numb, a gene required in determination of cell fate during sensory organ formation in Drosophila embryos

Neurons and support cells of each sensory organ in Drosophila embryos are most likely derived from a single precursor cell. This cell lineage is affected in numb mutants. Morphological alterations of sensory structures, as well as changes in the number of cells expressing cell type-specific markers, indicate that sensory neurons in numb mutant embryos are transformed into lineage-related nonneuronal support cells. Thus the numb gene controls the fate of progeny derived from sensory organ precursors. The numb gene has been isolated by the plasmid rescue method. The structure of its predicted product is discussed.

Three-dimensional scanning electron microscopic study of the normal hamster olfactory epithelium

The olfactory epithelium of the adult hamster (Mesocricetus auratus) was studied using the scanning electron microscope. A method that produced fractures in the epithelium exposed structures below the surface and made it possible to examine the morphological and structural relationships among cells. Three cell types were studied: supporting cells, olfactory neurons (receptor cells) and basal cells. Supporting cells were observed spanning the full extent of the epithelium, and had basal foot processes that terminated at or near the basal lamina. Along the lateral margin of supporting cells, cellular processes were observed extending outwards, reaching olfactory neurons and adjacent supporting cells. These cellular contacts among supporting cells and olfactory neurons were present at different levels of the epithelium. Olfactory neurons were located primarily in the middle and lower epithelial regions. Their dendritic processes reached the epithelial surface in a straight or tortuous manner, passing between the supporting cells. Olfactory axons were observed as thin unbranched processes that emerged from a conical hillock region, passed basally, and fasciculated into larger sensory bundles within the lamina propria. Basal cells were observed adjacent to the basal lamina as a row of single cells or clustered in groups. Within the lamina propria connective tissue, blood vessels, axon bundles and Bowman's glands were examined. Bowman's glands were composed of pyramidal secretory cells arranged about a single duct that extended to the epithelial surface. Scanning electron microscopy provided a unique three-dimensional analysis of cell structure within the olfactory epithelium. The results provide new and different observations on the detailed morphology and intimate relationships that exist among epithelial cells, and complement previous light and transmission EM observations.

T cell function and expression are dramatically altered in T cell receptor V gamma 1.1J gamma 4C gamma 4 transgenic mice

We have characterized transgenic mice carrying a functional T cell receptor (TCR) C gamma 4 (V gamma 1.1J gamma 4C gamma 4) gene. Results indicate that active transcription of the C gamma 4 transgene can influence expression of the endogenous C gamma 4, C gamma 1 (V gamma 3-, V gamma 4-, V gamma 2-, or V gamma 5J gamma 1C gamma 1) and C gamma 2 (V gamma 1.2J gamma 2C gamma 2) genes, while the ultimate expression of other TCR delta, alpha, and beta chain genes, as well as the adult T cell response, are relatively unaltered. Cells expressing transgenic C gamma 4 and endogenous delta TCR transcripts can migrate to the skin as dendritic epithelial cells (DEC) even though C gamma 4 cells are rarely, if at all, found in the skin. Transgenic and control mice were compared at 2 weeks, 6-7 weeks, and older. At 2 weeks, the thymus of transgenic mice, particularly the medulla, was much larger than control. Moreover, peripheral lymphoid tissues of younger mice were markedly (as much as 100-fold) more immunoreactive (both Con A response and alloreactivity). These differences, although persistent, became smaller in older mice. The data suggest that transgene expression has a major effect on T cell development and reactivity.

Dendritic morphology of identified retinal ganglion cells in Xenopus laevis: a comparison between the results of horseradish peroxidase and cobaltic-lysine retrograde labelling

Following the application either of cobaltic-lysine complex or a 30% solution of horseradish peroxidase (HRP) in a sealed tube to the cut end of the optic nerve of young adult Xenopus frogs, the dendritic morphology of large ganglion cells was studied in retinal wholemount preparations, and compared with that in animals of the same size as revealed by the short time administration of HRP crystals. In the former two groups of animals, after 24 h survival, the size of the dendritic arborization of characterized ganglion cell types, Types I and III, were found to be significantly larger (61-79% and 180-187%, respectively) than those which survived 3 days after the administration of HRP crystals. These findings suggest that the very fine dendritic branches of large ganglion cells may remain unlabelled after a short-time exposure to HRP.

Projection neurons in the rat dorsolateral septal nucleus possess recurrent axon collaterals

Projection neurons in the rat dorsolateral septal nucleus (DLSN) were labeled intracellularly with horseradish peroxidase (HRP) in an in vitro slice preparation. The labeled neurons exhibited widespread 'isodendritic' type dendritic fields. Each of the neurons was identified as a projection neuron by the tracing of its main axon out of DLSN. The axons of these neurons gave rise to intrinsic collaterals which branched to form an extensive axon plexus which was confined to DLSN. These axon collaterals exhibited numerous en passant swellings suggestive of boutons. It is proposed that the recurrent axon collaterals of DLSN projection neurons may form an anatomical substrate for local inhibition within DLSN.

Characteristics of microtubules at the different stages of neuronal differentiation and maturation

The developing nervous system has proved to be a very powerful tool to analyze how MT are involved in basic biological processes such as cell proliferation, cell migration, cell shaping, and transport. A better knowledge of the basic events occurring during neurogenesis also affords us the possibility of establishing the basis of experiments and trying to solve unanswered and important questions. Despite the considerable value of cell culture, we need to use more discrete regions of the developing brain in situ in order to analyze the MT and their modifications into cells developing their "natural" environment. One major problem remains the question of the mode of assembly and disassembly, that is, the behavior of MT in living cells. Dynamic instability and/or treadmilling are accurate interpretations of the dynamics of MT at least in vitro or in cell culture, but we do need more information on what happens in situ and in vitro. One of the main tasks of cell biologists is to devise satisfactory tests to approach this fundamental question. In this view, pharmacological manipulation of embryos treated in whole-embryo culture systems might be a possible way. Microtubules are ubiquitous cell components. However, the extensive heterogeneity of MAP and tubulin in the CNS confers on the neurons a wide range of capabilities of assembly of these proteins and suggests that the neuron has a unique potential of a relation between MT composition and cell function. We have seen that each major event during neurogenesis is related to a specific series of modifications of the MT components. It remains to be determined if there is a causal or just a correlative relationship between the appearance of specific isotypes and the occurrence of specific events and/or functions. We have also to determine the exact spatial and temporal relations among the different isotypes of MT proteins, tubulin, and MAP. Is there a close correspondence between a tubulin and a MAP isotype? Can the appearance of one isotype of tubulin influence the appearance and the assembly of a specific MAP, or vice versa? Recent results obtained with the Tyr- and Glu-MT shed light on these questions and suggest a whole series of possibilities for cells to modulate the structure, behavior, and function of MT in specific domains of the neuron or in specific regions of the brain, by only a minute modification of the molecule of tubulin. Microtubule protein heterogeneity raises also a number of questions.(ABSTRACT TRUNCATED AT 400 WORDS)

Shapes of nerve cells in the myenteric plexus of the guinea-pig small intestine revealed by the intracellular injection of dye

The shapes of myenteric neurons in the guinea-pig small intestine were determined after injecting living neurons with the dye Lucifer yellow via a microelectrode. The cells were fixed and the distribution of Lucifer yellow rendered permanent by an immunohistochemical method. Each of 204 nerve cells was examined in whole-mount preparations of the myenteric plexus and drawn using a camera lucida at 1250 x magnification. Four cell shapes were distinguished: (1) neurons with several long processes corresponding to type II of Dogiel; (2) neurons with a single long process and lamellar dendrites corresponding to type I of Dogiel; (3) neurons with numerous filamentous dendrites; and (4) small neurons with few processes. About 15% of the neurons could not be placed into these classes or into any single class. The type II neurons (39% of the sample) had generally smooth somata and up to 7 (average 3.3) long processes, most of which ran circumferentially. Dogiel type I neurons (34% of sampled neurons) had characteristic lamellar dendrites, i.e., broad dendrites that were flattened in the plane of the plexus. The filamentous neurons (7% of the sample), had, on average, 14 fine processes up to about 50 microns in length. Small neurons with smooth outlines and a few fine processes made up 5% of the neurons encountered. We conclude that myenteric neurons that have been injected with dye can be separated into morphologically distinct classes and that the different morphological classes probably correspond to different functional groupings of neurons.

Alterations in the morphology of ganglion cell dendrites in the adult rat retina after optic nerve transection and grafting of peripheral nerve segments

Transected ganglion cell axons from the adult retina are capable of reinnervating their central targets by growing into transplanted peripheral nerve (PN) segments. Injury of the optic nerve causes various metabolic and morphological changes in the retinal ganglion cell (RGC) perikarya and in the dendrites. The present work examined the dendritic trees of those ganglion cells surviving axotomy and of those whose served axons re-elongated in PN grafts to reach either the superior colliculus (SC), transplanted SC, or transplanted autologous thigh muscle. The elaboration of the dendritic trees was visualized by means of the strongly fluorescent carbocyanine dye DiI, which is taken up by axons and transported to the cell bodies and from there to the dendritic branches. Alternatively, retinofugal axons regrowing through PN grafts were anterogradely filled from the eye cup with rhodamine B-isothiocyanate. The transection of the optic nerve resulted in characteristic changes in the ganglion cell dendrites, particularly in the degeneration of most of the terminal and preterminal dendritic branches. This occurred within the first 1 to 2 weeks following axotomy. The different types of ganglion cells appear to vary in their sensitivity to axotomy, as reflected by a rapid degeneration of certain cell dendrites after severance of the optic nerve. The most vulnerable cells were those with small perikarya and small dendritic fields (type II), whereas larger cells with larger dendritic fields (type I and III) were slower to respond and less dramatically affected. Regrowth of the lesioned axons in peripheral nerve grafts and reconnection of the retina with various tissues did not result in a significant immediate recovery of ganglion cell dendrites, although it did prevent some axotomized cells from further progression toward posttraumatic cell death.

Polarity orientation of microtubules in hippocampal neurons: uniformity in the axon and nonuniformity in the dendrite

We have analyzed the polarity orientation of microtubules in the axons and dendrites of cultured rat hippocampal neurons. As previously reported of axons from other neurons, microtubules in these axons are uniform with respect to polarity; (+)-ends are directed away from the cell body toward the growth cone. In sharp contrast, microtubules in the mid-region of the dendrite, approximately 75 microns from the cell body, are not of uniform polarity orientation. Roughly equal proportions of these microtubules are oriented with (+)-ends directed toward the growth cone and (+)-ends directed toward the cell body. At distances within 15 micron of the growth cone, however, microtubule polarity orientation in dendrites is similar to that in axons; (+)-ends are uniformly directed toward the growth cone. These findings indicate a clear difference between axons and dendrites with respect to microtubule organization, a difference that may underlie the differential distribution of organelles within the neuron.

Induction of process outgrowth in vertebrate and invertebrate cell lines by a 2-pyridinyl thiosemicarbazone

Regulation of differentiation in cells of disparate origin is often mediated by widely differing molecular signals and receptor mechanisms. For example, two neuron-like cell lines used extensively as models for molecular control of differentiation, the steroid-sensitive Kc line from Drosophila and the polypeptide- and cyclic nucleotide-sensitive PC12 line from rat, share no obvious growth factor or hormone receptors. However, we have found that a thiosemicarbazone, 1-pyrrolidinecarbothioic acid [1-(2-pyridinyl)ethylidene] hydrazide, one of a class of synthetic antineoplastic agents, induces process outgrowth - a marker of cellular differentiation - in cells of both of these lines. Moreover, the thiosemicarbazone induces process outgrowth in cells of mutant clones of these lines that are refractory to treatment with growth factors or hormones. Activity of the thiosemicarbazone is dependent upon the alpha-(N)-heterocyclic ring. These findings show that the 2-pyridinyl thiosemicarbazone mimics the effects of diverse epigenetic factors in inducing process outgrowth similar to that seen in cellular differentiation of these cell lines induced by natural regulators. Regulation may be by a mechanism, common to both invertebrate and vertebrate cells, which occurs downstream from the receptors that have been previously shown to mediate epigenetically induced differentiation.

[Neuronal organization of the periamygdaloid cortex in the cat brain]

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

[Neuronal organization of field 4 of the motor cortex of the cat brain]

By means of the silver nitrate impregnation method after Golgi-Kopsch in kittens and young cats the field 4 in the cerebral motor cortex has been studied. The motor cortex of the field 4 possesses certain heteromorphism. Besides usual stellate and pyramidal neurons, that differ from real ones by some morphological signs: their body is often round, the apical dendrite is much thinner than the corresponding dendrite of a pyramidal neuron, it does not produce oblique branches along the course, never gets into the I layer, the spines arrange less densely. According to the mode of dendrites setting off, the atypical pyramidal neurons can be divided into multipolar and spindle-like with horizontal or vertical branching of the dendrites. According to the spines distribution, the multipolar atypical neurons can be divided into spinous, rare-spinous and aspinous. With respect to various cellular forms and distribution of various types of neurons in layers, every of the areas (gamma, alpha, sfu, fu) possesses specific peculiarities. The greatest variability of the neurons have the field 4 gamma and 4 alpha, where, besides stellate and pyramidal, atypical neurons can be found. The stellate neurons of the field 4 gamma are characterized with a deep arrangement, their number is essentially less, than in other areas of the field 4. In the field 4 alpha they are situated in the layers II-III. Suprafundal and fundal parts of the field do not possess pyramidal atypical neurons and are characterized with presence of large amount of the stellate neurons. In respect to the axonal branching in the suprafundal part of the field 4, 2 types of the stellate cells are distinguished.

Synaptic connections of an interneuron with axonal arcades in the cat visual cortex

A single, isolated interneuron with axonal arcades in the cat visual cortex was analysed in detail by both light and electron microscopy. The neuron was impregnated by the Golgi-Kopsch method, gold-toned, and processed for electron microscopy using the ethanolic phosphotungstic acid (PTA) staining method of Bloom & Aghajanian (1968). These methods, in combination, resulted in the successful identification of a large number of synaptic boutons arising from the axon of the cell under study. We examined serially at the electron microscope level 210 boutons of the axonal arborization of the cell. Of these, 152 formed identifiable symmetrical synaptic contacts with a variety of postsynaptic elements. The vast majority of the postsynaptic targets were dendritic profiles, which represented 95.7% of all the synaptic contacts identified. Only one example was observed of two labelled boutons making contacts with the same postsynaptic element; the rest were apparently on different elements. This distribution of synapses, characterized by the lack of convergence, is very similar to that reported by other authors for a certain kind of double bouquet cell which, in turn, shares some morphological features with the neurons with axonal arcades. It is suggested that fine details of the geometry of the axonal arborization of a given cell are an important reflection of the distribution of its synapses.

Dendritic maturation in cat retinal ganglion cells: a Lucifer yellow study

The dendritic morphology of developing cat alpha- and beta-retinal ganglion cells was investigated by intracellular injection of Lucifer yellow. In both cell classes the basic pattern of adult morphology was present at birth. However, the presence of transient small spiny protrusions along the dendrites was characteristic of early postnatal cells. Many alpha-cells were further distinguished by a small degree of dendritic bi-stratification which disappeared within the first 5 postnatal days. Therefore during the period before the eyes opened (P7-P10) there was a considerable degree of modification and maturation in dendritic morphology in both classes of retinal ganglion cells. alpha- and beta-cells exhibited differing temporal patterns of dendritic growth, which argues against a 'passive-stretching' hypothesis that explains dendritic field enlargement solely as an effect of retinal areal growth.

Effect of tetraploidy on dendritic branching in neurons and glial cells of the frog, Xenopus laevis

Morphological aspects of four different groups of Golgi impregnated brain cells from a tetraploid strain of Xenopus laevis frogs were compared to analogous cells in comparably sized diploid frogs. The cells examined included neurons from the telencephalon, caudal hypothalamus, and optic tectum, and radial glial cells from the optic tectum. The brains of tetraploid frogs appeared grossly normal and were the same size and contained similar cell types as diploid brains. As observed in previous studies on polyploid amphibia, somal diameters increased significantly in tetraploid cells for each of the four groups of cells examined. Also, the total length of the dendritic arbors in tetraploid brain cells increased significantly by factors ranging from 1.4 to 2.4 times the total length of the analogous processes in diploid cells. Tetraploid neurons in the telencephalon and hypothalamus increased their arbor lengths predominantly by increasing the number of dendritic branches, while maintaining the average distance between branch points in the dendritic segments. In contrast, the tetraploid large pear-shaped neurons in the optic tectum had significantly longer terminal dendritic segments than the analogous diploid neurons, although these tetraploid neurons maintained their average number of dendritic segments per cell. Tetraploid tectal radial glial cells appeared to increase both their number of branches and the lengths of their terminal segments. Thus, the mode by which tetraploid brain cells achieved longer dendritic arbors varied from cell type to cell type. These results suggest a hypothetical basis for possible effects of genomic size on vertebrate brain structure and evolution at the cellular level.

Stages in the structural differentiation of retinal ganglion cells

Using a cultured wholemount technique we have studied the morphological differentiation of ganglion cells in the retina of the rat and cat, during normal development. In both species the differentiation of ganglion cells begins in embryonic life, before embryonic day (E) 17 in the rat and E36 in the cat. It is useful to describe the morphological differentiation of ganglion cells as occurring in three stages. In the first stage, each germinal cell becoming a ganglion cell extends an axon into the fibre layer of the retina and towards the optic disc, and the soma of the cell moves towards the ganglion cell layer. As the soma approaches the ganglion cell layer, the processes that attach its poles to the inner and outer surfaces of the retina are withdrawn. When the soma reaches the ganglion cell layer, a stage of active dendritic growth begins, which lasts until shortly before birth in the cat and until several days after birth in the rat. The cell extends stem dendrites that branch profusely and are commonly tipped by growth cones. The major morphological classes of ganglion cell become distinct in the latter part of stage 2, as do the centroperipheral gradients in ganglion cell size apparent in the cat. During the third stage, the dendritic trees of ganglion cells no longer branch or extend by means of active growth cones. Very considerable growth of all parameters of the cell (soma size, dendrite calibre and length, axon calibre) occurs nevertheless, presumably by interstitial addition of membrane throughout the cell.

Polymorphism of age-related changes in stimulatory capacity of murine dendritic cells

All through life, regulatory and executive components of the immune system undergo changes, differing in rate and extent, dependent on the genetic background. We have, here, examined age-dependent changes in stimulatory capacity of dendritic cells (DC) in allogeneic mixed leukocyte reaction (MLR). DC of mice of five strains showed very little change as they aged. DC from mice of two other strains showed a significant age-related decrease of stimulatory activity and those of one strain showed an increase. The capacity of DC to stimulate syngeneic MLR was examined in three strains, as a function of age, and was found to decrease in one and to slightly increase in two. The underlying cause for this extensive polymorphism remains to be determined. We could not find supporting evidence for the view that the observed changes were related to changes in Ia density on dendritic cells.

Isolation of embryonic chick motoneurons and their survival in vitro

This is the first of a series of 4 papers in which we describe the regulation of excitatory amino acid receptors on embryonic chick motoneurons dissociated from the lateral motor column and maintained in cell culture. Techniques are described for labeling embryonic chick motoneurons in vivo with Lucifer Yellow or fluorescein isothiocyanate conjugates of wheat germ agglutinin (Fl-WGA). We estimate that 65-95% of the motoneurons in the lateral motor column survive tissue dissociation and settle on an appropriate culture surface. The number of fluorescent motoneurons observed in heterogeneous spinal cord cell cultures decreases with a half-life of 2 d. The decline is due to fading of the fluorescent tracer rather than to loss of cells. Techniques are also described for separating motoneurons from other spinal cord cells with a fluorescence-activated cell sorter. Approximately 24% of the motoneurons in the lateral motor column can be isolated, and motoneurons comprise more than 90% of the population in cultures seeded with sorted cells. The survival of sorted and unsorted motoneurons in vitro is enhanced in the presence of skeletal myotubes or muscle conditioned medium, but the survival of non-motoneurons is not influenced by muscle. Electrophysiologic properties of sorted and unsorted motoneurons determined with patch-clamp techniques are similar. Both differ from mature motoneurons in their lower resting membrane potential (-50 mV), larger input resistance (450 M omega), and longer time constant (39 msec). Also they do not exhibit anomalous rectification or a calcium-activated potassium after hyperpolarization. Motoneurons grown in the absence of interneurons differ from motoneurons in heterogeneous spinal cord cell cultures in that their neurites (dendrites) are shorter and they branch less often.

The sources of the nigrotectal pathway

The nigrotectal pathway plays a role in the generation of saccade related responses by cells in the deep layers of the superior colliculus. By using a retrograde horseradish peroxidase technique that homogeneously fills neurons, the present experiments demonstrate that the source of the nigrotectal projection to the intermediate gray layer of the grey squirrel (Sciurus carolinensis) is a heterogeneous population of neurons whose somas and dendrites are concentrated in the rostral pole of pars reticulata. This region of pars reticulata receives projections from the posterior caudate, which in turn is a target of both the pulvinar and visual cortex. In addition, these experiments reveal the presence of a second, distinct set of neurons projecting to the midbrain tectum that are located in pars lateralis of the substantia nigra. These neurons can be distinguished from those in pars reticulata by their homogeneity and by their prominent basal dendrites. Furthermore, pars lateralis of the squirrel substantia nigra is, on cytoarchitectonic and immunocytochemical grounds, a distinct subdivision that does not receive projections from the posterior caudate. We conclude that both pars reticulata and lateralis are sources of the nigrotectal pathway. In addition, our results suggest, on connectional grounds, that the rostral pole of pars reticulata may be specialized to subserve the visual guidance of orienting movements.

Morphology and electrophysiological properties of reticularis thalami neurons in cat: in vivo study of a thalamic pacemaker

Reticularis thalami neurons (RE neurons) were identified morphologically, and their electrophysiological properties were studied in cat under barbiturate anesthesia. Intracellular HRP injections showed that RE neurons possessed very long dendrites bearing numerous filopodia-like appendages and that their axons were directed toward main thalamic nuclei. As a rule, small axonal branches were also emitted within the RE nucleus itself. At rest, the membrane potential of RE neurons displayed 2 types of oscillations: a slow 0.1-0.2 Hz oscillation and fast 7-12 Hz oscillations occurring on the positive phase of the former. Episodes of spindle (7-12 Hz) waves lasted for 2-3 sec and were characterized by rhythmic depolarizations and burst discharges. Intracellular injections of QX314 and current pulse analyses revealed the presence in RE cells of 2 distinct inward currents: a persistent current that promoted tonic firing and a low-threshold current deinactivated by hyperpolarization that generated burst discharges. The low-threshold current deinactivated with large somatic hyperpolarizations (up to 30 mV) and produced depolarizing responses that lasted for about 70 msec. In addition, low-threshold responses appeared rhythmically at intervals of about 150 msec after recovery of the membrane potential from hyperpolarization. Because of their duration, voltage dependence, and persistence after intracellular injections of QX314, it is suggested that these responses resulted from activation of a low-threshold Ca2+ current at the dendritic level. In QX314-injected cells, selective components of spontaneous oscillations were abolished, among them the positive phase of the slow oscillation and late depolarizing humps that followed burst discharges within spindle sequences. However, the rhythmic occurrence of spindle episodes at 0.1-0.2 Hz was never affected by DC currents or by QX314 or Cl- injections, suggesting that oscillations within a particular RE neuron partly reflected the oscillatory behavior of a network of cells. On the basis of these electrophysiological results and the known morphological and neurochemical features, a new hypothesis is proposed to account for the rhythmicity of RE neurons.

Integrative mechanisms controlling directional sensitivity of an identified sensory interneuron

Several identified interneurons in the cricket cercal afferent system display directional sensitivity to wind stimuli: the spike frequency of these cells depends on the wind direction with respect to the animal's body. Factors determining the directional sensitivity of one of these identified interneurons (interneuron 10-3) were studied in detail. This cell has 3 dendritic branches that arborize in 3 distinct regions of the terminal abdominal ganglion. Using 2 independent methods, it was demonstrated that the dendrites have different receptive fields to wind stimuli. First, small patches of filiform hairs, whose afferents projected to individual dendrites, were isolated and selectively stimulated. In each case the response of the cell matched the receptive field of the afferents in the patch. Second, a laser beam directed through the stereo dissecting microscope was used to photoinactivate small portions of the cell in situ during intracellular recording. By isolating or ablating individual dendrites, the contributions of each of the 3 dendrites to the overall receptive field were assessed. Although the receptive field of the whole cell could be predicted by a summation of the receptive fields of all 3 dendrites, the precise directional sensitivity of the cell could not be predicted by a simple linear summation of the receptive fields of each dendrite. Two factors were found to account for this nonlinearity of summation. The first factor was polysynaptic inhibition from other interneurons within the terminal abdominal ganglion. Wind directions that activate inhibition in interneuron 10-3 were identified, and the specific classes of filiform afferents that activate the inhibitory pathway were determined. The net effect of the inhibition was to "sharpen" the directional sensitivity of 10-3 by selectively decreasing the cell's response to specific excitatory inputs. The second factor that contributed to directional sensitivity was the complex electroanatomy of the interneuron. The probable location of the spike-initiating zone (SIZ) was determined by using the laser photoinactivation technique. The relative efficacies of synaptic inputs onto the 3 different branches were then interpreted with respect to their different electrotonic distances from the SIZ. On the basis of the data obtained in this report, we present a qualitative model for the basis of directional sensitivity in this cell.

Retinal constraints on orientation specificity in cat visual cortex

Most retinal ganglion cells (Levick and Thibos, 1982) and cortical cells (Leventhal, 1983; Leventhal et al., 1984) subserving peripheral vision respond best to stimuli that are oriented radially, i.e., like the spokes of a wheel with the area centralis at the hub. We have extended this work by comparing directly the distributions of orientations represented in topographically corresponding regions of retina and visual cortex. Both central and peripheral regions were studied. The relations between the orientations of neighboring ganglion cells and the manner in which the overrepresentation of radial orientations is accommodated in the functional architecture of visual cortex were also studied. Our results are based on an analysis of the orientations of the dendritic fields of 1296 ganglion cells throughout the retina and the preferred orientations of 1389 cells located in retinotopically corresponding regions of cortical areas 17, 18, and 19 in the cat. We find that horizontal and vertical orientations are overrepresented in regions of both retina and visual cortex subserving the central 5 degrees of vision. The distributions of the orientations of retinal ganglion cells and cortical cells subserving the horizontal, vertical, and diagonal meridians outside the area centralis differ significantly. The distribution of the preferred orientations of the S (simple) cells in areas 17, 18 and 19 subserving a given part of the retina corresponds to the distribution of the dendritic field orientations of the ganglion cells in that part of retina. The distribution of the preferred orientations of C (complex) cells with narrow receptive fields in area 17 but not C cells with wide receptive fields in areas 17, 18, or 19 subserving a given part of the retina matches the distribution of the orientations of the ganglion cells in that part of retina. The orientations of all of the alpha-cells in 5-9 mm2 patches of retina along the horizontal, vertical, and oblique meridians were determined. A comparison of the orientations of neighboring cells indicates that other than a mutual tendency to be oriented radially, ganglion cells with similar orientations are not clustered in the retina. Reconstructions of electrode penetrations into regions of visual cortex representing peripheral retina indicate that columns subserving radial orientations are wider than those subserving nonradial orientations. Our results provide evidence that the distribution of the preferred orientations of simple cells in visual cortex subserving any region of the visual field matches the distribution of the orientations of the ganglion cells subserving the same region of the visual field.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunocytochemical localization of tubulin and microtubule-associated protein 2 during the development of hippocampal neurons in culture

In dissociated-cell cultures prepared from the embryonic rat hippocampus, neurons establish both axons and dendrites, which differ in geometry, in ultrastructure, and in synaptic polarity. We have used immunocytochemistry with monoclonal antibodies to study the regional distribution of beta-tubulin and micro-tubule-associated protein 2 (MAP2) in hippocampal cultures and their localization during early stages of axonal and dendritic development. After development for a week or more in culture, when axons and dendrites were well-differentiated, the distribution of these two proteins was quite different. Beta-tubulin was present throughout the nerve cell, in soma, dendrites, and axon. It was also present in all classes of non-neuronal cells, astrocytes, fibroblasts, and a presumptive glial progenitor cell. In contrast, MAP2 was preferentially localized to nerve cells; within neurons, MAP2 was present in soma and dendrites, but little or no immunostaining was detectable in axons. Both beta-tubulin and MAP2 were present in nerve cells at the time of plating. From the earliest stages of process extension, beta-tubulin was present in all neuronal processes, both axons and dendrites. Surprisingly, MAP2 was also initially present in both axons and dendrites, extending as far as the axonal growth cone. With subsequent development, MAP2 staining was selectively lost from the axon so that after 1 week in vitro little or no axonal staining remained. Taken together with earlier results (Cáceres et al., 1984a), these data indicate that the establishment of neuronal polarity, as manifested by the molecular differentiation of the axonal and dendritic cytoskeleton, occurs largely under endogenous control, even under culture conditions in which cell interactions are greatly restricted.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphology of HRP-injected spinocervical tract neurons: effect of dorsal rhizotomy

Twenty-five physiologically identified spinocervical tract (SCT) neurons in the sixth lumbar segment of the cat were filled with HRP by intracellular injection. All were reconstructed from sagittal sections using the camera lucida, and a subset (n = 18) was also reconstructed using a computer reconstruction system. Thirteen cells were in intact preparations, nine were in spared root preparations (L5, L6, S1, S2 cut; L7 spared), and three were in preparations with L5 through S2 cut. Analysis of the dendritic tree of these neurons revealed little change in gross morphology after partial deafferentation despite increased proportions sensitive to nociceptive input (Sedivec et al., 1983). The dendrites still largely respected the lamina II-III border, and relatively few dendrites were directed ventrally from the cell body, although the ratio of ventral to dorsal dendrites was greater than normal. The major change was an increase in surface area and volume caused by changes in diameter (but not length) of the dendrites. Larger-than-usual maximum branch order of individual dendritic trees of some cells was also observed after chronic deafferentation. Thus, SCT cells in deafferented segments do not undergo atrophy, but show, rather, limited signs of growth and the possibility of dendritic reorganization. We have also computed correlations between different parameters of these cells (cell body size, number and size of primary dendrites, total area and length of individual dendrites) and have found that, as in motoneurons, diameter of the primary dendrite measured 30 micron from the soma is significantly correlated with total dendritic surface area and length. SCT neurons tend to have more dendrites than spinal alpha-motoneurons, but total surface area is smaller for a given diameter of a proximal dendrite.

A functional organization of ON and OFF pathways in the rabbit retina

Intracellular electrophysiological recordings were obtained from amacrine and ganglion cells in an isolated, superfused retina-eyecup preparation of the rabbit. Cells were characterized physiologically, after which cell-staining was accomplished by intracellular iontophoresis of HRP. A computer-assisted image-processing system was used to study the dendritic stratification pattern of HRP-labeled neurons within the inner plexiform layer (IPL). Our results support the concept that the IPL is functionally divided into a distal OFF region and proximal ON layer. ON and OFF ganglion and amacrine cells show dendritic arborizations consistent with this division and ON-OFF ganglion cells have processes in both portions of the IPL. It appears that these functional subdivisions of the IPL reflect excitatory, but not necessarily inhibitory, inputs. Thus, the pattern of dendritic arborization of a cell appears to predict its physiological response polarity, regardless of the type of inhibition it receives.

Wide-spreading terminal axons in the inner plexiform layer of the cat's retina: evidence for intrinsic axon collaterals of ganglion cells

Extracellular, iontophoretic injections of horseradish peroxidase (HRP) were made directly into the cat's retina. The retinas were processed with the cobalt-enhanced diaminobenzidine method and prepared as whole-mounts. These retinas reveal HRP-filled axons that extend widely and terminate within the inner plexiform layer. The axons are morphologically distinct from ganglion and amacrine cell dendritic trees that were retrogradely labelled from the same injection sites. The axons are long and straight, approximately 1 micron in diameter, and in some cases can be traced for several millimeters in the inner plexiform layer. Each axon gives rise to many short, terminal branches that extend, on average, 100 microns from the parent axon and bear clusters of boutons. The terminal branches are widely spaced so that the bouton clusters are distributed in small, isolated patches along the length of the axon. Bouton clusters vary in size and contain from two to over 100 loosely arranged boutons. Single boutons are frequently large, up to 3 microns in diameter. In one case a terminal axon was traced to its origin from the parent axon of an HRP-filled ganglion cell. It is suggested, therefore, that these axons are intrinsic to the retina and originate as primary collaterals of ganglion cells.

Dendritic plasticity in the early postnatal feline retina: quantitative characteristics and sensitive period

Retinal lesions were made in kittens between 3 and 60 days postnatal age and in adult cats. After postlesion survival times ranging from 4 to 11 months the dendritic morphology of retinal ganglion cells was revealed by retrograde labeling with horseradish peroxidase or with neurofibrillar staining techniques. After retinal lesions on the third postnatal day changes of dendritic morphology were observed in retinal ganglion cells adjacent to regions of retrograde degeneration. Originating from eccentrically positioned somata the dendritic fields extended into the regions that were free of neighboring cells. The dendrites oriented toward the ganglion-cell-free region were elongated and thicker than normal. The density of dendrites per unit area was increased in this part of the dendritic trees. Lesions on the 20th, 38th, and 56th postnatal days elicited increasingly weaker changes of dendritic morphology. The sensitive period for the type of dendritic plasticity described ends between 40 and 60 days postnatally.

Dendritic development in the neocortex of adult rats subjected to postnatal malnutrition

The Golgi-Cox method was used to study the maturation of the large pyramidal cells of the Vth cortical layer in two groups of adult rats, one subjected to early postnatal malnutrition and another malnourished only during the second month of life. The main alterations were observed in the pyramidal cells of cortical layer V of rats malnourished during the first month of life. They consist of a decrease in the number and span of dendritic basilar processes. In animals malnourished during the second month of life, the number and span of basilar dendritic processes in pyramidal cells of layer V, were normal. It is postulated that early postnatal malnutrition induced immediately after birth, profoundly disturbs the process of neuronal maturation in the neocortex of the rat brain, probably with permanent effects.

Correlations between the structural and functional characteristics of neurons in the superficial laminae and the hamster's superior colliculus

Intracellular recording, receptive field mapping, and horseradish peroxidase (HRP) injection techniques were used to determine the structural and functional characteristics of neurons in the superficial laminae (stratum griseum superficiale and stratum opticum) of the hamster's superior colliculus (SC). Fifty-nine neurons (from 38 different hamsters) were successfully characterized, injected with HRP, and recovered. Of these, 8 were marginal cells, 14 had stellate morphology, 10 had narrow, vertically oriented dendritic trees, 12 had wide, vertically oriented dendritic arbors, and 8 were horizontal cells. Seven neurons had somatodendritic morphologies which did not fall into any of these groups. Overall, the distribution of receptive field properties for these cells matched that obtained in previous extracellular recordings from the superficial SC laminae in this species (Chalupa, L.M., and R.W. Rhoades (1977) J. Physiol. (Lond.) 270: 595-626; Chalupa, L.M. and R.W. Rhoades (1978) J. Physiol. (Lond.) 274: 571-592). There were significant correlations between receptive field properties and morphology. Sixty-four percent of the stellate cells and 75% of the marginal cells were directionally selective. Only 17% of the other cell types exhibited this response property. In addition, only 36% of the stellate cells and 25% of the marginal neurons were discharged by stationary, flashed spots. Eighty-one percent of the other recovered cells gave reliable responses to such stimuli. Stellate and marginal cells could also be differentiated from the other cell types on the basis of speed selectivity. Only 29% of the stellate and 13% of the marginal cells responded to stimulus speeds in excess of 20 degrees/sec.(ABSTRACT TRUNCATED AT 250 WORDS)

The dendritic architecture of the medial terminal nucleus of the accessory optic system in the rat, rabbit, and cat

The neurons of the medial terminal nucleus (MTN) of the accessory optic system (AOS) have been studied in the rat, rabbit and cat in Golgi-Cox and Golgi-Kopsch impregnated brain sections. The present anatomical findings permit a division of the MTN of these species into dorsal and ventral components (MTNd, MTNv), in agreement with other investigations. The MTNd contains predominantly linear-bipolar and linear-multipolar shaped neurons with cell bodies that measure in the range of 25-50 microns. These neurons have 2 to 4 primary dendrites which, along with their smaller dendritic branches, are oriented in the plane of the long axis of the MTN (i.e. from ventromedial to dorsolateral). These linear-bipolar and linear-multipolar cells represent 70-80% of the neurons of the MTNd as seen in the Golgi impregnated sections. The remaining 20-30% of the MTNd neurons are nearly all multipolar in shape with somata measuring in the range of 15-25 microns. An occasional multipolar neuron is larger, has a soma that measures around 30-60 microns and has dendrites which extend outward from the cell body to cover large areas of the MTNd. There was considerable extension of the dendrites of MTNd neurons into the MTNv; however, the dendrites of MTNd neurons were not observed extending into the adjacent substantia nigra (SN) or ventral tegmental area (VTA) of Tsai (1925). Conversely, the dendrites of neurons in the neighboring SN and VTA course along the borders of the MTN but only occasionally extend into the MTN.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphologic and functional abnormalities that develop in kitten Purkinje neurons during maintenance for months after maturation in organotypic cultures

The morphologic and functional properties of the Purkinje cells (P-cells) grown for 10-11 weeks in organotypic cultures from newborn kitten cerebella were studied and compared to cultures which had been grown for 4-5 weeks under the same standard conditions. Electrophysiological and morphological data were obtained from HRP iontophoretically labeled neurons and were quantified by means of computerized techniques. Extracellular recordings of spontaneous activity showed that the 10-11-week-old P-cells had a pacemaker-like firing rate whereas the P-cells aged 4-5 weeks in vitro displayed a bursting activity. The qualitative morphological data evidenced abnormal swellings both on dendritic and axonal processes of the 10-11-week-old P-cells which were not present on the 4-5-week-old P-cells. The quantitative data revealed a significant decrease in the overall size of the dendritic network of the 10-11-week-old P-cells mainly due to a reduction in the total dendritic length and in the total number of dendritic segments, whereas the individual segment lengths remained almost unchanged. Dendritic spine counts showed no decrease in the dendritic density of these older P-cells. Such data suggest that the changes observed in 10-11-week-old cultured P-cells may be compared to the age-related changes occurring in vivo and that such in vitro models could be useful tools in the study of the pathology of aging. However, alternative factors other than senescence are discussed since they may account for some degenerative changes observed in the older cultured P-cells.

Independent steroid control of the fates of motoneurons and their muscles during insect metamorphosis

The metamorphosis of insects is controlled by the blood titers of a small number of developmental hormones including a class of steroids, the ecdysteroids. We have studied the developmental fates of several muscles and their motoneurons during the larval-pupal transformation of the tobacco hornworm, Manduca sexta. The endocrine events which trigger pupal development are first, a fall in the blood titer of juvenile hormone, followed by two subsequent elevations of blood ecdysteroids. The small "commitment pulse" of ecdysteroids commits tissues to pupal development, whereas the sustained "prepupal peak" causes the new pupa to be formed (Riddiford, L. M. (1980) In Progress in Ecdysone Research, J.A. Hoffmann, ed., pp. 409-430, Elsevier/North-Holland Biomedical Press, Amsterdam). In the present experiments we were able to correlate specific aspects of the changing blood steroid titers with the degeneration of larval muscles, and with the dendritic regression and death of their motoneurons. The abdominal prolegs, which are the principal locomotory appendages of the caterpillar, are lost during the larval-pupal transformation. We have followed the fates of a proleg retractor muscle, PPRM, and its single motoneuron, PPR. Two other differently fated abdominal muscles not associated with the proleg were also studied. Surgical and endocrinological manipulations showed that PPRM degenerates in response to the rising phase of the prepupal ecdysteroid peak and that interactions with its motoneuron are not involved in the muscle's death. Motoneuron PPR responds to the rising prepupal peak by first reducing its dendritic arbor by 40% and then dying. Other proleg motoneurons regress but do not die, indicating that dendritic regression is programmed separately from neuronal death. Neither the dendritic reduction nor the death of PPR involves interactions with its target muscle. These results indicate that ecdysteroids have independent and parallel effects in the periphery, where they cause muscle degeneration, and in the central nervous system, where they cause dendritic regression and death of motoneurons.

The morphology of physiologically identified GABAergic neurons in the somatic sensory part of the thalamic reticular nucleus in the cat

Neurons with somatic sensory receptive fields were examined electrophysiologically in the thalamic reticular nucleus of the cat. All cells had receptive fields much larger than those of neurons in the ventral posterior nucleus and were driven by less readily defined somesthetic stimuli. Response latencies to peripheral or medial lemniscal stimulation were, on average, longer than in the ventral posterior nucleus and suggested activation of the reticular nucleus cells by collaterals of thalamocortical relay cell axons arising in the ventral posterior nucleus. When injected intracellularly with horseradish peroxidase, reticular nucleus cells displayed thin axons with intrareticular collaterals and diffuse branches through much of the ventral posterior and posterior thalamic nuclei. Dendrites ended in processes resembling synaptic terminals. Electron microscopic immunocytochemistry of the same part of the reticular nucleus revealed processes immunoreactive for glutamic acid decarboxylase and identifiable as both collateral axon terminals and presynaptic dendrites of GABAergic reticular nucleus cells. These synaptically linked reticular nucleus cells and, in addition, immunoreactive somata and presynaptic dendrites received synapses from at least three varieties of nonimmunoreactive profiles.

The dendritic morphology of hippocampal dentate granule cells varies with their position in the granule cell layer: a quantitative Golgi study

The dendritic morphology of Golgi-stained hippocampal dentate granule cells was evaluated by measuring the amount and location of dendrite, and the number of length of dendritic branches. Granule cells with somata in the superficial third of the granule cell layer has substantially more dendritic material than those with somata in the deep portions of the cell layer; this difference occurred throughout the extent of the molecular layer. Superficial cells also had different dendritic branching patterns and wider dendritic fields than did cells located in the deeper two-thirds of the granule cell layer. These results indicate that the position of neurons within the cell layer should be taken into account when quantifying the dendritic fields of dentate granule cells.

The function of dendritic spines: a theoretical study

A modeling procedure is proposed which introduces the cable equivalent of dendritic spines into the Rall model of spiny interneurons in the spinal cord. At this point combined morphological and physiological works have given some insight into the possible role of a single spine and the function of a single spine has been studied by theoretical computations [Jack, Noble and Tsien (1975) Electric Current Flow in Excitable Cells, pp. 218-223. Oxford University Press, Oxford; Koch and Poggio (1983) Trends Neurosci. 6, 80-83; Perkel (1983) J. Physiol., Paris 78, 695-699]. The goal of the present paper is two-fold: (a) to stress the gross function of the spine system in the excitability of dendrites; and (b) to emphasize the role of spines in the dynamic input/output function of neurons. The simulation procedure is based on the well-known compartmental method. (1) The kinetics of active somatic and dendritic compartments are taken from a currently available spinal interneuron model to match the physiological data of large dorsal horn neurons carrying spines. (2) Beside the prolongation of the somatic excitatory postsynaptic potential, the model suggests that the spiny neuron increases the differences in the latency and height of excitatory postsynaptic potential as a function of the electrotonic position of input. The characteristics of the excitatory postsynaptic potential can be modified by the changes in spine geometry and the ratio of cytoplasmic resistances of spine stalk to that of main dendritic shaft. (3) Dendritic electroresponsiveness, which was already postulated for dorsal horn neurons, is analysed by the model including calcium and slow potassium systems. It is concluded that the participation of the spine stalk in active processes can highly modify the input dependence of response pattern. Depolarization-dependent Ca2+ accumulation in spines may reflect the interaction of spine stalks. (4) Passive antidromic spread of action potential can be suppressed in spiny cells. Analysis of active antidromic spread shows the probable importance of spines located near the soma. Centripetal vs centrifugal conduction of dendritic action potential may depend on the spine distribution along the tree and change in electrical parameters of spines.

A morphological investigation of thalamic neurons by intracellular HRP staining in cats

Morphological analysis of 77 neurons in the ventroanterior (VA), ventrolateral (VL), ventromedial (VM), and central lateral (CL) nuclei was performed by intracellular HRP staining in combination with electrophysiological studies. The neurons were classified into four groups according to either electrophysiological or morphological criteria, i.e., 20 relay neurons (18 thalamocortical (T-C) and two thalamocaudate (T-Cd) relay neurons), 17 projection neurons, 36 unidentified neurons, and four presumed interneurons. All 36 unidentified neurons had morphological features similar to those of relay and projection neurons. All neurons except four presumed interneurons had dendrites sparsely covered with spinelike appendages. Most of their dendrites displayed a spherically radiating branching pattern, and a few showed a tufted or linearly oriented pattern. Sizes of somata and dendritic radii were compared in entopeduncular (Ent)-responsive (n = 25) and cerebellar (CN)-responsive groups (n = 37) in VA, VL, and VM nuclei. The soma size was similar in VL (18-21 X 29-34 micron) and VM (15-19 X 29-31 micron), but in VA, CN-responsive neurons (15 X 30 micron) seemed to be smaller than Ent-responsive ones (22 X 36 micron). The largest dendritic field of neurons in each thalamic nucleus was similar in both groups. They were about 250-320 micron in radius. Diameters of axons were also compared but no statistically significant difference was detected (i.e., 1.5 +/- 0.3 (mean +/- S.D.) micron for the Ent group and 1.7 +/- 0.5 micron for the CN group). Three types of axonal trajectories were noted, i.e., neurons projecting their axons dorsolaterally, ventrolaterally, or horizontally. Fourteen neurons out of 37 relay and projection neurons gave off several fine distal axon collaterals in the thalamic reticular nucleus, and one T-Cd, three projection, and one unidentified neurons gave off proximal axon collaterals near the soma-dendritic domain in addition to those in the thalamic reticular nucleus. Four neurons classified as presumed interneurons had smaller somata (9-13 X 18-23 micron) and varicose dendrites. Three of them received Ent-induced inhibitory postsynaptic potentials (IPSPs) or CN-induced excitatory postsynaptic potentials (EPSPs). Several presumed axon terminals were found to cover the soma of an adjacent neuron, which seemed to indicate their inhibitory nature. The proximal axon collaterals in the ventral thalamic nuclei may consist of local inhibitory circuits with presumed interneurons in addition to other inhibitory circuits with thalamic reticular neurons.

Light microscopic analysis of Golgi-impregnated rat subthalamic neurons

The neuronal morphology of the rat subthalamic nucleus (STH) was studied using Golgi techniques and Nissl stain. The results show that the somatic shapes of STH neurons vary from fusiform to oval or polygonal. Somatic cross-sectional areas vary between 140 microns2 and 440 microns2. Some of the cells have a few somatic spines. Two to six primary dendrites gave rise to tapering daughter dendrites which extend up to 500 microns. These dendrites are sparsely covered with spines. Some distal dendrites and primary dendrites of the STH also bear filiform appendages. Neurons located in the deep portion of the STH have oval dendritic fields whose long axis is parallel to the long axis of the nucleus in frontal or sagittal planes. Some of these neurons have one or two dendrites which cross the borders of the STH into the zona incerta, the lateral hypothalamus, or the cerebral peduncle. Generally, neurons located at the borders of the STH have their dendritic fields extending parallel to the borders and are confined to the nucleus. However, some neurons adjacent to the ventrolateral border of the nucleus have some dendrites extending into the cerebral peduncle. Quantitative analysis of the STH neurons showed a unimodal distribution of somatic sizes as well as the number of primary dendrites. No neurons with obvious Golgi type II characteristics were found. Two types of afferent fibers were observed entering the STH. One type consists of axon collaterals arising from the cerebral peduncle ventrolaterally, or the internal capsule rostrally, while the other enters the nucleus after crossing the internal capsule rostrally. These results suggest that the rat STH is an open nucleus in contrast to other species such as man, monkey, and cat, where it is closed, and that the rat STH may contain only one type of neuron.

Postnatal development of the superficial layers in the rat superior colliculus: a study with Golgi-Cox and Klüver-Barrera techniques

The postnatal development of the superficial (optic) layers of the rat superior colliculus has been studied using Klüver-Barrera staining and Golgi impregnation in rats aged 3-45 days. The Klüver-Barrera staining reveals that the SC of 3 day old rats is morphologically immature with no obvious lamination. It contains densely packed cells of uniform size. The packing density of the cells gradually decreases between 9 and 15 days as the thickness of the layers increases. The first myelinated fibres in the SC appear at 15 days but the stratum opticum is still not recognizable. By 30 days, the SC has a distinctly laminated appearance, but the thickness of the superficial layers continues to increase until day 45 postnatal. Golgi-Cox impregnation displays the range of neuronal types in the superficial layers of the SC previously described by Langer and Lund (1974). Using the morphological criteria of these authors for classification of the neurons, the developmental changes of the marginal cells, horizontal cells, ganglion cells types I, II, III and stellate cells have been followed. The SC of 3 day old rats contains immature neurons; only a few larger cells have branched dendrites. In 9 days old SC the neuronal types present in the adult are recognizable, although their appearances are still immature. By 15 days neurons have adult-looking dendritic trees but dendritic growth continues beyond 30 days. The visual part of the SC has a protracted period of postnatal development, the sequence of developmental changes being similar for the different types of collicular neurons. Features common to development are the increasing size of neuronal somata, the increasing length of dendrites and the acquisition of a complex pattern of dendritic arborization. Larger cells appear to commence development earlier than small cells, although the rate of developmental changes is different for each of the various types of collicular neurons.

Ultrastructural documentation of M241 glycoprotein on dendritic and endothelial cells in normal human skin

M241 is a glycoprotein that recently has been demonstrated to be present in human thymus in a distribution similar to T6. Studies in skin, however, suggest that M241, in contrast to T6, is detected only on a subset of Langerhans cells and on a population of dendritic cells in the superficial dermis. We compared the reactivities of monoclonal antibodies to M241 and T6 with dendritic cells in normal human skin using immunoelectron microscopy. Our findings indicate that M241 is present on a minority of Langerhans cells and on a substantial number of other predominantly dermal dendritic cells with morphologic features of indeterminate cells. Anti-M241 reactivity was generally restricted to the cell membrane, although cytoplasmic reactivity was detected in some Langerhans cells. Dermal endothelial cells, which like dendritic cells are capable of antigen presentation, were also reactive with anti-M241 antibody. M241 is a glycoprotein, different from T6, with a tissue distribution potentially relevant to the understanding of antigen-presenting cells in the skin.

Dendritic development in the isthmo-optic nucleus of chick embryos

In the mature isthmo-optic nucleus, the neuronal perikarya are arranged in a convoluted lamina surrounding the neuropil, and the primary dendrites of each neuron project perpendicular to the lamina into the neuropil. Thus, the neurons are highly polarized. It was previously believed that this mature morphology was the result of remodelling during the last week of embryogenesis, and that the neurons were initially multipolar and nonpolarized. We here show that as early as embryonic day 12 the neurons are already polarized, with a morphology resembling that in older embryos and hatched chicks. However, the neurons in the core of the isthmo-optic nucleus are almost all polarized ventrally or ventromedially at this age, whereas they later take on many different orientations. In contrast, most neurons near the border of the nucleus already have inwardly polarized dendrites, as in hatched chicks.

A golgi study of the optic tectum of the tegu lizard, Tupinambis nigropunctatus

The dendritic patterns of cells in the optic tectum of the tegu lizard, Tupinambis nigropunctatus, were analyzed with the Ramon-Moliner modification of the Golgi-Cox technique. Cell types were compared with those described by other authors in the tectum of other reptiles; particular comparisons of our results were made with the description of cell types in the chameleon (Ramń, 1896), as the latter is the most complete analysis in the literature. The periventricular gray layers 3 and 5 consist primarily of two cell types--piriform or pyramidal shaped cells and horizontal cells. Cells in the medial portion of the tectum, in an area coextensive with the bilateral spinal projection zone, possess dendrites that extend across the midline. The latter cells have either fusiform or pyramidal shaped somas. The central white zone, layer 6, contains fibers, large fusiform or pyramidal shaped cells, fusiform cells, and small horizontal cells. The central gray zone, layer 7, is composed predominately of fusiform cells which have dendrites extending to the superficial optic layers, large polygonal cells, and horizontal cells. The superficial gray and white layers, layers 8-13, contain polygonal, fusiform, stellate, and horizontal elements. Layer 14 is composed solely of afferent optic tract fibers. Several differences in the occurrence and distribution of cell types between the tegu and the other reptiles studied are noted. Additionally, the laminar distribution of retinal, tectotectal, telencephalic, and spinal projections in the tegutectum can be related to the distribution of cell types, and those cells which may be postsynaptic to specific inputs can be identified. The highly differentiated laminar structure of the reptilian optic tectum, both in regard to cell type and to afferent and efferent connections, may serve as a model for studying some functional properties of lamination common to cortical structures.

Dendritic alteration of rat spinal motoneurons after dorsal horn mince: computer reconstruction of dendritic fields

Mammalian spinal motoneuron dendrites respond with cyclic degeneration and regeneration after ventral root crush. In the following experiments, the cross-sectional dendritic profile of rat lamina IX, medial, motoneurons under the T2 vertebra were analyzed after mincing the dorsal horn (normals, 14, 30, 60, 90 days postoperative (DPO); N = 6 animals/DPO). The spinal cords were impregnated by the tungstate modification of the Golgi technique. Individual lengths along dendritic segments between branching points were measured from coded slides, the data were computerized, and the dendrites were reconstructed by computer. Interanimal statistical comparisons were made by ANOVA a priori and Newman-Keuls test a posteriori. At 14 DPO, there was a statistically significant (P less than 0.05) increase in the number of dendritic segments, dendritic and serpentine length, and number of segments emanating from the soma compared with normal intact rats and with all other postoperative days. At 30 and 60 DPO, these parameters returned to normal values; however, there were many long, unbranched dendrites. At 90 DPO, there was a statistically significant (P less than 0.05) decrease in motoneuron dendritic serpentine length and segments. These data show that partially deafferented rat spinal motoneurons undergo a biphasic response; an initial growth phase followed by a degenerative phase.

A Golgi study of the parvocellular neurons in the paraventricular nucleus of the domestic fowl

The present study was focussed on the typology of small and medium-sized neurons in the hypothalamic paraventricular nucleus (PVN) of the domestic fowl as revealed by means of Golgi impregnation. This region is provided with different systems of neurons that can be distinguished on the basis of their location and dendritic morphology. Intraependymal neurons and CSF-contacting nerve cells are found in the periventricular layer together with bipolar elements endowed with processes extending parallel to the surface of the third ventricle. The short axons of these neurons may contact the magnocellular elements. Numerous isodendritic neurons are scattered throughout the entire PVN; these nerve cells possessing short and branched axons may be considered as local-circuit neurons. The complex intrinsic organization of the PVN of the domestic fowl might provide the structural basis for local interactions among the neuronal elements of this hypothalamic region.

The morphology of physiologically identified deep spinothalamic tract cells in the lumbar spinal cord of the cat

1. The morphology of eleven physiologically identified, deep, spinothalmic tract (s.t.t.) cells in the seventh lumbar segment of the cat were studied after being intracellularly injected with horseradish peroxidase (HRP).2. Four of these cells, prepared for combined light and electron microscopy, did not appear to be as well filled with HRP as the other cells which were prepared solely for the light microscope. In these four cells the axons were not stained and significantly fewer distal dendrites were stained.3. The axons of the other seven cells projected medially, crossed the mid line in the ventral white commissure and ascended in the contralateral ventral funiculus. No axon collaterals were found.4. The dendrites of eight cells could be divided into three groups. The first group projected laterally across lamina VII, usually passing through the ventrolateral portion of lamina VI before entering the lateral funiculus. The second group projected ventrally, ventromedially and ventrolaterally through the ventral parts of laminae VII and VIII and into the ipsilateral ventral funiculus. The third group projected towards the central canal, the ventral border of the dorsal columns and the dorsal parts of the ipsilateral ventral funiculus. This group usually branched profusely and projected into lamina X.5. Of the remaining three cells, one was located more deeply than any other cell, one was probably incompletely filled, and one was located more laterally. The first two cells had dendritic trees which bore strong similarities to the other eight cells described above.6. In all, 12.3-37.5% of dendritic tips were found in the white matter of the ventral or lateral funiculi.7. Dendrites never entered the dorsal columns but they could often be traced to points very close to the dorsal columns before they turned abruptly and ran parallel to the grey-white border.8. These data are discussed in relation to the excitatory and inhibitory responses of s.t.t. cells to somatic stimuli and the axonal projections of physiologically identified primary afferents and spinal interneurones.