Brain Peptides Research Articles

Suppressed Retinal Degeneration in Aged Wild Type and APPswe/PS1ΔE9 Mice by Bone Marrow Transplantation

Alzheimer's disease (AD) is an age-related condition characterized by accumulation of neurotoxic amyloid β peptides (Aβ) in brain and retina. Because bone marrow transplantation (BMT) results in decreased cerebral Aβ in experimental AD, we hypothesized that BMT would mitigate retinal neurotoxicity through decreased retinal Aβ. To test this, we performed BMT in APPswe/PS1ΔE9 double transgenic mice using green fluorescent protein expressing wild type (wt) mice as marrow donors. We first examined retinas from control, non-transplanted, aged AD mice and found a two-fold increase in microglia compared with wt mice, prominent inner retinal Aβ and paired helical filament-tau, and decreased retinal ganglion cell layer neurons. BMT resulted in near complete replacement of host retinal microglia with BMT-derived cells and normalized total AD retinal microglia to non-transplanted wt levels. Aβ and paired helical filament-tau were reduced (61.0% and 44.1% respectively) in BMT-recipient AD mice, which had 20.8% more retinal ganglion cell layer neurons than non-transplanted AD controls. Interestingly, aged wt BMT recipients also had significantly more neurons (25.4%) compared with non-transplanted aged wt controls. Quantitation of retinal ganglion cell layer neurons in young mice confirmed age-related retinal degeneration was mitigated by BMT. We found increased MHC class II expression in BMT-derived microglia and decreased oxidative damage in retinal ganglion cell layer neurons. Thus, BMT is neuroprotective in age-related as well as AD-related retinal degeneration, and may be a result of alterations in innate immune function and oxidative stress in BMT recipient mice.

β2 Adrenergic Receptor, Protein Kinase A (PKA) and c-Jun N-terminal Kinase (JNK) Signaling Pathways Mediate Tau Pathology in Alzheimer Disease Models

Alzheimer disease (AD) is characterized by neurodegeneration marked by loss of synapses and spines associated with hyperphosphorylation of tau protein. Accumulating amyloid β peptide (Aβ) in brain is linked to neurofibrillary tangles composed of hyperphosphorylated tau in AD. Here, we identify β2-adrenergic receptor (β2AR) that mediates Aβ-induced tau pathology. In the prefrontal cortex (PFC) of 1-year-old transgenic mice with human familial mutant genes of presenilin 1 and amyloid precursor protein (PS1/APP), the phosphorylation of tau at Ser-214 Ser-262 and Thr-181, and the protein kinases including JNK, GSK3α/β, and Ca(2+)/calmodulin-dependent protein kinase II is increased significantly. Deletion of the β2AR gene in PS1/APP mice greatly decreases the phosphorylation of these proteins. Further analysis reveals that in primary PFC neurons, Aβ signals through a β2AR-PKA-JNK pathway, which is responsible for most of the phosphorylation of tau at Ser-214 and Ser-262 and a significant portion of phosphorylation at Thr-181. Aβ also induces a β2AR-dependent arrestin-ERK1/2 activity that does not participate in phosphorylation of tau. However, inhibition of the activity of MEK, an upstream enzyme of ERK1/2, partially blocks Aβ-induced tau phosphorylation at Thr-181. The density of dendritic spines and synapses is decreased in the deep layer of the PFC of 1-year-old PS1/APP mice, and the mice exhibit impairment of learning and memory in a novel object recognition paradigm. Deletion of the β2AR gene ameliorates pathological effects in these senile PS1/APP mice. The study indicates that β2AR may represent a potential therapeutic target for preventing the development of AD.

Neuropeptide-Gated Perception of Appetitive Olfactory Inputs in Drosophila Larvae

Understanding how smell or taste translates into behavior remains challenging. We have developed a behavioral paradigm in Drosophila larvae to investigate reception and processing of appetitive olfactory inputs in higher-order olfactory centers. We found that the brief presentation of appetitive odors caused fed larvae to display impulsive feeding of sugar-rich food. Deficiencies in the signaling of neuropeptide F (NPF), the fly counterpart of neuropeptide Y (NPY), blocked appetitive odor-induced feeding by disrupting dopamine (DA)-mediated higher-order olfactory processing. We have identified a small number of appetitive odor-responsive dopaminergic neurons (DL2) whose activation mimics the behavioral effect of appetitive odor stimulation. Both NPF and DL2 neurons project to the secondary olfactory processing center; NPF and its receptor NPFR1 mediate a gating mechanism for reception of olfactory inputs in DL2 neurons. Our findings suggest that eating for reward value is an ancient behavior and that fly larvae are useful for studying neurobiology and the evolution of olfactory reward-driven behavior.

Kisspeptins and RFRP-3 Act in Concert to Synchronize Rodent Reproduction with Seasons

Seasonal mammals use the photoperiodic variation in the nocturnal production of the pineal hormone melatonin to synchronize their reproductive activity with seasons. In rodents, the (SD) short day profile of melatonin secretion has long been proven to inhibit reproductive activity. Lately, we demonstrated that melatonin regulates the expression of the hypothalamic peptides kisspeptins (Kp) and RFamide-related peptide-3 (RFRP-3), recently discovered as potent regulators of gonadotropin-releasing hormone (GnRH) neuron activity. In the male Syrian hamster, Kp expression in the arcuate nucleus is down-regulated by melatonin independently of the inhibitory feedback of testosterone. A central or peripheral administration of Kp induces an increase in pituitary gonadotropins and gonadal hormone secretion, but most importantly a chronic infusion of the peptide reactivates the photo-inhibited reproductive axis of Syrian hamsters kept in SD conditions. RFRP-3 expression in the dorsomedial hypothalamus is also strongly inhibited by melatonin in a SD photoperiod. Although RFRP-3 is usually considered as an inhibitory component of the gonadotropic axis, a central acute administration of RFRP-3 in the male Syrian hamster induces a marked increase in gonadotropin secretion and testosterone production. Furthermore, a chronic central infusion of RFRP-3 in SD-adapted hamsters reactivates the reproductive axis, in the same manner as Kp. Both Kp and RFRP-3 neurons project onto GnRH neurons and both neuropeptides regulate GnRH neuron activity. In addition, central RFRP-3 infusion was associated with a significant increase in arcuate Kp expression. However, the actual sites of action of both peptides in the Syrian hamster brain are still unknown. Altogether our findings indicate that Kp and RFRP neurons are pivotal relays for the seasonal regulation of reproduction, and also suggest that RFRP neurons might be the primary target of the melatoninergic message.

The protective effect of hyperbaric oxygen and Ginkgo biloba extract on Aβ25–35-induced oxidative stress and neuronal apoptosis in rats

Alzheimer's disease (AD) is characterized by accumulation and deposition of Aβ peptides in human brains. The present study aimed to determine the protective effect of HBO and EGB761 on Aβ25–35 peptides induced cognitive impairment and neuronal toxicity in rats. Characteristics of AD were induced in rats by the administration of Aβ25–35 in hippocampus. Rats were treated with HBO (2ATA 60min/day), EGB761 (20mg/kg/day), and the combination of HBO+EGB761 (20mg/kg/day+2ATA). The Morris water maze was used to detect the protective effects of HBO and EGB761 against cognitive impairment. The activities of SOD and GSH, the apoptosis-related genes and proteins and the apoptosis rate of hippocampus were detected. Compared to the model group, EGB761 and HBO treatments synergistically improved the escape latency. Furthermore, the activities of SOD and GSH in rat hippocampal tissue were found to have increased with a concomitant reduction in MDA levels, Bax expression, cytochrome c release, and the activity of caspase-9/3. Accordingly, a significant reduction was observed in the apoptosis rate following the treatment with EGB761 and HBO in this model of AD. Our findings suggest that HBO and EGB761 reduce cell toxicity and oxidative stress by blocking mitochondria-mediated apoptosis signaling in AD, and the combined treatment of HBO and Ginkgo further enhances these effects.

Brain Ischemia Activates β- and γ-Secretase Cleavage of Amyloid Precursor Protein: Significance in Sporadic Alzheimer’s Disease

Amyloid precursor protein cleavage through β- and γ-secretases produces β-amyloid peptide, which is believed to be responsible for death of neurons and dementia in Alzheimer’s disease. Levels of β- and γ-secretase are increased in sensitive areas of the Alzheimer’s disease brain, but the mechanism of this process is unknown. In this review, we prove that brain ischemia generates expression and activity of both β- and γ-secretases. These secretases are induced in association with oxidative stress following brain ischemia. Data suggest that ischemia promotes overproduction and aggregation of β-amyloid peptide in brain, which is toxic for ischemic neuronal cells. In our review, we demonstrated the role of brain ischemia as a molecular link between the β- and the γ-secretase activities and provided a molecular explanation of the possible neuropathogenesis of sporadic Alzheimer’s disease.

Mass spectrometric characterization of recombinant rat 5‐hydroxytryptamine receptor 1A (5‐HT1AR) expressed in tsA201 human embryonic kidney cells

The 5-hydroxytryptamine 1A receptor (serotonin 1A receptor; 5-HT(1A) R) is involved in a large series of brain functions, and roles in anxiety, depression, and cognition have been reported. So far, published information on mass spectrometrical characterization of 5-HT(1A) R is limited to the presence of two 5-HT(1A) R peptides in rat's whole brain as observed by in-solution digestion followed by LC-MS/MS. Knowledge about the protein sequence and PTMs, however, would have implications for generation of specific antibodies and designing studies on the 5-HT(1A) R at the protein level. A rat recombinant 5-HT(1A) R was extracted from the tsA201 cell line, run using several gel-based principles with subsequent in-gel digestion with several proteases, chymotrypsin, trypsin, AspN, proteinase K, and pepsin followed by nano-LC-ESI-MS/MS analysis on a high capacity ion trap and an LTQ Orbitrap Velos. Using two search engines, Mascot and Modiro™, the recombinant 5-HT(1A) R was identified showing 94.55% sequence coverage. A single phosphorylation at S301 was identified and verified by phosphatase treatment and a series of amino acid substitutions were detected. Characterization of 5-HT(1A) R, a key player of brain functions and neurotransmission, was shown and may enable generation of specific antibodies, design of future, and interpretation of previous studies in the rat at the protein level.

Design and Synthesis of β-Site Amyloid Precursor Protein Cleaving Enzyme (BACE1) Inhibitors with in Vivo Brain Reduction of β-Amyloid Peptides

The evaluation of a series of aminoisoindoles as β-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitors and the discovery of a clinical candidate drug for Alzheimer's disease, (S)-32 (AZD3839), are described. The improvement in permeability properties by the introduction of fluorine adjacent to the amidine moiety, resulting in in vivo brain reduction of Aβ40, is discussed. Due to the basic nature of these compounds, they displayed affinity for the human ether-a-go-go related gene (hERG) ion channel. Different ways to reduce hERG inhibition and increase hERG margins for this series are described, culminating in (S)-16 and (R)-41 showing large in vitro margins with BACE1 cell IC(50) values of 8.6 and 0.16 nM, respectively, and hERG IC(50) values of 16 and 2.8 μM, respectively. Several compounds were advanced into pharmacodynamic studies and demonstrated significant reduction of β-amyloid peptides in mouse brain following oral dosing.

Ontogeny of cocaine- and amphetamine-regulated transcript peptide in brain of frog, Microhyla ornata

The cocaine- and amphetamine-regulated transcript (CART) peptide is widely distributed in the brains of adult vertebrates including amphibians. Several physiological roles of CART have been intensely investigated in mammals. Despite these studies, the expression of CART during development of brain has not been studied in amphibians. In the present study, distribution of CART was investigated during development in the post hatched stage 23 to premetamorphic stage 30 of frog Microhyla ornata. CART is expressed as early as in stage 23 in ventral thalamus and rhombencephalon. As development progressed, CART immunoreactivity was observed in the olfactory bulb, telencephalon, rhombencephalon and spinal cord in stage 24. At stage 25, the CART immunoreactivity was observed in the ventromedial thalamic nucleus, posterocentral thalamic nucleus, torus nucleus, central gray and inferior reticular nucleus. In stage 26, CART reactivity was seen in the medial septum, preoptic area, nucleus entopeduncularis, magnocellular nucleus, median eminence, optic tectum, hypophysis and cerebellum. Additionally, CART immunoreactivity was observed in the medial pallium, anterior commissure, nucleus infundibularis dorsalis, ventralis and raphe nucleus at stage 30. The occurrences of CART immunoreactivity at early stage of development suggest that the peptide may have a functional significance during development. The wider appearance of CART in the brain of tadpoles, M. ornata suggests that the peptide may act as a neurohormone during the ontogeny.

The brain renin-angiotensin system and cardiovascular responses to stress: insights from transgenic rats with low brain angiotensinogen

The renin-angiotensin system (RAS) has been identified as an attractive target for the treatment of stress-induced cardiovascular disorders. The effects of angiotensin (ANG) peptides during stress responses likely result from an integration of actions by circulating peptides and brain peptides derived from neuronal and glial sources. The present review focuses on the contribution of endogenous brain ANG peptides to pathways involved in cardiovascular responses to stressors. During a variety of forms of stress, neuronal pathways in forebrain areas containing ANG II or ANG-(1-7) are activated to stimulate descending angiotensinergic pathways that increase sympathetic outflow to increase blood pressure. We provide evidence that glia-derived ANG peptides influence brain AT(1) receptors. This appears to result in modulation of the responsiveness of the neuronal pathways activated during stressors that elevate circulating ANG peptides to activate brain pathways involving descending hypothalamic projections. It is well established that increased cardiovascular reactivity to stress is a significant predictor of hypertension and other cardiovascular diseases. This review highlights the importance of understanding the impact of RAS components from the circulation, neurons, and glia on the integration of cardiovascular responses to stressors.

Levetiracetam suppresses neuronal network dysfunction and reverses synaptic and cognitive deficits in an Alzheimer's disease model.

In light of the rising prevalence of Alzheimer's disease (AD), new strategies to prevent, halt, and reverse this condition are needed urgently. Perturbations of brain network activity are observed in AD patients and in conditions that increase the risk of developing AD, suggesting that aberrant network activity might contribute to AD-related cognitive decline. Human amyloid precursor protein (hAPP) transgenic mice simulate key aspects of AD, including pathologically elevated levels of amyloid-β peptides in brain, aberrant neural network activity, remodeling of hippocampal circuits, synaptic deficits, and behavioral abnormalities. Whether these alterations are linked in a causal chain remains unknown. To explore whether hAPP/amyloid-β-induced aberrant network activity contributes to synaptic and cognitive deficits, we treated hAPP mice with different antiepileptic drugs. Among the drugs tested, only levetiracetam (LEV) effectively reduced abnormal spike activity detected by electroencephalography. Chronic treatment with LEV also reversed hippocampal remodeling, behavioral abnormalities, synaptic dysfunction, and deficits in learning and memory in hAPP mice. Our findings support the hypothesis that aberrant network activity contributes causally to synaptic and cognitive deficits in hAPP mice. LEV might also help ameliorate related abnormalities in people who have or are at risk for AD.

P2‐151: PICALM regulates Aβ42 production by modulation of gamma‐secretase trafficking

Alzheimer disease (AD) is the most common type of dementia worldwide. Several lines of evidence suggest that aberrant production, clearance and aggregation of amyloid-beta peptide (Aβ) in human brain are linked to the etiology of AD. Recently, genome-wide association studies in late-onset AD patients have reported evidence that variation in phosphatidylinositol binding clathrin assembly protein (PICALM) gene confer genetic risk for AD. To investigate the role of PICALM in Aβ generation, we analyzed the effects of knockdown or overexpression of PICALM in cultured cells on the processing of amyloid precursor protein (APP). We also monitored the trafficking of the gamma-secretase by monoclonal antibody A5226A, which recognizes the extracellular domain of mature Nicastrin on the cell surface (Hayashi et al., Oncogene 2011). Depletion of PICALM caused a decrease in the production ratio of Aβ42, the most aggregable Aβ species. Moreover, PICALM RNAi altered the endocytic rate of gamma-secretase, while the endocytosis of transferrin, one of the typical cargo proteins for clathrin-mediated endocytosis, was not affected. In contrast, total Aβ levels as well as Aβ42 ratio were increased by the overexpression of PICALM. These results suggest PICALM modulates gamma-secretase activity by regulating its clathrin-mediated endocytosis. Alteration in endocytic rate of gamma-secretase by PICALM RNAi/overexpression may change its steady-state subcellular localization, leading to alteration in both the total Aβ generation and the Aβ42 ratio.

The neurotoxicity of β-amyloid peptide toward rat brain is associated with enhanced oxidative stress, inflammation and apoptosis, all of which can be attenuated by scutellarin

This study was designed to investigate the processes underlying the neurotoxicity induced by β-amyloid peptide (Aβ) in the rat brain, as well as to examine whether scutellarin (Scu) can prevent this neurotoxicity. Thirty Wistar rats were randomly divided into 3 groups, i.e., untreated (control), treated with Aβ and treated with both Aβ and Scu. The treated rats were subjected to bilateral intracerebroventricular injection of Aβ(25-35) with or without subsequent dietary exposure to Scu. Learning and memory were assessed with the Morris water maze test; the activities of superoxide dismutase (SOD) and monoamine oxidase (MAO) were assayed biochemically; expression of the interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) proteins was determined by immunohistochemistry; and neuronal apoptosis was detected with Annexin staining followed by flow cytometry. The animals treated with Aβ exhibited impaired learning and memory; reduced SOD and elevated MAO activity, elevated protein levels of IL-1β, IL-6 and TNF-α; and a higher percentage of apoptotic neurons in the brain. Interestingly, all of these effects were ameliorated by administration of Scu. These findings indicate that the deficits in learning and memory demonstrated by the rats receiving Aβ are due to elevated oxidative stress and inflammation, which result in apoptosis and that Scu may prevent these deleterious effects.

Lysosomal Dysfunction in a Mouse Model of Sandhoff Disease Leads to Accumulation of Ganglioside-Bound Amyloid-β Peptide

Alterations in the lipid composition of endosomal-lysosomal membranes may constitute an early event in Alzheimer's disease (AD) pathogenesis. In this study, we investigated the possibility that GM2 ganglioside accumulation in a mouse model of Sandhoff disease might be associated with the accumulation of intraneuronal and extracellular proteins commonly observed in AD. Our results show intraneuronal accumulation of amyloid-β peptide (Aβ)-like, α-synuclein-like, and phospho-tau-like immunoreactivity in the brains of β-hexosaminidase knock-out (HEXB KO) mice. Biochemical and immunohistochemical analyses confirmed that at least some of the intraneuronal Aβ-like immunoreactivity (iAβ-LIR) represents amyloid precursor protein C-terminal fragments (APP-CTFs) and/or Aβ. In addition, we observed increased levels of Aβ40 and Aβ42 peptides in the lipid-associated fraction of HEXB KO mouse brains, and intraneuronal accumulation of ganglioside-bound Aβ (GAβ) immunoreactivity in a brain region-specific manner. Furthermore, α-synuclein and APP-CTFs and/or Aβ were found to accumulate in different regions of the substantia nigra, indicating different mechanisms of accumulation or turnover pathways. Based on the localization of the accumulated iAβ-LIR to endosomes, lysosomes, and autophagosomes, we conclude that a significant accumulation of iAβ-LIR may be associated with the lysosomal-autophagic turnover of Aβ and fragments of APP-containing Aβ epitopes. Importantly, intraneuronal GAβ immunoreactivity, a proposed prefibrillar aggregate found in AD, was found to accumulate throughout the frontal cortices of postmortem human GM1 gangliosidosis, Sandhoff disease, and Tay-Sachs disease brains. Together, these results establish an association between the accumulation of gangliosides, autophagic vacuoles, and the intraneuronal accumulation of proteins associated with AD.

Neuroprotective effect of undecylenic acid extracted from Ricinus communis L. through inhibition of μ-calpain

The key neuropathological features of Alzheimer’s disease are abnormal deposition of Aβ plaques and insoluble Aβ peptides in extracellular brain and intracellular neurofibril tangles induced by abnormal tau hyperphosphorylation. μ-Calpain is one of the factors that bridge these Aβ- and hyperphosphorylated tau-mediated pathological pathways. Undecylenic acid (UDA), a naturally occurring unsaturated fatty acid, was discovered as a μ-calpain inhibitor by screening a chemical library using a substrate specific μ-calpain assay method. UDA inhibited Aβ oligomerization and Aβ fibrillation and reversed Aβ-induced neuronal cell death. In addition, UDA scavenged ROS and reversed the levels of proapoptotic proteins induced by ROS in SH-SY5Y cells. UDA inhibited μ-calpain activity with better potency than the known peptide-like μ-calpain inhibitor, MDL28170, in SH-SY5Y and HEK293T cells transfected with the catalytic subunit of μ-calpain. These results suggest that UDA is a novel non-peptide-like μ-calpain inhibitor with good cell permeability and potent neuroprotective effect.

Hyperbaric Oxygen and Ginkgo Biloba Extract Inhibit Aβ25-35-induced Toxicity and Oxidative Stress in vivo: A Potential Role in Alzheimer's Disease

ABSTRACTAlzheimer's disease is characterized by the accumulation and deposition of Aβ peptides in human brains and Aβ induced free radical-mediated damage is one of the hypotheses. In the present study, we explored the protective effects of hyperbaric oxygen (HBO) and Ginkgo Biloba extract (EGB761) on Aβ25-35-induced brain toxicity. Our results demonstrated that EGB761, HBO, and the combination HBO and EGB761, could significantly improve the cognitive function in AD rats' model, especially the combination group. What's more, the activities of superoxide dismutase (SOD) in rat hippocampal tissue were obviously enhanced followed by evidently reduced malondialdehyde (MDA) levels in the same treatment groups mentioned earlier. There were no differences of nitric oxide (NO) productions in the group of EGB761, HBO, and HBO and EGB761, but they were all lower than that of model group. These findings suggest that both HBO and EGB761 may relieve cell toxicity and oxidative stress in AD and thus play a potential protective role in AD. Furthermore, the combination could have better effects compared with single one.

Myoinhibitory peptides in the brain of the cockroach Leucophaea maderae and colocalization with pigment-dispersing factor in circadian pacemaker cells

Myoinhibitory peptides (MIPs) are a family of insect W(X(6))Wamides with inhibitory effects on visceral muscles and juvenile hormone synthesis. Although MIPs are widely distributed within the nervous system, a detailed analysis of their distribution and function in insect brains is still missing. We analyzed the distribution of MIPs in the brain of the cockroach Leucophaea maderae. We focused on the accessory medulla (AMe), a small neuropil near the medulla that acts as the master circadian clock. Matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) and Nano-LC electrospray ionization (ESI) mass spectrometry revealed five Lem-MIPs in preparations of the AMe and corpora cardiaca. The complete sequences of two of these peptides were identified. Immunocytochemistry revealed wide distribution of MIP-related peptides in the cockroach brain. The superior median protocerebrum, parts of the central complex, and the tritocerebrum showed particularly dense immunostaining. In contrast, only a few local interneurons were stained in the antennal lobe and a few extrinsic neurons in the mushroom body, including a giant neuron innervating the calyces. The noduli of the AMe showed dense immunostaining, and neurons in all AMe cell groups except the anterior neurons were labeled. Pigment-dispersing factor- (PDF) and MIP immunostaining was colocalized in two neurons of the AMe. No colocalization of MIP- and PDF immunostaining was detected in the anterior optic commissure, but two small PDF-immunoreactive commissural fibers near the posterior optic commissure showed colocalized MIP immunostaining. The results suggest that several MIPs participate in different functional circuits of the circadian system and are involved in multiple brain circuits of the Madeira cockroach.

Substance P activates ADAM9 mRNA expression and induces α-secretase-mediated amyloid precursor protein cleavage

Altered levels of Substance P (SP), a neuropeptide endowed with neuroprotective and anti-apoptotic properties, were found in brain areas and spinal fluid of Alzheimer's disease (AD) patients. One of the hallmarks of AD is the abnormal extracellular deposition of neurotoxic beta amyloid (Aβ) peptides, derived from the proteolytic processing of amyloid precursor protein (APP). In the present study, we confirmed, the neurotrophic action of SP in cultured rat cerebellar granule cells (CGCs) and investigated its effects on APP metabolism. Incubation with low (5 mM) potassium induced apoptotic cell death of CGCs and amyloidogenic processing of APP, whereas treatment with SP (200 nM) reverted these effects via NK1 receptors. The non-amyloidogenic effect of SP consisted of reduction of Aβ1–42, increase of sAPPα and enhanced α-secretase activity, without a significant change in steady-state levels of cellular APP. The intracellular mechanisms whereby SP alters APP metabolism were further investigated by measuring mRNA and/or steady-state protein levels of key enzymes involved with α-, β- and γ-secretase activity. Among them, Adam9, both at the mRNA and protein level, was the only enzyme to be significantly down-regulated following the induction of apoptosis (K5) and up-regulated after SP treatment. In addition to its neuroprotective properties, this study shows that SP is able to stimulate non-amyloidogenic APP processing, thereby reducing the possibility of generation of toxic Aβ peptides in brain.

Identification, Expression, and Physiological Functions of Siberian Hamster Gonadotropin-Inhibitory Hormone

Gonadotropin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide that inhibits gonadotropin secretion in birds and mammals. To further understand its physiological roles in mammalian reproduction, we identified its precursor cDNA and endogenous mature peptides in the Siberian hamster brain. The Siberian hamster GnIH precursor cDNA encoded two RFamide-related peptide (RFRP) sequences. SPAPANKVPHSAANLPLRF-NH(2) (Siberian hamster RFRP-1) and TLSRVPSLPQRF-NH(2) (Siberian hamster RFRP-3) were confirmed as mature endogenous peptides by mass spectrometry from brain samples purified by immunoaffinity chromatography. GnIH mRNA expression was higher in long days (LD) compared with short days (SD). GnIH mRNA was also highly expressed in SD plus pinealectomized animals, whereas expression was suppressed by melatonin, a nocturnal pineal hormone, administration. GnIH-immunoreactive (-ir) neurons were localized to the dorsomedial region of the hypothalamus, and GnIH-ir fibers projected to hypothalamic and limbic structures. The density of GnIH-ir perikarya and fibers were higher in LD and SD plus pinealectomized hamsters than in LD plus melatonin or SD animals. The percentage of GnRH neurons receiving close appositions from GnIH-ir fiber terminals was also higher in LD than SD, and GnIH receptor was expressed in GnRH-ir neurons. Finally, central administration of hamster RFRP-1 or RFRP-3 inhibited LH release 5 and 30 min after administration in LD. In sharp contrast, both peptides stimulated LH release 30 min after administration in SD. These results suggest that GnIH peptides fine tune LH levels via its receptor expressed in GnRH-ir neurons in an opposing fashion across the seasons in Siberian hamsters.

Brainstem Neuropeptides and Vagal Protection of the Gastric Mucosal Against Injury: Role of Prostaglandins, Nitric Oxide and Calcitonin-Gene Related Peptide in Capsaicin Afferents

Earlier experimental studies indicated that the integrity of vagal pathway was required to confer gastric protection against damaging agents. Several peptides located in the brainstem initially identified to influence vagal outflow to the stomach, as assessed by electrophysiological approach or by vagal dependent alterations of gastric secretory and motor function, were investigated for their influence in the vagal regulation of the resistance of the gastric mucosa to injury. Thyrotropin releasing hormone (TRH), or its stable TRH analog, RX-77368, injected at low doses into the cisterna magna or the dorsal motor nucleus (DMN) was the first peptide reported to protect the gastric mucosa against ethanol injury through stimulation of vagal cholinergic pathways, inducing the release of gastric prostaglandins/nitric oxide (NO) and the recruitment of efferent function of capsaicin sensitive afferent fibers containing calcitonin-gene related peptide (CGRP). Activation of endogenous TRH-TRH1 receptor signaling located in the brainstem plays a role in adaptive gastric protection against damaging agents. Since then, an expanding number of peptides, namely peptide YY, CGRP, adrenomedullin, amylin, glugacon-like peptide, opioid peptides acting on µ, δ1 or δ2 receptors, nocicpetin, nocistatin, ghrelin, leptin and TLQP-21, a peptide derived from VGF prohormone, have been reported to act in the brainstem to afford gastric protection against ethanol injury largely through similar peripheral effectors mechanisms than TRH. Therefore gastric prostaglandins and CGRP/NO pathways represent a common final mechanism through which brain peptides confer vagally mediated gastroprotection against injury. A better understanding of brain circuitries through which these peptides are released will provide new strategies to recruit integrated and multifaceted gastroprotective mechanisms.