Fine structural aspects of the synaptic organization of the spinal trigeminal nucleus (pars interpolaris) of the cat

Synapse development within the spinal trigeminal nucleus

Pars interpolaris of the spinal trigeminal nucleus of kittens has been studied with the electron microscope at birth and at several subsequent ages during the first month of life. Attention has been given to ultrastructural maturational changes that occur in this neuropil, especially events in synaptogenesis. The results of this investigation include the following observations: (1) the neuropil, even at the earliest ages studied (three-hour-old kittens), is strikingly mature, necessitating a quantitative assessment in order to determine subtle developmental changes in synaptic patterns; (2) the number of axoaxonic contacts at birth are few, and their emergence is essentially a postnatal phenomenon; (3) it appears that the immature Gray type II or symmetrical synapse possesses distinct cleft material and dense, parallel membrane specializations. Synaptic vesicle accumulation at this contact appears to occur after the membrane specializations have formed. A previous study by Kerr26 has shown a reduced potential for primary afferent reorganization with the spinal trigeminal nucleus when kittens are subjected to trigeminal rhizotomy after three days of age. Our observations on the development of axoaxonic synaptic arrangements in the neonatal period may provide an explanation for these earlier results.

The effects of denervation and stimulation upon synaptic ultrastructure

Quantitative studies of synaptic ultrastructure were made in the upper layers of cat cerebral cortex. Tissues were from intact cortex and from long-term (chronic) undercut cortex with or without electrical stimulation. The synaptic effects of chronic electrical stimulation of denervated cortex are most readily understood as growth and remodeling of synaptic elements. Associated with chronic stimulation were increases in: symmetric membrane contacts; areas of round and flat vesicle containing terminals; dendritic shaft contacts; and synaptic contact lengths. Even without stimulation there were indications of synaptic plasticity in denervated cortex; compared with intact cortex, synapses having symmetric membrane contacts showed an increase in bouton area and an increase in synaptic contacts on dendritic shafts. These data are consistent with the observations of others in which axonal terminal growth occurred after differentation. But it appears that chronic electrical stimulation in the adult nervous system promotes significantly more plasticity than occurs without stimulation. In a functional sense stimulation in the present experiments produced effective inhibition which did not occur with denervation alone. Thus the plasticity observed with stimulation had both structural and functional components.

Study of axonal dystrophy. I. Pathology of the neuropil of the gracile and the cuneate nuclei in ageing and old rats: a stereological study

The changes with age in the neuropil of the gracile and the cuneate nuclei of rats were studied using stereological techniques, in relation to the occurrence of axonal dystrophy. The following were found: (1) significant difference in the volume fraction of presynaptic boutons between the gracile and the cuneate nuclei throughout the whole life span (17% and 13% respectively at 100 days of age); (2) progressive decrease in the volume fraction (34% decrease in the gracile nucleus between 100 and 800 days of age) and in the numerical density of presynaptic boutons, the decline being evident as soon as the animals reached maturity and before axonal dystrophy became manifest; (3) significant differences in the volume fractions of dendrites and of nerve cell bodies between the two nuclei throughout the whole life span of the animals, both being greater in the cuneate than in the gracile nucleus; an age-related decrease in the volume fraction of dendrites was also suspected in the gracile nucleus; (4) progressive increase in the volume fraction of fibrous astrocytic processes (from 3% at 100 days to 10.5% at 800 days in the gracile nucleus); (5) the above described age-related changes of presynaptic boutons and fibrous astrocytic processes were significant only in the gracile nucleus, not in the cuneate. The loss of boutons in ageing gracile nuclei was partially reflected in the appearance of degenerating nerve fibres in ageing gracile tract in the rostral cervical cord. Involutional loss of boutons and dystrophic formation of spheroids both appear and progress closely related in time and space. It was suggested that this set of changes can be understood as one integrated whole in which axonal dystrophy may represent only one side of the coin. The question of the causal mechanisms of axonal dystrophy still remains unanswered.

Patterns of degeneration in the external cuneate nucleus after multiple dorsal rhizotomies

Unilateral, intradural dorsal rhizotomies (C3-Cs) were performed on adult rats to study the patterns of synaptic organization of ascending dorsal root fibers in the external cuneate nucleus (ECN). Animals were permitted to survive for periods of time ranging from 3 hours to 12 days. Sham-operated animals presented a morphology indistinguishable from that of normal, unoperated animals. In rhizotomized animals, degeneration was observed ipsilaterally at all survival periods. After postoperative survivals of 3 to 14 hours some terminal boutons displayed clumping and diminution in numbers of synaptic vesicles and, in addition, degeneration myelinated axons were observed at this time. There was considerable degeneration in the neuropil between 24 and 48 hours postoperative. Two forms of degeneration occurred in axons and terminal boutons with comparable frequency: electron lucent degeneration and electron opaque degeneration. Reactive phagocytic glial cells contained degenerated masses, lipoid droplets, lysosome-like structures and myelin fragments. After postoperative survivals of four to six days, lucent and opaque degenerating terminals were less numerous. Neurofilamentous degeneration was observed only occasionally. Unaltered synaptic membrane specializations were present and were usually abutted by glia. At 12 days postoperative, synaptic glomeruli and serial synapses were not seen. Invaginating dendritic spines were rarely seen. Bouton populations that remained unualtered were: small (0.3-3.0 micron) boutons that contact dendritic shafts and somata, nodal synaptic boutons and boutons containing granular vesicles (80-100 nm).

Synaptic organization of the external cuneate nucleus in the rat

The normal synaptic organization of the rat external cuneate nucleus (ECN) has been investigated. The characteristic feature of the ECN neuropil is complex synaptic arrangements termed synaptic glomeruli. These involve both axo-dendritic and axo-axonic synapses and usually are isolated from the surrounding neuropil by lamellar glial sheaths. Glial isolation of synaptic glomeruli is conspicuous near capillaries. Central glomerular bouton profiles vary in size (2-9 micron diam) and configuration. They form asymmetrical synapses onto dendritic shafts and spines and occasionally receive symmetrical synapses from en passant bouton profiles. Other forms of axo-dendritic synapses not associated with synaptic glomeruli are observed. The type frequently observed is formed by one or more boutons (0.5 4.0 micron diam) synapsing onto a dendrite or dendritic spine. "Isolated" axo-dendritic synapses are surrounded by glial lamellae. Elongated "giant" boutons make multiple synaptic contacts along a dendritic shaft. Serial axo-axonic synapses are found mainly in caudal regions of the nucleus. Axo-somatic synapses are formed by small boutons (0.3.2.0 micron diam) contacting medium (16-24 micron) and small (9-14 micron) neurons. The least frequently observed bouton type in the rat ECN contains numerous granular vesicles, 80-100 nm in diameter. These boutons may contact dendrites, neuronal somas or other boutons.

Electron microscopy of degenerating axons and terminals in spinal trigeminal nucleus after tooth pulp extirpations

Following multiple tooth pulp extirpations, electron microscopic preparations show degenerating axons and synaptic terminals in the same region of the brain stem trigeminal nucleus previously demonstrating degeneration by light-optical methods. The observations confirm the phenomenon of transganglionic degeneration in this system and identify the class of central nervous system axons and synapses specifically related to innervation of the teeth.

Effects of neonatal deafferentation on the superficial laminae of the superior colliculus

The effect of neonatal unilateral enucleations or combined enulcleations-visual cortex ablation on the neurons of the superior colliculus has been studied, Enucleation alone leads to a shrinkage of neurons in the upper portion of the stratum grieseum superficiale but does not affect those in the lower half. The ratio of asymmetric/symmetric synaptic terminals is decreased from 85/15 to 75/25. A small number of abnormal synapses is also found. When both eye and contralateral visual cortex are removed at birth, neurons throughout the stratum griseum superficiale are reduced in size 20-25%. The synaptic ratio is reduced further to 55/45, and about 15% of the post-synaptic structures encountered have abnormal presynaptic profiles attached. It is concluded that the extent of transneuronal atrophy and synaptic disruption is proportional to the amount of afferent input removed. Also, the synaptic modifications made in the upper layers of the superior colliculus appear to be local in nature and there is no evidence of a significant sprouting or new growth of the remaining axons.

An electron microscopic study of lesion-induced synaptogenesis in the dentate gyrus of the adult rat. II. Reappearance of morphologically normal synaptic contacts

Intact synapses in the denervated area of the rat dentate gyrus are reduced to 14% of those normally present 2-4 days following a unilateral entorhinal lesion. By 160-240 days after lesion, the former entorhinal terminal zone is repopulated with new synapses. In all, there is more than a 5-fold increase in the density of intact synapses in the denervated zone between 2 and 240 days post-lesion, and the denervated zone of the molecular layer is restored to 80% of control values. The synapses are Gray type I and are formed on simple and complex spines which closely resemble those normally present. A few boutons have an abnormally large number of synaptic junctions. Reinnervation seems to progress at differential rates. Synapses are rapidly regained up to 30 days after operation, but thereafter the reacquisition of synaptic connections is much slower. Reinnervation is more rapid in the portion of the denervated zone nearest the granule cells, where the maximal densities are attained within 30 days. The time course of reinnervation differed from that of degeneration. A portion of the new synapses in the reinnervated molecular layer appear to arise by the assembly of new synaptic junctions. Over time, the number of post-synaptic contact sites along a given length of dendritic surface recovers, suggesting the formation of new synaptic sites. Our data indicate that granule cells retain a capacity even into adulthood to manufacture, position and assemble postsynaptic components of a synapse and, in concert with reactive afferents, form normal-appearing synapses.

An electron microscopic study of lesion-induced synaptogenesis in the dentate gyrus of the adult rat. I. Magnitude and time course of degeneration

Synapses in the rat dentate gyrus are rapidly lost after removal of the primary input from the entorhinal cortex. In this paper we describe the extent and time course of degeneration and in the subsequent paper the nature of the reinnervation processes. They synapses of entorhinal afferents are remarkably concentrated in their zone of termination. Unilateral removal of the rat entorhinal cortex results in the loss of about 86% of all synapses in the outer three-fourths of the molecular layer of the epsilateral dentate gyrus. Entorhinal synapses are all asymmetric (Gray type I) and terminate on dendritic spines. Analysis of the degeneration reaction provides a means to examine the characteristics of the loss of a relatively homogeneous afferent on a single cell type. The morphological characteristics of the the degenerating terminals showed some heterogeneity; both the electron lucent and electron dense types of degenerating terminals were identified. The electron lucent type was observed only at short survival times. The time course of the loss of degenerating terminals was resolvable into two components, each of which followed first order decay kinetics. Thus degenerating entorhinal terminals behaved as a population which disappeared randomly at a rate dependent on the fraction of terminals present at any time. The loss of degenerating terminals was accompanied by the loss of postsynaptic sites. At short survival times the majority of postsynaptic sites (defined by the presence of a postsynaptic density) had disappeared. There was also a loss of complex spines and some shrinkage of the molecular layer.

Acetylcholinesterase activity of synaptic structures in the spinal trigeminal nucleus

The electron microscope has been used to study the localization of acetylcholinesterase (AChE) activity in the spinal trigeminal nucleus of normal cats with special emphasis on the distribution near synaptic structures. Reaction product is found around both round and flattened synaptic vesicle-containing axon terminals, particularly in synaptic clefts and often specifically associated with the presynaptic, or less frequently the postsynaptic membrane. The presence of reaction product at these specific sites suggests that these are areas of high AChE activity and that acetylcholine may be important in neurotransmission in these regions.

A quantitative autoradiographic and electrophysiological study of the reinnervation of the dentate gyrus by the contralateral entorhinal cortex following ipsilateral entorhinal lesions

The post-lesion proliferation of contralateral enthorhinal afferents which occurs in response to ipsilateral entorhinal lesions was quantitatively analyzed with autoradiographic and electrophysiological techniques. In both cases, the extent of the crossed projection to the dentate granule cells was quantified on the basis of a contralateral/ipsilateral (C/I) ratio. Autoradiographic measures of grain density in the entorhinal terminal field indicates that the very sparse crossed entorhinal projection in intact animals proliferates approximately 6-fold following unilateral entorhinal lesions (on the basis of an increased C/I ratio of grain density in animals with long standing unilater entorhinal lesions). Furthermore, the total number of grains in the entorhinal terminal zone (obtained by subtracting background from non-terminal regions) also increases approximately 6-fold, indicating that compression of the neuropil cannot be the factor responsible for the increased grain density. These increases in the anatomical extent of the crossed projection as a consequence of unilateral entorhinal lesions are also reflected electrophysiologically. In operated animals, the C/I ratio of the extracellular population EPSP (a measure of the synaptic current generated by the crossed projections) also increase 5-8 fold. In addition, while in normal animals, no population spikes are observed following stimulation of the contralateral entorhinal area (indicating an absence of synchronous grnaule cell discharge in response to contralateral entorhinal input), such population spikes are quite prominent in the reinnervated dentate gyrus, indicating a large increase in the effective synaptic drive of the proliferated crossed projections.

The ventral lateral geniculate nucleus, pars lateralis of the rat. Synaptic organization and conditions for axonal sprouting

The synaptic organization of the pars lateralis portion of the ventral lateral geniculate nucleus is similar to that of other thalamic nuclei. There are four types of synaptic knobs (RL, RS, F1, F2). RL knobs are large and irregularly shaped, contain round synaptic vesicles and make multiple asymmetrical junctions. They are found primarily in "synaptic islands" making contact with gemmules, spines, small dendrites, and other synaptic profiles containing pleiomorphic synaptic vesicles (F2). Smaller RS knobs contain round vesicles and make asymmetrical junctions with the same type of elements as RL knobs, with the exception of the F2 profiles, but are seldom found in synaptic islands. F1 knobs contain flattened synaptic vesicles and form symmetrical junctions with F2 knobs, gemmules, spines, and small-medium dendrites in synaptic islands, throughout the neuropil, and on the proximal dendrites and soma of the largest type of neuron. F2 knobs are irregularly shaped, contain pleiomorphic synaptic vesicles and make symmetrical junctions primarily with gemmules and spines in synaptic islands. They are postsynaptic to RL and F1 knobs. Occipital decortication indicates that cortical terminals are of the RS type. Bilateral enucleation indicates that retinal terminals are of both the FL and RS type. The large amount of geographic overlap of retinal and cortical terminals on gemmules, spines, and small dendrites found in the neuropil outside of synaptic islands logically would maximize axonal sprouting between these two sources.

Dendroaxonic synapses in the substantia gelatinosa glomeruli of the spinal trigeminal nucleus of the cat

The glomeruli in the substantia gelatinosa layer of the spinal trigeminal nucleus of the cat contain three kinds of dendritic processes. One of these, the type 2 dendrite, contains large synaptic vesicles in its spine heads and in its shafts. The type 2 dendrite receivers axodendritic synapses from primary trigeminal afferent (C) axons and an occasional axodendritic synapse from small axonal (P) endings with small synaptic vesicles. The type 2 dendrites in turn form dendroaxonic synapses on the C endings. The dendroaxonic synapse and the axodendritic synapse of the C ending typically occur in reciprocal pairs. The axodendritic synapse usually lies in the depths of scalloped depressions in the surface of the C ending while the dendroaxonic synapse is found on the rim of the depression. Type 1 spines, i.e., dendritic spines receiving axodendritic synapses from the primary ending and lacking synaptic vesicles, also receive dendrodentritic synapses from type 2 dendrites. The type 2 dendrite with its large, rounded synaptic vesicles is considered to be excitatory at its dendroaxonic and dendrodendritic synapses. The type 2 dendrites course from glomerulus to glomerulus receiving their excitatory input through the axodendritic synapses of C axons. A type 2 dendrite, in response to C axon excitation would activate type 1 spines directly through their dendrodendritic synapses (C leads to 2 leads to 1) and indirectly by increasing transmitter release at the axodendritic synapses of the C axonal endings through their dendroaxonic synapses (2 leads to C leads to 1). The type 2 dendrites could serve two functions. First, they may prolong transmitter release from the axodendritic synapses of C axonal endings beyond the time of arrival of incoming potentials because of the reciprocal pairing of dendroaxonic and axodendritic synapses (C in equilibrium 2). Second, they may extend the spatial range of the excitatory output of active primary afferent axons to type 1 spines of glomeruli whose primary afferent axons may be inactive (C leads to 2 leads to 1).

Early terminal degeneration of cerebellar climbing fibers after destruction of the inferior olive in the rat. Synaptic relationships in the molecular layer

The cerebellar molecular layer in adult rats has been studied with the electron microscope at several early and consecutive survival times following 3-acetylpyridine intoxication. Climbing fiber (CF) terminals underwent a fast process of electron-dense degeneration which became apparent from 16 hours onwards. A small proportion of degenerating terminals were depleted of vesicles and filled with a dark flocculent and granular homogeneous matrix. Microtubular changes in degenerating CF tendrils were observed. CF terminals were found in relation with every Purkinje cell in normal animals and completely disappeared within 72 hours after the treatment. CF synapses were found on Purkinje dendritic and somatic thorns, sometimes also on the dendritic shafts or even on the Purkinje soma. Convincing evidencd of synaptic contacts of CF varicosities on either basket or stellate cells could not be obtained. CF synapses with Golgi II cell dendrites in the molecular layer were described. Decrease in the number of post-synaptic dendritic thorns normally assigned for CF synapses was observed consequential to CF anterograde degeneration. The observations are consistent with previous conclusions drawn from light microscopic studies that the clearing up of CF debris in the molecular layer is completed within the short time of three days, and that the inferior olive seems to be the only source of CFs.

An autoradiographic identification of Purkinje axon terminals in the cat

The Purkinje axon boutons terminating in nuclei fastigii and interpositus in the cat have been identified after injection of 3H leucine into the cerebellar cortex overlying the nuclei. The animals survived from 4-48 h after injection of the isotope. Semithin and ultrathin sections were coated and exposed for 3 and 14 weeks, respectively. The electron micrographs showed labelling over myelinated axons down to a diameter of 0.8 mum, and over boutons. Fifty labelled boutons were used for identification of the shape of their synaptic vesicles. The statistical analysis including the test for skewness showed that 39 boutons (78%) fall in one group. Most of the synaptic vesicles in this group are elliptical (ration from 1:1.1 - 1:1.7). Slightly ovoid vesicles (ration up to 1:1.3) are frequent, but flattened vesicles (ration above 1:1.7) are relatively few in this group of boutons. 8% of the boutons have a rather homogeneous vesicle population (prevalence of round vesicles, ratio 1:1). Synaptic specializations of Gray's type II or of an intermediate type were found in the boutons belonging to the first group (78% of the boutons). Specializations of Gray's type I were found in the other bouton groups (8% of the boutons).

Catecholaminergic axo-axonic synapses in the nucleus of the tractus solitarius (pars commissuralis) of the cat: possible relation to presynaptic regulation of baroreceptor reflexes

A study was performed on adult cats to investigate synaptic structures of nerve terminals in the commissural portion of the nucleus of the tractus solitarius (NTS); a site where the cardiovascular afferent fibers terminate and where a dense plexus of adrenergic element also resides. Synaptic contacts observed in the commissural portion were predominantly axo-dendritic but a smaller number of axo-somatic synapses were also recognized. A third type of junction, axo-axonic, appears to be unique to the commissural portion of the nucleus, since no axo-axonic contacts were encountered in the medial and ventrolateral portions of the NTS. By labeling with the 'false' neurotransmitter 5-hydroxydopamine (5-OHDA), three types of axo-axonic contacts with different presynaptic components could be identified; namely, axon varicosities with small clear spherical vesicles, axon varicosities containing flat synaptic vesicles and others with small cord vesicles labeled with 5-OHDA. Postsynaptic components were always axon varicosities with clear spherical vesicles. After surgical denervation of the IXth and Xth cranial nerves, no degenerated axon varicosities were observed in the presynaptic side in the axo-axonic contact. The present study clearly demonstrates that the commissural portion of the NTS contains axo-axonic synapses and some of the adrenergic axons in this area provide the presynaptic components for this type of synapse. Possible roles of adrenergic nerves to presynaptic regulation of baroreceptor reflexes are discussed.

Hypertrophy and redistribution of astrocytes in the deafferented dentate gyrus

The response of the astroglial population of the dentate gyrus molecular layer to removal of that region's primary afferent was investigated using Cajal's gold sublimate method. Deafferentation caused the astrocytes to hypertrophy, an effect which was detectable at 24 hr and maximal at 72-96 hr post-lesion. Following this, the astroglia entered a lengthy period of gradual atrophy. Counts of the astrocytes in the various sublayers of the molecular layer led to the conclusion that these cells migrate into denervated dendritic areas from neighboring, nondeafferented zones.

Lesion-induced synaptogenesis in brain: a study of dynamic changes in neuronal membrane specializations

When incoming fibers to a given brain region are damaged and degenerate, the remaining undamaged fibers can, in some cases, form new synapses, and restore physiologically functional circuitry. Synaptic membrane events underlie this reconstruction: the connection between membranes is broken and reformed.

Electron microscopy of synaptic structures in olfactory cortex of early postnatal rats

Layer 1 of the rat olfactory cortex has been studied with the electron microscope at birth and at several consecutive postnatal days up to 14 days of age. Special attention was directed towards synaptic structures and axons of the lateral olfactory tract (LOT). Numerous mature synapses are seen at birth and estimates were made of their subsequent increase in number. In addition, immature synapses are seen and mature postsynaptic sites occur with atypical, partial, multiple or no contact. The findings suggest: (1) considerable prenatal synaptogenesis in contrast to other cortical systems; (2) the maturation of the postsynaptic site may precede that of the presynaptic contact and vesicle accumulation; (3) there may be competition by more than one process for one postsynaptic specialization; (4) the non-innervated sites may result from deafferentation caused by prenatal cell death, although no degeneration was seen, and the atypical contacts may be a stage in the reinnervation of these sites; (5) the LOT develops in parallel with the synaptic neuropil and (6) by 14 days of age the area closely resembles adult tissue.

Diversity of mossy fibres in the cerebellar cortex in relation to different afferent systems: an experimental electron microscopic study in the cat

The evolution of the terminal degeneration has been compared in two systems of mossy fibres: the spinocerebellar and the pontocerebellar projections. The two systems exhibit both dense and clear types of terminal degeneration. However, there are important differences between the evolutive processes of terminal degeneration in the two systems: (i) the time course of the degenerating process is much faster for spinocerebellar than for pontocerebellar rosettes, and (ii) the glial phagocytic process accompanying the dense type of degeneration is different for the two systems. Spinocerebellar rosettes are generally removed from their glomerular central position by reactive glia, leaving fragments of the presynaptic membrane attached to their postsynaptic partner. This feature is exceptional for pontocerebellar rosettes which, in the course of their glial engulfment, leave free the postsynaptic differentiation of their former target granule cell dendrites. These differences of terminal degenerative processes have been reconciled with optical microscope observations by Brodal and Drablos1 of morphological differences between the rosettes of two different fibre systems.

Anatomical, physiological and biochemical studies of the cerebellum from mutant mice. II. Morphological study of cerebellar cortical neurons and circuits in the weaver mouse

The vermis of the homozygous weaver mice has been examined with Golgi and electron microscopic techniques. In addition to the findings already reported by previous authors 12, 29, new cytological features concerning all the cerebellar neuronal types and the synaptic reorganization of the cerebellar circuitry are described. As in other agranular cerebella, Purkinje cells do not develop spiny branchlets and have a randomly oriented dendritic tree. By contrast, their thick dendrites are studded with spines; according to their size and shape these were classified into: (a) small stubby spines which are the normal postsynaptic targets for climbing fibers; (b) tertiary-like spines, most of which are free of axonal contacts; (c) dolichoderus spines; (d) branching spines; and (e) hypertrophic spines. The last 3 types do not exist in normal cerebellum. Postsynaptic-like differentiations are frequently undercoating the smooth surface of the Purkinje dendrites. As it happens in the case of the free spines, free postsynaptic sites in the shafts of the dendrites develop an extracellular material similar to the material present in synaptic clefts. Basket and stellate cells also develop postsynaptic-like differentiations undercoating the somatic and dendritic plasma membranes. These free postsynaptic sites can reach a gigantic size, being longer than 3 mum in length. The rare postmigrative granule cells which persist in wv exhibit claw-endings not only at the dendritc terminal segments, but at the proximal dendritic stems as well. Some of these granule cells, besides having fully achieved migration, undergo a degenerative process indicating that they are probably directly affected by the mutation. Concerning the cerebellar circuitry, and despite the great number of free postsynaptic sites, the large majority of the synaptic contacts keep their specificity. However, some quantitative variations have been disclosed. The surface density of climbing varicosities is increased, whereas that of mossy rosettes is decreased. Stellate and basket fibers are present and their density also decreased. Furthermore, the pinceau formation around the initial segment of the Purkinje cell axon is missing. In addition to all normal synapt iccontacts (with the exception of the'parallel fiber-omnicellularsystem') present in weaver, heterologous synapses have also been encountered, mainly concerning the Purkinje dendritic spines, which can be contacted by mossy rosettes, granule cell bodies and/or dendrites. Morphological signs of partial innervation of the free postsynaptic sites on the smooth surface of Purknje dendrites and the perikarya and dendrites of interneurons have also been observed. These results confirm the existence of synaptic remodeling in wv cerebellum

Observation on the localization of mechanoreceptors in the kidney and afferent nerve fibres in the renal nerves in the rabbit

1. The distribution and localization of mechanoreceptors in the kidney were studied by recording afferent impulses from the renal nerve bundle or from single nerve fibres in the isoloted kidney preparation in the rabbit. 2. It was observed that mechanoreceptors are distributed in the cranial, central and caudal portions as well as the pelvic portion of the kidney. Diameter range of single nerve fibres from which afferent impulses were recorded was from 2 to 8 mum. 3. Histological studies show that the renal nerve possesses abundant non-myelinated nerve fibres with a relatively small number of myelinated nerve fibres. The myelinated axons had diameters ranging from 0-5 to 13-4 mum and the peak of the unimodal distribution curve was 1-5--2-4 mum.

Cerebellar alterations in the weaver mouse

The fine structure of the cerebellum of weaver mouse was examined and the paucity of granule cells and their axons, the parallel fibers, was confirmed. Unexpectedly, however, the dendritic spines of the Purkinje cells which, in normal animals, are the postsynaptic mates of the parallel fibers, were present. Furthermore, their essential morphology and their staining reactions were indistinguishable from those of the Purkinje cell dendritic spines in normal animals. Possible mechanisms of development are discussed.