Focal cerebral ischaemia in the rat: 1. Description of technique and early neuropathological consequences following middle cerebral artery occlusion

A procedure for occluding the stem of the proximal middle cerebral artery of the rat is described. The operation is performed under anaesthesia through a small subtemporal craniectomy. After occlusion, 3 animals were perfused with carbon block and 8 with a FAM fixative (40% formaldehyde, glacial acetic acid, and methanol). The findings were compared with sham-operated animals. Carbon black studies demonstrated an area of impaired perfusion corresponding to the territory of the occluded artery in each animal. Neuropathological studies invariably showed that there was ischaemic brain damage in the cortex and basal ganglia. The frontal cortex was involved in every animal, as was the lateral part of the neostriatum; the sensorimotor and auditory cortex were involved in most animals, whereas the occipital cortex and medial striatum were involved only infrequently. The damage produced by ischaemia could be readily distinguished from the small local lesion seen at the surgical site in sham-operated animals. The ability to produce a consistent focal ischaemic lesion in the rodent brain provides a technical approach that is sufficiently reproducible to enable investigation of the pathophysiology of ischaemia using recently developed autoradiographic and neurochemical methods.

The glutamate antagonist MK-801 reduces focal ischemic brain damage in the rat

Excessive activation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor has been implicated in the sequence of neurochemical events that results in irreversible neuronal damage in cerebral ischemia. The effects of the NMDA antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) upon the amount of ischemic brain damage has been assessed quantitatively in the lightly anesthetized rat. Focal cerebral ischemia was produced by the permanent occlusion of one middle cerebral artery (MCA), and the animals were killed 3 hours after the arterial occlusion. MK-801 (0.5 mg/kg) was administered intravenously either 30 minutes prior to MCA occlusion or 30 minutes after the induction of ischemia. Pretreatment with MK-801 reduced the volume of ischemic damage both in the cerebral cortex (by 38% compared with untreated rats with MCA occlusion; p less than 0.01) and in the caudate nucleus (by 18% compared with controls; p less than 0.05). Treatment with MK-801, initiated 30 minutes after MCA occlusion, reduced the volume of ischemic damage in the cerebral cortex (by 52% compared with controls; p less than 0.01). The volume of ischemic damage in the caudate nucleus was minimally influenced by MK-801 treatment initiated after MCA occlusion. The antiischemic effects of MK-801 were readily demonstrable despite the hypotension that MK-801 induced in rats anesthetized with halothane (0.5%), nitrous oxide (70%), and oxygen (30%). The potency of MK-801 in reducing ischemic brain damage, even when administered after the induction of ischemia, highlights the potential use of NMDA receptor antagonists for the treatment of focal cerebral ischemia in humans.

Reversible neural inactivation reveals hippocampal participation in several memory processes

Studies of patients and animals with brain lesions have implicated the hippocampal formation in spatial, declarative/relational and episodic types of memory. These and other types of memory consist of a series of interdependent but potentially dissociable memory processes-encoding, storage, consolidation and retrieval. To identify whether hippocampal activity contributes to these processes independently, we used a novel method of inactivating synaptic transmission using a water-soluble antagonist of AMPA/kainate glutamate receptors. Once calibrated using electrophysiological and two-deoxyglucose techniques in vivo, drug or vehicle was infused chronically or acutely into the dorsal hippocampus of rats at appropriate times during or after training in a water maze. Our findings indicate that hippocampal neural activity is necessary for both encoding and retrieval of spatial memory and for either trace consolidation or long-term storage.

Calcitonin gene-related peptide: functional role in cerebrovascular regulation

Distribution studies disclosed that all major cerebral arteries and cortical arterioles of the cat were invested with fine varicose nerve fibers that contained calcitonin gene-related peptide (CGRP)-like immunoreactivity; the trigeminal ganglia likewise contained CGRP immunoreactivity. Sequential immunostaining with antibodies to CGRP and to substance P (SP) revealed identical distributions of these two peptides in trigeminal ganglia and cerebrovascular nerve fibers, suggesting that CGRP and SP are colocalized in these nerves. CGRP completely disappeared from ipsilateral blood vessels after unilateral section of the trigeminal nerve. Exogenous CGRP was a potent relaxant of feline middle cerebral arteries in vitro (maximum relaxation, 10.5 +/- 1.5 mN; concentration eliciting half-maximal response, 9.6 +/- 1.3 nM). Perivascular microapplication of CGRP to individual cortical arterioles of chloralose-anesthetized cats provoked dose-dependent dilatations (maximum increase in diameter, 38 +/- 5%; concentration eliciting half-maximal response, approximately equal to 3 nM). CGRP was significantly more potent than SP as a cerebrovascular dilator, both in vitro and in situ. Chronic division of the ipsilateral trigeminal nerve in cats did not modify the magnitude of arteriolar responses to perivascular microapplication of either vasoconstrictor or vasodilator agents, but the duration of vasoconstrictor responses to norepinephrine (0.1 mM) or alkaline solutions (pH 7.6) was significantly increased. The cerebrovascular trigeminal neuronal system, in which CGRP is the most potent vasoactive constituent, may participate in a reflex or local response to excessive cerebral vasoconstriction that restores normal vascular diameter.

Innervation of the feline cerebral vasculature by nerve fibers containing calcitonin gene-related peptide: trigeminal origin and co-existence with substance P

The presence of a population of nerve fibers containing immunoreactive calcitonin gene-related peptide (CGRP) has been demonstrated around cerebral arteries of the cat with immunocytochemistry and radioimmunoassay. CGRP immunoreactivity in the feline cerebral vasculature, as characterized by high-performance liquid chromatography, is similar to authentic rat CGRP. Numerous perikarya containing CGRP are present in the trigeminal ganglia, and surgical lesions of the trigeminal ganglia significantly reduce the levels of CGRP in the cerebral vasculature, suggesting that this cranial nerve is the principal origin of these cerebrovascular nerve fibers. As demonstrated by sequential immunocytochemistry, CGRP coexists with substance P both in the trigeminal ganglion and nerve fibers around cerebral blood vessels. The presence of CGRP in the cerebrovascular trigeminal innervation provides further versatility and complexity for this sensory afferent system putatively involved in the transmission of intracranial pain.

Protective effect of the glutamate antagonist, MK-801 in focal cerebral ischemia in the cat

The effects of the glutamate N-methyl-D aspartate (NMDA) receptor antagonist, MK-801, upon ischemic brain damage has been examined in anesthetized cats. Focal cerebral ischemia was produced by permanent occlusion of one middle cerebral artery and the animal were killed 6 h later. The amount of early ischemic damage was assessed in coronal sections at 16 predetermined stereotactic planes. Pretreatment with MK-801 (5 mg/kg, i.v.), 30 min before occlusion of the middle cerebral artery significantly reduced the volume of ischemic damage (from 32.7 +/- 4.0% of the cerebral hemisphere in vehicle-treated cats to 16.2 +/- 4.5% in MK-801-treated cats). NMDA receptor antagonists that penetrate the blood-brain barrier, such as MK-801, merit further study as protective agents against ischemic brain damage.

Focal cerebral ischaemia in the rat: 2. Regional cerebral blood flow determined by [14C]iodoantipyrine autoradiography following middle cerebral artery occlusion

Local cerebral blood flow has been measured by quantitative autoradiography, employing [14C]iodoantipyrine as tracer, in rats killed half an hour after occlusion of the middle cerebral artery. The results were compared with pattern of local cerebral blood flow (CBF) in sham-operated rats and with neuropathological findings. In every animal there was a profound reduction (to 13% of control levels)in blood flow in the neocortex previously by the occluded artery. The level of blood flow in the areas in which ischaemic brain damage occurred was 0.24 +/- 0.03 ml g-1 min-1 (mean +/- SEM). this level of CBF is considerably greater than that reported following a similar surgical procedure in cats and primates. Moderate reductions in blood flow were also seen outside the territory of the occluded artery and in parts of the opposite hemisphere. Absolute increases in blood flow (hyperaemia) were seen only in the substantia nigra and globus pallidus ipsilateral to the occlusion. It is of the middle cerebral artery are reflections of alterations in neuronal function and metabolic activity secondary to the ischaemic lesion.

Neuropeptide Y: cerebrovascular innervation and vasomotor effects in the cat

Avian pancreatic polypeptide (APP) has been proposed to be a neurotransmitter in a subpopulation of sympathetic nerves. Here, we present immunocytochemical and pharmacological evidence that the structurally related peptide, neuropeptide Y (NPY), is likely to be the biologically active material in these nerves. Cerebral arteries from cats are invested with a dense network of NPY-containing nerve fibres, as demonstrated by immunocytochemistry. This immunoreaction is abolished by prior removal of the superior cervical ganglion. NPY causes strong contractions of cerebral arteries in vitro whereas APP has small effects on the vasomotor reactivity. The NPY-induced contractions were not inhibited by the alpha 2-adrenoceptor antagonist rauwolscine (10(-7) M) or the 5-hydroxytryptamine antagonist ketanserin (10(-7) M). The contractions were, however, sensitive to calcium removal or to the calcium antagonist diltiazem (10(-4) M).

Quantitative assessment of early brain damage in a rat model of focal cerebral ischaemia

A method for the volumetric assessment of early cerebral infarction, together with its statistical and biological validation, is described. In halothane anaesthetised rats the stem of the right middle cerebral artery was occluded and 3 hours later (with full monitoring of respiratory and cardiovascular status) the animals were killed by perfusion fixation. In normotensive normocapnic animals the volume of infarction was 52 +/- 4 mm3 in the cerebral cortex and 21 +/- 1 mm3 in the corpus striatum. The reproducibility of the volumetric assessment was found to be excellent (coefficient of correlation 0.995 on 18 replicate measurements). The minimum number of stereotactic levels which must be assessed to yield accurate volumetric measurements of infarction is 8. The method is sensitive at detecting alterations in the amount of infarction. For example, it can readily detect the increase in amount of structural damage in cerebral cortex following a transient episode of hypotension. This approach allows an objective assessment of drug therapy and management strategies in the treatment of cerebral infarction.

Calcitonin gene-related peptide and cerebral blood vessels: distribution and vasomotor effects

The innervation of cerebral blood vessels by nerve fibers containing calcitonin gene-related peptide (CGRP) and the vasomotor effects of this peptide are described for a number of different mammalian species. CGRP-immunoreactive nerve fibers were present in the adventitia of cerebral arteries in all species examined (guinea pig, cat, rabbit, rat, and mouse). Numerous perikarya containing CGRP immunoreactivity are demonstrable in the trigeminal ganglion of all species. In the cerebral perivascular nerve fibers and in trigeminal perikarya, CGRP is often colocalized with substance P and neurokinin A. Marked interspecies differences exist both in the density of CGRP-immunoreactive nerve fibers and in the cerebrovascular levels measured with radioimmunoassay. The highest concentrations were observed in cerebral vessels from guinea pigs, the lowest concentration in rabbit vessels, and intermediate levels in the feline and human cerebral vasculature. CGRP is a potent dilator of cerebral arteries in all species examined (human pial, feline middle cerebral, rabbit, guinea pig and rat basilar arteries). The concentration of CGRP eliciting half-maximal responses ranged from 0.4 nM (human pial artery) to 3 nM (rat and rabbit basilar arteries). Pretreatment of cerebral arteries with low concentrations of either substance P (0.1 nM) or neurokinin A (3 nM) attenuated slightly the CGRP-induced relaxations of guinea pig basilar arteries. Calcitonin was found to be a very weak dilator of cerebral arteries from human and guinea pig. Thus, cardiovascular nerve fibers containing CGRP appear to be present in all mammalian species (although to varying degrees) and CGRP is invariably a potent dilator of the cerebral arteries for all species.

Correlation between amino acid release and neuropathologic outcome in rat brain following middle cerebral artery occlusion

Using in vivo brain microdialysis, we studied amino acid release in the striatum and cortex of eight rats following permanent middle cerebral artery occlusion. We then processed all brains for histopathologic assessment of the volume of ischemic damage 4 hours after occlusion. Ischemic damage was varied by occlusion of the middle cerebral artery at a point either proximal (n = 4) or distal (n = 4) to the lenticulostriate vessels. Proximal occlusion elevated the dialysate contents of all amino acids. The largest increases occurred for the potentially neurotoxic amino acids aspartate and glutamate and for taurine (800-2,800% of basal efflux). We observed smaller increases for the "metabolic" amino acids (280-580% of basal efflux). Distal occlusion did not affect amino acid efflux in the striatum, and release in the cortex was significantly lower than that following proximal occlusion. We compared release data with acute histopathologic outcome. Proximal occlusion resulted in a large volume of ischemic damage in the cortex and striatum (25-48% of hemispheric volume). A smaller volume of ischemic damage was noted following distal occlusion (0-21% of hemispheric volume). The volume of ischemic damage and the amount of amino acid release were significantly correlated (p less than 0.05).

Cerebral circulation and norepinephrine: relevance of the blood-brain barrier

The systemic administration of norepinephrine has minimal effects on the cerebral circulation, perhaps due to blood-brain barrier mechanisms. To test hypothesis, the cerebrovascular effects of norepinephrine beyond the blood-brain barrier were studied in anesthetized baboons, Intraventricular norepinephrine (40 mug/kg) resulted in significant increases in cerebral blood flow (40%), cerebral oxygen consumption (21%), and cerebral glucose uptake (153%). Intracarotid hypertonic urea opens the blood-brain barrier by osmotic disruption; Consequent to hypertonic urea, the intracarotid infusion of norepinephrine, 50 ng/kg-min, significantly increase cerebral blood flow (49%), cerebral oxygen consumption (21%), and cerebral glucose uptake (76%), It appears probable that the cerebrovascular responses to norepinephrine are dependent on the integrity of the blood-brain barrier; It is likely that the increase in cerebral blood flow, associated with norepinephrine when it bypasses the barrier, is secondary to an increase in cerebral metabolism.

Focal cerebral ischaemia in the cat: treatment with the glutamate antagonist MK-801 after induction of ischaemia

The effects of the glutamate N-methyl-D-aspartate receptor antagonist MK-801 in reducing ischaemic brain damage have been examined in anaesthetised cats, with drug treatment being initiated 2 h after the induction of cerebral ischaemia. Focal cerebral ischaemia was produced by permanent occlusion of one middle cerebral artery, and the animals were killed 6 h later. The amount of early irreversible ischaemic damage was assessed at 16 predetermined stereotactic planes. Treatment with MK-801 (5 mg/kg, i.v.) 2 h after middle cerebral artery occlusion reduced significantly the volume of ischaemic damage (from 1,625 +/- 384 mm3 of the cerebral hemisphere in vehicle-treated cats to 792 +/- 385 mm3 in MK-801-treated cats). The demonstration of reduced ischaemic brain damage with MK-801, when the agent is administered after the induction of ischaemia, extends the therapeutic potential of such agents in the treatment of focal cerebral ischaemia in humans.

Substance P: immunohistochemical localization and effect upon cat pial arteries in vitro and in situ

1. Nerve fibres containing substance P immunoreactivity were present in the adventitia and the adventitia-media border of all cat cerebral arteries which were examined. Substance P immunoreactivity was most abundant in cerebral arteries from the rostral portion of the circle of Willis. 2. Substance P effected a dose-dependent relaxation of feline middle cerebral arteries which had been contracted with prostaglandin F2 alpha. The maximum relaxation (16 +/- 0.3 mN) was achieved with substance P at a concentration of 10-6 M. 3. In cats anaesthetized with alpha-chloralose, the perivascular microinjection of substance P effected dose-dependent increases in arteriolar calibre. The maximum increase in calibre (19 +/- 3%) was observed following the injection of 10(-6) M-substance P.

Endothelin-1-induced reductions in cerebral blood flow: dose dependency, time course, and neuropathological consequences

The capacity of endothelin-1 to induce severe reductions in cerebral blood flow and ischaemic neuronal damage was assessed in anaesthetised rats. Endothelin-1 (25 microliters of 10(-7)-10(-4) M) was applied to the adventitial surface of an exposed middle cerebral artery and striatal blood flow assessed by the hydrogen clearance technique. Endothelin-1 induced severe dose-dependent reductions in cerebral blood flow (e.g., minimum CBF at 10(-5) M of 9 +/- 11 ml 100 g-1 min-1 compared to 104 +/- 22 ml 100 g-1 min-1 with vehicle, p < 0.05), which persisted for at least 60 min at each concentration of endothelin-1. Application of endothelin-1 to the middle cerebral artery produced dose-dependent ischaemic brain damage (e.g., volume of damage of 65 +/- 34 mm3 at 10(-5) M compared to 0.22 +/- 0.57 mm3 for vehicle, p < 0.01). These data demonstrate that endothelin-1 is capable of reducing blood flow to pathologically low levels and provide a new model of controlled focal ischaemia followed by reperfusion.

Effect of pretreatment with the calcium antagonist nimodipine on local cerebral blood flow and histopathology after middle cerebral artery occlusion

We used the [14C]iodoantipyrine autoradiography technique to study the effect of pretreatment with the calcium antagonist nimodipine on local cerebral blood flow (lCBF) in rats that underwent middle cerebral artery (MCA) occlusion. In untreated control animals there were profound localized reductions in 1CBF 30 minutes after MCA occlusion. These were most pronounced in neocortical areas and in the caudate nucleus ipsilateral to the MCA occlusion. In animals pretreated with nimodipine (1 microgram X kg-1 X min-1 for 30 minutes before and 30 minutes after MCA occlusion), the ipsilateral decrease in 1CBF in cortical regions was significantly less than that in control animals. The drug did not appear to alter 1CBF in the ipsilateral caudate nucleus. Neuropathological quantification of the ischemic damage present 3 hours after occlusion showed that nimodipine pretreatment reduced the volume and extent of cellular damage in the periphery but not in the core of the lesion.

Neuropeptide Y: Immunocytochemical localization to and effect upon feline pial arteries and veins in vitro and in situ

Plexuses of nerve fibres containing neuropeptide Y (NPY)-like immunoreactivity invest pial arteries belonging to the circle of Willis, pial arterioles, occasionally penetrating arterioles and large veins. A more sparse supply of NPY-like fibres were observed around pial veins and venules. The NPY-immunoreactive fibres are located within the adventitia or at the adventitia-media border. Only occasional fibres are present in cerebral vessels of animals in which the superior cervical ganglion has been removed one week previously. Administration of NPY resulted in strong, concentration-dependent contractions of isolated feline middle cerebral arteries whereas administration of avian pancreatic polypeptide (APP) elicited weak contractions. In chloraloseanaesthetized cats, perivascular microapplication of NPY in situ resulted in marked concentration-dependent contractions of cerebral pial arterioles (34.7 +/- 6.6%; maximum decrease in calibre with NPY. Perivascular administration of NPY resulted in the constriction of pial veins but the magnitude of the venous calibre reductions was smaller than the response of arterioles at each reductions was smaller than the response of arterioles at each concentration examined. APP did not elicit contraction of pial arterioles or veins during in situ conditions. The pharmacological and immunocytochemical results strongly indicate the existence of a novel perivascular neuronal system containing NPY, which mediates contraction of cerebral blood vessels and NPY is colocalized with NA in sympathetic nerves.

Correlation of the extracellular glutamate concentration with extent of blood flow reduction after subdural hematoma in the rat

The excitatory neurotransmitters glutamate and aspartate are an important factor in the causation of ischemic brain damage. The concentration of glutamate and aspartate was serially measured in extracellular fluid using in vivo microdialysis after induction of a subdural hematoma or after a sham operation in the rat. Measurements were made in the cortex underlying the hematoma and in the ipsilateral hippocampus, and these findings were correlated with regional cerebral blood flow (CBF), measured autoradiographically 2 hours after hematoma induction. In the severely ischemic cortex underlying the hematoma (mean CBF less than 25 ml/100 gm/min), glutamate and aspartate content increased more than 750% over basal levels. In individual animals the magnitude of glutamate release correlated with the extent of the focal ischemic zone under the hematoma (r = 0.907). Hippocampal glutamate levels rose 339%, yet regional CBF was preserved (114 ml/100 gm/min). This accords with focal hypermetabolism in this model, and may imply a glutamate-mediated "excitotoxic" process after subdural hematoma.

Transthyretin quaternary and tertiary structural changes facilitate misassembly into amyloid

Human transthyretin (TTR) can be transformed into amyloid fibrils by partial acid denaturation to yield a monomeric amyloidogenic intermediate that self-associates into amyloid through quaternary structural intermediates, which are identified by sedimentation velocity methods. The monomeric amyloidogenic intermediate has substantial beta-sheet structure with a nonnative but intact tertiary structure as discerned from spectroscopic methods. Proteolysis sensitivity studies suggest that the C-strand-loop-D-strand portion of TTR becomes disordered and moves away from the core of the beta-sandwich fold upon formation of the monomeric amyloidogenic intermediate over the pH range 5.1-3.9. The single site mutations that are associated with early onset amyloid disease [familial amyloid polyneuropathy (FAP)] function by destabilizing tetrameric TTR. Under mild denaturing conditions, the FAP variants populate the monomeric amyloidogenic intermediate conformation, which assembles into amyloid, whereas wild-type TTR remains tetrameric and nonamyloidogenic. The FAP mutations do not significantly alter the native folded structure; instead, they appear to act by making the thermodynamics and perhaps the kinetics more favorable for formation of the amyloidogenic intermediate. Suppressor mutations have also been characterized that strongly stabilize tetrameric TTR and disfavor the formation of the monomeric amyloidogenic intermediate, thus inhibiting amyloid formation. The mechanistic details characterizing transthyretin amyloid fibril formation available from the biophysical studies outlined within have been utilized to develop a new therapeutic strategy for intervention in human amyloid disease. This approach features small molecules that bind with high affinity to the normal fold of transthyretin, inhibiting the quaternary and tertiary structural changes associated with the formation of the monomeric amyloidogenic intermediate that self-assembles into amyloid. Ligand binding to TTR stabilizes the native tetrameric fold, which is nonamyloidogenic.

Nimodipine and the haemodynamic and histopathological consequences of middle cerebral artery occlusion in the rat

The effect of the administration of nimodipine (1 microgram kg-1 min-1), initiated 5 min after occlusion of a middle cerebral artery (MCA), upon cerebral haemodynamics ([14C]iodoantipyrine autoradiography) and neuropathological outcome (volume of histologically ischaemic tissue) was investigated in anaesthetized rats. Measurements were made of the level of local CBF (LCBF) in a total of 37 neuroanatomically defined areas, either ipsilateral or contralateral to the occluded vessel, and the autoradiograms were examined using a new approach to quantitative densitometry that employed a frequency distribution analysis of the CBF in sections of the brain at different coronal planes. Both methods of analysis showed that nimodipine, administered after the ischemic event, did not modify the pattern of CBF distribution after MCA occlusion. The extent of ischaemic brain damage was determined by histological examination. There was no evidence that the extent of ischaemic damage, either in sections at eight different coronal planes or in overall volume, was significantly different in animals that received nimodipine from that observed in animals that received only the vehicle used to dissolve the drug. The lack of cerebral circulatory and neuropathological alterations when nimodipine administration is initiated after occlusion of the MCA is contrasted with the higher levels of LCBF and the reductions in the volume of ischaemic tissue that were found when nimodipine was administered before occlusion of the artery.

Influence of endogenous norepinephrine on cerebral blood flow and metabolism

The influence of brain norepinephrine on cerebral metabolism and blood flow was examined because exogenous norepinephrine, administered in a way that the blood-brain barrier is bypassed, has been shown to effect pronounced changes in the cerebral circulation. Reserpine (40 mug/kg, by intracarotid infusion) was administered in order to release brain norepinephrine in five anesthetized baboons. Reserpine significantly increased cerebral oxygen consumption (23%) and cerebral blood flow (50%). This response lasted for approximately 60 min. In a further five animals, effects of central beta-adrenoreceptor blockade were studied. Pro pranolol (12 mug/kg-min) produced an immediate, significant reduction in both cerebral oxygen consumption (40%) and cerebral glucose uptake (39%). Cerebral blood flow was reduced minimally. However, the responsiveness of the cerebral circulation to induced hypercapnia was severely attenuated from a gradient of 3.22 before, to 1,11 after, administration. These experiments suggest that central norepinephrine can influence the cerebral circulation primarily through noradrenergic effects on brain metabolism.

Focal cerebral ischemia in the rat: topography of hemodynamic and histopathological changes

We studied local cerebral blood flow, as measured by autoradiography with digital image processing and by tissue morphology, in six rats 4 hours after occlusion of the proximal middle cerebral artery. A consistent, three-dimensional pattern of graded reductions in local cerebral blood flow involved the affected hemisphere, with a densely ischemic zone (local cerebral blood flow less than 3 ml/100 gm/min) in the dorsolateral caudate putamen and the adjacent frontoparietal cortex. In the frontoparietal cortex, the normal laminar pattern of local cerebral blood flow was disrupted, and there was a transcortical gradient in flow, with pronounced ischemia in deeper layers and relatively preserved superficial flow. Comparisons of autoradiographic findings with histopathological abnormalities in adjacent frozen sections showed that the region of ischemic damage corresponded closely with the area of greatest reduction in blood flow. Although around this region local cerebral blood flow increased centrifugally, a striking finding was that flow density changed abruptly (a tenfold variation in flow within a 1 to 2 mm interval) at the edge of the pathological lesion. Penumbral conditions may therefore exist in only a very narrow zone 4 hours after onset of focal ischemia. After occlusion of a major cerebral artery, the pattern of local cerebral blood flow changes appears to depend on interactions among vascular architecture, reductions in perfusion pressure, alterations in metabolic demands, and variations in local vascular resistance.

Excitatory amino acid antagonists and their potential for the treatment of ischaemic brain damage in man

1. A wide range of therapeutic strategies has been explored in humans and experimental animals with the aim of improving outcome after brain ischaemia but few have shown convincing clinical benefit. 2. The massive increase in the extracellular concentration of glutamate which occurs in cerebral ischaemia is a key component in the sequence of neurochemical events which leads to neuronal death. Pharmacological blockade of the action of glutamate at the N-methyl-D-aspartate (NMDA) receptor, (the glutamate receptor subtype principally involved in the neurotoxic effects of the amino acid) provides a novel therapeutic approach to cerebral ischaemia. 3. The effects of NMDA receptor antagonists in animal models of focal cerebral ischaemia are uniquely consistent, viz, a marked reduction in the amount of irreversible ischaemic damage irrespective of the species, the model of cerebral ischaemia, when the animals are sacrificed after the ischaemic episode, whether ischaemia is permanent or temporary and followed by reperfusion and which particular NMDA antagonist was employed. 4. NMDA receptor antagonists have marked effects on brain function in normal animals. The balance between these potential adverse effects and the anti-ischaemic efficacy of these drugs will ultimately determine the clinical utility of this class of drugs. 5. The data which are reviewed provide the basis for the current clinical evaluation of NMDA receptor antagonists in stroke and head trauma.

Effect of apomorphine on the relationship between local cerebral glucose utilization and local cerebral blood flow (with an appendix on its statistical analysis)

The alterations in local glucose utilization and local blood flow in 36 discrete regions of the central nervous system (CNS) that occur following the intravenous administration of the putative dopaminergic agonist, apomorphine (0.5 mg/kg), have been measured using the quantitative autoradiographic 14C-2-deoxyglucose and 14C-iodoantipyrine techniques. In eight of the regions examined (frontal and sensory-motor cortices, ventral thalamus, caudate nucleus, globus pallidus, substantia nigra, subthalamic nucleus, and posterior cerebellar hemisphere), significant elevations of local cerebral blood flow (CBF) were observed following apomorphine administration. In these eight regions, proportionately similar, significant elevations in local glucose utilization were observed following apomorphine. In two of the regions investigated (anterior cingulate cortex and lateral habenular nucleus), significant reductions in both local blood flow and glucose utilization were observed following apomorphine administration. In the majority of regions examined (26 of the total 36), apomorphine did not alter significantly either blood flow or glucose use. Using a statistical approach, described in detail in an appendix, the relationship between local rates of glucose utilization and local levels of tissue blood flow was analyzed. A relationship between local CBF and local glucose utilization was found following apomorphine, and the nature of this relationship was indistinguishable from that observed in control animals. In no region of the CNS was a significant deviation from the normal CBF–glucose use relationship demonstrated following apomorphine administration. These results point to the greater importance of the effects of apomorphine upon tissue metabolic activity, rather than its direct vascular action, as being the major mechanism underlying the observed alterations in local CBF. The statistical methods provide a rigorous analytical approach to the analysis of alterations in the relationship, both locally and globally, of blood supply to glucose utilization.

Costs and use of mental health services before and after managed care

This paper tracks access, utilization, and costs of mental health care for a private employer over nine years during which mental health benefits were carved out of the medical plan and managed care was introduced. Prior to the carve-out, mental health costs increased by around 30 percent annually; in the first year after the change, costs dropped by more than 40 percent; in the six follow-up years, costs continued to decline slowly. This cost reduction was not attributable to decreased initial access, as the number of persons using any mental health care increased following the change. Instead, the cost reduction was the result of (1) fewer outpatient sessions per user, (2) reduced probability of an inpatient admission, (3) reduced length-of-stay for an inpatient episode, and (4) substantially lower costs per unit of service.