Circulatory and metabolic effects in the brain induced by amphetamine sulphate

Bedside interpretation of cerebral energy metabolism utilizing microdialysis in neurosurgical and general intensive care

The microdialysis technique was initially developed for monitoring neurotransmitters in animals. In 1995 the technique was adopted to clinical use and bedside enzymatic analysis of glucose, pyruvate, lactate, glutamate and glycerol. Under clinical conditions microdialysis has also been used for studying cytokines, protein biomarkers, multiplex proteomic and metabolomic analyses as well as for pharmacokinetic studies and evaluation of blood-brain barrier function. This review focuses on the variables directly related to cerebral energy metabolism and the possibilities and limitations of microdialysis during routine neurosurgical and general intensive care. Our knowledge of cerebral energy metabolism is to a large extent based on animal experiments performed more than 40 years ago. However, the different biochemical information obtained from various techniques should be recognized. The basic animal studies analyzed brain tissue homogenates while the microdialysis technique reflects the variables in a narrow zone of interstitial fluid surrounding the probe. Besides the difference of the volume investigated, the levels of the biochemical variables differ in different compartments. During bedside microdialysis cerebral energy metabolism is primarily reflected in measured levels of glucose, lactate and pyruvate and the lactate to pyruvate (LP) ratio. The LP ratio reflects cytoplasmatic redox-state which increases instantaneously during insufficient aerobic energy metabolism. Cerebral ischemia is characterized by a marked increase in intracerebral LP ratio at simultaneous decreases in intracerebral levels of pyruvate and glucose. Mitochondrial dysfunction is characterized by a moderate increase in LP ratio at a very marked increase in cerebral lactate and normal or elevated levels of pyruvate and glucose. The patterns are of importance in particular for interpretations in transient cerebral ischemia. A new technique for evaluating global cerebral energy metabolism by microdialysis of the draining cerebral venous blood is discussed. In experimental studies it has been shown that pronounced global cerebral ischemia is reflected in venous cerebral blood. Jugular bulb microdialysis has been investigated in patients suffering from subarachnoid hemorrhage, during cardiopulmonary bypass and resuscitation after out of hospital cardiac arrest. Preliminary results indicate that the new technique may give valuable information of cerebral energy metabolism in clinical conditions when insertion of an intracerebral catheter is contraindicated.

Corticosterone and exogenous glucose alter blood glucose levels, neurotoxicity, and vascular toxicity produced by methamphetamine

Our previous studies have raised the possibility that altered blood glucose levels may influence and/or be predictive of methamphetamine (METH) neurotoxicity. This study evaluated the effects of exogenous glucose and corticosterone (CORT) pretreatment alone or in combination with METH on blood glucose levels and the neural and vascular toxicity produced. METH exposure consisted of four sequential injections of 5, 7.5, 10, and 10 mg/kg (2 h between injections) D-METH. The three groups given METH in combination with saline, glucose (METH+Glucose), or CORT (METH+CORT) had significantly higher glucose levels compared to the corresponding treatment groups without METH except at 3 h after the last injection. At this last time point, the METH and METH+Glucose groups had lower levels than the non-METH groups, while the METH+CORT group did not. CORT alone or glucose alone did not significantly increase blood glucose. Mortality rates for the METH+CORT (40%) and METH+Glucose (44%) groups were substantially higher than the METH (< 10%) group. Additionally, METH+CORT significantly increased neurodegeneration above the other three METH treatment groups (≈ 2.5-fold in the parietal cortex). Thus, maintaining elevated levels of glucose during METH exposure increases lethality and may exacerbate neurodegeneration. Neuroinflammation, specifically microglial activation, was associated with degenerating neurons in the parietal cortex and thalamus after METH exposure. The activated microglia in the parietal cortex were surrounding vasculature in most cases and the extent of microglial activation was exacerbated by CORT pretreatment. Our findings show that acute CORT exposure and elevated blood glucose levels can exacerbate METH-induced vascular damage, neuroinflammation, neurodegeneration and lethality. Cover Image for this issue: doi. 10.1111/jnc.13819.

Mitochondria: key players in the neurotoxic effects of amphetamines

Amphetamines are a class of psychotropic drugs with high abuse potential, as a result of their stimulant, euphoric, emphathogenic, entactogenic, and hallucinogenic properties. Although most amphetamines are synthetic drugs, of which methamphetamine, amphetamine, and 3,4-methylenedioxymethamphetamine ("ecstasy") represent well-recognized examples, the use of natural related compounds, namely cathinone and ephedrine, has been part of the history of humankind for thousands of years. Resulting from their amphiphilic nature, these drugs can easily cross the blood-brain barrier and elicit their well-known psychotropic effects. In the field of amphetamines' research, there is a general consensus that mitochondrial-dependent pathways can provide a major understanding concerning pathological processes underlying the neurotoxicity of these drugs. These events include alterations on tricarboxylic acid cycle's enzymes functioning, inhibition of mitochondrial electron transport chain's complexes, perturbations of mitochondrial clearance mechanisms, interference with mitochondrial dynamics, as well as oxidative modifications in mitochondrial macromolecules. Additionally, other studies indicate that amphetamines-induced neuronal toxicity is closely regulated by B cell lymphoma 2 superfamily of proteins with consequent activation of caspase-mediated downstream cell death pathway. Understanding the molecular mechanisms at mitochondrial level involved in amphetamines' neurotoxicity can help in defining target pathways or molecules mediating these effects, as well as in developing putative therapeutic approaches to prevent or treat the acute- or long-lasting neuropsychiatric complications seen in human abusers.

Persistent cerebrovascular effects of MDMA and acute responses to the drug

Acutely, 3,4,-methylenedioxymethamphetamine (MDMA) induces cerebrovascular dysfunction [Quate et al., (2004)Psychopharmacol., 173, 287-295]. In the longer term the same single dose results in depletion of 5-hydroxytrptamine (5-HT) nerve terminals. In this study we examined the cerebrovascular consequences of this persistent neurodegeneration, and the acute effects of subsequent MDMA exposure, upon the relationship that normally exists between local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCMRglu). Dark agouti (DA) rats were pre-treated with 15 mg/kg i.p. MDMA or saline. Three weeks later, rats from each pre-treatment group were treated with an acute dose of MDMA (15 mg/kg i.p.) or saline. Quantitative autoradiographic imaging was used to measure LCBF or LCMRglu with [(14)C]-iodoantipyrine and [(14)C]-2-deoxyglucose, respectively. Serotonergic terminal depletion was assessed using radioligand binding with [(3)H]-paroxetine and immunohistochemistry. Three weeks after MDMA pre-treatment there were significant reductions in densities of 5-HT transporter (SERT)-positive fibres (-46%) and [(3)H]-paroxetine binding (-47%). In animals pre-treated with MDMA there were widespread significant decreases in LCMRglu, but no change in LCBF indicating a persistent loss of cerebrovascular constrictor tone. In both pre-treatment groups, acute MDMA produced significant increases in LCMRglu, while LCBF was significantly decreased. In 50% of MDMA-pre-treated rats, random areas of focal hyperaemia indicated a loss of autoregulatory capacity in response to MDMA-induced hypertension. These results suggest that cerebrovascular regulatory dysfunction resulting from acute exposure to MDMA is not diminished by previous exposure, despite a significant depletion in 5-HT terminals. However, there may be a sub-population, or individual circumstances, in which this dysfunction develops into a condition that might predispose to stroke.

Effects of sedation, stimulation, and placebo on cerebral blood oxygenation: a magnetic resonance neuroimaging study of psychotropic drug action

The effects of pharmacologic depression and stimulation of cerebral activity were investigated in seven healthy young volunteers using blood oxygenation-sensitive MRI at 2.0 T. Dynamic gradient-echo imaging (7 min) was performed before, during and after the intravenous application of 10 mg diazepam and 15 mg metamphetamine as well as of the corresponding drug placebos (isotonic saline) in a brain section covering frontotemporal gray matter, subcortical gray matter structures, and cerebellum. The MRI responses were significantly different for the two drugs applied (p = 0.01). Relative to signal strength during injection, metamphetamine elicited a signal increase of 0.97 +/- 0.03% (mean +/- SD, p = 0.02) within the whole section 4-5 min after injection. Similarly, both placebo conditions led to a small signal increase, i.e. 0.50 +/- 0. 03% (n.s.) for the metamphetamine placebo and 0.40 +/- 0.07% (p = 0. 03) for the diazepam placebo. Diazepam abolished this signal increase. A topographic analysis revealed the metamphetamine-induced signal increase to be more pronounced in subcortical gray matter structures (p = 0.01) and cerebellum (p = 0.02) than in frontotemporal cortical gray matter (p = 0.04). This finding is in agreement with the hypothesis that pertinent responses not only reflect global cerebral hemodynamic adjustments, but also localized perfusion changes coupled to alterations in synaptic activity. The occurrence of a placebo response is best explained by expectancy and may provide a confounding factor in the design of functional activation experiments.

Functional MRI of basal ganglia responsiveness to levodopa in parkinsonian rhesus monkeys

Functional MRI (fMRI) was used to study striatal sensitivity to levodopa in hemiparkinsonian rhesus monkeys. Responses consistent with increased neuronal activity were seen in areas whose normal dopaminergic input from the substantia nigra pars compacta had been ablated by MPTP. Sites of increased activity following levodopa included the lateral putamen, the ventral region of the caudate head, septal areas, and midlateral amygdala in the MPTP-lesioned hemisphere. Increased activity was also observed in the same areas in the nonlesioned hemisphere, but was less pronounced in spatial extent and magnitude, suggesting either subclinical contralateral damage and/or functional adaptations in the contralateral dopamine systems. The increases in neuronal activity following levodopa treatment were temporally correlated with increases in striatal dopamine levels. Chronic levodopa treatment reduced behavioral responsiveness to levodopa and abolished the fMRI response. These results suggest that fMRI can detect changes in dopamine receptor-mediated neuronal sensitivity to dopaminergic agents.

Effects of high amphetamine dose on mood and cerebral glucose metabolism in normal volunteers using positron emission tomography (PET)

The effects of high euphorigenic doses of D-amphetamine (0.9-1.0 mg/kg p.o.) on regional cerebral glucose metabolism (rCMRglu) and psychological measures were investigated in 10 healthy human volunteers using a within-subject design and [F-18]-fluorodeoxyglucose positron emission tomography (FDG-PET) and a variety of psychological assessments. At the dose tested, D-amphetamine produced a mania-like syndrome concomitantly with a widespread increase in absolute cerebral metabolism, which was significant in the anterior cingulate cortex, caudate nucleus, putamen, and thalamus. An exploratory analysis revealed that: (1) certain aspects of this mania-like syndrome correlated positively with the metabolic changes seen in the frontal cortex, caudate nucleus and putamen; and (2) some of the amphetamine-induced changes in CMRglu correlated with D-amphetamine plasma levels. The present findings of cortical and subcortical increases in cerebral metabolism after D-amphetamine application in humans accord with previous studies in animals, demonstrating that relatively high doses of D-amphetamine (presumably at least 1 mg/kg) are needed to increase cerebral glucose metabolism.

Increase of creatine kinase activity in the visual cortex of human brain during visual stimulation: a 31P magnetization transfer study

31P magnetic resonance spectroscopy was used to investigate changes in high energy phosphate levels and creatine kinase (CK) kinetics induced in the human visual cortex during photic stimulation. CK kinetics was evaluated by measuring the apparent unidirectional rate constant (kf) in the "forward" direction (i.e., in the direction of ATP synthesis from phosphocreatine). kf increased 34% in the visual cortex areas during stimulation without significant changes of steady-state concentration of high energy phosphate compounds, indicating that CK turnover is elevated during increased neuronal activity.

PET measurement of dopamine D2 receptor-mediated changes in striatopallidal function

This study was designed to validate an in vivo measurement of the functional sensitivity of basal ganglia neuronal circuits containing dopamine D2 receptors. We hypothesized that a D2 agonist would decrease striatopallidal neuronal activity, and hence regional cerebral blood flow (rCBF) over the axon terminals in the globus pallidus. Quantitative pallidal blood flow was measured using positron emission tomography (PET) with bolus injections of H215O and arterial sampling in six baboons before and after intravenous administration of the selective D2 agonist U91356a. We also tested whether the response to U91356a was modified by previous acute administration of various antagonists. Another baboon had serial measurements of blood flow under identical conditions, but received no dopaminergic drugs. In all animals that received U91356a, pallidal flow decreased in a dose-related manner. Global CBF had a similar response, but the decline in pallidal flow was greater in magnitude and remained significant after accounting for the global effect. A D2 antagonist, but not antagonists of D1, serotonin-2, or peripheral D2 receptors, prevented this decrease. This work demonstrates and validates an in vivo measure of the sensitivity of D2-mediated basal ganglia pathways. It also supports the hypothesis that activation of the indirect striatopallidal pathway, previously demonstrated using nonselective D2-like agonists, can be mediated specifically by D2 receptors. We speculate that the U91356a-PET technique may prove useful in detecting functional abnormalities of D2-mediated dopaminergic function in diseases such as parkinsonism, dystonia, Tourette syndrome, or schizophrenia.

Dextroamphetamine enhances "neural network-specific" physiological signals: a positron-emission tomography rCBF study

Previous studies in animals and humans suggest that monoamines enhance behavior-evoked neural activity relative to nonspecific background activity (i.e., increase signal-to-noise ratio). We studied the effects of dextroamphetamine, an indirect monoaminergic agonist, on cognitively evoked neural activity in eight healthy subjects using positron-emission tomography and the O15 water intravenous bolus method to measure regional cerebral blood flow (rCBF). Dextroamphetamine (0.25 mg/kg) or placebo was administered in a double-blind, counterbalanced design 2 hr before the rCBF study in sessions separated by 1-2 weeks. rCBF was measured while subjects performed four different tasks: two abstract reasoning tasks--the Wisconsin Card Sorting Task (WCST), a neuropsychological test linked to a cortical network involving dorsolateral prefrontal cortex and other association cortices, and Ravens Progressive Matrices (RPM), a nonverbal intelligence test linked to posterior cortical systems--and two corresponding sensorimotor control tasks. There were no significant drug or task effects on pCO2 or on global blood flow. However, the effect of dextroamphetamine (i.e., dextroamphetamine vs placebo) on task-dependent rCBF activation (i.e., task - control task) showed double dissociations with respect to task and region in the very brain areas that most distinctly differentiate the tasks. In the superior portion of the left inferior frontal gyrus, dextroamphetamine increased rCBF during WCST but decreased it during RPM (ANOVA F (1,7) = 16.72, p < 0.0046). In right hippocampus, blood flow decreased during WCST but increased during RPM (ANOVA F(1,7) = 18.7, p < 0.0035). These findings illustrate that dextroamphetamine tends to "focus" neural activity, to highlight the neural network that is specific for a particular cognitive task. This capacity of dextroamphetamine to induce cognitively specific signal augmentation may provide a neurobiological explanation for improved cognitive efficiency with dextroamphetamine.

Acute changes in cranial blood flow after cocaine hydrochloride

Cerebral blood flow (CBF) was measured with the 133Xenon inhalation technique and forehead skin flow with laser Doppler, before and twice after 0.3 milligram/kilogram of cocaine hydrochloride and a placebo given intravenously to six cocaine abusers, during two visits, separated by a minimum of one week. After cocaine, subjects showed significant increases in intoxication and tension. Systolic blood pressure and pulse rate also increased significantly after the drug but not after the placebo. CBF, with and without correction for end-tidal CO2, showed increases in left and right hemisphere after cocaine. The CBF increase was maximal in frontal, central and parietal regions. CBF changes correlated only with changes in a rated level of intoxication. Forehead skin flow did not change after cocaine or placebo. In habitual cocaine abusers, 0.3 mg/kg of cocaine, given intravenously produced increased CBF and no changes in forehead skin flow.

Multi-slice MRI of rat brain perfusion during amphetamine stimulation using arterial spin labeling

When a single coil is used to measure perfusion by arterial spin labeling, saturation of macromolecular protons occurs during the labeling period. Induced magnetization transfer contrast (MTC) effects decrease tissue water signal intensity, reducing the sensitivity of the technique. In addition, MTC effects must be properly accounted for in acquiring a control image. This forces the image to a single slice centered between the labeling plane and the control plane. In this work, a two-coil system is presented as a way to avoid saturation of macromolecular spins during arterial spin labeling. The system consists of one small surface coil for labeling the arterial water spins, and a head coil for MRI, actively decoupled from the labeling coil by using PIN diodes. It is shown that no signal loss occurs due to MTC effects when the two-coil system is used for MRI of rat brain perfusion, enabling three-dimensional perfusion imaging. Using the two-coil system, a multi-slice MRI sequence was used to study the regional effects of amphetamine on brain perfusion. Amphetamine causes significant increases in perfusion in many areas of the brain including the cortex, cingulate, and caudate putamen, in agreement with previous results using deoxyglucose uptake to monitor brain activation.

Hyperaemia in rat neocortex produced by acute exposure to methylenedioxymethamphetamine

Cerebral blood flow and glucose utilization were measured in rat neocortex, hippocampus and striatum following methylenedioxymethamphetamine injection (5 mg/kg, i.v.), using the tracers [14C]iodoantipyrine and [14C]2-deoxyglucose, respectively. In control rats, blood flow was coupled to glucose metabolism, but in methylenedioxymethamphetamine-treated rats, marked hyperperfusion was measured in frontal and parietal cortex with no change in glucose use. This suggests that methylenedioxymethamphetamine has the potential to disrupt cerebrovascular control.

Acute cocaine alters cerebrovascular autoregulation in the rat neocortex

Although cocaine abuse has been associated with an increased incidence of cerebrovascular accident, the underlying mechanisms are unknown. In this study we have investigated the effects of cocaine upon the autoregulation of local cortical blood flow (lCBF) during hypertension. Hypertension was induced in conscious rats by intravenous infusion of angiotensin-II (5 micrograms/ml; 0.5-2.5 ml/h), and animals were subsequently injected IV with either cocaine-HCl (5 mg/kg) or saline, prior to the measurement of lCBF of glucose utilization (lCGU) using [14C]-iodoantipyrine or [14C]-2-deoxyglucose quantitative autoradiography, respectively. Hypertension alone (< 155 mmHg) did not significantly alter lCBF in any cortical areas examined. However, at higher mean arterial blood pressure (MABP), lCBF increased focally (+265%) in parietal cortex. Cocaine did not alter lCBF in normotensive animals, but with increasing levels of hypertension (MABP > 145 mmHg), all cocaine-treated rats showed focal increases (200-400%) in lCBF in parietal cortex. Glucose use remained relatively unaffected in all treatment groups. This hyperaemia in cocaine-treated rats at MABP below the normal upper limit of autoregulation may provide a mechanism to explain haemorrhagic stroke in cocaine abusers.

Dissociated effects of amphetamine on arousal and cortical blood flow in humans

The effects of intravenous amphetamine infusion (0.3 mg/kg) on cerebral blood flow (CBF) and measures of autonomic and behavioral arousal were studied in 12 normal male volunteers in a placebo-controlled crossover design. Nonsignificant decreases were seen in CBF (measured by 133Xe inhalation), despite significant increases in autonomic and behavioral arousal. The apparent dissociation of CBF and arousal appears to be compatible with other human experiments suggesting that amphetamine decreases CBF and metabolism, as well as with neurobiological findings on the effects of catecholamines on resting cortical activity and mechanisms of increased attention. The results differ substantially, however, from findings of increased CBF and metabolism in animals. Although the larger doses used in animals most likely explain the discrepancy, technical limitations in human brain imaging cannot be excluded.

The concept of coupling blood flow to brain function: revision required?

A tight coupling exists between brain function and cerebral perfusion in most situations. The Roy and Sherrington hypothesis has been widely accepted to account for the phenomenon: increased neuronal metabolic activity will give rise to the accumulation of vasoactive catabolites, which decrease vascular resistance and thereby increase blood flow until normal homeostasis is reestablished. However, the hypothesis does not account for the disproportionate increase in flow that occurs in a number of circumstances. There are additional difficulties in reconciling more recent experimental data with the Roy and Sherrington hypothesis. In this review we direct attention toward the rich perivascular nerve supply to all parts of the cerebral circulation as possibly being an alternative control system allowing for rapid parallel changes in flow and neuronal activity.

Effects of chronic administration of dextroamphetamine on enzymes of energy metabolism in regions of the rat brain

In the present study the effects of chronic administration of dextroamphetamine on energy metabolism in the brain of the rat were examined. The enzymes studied were: hexokinase (soluble and particulate forms), phosphofructokinase, pyruvate kinase, lactate dehydrogenase, citrate synthase, NAD+ and NADP+-dependent isocitrate dehydrogenases, succinate dehydrogenase and malate dehydrogenase. All the activities of the enzymes were assayed in four regions of the brain of the rat (cerebellum, medulla oblongata and pons, cererbral cortex and diencephalon). Rats were injected intaperitoneally once daily with dextroamphetamine for 20 consecutive days. The initial dose was 5 mg/kg/day and the dose was then increased by 1 mg/kg/every 5 days up to a total of 8 mg/kg/day on days 16-20. In the glycolytic enzymes a reduction of the activity of phosphofructokinase was found in the diencephalon and an increase of the activity of pyruvate kinase and lactate dehydrogenase in the diencephalon and medulla oblongata and pons, respectively. Citrate synthase was the only enzyme in the Krebs' cycle affected by chronic administration of dextroamphetamine. The results presented here show that chronic administration of dextroamphetamine produced important changes in some enzymes of glycolysis and the Krebs' cycle in the brain of the rat.

Protective effects of "cerebroactive drugs" in a model of acute hypoxia

A systematic study of the hypobaric hypoxia method was carried out, using a wide range of vasodilators and metabolic modifiers. In general cerebral metabolic modifiers have a more effective antihypoxic action than cerebral vasodilators. After a discussion, the conclusion is that hypobaric hypoxia is useful as an initial screening procedure.

Caffeine and cerebral blood flow

Two groups of normal volunteers had regional cerebral blood flow (rCBF) measured, by the 133Xenon inhalation technique, before and 30 minutes after 250 mg or 500 mg caffeine given orally. rCBF was measured in a third group of subjects, twice, at a similar interval under identical laboratory conditions. Subjects who received caffeine showed significant decreases in rCBF while the others showed no rCBF change from the first to the second measurement. However, the two caffeine groups did not differ in degrees of rCBF reduction. There were no regional variations in the post-caffeine decrease in cerebral blood flow. The three groups did not show significant changes in end-tidal carbon dioxide, pulse rate, blood pressure, forehead skin temperature and respiratory rate.

Cerebrovascular permeability and cerebral blood flow in hypertension induced by gammahydroxybutyric acid. An experimental study in the rat

A sustained increase in blood pressure was obtained by intraperitoneal (i.p.) or intravenous (i.v.) administration of gammahydroxybutyric acid (GHBA, 1 g/kg) in rats under nitrous oxide anesthesia and in conscious rats with indwelling catheters in the aorta and a jugular vein. Evans blue-albumin and 125I-labeled serum albumin, given i.v. before GHBA, were used to study the function of the blood-barrier in rats killed 60 min after the injection of the drug. Brains from rats subjected to acute hypertension while awake showed less extravasation of albumin than did brains from anesthetized rats. Sectioning of the cervical symphatetic nerves did not increase extravasation in conscious rats. The cerebral blood flow, determined with the 14C-ethanol technique, did not significantly differ in GHBA-treated rats and controls. Because of the sustained increase in blood pressure, GHBA-induced hypertension might be a useful model for the study of long-term effects on the brain of hypertensive opening of the blood-brain barrier.

Effects of methamphetamine on blood flow in the caudate-putamen after lesions of the nigrostriatal dopaminergic bundle in the rat

Methamphetamine was given to rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopaminergic bundle. In these animals local cerebral blood flow, measured autoradiographically with [14C]iodoantipyrine as the diffusible tracer, was more than twice as high in the denervated caudate-putamen as compared to control. Measurements of local glucose consumption with the [14C]deoxyglucose technique showed no corresponding change in local metabolic rate. In fact, glucose consumption was lower in the caudate-putamen on the lesion side. The results show that the amphetamine-induced increase in cerebral blood flow does not require an inact nigrostriatal dopaminergic system. Furthermore, dopamine released by amphetamine seems to constrict the vessels and reduce the blood flow in the caudate-putamen.

The increase in extracellular potassium concentration in the ischemic brain in relation to the preischemic functional activity and cerebral metabolic rate

The course of ischemic increase of extracellular potassium concentration ([K+]e) was studied in rat cerebral cortex with potassium selective microelectrodes and correlated to the preischemic functional and metabolic state. Complete cerebral ischemia was induced in artificially ventilated rats by cardiac arrest. Seven different functional states including conditions with cerebral hypermetabolism (seizures, amphetamine intoxication, hyperthermia) and hypometabolism (barbiturate anesthesia, hypothermia) were chosen in order to cover a wide range of cerebral metabolic rates (CMRO2 : 28.7--2.4 ml O2/(100 g)/min). The ischemic increase of [K+]e was delayed in conditions with low CMRO2 and accelerated in conditions with high CMRO2; the time interval to the terminal steep rise in extracellular potassium concentration varied within the extremes of 35 +/- 5 and 365 +/- 12 sec (means +/- S.E.M.), the control state (N2O-analgesia) being 116 +/- 5 sec. In groups with high CMRO2 electrocortical activity ceased within 15 sec and in groups with low CMRO2 within 22 sec. The rates of the ischemic [K+]e increase, measured as rate of change in the potassium electrode potential (mV/sec), remained high in conditions with high preischemic CMRO2 and low in conditions with low CMRO2, indicating a remaining influence of the preischemic metabolism on membrane ion permeability. These results support previous metabolic data indicating that the rate of consumption of high energy phosphates during ischemia mirrors the preischemic cerebral metabolic rate. Phenobarbital anesthesia did not change the initial rate of [K+]e increase but reduced the rate of [K+]e increase later during ischemia, suggesting a special effect of barbiturates on partly depolarized membranes.

Cerebral circulatory and metabolic effects of piribedil

Two aspects of the cerebrovascular action of the putative dopaminergic agonist, piribedil, have been examined. The vasomotor responses of isolated feline middle cerebral artery to piribedil and its metabolite, S584, were first examined and the effects of piribedil upon cerebral blood flow, cerebral oxygen consumption and the electroencephalogram (EEG) were then investigated in anaesthetised baboons. Neither piribedil nor S584 displayed any marked vasomotor efficacy in vitro, with small changes in tension being observed only with large concentrations (greater than 10(-4) M). In the anaesthetised baboons, the administration of piribedil (0.1 and 1 mg/kg, i.v.) resulted in significant increases in cerebral blood flow (40 +/- 10% and 49 +/- 14%, respectively) (mean +/- S.E.M.) and cerebral oxygen consumption (13 +/- 10% and 17 +/- 6%) which were accompanied by an increase in low voltage fast activity of the EEG. Prior administration of the putative dopaminergic antagonist, pimozide (0.5 mg/kg), which itself was without significant effect upon cerebral blood flow and oxygen consumption, prevented the cerebral circulatory, metabolic and EEG alterations induced by piribedil (1 mg/kg). It would appear likely that the action of piribedil upon cerebral metabolic activity was principally responsible for the increases in cerebral tissue perfusion which followed its administration.

Regional cerebral blood flow in a case of amphetamine intoxication

The regional cerebral blood flow (133Xe-inhalation method) was measured during acute amphetamine intoxication in a male 25 years old addict. During the study the patient displayed symptoms of paranoia and slight euphoria and tension. The flow level was found to be elevated by about 30% compared to a study in non-intoxicated state. The augmentation was most marked in the left hemisphere and in frontal regions (local increases up to 100%). The results confirm earlier findings in animal models and indicate the central role of frontal cortical structures in the production of psychotic symptoms.