Identification of miRNA changes in Alzheimer's disease brain and CSF yields putative biomarkers and insights into disease pathways

MicroRNAs have essential functional roles in brain development and neuronal specification but their roles in neurodegenerative diseases such as Alzheimer's disease (AD) is unknown. Using a sensitive qRT-PCR platform we identified regional and stage-specific deregulation of miRNA expression in AD patient brains. We used experimental validation in addition to literature to reveal how the deregulated brain microRNAs are biomarkers for known and novel pathways in AD pathogenesis related to amyloid processing, neurogenesis, insulin resistance, and innate immunity. We additionally recovered miRNAs from cerebrospinal fluid and discovered AD-specific miRNA changes consistent with their role as potential biomarkers of disease.     

MicroRNAs as potential therapeutics for treating spinal cord injury

MicroRNAs are a class of recently discovered,small non-coding RNAs that have been shown to play essential roles in a vast majority of biological processes.Very little is known about the role of microRNAs during spinal cord injury.This review summarizes the changes in expression levels of microRNAs after spinal cord injury.These aberrant changes suggest that microRNAs play an important role in inflammation,oxidative stress,apoptosis,glial scar formation and axonal regeneration.Given their small size and specificity of action,microRNAs could be potential therapeutics for treating spinal cord injury in the future.There are rapidly developing techniques for manipulating microRNA levels in animals;we review different chemical modification and delivery strategies.These may provide platforms for designing efficient microRNA delivery protocols for use in the clinic.     

A tripartite organization of the urbilaterian brain: developmental genetic evidence from Drosophila

Developmental genetic studies suggest that the embryonic vertebrate brain has a tripartite ground plan consisting of a forebrain/midbrain, a hindbrain, and an intervening midbrain/hindbrain boundary region, which are characterized by the specific expression of the Otx, Hox and Pax-2/5/8 genes. Recent studies in Drosophila reveal similarities in the expression and function of these genes in patterning the embryonic brains of flies and vertebrates. Thus, in Drosophila, as is vertebrates, a Pax2/5/8 domain is located between an anterior otd/Otx2 region and a posterior Hox region of the embryonic brain. Moreover, in Drosophila, as in vertebrates, this Pax2/5/8 domain is located at the interface of the otd/Otx2 domain and a posterior unplugged/Gbx2 domain. Furthermore, in Drosophila, as in vertebrates, inactivation of otd/Otx2 or of unplugged/Gbx2 results in a comparable mispositioning or loss of orthologous gene expression domains in the embryonic brain. These developmental genetic similarities suggest that the tripartite ground plan, which characterizes the developing vertebrate brain, is also at the basis of the developing insect brain. This, in turn, implies that a tripartite organization of the embryonic brain may characterize all extant bilaterians, and thus may already have been established in the last common urbilaterian ancestor of all bilaterians.     

The allometry of brain miniaturization in ants

Extensive studies of vertebrates have shown that brain size scales to body size following power law functions. Most animals are substantially smaller than vertebrates, and extremely small animals face significant challenges relating to nervous system design and function, yet little is known about their brain allometry. Within a well-defined monophyletic taxon, Formicidae (ants), we analyzed how brain size scales to body size. An analysis of brain allometry for individuals of a highly polymorphic leaf-cutter ant, Atta colombica, shows that allometric coefficients differ significantly for small (<1.4 mg body mass) versus large individuals (b = 0.6003 and 0.2919, respectively). Interspecifically, allometric patterns differ for small (<0.9 mg body mass) versus large species (n = 70 species). Using mean values for species, the allometric coefficient for smaller species (b = 0.7961) is significantly greater than that for larger ones (b = 0.669). The smallest ants had brains that constitute ～15% of their body mass, yet their brains were relatively smaller than predicted by an overall allometric coefficient of brain to body size. Our comparative and intraspecific studies show the extent to which nervous systems can be miniaturized in taxa exhibiting behavior that is apparently comparable to that of larger species or individuals.     

Regulation by orexin of feeding behaviour and locomotor activity in the goldfish

Orexin is a hypothalamic neuropeptide that is implicated in the regulation of feeding behaviour and the sleep-wakefulness cycle in mammals. However, in spite of a growing body of knowledge concerning orexin in mammals, the orexin system and its function have not been well studied in lower vertebrates. In the present study, we first examined the effect of feeding status on the orexin-like immunoreactivity (orexin-LI) and the expression of orexin mRNA in the goldfish brain. The number of cells showing orexin-LI in the hypothalamus of goldfish brain showed a significant increase in fasted fish and a significant decrease in glucose-injected fish. The expression level of orexin mRNA in the brains of fasted fish increased compared to that of fed fish. We also examined the effect of an i.c.v. injection of orexin or an anti-orexin serum on food intake and locomotor activity in the goldfish. Administration of orexin by i.c.v. injection induced a significant increase of food intake and locomotor activity, whereas i.p. injection of glucose or i.c.v. injection of anti-orexin serum decreased food consumption. These results indicate that the orexin functions as an orexigenic factor in the goldfish brain.     

Distribution of aromatase in the brain of the African cichlid fish Astatotilapia burtoni: Aromatase expression,but not estrogen receptors,varies with female reproductive-state

Estrogen synthesis and signaling in the brains of vertebrates has pleotropic effects ranging from neurogenesis to modulation of behaviors. The majority of studies on brain-derived estrogens focus on males, but estrogenic signaling in females likely plays important roles in regulation of reproductive cycling and social behaviors. We used females of the mouth brooding African cichlid fish, Astatotilapia burtoni, to test for reproductive state-dependent changes in estrogenic signaling capacity within microdissected brain nuclei that are important for social behaviors. Expression levels of the rate-limiting enzyme aromatase, but not estrogen receptors, measured by qPCR changes across the reproductive cycle. Gravid females that are close to spawning had higher aromatase levels in all brain regions compared to females with lower reproductive potential. This brain aromatase expression was positively correlated with circulating estradiol levels and ovarian readiness. Using chromogenic in situ hybridization we localized aromatase-expressing cells to ependymal regions bordering the ventricles from the forebrain to the hindbrain, and observed more abundant staining in gravid compared to mouth brooding females in most regions. Staining was most prominent in subpallial telencephalic regions, and diencephalic regions of the preoptic area, thalamus, and hypothalamus, but was also observed in sensory and sensorimotor areas of the midbrain and hindbrain. Aromatase expression was observed in radial glial cells, revealed by co-localization with the glial marker GFAP and absence of co-localization with the neuronal marker HuC/D. Collectively these results support the idea that brain-derived estradiol in females may serve important functions in reproductive state-dependent physiological and behavioral processes across vertebrates.     

Histaminergic neuron system in the brain: Distribution and possible functions

Recent immunocytochemical studies have identified the histaminergic neuron system in the brain. In the rat brain, histaminergic neuronal cell bodies are located in the tuberomammillary nucleus in the posterior hypothalamus, while histaminergic fibers are distributed in almost all regions of the brain. Similar distributions of histaminergic neuronal cell bodies and fibers have been reported in the brains of other mammals and nonmammalian vertebrates. As expected from the widespread distributions of the efferent fibers, the central histaminergic neuron system seems to be involved in multiple functions in the brain. The results of intracerebral injection of histamine and administration of alpha-fluoromethylhistidine (FMH), which depletes brain histamine level, suggest that the central histaminergic system may modulate feeding, drinking and sexual behaviors, sleep-wakefulness and circadian rhythm, neuroendocrine and cardiovascular controls and thermoregulation.     

The primary brain vesicles revisited: are the three primary vesicles (forebrain/midbrain/hindbrain) universal in vertebrates?

It is widely held that three primary brain vesicles (forebrain, midbrain, and hindbrain vesicles) develop into five secondary brain vesicles in all vertebrates (von Baer's scheme). We reviewed previous studies in various vertebrates to see if this currently accepted scheme of brain morphogenesis is a rule applicable to vertebrates in general. Classical morphological studies on lamprey, shark, zebrafish, frog, chick, Chinese hamster, and human embryos provide only partial evidence to support the existence of von Baer's primary vesicles at early stages. Rather, they suggest that early brain morphogenesis is diverse among vertebrates. Gene expression and fate map studies on medaka, chick, and mouse embryos show that the fates of initial brain vesicles do not accord with von Baer's scheme, at least in medaka and chick brains. The currently accepted von Baer's scheme of brain morphogenesis, therefore, is not a universal rule throughout vertebrates. We propose here a developmental hourglass model as an alternative general rule: Brain morphogenesis is highly conserved at the five-brain vesicle stage but diverges more extensively at earlier and later stages. This hypothesis does not preclude the existence of deep similarities in molecular prepatterns at early stages.     

Thalamo-telencephalic pathways in the fire-bellied toad Bombina orientalis

It was suggested that among extant vertebrates, anuran amphibians display a brain organization closest to the ancestral tetrapod condition, and recent research suggests that anuran brains share important similarities with the brains of amniotes. The thalamus is the major source of sensory input to the telencephalon in both amphibians and amniote vertebrates, and this sensory input is critical for higher brain functions. The present study investigated the thalamo-telencephalic pathways in the fire-bellied toad Bombina orientalis, a basal anuran, by using a combination of retrograde tract tracing and intracellular injections with the tracer biocytin. Intracellular labeling revealed that the majority of neurons in the anterior and central thalamic nuclei project to multiple brain targets involved in behavioral modulation either through axon collaterals or en passant varicosities. Single anterior thalamic neurons target multiple regions in the forebrain and midbrain. Of note, these neurons display abundant projections to the medial amygdala and a variety of pallial areas, predominantly the anterior medial pallium. In Bombina, telencephalic projections of central thalamic neurons are restricted to the dorsal striato-pallidum. The bed nucleus of the pallial commissure/thalamic eminence similarly targets multiple brain regions including the ventral medial pallium, but this is accomplished through a higher variety of distinct neuron types. We propose that the amphibian diencephalon exerts widespread influence in brain regions involved in behavioral modulation and that a single dorsal thalamic neuron is in a position to integrate different sensory channels and distribute the resulting information to multiple brain regions.     

Encephalization in vertebrates. A new mode of calculation for allometry coefficients and isoponderal indices

The conventional allometric power function, with its slope near 2/3, works well for interspecific scaling of brain vs. body weight in all groups of vertebrates. It fails, however, in extrapolation to vertebrates of the largest size within their groups: these have smaller brains than the equation would predict. We propose a correction, the hyperbolic tangent, to linearize the data over all sizes, and we discuss evolutionary reasons for the relatively small brain size of the largest vertebrates.     

Anterograde and retrograde filling of central neuronal systems with horseradish peroxidase under in vitro conditions

In this study, a simple technique for neuronal tracing with horseradish peroxidase (HRP) in vitro is described. It can be applied to excised small brains of poikilothermic vertebrates, or to trimmed blocks or slices of brain tissue from homoiothermic vertebrates. The filling technique relies on the diffusion of HRP into transected axons of supravital neurons, and gives a Golgi-like staining of the filled neuronal profiles. The incubation is carried out at 4 degrees C, which minimizes unspecific background staining caused by pinocytotic uptake of HRP. The technique was tested for visualizing (i) intrapineal neurons projecting to the brain in the rainbow trout, (ii) pinealofugal projections to the brain in the rainbow trout and the three-spined stickleback, (iii) retinal ganglion cells in the rainbow trout, and (iv) central pinealopetal projections in the golden hamster. The strength of this method lies in the possibility to perform very accurate applications of HRP to excised brains or brain slices under a stereo microscope, the simple processing of tissue, and the Golgi-like filling of the neuronal profiles. This technique may provide an important complement to currently used HRP-tracing techniques.     

Retinoic acid downregulates microRNAs to induce abnormal development of spinal cord in spina bifida rat model

Objects MicroRNAs have been found in the developing central nervous system, but little is known about their functions in development, especially in the abnormal development of spinal cord in spina bifida. To this end, we have studied the mechanism of microRNAs involved in the morphogenesis of the spinal cord in all-trans-retinoic acid (RA)-treated spina bifida rat fetus. Materials and methods Timed-pregnant rats were gavage-fed RA, and embryos were obtained on 13.5, 15.5, 17.5, and 19.5 days. MicroRNAs’ expression profile was analyzed by Northern blot. In situ apoptosis detection and microRNA in situ hybridization methods on sections of paraffin-embedded tissues were employed to explore the mechanism. Conclusion Administration of RA reduced the size of the spinal cord, probably as a consequence of increased cell death. There is a dramatic decrease in the expression of miR-9/9*, miR-124a and miR-125b, and Bcl2 and P53 as well in the sacral cord from E13.5 to E19.5 days post coitum. Our data showed that expression of these microRNAs was dysregulated in RA-treated spinal cord during embryonic development, suggesting that they may be involved in the development of the spinal cord.     

Neural steroid hormone receptors

(1) Cell nuclear and cytoplasmic receptors for estrogens, androgens, and glucocorticoids have been identified in brains and pituitary glands of vertebrates. With respect to topography, estradiol (E₂) receptors are localized primarily in the hypophysiotrophic area and amygdala; 5-α-dihydrotestosterone (DHT) receptors are found in hypothalamus and limbic regions in smaller amounts and more uniformly distributed than those for estradiol; and corticosterone receptors are found in the hippocampal formation, septum, entorhinal cortex and amygdala. (2) Where information is available, mainly for estrogen receptors, their neural topography shows a remarkable constancy among vertebrates. The neural topography of estrogen and glucocorticoid receptors of rat and rhesus monkey will be compared. (3) A complicating factor in the study of androgens interacting with the brain is the conversion of testosterone (T) in neural tissue to both estrogenic and androgenic metabolites. Two of the products, E₂ and DHT, are recovered attached to cell nuclear receptors in the rat brain, whereas only DHT and T itself are found in pituitary cell nuclei. Evidence from other laboratories suggests that interactions of E₂ and DHT or T with intracellular receptors each subserve different behavioral and neuroendocrine functions in the rat. (4) The topography of estrogen receptors in the rat brain provides an excellent opportunity for studying estrogen action on brain chemistry. Estrogen effects on monoamine oxidase, choline acetylase, and glucose-6-phosphate dehydrogenase activity will be described. The overall importance of the action of steroid hormones on gene expression will be briefly discussed.     

The blood-brain barrier and ventricular system of Myxine glutinosa.

Comparison of the rate and extent of penetration of test compounds from plasma into brain and muscle of the hagfish, Myxine glutinosa, indicates that the blood-brain barrier is poorly developed or absent in this species. We examined a series of hagfish brains in the light and electron microscope in order to relate the structure of the brain to the physiology of the blood-brain barrier and cerebrospinal fluid. The ventricular system consists of an ependymal cell-lined central canal extending from the spinal cord to the midbrain and two or more ependymal cell-lined cavities located more rostrally. A preoptic and an infundibular recess were present in the diencephalons of all brains and were isolated from each other and from the primary ventricular system. Since a typical choroid plexus could not be identified, this suggests that cerebrospinal fluid must be formed entirely by brain in this species. Cerebral capillaries differ significantly from those of other vertebrates in possessing large numbers of cytoplasmic vesicles and in the relative rarity of tight junctions between endothelial cells. These capillaries do not, therefore, appear to be morphologically specialized for barrier functions.     

Evolution of the amygdala: new insights from studies in amphibians

The histology of amphibian brains gives an impression of relative simplicity when compared with that of reptiles or mammals. The amphibian telencephalon is small and contains comparatively few and large neurons, which in most parts constitute a dense periventricular cellular layer. However, the view emerging from the last decade is that the brains of all tetrapods, including amphibians, share a general bauplan resulting from common ancestry and the need to perform similar vital functions. To what extent this common organization also applies to higher brain functions is unknown due to a limited knowledge of the neurobiology of early vertebrates. The amygdala is widely recognized as a brain center critical for basic forms of emotional learning (e.g., fear conditioning) and its structure in amphibians could suggest how this capacity evolved. A functional systems approach is used here to synthesize the results of our anatomical investigations of the amphibian amygdala. It is proposed that the connectivity of the amphibian telencephalon portends a capacity for multi-modal association in a limbic system largely similar to that of amniote vertebrates. One remarkable exception is the presence of new sensory-associative regions of the amygdala in amniotes: the posterior dorsal ventricular ridge plus lateral nuclei in reptiles and the basolateral complex in mammals. These presumably homologous regions apparently are capable of modulating the phylogenetically older central amygdala and allow more complex forms of emotional learning.