Search

Objectives: Dried bonito dashi , a traditional Japanese fish broth made from dried bonito tuna, enhances food palatability due to its specific umami flavor characteristics. However, the pattern of brain activation following dashi ingestion has not been previously investigated. Methods: We mapped activation sites of the rat brain after intragastric loads of dried bonito dashi by measuring neuronal levels of the Fos protein, a functional marker of neuronal activation. Results: Compared to intragastric saline, intragastric dashi administration produced enhanced Fos expression in four forebrain regions: the medial preoptic area, subfornical organ, habenular nucleus, and central nucleus of the amygdala. Interestingly, the medial preoptic area was found to be the only feeding-related hypothalamic area responsive to dashi administration. Moreover, dashi had no effect in the nucleus accumbens and ventral tegmental area, two connected sites known to be activated by highly palatable sugars and fats. In the hindbrain, dashi administration produced enhanced Fos expression in both visceral sensory (caudal nucleus of the solitary tract, dorsal part of the lateral parabrachial nucleus, and area postrema) and autonomic (rostral ventrolateral medulla, and caudal ventrolateral medulla) sites. Discussion: The results demonstrate the activation of discrete forebrain and hindbrain regions following intragastric loads of dried bonito dashi . Our data suggest that the gut-brain axis is the principal mediator of the postingestive effects associated with the ingestion of dashi .

l-glutamate, an umami taste substance, is a key molecule coupled to a food intake signaling pathway. Furthermore, recent studies have unveiled new roles for dietary glutamate on gut-brain axis communication via activation of gut glutamate receptors and subsequent vagus nerve. In the present study, we mapped activation sites of the rat forebrain after intragastric load of 60 mM monosodium l-glutamate (MSG) by measurement of Fos protein, a functional marker of neuronal activation. The same concentration of d-glucose (sweet) and NaCl (salty) was used as controls. MSG administration exclusively produced enhanced Fos expression in four hypothalamic regions (the medial preoptic area, lateral hypothalamic area, dorsomedial nucleus, and arcuate nucleus). On the other hand, glucose administration exclusively enhanced Fos induction in the nucleus accumbens. Both MSG and glucose enhanced Fos induction in three brain regions (the habenular nucleus, paraventricular nucleus, and central nucleus of the amygdala). However, MSG induced Fos inductions were more potent than those of glucose in the habenular nucleus and paraventricular nucleus. Importantly, the present study identified for the first time two brain areas (the paraventricular and arcuate hypothalamic nuclei) that are more potently activated by intragastric MSG loads compared with glucose and NaCl. Overall, our results suggest significant activation of a neural network comprising the habenular nucleus, amygdala, and the hypothalamic subnuclei following intragastric load with glutamate., (Copyright © 2011 IBRO. Published by Elsevier Ltd. All rights reserved.)

Recent studies suggest the protective effects of adrenomedullin (AM) on ischemic brain damage. The present study was aimed at investigating the effects of AM and its receptor antagonist, AM₂₂₋₅₂, on ischemia-induced cerebral edema and brain swelling in rats using magnetic resonance imaging. Rats were subjected to 60 min of middle cerebral artery occlusion (MCAO) followed by reperfusion. Intravenous injection of AM (1.0 μg/kg), AM₂₂₋₅₂ (1.0 μg/kg), or saline was made before MCAO. Effects of AM injection just after reperfusion were also investigated. One day after ischemia, increases in T₂-weighted signals in the brain were clearly observed. Total edema volume, as well as brain swelling, was greatly and significantly reduced by pre-treatment of AM (reduced by 53%). Extent of brain swelling was significantly correlated with the volume of cerebral edema. The protective effect of AM against edema was more clearly observed in the cerebral cortex (reduced by 63%) than the striatum (reduced by 31%). Increased T₂ relaxation time in the cortex was recovered partially by pre-treatment of AM. Post-treatment of AM had no effects. Pre-treatment of AM₂₂₋₅₂ tended to exacerbate the edema. In another line of experiment, cocktail administration of AM with melatonin, a pineal product having neuroprotective potential as a free radical scavenger, failed to enhance the protective effects of AM alone. The present study clearly suggests the prophylactic effects of AM against cerebral edema, especially the cortical edema, in a rat stroke model., (Copyright © 2010 Elsevier Inc. All rights reserved.)

l-Glutamate is a multifunctional amino acid involved in taste perception, intermediary metabolism, and excitatory neurotransmission. In addition, recent studies have uncovered new roles for l-glutamate in gut-brain axis activation and energy homeostasis. l-Glutamate receptors and their cellular transduction molecules have recently been identified in gut epithelial cells. Stimulation of such l-glutamate receptors by luminal l-glutamate activates vagal afferent nerve fibers and then parts of the brain that are targeted directly or indirectly by these vagal inputs. Notably, 3 areas of the brain-the medial preoptic area, the hypothalamic dorsomedial nucleus, and the habenular nucleus-are activated by intragastric l-glutamate but not by glucose or sodium chloride. Furthermore, the chronic, ad libitum ingestion of a palatable solution of monosodium l-glutamate (1% wt:vol) by rats has also been found to reduce weight gain, fat deposition, and plasma leptin concentrations compared with rats that ingest water alone. No difference in food intake was observed. Such effects may also be vagally mediated. Together, such findings contribute to the growing knowledge base that indicates that l-glutamate signaling via taste and gut l-glutamate receptors may influence multiple physiologic functions, such as thermoregulation and energy homeostasis.

Recent studies have demonstrated the existence of receptors for L-glutamate (GLU) and their transduction molecules in the gut mucosa as well as in the oral cavity. Among 20 amino acids, gastric vagal afferent fibers respond only to intragastric administration of GLU. Functional magnetic resonance imaging revealed activation of several forebrain regions in response to intragastric infusion of taste solutions (D-glucose [sweet], monosodium L-glutamate [MSG; umami], and NaCl [salty] at 60 mM) in rats. Glucose activated the nucleus accumbens. MSG activated the medial preoptic area, dorsomedial nucleus of the hypothalamus, and habenular nucleus. Both glucose and MSG activated the amygdala. Some areas, such as the insular cortex, anterior cingulate cortex, hippocampus, and caudate-putamen were activated by all three substances. Glucose-induced brain activation developed slowly and persisted for a long time, whereas activation by MSG developed rapidly during infusion and reduced rapidly after cessation of infusion. NaCl induced only small and transient activation. Thus, both activated areas and temporal response patterns in the brain were distinct between sweet and umami substances delivered in the stomach. Postoral taste substances may activate the brain via neural (vagal) and/or humoral pathways.

Monosodium L-glutamate (MSG) elicits a unique taste termed umami and is widely used as a flavor enhancer in a variety of cuisines. Recent studies suggest the existence of L-glutamate (GLU) receptors and its transduction molecules in the gut mucosa as well as in the oral cavity. The vagal gastric afferent fibers respond specifically to the luminal stimulation of GLU in the stomach. GLU administration in the stomach also activates several brain areas (insular cortex, basal ganglia, limbic system, and hypothalamus). Ingestion of MSG enhanced secretion of digestive juices and insulin. Spontaneous ingestion of an MSG solution at the most preferred concentration (1% (w/v)) reduced weight gain, fat deposition, and plasma leptin levels without affecting food intake, naso-anal length (an index of somatic development), and lean mass in rats. These results suggest that umami signaling via gustatory and visceral pathways may play an important role in the process of digestion, absorption, metabolism, and other physiological functions via activation of the brain.

Microangiography with spatial resolution in the micrometer range was carried out to depict vascular responses of the cerebral artery and arterioles in rats and mice using a real-time imaging system and a third generation synchrotron radiation source at SPring-8. An X-ray direct-conversion type detector with 6 microm spatial resolution was developed for real-time biomedical imaging. The X-ray image is converted directly into an electrical signal in the photoconductive layer without image blurring. In synchrotron radiation radiography, a long source-to-object distance and a small source spot can produce high-resolution images. Microangiographic images were obtained without image blurring and were stored in a digital frame memory system with a 1024 x 1024-pixel, 10-bit format. In imaging experiments, vasoconstriction and vasodilatation of small cerebral arteries were visualized in response to hypercapnia, hemorrhagic hypotension, and vasoactive agents after iodine contrast agent injection into the carotid artery.

Injection with 6-hydroxydopamine (6-OHDA) into the nigrostriatal pathway results in loss of nigrostriatal dopaminergic neurons, which has been used widely as an animal model of Parkinson's disease. In the present study, location and extent of lesions 1 day after 6-OHDA injections (2, 4, 8, or 16 microg as a free base) in the substantia nigra (SN) were evaluated in rats by T(2)-weighted magnetic resonance imaging (MRI). The changes in MRI were also compared to immunohistochemical and behavioral changes. Hyperintense area in MRI was found at the region corresponding to 6-OHDA injection in a dose-dependent manner and was accompanied by a loss of tyrosine hydroxylase (TH)-positive cells. The shape of hyperintense area in the SN appeared to be composed of two components (i.e., circular and longitudinal regions). Administration of a larger dose of 6-OHDA (8-16 microg) was accompanied by an increase in hyperintense area and loss of TH-positive cells beyond the SN. The hyperintense area was observed on the first and third days after 6-OHDA injection, but the size and intensity declined to near normal levels on the ninth day. Rotational behavior induced by methamphetamine reached maximal levels at 4 microg 6-OHDA, and the behavior was maintained with doses up to 16 microg of 6-OHDA. Intrastriatal injection with 6-OHDA was less effective. These results suggest that MRI provides highly valuable information for verifying the size and location of intended lesions as well as for determining the optimal dose of neurotoxins in individual animals.

It has been reported that antipsychotic dopamine-D2-receptor (D2R) antagonists affected other neurotransmitter systems. In the present study, the effects of a D2R agonist, bromocriptine, and a D2R antagonist, spiperone, on brain activity were investigated using wild-type mice (WT) with intact D2Rs, and D2R-knockout mice (D2R-KO) lacking D2Rs by functional magnetic resonance imaging. In the WT, flow-weighted signal intensity significantly increased after administration of bromocriptine in the hippocampal formation. In contrast, signal intensity significantly decreased after administration of spiperone in the somatosensory-motor cortices, thalamus, anterior cingulate cortex, caudate-putamen, nucleus accumbens, hippocampal formation, and amygdala. In the D2R-KO, however, no significant changes were observed after administration of either bromocriptine or spiperone. The present results indicated that the D2R-KO lacked sensitivity to D2R agonist and antagonist in agreement with its genetic defects, which confirmed that the changes in brain activity in the WT after administration of either drug were mediated through D2Rs. These results suggest that antipsychotic D2R antagonists affect activity of the same brain regions of human patients through D2Rs, as observed in the present study. These changes in brain activity might be related to therapeutic efficacy as well as side effects of antipsychotic drugs on schizophrenic patients.

Spatio-temporal dynamics of activated brain areas induced by drinking were investigated and visualized in behaving rats using functional magnetic resonance imaging (fMRI). The rats were trained to drink in the magnet bore, and the images were taken during and after drinking glucose and distilled water. During glucose ingestion, the signal intensity was increased continuously and maximally in the lateral hypothalamic area (LHA) and the ventromedial hypothalamus (VMH). Somewhat less intense activation in the central nucleus of the amygdala (AMc), and transient activation in the piriform cortex and the mediodorsal nucleus of the thalamus were observed. The signal intensities of other regions measured were largely unchanged. During post-ingestive periods, the signals re-increased in the hypothalamic areas and AMc. When water was given, LHA and VMH were similarly activated, however, the signal intensity in the amygdala was not significantly increased. The results indicate that these brain regions are activated differentially during drinking behavior, and that LHA and VMH play a central role in the control of not only feeding but also drinking. The regional activities in LHA and VMH are not principally related to the gustatory sensation, and the reactivation after drinking may be related to satisfaction or post-ingestive nutritional information. Also, the responses of AMc are probably due to reward value difference. To the best of our knowledge, this is the first report of mapping of brain areas using fMRI in behaving rats. The improved method described in this study for collecting fMRI data in behaving animals will be useful for studying functional network during animal behavior.

The precise mechanism of reversible opening of the blood-brain barrier (BBB) is elusive. Hyperosmotic mannitol at 1.4 to 1.6 M is commonly used for this purpose but intraarterial injection of such a hyperosmotic solution is known to have possible side effects on the brain. Cooling of the solution has recently been reported to have potential to open the BBB. The in situ brain perfusion technique with [(14)C]-sucrose was used first to quantify BBB permeability in rats after intraarterial injection of 1.1 M mannitol, which is less hyperosmotic than commonly used mannitol, at room temperature and at 4 degrees C. Mannitol at 4 degrees C produced an opening of the BBB but the duration of the opening was less than 30 min. We then investigated the effect of an Na(+)/Ca(2+) exchange blocker (KB-R7943) on this hypothermic BBB opening. KB-R7943 extended the BBB opening to 30 min without affecting the peak level of BBB permeability at 5 min. Simple manipulation of temperature can thus enhance the reversible BBB opening in mannitol and pharmacological manipulation of calcium dynamics works synergistically with hypothermic mannitol., (©2002 Elsevier Science (USA).)

The blood-brain barrier (BBB) is a permeability barrier of interconnected brain capillary endothelial cells. Intraarterial infusion of papaverine relieves cerebral vasospasms by inhibiting smooth muscle contractions and it may simultaneously lead to a disruption of BBB permeability. To date, the mechanism underlying this phenomenon and the quantification of BBB disruption remains elusive. We first examined the changes in cerebrovascular permeability after an intracarotid infusion of papaverine (0.20%) in rats by an in situ brain perfusion technique. We then demonstrated that changes in cerebrovascular permeability depend on the concentration of papaverine. This is the first study in which the degree of BBB disruption was accurately quantified in terms of [(14)C]sucrose and it was demonstrated that papaverine has a prolonged effect on cerebrovascular permeability. This result suggests the importance of in vivo experiments for a precise evaluation of permeability for many other agents, particularly for the central nervous system.

Osmotic disruption is currently being used to circumvent the blood-brain barrier (BBB) and enhance the delivery of therapeutic molecules in human brains. To date, however, the time course during the early phase of disruption has not been clarified. In order to demonstrate the rapid change in cerebrovascular permeability after BBB disruption in rats, we developed a method of in situ brain perfusion to demonstrate the earliest reversibility in cerebrovascular permeability. Osmotic BBB disruption was attained by intracarotid infusion of hypertonic mannitol. Perfusate containing [14C]-sucrose was infused at different time points following osmotic stress followed by measuring cerebrovascular permeability. The earliest BBB disruption was seen to occur 5 min after osmotic stress, after which the exact time course of cerebrovascular reversibility was studied. The protocol reported here, in contrast with those reported in previous studies, was shown to be qualitative, simple, and fast. In addition, the method can be applied to measure any low BBB permeability molecules. This protocol should be helpful for any research focused on enhancing drug delivery into the brain following osmotic BBB disruption.

A female patient who fulfilled the diagnostic criteria of Walker-Warburg syndrome had muscle biopsy finding of muscular dystrophy. There was normal expression of merosin (laminin alpha2 chain) and dystrophin and only slightly reduced dystrophin-associated glycoprotein expression. On genetic analysis, she had no specific haplotype, the common mutation of 3kb insertion, or point mutations in the Fukuyama-type congenital muscular dystrophy gene, suggesting that the two diseases are not genetically identical.

Human umbilical vein endothelial cells (HUVECs) were transplanted in athymic mouse brain and neovascularization of grafted endothelial cells was studied. HUVECs were transfected by a reporter gene pEGFPE-N1 in vitro and grafted stereotactically in unilateral striatum of adult nude mice. Histological studies in 4 weeks revealed that grafted HUVECs newly formed microvessels in brain, which were migrated and fused with host vessels. Intravenous injection of Evans blue before sacrificing animals resulted in no extravasation of dye, indicating that a blood-brain barrier (BBB) was formed by the grafted HUVECs. Immunohistochemistry demonstrated that host astrocytes extended glial feet on the grafted endothelial cells and a part of the newly formed vessels was positive with glucose transporter-1. These results indicate that endothelial cells from an ectopic origin have the potential to form a BBB after grafting in the central nervous system.

We used magnetic resonance imaging (MRI) to examine the brain of a typical Coffin-Lowry syndrome (CLS) patient. There were many small perivascular focal areas of hypointensity in the white matter on T1-weighted images, similar to those found in mucopolysaccharidosis or perivascular leukomalacia. However, these changes could not seen in another patient we examined. Both patients showed normal urinary mucopolysaccharide patterns with chromatographic analysis. The cause of the MRI result is not known, but it could have a heterogeneous origin, and this result could represent an important indication defining one type of CLS.

We studied the mechanism of reoxygenation injury of cerebral microvessels in cultured rat brain capillary endothelial cells (BCECs). BCECs were isolated from rat cerebral cortices by a two step enzymatic treatment. The monolayers of BCECs were subjected to anoxia for 20 minutes followed by reoxygenation for 3 hours. Cell damage was assessed by measuring the leakage of intracellular lactic dehydrogenase (LDH). The control group was anoxia/reoxygenated BCECs without any protective reagents. To study the protective effect of free radical scavengers and antioxidants, superoxide dismutase, catalase, deferoxamine, oxypurinol, indomethacin, or NG-nitro-L-arginine methyl ester (L-NAME) was applied during anoxia/reoxygenation. Thus 7 experimental conditions were established. Lactic dehydrogenase (LDH) leaked from reoxygenated BCECs due to cell membrane damage. This leakage was almost totally suppressed by superoxide dismutase, indicating that reoxygenation injury of BCECs is mediated by superoxide generation. The other scavengers and antioxidants partially suppressed LDH leakage. Reduction of Ca2+ in the culture medium from 1.6 mM to 0.016 mM also suppressed LDH leakage. These results indicate that BCECs subjected to anoxia/reoxygenation become potent generators of superoxide anion, which is thought to be responsible for reoxygenation injury. The superoxide generation partially depends on the xanthine oxidase and cyclooxygenase pathways. As L-NAME partially suppressed LDH leakage peroxynitrite may contribute to reoxygenation injury of BCECs. The extracellular Ca2+ concentration also plays a critical role in the reoxygenation injury of BCECs.

The transplantation of fetal dopamine neurons has previously been shown to ameliorate locomotor deficits in laboratory animals with nigrostriatal dopamine lesions. These studies have also demonstrated a reinstatement of striatal dopamine synthesis and release associated with the graft-to-host fiber innervation. More recent studies in the intact striatum indicate that striatal dopamine release can be regulated by corticostriatal glutamatergic projections. In the present study we hypothesized that secretion of dopamine by grafted neurons may also be regulated by similar mechanisms. To test this hypothesis we have measured dopamine release in the striatum of rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway and grafts containing dopamine neurons. Intrastriatal dopamine levels were determined using methods of in vivo microdialysis. The administration of dihydrokainic acid, an inhibitor of glutamate uptake, resulted in the release of striatal dopamine in grafted and normal rats. In contrast, dopamine was not detectable in animals with 6-OHDA lesions alone. Additional studies were conducted to determine the type of glutamate receptor mediating the release of striatal dopamine. Kainic acid administration into the perfusate of the dialysis probe resulted in the release of striatal dopamine in a dose-dependent fashion in both grafted and normal rats. N-methyl-D-aspartate had no effect on dopamine release except at abnormally high concentrations. These results demonstrate that dopamine neurons which are transplanted into the striatum of rats with 6-OHDA lesions become functionally incorporated into the neural circuitry of the host brain, and that the release of dopamine by grafted neurons can be regulated by afferent fibers from the host brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced glutathione (GSH) plays an important role in cellular protection against damage from free radicals and other electrophiles. GSH in the rat central nervous system was quantitatively analyzed. In adult brain, tissue from the cerebellum and cerebrum had higher GSH levels than that from the brainstem and spinal cord. Infant cerebrum and cerebellum contained lower levels of GSH than adult cerebrum and cerebellum. These data seem to suggest that the brainstem and spinal cord in adults, and the cerebrum and cerebellum in infants, are more vulnerable to injury by free radical-like radiation than the cerebrum and cerebellum in adults.