]>EXG5341S0531-5565(00)00153-410.1016/S0531-5565(00)00153-4Elsevier Science Inc.Fig. 1The plasma concentrations of glucose, immunoreactive glucagon (IRG), immunoreactive insulin (IRI), epinephrine, and norepinephrine after microinjection of saline (1μl; ○) or neostigmine (5×10−8mol; •) into 3rd cerebral ventricle. Values are means±SE for 7–22 rats. Significant differences between subjects and saline-treated controls at identical times (at least p<0.05).Fig. 2Relative contributions of the pathways to hyperglycemia induced by the injection of neostigmine into the central nervous system.Fig. 3The plasma concentrations of glucose, epinephrine, and norepinephrine after intrahippocampal injection of 5×10−8, 5×10−9mol of neostigmine, saline, or coinjection of 5×10−8mol of neostogmine and atropine.Fig. 4The concentrations of epinephrine(A), dopamine(B), and norepinephrine(C) in DAT, VD, and ND groups, respectively. One way ANOVA shows significant differences among the three groups (p=0.0261); epinephrine level in DAT subjects was significantly lower than that in ND by Scheffe's post hoc test (p=0.0332).Table 1Number of subjects, mean age, mean arterial pressure, and MMSE scores in DAT, VD, and ND groupsDATVDNDNumber of subjects662821Mean age (mean±S.D.)82.49±7.7782.86±5.8682.95±7.77Mean atrial pressure (mean±S.D.) (mmHg)92.64±10.9994.74±10.3194.56±12.09Mean score of MMSE (mean±S.D.)7.96±6.495.29±5.1924.52±2.86Table 2Plasma concentrations of epinephrine, norepinephrine, dopamine, glucose, and insulin in DAT, VD, and ND groupsDATVDNDEpinephrine (pg/ml)18.83±13.1124.93±20.4531.52±29.83Norepinephrine (pg/ml)286.25±172.89333.29±221.77357.14±259.69Dopamine (pg/ml)7.08±8.9213.61±22.5014.33±21.36Glucose (mg/dl)88.81±8.1889.86±9.6289.57±7.19Insuline (uU/ml)5.31±1.685.33±2.265.09±1.64The metabolism of plasma glucose and catecholamines in Alzheimer's diseaseHUmegakia*umegaki@tsuru.med.nagoya-u.ac.jpNTamayaaTShinkaibAIguchiaaDepartment of Geriatrics, Nagoya University Graduate School of Medicine, 65 Tsuruma-Cho, Showa-Ku, Nagoya, Aichi, 466-8550, JapanbDepartment of Cell Biology, Tokyo Metropolitan Institute of Gerontology, 35-3 Sakae-Cho, Itabashi-Ku, Tokyo, 173-0015, Japan*Corresponding author. Tel.: +81-52-744-2365; fax: +81-52-744-2371AbstractSeveral lines of evidence suggest that the cholinergic system in the hippocampus plays a pivotal roll in regulating the peripheral metabolism of glucose and catecholamines. The injection of cholinergic stimulators including neostigmine, the acetylcholine esterase inhibitor, into the third ventricle or the hippocampus induces the elevation of glucose or catecholamines in plasma in rats. Under stress conditions, release of acetylcholine in the hippocampus increases, which coincides with the elevation of plasma glucose and catecholamines. Age-related reduction in responsivity of the cholinergic system in the hippocampus has been well documented. The intrahippocampal neostigmine injection induces significantly attenuated responses in plasma glucose and catecholamines in rats, the finding suggested that changes in cholinergic system activity in the hippocampus could result in alteration of the peripheral metabolism of glucose and catecholamines. In Alzheimer's disease (AD), the most common type of dementia, degeneration of the hippocampal cholinergic system is one of the most robust pathological features. Measurement of plasma catecholamines during a fasting state in the groups of AD subjects, vascular dementia subjects, and non-demented control subjects showed significantly lower plasma epinephrine levels in the AD subjects.KeywordsHippocampusAcetylcholineAgingStressInsulinDementia1IntroductionThe close regulation of plasma glucose and catecholamines is essential to maintenance of life. Under acute stress, the plasma levels of glucose and catecholamines become elevated, and these reactions coincide with the activation of several brain regions including the hippocampus. Several studies have reported that acute stress induced acetylcholine (ACh) release in the hippocampus (Gilad, 1987; Imperato et al., 1991; Mizuno and Kimura, 1997). Tajima et al. (1996) also found that restraint stress induced the increase of ACh release in the hippocampus by using microdialysis, noting the elevation of plasma levels of glucose, epinephrine, and norepinephrine in rats.The stress reportedly affects the central nervous system (CNS). Chronic and acute stress has been shown to induce several changes in the CNS (Sapolsky, 1997; McEwen, 1999). Chronic stress has been shown to be associated with the alteration of synaptic terminal structures in the hippocampus (Magarinos et al., 1997). Several lines of evidence indicate that stress and glucocorticoids affect memory performance (Wolkowitz et al., 1997; de Quervain et al., 1998; Kim and Yoon, 1998; Sandi, 1998). Lupien et al. (1998) demonstrated that elevated cortisol, the major stress hormone, produced hippocampal atrophy and memory deficits in the human model. However, it is largely unknown how changes in CNS affect stress responses.Chemical stimulation of the CNS with various substances has been reported to induce hyperglycemia (Iguchi et al., 1984, 1985, 1986, 1988, 1991). These substances include adrenergic, cholinergic, histamine, neuropeptides such as bombesin, thyrotropin-releasing hormone, and 2-deoxyglucose. Iguchi et al. (1988) compared the potency to induce hyperglycemia of several substances, and reported that the muscarinic subtype of cholinergic receptors play an important role in CNS-mediated glucoregulation. Injection of neostigmine, the choline esterase inhibitor, into the third ventricle or hippocampus induces the increase of glucose and catecholamines in plasma, and these peripheral reactions resemble stress responses. Activity in the CNS, including the hippocampus, and particularly in the cholinergic system, must be involved in the regulation of glucose and catecholamines in plasma.Age-related changes in the hippocampal cholinergic system have been studied extensively. The overall findings remain controversial, although, several studies showed that the input of the cholinergic system into the hippocampus was attenuated with aging. We observed attenuated responses in plasma glucose and catecholamines after injection of neostigmine into the hippocampus of aged rats. This finding suggested that age-related changes in hippocampal formation could be associated with peripheral metabolic changes.Alzheimer's disease (AD) is one of the most common types of dementia. Pathologies in the AD brain include the substantial degeneration of several regions, including the cortex and the hippocampus (Jack et al., 1998). Degeneration of the cholinergic system in the hippocampus is one of the earliest and most severe features of AD pathology. Based on findings that strongly suggest the involvement of the hippocampus in the regulation of plasma glucose and catecholamines, we hypothesized that the metabolism of these substances could be altered.2Stimulation of the cholinergic system in CNSIguchi et al. (1986) reported that injection of neostigmine, the ACh esterase inhibitor, into the third ventricle of rats caused a dose-dependent increase of glucose, epinephrine, norepinephrine, and glucagon concentration in plasma (Fig. 1). This effect probably occurred through increase of endogenous ACh in the CNS, given that neostigmine inhibits ACh esterase, which degrades ACh. Neostigmine-induced hyperglycemia was prevented by coadministration of atropine, suggesting that this response was mediated by cholinergic receptors of muscarinic subtype.The mechanism of these reactions has not yet been fully elucidated, however, the hypothesized mechanism is given below. The secretion of epinephrine from the adrenal medulla is under neuronal control. Increase of epinephrine occurs probably via activation of the neurons regulating the adrenal medulla, which is triggered by the signals associated with the activation of the cholinergic system in the hippocampus. Most of the norepinephrine in plasma is spillover from the sympathetic nervous terminals. Increase of norepinephrine after neostigmine injection into the CNS should reflect the activation of the sympathetic nervous system. In the mechanism of neostigmine-induced elevation of plasma glucose, at least four possible pathways were hypothesized. First, the secreted epinephrine may directly act on the hepatic release of glucose. Second, epinephrine may induce the release of glucagon and the suppression of insulin secretion in the pancreas. Third, direct neuronal control in the pancreas causes glucagon secretion. Fourth, direct innervation in the liver activates the glucose release. The relative contribution to induction of hyperglycemia was 22% for glucagon, 29% for epinephrine, and 49% for other factors including direct neuronal innervation in the liver (Fig. 2) (Iguchi et al., 1988).Uemura et al. (1989) studied the involvement of the cholinergic system in the hippocampus in CNS-mediated glucoregulation. Intrahippocampal injection of neostigmine also caused the significant increase of plasma glucose and catecholamines in a dose-dependent manner. Coinjection of atropine into both the hippocampus and the ventromedial hypothalamus suppressed this reaction (Iguchi et al., 1991). This finding suggested that the activation of muscarinic receptors in the hippocampus induced the increase of plasma glucose and catecholamines partly through, at least in, the activation of muscarinic cholinergic receptors in the ventromedial hypothalamus.These findings, taken together, strongly suggested that the hippocampus plays a pivotal role in CNS-mediated regulation of plasma glucose, catecholamines, and other hormones.3Age-associated change in the response of the cholinergic systemAge-related changes in the cholinergic system in the CNS have been well investigated (Decker, 1987). However, data regarding the age-related changes of input of cholinergic neurons into the hippocampus are controversial. Age-related changes in the activity of choline acetyltransferase, the synthetic enzyme of ACh, the content of ACh in the hippocampus, or the number of cholinergic neurons in the basal forebrain, the origin of cholinergic innervation, have been inconsistently found. The responsivity of the cholinergic system in the hippocampus, however, has been consistently suggested to demonstrate age-related changes. ACh synthesis, stimulation-induced release of ACh, and the electrophysiological response of postsynaptic neurons are diminished during the process of aging. Lippa et al. (1980, 1981, 1985) have extensively studied the reduced responsivity of aged hippocampal neurons by using in vivo recording. Other studies using hippocampal slice preparations have reported diminished neuronal responsivity to ACh application (Segal, 1982; Haigler et al., 1985). Mizuno and Kimura (1997) reported attenuated hippocampal ACh release in aged rats by using microdialysis.Based on these findings, we hypothesized that reduced responsivity of hippocampal neurons to ACh could result in changes in the peripheral metabolism. We injected neostigmine into the hippocampus of both aged (24MO) and young (6MO) Fischer 344 rats (n=20 and n=25, respectively), and measured the levels of glucose, epinephrine, and norepineprine in plasma after injection. The results (Fig. 3) indicated attenuated responses of plasma glucose and catecholamines by stimulation of the cholinergic system in the hippocampus of the aged rats (unpublished data).This finding suggested that the age-associated decrease of activity in the hippocampal cholinergic system could result in alteration of the peripheral metabolism.4Metabolism of catecholamines and glucose in plasma in Alzheimer's diseaseThe metabolic alterations in the brain of Alzheimer's disease have been investigated extensively (Meier-Ruge and Bertoni-Freddari, 1996; Yamaguchi et al., 1997), and the alteration of glucose metabolism in the brain is involved in the impairment of cognitive function in this disease. However, metabolic changes in the body characteristic of this disease have been less clear. One of the robust features in Alzheimer's disease is degeneration in the hippocampus, particularly in the cholinergic system. Based on findings indicating that the hippocampal cholinergic system is closely associated with the peripheral metabolism, we hypothesized that impairment of the cholinergic system in Alzheimer's disease could lead to changes in the peripheral metabolism.Several studies have focused on the plasma glucose metabolism in Alzheimer's disease, though, their results are inconsistent. Landin et al. (1993) and Bucht et al. (1983) reported finding lower fasting plasma glucose in subjects with Alzheimer's disease than in non-demented subjects, whose finding contrasted with those in other reports, which failed to confirm this difference (Winograd et al., 1991; Kilander et al., 1993). In some studies, hyperinsulinemia and reduced insulin sensitivity were found in both fasting states and during glucose tolerance testing (Bucht et al., 1983; Fujisawa et al., 1991; Razay and Wilcock 1994; Craft et al., 1998), though, other reports indicated no difference between the level of insulin in AD subjects and that in controls (Winograd et al., 1991; Kilander et al., 1993).Other studies have focused on the level of catecholamines in AD. Findings in these studies are also markedly inconsistent. Elrod et al. (1997) reported that level of norepinephrine in the plasma of DAT subjects increased. Conversely, a study done by Vitiello et al. (1993) reported a trend toward decreased levels of plasma norepinephrine and epinephrine in DAT subjects.We previously investigated the level of plasma catecholamines, glucose, and insulin in fasting state in AD, vascular dementia (VD), and non-demented (ND) female subjects (Umegaki et al., 2000). The three groups in this study were age-matched (AD=82.49±7.77, VD=82.86±5.86, ND=82.95±7.77), and the subjects were non-smokers (Table 1); those who had chronic obstructive pulmonary diseases, diabetes mellitus, neurodegenerative disease, or abnormal thyroid function were excluded. What we found in this study was that AD subjects, though not VD subjects, had significantly lower plasma epinephrine levels than non-demented subjects (AD=18.83±13.11, ND=31.52±29.83pg/ml). The other catecholamines investigated, norepinephrine and dopamine, showed lower levels in AD subjects, although the difference did not reach significance (Fig. 4, Table 2). The VD and AD subjects recruited for this study had similar scores on the Mini-Mental State Examination, which is the most well-established assessment test for cognitive function (Folstein et al., 1975) (Table 1). Consequently, the low plasma epinephrine appears to be specific for AD; not for demented states in general. No differences in fasting plasma glucose and insulin were found among these three groups. Recently, Craft et al. (1998) reported that apolipoprotein E genotypes are closely related to the fasting plasma insulin level. AD subjects who are apolipoprotein E-e4 homozygotes had a normal plasma insulin level whereas AD subjects who are not e4 homozygotes had an elevated plasma insulin level. The apoE4 genotype of the subjects we recruited should be investigated. The mechanism behind the low-plasma epinephrine level in AD subjects remains to be elucidated, although we could find the reason in the impaired hippocampal cholinergic system. The cholinergic system in the hippocampus might regulate the basal tone of epinephrine release from the adrenal medulla as well as epinephrine release during the stimulated state.5ConclusionData from animal studies show that the cholinergic system in the hippocampus is deeply involved in the regulation of plasma glucose and catecholamines. Impairment of the cholinergic system in the hippocampus has been reported in both aged rats and AD subjects, and our findings in our studies suggest that the metabolism of glucose and/or catecholamines is altered in these conditions.ReferencesBucht et al., 1983GBuchtRAdolfssonFLithnerBWinbladChanges in blood glucose and insulin secretion with senile dementia of Alzheimer typeActa Med. Scand.2131983387392Craft et al., 1998SCraftEPeskindM.WSchwartzG.DSchellenbergMRaskindDPorteCerebrospinal fluid and plasma insulin levels in Alzheimer's diseaseNeurology501998164168Decker, 1987M.WDeckerThe effects of aging on hippocampal and cortical projections of the forebrain cholinergic systemBrain Res. Rev.121987423438Elrod et al., 1997RElrodE.RPeskindLDiGiacomoK.IBrodkinR.CVeithM.ARaskindEffects of Alzheimer's disease severity on cerebrospinal fluid norepinephrine concentrationAm. J. Psychiatry15419972529Folstein et al., 1975M.FFolsteinS.EFolsteinP.RMcHughMini-Mental State: a practical method for grading the cognitive state of patients for the clinicianJ. Psychiatr. Res.121975189198Fujisawa et al., 1991YFujisawaKSasakiKAkiyamaIncreased insulin levels after OGTT load in peripheral blood and cerebrospinal fluid of patients with dementia of Alzheimer typeBiol. Phychiatry30199112191228Gilad, 1987G.MGiladThe stress-induced response of the septo-hippocampal cholinergic system: a vectorial outcome of psychoneuroendocrinological interactionsPsychoneuroendocrinology121987167184Haigler et al., 1985H.JHaiglerLCahillMCahillECharlesAcetylcholine, aging and anatomy: differential effects in the hippocampusBrain Res.3621985157160Iguchi et al., 1984AIguchiHMatsunagaTNomuraMGotohGlucoregulatory effects of intrahypothalamic injections of bombesis and other peptidesEndocrinology1146198422422246Iguchi et al., 1985AIguchiHMatsunagaTGotohTNomuraAYatomiNSakamotoCentral hyperglycemic effect of adrenaline and carbocholActa Endocrinol.1091985440445Iguchi et al., 1986AIguchiHGotohHMatsunagaAYatomiAHonmuraMYanaseNSakamotoMechanism of central hyperglycemic effect of cholinergic agonists in fasted ratsAm. J. Physiol.2511986E431E437Iguchi et al., 1988AIguchiHGotohHMatsunagaAYatomiAHonmuraMYanaseNSakamotoRelative contribution of the nervous system and hormones to CNS-mediated hyperglycemiaAm. J. Physiol.2551988E920E927Iguchi et al., 1991AIguchiKUemuraYKunohHMiuraTIshiguroKNonogakiTTamagawaMGotohNSakamotoHyperglycemia induced by hippocampal administration of neostigmine is suppressed by intrahypothalamic atropineNeuropharmacology30199111291130Imperato et al., 1991AImperatoSPuglisi-AllegraPCasoliniLAngelucciChanges in brain dopamine and acetylcholine release during and following stress are independent of the pituitary-adenocortical axisBrain Res.5381991111117Jack et al., 1998C.RJackJrR.CPetersenY.CXuP.CO'brienS.CWaringE.GTangalosG.ESmithR.JInvikS.NThibodeauEKokmenHippocampal atrophy and apolipoprotein E genotype are independently associated with Alzheimer's diseaseAnn. Neurol.431998303310Kilander et al., 1993LKilanderMBobergHLithellPeripheral glucose metabolism and insuline sensitivity in Alzheimer's diseaseActa Neurol. Scand.871993294298Kim and Yoon, 1998J.JKimK.SYoonStress: metaplastic effects in the hippocampusTrends Neurosci.211998505509Landin et al., 1993KLandinK.LBlennowAWallinC.GGottfriesLow blood pressure and blood glucose levels in Alzheimer's disease. Evidence for a hypometabolic disorder?J. Internal Med.2331993363367Lippa, 1980A.SLippaR.WPelhamBBeerD.JCritchettR.LDeanR.TBartusBrain cholinergic dysfunction and memory in aged ratsNeurobiol. Aging119801319Lippa et al., 1981A.SLippaD.JCritchettFEhlertH.IYamamuraS.JEnnaR.TBartusAge-related alterations in neurotransmitter receptors: an electrophysiological and biochemical analysisNeurobiol. Aging2198138Lippa, 1985A.SLippaC.CLoullisJRotrosenD.MCordascoD.JCritchettJ.AJosephConformational changes in muscarinic receptors may produce diminished cholinergic neurotransmission and memory deficits in aged ratsNeurobiol. Aging61985317323Lupien et al., 1998S.JLupienMde LeonSde SantiAConvitCTarshishN.P.VNairMThakurB.SMcEwenR.LHaugerM.JMeaneyCortisol levels during human aging predict hippocampal atrophy and memory deficitsNature Neurosci.119986973Magarinos et al., 1997A.MMagarinosJ.MVerdugoB.SMcEwenChronic stress alters synaptic terminal structure in hippocampusProc. Natl. Acad. Sci.9425199714 00214 008McEwen, 1999B.SMcEwenStress and hippocampal plasticityAnnu. Rev. Neurosci.221999105122Meier-Ruge and Bertoni-Freddari, 1996WMeier-RugeCBertoni-FreddariThe significance of glucose turnover in the brain in the pathogenetic mechanism of Alzheimer's diseaseRev. Neurosci.71996119Mizuno and Kimura, 1997TMizunoFKimuraAttenuated stress response of hippocampal acetylcholine releases and adrenocortical secretion in aged ratsNeurosci. Lett.22219974952de Quervain et al., 1998D.Jde QuervainBRoozendaalJ.LMcGaughStress and glucocorticoids impair retrieval of long-term spatial memoryNature3941998787790Razay and Wilcock, 1994GRazayG.KWilcockHyperinsulinaemia and Alzheimer's diseaseAge Aging231994396399Sandi, 1998CSandiThe role and mechanism of action of glucocorticoid involvement in memory storageNeural Plasticity619984152Sapolsky, 1997R.MSapolskyWhy stress is bad for your brainScience2731997749750Segal, 1982MSegalChanges in neurotransmitter actions in the aged rat hippocampusNeurobiol. Aging31982121132Tajima et al., 1996TTajimaHEndoYSuzukiHIkariMGotohAIguchiImmobilization stress-induced increase of plasma epinephrine, norepinephrine and glucose in ratsBrain Res.7201996155158Uemura et al., 1989KUemuraAIguchiHYatomiAMiuraAHonmuraMYanaseNSakamotoInvolvement of the hippocampus in central nervous system-mediated glucoregulation in ratsEndocrinology1245198924552499Umegaki et al., 2000HUmegakiHIkariHNakahataJYoshimuraHEndoTYamamotoAIguchiLow plasma epinephrine in elderly female subjects of dementia of Alzheimer typeBrain Res.85820006770Vitiello et al., 1993BVitielloR.CVeithS.EMolchanR.AMartinezB.ALawlorJRadcliffeJ.LHillTSunderlandAutonomic dysfunction in patients with dementia of the Alzheimer typeBiol. Psychiatry341993428433Winograd et al., 1991C.HWinogradD.HJacobsonJ.RMinkoffC.APeabodyB.STaylorLWidrowJ.AYesavageBlood glucose and insuline response in patients with senile dementia of the Alzheimer's typeBiol. Psychiatry301991507511Wolkowitz et al., 1997O.MWolkowitzV.IReusJCanickBLevinSLupienGlucocorticoid medication, memory and steroid psychosis in medical illnessAnn. NY Acad. Sci.82319978196Yamaguchi et al., 1997SYamaguchiKMeguroMItohCHayasakaMShimadaHYamazakiAYamadoriDecreased cortical glucose metabolism correlated with hippocampal atrophy in Alzheimer's diseaseJ. Neurol., Neurosurg. Psychiatry621997596600