神经网络研究的成果,提出一个海马记忆功能的神经网络模型。模型由三个神经网络所组成;海马的ＣＡ１和ＣＡ３网络和大脑皮层联合区,ＣＡ３的功能是将不同感觉输入联合起来,而ＣＡ１的作用是将它们结成一个单一的记忆。而大脑皮层则是长期记忆的部位。在ＶＡＸ１１／７５０上进行计算机仿真,仿真证明模型有近期及长期记忆功能,破坏模拟海马的部分,模型显示出与顺行性遗忘症相似的特性。在     

Sequence learning by honeybees

Bees of several genera make foraging trips on which they visit a series of plants in a fixed order. To help understand how honeybees might acquire such routes, we examined whether (1) bees learn motor sequences, (2) they link motor instructions to visual stimuli, (3) their visual memories are triggered by contextual cues associated with the bees' position in a sequence.