A Novel Near-Infrared Fluorescence Probe THK-565 Enables In Vivo Detection of Amyloid Deposits in Alzheimer's Disease Mouse Model

PURPOSE

Noninvasive imaging of protein aggregates in the brain is critical for the early diagnosis, disease monitoring, and evaluation of the effectiveness of novel therapies for Alzheimer's disease (AD). Near-infrared fluorescence (NIRF) imaging with specific probes is a promising technique for the in vivo detection of protein deposits without radiation exposure. Comprehensive screening of fluorescent compounds identified a novel compound, THK-565, for the in vivo imaging of amyloid-β (Aβ) deposits in the mouse brain. This study assessed whether THK-565 could detect amyloid-β deposits in vivo in the AD mouse model.

PROCEDURES

The fluorescent properties of THK-565 were evaluated in the presence and absence of Aβ fibrils. APP knock-in (APP-KI) mice were used as an animal model of AD. In vivo NIRF images were acquired after the intravenous administration of THK-565 and THK-265 in mice. The binding selectivity of THK-565 to Aβ was evaluated using brain slices obtained from these mouse models.

RESULTS

The fluorescence intensity of the THK-565 solution substantially increased by mixing with Aβ fibrils. The maximum emission wavelength of the complex of THK-565 and Aβ fibrils was 704 nm, which was within the optical window range. THK-565 selectively bound to amyloid deposits in brain sections of APP-KI mice After the intravenous administration of THK-565, the fluorescence signal in the head of APP-KI mice was significantly higher than that of wild-type mice and higher than that after administration of THK-265. Ex vivo analysis confirmed that the THK-565 signal corresponded to Aβ immunostaining in the brain sections of these mice.

CONCLUSIONS

A novel NIRF probe, THK-565, enabled the in vivo detection of Aβ deposits in the brains of the AD mouse model, suggesting that NIRF imaging with THK-565 could non-invasively assess disease-specific pathology in AD.

In vivo [18F]THK-5351 imaging detected reactive astrogliosis in argyrophilic grain disease with comorbid pathology: A clinicopathological study

Quantification of in vivo reactive astrogliosis, which represents neural inflammation and remodeling in the brain, is an emerging methodology for the evaluation of patients with neurodegenerative diseases. [18F]THK-5351 is a positron emission tomography (PET) tracer for monoamine oxidase B (MAO-B), a molecular marker of reactive astrogliosis. We performed in vivo [18F]THK-5351 PET in a patient who at autopsy was found to have argyrophilic grain disease (AGD) with comorbid pathology to visualize reactive astrogliosis for the first time. We aimed to validate an imaging-pathology correlation using [18F]THK-5351 PET and the autopsy brain. The patient, a 78-year-old man, was pathologically diagnosed with AGD combined with limbic-predominant age-related transactive response DNA-binding protein of 43 kDa encephalopathy and Lewy body disease without Alzheimer disease-related neuropathological changes. Reactive astrogliosis in the postmortem brain was abundant in the inferior temporal gyrus, insular gyrus, entorhinal cortex, and ambient gyrus where premortem [18F]THK-5351 signals were high. We found a proportional correlation between the amount of reactive astrogliosis in the postmortem brain and the in vivo [18F]THK-5351 standardized uptake value ratio (r = 0.8535, p = 0.0004). These results indicated that reactive astrogliosis in AGD with comorbid pathology could be identified and quantified by in vivo MAO-B imaging.

Contribution of astrocytic histamine N-methyltransferase to histamine clearance and brain function in mice

Brain histamine acts as a neurotransmitter in the regulation of various brain activities. Previous studies have shown that histamine N-methyltransferase (HNMT), a histamine-metabolizing enzyme, controls brain histamine concentration and brain function. However, the relative contribution of astrocytic or neuronal HNMT to the regulation of the histaminergic system is still inconclusive. Here, we phenotyped astrocytes-specific HNMT knockout (cKO) mice to clarify the involvement of astrocytic HNMT in histamine clearance and brain function. First, we performed histological examinations using HNMT reporter mice and showed a wide distribution of HNMT in the brain and astrocytic HNMT expression. Then, we created cKO mice by Cre-loxP system and confirmed that HNMT expression in cKO primary astrocytes was robustly decreased. Although total HNMT level in the cortex was not substantially different between control and cKO brains, histamine concentration after histamine release was elevated in cKO cortex. In behavioral tests, impaired motor coordination and lower locomotor activity were observed in the cKO mice. However, anxiety-like behaviors, depression-like behaviors, and memory functions were not altered by astrocytic HNMT disruption. Although sleep analysis demonstrated that the quantity of wakefulness and sleep did not change, the increased power density of delta frequency during wakefulness indicated lower cortical activation in cKO mice. These results demonstrate that astrocytic HNMT contributes to histamine clearance after histamine release in the cortex and plays a role in the regulation of motor coordination, locomotor activity, and vigilance state.

Chemogenetic modulation of histaminergic neurons in the tuberomamillary nucleus alters territorial aggression and wakefulness

Designer receptor activated by designer drugs (DREADDs) techniques are widely used to modulate the activities of specific neuronal populations during behavioural tasks. However, DREADDs-induced modulation of histaminergic neurons in the tuberomamillary nucleus (HA^TMN neurons) has produced inconsistent effects on the sleep–wake cycle, possibly due to the use of Hdc-Cre mice driving Cre recombinase and DREADDs activity outside the targeted region. Moreover, previous DREADDs studies have not examined locomotor activity and aggressive behaviours, which are also regulated by brain histamine levels. In the present study, we investigated the effects of HA^TMN activation and inhibition on the locomotor activity, aggressive behaviours and sleep–wake cycle of Hdc-Cre mice with minimal non-target expression of Cre-recombinase. Chemoactivation of HA^TMN moderately enhanced locomotor activity in a novel open field. Activation of HA^TMN neurons significantly enhanced aggressive behaviour in the resident–intruder test. Wakefulness was increased and non-rapid eye movement (NREM) sleep decreased for an hour by HA^TMN chemoactivation. Conversely HA^TMN chemoinhibition decreased wakefulness and increased NREM sleep for 6 h. These changes in wakefulness induced by HA^TMN modulation were related to the maintenance of vigilance state. These results indicate the influences of HA^TMN neurons on exploratory activity, territorial aggression, and wake maintenance.

Organic Cation Transporters in Brain Histamine Clearance: Physiological and Psychiatric Implications

Histamine acts as a neurotransmitter in the central nervous system and is involved in numerous physiological functions. Recent studies have identified the causative role of decreased histaminergic systems in various neurological disorders. Thus, the brain histamine system has attracted attention as a therapeutic target to improve brain function. Neurotransmitter clearance is one of the most important processes for the regulation of neuronal activity and is an essential target for diverse drugs. Our previous study has shown the importance of histamine N-methyltransferase for the inactivation of brain histamine and the intracellular localization of this enzyme; the study indicated that the transport system for the movement of positively charged histamine from the extracellular to intracellular space is a prerequisite for histamine inactivation. Several studies on in vitro astrocytic histamine transport have indicated the contribution of organic cation transporter 3 (OCT3) and plasma membrane monoamine transporter (PMAT) in histamine uptake, although the importance of these transporters in in vivo histamine clearance remains unknown. Immunohistochemical analyses have revealed the expression of OCT3 and PMAT on neurons, emphasizing the importance of investigating neuronal histamine uptake. Further studies using knockout mice or fast-scan cyclic voltammetry will accelerate the research on histamine transporters. In this review article, we summarize histamine transport assays and describe the candidate transporters responsible for histamine transport in the brain.

Sleep-Wake Control by Melanin-Concentrating Hormone (MCH) Neurons: a Review of Recent Findings

PURPOSE OF THE REVIEW

Melanin-concentrating hormone (MCH)-expressing neurons located in the lateral hypothalamus are considered as an integral component of sleep-wake circuitry. However, the precise role of MCH neurons in sleep-wake regulation has remained unclear, despite several years of research employing a wide range of techniques. We review recent data on this aspect, which are mostly inconsistent, and propose a novel role for MCH neurons in sleep regulation.

RECENT FINDINGS

While almost all studies using "gain-of-function" approaches show an increase in rapid eye movement sleep (or paradoxical sleep; PS), loss-of-function approaches have not shown reductions in PS. Similarly, the reported changes in wakefulness or non-rapid eye movement sleep (slow-wave sleep; SWS) with manipulation of the MCH system using conditional genetic methods are inconsistent. Currently available data do not support a role for MCH neurons in spontaneous sleep-wake but imply a crucial role for them in orchestrating sleep-wake responses to changes in external and internal environments.

Histamine H1 receptor on astrocytes and neurons controls distinct aspects of mouse behaviour

Histamine is an important neurotransmitter that contributes to various processes, including the sleep-wake cycle, learning, memory, and stress responses. Its actions are mediated through histamine H₁–H₄ receptors. Gene knockout and pharmacological studies have revealed the importance of H₁ receptors in learning and memory, regulation of aggression, and wakefulness. H₁ receptors are abundantly expressed on neurons and astrocytes. However, to date, studies selectively investigating the roles of neuronal and astrocytic H₁ receptors in behaviour are lacking. We generated novel astrocyte- and neuron-specific conditional knockout (cKO) mice to address this gap in knowledge. cKO mice showed cell-specific reduction of H₁ receptor gene expression. Behavioural assessment revealed significant changes and highlighted the importance of H₁ receptors on both astrocytes and neurons. H₁ receptors on both cell types played a significant role in anxiety. Astrocytic H₁ receptors were involved in regulating aggressive behaviour, circadian rhythms, and quality of wakefulness, but not sleep behaviour. Our results emphasise the roles of neuronal H₁ receptors in recognition memory. In conclusion, this study highlights the novel roles of H₁ receptors on astrocytes and neurons in various brain functions.

Lateral hypothalamic neurotensin neurons promote arousal and hyperthermia

Sleep and wakefulness are greatly influenced by various physiological and psychological factors, but the neuronal elements responsible for organizing sleep-wake behavior in response to these factors are largely unknown. In this study, we report that a subset of neurons in the lateral hypothalamic area (LH) expressing the neuropeptide neurotensin (Nts) is critical for orchestrating sleep-wake responses to acute psychological and physiological challenges or stressors. We show that selective activation of Nts^LH neurons with chemogenetic or optogenetic methods elicits rapid transitions from non-rapid eye movement (NREM) sleep to wakefulness and produces sustained arousal, higher locomotor activity (LMA), and hyperthermia, which are commonly observed after acute stress exposure. On the other hand, selective chemogenetic inhibition of Nts^LH neurons attenuates the arousal, LMA, and body temperature (Tb) responses to a psychological stress (a novel environment) and augments the responses to a physiological stress (fasting).

A neurotensin-producing subset of neurons in the lateral hypothalamus promote arousal and thermogenesis; these neurons are necessary for appropriate sleep-wake and body temperature responses to various stressors.

Adjusting sleep-wake behavior in response to environmental and physiological challenges may not only be of protective value, but can also be vital for the survival of the organism. For example, while it is crucial to increase wake to explore a novel environment to search for potential threats and food sources, it is also necessary to decrease wake and reduce energy expenditure during prolonged absence of food. In this study, we report that a subset of neurons in the lateral hypothalamic area (LH) expressing the neuropeptide neurotensin (Nts) is critical for orchestrating sleep-wake responses to such challenges. We show that brief activation of Nts^LH neurons in mice evokes immediate arousals from sleep, while their sustained activation increases wake, locomotor activity, and body temperature for several hours. In contrast, when Nts^LH neurons are inhibited, mice are neither able to sustain wake in a novel environment nor able to reduce wake during food deprivation. These data suggest that Nts^LH neurons may be necessary for generating appropriate sleep-wake responses to a wide variety of environmental and physiological challenges.

Melanin-concentrating hormone neurons promote rapid eye movement sleep independent of glutamate release

Neurons containing melanin-concentrating hormone (MCH) in the posterior lateral hypothalamus play an integral role in rapid eye movement sleep (REMs) regulation. As MCH neurons also contain a variety of other neuropeptides [e.g., cocaine- and amphetamine-regulated transcript (CART) and nesfatin-1] and neurotransmitters (e.g., glutamate), the specific neurotransmitter responsible for REMs regulation is not known. We hypothesized that glutamate, the primary fast-acting neurotransmitter in MCH neurons, is necessary for REMs regulation. To test this hypothesis, we deleted vesicular glutamate transporter (Vglut2; necessary for synaptic release of glutamate) specifically from MCH neurons by crossing MCH-Cre mice (expressing Cre recombinase in MCH neurons) with Vglut2^flox/flox mice (expressing LoxP-modified alleles of Vglut2), and studied the amounts, architecture and diurnal variation of sleep-wake states during baseline conditions. We then activated the MCH neurons lacking glutamate neurotransmission using chemogenetic methods and tested whether these MCH neurons still promoted REMs. Our results indicate that glutamate in MCH neurons contributes to normal diurnal variability of REMs by regulating the levels of REMs during the dark period, but MCH neurons can promote REMs even in the absence of glutamate.

Melanin-concentrating hormone neurons contribute to dysregulation of rapid eye movement sleep in narcolepsy

The lateral hypothalamus contains neurons producing orexins that promote wakefulness and suppress REM sleep as well as neurons producing melanin-concentrating hormone (MCH) that likely promote REM sleep. Narcolepsy with cataplexy is caused by selective loss of the orexin neurons, and the MCH neurons appear unaffected. As the orexin and MCH systems exert opposing effects on REM sleep, we hypothesized that imbalance in this REM sleep-regulating system due to activity in the MCH neurons may contribute to the striking REM sleep dysfunction characteristic of narcolepsy. To test this hypothesis, we chemogenetically activated the MCH neurons and pharmacologically blocked MCH signaling in a murine model of narcolepsy and studied the effects on sleep-wake behavior and cataplexy. To chemoactivate MCH neurons, we injected an adeno-associated viral vector containing the hM3Dq stimulatory DREADD into the lateral hypothalamus of orexin null mice that also express Cre recombinase in the MCH neurons (MCH-Cre::OX-KO mice) and into control MCH-Cre mice with normal orexin expression. In both lines of mice, activation of MCH neurons by clozapine-N-oxide (CNO) increased rapid eye movement (REM) sleep without altering other states. In mice lacking orexins, activation of the MCH neurons also increased abnormal intrusions of REM sleep manifest as cataplexy and short latency transitions into REM sleep (SLREM). Conversely, a MCH receptor 1 antagonist, SNAP 94847, almost completely eliminated SLREM and cataplexy in OX-KO mice. These findings affirm that MCH neurons promote REM sleep under normal circumstances, and their activity in mice lacking orexins likely triggers abnormal intrusions of REM sleep into non-REM sleep and wake, resulting in the SLREM and cataplexy characteristic of narcolepsy.

JNJ10181457, a histamine H3 receptor inverse agonist, regulates in vivo microglial functions and improves depression-like behaviours in mice

Brain histamine acts as a neurotransmitter and regulates various physiological functions, such as learning and memory, sleep-wake cycles, and appetite regulation. We have recently shown that histamine H3 receptor (H3R) is expressed in primary mouse microglia and has a strong influence on critical functions in microglia, including chemotaxis, phagocytosis, and cytokine secretion in vitro. However, the importance of H3R in microglial activity in vivo remains unknown. Here, we examined the effects of JNJ10181457 (JNJ), a selective and potent H3R inverse agonist, on microglial functions ex vivo and in vivo. First, we injected ATP, which is a typical chemoattractant, into hippocampal slices to investigate the effect of JNJ on chemotaxis. ATP-induced microglial migration toward the injected site was significantly suppressed by JNJ treatment. Next, we examined whether JNJ affected microglial phagocytosis in hippocampal slices and in the prefrontal cortex. Microglial engulfment of dead neurons induced by N-methyl-_d-aspartate was inhibited in the presence of JNJ. The increase in zymosan particle uptake by activated microglia in the prefrontal cortex was prevented by JNJ administration. Finally, we determined the importance of JNJ in a lipopolysaccharide (LPS)-induced depression model. JNJ reduced the LPS-induced upregulation of microglial pro-inflammatory cytokines and improved depression-like behaviour in the tail-suspension test. These results demonstrate the inhibitory effects of JNJ on chemotaxis, phagocytosis, and cytokine production in microglia inside the brain, and highlight the importance of microglial H3R for brain homeostasis.

Characterization of murine polyspecific monoamine transporters

The dysregulation of monoamine clearance in the central nervous system occurs in various neuropsychiatric disorders, and the role of polyspecific monoamine transporters in monoamine clearance is increasingly highlighted in recent studies. However, no study to date has properly characterized polyspecific monoamine transporters in the mouse brain. In the present study, we examined the kinetic properties of three mouse polyspecific monoamine transporters [organic cation transporter 2 (Oct2), Oct3, and plasma membrane monoamine transporter (Pmat)] and compared the absolute mRNA expression levels of these transporters in various brain areas. First, we evaluated the affinities of each transporter for noradrenaline, dopamine, serotonin, and histamine, and found that mouse ortholog substrate affinities were similar to those of human orthologs. Next, we performed drug inhibition assays and identified interspecies differences in the pharmacological properties of polyspecific monoamine transporters; in particular, corticosterone and decynium‐22, which are widely recognized as typical inhibitors of human OCT3, enhanced the transport activity of mouse Oct3. Finally, we quantified absolute mRNA expression levels of each transporter in various regions of the mouse brain and found that while all three transporters were ubiquitously expressed, Pmat was the most highly expressed transporter. These results provide an important foundation for future translational research investigating the roles of polyspecific monoamine transporters in neurological and neuropsychiatric disease.

Histamine H3 receptor in primary mouse microglia inhibits chemotaxis, phagocytosis, and cytokine secretion

Histamine is a physiological amine which initiates a multitude of physiological responses by binding to four known G-protein coupled histamine receptor subtypes as follows: histamine H1 receptor (H1 R), H2 R, H3 R, and H4 R. Brain histamine elicits neuronal excitation and regulates a variety of physiological processes such as learning and memory, sleep-awake cycle and appetite regulation. Microglia, the resident macrophages in the brain, express histamine receptors; however, the effects of histamine on critical microglial functions such as chemotaxis, phagocytosis, and cytokine secretion have not been examined in primary cells. We demonstrated that mouse primary microglia express H2 R, H3 R, histidine decarboxylase, a histamine synthase, and histamine N-methyltransferase, a histamine metabolizing enzyme. Both forskolin-induced cAMP accumulation and ATP-induced intracellular Ca(2+) transients were reduced by the H3 R agonist imetit but not the H2 R agonist amthamine. H3 R activation on two ubiquitous second messenger signalling pathways suggests that H3 R can regulate various microglial functions. In fact, histamine and imetit dose-dependently inhibited microglial chemotaxis, phagocytosis, and lipopolysaccharide (LPS)-induced cytokine production. Furthermore, we confirmed that microglia produced histamine in the presence of LPS, suggesting that H3 R activation regulate microglial function by autocrine and/or paracrine signalling. In conclusion, we demonstrate the involvement of histamine in primary microglial functions, providing the novel insight into physiological roles of brain histamine.

Role of histamine H3 receptor in glucagon-secreting αTC1.6 cells

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Histamine H₃ receptor is expressed in pancreatic α-cells.

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Histamine H₃ receptor negatively regulates glucagon secretion from αTC1.6 cells.

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Immepip, a selective H₃ receptor agonist, decreases serum glucagon concentration in rats.

Pancreatic α-cells secrete glucagon to maintain energy homeostasis. Although histamine has an important role in energy homeostasis, the expression and function of histamine receptors in pancreatic α-cells remains unknown. We found that the histamine H₃ receptor (H₃R) was expressed in mouse pancreatic α-cells and αTC1.6 cells, a mouse pancreatic α-cell line. H₃R inhibited glucagon secretion from αTC1.6 cells by inhibiting an increase in intracellular Ca²⁺ concentration. We also found that immepip, a selective H₃R agonist, decreased serum glucagon concentration in rats. These results suggest that H₃R modulates glucagon secretion from pancreatic α-cells.

Insufficient intake of L-histidine reduces brain histamine and causes anxiety-like behaviors in male mice

L-histidine is one of the essential amino acids for humans, and it plays a critical role as a component of proteins. L-histidine is also important as a precursor of histamine. Brain histamine is synthesized from L-histidine in the presence of histidine decarboxylase, which is expressed in histamine neurons. In the present study, we aimed to elucidate the importance of dietary L-histidine as a precursor of brain histamine and the histaminergic nervous system. C57BL/6J male mice at 8 wk of age were assigned to 2 different diets for at least 2 wk: the control (Con) diet (5.08 g L-histidine/kg diet) or the low L-histidine diet (LHD) (1.28 g L-histidine/kg diet). We measured the histamine concentration in the brain areas of Con diet-fed mice (Con group) and LHD-fed mice (LHD group). The histamine concentration was significantly lower in the LHD group [Con group vs. LHD group: histamine in cortex (means ± SEs): 13.9 ± 1.25 vs. 9.36 ± 0.549 ng/g tissue; P = 0.002]. Our in vivo microdialysis assays revealed that histamine release stimulated by high K(+) from the hypothalamus in the LHD group was 60% of that in the Con group (P = 0.012). However, the concentrations of other monoamines and their metabolites were not changed by the LHD. The open-field tests showed that the LHD group spent a shorter amount of time in the central zone (87.6 ± 14.1 vs. 50.0 ± 6.03 s/10 min; P = 0.019), and the light/dark box tests demonstrated that the LHD group spent a shorter amount of time in the light box (198 ± 8.19 vs. 162 ± 14.1 s/10 min; P = 0.048), suggesting that the LHD induced anxiety-like behaviors. However, locomotor activity, memory functions, and social interaction did not differ between the 2 groups. The results of the present study demonstrated that insufficient intake of histidine reduced the brain histamine content, leading to anxiety-like behaviors in the mice.

Predominant role of plasma membrane monoamine transporters in monoamine transport in 1321N1, a human astrocytoma-derived cell line

Monoamine neurotransmitters should be immediately removed from the synaptic cleft to avoid excessive neuronal activity. Recent studies have shown that astrocytes and neurons are involved in monoamine removal. However, the mechanism of monoamine transport by astrocytes is not entirely clear. We aimed to elucidate the transporters responsible for monoamine transport in 1321N1, a human astrocytoma-derived cell line. First, we confirmed that 1321N1 cells transported dopamine, serotonin, norepinephrine, and histamine in a time- and dose-dependent manner. Kinetics analysis suggested the involvement of low-affinity monoamine transporters, such as organic cation transporter (OCT) 2 and 3 and plasma membrane monoamine transporter (PMAT). Monoamine transport in 1321N1 cells was not Na(+) /Cl(-) dependent but was inhibited by decynium-22, an inhibitor of low-affinity monoamine transporters, which supported the importance of low-affinity transporters. RT-PCR assays revealed that 1321N1 cells expressed OCT3 and PMAT but no other neurotransmitter transporters. Another human astrocytoma-derived cell line, U251MG, and primary human astrocytes also exhibited the same gene expression pattern. Gene-knockdown assays revealed that 1321N1 and primary human astrocytes could transport monoamines predominantly through PMAT and partly through OCT3. These results might indicate that PMAT and OCT3 in human astrocytes are involved in monoamine clearance.

Molecular mechanism of histamine clearance by primary human astrocytes

Histamine clearance is an essential process for avoiding excessive histaminergic neuronal activity. Previous studies using rodents revealed the predominant role of astrocytes in brain histamine clearance. However, the molecular mechanism of histamine clearance has remained unclear. We detected histamine N-methyltransferase (HNMT), a histamine-metabolizing enzyme, in primary human astrocytes and the astrocytes of human brain specimens. Immunocytochemical analysis and subcellular fractionation assays revealed that active HNMT localized to the cytosol, suggesting that histamine transport into the cytosol is crucial for histamine inactivation. We showed that primary human astrocytes transported histamine in a time-dependent manner. Kinetics analysis showed that two low-affinity transporters were involved in histamine transport. Histamine uptake by primary human astrocytes was not dependent on the extracellular Na(+) /Cl(-) concentration. Histamine is reported to be a substrate for three low-affinity and Na(+) /Cl(-) -independent transporters: organic cation transporter 2 (OCT2), OCT3, and plasma membrane monoamine transporter (PMAT). RT-PCR analysis revealed that OCT3 and PMAT were expressed in primary human astrocytes. Immunohistochemistry confirmed OCT3 and PMAT expression in the astrocytes of human brain specimens. Drug inhibition assays and gene knockdown assays revealed the major contribution of PMAT and the minor contribution of OCT3 to histamine transport. The present study demonstrates for the first time that the molecular mechanism of histamine clearance is by primary human astrocytes. These findings might indicate that PMAT, OCT3 and HNMT in human astrocytes play a role in the regulation of extraneuronal histamine concentration and the activities of histaminergic neurons.

[(11)C]Doxepin binding to histamine H1 receptors in living human brain: reproducibility during attentive waking and circadian rhythm

Molecular imaging in neuroscience is a new research field that enables visualization of the impact of molecular events on brain structure and function in humans. While magnetic resonance-based imaging techniques can provide complex information at the level of system, positron emission tomography (PET) enables determination of the distribution and density of receptor and enzyme in the human brain. Previous studies using [(11)C]raclopride and [(11)C]FLB457 revealed that the release of neuronal dopamine was increased in human brain by psychostimulants or reward stimuli. Following on from these previous [(11)C]raclopride studies, we examined whether the levels of neuronal release of histamine might change [(11)C]doxepin binding to the H1 receptors under the influence of physiological stimuli. The purpose of the present study was to evaluate the test-retest reliability of quantitative measurement of [(11)C]doxepin binding between morning and afternoon and between resting and attentive waking conditions in healthy human subjects. There was a trend for a decrease in [(11)C]doxepin binding during attentive calculation tasks compared with that in resting conditions, but the difference (less than 10%) was not significant. Similarly, the binding potential of [(11)C]doxepin in the cerebral cortex was slightly higher in the morning than that in the afternoon, but it was also insignificant. These data suggest that higher histamine release during wakefulness could not decrease the [(11)C]doxepin binding in the brain. This study confirmed the reproducibility and reliability of [(11)C]doxepin in the previous imaging studies to measure the H1 receptor.

Involvement of both granular cells and plasmatocytes in phagocytic reactions in the greater wax moth, Galleria mellonella

Although it has been previously found by most authors that only plasmatocytes are involved in phagocytosis of non-self in the greater wax moth, Galleria mellonella, in the present study we demonstrate that in vitro, both granular cells and plasmatocytes are involved in this reaction, using monolayers of these haemocytes prepared from larval haemolymph by a differential cell fractionation method. The adhesion of granular cells to glassware and phagocytosis by granular cells of FITC-labelled silica beads were both greatly reduced by the presence of p-NPGB, a serine proteinase inhibitor, which is known to inhibit the activation of the prophenoloxidase cascade, but the reactions were only partly influenced by PTU, an inhibitor of phenoloxidase. These results suggest that an enhancing factor for both reactions is phenoloxidase itself or a component induced during the course of activation of the prophenoloxidase cascade, but not the melanised substance produced by the action of this reaction. For plasmatocytes, attachment to non-self was totally blocked by the absence of CaCl(2) or by the presence of EDTA at concentrations greater than 20 mM, and phagocytosis was greatly enhanced by CaCl(2), but suppressed by EDTA. These results suggest that calcium is a factor required for adhesion of plasmatocytes, and that it also functions to enhance their phagocytic action.

A Na+-H+ exchange inhibitor (SM-20550) protects from microvascular deterioration and myocardial injury after reperfusion

Na+-H+ exchange inhibitors may reduce myocardial damage after reperfusion. However, their effects on microvascular deterioration are not known. We examined the potency of a novel Na+-H+ exchange inhibitor, SM-20550 [ N-(Aminoiminomethyl)-1,4-dimethyl-1H-indole-2-carboxamide methanesulfonate], and its effects on microvascular damage after reperfusion. In an in vitro study, the Na+-H+ exchange inhibiting activity of SM-20550 was about 10 times greater than that of ethylisopropyl amiloride. In in vivo experiments, we occluded the left circumflex coronary artery in 29 dogs for 2 h and then reperfused for 5 h. SM-20550 was administered either before ischemia (n = 11) or before reperfusion (n = 7). Another 11 dogs served as controls. We found that SM-20550 not only improved coronary vasodilator responses to acetylcholine and adenosine after reperfusion, but also reduced infarct size (P < 0.01). Intramyocardial bleeding, which should reflect microvascular damage, was not found in dogs with SM-20550 treatment. Infarct size was correlated inversely with collateral blood flow in control (both, P < 0.01) but not in SM-20550-treated animals. Furthermore, SM-20550 significantly suppressed ventricular fibrillation during both ischemia and reperfusion. These results suggest that protective effects of Na+-H+ exchange inhibitors on reperfused myocardium are due at least in part to microvascular protection.

Bilateral coronary ostial stenosis and aortic regurgitation due to syphilitic aortitis

Coronary ostial stenosis in otherwise normal coronary vessels, is a rare complication of syphilitic aortitis, and most of the cases are found at autopsy. We report here a case in which bilateral coronary ostial stenosis and aortic regurgitation due to syphilitic aortitis was diagnosed; coronary artery bypass graft and aortic valve replacement were then performed. The macroscopic finding and the histopathological examination of the ascending aorta revealed the presence of syphilitic aortitis. It is important to note that syphilis is one of the causes of coronary ostial stenosis in young adults associated with aortic regurgitation.

Ventricular unloading and improvement in left ventricular function after angiotensin converting enzyme inhibition with enalapril in patients with chronic congestive heart failure

To clarify how angiotensin converting enzyme inhibition affects left ventricular function through ventricular unloading, ventricular wall stress, ventricular volumes, and other cardiac indices and exercise tolerance were evaluated in 17 patients with mild to moderate chronic congestive heart failure before and after 3 months of treatment with enalapril. Echocardiographic examination revealed that treatment with this angiotensin converting enzyme inhibitor resulted in significant reductions in end-systolic wall stress (117 +/- 25 to 89 +/- 28 g/cm2, p < 0.01) and left ventricular volume indices (end-diastolic: 163 +/- 56 to 143 +/- 60; end-systolic 99 +/- 51 to 77 +/- 57 ml/m2 p < 0.01). Ejection fraction (42 +/- 11 to 48 +/- 13%, p < 0.01) and systolic blood pressure/end-systolic volume (SBP/ESV; 1.06 +/- 0.30 to 1.33 +/- 0.48 mmHg/ml, p < 0.01) were both increased. By radionuclide ventriculography, ejection fraction and peak ejection rate (2.30 +/- 0.74 to 2.80 +/- 0.76 EDV/sec, p < 0.01) were increased, while time to peak ejection, time to peak filling, and peak filling rate were unchanged. Heart rate and double product at exercise were decreased and delta EF was significantly increased (-1.4 +/- 4.1 to 1.6 +/- 4.4%, p < 0.02). The decrease in end-systolic wall stress was consistently related to both the increase in ejection fraction and SBP/ESV, while the decrease in end-diastolic volume was related only to SBP/ESV and not to ejection fraction. Furthermore, there was a direct relationship between the decrease in systolic wall stress and the decrease in end-diastolic volume.(ABSTRACT TRUNCATED AT 250 WORDS)