Inhibition of Indoleamine 2,3-Dioxygenase Exerts Antidepressant-like Effects through Distinct Pathways in Prelimbic and Infralimbic Cortices in Rats under Intracerebroventricular Injection with Streptozotocin.

The application of intracerebroventricular injection of streptozotocin (ICV-STZ) is considered a useful animal model to mimic the onset and progression of sporadic Alzheimer's disease (sAD). In rodents, on day 7 of the experiment, the animals exhibit depression-like behaviors. Indoleamine 2,3-dioxygenase (IDO), a rate-limiting enzyme catalyzing the conversion of tryptophan (Trp) to kynurenine (Kyn), is closely related to depression and AD. The present study aimed to investigate the pathophysiological mechanisms of preliminary depression-like behaviors in ICV-STZ rats in two distinct cerebral regions of the medial prefrontal cortex, the prelimbic cortex (PrL) and infralimbic cortex (IL), both presumably involved in AD progression in this model, with a focus on IDO-related Kyn pathways. The results showed an increased Kyn/Trp ratio in both the PrL and IL of ICV-STZ rats, but, intriguingly, abnormalities in downstream metabolic pathways were different, being associated with distinct biological effects. In the PrL, the neuroprotective branch of the Kyn pathway was attenuated, as evidenced by a decrease in the kynurenic acid (KA) level and Kyn aminotransferase II (KAT II) expression, accompanied by astrocyte alterations, such as the decrease in glial fibrillary acidic protein (GFAP)-positive cells and increase in morphological damage. In the IL, the neurotoxicogenic branch of the Kyn pathway was enhanced, as evidenced by an increase in the 3-hydroxy-kynurenine (3-HK) level and kynurenine 3-monooxygenase (KMO) expression paralleled by the overactivation of microglia, reflected by an increase in ionized calcium-binding adaptor molecule 1 (Iba1)-positive cells and cytokines with morphological alterations. Synaptic plasticity was attenuated in both subregions. Additionally, microinjection of the selective IDO inhibitor 1-Methyl-DL-tryptophan (1-MT) in the PrL or IL alleviated depression-like behaviors by reversing these different abnormalities in the PrL and IL. These results suggest that the antidepressant-like effects linked to Trp metabolism changes induced by 1-MT in the PrL and IL occur through different pathways, specifically by enhancing the neuroprotective branch in the PrL and attenuating the neurotoxicogenic branch in the IL, involving distinct glial cells.

Ganoderma lucidum spore extract improves sleep disturbances in a rat model of sporadic Alzheimer's disease.

Introduction: Ganoderma lucidum (G. lucidum, Lingzhi) has long been listed as a premium tonic that can be used to improve restlessness, insomnia, and forgetfulness. We previously reported that a rat model of sporadic Alzheimer's disease (sAD) that was induced by an intracerebroventricular injection of streptozotocin (ICV-STZ) showed significant learning and cognitive deficits and sleep disturbances. Treatment with a G. lucidum spore extract with the sporoderm removed (RGLS) prevented learning and memory impairments in sAD model rats. Method: The present study was conducted to further elucidate the preventive action of RGLS on sleep disturbances in sAD rats by EEG analysis, immunofluorescence staining, HPLC-MS/MS and Western blot. Results: Treatment with 720 mg/kg RGLS for 14 days significantly improved the reduction of total sleep time, rapid eye movement (REM) sleep time, and non-REM sleep time in sAD rats. The novelty recognition experiment further confirmed that RGLS prevented cognitive impairments in sAD rats. We also found that RGLS inhibited the nuclear factor-κB (NF-κB)/Nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammatory pathway in the medial prefrontal cortex (mPFC) in sAD rats and ameliorated the lower activity of γ-aminobutyric acid (GABA)-ergic neurons in the parabrachial nucleus (PBN). Discussion: These results suggest that inhibiting the neuroinflammatory response in the mPFC may be a mechanism by which RGLS improves cognitive impairment. Additionally, improvements in PBN-GABAergic activity and the suppression of neuroinflammation in the mPFC in sAD rats might be a critical pathway to explain the preventive effects of RGLS on sleep disturbances in sAD.

Sporoderm-removed Ganoderma lucidum spores ameliorated early depression-like behavior in a rat model of sporadic Alzheimer's disease.

Introduction: Ganoderma lucidum: (G. lucidum, Lingzhi) is a medicinal and edible homologous traditional Chinese medicine that is used to treat various diseases, including Alzheimer's disease and mood disorders. We previously reported that the sporoderm-removed G. lucidum spore extract (RGLS) prevented learning and memory impairments in a rat model of sporadic Alzheimer's disease (sAD), but the effect of RGLS on depression-like behaviors in this model and its underlying molecular mechanisms of action remain unclear. Method: The present study investigated protective effects of RGLS against intracerebroventricular streptozotocin (ICV-STZ)-induced depression in a rat model of sAD and its underlying mechanism. Effects of RGLS on depression- and anxiety-like behaviors in ICV-STZ rats were assessed in the forced swim test, sucrose preference test, novelty-suppressed feeding test, and open field test. Results: Behavioral tests demonstrated that RGLS (360 and 720 mg/kg) significantly ameliorated ICV-STZ-induced depression- and anxiety-like behaviors. Immunofluorescence, Western blot and enzyme-linked immunosorbent assay results further demonstrated that ICV-STZ rats exhibited microglia activation and neuroinflammatory response in the medial prefrontal cortex (mPFC), and RGLS treatment reversed these changes, reflected by the normalization of morphological changes in microglia and the expression of NF-κB, NLRP3, ASC, caspase-1 and proinflammatory cytokines. Golgi staining revealed that treatment with RGLS increased the density of mushroom spines in neurons. This increase was associated with elevated expression of brain-derived neurotrophic protein in the mPFC. Discussion: In a rat model of ICV-STZ-induced sAD, RGLS exhibits antidepressant-like effects, the mechanism of which may be related to suppression of the inflammatory response modulated by the NF-κB/NLRP3 pathway and enhancement of synaptic plasticity in the mPFC.

Chronic Stress-Induced Elevation of Melanin-Concentrating Hormone in the Locus Coeruleus Inhibits Norepinephrine Production and Associated With Depression-Like Behaviors in Rats.

BACKGROUND: Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that projects throughout the central nervous system, including the noradrenergic locus coeruleus (LC). Our previous study suggested that MCH/MCH receptor 1 (MCHR1) in the LC may be involved in the regulation of depression. The present study investigated whether the role of MCH/MCHR1 in the LC in depression-like behaviors is associated with the regulation of norepinephrine. METHOD: Chronic unpredictable stress (CUS) and an acute intra-LC microinjection of MCH induced depression-like behaviors in rats. The MCHR1 antagonist SNAP-94847 was also microinjected in the LC in rats that were suffering CUS or treated with MCH. The sucrose preference, forced swim, and locomotor tests were used for behavioral evaluation. Immunofluorescence staining, enzyme-linked immunosorbent assay, western blot, and high-performance liquid chromatography with electrochemical detection were used to explore the mechanism of MCH/MCHR1 in the regulation of depression-like behaviors. RESULTS: CUS induced an abnormal elevation of MCH levels and downregulated MCHR1 in the LC, which was highly correlated with the formation of depression-like behaviors. SNAP-94847 exerted antidepressant effects in CUS-exposed rats by normalizing tyrosine hydroxylase, dopamine ß hydroxylase, and norepinephrine in the LC. An acute microinjection of MCH induced depression-like behaviors through its action on MCHR1. MCHR1 antagonism in the LC significantly reversed the MCH-induced downregulation of norepinephrine production by normalizing MCHR1-medicated cAMP-PKA signaling. CONCLUSIONS: Our study confirmed that the MCH/MCHR1 system in the LC may be involved in depression-like behaviors by downregulating norepinephrine production. These results improve our understanding of the pathogenesis of depression that is related to the MCH/MCHR1 system in the LC.

Reduction of BDNF Levels and Biphasic Changes in Glutamate Release in the Prefrontal Cortex Correlate with Susceptibility to Chronic Stress-Induced Anhedonia.

Chronic stress has been considered to induce depressive symptoms, such as anhedonia, particularly in susceptible individuals. Synaptic plasticity in the prefrontal cortex (PFC) is closely associated with susceptibility or resilience to chronic stress-induced anhedonia. However, effects of chronic stress with different durations on the neurobiological mechanisms that underlie susceptibility to anhedonia remain unclear. The present study investigated effects of chronic mild stress (CMS) for 14, 21, and 35 d on anhedonia-like behavior and glutamate synapses in the PFC. We found that brain-derived neurotrophic factor (BDNF) levels in the PFC significantly decreased only in anhedonia-susceptible rats that were exposed to CMS for 14, 21, and 35 d. Additionally, 14 d of CMS increased prefrontal glutamate release, and 35 d of CMS decreased glutamate release, in addition to reducing synaptic proteins and spine density in the PFC. Moreover, we found that anhedonia-like behavior in a subset of rats spontaneously decreased, accompanied by the restoration of BDNF levels and glutamate release, on day 21 of CMS. Ketamine treatment restored the reduction of BDNF levels and biphasic changes in glutamate release that were induced by CMS. Our findings revealed a progressive reduction of synaptic plasticity and biphasic changes in glutamate release in the PFC during CMS. Reductions of BDNF levels may be key neurobiological markers of susceptibility to stress-induced anhedonia.

Anti-stress effects of combined block of glucocorticoid and mineralocorticoid receptors in the paraventricular nucleus of the hypothalamus.

BACKGROUND AND PURPOSE: Mineralocorticoid receptors (MRs), glucocorticoid receptors (GRs) and corticotropin-releasing factor (CRF) in the paraventricular nucleus of hypothalamus (PVN) are involved in the response to stress. The present study investigated the role of GRs and MRs in the PVN in regulating depressive and anxiety-like behaviours. EXPERIMENTAL APPROACH: To model chronic stress, rats were exposed to corticosterone treatment via drinking water for 21 days, and GR antagonist RU486 and MR antagonist spironolactone, alone and combined, were directly injected in the PVN daily for the last 7 days of corticosterone treatment. Behavioural tests were run on days 22 and 23. Depressive- and anxiety-like behaviours were evaluated in forced swim test, sucrose preference test, novelty-suppressed feeding test and social interaction test. The expression of GRs, MRs and CRF were detected by western blot. KEY RESULTS: Rats exposed to corticosterone exhibited depressive- and anxiety-like behaviours. The expression of GRs and MRs decreased, and CRF levels increased in the PVN. The intra-PVN administration of RU486 increased the levels of GRs and CRF without influencing depressive- or anxiety-like behaviours. The spironolactone-treated group exhibited an increase in MRs without influencing GRs and CRF in the PVN and improved anxiety-like behaviours. Interestingly, the intra-PVN administration of RU486 and spironolactone combined restored expression of GRs, MRs and CRF and improved depressive- and anxiety-like behaviours. CONCLUSION AND IMPLICATIONS: In this rat model of stress, the simultaneous restoration of GRs, MRs and CRF in the PVN might play an important role in the treatment of depression and anxiety.

Prophylactic effects of sporoderm-removed Ganoderma lucidum spores in a rat model of streptozotocin-induced sporadic Alzheimer's disease.

ETHNOPHARMACOLOGICAL RELEVANCE: Ganoderma lucidum (G. lucidum, Lingzhi), also known as "immortality mushroom" has been broadly used to improve health and longevity for thousands of years in Asia. G. lucidum and its spores have been used to promote health, based on its broad pharmacological and therapeutic activity. This species is recorded in Chinese traditional formula as a nootropic and has been suggested to improve cognitive dysfunction in Alzheimer's disease. However, little is known about the nootropic effects and molecular mechanism of action of G. lucidum spores. AIM OF THE STUDY: The present study investigated the protective effects of sporoderm-deficient Ganoderma lucidum spores (RGLS) against learning and memory impairments and its mechanism of action. MATERIALS AND METHODS: In the Morris water maze, the effects of RGLS on learning and memory impairments were evaluated in a rat model of sporadic Alzheimer's disease that was induced by an intracerebroventricular injection of streptozotocin (STZ). Changes in amyloid ß (Aß) expression, Tau expression and phosphorylation, brain-derived neurotrophic factor (BDNF), and the BDNF receptor tropomyosin-related kinase B (TrkB) in the hippocampus were evaluated by Western blot. RESULTS: Treatment with RGLS (360 and 720 mg/kg) significantly enhanced memory in the rat model of STZ-induced sporadic Alzheimer's disease and reversed the STZ-induced increases in Aß expression and Tau protein expression and phosphorylation at Ser199, Ser202, and Ser396. The STZ-induced decreases in neurotrophic factors, including BDNF, TrkB and TrkB phosphorylation at Tyr816, were reversed by treatment with RGLS. CONCLUSION: These findings indicate that RGLS prevented learning and memory impairments in the present rat model of STZ-induced sporadic Alzheimer's disease, and these effects depended on a decrease in Aß expression and Tau hyperphosphorylation and the modulation of BDNF-TrkB signaling in the hippocampus.

VAMP3 and SNAP23 as Potential Targets for Preventing the Disturbed Flow-Accelerated Thrombus Formation.

Disturbed blood flow has been recognized to promote platelet aggregation and thrombosis via increasing accumulation of von Willebrand factor (VWF) at the arterial post-stenotic sites. The mechanism underlying the disturbed-flow regulated endothelial VWF production remains elusive. Here we described a mouse model, in which the left external carotid artery (LECA) is ligated to generate disturbed flow in the common carotid artery. Ligation of LECA increased VWF accumulation in the plasma. Carotid arterial thrombosis was induced by ferric chloride (FeCl3) application and the time to occlusion in the ligated vessels was reduced in comparison with the unligated vessels. In vitro, endothelial cells were subjected to oscillatory shear (OS, 0.5 ± 4 dynes/cm2) or pulsatile shear (PS, 12 ± 4 dynes/cm2). OS promoted VWF secretion as well as the cell conditioned media-induced platelet aggregation by regulating the intracellular localization of vesicle-associated membrane protein 3 (VAMP3) and synaptosomal-associated protein 23 (SNAP23). Disruption of vimentin intermediate filaments abolished the OS-induced translocation of SNAP23 to the cell membrane. Knockdown of VAMP3 and SNAP23 reduced the endothelial secretion of VWF. Systemic inhibition of VAMP3 and SNAP23 by treatment of mice with rapamycin significantly ameliorated the FeCl3-induced thrombogenesis, whereas intraluminal overexpression of VAMP3 and SNAP23 aggravated it. Our findings demonstrate VAMP3 and SNAP23 as potential targets for preventing the disturbed flow-accelerated thrombus formation.

A common neuronal mechanism of hypertension and sleep disturbances in spontaneously hypertensive rats: Role of orexinergic neurons.

Epidemiologic studies have shown that sleep disorders are associated with the development of hypertension. The present study investigated dynamic changes in sleep patterns during the development of hypertension across the lifespan in spontaneously hypertensive rats (SHRs) and the neural mechanism that underlies these comorbidities, with a focus on the orexinergic system. Blood pressure in rats was measured using a noninvasive blood pressure tail cuff. Sleep was monitored by electroencephalographic and electromyographic recordings. Immunohistochemistry was used to detect the density and activity of orexinergic neurons in the perifornical nucleus. Hcrt2-SAP (400 or 800 ng) was microinjected in the lateral hypothalamus to lesion orexinergic neurons. Compared with Wistar-Kyoto rats, SHRs exhibited various patterns of sleep disturbances. In SHRs, dynamic changes in hypersomnia in the rats' active phase was not synchronized with the development of hypertension, but hyperarousal in the inactive phase and difficulties in falling asleep were observed concurrently with the development of hypertension. Furthermore, the density and activity of orexinergic neurons in the perifornical nucleus were significantly higher in SHRs than in age-matched Wistar-Kyoto rats. The reduction of orexinergic neurons in the lateral hypothalamus partially ameliorated the development of hypertension and prevented difficulties in falling asleep in SHRs. These results indicate that although the correlation between sleep disturbances and hypertension is very complex, common mechanisms may underlie these comorbidities in SHRs. Overactivity of the orexin system may be one such common mechanism.

Serotonergic system may be involved in alterations of sleep homeostasis in spontaneously hypertensive rats.

Hypertension is associated with sleep disorders. Spontaneously hypertensive rats are derived from Wistar-Kyoto rats and widely used in research on hypertension. The present study investigated the propensity to sleep and electroencephalographic spectrum changes over 24 hr in spontaneously hypertensive rats, and proposed the involvement of the serotonergic system in these alterations. Time-course analysis showed that spontaneously hypertensive rats exhibit hyperarousal during the light phase but hypersomnia during the dark phase. Spontaneously hypertensive rats also exhibited less slight fluctuation in electroencephalographic delta power density over 24 hr as compared with Wistar-Kyoto rats, suggesting that the accumulation or elimination of sleep pressure was disrupted. Sleep deprivation disrupted the regulation of sleep homeostasis in spontaneously hypertensive rats, reflected by less sleep time and poor sleep quality during the recovery period. The density and activity of serotonergic neurons in the dorsal raphe nucleus were higher in spontaneously hypertensive rats compared with Wistar-Kyoto rats. Interestingly, we observed the absence of fluctuations in 5-hydroxytryptamine and 5-hydroxyindoleacetic acid across the sleep, wake, sleep deprivation and sleep recovery stages in spontaneously hypertensive rats, which were dramatically different from Wistar-Kyoto rats. These results indicate that the disruption of sleep-wake pattern and sleep homeostasis in spontaneously hypertensive rats might be related to abnormalities of the serotonergic system.

Protection from Amyloid ß Peptide-Induced Memory, Biochemical, and Morphological Deficits by a Phosphodiesterase-4D Allosteric Inhibitor.

Recent imaging studies of amyloid and tau in cognitively normal elderly subjects imply that Alzheimer's pathology can be tolerated by the brain to some extent due to compensatory mechanisms operating at the cellular and synaptic levels. The present study investigated the effects of an allosteric inhibitor of phosphodiesterase-4D (PDE4D), known as BPN14770 (2-(4-((2-(3-Chlorophenyl)-6-(trifluoromethyl)pyridin-4-yl)methyl)phenyl)acetic Acid), on impairment of memory, dendritic structure, and synaptic proteins induced by bilateral microinjection of oligomeric amyloid beta (Aß 1-42 into the hippocampus of humanized PDE4D (hPDE4D) mice. The hPDE4D mice provide a unique and powerful genetic tool for assessing PDE4D target engagement. Behavioral studies showed that treatment with BPN14770 significantly improved memory acquisition and retrieval in the Morris water maze test and the percentage of alternations in the Y-maze test in the model of Aß impairment. Microinjection of oligomeric Aß 1-42 caused decreases in the number of dendrites, dendritic length, and spine density of pyramid neurons in the hippocampus. These changes were prevented by BPN14770 in a dose-dependent manner. Furthermore, molecular studies showed that BPN14770 prevented Aß-induced decreases in synaptophysin, postsynaptic density protein 95, phosphorylated cAMP-response element binding protein (CREB)/CREB, brain-derived neurotrophic factor, and nerve growth factor inducible protein levels in the hippocampus. The protective effects of BPN14770 against Aß-induced memory deficits, synaptic damage, and the alteration in the cAMP-meditated cell signaling cascade were blocked by H-89 (N-[2-(p-Bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride), an inhibitor of protein kinase A. These results suggest that BPN14770 may activate compensatory mechanisms that support synaptic health even with the onset of amyloid pathology in Alzheimer's disease. SIGNIFICANCE STATEMENT: This study demonstrates that a phosphodiesterase-4D allosteric inhibitor, BPN14770, protects against memory loss and neuronal atrophy induced by oligomeric Aß 1-42. The study provides useful insight into the potential role of compensatory mechanisms in Alzheimer's disease in a model of oligomeric Aß 1-42 neurotoxicity.

Ginsenoside Rg1 promotes sleep in rats by modulating the noradrenergic system in the locus coeruleus and serotonergic system in the dorsal raphe nucleus.

Panax ginseng Mayer has been used as tranquilizer to improve sleep disorder, but its active component is not defined. This study investigated the effects of the most abundant constituents of P. ginseng-protopanaxatriol ginsenoside Rg1 and protopanaxadiol ginsenoside Rb1-on sleep in rats. Male Sprague-Dawley rats received intragastrical injections of Rg1 and Rb1 for 3 days (5, 10, and 20 mg/kg/day). Sleep parameters were analyzed using electroencephalogram and electromyogram. Neuronal activation and monoaminergic neurotransmitters were evaluated using immunohistochemical fluorescence staining and HPLC, respectively. Rg1 treatment significantly increased the duration of total sleep, rapid eye movement sleep (REMS) and Non-REMS at the dose of 5, 10 and 20 mg/kg/day, and also prolonged the proportion of slow-wave sleep in the total sleep. The Non-REMS episodes were increased and the mean duration of each wakefulness episode was depressed by Rg1 treatment. Rb1 had no effect on sleep parameters. Rg1 treatment decreased the activity of noradrenergic neurons in locus coeruleus (LC) and increased the activity of serotonergic neurons in the dorsal raphe nucleus (DRN). Besides, Rg1 depressed extracellular norepinephrine concentrations in both LC and DRN and in other sleep-regulating brain regions of which functions can be modulated by monoaminergic neurotransmitters discharged from projecting noradrenergic and serotonergic neurons. In conclusion, Rg1 might be the sleep-promoting component in P. ginseng and its mechanism may be related to the modulation of noradrenergic and serotonergic systems. Our findings also highlight functional differences between Rg1 and Rb1.

Melanin-Concentrating Hormone (MCH) and MCH-R1 in the Locus Coeruleus May Be Involved in the Regulation of Depressive-Like Behavior.

Background: Previous anatomical and behavioral studies have shown that melanin-concentrating hormone is involved in the modulation of emotional states. However, little is known about brain regions other than the dorsal raphe nucleus that relate the melanin-concentrating hormone-ergic system to depressive states. Numerous studies have shown that the locus coeruleus is involved in the regulation of depression and sleep. Although direct physiological evidence is lacking, previous studies suggest that melanin-concentrating hormone release in the locus coeruleus decreases neuronal discharge. However, remaining unclear is whether the melanin-concentrating hormone-ergic system in the locus coeruleus is related to depressive-like behavior. Method: We treated rats with an intra-locus coeruleus injection of melanin-concentrating hormone, intracerebroventricular injection of melanin-concentrating hormone, or chronic subcutaneous injections of corticosterone to induce different depressive-like phenotypes. We then assessed the effects of the melanin-concentrating hormone receptor 1 antagonist SNAP-94847 on depressive-like behavior in the forced swim test and the sucrose preference test. Results: The intra-locus coeruleus and intracerebroventricular injections of melanin-concentrating hormone and chronic injections of corticosterone increased immobility time in the forced swim test and decreased sucrose preference in the sucrose preference test. All these depressive-like behaviors were reversed by an intra-locus coeruleus microinjection of SNAP-94847. Conclusions: These results suggest that the melanin-concentrating hormone-ergic system in the locus coeruleus might play an important role in the regulation of depressive-like behavior.

Depression-like behaviors induced by chronic corticosterone exposure via drinking water: Time-course analysis.

Hypothalamic-pituitary-adrenal (HPA) axis activity is commonly dysregulated in stress-related psychiatric disorders. The corticosterone rat model was developed to understand the influence of stress on depression-like symptomatology. To further understand the effects of corticosterone on the development of depression-like behavior, rats were continuously exposed to corticosterone (200 µg/ml) or vehicle via drinking water daily for 21 days. The rats underwent a series of behavioral tests, and electroencephalographical recordings were performed after 7, 14, and 21 days of treatment. The measurements included immobility time (i.e., despair) in the forced swim test, locomotor activity in the open field test, sucrose consumption (i.e., anhedonia) in the sucrose preference test, and sleep-wake parameters. The rats in the 7-day corticosterone exposure group exhibited depression-like behavior, including increases in despair, anhedonia, anxiety, and sleep impairments. The rats in the 14-day corticosterone exposure group exhibited normal patterns of behavior and sleep structure. When corticosterone exposure was extended to 21 days, depression-like symptoms recurred, including despair, anhedonia, anxiety, and sleep disturbances. Overall, the present study observed U-shaped depression-like effects across 3 weeks of corticosterone exposure via drinking water.

Intracerebroventricular streptozotocin-induced Alzheimer's disease-like sleep disorders in rats: Role of the GABAergic system in the parabrachial complex.

AIM: Sleep disorders are common in Alzheimer's disease (AD) and assumed to directly influence cognitive function and disease progression. This study evaluated sleep characteristics in a rat model of AD that was induced by intracerebroventricular streptozotocin (STZ) administration and assessed the possible underlying mechanisms. METHODS: Cognition ability was assessed in the Morris water maze in rats. Sleep parameters were analyzed by electroencephalographic and electromyographic recordings. Neuronal activity in brain areas that regulate sleep-wake states was evaluated by double-staining immunohistochemistry. High-performance liquid chromatography with electrochemical detection was used to detect neurotransmitter levels. RESULTS: Fourteen days after the STZ injection, the rats exhibited sleep disorders that were similar to those in AD patients, reflected by a significant increase in wakefulness and decreases in nonrapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. The c-Fos expression analysis indicated that neuronal activity and the number of neurons in the dorsal raphe nucleus and locus coeruleus decreased in STZ-injected rats. In the ventrolateral preoptic nucleus (VLPO), the activity of γ-aminobutyric acid (GABA) neurons was suppressed. In the arousal-driving parabrachial nucleus (PBN), GABAergic activity was suppressed, whereas glutamatergic activity was promoted. The neurotransmitter analysis revealed a reduction in GABA in the VLPO and PBN and elevation of glutamate in the PBN. A direct injection of the GABAA receptor antagonist bicuculline in the PBN in normal rats induced a similar pattern of sleep disorder as in STZ-injected rats. A microinjection of GABA in the PBN improved sleep disorders that were induced by STZ. CONCLUSION: These results suggest that the reduction in GABAergic inhibition in the PBN and VLPO may be involved in sleep disorders that are induced by STZ. Our novel findings encourage further studies that investigate mechanisms of sleep regulation in sporadic AD.

Sleep patterns deteriorate over time in chronic corticosterone-treated rats.

Repeated corticosterone (CORT) injections reliably produce depressive-like behavior in rodents. Our previous study showed that sleep parameters were altered in rats after daily injections of CORT for 7 days, and sleep disturbances appeared to be correlated with depressive-like behavior. The aim of the present study was to investigate time-dependent correlations between changes in sleep parameters and the formation of depressive-like behavior in rats after more prolonged treatment with CORT. Rats received daily injections of CORT (40 mg/kg, s.c.) for 7, 14, or 21 days. Electroencephalographic recordings were performed to study sleep parameters. The sucrose preference test and forced swim test were performed to evaluate depressive-like behavior. Western blot was used to detect protein levels. Our results showed that 7-day CORT treatment resulted in no significant depressive-like behavior or changes in rapid-eye-movement (REM) sleep. However, the duration of non-REM sleep significantly decreased, tyrosine hydroxylase (TH) levels significantly increased, and glucocorticoid receptor (GR) expression decreased in the locus coeruleus. Treatment with CORT for 14 and 21 days increased depressive-like behavior, enhanced REM sleep, shortened REM sleep latency, decreased TH and GR levels, and increased the levels of the chaperone FK506 binding protein 51 (FKBP51) in the locus coeruleus. These results indicate that the development of depression after chronic CORT treatment may be related to the formation of sleep disorders. Abnormalities of REM sleep may be a characteristic of sleep in models of depression that is induced by chronic CORT administration in rats. The noradrenergic system and GR pathway in the locus coeruleus may be involved in the formation of depression concomitant with sleep disturbances.

Dysfunction of GABAergic neurons in the parafacial zone mediates sleep disturbances in a streptozotocin-induced rat model of sporadic Alzheimer's disease.

Sleep disturbances are prevalent among patients with Alzheimer's disease (AD) and often precede the onset and progression of dementia. However, there are no reliable animal models for investigating sleep disturbances in patients with sporadic AD (sAD), which accounts for more than 90% of all AD cases. In the present study, we characterize the sleep/wake cycles and explore a potential mechanism underlying sleep disturbance in a rat model of sAD induced via intracerebroventricular (icv) injection of streptozotocin (STZ). STZ-icv rats exhibited progressive decreases in slow wave sleep (SWS) during the light phase and throughout the light/dark cycle beginning from 7 days after STZ-icv. Additionally, increased wakefulness and decreased rapid-eye-movement (REM) and non-REM (NREM) sleep were observed from 14 days after STZ-icv. Beginning on day 7, STZ-icv rats exhibited significant decreases in delta (0.5-4.0 Hz) power accompanied by increased power in the beta (12-30 Hz) and low gamma bands (30-50 Hz) during NREM sleep, resembling deficits in sleep quality observed in patients with AD. Immunohistochemical staining revealed a significant reduction in the ratio of c-Fos-positive GABAergic neurons in the parafacial zone (PZ) beginning from day 7 after STZ-icv. These results suggest that the STZ-icv rat model is useful for evaluating sleep disturbances associated with AD, and implicate the dysregulation of GABAergic neuronal activity in the PZ is associated with sleep disturbance induced by STZ.

Tenuifolin, a saponin derived from Radix Polygalae, exhibits sleep-enhancing effects in mice.

BACKGROUND: Radix Polygalae, the dried root of Polygala tenuifolia, has been extensively used as a traditional Chinese medicine for promoting intelligence and tranquilization. Polygalasaponins extracted from the root of P. tenuifolia possess evident anxiolytic and sedative-hypnotic activities. Previous studies have reported that tenuifolin was a major constituent of polygalasaponins. PURPOSE: The currently study aims to investigate the hypnotic effect and possible mechanism of tenuifolin in freely moving mice. DESIGN/METHODS: The hypnotic effects of tenuifolin (20, 40 and 80mg/kg, p.o.) were assessed by electroencephalographic (EEG) and electromyographic (EMG) analysis. Double-staining immunohistochemistry test was performed to evaluate the neuronal activity of sleep-wake regulating brain areas. High performance liquid chromatograph- electrochemical detection (HPLC-ECD) and ultrafast liquid chromatography-mass spectrometry (UFLC-MS) were used for the detection of neurotransmitters. Locomotor activity was measured by Open-field Test. RESULTS: Tenuifolin at doses of 40 and 80mg/kg (p.o.) significantly prolonged the total sleep time by increasing the amount of non-rapid eye movement (NREM) and rapid eye movement (REM) sleep, associated with the significant increase in the bouts of episodes respectively. After administration of tenuifolin, the cortical EEG power spectral densities during NREM and REM sleep were similar to that of natural sleep (vehicle) and thus compatible with physiological sleep. Double-immunohistochemistry staining test showed that tenuifolin increased the c-Fos positive ratios of GABAergic NREM sleep-promoting neurons in ventrolateral preoptic area (VLPO), cholinergic REM sleep-promoting neurons in laterodorsal tegmental area (LDT) and pontomesencephalic tegmental area (PPT) and decreased the c-Fos positive ratios in wake-promoting neurons (locus coeruleus (LC) and perifornical area (Pef)). Neurotransmitter detections revealed that tenuifolin significantly reduced the noradrenaline (NA) levels in LC, VLPO, PPT and LDT, elevated the GABA levels in VLPO, LC and Pef and increased the acetylcholine (Ach) levels in LDT and PPT. In addition, tenuifolin did not cause any change to locomotor activity. CONCLUSION: Taken together, these results provide the first experimental evidence of the significant sleep-enhancing effect of tenuifolin in mice. This effect appears to be mediated, at least in part, by the activation of GABAergic systems and/or by the inhibition of noradrenergic systems. Moreover, this study adds new scientific evidence and highlights the therapeutic potential of the medicinal plant P. tenuifolia in the development of phytomedicines with hypnotic properties.

Tetrandrine, an alkaloid from S. tetrandra exhibits anti-hypertensive and sleep-enhancing effects in SHR via different mechanisms.

BACKGROUND: Sleep disorders have been found to be associated with hypertension in both cross-sectional and longitudinal epidemiological studies. Tetrandrine, a major component of Stephania tetrandra, is well known as an antihypertensive agent. The anti-hypertension mechanism mainly relies on its L-type calcium channel blocking property. In the previous study, tetrandrine revealed both anti-hypertension and hypnotic effects in spontaneously hypertensive rats (SHRs). PURPOSE: This study aims to elucidate whether the antihypertensive mechanism of tetrandrine in SHRs is relevant to its hypnotic effect. DESIGN/METHODS: Sleep-wake behavior of the SHRs was detected by electroencephalography (EEG) and electromyography (EMG) recordings. Blood pressure was measured by noninvasive blood pressure tail cuff test. Immunohistochemistry was performed to evaluate the noradrenergic neuronal activity. The level of norepinephrine (NE) was detected by HPLC-ECD. RESULTS: Amlodipine (100mg/kg, i.g.), the well-known L-type Ca2+ channel blockers (CCBs) exhibited remarkable antihypertensive activities in SHRs, but did not show effects on sleep of SHRs. Tetrandrine (30 and 60mg/kg/day, i.g.) significantly suppressed blood pressure of SHRs. Meanwhile, tetrandrine (60mg/kg/day, i.g.) remarkably increased non-rapid eye movement sleep (NREMS) time, bouts and mean duration. The hypnotic effect of tetrandrine was potentiated by prazosin (0.5mg/kg, i.p.) but attenuated by yohimbine (2mg/kg, i.p.). Administration of tetrandrine (60mg/kg/day, i.g.) not only significantly decreased c-Fos positive ratio of noradrenergic neurons in the locus coeruleus (LC), but also significantly decrease NE in the endogenous sleep-wake regulating pathways including LC, hypothalamus and ventrolateral preoptic nucleus (VLPO). CONCLUSION: In spite of a good potency in blocking L-type Ca2+ channel, the hypnotic effects of tetrandrine may be related to its suppressing effects on the noradrenergic system other than to block calcium channels. As a multi-targets drug, tetrandrine might be favorable to the hypertension patients who suffered poor sleep.

Ca(2+) in the dorsal raphe nucleus promotes wakefulness via endogenous sleep-wake regulating pathway in the rats.

Serotonergic neurons in the dorsal raphe nucleus (DRN) are involved in the control of sleep-wake states. Our previous studies have indicated that calcium (Ca(2+)) modulation in the DRN plays an important role in rapid-eye-movement sleep (REMS) and non-REMS (NREMS) regulation during pentobarbital hypnosis. The present study investigated the effects of Ca(2+) in the DRN on sleep-wake regulation and the related neuronal mechanism in freely moving rats. Our results showed that microinjection of CaCl2 (25 or 50 nmol) in the DRN promoted wakefulness and suppressed NREMS including slow wave sleep and REMS in freely moving rats. Application of CaCl2 (25 or 50 nmol) in the DRN significantly increased serotonin in the DRN and hypothalamus, and noradrenaline in the locus coeruleus and hypothalamus. Immunohistochemistry study indicated that application of CaCl2 (25 or 50 nmol) in the DRN significantly increased c-Fos expression ratio in wake-promoting neurons including serotonergic neurons in the DRN, noradrenergic neurons in the locus coeruleus, and orxinergic neurons in the perifornical nucleus, but decreased c-Fos expression ratio of GABAergic sleep-promoting neurons in the ventrolateral preoptic nucleus. These results suggest that Ca(2+) in the DRN exert arousal effects via up-regulating serotonergic functions in the endogenous sleep-wake regulating pathways.