Biochemical evidence for cholinergic innervation of intracerebral blood vessels

Muscarinic cholinergic receptor sites were detected with [3H]quinuclidinylbenzilate (QNB) binding techniques in two fractions of bovine intracerebral vessels; one of the fractions contained primarily small arteries and veins with some attached capillaries, and the other one was highly enriched in capillaries. The amounts of binding were similar in equivalent vascular fractions isolated from cerebral cortex, caudate nucleus and cerebellar cortex in spite of large differences among the 3 regions in [3H]QNB binding to brain tissue. The different distribution of muscarinic receptors in brain tissue and blood vessels argues against the possibility that the receptors represent a contamination of the vascular fractions by brain parenchyma. Cerebral endothelial cells, which were isolated by treating capillaries with collagenase, bound [3H]QNB to the same extent as did cerebral capillaries. This is consistent with an endothelial localization of capillary muscarinic receptors. Choline acetyltransferase (ChAT) activity, a marker for cholinergic neurons, also was present in the vascular preparations. Within each brain region, ChAT activities in capillaries and larger vessels were similar, but significant regional differences were found for vascular ChAT activity, with the highest values in the caudate. Isolated endothelial cells contained significantly lower levels of ChAT activity than intact capillaries, suggesting a periendothelial location of the enzyme, as would also be the case for attached nerve terminals. The presence of [3H]QNB binding sites and ChAT activity in intracerebral blood vessels is consistent with an innervation of the cerebral vasculature by a cholinergic system that may regulate cerebral blood flow and capillary permeability.     

Sphenopalatine ganglion stimulation increases regional cerebral blood flow independent of glucose utilization in the cat

Regional cerebral blood flow was determined using the tracer [14C]iodoantipyrine and regional brain dissection, and regional cerebral glucose utilization determined using the 2-deoxyglucose method, in the alpha-chloralose-anesthetized cat to evaluate the effect of electrical stimulation of the sphenopalatine (pterygopalatine) ganglion. Unilateral stimulation for either a short period (7-10 min) or a longer period (45 min) resulted in increases in blood flow in the ipsilateral cerebral cortex of up to 45% (parietal cortex) with, in addition, increased flow in the white matter of the corpus callosum (42%). The flow changes for both brief and prolonged stimulation were not significantly different. Flow was not altered in either the brainstem or basal ganglia (caudate nucleus). In contrast to these changes in cerebral blood flow no changes in cerebral glucose utilization were seen in any of the brain areas studied and in particular there were no changes in the areas in which blood flow increased. These data provide clear evidence that the innervation of the cerebral vasculature from the main parasympathetic ganglion can alter cerebral blood flow independent of cerebral metabolism.     

Choline acetyltransferase activity associated with cerebral cortical microvessels does not originate in basal forebrain neurons

Cerebral cortical microvessels are innervated by cholinergic fibers that are probably involved in the regulation of local cerebral blood flow and blood-brain barrier permeability. The possibility exists that the cholinergic terminals associated with the cortical microvasculature belong to neurons from the nucleus basalis magnocellularis (NBM), where 70% of the cortical cholinergic projections originate. To test this hypothesis, ibotenic acid (25 nmol) was injected unilaterally in the NBM in rats, and 14 days later, choline acetyltransferase (ChAT) activity was measured in the frontoparietal cortex and in a blood vessel fraction isolated from this region. Lesions of the NBM resulted in a 50% decrease of cortical ChAT as compared with control or sham-operated hemispheres; however, no changes were observed in the ChAT activity associated with cortical microvessels. These results indicate that, in rat cerebral cortex, the perivascular cholinergic terminals do not originate in the basal forebrain.     

Glucose transporter localization in brain using light and electron immunocytochemistry

A polyclonal antibody to a synthetic 13 amino acidpeptide found at the carboxyl-terminal end of the glucose transporter protein was raised in rabbit and used in light and electron immunocytochemical studies of human and canine brain. This antibody identified a broad band of polypeptide of average Mr 55,000 on immunoblots (immunogold-silver stains) of electrophoresed membrane proteins from human red blood cells. A similar polypeptide band (Mr 45,000-60,000) was identified on immunoblots of microvessel membrane proteins isolated from canine cerebrum, suggesting that this antibody is a useful tool for studying the distribution and abundance of the glucose transporter protein in mammalian nervous tissue. Peroxidase antiperoxidase stains of cerebrum using this antibody demonstrated that transporters are abundant in the intima pia, in the endothelium of blood vessels in the subarachnoid space, and in the endothelium of arterioles, venules, and capillaries of gray and white matter. In cerebellum, reaction product was localized in the vessels of the subarachnoid space and in microvessels of the molecular layer, the granular layer, and the white matter. However, transporters were not found in the intima pia of cerebellum. In medulla oblongata, transporters were found in the intima pia, the endothelium of some subarachnoid vessels, and the microvessels of gray and white matter. In pituitary, microvessels in adenohypophysis contained no reaction product, but the antigen was detected in some microvessels in neurohypophysis. Electron microscopy of cerebral cortex using a protein A-gold technique demonstrated that glucose transporters are equally abundant on the luminal and abluminal membranes of microvessel endothelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Basal forebrain nitric oxide synthase (NOS)-containing neurons project to microvessels and NOS neurons in the rat neocortex: cellular basis for cortical blood flow regulation

Stimulation of basal forebrain neurons results in local increases in cortical cerebral blood flow that are dependent upon cholinergic and nitrergic mechanisms. In the present study, we investigated the possibility that basal forebrain nitric oxide synthase (NOS)-containing neurons project to microvessels and NOS interneurons in the rat cerebral cortex. We performed quisqualic (QUIS) acid lesions of the basal forebrain and evaluated their effects on cortical NOS immunostained nerve terminals, with emphasis on those associated with microvessels and NOS interneurons, both at the light and/or electron microscopic levels. The results show that basal forebrain NOS neurons provide about one third of the overall cortical NOS innervation. Further, the data indicate that basalocortical NOS fibres establish privileged associations with microvessels and NOS neurons, as respective denervations of 60 and 45% were observed following lesion. At the electron microscopic level, most perivascular NOS neuronal elements corresponded to nerve terminals and a majority ( approximately 25%) of these were located in the immediate vicinity of the blood vessels, similar to the perivascular distribution reported previously for classic neurotransmitters/neuromediators. NOS terminals abutting on cortical NOS neurons were primarily nonjunctional. Altogether, these results raise the possibility that not only cholinergic but also nitrergic basal forebrain neurons are involved in the flow response observed following stimulation of the basal forebrain. Further, they suggest interactions between basalocortical and intracortical NOS neurons. We conclude that these interactions are involved in the spatial and temporal regulation of cortical perfusion following basal forebrain activation, and that they may become dysfunctional in pathologies such as Alzheimer's disease which affects both the basal forebrain and the cortical NOS neurons.     

The topographic distribution of brain atrophy in Huntington's disease and progressive supranuclear palsy

Summary The topographic distribution of brain atrophy was quantified by image analysis of fixed coronal brain slices from 12 patients dying with Huntington's disease (HD) and from 4 other patients dying with progressive supranuclear palsy (PSP). In HD, atrophy was maximal within the caudate nucleus, putamen and globus pallidus. However, the cerebral cortex was also atrophied with reductions in cross-sectional area within frontal, temporal and parietal lobes. In general, more white matter than grey matter was lost leading to an elevation in the grey/white matter ratio. The amygdala and thalamus were reduced in area. In PSP, lesser reductions in cortical area than those of HD were seen, these again being mostly due to a loss of white matter, resulting in an elevation of the grey/white ratio. The globus pallidus and thalamus were decreased in area, but no changes in the caudate nucleus and putamen were measured.Supported in part by an intercalated BSc studentship (RO) from the Medical Research Council     

Thy-1-like immunoreactivity in human brain during development

Thy-1-like immunoreactivity was found in several areas of the immature and adult human brain, using indirect immunofluorescence techniques. In the fetal brain (31 gestational weeks) most immunoreactivity was located in the white matter with an overall granular diffuse distribution and stray fluorescent fibrous structures radiating into grey matter. At 2 months postnatally, the large axon bundles of the internal capsule traversing the caudate nucleus were strongly positive, whereas surrounding neuropil seemed to be negative. In the adult caudate nucleus no such fluorescent fibre bundles could be observed. At 8 months of age, both cerebellum and frontal cerebral cortex contained large numbers of fibrous structures in the grey matter in addition to white matter fluorescence. The molecular layer of both areas was negative. The 8-month-old cerebellum had a Thy-1 distribution similar to the adult, while in the frontal cortex cerebri the density of fluorescent structures increased gradually until adulthood. However, in the 5-year-old frontal cortex the immature granular appearance of 2-month-old cortex could still be seen, but with a greater number of radiating fluorescent bundles. In the adult brain, cerebellum contained a dense pattern of thick, fibrous fluorescent structures in white matter and the internal granular layer and in the frontal cortex thick bundles radiated into grey matter to form a plexus of coarse individual fibres in layers II and III. The hippocampal formation of the 31-week-old fetus contained a network of thin varicose fibres, ascending from the white matter. Stratum radiatum at this stage contained numerous small spots of Thy-1-like immunoreactivity, but no visible fluorescent fibres.(ABSTRACT TRUNCATED AT 250 WORDS)     

遗忘型轻度认知损害和非痴呆血管性认知损害的局部脑血流量

目的 探讨遗忘型轻度认知损害(aMCI)和非痴呆血管性认知损害(VCI-ND)的局部脑血流量(rCBF)改变的特征.方法 健康中老年人16名,aMCI组患者10例,VCI-ND组患者12例,年龄在50～80岁,教育程度均在初中毕业及以上,全部完成头颅CT或MRI检查.应用Xe-CT技术定量测定38例研究对象脑不同部位的rCBF.结果 (1)静息状态健康中老年人(NC)组脑不同部位的rCBF分布情况:由高到低分别为基底节核团(76.4±8.6)ml·100 g-1·min-1、皮质(48.0±7.1)ml·100 g-1·min-1和白质(20.5±1.7)ml·100 g-1·min-1.(2)NC组、aMCI组和VCI-ND组患者的rCBF表现比较:aMCI组颞、顶、枕叶的rCBF值呈一定趋势的减少,VCI-ND组额叶的rCBF值呈一定趋势的减少,而VCI-ND组rCBF下降最明显的部位集中在白质区域[(17.7±2.3)ml·100 g-1·min-1,F=5.740,P=0.002],从深度看覆盖了脑室旁白质和皮质下深部白质两部分,从长度看覆盖了白质的前后区域.3组基底节区核团包括尾状核、豆状核和丘脑的rCBF值比较差异无统计学意义.结论 aMCI和VCI-ND的rCBF值的差异反映了两者在病理机制方面的差异.     

Distribution of amyloid deposits in the cerebral white matter of the Alzheimer’s disease brain: relationship to blood vessels

The relationship between blood vessels and amyloid β (Aβ)-protein deposits in the cortex of the Alzheimer’s disease (AD) brain is still controversial. It is difficult to distinguish whether the Aβ deposits are associated with blood vessels or neurons because of their widespread and complicated distribution. In this study, we investigated the distribution of Aβ deposits in the cerebral white matter of the AD brain as a means of removing the bias of neuronal distribution. An immunohistochemical study of 100 serial sections, after pretreatment with formic acid for 24 h, revealed the presence of Aβ deposits in the cerebral white matter of the AD brain. There are various morphological types of plaques containing Aβ deposits in the white matter, the same as in the gray matter. While the majority of Aβ deposits was of a circumscribed type such as “classic” and “primitive” plaques, “compact” and “diffuse” plaques were also observed in the white matter. The location of the Aβ deposits was, for the most part, immediately beneath the gray matter. The distribution of Aβ deposits in the white matter was found to correspond to the orientation of the blood vessels. Serial sections also revealed that these Aβ deposits were distributed along a single blood vessel. These findings suggest that the deposition of Aβ in the cerebral white matter is primarily related to the blood vessels. Received: 7 March 1996 / Revised: 10 October 1996     

Cholinergic innervation of the human striatum, globus pallidus, subthalamic nucleus, substantia nigra, and red nucleus.

The anatomical organization of cholinergic markers such as acetylcholinesterase, choline acetyltransferase, and nerve growth factor receptors was investigated in the basal ganglia of the human brain. The distribution of choline acetyltransferase-immunoreactive axons and varicosities and their relationship to regional perikarya showed that the caudate, putamen, nucleus accumbens, olfactory tubercle, globus pallidus, substantia nigra, red nucleus, and subthalamic nucleus of the human brain receive widespread cholinergic innervation. Components of the striatum (i.e., the putamen, caudate, olfactory tubercle, and nucleus accumbens) displayed the highest density of cholinergic varicosities. The next highest density of cholinergic innervation was detected in the red nucleus and subthalamic nucleus. The level of cholinergic innervation was of intermediate density in the globus pallidus and the ventral tegmental area and low in the pars compacta of the substantia nigra. Immunoreactivity for nerve growth factor receptors (NGFr) was confined to the cholinergic neurons of the basal forebrain and their processes. Axonal immunoreactivity for NGFr was therefore used as a marker for cholinergic projections originating from the basal forebrain (Woolf et al., '89: Neuroscience 30:143-152). Although the vast majority of striatal cholinergic innervation was NGFr-negative and, therefore, intrinsic, the striatum also contained NGFr-positive axons, indicating the existence of an additional cholinergic input from the basal forebrain. This basal forebrain cholinergic innervation was more pronounced in the putamen than in the caudate. The distribution of NGFr-positive axons suggested that the basal forebrain may also project to the globus pallidus but probably not to the subthalamic nucleus, substantia nigra, or red nucleus. The great majority of cholinergic innervation to these latter three structures and to parts of the globus pallidus appeared to come from cholinergic neurons outside the basal forebrain, most of which are probably located in the upper brainstem. These observations indicate that cholinergic neurotransmission originating from multiple sources is likely to play an important role in the diverse motor and behavioral affiliations that have been attributed to the human basal ganglia.     

Monoamine oxidase activity in the cerebral vasculature: comparison between fresh microvessels from different structures and cell cultures derived from microvessels

Monoamine oxidase (MAO) activity was studied in various preparations of porcine brain microvessels to explore further the role of this enzyme in the blood-brain barrier to catecholamines. No difference was noted (Vm and Km) between microvessels isolated from three structures (caudate nucleus, thalamus, and cerebral cortex) in which the responses to circulating catecholamines in vivo are markedly different. Large and small microvessels from the caudate nucleus and the thalamus presented the same specific activity. Cell cultures obtained from small microvessels were rich in endothelial cells as identified by the presence of Factor VIII-related antigen. These preparations displayed an MAO activity about ninefold less than freshly isolated microvessels, although their prostaglandin synthetase activity appeared normal. These results suggest that MAO activity is not the main factor determining the regional differences in the cerebrovascular reactions to catecholamines, that MAO is not specifically localized in the endothelium but must be also present in the smooth muscle, and that the MAO activity is greatly decreased during cell culture.     

Neuronal and endothelial sites of acetylcholine synthesis and release associated with microvessels in rat cerebral cortex: ultrastructural and neurochemical studies

We sought to establish what proportion of the cholinergic innervation of the cerebral cortex (CX) is associated with intraparenchymal blood vessels by using immunocytochemical and neurochemical techniques, and whether [3H]acetylcholine ([3H]ACh) is synthesized and released by elements associated with cortical microvessels (MV). MVs and, for comparison, tissue homogenates were prepared using sucrose gradient/differential ultracentrifugation methods. Efficacy of the separation technique was indicated by the activity of gamma-glutamyltranspeptidase (up to 29.2-fold enrichment), an endothelial cell marker enzyme, in the MV fraction and microscopy. The size of isolated microvessels ranged from 5 to 40 micron (o.d.) with 67.7% of the vessels less than 10 micron and 32.2% between 11 and 40 micron (690 vessels measured from 4 animals). By electron microscopy immunoreactive choline acetyltransferase (ChAT), the biosynthetic enzyme for ACh, was localized to: (a) axons and axon terminals opposed to the basal laminae of capillaries and small arterioles, and (b) capillary endothelial cells. ChAT-labeled elements associated with MVs were most prominent in layers I, III and V of the CX consistent with the local pattern of cholinergic innervation. The absolute amount of ACh synthesized (pmol Ach/100 mg wet wt.) by elements associated with cortical MVs was relatively small (2.3% total cortical homogenate activity). Inhibition of MV ChAT activity to 5% of control by the specific ChAT inhibitor, 4-naphthylvinylpyridine, and HPLC analysis of the product, indicated that authentic ACh was measured. Other tissues similarly synthesized small amounts of ACh relative to the CX, caudate nucleus (CN, 2.4%), cerebellum (CRB, 1.4%) and liver (LIV, 3.9%). Consistent with the known extent of the cholinergic innervation of the tissues examined, the rank order of ChAT associated for both MVs and homogenate were: CN greater than CX much greater than CRB greater than LIV. However, based on the specific activities of ChAT, cortical MVs have the remarkable capacity to synthesize ACh at rates 95% greater than cortical (S1 fraction) homogenate (59.0 +/- 3.5 nmol/mg protein/40 min; n = 7), which is enriched in nerve terminals. Except for LV (+11%), other tissues also had remarkably high ChAT activity in MV (% above corresponding homogenate; P less than 0.05, n = 5): CN (+269) and CRB (+313). Release of [3H]ACh from MVs and, for comparison, nerve terminals were graded to K+ depolarization stimulus (5-55 mM), maximal with 55 mM K+ and Ca2+ dependent.(ABSTRACT TRUNCATED AT 400 WORDS)     

Endothelial nitric oxide synthetase (eNOS) in astrocytes: another source of nitric oxide in neocortex.

The distribution of the endothelial form of nitric oxide synthetase (eNOS) was examined in the visual cortex of three species of primate and in the rat using immunocytochemistry. Labeled cells were found in both the gray and white matter. These cells were stellate in appearance and labeled cell processes were seen contacting blood vessels or the pia, suggesting that, by morphological criteria, the cells were astrocytes. All eNOS positive cells were double labeled with an antibody against S100beta. Although all cells were double labeled in the white matter, in the gray matter, some S100beta positive cells did not contain detectable levels of eNOS. eNOS positive astrocytic processes appeared to form prominent and distinctive structures next to neurons, especially in cortical layer IIIC. We postulate that these eNOS-positive structures form astrocytic perisynaptic sheaths on neuronal somas in the cortex. If this is true, then nitric oxide can influence neuronal transmission directly at axosomatic synapses in the cortex. In addition, the presence of eNOS in astrocytes and in their processes that contact blood vessels suggests that the link between local cortical activity and changes in cerebral blood flow could be mediated by astrocytic release of nitric oxide.     

A case of familial juvenile Alzheimer's disease with apallic state at the relatively early stage and various neurological features--a clinicopathological study

A case of familial juvenile Alzheimer's disease with apallic state at the relatively early stage and various neurological features was reported. A 33-year-old woman showed a progressive dementia followed by apallic state at the relatively early stage, and died of cardiac failure at the age of 45. Neurological examination disclosed chorea, myoclonus, rigidity, pyramidal sign, and generalized convulsion. Neuropathologically, extensive senile changes such as senile plaques, neurofibrillary tangles, and granurovascular degenerations were observed in the brain, chiefly in the cerebral cortex and limbic system. The present case was characterized by a severe neuronal loss in the subcortical gray matter such as the caudate nucleus, dentate nucleus, substantia nigra, and thalamus as well as a marked myelin loss and axonal damages in the cerebral white matter. This case suggested a combination of multisystemic degeneration and a primary degeneration of the cerebral white matter. The additional peculiar aspects in this case were the senile plaques and amyloid angiopathy in the cerebellar cortex, and the senile plaques and grumose degeneration in the cerebellar dentate nucleus. In the clinicopathological standpoint, the apallic state in this case could be attributed to a severe degeneration of the cerebral white matter in addition to the cerebral cortical deterioration. Furthermore, the occurrence of chorea and myclonus might be contributed to the severe degeneration of the caudate nucleus and to the degeneration of the dentate nucleus, particularly to the grumose degeneration, respectively.     

Observations on cerebral ischaemia in cats at injury threshold levels

Abstract

The potential for recovery of brain tissue subjected to ischaemia at a threshold level of injury was evaluated in cats subjected to 20 min middle cerebral artery occlusion. In addition to assessment of regional cerebral blood flow and water content, the permeability of the bloodbrain barrier and morphological changes detected by light microscopy were studied at various time intervals. Our observations revealed that although a similar reduction of blood flow during arterial occlusion was found both in the caudate nucleus and the cerebral cortex, the reactive hyperaemia was consistently higher in the caudate nucleus than in the cortex. After 24 h the caudate nucleus also revealed a significantly higher water content and increased vascular permeability than the cortex. Morphological observations at 24 h in areas affected by ischaemia showed widespread, marked ischaemic neuronal injury, whereas at 3 d there was, in addition, a vigorous proliferative reaction of vascular elements. Cats sacrificed at 14 d revealed a remarkably good preservation of neurons, both in the caudate nucleus and cortex which otherwise showed a few circumscribedsmall, infarcts surrounded by normal nerve cells. Our study suggests that neurons injured at threshold level have a considerable capacity for recovery. Otherwise, with a similar degree of ischaemiathe caudate nucleus appears more prone to increased vascular permeability and oedema than the cerebral cortex.     

Degeneration of the basalocortical pathway from the cortex induces a functional increase in galaninergic markers in the nucleus basalis magnocellularis of the rat.

The present work aimed 1) to evaluate whether an increase in galanin or galanin receptors could be induced in the nucleus basalis magnocellularis (nbm) by degeneration of the basalocortical neurons from the cortex and 2) to analyze the consequences of such an increase on cortical activity. First, a mild ischemic insult to the frontoparietal cortex was performed to induce the degeneration of the basalocortical system; galanin immunoreactivity, galanin binding sites, and cholinergic muscarinic receptors were quantified through immunocytochemistry and autoradiography. Second, galanin infusions in the nbm were undertaken to mimic a local increase of the galaninergic innervation; cortical acetylcholine release, cerebral glucose use, and cerebral blood flow were then measured as indices of cortical activity. As a result of the cortical ischemic lesion, the postsynaptic M1 and presynaptic M2 muscarinic receptors were found to be reduced in the altered cortex. In contrast, galaninergic binding capacity and fiber density were found to be increased in the ipsilateral nbm in parallel with a local decrease in the cholinergic markers such as the muscarinic M1 receptor density. Galanin infusion into the nbm inhibited the cortical acetylcholine release and cerebral blood flow increases elicited by the activation of the cholinergic basalocortical system but failed to affect acetylcholine release, cerebral blood flow, and cerebral glucose use when injected alone in the nbm. These results demonstrate that degeneration of the basalocortical system from the cortex induces an increase in galaninergic markers in the nbm, a result that might suggest that the galaninergic overexpression described in the basal forebrain of patients with Alzheimer's disease can result from a degeneration of the cholinergic basalocortical system from the cortex. Because galanin was found to reduce the activity of the basalocortical cholinergic system only when this one is activated, galanin might exert its role rather during activation deficits than under resting conditions such as the resting cortical hypometabolism, which is characteristic of Alzheimer's disease.     

The cerebrovascular role of the cholinergic neural system in Alzheimer's disease

The intrinsic cholinergic innervation of the cortical microvessels contains both subcortical pathways and local cortical interneurons mediated by muscarinic and nicotinic acetylcholine receptors. Stimulation of this system leads to vasodilatation. In the extrinsic innervation, choline acts as a selective agonist for the α7-nicoticinic acetylcholine receptor on the sympathetic nerves to cause vasodilatation, and through this mechanism, cholinergic modulation may affect this sympathetic vasodilatation. Alzheimer's disease is characterized by a cerebral cholinergic deficit and cerebral blood flow is diminished. Cholinesterase inhibitors, important drugs in the treatment of Alzheimer's disease, could influence the cerebral blood flow through stimulation of the intrinsic cholinergic cerebrovascular innervation. Indeed, cholinesterase inhibitors improve cerebral blood flow in Alzheimer patients who respond to treatment. Further, cerebrovascular reactivity and neurovascular coupling are impaired in Alzheimer's disease and both can be improved by cholinesterase inhibitors. Conversely, cholinesterase inhibitors inhibit the α7-nicoticinic acetylcholine receptor on extrinsic sympathetic nerves and thus may impair vasodilatation. The net outcome of these opposing effects in clinical practice remains unknown. Moreover, it is uncertain whether the regulation of cerebral blood flow during blood pressure changes (cerebral autoregulation) is impaired in patients with Alzheimer's disease. Technological developments now allow us to dynamically measure blood pressure, cerebral blood flow, and cerebral cortical oxygenation. Using simple maneuvers like single sit-stand and repeated sit-stand maneuvers, the regulation of cerebral perfusion in patients with Alzheimer's disease can easily be measured. Sit-stand maneuvers can be considered as a provocation test for cerebral autoregulation, and provide excellent opportunities to study the cerebrovascular effects of cholinesterase inhibitors.     

Association of histamine with cerebral microvessels in regions of bovine brain

Intracerebral blood vessels of diameter< 100 μm (microvessels) were isolated from homogenates of bovine brain regions by a sieving procedure which yielded a preparation suitable for biochemical analysis. It was found that microvessels isolated from cerebral cortex grey matter had levels of endogenous histamine which were approximately 23-fold greater than the concentration found in the initial homogenate. Microvessels isolated from the striatum and hippocampus also had concentrations of endogenous histamine which were 5- to 6-fold greater than the initial homogenate. It was calculated that approximately half of the endogenous histamine in bovine cerebral cortex grey matter and one tenth of the endogenous histamine in striatum and hippocampus was associated with the microvasculature.The results of biochemical analysis of microvessel preparations from the cerebral cortex grey matter indicated that: (1) most of endogenous histamine was recovered in the crude nuclear pellet after subcellular fractionation of homogenates; and (2) the endogenous level of histamine was associated with minimal histidine decar☐ylase activity. The above features are characteristic of most cells and it is speculated that histamine in these microvessels was localized in mast cells.     

Positron emission tomography in neuropsychology

By positron emission tomography (PET) of 18F-2-fluoro-2-deoxy-D-glucose (FDG) local cerebral metabolic rate for glucose (LCMRGl) can be measured in man. Normal values in cerebral cortex and basal ganglia range from 35 to 50 mumol/100 g/min, the values in gray matter structures of the posterior fossa were 25-30 mumol/100 g/min, the lowest LCMRGl was found in the white matter (15-20 mumol/100 g/min). During sensory stimulation by various modalities functional activation increases LCMRGl in the respective special areas, while sleep decreases metabolic rate in all cortical and basal gray matter structures. In many neurological disorders CMRGl is altered in a disease-specific pattern. In dementia of the Alzheimer type CMRGl is impaired even in early stages with accentuation in the parieto-temporal cortex, while in multi-infarct dementia glucose uptake is mainly reduced in the multifocal small infarcts. In Huntington's chorea the most conspicuous changes are found in the caudate nucleus and putamen. In cases of focal lesions (e.g. ischemic infarcts) metabolic disturbances extend far beyond the site of the primary lesion and inactivation of metabolism is found in intact brain structures far away from the anatomical lesion. Additional applications of PET include determination of the metabolism of various substrates, of protein synthesis, of function and distribution of receptors, of tumor growth and of the distribution of drugs as well as the measurement of oxygen consumption, blood flow and blood volume.     

Autoradiographic distribution of cerebral blood flow increases elicited by stimulation of the nucleus basalis magnocellularis in the unanesthetized rat

The nucleus basalis magnocellularis (NBM) of the rat, equivalent of Meynert's nucleus in the primate, is the origin of the main cholinergic innervation of the cerebral cortex. Stimulation of this area has been previously shown to induced marked, cholinergically mediated, blood flow increases in the frontal and parietal cortices. However, the complete distribution of the cerebrovascular effects of NBM stimulation within the whole brain has not been determined. In the present study, we used the [¹⁴C]iodoantipyrine autoradiographic method to measure local cerebral blood flow (CBF) in the unanesthetized rat, chronically implanted with a stimulation electrode. We performed unilateral electrical stimulation of the NBM in order to compare both the interhemispheric differences in blood flow and the differences with a group of sham-stimulated rats. Considerable blood flow increases were found in most neocortical areas, exceeding 400% in the frontal area, compared to the control group. Marked responses also appeared in discrete subcortical regions such as the zona incerta, some thalamic nuclei and structures of the extrapyramidal system. These responses were mostly ipsilateral to the stimulation. The significance and the distribution of these blood flow increases are related first, to anatomical and functional data on mainly the cholinergic projections from the NBM, but also non-cholinergic pathways connected with the NBM, second, to biochemical data on the basalocortical system, and third, to the limited ultrastructural data on the innervation of microvascular elements. This cerebrovascular study represents a step in the elucidation of the function of the basalocortical system and provides data which may be related to certain deficits of degenerative disorders such as Alzheimer's disease in which this system is consistently affected.