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R M Sapolsky

Publications and source records attributed to R M Sapolsky.

At least 19 recordsLinked to original sources
PubMed2004

Restructuring the neuronal stress response with anti-glucocorticoid gene delivery.

Glucocorticoids, the adrenal steroids released during stress, compromise the ability of neurons to survive neurological injury. In contrast, estrogen protects neurons against such injuries. We designed three genetic interventions to manipulate the actions of glucocorticoids, which reduced their deleterious effects in both in vitro and in vivo rat models. The most effective of these interventions created a chimeric receptor combining the ligand-binding domain of the glucocorticoid receptor and the DNA-binding domain of the estrogen receptor. Expression of this chimeric receptor reduced hippocampal lesion size after neurological damage by 63% and reversed the outcome of the stress response by rendering glucocorticoids protective rather than destructive. Our findings elucidate three principal steps in the neuronal stress-response pathway, all of which are amenable to therapeutic intervention.

11-beta-Hydroxysteroid Dehydrogenase Type 2↗
PubMed2004

Overexpression of calbindin D(28k) in dentate gyrus granule cells alters mossy fiber presynaptic function and impairs hippocampal-dependent memory.

Calcium is a key signaling ion for induction of synaptic plasticity processes that are believed to influence cognition. Mechanisms regulating activity-induced increases in neuronal calcium and related synaptic modifications are not fully understood. Moreover, involvement of specific synapses in discrete aspects of spatial learning remains to be elucidated. We used herpes simplex amplicons to overexpress calbindin D(28k) (CaBP) selectively in dentate gyrus (DG) granule cells. We then examined the effects on hippocampal network activity by recording evoked synaptic responses in vivo and in vitro and analyzing hippocampal-dependent behavior. Relative to Lac-Z- and sham-infected controls, CaBP overexpression increased mossy fiber (MF-CA3) excitatory postsynaptic potentials and reduced paired-pulse facilitation (PPF), suggesting an increase in presynaptic strength. Additionally, CaBP overexpression reduced long-term potentiation (LTP), caused a frequency-dependent inhibition of post-tetanic potentiation (PTP), and impaired spatial navigation. Thus, increasing CaBP levels selectively in the DG disrupts MF-CA3 presynaptic function and impairs spatial cognition. The results demonstrate the power of gene delivery in the study of the neural substrates of learning and memory and suggest that mossy fiber synaptic plasticity is critical for long-term spatial memory.

Animals↗
PubMed2004

Gene expression profiles associated with survival of individual rat dentate cells after endogenous corticosteroid deprivation.

Removal of circulating corticosterone by adrenalectomy (ADX) leads to apoptosis after 3 days in a small population of rat dentate granule neurons, whereas most surrounding cells remain viable. Interestingly, a specific expression profile is triggered in surviving granule cells that may enhance their survival. Hippocampal slices prepared 1, 2 or 3 days after ADX or sham operation were stained ex vivo with Hoechst 33258, which serves to identify apoptotic neurons. After electrophysiological analysis, multiple gene expression in surviving individual granule cells was assessed by linear antisense RNA amplification and hybridization to slot blots containing various neuronal cDNAs. Hierarchical clustering and principal component analysis was performed on two physiological variables and 14 mRNA ratios from ADX cells from every time point. Our results indicate that surviving 3-day ADX granule cells display lower membrane capacitance, lower relative N-methyl-d-aspartate (NMDA) R1 mRNA expression and higher relative mineralocorticoid receptor (MR), alpha1A voltage-gated Ca-channel, Bcl-2 and NMDA R2C mRNA expression. Some 1- and 2-day ADX cells cluster with these 3-day survivors; therefore, one or more components of their mRNA expression profile may represent predictive markers for apoptosis resistance. The functional relevance of two candidate genes was tested by in vivo local over-expression in the same model system; of these, Bcl-2 conferred partial protection when induced shortly before ADX. Therefore, removal of corticosteroids triggers a specific gene expression profile in surviving dentate granule cells; key components of this profile may be associated with their survival.

Adrenalectomy↗
PubMed2003

Glutathione peroxidase overexpression inhibits cytochrome C release and proapoptotic mediators to protect neurons from experimental stroke.

BACKGROUND AND PURPOSE: Ischemic injury and reperfusion increases superoxide (O2-) production and reduces the ability of neurons to scavenge free radicals, leading to the release of cytochrome c and apoptosis. Here we test whether overexpression with the use of gene therapy of the antioxidant glutathione peroxidase (Gpx), delivered before or after experimental stroke, is protective against ischemic injury. METHODS: Sixty-two rats underwent middle cerebral artery occlusion for 1 hour. Defective herpes simplex viral vectors expressing Gpx/lacZ or lacZ alone (control) were delivered into each striatum 12 hours before or 2 or 5 hours after ischemia onset. RESULTS: Striatal neuron survival at 2 days was improved by 36% when Gpx was delivered 12 hours before ischemia onset, 26% with a 2-hour delay, and 25% when delayed 5 hours. After ischemia, Gpx overexpression significantly reduced cytosolic translocation of cytochrome c and increased the proportion of Bcl-2-positive cells compared with cells transfected with control vector. Bax and activated caspase-3, while present in control-transfected neurons after ischemia, were rarely noted in Gpx-transfected cells. CONCLUSIONS: Expression from these herpes simplex viral vectors begins 4 to 6 hours after injection, which suggests a 9- to 11-hour temporal therapeutic window for Gpx. This is the first study to show that overexpression of Gpx with the use of gene therapy protects against experimental stroke, even with postischemic transfection, and the neuroprotective mechanism involves attenuation of apoptosis-related events.

Animals↗
PubMed2003

Are subordinates always stressed? A comparative analysis of rank differences in cortisol levels among primates.

Among primate species there is pronounced variation in the relationship between social status and measures of stress physiology. An informal meta-analysis was designed to investigate the basis of this diversity across different primate societies. Species were included only if a substantial amount of published information was available regarding both social behavior and rank-related differences in stress physiology. Four Old World and three New World species met these criteria, including societies varying from small-group, singular cooperative breeders (common marmoset and cotton top tamarin) to large-troop, multi-male, multi-female polygynous mating systems (rhesus, cynomolgus, talapoin, squirrel monkeys, and olive baboon). A questionnaire was formulated to obtain information necessary to characterize the stress milieu for individuals in particular primate societies. We standardized cortisol values within each species by calculating the ratio of basal cortisol concentrations of subordinates to those of dominants in stable dominance hierarchies and expressing the ratio as a percentage (relative cortisol levels). The meta-analysis identified two variables that significantly predicted relative cortisol levels: subordinates exhibited higher relative cortisol levels when they (1). were subjected to higher rates of stressors, and (2). experienced decreased opportunities for social (including close kin) support. These findings have important implications for understanding the different physiological consequences of dominant and subordinate social status across primate societies and how social rank may differ in its behavioral and physiological manifestations among primate societies.

Aggression↗
PubMed2003

Reproduction and resistance to stress: when and how.

Environmental and social stresses have deleterious effects on reproductive function in vertebrates. Global climate change, human disturbance and endocrine disruption from pollutants are increasingly likely to pose additional stresses that could have a major impact on human society. Nonetheless, some populations of vertebrates (from fish to mammals) are able to temporarily resist environmental and social stresses, and breed successfully. A classical trade-off of reproductive success for potential survival is involved. We define five examples. (i) Aged individuals with minimal future reproductive success that should attempt to breed despite potential acute stressors. (ii) Seasonal breeders when time for actual breeding is so short that acute stress should be resisted in favour of reproductive success. (iii) If both members of a breeding pair provide parental care, then loss of a mate should be compensated for by the remaining individual. (iv) Semelparous species in which there is only one breeding period followed by programmed death. (v) Species where, because of the transience of dominance status in a social group, individuals may only have a short window of opportunity for mating. We suggest four mechanisms underlying resistance of the gonadal axis to stress. (i) Blockade at the central nervous system level, i.e. an individual no longer perceives the perturbation as stressful. (ii) Blockade at the level of the hypothalamic-pituitary-adrenal axis (i.e. failure to increase secretion of glucocorticosteroids). (iii) Blockade at the level of the hypothalamic-pituitary-gonad axis (i.e. resistance of the reproductive system to the actions of glucocorticosteroids). (iv) Compensatory stimulation of the gonadal axis to counteract inhibitory glucocorticosteroid actions. Although these mechanisms are likely genetically determined, their expression may depend upon a complex interaction with environmental factors. Future research will provide valuable information on the biology of stress and how organisms cope. Such mechanisms would be particularly insightful as the spectre of global change continues to unfold.

Animals↗
PubMed2002

HSV-mediated delivery of virally derived anti-apoptotic genes protects the rat hippocampus from damage following excitotoxicity, but not metabolic disruption.

Studies utilizing gene delivery to the nervous system indicate that various strategies are protective following acute neurological insults such as seizure and stroke. We have found that inhibitors of apoptosis are protective against excitotoxicity and heat stress but not energetic impairment in vitro. Here we studied the neuroprotective efficacy in vivo of these mediators: viral genes (crmA, p35, gamma34.5 KsBcl-2) that have evolved to suppress suicidal host responses to infection, by inhibiting apoptosis. We investigated these effects by utilizing modified herpes vectors to deliver the anti-apoptotic agents intracerebrally and examined them in the face of excitotoxic and metabolic insults. We found that p35 and gamma34.5 reduced by 45% a hippocampal CA3 lesion caused by kainic acid, while crmA and KsBcl-2 did not. None of the inhibitors protected the dentate gyrus of the hippocampus following 3-acetylpyridine, a hypoglycemia model, but we found crmA to worsen the damage. These data are similar to our results in neuronal cultures where the inhibitors protected against the excitotoxin domoic acid, but not against the metabolic poison, cyanide. Together, the results suggest that inhibitors of various apoptotic elements are capable of protecting under acute insult conditions both in vitro and in vivo, suggesting possible future therapeutic applications.

Animals↗
PubMed2001

Sleep deprivation elevates plasma corticosterone levels in neonatal rats.

Plasma corticosterone (CORT) levels were measured after short periods of sleep deprivation in rats at postnatal days 12, 16, 20, and 24. There was an age-dependent increase in basal CORT levels and sleep deprivation significantly elevated CORT at all ages compared to non-sleep deprived controls. The levels of CORT after sleep deprivation in P16, P20 and P24 animals were similar, resulting in an age-dependent decrease of the magnitude of the response. Sleep deprived P12 animals had lower levels of CORT. However, the observed response to sleep deprivation suggests that sleep loss is a significant stressor at this age. These observations suggest that younger animals are more sensitive to the effects of mild sleep deprivation than older ones.

Aging↗
PubMed2001

Gene therapy and the aging nervous system.

In recent years, the first attempts have been made to apply gene transfer technology to protect neurons from death following neurological insults. There has been sufficient progress in this area that it becomes plausible to consider similar gene therapy approaches meant to delay aspects of aging of the nervous system. In this review, we briefly consider such progress and how it might be applied to the realm of the aging brain. Specifically, we consider: (a) the means of delivery of such therapeutic genes; (b) the choice of such genes; and (c) technical elaborations in gene delivery systems which can more tightly regulate the magnitude and duration of transgene protection.

Aging↗
PubMed2001

Cortisol levels predict cognitive impairment induced by electroconvulsive therapy.

BACKGROUND: Elevated glucocorticoids may increase the vulnerability of the brain to the adverse effects of repeated seizures. This study tested the hypothesis that higher ambient cortisol levels would predict increased cognitive impairment in depressed patients subsequent to receiving electroconvulsive therapy (ECT) for major depression. METHODS: Sixteen subjects provided three samples of saliva the day before receiving unilateral nondominant ECT. Measures of mood, global cognitive functioning, attention, executive function, verbal and visuospatial memory, and visuospatial processing speed were obtained 1 day before the first ECT and 1 day after the sixth ECT treatment. The relationship between basal salivary cortisol obtained before the first ECT treatment and the change score of each cognitive measure after the sixth ECT treatment was examined and tested with Pearson correlation coefficients. RESULTS: Electroconvulsive therapy treatments delivered over 2 weeks resulted in a significant improvement in mood and a decline in most measures of cognitive performance. Elevated basal cortisol was associated with a greater decline in performance of executive function, visuospatial processing speed, and verbal memory. CONCLUSIONS: Although this study is limited by the small number of subjects and the high number of comparisons, all significant correlations were consistent with the hypothesis that elevated cortisol predicts a greater degree of ECT-induced cognitive impairment.

Adult↗
PubMed2001

Neuroprotective effects of an adenoviral vector expressing the glucose transporter: a detailed description of the mediating cellular events.

Considerable knowledge exists concerning the events mediating neuron death following a necrotic insult; prompted by this, there have now been successful attempts to use gene therapy approaches to protect neurons from such necrotic injury. In many such studies, however, it is not clear what sequence of cellular events connects the overexpression of the transgene with the enhanced survival. We do so, exploring the effects of overexpressing the Glut-1 glucose transporter with an adenoviral vector in hippocampal cultures challenged with the excitotoxin kainic acid (KA). Such overexpression enhanced glucose transport, attenuated the decline in ATP concentrations, decreased the release of excitatory amino acid neurotransmitters, and decreased the total free cytosolic calcium load. Commensurate with these salutary effects, neuronal survival was enhanced with this gene therapy intervention. Thus, the neuroprotective effects of this particular gene therapy occurs within the known framework of the mechanisms of necrotic neuronal injury.

Adenosine Triphosphate↗
PubMed2001

Neuroprotection with herpes simplex vectors expressing virally derived anti-apoptotic agents.

A large body of literature dealing with neurotoxicity has focused on trying to define the exact nature of cell death following a neurological insult. While there is some debate in the field, it has been shown that a number of neurons in a given population can respond to an acute insult stimulus by activating the apoptotic cascade. To what extent, however, these insults result in the classical manifestations of either apoptosis or necrosis, or whether a mixture of the two results, is highly controversial, in part dependent on the particular system utilized. In this paper, we investigate the role of particular apoptotic signals in cultured rat hippocampal neurons, following acute excitotoxicity, metabolic poisoning, and heat stress. In particular, we examine these effects by utilizing a modified herpes simplex viral vector to specifically deliver viral anti-apoptotic genes. We have selected a battery of viral genes (crmA, p35, gamma34.5, KsBcl-2) that have evolved to suppress suicidal host responses to infection. We examine these inhibitors in the face of the above classes of insults and report that each viral agent tested has a unique profile in its ability to protect hippocampal neurons following acute neurological insults. Specifically, the effects of domoic acid excitotoxicity can be alleviated only with crmA, p35 and gamma34.5 whereas all genes tested can protect against heat stress. Conversely, no genes tested can protect against metabolic poisoning by cyanide. Such a study helps us to further understand the nature of apoptotic signals in different insults.

Animals↗
PubMed2001

Interactions among glucose, lactate and adenosine regulate energy substrate utilization in hippocampal cultures.

Glucose is the major energy source during normal adult brain activity. However, it appears that glial-derived lactate is preferred as an energy substrate by neurons following hypoxia-ischemia. We examined factors influencing this switch in energetic bias from glucose to lactate in cultured hippocampal neurons, focusing on the effects of the physiological changes in lactate, glucose and adenosine concentrations seen during hypoxia-ischemia. We show that with typical basal concentrations of lactate and glucose, lactate had no effect on glucose uptake. However, at the concentrations of these metabolites found after hypoxia-ischemia, lactate inhibited glucose uptake. Reciprocally, glucose had no effect on lactate utilization regardless of glucose and lactate concentrations. Furthermore, we find that under hypoglycemic conditions adenosine had a small, but significant, inhibitory effect on glucose uptake. Additionally, adenosine increased lactate utilization. Thus, the relative concentrations of glucose, lactate and adenosine, which are indicative of the energy status of the hippocampus, influence which energy substrates are used. These results support the idea that after hypoxia-ischemia, neurons are biased in the direction of lactate rather than glucose utilization and this is accomplished through a number of regulatory steps.

Adenosine↗
PubMed2001

Mechanisms of estrogenic protection against gp120-induced neurotoxicity.

gp120, an HIV coat glycoprotein that may play a role in AIDS-related dementia complex (ADC), induces neuronal toxicity characterized by NMDA receptor activation, accumulation of intracellular calcium, and downstream degenerative events including generation of reactive oxygen species and lipid peroxidation. We have previously demonstrated estrogenic protection against gp120 neurotoxicity in primary hippocampal cultures. We here characterize the mechanism of protection by blocking the classical cytosolic estrogen receptors and by measuring oxidative end points including accumulation of extracellular superoxide and lipid peroxidation. Despite blocking ERalpha and ERbeta with 1 microM tamoxifen, we do not see a decrease in the protection afforded by 100 nM 17 beta-estradiol against 200 pM gp120. Additionally, 17alpha-estradiol, which does not activate estrogen receptors, protects to the same extent as 17beta-estradiol. 17beta-Estradiol does, however, decrease gp120-induced lipid peroxidation and accumulation of superoxide. Together the data suggest an antioxidant mechanism of estrogen protection that is independent of receptor binding.

Animals↗
PubMed2001

Differential sensitivity of murine astrocytes and neurons from different brain regions to injury.

Different brain regions show differential vulnerability to ischemia in vivo. Despite this, little work has been done to compare vulnerability of brain cells isolated from different brain regions to injury. Relatively pure neuronal and astrocyte cultures were isolated from mouse cortex, hippocampus, and striatum. Astrocyte vulnerability to 6 h oxygen-glucose deprivation was greatest in striatum (81.8 +/- 4.6% cell death), intermediate in hippocampus (59.8 +/- 4.8%), and least in cortex (37.0 +/- 3.5%). In contrast neurons deprived of oxygen and glucose for 3 h showed greater injury to cortical neurons (71.1 +/- 5.2%) compared to striatal (39.0 +/- 3.1%) or hippocampal (39.0 +/- 5.3%) neurons. Astrocyte injury from glucose deprivation or H(2)O(2) exposure was significantly greater in cells from cortex than from striatum or hippocampus. Neuronal injury resulting from serum deprivation was greater in cortical neurons than in those from striatum or hippocampus, while excitotoxic neuronal injury was equivalent between regions. Antioxidant status and apoptosis-regulatory genes were measured to assess possible underlying differences. Glutathione was higher in astrocytes and neurons isolated from striatum than in those from hippocampus. Superoxide dismutase activity was significantly higher in striatal astrocytes, while glutathione peroxidase activity and superoxide did not differ by brain region. Bcl-x(L) was significantly higher in striatal astrocytes than in astrocytes from other brain regions and higher in striatal and hippocampal neurons than in cortical neurons. Both neurons and astrocytes isolated from different brain regions demonstrate distinct patterns of vulnerability when placed in primary culture. Antioxidant state and levels of expression of bcl-x(L) can in part account for the differential injury observed. This suggests that different protective strategies may have different efficacies depending on brain region.

Animals↗
PubMed2001

Gene therapy against neurological insults: sparing neurons versus sparing function.

Increasing knowledge of neuron death mediators has led to gene therapy techniques for neuroprotection. Overexpression of numerous genes enhances survival after necrotic or neurodegenerative damage. Nonetheless, although encouraging, little is accomplished if a neuron is spared from death, but not from dysfunction. This article reviews neuroprotection experiments that include some measure of function, and synthesizes basic principles relating to its maintenance. Variations in gene delivery systems, including virus-type and latency between damage onset and vector delivery, probably impact the therapeutic outcome. Additionally, functional sparing might depend on factors related to insult severity, neuron type involved or the step in the death cascade that is targeted.

Animals↗