The section-Golgi-impregnation procedure--3. Combination of Golgi-impregnation with enzyme histochemistry and electron microscopy to characterize acetylcholinesterase-containing neurons in the rat neostriatum

Acetylcholinesterase reactivity in the frontal cortex of human and monkey: contribution of AChE-rich pyramidal neurons

Light and electron microscopic histochemistry were used to analyze the distribution of the enzyme acetylcholinesterase (AChE) in the frontal cortex of macaque monkey and human. In prefrontal, premotor, prelimbic, and medial paralimbic areas, AChE reactivity showed a characteristic bilaminar appearance due to a combination of positive neuronal and fiber labeling in deep layer III and layer V. In addition, layer I contained dense AChE-reactive fiber plexuses labeled throughout the frontal areas. One of the major issues addressed in this study was whether pyramidal neurons in the nonhuman primate cortex express AChE reactivity, as has been reported for humans. Three different histochemical methods were applied to provide confidence in the reliability of the results. Light microscopic analysis revealed strongly reactive, intensely stained pyramidal neurons in monkey as well as in the human. Further, these AChE-rich neurons exhibited the same pattern of laminar and regional variation in both species. In the prefrontal and premotor areas, AChE-rich pyramidal neurons predominated in layer III. In the motor cortex, they were also concentrated in layer III, but numerous AChE-rich pyramids were observed in layer V. In contrast, medial paralimbic areas had more AChE-rich neurons in layer V than in layer III. Finally, at the electron microscopic level, the subcellular distribution of AChE histochemical product in pyramidal neurons was identical in both monkey and human. The only difference noted between the two species was that the density of AChE-rich pyramidal neurons was greater in humans than in monkeys. Since nonhuman primates possess a system of AChE-reactive pyramidal neurons similar to human, they provide a potentially useful animal model for analyzing acetylcholinesterase neuronal systems in the cortex, which are compromised in various neuropathological diseases like Alzheimer's disease.

Differential inhibition of acetylcholinesterase molecular forms in normal and Alzheimer disease brain

Molecular forms of acetylcholinesterase were studied in three brain regions from Alzheimer disease patients and non-demented, age-matched controls. In Alzheimer disease patients, the membrane-bound G4 form was decreased in frontal (-71%) and parietal cortex (-45%) and in the caudate-putamen (-47%) from control levels. We also found a decrease of aqueous-soluble acetylcholinesterase molecular forms in the aqueous-soluble acetylcholinesterase molecular forms in the caudate-putamen region. The effect of three clinically significant acetylcholinesterase inhibitors, heptyl-physostigmine, physostigmine and edrophonium, on aqueous-soluble acetylcholinesterase molecular forms of the caudate-putamen was investigated. Heptyl-physostigmine, a physostigmine analogue, showed preferential inhibition for the G1 form. On the contrary, edrophonium inhibited the G4 form more potently than the G1 form. Physostigmine inhibited both forms with similar potency. The clinical implications of selective acetylcholinesterase inhibitors are discussed.

Morphological taxonomy of the neurons of the primate striatum

A quantitative taxonomy of primate striatal neurons was elaborated on the basis of the morphology of Golgi-impregnated neurons. Dendritic arborizations were reconstructed from serial sections and digitized in three dimensions by means of a video computer system. Topological, metrical, and geometrical parameters were measured for each neuron. Groups of neurons were isolated by using uni- and multidimensional statistical tests. A neuronal species was defined as a group of neurons characterized quantitatively by a series of nonredundant parameters, differing statistically from other groups, and appearing as a separate cluster in principal component analysis. Four neuronal species were isolated: (1) the spiny neuronal species (96% of striatal neurons) characterized by spine-free proximal dendrites (up to 31 microns) and spine-laden distal dendrites, which are more numerous, shorter, and less spiny in the human than in the monkey, (2) the leptodendritic neuronal species (2%) characterized by a small number of long, thick, smooth, and sparsely ramified dendrites, (3) the spidery neuronal species (1%) characterized by very thick dendritic stems and a large number of varicose recurrent distal processes, and (4) the microneuronal species (1%) characterized by numerous short, thin, and beaded axonlike processes. All striatal neurons give off a local axonal arborization. The size and shape of cell bodies were analyzed quantitatively in Golgi material and in materials treated for Nissl-staining, immunohistochemical demonstration of parvalbumin and histochemical demonstration of acetylcholinesterase. Only three types were distinguishable: small, round cell bodies corresponding to either spiny neurons or microneurons, medium-size elongated cell bodies, which were parvalbumin-immunoreactive and corresponded to leptodendritic neurons, and large round cell bodies, which were acetylcholinesterase-positive and corresponded to spidery neurons. Thorough analysis of previously elaborated classifications revealed that spidery neurons do not exist in rats and cats and that large cholinergic neurons in these species correspond to leptodendritic neurons. From this, it can be assumed that the dendritic domain of striatal cholinergic neurons is considerably smaller in primates than in other species. Computer simulations based on both the frequency of each neuronal species and their three-dimensional dendritic morphology revealed that the striatum consists of two intertwined dendritic lattices: a fine-grain lattice (300-600 microns) formed by the dendritic arborizations of spiny, spidery, and microneurons, and a large-grain lattice (1,200 microns) formed by the dendritic arborizations of leptodendritic neurons. This suggests that cortical information can be processed in the striatum through two different systems: a fine-grain system that would conserve the precision of the cortical input, and a large-grain system that would blur it.

Plasmalemmal appositions between cholinergic and non-cholinergic neurons in rat caudate-putamen nuclei

We have observed that in rat caudate-putamen nuclei, neurons immunolabeled for choline acetyltransferase were sometimes in direct apposition to unlabeled perikarya and dendrites [Pickel V. M. and Chan J. (1990) J. Neurosci. Res. 25, 263-280]. Similar juxtapositions between plasmalemmas of nerve cells each receiving input from one common terminal have been associated with activation of certain central neurons [Theodosis D. T. and Poulain D. A. (1989) Brain Res. 484, 361-366]. Thus, we sought to determine the relative abundance and ultrastructure of the appositions and the frequencies of shared synapses between choline acetyltransferase-labeled and unlabeled neurons in the rat striatum. A monoclonal antibody raised against choline acetyltransferase was localized in semi-adjacent ultrathin sections through 24 neurons in the dorsolateral caudate-putamen nuclei. Five of these choline acetyltransferase-labeled perikarya showed direct somatic appositions with unlabeled neurons. The remaining 19 of the choline acetyltransferase-labeled perikarya did not show somatic appositions with unlabeled perikarya; however, when traced through multiple (20-100) semi-adjacent sections their dendrites always showed extensive plasmalemmal juxtapositions with one or more unlabeled perikarya. The apposed perikarya had round nuclei and other characteristics of medium, spiny neurons. The majority of the apposed cholinergic and non-cholinergic neurons were postsynaptic to at least one common unlabeled terminal. These terminals usually formed symmetric junctions. At sites of appositions, the plasmalemmas of choline acetyltransferase-immunoreactive soma or dendrites and unlabeled neurons were closely spaced without intervening astrocytic processes. The appositions lacked the ultrastructural features typical of gap-junctions, but did occasionally show parallel arrays of thin (1-2 nm) electron-dense bands. In both labeled and unlabeled perikarya, the nuclei were separated from the appositional zones by narrow (0.7-3.3 microns) rims of cytoplasm. This cytoplasmic rim contained subsurface cisternae and other less specialized smooth and rough endoplasmic reticulum, and vesicular structures. The findings suggest that in the caudate-putamen nuclei (1) the tonically active cholinergic neurons [Wilson C. J. et al. (1990) J. Neurosci. 10, 508-519] may modulate or be modulated by non-cholinergic spiny neurons through non-synaptic somatic or dendritic appositions, and (2) that both neurons may be simultaneously inhibited by shared afferent input. Activation of this system could facilitate coordinated movements through synchronization of cholinergic interneurons and spiny projection neurons containing GABA or other transmitters.

Factors regulating the expression of acetylcholinesterase-containing neurons in striatal cultures: effects of chemical depolarization

The influence of chemical depolarization on the survival and differentiation of acetylcholinesterase (AChE)-containing neurons was examined in primary rat striatal cultures, maintained in different types of media (serum-free and serum-supplemented) and substrate (poly-ornithine and astrocyte monolayer). Chronic application of 5 microM veratridine resulted in a significant loss of neurites by AChE-positive cells, while a higher concentration (20 microM) reduced the number of stained cell bodies. These effects appeared to be selective with regard to AChE-positive cells, as indicated by morphological observations of the cells in the treated cultures and receptor binding measurements. Similarly, elevation of extracellular KCl levels (20-60 mM) produced a dose-dependent neurite loss by AChE-containing cells. Blockers of voltage-sensitive Ca2+ channels--verapamil (1 microM) and nifedipine (1 microM)--did not affect the veratridine-induced neurite loss, while tetrodotoxin (0.1 microM) had a partial effect. When cultures treated with 5 microM veratridine were allowed to recuperate for several days, the number of AChE-positive cells possessing neurites returned close to control values, thus indicating the reversibility of the effect of chemical depolarization. The possibility that chronic neuronal depolarization in the striatum might play a role in regulation of the neuronal processes outgrowth by AChE-containing cells is discussed.

Synaptic connections of neurones identified by Golgi impregnation: characterization by immunocytochemical, enzyme histochemical, and degeneration methods

For more than a century the Golgi method has been providing structural information about the organization of neuronal networks. Recent developments allow the extension of the method to the electron microscopic analysis of the afferent and efferent synaptic connections of identified, Golgi-impregnated neurones. The introduction of degeneration, autoradiographic, enzyme histochemical, and immunocytochemical methods for the characterization of Golgi-impregnated neurones and their pre- and postsynaptic partners makes it possible to establish the origin and also the chemical composition of pre- and postsynaptic elements. Furthermore, for a direct correlation of structure and function the synaptic interconnections between physiologically characterized, intracellularly HRP-filled neurones and Golgi-impregnated cells can be studied. It is thought that most of the neuronal communication takes place at the synaptic junction. In the enterprise of unravelling the circuits underlying the synaptic interactions, the Golgi technique continues to be a powerful tool of analysis.

Fetal neostriatal transplants in the rat: a light and electron microscopic Golgi study

Fetal striatal neurons were transplanted into the ibotenic acid lesioned rat striatum. Three months after transplantation the grafted tissue was Golgi-impregnated and examined at the light microscopic level to determine the morphological characteristics of the transplanted neurons. Golgi-impregnated neurons were then gold-toned and examined at the electron microscopic level. The transplanted neurons were classified by both somatic size and somatic and dendritic morphology, which demonstrated that at least seven distinct cell types are present in striatal grafts. Type I large neurons had aspinous somata, sparsely spined dendrites, and indented nuclei, whereas type II large neurons displayed somatic spines, sparsely spined dendrites, and indented nuclei. Type I medium neurons exhibited aspinous somata and proximal dendrites, heavily spined distal dendrites, and unindented nuclei. Type II medium neurons had somatic spines, sparsely spined dendrites, and indented nuclei. Type III medium neurons had aspinous somata, poorly branched and sparsely spined dendrites, and indented nuclei, while type IV medium neurons had aspinous somata, highly branched and sparsely spined dendrites, and indented nuclei. Type V medium neurons displayed aspinous somata, varicose dendrites, and indented nuclei. These results demonstrate that transplanted fetal striatal neurons differentiate into morphologically and ultrastructurally distinct striatal cell types.

Ultrastructural localization of [125I]neurotensin binding sites to cholinergic neurons of the rat nucleus basalis magnocellularis

The distribution of specifically-labeled neurotensin binding sites was examined in relation to that of cholinergic neurons in the rat nucleus basalis magnocellularis at both light and electron microscopic levels. Lightly prefixed forebrain slices were either labeled with [125I](Tyr3) neurotensin alone or processed for combined [125I]neurotensin radioautography and acetylcholinesterase histochemistry. In light microscopic radioautographs from 1-microns-thick sections taken from the surface of single-labeled slices, silver grains were found to be preferentially localized over perikarya and proximal processes of nucleus basalis cells. The label was distributed both throughout the cytoplasm and along the plasma membrane of magnocellular neurons all of which were found to be cholinesterase-positive in a double-labeled material. Probability circle analysis of silver grain distribution in electron microscopic radioautographs confirmed that the major fraction (80-89%) of specifically-labeled binding sites associated with cholinesterase-reactive cell bodies and dendrites was intraneuronal. These intraneuronal sites were mainly dispersed throughout the cytoplasm and are thus likely to represent receptors undergoing synthesis, transport and/or recycling. A proportion of the specific label was also localized over the nucleus, suggesting that neurotensin could modulate the expression of acetylcholine-related enzymes in the nucleus basalis. The remainder of the grains (11-20%) were classified as shared, i.e. overlied the plasma membrane of acetylcholinesterase-positive neuronal perikarya and dendrites. Extrapolation from light microscopic data, combined with the observation that shared grains were detected at several contact points along the plasma membrane of cells which also exhibited exclusive grains, made it possible to ascribe these membrane-associated receptors to the cholinergic neurons themselves rather than to abutting cellular profiles. Comparison of grain distribution with the frequency of occurrence of elements directly abutting the plasma membrane of neurotensin-labeled/cholinesterase-positive perikarya indicated that labeled cell surface receptors were more or less evenly distributed along the membrane as opposed to being concentrated opposite abutting axon terminals endowed or not with a visible junctional specialization. The low incidence of labeled binding sites found in close association with abutting axons makes it unlikely that only this sub-population of sites corresponds to functional receptors. On the contrary, the dispersion of labeled receptors seen here along the plasma membrane of cholinergic neurons suggests that neurotensin acts primarily in a paracrine mode to influence the magnocellular cholinergic system in the nucleus basalis.

The postnatal expression of acetylcholinesterase in somatostatin-positive cells of mouse hippocampus

The neuroanatomical distributions of acetylcholinesterase (AChE) staining and somatostatin-like immunoreactivity (SOMLI) of neurons intrinsic to the mouse hippocampal formation have been evaluated during postnatal development. Besides the progressive development of neuropil staining for AChE, as a consequence of the septohippocampal innervation, intense AChE staining was also expressed in a subpopulation of neurons intrinsic to the stratum oriens and the hilus of dentate gyrus. In the stratum oriens, the number of AChE-positive cells increased between postnatal day (PND) 3 and PND 10 and declined slightly after PND 21. In the hilus of the dentate gyrus, the number of AChE-stained cell bodies increased progressively until PND 21 when the adult complement was achieved. The AChE-positive neurons of strata radiatum and lacunosum-moleculare, which were few and scattered, increased progressively from PND 7 until adulthood. SOMLI-positive neurons were present in the hippocampal formation by PND 3, and their density showed initial increases followed by decreases in the second to third postnatal week. SOMLI cell distribution on the other hand did not change remarkably during subsequent maturation. Because of the similar developmental time course and localization of AChE and SOMLI neurons, co-localization was assessed by a double-staining method. A large percentage of the neurons staining for one of these markers also stained for the other. In the stratum oriens, from PND 3 to PND 10, the number of SOMLI neurons expressing AChE was increased while a slight decrease from the PND 21 to adulthood was evident. Virtually all SOMLI-positive neurons in the dentate gyrus stained for AChE from PND 7 through adulthood, although the intensity of AChE reactivity declined with maturation.

Distribution of dopamine D-2 receptors in the rat striatal complex and its comparison with acetylcholinesterase

The distribution of D-2 dopamine receptors in the rat striatal complex was studied with autoradiography after specific in vivo labeling with the dopamine agonist [3H]N-n-propylnorapomorphine and subsequent irreversible fixation. This labeling technique allows the visualization of D-2 receptors at the cellular level by light microscopic emulsion autoradiography. During the preparation of emulsion autoradiograms, the recovery of the label was 75%, the specific and the aspecific label being equally affected. The distribution of label before and after the loss of radioactive label occurred, did not show differences. In rat neostriatum, dopamine D-2 receptors are not homogeneously distributed: in the caudate-putamen the density is laterally higher than medially. Moreover, there exists a mosaic-like pattern of receptor density. In the ventral striatum, comprising the fundus striati, nucleus accumbens septi and olfactory tubercle, the receptor density is lower than in the caudate-putamen, except for the core regions in the islands of Calleja and the rim of these islands, which contain high (as high as the lateral caudate-putamen) and a moderate density of receptors, respectively. In caudate-putamen and lateral nucleus accumbens it appeared that the intensity of acetylcholinesterase staining parallels more or less the distribution of dopamine D-2 receptors. In medial nucleus accumbens and in olfactory tubercle, the high intensity of acetylcholinesterase is not paralleled by a high D-2 receptor labeling density. This receptor labeling density does not seem to be matched by differences in densities of medium-sized neuronal cell bodies.

Basal forebrain neurons undergo somatal and dendritic remodeling during postnatal development: a single-section Golgi and choline acetyltransferase analysis

In attempt to determine whether or not morphologic changes occur in the cholinergic basal forebrain during postnatal development. Golgi-impregnated and choline acetyltransferase-positive cells were examined in adult and postnatal day (P) 10, 14, 18, and 27 rats. Light microscopic analyses revealed progressive increases in in cross-sectional cell body area, number of primary dendrites, number of dendritic branch points, and length of the longest dendrite that peaked at P18 and thereafter decreased to smaller adult values with the exception of dendritic length which monotonically increased until adulthood. These findings suggest that extensive remodeling of cholinergic neurons in the basal complex occurs even at relatively late postnatal periods.

Cortical projection of giant neostriatal neurons in the cat. Light and electron microscopic horseradish peroxidase study

Following voluminous injections of horseradish peroxidase (HRP) in various neocortical fields, a small number of labeled large neurons are observed ipsilaterally in the putamen, striatal ponticuli, caudate nucleus, and nucleus accumbens septi. The bulk of the corticopetal cells are found in the putamen and in the striatal ponticuli. A more significant number of labeled neurons is encountered following injections in auditory and sensorimotor cortex, followed by the prefrontal and premotor cortex; very few cells project to the visual cortex. Ultrastructurally, the large HRP-labeled neurons display an eccentrically located, indented nucleus, abundant granular endoplasmic reticulum forming Nissl bodies, well developed Golgi zones, and numerous dense bodies. The simultaneous demonstration of retrogradely transported HRP and acetylcholinesterase (AChE) suggest that the large neurons are presumably cholinergic. These results provide evidence that at least some of the giant striatal neurons are efferent cells. The coincidence of cytological, histochemical, and hodological criteria invite the speculation that the giant corticopetal neostriatal neurons might be related to the magnocellular cholinergic groups of the basal forebrain (especially the Ch4 group).

Three-dimensional organization of the striosomal compartment and patchy distribution of striatonigral projections in the matrix of the cat caudate nucleus

Acetylcholinesterase staining on successive frontal or sagittal sections was used to determine the three-dimensional organization of the striosomal and matrix compartments in the adult cat caudate nucleus. Reconstruction drawings of the acetylcholinesterase-poor zones (striosomes) indicated that the striosomal compartment is a labyrinthine network organized in the rostrocaudal and mediolateral axis which is reproducible from one animal to another. Four main anteroposterior channels converging in the mediorostral pole of the caudate nucleus were distinguished. Seven to eight diagonally oriented channels crossing the previous ones were seen also in the mediolateral axis on the central core of the caudate nucleus. The pattern of organization of the numerous and tortuous striosomal channels was more complicated medially, while the lateral part of the caudate nucleus was represented mainly by the matrix compartment. In addition, a sub-compartmentation of the matrix was demonstrated by retrograde tracing studies made by injecting either horseradish peroxidase-wheat germ agglutinin, [14C]amino acids or a mixture of horseradish peroxidase-wheat germ agglutinin and [14C]amino acids in several areas of the substantia nigra pars reticulata. Labelled patches were seen with both tracers, their topographical localization depended on the nigral injection site but reconstruction analysis indicated that the populations of cells which innervate the substantia nigra pars reticulata originate in the two third lateral parts of the caudate nucleus all along its rostrocaudal extension. Examination of horseradish peroxidase-wheat germ agglutinin labelled cells indicated that not all cells were labelled in patches suggesting a further sub-compartmentation of these patches. Finally, a comparison of the topographical distributions of labelled patches and of striosomes revealed that most patches were located in the extrastriosomal matrix.

Acetylcholinesterase on the dendrites of central cholinergic neurons: an electron microscopical study in the ferret

A combination of choline acetyltransferase immunohistochemistry and acetylcholinesterase histochemistry was used to characterize the ultrastructural distribution of acetylcholinesterase in identified cholinergic and non-cholinergic neurons in the ferret brain. Previous studies have shown that most of the cholinergic input to the brain arises from choline acetyltransferase-positive neurons found in the neostriatum, basal forebrain and dorsolateral pontine tegmentum. In all these cells intense staining for acetylcholinesterase was localized within the cisternae of the rough endoplasmic reticulum, in the nuclear envelope and Golgi apparatus, and along the plasma membranes of the soma and dendrites. In contrast, the distribution of acetylcholinesterase in non-cholinergic neurons was restricted mainly to the cisternae of the endoplasmic reticulum and the nuclear envelope. Since previous studies have associated high levels of acetylcholinesterase staining with non-cholinergic neurons in the locus coeruleus and substantia nigra zona compacta, these areas were examined as well. The ultrastructural localization of acetylcholinesterase in the principal locus coeruleus neurons was as observed in typical non-cholinergic neurons. On the other hand, the distribution of acetylcholinesterase in the principal cells of the zona compacta of the substantia nigra was more like that found in cholinergic neurons. In conclusion, the subcellular distribution of acetylcholinesterase in the principal cholinergic neurons of the brain follows a characteristic pattern which, with one exception, is different from that of acetylcholinesterase-positive non-cholinergic neurons.

The distribution and compartmental organization of the cholinergic neurons in nucleus accumbens of the rat

In this study the distribution of the cholinergic neurons was examined in relation to the compartmental organization of nucleus accumbens. This was accomplished by charting the location of the choline acetyltransferase-immunoreactive neurons and mapping their distribution in relation to cytoarchitectural features and the patterns of acetylcholinesterase activity and enkephalin immunoreactivity. Choline acetyltransferase-containing perikarya are inhomogeneously distributed in nucleus accumbens. Their density is lowest at the rostral pole and highest, caudomedially, at the septal pole. The cells form a compact, medial column and a diffuse, lateral zone and, moreover, there are distinct gradients in their distribution. The highest numbers of immunoreactive perikarya occur within the intensely immunostained zones of choline acetyltransferase-immunoreactive neuropil in ventral and ventromedial parts of the nucleus, whereas lower numbers coincide with choline acetyltransferase-poor zones in the central part of the nucleus. Zones of intensely choline acetyltransferase-immunoreactive neuropil are largely in register with regions of high acetylcholinesterase activity in middle and caudal parts of the nucleus but do not coincide rostrally. Choline acetyltransferase-rich zones correspond to moderate enkephalin immunoreactivity in the outer shell of the nucleus, but a moderately choline acetyltransferase-immunostained matrix surrounds "patches" of intense enkephalin immunoreactivity in the core. Small aggregates of cells, which feature commonly in nucleus accumbens, seem to be avoided by both choline acetyltransferase- and enkephalin-immunoreactive zones. Choline acetyltransferase-immunoreactive processes are mostly confined by the boundaries of their respective immunoreactive zones. Few choline acetyltransferase-immunoreactive neurons lie in the enkephalin-rich patches and those that lie close to the patches show little preference in the directionality of their processes such that some cross the borders, whereas others do not. Thus, our findings show that the cholinergic elements are differentially distributed within nucleus accumbens; that these elements are compartmentally ordered; and that, in light of their limited access to other compartments, they possibly play only a minor role in intercompartmental communication.

New perspectives in basal forebrain organization of special relevance for neuropsychiatric disorders: the striatopallidal, amygdaloid, and corticopetal components of substantia innominata

The basal forebrain is critically involved in functions representing the highest levels of integration. Only recently has a relatively clear anatomical picture of this important area begun to emerge. The territory that has generally been referred to as the "substantia innominata" appears to be composed of portions of three recognizable forebrain structures: the ventral striatopallidal system, the extended amygdala and the magnocellular corticopetal system. (1) Rostrally, the striatopallidal system reaches ventrally to the base of the brain. (2) Caudal to the ventral extension of the striatopallidal system elements of the centromedial amygdala and bed nucleus of the stria terminalis are merged so that these two areas together with this subpallidal corridor form a large forebrain unit that might be described as an "extended amygdala". (3) Large cholinergic and non-cholinergic corticopetal neurons form a more or less continuous aggregate that is interwoven with the striatopallidal and extended amygdala systems in basal forebrain. Consideration of morphological and connectional characteristics of basal forebrain suggests that the corticopetal cell groups, together with magnocellular elements of the striatum, serve similar functional roles for the striatopallidal system, the extended amygdala, and the septal-diagonal band complex. Specifically, the output of medium spiny neurons in striatum, extended amygdala, and lateral septum are directed toward somewhat larger sparsely or moderately spiny neurons with radiating dendrites which in turn project to diencephalon and brainstem or provide either local feedback (e.g. in striatum) or distal feedback to cortex. The functional implications of this parallel processing of descending forebrain afferents are discussed.

Regional differences in reappearance of D2-dopamine receptors in the rat caudate-putamen complex after irreversible inactivation

The reappearance of D2-receptors in the striatum of the rat was studied by autoradiography after in vivo labeling with [3H]N-n-propylnorapomorphine ([3H]NPA) at various time intervals after the inactivation of dopamine receptors by intraperitoneal administration of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). Within two days after inactivation the labeling had decreased to 18% of controls. Thereafter, the label reappeared and after 8 days or more reached levels of 80% of that of untreated controls. Autography showed that 4 h after EEDQ treatment no preferential labeling of the striatum can be seen. Five days after EEDQ a slight difference in labeling density between the medial and lateral striatum was detected, whereas after 18 days a prominent lateromedial gradient in silver grain density was seen, resembling the gradient seen without EEDQ treatment. This silver grain gradient is not paralleled by the density of medium-sized neuronal cell bodies. This suggests a difference in synthesis rate of receptors either in other cells than the medium-sized neuron or, alternatively, in otherwise indistinguishable medium-sized neurons. Five days after EEDQ treatment, clusters of silver grains in the lateral striatum were seen. These clusters have a diameter of 150-400 microns and are separated from each other at 200-500 microns. Each cluster may represent newly synthesized receptors of a single neuron (e.g. cholinergic or somatostatinergic interneuron).

Distribution of enkephalin-immunoreactive nerve fibres and terminals in the region of the nucleus basalis magnocellularis of the rat: a light and electron microscopic study

This investigation was carried out on the distribution of enkephalin-containing nerve fibres and terminals in the region of the nucleus basalis magnocellularis (NBM) of the rat. At the light microscope (LM) level, enkephalin-immunoreactive sites and endogenous choline acetyltransferase (ChAT) were demonstrated by employing the two-colour immunoperoxidase staining technique, using highly specific monoclonal antibodies against enkephalin and ChAT. A pharmacohistochemical procedure to reveal acetylcholinesterase (AChE)-synthesizing neurons combined with the peroxidase-antiperoxidase (PAP) immunocytochemical technique to detect endogenous enkephalins, provided ultrastructural data on the relationships of neuronal elements containing AChE and enkephalins in the region of the NBM. At the LM level, cholinergic neurons of the NBM were surrounded by a dense network of enkephalin-immunoreactive nerve fibres. Electron microscopic (EM) observations of histochemically characterized structures, that were first identified in the LM, revealed that intensely AChE-stained structures in the region of the NBM received sparse synaptic inputs from enkephalin immunoreactive terminals. Synaptic inputs of immunoreactive terminals onto intensely AChE-stained neuron cell bodies were not detected. Synaptic contacts onto proximal AChE-positive dendrites were sparse, but the density increased on more distal regions of the dendrites. All immunoreactive boutons studied established symmetrical synaptic contacts with AChE-positive post-synaptic structures. The pattern of the synaptic input to these cells differs strikingly from that onto typical globus pallidus neurons. The perikarya and dendrites of the latter neurons were characteristically ensheathed in immunoreactive synaptic boutons. Results are consistent with the view that enkephalin-like substances in the rat might be synaptic transmitters or neuromodulators in the area of the NBM and that cholinergic neurons of the NBM (Ch4) are integrated into the circuitry of the basal ganglia. Enkephalins may play an important role regulating the extrinsic cholinergic innervation of the neocortex.

Glutamate decarboxylase immunoreactive neurons in rat neostriatum: their morphological types and populations

Morphological types and populations of glutamate decarboxylase (GAD)-immunoreactive neurons in rat neostriatum (Str) were studied. Str of colchicine-treated animals contained 3 types of neurons immunoreactive for GAD. The first type, which makes up 80-84% of Str neurons, was medium in size and showed moderate intensity GAD-staining. The somatic morphology of the neurons was identical to the medium-spiny projection neuron. The second type, 3-5% of Str neurons, was small to medium in size and was intensely stained for GAD. The somata of the neurons were round or oval and contained a narrow ring of cytoplasm surrounding the nucleus, which often had nuclear invaginations. There were only a few in each section of the third type, which were large, polygonal, and intensely stained, GAD-immunoreactive neurons, including all 3 types, ranged from 85-87% of the total neuron population. The present study indicated that GABAergic neurons in the Str are not a single morphological type and that most Str projection neurons are GABAergic.

Cholinergic synaptic input to different parts of spiny striatonigral neurons in the rat

The postsynaptic targets of cholinergic boutons in the rat neostriatum were assessed by examination in the electron microscope of boutons that were immunoreactive for choline acetyltransferase, the synthetic enzyme for acetylcholine. These boutons formed symmetrical synaptic specializations with neostriatal neurons. Of 209 immunoreactive synaptic boutons observed in random searches of the neostriatum, 45% made contact with dendritic shafts, 34% with dendritic spines, and 20% with neuronal perikarya. Many of the postsynaptic structures had ultrastructural characteristics of the most common type of striatal neuron, the medium-size densely spiny neuron. This was confirmed by the examination in the electron microscope of Golgi-impregnated medium-size spiny neurons from sections that had also been immunostained for choline acetyltransferase. Immunoreactive boutons formed symmetrical synaptic specializations with all parts of the neurons examined, i.e., perikarya, proximal and distal dendritic shafts, and dendritic spines. Two of the Golgi-impregnated medium-size spiny neurons that received input from the cholinergic boutons were also retrogradely labelled with horseradish peroxidase that had been injected into the substantia nigra, they were thus further characterized as striatonigral neurons. Similarly, seven retrogradely labelled perikarya of striatonigral neurons were found to receive input from the cholinergic boutons. It is concluded that cholinergic boutons in the neostriatum form synaptic specializations and that one of their major targets is the medium-size densely spiny neuron that projects to the substantia nigra. The topography of the cholinergic afferents of these cells is distinctly different from that of other boutons derived from local neurons and from boutons that form asymmetrical synaptic specializations, but it is similar to that of the dopaminergic boutons originating from neurons in the substantia nigra.

Cellular substrate of the histochemically defined striosome/matrix system of the caudate nucleus: a combined Golgi and immunocytochemical study in cat and ferret

In order to learn what morphological substrate might underly the histochemical compartments of the neostriatum, sections of the caudate nucleus and the putamen of cats and ferrets were stained immunocytochemically with antisera directed against several neuropeptides and transmitter-related enzymes and were then Golgi-impregnated. Adjacent sections were stained to reveal acetylcholinesterase activity to identify the acetylcholinesterase-poor striosomes. The immunostaining produced by several of the antibody preparations was in register with the acetylcholinesterase-poor striosomes but the most prominent staining of these zones occurred with the antibodies directed against substance P. The striosomes were delineated by intense substance P-immunostaining of neuronal perikarya and dendrites, and in the rostral and dorsal caudate nucleus the boundary between substance P-immunostained and extrastriosomal matrix was abrupt. For these reasons we analysed Golgi-impregnated neurons in sections immunostained for substance P in order to assess the influence of the chemically defined striosomal architecture on the position and dendritic arborization of neurons located both within the striosomes and within the extrastriosomal matrix. The most commonly impregnated neurons were of the medium-size densely spiny class. Those that were present within the striosomes and lay within one dendritic radius of the boundary were divided into two types: (1) neurons whose dendritic arborization was apparently not influenced by the boundary and (2) neurons whose dendritic arborization was markedly influenced by the boundary. For neurons of the latter type, dendrites either emerged from the parts of the perikaryon away from the boundary, so avoiding crossing it, or they exhibited abrupt changes in their course, apparently to avoid crossing the boundary. Spiny neurons located in the extrastriosomal matrix but close to the striosomal boundary had dendrites that were either influenced by, or not influenced by the compartmental boundary. We conclude that there is a specific cytoarchitecture underlying the histochemical compartments of the neostriatum and that different sub-populations of medium-size spiny neurons underly (1) the segregation of information flow in striosomes and the extrastriosomal matrix and (2) communication between striosomes and the extrastriosomal matrix.

Neurotransmitters in the mammalian striatum: neuronal circuits and heterogeneity

The major input and output pathways of the mammalian striatum have been well established. Recent studies have identified a number of neurotransmitters used by these pathways as well as by striatal interneurons, and have begun to unravel their synaptic connections. The major output neurons have been identified as medium spiny neurons which contain gamma-aminobutyric acid (GABA), endogeneous opioids, and substance P. These neurons project to the pallidum and substantia nigra in a topographic and probably chemically organized manner. The major striatal afferents from the cerebral cortex, thalamus, and substantia nigra terminate, at least in part, on these striatal projection neurons. Striatal interneurons contain acetylcholine, GABA, and somatostatin plus neuropeptide Y, and appear to synapse on striatal projection neurons. In recent years, much activity has been directed to the neurochemical and hodological heterogeneities which occur at a macroscopic level in the striatum. This has led to the concept of a patch-matrix organization in the striatum.

Neostriatal cholinergic neurons receive direct synaptic inputs from dopaminergic axons

We used an electron microscopic 'mirror technique' to determine whether cholinergic neurons are in direct synaptic contact with dopaminergic axons in the rat neostriatum. Tyrosine hydroxylase-immunoreactive axons make synaptic contacts with the somata and proximal dendrites of large choline acetyltransferase-immunoreactive striatal neurons which are thought to be interneurons. This provides morphological evidence that nigrostriatal dopaminergic neurons can influence monosynaptically the striatal cholinergic neurons.

Sparing of acetylcholinesterase-containing striatal neurons in Huntington's disease

The present study demonstrates that large aspiny neurons, containing the enzyme acetylcholinesterase (AChE), are relatively preserved in the caudate nucleus and putamen in Huntington's disease (HD). Although histochemical evidence indicates that AChE and choline acetyltransferase (ChAT) co-localize within the same striatal neurons, measurements of ChAT activity showed significant reductions in enzyme activity, as others have reported. Reduced ChAT activity in the presence of presence of persistent AChE-positive neurons may be a consequence of loss of synaptic terminals resulting from the death of spiny neurons. The selectivity of neuronal sparing in HD may be related to the patterns of synaptic contact or a paucity of excitatory amino acid receptors on striatal aspiny neurons.

Identification of acetylcholinesterase-reactive neurons and neuropil in neostriatal transplants

To identify and describe neurons in neostriatal transplants that synthesize acetylcholinesterase (AChE), the present study has utilized the irreversible AChE inhibitor diisopropylfluorophosphate (DFP) combined with AChE histochemistry. Dissociated suspensions of tissue taken from the striatal ridge of embryos at 14 days of gestation were transplanted into the neostriatum of adult rats 5 days after intrastriatal kainic acid lesions. Two types of AChE neurons have been identified in transplants treated with DFP. One type resembled the large intensely reactive AChE neuron that is thought to be a cholinergic interneuron of the normal neostriatum. The other type resembled smaller, less reactive AChE neurons of the neostriatum, as well as medium-sized, lightly reactive AChE neurons of the globus pallidus. Qualitative observations suggest that these less reactive AChE neurons were more numerous in transplants compared to the normal neostriatum. Both AChE neuronal types were found in segregated clusters throughout the grafts. Transplants processed for AChE histochemistry without DFP treatment contained two types of AChE neuropil. Dark areas of AChE neuropil similar in intensity to the normal neostriatum were found between larger areas of lighter AChE neuropil. These results demonstrate that neostriatal transplants contain AChE neurons and suggest that these neurons contribute to the AChE reactivity within the graft.

Characterization of substance P- and [Met]enkephalin-immunoreactive neurons in the caudate nucleus of cat and ferret by a single section Golgi procedure

Modifications of the single-section Golgi-impregnation procedure of Gabbott and Somogyi are described. The modifications allow easier and more rapid preparation of the sections for Golgi-impregnation and easier handling of large numbers of serial sections. The technique consists of placing a section that has been treated with osmium tetroxide and potassium dichromate on a microscope slide and "sandwiching" it with a second microscope slide. The two slides are held together at one end by tape and the assembly is dipped into a solution of silver nitrate. Golgi-impregnation of neurons occurs within a few hours and is generally complete within 12 h. The technique has been applied to sections through the caudate nucleus of the cat and ferret in order to define the morphological characteristics of striatal substance P- and methionine enkephalin-immunoreactive neurons. Sections were first incubated to reveal the immunoreactive structures and then subjected to the Golgi method. Golgi-impregnated neurons that were immunoreactive for either substance P or methionine enkephalin had medium-size perikarya from which several dendrites emerged. The dendrites branched close to the perikaryon; secondary and higher order dendrites were densely laden with spines, as many as 15 spines per 10 microns of dendrite. It is concluded that both striatal substance P-containing and methionine enkephalin-containing neurons are of the medium-size densely spiny type. Medium-size densely spiny neurons may be homogeneous with respect to their somatodendritic morphology but heterogeneous with respect to their chemical characteristics and axonal morphology.

Synaptic organization of cholinergic neurons in the monkey neostriatum

Cholinergic neurons in the monkey neostriatum were examined at the light and electron microscopic level by immunohistochemical methods in order to localize choline acetyltransferase (ChAT), the synthesizing enzyme for acetylcholine. At the light microscopic level a sparse distribution of cholinergic neurons was identified throughout the caudate nucleus. Neurons had large (25-30 microns) somata, eccentric invaginated nuclei, primary dendrites of unequal diameters, and varicosities on distal dendritic branches. Ultrastructural study showed that the cholinergic cells had a cytoplasm abundant in organelles. Within dendritic branches, mitochondria and cisternae were localized primarily to varicosities. Synaptic inputs were distributed mostly to the dendrites and at least four types that formed symmetric or asymmetric synapses were observed. Immunoreactive fibers were relatively numerous within the neuropil and exhibited small diameters (0.1-0.15) micron) and swellings at frequent intervals. Cholinergic boutons that formed synapses were compared to unlabeled terminals making asymmetric synapses with dendritic spines. Results showed that ChAT-positive axons had significantly smaller cross-sectional areas, shorter synaptic junctions, and a higher density and surface area of mitochondria than the unlabeled boutons. Cholinergic axons formed symmetric synapses mostly with dendritic spines (53%) and the shafts of unlabeled primary and distal dendrites (37%). A relatively small proportion of the boutons contacted axon initial segments (1%) and cell bodies (9%) that included medium-sized neurons with unindented (spiny) and indented (aspiny) nuclei. The majority of dendritic spines contacted by cholinergic axons were also postsynaptic to unlabeled boutons forming asymmetric synapses. The results suggest that cholinergic neurons in the primary neostriatum belong to a single morphological class corresponding to the large aspiny (type II) interneuron identified in previous Golgi studies. Present results along with earlier Golgi-electron microscopic observations from this laboratory suggest that neostriatal cholinergic cells integrate many sources of intrinsic and extrinsic inputs. The observed convergence of ChAT-immunoreactive boutons and unlabeled axons onto the same dendritic spines suggests that intrinsic cholinergic axons modulate extrinsic inputs onto neostriatal spiny neurons at postsynaptic sites close to the site of afferent input.

Release of acetylcholinesterase from the caudate nucleus of the rat

Acetylcholinesterase (AChE) can be released in the perfusate of rat caudate nucleus (CN) slices by two different modes of stimulation, with electrical stimulation at 5 Hz and with high concentrations of K+ (105 mM) using K+-propionate. We were unable to demonstrate AChE release with lower K+ concentrations (50 mM); however, at this concentration the drop in AChE activity seen in resting conditions was prevented. Practically all (95%) cholinesterase (ChE) found in the rat CN is AChE, which is represented by two major molecular forms (4S and 10S). In the perfusate, only AChE activity could be detected. A comparison of acetylcholine (ACh) and AChE release showed that maximal 3H-outflow and AChE release occurred at the same frequency (5 Hz), but the onset of AChE release was delayed. With high K+ (105 mM) depolarization, AChE release started after termination of the stimulation and continued for at least 50 min. These findings are consistent with the view that soluble form(s) of AChE can be slowly released from neurons under specific conditions of depolarization. In the caudate of the rat, the most likely sites for this release are processes of cholinergic interneurons. A hypothesis of AChE release is presented, and possible physiological and pathological implications of such a mechanism are discussed.

Histochemical localization of acetylcholinesterase in relation to motor neurons and internuclear neurons of the cat abducens nucleus

Three distinct patterns of AChE localization have been observed in relation to cat abducens motor neurons and internuclear neurons labelled by retrograde transport of horseradish peroxidase. First, AChE was localized predominantly within cisternae of granular endoplasmic reticulum and agranular reticulum of motor neuron somata, dendrites and axons, but was absent from internuclear neurons. AChE was also associated with saccules of the Golgi apparatus in the motor neurons, but was was absent from all other cytoplasmic organelles. Second, AChE was observed on the soma-dendritic and axonal surface membrane of the motor neurons, particularly at sites of apposition of synaptic endings of all morphological types, but was usually absent from the surface membranes of internuclear neurons. Third, AChE was associated both extracellularly and intracellularly with certain synaptic endings that contained spheroidal synaptic vesicles and that contacted both motor neurons and internuclear neurons. A similar pattern of staining of synaptic endings was observed at the neuromuscular junctions in the lateral rectus muscle. Axotomy of the VIth nerve resulted in loss of intracellular AChE associated with the Golgi apparatus and extracellular AChE on the somatic surface membrane of the motor neurons. The patterned localization of AChE contrasted with the localization of butyrylcholinesterase, which was associated predominantly with astrocytes. The findings suggest different roles of AChE as a function of the different patterns of localization.

Large neurons in the primate neostriatum examined with the combined Golgi-electron microscopic method

Large neurons in the monkey neostriatum were examined in the electron microscope in tissue treated with the rapid-Golgi impregnation method followed by the gold-toning procedure. Two types of large neurons were investigated: an aspiny neuron (aspiny type II; N = 5) with numerous varicose dendrites and a spiny cell (spiny type II; N = 1) with few sparsely spined dendrites. The large aspiny neurons had variably shaped somata, an eccentric highly invaginated nucleus, and a cytoplasm rich in organelles. Mitochondria were distributed unevenly in dendrites and were localized primarily in varicosities. Some mitochondria exhibited dense bodies 80-300 nm in size. Most synapses (84%) onto large aspiny neurons occurred 20 micron or more from the cell body and contacted dendritic varicosities (63%). A smaller proportion of boutons (21%) contacted constricted portions of varicose segments. A low incidence of synaptic boutons was observed on smooth primary and secondary dendrites (11%), cell bodies (3%), and branch points (2%). Seven percent of the axons that synapsed with large aspiny neurons also contacted nearby dendrites or spines of medium-sized spiny neurons. At least eight morphologically distinct types of axons making synapses with large aspiny neurons were identified and included both symmetric and asymmetric types. The large spiny neuron was different from the large aspiny neuron in its subcellular characteristics. Synapses were found on all portions of the cell, including the axon initial segment, but fewer types of axonal inputs were identified. These findings confirm that the two types of large neurons identified in Golgi impregnations of the primate neostriatum are also different at the ultrastructural level, both in their cytological features and in their synaptic organization. The large aspiny neuron integrates synaptic inputs that innervate a relatively large area of caudate neuropil and appear to arise from a variety of extrinsic and intrinsic sources. The high density of synaptic inputs to dendritic varicosities suggests that they have an important functional role.

Distinct sites of functional interaction between dopamine, acetylcholine and gamma-aminobutyrate within the neostriatum: an electromyographic study in rats

In order to study the functional interaction between dopamine, acetylcholine and gamma-aminobutyrate within the rat neostriatum, we investigated the effect of intrastriatal injection of different drugs acting on these transmitter systems on muscle tone measured as tonic activity in the electromyogram of the gastrocnemius muscle. Bilateral injection of haloperidol (500 ng) into the rostral neostriatum (rostral injection: A8920-9650(46] induced tonic activity in the electromyogram, whereas injection into the intermediate part (intermediate injection; A7020-7890(46] was ineffective. Muscimol (25 ng) induced tonic activity in the electromyogram, when injected into the intermediate part and not into the rostral part, while bethanechol (1 microgram) was effective when injected into either site. Haloperidol-induced tonic activity in the electromyogram was prevented by coadministration of apomorphine (500 ng) or scopolamine (1 microgram), but not of bicuculline (300 ng). Haloperidol-induced tonic activity in the electromyogram was also reduced by subsequent intermediate injection of scopolamine or bicuculline, while apomorphine was ineffective. Tonic activity in the electromyogram induced by rostral injection of bethanechol was prevented by coadministration of scopolamine, but not of apomorphine. Intermediate injection of scopolamine or bicuculline reduced the tonic activity in the electromyogram after rostral or intermediate injection of bethanechol. Tonic activity in the electromyogram induced by intermediate injection of muscimol was prevented by coadministration of bicuculline, but not of scopolamine. Rostral injection of apomorphine or scopolamine failed to alter the tonic activity in the electromyogram induced by intermediate injection of bethanechol or muscimol. These results point to the existence of: a functional interaction between dopamine and acetylcholine in the rostral neostriatum; a functional interaction between acetylcholine and gamma-aminobutyrate in the intermediate neostriatum, and a functional flow of information from the rostral to the intermediate neostriatum.

The localization of central cholinergic neurons

Over the past decade our understanding of the localization of central cholinergic neurons has greatly increased. Interest in these systems has also intensified due to the involvement of cholinergic mechanisms in Alzheimer's disease. The distribution of central cholinergic neurons is reviewed, focusing on recent work in experimental animals. The pharmacohistochemical procedure for acetylcholinesterase and the development of antibodies to choline acetyltransferase are two of the major technical advances that have shaped our knowledge of the distribution of central cholinergic neurons. The results, advantages and limitations of both techniques are discussed. A discussion of the phenomenon of coexistence of acetylcholine with neuroactive peptides in central neurons is also included.

A correlated light and electron microscopic study of identified cholinergic basal forebrain neurons that project to the cortex in the rat

Cholinergic neurons in the basal forebrain which project to the frontal cortex were studied by combining the retrograde transport of a conjugate of horseradish peroxidase and wheat germ agglutinin with choline acetyltransferase immunohistochemistry. Neurons that were both retrogradely labelled and immunoreactive were found on the medial, lateral, and ventral borders of the globus pallidus, within the globus pallidus, as well as in the substantia innominata and ventral pallidum region. The cell bodies averaged 31 by 19 micron in size and had sparsely branching dendrites. Cells which were labelled by both techniques were first characterised in the light microscope and then studied in the electron microscope. The perikarya had large amounts of cytoplasm with abundant organelles. The nuclei were indented, were usually eccentrically placed, and contained prominent nucleoli. The synaptic input onto the cell bodies and their dendrites was studied in serial sections. The synaptic input onto the perikarya and proximal dendrites was sparse but the density increased on more distal regions of the dendrites. Subjunctional bodies were associated with the postsynaptic membrane in 20-30% of the synaptic contacts and these were classified as asymmetrical; the remaining contacts could not be classified because of an association of the immunoreaction product with the postsynaptic membrane. The synaptic input to these cells was distinctly different from that onto typical globus pallidus cells, the perikarya and dendrites of which were characteristically ensheathed in synaptic boutons.

Immunocytochemical localization of choline acetyltransferase within the rat neostriatum: a correlated light and electron microscopic study of cholinergic neurons and synapses

Monoclonal antibodies to choline acetyltransferase (ChAT) were used in an immunocytochemical study to characterize putative cholinergic neurons and synaptic junctions in rat caudate-putamen. Light microscopy (LM) revealed that ChAT-positive neurons are distributed throughout the striatum. These cells have large oval or multipolar somata, and exhibit three to four primary dendrites that branch and extend long distances. Quantitative analysis of counterstained preparations indicated that ChAT-positive neurons constitute 1.7% of the total neuronal population. Electron microscopy (EM) of immunoreactive neurons initially studied by LM revealed somata characterized by deeply invaginated nuclei and by abundant amounts of organelle-rich cytoplasm. Surfaces of ChAT-positive neurons are frequently smooth, but occasional somatic protrusions and dendritic spines occur. Although infrequently observed, axons of ChAT-positive neurons branch, receive synapses, and become myelinated. Unlabeled boutons make both symmetrical and asymmetrical synapses with ChAT-positive somata and proximal dendrites, but are more numerous on distal dendrites. In addition, some unlabeled terminals form asymmetrical synapses with ChAT-positive somata and dendrites that are distinguished by prominent subsynaptic dense bodies. Light microscopy demonstrated a dense distribution of ChAT-positive fibers and punctate structures in the striatum, and these structures appear to correlate, respectively, with labeled preterminal axons and presynaptic boutons identified by EM. ChAT-positive boutons contain pleomorphic vesicles, and make symmetrical synapses primarily with unlabeled dendritic shafts. Furthermore, they establish synaptic contacts with somata, dendrites and axon initial segments of unlabeled neurons that ultrastructurally resemble medium spiny neurons. These observations, together with the results of other investigations, suggest that medium spiny GABAergic projection neurons receive a cholinergic innervation that is probably derived from ChAT-positive striatal cells. The results of this study also indicate that cholinergic neurons within caudate-putamen belong to a single population of cells that have large somata and extensive sparsely spined dendrites. Such neurons, in combination with dense concentrations of ChAT-positive fibers and terminals, are the likely basis for the large amounts of ChAT and acetylcholine detected biochemically within the neostriatum.

Topography of cholinergic perikarya and nerve fibres as well as cholinergic vesicles in the rat duodenum

Using the acetylthiocholine staining method, it was possible to visualize acetylcholinesterase (AChE)-stained neuronal cell bodies and nerve endings as well as AChE-positive vesicles in the rat duodenum. AChE-reactive perikarya were seen with certainty only in the myenteric plexus. They were 40 micron in diameter and were mostly localized in groups within the ganglia (3-6 neurons per ganglion). Some thick, AChE-reactive nerve processes, running over a long distance in interconnecting nerve fibre strands, had their origin from AChE-containing myenteric plexus perikarya. AChE-stained nerve fibres were detected in the myenteric and submucosal plexus as well as in the longitudinal and circular smooth muscle cell layer. AChE-positive nerve fibres were in close contacts with blood vessels, probably arterioles, Brunner's gland cells and epithelial cells. A conspicuously high density of AChE-positive nerve fibres was noted in the longitudinal smooth muscle layer, while AChE-stained nerve fibres were visualized only sporadically in the circular smooth muscle layer. Some Brunner's gland cells and epithelial cells contained AChE-reactive vesicles, which were constantly localized on the basal cell portion. The present findings might indicate that acetylcholine possesses important physiological roles as neurotransmitter and/or neuromodulator in the rat duodenum.

Glutamate decarboxylase-immunoreactive structures in the rat neostriatum: a correlated light and electron microscopic study including a combination of Golgi impregnation with immunocytochemistry

An antibody to glutamate decarboxylase has been used in a light and electron microscopic study of the neostriatum of rats that had received intracerebral injections of colchicine. In the light microscope, neuronal perikarya and small punctate structures that displayed immunoreactivity were found. The perikarya could be divided into two classes based on their sizes: small-to-medium-sized and large. Proximal dendrites, axon initial segments, and axon collaterals were occasionally stained. When the nuclei of the neurons were visible, they possessed indentations. The immunoreactive punctate structures were spread evenly throughout the neostriatum but occasionally were associated with immunoreactive and nonimmunoreactive perikarya. When the same sections were examined in the electron microscope, the small-to-medium-sized immunoreactive perikarya were found to be similar in morphology and synaptic input to a class of Golgi-impregnated neuron that has been previously shown to accumulate locally administered, radiolabelled gamma-aminobutyric acid. Neurons with the ultrastructural characteristics of typical striatonigral neurons did not display immunoreactivity. As neurons in this pathway probably contain gamma-aminobutyric acid, it is possible that our procedure or our antibody does not stain all gamma-aminobutyric-acid-containing structures in the neostriatum. A total of 404 immunoreactive punctate structures were examined by correlated light and electron microscopy or by electron microscopy alone. They were identified as immunoreactive axonal boutons and each of them, when examined in serial sections, displayed typical synaptic specialisations. Membrane specialisations were always of the symmetrical type. At least five distinct targets of the immunoreactive terminals were identified: neurons that were themselves immunoreactive for glutamate decarboxylase; the immunoreactive terminals made synaptic contact with all parts of the neurons examined, i.e., perikarya, proximal dendrites, and axon initial segments. Neurons identified by Golgi impregnation of the same sections as medium-sized and densely spiny; the immunoreactive terminals made contact predominantly with the perikarya and dendritic shafts. Large neurons found only in the ventral caudate-putamen, whose somata and dendrites were ensheathed in immunoreactive terminals. Medium-sized nonimmunoreactive perikarya that possessed nuclear indentations. Large nonimmunoreactive perikarya that had the typical structural features of striatal cholinergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic synapses in the rat brain: a correlated light and electron microscopic immunohistochemical study employing a monoclonal antibody against choline acetyltransferase

Using a monoclonal antibody to choline acetyltransferase, immunoreactive synaptic boutons were identified in the neostriatum, cingulate cortex, basolateral nucleus of the amygdala, hippocampus and interpeduncular nucleus of the rat. The synapses were generally symmetrical although some asymmetrical membrane specializations were observed. Postsynaptic targets included perikarya, dendritic shafts and dendritic spines.

Characterization of cholinergic neurons in the rat neostriatum. A combination of choline acetyltransferase immunocytochemistry, Golgi-impregnation and electron microscopy

Immunocytochemistry with a monoclonal antibody against choline acetyltransferase has been used to characterise cholinergic neurons in the rat neostriatum. The light microscopic morphology, ultrastructure and synaptic input of these neurons was compared to that of the three types of large neuron found in Golgi preparations of the striatum. The cholinergic neurons are large and have long infrequently branching dendrites. Two of the immunoreactive neurons were also Golgi-impregnated and showed characteristics of the "classical" large neurons of the striatum. Examination in the electron microscope revealed that the synaptic input to perikarya and proximal dendrites is sparse, thus distinguishing them from another large type of neuron, found in the ventral regions of the striatum, whose dendrites and perikarya are ensheathed in synaptic boutons. It is concluded that one of the three morphologically distinguishable classes of large neuron in the striatum is a cholinergic neuron.

Aspiny neurons and their local axons in the neostriatum of the rat: a correlated light and electron microscopic study of Golgi-impregnated material

Three types of neuron with smooth (aspiny) dendrites could be distinguished in the Golgi-impregnated rat neostriatum. Examples of each type of aspiny neuron were found with local axon collaterals within the neostriatum and these were selected for gold- toning and examination in the electron microscope. One type of aspiny neuron had an elongated, usually spindle-shaped, medium-size soma with two, or rarely three, primary dendrites originating from opposite poles of the cell; one example of this type of neuron had two separate axons. The second type of aspiny neuron had a nearly round, medium-size soma with four primary dendrites that branched profusely quite close to the cell body. A third type of aspiny neuron had a very large polygonal-shaped cell body. Afferent axon terminals were found in synaptic contact with the dendrites and cell bodies of all three types of aspiny neuron. Axon collaterals of each type of neuron displayed varicosities which, when examined in the electron microscope, were frequently found to be boutons making synaptic contact. All such synaptic contacts had symmetrical membrane specializations and the most common postsynaptic targets were dendritic shafts, sometimes spine-bearing. Dendritic spines themselves also received synapses from each type of neuron. No axosomatic synapses involving boutons of identified axons were found. One example of a synapse between an axon collateral of an aspiny neuron and one of the same neuron's dendrites (an ' autapse ') was demonstrated by electron microscopy. It is concluded that the synaptic terminals of at least four types of neuron, the three aspiny types described here and the medium-size densely spiny neuron, participate in local circuit interactions in the neostriatum.