The organization of synaptic junctions in cat putamen

Three-dimensional analysis of dendritic spines. II. Spine apparatus and other cytoplasmic components

A total of 342 dendritic spines (193 from the visual and 149 from the cerebellar cortex of the mouse) were analyzed in serial and several hundred of thousands of them in single sections, with respect to the presence and organization of the spine apparatus and other cytoplasmic components. The continuity of the spine apparatus with the smooth endoplasmic reticulum of the dendritic trunk was shown in three-dimensional reconstructions. The dense material of the spine apparatus was divided into "inner dense plate" and "outer dense plate". The close relationship between the outer dense plate and the postsynaptic density suggests that the spine apparatus functions as a postsynaptic protein synthesizing centre. The material from the outer dense plate could be used for a dynamic extension of the synaptic active zone. An extraspinous spine apparatus of the axon initial segment was partially reconstructed. Polyribosomes were found in all large spines of the visual cortex but were not so frequent in small spines and in Purkinje cell dendritic spines. Microfilamentous network and intermediate filaments occurred in the spines. The smooth endoplasmic reticulum of Purkinje cell dendritic spines was reconstructed. No spine apparatus and dense material were present in these spines.

A theory of the functional organization of the neostriatum and the neostriatal control of voluntary movement

A theory of the intrinsic, functional organization of the neostriatum and the neostriatal control of voluntary movement is presented. The cell types of neostriatum are described in accordance with the classification scheme of Pasik, Pasik and DiFiglia (ref. 204) and their suspected neurotransmitters are identified. The functional relations between the afferent projections to neostriatum and the intrinsic elements of neostriatum are described. A division of the neostriatal efferents into two functional cell systems is conceived, in which one efferent system, the Spiny I cell matrix, is thought to be represented by a lateral inhibitory network comprised of the common Spiny I neurons which inhibit their targets, while another is termed the Spiny II cell cluster and consists of the far less numerous excitatory efferents of neostriatum (the Spiny II cells) and is represented by clusters of neurons, the members of each cluster consisting of one excitatory efferent neuron and three interneurons. The implications of this view for neostriatal input--output relations are discussed, and the theory is developed by reference to a variety of converging lines of empirical evidence, and is used to interpret the effects of various pharmacologic strategies which have been employed to achieve symptom management in disorders of voluntary movement. In the course of this review, there emerges an integrative theory of the principles governing the neostriatal control of voluntary movement.

Corticostriate projections from the primary motor cortex in the dog

Corticostriate projections from the hindlimb and forelimb areas of the primary motor cortex in the dog were traced using the autoradiographic technique. Injections of tritiated leucine into the hindlimb area resulted in discrete oval or semicircular patches of label confined to the dorsolateral corner of the head and body of the caudate nucleus. No label was found over the putamen. Injections into the forelimb area yielded irregularly shaped patches of label over the dorsolateral part of the head and body of the caudate nucleus as well as more diffuse label over the dorsal-most part of the putamen. In both instances diffuse terminal fields were noted in the dorsolateral part of the contralateral caudate nucleus. A comparison of results in the caudate nucleus indicates that projections from the forelimb area terminate somewhat more caudally and slightly more ventrally and medially than do projections from the hindlimb area. The results further suggest that although terminal fields from these areas may to some extent interdigitate with one another, they also overlap each other to a significant degree.

Acetylcholinesterase-containing neurons in cat neostriatum: a morphological and quantitative analysis

When examined in brain sections prepared according to the Butcher's pharmaco-histochemical method, the large acetylcholinesterase (AChE)-containing cells in cat putamen appear morphologically different, more numerous per mm2, and significantly larger than those in caudate nucleus. Such a finding supports the view that the feline neostriatum is not a homogeneous structure. In addition, horseradish peroxidase (HRP) injected into the various target nuclei of neostriatum labels numerous medium-sized striatal cells and a few large-sized putaminal neurons. However, no HRP material could be detected in the large AChE cells themselves, suggesting that these cells are not output neurons.

Ultrastructure of Golgi-impregnated and gold-toned spiny and aspiny neurons in the monkey neostriatum

Golgi-impregnated, gold-toned spiny and aspiny neurons in the monkey neostriatum were deimpregnated and examined at the electron microscope level. Spiny type I neurons have relatively large nuclei with few indentations and aggregates of chromatin under the nuclear membrane which in some regions give the appearance of a dark rim. The small quantity of surrounding cytoplasm is poor in organelles. Aspiny type I neurons have eccentric, highly indented nuclei. The relatively large proportion of cytoplasm is rich in organelles especially Golgi apparatus and rough endoplasmic reticulum which often appears in stacks. Synapses with symmetric membrane densities are common on the somata of spiny type I neurons. Those on the proximal and distal dendritic shafts are few in number and asymmetric, and those on spines more frequent and primarily asymmetric. Aspiny type I neurons have few synapses on their cell bodies. Proximal and distal dendrites, however, are contacted by numerous profiles which contain small round vesicles and make both symmetric and asymmetric synapses. The same axon terminals also synapse with dendritic spines of spiny neurons, indicating that an input, most likely of afferent origin, is shared by both cell types. Other less frequently occurring profiles forming symmetric membrane densities also contact the dendrites of aspiny and spiny neurons. The axon hillocks and initial segments of both neuronal types receive a synaptic input, which is more common on spiny cells. Results offer unequivocal evidence for the differences in the ultrastructure of these two most common categories of medium-size neostriatal neurons, which may help in their proper identification in standard material, as well as information on the types and distributions of synaptic inputs onto these neurons. Moreover, the findings clarify some controversies in the literature probably originating from observations on a mixed population of cells of medium size.

A study of the axon initial segment and proximal axon of neurons in the primate motor and somatic sensory cortices

The axon initial segments of pyramidal cells and large and small stellate cells in the primate sensori-motor cortex have a typical membrane undercoating and bundles of neurotubules. Those of pyramidal cells are directed towards the white matter whereas those of large and small stellate cells often run obliquely or towards the cortical surface and may be curved. Cisternal organs in these initial segments are related to symmetrical axon terminals, frequently coming into close apposition to the non-synaptic part of these terminals adjacent to the synapse between the axon terminal and initial segment. The dense plates of cisternal organs and the membrane undercoating of the initial segment are specifically stained by ethanolic phosphotungstic acid (ethanolic PTA). Pyramidal initial segments have spines which receive only symmetrical synapses, as do the shafts of the initial segments of each cell type. The full length of the initial segment was studied for fourteen pyramidal and two large stellate cells. All gave rise to myelinated axons although two pyramidal cells had lengths of unmyelinated axon between the initial segment and myelinated axon. One of these lengths of unmyelinated axon made an asymmetric synapse on to a dendrite just after losing its initial segment features. Quantitative analysis of these complete initial segments showed that whereas the diameter of the initial segment and the axon it gave rise to were approximately proportional to the size of the parent cell soma over a considerable range of cell diameters, the length of the initial segment appeared to be unrelated to either its diameter or the size of its parent soma but varied between 30 and 55 μm apparently at random. Synapses were evenly distributed along the full length of the complete pyramidal initial segments, but the density of synapses on the initial segments of supragranular pyramids was about three times that on those of infragranular pyramids and cisternal organs were similarly more frequent in the initial segments of supragranular pyramids.

The postnatal development of the caudate nucleus: a Golgi and electron microscopic study of kittens

This study used light and electron microscopy to describe changes in the synaptic organization of developing caudate nucleus and to quantitate postnatal synaptogenesis in this region. Observation at the light microscopic level focus on the perinatal period and suggest an early maturation of spiny interneurons of the caudate nucleus. Golgi impregnation of these cells at early postnatal ages (birth to 7 days) reveals 3-5 primary dendrites which radiate from the cell body and extend for distances of 8-16 micron before branching. Secondary dendritic branches contain spines and extend, with further branching, for additional distances of 60-160 micron. The dendritic fields of neighboring caudate neurons overlap and the axons which arise from these cells course and branch within the dendritic fields. Examination of perinatal caudate neuropil (birth to 5 days) by electron microscopy reveals an extensive and well-developed axodendritic connectivity. Axonal profiles form multiple synapses en passant along single dendrites and dendritic spines or on several adjacent dendritic branches. At these ages, terminals contain few synaptic vesicles and synaptic junctions are slightly asymmetrical. By the fifteenth postnatal day, boutons are filled with vesicles, junctional complexes are distinctly asymmetrical, and axondendritic connectivity has been modified by the increase of dendritic spines and branchlets. Thus, the basic pattern underlying the organization of synapses in the mature caudate nucleus, is established within the first week postpartum and subsequent changes are primarily quantitative.

The effect of blocking dopamine release on synthesis rate of dopamine in the striatum of the rat

Two experiments were carried out in rats to investigate the mechanisms by which dopamine (DA) synthesis is regulated. First, a unilateral lesion was made in the substantia nigra, thus interrupting the nervous impulse flow of the nigro-striatal pathway. Secondly, the release of DA in the striatum was blocked by means of 1-hydroxy-3-amino-pyrrolidone-2 (HA-966). In both experiments the synthesis rate of DA was accelerated as was shown by analysing the time course of the specific activity of striatal DA after an i.v. injection of 3,5-3H-tyrosine. Furthermore the influence of apomorphine on the rate of DA synthesis, accelerated by HA-966 or by lesion, was investigated. Apomorphine appeared to block the increase of DA synthesis. The results are discussed in the light of a transsynaptic feedback mechanism.

Dopamine-containing neurons of the substantia nigra and their terminals in the neostriatum

Tne ultrastructural and fluorescence histochemical characteristics of the mature rabbit substantia nigra and neostriatum have been reviewed as a frame of reference for the developmental study. Biochemical investigations were reported on neostriatal dopamine concentrations and the relative uptake and accumulation of 3H-dopamine by this tissue from fetal to adult stages, to provide quantitative data for correlation with the fluorexcence information. The development of the neurons of the substantia nigra and their axons which project to the neostriatum has been presented from their appearance at day 14 of gestation to their maturation in early postnatal life. The initial bipolar neuroblasts, which develop in the midline of the caudal mesencephalon, are fluorescent as soon as they emerge from the ependymal zone. Their fluorescent axons, which form the nigroneostriatal pathway, reach the telencephalon at day 16 of gestation and ramify extensively in the putamen by day 20, but do not enter the caudate nucleus until several days later. Some of the early fluorescent axonal profiles in the putamen are extremely large. Electron microscopic study of theis stage suggests that the large fluorescent profiles may correspond to axonal growth cones or early synapses. A distinct substantia nigra, pars compacta and reticulata, can be recognized by fluorescence microscopy by day 20 of gestation. Electron microscopy reveals that the young neurons are multipolar with numerous developing dendrites, some of which exhibit early synaptic junctions. The subsequent maturaition of these cells and the neuropil is described. The fluorescent axons of the substantia nigra grow into the putamen and caudate nucleus in a nonuniform manner forming fluorescent islands throughout the neostriatum in late fetal life. Occasionally, minute beaded fluorescent axons are found. These profiles might correspond to some of the axons with varicosities "en passage" revealed by electron microscopy. In an attempt to identify further the dopamine-containing axon, the ultratructure of adult neostriatum incubated in 5-hydroxydopamine was reported. Axonal varicosities "en passage" containing a dense "tag" in the vesicles were found. Most of the tagged boutons did not exhibit synaptic contacts. The possible significance of these finding s as related to dopamine secretion are discussed.

The synaptic organization of the caudate nucleus

The synaptic organization of the caudate nucleus appears to be homogeneous with no specialized groupings of axon terminals and postsynaptic profiles. The nerve terminals in the caudate nucleus fall into two size groups, one about 1 fim in diameter and the other about 5 /itn diameter. The smaller size group, which comprises the majority of terminals, may be subdivided into three varieties on the basis of vesicle morphology and the type of membrane thickening. Most contain round, 45 nm diameter vesicles and are associated with asymmetrical membrane thickenings. Others contain 48 nm diameter, polymorphic vesicles, which become flat in material washed in cacodylate buffer, and are associated with symmetrical membrane thickenings. A few other terminals with symmetrical membrane thickenings contain flat 42 nm vesicles. The large terminals contain round 45 nm diameter vesicles and have asymmetrical membrane thickenings. Axon terminals with asymmetrical membrane thickenings are found most frequently in contact with dendritic spines, but also with dendritic shafts and cell somata. Terminals with symmetrical membrane thickenings contact dendritic shafts and cell somata, and occasionally dendritic spines with which a terminal with asymmetrical thickenings is also making contact. The two types of terminal with symmetrical contact regions also form synapses onto the initial segments of axons. It is probable that such contact regions are invariably associated with cisternal organs in the initial segments. Serial synapses are found occasionally.