Ischemic anoxia and cerebral serotonin levels

Exposure to prenatal carbon monoxide and postnatal hyperthermia: short and long-term effects on neurochemicals and neuroglia in the developing brain

The effects of prenatal exposure to carbon monoxide (CO), a major component of cigarette smoke, was studied alone or in combination with postnatal hyperthermia, on the structural and neurochemical development of the postnatal brain at 1 and 8 weeks. Pregnant guinea pigs (n = 11) were exposed to 200 p.p.m CO for 10 h/day from midgestation until term (68 days), whereas control mothers (n = 10) breathed room air. On postnatal day 4, neonates from the control and CO-exposed pregnancies were exposed to hyperthermia (35 degrees C) for 75 min or remained at ambient (23 degrees C) temperature. Using semiquantitative immunohistochemical techniques the following neurotransmitter alterations were found in the medulla at 1 week: a decrease in met-enkephalin-immunoreactivity (IR) following postnatal hyperthermia and an increase in 5-hydroxytryptamine-IR following a combination of CO and hyperthermia. No alterations were observed in substance P- or tyrosine-hydroxylase-IR in any paradigm. At 8 weeks of age the combination of prenatal CO exposure followed by a brief hyperthermic stress postnatally resulted in lesions throughout the brain and an increase in glial fibrillary acidic protein-IR in the medulla. Such effects on brain development could be of relevance in cardiorespiratory control in the neonate and could have implications for the etiology of Sudden Infant Death Syndrome, where smoking and hyperthermia are major risk factors.

The neuroprotective effect of DL-tetrahydropalmatine in rat heatstroke

After the onset of heatstroke, rats with saline injection displayed hyperthermia, decreased mean arterial pressure, decreased cerebral blood flow, increased brain monoamine release, and increased neuronal damage score compared with those of normothermia, control rats. The heatstroke-induced hyperthermia, arterial hypotension, cerebral ischemia, brain monoamine overload, and cerebral neuronal injury were attenuated by pretreatment with dl-tetrahydropalmatine. The data indicate that DL-tetrahydropalmatine pretreatment provides neuroprotective effect in heatstroke.

Heatstroke-induced cerebral ischemia and neuronal damage. Involvement of cytokines and monoamines

Experiments were carried out to ascertain whether the levels of brain monoamines and cytokines are involved in the heatstroke-induced cerebral ischemia and neuronal damage. Heatstroke was induced by exposing anesthetized rats to a high ambient temperature of 42 degrees C; the moment at which the mean arterial pressure began to decrease from its peak level was taken as the onset of heatstroke. It was found that, during the heatstroke-induced cerebral ischemia and neuronal damage, the extracellular concentration of either dopamine, serotonin or norepinephrine were increased in the hypothalamus, the corpus striatum and other brain regions. In addition, the concentration of interleukin-1 (IL-1), IL-6 and tumor necrosis factor in both the plasma and brain was also increased during heatstroke-induced cerebral ischemia and neuronal damage. Heatstroke-induced cerebral ischemia and neuronal damage were attenuated by depletion of brain dopamine or serotonin produced by intracerebral injection of 6-hydroxydopamine or 5,7-dihydroxytryptamine, respectively. Accordingly, the survival of these heatstroke rats was increased after brain dopamine or serotonin depletion. Furthermore, heatstroke-induced cerebral ischemia, neuronal damage and monoamine accumulation were attenuated by blockade of IL-1 receptor produced by treatment with an IL-1 receptor antagonist. The survival of the heatstroke rats was also increased after induction of heat shock protein. The results suggest that marked accumulation of either dopamine, serotonin or IL-1 in brain is important for the occurrence of heatstroke-induced cerebral ischemia and neuronal damage in rats. The survival of these heatstroke rats can be increased by inhibition of IL-1 receptors or monoamine system in brain as well as by induction of heat shock protein.

Impairment of blood-brain barrier function by serotonin induces desynchronization of spontaneous cerebral cortical activity: experimental observations in the anaesthetized rat

The possibility that elevation of serotonin in the circulation, which is found in various pathological states, influences the spontaneous cerebral cortical activity was examined in a rat model. The electroencephalogram was recorded using bipolar epidural electrodes placed over the frontal and parietal cerebral cortex. Intravenous infusion of serotonin (10 micrograms/kg per min for 10 min) decreased the electroencephalogram amplitude in both frontal and parietal recordings within 4 min of infusion. This decrease in amplitude was reversible, Pretreatment with cyproheptadine (a potent serotonin2 receptor antagonist) prevented the serotonin-induced decrease of the electroencephalogram amplitude. The blood-brain barrier permeability to Evans Blue and [131I]sodium was increased in frontal and parietal cortex. This increase in blood-brain barrier permeability was absent in animals pretreated with cyproheptadine. These results provide direct evidence that an elevated level of serotonin in blood has the capacity to influence spontaneous cortical electrical activity. This effect of serotonin on electroencephalogram appears to be due to its ability to enter into the brain parenchyma by inducing a short-term breakdown of the blood-brain barrier, probably via serotonin2 receptors.

Mechanisms of drug actions against neuronal damage caused by ischemia--an overview

1. Oxygen and energy deficits induces a cascade of pathological processes which lead to neuronal dysfunction and cell death. 2. The pathogenesis of ischemia-induced neuronal damage includes a disturbed calcium homeostasis, an excessive release of EAA and an enhanced formation of free oxygen radicals. 3. Calcium antagonists inhibit Ca2+ influx into the neuronal cell via VSCC. 4. Glutamate antagonists reduce intracellular Ca2+ concentration by inactivation of NMDA receptor-associated calcium channels (NMDA antagonists) or AMPA/quisqualate receptor-linked sodium channels (non-NMDA antagonists). 5. Furthermore, oxygen radical scavengers can avoid neuronal damage. 6. Agonists of the adenosinergic and serotonergic transmitter systems contribute to neuroprotection by hyperpolarization of the neuronal membrane due to an increase of K+ permeability.

Serotonin release into plasma during common carotid artery thrombosis in rats

BACKGROUND AND PURPOSE

We have tested the hypothesis that platelet-derived serotonin is released into the bloodstream during cerebrovascular thrombosis.

METHODS

Nonocclusive common carotid artery thrombosis was produced photochemically in 22 anesthetized adult male Wistar rats using the photosensitizing dye rose bengal and irradiation with an argon-pumped dye laser. Plasma serotonin levels were recorded before, during, and after photothrombosis by intra-arterial in vivo microdialysis with the probe placed distal to the site of thrombosis.

RESULTS

During and immediately after the common carotid artery thrombosis, serotonin levels increased significantly to a peak value of 781 nmol/l (p less than 0.001 by analysis of variance), representing a 15-fold increase compared with baseline levels. The increased serotonin levels gradually decreased but remained significantly elevated for 90 minutes. Ultrastructural analysis of the carotid thrombi identified a dense mass of aggregated platelets at various stages of degranulation.

CONCLUSIONS

These results are the first to demonstrate directly that serotonin accumulation occurs in plasma during and after the acute phase of common carotid artery thrombosis. Increased plasma serotonin levels may play a major role in the cerebral blood flow and blood-brain barrier abnormalities previously documented in this model of large-vessel thrombotic stroke.

Serotonin may have neurotoxic properties

Serotonin (5HT), a major platelet secretory product, has been shown to suppress CNS function in vivo. As part of an ongoing project to study interactions between neuron and platelet, we used organotypic explant cultures of rat spinal cord to study if 5HT had a morphologically demonstrable neurotoxic effect. The results suggest that serotonin may be neurotoxic, and that this effect may be prevented by ketanserin, a specific 5HT2 antagonist. Related experiments, using acetylcholinesterase (AChE) enzyme activity as a biochemical parameter, indicate that 5HT hastens the decline of enzyme activity. The concentrations of 5HT at which neurotoxicity was demonstrated were comparable to the calculated 5HT concentration potentially present in the vicinity of an acute cerebral thrombus. These findings could provide new insight into the mechanism of ischemic neuronal injury.

Platelet secretory products may contribute to neuronal injury

BACKGROUND

We do not fully understand the mechanisms for neuronal damage following cerebral arterial occlusion by a thrombus that consists mainly of platelets. The view that certain endogenous substances, such as glutamate, may also contribute to neuronal injury is now reasonably well established. Blood platelets are known to contain and secrete a number of substances that have been associated with neuronal dysfunction. Therefore, we hypothesize that a high concentration (approximately several thousand-fold higher than in plasma, in our estimation) of locally released platelet secretory products derived from the causative thrombus may contribute to neuronal injury and promote reactive gliosis.

SUMMARY OF COMMENT

We have recently been able to report some direct support for this concept. When organotypic spinal cord cultures were exposed to platelet and platelet products, a significant reduction in the number and the size of the surviving neurons occurred in comparison with those in controls. We further observed that serotonin, a major platelet product, has neurotoxic properties. There may be other platelet components with similar effect.

CONCLUSIONS

The hypothesis of platelet-mediated neurotoxicity gains some support from these recent in vitro findings. The concept could provide a new area of research in stroke, both at the clinical and basic levels.

Changes in blood-brain barrier and cerebral blood flow following elevation of circulating serotonin level in anesthetized rats

Plasma serotonin (5-HT) was elevated by an intravenous infusion of this amine into urethane-anaesthetized rats and the concentration approximated that present in various neurological diseases and mental abnormalities. An infusion of 10 micrograms per kg body weight for 10 min significantly increased blood-brain barrier (BBB) permeability to Evans blue and 131I-sodium measured in whole brain. Regional BBB determinations with labelled 131I-sodium showed that the permeability to this compound was increased in the cerebral cortex, hippocampus, caudate nucleus, hypothalamus, colliculus and the cerebellum but not in the pons and the medulla oblongata. Regional blood flow was reduced in the same parts which showed BBB abnormality tested with 125I-labeled microspheres. Pretreatment with cyproheptadine, a 5-HT2 receptor antagonist, prevented the BBB increase and the regional blood flow was near normal values. Similar effects were obtained with indomethacin, a prostaglandin synthesis inhibitor. Vinblastine, known to influence vesicular transport, eliminated extravasation of the tracers but the regional blood flow remained depressed. A hypothesis is put forward that serotonin after binding to its receptor in the cerebral vessels stimulates prostaglandin which either directly or by means of cyclic adenosine monophosphate causes an increased vesicular transport across the endothelial cells and thus an extravasation of tracer substances in the brain. Obviously, this form of exudation can be influenced by pharmacological means.

Effect of the serotonin antagonist ketanserin on the hemodynamic and morphological consequences of thrombotic infarction

The effect of the serotonin (5-hydroxytryptamine, 5-HT) antagonist ketanserin on the remote hemodynamic consequences of thrombotic brain infarction was studied in rats. Treated rats received an injection of 1 mg/kg ketanserin 30 min before and 1 h following photochemically induced cortical infarction. Local CBF (LCBF) was assessed autoradiographically with [14C]iodoantipyrine 4 h following infarction, and chronic infarct size was documented at 5 days. Thrombotic infarction led to significant decreases in LCBF within noninfarcted cortical regions. For example, mean LCBF was decreased to 63, 55, and 65% of control (nontreated normal rats) in ipsilateral frontal, lateral, and auditory cortices, respectively. In rats treated with ketanserin, significant decreases in LCBF were not documented within remote cortical areas compared with controls. In contrast to these hemodynamic effects, morphological analysis of chronic infarct size demonstrated no differences in infarct volume between treated (27 +/- 3 mm3) and nontreated (27 +/- 6 mm3) rats. These data are consistent with the hypothesis that 5-HT is involved in the widespread hemodynamic consequences of experimentally induced thrombotic infarction. Remote hemodynamic consequences of acute infarction can be inhibited without altering final infarct size.

Impairment of cerebellar blood flow autoregulation during cerebral ischemia in spontaneously hypertensive rats

Participation of the autonomic nervous system in cerebellar autoregulation during supratentorial cerebral ischemia induced by bilateral carotid ligation was studied using 23 spontaneously hypertensive rats. Cerebral and cerebellar blood flows measured by a hydrogen clearance method were evaluated under stepwise hemorrhagic hypotension before and 30 minutes after ligation and after a 30-minute recirculation period following 1 hour of ligation. alpha-Adrenergic blockade with phenoxybenzamine, beta-adrenergic blockade with propranolol, and muscarinic cholinergic blockade with atropine were selectively administered before ligation for inhibition of sympathetic and parasympathetic tone. Cerebral blood flow autoregulation was severely impaired during and after cerebral ischemia in each treatment group. During cerebral ischemia, cerebellar blood flow autoregulation was also significantly impaired in both the propranolol and atropine groups although it was better preserved in the phenoxybenzamine group. After recirculation, cerebellar blood flow autoregulation recovered almost to the normal range in the phenoxybenzamine and atropine groups but remained impaired in the propranolol group. Our results suggest that impaired cerebellar blood flow autoregulation in supratentorial cerebral ischemia is partly modulated by the alpha-adrenoceptor system, which is activated by hypertensive stimuli and cerebral ischemia, leading to vasoconstriction in the cerebellum.

A follow-up study of platelet-rich plasma serotonin in clinical subtypes of cerebral infarction

The serotonin concentration in the platelet-rich plasma of 32 patients with single and multiple stroke type cerebral infarction was investigated at various stages. Serotonin levels were decreased in the acute period. The incidence of serotonin abnormality was higher in multiple types than in the single type. Serotonin levels were significantly decreased in treated hypertensive patients compared with untreated patients. Serotonin levels, therefore, varied according to the type and stage of cerebral infarction.

Photochemically induced cerebral infarction. II. Edema and blood-brain barrier disruption

Alterations in the blood-brain barrier to proteins, and regional water and electrolyte content were documented in a rat model of photochemically induced small-vessel thrombosis leading to infarction. Horseradish peroxidase (HRP) or Evans blue was given immediately following a 2-min photochemical sensitization period. At 5 min following irradiation, multifocal sites of peroxidase extravasation were noted within the irradiated area. Ultrastructural examination revealed endothelial cells filled with HRP which in some cases extended into the basal lamina and extracellular spaces. At 15 min, protein leakage was more pronounced within the irradiated zone and reaction product was also apparent within the subarachnoid and perivascular spaces of brain regions remote from the site of irradiation. Widespread staining on the surface of the irradiated hemisphere was apparent in rats perfused 8 h following Evans blue infusion. Water content increased significantly by 15 min within the irradiated zone but not in brain regions remote from this site. Although vasogenic edema is an early event in this stroke model, increases in water content are restricted to the irreversibly damaged site. In contrast, protein tracer escaping from microvessels coursing within the irradiated zone was widely distributed. These findings implicate endothelial barrier dysfunction in the genesis of tissue injury in this model. Morphological evidence for the capability of macromolecules to escape from a site of evolving infarction and to migrate to distances remote from the area of primary microvascular damage is also discussed.

Photochemically induced cortical infarction in the rat. 1. Time course of hemodynamic consequences

Alterations in local CBF (LCBF) were assessed autoradiographically in the rat at several time points following photochemically induced cortical infarction. Cortical infarction of consistent size and location was produced by irradiating the brain with green light through the intact skull for 20 min following the systemic injection of rose bengal. A consistent pattern of altered LCBF was recorded in both ipsilateral and contralateral brain regions over the course of the study. At 30 min, a severely ischemic zone surrounded by regions of cortical hyperemia was apparent. LCBF was also depressed relative to control values in ipsilateral cortical regions remote from the irradiated area, while contralateral cortical structures were mildly hyperemic. By 4 h, the zone of severe ischemia had enlarged and its margins were no longer hyperemic. Ipsilateral cortical and some subcortical structures demonstrated significantly depressed levels of LCBF. At 5 days, LCBF throughout both ipsilateral and contralateral cortices was depressed compared with control values. By 15 days, LCBF had returned to control levels in most brain structures shown histopathologically not to be irreversibly damaged. The temporal sequence and magnitude of these hemodynamic alterations are consistent with findings in clinical studies in which repeated measurements of CBF have been carried out in patients with acute stroke. The ability to produce a cortical infarct that results in a consistent pattern of altered CBF should facilitate the investigation of stroke mechanisms responsible for these hemodynamic abnormalities.

Biochemical effects of cerebral ischemia: relevance to migraine

Although decreased CBF has now been reported during the prodrome of migraine, the cause of the decreased flow is still unknown. It is particularly unclear whether these phenomena are related to vasospasm and "steal" between the extracranial and intracranial circulation or to the spreading depression of Leao and the accompanying metabolic depression. In the present paper, metabolic changes in the brain during ischemia and reperfusion are reviewed and compared with CNS biochemical changes during migraine attack. In addition, the technique of Topical Magnetic Resonance (TMR) as applied to the in vivo study of energy phosphate metabolism in extracranial tissues and brain is described and the potential of this technique to evaluate shifts in energy metabolism and pH in stroke and migraine is discussed.

Changes in ambulation and drinking behavior related to stroke in stroke-prone spontaneously hypertensive rats

In order to elucidate the behavioral changes related to stroke, ambulatory activity and water drinking were observed in stroke-prone spontaneously hypertensive rats (SHRSP). Age matched male SHRSP and Wistar Kyoto rats (WKY) were subjected to a 12 hour light and dark alternation cycle. Ambulation and drinking activity counts were determined simultaneously with an Ambulo-Drinkometer. Before stroke, ambulation and drinking activity counts in the dark phase (82%) were higher than those in the light phase (18%). Both parameters were well synchronized with the light and dark alternation cycle. With aging, daily ambulation decreased while daily drinking activity increased in SHRSP and WKY. Daily ambulation and drinking activity in 15 and 30 week old SHRSP were greater than those of WKY. It was demonstrated with an Ambulo-Drinkometer that SHRSP undergo specific behavioral changes before the onset of stroke. For instance, the 40-60 week old SHRSP showed significant individual variation in both ambulation and drinking activity. This desynchronization with the light and dark alternation cycle was followed by stroke. Twenty seven autopsies showed 11 cerebral infarctions, 10 cerebral hemorrhage and 6 cerebral hemorrhage with infarctions to be the causes of death.

Immunohistochemical and electron microscopic demonstration of vascular innervation in the mammalian brainstem

Ultrastructural morphological relationship between microvessels and neural elements containing serotonin-like immunoreactivity, substance P and methionine-enkephalin like immunoreactivity were studied in the monkey and cat brain. A close relationship between serotonin-like immunoreactive dendritic processes, enkephalin-like immunoreactive profiles and capillary basement membrane was observed; they were usually separated by a double layer of glial membrane. More importantly, serotonin and substance P-like immunoreactive dendritic profiles are reported in close approximation with capillary basement membrane with no glial limitans at the site of contact. These intimate morphological associations may be the basis for neural regulation of tonicity, permeability and chemosensor function in the brain microvasculature.

Effect of omental transposition on to the brain on the cortical content of norepinephrine, dopamine, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in experimental cerebral ischaemia

Local cerebral ischaemia causes a significant decrease in norepinephrine, dopamine, 5-hydroxytryptamine in the cortical brain tissue of rabbits, associated with an increase in 5-hydroxyindoleacetic acid. Previous transposition of the omentum on to the brain surface maintains, to a large extent, physiological levels of these metabolites. This study stresses the role of the transposed omentum in reducing the effects of experimental occlusion of a major cerebral artery.

Brain hypoxia: the turning-point in the genesis of the migraine attack?

The hypothesis postulates that a brief episode of focal cerebral hypoxia occurs in every attack of migraine. Clinical biochemical and technical (EEG and CT scans) evidence is summarized suggesting that cerebral hypoxia is seen as the turning-point in the pathogenesis of the attack. It may be provoked by different mechanisms in different patients; the potential role of decreased oxygen supply and of increased oxygen need are reviewed and excess sympathetic drive is considered a potential key mechanism in a majority of patients. Whether or not focal hypoxia leads to a genuine migraine attack, depends largely upon the quality of the whirlpool of biochemical, vascular and hematological changes that follow the hypoxic episode. These changes are discussed and it is concluded that those which have been reported to occur during migraine attacks could be due to a preceding hypoxic event. Finally, the hypoxia viewpoint is confronted with some popular theories about the pathogenesis of migraine. It is found that the other points of view are compatible with the hypoxia hypothesis.

Cortical injury without ischemia produced by topical monoamines

Responses to monoamines perfused over the cortical surface through modified pial windows were monitored in 106 cats. Norepinephrine (NE) and serotonin (5-HT) were diluted in mock CSF to concentrations of 50 and 500 ng/ml respectively, levels at or near the maximum concentrations to which the cortical surface might be exposed in subarachnoid hemorrhage or damage to nearby neurons. Each cat had simultaneous one-hour perfusions of monoamine solution over one hemisphere and a control solution over the other hemisphere thus serving as its own control. The perfusion solutions were observed to be restricted to the area of the pial window, and minimal histological damage was seen with the perfusion technique. The 5-HT perfusions were associated with an almost 20% narrowing of small pial arteries and arterioles but no significant effect on regional cerebral blood flow (rCBF), cortical water content or cortical function as monitored by EEG and somatosensory evoked potentials (SEP). In contrast, NE caused cortical edema and changes in the EEG and SEP's without significant vascular effect. These results suggest a non-ischemic toxicity of NE released by subarachnoid hemorrhage or cerebral damage.

Nerve endings and pharmacological receptors in cerebral vessels

1. The cerebral vessels possess adrenergic, cholinergic, serotonergic and peptidergic innervations. 2. The cerebral vessels have alpha- and beta-adrenergic, cholinergic, serotonergic, histaminergic H1 and H2 and dopaminergic receptors whose activation by different agents causes vasomotor responses. 3. The induced effects by noradrenaline, adrenaline and serotonin are characterized by a cerebral vasoconstriction clearly manifested in man, the awake or anesthetized animal and isolated vessels. The vasoconstrictor response generally obeys an activation of specific receptors. 4. Under experimental conditions acetylcholine, histamine, dopamine and isoproterenol relax these vessels, in which cholinergic, H2-histaminergic, dopaminergic and beta-adrenergic (beta 1) receptors are implicated, respectively.

Histochemical changes of brain dopamine in an acute stage of cerebral ischemia in gerbils

The fluorescence histochemical method of Falck et al. was applied to 40 gerbil brains after ligation of a unilateral common carotid artery to investigate alterations of brain dopamine in the acute stage of cerebral ischemia. The distribution of dopaminergic terminals and cell bodies in gerbils is the same as in other mammals. On the ligated side after one hour of ischemia, diffuse green fluorescence of dopaminergic terminals showed only a slight decrease in intensity when compared to the nonligated side. But white matter and bundles of myelinated fibers adjacent to and in the dopamine-rich regions had an intense green fluorescence in contrast to the non-ligated side where they are normally non-fluorescent. This is considered to indicate the extraneuronal leakage and diffusion of dopamine. The intensity of extraneuronal green fluorescence was especially high in glial cells. Occasionally, there was also an unusual green fluorescence in the lumen of small vessels in dopamine-rich regions on the ligated side. Dopaminergic cell bodies in the substantia nigra on the ligated side revealed a conspicuous reduction in the fluorescence intensity in severely affected cases. After 2 or 3 hours of ischemia, there was a marked reduction or disappearance of the diffuse green fluorescence on the ligated side. This may be attributed in part to further diffusion of leaked dopamine.

Homovanillic acid and 5-hydroxyindoleacetic acid in the ventricular CSF of comatose patients with obstructive hydrocephalus

Ventricular cerebrospinal fluid (CSF) levels of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were determined every 2 to 4 hours over a period of 1 to 4 days in 12 patients, consisting of seven cases of brain tumor, two cases of cerebrovascular disease, and three cases of head injury. The concentrations of HVA and 5-HIAA varied with time in all cases, and significant correlations were found between the two values in eight cases. However, the relationship between variations of HVA and 5-HIAA levels and rhythms of sleep and waking could not be clarified. Both HVA and 5-HIAA concentrations varied at high levels in two patients whose CSF flow was completely blocked by tumor at the site of the fourth ventricle and aqueduct, respectively. On the contrary, in a case with craniopharyngioma in the third ventricle which blocked the bilateral foramina of Monro, although the HVA values were high, the 5-HIAA values varied at low levels. Of five comatose patients, two had cerebrovascular lesions and three had sustained head injury, and, in four of the five, the values of either one or both of HVA and 5-HIAA were low, but in the fifth case the 5-HIAA value was high. Estimation of HVA and 5-HIAA concentrations in ventricular CSF may be a valuable tool in the investigation of brain monoamine metabolism. However, many factors must be considered in the interpretation of results of clinical studies.

Survival of the ischemic brain: a progress report

The number of patients with cerebral infarctions increases as the population ages, despite campaigns against hypertension, the greatest risk factor. Cerebral ischemia initiates events that are presumed to defer the stage of irreversible injury. These events cause an increase of perfusion around the central ischemic zone and trigger the Bohr effect, both of which preserve tissue viability. Almost simultaneously, mitochondrial function fails, resulting in insufficient energy for the enzyme systems to control Na and K ion equilibrium. At the same time, protein synthesis slows and cellular respiratory enzymes decrease their activity, initiating an irreversible state of tissue change. Tissue fatty acids increase as a result of dissolution of cell membrane lipoprotein structure. Barbiturates reduce the extent of experimental infarction. Resperine and aminophylline are also effective, but there are no corroborative clinical trials. That ischemic brain damage may be the result of toxic substances in the ischemic tissue represents a new concept.

Influence of cerebral embolism on brain monoamines

In baboons the right cerebral hemisphere was embolised by a shower of microemboli, immediately followed by one large embolus designed to occlude the middle cerebral artery (MCA). One hour after embolism a significant, though small, reduction in blood flow and oxygen consumption of the embolised hemisphere was recorded, at which time the animals were killed and brain monoamines measured. Dopamine was reduced in the ipsilateral caudate nucleus, the reported site of maximal ischaemic damage in this model. Dopamine levels were increased in frontal and occipital grey matter sampled from areas surrounding the occluded MCA territory and in similar brain areas of the opposite non-embolised hemisphere. Noradrenaline was increased in grey matter from both cerebral hemispheres, as well as subcortical structures bilaterally. Brain 5-hydroxytryptamine levels were unaltered, but increased 5-hydroxyindoleacetic acid in cisternal cerebrospinal fluid suggested transient alteration in 5-hydroxytryptamine metabolism after embolism. The effects of cerebral embolism on brain monoamine metabolism appear to be different from the effects of permanent surgical occlusion of major cerebral vessels. The bilaterality of effects after unilateral hemispheric embolism might be related to diaschisis. The mechanisms of the observed changes, as well as their relevance to the progression of cerebral ischaemia and the complications associated with cerebral embolism, still require to be established.

New ultrastructural evidence for a protein transport system in endothelial cells of gerbil brains

Pathways for transfer of horseradish peroxidase (HRP) across the cerebral microvasculature were studied in Mongolian gerbils after inducing either unilateral carotid-artery ligation or intracarotid air embolism. Electron microscopy on samples from both ipsilateral and contralateral brain hemispheres showed the reaction product (HRP) in the endothelial cytoplasm of capillaries and arteriols in all animals; in the basal lamina, HRP was seen only after long (3--4 h) ischemic periods. HRP was seen within both spherical and tubular structures, with the latter appearing in obliquely or longitudinally sectioned blood vessels. These endothelial channel-like structures are part of a tubulovesicular network which seemingly exists in the normal endothelium of the gerbil brain. The tubules serve as pathways for proteins into the brain; protein transfer becomes enhanced following circulatory injuries such as ischemia.

Plasma serotonin contents in cerebrovascular disease

The plasma serotonin contents of fourty-three cerebrovascular patients were examined. 1. Abnormal serotonin contents were found in 72 per cent of fourty-three cerebrovascular patients. 2. In cerebral hemorrhage, serotonin contents were significantly low in the acute period. 3. Serotonin contents in cerebral hemorrhage and subarachnoid hemorrhage, had an increasing tendency from the fourth week to the eigth week, but after the eighth week, they returned to normal.

Ischemia-induced seizures and cortical monoamine levels

Seizure activity as a component of the ischemic process possibly responsible for monoamine changes described in the gerbil stroke model was the subject of this study. Abnormal motor activity suggestive of seizures developed one to three hours after unilateral ligation of the common carotid artery in approximately 50% of gerbils that exhibited signs of stroke. Reduction of cortical levels of dopamine and norepinephrine was observed only when seizures occurred in association with stroke. The levels of 5-hydroxytryptamine were reduced bilaterally in animals with and without signs of stroke and were reduced further in animals with stroke plus seizures. Further study is needed to establish whether the catecholamine changes associated with ischemia-induced seizures are primary and causative or secondary to seizure activity itself. In the ischemic brain, 5-hydroxytryptamine metabolism appears disordered independent of seizure activity. Seizure activity must be taken into account when the mechanisms of disordered monoamine metabolism are being examined in the gerbil stroke model.

Cathecholamine and 5-hydroxytryptamine levels in ischemic brain. Influence of p-chlorophenylalanine

The effect of ischemia on catecholamine and 5-hydroxytryptamine (5-HT) levels in brain cortex was examined in the gerbil stroke model. Unilateral common carotid artery occlusion produced bilateral decrease in cortical dopamine levels in gerbils both symptomatic and asymptomatic of cerbral ischemia. The 5-HT progressively decreased only in the occluded hemisphere of ischemic animals. In p-chlorophenylalanine (PCPA)-treated gerbisl, dopamine decreased only in the occluded hemisphere of symptomatic animals, but norepinephrine became decreased bilaterally compared with controls. The 5-HT decrease was twice that seen in untreated animals. It is suggested that these results indicate initial release together with reduced synthesis of monoamines in ischemic brain. The incidence of ischemia induced by carotid occlusion decreased from 44% to 26% in PCPA-treated animals, which also suggests that depletion of 5-HT available for neuronal release prior to the induction of ischemia may reduce stroke incidence by limiting impairment of collateral vasocapacitance. PCPA pretreatment did not influence the development of edema in the occluded hemisphere of ischemic animals once ischemia was established.

Coagulopathy following experimental cerebral ischemia

In adult normothermic cats cerebral blood flow was interrupted for 1 hour by clamping the innominate and subclavian arteries. Following ischemia the brains were recirculated with blood, and the coagulation system was investigated by measuring coagulation times and blood content of fibrinogen and platelets. Ischemia induced progressive consumption coagulopathy with an increase in coagulation times and a decrease of platelets and fibrinogen by more than 40%. Coagulopathy was accompanied by a respiratory distress syndrome with a significant increase in the alveolar-arterial carbon dioxide gradient from --3.3 to --13.5 mm Hg. A correlation was found between plasma fibrinogen concentration, cerebral blood flow and electrophysiological function, indicating that a relationship exists between the severity of postischemic coagulopathy and functional recovery following prolonged cerebral ischemia.

[Sleep EEG alterations in patients suffering from circulatory disturbances. Relation to neurological and psychopathological changes (author's transl)]

In 30 conscious patients (24 men, 6 women) aged 30-74 years suffering from ischemic lesions in the cerebral hemispheres, polygraphic night sleep recordings were performed about 45 days after the beginning of the illness. The alterations in sleep were characterized by a delay in the onset of sleep, prolonged waking periods, and a reduction of deep synchronous sleep. Statistical analysis revealed a relationship between prolonged waking time with higher age as well as with high complex reaction time and euphoric state of mind, which can be considered as a sign of psycho-organic impairment. In contrast thereto, the degree of the neurological symptomatology is of less importance for the kind and extent of the sleep disturbances.

Experimental cerebral ischemia in Mongolian gerbils. IV. Behaviour of biogenic amines

Behaviour of biogenic amines was studied in the brains of Mongolian gerbils subjected to unilateral occlusion of the common carotid artery. Assays on the hemispheres ipsilateral to occlusion revealed in symptom-positive animals a progressive decrease in norepinephrine and dopamine, and an increase in serotonin throughout the duration of an ischemic insult. In post-ischemic periods following the release of the clip, changes in biogenic amine levels generally conformed to the principles of a previously described "maturation" phenomenon, with delayed reactions occurring after the shorter ischemic insults.

XIII. Cerebral circulation and metabolism in stroke. Cerebral circulation and metabolism in stroke study group

An understanding of the cerebral circulation is so fundamental to comprehension of the pathogenesis of stroke that cerebral blood flow and metabolism merit review in this series of reports. The authors recognize that the research described here is very technical in nature and may appear to have little practical application to clinical medicine. Nevertheless, these matters are basic to the development of precise methods for the measurement of regional cerebral blood flow in man which could be used to monitor the therapy of stroke with greater success than is possible at present.

Constriction of pial arterioles produced by prostaglandin F2alpha

Prostaglandin F2alpha constricted pial arterioles when locally applied to the cerebral surface. Norepinephrine and serotonin each elicted similar contractile effects. The constriction produced by F2alpha in combination with either biogenic amine was greater than the constriction elicited by F2alpha or amine acting alone. The effect of one agent on the other was additive rather than potentiating. Since F2alpha norepinephrine and serotonin are all naturally occurring agents, it is possible that their combined effect is important under pathological circumstances and this combined effect should not be overlooked in the search for single spasmogens of great potency. Before ascribing a pathologically important effect of F2alpha, either alone or in combination, evidence is required showing that doses effective in experiments are similar to the concentrations occurring during disease states and/or that vessels may become hypersensitive to F2alpha during such states.

Enhanced vesicular transport of exogenous peroxidase across cerebral vessels, induced by serotonin

Previous studies have revealed that the endothelial cells of cerebral vessels are linked by tight junctions preventing an intercellular passage of exogenous peroxidase. However, under normal conditions, vesicular transport of the tracer has been demonstrated in parts of cerebral vessels, especially in arterioles with a diameter of 30-100 mu. Solutions, containing 50-800 mug of buffered 5-hydroxytryptamine sulphate (serotonin), were perfused through the cerebral ventricles on mice after intravenous injection of horseradish peroxidase. Usually, the biogenic amine enhanced the vesicular transport of exogenous peroxidase. The serotonin-induced increased transport was observed in vessels on the surface of the brain as well as in vessels located in the parenchyma. No cell damage was observed. Increased transport was observed in arterioles, venules, and in capillaries. Therefore, it is not likely that the serotonin effect is a constriction of smooth muscle cells causing an opening of the tight junctions followed by an intercellular movement of tracer. The most reasonable assumption behind the mechanism is that serotonin affects the plasmamembrane of endothelial cells resulting in an enhanced production and transfer of cytoplasmic vesicles.

Cerebral metabolic changes during treatment of subacute cerebral infarction by alpha and beta adrenergic blockade with phenoxybenzamine and propranolol

Cerebral hemispheric blood flow (HBF) and metabolism were measured in 30 patients with acute and subacute cerebral infarction before and after intracarotid infusion of the alpha adrenergic blocking agent phenoxybenzamine (PBZ) or the beta adrenergic blocker propranolol (PPL) dissolved in saline. Following intracarotid injection of 7 µg per kilogram per minute PBZ, HBF showed no change but cerebral hemispheric oxygen consumption (HMIO 2 ) and carbon dioxide production (HMICO 2 ) decreased. Glucose consumption (HMIGl) was unchanged but the glucose to oxygen utilization ratio (HG:O) increased. Intracarotid injection of 1.45 µg per kilogram per minute PPL caused reduction of HBF, HMIO 2 , HMICO 2 , HMIGl and HG:O. After PBZ infusion, mean systemic arterial blood pressure (MABP) decreased slightly, intracranial venous pressure (ICVP) and CSF pressure (CSFP) increased, and central venous pressure (CVP) remained unchanged. PPL infusion had no effect on intracranial dynamics.

Possible mechanisms whereby PBZ and PPL influence cerebral metabolism and function were discussed. Inhibition of uncoupling of oxidative phosphorylation appeared to be the most likely explanation for the improvement in brain function and metabolic change associated with each of the drugs. These data support the concept that catecholamines released into brain tissue are a possible cause of uncoupled oxidative phosphorylation.

Presently available evidence suggests that adrenergic blocking agents warrant clinical evaluation in the treatment of acute cerebral ischemia, infarction, hemorrhage, and anoxia.

Barbiturate protection in acute focal cerebral ischemia

We have found that anesthetic technique modifies the neurological and pathological sequelae of unilateral middle cerebral artery and internal carotid artery occlusion in dogs. Occlusion was performed in seven groups of six dogs during each of the following anesthetic regimens: light (0.8%) halothane, "awake," deep (1.9%) halothane, deep halothane with mean arterial pressure reduced to 55 torr, pentobarbital (56 mg per kilogram), light halothane plus 40 mg per kilogram thiopental begun just before cerebral artery occlusion, and light halothane plus 40 mg per kilogram thiopental begun 15 minutes after occlusion. Body temperature, arterial P co co 2 P o o 2 pH, and blood pressure (except as noted above) were maintained normal. Neurological examinations were performed daily. On the seventh day the dogs were killed and their brains removed for pathological study. Hemiparesis occurred in five of six dogs under light halothane and five of six awake dogs; a mean of 10.8% and 9.6%, respectively, of their right hemispheres were infarcted. In the deep halothane groups, all of the normotensive and five of the six hypotensive dogs became severely hemiplegic; mean infarction size was 28.2% and 34.1%, respectively. Only one of the 18 dogs who received a barbiturate sustained a neurological deficit -- a transient unilateral weakness. Means of 1.4%, 2.7%, and 0.1% of the right hemisphere were infarcted in the barbiturate animals. The protective action of barbiturates in canine acute focal cerebral ischemia suggests that they should be considered for anesthesia in surgery requiring cerebral vessel occlusion and perhaps even for treatment of acute stroke.

Cerebrovascular response to intracarotid injection of serotonin before and after middle cerebral artery occlusion

The effect of intracarotid injection of serotonin (5-HT) on internal carotid artery flow and oxygen availability (O(2)a) of the cerebral cortex was studied in 10 baboons. Vasoconstriction occurred in the vascular bed of the territory supplied by the injected artery. After one middle cerebral artery was occluded the vasoconstrictor effect of 5-HT was more pronounced, particularly in the non-ischaemic hemisphere. The capacity of the cerebral vessels to provide collateral blood flow was reduced in both ischaemic and non-ischaemic areas of brain. As a result of focal cerebral ischaemia, 5-HT may accumulate in the brain and contribute to the progression of infarction.