Ultrastructural Changes of Caudate Nucleus in Mice Chronically Treated with Manganese.

Manganese (Mn) is able to cross the blood-brain barrier and induces functional and structural alterations during the intoxication by this metal. Therefore, the effects of chronic administration of Mn in the caudate nucleus of mice were evaluated by electron microscopy. Male albino mice were injected intraperitoneally with MnCl2 (5 mg/kg/d) 5 d per week during 9 weeks. The control group received only 0.9% of NaCl solution. The caudate nuclei were extracted and subsequently processed to be observed on a conventional transmission electron microscope at 2, 4, 6, and 9 weeks after treatment. A high percentage of vacuolated and swollen mitochondria were found throughout all the analyzed periods. Myelin disarrangement and ultrastructural alterations related to edema were observed increased in Mn-treated mice at week 9. Granular degeneration of myelin at week 9 accompanied with deposition of electron dense granules in the neuropil was also observed. Edema in neuropil and glial cells was detected from week 2 to week 9 accompanied by swollen mitochondria. Neuronal bodies, synaptic terminals, and perivascular cells were found swollen. Decreased electron density in postsynaptic areas and decreased and dispersed synaptic vesicles in presynaptic areas were noted in Mn-treated animals. Some neurons from Mn-treated mice showed cisternae dilation of the Golgi apparatus. These results suggest that Mn-treatment produces structural alterations in the caudate nucleus that could be responsible for some of the neurotoxic effects of this metal.

A model system for in vivo gene transfer into the central nervous system using an adenoviral vector.

Previous methods of in vivo gene transfer to differentiated neurons of the adult mammalian brain have been inefficient and associated with technical problems. We have therefore developed a model system of direct gene transfer using a replication-defective adenoviral vector containing a beta-galactosidase gene to transduce brain neurons. Following injection of purified high titre recombinant adenovirus into the caudate putamen of seven week old mice, lacZ activity was evident in neural components of the central nervous system (CNS) for at least 8 weeks post infection. The efficiency of adenoviral gene transfer was very high compared to other techniques, suggesting an attractive and efficient alternative for neuronal gene transfer in vivo.

Regional differences in human ependymal and subventricular zone cytoarchitecture are unchanged in neuropsychiatric disease.

Much work has focused on the possible contribution of adult hippocampal neurogenesis to neuropsychiatric diseases. The hippocampal subgranular zone and the other stem cell-containing neurogenic niche, the subventricular zone (SVZ), share several cytological features and are regulated by some of the same molecular mechanisms. However, very little is known about the SVZ in neuropsychiatric disorders. This is important since it surrounds the lateral ventricles and in schizophrenia ventricular enlargement frequently follows forebrain nuclei shrinkage. Also, adult neurogenesis has been implicated in pharmacotherapy for affective disorders and many of the molecules associated with neuropsychiatric disorders affect SVZ biology. To assess the neurogenic niche, we examined material from 60 humans (Stanley Collection) and characterized the cytoarchitecture of the SVZ and ependymal layer in age-, sex- and post mortem interval-matched controls, and patients diagnosed with schizophrenia, bipolar illness, and depression (n = 15 each). There is a paucity of post mortem brains available for study in these diseases, so to maximize the number of possible parameters examined here, we quantified individual sections rather than a large series. Previous work showed that multiple sclerosis is associated with increased width of the hypocellular gap, a cell-sparse region that typifies the human SVZ. Statistically there were no differences between disease groups and controls in the width of the hypocellular gap or in the density of cells in the hypocellular gap. Because ventricular enlargement in schizophrenia may disrupt ependymal cells, we quantified them, but observed no difference between diagnostic groups and controls. There are significant differences in the prevalence of neuropsychiatric illness between the sexes. Therefore, we looked for male versus female differences, but did not observe any in the parameters quantified. We next turned to a finer spatial resolution and asked if there were differences amongst the disease groups in dorsal ventral subdivisions of the SVZ. Similar to when we treated the SVZ as a whole, we did not find such differences. However, compared to the dorsal SVZ, the ventral SVZ had a wider hypocellular gap and more ependymal cells in all four groups. In contrast, cell density was similar in dorsal ventral subregions of the SVZ hypocellular gap. These results show that though there are regional differences in the SVZ in humans, neuropsychiatric disorders do not seem to alter several fundamental histological features of this adult neurogenic zone.

[Organization of the projections of the substructures of deep mesencephalic nucleus to the striatum in the dog brain].

Method of retrograde axonal transport of horseradish peroxidase was used to study the organization of the projections of the individual substructures of the deep mesencephalic nucleus complex to the functionally diverse regions of striatal structures of the dog brain (n=20). It was shown that the projection fibers of the neurons of the nucleus profundus mesencephali were directed to the ventro-lateral segment of the nucleus caudatus and the ventral segment of the putamen. The dorsal segment of the putamen obtains the fibers from the neurons of the nucleus cuneiformis, while the lateral segment of the nucleus accumbens received them from the neurons of the nucleus subcuneiformis. The possible pathways for conduction of the functionally diverse information and its integration in the investigated projection systems are discussed.

[Fusion of brain neurons in rat embryos].

Syncytial interneuronal connections were studied in the sensomotor cortex and caudate nucleus of twenty 14-22 day rat embryos. It was shown that with the extremely weak development of glial processes, many neuronal bodies and their processes were in the direct contact with each other. The contacting membranes in these areas formed oblong and dot-like contacts resembling gap and tight junctions. As a result, the intercellular cleft experienced varicose-like deformations. In the area of contacts, barely visible membrane pores were formed that broadened to form large perforations. The perforation margins presented the rounded shape of fused plasma membranes of adjacent neurons. Inside the perforations, residual vesicular membranous bodies were formed. The areas of the paired membranes between perforations were fragmented, thus increasing the number of residual vesicles, until the neurons fused with each other completely by unifying the neuroplasm of contacting cells. The results of these studies suggest that that the fusion of neurons in vertebrate brain cortex and brainstem nuclei could occur not only in pathology, but also in normal animals at the stage of embryonic development.

[Structural basis for the inhibitory function of the parietal cortex efferent systems].

Relative quantitative distribution of all the associative and descending efferent fibers and the ultrastructural organization of the terminals of the parietal cortex areas 5 and 7 in the caudate (NC) and red nucleus (NR) in the cat were analyzed after a local, pointed destruction of the cortex of these areas. The maximal numbers of the associative fibers were found to project to the fundus areas of the motor cortex and to the area of Clare-Bishop; moderate projections were detected to the areas 31, 19 and single degenerating fibers were registered in the areas 1,2, 3a, 3b, 30, and 23. The descending efferents were maximally projecting to NC, NR, reticular nuclei of the thalamus, midbrain, and pons, in all of which, according to the immunocytochemical studies, GABA-ergic terminals are prevalent. On the basis on the electron microscopical studies, it was suggested that the influence of the parietal cortex is mediated by the axo-spinal synapses of the medium shortaxonal spiny cells of the dorsolateral part of NC caput and by the axo-dendritic synapses of Golgi II cells of the parvocellular part of NR. On the basis of the maximal involvement of the fundus areas of the motor cortex, as well as of the inhibitory subcortical (NC) and stem nuclei (NR, reticular nuclei of the thalamus, midbrain, and nuclei pontis), it is suggested that these structures serve as the morphological substrates for the realization of the inhibitory, integrative function of the parietal cortex.

Time-dependent exposure of nicotine and smoke modulate ultrasubcellular organelle localization of dopamine D1 and D2 receptors in the rat caudate-putamen.

The correlation of the subcellular localization of dopamine D(1) and D(2) receptors (DA D(1) R, DA D(2) R) with nicotine addiction has not been studied. We demonstrated the ultrasubcellular organelle localization of DA D(1) and D(2) Rs in the caudate-putamen (CPu) area of rat brain in vivo exposed to nicotine (3 mg/day; oral) and passive cigarette smoking (500 ml each; 3 times/day) for 1, 4, and 12 weeks, respectively. Our results revealed DA D(1) R localization in the presynaptic and postsynaptic dendrites, endocytic vesicles, and secretory granules, and DA D(2) R localization in the presynaptic dendrites and vesicles. DA D(1) R immunogold particles were highly decreased in the secretory granules of CPu, and increased in the postsynaptic area and vesicles after prolonged nicotine and smoking exposures, suggesting the strong influence of long time smoking and nicotine exposures on DA D(1) R subcellular organelle localization. DA D(2) R immunoreactivity was comparatively less changed than that of the DA D(1) R. Western blot analysis also showed the differential expression of DA D(1) and D(2) R proteins upon nicotine and smoking exposures as compared to the untreated controls. Taken together, the results for the first time suggests the execution of addictive behavior of nicotine through modulation of mesolimbic dopaminergic system targeting subcellular organelle of DA D(1) and D(2) Rs in the CPu of adult rat brain that may lead to novel therapeutic approaches related to nicotine's neuropsychological disorders including drug addiction.

Immunocytochemical localization studies of myelin basic protein.

The location of myelin encephalitogenic or basic protein (BP) in peripheral nervous system (PNS) and central nervous system (CNS) was investigated by immunofluorescence and horseradish peroxidase (HRP) immunocytochemistry. BP or cross-reacting material could be clearly localized to myelin by immunofluorescence and light microscope HRP immunocytochemistry. Fine structural studies proved to be much more difficult, especially in the CNS, due to problems in tissue fixation and penetration of reagents. Sequential fixation in aldehyde followed by ethanol or methanol provided the best conditions for ultrastructural indirect immunocytochemical studies. In PNS tissue, anti-BP was localized exclusively to the intraperiod line of myelin. Because of limitations in technique, the localization of BP in CNS myelin could not be unequivocally determined. In both PNS and CNS tissue, no anti-BP binding to nonmyelin cellular or membranous elements was detected.

Cilia formation in the adult cat brain after pargyline treatment.

The brains of four adult cats treated with pargyline (a nonhydrazide monoaminoxidase inhibitor) were examined at both the light and electron microscopic levels. Formation of typical mature cilia with the 9 + 2 pattern was observed in neural cells in the following areas: habenula nuclei, interpeduncular nuclei, hippocampus, mammillary bodies, thalamus, and caudate nucleus. The most marked ciliation occurs in the habenula nuclei. In general, glial cells greatly predominate in the formation of cilia. It is not clear whether ciliation in the central nervous system is the direct result of pargyline or if it occurs indirectly as a result of inhibition of monoaminoxidase. These findings are compared with the serotonin effect on ciliation in the embryogenesis of lower forms. It is suggested that pharmacological stimulation of centriolar reproduction without subsequent mitosis may lead to ciliary formation.

Transgenic minipig model of Huntington's disease exhibiting gradually progressing neurodegeneration.

Recently developed therapeutic approaches for the treatment of Huntington's disease (HD) require preclinical testing in large animal models. The minipig is a suitable experimental animal because of its large gyrencephalic brain, body weight of 70-100 kg, long lifespan, and anatomical, physiological and metabolic resemblance to humans. The Libechov transgenic minipig model for HD (TgHD) has proven useful for proof of concept of developing new therapies. However, to evaluate the efficacy of different therapies on disease progression, a broader phenotypic characterization of the TgHD minipig is needed. In this study, we analyzed the brain tissues of TgHD minipigs at the age of 48 and 60-70 months, and compared them to wild-type animals. We were able to demonstrate not only an accumulation of different forms of mutant huntingtin (mHTT) in TgHD brain, but also pathological changes associated with cellular damage caused by mHTT. At 48 months, we detected pathological changes that included the demyelination of brain white matter, loss of function of striatal neurons in the putamen and activation of microglia. At 60-70 months, we found a clear marker of neurodegeneration: significant cell loss detected in the caudate nucleus, putamen and cortex. This was accompanied by clusters of structures accumulating in the neurites of some neurons, a sign of their degeneration that is also seen in Alzheimer's disease, and a significant activation of astrocytes. In summary, our data demonstrate age-dependent neuropathology with later onset of neurodegeneration in TgHD minipigs.

Thalamic degeneration in MPTP-treated Parkinsonian monkeys: impact upon glutamatergic innervation of striatal cholinergic interneurons.

In both Parkinson's disease (PD) patients and MPTP-treated non-human primates, there is a profound neuronal degeneration of the intralaminar centromedian/parafascicular (CM/Pf) thalamic complex. Although this thalamic pathology has long been established in PD (and other neurodegenerative disorders), the impact of CM/Pf cell loss on the integrity of the thalamo-striatal glutamatergic system and its regulatory functions upon striatal neurons remain unknown. In the striatum, cholinergic interneurons (ChIs) are important constituents of the striatal microcircuitry and represent one of the main targets of CM/Pf-striatal projections. Using light and electron microscopy approaches, we have analyzed the potential impact of CM/Pf neuronal loss on the anatomy of the synaptic connections between thalamic terminals (vGluT2-positive) and ChIs neurons in the striatum of parkinsonian monkeys treated chronically with MPTP. The following conclusions can be drawn from our observations: (1) as reported in PD patients, and in our previous monkey study, CM/Pf neurons undergo profound degeneration in monkeys chronically treated with low doses of MPTP. (2) In the caudate (head and body) nucleus of parkinsonian monkeys, there is an increased density of ChIs. (3) Despite the robust loss of CM/Pf neurons, no significant change was found in the density of thalamostriatal (vGluT2-positive) terminals, and in the prevalence of vGluT2-positive terminals in contact with ChIs in parkinsonian monkeys. These findings provide new information about the state of thalamic innervation of the striatum in parkinsonian monkeys with CM/Pf degeneration, and bring up an additional level of intricacy to the consequences of thalamic pathology upon the functional microcircuitry of the thalamostriatal system in parkinsonism. Future studies are needed to assess the importance of CM/Pf neuronal loss, and its potential consequences on the neuroplastic changes induced in the synaptic organization of the thalamostriatal system, in the development of early cognitive impairments in PD.

[Ultrastructural changes of myelinated fibers in the brain in continuous and attack-like paranoid schizophrenia]. / Ul'trastrukturnye izmeneniya mielinovykh volokon v golovnom mozge pri nepreryvnotekushchei i pristupoobraznoi paranoidnoi shizofrenii.

AIM: Previously the authors have reported the ultrastructural pathology of myelinated fibers (MF) in the brain in schizophrenia. The aim of the present study was to compare the effect of disease course on ultrastructural changes of MF. MATERIAL AND METHODS: Postmortem electron microscopic morphometric study of MF was performed in the prefrontal cortex, caudate nucleus and hippocampus in 19 cases of paranoid schizophrenia. Fourteen cases of continuous schizophrenia, 5 cases of attack-like schizophrenia and 25 normal matched control cases were studied. The proportion (percentage) of pathological MF was estimated in the prefrontal cortex, layer 5, CA3 area of hippocampus, pyramidal layer, and in the head of the caudate nucleus. RESULTS: The percentage of MF having axonal atrophy and swelling of periaxonal oligodendrocyte process was significantly higher in both continuous and attack-like schizophrenia in all brain structures studied as compared to the control group. In the hippocampus and caudate nucleus, this parameter was increased significantly in attack-like schizophrenia as compared to continuous schizophrenia. In the prefrontal cortex. The percentage of the pathological MF having signs of deformation and destruction of myelin sheaths increased significantly only in continuous schizophrenia as compared to the control group. CONCLUSION: MF pathology is similar in attack-like and continuous paranoid schizophrenia but differ by the degree of severity of pathological MF. Abnormalities in MF contribute to the disconnectivity between the prefrontal cortex, caudate nucleus and hippocampus.

Ultrastructural localization of nitrotyrosine within the caudate-putamen nucleus and the globus pallidus of normal rat brain.

Nitration of protein tyrosine residues by nitric oxide (NO)-derived reactive species results in the production of stable nitrotyrosine (NT) moieties that are immunochemically detectable in many regions of normal brain and enriched in those areas containing constitutive nitric oxide synthase (cNOS). These include the caudate-putamen nucleus (CPN) and the globus pallidus, which receives major inhibitory input from the CPN. To determine the functional sites for NT production in these critical motor nuclei, we examined the electron microscopic immunocytochemical localization of NT and cNOS in rat brain. In the CPN, NT was localized to the somata and dendrites of cNOS-containing interneurons and spiny neurons, some of which received input from cNOS-labeled terminals. The NT immunoreactivity was most prevalent on outer mitochondrial membranes and nearby segments of the plasma membranes in dendrites and within asymmetric synapses on dendritic spines. In the CPN and globus pallidus, there was also a prominent labeling of NT in astrocytic processes, small axons, and tubulovesicles and/or synaptic vesicles in axon terminals. These terminals formed mainly asymmetric synapses in the CPN and inhibitory-type synapses in the globus pallidus where they often apposed cNOS-containing terminals that also formed asymmetric, excitatory-type synapses. Our results suggest that NT is generated by mechanisms requiring the dual actions of excitatory transmitters and NO derived either from interneurons in the CPN or from excitatory afferents in the globus pallidus. The findings also implicate NT in the physiological actions of NO within the striatal circuitry and, particularly, in striatopallidal neurons severely affected in Huntington's disease.

Ultrastructural localization of the CB1 cannabinoid receptor in mu-opioid receptor patches of the rat Caudate putamen nucleus.

Cannabinoids and opioids are widely consumed drugs of abuse that produce motor depression, in part via respective activation of the cannabinoid subtype 1 receptor (CB1R) and the mu-opioid receptor (muOR), in the striatal circuitry originating in the caudate putamen nucleus (CPN). Thus, the CB1R and muOR may show similar targeting in the CPN. To test this hypothesis, we examined the electron microscopic immunocytochemical labeling of CB1R and muOR in CPN patches of rat brain. Of the CB1R-labeled profiles, 34% (588) were dendrites, presumably arising from spiny as well as aspiny-type somata, which also contained CB1R immunoreactivity. In dendrites, CB1R often was localized to nonsynaptic and synaptic plasma membranes, particularly near asymmetric excitatory-type junctions. Almost one-half of the CB1R-labeled dendrites contained muOR immunoreactivity, whereas only 20% of all muOR-labeled dendrites expressed CB1R. Axons and axon terminals as well as abundant glial processes also showed plasmalemmal CB1R and were mainly without muOR immunoreactivity. Many CB1R-labeled axon terminals were small and without recognizable synaptic junctions, but a few also formed asymmetric, or more rarely symmetric, synapses. The CB1R-labeled glial processes were often perivascular or perisynaptic, surrounding asymmetric excitatory-type axospinous synapses. Our results show that in CPN patches CB1R and muOR are targeted strategically to some of the same postsynaptic neurons, which may account for certain similarities in motor function. Furthermore, they also provide evidence that CB1R may play a major role in the modulation of presynaptic transmitter release and glial functions that are unaffected in large part by opioids active at muOR in CPN.

Hereditary striatonigral and cerebello-olivary degeneration of the Kerry Blue Terrier. II. Ultrastructural lesions in the caudate nucleus and cerebellar cortex.

The character and progression of ultrastructural lesions in the caudate nucleus and cerebellar cortex were studied in four Kerry Blue Terriers afflicted with a hereditary neurodegenerative disease. In the caudate nucleus, the initial lesion was mitochondrial hypertrophy in dendrites of intrinsic neurons. Degeneration of these neurons became widespread while axons of passage and terminal boutons were spared. During the final stages, there was severe disruption of the neuropil with loss of both neurons and glia. A narrow zone bordering the lateral ventricles, however, remained unaffected. In the cerebellar cortex, the lesions involved principally Purkinje cells and progressed through a pattern of degeneration comparable to that involving intrinsic neurons of the caudate nucleus. In the later stages, there was astroglial scarring of the molecular layer. In contrast to the caudate nucleus, there was no disruption of the neuropil with loss of structure in the cerebellum. The fact that progression of lesions during the early stages of the disease in both the caudate nucleus and cerebellar cortex was similar suggested a common mechanism for the neurodegeneration .

Differential corticosteroid regulation of type II glucocorticoid receptor-like immunoreactivity in the rat central nervous system: topography and implications.

Neuronal type II glucocorticoid receptor-like immunoreactivity in the central nervous system shows heterogeneity in intensities and relative densities. This might predict variations in the regional responses of neuronal immunoreactivity to corticosteroids. We investigated changes in the intracellular location of immunoreactivity in the rat central nervous system after adrenalectomy and corticosteroid treatment, and carried out detailed statistical analysis of changes in neuronal nuclear immunoreactivity in the hippocampus and caudateputamen. Three types of responses were observed. The majority of neurons, classified type A, showed a predominant nuclear immunoreactivity in intact rats, lost nuclear and eventually cytoplasmic immunoreactivity after adrenalectomy, and regained nuclear immunoreactivity within 5 min of corticosterone and 2 h of aldosterone treatment, respectively. A subgroup of neurons in the hippocampus, striatum, septum, and habenula, classified type B, were not immunoreactive in intact rats, showed intense cytoplasmic immunoreactivity after adrenalectomy, and disappeared rapidly after corticosterone treatment and later in response to aldosterone. A subgroup of vermal cerebellar Purkinje neurons, classified type C, developed an intense cytoplasmic immunoreactivity after adrenalectomy, increased in number in response to corticosterone, and did not respond to aldosterone.

Dendritic domains of medium spiny neurons in the primate striatum: relationships to striosomal borders.

Medium spiny neurons are the projection neurons of the striatum. They receive the majority of striatal afferents, and they make up the vast majority of all neurons in the striatum. These densely spiny cells thus constitute a major substrate for input-output processing in the striatum. In the experiments described here we analyzed the dendritic fields of spiny neurons in the squirrel monkey striatum and plotted their orientations with respect to the borders between striosomes and matrix. Medium-sized spiny neurons in the caudate nucleus were filled intracellularly in a fixed-slice preparation with the fluorescent dye Lucifer Yellow. Dendritic arbors were reconstructed following immunostaining of the injected neurons with antiserum to Lucifer Yellow and counterstaining for striosome/matrix compartments. A majority of the medium spiny neurons studied had dendritic arborizations that remained within their compartment of origin. Thus the striosome/matrix subdivision not only partitions neurotransmitter molecules and extrinsic striatal connections into two domains in the primate caudate nucleus, but also constrains the dendritic arbors of many projection neurons there. Other medium spiny neurons, however, in both striosomes and matrix, had dendrites that crossed from one compartment into the other. About a quarter of the spiny neurons reconstructed had at least one such crossing dendrite. These results suggest that compartmentalization of afferent and efferent processing by projection neurons in the primate striatum is not absolute. For a subpopulation of spiny neurons in striosomes and matrix, inputs to one compartment could have a direct influence on output cells of the other.

Fine structure and synaptic connections of the common spiny neuron of the rat neostriatum: a study employing intracellular inject of horseradish peroxidase.

Medium-sized spiny neurons of the neostriatum, identified by intracellular injection of horseradish peroxidase, were examined at both light and electron microscopic levels. These neurons were characterized by their heavy investment of dentritic spines, beginning about 20 micron from the soma and continuing to the tips of the dendrites. Their axons arose from the soma or from a large dendritic trunk very near the soma, and tapered rapidly to form a main axonal branch from which arose several smaller initial collaterals. These arborized extensively throughout an area of about the same size as, and highly overlapping with, the dendritic field of the cell, while the main axon could be followed for distances of up to 1 mm in the direction of the globus pallidus. Three major synaptic types were seen in contact with spiny neurons. Boutons containing small round synaptic vesicles formed synapses exclusively with spiny regions of the dendrites, and most of these were axo-spinous. Small, very pleomorphic synaptic vesicles characterized a second bouton type of unknown origin, which made contacts with somata, initial segments, and dendrites, but not dendritic spines. Boutons containing large pleomorphic synaptic vesicles had the most widespread distribution, contacting all regions including dendritic spines. Spines receiving these contacts also were postsynaptic to boutons containing small round vesicles. Axon collaterals of spiny cells formed synapses with large pleomorphic vesicles and made synapses with somata, initial segments of axons, dendrites, and dendritic spines of striatal neurons, including other spiny cells.

Dendritic arbors of spiny neurons in the primate striatum are directionally polarized.

Despite the relatively unfeatured cytoarchitecture of the striatum, this large subcortical region has been found to have a modular macroscopic substructure comprising the neurochemically distinct striosomes and matrix, and, within the matrix, patchy input and output arrangements called matrisomes. In the study reported here, we explored the possibility that the cellular architecture of the striatum is also more specialized than previously suspected. We injected medium spiny neurons in lightly fixed slices of the squirrel monkey caudate nucleus, reconstructed their dendritic arbors, and analyzed the orientations of these arbors with respect to the cardinal planes of the striatum. The data were unequivocal in suggesting that many spiny neurons, whether near striosomes or not, have dendritic arbors with preferred orientations along a diagonal axis running from rostral, dorsal, and medial to caudal, ventral, and lateral. This axis corresponds to the orientations of many striosomes and matrisomes in the squirrel monkey's caudate nucleus. We therefore suggest that the primate striatum is characterized not only by a macroscopic organization dividing it into striosomes and matrisomes, but also by a microscopic architecture observed by the dendritic arbors of many of its projection neurons. We obtained comparable supplementary observations for the ferret caudate nucleus, suggesting that such spatial alignment of spiny dendritic arbors may be a general feature of striatal organization. These polarized dendritic arrangements could provide a cellular framework for compartmental input-output processing within the striatum.

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.