Subsurface cisterns and lamellar bodies: particular forms of the endoplasmic reticulum in the neurons

Membrane Organelles in Developing Hamster Frontal Cortex

Changes in the morphology of the protein-synthetic organelles in pyramidal cells from the frontal cortex were studied in the newborn, 5-, 10-, 15-, 20- day, and adult golden hamster (Mesocricetus auratus). The rough endoplasmic reticulum (RER) was of special interest since it forms the characteristic Nissl substance of adult neurons, as well as other occasional specializations including the subsurface cistern, the lamellar body, the nebenkem, the multilaminated body, the annulate lamella, and the spine apparatus. During the course of this investigation, a sequential pattern was noted in the appearance of the subsurface cisterns and the lamellar bodies, which were the only two specializations of RER observed.

The animals were perfused with glutaraldehyde-paraformaldehyde in cacodylate buffer (pH 7.3) after the method of Peters. Tissue samples were subsequently post-fixed in 2% osmium tetroxide, dehydrated in acetone, and embedded in Epon-Araldite resin.

Stimulation-induced structural changes at the nucleus, endoplasmic reticulum and mitochondria of hippocampal neurons

Neurons exhibit stimulation-induced ultrastructural changes such as increase of thickness and curvature of the postsynaptic density, decrease in contact area between subsurface cistern and plasma membrane, and formation of CaMKII clusters and synaptic spinules. These structural characteristics help in identifying the activity state of the neuron and should be taken into consideration when interpreting ultrastructural features of the neurons. Here in organotypic hippocampal slice cultures where experimental conditions can be easily manipulated, two additional features are documented in forebrain neurons as reliable benchmarks for stimulation-induced structural changes: (1) The neuronal nucleus showed conspicuous clustering of dark chromatin, and (2) the endoplasmic reticulum formed stacks with a uniform gap of ~ 13 nm filled with dark materials. Both structural changes progressed with time and were reversible upon returning the slice cultures to control medium. These stimulation-induced structural changes were also verified in dissociated hippocampal neuronal cultures and perfusion-fixed brains. In hippocampal slice cultures, the neuronal chromatin clustering was detectable within 30 s of depolarization with high K⁺ (90 mM) or treatment with NMDA (50 μM). In contrast, the formation of ER cisternal stacks did not become apparent for another 30 s. Importantly, in dissociated neuronal cultures, when the extracellular calcium was chelated by EGTA, treatment with high K⁺ no longer induced these changes. These results indicate that the stimulation-induced chromatin clustering and formation of ER stacks in neurons are calcium-dependent. Additionally, mitochondria in neuronal somas of tissue culture samples consistently became swollen upon stimulation. However, swollen mitochondria were also present in some neurons of control samples, but could be eliminated by blocking basal activity or calcium influx. This calcium-dependent structural change of mitochondria is specific to neurons. These structural changes may bring insights to the neuron’s response to intracellular calcium rise upon stimulation.

Subsurface cistern (SSC) proliferation in Purkinje cells of the rat cerebellum in response to acute and chronic exposure to paint thinner: A light and electron microscopy study

Intentional inhalation and occupational exposure are two ways humans are exposed to thinner, a widely employed solvent in industry. Inhalation of thinner induces toxic effects in various organs, with the cerebellum being one of the most affected structures of the CNS. The aim of this work was to describe specific structural alterations of cerebellum Purkinje cells in rats following exposure to thinner for 16 weeks. A histological analysis of the cerebellum of solvent-exposed rats revealed swollen Purkinje cell dendrites surrounded by empty space, and electronic microscopy showed an increase in the number of subsurface cisterns (SSCs) within their dendritic processes. After a period of non-exposure, the number of SSCs decreased without reaching normal levels, suggesting a degree of plasticity. Purkinje cell SSCs, which are derived from smooth endoplasmic reticulum, contain inositol trisphosphate receptors (IP3Rs), ryanodine receptors (RR), and a recently identified characteristic cluster of large conductance calcium-activated potassium (BKCa) channels. We found that SSCs in Purkinje cell dendrites were closely associated with mitochondria, and immunofluorescence microscopy showed higher levels of RR and calbindin receptors (CB), in Purkinje cells of exposed than normal rats. These changes are probably related to behavioral manifestations of cerebellar alterations, such as imbalance and ataxia, consistent with the suggested involvement of increases in SSCs in ataxia in rats and humans. This increase in SSCs, taken together with the localization of RR, IP3R and BKCa proteins in this structure, suggests altered intracellular calcium-buffering processes in the Purkinje cells of thinner-exposed rats.

Two distinct pools of large-conductance calcium-activated potassium channels in the somatic plasma membrane of central principal neurons

Although nerve cell membranes are often assumed to be uniform with respect to electrical properties, there is increasing evidence for compartmentalization into subdomains with heterogeneous impacts on the overall cell function. Such microdomains are characterized by specific sets of proteins determining their functional properties. Recently, clustering of large-conductance calcium-activated potassium (BK_Ca) channels was shown at sites of subsurface membrane cisterns in cerebellar Purkinje cells (PC), where they likely participate in building a subcellular signaling unit, the 'PLasmERosome'. By applying SDS-digested freeze-fracture replica labeling (SDS-FRL) and postembedding immunogold electron microscopy, we have now studied the spatial organization of somatic BK_Ca channels in neocortical layer 5 pyramidal neurons, principal neurons of the central and basolateral amygdaloid nuclei, hippocampal pyramidal neurons and dentate gyrus (DG) granule cells to establish whether there is a common organizational principle in the distribution of BK_Ca channels in central principal neurons. In all cell types analyzed, somatic BK_Ca channels were found to be non-homogenously distributed in the plasma membrane, forming two pools of channels with one pool consisting of clustered channels and the other of scattered channels in the extrasynaptic membrane. Quantitative analysis by means of SDS-FRL revealed that about two-thirds of BK_Ca channels belong to the scattered pool and about one-third to the clustered pool in principal cell somata. Overall densities of channels in both pools differed in the different cell types analyzed, although being considerably lower compared to cerebellar PC. Postembedding immunogold labeling revealed association of clustered channels with subsurface membrane cisterns and confirmed extrasynaptic localization of scattered channels. This study indicates a common organizational principle for somatic BK_Ca channels in central principal neurons with the formation of a clustered and a scattered pool of channels, and a cell-type specific density of this channel type.

Large-conductance calcium-activated potassium channels in purkinje cell plasma membranes are clustered at sites of hypolemmal microdomains

Calcium-activated potassium channels have been shown to be critically involved in neuronal function, but an elucidation of their detailed roles awaits identification of the microdomains where they are located. This study was undertaken to unravel the precise subcellular distribution of the large-conductance calcium-activated potassium channels (called BK, KCa1.1, or Slo1) in the somatodendritic compartment of cerebellar Purkinje cells by means of postembedding immunogold cytochemistry and SDS-digested freeze-fracture replica labeling (SDS-FRL). We found BK channels to be unevenly distributed over the Purkinje cell plasma membrane. At distal dendritic compartments, BK channels were scattered over the plasma membrane of dendritic shafts and spines but absent from postsynaptic densities. At the soma and proximal dendrites, BK channels formed two distinct pools. One pool was scattered over the plasma membrane, whereas the other pool was clustered in plasma membrane domains overlying subsurface cisterns. The labeling density ratio of clustered to scattered channels was about 60:1, established in SDS-FRL. Subsurface cisterns, also called hypolemmal cisterns, are subcompartments of the endoplasmic reticulum likely representing calciosomes that unload and refill Ca2+ independently. Purkinje cell subsurface cisterns are enriched in inositol 1,4,5-triphosphate receptors that mediate the effects of several neurotransmitters, hormones, and growth factors by releasing Ca2+ into the cytosol, generating local Ca2+ sparks. Such increases in cytosolic [Ca2+] may be sufficient for BK channel activation. Clustered BK channels in the plasma membrane may thus participate in building a functional unit (plasmerosome) with the underlying calciosome that contributes significantly to local signaling in Purkinje cells.

Morphology, characterization, and distribution of retinal photoreceptors in the Australian lungfish Neoceratodus forsteri (Krefft, 1870)

The Australian lungfish Neoceratodus forsteri (Dipnoi) is an ancient fish that has a unique phylogenetic relationship among the basal Sarcopterygii. Here we examine the ultrastructure, histochemistry, and distribution of the retinal photoreceptors using a combination of light and electron microscopy in order to determine the characteristics of the photoreceptor layer in this living fossil. Similar proportions of rods (53%) and cones (47%) reveal that N. forsteri optimizes both scotopic and photopic sensitivity according to its visual demands. Scotopic sensitivity is optimized by a tapetum lucidum and extremely large rods (18.62 +/- 2.68 microm ellipsoid diameter). Photopic sensitivity is optimized with a theoretical spatial resolving power of 3.28 +/- 0.66 cycles degree(-1), which is based on the spacing of at least three different cone types: a red cone containing a red oil droplet, a yellow cone containing a yellow ellipsoidal pigment, and a colorless cone containing multiple clear oil droplets. Topographic analysis reveals a heterogeneous distribution of all photoreceptor types, with peak cone densities predominantly found in temporal retina (6,020 rods mm(-2), 4,670 red cones mm(-2), 900 yellow cones mm(-2), and 320 colorless cones mm(-2)), but ontogenetic changes in distribution are revealed. Spatial resolving power and the diameter of all photoreceptor types (except yellow cones) increases linearly with growth. The presence of at least three morphological types of cones provides the potential for color vision, which could play a role in the clearer waters of its freshwater environment.

Distribution of calcium pyroantimonate precipitates in Xenotoca Mauthner cells at normal and increased functional activity

The pyroantimonate method was used for the ultrastructural localization of calcium ions (Ca2+) in Xenotoca Mauthner cells under normal conditions and after prolonged natural stimulation. In normal state, the highest concentration of these ions was observed as compact electron-dense precipitates inside the synaptic cleft exactly at the synaptic active zones. Some amount of dotted precipitates was revealed in the synaptic boutons. In the extracellular space and in the cytoplasm the precipitates are seen mainly as single membrane-bound dots. After prolonged stimulation significant redistribution of the precipitates was observed. They were entirely absent in the presynaptic areas, became diffuse and discontinuous or disappeared completely at the synaptic active zones. On the contrary, in the cytoplasmic organelles (subsynaptic cisternae, vacuoles, smooth reticulum, mitochondria) the precipitates were aggregated into continuous dense clusters inside the membranous compartments or on their surfaces. Also, large amounts of granules, not associated with membranes, were localized inside the cytoplasm directly at the cytoskeletal elements. It is suggested that membrane subsynaptic organelles are the primary structures which sequestrate, accumulate and retain Ca2+. Thus, these elements, together with deeper elements of smooth cytoplasmic reticulum, may control the cytoplasmic activity of Ca2+ and, as a consequence, control many physiologically significant reactions of the neurons.

C-terminals on motoneurons: electron microscope localization of cholinergic markers in adult rats and antibody-induced depletion in neonates

C-terminals on motoneurons are defined as those accompanied by characteristic postsynaptic specializations termed subsurface cisterns. We have previously shown, by light microscope immunolabelling methods, that subsurface cisterns occur regularly beneath choline acetyltransferase- and acetylcholinesterase-containing boutons on motoneurons. In the present study, the cholinergic nature of C-terminals suggested by these results was further investigated by immunohistochemistry and electron microscopy in adult rats and in neonates treated with a murine monoclonal acetylcholinesterase antibody which was previously shown to cause immunological lesions of central cholinergic systems. In both the facial nucleus and lumbar segment of spinal cord of adult rats, C-terminals were seen intensely immunostained for the cholinergic markers choline acetyltransferase and acetylcholinesterase. Immunolabelled terminals made contact with either neuronal somata or large calibre dendrites, which were positive for the cholinergic markers, and exhibited club-shaped or thin elongated morphologies suggestive of terminal or en passant type synaptic interactions. The close relationship found between cholinergic markers and immunolabelled subsurface cisterns in adults was maintained on motoneurons of eight-day-old rats. While subcutaneous treatment of newborn rat with acetylcholinesterase antibody appeared to have no effect on the distribution of immunopositive subsurface cisterns in motoneurons when examined on postnatal day 8, the density of labelling for the two cholinergic markers around these neurons was reduced. Areas of neuropil immediately surrounding motoneurons in treated animals often showed signs of extensive swelling and deterioration indicative of a lesion event, and these motoneurons frequently displayed subsurface cisterns unapposed to C-terminals. These results support our earlier conclusion, based on light microscope investigation, that the majority if not all C-terminals are cholinergic in the areas investigated and demonstrate the potential utility of immunolesion methods in the study of C-terminal function.

Fine structure of the supramammillary nucleus of the rat: analysis of the ultrastructural character of dopaminergic neurons

The supramammillary nucleus projecting to widespread regions contains dopaminergic and non-dopaminergic neurons. The present study provided a comprehensive electron microscopic analysis of these dopaminergic and non-dopaminergic neurons in the supramammillary nucleus of the rat. The normal supramammillary nucleus was composed of round or spindle-shaped, small and medium-sized neurons (12.7 x 8.0 microns, 78.0 microns 2) containing a light oval nucleus with invaginated envelope, mitochondria, Golgi apparatus, lysosomes, less-developed rough endoplasmic reticulum, and no Nissl bodies. The majority of terminals (more than 70%) in the normal neuropil were small (diameter less than 1.0 microns) and contained round vesicles forming asymmetric synaptic contacts. The terminals often contained dense-cored vesicles. To determine the morphological features of dopaminergic neurons, we examined the ultrastructural localization of tyrosine hydroxylase (TH) immunoreactivity, which is the synthetic enzyme of dopamine, and compared TH-immunoreactive neurons to non-TH-immunoreactive neurons. Their shape and size were similar. The average number of axosomatic terminals in a sectional plane was 5.0 in TH-neurons and 2.4 in non-TH-neurons; the bouton covering ratio was 16.5% in the former and 8.6% in the latter. Both numbers were significantly larger in TH-neurons than in non-TH-neurons. Serial ultrathin sections of these neurons revealed that the average total number of axosomatic terminals was 55.7 in the TH-neuron and 28.4 in the non-TH-neuron. Characteristic lamellar bodies and sub-surface cisternae were often present in TH neurons. There were no TH-labeled terminals. These results indicate that dopaminergic neurons receive more inputs than neurons containing other neurotransmitters.

The influence of age on supraoptic nucleus glial cells of the mouse

In 2-year-old mice, astrocytes of the supraoptic nucleus (SON) of the hypothalamus, placed in close contact with the meningeal covering contained concentric arrangements of cisterns in their cytoplasm called glial concentric bodies (GCBs). They are formed by a variable number of flattened cisterns without pores, and no anastomosis was observed between adjacent cisterns. Rough endoplasmic reticulum (RER) cisterns do not show continuity with fully developed GCBs, although a close continuity between RER cisterns and GCBs was present in images suggesting GCB formation. Concomitantly with the appearance of GCBs, ventral neurosecretory neurons of the SON showed a cytoplasmic membrane reinforced by the apposition of glial prolongations. The possible origin and function of these GCBs and lamellae are discussed here.

Krabbe's disease with giant lamellar bodies in Purkinje cells

An autopsy case of Krabbe's disease in a child aged 6 years 7 months 1s reported. Histologically, globoid cells, loss of myelin, oligodendroglia and axons, and marked gliosis were observed in the white matter. In addition, there was severe neuronal loss in the thalamus, pontine nucleus, dentate nucleus and olivary nuclei. The cerebellar cortex showed extensive loss of granular cells and moderate loss of Purkinje cells. There were numerous eosinophilic inclusion bodies, ranging from 2 to 15 microns in diameter, in the dendrites of Purkinje cells. The ultrastructural findings for the inclusion bodies were consistent with those of giant lamellar bodies. In addition, smaller lamellar bodies were frequently observed in the perikarya and dendrites. Although loss of granular cells was more prominent in the hemispheres than in the vermis, the inclusion bodies were observed in hemispheres but were infrequently observed in the vermis. They were found in degenerated Purkinje cells which had lost afferent fibers. It is considered that these giant lamellar body inclusions are an unusual type of degenerative structure specific to Purkinje cells.

Neuronal ultrastructure and somatostatin immunolocalization in the ciliary ganglion of chicken and quail

Ciliary and choroid neurons of the avian ciliary ganglion innervate different targets in the eye bulb. By light microscopic immunocytochemistry, somatostatin (SOM) has been localized to a subset of ganglionic neurons believed to be, for the most part, choroid neurons. Although several studies have been published on the physiology, afferent and efferent innervation, and response to experimental injury of this population of cells, their morphological features are still unclear. This has led us to perform a fine structural and immunocytochemical study on the ciliary ganglia of adult chickens and quails to provide the first thorough characterization of the choroid neurons and to analyze whether or not they can be unequivocally identified by expression of SOM. Here, we show that standard and immuno-electron microscopy provide firm criteria for the distinction of ciliary and choroid neurons, whose populations overlap in cell size and territory of distribution. The satellite cell sheaths form compact myelin lamellae around ciliary neurons and flattened processes around choroid neurons. Moreover, ciliary neurons are innervated by a larger number of boutons than choroid neurons. Chicken ciliary neurons are invested by boutons only over one pole of the cell body, while their quail counterparts have an almost complete shell of presynaptic boutons over the entire cell body. Ciliary neurons form mixed synaptic junctions (chemical and electrical), while choroid neurons form only chemical synapses. Crest synapses are present in ciliary neurons of both species. Nematosomes occur in both ciliary and choroid neurons. Choroid neurons contain a larger complement of large dense core vesicles than ciliary neurons and their Golgi apparatuses are more prominent. In the light microscope, somatostatin-immunostaining appears noticeably different in the two species: mostly granular in the chicken and skein-shaped in the quail. Immuno-electron microscopy reveals that somatostatin-like immunoreactivity is localized to Golgi apparatus and large dense core vesicles. Somatostatin is expressed by all the choroid neurons, but not by the ciliary neurons. This neuropeptide is, therefore, a true cell population marker.

Evidence for the cholinergic nature of C-terminals associated with subsurface cisterns in alpha-motoneurons of rat

C-terminals can be distinguished at the ultrastructural level from other types of nerve endings on motoneurons by their prominent and regularly occurring postsynaptic specializations termed subsurface cisterns (SSC). We have previously shown (Yamamoto et al., 1991) that an antibody directed against a sequence within the gap junction protein connexin32 immunolabels these motoneuronal SSCs and can therefore serve as a immunohistochemical tool to visualize indirectly the location of C-terminals on motoneurons at the light microscope level. Here we have used this anti-SSC antibody in combination with antibodies against choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) to determine whether C-terminals on motoneurons contain these cholinergic enzyme markers. In sections at all major spinal cord levels and in several cranial motor nuclei examined, motoneuronal cell bodies and their proximal dendrites were studded with large ChAT-immunoreactive (ChAT-IR) boutons. Boutons having a similar distribution and appearance on motoneurons were also immunolabeled for AChE. In addition, motoneurons were surrounded by a dense plexus of AChE-immunoreactive (AChE-IR) varicose fibers and fine preterminal axons. In double-labeled sections, AChE-IR boutons corresponded to those immunolabeled for ChAT. In sections processed for simultaneous immunofluorescence detection of ChAT and SSCs, ChAT-IR boutons were very often found in apposition to immunolabeled SSCs. In sections processed for simultaneous labeling of AChE and SSCs. AChE-IR boutons were again frequently seen abutting labeled SSCs. These results provide the first strong evidence at the LM level that a large proportion, if not the entirety, of C-terminals are cholinergic and show that these terminals consist in part of relatively large varicosities along highly varicose axons that form en passant type contacts on motoneurons. At the same time, our results substantially narrow possibilities regarding the as yet undetermined source of C-terminals, which can now be considered to originate from cholinergic neurons, such as those located in the brainstem and/or the spinal cord.

Tridimensional organization of Purkinje neuron cisternal stacks, a specialized endoplasmic reticulum subcompartment rich in inositol 1,4,5-trisphosphate receptors

Stacks of regularly spaced, flat, smooth-surfaced endoplasmic reticulum cisternae frequently observed in both the cell body and dendrites of cerebellar Purkinje neurons, were previously shown by immunocytochemistry to be highly enriched in receptors for the second messenger, inositol 1,4,5-trisphosphate. Morphometric analyses have been carried out on randomly selected thin section images of rat Purkinje neurons to reveal the tridimensional organization of these structures. Individual stacked cisternae (on the average approximately 3.5 per stack) were shown to be separated from each other by a 23.5 nm space occupied by perpendicular bridges, approximately 20 nm in diameter, most probably composed by two apposed receptor homotetramer molecules, inserted into the parallel membranes in their hydrophobic domains. In the stacked membranes the density of the bridges was approximately 500 microns -2, corresponding to approximately 15% of the surface area. The lateral distribution of bridges was not random, but revealed regular distances that might correspond to unoccupied receptor slots. In each stack, the external cisternae were often in direct lumenal continuity with conventional elements of the endoplasmic reticulum, whereas the internal cisternae were not. Since continuities between stacked cisternae were never observed, the results indicate that the internal cisternae are at least transitorily discrete, i.e. they are not in permanent lumenal continuity with the rest of the endoplasmic reticulum. To our knowledge this is the first demonstration of a physical subcompartmentalization of the latter endomembrane system in a non-mitotic cells. A model for the biogenesis of cisternal stacks, based on the head-to-head binding and lateral interaction of the inositol 1,4,5-trisphosphate receptor molecules in the plane of the interacting membranes, is proposed and critically discussed.

The confronting cisternae in the hippocampal neurons of rats and Japanese monkeys

The ultrastructure of the neurons in the hippocampal formation of Wistar rats and Japanese monkeys was investigated. Confronting cisternae were observed in the cytoplasm of pyramidal neurons and granule cells. The structures were composed of closely apposed parallel cisternae, presumably continuous with the cisternae of the rough endoplasmic reticulum. The cytoplasmic matrix between the confronting cisternae contained electron dense flocculent material. In the pyramidal neurons irregular confronting cisternae were also observed. Possible functions of the confronting cisternae are discussed.

The endoplasmic reticulum of Purkinje neuron body and dendrites: molecular identity and specializations for Ca2+ transport

Immunofluorescence and immunogold labeling, together with sucrose gradient separation and Western blot analysis of microsomal subfractions, were employed in parallel to probe the endoplasmic reticulum in the cell body and dendrites of rat cerebellar Purkinje neurons. Two markers, previously investigated in non-nerve cells, the membrane protein p91 (calnexin) and the lumenal protein BiP, were found to be highly expressed and widely distributed to the various endoplasmic reticulum sections of Purkinje neurons, from the cell body to dendrites and dendritic spines. An antibody (denominated anti-rough-surfaced endoplasmic reticulum), which recognized two membrane proteins, p14 and p40, revealed a similar immunogold labeling pattern. However, centrifugation results consistent with a widespread distribution were obtained for p14 only, while p40 was concentrated in the rough microsome-enriched subfractions. The areas enriched in the inositol 1,4,5-triphosphate receptor and thus presumably specialized in Ca2+ transport (stacks of multiple smooth-surfaced cisternae; the dendritic spine apparatus) also exhibited labeling for BiP and p91, and were positive for the anti-rough-surfaced endoplasmic reticulum antibody (presumably via the p14 antigen). Additional antibodies, that yielded inadequate immunocytochemical signals, were employed only by Western blotting of the microsomal subfractions, while the ryanodine receptor was studied by specific binding. The latter receptor and the Ca2+ ATPase, known in other species to be concentrated in Purkinje neurons, exhibited bimodal distributions with a peak in the light and another in the heavy subfractions. A similar distribution was also observed with another lumenal protein, protein disulfide isomerase. Taken as a whole, the results that we have obtained suggest the existence in the endoplasmic reticulum of Purkinje neurons of two levels of organization; the first identified by widespread, probably general markers (BiP, p91, possibly p14 and others), the second by specialization markers, such as the inositol 1,4,5-triphosphate receptor and, possibly, p40, which appear restricted to areas where specific functions appear to be localized.

Subsurface cisterns in alpha-motoneurons of the rat and cat: immunohistochemical detection with antibodies against connexin32

A monoclonal antibody against amino acids 224-234 of the gap junction protein connexin32 was found by immunohistochemistry to label subsurface cisterns (SSCs) in alpha-motoneurons of the rat (Yamamoto et al., 1990) and was used here to document by light (LM) and electron microscopy (EM) the appearance of immunoreactive SSCs in motoneurons of the rat and cat. This antibody and a polyclonal antibody against connexin32 labelled gap junctions in rat liver as well as SSCs in facial motoneurons. By LM, SSCs were seen as labelled puncta on motoneuronal perikarya and proximal dendrites. In the rat, they appeared to be present on all motoneurons at cranial and spinal levels, but varied considerably in size and number among motor nuclei. Labelled SSCs were the smallest and most sparse in motoneurons of the dorsal vagal motor nucleus, moderate in size and most numerous in the trochlear, oculomotor, and trigeminal motor nuclei, and largest though less densely distributed in spinal motoneurons. Dendrites were seen to contain SSCs for distances of up to 230 micron from their somal origin. Labelling within individual SSCs seen en face consisted of either numerous small puncta or linear arrays of immunoreactivity. By EM, labelled SSCs in the rat facial nucleus were always seen beneath a cluster of C-terminals. Immunolabelling was most dense in the space between the plasma membrane and SSC, which we define as the subsurface cisternal cleft. The SSCs were usually intermittently labelled along their length and exhibited a narrow luminal space ranging from 2 to 5 nm. On the basis of structural analogies between SSCs in neurons and the sacroplasmic reticulum terminal cistern/T-tubule complex in muscle, SSCs have previously been suggested to be important sites of calcium mobilization. The constant association of C-terminal with SSCs in motoneurons may represent a useful model in which to study SSC function as well as to investigate the possible presence of a connexinlike protein at regions of SSCs that form a narrow lumen similar to that at gap junctions.

Pinealocyte subsurface cisterns. I: Cytological aspects including three-dimensional structure

Subsurface cisterns (ssc) in the pineal gland of Meriones unguiculatus have been characterized with transmission electron microscopy, freeze-fracture, morphometry, and three-dimensional reconstruction. Subsurface cisterns (which are observed only in pinealocytes and never in gliocytes) are cisterns of the endoplasmic reticulum (ER) approaching the plasmalemma at a distance of 15-20 nm. Freeze-fracture preparations show that except for some ribosomes at the cytoplasmic face, the cistern membranes as well as the related portions of the plasmalemma are free of special or specifically arranged particles or pores. All ssc have a lumen of 15-20 nm width and underlie 5.6% of the plasmalemma in a single layer; neither collapsed types nor stacks of ssc could be observed. As seen from reconstructions, large ssc are fenestrated and are situated preferentially in regions where the neighboring pinealocyte also bears large ssc. As a consequence, double-sided ssc, which can be observed in sections of (mostly large) ssc, are not a random phenomenon. In regions of the large ssc, adhering junctions are also concentrated. Tubules of 20-nm diameter link ssc with deeper parts of the ER, particularly with the perinuclear cistern and with the tubulo-cisternal network at the trans-side of the Golgi apparatus. Besides ssc proper, a lot of small endplates of ER-tubules are seen close to the plasmalemma. It is suggested that ssc form by the widening and fusing of such ER-tubules and decrease by retraction of ER-tubules from the cell surface.

Ultrastructure of substance P immunoreactive elements in the periaqueductal gray matter of the rat

Substance P (SP) is a non-opioid peptide that generates a potent analgesia when injected into the periaqueductal gray matter (PAG). The aim of this study was to investigate the fine neuronal structures and synaptic circuits involved in SP action in rats by means of electron microscopy, using immunocytochemical (ICC) pre-embedding methods. A conventional ultrastructural study, carried out to interpret the ICC data correctly, shows small sized nerve cell bodies with a high nucleus-cytoplasmic ratio; absence of an extensive granular endoplasmic reticulum; and few axo-somatic contacts having symmetrical and asymmetrical junctions in equal proportions. The large neuropil is characterized by numerous thin unmyelinated axons and axo-dendritic synapses mainly showing pleomorphic vesicles and asymmetrical junctions. The ICC analysis showed moderately labeled nerve cell bodies with the same structural, synaptic, and dimensional features as the negative cells. In the neuropil SP immunoreactivity is shown by dendrites, synapses, and thin elements which are unidentifiable structurally. No SP terminals synapsing on SP nerve cell bodies were found and only occasional SP light labeled terminals synapsing on negative perikarya were seen. The SP boutons generally have pleomorphic vesicles and asymmetrical junctions. On the basis of these data a possible excitatory activity of PAG SP synapses could be hypothesized. This activity would take place on postsynaptic neurons generally at a dendritic level. Our ultrastructural findings give support to an excitatory role carried out by SP neurons of the PAG, as suggested by the role of PAG circuitry on spinal nociception.

Epitopes of gap junctional proteins localized to neuronal subsurface cisterns

Several lines of evidence indicate the existence of channels that mediate the movement of calcium from the extracellular space directly into some intracellular calcium storage compartment and from one intracellular membrane-bounded compartment to another. The possibility that such channels resemble intercellular communication pathways formed by gap junction proteins (connexins) was investigated in rat brain. Antibodies against a rat liver gap junction protein (connexin32) were found to recognize several distinct proteins on Western blots of brain homogenates. In motoneurons these antibodies immunohistochemically labelled portions of neuronal endoplasmic reticulum membranes that form subsurface cisterns (SSCs) adjacent to the plasma membrane. These results suggest that SSCs and connexin-like proteins may be involved in the process of calcium mobilization in neurons.

"Grumose degeneration" of the dentate nucleus. A light and electron microscopic study in progressive supranuclear palsy and dentatorubropallidoluysial atrophy

So-called "grumose degeneration" (GD) of the dentate nucleus (DN) which is a unique alteration in progressive supranuclear palsy and dentatorubropallidoluysial atrophy was studied by light and electron microscope. Light microscopically, the presence of a large amount of eosinophilic granular and/or amorphous material around the neurons is the most conspicuous feature of GD. In addition, the number of neurons is decreased and some of them are swollen as with central chromatolysis. Electron microscopically, the granular and/or amorphous material mainly consists of the altered axon terminals of the Purkinje cells (Pax), which are relatively electron-dense and characteristically contain varying numbers of deformed lamellar bodies, highly electron-dense mitochondria and many vacuoles which are adherent to the astrocytic processes. GD is a unique histological change of both the chromatolytic DN neurons and the grumose appearance of the altered Pax. Possible mechanisms are discussed.

Lamellar bodies are markers of cholinergic neurons in ferret nucleus basalis

Lamellar bodies are composed of stacks of closely-packed, ribosome-free cisterns which are in continuity with the rough endoplasmic reticulum. In the ferret nucleus basalis stained for choline acetyltransferase it was shown, by correlating light with electron microscopy, that only the cholinergic cells there possess lamellar bodies. The significance of lamellar bodies in the cholinergic neurons of the nucleus basalis is not known, but these structures may reflect a peculiar aspect of the functioning of the cholinergic cells which will need to be investigated further.

Structure of the subrhabdomeric cisternae in the photoreceptor cells of Drosophila melanogaster

The structure of subrhabdomeric cisternae (SRC) and related structures in the photoreceptor cells (retinular cells) of Drosophila melanogaster in normal flies and visual mutants were compared by electron microscopic observation of semithin sections of osmium-impregnated specimens. The three-dimensional organization of SRC and the other cell organelles was demonstrated by stereoscopy. Both light- and dark-adapted normal retinular cells contained elaborate networks of anastomosing tubules of SRC immediately beneath the rhabdomeres. Tubules connecting the SRC and rough endoplasmic reticulum were frequently seen. The SRC were absent from the retinular cells of rdgAKS60 whose rhabdomeres degenerate gradually after eclosion. Instead, numerous smooth vesicles were observed in the subrhabdomeric regions. In rdgBEE170, in which rhabdomere degeneration is light dependent, the SRC appeared normal in the dark-adapted flies. But their SRC gradually disintegrated after exposure to light. In norpASB37, whose rhabdomeres are small but do not degenerate, SRC appeared normal. These results suggest that the SRC is a significant structure for the maintenance of the structure of photoreceptive membrane in the retinular cells of Drosophila.

Unusual configurations of endoplasmic reticulum in pinealocytes of the Djungarian hamster (Phodopus sungorus)

Ultrastructural observations of the pineal gland of Phodopus sungorus revealed different morphological forms of endoplasmic reticulum. These included crystalloids composed of 200A-wide tubules with an intervening space of 200A and connected at right angles to form a rectangular lattice; complexes of undulating 500A-wide tubules in an electron-dense cytoplasmic matrix; and stacks of flattened cisternae covered with granular electron-dense material. All these structures are continuous with the surrounding endoplasmic reticulum. Frequently one structure is directly connected with another. The exact function of these structures derived from the endoplasmic reticulum is still unclear, but they can be assumed to be morphological features of augmented secretory activity.

Ultrastructural pathology of dendritic spines in epitumorous human cerebral cortex

Ultrastructural changes in the human epitumorous cerebral cortex were examined. A swelling of nerve cell perikarya, dendrites and axon terminals, and an occasional hyperplasia and disarray of microtubules and neurofilaments were observed. Accumulations of lysosomes, tubuloreticular structures and intracytoplasmic or intramitochondrial crystalloid inclusions were also found. Some myelinated axons were degenerated. Astrocytes and their processes were focally swollen. A mild swelling was found also in microgliocytes. Oligodendrocytes occasionally contained accumulations of dense bodies. Special attention was paid to dendritic spines. The spine surface morphology changed distinctly on swollen dendritic segments. The necks of most spines were short and wide, and numerous sessile forms were present in this location. The spine apparatus was often hypertrophied and disorganized. Smoothing out of spines on swollen dendrites is described and a possible functional significance of the observed changes in the symptomatology of brain tumors is hypothesized.

Process of differentiation of cerebellar Purkinje neurons in the chick embryo

The microscopic and ultrastructural differentiation of Purkinje neurons has been studied in 40 chicken embryo cerebella, from the 10th incubation day to hatching, and the transverse diameter of the cell body measured, for each developmental stage, on 30 electron micrographs of sagittally cut Purkinje cells. The developing Purkinje cell bodies, bipolar, at first, given the presence of two processes emerging from the opposite poles of the oval perikaryon, grow progressively in size. After the 12th incubation day, they develop a branched dendritic tree, and, shortly before hatching time, the cells acquire the characteristic flask or pear-shaped configuration. On the 10th incubation day, microtubules are already detectable together with Golgi complexes and a few vesicles of rough endoplasmic reticulum; on the 14th incubation day, RER cisterns are recognizable in the supranuclear cytoplasm, later extending into the whole perikaryon, and attaining their definitive distribution by the 18th incubation day. Pinocytotic and coated vesicles, as well as subsurface cisterns are seen during the whole embryonic life. In the earliest stages of development, three distinct types of junctional contacts between Purkinje cells and surrounding axons are described, and their functional role in relation to synaptogenetic processes is discussed. Beginning with the 16th incubation day, some Purkinje neurons undergo degenerative changes similar to those described in other types of neurons of the central and peripheral nervous system.

Ultrastructural features of the ventromedial region of the laminar nucleus in the red-eared turtle (Chrysemys scripta elegans)

The nuclei of the torus semicircularis, in particular the laminar nucleus, have been functionally implicated in sound localization, vocalization, and mating behavior. In the red-eared turtle the ventromedial region of the laminar nucleus (containing two discrete dense cellular areas and the surrounding neuropil) was examined electron microscopically in the present study. Neuronal cell bodies in the two cellular areas were different in size, shape, cytoplasmic constituents, and their relationship to each other. Cell bodies in the layer beneath the ependymal surface were almost always surrounded by lamellae while cell bodies in the layer above the central nucleus were in close apposition. We are speculating that cell bodies in the superficial layer may be neuroendocrine in nature. This speculation is based on the presence of lipidlike droplets within cell bodies, and previous findings indicating steroid binding and synthesis in this region in reptilian brains. Cell bodies located above the central nucleus were characteristic in that they contained lamellar bodies and extensive well-developed Golgi regions. Closely apposed groups of these cell bodies were frequently surrounded by or in close apposition to large axonal profiles. These profiles were filled with clear core vesicles, numerous mitochondria, and clusters of small dense core particles. Synaptic contacts between large axonal profiles and cell bodies were not observed. The neuropil surrounding cell bodies of the inner layer of this region of the laminar nucleus contained glomeruli composed of a central axon surrounded, and in synaptic contact, with dendrites. Throughout the area of the laminar nucleus studied, synapses appeared to be primarily of the asymmetrical type.

Qualitative and quantitative ultrastructural observations on retinal ganglion cell layer of rat after intraorbital optic nerve crush

Rat retinal ganglion cell layer (GCL) was examined ultrastructurally 1-180 days after intraorbital crushing of one optic nerve. It was confirmed quantitatively that axotomized ganglion cells lost cisternal membranes of the rough endoplasmic reticulum (RER) and showed disintegration of Nissl bodies and ribosomal rosettes 3 days postoperatively. Between 60 and 180 days after neurotomy there was partial reversion of the RER towards normal. At postoperative intervals of 14-60 days, chromatin aggregation became conspicuous and some nuclei were prominently furrowed and contained electron-dense inclusions. Concurrently, profiles of dead ganglion cells were encountered. Mean mitochondrial area increased in axotomized neurons but mitochondrial density declined, while the Golgi apparatus, lamellar specializations of the RER and the size of nuclei did not change significantly. Cytoplasmic atrophy was profound, however. Small nerve cells of the GCL appeared morphologically distinct from ganglion cells and did not undergo appreciable alteration. A decline in neuronal density, approximating 35%, occurred between the third and seventh postoperative day and progressed slowly thereafter. Neuronal density was 32% of normal 180 days postoperatively. A temporary increase in glial density 3-28 days after operation was due to microglial hyperplasia. Müller cell and astrocytic processes hypertrophied, infiltrated nerve fibre bundles, and surrounded and intruded into neuronal somata. Bundles of unmyelinated small axons, invested by astrocytes and basal lamina, were present within the necrotic cavity of the lesioned nerve 28-90 days postoperatively and had cytologic features of regenerative axonal sprouts. We conclude that intraorbital optic nerve crush is followed by a noteworthy degree of regenerative axonal sprouting which occurs and persists against a background of slow but relentless decline in the retinal ganglion cell population. This slow decline follows a rapidly-sustained loss of approximately one-third of the axotomized retinal ganglion cells during the first postoperative week. Intraorbital, as opposed to intracranial, injury of the optic nerve appears, paradoxically, to induce both a greater degree of ganglion cell death and a greater amount of regenerative axonal sprouting. Cytologic changes in axotomized retinal ganglion cells resemble those described for other populations of mammalian intrinsic neurons subjected to like injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrophysiological and morphological correlates of axotomy-induced deafferentation of the goldfish Mauthner cell

Axotomy-induced changes in afferent synapses to the goldfish Mauthner cell have been analyzed with intracellular recordings and with electron microscopy. The studies encompassed 7-208 days after cervical spinal cord transection. The physiological findings suggest a persistent and specific reduction in excitatory chemical inputs to the soma and proximal lateral dendrite, with no changes in somatic inhibition or in the electrotonic and chemical inputs to the more distal regions of the lateral dendrite. Corroborative morphological evidence includes swelling of the M-cell soma, as indicated by a 35% increase in the length of its minor diameter, an increased spacing and a quantitatively lower density of terminals on the soma, and the appearance of astrocytic processes partially or completely engulfing the terminals in that region. Similar changes were observed on the inferior dendrites projecting from the ventral surface of the soma, although these dendrites do not exhibit the chromatolytic changes observed at the soma. In contrast, there are no noticeable changes in either the synaptic investment of the lateral dendrite or its ultrastructure. Quantitative and qualitative data support the conclusion that there is a restricted and specific reduction in the proximal excitatory inputs to the M-cell. The evidence also suggests that electrotonic junctions between afferents and the M-cell remain intact, functionally and structurally.

Acetylcholinesterase activity and type C synapses in the hypoglossal, facial and spinal-cord motor nuclei of rats. An electron-microscope study

Using the electron-microscope technique of Lewis and Shute, we studied the localization of the acetylcholinesterase (AChE) activity in the hypoglossal, facial and spinal-cord motor nuclei of rats. The technique used selectively detects synapses with subsynaptic cisterns (type C synapses) as well as heavy deposits of reaction products in the rough endoplasmic reticulum, in fragments of the nuclear envelope, in some Golgi zones and on parts of the pericaryal plasma membrane, the axolemma and the dendritic membrane. In C synapses, AChE activity was located in the synaptic cleft and on the membrane of presynaptic boutons. Some C synapses exhibited distinct synaptic specialization in the form of multiple 'active zones'. These zones were characterized by dense presynaptic projections, short dilations of the synaptic cleft, and postsynaptic densities localized between the postsynaptic membrane and the outer membrane of the subsynaptic cistern. Within the postsynaptic densities, rows of rod- or channel-like structures were observed. The subsynaptic cisterns were continuous with the positive rough endoplasmic reticulum. The results are discussed in terms of the possible role of C synapses in the regulation of AChE synthesis in postsynaptic cholinergic neurons and/or in the regulation of AChE release into the extracellular space as well as in the establishment of new synaptic contacts.

Degeneration of thalamic neurons in "Purkinje cell degeneration" mutant mice. II. Cytology of neuron loss

The cytology of thalamocortical relay neuron degeneration in the ventral medial geniculate nucleus (vMG) of mice homozygous for the autosomal recessive Purkinje cell degeneration (pcd) mutation has been studied by light and electron microscopy. More limited sampling of the submedial and mediodorsal nuclei suggested that cytological alterations in the vMG were typical of all degenerating thalamic nuclei. The number of vMG neurons in pcd mutants was comparable to controls at and prior to postnatal day 40 (P40). By P60 seventy percent, and by P90 approximately 90%, of the original complement of vMG neurons had degenerated in mutant mice. At P30, the general cytological organization of vMG neurons closely resembled that of neurons in littermate (+/+ or +/pcd) controls, but neurons in mutants were distinguished by the presence of small aggregates of fine granules (approximately 9 nm in diameter) that were commonly associated with otherwise normal cisternae of rough endoplasmic reticulum; neither the number nor the size of these granular aggregates increased in older mutants. By P50 cytoplasmic organelles were curiously distributed in more severely affected neurons: large areas of cytoplasm were occupied exclusively by polysomes, while profiles of endoplasmic reticulum and the Golgi apparatus appeared to be reduced. Before frank degenerative changes were apparent (at P50), all classes of synaptic terminals identified in normal mice were found to have made morphologically normal synaptic contacts on mutant vMG neuron dendrites. In contrast to the homologous nuclear complex in the cat, presynaptic dendrites were not apparent in synaptic glomeruli in wild-type or mutant murine vMG. Cytopathological alterations in the neuropil of P50 and older mutants were dominated by degenerating dendritic profiles; there was no evidence that the loss of thalamic neurons in pcd mutants was associated with synaptic agenesis or dysgenesis or the prior or concurrent degeneration of afferent synaptic terminals.

Presynaptic inclusions in mossy fibre terminals of the cerebellar cortex following long-term undernutrition in adult rats

Past work on the C.N.S. of nutritionally deprived immature rats shows widespread structural and functional alterations that were not found in nutritionally deprived adults. In the present work we studied cerebellar mossy fibre terminals of adult rats, given a 8% casein diet for periods of 6, 12 and 18 months. After 12 months of the diet, mossy fibre terminals presented a large number of spherical or disc-shaped membrane-free inclusions herein referred to as presynaptic inclusions, with diameters up to 1.3 micron and formed by fine-textured subunits, compacted into 3 nm strands. This material is an extension of the cytoplasmic network of the terminal. No special relationship was observed with the active zones; synaptic vesicles found in the proximity or embedded in these inclusions were often of the flat type, whereas those close to the active zones always appeared spherical. These results show that even in adult rats synaptic terminals are areas sensitive to protein deprivation.

Quantitative analysis of rough endoplasmic reticulum approaches to the cell membrane in the secretory ameloblast of the rat incisor

The distribution of approaches of rough endoplasmic reticulum to the cell membrane within the supranuclear region of the secretory ameloblast of the rat incisor was quantitated using a Zeiss MOP-3. In ameloblasts cut in cross section, most of these approaches appear as circular profiles representing cross sections of elongated cisternae, which are aligned parallel to the long axis of the cell. Because of their position, orientation, and distribution of ribosomes, these approaches were consistent with the appearance of subsurface cisternae. Using cross-sectioned ameloblasts, the lengths of apposed plasma membranes either between or within rows of cells were measured from electron micrographs. Along these lengths, matched approaches of rough endoplasmic reticulum from opposite sides of the apposed plasma membranes were counted. Approaches from either side that were unmatched were also counted. Thirteen percent of the approaches were matched between rows of ameloblasts, and 13.5% of the approaches were matched within rows, demonstrating no significant difference between the two sites. Furthermore, mathematical analysis showed that the theoretical probability of two approaches coinciding is 17%. The experimental values are not statistically different from the theoretical probability, and it is concluded that the matching of rough endoplasmic reticulum approaches to the plasma membrane, or subsurface cisternae, occurs at random.

Acidophilic crystalline inclusion body in the caudate nerve cells

Acidophilic crystalline inclusion bodies (ACBs) within the cytoplasm of large neurons of the caudate nucleus and putamen were described. ACB was eosinophilic needle-shaped intracytoplasmic material and electronmicroscopically composed of filamentous material. Some were found in the cisterns of rough-surfaced endoplasmic reticulum. There was no histochemical and electronmicroscopic similarity between ACB and Mallory's hyaline bodies of hepatocytes. Though ACBs were noted in a high incidence in alcohol drinkers (65.7%), particularly suffering of alcoholic encephalopathy (72.2%), they were also found in patients without drinking habit (53.9%). In the latter cases, the incidence was high in aged people and patients dying of debilitating diseases (75%) or malignant tumors (57.1%). Consequently, ACB is not pathognomonic for chronic alcoholisms. On histochemical and electron microscopic studies, ACB was considered as a proteinic material, originated from rough-surfaced endoplasmic reticulum, and resulted from some disordered protein synthesis of the neurons.

Ontogeny of the photoreceptors in the embryonic retina of the viviparous guppy, Poecilia reticulata P. (Teleostei). An electron-microscopical study

Ultrastructural analyses of retinal development in the guppy embryo show that at midgestation all types of photoreceptors are differentiated in the fundus, and at birth differentiation extends over the whole retina. Formation of discs of outer segments is more rapid in rods than in cones. Double cones differentiate simultaneously with long single cones and are formed by the adhesion of two primordial inner segments; short single cones develop last. Wherever cones are differentiated, they are arranged in an adult-type square mosaic. The rods in the embryo, as opposed to the adult, are likewise regularly arranged within the mosaic unit. These results are at variance with the generally held opinion that adult teleosts which possess duplex retinae have larvae with pure cone retinae, and that rods, double cones and mosaics appear in late larval life or only at metamorphosis. In the double cones of the guppy embryo subsurface cisternae develop along the adjoining primordial inner segments. Additionally, regularly distributed subsurface cisternae are formed in the regions of intimate contact of long single cones with double cones and rods. We suggest that the early development of rods and double cones, and a square-mosaic with regular distribution of rods and subsurface cisternae, provide the newly born with a fully functional optical apparatus, especially suited to perception of movements. This is necessary for its survival against predatory, especially maternal, attacks.

Fine structure of the sensory epithelium of guinea-pig organ of Corti: subsurface cisternae and lamellar bodies in the outer hair cells

The fine structure of subsurface cisternae and lamellar bodies in the outer hair cells of the guinea-pig organ of Corti was studied with thin sections and freeze-fracture replicas. Subsurface cisternae in the outer hair cells consist of multilayers along the lateral plasma membrane of the cell. The outermost layer is a flattened cistern in the upper part of the supranuclear region, but comprises a series of tubules in the lower part. Deeper layers are fenestrated cisternae in which disc-like areas are found in the upper part of the supranuclear region. Lamellar bodies consist of concentric layers of fenestrated cisternae and are located in the apical cytoplasm beneath the cuticular plate. They are continuous with the subsurface cisternae. In the supranuclear cytoplasm, bulges of the subsurface cisternae and the lamellar bodies are found. Dilated cisternae are also present. Some dilated cisternae contain many small vesicles, which display acid phosphatase activity. The dilated cisternae are considered as forms of the bulges undergoing transformation into multivesicular bodies. The possible role of the lamellar bodies, and the origin and fate of the subsurface cisternae are discussed.

Fetal development of primate chemosensory corpuscles. I. Synaptic relationships in late gestation

Fetal macaque chemosensory corpuscles during the last part of gestation contained chemosensory, sustentacular, and undifferentiated basal cells. Sustentacular cells had apical secretory granules and no specialized contacts with axons. Chemosensory cells contained basal collections of 80-100 nm dense core granules, and specialized axonal contacts of three types--afferent synapses, efferent synapses, and subsurface cisternae. Afferent synapses were commonly present on electron opaque cells with many 80-100-nm granules, typical 40-60-nm synaptic vesicles, and a few cisternae of smooth or granular endoplasmic reticulum. Cells with subsurface cisternae and/or efferent synapses were usually electron lucent, lacked vesicles and granules, and contained numerous intracytoplasmic cisternal elements. A continuum of intermediate forms was observed. It is postulated that transition of synaptic arrays accompanies the maturation of individual chemosensory cells.

Lamellar bodies in heterotopic neurons of the cerebellum

Small eosinophilic inclusion bodies were observed in the cytoplasm and processes of heterotopic neurons of the cerebellum in a case of Werdnig-Hoffmann disease. They were oval, triangular, or rod-shaped and measured 2-10 microns. Histochemically, these bodies contained a considerable amount of protein, lipid, and some polysaccharide, but no nucleic acid. The inclusion bodies were ultrastructurally identified with giant lamellar bodies. It was suggested that this body was a pathologic intraneuronal structure which is possibly related to the degenerating process of neurons.

'Free' postsynaptic-like densities in normal adult brain: their occurrence, distribution, structure and association with subsurface cisterns

Samples of cerebral cortex (parietal and occipital) and thalamic nuclei (ventrobasal, posterolateral, dorsal lateral geniculate) from normal, adult, aldehyde perfusion fixed mice and rats were examined by electron microscopy for the presence of free postsynaptic-like densities (FPSDs). FPSDs are plaques of intracellular paramembranous electron-dense material, ultrastructurally indistinguishable from postsynaptic densities, but not aligned with a presynaptic specialization. In a systematic survey of the neuropil around 6000 neuronal perikarya, 250 FPSDs were encountered. Almost all of these were within dendritic spines and shafts and about 90% of them were apposed by a neuronal perikaryon, the remainder by a dendritic shaft. In every case a subsurface cistern (SSC) was present in the cell body or dendrite apposed to the FPSD, and was flattened along the extent of the FPSD. In none of the material were the FPSDs associated, even remotely, with degenerating elements, suggesting that they are not formed by degeneration of presynaptic boutons. The incidence of FPSD-SSC complexes was higher in thalamus than in cerebral cortex which, together with previous observations indicating their absence from normal cerebellar cortex, suggests significant regional variations in distribution. It is suggested that FPSDs might represent synaptic precursors perhaps induced to form as a response to loss (possibly age-dependent loss) of synaptic contacts on a neuron and that the SSCs are somehow involved in maintaining the FPSDs and/or preparing them for innervation by adjacent axon terminals to form new synaptic contacts.

Subsurface cisterns and lamellar bodies in the granule cells of the guinea-pig fascia dentata

Subsurface cisterns (SSC's) and less frequent lamellar bodies (LB's) were identified in the granule cells of the guinea-pig fascia dentata. Both structures, composed of flattened or collapsed agranular cisterns, are continuous with the regular rough endoplasmic reticulum and occasionally connected with each other forming LB-SSC complexes. The SSC's are apposed to glia, synaptic boutons, and nerve cell processes as well as to neighbouring granule cells appearing here singly and in confronting pairs. The quantitative analysis of the various cisternal appositions compared to the distribution of the tissue components on the granule cell soma shows that the overwhelming majority of SSC's are related to glial cells.

Development of axosomatic synapses of the Xenopus spinal cord with special reference to subsurface cisterns and C-type synapses

The relationships of highly flattened subsurface cisterns (SCCs) were investigated electron microscopically in the spinal cord at various developmental stages of tadpoles and adult toads, Xenopus laevis. In medial ventral motor cells (MVCs) of the adult, more than 90% of 156 SSCs examined were situated postsynaptically. Similarly, more than 90% of 540 SSCs in lateral motor column cells (LMCs) were postsynaptic. By contrast, in early developmental stages, the SSCs were initially formed by regional flattening of cisterns of rough-surfaced endoplasmic reticulum just beneath the cell surfaces opposite to glial processes. Then, the glial processes were displaced by nerve endings with an elongated bouton, and thus the C-type synapses were formed. The ratio of postsynaptic SSCs to the total SSCs reached the adult level at around Stage 60. This finding suggests that the SSCs in the MVCs and LMCs draw a certain type of nerve ending to form C-type synapses. Such a mechanism is totally lacking in the dorsal and lateral small nerve cells, since the SSCs in these cells were always situated under the surface opposite to glial processes throughout the developmental stages and in the adult. In mature C-type synapses, an aggregate of synaptic vesicles and a structural specialization of presynaptic membrane occurred only at the region where the postsynaptic membrane was associated with the SSC. The postsynaptic membrane itself of the C-type synapse showed no marked structural specialization at any stage of development or in the adult. The postsynaptic SSC In the mature C-type synapse seems to be involved in some way in the reception of synaptic transmission.

Morphology and distribution of the synapses to the spinal motoneuron of the frog

The quantitative distribution of the different structural elements on the surface of the motoneurons (MN) in the spinal cord of the frog was studied in thin sections and freeze-fracture replicas. In particular, the different synaptic types and their distribution on the MN soma and dendrites are described. In thin sections three types of synapses were discerned: the S-type with spherical vesicles, the F-type with flattened vesicles, and finally the C-type synapse with spherical vesicles and a subsynaptic cistern. The synaptic covering at the MN surface as determined by thin sections is about 36%. In freeze-fracture replicas were observed boutons with and without gap junctions, and C-type boutons. When using the latter technique the synaptic covering was found to be 43%. With both techniques special attention was paied to the morphology of the C-type bouton and both the subsynaptic and extrasynaptic cisterns. The soma membrane over the sub- and extrasynaptic cisterns reveals characteristic and very similar morphological features with respect to both the distribution and size of the membrane particles. the possible functions of the two cisternal types are discussed.

The occurrence of cytoplasmic lamellar bodies in normal and pathologic conditions

Lamellar bodies are stacks of parallel cisternae of approximately regular spacing derived from ergastoplasm. Their occurrence was studied in various nervous and epithelial cells of different animal species in both normal and diseased subjects. This organelle appears to be, at least for some cell types, a normal cytoplasmic feature. The number of lamellar bodies increases in some pathologic conditions and when the cell metabolism is elevated.

Focal laminate segments in cytoplasmic processes of mouse myocardial fibroblasts

In mouse ventricular myocardium, we have found unusual fibroblasts whose cellular processes in some regions are particularly flattened and which contain linearly-arranged, electron-opaque structures ('central laminae"). The morphology of these focal laminate segments of fibroblast processes suggests that the intracellular laminae are adhesive entities which hold the plasmalemmata above and below them in close parallel apposition for short distances.