Summary Neuromodulation of arousal states ensures that an animal appropriately responds to its environment and engages in behaviors necessary for survival. However, the molecular and circuit properties underlying neuromodulation of arousal states such as sleep and wakefulness remain unclear. To tackle this challenge in a systematic and unbiased manner, we performed a genetic overexpression screen to identify genes that affect larval zebrafish arousal. We found that the neuropeptide neuromedin U (Nmu) promotes hyperactivity and inhibits sleep in zebrafish larvae, whereas nmu mutant animals are hypoactive. We show that Nmu-induced arousal requires Nmu receptor 2 and signaling via corticotrophin-releasing hormone (Crh) receptor 1. In contrast to previously proposed models, we find that Nmu does not promote arousal via the hypothalamic-pituitary-adrenal axis, but rather likely acts via brainstem crh-expressing neurons. These results reveal an unexpected functional and anatomical interface between the Nmu system and brainstem arousal systems that represents a novel wake-promoting pathway.

In adult primary visual cortex (V1), dendritic spines are more persistent than during development. Brain-derived neurotrophic factor (BDNF) increases synaptic strength, and its levels rise during cortical development. We therefore asked whether postsynaptic BDNF signaling through its receptor TrkB regulates spine persistence in adult V1. This question has been difficult to address because most methods used to alter TrkB signaling in vivo affect cortical development or cannot distinguish between pre-and postsynaptic mechanisms. We circumvented these problems by employing transgenic mice expressing a dominant negative TrkB-EGFP fusion protein in sparse pyramidal neurons of the adult neocortex and hippocampus, producing a Golgi-staining-like pattern. In adult V1, expression of dominant negative TrkB-EGFP resulted in reduced mushroom spine maintenance and synaptic efficacy, accompanied by an increase in long and thin spines and filopodia. In contrast, mushroom spine maintenance was unaffected in CA1, indicating that TrkB plays fundamentally different roles in structural plasticity in these brain areas.adult cortical plasticity ͉ BDNF signaling ͉ synapse stability ͉ transgenic mice D uring development, synapse formation and elimination are regulated by molecular cues, spontaneous activity, and experience (1, 2). Most glutamatergic synapses on excitatory neurons are situated on dendritic spines. Live imaging of neurons expressing GFP has provided important information on the dynamics of spine formation and maintenance (3-8). Filopodia are short-lived fingershaped protrusions and believed to be precursors of dendritic spines (9, 10). Newly formed spines are often thin or long and appear and disappear within days. Some mature into mushroom or stubby spines, which are more stable and often persist for months (7,8). There are strong correlations between spine size, spine persistence, synaptic efficacy, and the number of ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs) at the postsynaptic density (8,11,12). With development and aging of the cortex, there is a shift toward larger and more persistent spine types (3,7,13).Spine dynamics are influenced by plasticity. Long-term potentiation in hippocampus is associated with an increase in spine size (14) and spine formation (15), whereas term depression is associated with spine elimination (16). Interestingly, reducing synaptic input results in an increase in spine numbers, probably due to homeostatic mechanisms (17)(18)(19).Ocular dominance plasticity in V1 is associated with initial pruning and later formation and stabilization of spines (20,21) and occurs predominantly during a critical period of development. Maturation of the extracellular matrix is a major factor in ending the critical period, probably by increasing spine and axon stability (20)(21)(22) BDNF signaling through TrkB receptors is a key player in visual plasticity (23,24). It drives the development of inhibitory innervation, an important factor in ocular dominance plasticity (25,26). BDNF is...

2The limits of visual acuity and contrast sensitivity are set by the eye, but what we perceive is determined by the visual cortex 1 . In healthy, mature people and animals, the visual acuities of the retina and the cortex are well-matched 2 , but this match is neither automatic nor unbreakable. Differences between cortical and retinal acuity are most apparent during development, when cortical acuity continues to rise after retinal development is completed 3 , and during aging, when behavioral acuity falls even without obvious changes in the eye or the thalamus 4 . Differences also occur as a result of cortical injury or erroneous development. This is the case with amblyopia, the most prevalent (2-4%) visual impairment in young people. Amblyopia is a reduced psychophysical acuity in one or both eyes. It is believed to be caused by deficient processing in the visual cortex 5 , but the mechanisms underlying the dissociations of retinal and cortical acuity in amblyopia and in the healthy aging and developing brain are unclear. Interestingly, there is a good match between changes in the cortical expression level of brain-derived neurotrophic factor (BDNF) and changes in visual acuity.During development, acuity and BDNF levels rise 6 , while both slowly decrease with age 4,7 . This relationship between BDNF and acuity also holds for experimentally induced amblyopia. BDNF mRNA and protein levels 8,9 and acuity 10 in the primary visual cortex (V1) responding to a monocularly deprived eye are all below normal. In amblyopic rats receiving environmental enrichment 11 or antidepressant treatment 12 , increased BDNF expression in the cortex was seen in parallel to the restoration of visual acuity. Moreover, transgenic mice overexpressing BDNF in the forebrain show a faster rise of cortical acuity 6 even when reared in darkness 13 . Although there is a wealth of data on the involvement of BDNF and its main receptor TrkB in neuronal development 14 , synaptic efficacy 15 , -morphology 16 and -plasticity 17,18 , it has remained unknown how BDNF promotes visual acuity at the coding level and whether BDNF signaling plays a role in acuity in the mature cortex. For these reasons we studied visual acuity in adult transgenic mice where, after normal development is completed, cortical TrkB/BDNF signaling is impaired. We found a loss of acuity, caused by a reduction in apparent contrast. Using a combination of experiments and modeling, we show the involvement of cortical gain control in the selective loss of responses to visual stimuli with high spatial frequencies and the maintenance of responses to low spatial frequencies. RESULTS Genetic inhibition of TrkB signaling in the adult cortexTo investigate the role of TrkB signaling in cortical acuity in the mature animal we overexpressed a dominant negative TrkB.T1-EGFP fusion protein 19 in a large proportion of pyramidal cells after the maturation of cortical acuity. This was achieved by crossing mice carrying a Cre-dependent TrkB.T1-EGFP-transgene under the control of the Thy-1 promoter ...

'AT(4) receptors' through which Angiotensin IV (Ang IV) improves memory acquisition, were recently identified as insulin regulated aminopeptidase (IRAP). Radioligand binding studies have hitherto been performed with iodinated Ang IV in the presence of divalent cation chelators EDTA and 1,10-phenanthrolin. Hence, they referred to the apo-form of IRAP. Presently, binding of [(3)H]Ang IV and [(3)H]AL-11, a stable Ang IV analog, was compared on Chinese hamster ovary (CHO-K1) and mouse hippocampal (P40H1) cell membranes. With chelators, their high affinity sites showed the same pharmacological profile as for [(125)I]Ang IV binding. Without chelators, only high affinity binding was perceived for [(3)H]AL-11. The same pharmacological profile was recorded in both membrane preparations; it was different from the one in the presence of chelators and corresponded to catalytically active IRAP (despite the concurrent presence of aminopeptidase N (APN) in P40H1 cell membranes). This confirms that the active and apo-forms of IRAP have a distinct pharmacological profile.

Background: Inactivating genes in vivo is an important technique for establishing their function in the adult nervous system. Unfortunately, conventional knockout mice may suffer from several limitations including embryonic or perinatal lethality and the compensatory regulation of other genes. One approach to producing conditional activation or inactivation of genes involves the use of Cre recombinase to remove loxP-flanked segments of DNA. We have studied the effects of delivering Cre to the hippocampus and neocortex of adult mice by injecting replication-deficient adeno-associated virus (AAV) and lentiviral (LV) vectors into discrete regions of the forebrain.

Compounds routinely used to increase the quality of life and combat disease undergo stringent potency and biosafety tests before approval. However, based on the outcome of ongoing research, new norms need to be effected to ensure that the compounds conform to biosafety at all target levels of activity. Whereas in vitro tests used to assess biosafety lack the potency and the translational attribute of a whole animal, mammalian preclinical models are expensive and time exhaustive. Zebrafish (Danio rerio) has emerged as an attractive alternative for biosafety studies due to its small size, genetics, breeding capabilities, and most importantly, similarity at the molecular and physiological levels with humans. It has been used extensively for testing various forms of toxicity, including developmental toxicity, cardiotoxicity, nephrotoxicity, and hepatotoxicity. We review here the utility of zebrafish as a powerful, sensitive, quantitative, noninvasive, and high-throughput whole-animal assay to screen for toxicity. Different forms of toxicity will be discussed briefly before we highlight the present state of genotoxicity study in zebrafish. This review, a first in this research area, will serve as a comprehensive introduction to the field of genotoxicity assay using zebrafish, a nascent but promising field that assays compounds for DNA damage. We also discuss possible approaches that could potentially be pursued to overcome some of the shortcomings in current genotoxic studies.

We have demonstrated in our previous studies that ventral subicular lesion induces neurodegeneration of the hippocampus and produces cognitive impairment in rats. In the present study, the efficacy of transplanted green fluorescent protein (GFP)-labeled hippocampal cell line (H3-GFP) cells in establishing functional recovery in ventral subicular lesioned rats has been evaluated. The survival of H3-GFP transplants and their ability to express trophic factors in vivo were also investigated. Adult male Wistar rats were subjected to selective lesioning of ventral subiculum and were transplanted with H3-GFP cells into the cornu ammonis 1 (CA1) hippocampus. The transplants settled mainly in the dentate gyrus and expressed neurotrophic factors, brain-derived neurotrophic factor (BDNF), and basic fibroblast growth factor (bFGF). The ventral subicular lesioned (VSL) rats with H3-GFP transplants showed enhanced expression of BDNF in the hippocampus and performed well in eight-arm radial maze and Morris water maze tasks. The VSL rats without hippocampal transplants continued to show cognitive impairment in task learning. The present study demonstrated the H3-GFP transplants mediated recovery of cognitive functions in VSL rats. Our study supports the notion of graft meditated host regeneration and functional recovery through trophic support, although these mechanisms require further investigation.

BackgroundTransgenic mice with mosaic, Golgi-staining-like expression of enhanced green fluorescent protein (EGFP) have been very useful in studying the dynamics of neuronal structure and function. In order to further investigate the molecular events regulating structural plasticity, it would be useful to express multiple proteins in the same sparse neurons, allowing co-expression of functional proteins or co-labeling of subcellular compartments with other fluorescent proteins. However, it has been difficult to obtain reproducible expression in the same subset of neurons for direct comparison of neurons expressing different functional proteins.Principal FindingsHere we describe a Cre-transgenic line that allows reproducible expression of transgenic proteins of choice in a small number of neurons of the adult cortex, hippocampus, striatum, olfactory bulb, subiculum, hypothalamus, superior colliculus and amygdala. We show that using these Cre-transgenic mice, multiple Cre-dependent transgenes can be expressed together in the same isolated neurons. We also describe a Cre-dependent transgenic line expressing a membrane associated EGFP (EGFP-F). Crossed with the Cre-transgenic line, EGFP-F expression starts in the adolescent forebrain, is present in dendrites, dendritic protrusions, axons and boutons and is strong enough for acute or chronic in vivo imaging.SignificanceThis triple transgenic approach will aid the morphological and functional characterization of neurons in various Cre-dependent transgenic mice.