Large neostriatal neurons in the rat: an electron microscopic study of gold-toned Golgi-stained cells

The Tail of the Mouse Striatum Contains a Novel Large Type of GABAergic Neuron Incorporated in a Unique Disinhibitory Pathway That Relays Auditory Signals to Subcortical Nuclei

The most caudal part of the striatum in rodents, the tail of the striatum (TS), has many features that distinguish it from the rostral striatum, such as its biased distributions of dopamine receptor subtypes, lack of striosomes and matrix compartmentalization, and involvement in sound-driven behaviors. However, information regarding the TS is still limited. We demonstrate in this article that the TS of the male mouse contains GABAergic neurons of a novel type that were detected immunohistochemically with the neurofilament marker SMI-32. Their somata were larger than cholinergic giant aspiny neurons, were located in a narrow space adjacent to the globus pallidus (GP), and extended long dendrites laterally toward the intermediate division (ID) of the trilaminar part of the TS, the region targeted by axons from the primary auditory cortex (A1). Although vesicular glutamate transporter 1-positive cortical axon terminals rarely contacted these TS large (TSL) neurons, glutamic acid decarboxylase-immunoreactive and enkephalin-immunoreactive boutons densely covered somata and dendrites of TSL neurons, forming symmetrical synapses. Analyses of GAD67-CrePR knock-in mice revealed that these axonal boutons originated from nearby medium spiny neurons (MSNs) in the ID. All MSNs examined in the ID in turn received inputs from the A1. Retrograde tracers injected into the rostral zona incerta and ventral medial nucleus of the thalamus labeled somata of TSL neurons. TSL neurons share many morphological features with GP neurons, but their strategically located dendrites receive inputs from closely located MSNs in the ID, suggesting faster responses than distant GP neurons to facilitate auditory-evoked, prompt disinhibition in their targets.SIGNIFICANCE STATEMENT This study describes a newly found population of neurons in the mouse striatum, the brain region responsible for appropriate behaviors. They are large GABAergic neurons located in the most caudal part of the striatum [tail of the striatum (TS)]. These TS large (TSL) neurons extended dendrites toward a particular region of the TS where axons from the primary auditory cortex (A1) terminated. These dendrites received direct synaptic inputs heavily from nearby GABAergic neurons of the striatum that in turn received inputs from the A1. TSL neurons sent axons to two subcortical regions outside basal ganglia, one of which is related to arousal. Specialized connectivity of TSL neurons suggests prompt disinhibitory actions on their targets to facilitate sound-evoked characteristic behaviors.

Thinking Outside the Box (and Arrow): Current Themes in Striatal Dysfunction in Movement Disorders

The basal ganglia are an intricately connected assembly of subcortical nuclei, forming the core of an adaptive network connecting cortical and thalamic circuits. For nearly three decades, researchers and medical practitioners have conceptualized how the basal ganglia circuit works, and how its pathology underlies motor disorders such as Parkinson's and Huntington's diseases, using what is often referred to as the "box-and-arrow model": a circuit diagram showing the broad strokes of basal ganglia connectivity and the pathological increases and decreases in the weights of specific connections that occur in disease. While this model still has great utility and has led to groundbreaking strategies to treat motor disorders, our evolving knowledge of basal ganglia function has made it clear that this classic model has several shortcomings that severely limit its predictive and descriptive abilities. In this review, we will focus on the striatum, the main input nucleus of the basal ganglia. We describe recent advances in our understanding of the rich microcircuitry and plastic capabilities of the striatum, factors not captured by the original box-and-arrow model, and provide examples of how such advances inform our current understanding of the circuit pathologies underlying motor disorders.

Molecular regulation of dendritic spine dynamics and their potential impact on synaptic plasticity and neurological diseases

The structure and dynamics of dendritic spines reflect the strength of synapses, which are severely affected in different brain diseases. Therefore, understanding the ultra-structure, molecular signaling mechanism(s) regulating dendritic spine dynamics is crucial. Although, since last century, dynamics of spine have been explored by several investigators in different neurological diseases, but despite countless efforts, a comprehensive understanding of the fundamental etiology and molecular signaling pathways involved in spine pathology is lacking. The purpose of this review is to provide a contextual framework of our current understanding of the molecular mechanisms of dendritic spine signaling, as well as their potential impact on different neurodegenerative and psychiatric diseases, as a format for highlighting some commonalities in function, as well as providing a format for new insights and perspectives into this critical area of research. Additionally, the potential strategies to restore spine structure-function in different diseases are also pointed out. Overall, these informations should help researchers to design new drugs to restore the structure-function of dendritic spine, a "hot site" of synaptic plasticity.

Cholinergic interneurons in the dorsal and ventral striatum: anatomical and functional considerations in normal and diseased conditions

Striatal cholinergic interneurons (ChIs) are central for the processing and reinforcement of reward-related behaviors that are negatively affected in states of altered dopamine transmission, such as in Parkinson's disease or drug addiction. Nevertheless, the development of therapeutic interventions directed at ChIs has been hampered by our limited knowledge of the diverse anatomical and functional characteristics of these neurons in the dorsal and ventral striatum, combined with the lack of pharmacological tools to modulate specific cholinergic receptor subtypes. This review highlights some of the key morphological, synaptic, and functional differences between ChIs of different striatal regions and across species. It also provides an overview of our current knowledge of the cellular localization and function of cholinergic receptor subtypes. The future use of high-resolution anatomical and functional tools to study the synaptic microcircuitry of brain networks, along with the development of specific cholinergic receptor drugs, should help further elucidate the role of striatal ChIs and permit efficient targeting of cholinergic systems in various brain disorders, including Parkinson's disease and addiction.

GABAergic inputs from direct and indirect striatal projection neurons onto cholinergic interneurons in the primate putamen

Striatal cholinergic interneurons (ChIs) are involved in reward-dependent learning and the regulation of attention. The activity of these neurons is modulated by intrinsic and extrinsic γ-aminobutyric acid (GABA)ergic and glutamatergic afferents, but the source and relative prevalence of these diverse regulatory inputs remain to be characterized. To address this issue, we performed a quantitative ultrastructural analysis of the GABAergic and glutamatergic innervation of ChIs in the postcommissural putamen of rhesus monkeys. Postembedding immunogold localization of GABA combined with peroxidase immunostaining for choline acetyltransferase showed that 60% of all synaptic inputs to ChIs originate from GABAergic terminals, whereas 21% are from putatively glutamatergic terminals that establish asymmetric synapses, and 19% from other (non-GABAergic) sources of symmetric synapses. Double pre-embedding immunoelectron microscopy using substance P and Met-/Leu-enkephalin antibodies to label GABAergic terminals from collaterals of "direct" and "indirect" striatal projection neurons, respectively, revealed that 47% of the indirect pathway terminals and 36% of the direct pathway terminals target ChIs. Together, substance P- and enkephalin-positive terminals represent 24% of all synapses onto ChIs in the monkey putamen. These findings show that ChIs receive prominent GABAergic inputs from multiple origins, including a significant contingent from axon collaterals of direct and indirect pathway projection neurons.

Synapses of identified neurons in the neostriatum

Studies of the basal ganglia and particularly the neostriatum have described a complex array of neuron types, synapses and putative transmitters. One approach to the study of such an area is to examine identified neurons and thus establish the neural circuits that underlie function. Striatal neurons have been identified under the light microscope by one or more of the following methods: (1) structure, based on Golgi impregnation or the intracellular injection of horseradish peroxidase (HRP); (2) projection area, by the retrograde transport of HRP or the tracing of HRP-injected or Golgi-impregnated axons; (3) chemistry, by immunocytochemistry, histochemistry or autoradiography, to reveal the presence of a selective uptake system for a putative transmitter. Examination of identified neurons in the electron microscope allows the characterization of their afferent synapses (by immunocytochemistry or anterograde degeneration) and their local synaptic output. The afferent and efferent synapses of five classes of identified striatal neurons are discussed: (1) those neurons described in Golgi preparations as medium-size and densely spiny; (2) a large type of striatonigral neuron; (3) GABAergic interneurons; (4) cholinergic neurons; (5) somatostatin-immunoreactive neurons. It is concluded that medium-size densely spiny neurons provide the basic framework of the neural circuits of the neostriatum.

Acute effects of pulsed microwaves and 3-nitropropionic acid on neuronal ultrastructure in the rat caudate-putamen

Ultrastructure of the medium sized "spiny" neuron in rat dorsal-lateral caudate-putamen was assessed after administration of 3-nitropropionic acid (3-NP) and exposure to pulsed microwaves. Sprague-Dawley male rats were given two daily intraperitoneal doses of 0 or 10 mg/kg 3-NP and 1.5 h after each dose were exposed to microwave radiation at a whole body averaged specific absorption rate (SAR) of 0 (sham exposure), 0.6, or 6 W/kg for 30 min. Microwave exposure consisted of 1.25 GHz radiation delivered as 5.9 micros pulses with repetition frequency 10 Hz. Tissue samples taken 2-3 h after the second sham or microwave exposure showed no injury with light microscope methods. Blinded qualitative assessment of ultrastructure of randomly selected neurons from the same samples did reveal differences. Subsequent detailed, quantitative measurements showed that, when followed by sham exposure, administration of 3-NP significantly increased endoplasmic reticulum (ER) intracisternal width, ER area density, and nuclear envelope thickness. Microwave exposure at 6 W/kg alone also significantly increased these measures. Exposure of 3-NP treated animals at 6 W/kg significantly increased effects of 3-NP on ultrastructure. Although exposure at 0.6 W/kg alone did not affect ultrastructure measures, exposure of 3-NP treated animals at 0.6 W/kg reduced the effects of 3-NP. We concluded that 3-NP changed neuronal ultrastructure and that the microwave exposures used here changed neuronal ultrastructure in ways that depended on microwave SAR and neuron metabolic status. The apparent cancellation of 3-NP induced changes by exposure to pulsed microwaves at 0.6 W/kg indicated the possibility that such exposure can protect against the effects of mitochondrial toxins on the nervous system.

Neurogenesis and stereological morphometry of calretinin-immunoreactive GABAergic interneurons of the neostriatum

We determined the neurogenesis characteristics of a distinct subclass of rat striatum gamma-aminobutyric acidergic (GABAergic) interneurons expressing the calcium-binding protein calretinin (CR). Timed-pregnant rats were given an intraperitoneal injection of 5-bromo-2'-deoxyuridine (BrdU), a marker of cell proliferation, on designated days between embryonic day 12 (E12) and E21. CR-immunoreactive (-IR) neurons and BrdU-positive nuclei were labeled in the adult neostriatum by double immunohistochemistry, and the proportion of double-labeled cells was quantified. CR-IR interneurons of the neostriatum show maximum birth rates (>10% double labeling) between E14 and E17, with a peak at E15. CR-IR interneurons occupying the lateral half of the neostriatum become postmitotic prior to medial neurons. In the precomissural neostriatum, the earliest-born neurons occupy the lateral quadrants and the latest-born neurons occupy the dorsomedial sector. No significant rostrocaudal neurogenesis gradient is observed. CR-IR neurons make up 0.5% of the striatal population and are localized in both the patch and the matrix compartments. CR-IR neurons of the patch compartment are born early (E13-15), with later-born neurons (E16-18) populating mainly the matrix compartment. CR-IR cells of the neostriatum are a distinct subclass of interneurons that are born at an intermediate time during striatal development and share common neurogenesis characteristics with other interneurons and projection neurons produced in the ventral telencephalon.

Chemical anatomy of striatal interneurons in normal individuals and in patients with Huntington's disease

This paper reviews the major anatomical and chemical features of the various types of interneurons in the human striatum, as detected by immunostaining procedures applied to postmortem tissue from normal individuals and patients with Huntington's disease (HD). The human striatum harbors a highly pleomorphic population of aspiny interneurons that stain for either a calcium-binding protein (calretinin, parvalbumin or calbindin D-28k), choline acetyltransferase (ChAT) or NADPH-diaphorase, or various combinations thereof. Neurons that express calretinin (CR), including multitudinous medium and a smaller number of large neurons, are by far the most abundant interneurons in the human striatum. The medium CR+ neurons do not colocalize with any of the known chemical markers of striatal neurons, except perhaps GABA, and are selectively spared in HD. Most large CR+ interneurons display ChAT immunoreactivity and also express substance P receptors. The medium and large CR+ neurons are enriched with glutamate receptor subunit GluR2 and GluR4, respectively. This difference in AMPA GluR subunit expression may account for the relative resistance of medium CR+ neurons to glutamate-mediated excitotoxicity that may be involved in HD. The various striatal chemical markers display a highly heterogeneous distribution pattern in human. In addition to the classic striosomes/matrix compartmentalization, the striosomal compartment itself is composed of a core and a peripheral region, each subdivided by distinct subsets of striatal interneurons. A proper knowledge of all these features that appear unique to humans should greatly help our understanding of the organization of the human striatum in both health and disease states.

5-HT1B receptor binding in degenerative movement disorders

Using [3H]sumatriptan as a radioligand, 5-hydroxytryptamine (5-HT)1B receptors were examined in posterior striatum and midbrain post-mortem tissue sections of 12 patients who had died from representative degenerative movement disorders as compared to nine controls. In the control human basal ganglia, the highest densities of [3H]sumatriptan binding were observed in the globus pallidus and substantia nigra. No significant change in the density of [3H]sumatriptan binding sites was found in the striatum and substantia nigra of the six Parkinson's disease brains. In the two brains from patients with progressive supranuclear palsy an increase was found in the densities of [3H]sumatriptan binding sites, most marked in the substantia nigra. In contrast, [3H]sumatriptan labelling was almost absent in the striatonigral degeneration brain and was markedly reduced in the three Huntington's disease brains. This study indicates that the status of 5-HT1B receptors is different in each degenerative movement disorder and suggests that human 5-HT1B receptors are located somatodendritically on GABAergic and peptidergic caudate-putamen neurons which project to the substantia nigra and globus pallidus, where these receptors are presynaptic.

Glutamate decarboxylase-67 messenger RNA expression in normal human basal ganglia and in Parkinson's disease

Expression of glutamate decarboxylase-67 messenger RNA was examined in the basal ganglia of normal controls and of cases of Parkinson's disease using in situ hybridization histochemistry in human post mortem material. In controls glutamate decarboxylase-67 messenger RNA expression was detected in all large neurons in both segments of the globus pallidus and in three neuronal subpopulations in the striatum as well as in substantia nigra reticulata neurons and in a small sub-population of subthalamic neurons. In Parkinson's disease, there was a statistically significant decrease of 50.7% in glutamate decarboxylase-67 messenger RNA expression per neuron in the lateral segment of the globus pallidus (controls: mean 72.8 microns2 +/- S.E.M. 8.7 of silver grain/neuron, n = 12; Parkinson's disease: mean 35.9 microns2 +/- S.E.M. 9.7 of silver grain/neuron, n = 9, P = 0.01, Student's t-test). In the medial segment of the globus pallidus, there was a small, but non-significant decrease of glutamate decarboxylase-67 messenger RNA expression in Parkinson's disease (controls: mean 100.6 microns2 +/- S.E.M. 7.2 of silver grain/neuron, n = 11; Parkinson's disease: mean 84.8 microns2 +/- S.E.M. 13.0 of silver grain/neuron, n = 7, P = 0.1, Student's t-test). No significant differences in glutamate decarboxylase-67 messenger RNA were detected in striatal neuronal sub-populations between Parkinson's disease cases and controls. These results are the first direct evidence in humans that there is increased inhibitory drive to the lateral segment of the globus pallidus in Parkinson's disease, as suggested by data from animal models. We therefore provide theoretical support for current experimental neurosurgical approaches to Parkinson's disease.

Glutamatergic and GABAergic postsynaptic responses of striatal spiny neurons to intrastriatal and cortical stimulation recorded in slice preparations

Glutamatergic and GABAergic responses of the neostriatal spiny neurons to intrastriatal and cortical stimulation were characterized by intracellular recording in brain slice preparations. This study also demonstrated the role of each response in the spike activity of the spiny neuron. Single neostriatal stimulation induced postsynaptic potentials consisting of multiple components. The early part of the postsynaptic potential, which was isolated by the GABAA antagonist bicuculline methiodide and the N-methyl-D-aspartate antagonist 3-(2-carboxypiperzin-4-yl)-propyl-1-phosphonic acid (CPP), was mainly an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptor-mediated response. Perfusion of magnesium-free medium containing bicuculline methiodide and the AMPA/kainate antagonist 3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline (NBQX) disclosed a large, slow N-methyl-D-aspartate receptor-mediated response. The N-methyl-D-aspartate response in magnesium-containing perfusing medium was small in neurons at the resting membrane potential, but became a significant component when the neurons were depolarized to subthreshold membrane potential. The duration of the N-methyl-D-aspartate response was over 300 ms. The nicotinic antagonists dihydro-beta-erythroidine hydrobromide and mecamylamine failed to change responses to single stimulation. Repetitive intrastriatal stimulation induced a large, long-duration depolarization with action potentials in the spiny neurons. This stimulation-induced response resembles that of the depolarization stage observed in anesthetized animals. Bicuculline methiodide increased the response amplitude. In contrast, CPP reduced the amplitude of the response to the below the spike generation threshold. The CPP-sensitive N-methyl-D-aspartate response was large and lasted several hundred milliseconds after the termination of repetitive stimulation. Responses of the neostriatal neurons to cortical stimulation were similar to those induced after intrastriatal stimulation. CPP greatly reduced both the response amplitude and the number of spikes triggered from the response. Bicuculline methiodide, on the other hand, greatly increased the response amplitude and the number of spikes. The AMPA/kainate response alone, which was isolated by application of bicuculline methiodide and CPP, did not induce sustained depolarization in spiny neurons to repetitive cortical stimulation. Application of NBQX diminished GABAA response to cortical stimulation. This observation indicates that, for neostriatal spiny neurons to respond with GABAA response after cortical stimulation, the AMPA/kainate response must be induced in the GABAergic secondary neurons in the neostriatum. This study indicates that the main synaptic driving forces of neostriatal spiny neurons include AMPA/kainate, N-methyl-D-aspartate and GABAA responses. Although AMPA/kainate response is the main synaptic input, the generation of the action potentials in neostriatal neurons is greatly influenced by both GABAA and N-methyl-D-aspartate responses.

Identification and characterization of striatal cell subtypes using in vivo intracellular recording and dye-labeling in rats: III. Morphological correlates and compartmental localization

In the first two reports of this series, in vivo intracellular recording techniques were used to characterize the electrophysiological properties of two types of striatal neurons that had been identified by their distinct response patterns to stimulation of corticostriatal afferents. In this paper, we examined whether cells showing Type I or Type II response patterns also differed with respect to their morphology or compartmental localization by combining intracellular recording and Lucifer yellow staining with immunocytochemical localization of calbindin 28 kd immunoreactivity. In the majority of cases, both Type I and Type II neurons exhibited similar morphological characteristics, with 80% of the Type I cells (13/16) and all of the Type II cells (n = 40) being small or medium spiny neurons. In each case where the morphological class of the cell was different than the spiny cell class, the cell exhibited a Type I response pattern. These spiny neurons had somata that averaged 17.1 +/- 1.3 microns in diameter and gave rise to between four and eight primary dendrites. The axons typically arose from cell bodies (7/13 for Type I and 25/40 for Type II cells) and emitted extensive local axonal collaterals. However, the axons of Type I cells more frequently originated from the dorsal surface of the somata (9/13; 69%), whereas Type II axons more frequently arose from the ventral surface of the somata (25/35; 71%), which may account for their different extracellular waveforms. In coronally sectioned tissue (n = 18), the axons always projected laterally when the somata were located in the medial striatum and projected medially when the somata were in the lateral striatal region. In a subset of experiments (N = 22), Lucifer yellow-stained neurons were localized with respect to their position within the patch and matrix compartments of the striatum using subsequent staining for calbindin 28 kd immunoreactivity. Of the 20 labeled medium spiny neurons examined (Type II: N = 13; Type I: N = 7), 19 were located in the calbindin-positive matrix compartment. The only neuron localized to the patch compartment was a medium spiny cell that exhibited a Type II paired impulse response pattern. In addition, of the two aspiny neurons from this group with beaded dendrites, one was localized to the border between adjacent patch and matrix compartments, whereas the other was located completely within the matrix compartment. Therefore, despite their distinct paired impulse response patterns, the majority of both Type I and Type II neurons were medium spiny cells located in the matrix compartment of the striatum.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural features of the choline acetyltransferase-containing neurons and relationships with nigral dopaminergic and cortical afferent pathways in the rat striatum

The aim of this study was first to specify the morphology and neuronal environment of the large cholinergic neurons, and second to determine the distribution and mode of termination of the corticostriatal and dopaminergic inputs on these neurons in the rat striatum. Immunocytochemical procedures with a monoclonal antibody against choline acetyltransferase, Golgi staining and standard electron microscopic techniques were used to specify the ultrastructural features of the putatively cholinergic classical large neurons. The large/choline acetyltransferase-positive neurons are characterized by a voluminous, eccentric, and deeply indented nucleus leaving a large cytoplasmic area, and by the presence of an abundant granular endoplasmic reticulum and of many polysomes and free ribosomes. Serial ultrathin sectioning further indicated the presence of nematosomes or nucleolus-like bodies within the nucleus and the cytoplasm of the large neurons. In addition, these neurons were found to be in direct apposition with up to four surrounding neurons showing features typical of medium-sized spiny neurons. These data support the view that the putatively cholinergic neurons may have an intense metabolic activity and may be involved in striatal clusters. When choline acetyltransferase immunostaining was coupled with the identification of degenerating corticostriatal afferents after lesion of the cerebral cortex, degenerating terminals were seen to form synapses of an asymmetrical type on distal labelled dendrites, but these contacts were very rare. On the other hand, nigrostriatal dopaminergic axons, identified by means of either the degeneration method or tyrosine hydroxylase immunostaining, were often found to run directly for long distances around the choline acetyltransferase-positive cell bodies. Occasionally, dopaminergic terminals formed possible symmetrical synapses on choline acetyltransferase-positive cell bodies or proximal dendrites. These data provide evidence that the putatively cholinergic neurons are directly contacted by corticostriatal and dopaminergic nigrostriatal afferents. The respective positions and nature of the two types of contacts further provide morphological support for the hypothesis that postsynaptic interactions may occur between the corticostriatal and dopaminergic nigrostriatal afferents at the level of the cholinergic neurons.

Techniques for converting Golgi precipitate in CNS neurons into stable electron microscopic markers

Direct electron microscopy of nervous tissue stained with the Golgi impregnation method is unsatisfactory because the cytoplasm of the cell bodies and processes of the impregnated neurons are completely filled with a compact precipitate of electron dense silver chromate. This precipitate entirely obscures the cytological details of the impregnated neurons. Because of its solidity and instability in aqueous solutions, the silver chromate is also a source of inconvenience during the preparation of the ultrathin sections. This review summarizes methods that have been developed with the aim of replacing the Golgi precipitate in CNS neurons with a more convenient electron dense material--for example, heavy metal salts or metallic particles. Conversion of the precipitate into a stable electron dense marker is done before the material is embedded for electron microscopy. The methods include lead, gold, and bromide substitution, treatment with ammonia, direct chemical reduction into metallic silver, and photoreduction of the silver chromate into silver through irradiation with ultraviolet light.

Choline acetyltransferase- and substance P-like immunoreactive elements in fetal striatal grafts in the rat: a correlated light and electron microscopic study

Fetal striatal neurons were transplanted into the ibotenic acid-lesioned rat striatum. Three months after transplantation, the graft tissue was processed for choline acetyltransferase- and substance P-like immunoreactivity and was subsequently examined at the light and electron microscopic levels. The study demonstrated that choline acetyltransferase- and substance P-like-immunoreactive neurons were homogenously present throughout fetal striatal grafts, although in decreased numbers compared with those in the normal rat striatum. The majority of the choline acetyltransferase-immunoreactive neurons had fusiform, oval, or polygonal somata with somatic diameters greater than 20 microns and contained deeply invaginated nuclei surrounded by copious cytoplasm. In addition, choline acetyltransferase-immunoreactive neurons with somatic diameters between 10 and 20 microns were also demonstrated. The grafts' substance P-like-immunoreactive neurons, which had somatic diameters between 10 and 25 microns and had oval or polygonal perikarya, could be classified into two types based on their ultrastructural characteristics. Type I neurons contained an unindented nucleus which was surrounded by a thin rim or moderate amount of cytoplasm, whereas Type II immunoreactive neurons contained an indented nucleus which was surrounded by copious cytoplasm. Choline acetyltransferase- and substance P-like-immunoreactive dendrites in the grafts' neuropil were contacted by multiple unlabeled axon terminals. In addition, choline acetyltransferase- and substance P-like-immunoreactive axon terminals forming symmetric contacts with unlabeled dendrites were present within the graft. The study demonstrated that many of the neuroanatomical features of choline acetyltransferase- and substance P-like-immunoreactive elements found in the normal rat striatum are present in mature fetal striatal grafts.

Interneurons in the rat striatum: relationships between parvalbumin neurons and cholinergic neurons

A pre-embedding double-labeling immunocytochemical method was used to examine the synaptic relationships between cholinergic neurons and the parvalbumin immunoreactive (PV+) neurons. The PV+ neurons were labeled by silver-intensified colloidal gold particles, and the cholinergic neurons by immunoperoxidase reaction products. Cholinergic and PV+ axon terminals form synapses with both the somata and dendrites of PV+ neurons, as well as unlabeled medium-sized somata with round un-indented nuclei, a typical characteristic of the medium spiny projection neurons. These observations suggest that the PV+ and the cholinergic neurons have converging influences on both the projection neurons and the PV+ interneurons in the striatum.

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.

Large neurons in the neostriatum in Alzheimer's disease and progressive supranuclear palsy: a topographic, histologic and ultrastructural investigation

Large neurons in the neostriatum of patients with Alzheimer's disease (AD) and progressive supranuclear palsy (PSP) were investigated topographically, histologically and ultrastructurally. The number of large neurons whose nuclear area is greater than 101 microns2 was uniformly decreased in the neostriatum in PSP, but the decrease of these neurons in AD appeared to be more marked in the nucleus accumbens. Most of the remaining large neurons in both diseases contained neurofibrillary tangles (NFTs). In addition, some of the small neurons in PSP were positive for tau-immunostaining. Curly fibers were frequently observed in AD, but were absent in PSP. Ultrastructurally, NFTs in AD were composed mainly of paired helical filaments, whereas those in PSP contained straight tubules.

Distribution of DARPP-32 in the basal ganglia: an electron microscopic study

DARPP-32, a dopamine and cyclic AMP-regulated phosphoprotein, has been studied by light and electron microscopical immunocytochemistry in the rat caudatoputamen, globus pallidus and substantia nigra. In the caudatoputamen, DARPP-32 was present in neurons of the medium-sized spiny type. Immunoreactivity for DARPP-32 was present in dendritic spines, dendrites, perikaryal cytoplasm, most but not all nuclei, axons and a small number of axon terminals. Immunoreactive axon terminals in the caudatoputamen formed symmetrical synapses with immunolabeled dendritic shafts or somata. Neurons having indented nuclei were never immunoreactive. In the globus pallidus and substantia nigra pars reticulata, DARPP-32 was present in myelinated and unmyelinated axons and in axon terminals. The labelled axon terminals in these regions formed symmetrical synaptic contacts on unlabelled dendritic shafts or on unlabelled somata. These data suggest that DARPP-32 is present in striatal neurons of the medium-sized spiny type and that these DARPP-32-immunoreactive neurons form symmetrical synapses on target neurons in the globus pallidus and substantia nigra. The presence of DARPP-32 in these striatal neurons and in their axon terminals suggests that DARPP-32 mediates part of the response of medium-size spiny neurons in the striatum to dopamine D-1 receptor activation.

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.

The generation and differentiation of cholinergic neurons in rat caudate-putamen

By combining [3H]thymidine autoradiography with choline acetyltransferase (ChAT) immunocytochemistry, we have determined the generation pattern of the large cholinergic neurons in the neostriatum. All of these neurons are produced between embryonic days 12 and 17 (E12-E17), with 75% of them being born between E13 and 15. Cholinergic neurons appeared to be among the earliest cells produced in the neostriatum when compared with previous generation studies of all neurons in the rat caudate-putamen. The caudal-to-rostral neurogenic gradient reported in previous investigations of all neurons was the only spatiotemporal gradient observed for cholinergic neurons. The generation peak for these cells was E13 caudally, and E15 rostrally. Additional immunocytochemical studies detected ChAT immunoreactivity within somata and primary dendrites of 1 day postnatal (1 dpn) rat neostriatum, and subsequently demonstrated a dramatic increase in the intensity of reaction product and the complexity of dendritic arborizations by 14 dpn. Large ChAT-positive neurons of the basal forebrain contained within the same specimens appeared to differentiate their cholinergic phenotype earlier than those in the neostriatum. However, recent generation studies of basal forebrain neurons combined with the present results have demonstrated that both cholinergic populations are produced simultaneously along the same neurogenic gradients. This then represents an example of cholinergic projection (basal forebrain system) and local circuit (neostriatum) neurons that share similar generation patterns but differ with respect to sequences of transmitter phenotype expression. Thus, for cholinergic forebrain neurons, a cell's position along the neurogenic gradient and its transmitter phenotype appear to be more closely associated with its birth date than its ultimate projection or rate of differentiation.

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).

Golgi study of the mouse striatum: age-related dendritic changes in different neuronal populations

The Van der Loos modification of the Golgi-Cox method and morphometric analyses were used to study the neuronal types in the striatum of adult (3, 6, and 10 months) and aged (20, 25, and 30 months) C57BL/6N mice. In adult mice six types of striatal neurons were distinguished primarily on the basis of the morphology of their cell body and dendrites. Each of these types was compared with morphologically similar neurons from previous Golgi classifications in other species and discussed within the framework of recent immunocytochemical work. With similar methods the age-related changes occurring on the dendrites of three of the six striatal types were also analyzed. In the medium-sized neuron with spine-laden dendrites, various dendritic tree shapes and sizes were distinguished in all age groups studied. Qualitative observations as well as measurements of total dendritic length per cell suggested that the dendrites in this type may both grow and regress throughout the life span, although signs of dendritic atrophy and regression were observed only in the aged groups. In the other two types of neuron, one a medium aspiny cell with thin varicose dendrites and the other a large spiny neuron with many dendrites, measurements of total dendritic lengths revealed sustained growth of the tree well into advanced age, followed by moderate regression in the oldest groups. The present findings also indicate that the dendrites of each type of striatal neuron follow unique temporal patterns of growth and regression during the life span of the mouse.

Short- and long-term survival of large neurons in the excitotoxic lesioned rat caudate nucleus: a light and electron microscopic study

Large striatal neurons are spared in caudate tissue from postmortem brain of patients with Huntington's disease (HD) and in the rat caudate lesioned with excitotoxins at short postlesion intervals. In order to determine the survival of large neurons and other effects of excitotoxicity at longer postlesion intervals the rat caudate nucleus was examined 2, 7, and 30 weeks after intrastriatal injections of the excitotoxin, quinolinic acid. The caudate nucleus diminished in size progressively up to 30 weeks postlesion due to 1) shrinkage and compacting of the lesion zone and 2) reduction in area of intact caudate, apparently due to gradual loss of the remaining caudate neurons. In Nissl-stained sections of the lesion zone where total neuronal density was less than 5% of contralateral control, large neurons were present at all postlesion intervals, forming 38-58% of the remaining neurons. Unexpectedly, a fivefold reduction in the number of large neurons was observed between 2 and 30 weeks postlesion. Also, at 7 and 30 weeks postlesion most of the large neurons were confined to the peripheral region of the lesion. At all postlesion intervals, large neurons retained ultrastructural integrity and some synaptic inputs despite the severe disruption of the surrounding neuropil. Surrounding the lesion zone was a transition zone which exhibited a decrease in total neuronal density to 53-74% of control. In this region the density of large neurons was not diminished, and the proportion of large neurons was elevated in comparison to that of controls at all postlesion intervals. Findings suggest that following excitotoxic lesion of the caudate nucleus there are marked differences between short- and long-term postlesion intervals in the survival and distribution of large neurons. We speculate that an imbalance in the synaptic connections with other caudate neurons leads to the persistent loss of large neurons in the lesion zone at long postlesion intervals. A transition zone surrounding the lesion, where cell loss is less severe than in the lesion zone, exhibits features more characteristic of the neuropathology of HD.

Selective decrease of large neurons in the neostriatum in progressive supranuclear palsy

In order to evaluate the quantitative changes in the neostriatum in progressive supranuclear palsy (PSP), sections of the caudate head (CN) and putamen (PT) from 4 PSP patients were stained with Klüver-Barrera, and the cell body and nuclear area of the neurons were measured by a digitizer. Obtained results were compared to those of 6 age-matched control and 4 Alzheimer's disease and senile dementia of Alzheimer type (AD/SDAT) subjects which were previously reported. The number of large neurons (nuclear area greater than 101 microns 2) in PSP was about 40% (P less than 0.01) and 30% (P less than 0.01) of that of the controls in CN and PT, respectively. In contrast, the number of small neurons in PSP (nuclear area less than 100 microns 2) was well preserved. The values were quite similar to those in AD/SDAT. The implications and possible significance are discussed.

Dopamine-acetylcholine interaction in the rat striatum: a dual-labeling immunocytochemical study

The relationship between cholinergic neurons and dopaminergic axons in the rat striatum was examined by a dual-labeling immunocytochemical method. Cholinergic neurons were identified by their immunoreactivity for choline acetyltransferase (ChAT), and dopaminergic axon terminals were identified by their positive immunoreactivity for tyrosine hydroxylase (TH). Electron microscopic analysis of dual-labeled sections revealed that while most TH-positive terminals formed synapses with unlabeled striatal neurons and dendrites, a number of TH-positive terminals formed close appositions, highly suggestive of synapses, with both large and small dendrites as well as somata of ChAT-positive neurons. Tight appositions were also found between TH-positive terminals and ChAT-positive terminals. Moreover, TH-positive terminals and ChAT-positive terminals were found to form synapses with common dendrites of unlabeled striatal neurons. These results indicated that 1) dopaminergic axon terminals could interact directly with striatal cholinergic interneurons via tight appositions with distances comparable to conventional synapses; and 2) there is a convergence of dopaminergic and cholinergic axon terminals on noncholinergic striatal neurons.

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.

Age-related changes in the nigrostriatal system

These data support the view that the rate at which an organism ages is a summation of factors throughout life. While some cells seem to remain stable or even grow with age, others show significant regression. In this regard, different populations of striatal neurons show unique and different patterns of growth and development with advancing age. While aspiny II neurons show peak growth by 10 months of age, aspiny I and medium spiny I cells do not reach a growth peak until much later in life. In addition, our data support the notion that the occurrence and severity of structural changes in the aged brain are not distributed homogeneously and that many of the so-called "age-related" changes that were once generalized to the entire brain are brain-region, cell-type, and species specific. Furthermore, our data reinforces the concept that the correlation of structure and function is central to the analysis of an aging population because considerable differences may be found in data based on functionally impaired and unimpaired groups.

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.

Glutamate decarboxylase-like immunoreactive neurons in the rat caudate putamen

GAD-IR neurons were roughly divided into those with medium sized perikarya and large perikarya. The medium-sized GAD-IR neurons accounted for about 85% of the GAD-IR neurons. The medium-sized perikarya were further divided into two, those with a smooth nuclear membrane and those with an indented nucleus. The former were very similar to medium-sized spiny neurons and the latter corresponded to medium-sized aspiny neurons. The GAD-IR large cells that were identified by light microscopy, had nuclear indentations and were divided into two classes based on their ultrastructural features, type 1 large cells received few synaptic inputs and type 2 large cells received many synaptic contacts from non-immunoreactive or immunoreactive boutons. The former resembles Type I large cells and the latter Type II large cells identified recently by Chang and Kitai; the latter are also similar to the second type of projecting neurons identified by Bolam et al.

Selective involvement of large neurons in the neostriatum of Alzheimer's disease and senile dementia: a morphometric investigation

In order to evaluate the quantitative changes in the neostriatum of Alzheimer type (SDAT), sections of the caudate head (CN) and putamen (PT) from 4 AD/SDAT and 6 age-matched control cases were stained with Klüver-Barrera, and the cell body and nuclear areas of the neurons were measured by a digitizer. This study revealed a significant decrease in the number of large neurons (nuclear area; greater than 101 micron 2) and good preservation of the number of small neurons (nuclear area; less than 100 micron 2) in CN and PT of AD/SDAT.

Dopaminergic axons directly make synapses with GABAergic neurons in the rat neostriatum

We examined with an electron microscopic 'mirror technique' whether glutamic acid decarboxylase-immunoreactive (GAD-IR) neurons are in direct synaptic contact with tyrosine hydroxylase-immunoreactive (TH-IR) axons in the rat neostriatum. Three types of GAD-IR neurons were identified in the nucleus caudatus putamen based upon their size and ultrastructural characteristics. These were medium spiny, medium aspiny and large cells. All types of GAD-IR neurons made synaptic contact with TH-IR axonal boutons at least on perikarya and proximal dendrites. This provides ultrastructural evidence for catecholaminergic, presumably, nigrostriatal dopaminergic inputs to both long- and short-axon neurons most probably containing GABA.

The intercalated cells of the amygdala

The intercalated cell groups, or massa intercalata, of the amygdala have been studied in rodent brains with Golgi methods. They also have been examined in gallocyanin-chromalum-, AChE-, and Timm-stained rat brains. The Golgi data indicate that the intercalated cells are not confined to a series of isolated cell clumps but form a neuronal net that covers the rostral half of the lateral-basolateral nuclear complex, stretches across a major portion of rostral amygdala, and continues rostrally beneath the anterior commissure. There are two general types of intercalated neuron--medium and large neurons. The medium intercalated neurons are more common. They have round to elongate somata, 9-18 microns in diameter, and round to bipolar dendritic trees, depending on their location. Most of the dendrites are spine-bearing, as are 20% of the somata. Their axons often have locally ramifying collaterals. The parent axons apparently terminate in either the lateral-basolateral or central nuclei and some of them appear to enter the external capsule. There is a unique medium intercalated neuron that has nearly spine-free, varicose dendrites and an axon that is typical of short axon (Golgi II) cells. There are two varieties of large intercalated neuron-spiny and aspiny. Most of them are aspiny, although they usually have a few spines scattered along their dendrites. Both varieties have elongate, sometimes round, somata that can be as much as 60 microns long. Their dendrites are long, thick, and have few branch points. Only the initial part of the large aspiny cell axon has been impregnated. The large spiny cell axons have several local collaterals; the destination of the parent axons is unknown. The intercalated cells occur along fiber bundles, which are probably afferent to them. The axons that travel among the intercalated cells give off short collaterals and boutons en passant. The sources of these fibers are not known. From the published experimental data, it is likely that they originate in the piriform and entorhinal cortices, the lateral preoptic area, lateral hypothalamus, and ventral pallidum. Axon collaterals of basolateral nucleus pyramidal cells appear to terminate among the intercalated cells. It is suggested that the intercalated cells serve as sites for integration of the output of these various areas and, in turn, communicate it to the lateral-basolateral and central amygdaloid nuclei. The intercalated cells closely resemble neurons in the corpus striatum. Thus the question is raised and discussed of whether the intercalated cells are a ventral extension of the corpus striatum.

The olfactory tubercle of the cat. I. Morphological components

On the basis of morphology and arrangement of cell types, the olfactory tubercle (OT) of the cat is divided into two main components: a cortical part and the cap/hilus regions in which cortical characteristics are not recognizable. The cortical part undergoes a gradual transformation from a more cortex-like structure in the lateral half of the OT - possibly related to the presence of olfactory fibers - to a more striatum-like organization in the medial half. Cell bridges extend between the polymorph layer of the cortical part and the striatum and especially the n. accumbens. The cap regions form 8 or 9 superficial grooves running in a rostro-caudal direction. They contain dwarf and small pyramidal-like neurons and lie immediately ventral to the granule islands of Calleja. Dwarf and small pyramidal-like neurons give rise to an ascending axonal plexus which may contact large neurons in the hilus regions dorsal to the Calleja islands and in part also neurons of the ventral pallidum, the dendrites of which enter the lateral hilus zones. The proportion of dwarf cells to granule cells in the cap regions gradually reverses from lateral, where dwarf cells dominate, to medial, where the caps contain almost exclusively granule cells. No interconnections are observed between the two components of the OT.

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.

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.

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)

Correspondence between the dopamine islands and striosomes of the mammalian striatum

During the development of the mammalian striatum, the early-forming dopamine innervation is broken up into macroscopic patches called "dopamine islands". These express high tyrosine hydroxylase-like immunoreactivity and are also rich in acetylcholinesterase activity. The mature striatum has prominent macroscopic compartments called "striosomes" that were first characterized by their low acetylcholinesterase activity and since have been related to heterogeneities in striatal input-output organizations. This report describes two sets of experiments designed to determine the relationship between the dopamine islands and the striosomes. The distributions of striatal tyrosine hydroxylase-like immunoreactivity and acetylcholinesterase activity were first compared in a series of kittens and young cats ranging in age from 1-228 postnatal days. During this time, the pattern of tyrosine hydroxylase-like immunoreactivity changed from islandic (patchy) to diffuse, and the pattern of acetylcholinesterase staining changed from one of acetylcholinesterase-rich patches to one of acetylcholinesterase-poor striosomes. The dopamine islands were in register with the acetylcholinesterase-poor patches at early developmental stages and at later stages the islands matched striosomes. These observations establish a correspondence between the dopamine islands and striosomes and demonstrate that the acetylcholinesterase-rich patches of the immature caudate nucleus become the acetylcholinesterase-poor striosomes of the adult. In a second set of experiments, cat fetuses were exposed to [3H]thymidine at embryonic days 22-29 in order to label the clustered subpopulations of striatal neurons known from previous experiments to lie in striosomes [Graybiel and Hickey (1982) Proc. natn. Acad. Sci. U.S.A. 79, 198-202]. The [3H]thymidine-labeled brains were examined at late fetal (embryonic days 50-52), early postnatal (days 1-21) and later postnatal (days 62-199) ages. The clusters of [3H]thymidine-labeled neurons were aligned with tyrosine hydroxylase-rich, acetylcholinesterase-rich patches early in development, and with acetylcholinesterase-poor striosomes at later stages. There were marked dorsoventral differences in the intensity of tyrosine hydroxylase-like immunoreactivity in the dopamine islands and this was confirmed in neonatal rats. A "dorsal islandic system" was defined as having crisp, highly immunoreactive islands; ventrally, regions of low and medium tyrosine hydroxylase-like immunoreactivity formed a mosaic.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholinergic neurons in the nucleus tegmenti pedunculopontinus pars compacta and the caudoputamen of the rat: a light and electron microscopic immunohistochemical study using a monoclonal antibody to choline acetyltransferase

Large neurons in the nucleus tegmenti pedunculopontinus pars compacta (TPC) of the rat were shown to have choline acetyltransferase (ChAT) immunoreactivity by light and electron microscopic immunohistochemistry using a monoclonal antibody to ChAT. The ChAT-positive TPC neurons had triangular or multipolar cell bodies with diameters of 20-50 micron. The ultrastructural features of the ChAT-positive TPC neurons were similar to those of ChAT-positive neurons in the caudoputamen; each neuron had a distinct, pale nucleus with an indented nuclear envelope and large, cytoplasm-containing, well-developed endoplasmic reticulum and pale mitochondria.