Feeding acetyl-L-carnitine and lipoic acid to old rats significantly improves metabolic function while decreasing oxidative stress

Mitochondrial-supported bioenergetics decline and oxidative stress increases during aging. To address whether the dietary addition of acetyl-l-carnitine [ALCAR, 1.5% (wt/vol) in the drinking water] and/or (R)-alpha-lipoic acid [LA, 0.5% (wt/wt) in the chow] improved these endpoints, young (2-4 mo) and old (24-28 mo) F344 rats were supplemented for up to 1 mo before death and hepatocyte isolation. ALCAR+LA partially reversed the age-related decline in average mitochondrial membrane potential and significantly increased (P = 0.02) hepatocellular O(2) consumption, indicating that mitochondrial-supported cellular metabolism was markedly improved by this feeding regimen. ALCAR+LA also increased ambulatory activity in both young and old rats; moreover, the improvement was significantly greater (P = 0.03) in old versus young animals and also greater when compared with old rats fed ALCAR or LA alone. To determine whether ALCAR+LA also affected indices of oxidative stress, ascorbic acid and markers of lipid peroxidation (malondialdehyde) were monitored. The hepatocellular ascorbate level markedly declined with age (P = 0.003) but was restored to the level seen in young rats when ALCAR+LA was given. The level of malondialdehyde, which was significantly higher (P = 0.0001) in old versus young rats, also declined after ALCAR+LA supplementation and was not significantly different from that of young unsupplemented rats. Feeding ALCAR in combination with LA increased metabolism and lowered oxidative stress more than either compound alone.     

Age-associated mitochondrial oxidative decay: improvement of carnitine acetyltransferase substrate-binding affinity and activity in brain by feeding old rats acetyl-L- carnitine and/or R-alpha -lipoic acid

We test whether the dysfunction with age of carnitine acetyltransferase (CAT), a key mitochondrial enzyme for fuel utilization, is due to decreased binding affinity for substrate and whether this substrate, fed to old rats, restores CAT activity. The kinetics of CAT were analyzed by using the brains of young and old rats and of old rats supplemented for 7 weeks with the CAT substrate acetyl-l-carnitine (ALCAR) and/or the mitochondrial antioxidant precursor R-alpha-lipoic acid (LA). Old rats, compared with young rats, showed a decrease in CAT activity and in CAT-binding affinity for both substrates, ALCAR and CoA. Feeding ALCAR or ALCAR plus LA to old rats significantly restored CAT-binding affinity for ALCAR and CoA, and CAT activity. To explore the underlying mechanism, lipid peroxidation and total iron and copper levels were assayed; all increased in old rats. Feeding old rats LA or LA plus ALCAR inhibited lipid peroxidation but did not decrease iron and copper levels. Ex vivo oxidation of young-rat brain with Fe(II) caused loss of CAT activity and binding affinity. In vitro oxidation of purified CAT with Fe(II) inactivated the enzyme but did not alter binding affinity. However, in vitro treatment of CAT with the lipid peroxidation products malondialdehyde or 4-hydroxy-nonenal caused a decrease in CAT-binding affinity and activity, thus mimicking age-related change. Preincubation of CAT with ALCAR or CoA prevented malondialdehyde-induced dysfunction. Thus, feeding old rats high levels of key mitochondrial metabolites can ameliorate oxidative damage, enzyme activity, substrate-binding affinity, and mitochondrial dysfunction.     

Short-term supplementation with acetyl-l-carnitine and lipoic acid alters plasma protein carbonyl levels but does not improve cognition in aged beagles

Previous work has shown that a diet enriched with antioxidants and mitochondrial co-factors improves cognition in aged dogs, which is accompanied by a reduction in oxidative damage in the brain. The objective of the present study was to assess the effects of supplementation with mitochondrial co-factors on cognition and plasma protein carbonyl levels in aged dogs. Specifically, we aimed to test whether the individual or combined action of lipoic acid (LA) and acetyl-l-carnitine (ALCAR) could account for the beneficial effects of the enriched diet that contained both plus antioxidants. Dogs were given LA or ALCAR, alone and then in combination and cognition was assessed using a spatial learning task and two discrimination and reversal paradigms. Dogs receiving the ALCAR supplement showed an increase in protein carbonyl levels that was associated with increased error scores on the spatial task, and which was reduced upon additional supplementation with LA. We did not observe significant positive effects on cognition. The present findings suggest that short-term supplementation with LA and ALCAR is insufficient to improve cognition in aged dogs, and that the beneficial effects of the full spectrum diet arose from either the cellular antioxidants alone or their interaction with LA and ALCAR.     

A cluster analysis study of acetyl-l-carnitine effect on NMDA receptors in aging

Aging is associated with a reduction in the maximum density of n-methyl-d-aspartate (NMDA)-sensitive glutamate binding sites in the hippocampus of Fischer 344 rats. This study was designed to investigate the effect of acetyl-l-carnitine (ALCAR) on NMDA receptors in the old rat (24 months) after chronic or single-dose treatments. The number of NMDA receptors was significantly decreased in the old rat hippocampus by 19.5% compared with the young rat. A six-month treatment with ALCAR in the old rat attenuated the loss of NMDA binding sites in the hippocampus. A single-dose treatment with ALCAR in the old rat increased the B_max value by 35%, while no change was observed in the young group. We conclude that ALCAR can exert two actions: a trophic/neuro-preserving one when chronically administered during aging, and a stimulatory one when given at a single dose in the aged rat.     

Chronic dietary iron overload in rats results in impaired calcium sequestration by hepatic mitochondria and microsomes [corrected

The purpose of these experiments was to determine whether chronic dietary iron overload causes impairment of hepatic mitochondrial and/or microsomal calcium sequestration. Experimental iron overload was produced by feeding three groups of rats a chow diet supplemented with 3.0% (wt/wt) carbonyl iron for up to 8 weeks achieving graded increases in hepatic iron concentrations ranging from 1360 to 3170 micrograms/g. At low levels of iron overload, there were no changes in mitochondrial oxidative metabolism or calcium sequestration, whereas at moderate and high degrees of iron loading, both of these parameters were significantly reduced. In contrast, there were significant decreases in microsomal cytochrome P450 levels and microsomal calcium sequestration at all three levels of iron loading. These abnormalities occurred at hepatic iron concentrations at which the authors have previously found evidence of hepatic organelle lipid peroxidation. These alterations in organelle calcium sequestration may impair intracellular calcium homeostasis in the liver and contribute to subsequent cellular injury.     

Effect of exercise on learning and memory in a rat model of developmental stress

Adverse life events occurring in early development can result in long-term effects on behavioural, physiological and cognitive processes. In particular, perinatal stressors impair neurogenesis in the hippocampus which consequently impairs memory formation. Exercise has previously been shown to have antidepressant effects and to increase cognitive functioning by increasing neurogenesis and neurotrophins in the hippocampus. The current study examined the effects of maternal separation, which has been shown to model anxiety in animals, and the effects of exercise on learning and memory. Forty-five male Sprague-Dawley rats were divided into four groups, maternally separated / non-runners, maternally separated / runners, non-separated / runners and non-separated / non-runners. Maternal separation occurred from postnatal day 2 (P2) to 14 (P14) for 3 h per day. Exercised rats were given voluntary access to individual running wheels attached to their cages from P29 to P49. Behavioural testing (Morris water maze (MWM) and object recognition tests) took place from P49 to P63. Maternally separated rats showed no significant difference in anxiety levels in the elevated plus maze and the open field compared to the normally reared controls. However, rats that were allowed voluntary access to running wheels showed increased levels of anxiety in the elevated plus maze and in the open field. Maternal separation did not have any effect on memory performance in the MWM or the object recognition tasks. Exercise increased spatial learning and memory in the MWM with the exercised rats displaying a decreased latency in locating the hidden platform than the non-exercised rats. The exercised rats spent significantly less time exploring the most recently encountered object in the temporal order task in comparison to the non-exercised controls, therefore showing improved temporal recognition memory. All groups performed the same on the other recognition tasks, with all rats showing intact memory performance. Results indicate that maternal separation had little effect on the rats whereas exercise enhanced both spatial and recognition memory.     

Forty percent and eighty percent methionine restriction decrease mitochondrial ROS generation and oxidative stress in rat liver

Dietary restriction (DR) lowers mitochondrial reactive oxygen species (ROS) generation and oxidative damage and increases maximum longevity in rodents. Protein restriction (PR) or methionine restriction (MetR), but not lipid or carbohydrate restriction, also cause those kinds of changes. However, previous experiments of MetR were performed only at 80% MetR, and substituting dietary methionine with glutamate in the diet. In order to clarify if MetR can be responsible for the lowered ROS production and oxidative stress induced by standard (40%) DR, Wistar rats were subjected to 40% or 80% MetR without changing other dietary components. It was found that both 40% and 80% MetR decrease mitochondrial ROS generation and percent free radical leak in rat liver mitochondria, similarly to what has been previously observed in 40% PR and 40% DR. The concentration of complexes I and III, apoptosis inducing factor, oxidative damage to mitochondrial DNA, five different markers of protein oxidation, glycoxidation or lipoxidation and fatty acid unsaturation were also lowered. The results show that 40% isocaloric MetR is enough to decrease ROS production and oxidative stress in rat liver. This suggests that the lowered intake of methionine is responsible for the decrease in oxidative stress observed in DR.     

Age-dependent nerve cell loss in the brain of Sprague-Dawley rats: effect of long term acetyl-L-carnitine treatment

The age dependent loss of nerve cells was investigated in 22 brain areas from young (3 month), adult (13 month) and old (25 month) Sprague-Dawley rats. As in previous studies, we observed an age-related neuronal loss primarily in the archicortex and in the hippocampus and in other subcortical structures (amigdaloid nucleus, pontine nuclei, cerebellar cortex). In sensory areas of cerebral cortex the neuronal loss was less marked. The effect of a 6 month treatment with acetyl-L-carnitine (ALCAR) on the number of nerve cells in the same brain areas was also investigated. ALCAR treatment began when the rats were aged 16 months. ALCAR treatment was able to counteract the age-dependent decrease in nerve cell number primarily in the temporal and occipital cortical areas, in the archicortex and hippocampus. The above findings suggest that long term ALCAR treatment may be effective in slowing down the age-related nerve cell loss in some rat brain areas.     

Regulation of longevity and oxidative stress by nutritional interventions: Role of methionine restriction

Comparative studies indicate that long-lived mammals have low rates of mitochondrial reactive oxygen species production (mtROSp) and oxidative damage in their mitochondrial DNA (mtDNA). Dietary restriction (DR), around 40%, extends the mean and maximum life span of a wide range of species and lowers mtROSp and oxidative damage to mtDNA, which supports the mitochondrial free radical theory of aging (MFRTA). Regarding the dietary factor responsible for the life extension effect of DR, neither carbohydrate nor lipid restriction seems to modify maximum longevity. However protein restriction (PR) and methionine restriction (at least 80% MetR) increase maximum lifespan in rats and mice. Interestingly, only 7 weeks of 40% PR (at least in liver) or 40% MetR (in all the studied organs, heart, brain, liver or kidney) is enough to decrease mtROSp and oxidative damage to mtDNA in rats, whereas neither carbohydrate nor lipid restriction changes these parameters. In addition, old rats also conserve the capacity to respond to 7 weeks of 40% MetR with these beneficial changes. Most importantly, 40% MetR, differing from what happens during both 40% DR and 80% MetR, does not decrease growth rate and body size of rats. All the available studies suggest that the decrease in methionine ingestion that occurs during DR is responsible for part of the aging-delaying effect of this intervention likely through the decrease of mtROSp and ensuing DNA damage that it exerts. We conclude that lowering mtROS generation is a conserved mechanism, shared by long-lived species and dietary, protein, and methionine restricted animals, that decreases damage to macromolecules situated near the complex I mtROS generator, especially mtDNA. This would decrease the accumulation rate of somatic mutations in mtDNA and maybe finally also in nuclear DNA.     

Melatonin preserves fetal growth in rats by protecting against ischemia/reperfusion-induced oxidative/nitrosative mitochondrial damage in the placenta

We have previously demonstrated that melatonin protects against ischemia/reperfusion-induced oxidative damage to mitochondria in the fetal rat brain. The purpose of the present study was to evaluate the effects of maternally administered melatonin on ischemia/reperfusion-induced oxidative placental damage and fetal growth restriction in rats. The utero-ovarian arteries were occluded bilaterally for 30 min in rats on day 16 of pregnancy to induce fetal ischemia. Reperfusion was achieved by releasing the occlusion and restoring circulation. Melatonin solution (20 microg/mL) or the vehicle alone was administered orally during pregnancy. A sham operation was performed in control rats, which were treated with vehicle alone. Laparotomy was performed on day 20 of pregnancy and the number and weight of fetal rats and placentas were measured. Placental mitochondrial respiratory control index (RCI), a marker of mitochondrial respiratory activity, was also calculated for each group. Using immunohistochemistry, we investigated the degree of immunostaining of 8-hydroxy-2-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, and redox factor-1(ref-1), which repairs DNA damage and acts as a redox-modifying factor in rat placenta. Predictably, the ischemia/reperfusion operation significantly decreased the weight of fetal rats and placentas and the RCI. Melatonin prevented ischemia/reperfusion-induced changes in RCI (1.55 +/- 0.05 to 1.83 +/- 0.09, P < 0.05) and fetal growth (3.04 +/- 0.17 to 3.90 +/- 0.1, P < 0.0001). Immunohistochemistry revealed significant positive staining for 8-OHdG and ref-1 following ischemia/reperfusion; these effects were also reduced by melatonin treatment. Results indicated that ischemia/reperfusion-induced oxidative placental DNA and mitochondrial damage and fetal growth restriction can be prevented by maternally administered melatonin.     

Antioxidant treatment prevents cognitive impairment and oxidative damage in pneumococcal meningitis survivor rats

Pneumococcal meningitis is associated with the highest fatality case ratios in the world. Most of patients that survive present neurologic sequelae at later times as well as biochemicals alterations such as oxidative stress in both earlier and later times after central nervous system infection. In this context, we evaluated the effect of antioxidant treatment on memory and oxidative parameters in the hippocampus of meningitis survivor rats 10 days after infection. To this aim, the animals underwent a magna cistern tap receiving either 10 μL sterile saline as a placebo or an equivalent volume of a Streptococcus pneumoniae suspension at the concentration 5x10⁹ cfu/mL. The animals submitted to meningitis were divided into the following groups: 1) treated with antibiotic, 2) treated with basic support plus N-acetylcysteine, 3) treated with basic support plus deferoxamine, 4) treated with basic support plus N-acetylcysteine and deferoxamine, or 5) treated with N-acetylcysteine plus deferoxamine. Ten days after meningitis, the animals underwent inhibitory avoidance and habituation to an open field tasks and, immediately after, were assessed for oxidative damage in the hippocampus and cortex. The meningitis group showed significantly decreased performance in latency retention compared with the sham group in the inhibitory avoidance task. In the open-field task, the meningitis group presented memory impairment after meningitis. All these memory impairments were prevented by N-acetylcysteine plus deferoxamine with or without basic support and its isolate use. In addition, there was an increase of lipid phosphorylation in cortex and hippocampus and all the combined antioxidants attenuated lipid phosphorylation in both structures. On the other hand, there was an increase of protein phosphorylation in cortex and N-acetylcysteine plus deferoxamine with or without basic support prevented it. Thus, we hypothesize that oxidative stress may be related to cognitive impairment in pneumococcal meningitis.     

Ethanol Attenuates Spatial Memory Deficits and Increases mGlu1a Receptor Expression in the Hippocampus of Rats Exposed to Prenatal Stress

Background: Although it is generally believed that chronic ethanol consumption impairs learning and memory, results obtained in experimental animals are not univocal, and there are conditions in which ethanol paradoxically improves cognitive functions. In the present work, we investigated the effects of prenatal stress and of chronic ethanol exposure during adulthood on spatial memory in rats. Methods: Rats were subjected to a prenatal stress delivered as 3 daily 45‐minute sections of restraint stress to the mothers during the last 10 days of pregnancy (PRS rats). After 7 months of ethanol exposure (ethanol 10%, oral intake), memory performances were evaluated in a spatial discrimination test in control and PRS male rats. Then, the oxidative damages and the expression of metabotropic glutamate (mGlu) receptors were assessed in their hippocampus. Results: Chronic ethanol exposure resulted in a reduced performance in a spatial recognition task in control animals. Unexpectedly, however, the same treatment attenuated spatial memory deficits in rats that had been subjected to prenatal stress. This paradigm of ethanol administration did not produce detectable signs of oxidative damage in the hippocampus in either unstressed or PRS rats. Interestingly, ethanol intake resulted in differential effects in the expression of mGlu receptor subtypes implicated in mechanisms of learning and memory. In control rats, ethanol intake reduced mGlu2/3 and mGlu5 receptor levels in the hippocampus; in PRS rats, which exhibited a constitutive reduction in the levels of these mGlu receptor subtypes, ethanol increased the expression of mGlu1a receptors but did not change the expression of mGlu2/3 or mGlu5 receptors. Conclusion: Our findings support the idea that stress‐related events occurring before birth have long‐lasting effects on brain function and behavior, and suggest that the impact of ethanol on cognition is not only dose‐ and duration‐dependent, but also critically influenced by early life experiences.     

Human amnesia and the medial temporal lobe illuminated by neuropsychological and neurohistological findings for patient E.P.

We present neurohistological information for a case of bilateral, symmetrical damage to the medial temporal lobe and well-documented memory impairment. E.P. developed profound memory impairment at age 70 y and then was studied for 14 y He had no capacity for learning facts and events and had retrograde amnesia covering several decades. He also had a modest impairment of semantic knowledge. Neurohistological analysis revealed bilaterally symmetrical lesions of the medial temporal lobe that eliminated the temporal pole, the amygdala, the entorhinal cortex, the hippocampus, the perirhinal cortex, and rostral parahippocampal cortex. The lesion also extended laterally to involve the fusiform gyrus substantially. Last, the superior, inferior, and middle temporal gyri were atrophic, and subjacent white matter was gliotic. Several considerations indicate that E.P.’s severe memory impairment was caused by his medial temporal lesions, whereas his impaired semantic knowledge was caused by lateral temporal damage. His lateral temporal damage also may have contributed to his extensive retrograde amnesia. The findings illuminate the anatomical relationship between memory, perception, and semantic knowledge.The medial temporal lobe has been associated with memory function for more than a century (1–3). The development of an animal model of human memory impairment in the nonhuman primate (4) led to the identification of the specific structures that are important: the hippocampus [including the cornu ammonis (CA) fields, dentate gyrus, and subicular complex] and the adjacent entorhinal, perirhinal, and parahippocampal cortices (5). This work demonstrated further that memory impairment is less severe when bilateral removal is limited to the hippocampus than when the lesion is enlarged to include the adjacent cortical structures (6).Studies of memory-impaired patients demonstrated this same point. For example, the noted patient H.M (1), who sustained a large bilateral medial temporal lobe resection to relieve epilepsy, had very severe memory impairment. In contrast, patients with damage limited to the hippocampus are less severely impaired (7).The most useful information about the functional neuroanatomy of human memory comes from cases in which there are opportunities to carry out extensive neuropsychological testing as well as postmortem neurohistological analysis. This testing has been accomplished for patients with damage limited to the hippocampus proper (8–11). However, less information is available for patients with larger medial temporal lobe lesions. Patient P.B. developed memory impairment following surgical resection of the right medial temporal lobe and, as discovered later in postmortem examination, a sclerotic lesion of the left hippocampus (12, 13). P.B. was less severely impaired than H.M. (14). Patient N.T. developed memory impairment following right temporal lobectomy and, as discovered later, a lesion of the left hippocampus (15, 16). In both these cases, the lesions were asymmetrical, and it is difficult to know to what extent the right extrahippocampal damage contributed to the neuropsychological findings, particularly for N.T., for whom both medial and lateral right temporal cortex was removed.Here we present neuropsychological and neurohistological findings for patient E.P. (17). E.P. developed profound memory impairment in 1992 after viral encephalitis, an impairment that proved to be even more severe than that in patient H.M. Structural MRI revealed bilateral and symmetrical damage to his medial temporal lobe (Fig. 1). Beginning in 1994, E.P. was studied for 14 y before he died in 2008. Neurohistological information in cases of large, bilaterally symmetrical medial temporal lobe lesions and well-documented, severe memory impairment is quite rare. This information makes it possible to address two fundamental questions: What anatomical damage is sufficient to cause profound, nearly absolute impairment in memory? Can damage to the medial temporal lobe also impair perception and semantic knowledge along with memory, as suggested in recent studies (18, 19)?Open in a separate windowFig. 1.T2-weighted MRI images of E.P.’s brain from 1994. Axial sections are arranged from ventral to dorsal (A–D). Note areas of hyperintensity in the medial temporal lobe indicated by white arrows. Regions included within the abnormal hyperintensity include the temporopolar cortex (TPC), amygdaloid complex (A), and hippocampal formation bilaterally (H). The left side of each image illustrates the left side of the brain.     

Chronic ethanol consumption alters the glutathione/glutathione peroxidase-1 system and protein oxidation status in rat liver

BACKGROUND: Alcohol-induced liver damage is associated with oxidative stress, which might be linked to disturbances in liver antioxidant defense mechanisms. The effect of chronic ethanol consumption on the mitochondrial and cytosolic glutathione/glutathione peroxidase-1 (GSHPx-1) system and oxidative modification of proteins was therefore studied in the rat. METHODS: Male Sprague-Dawley rats were fed liquid diets that provided 36% total calories as ethanol for at least 31 days. Pair-fed controls received isocaloric diets with ethanol calories substituted with maltose-dextrins. Mitochondrial and cytosolic fractions were prepared from livers and assayed for GSHPx-1 and glutathione reductase activities and total and oxidized concentrations of glutathione. Catalase activity was measured in the postmitochondrial supernatant. Levels of GSHPx-1, lactate dehydrogenase, and the beta subunit of the F1 portion of the ATP synthase protein were determined by western blot analysis. Concentrations of mitochondrial and cytosolic protein carbonyls were measured to assess ethanol-induced oxidation of proteins. RESULTS: Chronic ethanol consumption significantly decreased cytosolic and mitochondrial GSHPx-1 activities by 40% and 30%, respectively. Levels of GSHPx-1 protein in cytosol were unaffected by ethanol feeding, whereas there was a small decrease in GSHPx-1 protein levels in mitochondria isolated from ethanol-fed rats. Glutathione reductase activities were increased in both intracellular compartments and catalase activity was increased as a consequence of ethanol exposure. Cytosolic total glutathione was mildly decreased, whereas ethanol feeding increased mitochondrial levels of total glutathione. Chronic ethanol feeding significantly increased both cytosolic and mitochondrial concentrations of protein carbonyls by 30% and 60%, respectively. CONCLUSIONS: This study demonstrates that chronic ethanol-induced alterations in the glutathione/GSHPx-1 antioxidant system might promote oxidative modification of liver proteins, namely those of the mitochondrion, which could contribute to the adverse effects of ethanol on the liver.     

Carvedilol reduces mitochondrial damage induced by hypoxanthine/xanthine oxidase: relevance to hypoxia/reoxygenation injury

The cardioprotective properties of new pharmaceuticals such as carvedilol might be explained by enhanced mitochondrial protection. The aim of this work was to determine the role of carvedilol in the protection of heart mitochondria from oxidative damage induced by hypoxanthine/xanthine oxidase, a known source of oxidative stress in the vascular system. Carvedilol reduced oxidative-stress-induced mitochondrial injury, as seen by the delay in the loss of the mitochondrial transmembranar potential (Delta Psi), the decrease in mitochondrial swelling, and the increase in mitochondrial calcium uptake. Carvedilol improved the mitochondrial respiratory activity in state III and offered an overall protection in the respiratory control and in the P/O ratios in mitochondria under oxidative stress. The data indicated that carvedilol was able to partly protect heart mitochondria from oxidative stress-induced damage. Our results suggest that mitochondria can be important targets for some cardioprotective pharmaceuticals.     

Bidirectional changes to hippocampal theta–gamma comodulation predict memory for recent spatial episodes

Episodic memory requires the hippocampus, which is thought to bind cortical inputs into conjunctive codes. Local field potentials (LFPs) reflect dendritic and synaptic oscillations whose temporal structure may coordinate cellular mechanisms of plasticity and memory. We now report that single-trial spatial memory performance in rats was predicted by the power comodulation of theta (4–10 Hz) and low gamma (30–50 Hz) rhythms in the hippocampus. Theta–gamma comodulation (TGC) was prominent during successful memory retrieval but was weak when memory failed or was unavailable during spatial exploration in sample trials. Muscimol infusion into medial septum reduced the probability of TGC and successful memory retrieval. In contrast, patterned electrical stimulation of the fimbria-fornix increased TGC in amnestic animals and partially rescued memory performance in the water maze. The results suggest that TGC accompanies memory retrieval in the hippocampus and that patterned brain stimulation may inform therapeutic strategies for cognitive disorders.     

Chronic ethanol consumption causes alterations in the structural integrity of mitochondrial DNA in aged rats.

Chronic ethanol consumption adversely affects the respiratory activity of rat liver mitochondria. It causes increased cellular production of oxygen radical species and selectively decreases mitochondrial glutathione (GSH) levels. Here we show, using Southern hybridization techniques on total rat genomic DNA, that long-term (11-13 months) ethanol feeding, using the Lieber-DeCarli diet, results in a 36% (P <.05; n = 4) decrease in hepatic mitochondrial DNA (mtDNA) levels when compared with paired controls. UV quantitation of mtDNA isolated from hepatic mitochondria showed that chronic ethanol intake (11-13 months) causes a 44% (P <.01; n = 6) decrease in the amount of mtDNA per milligram of mitochondrial protein. No significant decline in mtDNA levels was seen in ethanol-fed animals maintained on the diet for 1 to 5 months. Ethanol feeding caused a 42% (P <.01; n = 4) and a 132% (P <.05; n = 3) increase in 8-hydroxydeoxyguanosine (8-OHdG) formation in mtDNA in animals maintained on the diet for 3 to 6 months and 10 to 11 months, respectively. In addition, agarose gel electrophoresis revealed a 49% increase (P <.05; n = 3) in mtDNA single-strand breaks (SSB) in animals fed ethanol for more than 1 year. These findings suggest that chronic ethanol consumption causes enhanced oxidative damage to mtDNA in older animals along with increased strand breakage, and that this results in its selective removal/degradation by mtDNA repair enzymes.     

Spatial memory and the human hippocampus

The hippocampus and adjacent medial temporal lobe structures are known to support declarative memory, but there is not consensus about what memory functions the hippocampus might support that are distinct from the functions of the adjacent cortex. One idea is that the hippocampus is specifically important for allocentric spatial memory, e.g., the hippocampus is especially needed to remember object locations when there is a shift in viewpoint between study and test. We tested this proposal in two experiments. Patients with damage limited to the hippocampus were given memory tests for object locations in a virtual environment. In the first experiment, participants studied locations of a variable number of images (one to five) and tried to remember the image locations from either the same viewpoint as during study (shift of 0 degrees) or a different viewpoint (shift of 55 degrees, 85 degrees, or 140 degrees). In each viewpoint condition (shifts of 0 degrees, 55 degrees, 85 degrees, and 140 degrees), patients performed normally when remembering one or two image locations. Further, performance declined to a similar degree in each viewpoint condition as patients tried to remember increasing numbers of image locations. In the second experiment, participants tried to remember four images after viewpoint shifts of 0 degrees, 55 degrees, 85 degrees, or 140 degrees. Patients were mildly impaired at all conditions (shifts of 0 degrees, 55 degrees, 85 degrees, and 140 degrees), and the impairment was no greater when viewpoint shifted. We conclude that damage to the hippocampus does not selectively impair viewpoint-independent spatial memory. Rather, hippocampal damage impairs memory as the memory load increases.