Edythe D. London

Gender-Linked Brain Injury in Experimental Stroke

BACKGROUND AND PURPOSE Premenopausal women are at lower risk than men for stroke, but the comparative vulnerability to tissue injury once a cerebrovascular incident occurs is unknown. We hypothesized that female rats sustain less brain damage than males during experimental focal ischemia and that the gender difference in ischemic outcome can be eliminated by ovariectomy. METHODS Age-matched male (M), intact female (F), and ovariectomized female (O; plasma estradiol: 4.1+/-1.6 pg/mL compared with 7.4+/-1.5 in F and 4.0+/-1.1 in M) rats from two different strains, normotensive Wistar and stroke-prone spontaneously hypertensive rats, were subjected to 2 hours of intraluminal middle cerebral artery occlusion, followed by 22 hours of reperfusion. Cerebral blood flow (CBF) was monitored throughout the ischemic period by laser-Doppler flowmetry. Infarction volume in the cerebral cortex (Ctx) and caudoputamen (CP) was determined by 2,3,5-triphenyltetrazolium chloride staining. In a separate cohort of M, F, and O Wistar rats, absolute rates of regional CBF were measured at the end of the ischemic period by quantitative autoradiography using [14C]iodoantipyrine. RESULTS F rats of either strain had a smaller infarct size in Ctx and CP and a higher laser-Doppler flow during ischemia compared with respective M and O rats. Mean end-ischemic CBF was higher in F compared with M and O rats in CP, but not in Ctx. Cerebrocortical tissue volume with end-ischemic CBF < 10 mL/100 g/min was smaller in F than M rats, but not different from O rats. CONCLUSIONS We conclude that endogenous estrogen improves stroke outcome during vascular occlusion by exerting both neuroprotective and flow-preserving effects.

Structural Abnormalities in the Brains of Human Subjects Who Use Methamphetamine

We visualize, for the first time, the profile of structural deficits in the human brain associated with chronic methamphetamine (MA) abuse. Studies of human subjects who have used MA chronically have revealed deficits in dopaminergic and serotonergic systems and cerebral metabolic abnormalities. Using magnetic resonance imaging (MRI) and new computational brain-mapping techniques, we determined the pattern of structural brain alterations associated with chronic MA abuse in human subjects and related these deficits to cognitive impairment. We used high-resolution MRI and surface-based computational image analyses to map regional abnormalities in the cortex, hippocampus, white matter, and ventricles in 22 human subjects who used MA and 21 age-matched, healthy controls. Cortical maps revealed severe gray-matter deficits in the cingulate, limbic, and paralimbic cortices of MA abusers (averaging 11.3% below control; p < 0.05). On average, MA abusers had 7.8% smaller hippocampal volumes than control subjects (p < 0.01; left, p = 0.01; right, p < 0.05) and significant white-matter hypertrophy (7.0%; p < 0.01). Hippocampal deficits were mapped and correlated with memory performance on a word-recall test (p < 0.05). MRI-based maps suggest that chronic methamphetamine abuse causes a selective pattern of cerebral deterioration that contributes to impaired memory performance. MA may selectively damage the medial temporal lobe and, consistent with metabolic studies, the cingulate-limbic cortex, inducing neuroadaptation, neuropil reduction, or cell death. Prominent white-matter hypertrophy may result from altered myelination and adaptive glial changes, including gliosis secondary to neuronal damage. These brain substrates may help account for the symptoms of MA abuse, providing therapeutic targets for drug-induced brain injury.

Drug abusers show impaired performance in a laboratory test of decision making.

A defining feature of drug addiction is persistent drug use despite long-term adverse consequences. This study examined the performance of drug abusers on a neuropsychological test that requires evaluation of long-term outcomes in the presence of a complex set of mixed reward/punishment contingencies (the Gambling Task). In order to control for generalized deficits related to choice and planning, subjects were also administered the Wisconsin Card Sorting Task. Thirty polysubstance abusers were compared to a comparison group of 24 subjects who did not use illicit drugs of abuse. Drug abusers performed much more poorly on the Gambling Task (net score = 10.2 +/- 4.7, mean +/- s.e.m.) than controls (26.0 +/- 5.3), but did not differ from controls on the Wisconsin Card Sorting Task. The results show that drug abusers are more likely to make maladaptive decisions in the Gambling Task that result in long-term losses exceeding short-term gains. These findings indicate that the Gambling Task may be a useful model in laboratory studies of cognitive dysfunctions associated with drug abuse.

Orbitofrontal cortex dysfunction in abstinent cocaine abusers performing a decision-making task

Cocaine abusers demonstrate faulty decision-making as manifested by their inability to discontinue self-destructive drug-seeking behaviors. The orbitofrontal cortex (OFC) plays an important role in decision-making. In this preliminary study we tested whether 25-day-abstinent cocaine abusers show alterations in normalized cerebral blood flow (rCBF) in the OFC using PET with (15)O during the Iowa Gambling Task (a decision-making task). This task measures the ability to weigh short-term rewards against long-term losses. A control task matched the sensorimotor aspects of the task but did not require decision-making. Cocaine abusers (N = 13) showed greater activation during performance of the Iowa Gambling Task in the right OFC and less activation in the right dorsolateral prefrontal cortex (DLPFC) and left medial prefrontal cortex (MPFC) compared to a control group (N = 13). Better Iowa Gambling Task performance was associated with greater activation in the right OFC in both groups. Also, the amount of cocaine used (grams/week) prior to the 25 days of enforced abstinence was negatively correlated with activation in the left OFC. Greater activation in the OFC in cocaine abusers compared to a control group may reflect differences in the anticipation of reward while less activation in the DLPFC and MPFC may reflect differences in planning and working memory. These findings suggest that cocaine abusers show persistent functional abnormalities in prefrontal neural networks involved in decision-making and these effects are related to cocaine abuse. Compromised decision-making could contribute to the development of addiction and undermine attempts at abstinence.

The neurosteroid dehydroepiandrosterone sulfate is an allosteric antagonist of the GABAA receptor

Binding of the neurosteroid dehydroepiandrosterone sulfate (DHEAS) to rat brain synaptosomal membranes was studied in vitro, and the interaction of DHEAS with the GABAA receptor was tested using biochemical and electrophysiological assays. DHEAS bound to two populations of sites, and its binding was inhibited by barbiturates. DHEAS interfered with barbiturate-mediated enhancement of benzodiazepine binding. In cultured neurons from ventral mesencephalon, DHEAS reversibly blocked GABA-induced currents, behaving as an allosteric antagonist of the GABAA receptor.

Neural Systems and Cue-Induced Cocaine Craving

We have extended our previous work investigating the neural correlates of cue-induced cocaine craving through the use of positron emission tomography with greater spatial resolution (<4.6 mm), an evocative script, and a pixel-by-pixel analysis. Craving and cerebral glucose metabolism were measured after presentation of cocaine-related or neutral cues to 11 cocaine abusers. Cocaine cues elicited a higher degree of craving than has been previously reported and resulted in left hemispheric activation of lateral amygdala, lateral orbitofrontal cortex, and rhinal cortex and right hemispheric activation of dorsolateral prefrontal cortex and cerebellum. The intensity of activation in these areas (except cerebellum), as well as left insula, was also correlated with craving. Deactivation occurred in left ventral pole and left medial prefrontal cortex. The results suggest that induction of drug craving involves a neural network that assigns incentive motivational value to environmental stimuli through the coactivation of brain regions that process information about memories and emotions.

Decision-making in a Risk-taking Task: A PET Study

As decision-making is central to motivated behavior, understanding its neural substrates can help elucidate the deficits that characterize various maladaptive behaviors. Twenty healthy adults performed a risk-taking task during positron emission tomography with 15O-labeled water. The task, a computerized card game, tests the ability to weigh short-term rewards against long-term losses. A control task matched all components of the risk-taking task except for decision-making and the difference between responses to contingent and non-contingent reward and punishment. Decision-making (2 runs of the active task minus 2 runs of the control task) activated orbital and dorsolateral prefrontal cortex, anterior cingulate, insula, inferior parietal cortex and thalamus predominantly on the right side, and cerebellum predominantly on the left side. In an exploratory analysis, guessing (run 1 minus run 2 of the active task) accompanied activation of sensory-motor associative areas, and amygdala on the left side, whereas informed decision-making (run 2 minus run 1) activated areas that subserve memory (hippocampus, posterior cingulate) and motor control (striatum, cerebellum). The findings provide a framework for future investigations of decision-making in maladaptive behaviors.

Higher levels of nicotine in arterial than in venous blood after cigarette smoking

We examined differences between arterial and venous concentrations of nicotine in human subjects. Shortly after smoking a cigarette, levels of nicotine in arterial plasma were more than double those in venous plasma. The time course of the rise in arterial nicotine levels and the magnitude of the arteriovenous difference varied considerably among subjects. For some subjects, arterial nicotine concentrations after one cigarette were similar to venous concentrations typically observed after 20 cigarettes and were nearly 10 times greater than venous concentrations. Our findings have implications for understanding the high degree of addictiveness and cardiovascular toxicity of smoked forms of drugs.

Differences between smokers and nonsmokers in regional gray matter volumes and densities

BACKGROUND Magnetic resonance imaging (MRI) studies have demonstrated large-scale brain abnormalities in cigarette smokers, such as ventricular enlargement and atrophy. Converging lines of evidence point to functional differences between smokers and nonsmokers in specific brain regions, namely the lateral prefrontal cortex (PFC), anterior cingulate cortex (ACC), ventral striatum, and thalamus. Using MRI, we examined these regions for differences in gray matter between smokers and nonsmokers. METHODS Thirty-six otherwise healthy adults (19 smokers and 17 nonsmoking control subjects) underwent three-dimensional Fourier-transform spoiled-gradient-recalled acquisition MRI of the brain. Both hand-drawn regions of interest and the computer program voxel-based morphometry were used to assess group differences in regional gray matter volumes and densities, respectively. RESULTS Smokers had smaller gray matter volumes and lower gray matter densities than nonsmokers in the PFC bilaterally, along with smaller volumes in the left dorsal ACC and lower gray matter densities in the right cerebellum. Smokers also had negative associations between pack-year smoking history and PFC gray matter densities. CONCLUSIONS Smokers and nonsmokers differed in regional gray matter in brain areas previously linked with nicotine dependence. These findings might reflect effects of chronic smoking, predisposing traits that lead to smoking, or some combination of these factors.

17β-Estradiol Reduces Stroke Injury in Estrogen-Deficient Female Animals

BACKGROUND AND PURPOSE The importance of postmenopausal estrogen replacement therapy for stroke in females remains controversial. We previously showed that female rats sustain less infarction in reversible middle cerebral artery occlusion (MCAO) than their ovariectomized counterparts and that vascular mechanisms are partly responsible for improved tissue outcomes. Furthermore, exogenous estrogen strongly protects the male brain, even when administered in a single injection before MCAO injection. The present study examined the hypothesis that replacement of 17beta-estradiol to physiological levels improves stroke outcome in ovariectomized, estrogen-deficient female rats, acting through blood flow-mediated mechanisms. METHODS Age-matched, adult female Wistar rats were ovariectomized and treated with 0, 25, or 100 microgram of 17beta-estradiol administered through a subcutaneous implant or with a single Premarin (USP) injection (1 mg/kg) given immediately before ischemia was induced (n=10 per group). Each animal subsequently underwent 2 hours of MCAO by the intraluminal filament technique, followed by 22 hours of reperfusion. Ipsilateral parietal cortex perfusion was monitored by laser-Doppler flowmetry throughout ischemia. Cortical and caudate-putamen infarction volumes were determined by 2,3, 5-triphenyltetrazolium chloride staining and digital image analysis. End-ischemic regional cerebral blood flow was measured in ovariectomized females with 0- or 25-microgram implants (n=4 per group) by (14)C-iodoantipyrine quantitative autoradiography. RESULTS Plasma estradiol levels were 3.0+/-0.6, 20+/-8, and 46+/-10 pg/mL in the 0-, 25-, and 100-microgram groups, respectively. Caudate-putamen infarction (% of ipsilateral caudate-putamen) was reduced by long-term, 25-microgram estrogen treatment (13+/-4% versus 31+/-6% in the 0-microgram group, P<0.05, and 22+/-3% in the 100-microgram group). Similarly, cortical infarction (% of ipsilateral cortex) was reduced only in the 25-microgram group (3+/-2% versus 12+/-3% in the 0-microgram group, P<0.05, and 6+/-3% in the 100-microgram group. End-ischemic striatal or cortical blood flow was not altered by estrogen treatment at the neuroprotective dose. Infarction volume was unchanged by acute treatment before MCAO when estrogen-treated animals were compared with saline vehicle-treated animals. CONCLUSIONS Long-term estradiol replacement within a low physiological range ameliorates ischemic brain injury in previously ovariectomized female rats. The neuroprotective mechanism is flow-independent, not through preservation of residual ischemic regional cerebral blood flow. Furthermore, the therapeutic range is narrow, because the benefit of estrogen in transient vascular occlusion is diminished at larger doses, which yield high, but still physiologically relevant, plasma 17beta-estradiol levels. Lastly, unlike in the male brain, single-injection estrogen exposure does not salvage ischemic tissue in the female brain. Therefore, although exogenous steroid therapy protects both male and female estrogen-deficient brain, the mechanism may not be identical and depends on long-term hormone augmentation in the female.