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

Regulation of cerebral blood flow--a brief review

Cerebral blood flow is largely independent of perfusion pressure when autoregulation is intact. Cerebral circulation is regulated mainly by changes of vascular resistance. Resistance can be modulated by local-chemical and endothelial factors, by autacoids, and by release of transmitters from perivascular nerves. Local-chemical factors such as H(+)-, K(+)-, Ca(2+)-ions, adenosine, and osmolarity are involved in the regulation of cerebrovascular resistance during cortical activation and under pathological conditions such as hypoxia or ischaemia. Endothelial factors such as thromboxane A2, endothelin (ET), endothelium derived constrictor factor and endothelium derived relaxing (EDRF, identified as nitric oxide, NO) or hyperpolarizing (EDHF) factor, and prostacyclin (PGI2), can be released by physical stimuli such as shear stress or haemorrhage, by autacoids, by neurotransmitters, and by cytokines. Several of these factors (NO, PGI2, ET) can also be released from neurons and astrocytes thus enabling a coupling between parenchymal function and flow. Autacoids like histamine, bradykinin, eicosanoids, and free radicals influence cerebrovascular resistance, capacitance vessels and the permeability of the blood-brain barrier under pathological conditions. They are released by trauma, ischaemia, seizures and inflammation. Cerebral arteries are innervated by several systems. The sympathetic-noradrenergic fibres originate from the superior cervical ganglion. By releasing the constricting transmitters norepinephrine and neuropeptide Y this system extends the range of autoregulation. The parasympathetic cholinergic system with the dilating transmitters acetylcholine and vasoactive intestinal polypeptide may prevent ischaemia. Besides the intracerebral noradrenergic and serotonergic perivascular innervation with an unclear function, a trigeminal innervation has been described.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional cortical interaction patterns in visual perception and visuospatial problem solving

To explore the integration of functional neuronal interactions in human higher cortical functions, we applied multivariate mathematical techniques to regional cerebral blood flow (rCBF) increases induced by mental activity. rCBF was measured using the intravenous xenon-133 clearance technique with 32 bihemispheric detectors in 84 normal volunteers at rest and during both a visuoperceptual accuracy task and a visuospatial problem solving task. Both paradigms activated rCBF in bilateral premotor, motor and postcentral regions. Bilateral prefrontal activation occurred during problem solving but not during the perceptual accuracy task. Partial correlations coefficients and factor analysis identified significant interactions between numerous cortex regions in both tasks. There were highly ordered and integrated patterns of functional interaction patterns between cortex areas subserving elementary subfunctions of complex behavior. Cortical interaction analysis by such techniques is a useful tool to describe the functional anatomy of large-scale neurocognitive networks in the intact human brain. Imaging functional interactions between active cortex areas are complementary to other experimental neurophysiologic methods to explore brain-behavior relationships in health and disease.

Single photon emission computed tomography using perfusion tracers in seizure disorders

Single photon emission computed tomography (SPECT) using perfusion tracers makes it possible to estimate regional cerebral blood flow (rCBF) and, indirectly, local brain metabolism. It may be possible to detect and follow physiopathological alterations, such as may be seen in seizure disorders. The authors review the principles of and some data on perfusion SPECT in seizure disorders, stress advantages as well as major drawbacks and add their initial experience with Tc-99m hexamethylpropyleneamine oxime (HMPAO) SPECT in febrile convulsions.

Efferent microvascular responses to electrical stimulation of the area postrema in rats

As part of its role to transduce blood-borne and afferent neural stimuli to the brain, the area postrema conducts efferent projections monosynaptically to individual nuclei of the medulla oblongata and pons. We hypothesized that electrical activation of the area postrema would mimic this transduction process and couple microvascular responses in efferent sites to local increases in tissue metabolism reported previously. We used quantitative autoradiographic techniques and image analysis to measure capillary transfer constants for [14C]alpha-aminoisobutyric acid (AIB, a small, neutral amino acid) and blood flow (iodo[14C]antipyrine) in individual brainstem structures of anesthetized rats. The area postrema was stimulated electrically by means of a monopolar microelectrode positioned stereotaxically 100 microns deep in the dorsocentral aspect of the organ. There were no significant effects of stimulation on [14C]AIB influx or blood flow in control hindbrain structures where postremal projections are sparse or absent--the spinal trigeminal nucleus, reticular formation, or cerebellar vermis. Stimulation of the area postrema produced equivalent increases in transcapillary influx of [14C]AIB and capillary blood flow in the nucleus of the solitary tract, dorsal motor nuclei of the vagus nerves, ventrolateral medullary C1 region, locus coeruleus, dorsal tegmental nuclei, and lateral parabrachial nuclei. Formation of ratios interrelating rates of [14C]AIB influx and blood flow with previously assessed values of tissue glucose metabolism indicated that these measures increased proportionately during postremal stimulation. Such proportional increases in capillary [14C]AIB transfer and blood flow during tissue activation by area postrema stimulation are consistent with interpretation that the increase in blood flow resulted from recruitment of unused surface area in the capillary networks of individual efferent nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)

Does nitric oxide mediate the increases in cerebral blood flow elicited by hypercapnia?

The endothelium-derived relaxing factor (EDRF), probably nitric oxide (NO) or a closely related compound (EDRF/NO), is a potent vasodilator that appears to regulate vascular tone in several vascular beds. I have investigated whether EDRF/NO is also involved in the regulation of the cerebral circulation--in particular, whether EDRF/NO participates in the increases in cerebral blood flow elicited by hypercapnia. Rats were anesthetized with halothane, 1-2% (vol/vol), paralyzed, and artificially ventilated. Arterial pressure was monitored and blood gases were controlled. Cerebral blood flow was continuously monitored through a cranial window over the sensory cortex by a laser-Doppler probe. The window was superfused with Ringer's solution (pH 7.3-7.4 at 37 degrees C). During superfusion with Ringer's solution, hypercapnia (PCO2 = 55.8 +/- 0.8 mmHg) increased cerebral blood flow by 121 +/- 6% (n = 27; P less than 0.001; analysis of variance). Topical superfusion with the NO synthase inhibitors N omega-nitro-L-arginine (1 mM) attenuated the cerebrovasodilation by 93 +/- 6% (n = 8). In contrast, the vasodilation elicited by topical papaverine (1 mM) was not affected by N omega-nitro-L-arginine (n = 10). Application of N omega-nitro-D-arginine (1 mM) did not affect the cerebrovasodilation elicited by hypercapnia (P greater than 0.05; n = 8). N omega-Methyl-L-arginine (1 mM) attenuated the cerebrovasodilation elicited by hypercapnia by 44 +/- 4% (n = 8; P less than 0.001), an effect completely reversed by coapplication of L-arginine (10 mM; P greater than 0.05; n = 13). These findings indicate that the powerful effects of CO2 on the cerebral circulation are mediated by arginine-derived EDRF/NO. EDRF/NO is an important molecular signal whose actions may also include the regulation cerebral circulation.

Unilateral naris closure and vascular development in the rat olfactory bulb

The blood supply to the brain has been linked closely to nervous system function and metabolism, thereby possibly playing a direct role in brain maturation. Previously, we demonstrated that closure of an external naris early in life results in large changes within the olfactory bulb, including reductions in laminar volume and cell number and a rapid decline in metabolism and protein synthesis. To understand the role of the blood supply in the dramatic changes following naris closure, the present study examines the development of olfactory bulb vasculature in unilaterally odor-deprived and control rats. On post-partum day 1 (P1; the day after birth), littermate rat pups underwent either unilateral naris occlusion or sham surgery. On P5, P10, P15, P20, P30 and P60, animals were perfused with an india ink-gelatin mixture to assess blood vessel amount and complexity. Densitometric analyses were performed to obtain values of blood vessel area ratios (vessel area/tissue area), branch point number and branch point density. Considerable vessel development in all bulbs occurred over the first two to three weeks post-partum. By P20, large reductions in vessel area ratios were observed in all constituent laminae of deprived bulbs. While similar reductions in number of vessel branch points/tissue area were seen, few changes were noted in the number of branch points/vessel area. The effects were primarily confined to early developmental periods: bulb vasculature in animals deprived at older ages (P40) appeared normal. The results indicate that the vasculature responds to alterations in sensory stimulation early in life, therefore potentially playing an important regulative role in neural development.

Technetium-99m hexamethylpropylene amine oxime single photon emission tomography in febrile convulsions

We report our initial experience with technetium-99m hexamethyl propylene amine oxime (99mTC-HMPAO) brain single photon emission tomography (SPET) in the investigation of 19 children presenting with febrile convulsions. Two patients with complex febrile convulsions showed focal SPET lesions contralateral to the neurological deficit. However, in 9 out of 17 patients with simple febrile convulsions, focally disturbed perfusion was shown. In 4 out of 6 patients with electroencephalogram (EEG) abnormalities on admittance, SPET revealed at least 2 focal lesions. The temporofrontal region was the one most commonly involved. The SPET findings presented here also suggest a temporal relationship with the febrile convulsions, with markedly fewer lesions if examined after 12 days. In our initial experience, perfusion SPET did not show any particular pattern helpful in the differential diagnosis of the child presenting with febrile convulsions. Physiopathologically, our findings may support the hypothesis that brain tissue is regionally more vulnerable to fever, in patients presenting with febrile convulsions.

The onset of postischemic hypoperfusion in rats is precipitous and may be controlled by local neurons

BACKGROUND AND PURPOSE

Reperfusion following transient global cerebral ischemia is characterized by an initial hyperemic phase, which precedes hypoperfusion. The pathogenesis of these flow derangements remains obscure. Our study investigates the dynamics of postischemic cerebral blood flow changes, with particular attention to the role of local neurons.

METHODS

We assessed local cortical blood flow continuously by laser Doppler flowmetry to permit observation of any rapid flow changes after forebrain ischemia induced by four-vessel occlusion for 20 minutes in rats. To investigate the role of local cortical neurons in the regulation of any blood flow fluctuations, five rats received intracortical microinjections of a neurotoxin (10 micrograms ibotenic acid in 1 microliter; 1.5-mm-depth parietal cortex) 24 hours before ischemia to induce selective and localized neuronal depletion in an area corresponding to the sample volume of the laser Doppler probe (1 mm3). Local cerebral blood flow was measured within the injection site and at an adjacent control site.

RESULTS

Ischemia was followed by marked hyperemia (235 +/- 23% of control, n = 7), followed by secondary hypoperfusion (45 +/- 3% of control, n = 7). The transition from hyperemia to hypoperfusion occurred not gradually but precipitously (maximal slope of flow decay: 66 +/- 6%/min; n = 7). In ibotenic acid-injected rats, hyperemia was preserved at the injection site, but the sudden decline of blood flow was abolished (maximal slope of flow decay: 5 +/- 3%/min compared with 53 +/- 8%/min at the control site; n = 5, p less than 0.001) and no significant hypoperfusion developed (103 +/- 20% of control at 60 minutes).

CONCLUSIONS

These data suggest that the rapid transition to cortical hypoperfusion after forebrain ischemia may be triggered locally by a neuronal mechanism but that this mechanism does not underlie the initial hyperemia.

Cerebral lateralization and color perception: a transcranial Doppler study

Eight normal subjects were examined in dark, light and color conditions. Mean cerebral blood flow velocity (MBFV) were recorded almost simultaneously from their posterior cerebral arteries (PCA) using transcranial Doppler (TCD) ultrasound. The side-to-side difference was significant during the dark (p = 0.0159) and color stimulation (p = 0.0001) but not in light condition. This side-to-side difference in MBFV was used to characterize lateralization of color perception. This showed that the right PCA was always greater than the left during the presentation of color stimuli. Primary psychological colors (blue, yellow, red and green) induced greater lateralization as compared with color resulting from a mixed blue-green wavelength. This suggests that the right visual cortex is selectively sensitive to wavelengths.

Crossed cerebellar diaschisis accompanied by hemiataxia: a PET study

To study crossed cerebellar diaschisis (CCD), cerebellar blood flow and oxygen metabolism were measured with positron emission tomography (PET) in 12 patients who showed a minimal degree of hemiparesis due to single unilateral supratentorial lesion. Six patients presenting with mild to moderate cerebellar type hemiataxia showed CCD, that is, decreased blood flow and oxygen metabolism in the cerebellar hemisphere contralateral to the side of supratentorial lesion. Hemiataxia and reduced cerebellar blood flow and metabolism occurred in the ipsilateral side. Lesions were located in the thalamus in four patients and the parietal lobe and internal capsule in one each. The other six patients did not exhibit ataxia, and oxygen metabolism was not reduced in the contralateral cerebellar hemisphere. In two of these cases, however, reduced cerebellar perfusion was observed in the contralateral cerebellar hemisphere. These findings indicate that CCD occurs with hemiataxia and suggest that it results not only from disruption of the corticopontocerebellar pathway but also of the dentatorubrothalamic pathway. CCD associated with hemiataxia, demonstrated in patients with thalamic lesions, was presumed to result from retrograde deactivation of the cerebellar hemisphere via the dentatorubrothalamic pathway.

Blood-brain barrier dysfunctions following systemic injection of kainic acid in the rat

Changes in blood-brain barrier (BBB) permeability and cerebral metabolic activity following intravenous injection of kainic acid (KA; 6, 12 mg/Kg) in rats were assessed by calculating respectively a blood-to-brain transfer constant (Ki) for [14C]alpha-aminoisobutyric acid and local cerebral glucose utilization (LCGU) values, at different times (1 h, or acute seizures phase, and 48 h, or chronic pathology phase) after the induction of seizures. A significant increase in the local permeability of the BBB was observed 1 h after the injection of KA 6 mg/Kg (eliciting no significant changes in cerebral metabolic activity, except within the frontal cortex and the hippocampus) and 12 mg/Kg (which induced a marked and widespread enhancement of LCGU). On the contrary, during the pathology phase, persistent regional increases in Ki values were evidenced in rats treated with the lowest dose of the convulsant, but not in rats injected with KA 12 mg/Kg (a dose able to cause extensive neuronal damage). Thus one can speculate that: 1) KA-induced regional changes in the permeability of the BBB are not correlated with changes in neuronal activity; 2) opening of the BBB is not reliably associated with neuronal injury.

Focal elevations in neocortical interstitial K+ produced by stimulation of the fastigial nucleus in rat

We studied whether K+, a potent cerebrovasodilator released by active neurons, participates in the increase in cortical cerebral blood flow (CBF) elicited by stimulation of the cerebellar fastigial nucleus (FN). Rats were anesthetized by continuous administration of halothane (1-3%), paralyzed and artificially ventilated. FN was stimulated electrically (8 s trains, 50 Hz, 5-10 V) through microelectrodes positioned stereotaxically. K+o (mM) was measured in sensory cortex by K(+)-sensitive micropipettes. In some experiments neocortical CBF was monitored continuously by laser-doppler flowmetry. Stimulation of the FN produced significant increases in K+o that averaged 0.91 +/- 0.16 mM (range 0.5-2.9 mM; n = 19) and were confined to sites corresponding to the intermediate cortical laminae (P less than 0.05, ANOVA). To determine whether such K+o elevations were able to produce increases in CBF comparable to those elicited by FN stimulation, cortical K+o was increased by superfusing the sensory cortex with 20-30 mM K+ in Ringer. K+o elevations of 2.8 +/- 0.6 mM increased CBF by 17 +/- 2% (n = 5), an increase considerably smaller than that elicited by FN stimulation in cerebral cortex. We conclude that K+ is unlikely to mediate the cortical cerebrovasodilation. Furthermore, the restricted spatial distribution of the K+o increase indicates that the cortical neural activity evoked by FN stimulation is highly focal. Thus the findings support the hypothesis that, in cortex, the vasodilation is mediated by activation of a restricted group of neural elements, perhaps neurons in laminae III-IV.

(99mTc)-HM-PAO SPECT and cognitive impairment in Parkinson's disease: a comparison with dementia of the Alzheimer type

Regional cerebral perfusion was evaluated by single photon emission tomography (SPECT) using (99mTc)-HM-PAO as a tracer, in thirty Parkinsonian patients with (n = 15) or without (n = 15) dementia, nineteen patients with dementia of the Alzheimer type (DAT) and thirteen control subjects. HM-PAO uptake was measured in the frontal, parietal, temporal and occipital cortex and tracer perfusion was expressed as cortical/cerebellar activity ratios. Regional HM-PAO ratios in nondemented Parkinsonian patients did not differ from controls, whereas in demented patients with Parkinson's disease (DPD) a significant reduction was found in the parietal, temporal and occipital cortex. Tracer uptake ratios were significantly reduced in all regions in the DAT group. Thus DPD and DAT shared a common pattern of marked posterior hypoperfusion, although the perfusion defect was greater and more extensive in the DAT patients.

Effects of HA1077, an intracellular calcium antagonist, on neurotransmitter metabolism in rat brain in vivo

The effect of HA1077, an intracellular calcium antagonist, on neurotransmitter metabolism in rat brain was investigated in vivo. After administration of HA1077, at doses of 0.1, 0.3, and 3 mg/kg, 5-hydroxyindoleacetic acid (5-HIAA) levels increased in most regions except midbrain. In the striatum, parallel increases of both serotonin (5-HT) and 5-HIAA levels were observed at 0.3 mg/kg, but only the 5-HT level increased at 0.1 mg/kg. These results suggest that HA1077 may activate the turnover or synthesis of 5-HT. After administration of HA1077 at 0.3, 1, and 3 mg/kg, the dopamine (DA) level was increased in the striatum, but 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid levels were unchanged. After HA1077 administration at 1 mg/kg, both DA and DOPAC levels increased in the hypothalamus and only DA level increased in the cerebral cortex. By contrast, DOPAC level decreased in the midbrain after HA1077 treatment at 0.1 and 0.3 mg/kg, and in the brainstem at 0.1 and 10 mg/kg. The ratio of [3H]-N-methylspiperone accumulation relative to that in the cerebellum did not change after HA1077 treatment at any of the doses employed. Thus, the effects of HA1077 on neurotransmitter metabolism are complex and vary depending on the dosage and sites of the brain. Although the dose-dependent effects of HA1077 on neurotransmitter metabolism are similar to those of calcium entry blockers, HA1077 can facilitate DA synthesis in the hypothalamus and striatum, unlike the calcium entry blockers.

Control of cerebral circulation in the high-risk neonate

A knowledge of neonatal cerebrovascular physiology is essential to the understanding of diseases that frequently affect the subsequent development of the newborn brain. Recent observations indicate that the cerebral vessels of the healthy newborn infant, even the very preterm, respond to physiological stimuli in the same manner as in the mature organism. Thus, cerebral blood flow changes with changes in arterial carbon dioxide tension (PaCO2), oxygen concentration (CaO2), or glucose concentration, whereas cerebral blood flow remains constant at minor fluctuations in arterial blood pressure. In pathological states, pressure autoregulation may become impaired, and in severe cases the vessels do not react to chemical or metabolic stimuli. These infants are at high risk for developing cerebral lesion, and they may be candidates for new "brain-protecting regimens."

Alterations of local cerebral blood flow and glucose uptake by electroconvulsive shock in rats

The effects of single and repeated electroconvulsive shock (ECS) treatment on regional cerebral blood flow (rCBF) and on rates of glucose flow from blood to local brain areas (rCGF), were investigated in pentobarbital-anesthetized rats, using quantitative autoradiographic techniques. Effects of single ECS on rCBF were assessed at two average time points of 15 and 55 sec after the application of the electric current, whereas the effects on rCGF were assessed at 70 and 110 sec. Effects of repeated ECS were assessed 24 hr after the last ECS in a series of eight daily treatments. Single ECS caused marked increases in rCGF in different brain structures, but no significant effects were observed after repeated ECS. Similarly, substantial increases in rCBF were seen during and immediately after the ECS-induced seizure, but not 24 hr after the last treatment of repeated ECS. Single ECS appeared to have differential effects on rCBF in hind-brain structures as compared to more anterior regions. A linear relationship between rCBF and rCGF values was established in control animals, indicating coupling of these two variables with a constant rCBF/rCGF ratio. ECS caused an apparent increase in the CBF/CGF ratio, which might be attributed to the different temporal resolution of the two methods used here to estimate rCGF and rCBF. Analysis of the increments of rCGF and rCBF extrapolated to the same point in time after a single ECS (10 sec), revealed that in many of the examined structures the CBF/CGF ratio was similar to that observed in control animals, indicating that the coupling of CBF and CGF is maintained during the seizure. But in some brain stem structures such as the dorsal raphe, inferior colliculi, superior olivary nucleus, and the vestibular nucleus there were large increases in CGF associated with a marked drop in the CBF/CGF ratio. This observation suggests that high metabolic demands can be met by increased local blood flow up to a given "ceiling" keeping the glucose clearance from blood to brain tissue constant. However, when the metabolic demands exceed this upper limit, the additional demands could be met by an increased clearance of glucose without a change in CBF.

Flicker evoked increase in optic nerve head blood flow in anesthetized cats

The effect of diffuse luminance flicker stimulation of a large area (approximately 30 degrees diameter) on red blood cell flux (F) in the optic nerve head was measured in the anesthetized cat. F increased markedly during sustained flicker. The F-response to the initiation and cessation of the stimulation was found to occur within a few seconds. Upon sustained stimulation, the increase in F reached a plateau within approximately 2 min. Its level depended upon the intensity, frequency and wavelength of the stimulation and the state of adaptation of the retina. This stimulus offers a new and powerful means of investigating blood flow regulation in the optic nerve head (ONH).

Decreases in regional cerebral blood flow with normal aging

Positron emission tomographic (PET) images of regional cerebral blood flow (rCBF) from 30 normal, resting volunteers aged 30 to 85 years were analysed to identify areas where rCBF fell with age. Images were anatomically normalised, and a pixel-by-pixel linear regression was performed to remove differences in global CBF between subjects. Pixels at which rCBF then showed a significant (p less than 0.01) negative correlation with age were identified. They were displayed as a statistical parametric map (SPM) of correlations. We demonstrate an age-related decrease in adjusted rCBF in the cingulate, parahippocampal, superior temporal, medial frontal, and posterior parietal cortices bilaterally, and in the left insular and left posterior prefrontal cortices (omnibus significance, chi 2 = 2,291, p less than 0.0001, df = 1). Decreases in rCBF suggest a regionally specific loss of cerebral function with age. The affected areas were all limbic, or association, cortices. Therefore, these decreases may constitute the cerebral substrate of the cognitive changes that occur during normal aging.

Acute cocaine administration: effects on local cerebral blood flow and metabolic demand in the rat

Local cerebral blood flow and glucose utilisation were measured in both saline (n = 10) and cocaine (10 mg/kg; n = 10) treated rats using [14C]iodoantipyrine and [14C]2-deoxyglucose quantitative autoradiography respectively. In control animals, the ratio of flow to metabolism was 1.40 (r = 0.92) for the 40 brain regions examined. Cocaine treatment altered neither the correlation (r = 0.83) nor the ratio (1.49). Thus, the fundamental relationship between CBF and metabolism remains intact following acute cocaine exposure.

Active microwave computed brain tomography: the response to a challenge

The potential application of active microwave techniques to brain imaging is studied by numerical simulations and experimentally using a recently developed cylindrical microwave scanner. The potential advantages and limitations of this method in static and dynamic brain imaging are presented and compared with other imaging techniques.

SPECT in the diagnosis of Alzheimer's disease and multi-infarct-dementia

SPECT with Tc-99m HM-PAO as a radiopharmaceutical was performed in 17 patients meeting research criteria for Alzheimer's disease (AD), in 10 patients with a clinical diagnosis of multi-infarct-dementia (MID) and in 12 healthy volunteers. Regional tracer uptake was measured in frontal, parietal, and temporoparietal regions. A statistically significant decrease of tracer uptake in the temporoparietal region was found in AD-patients compared with controls. AD-patients showed less activity in this region than MID-patients, but this difference did not reach statistical significance. In both AD- and MID-patients decrease of tracer uptake was not correlated with dementia severity. We conclude that SPECT brain imaging is not yet ready for routine use in the distinction between AD and MID.

Normal cerebrovascular regulatory mechanisms are present in intracerebral neuronal transplants

Local cerebral blood flow and local cerebral glucose utilization were measured using quantitative autoradiography in parallel groups of rats (n = 5-7) which 12-15 weeks previously had undergone limited unilateral ibotenate-induced lesion of the nucleus basalis magnocellularis, followed by implantation into ipsilateral neocortex of primordial basal forebrain cell suspensions. Surviving transplants were visualized by acetylcholinesterase histochemistry. Neither lesion alone nor the presence of a transplant produced significant side-to-side differences in either blood flow or glucose use in any of the 20 brain areas measured. Glucose use within the transplant was independent of the site of implantation. When sited in neocortex, glucose use in the transplant (66 +/- 4 mumol/100 g per min) was significantly lower than in the corresponding contralateral site (113 +/- 3 mumol/100 g per min), whereas when sited in subcortical white matter, glucose use (53 +/- 3 mumol/100 g per min) was significantly higher than in the contralateral side (29 +/- 4 mumol/100 g per min). In the host brain as a whole, the ratio of blood flow to glucose use ipsilateral to the transplant (m = 1.27, r = 0.88) was not significantly different from that of the contralateral side (m = 1.30, r = 0.94). This relationship was also observed within the transplanted tissue itself despite the fact that alkaline phosphatase histochemistry revealed a relative hypervascularization associated with the implantation site.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative technetium 99m hexamethylpropylene amine oxime SPET study in different types of dementia

Regional cerebral perfusion was evaluated by single photon emission computed tomography (SPET) using technetium 99m hexamethylpropylene amine oxime (99mTc-HMPAO) as a tracer, in 13 control subjects and 44 age-matched patients suffering from dementia of the Alzheimer's type (DAT, n = 19), presumed Pick's disease (n = 5), idiopathic Parkinson's disease with dementia (DPD, n = 15) and progressive supranuclear palsy (PSP, n = 5). HMPAO uptake was measured in the superior frontal, inferior frontal, parietal, temporal and occipital cortices, and the perfusion values were expressed as cortical/cerebellar activity ratios. As compared with controls, tracer uptake ratios in the DAT group were significantly reduced over all cortical regions, with the largest defects in the parieto-temporal and superior frontal cortices. A marked hypoperfusion affecting the superior and inferior frontal cortices was found in Pick's disease, whereas a mild but significant hypoperfusion was observed only in the superior frontal cortex of patients with PSP. In the DPD group, HMPAO uptake was significantly reduced in the parietal, temporal and occipital cortices, but not in the frontal cortex. These results show that DAT and DPD share an opposite anteroposterior HMPAO uptake defect as compared with the Pick's and PSP groups.

Cortical functional architecture and local coupling between neuronal activity and the microcirculation revealed by in vivo high-resolution optical imaging of intrinsic signals

We have shown previously the existence of small, activity-dependent changes in intrinsic optical properties of cortex that are useful for optical imaging of cortical functional architecture. In this study we introduce a higher resolution optical imaging system that offers spatial and temporal resolution exceeding that achieved by most alternative imaging techniques for imaging cortical functional architecture or for monitoring local changes in cerebral blood volume or oxygen saturation. In addition, we investigated the mechanisms responsible for the activity-dependent intrinsic signals evoked by sensory stimuli, and studied their origins and wavelength dependence. These studies enabled high-resolution visualization of cortical functional architecture at wavelengths ranging from 480 to 940 nm. With the use of near-infrared illumination it was possible to image cortical functional architecture through the intact dura or even through a thinned skull. In addition, the same imaging technique proved useful for imaging and discriminating sensory-evoked, activity-dependent changes in local blood volume and oxygen saturation (oxygen delivery). Illumination at 570 nm allowed imaging of activity-dependent blood volume increases, whereas at 600-630 nm, the predominant signal probably originated from activity-dependent oxygen delivery from capillaries. The onset of oxygen delivery started prior to the blood volume increase. Thus, optical imaging based on intrinsic signals is a minimally invasive procedure for monitoring short- and long-term changes in cerebral activity.

Ultrastructural evidence for a close relationship between dopamine cell processes and blood capillary walls in Macaca monkey and rat retina

In the retina, tyrosine-hydroxylase (TH) antiserum specifically labels intrinsic dopamine (DA)-neurons. In order to clarify the relationship between capillaries and DA-processes already observed by light microscopy, we have performed TH-immunocytochemistry on rat and monkey retinas at the electron microscope level. Close contacts were observed between DA-varicosities and the basal lamina of both pericytes and endothelial cells. As in the brain, these anatomical findings suggest that intrinsic DA-neurons could contribute to the regulation of local retinal blood flow and/or permeability.

Uncoupling of cerebral blood flow and glucose metabolism in conscious rats with chronic renal hypertension

In an analysis of 46 individual brain structures and regions, we found that 12-14 weeks of renal hypertension in rats were associated with a 42% increase in cerebrovascular resistance, an average 28% reduction in cerebral blood flow, and no general change in cerebral glucose metabolism. A specific increase in metabolic activity, however, was identified in locus coeruleus. Generalized cerebral vasoconstriction resulting from central noradrenergic innervation originating in locus coeruleus is a possible explanation for the uncoupling of cerebral blood flow and metabolism in rats with chronic renal hypertension.

Blood flow changes in chicken brain stem auditory nuclei following cochlea removal

Cochlea removal results in rapid and persistent metabolic and morphological changes in avian brain stem auditory nuclei. Because such changes in the central nervous system are often associated with changes in local blood flow, we examined blood flow in second-order auditory nucleus magnocellularis (NM) and third-order nucleus laminaris (NL). The diffusible tracer [14C]-iodoantipyrine was infused intravenously into 20- to 26-day-old chickens either 30 min or 6 h after unilateral cochlea removal. This tracer rapidly equilibrates between blood and tissue in proportion to local blood flow. Unoperated animals served as controls. Thirty seconds after tracer infusion, brains were removed and frozen. Cryostat sections were prepared for quantitative film autoradiography. Blood flow in normal and deafferented areas within NM and NL was compared. Nucleus magnocellularis receives its only excitatory input from the ipsilateral cochlea via the eighth nerve. Axons from NM bifurcate and project to the ipsilateral dorsal dendritic region of NL (NLd) and the contralateral ventral dendritic region of NL (NLv). Thirty minutes after cochlea removal, blood flow in ipsilateral NM decreases by 30%. This decrease persists at 6 hours. Blood flow in NL does not change in accordance with the pattern of afferent input from NM. Rather, blood flow in NLd and NLv ipsilateral to cochlea removal is significantly decreased 6 h post lesion. These results are in contrast to the pattern of morphological and metabolic changes observed in NL after cochlea removal.

Hereditary cerebral hemorrhage with amyloidosis--Dutch type. Tc-99m HM-PAO single photon emission computed tomography

We performed single photon emission computed tomography (SPECT) and cerebral CT-scans in nine patients with hereditary cerebral amyloid angiopathy. CT-scans showed 23 focal hypodense lesions, 13 of which were visible on SPECT as a CBF-defect. One patient showed a CBF-defect on SPECT without CT-scan lesion and had a cerebral hemorrhage three months later in that particular region. In two additional patients, who were 50% at risk for this autosomal dominant disease, CBF-defects on SPECT, but no cortical lesions on CT-scan were found. CT-scans may be more sensitive than SPECT to detect chronic lesions caused by cerebral hemorrhages, but another possibility is that hemorrhages do not always lead to persistent CBF-defects. SPECT can show the effect of amyloid deposits on CBF before the angiopathy causes clinical symptoms.

Redistribution of cerebral activity during childhood

Data on the functional development of brain structures in early childhood are scarce. Cognition changes markedly from pre-school age to school age, and we thought it of interest to examine the level of functional activity of selected brain regions. Nine preschool children were studied and compared with eight school children and eighteen adults. Xe133 emission tomography was used for determination of regional cerebral blood flow (rCBF). It was demonstrated that activity in the striatal regions is low in early childhood. In school age the proportion of flow to these regions is increased by about 11-14 per cent (difference between medians). Perfusion of the occipital lobes decreased with age when studied with open eyes and closed eyes, possibly reflecting loss of synapses and decreased plasticity.

Maintenance of local cerebral blood flow after acute neuronal death: possible role of non-neuronal cells

In brain, a major factor regulating local perfusion is local neuronal activity. However, we have recently discovered that, in rat, five days after selective neuronal destruction in the parietal cortex by local microinjections of the excitotoxin ibotenic acid, local cerebral blood flow, within the lesion, remains in the normal range. We studied whether proliferating non-neuronal cells and/or local changes in microvascular density participate to maintain local cerebral blood flow. Rats were anesthetized (halothane 1-3%), ibotenic acid (10 micrograms in 1 microliter) was locally microinjected in a restricted region of the parietal cortex, and animals were allowed to recover. Three, five, seven, 11, 30 days later local cerebral blood flow was measured autoradiographically under chloralose anesthesia (40 mg/kg, s.c.) by the [14C]iodoantipyrine technique. Cellular density or microvascular area were determined on sections stained with Thionine or processed for the endothelial marker alkaline phosphatase, respectively. Local neurons were destroyed by 24 h after microinjections of ibotenic acid. However, from three to 11 days after lesion local cerebral blood flow was unchanged (P greater than 0.05; n = 5), thereafter declining so that by 30 days blood flow was 48 +/- 6% of control (P less than 0.05; n = 5). Cellular density increased within the lesion by 17.5-fold at seven to 11 days (P less than 0.01) and declined to a 11.7-fold elevation above control at day 30 (P less than 0.01). New cells consisted of macrophages, endothelium and glial fibrillary acidic protein-positive astrocytes. The microvascular area increased 4.2-fold from three to 11 days (P less than 0.01). The patency of the presumably newly formed vessels was determined by the presence of intravascular red blood cells, which were revealed histochemically. The area occupied by red blood cells within cerebral microvessels, in contrast to microvascular area, did not increase until seven days after lesion, reaching a 3.2-fold increase at 11 days. Thus within the lesion, local cerebral blood flow remains constant during the phase in which cellular and microvascular density increases. The presumably newly formed vessels cannot contribute to maintain local cerebral blood flow since during this phase they are not patent; rather patency develops coincident with the decline in local cerebral blood flow. We conclude that non-neuronal cells, most likely activated macrophages, may be an important factor regulating local cerebral perfusion, after acute neuronal death.

Cerebral blood flow and metabolism in sleep

A review is presented of the electrical activity of the brain and its global and regional blood flow and metabolism in the different stages of sleep and in wakefulness in animals and humans. During slow-wave sleep (SWS), the blood flow and metabolism of the brain decrease slightly below the level of wakefulness. During rapid eye movement the activity of the brain increases above that of SWS and sometimes above that of wakefulness. Some studies suggest that both at sleep onset and at arousal the brain stem-cerebellar complex (BSC) may be activated before the cortex and the right hemisphere before the left. Variation of hemispheric dominance seems to be a phenomenon of both wakefulness and sleep.

The effects of the GABA agonist muscimol upon blood flow in different vascular territories of the rat cortex

Local cerebral blood flow was measured in five regions of rat cortex immediately following intravenous administration of the gamma-aminobutyric acid (GABA) agonist muscimol. In contrast to recent observations, no increases in blood flow were found at either of the two time points analysed, and the data revealed that decreases in blood flow previously reported 30 min after muscimol treatment were in evidence as early as 30 s. These results are totally consistent with the conclusion that the overall effects of GABA agonists in the intact animal are to reduce blood flow in line with reduced metabolic demand in the neuropil. However, the heterogeneity of the reductions in cortical blood flow found here possibly suggests a biological role for vascular GABA systems in providing a mitigating influence on fluctuating tissue perfusion.

Modifications of the permeability of the blood-brain barrier and local cerebral metabolism in pentobarbital- and ketamine-anaesthetized rats

The state of deep surgical anaesthesia, induced by intraperitoneal injection of pentobarbital sodium (54 mg/kg) or ketamine hydrochloride (150 mg/kg) in the rat, was accompanied by a significant reduction in the permeability of the blood-brain barrier evaluated by calculating a unidirectional blood-to-brain constant (Ki) for the circulating tracer [14C]alpha-aminoisobutyric acid. Pentobarbital-induced anaesthesia was also characterized by a widespread and marked depression of local cerebral glucose utilization; on the contrary, when rats were anaesthetized with ketamine, cerebral glucose utilization increased in the striatum and hippocampus and decreased in the cerebellum and brain-stem. It is suggested, as a hypothesis, that two different mechanisms, depending on the kind of the anaesthetic drug used, may be involved in the changes in the permeability of the blood-brain barrier, observed in anaesthetized animals: (a) a neurogenic component; (b) a direct interaction of the anaesthetic with elements of the microvasculature.

Dynamics of regional cerebral blood flow for various visual stimuli

Isotope tracer methods for measuring regional cerebral blood flow or metabolism do not provide data on the dynamics of the fast adjustment of local cerebral blood flow. Measuring intracranial flow patterns of the posterior cerebral artery by means or 2 MHz pulsed transcranial Doppler ultrasonography demonstrated that detailed dynamic effects of various visual patterns on local cerebral perfusion can be recorded, and that visual stimuli of different complexity as well as the strategy of stimulus perception cause distinct flow velocity changes in the occipital cortex involved in information processing. This type of on--line analysis may become a powerful tool for detecting fast autoregulatory mechanisms in relation to purely functional cerebral changes.

Selective enhancement of intratumoural blood flow in malignant gliomas: experimental study in rats by intracarotid administration of adenosine or adenosine triphosphate

We studied the effect of intravenous and intracarotid infusion of adenosine and adenosine triphosphate (ATP) on the regional blood flow of intracerebrally transplanted RG-C6 tumours in rats, using the hydrogen clearance method. The intracarotid administration of adenosine or ATP selectively increased blood flow in the tumour, but did not produce any significant change either in the regional cerebral blood flow of the extratumoural ipsilateral hemisphere or in the ipsilateral hemisphere without tumour. The intracarotid administration of ATP at a dose of 10 micrograms/kg/min produced the most effective increase in the tumour blood flow (+51.5 +/- 16.8%). In contrast, both the intravenous administration of adenosine and that of ATP failed to increase tumour blood flow. These results may possibly indicate that intracarotid administration of the adenosine or ATP might contribute in selectively enhancing the delivery of anti-cancer agents to malignant brain tumours.

Effect of methotrexate on local cerebral blood flow in conscious rats

The effect of methotrexate (MTX) on local cerebral blood flow (I-CBF) was studied with autoradiographic [14C]-iodoantipyrine methods in normal conscious rats. I-CBF was reduced by 30-57% in the rats given MTX (100 mg or 200 mg/body) as compared to that in the saline injected control group, but no dose-dependent effect was observed. The mechanism of I-CBF reduction by MTX was discussed.