Pattern conserving data structure and algorithms for computations on dendritic trees

The linked list is offered as a pattern conserving data structure, useful for storing neuronal dendritic trees. A BASIC language algorithm is described. Modifications of this algorithm for building linked lists, graphing dendritic trees, and tarry ordering trees are presented. Brief mention is made of the last in first out stack as a alternative data structure for computations on dendritic trees.

Intracellular labeling of afferents to the lateral superior olive in the bat, Eptesicus fuscus

An in vitro tissue slice preparation of the bat brain stem was used to label intracellularly individual axons projecting to the lateral superior olive from two different sources: the medial nucleus of the trapezoid body (MNTB) and the anteroventral cochlear nucleus (AVCN). The tracing of individually labeled MNTB axons into the lateral superior olive reaffirms the long accepted indirect route by which information from the contralateral ear reaches the lateral superior olive. While the MNTB appears to relay input from the contralateral AVCN, information from the ipsilateral ear reaches the lateral superior olive via a direct projection from the ipsilateral AVCN. Axons from the contralateral and ipsilateral pathways have different distribution patterns upon the fusiform cells of the lateral superior olive. Axon terminals of MNTB principal cells have a perisomatic and proximal dendritic distribution pattern. Axon terminal varicosities from the ipsilateral anteroventral cochlear nucleus are distributed primarily to more distal dendrites.

Reticulo-spinal neurons participating in the control of synergic eye and head movements during orienting in the cat. II. Morphological properties as revealed by intra-axonal injections of horseradish peroxidase

Previously we described physiological properties of pontine reticulo-spinal neurons which generate bursts and decaying tonic discharges related to eye movements and neck muscle activity during ipsiversive gaze shifts (Grantyn and Berthoz 1987). Two of these "eye-neck reticulo-spinal neurons" (EN-RSN) were labeled by intra-axonal injections of HRP. The present report provides a detailed description of their morphology with an emphasis on the topography of axon collaterals, bouton numbers, and the structure of preterminal ramifications in different target areas. The cell bodies of labeled EN-RSNs were located rostro-ventrally to the abducens nucleus. Their descending axons issued 8 and 13 collaterals (left and right EN-RSN, respectively) at different rostro-caudal levels, between the abducens nucleus and the pyramidal decussation. On the basis of the size of their cell bodies, the isodendritic type of dendritic branching and their multiple collateralization, EN-RSNs correspond to the class of "generalized" reticular neurons, often referred to as The Scheibels' neurons. Collaterals of EN-RSNs terminated in the following structures: the abducens and facial nuclei, the medial and lateral vestibular nuclei, the nn. prepositus and intercalatus, and the bulbar reticular formation. As judged from bouton numbers, the strongest connection of both neurons was with the abducens nuclei. Terminations in the rostral part of the medial vestibular and prepositus nuclei indicate that EN-RSNs may also influence oculomotor output activity through these indirect routes. In the facial nucleus, a majority of terminations was found in its medial subdivision containing motoneurons of ear muscles. However, other subdivisions were also contacted by EN-RSNs. Most terminations in the rostral bulbar reticular formation are distributed to the dorsal, gigantocellular field. Within this field, there is a substantial contribution to the zone characterized by the highest density of reticulo-spinal neurons projecting directly to neck motoneurons. Other target areas which may participate in the modulation of spinal cord activity by EN-RSNs are the ventral reticular nucleus in the caudal medulla and the lateral vestibular nucleus. EN-RSNs also establish connections with precerebellar structures: the prepositus and the paramedian reticular nuclei. The numbers of boutons on collaterals issued within 6 mm of the injection site varied between 37 and 469. The occurrence of presumed axo-somatic contacts was low (0-8.2%) and not characteristic for any particular target area. Local accumulations of boutons in the form of small and large field clusters was a common observation.(ABSTRACT TRUNCATED AT 400 WORDS)

A Golgi study of the proximal portion of the human Purkinje cell axon

The proximal portion of the Purkinje cell axon in normal cerebellum was investigated using the Golgi-Cox method. The axon emerging from the axon hillock tapered as it proceeded distally along the initial segment. The most distal portion of the initial segment was the narrowest (about 1 micron). Then the axon became thicker again in the probable myelinated portion. The length of the axon hillock plus the initial segment ranged from 21 micron to 52 micron, 35 +/- 6 micron on average +/- SD. The axon arose from any site of the soma and the primary dendrite of the Purkinje cell. Almost half of the axons emanated from a lateral surface of the soma. The dendritic arbores of the Purkinje cell with a torpedo were atrophic.

Retinal ganglion cells: a functional interpretation of dendritic morphology

The electrical properties of the different anatomical types of retinal ganglion cells in the cat were calculated on the basis of passive cable theory from measurements made on histological material. Standard values for the electrical parameters were assumed (R1= 70 Ω cm, Cm= 2 μF cm-2,Rm= 2500 Ω cm2). We conclude that these neurons need not be equipotential despite their small dimensions, mainly because of their extensive branching. The interactions between excitation and inhibition when the inhibitory battery is near the resting potential can be strongly nonlinear in these cells. To characterize the different types of ganglion cells in terms of this property we introduce the factor by which the soma depolarization induced by a given excitatory input is reduced by inhibition. In this framework we analyse some of the integrative properties of an arbitrary passive dendritic tree and we then derive the functional properties that are characteristic for the various types of ganglion cells. Our main results are: (i) Nonlinear saturation at the synapses may be made effectively smaller by spreading the same (conductance) input among several subunits on the dendritic field. Subunits are defined as regions of the dendritic field that are somewhat isolated from each other and roughly equipotential within. (ii) Shunting inhibition can specifically veto an excitatory input, if it is located on the direct path to the soma. TheFvalues can then be very high even when the excitatory inputs are much larger than the inhibitory, as long as the absolute value of inhibition is not too small. Inhibition more distal than excitation is much less effective. (iii) Specific branching patterns coupled with suitable distribution of synapses are potentially able to support complex information processing operations on the incoming excitatory and inhibitory signals. The quantitative analysis of the morphology of cat retinal ganglion cells leads to the following specific conclusions: (i) None of the cells examined satisfies Rail’s equivalent cylinder condition. The dendritic tree cannot be satisfactorily approximated by a non-tapering cylinder. (ii) Under the assumption of a passive membrane, the dendritic architecture of the different types of retinal ganglion cells reflects characteristically different electrical properties, which are likely to be relevant for their physiological function and their information processing role: (a) α cells have spatially inhomogeneous electrical properties, with many subunits. Within each subunit nonlinear effects may take place; between subunits good linear summation is expected.Fvalues are relatively low. (b) β cells at small eccentricities have rather homogeneous electrical properties. Even distal inputs are weighted rather uniformly. Electrical inhomogeneities of the a type appear for P cells at larger eccentricities.Fvalues are low. (c) γ-like cells have few subunits, each with high input resistance underlying nonlinear saturation effects possibly related to a sluggish character.Fvalues are high: inhibition of the shunting type can interact in a strongly nonlinear way with excitatory conductance inputs. (d) δ-like cells show many subunits with a high input resistance, covering well the dendritic area. Within each subunit inhibition on the direct path to the soma can specifically veto a more distal excitation. It is conjectured that such a synaptic organization superimposed on the δ cell morphology underlies directional selectivity to motion. (iii) Most of our data refer to steady-state properties. They probably apply, however, to all light evoked signals, since transient inputs with time to peak of 30 ms or more can be treated in terms of steady-state properties of the ganglion cells studied. (iv) All our results are affected only slightly by varying the parameter values within reasonable ranges. If, however, the membrane resistance were very high, all ganglion cells would approach equipotentiality. ForRm= 8000 Ω cm2subunits essentially disappear in all types of ganglion cells (for steady state inputs). Our results concerning nonlinear interaction of excitation and inhibition ( values) would, however, remain valid even for much larger values ofRmand for any value ofR1larger than 30-50 Ω cm. The critical requirement is that peak inhibitory conductance changes must be sufficiently large (around 5 x 10-8S) with an equilibrium potential close to the resting potential. Underestimation of the diameters of the dendritic branches may affect these conclusions (Fcould be significantly lower).

Direct observations on the contacts made between Ia afferent fibres and alpha-motoneurones in the cat's lumbosacral spinal cord

1. The enzyme horseradish peroxidase was injected into identified lumbosacral alpha-motoneurones and Group Ia afferent fibres in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. Subsequent histological examination allowed the determination of (a) the extent of the motoneuronal dendritic trees, (b) the number and location of Ia synapses upon the motoneurones. 2. alpha-motoneurones had seven to eighteen primary dendrites and each produced daughter branches up to the fourth to the sixth order. At dendritic bifurcations Rall's 3/2 Power Law was obeyed. There was little or no dendritic tapering up to about 800 micrometers from the soma. Beyond this distance, however, there was considerable tapering. 3. Horseradish peroxidase injections revealed that motoneuronal dendrites are much longer than previously thought. Individual dendrites could be traced for up to 1600 micrometers from the soma and dendritic trees were usually 2-3 mm from tip to tip. Nearly all the motoneurones had dendrites that entered the white matter of the cord. Dendrites could also reach as far dorsally as laminae V and VI. 4. Ia synapses upon motoneuronal somata were examined in cords counterstained with cresyl violet or methylene green. About 10% of Ia boutons in lamina IX were on somata and each Ia collateral terminated on 3.66 motoneuronal somata or the most proximal (30 micrometer) dendrites, with on average about two contacts per motoneurone. 5. Ten Ia afferent fibre-motoneurone pairs were injected with horseradish peroxidase. The following conclusions were drawn: (i) only one collateral of any given Ia axon makes contact with a motoneurone even though other collaterals from the same axon might pass through the dendritic tree, (ii) usually all contacts made between a Ia fibre and a motoneurone are at about the same geometrical distance from the soma, even when on different dendrites, (iii) between two and five contacts are made upon the dendritic tree (average 3.4) at distances of between 20 and 820 micrometers from the soma. 6. The results are discussed in relation to previous anatomical and electrophysiological work.

Localization and morphology of cat retractor bulbi motoneurons

1. Motoneurons innervating the cat retractor bulbi muscle have been identified by retrograde axonal transport of horseradish peroxidase (HRP). Following injections of the four slips of the retractor bulbi muscle, labeled motoneurons were found in the abducens nucleus overlapping the distribution of lateral rectus motoneurons and in the oculomotor nucleus partially overlapping the distribution of medial rectus motoneurons. Retractor bulbi motoneurons also were found in the accessory abducens nucleus situated ventral and lateral to the abducens nucleus. 2. Retractor bulbi motoneurons varied considerably in shape and size, but in all instances contained similar cytoplasmic organelles. Quantitative analyses of mean soma diameter indicated that the average size of retractor bulbi motoneurons was larger than the average size of lateral rectus and medial rectus motoneurons. 3. Retractor bulbi motoneurons in the accessory abducens nucleus were identified electrophysically and stained by intracellular injection of HRP. Neuronal reconstructions demonstrated a dorsomedial axonal trajectory directed toward the abducens nucleus and elongated dendritic fields oriented in a dorsomedial-ventrolateral axis. Another major dendritic extension was directed toward the magnocellular division of the spinal trigeminal nucleus, a major source of excitatory input to these motoneurons. 4. Quantitative analyses of synaptic density indicated that the somata of retractor bulbi motoneurons were contacted by significantly fewer synaptic endings than the somata of motoneurons in the abducens nucleus. Retractor bulbi motoneurons in the abducens nucleus exhibited variations in synaptic density that were similar to the densities on lateral rectus motoneurons. 5. Given the morphological differences in location, size, and somadendritic extent between motoneurons in the accessory abducens, abducens and oculomotor nuclei, it is suggested that such features reflect functional differences between the motoneurons with respect to fiber composition of the muscles they innervate, and subsequently to the role each muscle plays in eye movement. 6. Since the morphological features of retractor bulbi motoneurons in the accessory abducens nucleus are quite different from those in either the abducens or oculomotor nuclei, it appears that each motoneuronal population may perform unique oculomotor functions.

Kitten ganglion cells: dendritic field size at 3 weeks of age and correlation with receptive field size

A Golgi study of beta (brisk-X type) ganglion cells has been done to compare ganglion cells in the retina of 3-week-old and adult cats. An anatomical basis for the large receptive field centers found in the immature kitten retina was sought. Kitten beta-type ganglion cells have significantly smaller dendritic spreads than adult beta cells; the dendrites of the kitten cells must still grow to reach their final adult size. Therefore a synaptic basis for the large receptive field size of the immature cells is suggested.

Dendrite bundles, central programs and the olfactory bulb

The long secondary dendrites of mitral cells in the olfactory bulb are well developed in the mammalian neonate and show a considerable degree of interweaving and coiling characteristic of dendrite bundles. In a number of other areas throughout the central nervous system, we have made a provisional correlation between the appearance of these bundles and the development of specific items of output performance characteristic of the aras involved. On this basis we have suggested that the dendrite bundles may serve as a repository for the central program shaping the response. This hypothesis is explored further in the case of the olfactory bulb. Mechanisms are suggested whereby rudimentary appetitive programs already encoded along facing dendrite membrane pairs within the specialized intrafascicular milieu, may trigger and control nipple search and suckling in the still blind and only primitively mobile neonate.

The organization of a cephalopod ganglion

The stellate ganglion of cephalopods is sharply divided into a ventral part containing only large cells and a dorsal part where there are also microneurons (amacrine cells). Axons proceed from the larger cells of the ganglion to the stellar nerves in distinct dorsal and ventral roots, which join as they leave the ganglion. The ventral roots contain only large motor fibres, one arising from each of the 30000 ventral cells. The input to this part is from less than 2000 large fibres of the pallial nerve. These fibres branch abundantly in the ventral neuropil. After severing the pallial nerve massive degeneration occurs there, producing shrinkage of the whole ganglion. There is also degeneration in the dorsal neuropil, which therefore also has input from the pallial nerve. The dorsal roots contain some large fibres, being the axons of the larger dorsal cells. In addition, they contain numerous small fibres. These include efferent chromatophore fibres, which degenerate after severing the pallial nerve and therefore pass through the ganglion presumably without synapse. There are also afferent fibres from the periphery in the dorsal roots and, after severing stellar nerves, degeneration appears in the outer layers of the dorsal neuropil and in the pallial nerve. No degeneration occurs in the central stumps of the ventral roots after this operation. The trunks of the small cells of the dorsal part form characteristic bundles of fine fibres in the outer dorsal neuropil and dorsal roots. These bundles carry varicosities and make plexuses in the bases of the dorsal roots, intertwined with collaterals of the outgoing large fibres and branches of the incoming afferents from the periphery. Probably these microneurons terminate within the ganglion and are concerned with reflex modulation of the output of the dorsal neuropil. The arrangement of the dorsal and ventral divisions of the ganglion and roots of the stellar nerves is similar in Sepia and Loligo to that in Octopus. There are more numerous large terminal knobs in the neuropils of these decapods and these endings are also found within the cell layers, especially in the hind part of the dorsal region. The course of degeneration within the ganglion was followed after section of the pallial and stellar nerves in all three species, more in detail in Octopus. Degeneration of terminations is already advanced 15 h after severing the pallial nerve (at about 24 °C); break-up within the nerve trunks comes later. Degeneration granules have mostly disappeared 3 days after the lesion. Severed stellar nerves of Octopus show very abundant sprouting from the central stump, the fibres turning back to invade the ganglion and form terminal knobs in the neuropil and throughout the cell layers.

Dendritic-tree anatomy codes form-vision physiology in tadpole retina

In tadpole frog retina, the development of four classes of visual form detectors matched the growth of four types of ganglion cell dendritic trees. From this correlation of electrophysiology and anatomy we concluded that the structure of retinal ganglion cell dendritic trees provides the code for detection of visual shapes.

Motoneuron morphology and synaptic contacts: determination by intracellular dye injection

The structure and dendritic connections of an identified crustacean motoneuron were analyzed by intracellular injection of dye. Some processes of the neuron end in the ganglionic neuropil, but most terminate on axons which pass through the ganglion in specific, identifiable tracts. The former processes are ipsilateral to the soma, while the latter, as well as their connections, display bilateral symmetry. Structural and functional evidence suggests that the demonstrated contacts are synaptic junctions, and that the approach can therefore be used to study patterns of synaptic organization in complex neural networks.