Cerebral functional, metabolic and circulatory effects of intravenous infusion of adrenaline in the rat

Evidence on Adrenaline Use in Resuscitation and Its Relevance to Newborn Infants: A Non-Systematic Review

AIM

Guidelines for newborn resuscitation state that if the heart rate does not increase despite adequate ventilation and chest compressions, adrenaline administration should be considered. However, controversy exists around the safety and effectiveness of adrenaline in newborn resuscitation. The aim of this review was to summarise a selection of the current knowledge about adrenaline during resuscitation and evaluate its relevance to newborn infants.

METHODS

A search in PubMed, Embase, and Google Scholar until September 1, 2015, using search terms including adrenaline/epinephrine, cardiopulmonary resuscitation, death, severe brain injury, necrotizing enterocolitis, bronchopulmonary dysplasia, and adrenaline versus vasopressin/placebo.

RESULTS

Adult data indicate that adrenaline improves the return of spontaneous circulation (ROSC) but not survival to hospital discharge. Newborn animal studies reported that adrenaline might be needed to achieve ROSC. Intravenous administration (10-30 μg/kg) is recommended; however, if there is no intravenous access, a higher endotracheal dose (50-100 μg/kg) is needed. The safety and effectiveness of intraosseous adrenaline remain undetermined. Early and frequent dosing does not seem to be beneficial. In fact, negative hemodynamic effects have been observed, especially with doses ≥30 μg/kg intravenously. Little is known about adrenaline in birth asphyxia and in preterm infants, but observations indicate that hemodynamics and neurological outcomes may be impaired by adrenaline administration in these conditions. However, a causal relationship between adrenaline administration and outcomes cannot be established from the few available retrospective studies. Alternative vasoconstrictors have been investigated, but the evidence is scarce.

CONCLUSION

More research is needed on the benefits and risks of adrenaline in asphyxia-induced bradycardia or cardiac arrest during perinatal transition.

Microdialysate concentration changes do not provide sufficient information to evaluate metabolic effects of lactate supplementation in brain-injured patients

Cerebral microdialysis is a widely used clinical tool for monitoring extracellular concentrations of selected metabolites after brain injury and to guide neurocritical care. Extracellular glucose levels and lactate/pyruvate ratios have high diagnostic value because they can detect hypoglycemia and deficits in oxidative metabolism, respectively. In addition, patterns of metabolite concentrations can distinguish between ischemia and mitochondrial dysfunction, and are helpful to choose and evaluate therapy. Increased intracranial pressure can be life-threatening after brain injury, and hypertonic solutions are commonly used for pressure reduction. Recent reports have advocated use of hypertonic sodium lactate, based on claims that it is glucose sparing and provides an oxidative fuel for injured brain. However, changes in extracellular concentrations in microdialysate are not evidence that a rise in extracellular glucose level is beneficial or that lactate is metabolized and improves neuroenergetics. The increase in glucose concentration may reflect inhibition of glycolysis, glycogenolysis, and pentose phosphate shunt pathway fluxes by lactate flooding in patients with mitochondrial dysfunction. In such cases, lactate will not be metabolizable and lactate flooding may be harmful. More rigorous approaches are required to evaluate metabolic and physiological effects of administration of hypertonic sodium lactate to brain-injured patients.

Arousal withiv epinephrine depends on the depth of anesthesia

PURPOSE

To investigate whether the depth of anesthesia affects the change in the bispectral index (BIS) caused by iv epinephrine during propofol anesthesia.

METHODS

Forty women undergoing elective lower abdominal surgery received a propofol target controlled infusion (TCI) to maintain a modified Observer's Assessment of Alertness/Sedation (OAA/S) score of 2 (sedation period). Subsequently anesthesia was induced with propofol TCI 5 mug.mL(-1) and rocuronium 0.9 mg.kg(-1), and propofol continued so as to maintain general anesthesia at a BIS of 50 (general anesthesia period). Intravenous epinephrine at a dose of 10 mug.5 mL(-1) in normal saline (epinephrine group, n = 20) or normal saline 5 mL (control group, n = 20) was administered during both periods. The BIS, mean arterial pressure (MAP) and heart rate (HR) were measured immediately before, and one, two, three, four, six, eight, and ten minutes after injection. The modified OAA/S scale was evaluated during the sedation period.

RESULTS

There was no significant change in the modified OAA/S scale, BIS, or hemodynamic variables compared to preinjection values during either sedation or general anesthesia in the control group. Intravenous epinephrine increased the BIS and modified OAA/S scale during sedation, but there was no increase in BIS during general anesthesia. Increases in HR and MAP were observed during both periods after iv epinephrine.

CONCLUSION

Intravenous epinephrine 10 mug resulted in an arousal effect and an increase in BIS during sedation, but did not change the BIS during general anesthesia. These results suggest that the arousal effect of iv epinephrine during propofol anesthesia depends on anesthetic depth.

Pre-test metyrapone impairs memory recall in fear conditioning tasks: lack of interaction with β-adrenergic activity

Cognitive processes, such as learning and memory, are essential for our adaptation to environmental changes and consequently for survival. Numerous studies indicate that hormones secreted during stressful situations, such as glucocorticoids (GCs), adrenaline and noradrenaline, regulate memory functions, modulating aversive memory consolidation and retrieval, in an interactive and complementary way. Thus, the facilitatory effects of GCs on memory consolidation as well as their suppressive effects on retrieval are substantially explained by this interaction. On the other hand, low levels of GCs are also associated with negative effects on memory consolidation and retrieval and the mechanisms involved are not well understood. The present study sought to investigate the consequences of blocking the rise of GCs on fear memory retrieval in multiple tests, assessing the participation of β-adrenergic signaling on this effect. Metyrapone (GCs synthesis inhibitor; 75 mg/kg), administered 90 min before the first test of contextual or tone fear conditioning (TFC), negatively affected animals’ performances, but this effect did not persist on a subsequent test, when the conditioned response was again expressed. This result suggested that the treatment impaired fear memory retrieval during the first evaluation. The administration immediately after the first test did not affect the animals’ performances in contextual fear conditioning (CFC), suggesting that the drug did not interfere with processes triggered by memory reactivation. Moreover, metyrapone effects were independent of β-adrenergic signaling, since concurrent administration with propranolol (2 mg/kg), a β-adrenergic antagonist, did not modify the effects induced by metyrapone alone. These results demonstrate that pre-test metyrapone administration led to negative effects on fear memory retrieval and this action was independent of a β-adrenergic signaling.

Interacting brain systems modulate memory consolidation

Emotional arousal influences the consolidation of long-term memory. This review discusses experimental approaches and relevant findings that provide the foundation for current understanding of coordinated interactions between arousal activated peripheral hormones and the brain processes that modulate memory formation. Rewarding or aversive experiences release the stress hormones epinephrine (adrenalin) and glucocorticoids from the adrenal glands into the bloodstream. The effect of these hormones on memory consolidation depends upon binding of norepinephrine to beta-adrenergic receptors in the basolateral complex of the amygdala (BLA). Much evidence indicates that the stress hormones influence release of norepinephrine in the BLA through peripheral actions on the vagus nerve which stimulates, through polysynaptic connections, cells of the locus coeruleus to release norepinephrine. The BLA influences memory storage by actions on synapses, distributed throughout the brain, that are engaged in sensory and cognitive processing at the time of amygdala activation. The implications of the activation of these stress-activated memory processes are discussed in relation to stress-related memory disorders.

Sympathetic influence on cerebral blood flow and metabolism during exercise in humans

This review focuses on the possibility that autonomic activity influences cerebral blood flow (CBF) and metabolism during exercise in humans. Apart from cerebral autoregulation, the arterial carbon dioxide tension, and neuronal activation, it may be that the autonomic nervous system influences CBF as evidenced by pharmacological manipulation of adrenergic and cholinergic receptors. Cholinergic blockade by glycopyrrolate blocks the exercise-induced increase in the transcranial Doppler determined mean flow velocity (MCA Vmean). Conversely, alpha-adrenergic activation increases that expression of cerebral perfusion and reduces the near-infrared determined cerebral oxygenation at rest, but not during exercise associated with an increased cerebral metabolic rate for oxygen (CMRO(2)), suggesting competition between CMRO(2) and sympathetic control of CBF. CMRO(2) does not change during even intense handgrip, but increases during cycling exercise. The increase in CMRO(2) is unaffected by beta-adrenergic blockade even though CBF is reduced suggesting that cerebral oxygenation becomes critical and a limited cerebral mitochondrial oxygen tension may induce fatigue. Also, sympathetic activity may drive cerebral non-oxidative carbohydrate uptake during exercise. Adrenaline appears to accelerate cerebral glycolysis through a beta2-adrenergic receptor mechanism since noradrenaline is without such an effect. In addition, the exercise-induced cerebral non-oxidative carbohydrate uptake is blocked by combined beta 1/2-adrenergic blockade, but not by beta1-adrenergic blockade. Furthermore, endurance training appears to lower the cerebral non-oxidative carbohydrate uptake and preserve cerebral oxygenation during submaximal exercise. This is possibly related to an attenuated catecholamine response. Finally, exercise promotes brain health as evidenced by increased release of brain-derived neurotrophic factor (BDNF) from the brain.

Cerebral non-oxidative carbohydrate consumption in humans driven by adrenaline

During brain activation, the decrease in the ratio between cerebral oxygen and carbohydrate uptake (6 O(2)/(glucose + (1)/(2) lactate); the oxygen-carbohydrate index, OCI) is attenuated by the non-selective beta-adrenergic receptor antagonist propranolol, whereas OCI remains unaffected by the beta(1)-adrenergic receptor antagonist metroprolol. These observations suggest involvement of a beta(2)-adrenergic mechanism in non-oxidative metabolism for the brain. Therefore, we evaluated the effect of adrenaline (0.08 microg kg(-1) min(-1) i.v. for 15 min) and noradrenaline (0.5, 0.1 and 0.15 microg kg(-1) min(-1) i.v. for 20 min) on the arterial to internal jugular venous concentration differences (a-v diff) of O(2), glucose and lactate in healthy humans. Adrenaline (n = 10) increased the arterial concentrations of O(2), glucose and lactate (P < 0.05) and also increased the a-v diff for glucose from 0.6 +/- 0.1 to 0.8 +/- 0.2 mM (mean +/- s.d.; P < 0.05). The a-v diff for lactate shifted from a net cerebral release to an uptake and OCI was lowered from 5.1 +/- 1.5 to 3.6 +/- 0.4 (P < 0.05) indicating an 8-fold increase in the rate of non-oxidative carbohydrate uptake during adrenaline infusion (P < 0.01). Conversely, noradrenaline (n = 8) did not affect the OCI despite an increase in the a-v diff for glucose (P < 0.05). These results support that non-oxidative carbohydrate consumption for the brain is driven by a beta(2)-adrenergic mechanism, giving neurons an abundant provision of energy when plasma adrenaline increases.

Some hormonal influences on glucose and ketone body metabolism in normal human subjects

Control of glucose and ketone body metabolism is integrated by a variety of hormones. Insulin is the major anabolic hormone, and its actions are antagonized by rapidly acting catabolic hormones, such as glucagon and the catecholamines, and by others such as cortisol, growth hormone and the thyroid hormones, which generally have more delayed effects. In the normal human subject, the effects of catabolic hormones to raise blood glucose are limited by a compensatory increase in insulin secretion, and these effects are enhanced in insulin deficiency. Hyperketonaemic actions of the catabolic hormones may result from increased supply of non-esterified fatty acids from lipolysis, although glucagon has a major direct action to increase ketogenesis at the liver. As expected, these actions are also restricted in normal humans by the compensatory rise in insulin secretion. Hyperketonaemia does, however, occur with adrenaline (epinephrine) and noradrenaline (norepinephrine), even in the presence of mildly elevated insulin concentrations. These catecholamines may assume particular importance in mobilization of lipid fuels in milder forms of stress, when insulin secretion is normal or mildly increased. In severe stress, when there is catecholamine-induced suppression in insulin secretion, lipolytic and hyperketonaemic effects of all the catabolic hormones may be manifest. Starvation in humans also results in diminished insulin secretion and increased catabolic hormone secretion. The relative importance of individual hormones in lipid mobilization during starvation is uncertain, although glucagon, growth hormone, noradrenaline and, possibly, dopamine may all play a part.

Vasopressors for cardiopulmonary resuscitation. Does pharmacological evidence support clinical practice?

Adrenaline (epinephrine) has been used for cardiopulmonary resuscitation (CPR) since 1896. The rationale behind its use is thought to be its alpha-adrenoceptor-mediated peripheral vasoconstriction, causing residual blood flow to be diverted to coronary and cerebral circulations. This protects these tissues from ischaemic damage and increases the likelihood of restoration of spontaneous circulation. Clinical trials have not demonstrated any benefit of adrenaline over placebo as an agent for resuscitation. Adrenaline has deleterious effects in the setting of resuscitation, predictable from its promiscuous pharmacological profile. This article discusses the relevant pharmacology of adrenaline in the context of CPR. Experimental and clinical evidences for the use of adrenaline and alternative vasopressor agents in resuscitation are given, and the properties of an ideal vasopressor are discussed.

Does induced hypertension reduce cerebral ischaemia within the traumatized human brain?

Recent changes in published guidelines for the management of patients with severe head injury are based on data showing that aggressive maintenance of cerebral perfusion pressure (CPP) can worsen outcome due to extracranial complications of therapy. However, it remains unclear whether CPP augmentation could reduce cerebral ischaemia, a finding which might prompt the search for CPP augmentation protocols that avoid these extracranial complications. We studied 10 healthy volunteers and 20 patients within 6 days of closed head injury. All subjects underwent imaging of cerebral blood flow (CBF), blood volume (CBV), oxygen metabolism (CMRO2) and oxygen extraction fraction (OEF) using 15O PET. In addition, for patients, the EEG power ratio index (PRI), burst suppression ratio and somatosensory evoked potentials (SEP) were obtained and CPP was increased from 68 +/- 4 to 90 +/- 4 mmHg using an infusion of norepinephrine and measurements were repeated. Following elevation of CPP, CBF and CBV were increased and CMRO2 and OEF were reduced (P < 0.001 for all comparisons). Regions with a reduction in CMRO2 were associated with the greatest reduction in OEF (r2 = 0.3; P < 0.0001). Although CPP elevation produced a significant fall in the ischaemic brain volume (IBV) (from 15 +/- 16 to 5 +/- 4 ml; P < 0.01) and improved flow metabolism coupling, the IBV was small and clinically insignificant in the majority of these patients. However, the reduction in IBV was directly related to the baseline IBV (r2 = 0.97; P < 0.001) and patients with large baseline IBV showed substantial and clinically significant reductions. CPP augmentation increased the EEG PRI (5.0 +/- 1.5 versus 4.3 +/- 1.4, P < 0.01), implying an overall decrease in neural activity, but these changes did not correlate with the reduction in CMRO2 and there was no change in SEP cortical amplitude (N20-P27). These data provide support for recent changes in recommended CPP levels for head injury management across populations of patients with significant head injury. However, they do not provide guidance on whether the intervention may be more appropriate at earlier stages after injury, or in patients selected because of high baseline IBV. It also remains unclear whether CPP values below 65 mmHg can be safely used in this population. Clarification of the significance of a reduction in CMRO2 and neuronal electrical function will require further study.

Role of epinephrine in acute stress

This article presents the likely pathway of stimuli generated by the recognition of high-intensity stressors to ultimately produce a fight-or-flight response. A key element is the recognition that psychological stressors that do not directly alter the internal environment represent the most important etiology of a fight-or-flight response. Adrenomedullary secretion is a critical component of that response; impromptu stimulation of the adrenal medulla can produce plasma epinephrine concentrations greater than 10,000 pg/mL. When these plasma levels reach the hypothalamus to act on the CNS, the result is facilitation of the decision making, and decision execution processes (fight-or-flight), and perhaps further sympathetic stimulation and vasopressin release. Subjects with underlying cardiovascular and/or metabolic pathology may be particularly susceptible to potentially lethal reactions to this neuroendocrine response. Additionally, since this biological reaction may be triggered by sudden changes in the social environment, the coordinated actions of epinephrine, sympathetic stimulation and vasopressin must be directed at not only optimizing the chances for survival, but also at attaining maximal preservation of the individual environmental and social domains.

Norepinephrine activation of basal cerebral metabolic rate for oxygen (CMRO2) during hypothermia in rats

In an earlier study on the effect of mild hypothermia (34 degrees C) on the cerebral metabolic rate for oxygen (CMRO2) in rats, we used norepinephrine (NE) to support arterial blood pressure while inducing isoelectricity on the electroencephalogram (EEG) with thiopental (TP). Even with administration of sufficient TP to reduce a fully active EEG to an isoelectric EEG, CMRO2 was often unchanged. Based on this observation, we hypothesized that NE had activated CMRO2 despite thiopental coma. Therefore, we studied the effect of NE compared with donor blood (DB) infusion to maintain arterial blood pressure during TP-induced isoelectric EEG on whole-brain CBF (H2 clearance) and CMRO2 during normothermia (38 degrees C) and mild hypothermia (34 degrees C) in rats during 70% N2O/30% O2 analgesia. Cerebral blood flow (CBF) and CMRO2 were measured in four groups of rats at 38 degrees C followed by measurements at either 38 degrees C (two groups) or 34 degrees C (two groups) and during TP-induced EEG isoelectricity. Within each of the two groups at 38 degrees C and 34 degrees C, arterial pressure was sustained by either DB (n = 10) or NE (n = 9) infusion. At 38 degrees C, CMRO2 in the DB and NE groups was 7.92 +/- 1.05 and 6.4 +/- 0.80 mL x 100 g-1.min-1 and decreased to 50% of normal (3.95 +/- 0.70 and 3.32 +/- 0.40 mL x 100 g-1.min-1, respectively) during TP isoelectricity for a functional:basal CMRO2 distribution of 50% +/- 4% and 50% +/- 4%. At 34 degrees C, CMRO2 values in the DB and NE groups were 6.31 +/- 1.41 and 5.41 +/- 2.02 mL x 100 g-1.min-1, respectively. During TP-induced isoelectricity, CMRO2 values in both groups were reduced to 2.37 +/- 0.43 and 3.55 +/- 1.27 mL x 100g-1.min-1, respectively, resulting in a functional:basal CMRO2 distribution of 61%:38% in the DB group and the reverse, or 27%:73%, in the Ne group. Basal CMRO2 was significantly (P < 0.05) larger in the NE-infused rats. These results suggest that NE infusion, by increasing CMRO2 during mild hypothermia, could nullify its protective effects in the ischemic brain.

Mania: sympathoadrenal function and clinical state

We investigated sympathoadrenal and sympathetic nervous system activity, catecholamine disposition, and clinical state in 19 hospitalized manic patients. Severity of the core manic syndrome, anxiety, and hostility correlated with 24-hour urinary excretion of epinephrine relative to its metabolites, but only weakly with norepinephrine. Agitation, however, correlated most strongly and significantly with norepinephrine. Eight of the patients had mixed states: concurrent manic and depressive syndromes. There were no differences between mixed and pure manic patients with respect to catecholamine or metabolite excretion or precursor/product ratios, but mixed manic patients tended to have higher excretion of norepinephrine and had increased variance with respect to catecholamine measures. These data suggest that the function of the adrenal medulla, whether directly or indirectly, is important in the symptoms of both mixed and pure mania.

Shy-Drager syndrome. Effect of fludrocortisone and L-threo-3,4-dihydroxyphenylserine on the blood pressure and regional cerebral blood flow

In nine cases of Shy-Drager syndrome, the changes in blood pressure and cerebral blood flow on sitting up from a supine position were studied. The influence of fludrocortisone, a synthetic mineralocorticoid, and L-threo-3,4-dihydroxyphenylserine (DOPS), a precursor of norepinephrine, on these changes was examined. On sitting up, the regional cerebral blood flow (rCBF) measured by Xe133 inhalation showed a tendency to decrease. Fludrocortisone reduced the fall of the mean blood pressure significantly. DOPS reduced the fall of both the diastolic blood pressure and rCBF significantly.

Plasma epinephrine modulates the cerebrovasodilation evoked by electrical stimulation of dorsal medulla

We examined whether plasma epinephrine contributes to the increase in regional cerebral blood flow (rCBF) evoked by electrical stimulation of the dorsal medullary reticular formation (DMRF). Rats were anesthetized (alpha-chloralose, 30 mg/kg, s.c.), paralyzed and artificially ventilated. The DMRF was electrically stimulated through microelectrodes stereotaxically implanted. During stimulation, blood gases and arterial pressure were monitored and maintained within normal range. rCBF was determined in 11 dissected brain regions using the [14C]iodoantipyrine technique. Plasma epinephrine and norepinephrine were measured radioenzymatically in rats with intact adrenals or adrenalectomy, and with or without infusion of epinephrine. DMRF stimulation induced widespread increases in rCBF associated with a 50-fold increase in plasma epinephrine and a 20-fold increase in norepinephrine without changes in the electroencephalogram. In contrast, stimulation of the adjacent medial longitudinal fasciculus had no effect upon rCBF or plasma catecholamines. Acute bilateral adrenalectomy produced regionally selective reductions in the stimulation-coupled increases in rCBF throughout brain (P less than 0.05). Infusion of epinephrine in adrenalectomized rats to levels comparable to those observed in intact animals during DMRF stimulation did not by itself modify rCBF. However, when infused in conjunction with stimulation of the DMRF, but not medial longitudinal fasciculus, epinephrine fully restored the stimulus-related increases in rCBF in all brain regions to levels comparable to those observed in intact rats. We conclude that stimulation of the DMRF elevates rCBF through two mechanisms; by a neurally-mediated increase in local metabolism and thereby flow (adrenal independent secondary vasodilation) and by releasing epinephrine from adrenal medulla which secondarily acts to increase rCBF by an action on brain.

Regional cerebral blood flow in acute hypertension induced by adrenaline, noradrenaline and phenylephrine in the conscious rat

Hypertension was induced in conscious rats by intravenous infusion of phenylephrine (3, 6 or 12 micrograms kg-1 min-1), noradrenaline (3 micrograms min-1) or adrenaline (3 micrograms kg-1 min-1). Local cerebral blood flow was measured autoradiographically in 24 defined brain structures using [14C]iodoantipyrine as the diffusible tracer. The mean arterial pressure induced by adrenaline, noradrenaline and the two higher doses of phenylephrine was 158-168 mmHg with no significant differences between the groups. Only adrenaline significantly increased local cerebral blood flow in nine of the 24 structures studied. The smaller capacity for autoregulation after adrenaline compared with other drugs might be related to a beta-adrenoreceptor-stimulating effect.

Effect of momentary stress on brain energy metabolism in weanling mice: apparent use of lactate as cerebral metabolic fuel concomitant with a decrease in brain glucose utilization

The hypothesis that the anxiety induced by repeated injections affects brain energy metabolism was tested. Normal 19- to 21-day-old mice were stressed by two sham intraperitoneal injections within 4 min, at which time they were decapitated. Noninjected, control littermates were quickly decapitated. Momentary stress increased plasma glucose (12%), glycerol (85%), beta-hydroxybutyrate (108%), and lactate (153%)--a reflection of elevated plasma cortisol (25%) and glucagon (45%). In brain, stress increased levels of glucose-6-P (15%) and fructose-6-P (17%). The brain pyruvate concentration increased 74%; lactate 76%. Citrate, alpha-ketoglutarate, and malate increased 15, 95, and 37%, respectively. Levels of glycogen, glucose, phosphocreatine, ATP, ADP, and AMP were unchanged. The brain lactate/pyruvate ratio was normal but the brain/plasma lactate ratio fell 32%. Metabolite changes in the stressed animals were compatible with a decrease in the glycolytic flux at the phosphofructokinase step and a paradoxical increased flux in the Krebs citric acid cycle. The decreased brain/plasma lactate ratio supported increased uptake of lactate from plasma and increased brain lactate oxidation. Metabolite changes similar to those described above occurred in unstressed mice injected with lactate. Findings confirm a positive effect of stress on brain metabolism, support a role for lactate as an oxidative fuel for brain, and caution that the rate of cerebral glucose utilization may not always reflect brain energy (oxidative) metabolism accurately.

Adrenaline-induced hypertension: morphological consequences of the blood-brain barrier disturbance

Acute hypertension may transiently open the blood-brain barrier (BBB). To determine whether such temporary exposure of the brain parenchyma to plasma constituents may lead to permanent morphological alterations, acute hypertension was induced by i.v. adrenaline in conscious rates given Evan's blue and horseradish peroxidase as tracers. The brain were perfused in situ 24 h later: 17 of 21 brains showed multifocal sites of extravasation of the tracers and of endogenous plasma albumin, fibrinogen and fibronectin identified by immunohistochemistry. The proteins spread locally in the parenchyma and were taken up by neurons. Within the leaking sites in the cortex, hippocampus, thalamus and basal ganglia some shrunken and grossly distorted acidophilic neurons were present. Focal areas of sponginess were observed in the subpial and subependymal zones. Thus, a transient opening of the BBB may lead to neuronal damage.

A transient hypertensive opening of the blood-brain barrier can lead to brain damage. Extravasation of serum proteins and cellular changes in rats subjected to aortic compression

A transient increase in blood pressure was induced in 15 male Sprague Dawley rats by clamping the upper abdominal aorta for 8-10 min. Three rats served as controls. The brains were fixed by perfusion 2 h or 7 days later. Evan's blue-albumin (EBA) was used for macroscopic evaluation of the blood-brain barrier (BBB) integrity. Extravasated plasma albumin, fibrinogen and fibronectin were demonstrated by immunohistochemistry on paraffin sections. Glial fibrillary acidic protein (GFAP) was visualized in the same way. Parallel sections were analyzed for possible parenchymal changes associated with the BBB breakdown. Multiple focal areas of BBB opening were seen in the brains of the three rats killed 2 h after the hypertensive episode. The plasma proteins were present in the vascular wall, extracellular space and within certain neurons. Shrunken acid fuchsin positive neurons were seen in some areas of extravasation. After 7 days, in 5 out of 12 rats a few local lesions with EBA leakage and positive immunostaining for plasma proteins were seen. Structurally these lesions were characterized by shrinkage, fuchsinophilia and disintegration of neurons and proliferation of astrocytes. Thus, a transient opening of the BBB by acute hypertension may lead to permanent tissue damage.

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.

Modulating effects of posttraining epinephrine on memory: involvement of the amygdala noradrenergic system

These experiments examined the effects, on retention, of posttraining intra-amygdala administration of norepinephrine (NE), and propranolol. Rats were trained on a one-trial step-through inhibitory avoidance task and tested for retention 24 h later. Injections were administered bilaterally (1.0 microliter/injection) through chronically-implanted cannulae. Low doses of NE (0.1 or 0.3 microgram) administered shortly after training enhanced retention while higher doses (1.0 or 5.0 micrograms) were ineffective. Retention was not affected by NE administered 3 h after training. The effect of intra-amygdala NE on retention is blocked by simultaneous administration of propranolol (0.2 microgram). This finding suggests that the memory-enhancing effect of NE may be mediated by beta-receptors. Posttraining intra-amygdala NE also attenuated the retention deficit produced by adrenal demedullation. Further, intra-amygdala injections of propranolol (0.2 microgram) blocked the enhancing effect, on retention, of posttraining s.c. injections of epinephrine. These findings suggest that activation of noradrenergic receptors in the amygdala may be involved in memory processing and may play a role in the memory-modulating effect of peripheral epinephrine.

Regional cerebral blood flow (rCBF) in man during perception of radiant warmth and heat pain

The present study concerns the effects of experimental pain (radiant warmth and heat pain) on regional cerebral blood flow (rCBF) in pretrained subjects. The radiant warmth caused a general rCBF increase. However, if anxiety was avoided, heat pain caused the general rCBF level to return towards the level at rest. Thus, pain sensation per se may not cause a larger rCBF (and metabolic) response than that of the localized tactile stimulation, provided that the element of psychic apprehension and anxiety is eliminated or controlled.

Peripheral epinephrine modulates the effects of post-training amygdala stimulation on memory

The present study investigated the role of adrenal epinephrine in the memory modulatory effects of post-training amygdala stimulation. Adrenal demedullated (ADMX) or sham demedullated (SHAM) rats received electrical stimulation of the amygdala immediately after training on inhibitory and active avoidance tasks. With both tasks, the stimulation impaired retention only in the rats with intact adrenal medullae: the retention performance of the ADMX in the rats with intact adrenal medullae: the retention performance of the ADMX rats given post-training stimulation was better than that of the unstimulated ADMX group with implanted electrodes. However, ADMX rats given post-training epinephrine (1.0 mg/kg, s.c.) immediately before the amygdala stimulation had retention deficits comparable to those of the SHAM group given amygdala stimulation. If epinephrine was administered a short time after rather than before the post-training amygdala stimulation, retention of the ADMX animals was not impaired. The findings are interpreted as indicating that circulating epinephrine present at the time of amygdala stimulation modulates the effects of amygdala stimulation on memory.

Brain catecholamines and memory modulation: effects of footshock, amygdala implantation, and stimulation

The results of previous studies indicate that the extent of a transient decline in brain norepinephrine (NE) levels shortly after training and administration of any of several memory modulating treatments is correlated with later retention performance. The present experiment assessed such changes after one-trial inhibitory (passive) avoidance training and, in addition, measured concentration changes in 3-methoxy-4-hydroxyphenylglycol (MHPG), the major metabolite of brain NE, as well as dopamine (DA) and epinephrine (EPI) levels. The results indicate that the decreases in brain NE after footshock are accompanied by an increase in MHPG, thus providing additional evidence that brain NE is released after training. DA levels were unchanged after training; brainstem EPI levels increased after the training footshock, but forebrain EPI levels were unchanged. A second experiment examined brain catecholamine levels in animals which received post-training electrical stimulation of the amygdala. The findings of this experiment indicate that the amygdala damage which accompanies electrode implantation apparently results in a chronic change in whole brain NE levels and metabolism. After amygdala, NE concentrations in both brainstem and forebrain samples were reduced by 20% and MHPG was increased by 22-34%. Furthermore, NE levels were not responsive to training in implanted animals. Thus, brain NE levels after training were not predictive of retention performance in amygdala-implanted or -stimulated animals. However, the significance of such findings for understanding the possible role of central NE in memory storage is complicated by the severe modification of the dynamics of brain aminergic systems in animals bearing amygdala electrodes.

Cerebral oxygen and energy metabolism during and after 30 minutes of moderate hypoxia

Sixty-four isolated canine brain preparations were subjected to either 15 or 30 min of perfusion with blood equilibrated at either Pao2 30 mmHg or Pao2 40 mmHg followed by up to 60 min of reoxygenation with blood having a Pao2 greater than 100 mmHg. Pao2 30 mmHg perfusion decreased oxygen availability and the cerebral metabolic rate for oxygen (CMRo2) to 44 and 49% of normal, respectively, whereas Pao2 40 mmHg perfusion decreased oxygen availability and CMRo2 to 64 and 70% of normal, respectively. Creatine phosphate was markedly decreased (0.6 and 4% of normal, respectively) and ATP was only slightly decreased (73 and 90% of normal, respectively) in these preparations during the hypoxic period. Although ATP returned to normal during the reoxygenation period in both groups, creatine phosphate and CMRo2 returned to normal only in the Pao2 40 mmHg preparations. In brains perfused at various Pao2 levels for periods ranging from 6 to 30 min, the total oxygen deficit (the cumulative difference over time between normal and actual CMRo2) rather than tissue lactate levels appeared to influence the restoration of CMRo2 to normal following hypoxia. An oxygen deficit in excess of 25 mumol/g precluded return to a normal CMRo2 following reoxygenation.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuation of epileptogenesis: proactive effect of a single epinephrine injection of amygdaloid kindling

Repeated daily electrical stimulation of the amygdala can lead to a progressive increase in brain and behavioral seizures. This phenomenon, termed kindling, has been viewed as a model for epileptogenesis. The results reported here demonstrate that a single systemic epinephrine injection can significantly retard such epileptogenesis for a period of at least several days. These findings suggest that peripheral catecholamines, responding either to stress near the time of seizure initiation or to treatments administered at that time, may be important in regulating the development of epileptic states. In addition, the results indicate that an acute episode of high plasma epinephrine levels may result in a durable modification of brain function.

Regional blood flow in canine brain during nicotine infusion: effect of autonomic blocking drugs

Radioactive microspheres (15 mu) were used to measure regional cerebral blood flow during intravenous infusion of nicotine (36 micrograms/kg/min) in anesthetized, open chest dogs. Experiments were conducted with uncontrolled mean aortic pressure and intact autonomic receptors (Series I; n = 9), and in four groups of dogs with mean aortic pressure held constant (Series II); 1) with intact autonomic receptors (n = 6), 2) after beta adrenergic blockade (n = 8), 3) after alpha and beta adrenergic blockade (n = 6), 4) after alpha and beta adrenergic and cholinergic blockade (n = 4). In Series I, nicotine raised mean aortic pressure (+ 72%) and increased flow in cerebral cortex (+ 67%), cerebellum (+ 38%), pons (+ 46%), medulla (+ 39%), and spinal cord (+ 48%). In all regions, but cortex, increases in vascular resistance limited nicotine-induced increases in flow. In Series II, nicotine changed flow only in cortex. Without blockade, nicotine increased cortical flow (+ 38%); but beta blockade abolished this increase in flow. After alpha and beta blockade nicotine again raised cortical flow (+ 29%), and additional cholinergic blockade had no effect on this response. It is concluded that nicotine causes predominant beta receptor mediated vasodilation in cerebral cortex, although it also activates alpha (vasoconstrictor) receptors and a non-adrenergic, non-cholinergic vasodilator mechanism in this region of brain.

The effects of intravenous norepinephrine on the local coupling between glucose utilization and blood flow in the rat brain

Norepinephrine was infused intravenously in two groups of normal, awake rats. In one group local cerebral glucose utilization (LCGU) was measured by the deoxyglucose method (Sokoloff et al. 1977b); in the other group local cerebral blood flow (LCBF) was determined by the iodoantipyrine method (Sakurada et al. 1978). The experiments were performed during a stable state in which the heart rate was reduced between 36% (LCGU experiments) and 27% (LCBF experiments). Norepinephrine infusion reduced LCGU in all 39 structures measured between - 18 and - 37% from control values obtained in a group of normal non-infused rats. The decrease in LCGU was significant (P less than 0.05) in 38 of the 39 structures tested. LCBF was increased but not statistically significantly in most of the structures examined. When the LCGU values of the various structures during norepinephrine infusion were correlated with their corresponding LCBF values, a tight correlation (r = 0.94) was found indicating a close coupling between LCGU and LCBF during norepinephrine infusion. When compared to the relationship between LCGU and LCBF in a normal, non-infused control group, the slope of the regression line was increased significantly (P less than 0.01) by the norepinephrine infusion, indicating a resetting of the coupling mechanism. This means that, at a given metabolic rate, a higher blood flow is needed to perfuse a brain structure during norepinephrine infusion than during control conditions.

Effect of diazepam on cerebral monoamine synthesis during hypoxia and hypercapnia in the rat

In view of the fact that diazepam has been shown to prevent an increase in catecholamine synthesis and/or turnover rates in stressful situations, and to modify the cerebral metabolic (and circulatory) response to hypoxia and hypercapnia, the influence of the drug on synthesis rates of DOPA and 5-HTP in three regions of the rat brain were studied under normoxic-normocapnic conditions, as well as in hypoxia and hypercapnia. In order to exclude a modifying influence of variations in tissue pO2 during hypercapnia, cerebral venous pO2 was kept at control values by moderate arterial hypoxia. When compared to the control state (paralyzed animals maintained on 70% N2O) normoxic and normocapnic animals given diazepam (in the absence of N2O) showed a slightly enhanced DOPA synthesis in limbic structures and reduced 5-HTP synthesis in limbic structures and striatum. In hypoxia, the drug considerably curtailed DOPA synthesis in limbic structures and striatum but had no effect on synthesis rate in cortex. The drug also appeared to exaggerate the generalized reduction in 5-HTP synthesis observed under 70% N2O. In hypercapnia, diazepam reduced the enhanced rate of DOPA synthesis (observed under 70% N2O) in striatum but left that in the cortex unchanged. The drug prevented the hypercapnia-induced increase in 5-HTP synthesis, observed under 70% N2O. It is concluded that diazepam significantly alters dopamine and serotonin synthesis in hypoxia and hypercapnia. Probably an indirect action, perhaps related to the stress-alleviating effect of diazepam, is involved. The results suggest that the effect of the drug on cerebral metabolic rate and blood flow in hypoxia and hypercapnia is unrelated to changes in noradrenaline synthesis or turnover. Furthermore, although the results demonstrate that diazepam modulates dopamine metabolism in hypoxia and hypercapnia it seems questionable that this influence can explain the metabolic and circulatory effects of diazepam in these conditions.

Anesthetics affect the cerebral metabolic response to circulatory catecholamines

This study examined whether the effect of intravenous infusions of either epinephrine or norepinephrine on cerebral metabolic rate for oxygen (CMRO2) in the dog was modified by different anesthetics. Infusions of either epinephrine or norepinephrine at rates of 0.1-0.25 mu.kg-1.min-1 reversibly increased the CMRO2 by 17-23% during anesthesia with cyclopropane 20% and nitrous oxide 50% in oxygen, whereas infusions at rates of 0.1-25.0 micrograms.kg-1.min-1 had no effect in dogs anesthetized with other inhalational or intravenous agents. Cyclopropane/nitrous oxide also increased permeability of the blood-brain barrier to Evan's blue dye whereas the other anesthetics tested did not. It is concluded that epinephrine and norepinephrine crossed the blood-brain barrier during cyclopropane anesthesia, accounting for the increase in CMRO2. The authors speculate that cyclopropane may have increased blood-brain barrier permeability by a direct effect on endothelial cells or by affecting central adrenergic systems and that epinephrine or norepinephrine may increase CMRO2 either by a direct action on neuronal receptors or via metabolically coupled synaptic events.

Effect of propranolol on local cerebral blood flow under normocapnic and hypercapnic conditions

The effect of propranolol (2.5 mg kg-1, i.v.) on local cerebral blood flow (CBF) in normocapnia was studied in rats maintained artificially ventilated on 70% N2O and 30% O2. The method used was autoradiography with [14C]iodoantipyrine. Although a single dose of propranolol, given 30 min prior to CBF measurements, somewhat reduced mean CBF values in all of the 22 structures analysed, none of the changes were significant. The results confirm previous ones, in which overall CBF was measured, in showing that beta-adrenergic mechanisms have little effect on normal cerebrovascular tone. Following a single dose of propranolol, results obtained in hypercapnia were equally negative; neither did CBF fall significantly when propranolol was given by constant infusion during 15 min. Furthermore, local CBF did not differ between animals infused with dl-propranolol and d-propranolol. It is concluded that in the rat, propranolol has but small effects on the CBF response to hypercapnia, if any. The results reveal that local CO2 responsiveness, calculated as delta CBF/delta PCO2, varies with normocapnic flow rates.

Effects of immobilization stress on regional cerebral blood flow in the conscious rat

Immobilization stress of conscious, normotensive, freely breathing 10-month-old Wistar-Kyoto rats produced an overall decline in regional cerebral blood flow (rCBF), as measured with [14C]iodoantipyrine, except at the frontal lobe. In 14 brain regions, rCBF fell by an average of 14.3% after 5 min of immobilization and by 11.9% after 15 min. Immobilization stress also stimulated hyperventilation and thereby reduced PaCO2. The slope relating rCBF to PaCO2 averaged 1.5 ml 100 g-1 min-1 mm Hg-1 in 9 significantly affected regions. The findings suggest that rCBF declines during immobilization stress because of cerebrovascular constriction caused by a reduction in PaCO2. Comparison of the average slope with published values in indicates furthermore that were PaCO2 to remain unchanged during immobilization, rCBF would increase by at most 20%.

Canine cerebral metabolism and blood flow during hypoxemia and normoxic recovery from hypoxemia

There are conflicting reports regarding the effects of hypoxemia on the cerebral metabolic rate for oxygen (CMRO2). Accordingly, we examined the changes in CMRO2 during normoxia, progressive hypoxia (PaO2 of 37, 27, and 23 mm Hg), and normoxic recovery from hypoxia. Measurements were made in dogs anesthetized with nitrous oxide (60-70%) and halothane (less than 0.1%) in oxygen. Arterial-cerebral venous blood oxygen content differences and cerebral blood flow (CBF) were measured simultaneously, the latter by a technique (collection of sagittal sinus outflow) previously validated for conditions of near-maximal CBF. The duration of each of the three hypoxic exposures was approximately 10 min. CMRO2 was significantly decreased (14%) only when the arterial blood oxygen tension was reduced to 23 mm Hg. CBF increased progressively to a maximum of 153% of control. Posthypoxemic brain biopsy values for cerebral metabolites obtained 40 min after normoxemia had been restored were normal. These results, in conjunction with an unchanged CMRO2 at 40 min normoxic recovery, suggest that no gross irreversible brain cell damage occurred. We conclude that with progressive hypoxemia, CMRO2 remains stable until oxygen demand exceeds oxygen delivery, resulting thereafter in a progressive reduction in CMRO2.