Selective reduction in ventral hippocampal acetylcholine release in awake galanin-treated rats and galanin-overexpressing transgenic mice

The neuropeptide galanin is an inhibitory modulator of hippocampal acetylcholine (ACh) release and cognitive functions. Anatomical evidence demonstrated some differences between the dorsal and ventral hippocampi notably in the expression of galanin receptor subtypes, and the neuronal population on which galanin-like immunoreactivity is expressed. This is suggestive of a differential role for this peptide in these two areas of the hippocampal formation. Using in vivo microdialysis, we investigated the role of galanin on ACh release in the dorsal and ventral hippocampi. Two models were studied: galanin-administered rats and transgenic mice over-expressing galanin (GAL-tg). In rats, galanin (2.0 and 10.0 microM) infused locally through the dialysis probe induced a significant decrease in ACh release in the ventral hippocampus, confirming previous findings, while no effect was seen in the dorsal hippocampus. Using the no net flux method, a significant reduction in ACh levels was noted only in the ventral hippocampus of GAL-tg compared to wild-type littermates. These results suggest that excess endogenous galanin can suppress basal ACh release, with anatomical specificity, to the ventral hippocampus. These results are of interest in the context of galanin receptor subtypes in the dorsal and ventral hippocampus, and the differential alterations of hippocampal subregions in neurological diseases such as Alzheimer's dementia.     

Effects of exposure to low level radiofrequency fields on acetylcholine release in hippocampus of freely moving rats

Some central cholinergic effects have been reported in animals after acute exposure to radiofrequency electromagnetic field at low intensity. We studied acetylcholine (ACh) release in the brain of freely moving rats exposed for 1 h during the day to a 2.45 GHz continuous wave radiofrequency field (RF) (2 or 4 mW/cm(2)) or exposed for 1 or 14 h during the night to a 800 MHz field modulated at 32 Hz (AM 200 mW/cm(2)). Measurements were performed by microdialysis using a membrane implanted through the upper CA1 region of the hippocampus. After irradiation with the 2.45 GHz RF, rats exposed at 2 mW/cm(2) did not show a significant modification of Ach release, whereas those exposed at 4 mW/cm(2) showed a significant 40% decrease in mean ACh release from hippocampus. This decrease was maximal at 5 h post exposure. Exposure to the 800 MHz RF for 1 h did not cause any significant effect, but exposure for 14 hrs induced a significant 43% decrease in ACh release during the period 11 p.m.-4 a.m. compared to control rats. In the control group we observed an increase of ACh release at the beginning of the night, which was linked to the waking period of rats. This normal increase was disturbed in rats exposed overnight to the 800 MHz RF. This work indicates that neurochemical modification of the hippocampal cholinergic system can be observed during and after an exposure to low intensity RF.     

Characterization of N-[3H]Methylcarbamylcholine Binding Sites and Effect of N-Methylcarbamylcholine on Acetylcholine Release in Rat Brain

The present experiments show that N-[3H]-methylcarbamylcholine ([3H]MCC) binds specifically and with high affinity to rat hippocampus, frontal cortex, and striatum. The highest maximal density of binding sites was apparent in frontal cortex and the lowest in hippocampus. [3H]MCC binding was potently inhibited by nicotinic, but not muscarinic, agonists and by the nicotinic antagonist dihydro-beta-erythroidine in all three brain regions studied. The effect of unlabeled MCC on acetylcholine (ACh) release from slices of rat brain was tested. The drug significantly enhanced spontaneous ACh release from slices of hippocampus and frontal cortex, but not from striatal slices. This effect of MCC to increase ACh release from rat hippocampus and frontal cortex was antagonized by the nicotinic antagonists dihydro-beta-erythroidine and d-tubocurarine, but not by alpha-bungarotoxin or by the muscarinic antagonist atropine. The MCC-induced increase in spontaneous ACh release from hippocampal and frontal cortical slices was not affected by tetrodotoxin. The results suggest that MCC might alter cholinergic transmission in rat brain by a direct activation of presynaptic nicotinic receptors on the cholinergic terminals. That this alteration of ACh release is apparent in hippocampus and frontal cortex, but not in striatum, suggests that there may be a regional specificity in the regulation of ACh by nicotinic receptors in rat brain.     

Evidence that Somatostatin Enhances Endogenous Acetylcholine Release in the Rat Hippocampus

The present experiments show that somatostatin (SS)-like immunoreactive material is present in the hippocampus and that its release can be increased by K+ stimulation of rat hippocampal slices, suggesting that SS-like peptides may be of significance to neurotransmission in the hippocampus. Exogenous SS-28 and SS-14 enhanced the K(+)-evoked release of endogenous acetylcholine (ACh) from rat hippocampal slices, whereas amino-terminal fragments of SS-28 did not. The increased ACh release in the presence of either peptide appeared to be mediated by an interaction with SS receptors because cyclo-SS, a putative SS antagonist, abolished the effects of both SS-28 and SS-14. In addition, the increase in ACh release induced by SS-14 or SS-28 was antagonized by the calcium channel antagonists omega-conotoxin GVIA, nifedipine, and cinnarizine, implicating voltage-sensitive calcium channels in this effect. Moreover, the effect was sensitive to tetrodotoxin, suggesting an indirect action of the peptides at a site distal to cholinergic nerve terminals. Cysteamine, which has been reported to deplete SS content and to increase SS release in brain, augmented the basal and evoked release of ACh from hippocampal slices, without affecting SS-like content and release. Finally, neuropeptide Y, which is colocalized with SS in many neurons of the hippocampal formation, did not alter ACh release, nor did it facilitate the SS-induced increase. The results suggest that in the rat hippocampus, both SS-28 and SS-14 interact with SS receptors to regulate ACh release indirectly by a mechanism that involves alterations of calcium influx during depolarization.     

Enhancement of hippocampal cholinergic neurotransmission through 5-HT1A receptor-mediated pathways by repeated lithium treatment in rats

Hippocampal cholinergic neuronal activity is reported to be regulated, at least partly, through serotonin1A (5-HT1A) receptors. Chronic lithium treatment has been shown to alter both behavioral and neurochemical responses mediated by postsynaptic 5-HT1A receptors. We investigated whether long-term lithium treatment affects central cholinergic neurotransmission through 5-HT1A receptor-mediated pathways. Changes in acetylcholine (ACh) release induced by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a 5-HT1A receptor agonist, in the rat hippocampus were measured using a microdialysis technique and a radioimmunoassay for ACh. Administration of lithium for 21 days resulted in a serum lithium concentration of 1.03 mM and caused little change in density or affinity of [3H]8-OH-DPAT binding sites in the hippocampus. The local application of 8-OH-DPAT into the hippocampus of lithium treated rats increased the ACh efflux in both the absence and the presence of physostigmine, a cholinesterase (ChE) inhibitor, in the perfusion fluid. The basal ACh efflux of lithium treated rats was not different from that of the control rats under normal conditions, but was significantly higher than that of the controls when ChE was inhibited. These results demonstrate that chronic lithium treatment increases spontaneous ACh release in the hippocampus under conditions of ChE inhibition, but not under normal conditions, and enhances cholinergic neurotransmission through 5-HT1A receptor-mediated pathways, and suggest that activation of 5-HT1A receptor function by lithium is related to the enhancement of hippocampal cholinergic neurotransmission.     

Output, Tissue Levels, and Synthesis of Acetylcholine During and After Transient Forebrain Ischemia in the Rat

Biochemical changes in the rat brain cholinergic system during and after 60 min of ischemia were studied using a four-vessel occlusion model. Extracellular acetylcholine (ACh) concentrations in the unanesthetized rat hippocampus markedly increased during ischemia and reached a peak (about 13.5 times baseline levels) at 5-10 min after the onset of ischemia. At 2-5 h after reperfusion, extracellular ACh concentrations were reduced to 64-72% of the levels of controls. ACh levels in the hippocampus, striatum, and cortex decreased significantly during ischemia and exceeded their control values just after reperfusion. A significant increase in hippocampal ACh level after 2 days of reperfusion and a decrease in [14C]ACh synthesis from [14C]glucose in hippocampal slices excised at 2 days after reperfusion were observed. The extracellular concentrations and tissue levels of choline markedly increased after ischemia. These results show that ACh is markedly released into the extracellular space in the hippocampus during ischemia, and they suggest that ACh synthesis is activated just after reperfusion and that cholinergic activity is reduced after 2-48 h of reperfusion in the hippocampus.     

Alterations in acetylcholine release in the rat hippocampus during sleep-wakefulness detected by intracerebral dialysis

Acetylcholine (ACh) release from the dorsal hippocampus was continuously monitored in freely moving rats during a light period using an intracerebral dialysis technique. A dialysate was collected every 6 min and polygraph recordings including cortical and hippocampal electroencephalograms, electromyogram, and electrooculogram were simultaneously made to determine the stage of sleep-wakefulness. The content of ACh was measured by high-performance liquid chromatography with electrochemical detection. ACh output showed profound and state-dependent fluctuations. ACh levels during waking increased approximately 300% compared to slow wave sleep. In contrast, the rate of ACh release during paradoxical sleep was as high as during waking and appeared to be even higher. These results revealed that the intracerebral dialysis technique provides a useful method to monitor changes in spontaneous neurotransmitter release during the sleep-waking cycle.     

Repeated Restraint Stress Alters Hippocampal Glutamate Uptake and Release in the Rat

Glutamatergic mechanisms are thought to be involved in stress-induced changes of brain function, especially in the hippocampus. We hypothesized that alterations caused by the hormonal changes associated with chronic and acute stress may affect glutamate uptake and release from hippocampal synaptosomes in Wistar rats. It was found that [3H]glutamate uptake and release by hippocampal nerve endings, when measured 24 h after 1 h of acute restraint, presented no significant difference. The exposure to repeated restraint stress for 40 days increased neuronal presynaptic [3H]glutamate uptake as well as basal and K+-stimulated glutamate release when measured 24 h after the last stress session. Chronic treatment also caused a significant decrease in [3H]glutamate binding to hippocampal membranes. We suggest that changes in the glutamatergic system are likely to take part in the mechanisms involved in nervous system plasticity following repeated stress exposure.     

Phorbol 12,13-dibutyrate enhances electrically stimulated neuromessenger release from rat dorsal hippocampal slices in vitro

The protein kinase C activator 4 beta-phorbol 12,13-dibutyrate (PDB) enhanced the electrically stimulated release of radiolabelled noradrenaline (NA), acetylcholine (ACh) and 5-hydroxytryptamine (5-HT) from dorsal hippocampal slices of the rat in vitro in a concentration-dependent manner. 4 alpha-Phorbol 12,13 didecanoate did not have an effect on the electrically stimulated release of any of the neuromessengers. Carbachol, which when present in the superfusion medium alone inhibited [14C]ACh release, significantly reduced the effect of PDB on the release of this neuromessenger. In the presence of either clonidine or [Leu5]enkephalin, which by themselves inhibited the electrically stimulated release of [3H]NA, the effect of PDB was significantly reduced. The enhancing effects of yohimbine and PDB on the electrically stimulated release of [3H]NA were additive. In all three cases, thus, the net effects of PDB were of a similar magnitude, whether the various compounds were present or not. Taken together, the present data suggest that the diacylglycerol/protein kinase C pathway is involved in the stimulus-evoked release of NA, ACh and 5-HT from dorsal hippocampal nerve terminals. Protein kinase C seems not to be involved in the modulation of the release of NA via presynaptic alpha 2-adrenoceptors and delta-opioid receptors and in that of ACh via presynaptic ACh receptors in that brain region.     

Effect of two distinct stressors on gene expression of the type 1 IP3 receptors

Inositol 1,4,5-trisphosphate (IP3) is one of the second messengers, which triggers calcium release from intracellular pools via IP3 receptors. Previously we have shown that single immobilization stress increased gene expression of both, the type 1 and type 2 IP3 receptors (IP3R1 and IP3R2, respectively). In this study we evaluated whether long-term exposure to softer stressor (cold exposure to 4 degrees C) can affect the response to single immobilization stress. We examined modulation of the type 1 IP3 receptor gene expression by each stressor separately, and then in their combination. Rats were immobilized for 30 min and 120 min and were decapitated immediately or 3 h after immobilization. Cold stress was performed by exposure of animals to 4 degrees C temperature for 1, 7 and 28 days. To determine the effect of both stressors in combination, animals exposed to cold for 28 days were afterwards exposed to immobilization for 120 min and decapitated 3 h after the end of stressful stimulus. Our results verify that single immobilization increases the IP3R1 gene expression in left atria of rat heart, while cold stress elevates the level of gene expression only after the exposure to cold for 7 days. The exposure to cold for 28 days did not increase the gene expression of the type 1 IP3 receptor compared to control. Application of both stressors (28 days of cold exposure followed by 120 min of immobilization with subsequent 3 h rest) showed the tendency of increased IP3R1 gene expression compared to absolute, nonstressed control, but level of the type 1 IP3 receptor mRNA was significantly lower compared to mRNA levels of solely immobilized animals. Thus, cold exposure affects the response of the gene expression of the type 1 IP3 receptor to immobilization stress.     

Regional Selectivity of a γ-Aminobutyric Acid-Induced [3H]Acetylcholine Release Sensitive to Inhibitors of γ-Aminobutyric Acid Uptake

The effects of gamma-aminobutyric acid (GABA) on the release of [3H]acetylcholine ([3H]ACh) were studied in synaptosomes prepared from rat hippocampus, cerebral cortex, hypothalamus, and striatum and prelabelled with [3H]choline. When synaptosomes were exposed in superfusion to exogenous GABA (0.01-0.3 mM) the basal release of newly synthesized [3H]ACh was increased in a concentration-dependent way in hippocampus, cortex, and hypothalamus nerve endings. In contrast, the release of [3H]ACh was not significantly affected by GABA in striatal synaptosomes. The effect of GABA was not antagonized significantly by bicuculline or picrotoxin. Muscimol caused only a slight not significant increase of [3H]ACh release when tested at 0.3 mM whereas, at this concentration, (-)-baclofen was totally inactive. The GABA-induced release of [3H]ACh was counteracted by SKF 89976A, SKF 100561, and SKF 100330A, three strong and selective GABA uptake inhibitors. The data suggest that, in selective areas of the rat brain, GABA causes release of [3H]ACh following penetration into cholinergic nerve terminals through a GABA transport system.     

Vasoactive Intestinal Peptide Increases Acetylcholine Synthesis by Rat Hippocampal Slices

The purpose of this study was to determine whether vasoactive intestinal peptide (VIP) might have a presynaptic modulatory effect at cholinergic terminals in the rat hippocampal formation. The exposure of rat hippocampal slices to VIP increased [3H]acetylcholine ([3H]ACh) synthesis from the precursor [3H]choline when tissue was incubated in normal or in high K+ medium; the maximal effect was apparent at 10(-8) M VIP and 10(-7) M VIP, respectively. Also, 10(-7) M VIP increased the activity of choline acetyltransferase (ChAT) in a hippocampal homogenate system. The increased synthesis by hippocampal slices was not the result of a VIP-induced alteration in either the basal release of ACh or the uptake of choline via the high-affinity uptake system. The increase in ACh synthesis induced by VIP in hippocampal slices was not associated with either adenylate cyclase or protein kinase C second messenger systems. There was no correlation between the effect of VIP on cyclic AMP production with that on ACh synthesis; also, forskolin, an activator of adenylate cyclase that increased cyclic AMP production 3.5-fold, did not mimic the effect of VIP on ACh synthesis. Similarly, there was no effect of the protein kinase C activator, phorbol myristate acetate, on ACh synthesis in hippocampal slices. However, the effect of VIP to increase ACh synthesis was not evident in the absence of extracellular calcium, suggesting that the effect of VIP is mediated by a calcium-requiring mechanism. The results suggest that, in the rat hippocampus, VIP has a presynaptic action at cholinergic terminals that results in enhanced synthesis of ACh, possibly by an action that alters ChAT activity.     

Choline availability and acetylcholine synthesis in the hippocampus of acetylcholinesterase-deficient mice

Mice deficient for acetylcholinesterase (AChE) have strongly increased extracellular levels of acetylcholine (ACh) in the dorsal hippocampus [Hartmann, J., Kiewert, C., Duysen, E.G., Lockridge, O., Greig, N.H., Klein, J., 2007. Excessive hippocampal acetylcholine levels in acetylcholinesterase-deficient mice are moderated by butyrylcholinesterase activity. J. Neurochem. 100, 1421-1429]. Using microdialysis, we found that increased ACh levels are accompanied by decreased levels of extracellular choline which were 1.60 microM in AChE-deficient mice and 4.36 microM in wild-type mice. Addition of choline (10 microM) to the perfusion fluid, while ineffective in wild-type animals, more than doubled extracellular ACh levels in AChE-deficient mice. High-affinity choline uptake (HACU), as measured ex vivo in corticohippocampal synaptosomes, was more than doubled in AChE-deficient mice. Inhibition of HACU by hemicholinium-3 (HC-3) in vivo reduced extracellular levels of ACh by 60% in wild-type mice but by more than 90% in AChE-deficient mice. Decreased ACh levels caused by infusion of HC-3 or tetrodotoxin (TTX) were accompanied by increased levels of free choline. Infusion of scopolamine (1 microM) caused a fivefold increase of ACh levels in wild-type animals but only a 50% increase in AChE-deficient mice. In conclusion, absence of AChE causes dynamic changes in the ratio of choline to ACh. High levels of extracellular ACh are accompanied by reduced levels of extracellular choline, and ACh release becomes strongly dependent on choline availability. Similar changes may take place in patients chronically exposed to AChE inhibitors.     

Metabolic and hormonal responses in theophylline-increased cold resistance in males

The effects of theophylline (a phosphodiesterase inhibitor-adenosine receptor antagonist) and substrate feeding (Ensure, 250 kcal/235 ml) on cold resistance were studied in seminude males undertaking submaximal (50% maximum O2 consumption), intermittent (34% of total time) exercise in the cold (-5 to 15 degrees C, individually adjusted) for 3 h. Each subject (n = 7) served as his own control and was tested on a weekly schedule. Under control treatment, rectal temperature (Tre) decreased by 0.9 degrees C to approximately 36.2 degrees C after cold exposure, whereas under theophylline and Ensure, the decrease of Tre was only 0.4 degrees C, indicating a significant increase (P less than 0.05) in cold resistance (50% better than control). The plasma concentration of theophylline was 4.8-5.9 micrograms/ml and was positively correlated with plasma concentration of free fatty acids. Plasma norepinephrine (NE) increased significantly during cold exposure; the absolute concentration was significantly higher after theophylline pretreatment. The plasma concentrations of glucose, epinephrine, cortisol, and adenosine 3',5'-cyclic monophosphate did not change and the changes of free thyroxine and triiodothyronine were minor. Together, the effectiveness of theophylline + Ensure in acutely increasing cold resistance may be due to increased substrate availability for thermogenesis, part of which, through theophylline's potentiation of both sympathetic release of NE and NE-stimulated lipolysis and part of which, through supplementary feeding of Ensure.     

Thermoregulatory responses of the immature rat following repeated postnatal exposures to 2,450-MHz microwaves

This study was designed to determine the changes that occur in the thermoregulatory ability of the immature rat repeatedly exposed to low-level microwave radiation. Beginning at 6-7 days of age, previously untreated rats were exposed to 2,450-MHz continuous-wave microwaves at a power density of 5 mW/cm2 for 10 days (4 h/day). Microwave and sham (control) exposures were conducted at ambient temperatures (Ta) which represent different levels of cold stress for the immature rat (ie, "exposure" Ta = 20 and 30 degrees C). Physiological tests were conducted at 5-6 and 16-17 days of age, in the absence of microwaves, to determine pre- and postexposure responses, respectively. Measurements of metabolic rate, colonic temperature, and tail skin temperature were made at "test" Ta = 25.0, 30.0, 32.5, and 35.0 degrees C. Mean growth rates were lower for rats exposed to Ta = 20 degrees C than for those exposed to Ta = 30 degrees C, but microwave exposure exerted no effect at either exposure Ta. Metabolic rates and body temperatures of all exposure groups were similar to values for untreated animals at test Ta of 32.5 degrees C and 35.0 degrees C. Colonic temperatures of rats repeatedly exposed to sham or microwave conditions at exposure Ta = 20 degrees C or to sham conditions at exposure Ta = 30 degrees C were approximately 1 degrees C below the level for untreated animals at test Ta of 25.0 degrees C and 30.0 degrees C. However, when the exposure Ta was warmer, rats exhibited a higher colonic temperature at these cold test Ta, indicating that the effectiveness of low-level microwave treatment to alter thermoregulatory responses depends on the magnitude of the cold stress.     

Effect of the exposure to chronic-intermittent cold on the thyrotropin and thyroid hormones in the rat

Rats exposed to acute cold (4 degrees C for 2 h), chronic cold (4 degrees C), and chronic-intermittent cold (4 degrees C for 2 h daily) were killed after 1, 2, 3, 4, and 10 days of cold exposure. The control group was maintained at 25 degrees C. In each animal, the plasma concentration of thyrotropine (THS), triiodothyronine (T3), and thyroxine (T4) was determined by radioimmunoassay. At the initial time of exposure, elevations in TSH, T3, and T4 were observed in the rats in each experimental group. However, on the 10th day, in rats exposed to chronic-intermittent cold, TSH, T3, and T4 decreased to values lower than the control values. In animals exposed to acute cold as well as to chronic cold no differences were found, with respect to the controls, in TSH and T4. In rats exposed to acute cold for 10 days, the T3 value was lower than the control value; however, in animals exposed to chronic cold, T3 was same as that in the controls. The results indicate that, in the rat, exposure to chronic-intermittent cold produces an inhibition in the secretion of TSH and thyroid hormones.     

Choline and acetylcholine metabolism in rat neostriatal slices

Choline (Ch) uptake and release and acetylcholine (ACh) synthesis and release have been studied by gas chromatography mass spectrometry (GCMS) in slices of rat neostriatum in vitro to assess the effects of depolarization by 25 mM K+ and the influence of elevated concentrations of Ch in the incubation medium. During the first 60 min after preparation, 25 mM K+ increased ACh release by 182% and reduced ACh levels by 40%. The rate of ACh synthesis was unchanged. After a 1-h equilibration period, the rate of ACh synthesis was considerably less (2.41 nmol mg-1 h-1, compared to 9.78 nmol mg-1 h-1). Exposure to 25 mM K+ during the second hour increased the rate to 6.47 nmol mg-1 h-1. During the first 10 min of exposure to 25 mM K+, ACh synthesis was reduced, regardless of incubation. Increasing concentrations of external [2H4]Ch apparently favored initial rates of net ACh synthesis, since the rank order of initial net ACh synthesis rates is the same as the rank order of external [2H4] Ch concentration under both normal and depolarized conditions. However, the only significant effect of external [2H4]Ch on ACh metabolism was that it increased ACh release during the initial 10 min, when the preparation was depolarized with K+. The efflux of endogenous [2H0]Ch was increased initially (10 min) and slowed over a 60-min period by 25 mM K+, and increased when [2H4]Ch in the medium was increased. Changes in ACh synthesis and release were dependent upon the time exposure of slices to high K+, and the results suggest that Ch favors initial rates of ACh synthesis, but that Ch influences ACh release primarily under conditions of stress (i.e., depolarization).     

Amyloid β-Peptide Inhibits High-Affinity Choline Uptake and Acetylcholine Release in Rat Hippocampal Slices

Abstract: The characteristic pathological features of the postmortem brain of Alzheimer's disease (AD) patients include, among other features, the presence of neuritic plaques composed of amyloid β-peptide (Aβ) and the loss of basal forebrain cholinergic neurons, which innervate the hippocampus and the cortex. Studies of the pathological changes that characterize AD and several other lines of evidence indicate that Aβ accumulation in vivo may initiate and/or contribute to the process of neurodegeneration and thereby the development of AD. However, the mechanisms by which Aβ peptide influences/causes degeneration of the basal forebrain cholinergic neurons and/or the cognitive impairment characteristic of AD remain obscure. Using in vitro slice preparations, we have recently reported that Aβ-related peptides, under acute conditions, potently inhibit K⁺-evoked endogenous acetylcholine (ACh) release from hippocampus and cortex but not from striatum. In the present study, we have further characterized Aβ-mediated inhibition of ACh release and also measured the effects of these peptides on choline acetyltransferase (ChAT) activity and high-affinity choline uptake (HACU) in hippocampal, cortical, and striatal regions of the rat brain. Aβ_1–40 (10^?8M) potently inhibited veratridine-evoked endogenous ACh release from rat hippocampal slices and also decreased the K⁺-evoked release potentiated by the nitric oxide-generating agent, sodium nitroprusside (SNP). It is interesting that the endogenous cyclic GMP level induced by SNP was found to be unaltered in the presence of Aβ_1–40. The activity of the enzyme ChAT was not altered by Aβ peptides in hippocampus, cortex, or striatum. HACU was reduced significantly by various Aβ peptides (10^?14 to 10^?6M) in hippocampal and cortical synaptosomes. However, the uptake of choline by striatal synaptosomes was altered only at high concentration of Aβ (10^?6M). Taken together, these results indicate that Aβ peptides, under acute conditions, can decrease endogenous ACh release and the uptake of choline but exhibit no effect on ChAT activity. In addition, the evidence that Aβ peptides target primarily the hippocampus and cortex provides a potential mechanistic framework suggesting that the preferential vulnerability of basal forebrain cholinergic neurons and their projections in AD could relate, at least in part, to their sensitivity to Aβ peptides.     

Chronic Stress and Lithium Treatments Alter Hippocampal Glutamate Uptake and Release in the Rat and Potentiate Necrotic Cellular Death After Oxygen and Glucose Deprivation

This study was undertaken to evaluate the effects of chronic variate stress and lithium treatment on glutamatergic activity and neuronal vulnerability of rat hippocampus. Male Wistar rats were simultaneously treated with lithium and submitted to a chronic variate stress protocol during 40?days, and afterwards the hippocampal glutamatergic uptake and release, measured in slices and synaptosomes, were evaluated. We observed an increased synaptosomal [(3)H]glutamate uptake and an increase in [(3)H]glutamate stimulated release in hippocampus of lithium-treated rats. Chronic stress increased basal [(3)H]glutamate release by synaptosomes, and decreased [(3)H]glutamate uptake in hippocampal slices. When evaluating cellular vulnerability, both stress and lithium increased cellular death after oxygen and glucose deprivation (OGD). We suggest that the manipulation of glutamatergic activity induced by stress may be in part responsible for the neuroendangerment observed after stress exposure, and that, in spite of the described neuroprotective effects of lithium, it increased the neuronal vulnerability after OGD.     

Seasonal dependence of the activity of antioxidant defence enzymes in the ground squirrel (Citellus citellus): the effect of cold.

1. The activity of antioxidant defense enzymes (SOD, CAT, GSH-Px and GST) was analysed during the autumn and winter in the ground squirrel adapted to 30 degrees C and subsequently exposed to cold for 6 and 24 hr. 2. The liver CAT activity as well as the IBAT CAT and GSH-Px activities differed between animals adapted to 30 degrees C, studied in autumn, and those studied in winter. 3. MnSOD activity in the liver was increased in autumn but decreased in winter after 6 hr cold exposure reaching the control level 24 hr later. Cold exposure induced a decrease in CAT activity (except after 24 hr cold exposure in winter) and an increase in GSH-Px activity. Lower GST activity was found after 24 hr exposure to cold in winter. 4. The IBAT SOD activity decreased under the influence of cold during both seasons with a tendency to return to the control level only in winter. Cold exposure produced a decrease in GST in both seasons and CAT activity in autumn. GSH-Px activity was increased in winter only. 5. The results indicate a seasonal dependence of the activity of antioxidant defence enzymes in the ground squirrel. Seasonal influence was evidenced in animals exposed to cold as well.