A cytoarchitectonic and histochemical study of nucleus basalis and associated cell groups in the normal human brain

Several recent studies have reported loss of neurons in the nucleus basalis in Alzheimer's disease. However, few detailed studies of the normal distribution of these neurons in the human brain have appeared. We have used Nissl staining and acetylcholinesterase histochemical staining of the human basal forebrain, alone or in combination to identify the organization of the nucleus basalis and associated cell groups, (or collectively, the magnocellular basal nucleus) in the normal human brain. The magnocellular basal nucleus includes a series of clusters of neurons and scattered perikarya extending from the medial septum and diagonal band nucleus rostrally, through the substantia innominata to the furthest caudal extent of the globus pallidus. This distribution is similar to that which has been described in the monkey. Furthermore, acetylcholinesterase-positive fibers in the human brain are seen in the two major pathways that have been identified as carrying magnocellular basal nucleus axons to the cerebral cortex in other species.These observations suggest that the topographic organization of the magnocellular basal projection to cerebral cortex in other species probably exists in man as well. It will therefore be important in future studies of the fate of these neurons in neurological degenerative diseases to assess the loss of neurons in the different components of the magnocellular basal nucleus in relation to the clinical evidence for dysfunction in the cortical areas which they innervate.     

Delayed treatment with nerve growth factor improves acquisition of a spatial task in rats with lesions of the nucleus basalis magnocellularis: evaluation of the involvement of different neurotransmitter systems.

Rats received bilateral lesions of the nucleus basalis magnocellularis by infusion of ibotenic acid. Fourteen days later, osmotic minipumps releasing human recombinant nerve growth factor (0.3 micrograms/day) were implanted subcutaneously. Starting one month after the lesion, spatial learning of the animals was tested using the Morris water maze. Acquisition of the task was impaired by the lesion, but treatment with nerve growth factor reduced the average latency to find the platform by approximately 9 s, which represents 28% of the lesion-induced behavioral deficit. Retention of this task and spatial acuity, tested in a trial in which the platform was not present, did not show a statistically significant improvement. Lesions of the nucleus basalis magnocellularis reduced the choline acetyltransferase activity in the neocortex, but not in the hippocampus. Treatment with nerve growth factor increased the choline acetyltransferase activity in the neocortex but not in the hippocampus. There was no significant difference in the levels of norepinephrine, dopamine, serotonin or their metabolites in the cortex or hippocampus between nerve growth factor-treated animals and lesioned control animals. There was no significant correlation between any of these neurochemical changes and behavioral performance (acquisition and spatial acuity). Treatment with nerve growth factor did not increase the number or the size of nerve growth factor receptor-immunoreactive neurons in the nucleus basalis magnocellularis. These data suggest that delayed treatment with nerve growth factor results in an improvement of spatial learning in rats with lesions of the nucleus basalis magnocellularis. A possible role for cholinergic mechanisms in this effect is discussed.     

Distribution and co-localization of choline acetyltransferase and p75 neurotrophin receptors in the sheep basal forebrain: implications for the use of a specific cholinergic immunotoxin

The basal forebrain cholinergic system is involved in different forms of memory. To study its role in social memory in sheep, an immunotoxin, ME20.4 immunoglobulin G (IgG)-saporin, was developed that is specific to basal forebrain cholinergic neurons bearing the p75 neurotrophin receptor. The distribution of sheep cholinergic neurons was mapped with an antibody against choline acetyltransferase. To assess the localization of the p75 receptor on basal forebrain cholinergic neurons, the distribution of p75 receptor-immunoreactive neurons with ME20.4 IgG was examined, and a double-labeling study with antibodies against choline acetyltransferase and p75 receptor was undertaken. The loss of basal forebrain cholinergic neurons and acetylcholinesterase fibers in basal forebrain projection areas was assessed in ewes that had received intracerebroventricular injections of the immunotoxin (50, 100 or 150 microg) alone, as well as, in some of the ewes treated with the highest dose, with bilateral immunotoxin injections in the nucleus basalis (11 microg/side). Results indicated that choline acetyltransferase- and p75 receptor-immunoreactive cells had similar distributions in the medial septum, the vertical and horizontal limbs of the band of Broca, and the nucleus basalis. The double-labeling procedure revealed that 100% of the cholinergic neurons are also p75 receptor positive in the medial septum and in the vertical and horizontal limbs of the band of Broca, and 82% in the nucleus basalis. Moreover, 100% of the p75 receptor-immunoreactive cells of these four nuclei were cholinergic. Combined immunotoxin injections into ventricles and the nucleus basalis produced a near complete loss (80-95%) of basal forebrain cholinergic neurons and acetylcholinesterase-positive fibers in the hippocampus, olfactory bulb and entorhinal cortex. This study provides the first anatomical data concerning the basal forebrain cholinergic system in ungulates. The availability of a selective cholinergic immunotoxin effective in sheep provides a new tool to probe the involvement of basal forebrain cholinergic neurons in cognitive processes in this species.     

Comparison of behavioral effects of nucleus basalis magnocellularis lesions and somatosensory cortex ablation in the rat

Cholinergic neurons in the nucleus basalis region of the forebrain project to various portions of the cerebral cortex, including somatosensory cortex. Degeneration of these neurons and their cortical projections is a major feature of the neuropathology of Alzheimer's disease. Injecting an excitotoxin into the basal forebrain to destroy nucleus basalis neurons provides a potentially useful animal model for studying the role of these neurons in Alzheimer's disease. Previously, we demonstrated that rats with nucleus basalis excitotoxin lesions performed poorly on a tactile discrimination task and on a test of working memory. In an effort to clarify further the role of impaired memory versus other types of impairment (e.g. disrupted somatosensory processing due to cholinergic deafferentation of somatosensory cortex), we compared a group of rats with bilateral nucleus basalis excitotoxin lesions and a group with bilateral somatosensory cortical ablations on a variety of behavioral tasks. Rats with nucleus basalis lesions performed as well as controls on a battery of neurological tests but exhibited increased emotionality unlike rats with somatosensory cortical ablations which performed poorly on the battery but were not hyperemotional. The two lesion groups were impaired significantly and to a comparable degree in performing two-choice tactile discriminations in a T-maze. In contrast, only rats with nucleus basalis lesions showed deficits in working memory as tested in an eight-arm radial maze. Both lesion groups performed comparably to sham controls on a test of reference memory involving a black/white discrimination in a T-maze. The findings suggest that rats with nucleus basalis lesions manifest disturbances in several of the same spheres (emotionality, somatosensory information processing, memory) that are disrupted in Alzheimer's disease and further confirm the utility of the excitotoxin lesion approach for studying the pathophysiology of Alzheimer's disease.     

Distribution of nerve growth factor receptor-like immunoreactivity in the adult rat central nervous system. Effect of colchicine and correlation with the cholinergic system--II. Brainstem, cerebellum and spinal cord

Multiple nuclei and fiber tracts in the adult rat brainstem and spinal cord were found to contain nerve growth factor receptor-related protein, as recognized by the monoclonal antibody 192-IgG. Both cholinergic and non-cholinergic sensory and motor regions demonstrated immunoreactive cell bodies and fibers. Nerve growth factor receptor-immunoreactive cells were seen in the mesencephalic nucleus of trigeminal nerve, superior colliculus, parabrachial, prepositus hypoglossal, raphe, dorsal and ventral cochlear, interstitial nucleus of the vestibular nerve, ambiguus and reticular nuclei, cerebellum and ventral spinal cord. Immunoreactive cells resembling neuroglia were distributed subpially along the superior colliculus. Intracerebroventricular injection of colchicine resulted in significantly increased nerve growth factor receptor immunoreactivity in all previously positive neurons and especially in certain neurons of the cochlear and ambiguus nuclei. It also resulted in the visualization of receptor immunoreactivity in certain neurons which were normally non-immunoreactive including cerebellar Purkinje cells, neurons of the central gray, locus coeruleus, facial, dorsal motor vagal and hypoglossal nuclei. In normal animals, nerve growth factor receptor-immunoreactive fibers and varicosities occurred in the trigeminal nerve nuclei, pontine, vestibular, parabrachial, facial, hypoglossal, dorsal motor vagal, solitary, gracile and cuneate nuclei and spinal cord. Although most fiber-like immunoreactive structures were probably axons and nerve terminals, neuroglial or extracellular localizations could not be excluded in some areas. For example, the medial nucleus of the inferior olive and most cerebellar nuclei contained diffuse non-fibrillar receptor immunoreactivity. The presence of nerve growth factor receptor-like immunoreactivity in cell bodies and fibers of several sensory and motor areas of the adult rat brainstem, cerebellum and spinal cord suggests multifocal actions of nerve growth factor or a nerve growth factor-like substance. Although the degree of overlap between nerve growth factor receptor- and choline acetyltransferase-containing regions in the brainstem is not as great as in the forebrain, our findings suggest a potential influence of nerve growth factor or nerve growth factor-like substances on cholinergic systems outside the forebrain. Furthermore, the disparities which occur imply that non-cholinergic nerve growth factor receptor-containing neurons of the brainstem, cerebellum and spinal cord may be affected by such trophic substances.     

The nucleus raphe interpositus in spinocerebellar ataxia type 3 (Machado-Joseph disease)

The nucleus raphe interpositus (RIP) plays an important role in the premotor network for saccades. Its omnipause neurons gate the activity of the burst neurons for vertical saccades lying within the rostral interstitial nucleus of the medial longitudinal fascicle and that for horizontal saccades residing in the caudal subnucleus of the pontine reticular formation. In the present study we investigated the RIP in five patients with clinically diagnosed and genetically confirmed spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease. Polyethylene glycol-embedded 100 microm serial sections stained for lipofuscin pigment and Nissl material as well as paraffin-embedded Nissl stained thin sections revealed the hitherto overlooked involvement of this pontine nucleus in the degenerative process underlying SCA3, whereby in four of our SCA3 patients the RIP underwent a conspicuous loss of presumed omnipause neurons. As observed in other affected brain structures, the RIP of all our SCA3 patients displayed reactive astrocytes and activated microglial cells, while some of the few of its surviving neurons harbored an ataxin-3-immunopositive intranuclear inclusion body. The findings of the present pathoanatomical study suggest that (1) neurodegeneration in the brain stem of terminal SCA3 patients is more widespread than previously thought and is not confined to cranial nerve nuclei involved in the generation of saccades but likewise involves the premotor network for saccades and (2) damage to the RIP may contribute to slowing of horizontal saccades in SCA3 patients but is not associated with saccadic oscillations as occasionally speculated.     

Cholinergic projections from the basal forebrain to the frontal cortex: a combined fluorescent tracer and immunohistochemical analysis in the rat

Cholinergic projections from the basal forebrain to some regions of the frontal cortex were studied by infusing propidium iodide (PI), a fluorescent tracer, into areas 6 and 10 and microscopically assessing the cellular co-localization of PI and immunohistochemically demonstrated choline-O-acetyltransferase (ChAT). The same brain sections were additionally processed for acetylcholinesterase (AChE, pharmacohistochemical regimen) and Nissl material (cresyl violet stain). Basal forebrain neurons projecting to the frontal cortex were found primarily in nucleus basalis, but others were located in association with the substantia innominata/lateral preoptic area, magnocellular preoptic area, and ansa lenticularis. These projection neurons were large (>25 μm in maximum soma extent), demonstrated ChAT-like immunoreactivity, stained intensely for AChE following systemic administration of bis-(1-methyl-ethyl)phosphorofluoridate, and were highly chromophilic.     

Fine structure of interleukin 18 (IL-18) receptor-immunoreactive neurons in the retrosplenial cortex and its changes in IL18 knockout mice

Interleukin 18 (IL-18) participates in the inflammatory immune response of lymphocytes. Delay in learning or memory are common in the IL-18 knockout mouse. Many IL-18-immunoreactive neurons are found in the retrosplenial cortex (RSC) and the subiculum. These neurons also contain the IL-18 receptor. We determined the location and the ultrastructure of the IL-18 receptor-immunoreactive neurons in the RSC and observed changes in the IL-18 receptor-immunoreactive neurons of the IL-18 knockout mouse. The IL-18 receptor-immunoreactive neurons were found specifically in layer V of the granular RSC. They were medium-sized neurons with a light oval nucleus and had little cytoplasm with many free ribosomes, rough endoplasmic reticulum and many mitochondria, but no Nissl bodies. The number of axosomatic terminals was about six per section. The IL-18 receptor-immunoreactive neurons were not found in the RSC in the IL-18 knockout mouse at 5 or 9 weeks of age. However, many small electron-dense neurons were found in layer V. Both the nucleus and cytoplasm were electron-dense, but not necrotic. The mitochondria and rough endoplasmic reticulum were swollen. The IL-18 receptor-immunoreactive neurons were presumed to be degenerating. The degeneration of the IL18-receptor-immunoreactive neurons in the RSC may cause the abnormal behaviors of the IL-18 knockout mice.     

Basal forebrain neurons provide major cholinergic innervation of primate neocortex

In 3 monkeys, lesions were made in the basal forebrain by microinjections of ibotenic acid into the nucleus basalis. Bilateral samples of multiple neocortical gyri were assayed for the activity of choline acetyltransferase. Compared to control hemispheres, enzyme activity was reduced up to 69% in the neocortex ipsilateral to the lesion; in addition, acetylcholinesterase staining was decreased at the lesioned site and in the ipsilateral cortex. These results support the concept that the principal cholinergic innervation of the primate neocortex is derived from axons and nerve terminals of neurons whose perikarya are located in the basal forebrain, particularly the nucleus basalis.     

The basal forebrain cholinergic system in the raccoon

The distribution of neurons displaying choline acetyltransferase (ChAT) immunoreactivity was examined in the raccoon basal forebrain using a rabbit antiscrum and a monoclonal antibody. Alternating sections were used for Nissl staining. ChAT-positive neurons were arranged in a continuous mass extending from the medial septum to the caudal pole of the pallidum. Based upon spatial relations to fibre tracts, the clustering of neuronal groups, and cytological criteria, the basal forebrain magnocellular complex can be subdivided into several distinct regions. Although clear nuclear boundaries were often absent, the ChAT-positive neurons were divided into: the nucleus tractus diagonalis (comprising pars septi medialis, pars verticalis and pars horizontalis); nucleus praeopticus magnocellularis; substantia innominata; and the nucleus basalis of Meynert. Comparison with Nissl-stained sections indicated the presence of varying proportions of non-cholinergic neurons clustered or arranged loosely within these basal forebrain subdivisions. These data provide a structural basis for studies concerned with the topographical and physiological aspects of the raccoon basal forebrain cholinergic projections and its comparison with the basal forebrains of other species.     

Atrophy of cholinergic neurons within the rat nucleus basalis magnocellularis following intracortical AF64A infusion

The rat nucleus basalis magnocellularis (nBM) was morphometrically analyzed following multiple intracortical AF64A infusions. At 3 weeks post-infusion, brains were histochemically double-stained for acetyl-cholinesterase and Nissl substance following diisopropylfluorophosphate pretreatment. Intracortical AF64A induced significant atrophy, but not degeneration, of nucleus basalis cholinergic cell bodies. These results suggest that retrograde cellular atrophy is associated with inhibition of presynaptic high-affinity choline transport on cortical terminals of nBM cholinergic neurons.     

Immunohistochemical evidence of substance P-like immunoreactivity in some 5-hydroxytryptamine-containing neurons in the rat central nervous system.

With the indirect immunofluorescence technique of Coons and collaborators a possible coexistence of 5-hydroxytryptamine (5-HT) and substance P in neurons of the lower medulla oblongata was explored. Antisera to 5-HT and to dopadecarboxylase (aromaticl-aminoacid decarboxylase), an enzyme probably present in immunologically indistinguishable forms both in catecholamine and 5-HT neurons, were used as markers for 5-HT neurons and an antiserum raised to synthetic substance P conjugated with bovine serum albumin for substance P-containing neurons. Five or 10 μm thick, consecutive sections were stained with the three antisera. Numerous cell somata in nucleus raphe magnus, nucleus raphe obscurus, nucleus raphe pallidus, pars α of the nucleus reticularis gigantocellularis and nucleus interfascicularis hypoglossi contained both substance P-like immunoreactivity and 5-HT (and dopadecarboxylase) immunoreactive material. After intraventricular or intracisternal injections of 5,6- or 5,7-dihydroxytryptamine, two neurotoxins assumed to cause degeneration mainly of 5-HT neurons, enlarged substance P and 5-HT (and dopadecarboxylase) positive fibres were seen in, around and lateral to the olivary complex. Furthermore, in these rats both substance P and 5-HT positive nerve terminals in the ventral horns of the spinal cord disappeared.These findings indicate that substance P and 5-HT may coexist not only in some cell bodies but also in axons and nerve endings. The latter conclusion must, however, remain tentative since the neurotoxins may cause unspecific damage and thus not only damage 5-HT (and postulated ‘SP-5-HT’) neurons.In further experiments reserpine was used, a drug known to deplete monoamines by affecting their storage sites. With a high dose of reserpine a marked depletion of 5-HT was obtained both in nerve terminals and cell bodies whereas substance P immunoreactive material seemed unaffected. Possible interpretations of these findings is that substance P and 5-HT have different storage sites within the neuron, or that reserpine selectively causes loss of 5-HT and not substance P from the same storage site.     

Differential effects of axotomy on substance P-containing and nicotinic acetylcholine receptor-containing retinal ganglion cells: time course of degeneration and effects of nerve growth factor.

The time course of degeneration of chick retinal ganglion cells was examined with Nissl stains and immunohistochemical methods for detection of substance P-like immunoreactive and nicotinic acetylcholine receptor immunoreactive neurons. Small lesions were made in the retinae, adjacent to the optic nerve head, and were subsequently sectioned parallel to the vitreal surface, permitting direct comparison of normal and axotomized retinal ganglion cells distal to the site of axon damage. At four and six days after surgery, a large number of degenerating cells with clear cytoplasm and pyknotic nuclei were seen. After eight, 10 and 14 days, many retinal ganglion cells displayed a chromatolytic response with dispersed Nissl granules, eccentric nuclei and the cells appeared crenulated. The number of apparently normal neurons in the ganglion cell layer in the axotomized region was reduced by about 50% six days following surgery, by about 70% on the 10th day and by about 75% on the 17th day. The remaining neurons in the ganglion cell layer were identified as displaced amacrine cells. From day 2 onwards, increased numbers of glial cells were present in the optic fibre, ganglion cell and inner plexiform layers. Many glial cells were enlarged and displayed extensive cytoplasmic processes, while others showed mitotic activity. Somata and proximal dendrites of retinal ganglion cells were intensely stained for substance P-like immunoreactivity at two and four days following surgery. At six, eight and 10 days, staining intensity was markedly reduced though still evident and at 14 and 17 days, substance P-like immunoreactivity had virtually disappeared. The persistence of limited substance P-like immunoreactive ganglion cells 10 days after surgery indicates that these cells have a relatively protracted response to axotomy. Nicotinic acetylcholine receptor-like immunoreactivity in the ganglion cells at two and four days following axotomy was substantially reduced. The majority of faintly stained nicotinic acetylcholine receptor-like immunoreactive ganglion cells, as visualized in counterstained sections, did not exhibit pyknosis in the immediate period following axotomy. Double label studies demonstrated that substance P-like immunoreactive ganglion cells were distinct from the nicotinic acetylcholine receptor-like immunoreactive ganglion cells. In a second set of experiments, nerve growth factor was then placed into the vitreous humor following intra-retinal axotomy. The somata, dendrites and proximal axons of lesioned substance P-like immunoreactive ganglion cells in these retinae were more intensely stained for a longer period of time and appeared more robust than cells from untreated retinae.(ABSTRACT TRUNCATED AT 400 WORDS)     

Distribution of nerve growth factor receptor immunoreactivity in the human hippocampus.

Nerve growth factor (NGF) receptor-like immunoreactivity has been demonstrated in the normal adult human hippocampus, using minimally fixed cryostat sections obtained from snap-frozen tissue and incubated with the mouse monoclonal antibody, ME 20.4. The majority of the reactivity was associated with nerve fibre processes and their terminals. Numerous fibres were apparent in the alveus, originating from the fornix, and extending into the stratum oriens and pyramidal layer of the hippocampal formation. A more diffuse particulate reactivity, presumed to be nerve terminal, was observed around the pyramidal neurons and in the stratum radiatum, stratum lacunosum moleculare and also in the dentate fascia. The pattern of hippocampal NGF receptor immunoreactivity was broadly similar to acetylcholinesterase histochemical localization, indicating a principal localization on cholinergic axons innervating this area. Preliminary observations indicate an overall reduction in NGF receptor-immunoreactive axons and terminals in old age and Alzheimer's disease.     

Distribution of nerve growth factor receptor-like immunoreactivity in the adult rat central nervous system. Effect of colchicine and correlation with the cholinergic system--I. Forebrain

Nerve growth factor receptor, as recognized by the monoclonal antibody 192-IgG, was localized to multiple regions of the adult rat forebrain. Immunoreactive cell bodies and fibers were seen in both sensory and motor regions which are known to contain cholinergic and non-cholinergic neurons. Specifically, nerve growth factor receptor immunoreactivity was present in cells lining the olfactory ventricle, rostral portion of the lateral ventricle, in basal forebrain nuclei, caudate putamen, globus pallidus, zona incerta and hypothalamus. Immunoreactive cells which were situated subpially along the olfactory ventricle and anterior portions of the lateral ventricle, and in the arcuate nucleus resembled neuroglia but could not definitively identified at the light microscopic level. Animals pretreated with intracerebroventricular colchicine displayed significantly increased nerve growth factor receptor immunoreactivity in all previously positive neurons and particularly in the medial preoptic area and ventral premammillary nucleus of the hypothalamus. In such animals, receptor immunoreactivity also appeared in previously non-immunoreactive cells of the hippocampal CA3 region and polymorph layer of the dentate gyrus as well as in the mitral cell layer of the olfactory bulb. Nerve growth factor receptor-immunoreactive fibers and varicosities were seen in the olfactory bulb, piriform cortex, neocortex, amygdala, hippocampus, thalamus, olivary pretectal nucleus and hypothalamus. In most regions, such fiber-like immunoreactive structures likely represented axon terminals, although in some areas, neuroglial or extracellular localizations could not be excluded. In this context, diffuse, non-fibrillar receptor immunoreactivity occurred in the lateral habenular nucleus and medial terminal nucleus of the accessory optic tract. Furthermore, intense nerve growth factor receptor immunoreactivity occurred along certain regions of the pial surface on the ventral surface of the brain. The distribution of nerve growth factor receptor-immunoreactive cell bodies and fibers in multiple sensory and motor nuclei suggests wide-spread influences of nerve growth factor throughout the adult rat forebrain. There is a high degree of overlap with regions containing choline acetyltransferase immunoreactivity. However, significant disparities exist suggesting that certain nerve growth factor receptor-containing non-cholinergic neurons of the rat forebrain may also be affected by nerve growth factor.     

Stability of neuronal number in the human nucleus basalis of Meynert with age

Numbers of neurons in the nucleus basalis of Meynert were estimated in seventeen non-demented patients who died of chronic hepatic or cardiopulmonary disease. Neurons were counted at the site of maximal neuronal density (SMND). This site was chosen by reviewing serial sections around the decussation of the anterior commissure and appeared to be comparable in different individuals. No correlation between numbers of neurons and age could be found. It appears that no uniform neuronal loss occurs in the nucleus basalis with age. Taken together with biochemical studies of cerebral cortical choline acetyltransferase activity, these findings suggest that there is no overall change in cholinergic input to cerebral cortex with age.     

Morphology of cochlear root neurons in the rat

Summary The morphology of large neurons in the cochlear nerve root of albino rat has been studied with a variety of techniques including Nissl and cell-myelin staining, Golgi impregnation, horseradish peroxidase back-filling of severed axons, transmission electron microscopy, and morphometry. The cells, called root neurons, resemble the globular cells of the ventral cochlear nucleus in having an oval cell body, an eccentric nucleus, an axon that projects centrally via the trapezoid body, and in receiving many primary-like axosomatic boutons. The root neurons, however, are larger than globular cells, and they have at least two types of dendrites oriented, respectively, parallel and across the cochlear nerve fibres. The soma, moreover, has less finely dispersed Nissl material, is less completely covered with terminals, and receives a smaller proportion of presumably inhibitory synapses. So far, this particular type of neuron has been observed only in rat and mouse.     

Striatal substance P cell clusters coincide with the high density terminal zones of the discontinuous nigrostriatal dopaminergic projection system in the cat: a study by combined immunohistochemistry and autoradiographic axon-tracing

A portion of the nigrostriatal projection that originates from presumably dopaminergic neurons in the caudal pars compacta of the substantia nigra and the suprajacent pars dorsalis (retrorubral area), was shown by [3H]amino acid autoradiographic tracing to distribute nonhomogeneously in the head of the caudate nucleus, such that zones of high density termination are in register with the archipelago of substance P cell clusters revealed immunohistochemically in the same and adjacent tissue sections of the cat's brain. Axons from this same portion of the substantia nigra distribute densely at caudal levels of the putamen where again substance P-immunoreactive striatal cells are numerous. In nearby tissue sections from the same cases, tyrosine hydroxylase-like immunoreactivity suggested only subtle variations in the density of the catecholamine axon network within the striatum. Thus, whereas dopamine axons are distributed densely throughout the striatum, those originating from cells in the caudal pars compacta et dorsalis of the substantia nigra and ending in the head of the caudate nucleus appear to terminate preferentially within the substance P cell clusters. These data suggest that the striatal substance P cells, which send their axons selectively to the entopeduncular nucleus and substantia nigra, but much less so the globus pallidus, are a major target of nigrostriatal dopamine transmission. This result is discussed with respect to the anatomical, neurochemical and functional organization of the striatifugal projection system.     

毁损Meynert基底核造成皮层及海马的乙酰胆硷酯酶减少行为学和形态学研究(英文)

本研究通过毁损Ｍ ｅｙｎｅｒｔ基底核（ｎｂＭ ）建立Ａｌｚｈｅｉｍ ｅｒ氏病（ＡＤ）动物模型。用乙酰胆硷酯酶（ＡＣｈＥ）细胞化学方法对模型动物大脑皮层及海马进行反应，评价ＡＣｈＥ 与ＡＤ 之间可能存在的关系。将４８ 只大鼠分成对照组及实验组，用Ｍｏｒｒｉｓ 水迷宫（ＭＷ Ｍ ）测定行为学变化。在实验组，以局部注射海人藻酸的方法毁损ｎｂＭ 。术后７ ｄ，再次检测其行为学变化。存活不同时间后，用ＡＣｈＥ 酶细胞化学技术染色脑切片，用图象分析系统测算海马层ＡＣｈＥ阳性神经元及纤维的体积密度。结果显示，毁损ｎｂＭ 鼠皮质及海马的ＡＣｈＥ阳性神经元纤维明显减少，其特征为片层结构缺失。这些变化在毁损ｎｂＭ 鼠３～４ 个月及９～１０ 个月组间无显著差异。本研究证明，毁损ｎｂＭ 出现的ＡＣｈＥ减少与ＡＤ 的发生关系密切，且与同一动物模型β 淀粉样蛋白及τ蛋白过度表达在时间上一致，后者是ＡＤ 病人的特征。     

Increased amyloid precursor protein expression and serotonergic sprouting following excitotoxic lesion of the rat magnocellular nucleus basalis: neuroprotection by Ca(2+) antagonist nimodipine

In the present study plastic neural responses to N-methyl-D-aspartate-induced excitotoxic lesions and the neuroprotective effects of the L-type voltage-dependent Ca(2+) channel antagonist nimodipine were investigated in the rat magnocellular nucleus basalis. Assessment of spontaneous behaviour in the elevated plus maze and small open-field paradigms on day 5 and day 14 post-surgery indicated anxiety and persistent hypoactivity of N-methyl-D-aspartate-lesioned rats, as compared with sham-operated controls. Nimodipine administration significantly alleviated the behavioural deficits. Quantitative histochemical analysis of acetylcholinesterase-positive fibre innervation of the somatosensory cortex and determination of the numbers of choline-acetyltransferase-positive proximal fibre branches of cholinergic projection neurons in the magnocellular nucleus basalis demonstrated a severe cholinergic deficit as a consequence of the excitotoxic lesion 14 days post-surgery. Nimodipine pre-treatment significantly attenuated the loss of cortical cholinergic innervation and preserved the functional integrity of cholinergic projection neurons in the magnocellular nucleus basalis. Double-labelling immunocytochemistry demonstrated increased amyloid precursor protein expression in shrinking and presumably apoptotic choline-acetyltransferase-positive neurons, whereas surviving cholinergic nerve cells were devoid of excessive amyloid precursor protein immunoreactivity. Moreover, as a consequence of N-methyl-D-aspartate infusion, rim-like accumulation of amyloid precursor protein-positive astrocytes was visualized in a penumbra-like zone of the excitotoxic injury. Furthermore, abundant sprouting of serotonergic projection fibres invading the damaged magnocellular nucleus basalis subdivision was demonstrated. Pharmacological blockade by the Ca(2+) antagonist nimodipine significantly attenuated both neuronal and glial amyloid precursor protein immunoreactivity and serotonergic fibre sprouting following N-methyl-D-aspartate infusion.The present data characterize plastic endogenous glial and neuronal responses in the magnocellular nucleus basalis model of acute excitotoxic brain damage. The increased amyloid precursor protein expression may indicate effective means of intrinsic neuroprotection, as secreted amyloid precursor protein isoforms are suggested to play a role in neuronal rescue following excitotoxic injury. From a pharmacological point of view, extensive sprouting of serotonergic projections in the damaged magnocellular nucleus basalis may also counteract N-methyl-D-aspartate excitotoxicity via serotonin-induced inhibition of Ca(2+) currents and membrane hyperpolarization. Hence, lesion-induced changes in spontaneous animal behaviour, such as anxiety and novelty-induced hypoactivity, may well be attributed to the considerable re-distribution of serotonergic projections in the basal forebrain. In conclusion, our present data emphasize a role of neuron-glia and neurotransmitter-system interactions in functional recovery after acute excitotoxic brain injury, and the efficacy of L-type Ca(2+) channel blockade by the selective 1,4-dihydropyridine antagonist nimodipine.