Afferent connections of the cat lateral vestibular nucleus

Location within the brain of HP-labeled neurons (origins of projections to the lateral vestibular nucleus) was investigated by iontophoretic injection of this enzyme. Bilateral projections to the following midbrain structures were revealed: the field of Forel, interstitial nuclei of Cajal, oculomotor nerve nuclei, and the red nucleus — to all parts of the lateral vestibular nucleus. Bilateral projections were also shown from more caudally located structures, viz. the superior, medial and inferior (descending) vestibular nuclei, Y groups of the vestibular nuclear complex, facial nucleus and hypoglossi, nucleus prepositus nervi hypoglossi and caudal nuclei of the trigeminal tract; ipsilateral projections from crus IIa of lobulus ansiformus of the cerebellar hemisphere; contralateral projections from the bulbar lateral reticular nucleus and Deiter's nucleus. A tonic organization pattern of afferent inputs from a number of brainstem formations to the dorsal and ventral lateral vestibular nucleus is revealed and trajectories of HP-labeled fiber systems projecting to Deiter's nucleus described.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 20, No. 4, pp. 494–503, July–August, 1988.     

The organization of synaptic interconnections in the laminae of the dorsal lateral geniculate nucleus of the cat

Summary Four axon types occur in the lateral geniculate nucleus. Two contain vesicles with mainly round profiles and these are distinguished from each other by their size, the appearance of their contents and by the types of contact they make. The larger RLP axons are interpreted as retinogeniculate and the smaller RSD axons as corticogeniculate fibers. The other two axon types contain many irregular or flattened vesicles and these F axons are regarded as two types of intrageniculate fiber.In laminae A and A 1 encapsulated synaptic zones form around grape-like dendritic appendages. These zones contain all axon types, but RSD axons are rare. Interstitial zones lie between the encapsulated zones and contain synapses formed by many RSD axons, some F and few RLP axons. The interstitial zones continue into the central interlaminar nucleus which forms a narrow band containing no encapsulated zones and few RLP axons. Lamina B contains relatively small RLP axons, very many RSD axons and only a few small encapsulated zones.Axosomatic junctions are rare throughout the nucleus. Axo-axonal junctions occur in all laminae but mostly in the encapsulated zones; the postsynaptic element is always an F axon, RLP or RSD axons generally form the presynaptic element.Supported by Grant NB 06662 from the USPHS. The skillful technical assistance given by Mrs. E. Langer during the course of this work is gratefully acknowledged.     

Developmental pattern of three vesicular glutamate transporters in the rat superior olivary complex

Vesicular glutamate transporters (VGLUTs) mediate the packaging of the excitatory neurotransmitter glutamate into synaptic vesicles. Three VGLUT subtypes have been identified so far, which are differentially expressed in the brain. Here, we have investigated the spatiotemporal distribution of the three VGLUTs in the rat superior olivary complex (SOC), a prominent processing center, which receives strong glutamatergic inputs and which lies within the auditory brainstem. Immunoreactivity (ir) against all three VGLUTs was found in the SOC nuclei throughout development (postnatal days P0–P60). It was predominantly seen in axon terminals, although cytoplasmic labeling also occurred. Each transporter displayed a characteristic expression pattern. In the adult SOC, VGLUT1 labeling varied from strong in the medial nucleus of the trapezoid body, lateral superior olive, and medial superior olive (MSO) to moderate (ventral and lateral nuclei of the trapezoid body) to faint (superior paraolivary nucleus). VGLUT2-ir was moderate to strong throughout the SOC, whereas VGLUT3 was only weakly expressed. These results extend previous reports on co-localization of VGLUTs in the auditory brainstem. As in the adult, specific features were seen during development for all three transporters. Intensity increases and decreases occurred with both VGLUT1 and VGLUT3, whereas VGLUT2-ir remained moderately high throughout development. A striking result was obtained with VGLUT3, which was only transiently expressed in the different SOC nuclei between P0 and P12. A transient occurrence of VGLUT1-immunoreactive terminals on somata of MSO neurons was another striking finding. Our results imply a considerable amount of synaptic reorganization in the glutamatergic inputs to the SOC and suggest differential roles of VGLUTs during maturation and in adulthood. This work was supported by the Graduate Research School Molecular, physiological and pharmacological analysis of cellular membrane transport, DFG GRK 845/1.     

Central connections of the olfactory bulb in the weakly electric fish,Gnathonemus petersii

Summary We have investigated the central connections of the classical olfactory system in the weakly electric fish Gnathonemus petersii using HRP and cobalt labelling techniques. The olfactory bulb projects bilaterally via the medial and lateral olfactory tracts to restricted areas of the telencephalon, namely to its rostromedial, lateral and posterior medial parts. The most extensive telencephalic target is the posterior terminal field, which arcs around the lateral forebrain bundle at levels posterior to the anterior commissure. Projections to the contralateral hemisphere cross in the ventral telencephalon rostral to the anterior commissure and via the posterior dorsal part of the anterior commissure; endings are also present within the anterior commissure. Bilateral projections to the preoptic area, to the nucleus posterior tuberis and to an area in the thalamus are apparent. In all cases, contralateral projections are less extensive than those on the side ipsilateral to the injected bulb. A projection via the medial olfactory tract can be followed to the contralateral bulb. Following injections into the olfactory bulb, retrogradely labelled neurons are found in the contralateral bulb and in six telencephalic areas; they are also present in the periventricular diencephalon and in an area lateral to the nucleus posterior tuberis. The present results support the suggestion that a reduction in olfactory input to the telencephalon occurs together with increased telencephalic differentiation in actinopterygian fishes.     

The fine structure of the hypothalamic secretory neurons of the White-crowned Sparrow,Zonotrichia leucophrys gambelii (Passeriformes: Fringillidae)

Summary The fine structures of the neurons and neuropils of the magnocellular supraoptic nucleus and the parvocellular nuclei of the rostral hypothalamus, including the suprachiasmatic and medial, lateral and periventricular preoptic nuclei, and the neuronal apparatus of the organum vasculosum laminae terminalis, have been examined in the male White-crowned Sparrow, Zonotrichia leucophrys gambelii, by correlated light and electron microscopy.The magnocellular supraoptic nucleus is characterized by large neurosecretory perikarya which contain a well developed Golgi complex and densecored granules 1,500–2,200 Å in diameter. The neuropil displays axons, dendrites and glial fibers. Some axonal profiles contain dense-cored vesicles 800–1,000 Å in diameter and clear vesicles 500 Å in diameter. Axo-somatic and axo-dendritic synapses are conspicuous in this nuclear region.The suprachiasmatic nucleus is characterized by an accumulation of small neurons with moderately developed cellular organelles and some dense-cored granules, approximately 1,000 Å in diameter. The profiles of axons within the neuropil contain dense-cored granules 800–1,000 Å in diameter and clear vesicles 500 Å in diameter.The neurons of the medial preoptic nucleus are relatively large and exhibit well developed cellular organelles and dense-cored granules 1,300 to 1,500 Å in diameter. Granular materials are formed within the Golgi complex. The medial preoptic nucleus is rich in secretory perikarya.Occasionally, neurons with granules 1,500–2,200 Å in diameter are encountered in the lateral preoptic and periventricular preoptic nuclei. They may be considered as scattered elements of the magnocellular (supraoptic and paraventricular) system.The organum vasculosum laminae terminalis consists of three layers, i.e., ependymal, internal and external zones, and exhibits a vascular arrangement similar to that of the median eminence. The perikarya of the parvocellular neurons and their axons in the internal zone contain numerous secretory granules ranging from 1,300 to 1,500 Å in diameter.This investigation was supported by Grant No. 5R040 Japan-U.S. Cooperative Science Program of the Japan Society for the Promotion of Science to Professor H. Kobayashi and Professor S.-I. Mikami, by a Scientific Research Grant No. 56019 from the Ministry of Education of Japan to S.-I. Mikami, by support from the Deutsche Forschungsgemeinschaft (Schwerpunktprogramm Biologie der Zeitmessung) to Prof. A. Oksche and by Grant No. GF 33334, U.S.-Japan Cooperative Science Program of the National Science Foundation to Prof. D.S. Farner.Herrn Professor Dr. Dres h.c. Wolfgang Bargmann zu seinem 70. Geburtstag am 27. Januar 1976 gewidmet.     

A putative suprachiasmatic nucleus of birds responds to visual motion

In mammals, the suprachiasmatic nucleus (SCN) is a pacemaker regulating daily rhythms. In birds, two retinorecipient nuclei have been called the avian SCN, one in the lateral hypothalamus and the other more medial and rostral. We asked whether the protooncogene c-fos is expressed in either nucleus after light exposure during subjective night, but not during subjective day, as is the case in the SCN of mammals.Chicks raised with one eye covered by a diffuser were exposed to vertically moving surroundings, after the difuser had been switched to the other eye.Surprisingly, we saw strong Fos label only in the lateral nucleus contralateral to the eye newly exposed to visual motion, but not in the ipsilateral nucleus nor in either medial SCN. No label was seen in animals kept in darkness or if the diffuser was not switched. Fos labeling did not differ between subjective day and night. The sensitivity to novel motion is also seen in motion-processing nuclei of the accessory optic system and pretectum; this suggests either that the lateral SCN is not the SCN, but part of the motion pathway, or that the avian SCN may be motion-sensitive during both day and night.     

Enzymatic degradation and quantitative lectin labeling for characterizing glycoconjugates which act as lectin acceptors in cat submandibular gland

Summary Sites of binding of eight different lectins (LTA, UEA I, WGA, SBA, DBA, CON A, PNA, RCA I) to cat submandibular gland were studied after exposure of tissue sections to sialidase, -fucosidase, -galactosidase, -mannosidase, -N-acetylglucosaminidase. All lectins were affected by enzymatic predigestion and the labeling of individual lectins was highly dependent upon the glycosidase used to pretreat the sections. Glycoconjugates of demilunar, acinar and ductal cells exhibited a different composition of terminal sequences. For example, fucose proved to form the disaccharide fucose-galactose in demilunar and acinar cells, whereas it was present with the sequence fucose-N-acetyl-d-glucosamine in striated duct cells. Sialic acid participated both to the terminal sequence sialic acid-galactose and sialic acid-N-acetyl-d-galactosamine either in demilunar or in ductal cells. Lectin labeling combined with glycosidase digestion was also helpful in verifying the influence of neighbouring oligosaccharides on the affinity of lectins for the respective sugars.     

Juxtaposition of the generative cell and vegetative nucleus in the mature pollen grain of amaryllis (Hippeastrum vitatum)

Summary Computer-generated, three-dimensional reconstructions from serial ultrathin sections were used to investigate the spatial organization and extent of association between the generative cell and vegetative nucleus within the mature pollen grain of amaryllis. In all cases examined, the highly lobed vegetative nucleus was found in close proximity and positioned laterally to the elongated, oval shaped generative cell. Numerous projections of the vegetative nucleus come to within 53 nm of the inner vegetative cell plasma membrane which surrounds the generative cell. These areas of close association may continue transversely around the generative cell for a distance of up to 4 m. Although an association exists between the generative cell and vegetative nucleus of the mature pollen grain, it is apparent that several changes must take place after pollination in order to achieve the high amount of close contact that occurs between the vegetative nucleus and the numerous terminal cell extensions of the leading sperm in the pollen tube of amaryllis (Mogensen 1986). Thus, this study demonstrates that the spatial organization among components of the male germ unit in the mature pollen grain does not necessarily reflect relationships that ultimately exist among these components within the pollen tube.     

The synaptic organization in the medial geniculate body of afferent fibres ascending from the inferior colliculus

Summary The ventral nucleus of the medial geniculate body has been examined electron microscopically 2–5 days after destruction of the inferior colliculus. In both the ipsi- and contralateral ventral nuclei, degenerating collicular afferents are of medium diameter (1–5 ) and their degenerating terminals are distributed mainly to synaptic aggregations (glomeruli) in which they end axo-axonically and axo-dendritically. Their distribution and mode of termination indicates that these terminals belong to a class which in normal material is large, contains round synaptic vesicles and ends by means of asymmetrical synaptic complexes upon dendrites and upon the second (pale) type of glomerular terminal. It also ends by means of adhesion plaques on the same dendrites.As the terminals of corticothalamic afferents to the nucleus are already known, only the origin of two types remains to be determined: the pale terminals, which arise from structures resembling dendrites and which end only axo-dendritically, and a small, less common terminal which ends axo-axonically, axo-dendritically and axo-somatically. Both types contain flattened synaptic vesicles and end by means of symmetrical synaptic complexes.Correlative Nauta and Golgi studies suggest that the collicular afferents have a very specific spatial distribution within the cellular laminae composing the ventral nucleus.The terminal degeneration commences as a neurofilamentous hyperplasia and quickly passes to one of increased electron density. There is evidence for early removal of degenerating terminals from the postsynaptic membrane.This work was supported by a grant from the Bank of New Zealand Medical Research Fund.We are indebted to Professor J. A. R. Miles for use of the electron microscope.     

The distribution of nuclear progesterone receptor in the hypothalamus and forebrain of the domestic hen

Summary Cell nuclei containing progesterone receptor were identified immunohistochemically in the hypothalamus and forebrain of the domestic hen using an antiserum to the steroid binding B subunit (110 kDa) of chicken oviduct progesterone receptor and the avidin-biotin complex procedure. Cell nuclei containing progesterone receptor were widely distributed in the anterior, medial and basal hypothalamus with the highest density occurring in the lamina terminalis and the preoptic area. Abundant, though less intensely reacting progesterone receptor was present in cell nuclei in the tuberal infundibular area and in the internal zone of the median eminence. A large group of cell nuclei containing progesterone receptor occurred in the dorsal anterior hypothalamus between the anterior commissure and the lateral ventricle. This group of nuclei extended anteriorly into the telencephalon. A small number of cell nuclei containing progesterone receptor was also found in the ventral telencephalon in the region of the nucleus accumbens.     

Activation of K+ channels by lanthanum contributes to the block of transmitter release in chick and rat sympathetic neurons

Summary We studied the effects of lanthanum (La³⁺) on the release of ³H-norepinephrine(³H-NE), intracellular Ca²⁺ concentration, and voltage clamped Ca²⁺ and K⁺ currents in cultured sympathetic neurons. La³⁺ (0.1 to 10 m) produced concentration-dependent inhibition of depolarization induced Ca²⁺ influx and ³H-NE release. La³⁺ was more potent and more efficacious in blocking ³H-NE release than the Ca²⁺-channel blockers cadmium and verapamil, which never blocked more than 70% of the release. At 3 m, La³⁺ produced a complete block of the electrically stimulated rise in intracellular free Ca²⁺ ([Ca²⁺] _i ) in the cell body and the growth cone. The stimulation-evoked release of ³H-NE was also completely blocked by 3 m La³⁺. However, 3 m La³⁺ produced only a partial block of voltage clamped Ca²⁺ current (I _Ca). Following La³⁺ (10 m) treatment ³H-NE release could be evoked by high K⁺ stimulation of neurons which were refractory to electrical stimulation. La³⁺ (1 m) increased the hyperpolarization activated, 4-aminopyridine (4-AP) sensitive, transient K⁺ current (I _A ) with little effect on the late outward current elicited from depolarized holding potentials. We conclude that the effective block of electrically stimulated ³H-NE release is a result of the unique ability of La³⁺ to activate a stabilizing, outward K⁺ current at the same concentration that it blocks inward Ca²⁺ current.     

Neurophysiological study of bulbar projections of different groups of superior laryngeal afferents

The projections of superior laryngeal afferents to bulbar neuronal structures were investigated using ortho- and antidromic testing during acute experiments on cats anesthetized with Nembutal. It emerged that endings of the most excitable (group A) afferent fibers were mostly distributed ipsilaterally within the solitary tract nucleus, the adjoining portion of the lateral tegmental field, and the rostral section of the retrofacial nucleus. High threshold (group A and A) afferent fibers also terminate in these nuclei, but are distributed over a wider area than low-threshold afferent projections in the solitary tract nucleus and the lateral tegmental field. The reverse applied to the retrofacial nucleus. Terminals of high threshold (group A) afferents extended to the caudal trigeminal nerve spinal tract nucleus, and possibly to the dorsal motor nucleus of the vagus nerve at obex level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 81–90, January–February, 1988.     

Purification and characterization of recombinant Escherichia coli-expressed Pichia etchellsii β-glucosidase II with high hydrolytic activity on sophorose

-Glucosidase II (Bgl II), encoded by the glu2 gene of the thermo-tolerant yeast Pichia etchellsii, was purified from recombinant Escherichia coli pBG22:JM109. The enzyme had a molecular mass of 176 kDa and was a dimer with an apparent subunit mass of 83 kDa. It exhibited broad substrate specificity and hydrolyzed -linked gluco-disaccharides and oligosaccharides, salicin, and cyanogenic glucoside amygladin. The unusually high hydrolytic activity of 7,680 units min^–1 g^–1 protein was obtained on sophorose. Competition experiments performed using differently linked -disaccharides indicated these to be hydrolyzed at the same active site. Transglycosylation activity leading to the biosynthesis of several disaccharides and oligosaccharides was observed. The enzyme was placed in glycosyl hydrolase family 3, based on a statistical approach using amino acid composition data. The involvement of His as a catalytically important residue was confirmed by diethylpyrocarbonate modification. Pre-incubation of the purified enzyme with 5 mM p-nitrophenyl--d-glucoside offered 2.5-fold higher residual activity compared with unbound enzyme, indicating protection at the active site. The feasibility of this enzyme as a biocatalyst of choice for the synthesis of glyco-conjugates is discussed.     

The neurosecretory system of the adult Calliphora erythrocephala

Summary Neurosecretory cells in the brain and suboesophageal ganglion of the adult female Calliphora erythrocephala have been studied in the light microscope. The paraldehydefuchsin stain (PAF) gave by far the clearest pictures.The medial neurosecretory cells of the protocerebrum (m.n.c.) show definite cyclic changes as to the size of the nuclei and the content of secretory material. The cytological changes depend on the age of the fly and the diet given and are correlated with ovarian development.The nuclear size is held to express the metabolic activity of the cells. Cells with large nuclei, as found in young sugar-flies (S1D) and meat-fed flies with developing ovaries (S4D/M2D), contain less secretory material which is released through the axons, while the m.n.c. of old sugar-flies (S6D) have small nuclei and are stuffed with secretory material which is stored in the perikarya.These results confirm those obtained by darkfield microscopy of living m.n.c. by Lea and E.Thomsen (1962 and unpublished).No really convincing evidence for the existence of more than one type of m.n.c. was found.Two small groups of lateral cells were observed. Possibly neurosecretory are further: 1-(2) cells at the base of each optic lobe, two groups of 2–3 cells on the caudal side of the brain, and 2 cells ventrally in the suboesophageal ganglion.Giant neurons of unknown function are situated very near the m.n.c. Their axons join those from the m.n.c., but end in the suboesophageal ganglion.The same region comprises a number of peculiar cells, each containing a large, fluid-filled vacuole (the vacuolated cells). Similar cells are associated with the possibly neurosecretory cells on the caudal side of the brain.My sincere thanks are due to my wife Dr. Ellen Thomsen, who made all the excisions of the brains and the measurements of the nuclei, to T.C.Normann for valuable assistance with the photographic work, and to Mrs. K. Bahnert for technical help with the gallocyanin method. The Carlsberg Foundation has supported the work with grants.     

Synaptic organization in the lateral geniculate nucleus of the monkey

Summary The synaptic organization in the lateral geniculate nucleus of the monkey has been studied by electron microscopy.The axon terminals in the lateral geniculate nucleus can be identified by the synaptic vesicles that they contain and by the specialized contacts that they make with adjacent neural processes. Two types of axon terminal have been recognized. The first type is relatively large (from 3–20 ) and contains relatively pale mitochondria, a great many vesicles and, in normal material, a small bundle of neurofilaments. These terminals have been called LP terminals. The second type is smaller (1–3 ), contains darker mitochondria, synaptic vesicles, and no neurofilaments. These have been called SD terminals.Both types of terminal make specialized axo-somatic and axo-dendritic synaptic contacts, but the axo-somatic contacts are relatively rare. In addition the LP terminals frequently make specialized contacts with the SD terminals, that is, axo-axonal contacts, and at these contacts the asymmetry of the membranes is such that the LP terminal must be regarded as pre-synaptic to the SD terminal.The majority of the synaptic contacts are identical to those that have been described previously (Gray, 1959 and 1963a) but, in addition, a new type of contact has been found. This is characterized by neurofilaments that lie close to the post-synaptic membrane, and by an irregular post-synaptic thickening. Such filamentous contacts have been found only where an LP terminal contacts a dendrite or a soma.The degeneration that follows removal of one eye demonstrates that the LP terminals are terminals of optic nerve fibres. The origin of the SD terminals is not known.The glial cells often form thin lamellae around the neural processes and tend to isolate synaptic complexes. These lamellae occasionally show a complex concentric organization similar to that of myelin.It is a pleasure to thank Prof. J. Z. Young for advice and encouragement and Dr. E. G. Gray for the considerable help he has given us. Dr. J. L. de C. Downer gave us much help with the care of the animals and with the operations. We also wish to thank Mr. K. Watkins for technical assistance and Mr. S. Waterman for the photography.     

Synapses in the cerebral ganglion of adult Ciona intestinalis

Summary Electron microscopy of the synaptic morphology of synapses in the cerebral ganglion of the adult ascidian (sea squirt) Ciona intestinalis reveals that the synapses are restricted to the central neuropil of the ganglion. Many of the synapses show a polarity of structure such that pre and post synaptic parts can be identified. The vesicles in the presynaptic bag are of two main diameters 80 and 30 nm respectively. The large vesicles have electron dense contents that vary both in their capacity and dimensions.The pre and postsynaptic membranes are more electron dense than the surrounding membranes, but they are only slightly thicker. Both the pre and post synaptic membranes have electron dense dots some 10 nm in diameter associated with their cytoplasmic surfaces. Sometimes the presynaptic membrane has larger peg-like projections between the vesicles. Associated with the post synaptic membrane are tubules some 10 nm in diameter. These tubules may be the dots cut obliquely.The synaptic cleft material is more electron dense than the surrounding intercellular material, and in it there is a dense line made up of granules about 3–5 nm in diameter. This dense line is usually mid way between the pre and post synaptic membranes, but may be nearer the postsynaptic membrane.No tight junctions between adjacent nerve process profiles have been observed.I wish to thank Professors J. Z. Young, F. R. S. and E. G. Gray for much advice and encouragement, also Dr. R. Bellairs for the use of electron microscope facilities and Mr. R. Moss and Mrs. J. Hamilton for skillful technical assistance.     

The fine structure of the olfactory tract in the teleost Carassius carassius L.

Summary Electronmicrographic montages of the olfactory tract at two levels in each of two fish (Carassius carassius L.) were constructed and fibre diameters measured using a Zeiss TGZ 3 particle size analyzer. Medial and lateral tract divisions, rhinocele and dorsal tela were identified. Ciliated ependymal cells line the rhinocele. Meninges form the outer covering of both tract divisions and the tela roofing the central canal.The lateral tract consists of 10–14 fasciculi in which myelinated nerve fibres are prominent. These fibres range in diameter between 0.2 and 1.8 (mean 0.7 ) consistent with conduction velocities averaging 0.6 m/sec recorded in the carp lateral olfactory tract.The medial division of the olfactory tract contains two larger fasciculi within which are numerous fine unmyelinated nerve fibres (mean diameter 0.17 ) arranged in bundles partly enveloped by glial cell processes. Myelinated nerve fibres are unevenly distributed within both fasciculi and have mean diameters of 0.6 .An interesting observation is the consistent presence of synapses within the largest bundle of the medial tract at all levels.Supported by Grant 5 Ro5 TW00154-03 from the National Institutes of Health, United States Public Health Service.The authors are indebted to the Fisheries and Wildlife Department who generously provided the fish from Snob's Creek Fish Hatchery, and gratefully acknowledge the technical assistance of Mr. T. Armitage, Mr. J. Simmons and Miss D. Harrison.     

The fine structure of cephalopod blood vessels III. Vessel innervation

Summary The cephalic aorta of Octopus vulgaris has a fairly complete endothelium lining the lumen, a thick complete basement membrane, a layer of circularly orientated and a layer of longitudinally orientated muscle fibres. Presumptive synaptic endings are of two types. In the circular muscle, axons containing vesicles, contact club-shaped projections of the muscle. The gap between the pre- and postsynaptic membranes is less than 100 Å and in some places apparently forms a tight junction. The second type of ending has been found in the longitudinal muscle; here axons full of vesicles end on the muscle. The ending is enclosed by a mesaxon of muscle and the synaptic gap is approximately 100 Å. In the smaller blood vessels, axons end on myofilament-containing pericytes of blood vessels (equivalent to small arterioles). The endings contain vesicles and have a synaptic gap of 100 Å. Only some of the pericytes seem to be innervated and transmission between one pericyte to another may be mediated by specialized junctions between the cells. The smaller non-myofilament containing vessels (equivalent to capillaries) are not thought to be innervated.We would like to thank Professor J. Z. Young and Dr. E. G. Gray for advice and encouragement, Mrs. Jane Astafiev for drawing Figs. 1 and 12, Mr. S. Waterman for photography, and Miss Cheryl Martin for secretarial assistance.     

A horseradish peroxidase study on the mammillothalamic tract in the rat

The mammillary projections to the anterior thalamic nuclei were investigated in the rat, using the horseradish peroxidase (HRP) method. Pars centralis of the medial mammillary nucleus projects to the medial portion of the ateromedial nucleus (AM). Pars medialis (Mm) of the medial mammillary nucleus sends fibers to the ipsilateral AM and sparsely to the medial portion of the contralateral side. The ventral and dorsal portions of Mm project to the anterior and posterior portions of AM, respectively. The pars latralis (Ml) and pars posterior (Mp) of the medial mammillary nucleus send fibers predominantly to the ipsilateral anteroventral nucleus and sparsely to the contralateral side. A slight difference between Ml and Mp projections was observed. The lateral mammillary nucleus projects bilaterally to the anterodorsal nucleus.     

The ventral lateral geniculate nucleus,pars lateralis of the rat

Summary 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 RL 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.We would like to thank Mr. Peter Rossetti for his excellent technical assistance on a major portion of this project, Ms. Judith Strauss for photographic assistance, and Ms. Nancy Wood for typing. Supported by grants NS 10579, NS 08724, 5 S01 RR 05402, and 2 T01 GM 00326