Plasticity and behavior: new genetic techniques to address multiple forms and functions

Inhibition of brain NOS activity impair spatial learning acquisition in fish

Nitric oxide plays a role in the long term potentiation mechanisms produced in the mammalian hippocampus during spatial learning. A great deal of data has demonstrated that the dorsolateral telencephalon of fish could be homologous to the mammalian hippocampus sharing functional similarities. In the present study, we analyzed the role of nitric oxide in spatial learning in teleost fish. In Experiment 1, we studied the effects of the inhibition of telencephalic nitric oxide in goldfish during the acquisition of a spatial task. The results showed that nitric oxide is involved in the learning of a spatial task. Experiment 2 evaluated the effects of the inhibition of telencephalic nitric oxide in goldfish for the retrieval of a learned spatial response. The results indicated that the retrieval of the information previously stored is not dependent of the nitric oxide. The last experiment analyzed the role of the telencephalic nitric oxide in place and cue learning. Results showed a clear impairment in place but not in cue learning. As a whole, these results indicate that fish and mammals, could have a relational memory system mediated by similar biochemical mechanisms.

Regulation of hippocampus-dependent memory by the zinc finger protein Zbtb20 in mature CA1 neurons

The mammalian hippocampus harbours neural circuitry that is crucial for associative learning and memory. The mechanisms that underlie the development and regulation of this complex circuitry are not fully understood. Our previous study established an essential role for the zinc finger protein Zbtb20 in the specification of CA1 field identity in the developing hippocampus. Here, we show that conditionally deleting Zbtb20 specifically in mature CA1 pyramidal neurons impaired hippocampus-dependent memory formation, without affecting hippocampal architecture or the survival, identity and basal excitatory synaptic activity of CA1 pyramidal neurons. We demonstrate that mature CA1-specific Zbtb20 knockout mice exhibited reductions in long-term potentiation (LTP) and NMDA receptor (NMDAR)-mediated excitatory post-synaptic currents. Furthermore, we show that activity-induced phosphorylation of ERK and CREB is impaired in the hippocampal CA1 of Zbtb20 mutant mice. Collectively, these results indicate that Zbtb20 in mature CA1 plays an important role in LTP and memory by regulating NMDAR activity, and activation of ERK and CREB.

Intrauterine environment-genome interaction and children's development (4): Brain-behavior phenotypying of genetically-engineered mice using a comprehensive behavioral test battery on research of neuropsychiatric disorders

Despite massive research efforts, the exact pathogenesis and pathophysiology of psychiatric disorders, such as schizophrenia and bipolar disorder, remain largely unknown. Animal models can serve as essential tools for investigating the etiology and treatment of such disorders. Some mutant mouse strains were found to exhibit behavioral abnormalities reminiscent of human psychiatric disorders. Here we outline our unique approach of extrapolating findings in mice to humans, and present studies on alpha-CaMKII heterozygous knockout (alpha-CaMKII+/-) mice as examples. Alpha-CaMKII+/- mice have profoundly dysregulated behavior and impaired neuronal development in the dentate gyrus (DG). The behavioral abnormalities include a severe working memory deficit and an exaggerated infradian rhythm, which are similar to symptoms seen in schizophrenia, bipolar mood disorder and other psychiatric disorders. By conducting a series of experiments, we discovered that almost all the neurons in the mutant DG were very similar to the immature DG neurons of normal rodents. In other words, alpha-CaMKII+/- mice have an "immature DG". We proposed that an "immature DG" in adulthood might induce alterations in behavior and serve as a promising candidate endophenotype of schizophrenia and other human psychiatric disorders. The impact of a large-scale mouse phenotyping on studies of psychiatric disorders and the potential utility of an "animal-model-array" of psychiatric disorders for the development of suitable therapeutic agents is also discussed.

Impact of brain-behavior phenotypying of genetically-engineered mice on research of neuropsychiatric disorders

Despite massive research efforts, the exact pathogenesis and pathophysiology of psychiatric disorders, such as schizophrenia and bipolar disorder, remain largely unknown. Animal models can serve as essential tools for investigating the etiology and treatment of such disorders. Since the introduction of gene targeting techniques, the functions of more than 10% of all known mouse genes have been investigated by creating mutant mice. Some of these mutant mouse strains were found to exhibit behavioral abnormalities reminiscent of human psychiatric disorders. In this review, we discuss the general requirements for animal models of human psychiatric disorders. We also outline our unique approach of extrapolating findings in mice to humans, and present studies on forebrain-specific calcineurin knockout mice as an example. We also discuss the impact of a large-scale mouse phenotyping on studies of psychiatric disorders and the potential utility of an "animal-model-array" of psychiatric disorders for the development of suitable therapeutic agents.

Two forms of long-term potentiation induced by different compounds

The purpose of this study was to investigate different forms of long-term potentiation (LTP) induced by different compounds. As shown in results, the influx of calcium via voltage-dependent calcium channels (VDCCs) was responsible for ( - )-clausenamide-induced LTP in hippocampus, while Rg1 induced LTP is mediated by the entry of calcium via N-methyl-d-aspartate glutamate (NMDA) receptor. The findings in the present study provide pharmacological basis for the nootropic mechanisms of these two compounds.

The pharmacology, neuroanatomy and neurogenetics of one-trial object recognition in rodents

Rats and mice are attracted by novel objects. They readily approach novel objects and explore them with their vibrissae, nose and forepaws. It is assumed that such a single explorative episode leaves a lasting and complex memory trace, which includes information about the features of the object explored, as well as where and even when the object was encountered. Indeed, it has been shown that rodents are able to discriminate a novel from a familiar object (one-trial object recognition), can detect a mismatch between the past and present location of a familiar object (one-trial object-place recognition), and can discriminate different objects in terms of their relative recency (temporal order memory), i.e., which one of two objects has been encountered earlier. Since the novelty-preference paradigm is very versatile and has some advantages compared to several other memory tasks, such as the water maze, it has become a powerful tool in current neurophamacological, neuroanatomical and neurogenetical memory research using both rats and mice. This review is intended to provide a comprehensive summary on key findings delineating the brain structures, neurotransmitters, molecular mechanisms and genes involved in encoding, consolidation, storage and retrieval of different forms of one-trial object memory in rats and mice.

Brain plasticity: From pathophysiological mechanisms to therapeutic applications

Cerebral plasticity, which is the dynamic potential of the brain to reorganize itself during ontogeny, learning, or following damage, has been widely studied in the last decade, in vitro, in animals, and also in humans since the development of functional neuroimaging. In the first part of this review, the main hypotheses about the pathophysiological mechanisms underlying plasticity are presented. At a microscopic level, modulations of synaptic efficacy, unmasking of latent connections, phenotypic modifications and neurogenesis have been identified. At a macroscopic level, diaschisis, functional redundancies, sensory substitution and morphological changes have been described. In the second part, the behavioral consequences of such cerebral phenomena in physiology, namely the "natural" plasticity, are analyzed in humans. The review concludes on the therapeutic implications provided by a better understanding of these mechanisms of brain reshaping. Indeed, this plastic potential might be 'guided' in neurological diseases, using rehabilitation, pharmacological drugs, transcranial magnetic stimulation, neurosurgical methods, and even new techniques of brain-computer interface - in order to improve the quality of life of patients with damaged nervous systems.

PolyADP-ribose polymerase-1 (PARP-1) and the evolution of learning and memory

PARP-1 is a multifunctional enzyme that can modulate gene expression. Cohen-Armon et al.(1) found that a homologue of PARP-1 is activated in the Aplysia nervous system as the animal responds to an aversive stimulus, which leads to sensitization, and during a more complex form of learning that involves feeding behavior. Significantly, inhibiting PARP-1 activation blocked the learning. Several key pathways in Aplysia neurons are activated both during learning and after injury, suggesting that mechanisms of learning evolved from primitive responses to injury. Since PARP-1 is evolutionarily conserved as a responder to various forms of stress, the finding that PARP-1 is activated during learning supports this idea.

New life in an old idea: the synaptic plasticity and memory hypothesis revisited

The notion that changes in synaptic efficacy underlie learning and memory processes is now widely accepted, although definitive proof of the synaptic plasticity and memory hypothesis is still lacking. This article reviews recent evidence relevant to the hypothesis, with particular emphasis on studies of experience-dependent plasticity in the neocortex and hippocampus. In our view, there is now compelling evidence that changes in synaptic strength occur as a consequence of certain forms of learning. A major challenge will be to determine whether such changes constitute the memory trace itself or play a less specific supporting role in the information processing that accompanies memory formation.

beta 2 nicotinic acetylcholine receptor subunit modulates protective responses to stress: A receptor basis for sleep-disordered breathing after nicotine exposure

Nicotine exposure diminishes the protective breathing and arousal responses to stress (hypoxia). By exacerbating sleep-disordered breathing, this disturbance could underpin the well established association between smoking and the increased risk of sudden infant death syndrome. We show here that the protective responses to stress during sleep are partially regulated by particular nicotinic acetylcholine receptors (nAChRs). We compared responses of sleeping wild-type and mutant mice lacking the beta2 subunit of the nAChR to episodic hypoxia. Arousal from sleep was diminished, and breathing drives accentuated in mutant mice indicating that these protective responses are partially regulated by beta2-containing nAChRs. Brief exposure to nicotine significantly reduced breathing drives in sleeping wild-type mice, but had no effect in mutants. We propose that nicotine impairs breathing (and possibly arousal) responses to stress by disrupting functions normally regulated by beta2-containing, high-affinity nAChRs.