Preparation of the spinal neurons and their bushy receptors for morphophysiological study

A preparation of the sensory neuron of the spinal ganglion with dendritic processes for simultaneous morphological and physiological investigations is described. It consists of a frog urinary bladder with bushy interoceptors in its wall, two vesicle neurons, two abdominal branches of the X spinal nerves and two IX spinal ganglia with ventral and dorsal roots branching off from them. The total length from the receptors to the ganglion neurons is 20-30 mm. In the ganglia a zone of the neuronal bodies localization is found, their processes form receptors; the zone includes as many as 9 neurons, 50-80 mkm in size. A vital fine structure of the ganglion cells and their satellites is traced. There are three types of cells in the ganglion--large, middle and small. Electrophysiological control has demonstrated that the preparation is viable for several hours.     

Fine structure of neurons synthesizing vasoactive intestinal peptide in the human colon from patients with Hirschsprung's disease

Summary The fine structure of neuronal perikarya and processes containing VIP-like immunoreactive material in the colon of patients with Hirschsprung's disease was investigated by immunoelectron microscopy. No VIP-like immunoreactive terminals were found in Auerbach's plexus of the ganglionic segment. However, VIP-like immunoreactive preterminal axons were frequently found to make synaptic contact with both immunoreactive and non-immunoreactive elements within Meissner's plexus. Therefore, the function of the VIP neurons in Auerbach's plexus seems to differ from that in Meissner's plexus. In the oligoganglionic segment, there were a few VIP-like immunoreactive processes, but no VIP-like immunoreactive synaptic formations. VIP-like immunoreactive processes were rarely encountered in the aganglionic segment. In both the oligo-and aganglionic segments, bowel relaxation is considered to be disturbed due to the lack of synaptic contacts of VIP-like immunoreactive neurons with other neuronal components.This work was supported in part by a grant (no. 57370002) from the Ministry of Education, Science and Culture, Japan     

Ultrastructural characteristics of axon terminals of the posterior lateral nucleus of the thalamus in the cat]

Two kinds of axon terminals: fine M-terminals with the diameter up to 2 mkm and large K-terminals with the diameter up to 6 mkm were found in electron microscopic study of the posterior lateral nucleus of the cat's thalamus. M-terminals comprising 88% of the total amount of the axon terminations under analysis are characterized by a great amount of densely packed light round synaptic vesicles and solitary mitochondria. These terminals form asymmetrical type of contacts in which the post-synaptic network is distinguished with a high degree of osmiophilia. The K-terminals contain a few rarely distributed round light synaptic vesicles and many mitochondria which are disposed in the central part of the termination. These terminals form a symmetrical type of synaptic contacts with poorly pronounced active zones in these formations. In axo-axonal contacts between the described kinds of terminals the K-terminals always serve as a presynapse. After extirpation of the sincipital cortex M-terminals underwent degeneration.     

Fine structure of neurons synthesizing vasoactive intestinal peptide in the human colon from patients with Hirschsprung's disease

The fine structure of neuronal perikarya and processes containing VIP-like immunoreactive material in the colon of patients with Hirschsprung's disease was investigated by immunoelectron microscopy. No VIP-like immunoreactive terminals were found in Auerbach's plexus of the ganglionic segment. However, VIP-like immunoreactive preterminal axons were frequently found to make synaptic contact with both immunoreactive and non-immunoreactive elements within Meissner's plexus. Therefore, the function of the VIP neurons in Auerbach's plexus seems to differ from that in Meissner's plexus. In the oligoganglionic segment, there were a few VIP-like immunoreactive processes, but no VIP-like immunoreactive synaptic formations. VIP-like immunoreactive processes were rarely encountered in the aganglionic segment. In both the oligo- and aganglionic segments, bowel relaxation is considered to be disturbed due to the lack of synaptic contacts of VIP-like immunoreactive neurons with other neuronal components.     

Axonal patterns of disc-shaped cells in the central nucleus of the cat inferior colliculus

The axonal patterns of disc-shaped cells (Dsc) and their distribution within the central nucleus (Cn) of the inferior colliculus was studied in young cats with the rapid Golgi method. Dsc were subdivided in three main cell varieties according to their axonal branching pattern. The first type possesses local axonal collaterals inside the lamina of origin but also gives collaterals and probably terminals to adjacent lamina. The second variety is characterized by a dense axonal plexus with a restricted zone of arborization. The third axonal pattern is distributed in a radiate fashion. These results demonstrate that Dsc contribute to the intrinsic axonal system of the Cn to a larger degree than previously supposed. Axon terminals of Dsc probably establish axo-dendritic contacts with medium sized Stc which probably establish contacts with neighbouring Dsc. This suggests that reciprocal connections between Dsc and Stc could exist in the Cn.     

Ultrastructure of the synapses of the initial axonal segment of the pyramidal neuron

Ultrastructure of the proximal part of the axon in the neurons, identified according to a number of morphological signs as pyramidal, has been studied in the layer III of the cat cerebral hemisphere sensomotor cortex. In sections, tangential to the cortical surface, in the initial axonal segment, a submembranous osmophilic layer and fasciculi of microtubules are revealed. On the initial segment spines are found, they contain cysterns resembling by their structure the spine system of the dendritic spines. Axonal terminals revealed along the axonal distribution are in contact both with the axonal trunk and with the spines. Regarding the initial segment, they are presynaptic, contain oval synaptic vesicles and form symmetric axo-axonal synapses only. In transversal sections axonal terminals are detected, arranging on the surface of the initial segment mostly as single ones, in longitudinal sections they are seen as clusters. Analysing the author's data and those from the literature, a conclusion is made that in intact animals the synaptic contacts at the initial segment of the axon are the only form of axo-axonal synapses in the neocortex.     

A survey of the cytology and synaptic organization of the insular trigeminal-cuneatus lateralis nucleus in the rat, including an identification of spinal afferent inputs

The cytology and synaptic organization of the insular trigeminal-cuneatus lateralis (iV-Cul) nucleus was examined in the rat. In addition, the ultrastructural morphology and synaptic connectivity of anterogradely labeled spinal afferent axons terminating in iV-Cul were examined following injection of horseradish peroxidase (HRP) into the cervical spinal cord. The uniformity of the ultrastructural features of iV-Cul neurons supports the presence of a homogeneous neuronal population. The most prominent feature of the iV-Cul neuropil is the presence of numerous interdigitating astrocytic processes, which extensively isolate neuronal somata and processes. iV-Cul contains a heterogeneous population of axonal endings that can be separated into three categories, depending upon whether they contain predominantly spherical-shaped agranular synaptic vesicles (R endings), predominantly pleomorphic-shaped agranular synaptic vesicles (P endings), or a heterogeneous population of dense-core vesicles (DC endings). The R endings represent the majority of axonal endings in iV-Cul and establish asymmetrical axodendritic and axospinous synaptic contacts, primarily along the distal portions of the dendritic tree. P endings establish symmetrical axosomatic, axodendritic, and axospinous synaptic contacts and exhibit a more generalized distribution along the somadendritic tree. DC terminals establish asymmetrical axodendritic synaptic contacts with distal dendritic processes and are the least frequently observed endings in the iV-Cul neuropil. Numerous synaptic glomeruli, exhibiting a single large central R bouton that establishes multiple axodendritic or axospinous synapses, characterize the iV-Cul neuropil. Axoaxonic synapses are conspicuously absent from the iV-Cul neuropil and glomeruli. The anterograde HRP labeling of spinal afferent axons that terminate in iV-Cul indicates that the terminals along these fibers are of the R type and that they are engaged predominantly in synaptic glomeruli. The results of this study indicate that the synaptic organization of iV-Cul is distinctly different from that of neighboring somatosensory nuclei, and supports the recent suggestion that this nucleus should be considered a separate precerebellar spinal relay nucleus in the lateral medulla.     

Neuronal organization of the periamygdaloid cortex in the cat brain

Neuronal organization of the fields Pmm, Pml2, Pe and epm of the periamygdaloid cortex of the cat brain has been studied by means of Golgi and Nissl methods. The field Pmm essentially differs from other fields of this cortex by primitiveness of its cytoarchitectonic an neuronal organization (two layers uniform by the composition of their neurons are distinguished, the structure of the latter is relatively primitive). In the medial part of this field long axonal rarely branching short dendritic, and in the lateral part--poorly differentiating pyramidal and spindle-like cells predominate. The field Pmm can be considered as a transitional formation between the subcortex (the medial nucleus of the amygdaloid body) and other fields of the periamygdaloid cortex. The fields Pml2, Pe and epm are built more complexly: the cells are organized in 4 layers, more complexly differentiated by their form and size than in the field Pmm and correspondingly more various (long axonal densely branching cells are observed: pyramidal and spindle-like--of the cortical type and bushy--of the subcortical type, as well as long axonal rarely branching reticular cells). The short axonal cells in the fields Pml2, Pe and epm are rather variable in their form, size and direction of axons; in the field Pmm they are less numerous. The field Pmm and the complex of the fields Pml2, Pe and epm are perhaps different in their function, this is evident from different projection of their neurons. Axons of the cells in the field Pmm get into less differentiated and the most ancient medial nucleus of the amygdaloid body and into the ancient system of connections of the latter--terminal strip, and neurons of the fields Pml2, Pe and epm are projected into the basolateral part of the amygdaloid body and into the external capsule--phylogenetically younger structures. Besides, poverty of the axonal collateralies in the long axonal neurons and a small amount and uniformity of the forms of the short axonal cells in the field Pmm and contrary, rich collateralies and variety of short axonal cells in the composition of other fields demonstrate more complex internal integrative function, performing in that composition.     

A Survey of the Cytology and Synaptic Organization of the Insular Trigeminal—Cuneatus Lateralis Nucleus in the Rat,Including an Identification of Spinal Afferent Inputs

The cytology and synaptic organization of the insular trigeminal—cuneatus lateralis (iV-Cul) nucleus was examined in the rat. In addition, the ultrastructural morphology and synaptic connectivity of anterogradely labeled spinal afferent axons terminating in iV-Cul were examined following injection of horseradish peroxidase (HRP) into the cervical spinal cord. The uniformity of the ultrastructural features of iV-Cul neurons supports the presence of a homogeneous neuronal population. The most prominent feature of the iV-Cul neuropil is the presence of numerous interdigitating astrocytic processes, which extensively isolate neuronal somata and processes. iV-Cul contains a heterogeneous population of axonal endings that can be separated into three categories, depending upon whether they contain predominantly spherical-shaped agranular synaptic vesicles (R endings), predominantly pleomorphic-shaped agranular synaptic vesicles (P endings), or a heterogeneous population of dense-core vesicles (DC endings). The R endings represent the majority of axonal endings in iV-Cul and establish asymmetrical axodendritic and axospinous synaptic contacts, primarily along the distal portions of the dendritic tree. P endings establish symmetrical axosomatic, axodendritic, and axospinous synaptic contacts and exhibit a more generalized distribution along the somadendritic tree. DC terminals establish asymmetrical axodendritic synaptic contacts with distal dendritic processes and are the least frequently observed endings in the iV-Cul neuropil. Numerous synaptic glomeruli, exhibiting a single large central R bouton that establishes multiple axodendritic or axospinous synapses, characterize the iV-Cul neuropil. Axoaxonic synapses are conspicuously absent from the iV-Cul neuropil and glomeruli. The anterograde HRP labeling of spinal afferent axons that terminate in iV-Cul indicates that the terminals along these fibers are of the R type and that they are engaged predominantly in synaptic glomeruli. The results of this study indicate that the synaptic organization of iV-Cul is distinctly different from that of neighboring somatosensory nuclei, and supports the recent suggestion that this nucleus should be considered a separate precerebellar spinal relay nucleus in the lateral medulla.     

Development of morphological diversity of dendrites in Drosophila by the BTB-zinc finger protein abrupt

Morphological diversity of dendrites contributes to specialized functions of individual neurons. In the present study, we examined the molecular basis that generates distinct morphological classes of Drosophila dendritic arborization (da) neurons. da neurons are classified into classes I to IV in order of increasing territory size and/or branching complexity. We found that Abrupt (Ab), a BTB-zinc finger protein, is expressed selectively in class I cells. Misexpression of ab in neurons of other classes directed them to take the appearance of cells with smaller and/or less elaborated arbors. Loss of ab functions in class I neurons resulted in malformation of their typical comb-like arbor patterns and generation of supernumerary branch terminals. Together with the results of monitoring dendritic dynamics of ab-misexpressing cells or ab mutant ones, all of the data suggested that Ab endows characteristics of dendritic morphogenesis of the class I neurons.     

Synaptic organization of the cat parietal association cortex (area 5b)

An electron microscopy study was made of synaptic organization in the cat association cortex, area 5b. A total of 1635 axonal terminals were discovered over 6215 µm² (240 electronic imagings of slices of different association cortex layers); i.e., an average of 263±16 terminals per 1000 µm² expanse. It was found that 75.5% of axon terminals contained synaptic vesicles and formed either one- or two-sided contact with postsynaptic structures; 24.5% of axonal terminals contained synaptic vesicles but formed no distinct synaptic contacts with nearby neurons; 84.9% of terminals contained round-shaped or slightly oval synaptic vesicles; 7.8% had both rounded and elongated shapes, and vesicles were very elongated in the remaining 7.3%. Of the axonal terminals having synaptic contacts, axo(dendritic)-spinal terminals accounted for 46.6%, and axodendritic and axosomatic endings amounted to 50.0% and 3.4% respectively (in all 77% of axosomatic terminals contained elongated vesicles and maintained symmetrical contact, while 23% had round-shaped vesicles and formed asymmetrical contact). Calculations show that for each 1 mm³ an average of 258 million axonal terminals are found forming synaptic contacts in the cat association cortex as well as 84 million terminals containing synaptic vesicles but not forming contact.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 174–185, March–April, 1989.     

Relais cells and afferent axons in the dorsal part of the lateral geniculate body in the albino rat under geometrical aspects]

1. The average volumes of dendritic domaines of relay neurons (P-neurons) were calculated and the quantitative relations to the neuronal elements situated in this area were investigated. Likewise we carried out measurements and calculations at the terminal parts of afferent axons, to find a conception concerning possible contacts between axons and P-neurons considering quantitative aspects. 2. The dendrites of one P-neuron are distributed in an area of about 0,008 mum3. In this area there are located somata of at least 120 other P-neurons and dendrites of altogether about 900 P-neurons. 3. The type-1-axons (cortical afferents) run almost linearly in the longitudinal system of the CGLd. Traversing a distance adequate to the diameter of a P-neuron (250 mum) the dendrites of 150 to 170 P-neurons may cross the course of one axon. At this distance the axon, however, has just set up about 50 boutons, thus synaptic contacts may be established with one third at most of the existing cells. A type-1-axon that is bifurcating in the entrance area into the CGLd is altogether of about 2000 mum in length and is able to develop about 420 presynaptic profiles. 4. The type-2-axons (retinal afferents) show a distinct terminal branching zone. The Golgi-Kopsch impregnated terminals of type-2a-axons are distributed in a space of 147000 mum3 capacity, the corresponding terminals of type-2b-axons in a space of 443000 mum3. The type-2a-axons having an average number of 23 boutons, may contact the dendritic branching zones of 25 P-neurons. There is a good reason to assume that type-2b-axons are in contact also with terminal dendritic parts of P-neurons. Thus the number of P-cells, which spread their dendrites into the terminal branching zone of one type-2b-axon may amount to 540. The average number of boutons of one type-2b-terminal, however, is only about 160. This means that synaptic contacts may be developed to the P-neurons-dendrites not exceeding 30% of them. 5. Various aspects of divergence of axon terminals in the albino rat's CGLd are discussed.     

Morphological characteristics of various segments of local connections in the rat somatosensory cortex

Pyramidal, aspinous, sparsely-spinous bipolar and multipolar neurons of the rat sensomotor cerebral cortex, impregnated after Golgi method, have been studied at an electron microscopical level. The ultrastructural characteristics of the pyramidal neurons differs from that of the nonpyramidal cells. Distribution of various synaptic contacts on the cellular surface and cortical postsynaptic targets of the axonal arborizations of the neurons are revealed. On the body of the pyramidal cells only symmetrical synapses exist, on large dendritic trunks symmetrical synapses prevail, on the spines and the terminal dendritic branches assymetrical synapses mainly predominate. Axonal collateralies of the pyramidal cells form asymmetrical synapses on the spines, small and middle dendrites. There are more axo-somatic synapses on the bodies of the nonpyramidal neurons than on the pyramidal cells, among them both symmetrical and asymmetrical types of the synapses occur. On the trunks and small dendrites of the nonpyramidal cells both types of synaptic contacts are revealed. In the distal direction of the dendrites the number of the asymmetrical synapses becomes predominating. Axons of the bipolar cells form asymmetrical synapses on the spines, small and middle dendrites. Axons of the multipolar cells form symmetrical synapses on the dendrites and the dendritic trunks of the nondifferentiated cells. Differences in the distribution character of the synaptic inlets and various postsynaptic targets of the axonal systems in the cells assume various functional role of the identified neurons.     

Localization of arginine vasotocin (AVT) mRNA in extrasomal compartments of magnocellular neurons in the chicken hypothalamo-neurohypophysial system

In the chicken, arginine vasotocin (AVT) is produced in and secreted by magnocellular neurons in the supraoptic (SON) and paraventricular (PVN) nuclei. To test the hypothesis of axonally transported AVT mRNA, the localization of AVT mRNA within extrasomal, axonal/dendritic compartments in the chicken hypothalamo-neurohypophysial system (HNS) were examined using AVT specific in situ hybridization histochemistry (ISHH) and RT-PCR. Many perikarya in the PVN and external--but none in the ventral subgroup of the SON show ISHH signals clearly extended into one or two processes, some with branching collaterals, traceable over a distance of more than 100 microns. Furthermore by using RT-PCR, AVT mRNA was detected in the median eminence and neurohypophysis representing the distal parts of the HNS, mainly consisting of axons and/or axon terminals. These observations of axonal mRNA offer new insights to the organization and function of the avian HNS.     

Synaptic patterns in the dorsal lateral geniculate nucleus of the monkey

Summary Synaptic junctions are found in all parts of the nucleus, being almost as densely distributed between cell laminae as within these laminae.In addition to the six classical cell laminae, two thin intercalated laminae have been found which lie on each side of lamina 1. These laminae contain small neurons embedded in a zone of small neural processes and many axo-axonal synapses occur there.Three types of axon form synapses in all cell laminae and have been called RLP, RSD and F axons. RLP axons have large terminals which contain loosely packed round synaptic vesicles, RSD axons have small terminals which contain closely packed round vesicles and F axons have terminals intermediate in size containing many flattened vesicles.RLP axons are identified as retinogeniculate fibers. Their terminals are confined to the cell laminae, where they form filamentous contacts upon large dendrites and asymmetrical regular synaptic contacts (with a thin postsynaptic opacity) upon large dendrites and F axons. RSD axons terminate within the cellular laminae and also between them. They form asymmetrical regular synaptic contacts on small dendrites and on F axons. F axons, which also occur throughout the nucleus, form symmetrical regular contacts upon all portions of the geniculate neurons and with other F axons. At axo-axonal junctions the F axon is always postsynaptic.Supported by Grant R 01 NB 06662 from the USPHS and by funds of the Neurological Sciences Group of the Medical Research Council of Canada. Most of the observations were made while R. W. Guillery was a visiting professor in the Department of Physiology at the University of Montreal. We thank the Department of Physiology for their support and Mr. K. Watkins, Mrs. E. Langer and Mrs. B. Yelk for their skillful technical assistance.     

Ultrastructural localization of immunolabeled substance P and methionine-enkephalin-octapeptide in the surface layer of the dorsal horn of rat spinal cord

Summary A preembedding dual immunolabeling technique and electron microscopy were utilized to demonstrate the localization of immunoreactive substance P and methionine-enkephalin-octapeptide (Enk-8) in ultrathin sections of the surface layer (laminae I and II) of rat spinal dorsal horn. The immunoreaction of Enk-8 was visualized as goldtoned silver particles and that of substance P as diaminobenzidine reaction products. Axonal terminals with immunoreactive substance P, and also unlabeled axonal terminals, formed synaptic junctions with the perikarya and dendritic processes of Enk-8-containing neurons. Dendritic profiles immunolabeled for substance P were synaptically linked with unlabeled axons but not with Enk-8-positive ones. Furthermore, it was found that Enk-8 axons and substance P axons terminated synaptically in juxtaposition to one another on the same immunonegative dendrites. Among the Enk-8-containing neurons axonal profiles also appeared to be synaptically associated with immunoreactive Enk-8 dendritic processes.     

Studies of cardiac ganglia in pre- and postnatal rabbits

Summary This investigation was undertaken to describe the ultrastructure of cardiac ganglia in rabbits from day 18 of gestation to day 35 postpartum. Special attention was directed to the types of synaptic contacts made with the principal neurons and with the small granule-containing cells. The cardiac ganglia in all animals consisted mainly of parasympathetic postganglionic neurons, supporting cells, and small granule-containing (small intensely fluorescent) cells. The neurons received afferent synaptic terminals of two types. One type contained mainly small clear vesicles typical of most cholinergic terminals. The second type contained mainly small dense-core vesicles (these were most prominent after treatment of the animal with 5-hydroxydopamine), and were considered to be adrenergic terminals. These adrenergic terminals are probably part of an inhibitory system in the ganglia. The small granule-containing cells received typical afferent synaptic terminals of the cholinergic type, and also formed specialized contacts with certain axonal terminals. These latter specializations are considered to be reciprocal synapses which probably have a role in modulating ganglionic transmission.Supported by the Kentucky Heart Association and the Heart Association of Louisville and Jefferson County     

Connections between neurons of sympathetic ganglia and the myenteric nerve plexus of the mammalian colon

By means of retrograde transport of the fluorescent marker primulin the initial part of the sympathetic innervation of the myenteric nervous plexus of the descending colon has been characterized in cats and guinea pigs. When primulin is injected into the myenteric nervous plexus, marked neurons are revealed in the caudal mesenteric ganglion, in the celiac plexus ganglia, in the sympathetic trunk ganglia. The marked nervous populations of the extramural sympathetic ganglia differ in their form, size, number of neurons and their distribution.     

Cytoangioarchitectonics of the parasympathetic ganglion of the frog bladder according to findings from studies during life]

The form of neuronal bodies and their interarrangement with capillaries was studied in prevital parasympathetic ganglia in the bladder of the frog (Rana temporaria). The size of the neurons and the diameter of the capillaries were measured. Most of the neurons were stated to have oval form and they are oriented by their long axis along the capillaries, about 20% neurons have contacts with 2--3 capillaries; some neurons have no contacts and their distance from the nearest capillary is 32--26 mkm. Intermediate structure may be either a connective tissue or neuroglia, or (seldom) other neuronal cells. Unequal conditions of neuronal blood supply, as the author believes, demonstrate their different metabolism and various levels of their functional activity.     

Characteristics of the interrelationships of gliocytes with neurocyte processes in rat celiac ganglia

While studying the ultrastructure of rat celiac nodes, it was stated that lemmocytes from the intercellular plexus develop around separate neuronal processes spiral membranes and multilayer membranes in the shape of concentric "musses". Similar membranes but of simpler structure develop perisomatic glyocytes. In old rats these types of glial membranes occur considerably rare. Both varieties of complicated types of glial membranes serve, evidently, for the isolation of preterminal sections of neuronal processes from probable unwanted contacts with other terminals.