A Golgi study of rat neostriatal neurons: light microscopic analysis

At least two types of large neurons (somatic cross-sectional areas, SA greater than 300 microns2) and five-types of medium neurons (SA between 100 and 300 microns2) were distinguished in Golgi preparations of the adult rat neostriatum. Type I large cells had aspinous somata with long, radiating, sparsely spined dendrites which were sometimes varicose distally, whereas type II large cells had spines on both somatic and dendritic surfaces. Type I medium cells had aspinous somata and proximal dendrites, but their distal dendrites were densely covered with spines. Type II medium cells had somatic spines, and their radiating dendrites were sparsely spined. Other medium cells had no somatic spines: Type III cells had poorly branched and sparsely spined dendrites. Type IV cells had profusely branched, sparsely spined dendrites. Type V cells had radiating and varicose dendrites which could also be sparsely spined. Several small neurons (SA mostly less than 100 microns2) were also found in the rat neostriatum: Some had aspinous soma with sparsely spined dendrites; others had somatic spines. Except for the type II large cells, intrinsic axon collaterals were observed for every type of neuron, indicating that they all had local integrating functions.     

Intracellular labeling of neurons in the medial accessory olive of the cat: I. Physiology and light microscopy

This study is the first of three reports on the detailed morphology of horseradish peroxidase injected neurons in the medial accessory olive of the cat. Intracellular, in vivo recordings of olivary cells were made and their response to mesodiencephalic stimulation was tested. In 44 units a short latency action potential could be recorded, which was very suggestive of a monosynaptic excitatory pathway. The short latency response was frequently followed by a long latency (mean 188 msec) or rebound action potential. Recordings were followed by intracellular iontophoresis of horseradish peroxidase. A total of 21 neurons, all located within the medial accessory olive were chosen for morphological analysis. Cells could be divided into two categories on the basis of their overall morphological appearance. Type I cells (n = 5) had sparsely branching dendrites that radiated away from the soma and were usually found in the caudal part of the medial accessory olive. The axon usually originated from the soma. Type II cells (n = 16) were located more rostrally. They had larger cell bodies with dendrites that ramified extensively, forming a globular structure (mean diam. 338 microns). The axon usually originated from a first order dendrite. No recurrent axon collaterals were observed on either type I or II cells. Both cell types carried long and complex spiny appendages; however, they were most numerous on the second and higher order dendrites of type II cells. Since the soma of these cells is usually not found in the centre of its dendritic field, even if the cell is located in the center area of the neuropil, it is suggested that the dendritic trees of up to 100 neurons may be intricately interwoven, establishing clusters with intensive intercommunication by means of dendritic gap junctions. The abundance, length and complexity of the spiny appendages suggest an important role in this process, but may also be relevant instruments in enhancing the computational capabilities of these neurons, especially in time sensitive processes. When relating the physiological and the morphological results, it was noted that both type I and type II cells could respond to mesodiencephalic stimulation and were both able to trigger a rebound action potential. No significant correlations were found between cell size and the latency of the rebound.     

The structure of the dorsal lateral geniculate nucleus in the mouse. A Golgi and electron microscopic study

Two types of neurons have been distinguished in Golgi and electron microscopic preparations of the dorsal lateral geniculate nucleus of young mice. In addition to a thalamo-striate relay cell (TSR neuron) with brush-like dendritic arbors and a thick, unbranched axon, a small tomedium size cell (PA neuron) of oval or spindle shaped body and few, long and seldom branched dendrites is frequently identified in our Golgi preparations. This second type of cell may exhibit none, one or several sparsely branched axon-like processes which terminate in the vicinity of the cell body. The dendrites of the PA neurons show characteristically large, spheroidal processes (p) 1–3 m? in diameter issuing forth singly, in clusters or as a “string of beads” from delicate, often long, pedicles attached to the dendritic shafts. Profiles comparable to these processes and in apparent continuity with PA dendrites have been identified with the electron microscope and show synaptic vesicles and a system of sacs of smooth E.R. The portions of the dendrites from which these vesicle-containing processes issue also show clusters of vesicles, ribosomes and an orderly array of microtubules. Golgi impregnated axons are followed from the optic tract and seen terminating as irregular enlargements (2–6 m?) on proximal dendrites of relay cells and on distal dendrites of the PA neuron. The intimate contact of the terminal branches of an optic collateral with a distal PA dendrite is carefully illustrated. Small calibered axons are likewise traced from the internal medullary lamina and seen to end by means of end-knobs on distal dendrites of both types of neurons. Electron microscopic observations substantiate the Golgi images and reveal three different types (I, II, III) of endings in the geniculate neuropil. The large type I endings correspond to the retinal afferents which generally make asymmetric synapti contact with type II profiles and/or with clusters of microspines on the TSR dendrites. Type II, thought to be the spheroidal dendritic appendages of the PA neurons, form symmetrical synaptic contacts with profiles of its own kind or more commonly with dendrites of the TSR neuron. The type III ending, probably cortical in origin, establishes asymmetrical synaptic contacts with small dendritic profiles. Only profiles of types I and II endings, together with those of other dendritic profiles, form part of the nest-like junctions known as the synaptic glomeruli. The significance of the unusual polarization of the geniculate interneurons is discussed.     

The inferior olivary connections to the cerebellum in the rat studied by retrograde axonal transport of horseradish peroxidase

Olivocerebellar projections were investigated in the rat using retrograde axonal transport of horseradish peroxidase. Discrete cell groups of the inferior olive were labelled, subsequent to injections in the paravermal region, the vermis, or the caudolateral hemisphere. Injections in the midrostrocaudal third of the paravermal area resulted in labelling of cells in the medial accessory olive (MAO), in cell group “b” at caudal levels, and in its lateral portion at mid-rostrocaudal levels. The rostral pole of the principal olive (PO), the dorsal accessory olive (DAO), and the dorsomedial cell column, were heavily labelled. By comparison, caudal paravermal injections resulted in labelling in the medial part of the mid-rostrocaudal levels of the MAO, but not in its caudal portion. The PO lamellae were labelled in their lateral half, excluding the lateral bend connecting them. Injections slightly lateral within this paravermal area gave no caudal MAO labelling, but did label cells in segments of both PO lamellae, medial to those in the previous case. From vermal injections, cell groups “b” and “c” of the caudal MAO were labelled, but no labelled cells were present in the PO. Subsequent to injections in the paramedian lobule, cells in the dorsal lamella of the PO were labelled. No cells of the MAO were labelled. These results are discussed in terms of specific labelling patterns and the general concepts of organization presently held for the Olivocerebellar system.     

Morphological study of the rostral interstitial nucleus of the medial longitudinal fasciculus in the monkey,Macaca mulatta by Nissl,Golgi, and computer reconstruction and rotation methods

We have studied the morphology of silver-impregnated neurons (rapid Golgi technique) in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), a center involved in the control of vertical and torsional saccadic eye movements. This morphological study of riMLF neurons in the rhesus monkey was undertaken to further our understanding of the functional circuitry of the oculomotor system. Our study employed Nissl, Golgi, and computer- assisted methods. The cytoarchitectonic boundaries of the riMLF and its relationships to neighboring structures were determined in both Nissl and Golgi preparations. Five (I–V) distinct morphological types of riMLF neurons were distinguished in the Golgi impregnations on the basis of soma size, dendritic size, numbers of primary dendrites, number of dendritic branch points, as well as form, number, and distribution of dendritic appendages. Type I neurons impregnated most frequently and had the most extensive and highly branched dendritic tree. Type II neurons displayed thick dendrites with complex dendritic appendages, but the dendritic tree was much more compact than that of type I cells. Type III and type V cells had fusiform somas and relatively unbranched dendritic trees but differed greatly in size as well as dendritic morphology. The type IV cell was the smallest neuron and had many characteristics of the local interneurons found in other thalamic, subthalamic, hypothalamic, and midbrain centers. The type V was the largest neuron, least frequently impregnated, and found only at rostral riMLF levels. Digitized reconstructions of each type of neuron were rotated by the computer, which revealed that the dendritic trees of types I, III, and V occupy a disk-like compartment in the riMLF neuropil. In contrast, the trees of types II and IV occupy a roughly spherical compartment. We suggest that three of the cell types are well suited for specific purposes: type II cells for receiving, topographically organized inputs that contain spatial information, type I cells for short-lead burst neuron output to the motor neurons or other premotor centers, and type IV cells for inhibitory inputs to type I cells. © 1994 Wiley-Liss, Inc.     

Light microscopic Golgi study of mitral/tufted cells in the accessory olfactory bulb of the adult rat.

Mitral/tufted cells (MTCs) of the accessory olfactory bulb (AOB) of adult rats were investigated light microscopically with the rapid Golgi method. The somata of the MTCs, appearing ovoid or triangular in shape, are distributed throughout the external plexiform layer. The soma size varies from small to large (12-26 microns). Apical dendrites originating from the soma enter the glomerular layer to provide branches that form the glomerular arbors. After making a glomerular arbor, some dendrites develop a second arbor (en passant and terminal arbors, respectively). The MTCs have a very diverse dendritic branching pattern and most have a variable number of glomerular arbors per cell (up to 6); we have tentatively classified the MTCs into simple, intermediate, and complex. Of the glomerular arbors, 80% have a diameter of less than 50 microns. The glomerular arbors have been classified as baskets (small spherical or ovoid) with short loopy processes; balls of yarn (large and nearly spherical) with loosely intermingled thick loops; and bushes (small to large and rather polymorphic) with irregular processes. The MTCs send dendritic arbors to terminate in one or more glomeruli where they are arranged in several different types of endings. Since it is generally believed that the dendrites of mitral and tufted cells of the main olfactory bulb terminate in only one glomerulus, the difference in the termination of the dendrites of the MTCs may represent a morphological characteristic that is relevant to the coding and/or integration of sensory information.     

Axonal branching of the olivocerebellar projection in the rat: a double-labeling study

Collateralization of olivocerebellar (climbing) fibers was studied in the rat by means of the fluorochrome double-labeling technique. Most of the olivocerebellar projection is crossed except for a minimal ipsilateral component which arises from the most rostal part of the inferior olivary nucleus (ION). ION neurons in the caudolateral part of the medial accessory olive (MAO) and the dorsal accessory olive (DAO) give off axons that branch to supply both hindlimb areas of the contralateral cerebellar cortex, i.e., the rostral anterior lobe and the caudal paramedian lobule. In addition, neurons in the middle one-third of the contralateral MAO and DAO send axons that divide to terminate in both the caudal part of the anterior lobe and the rostral part of the paramedian lobule (forelimb receiving areas). Neurons within the caudal part of the MAO, the lateral part of the DAO, the ventral lamella of the principal olive (PO), and the dorsomedial cell column (DMCC) send axonal branches that terminate within at least two different areas of the same sagittal zones throughout the contralateral cerebellar cortex. Thus, the ION contains specialized cells that provide a divergence of integrated information from the ION to at least two cerebellar regions.     

Cytoarchitecture and visual receptive neurons in the Wulst of the Japanese quail (Coturnix coturnix japonica)

The cellular organization of the Wulst was studied in Nissl- and Golgi-stained brain sections in order to identify the visual receptive neurons. Golgi-impregnated neurons were divided into four types according to their soma size, dendritic configuration, and density of spine distribution. Type I neurons, the largest cells in the Wulst, have long, straight dendrites with many spines. Type II neurons are medium-sized cells with long, straight dendrites. These dendrites have numerous spines. Type III neurons are medium-sized or small cells with spine-free dendrites. Type IV neurons, the smallest cells in the Wulst, have short dendrites with sparse spines. The projections of the nucleus dorsolateralis anterior thalami pars lateralis (DLL) to the Wulst were determined by the Fink-Heimer method. After lesions of the DLL, degenerating terminals are seen in a dorsolateral portion of the nucleus intercalatus hyperstriatum accessorium where the types II, III, and IV neurons are distributed. Postsynaptic elements to the DLL axons were identified by reconstruction of electron microscopic serial sections. Most of the postsynaptic elements were dendritic spines of the type II and IV neurons and a few were dendritic shafts of the type III neurons.     

Golgi studies of the neurons in layer II of the dorsal horn of the medulla (trigeminal nucleus caudalis)

The translucent band which lies just beneath the spinal V tract at the lower end of the spinal trigeminal nucleus (nucleus caudalis) can be divided into three layers. These three layers are distinguished by textural differences in their neuropil and by the morphology and laminar distribution of the axons and dendrites of their neurons. Layer II contains four different kinds of interneurons. Stalked cells are named after their short, stalk-like branches. Their cell bodies are found in greatest numbers in the outer half of layer II. Their coneshaped dendritic arbors extend medially across layers II and III and sometimes extend into layer IV. Their axons form extensive, canopy-like arborizations in layer I. Stalked cells are considered to be excitatory interneurons receiving input on their dendritic spines from primary axonal endings in the layers II and III glomeruli and transferring it to the dendrites of the layer I projection neurons. Layer II contains three kinds of Golgi type II inteneurons, i.e, neurons whose axons branch repeatedly within the confimes of their dendritic arbors. Islet cells similar to those found in layer III (Gobel), '75a), are found in small clusters in layer II. Their dendrites and axons are largely confined in layer II. The dendrites of the arboreal cell burst, in tree-like fashion, into highly focal dendritic arbors confined largely in layer II while the extensive rostral and caudal dendritic arbors of the II-III border cell lie largely in layers II and III with a few branches extending into layer I. The axons of both of these interneurons arborize in layers II and III with a few collaterals extending into layer I. Islet cells, arboreal cells and II-III border cells are considered to be inhibitory interneurons. They are strategically situated to interrupt transmission between primary axonal endings in layers II and III and the layer I projection neurons by altering the output of the stalked cells.     

Theta ganglion cell type of cat retina

We define a new bistratified ganglion cell type of cat retina using intracellular staining in vitro. The theta cell has a small soma, slender axon, and delicate, highly branched dendritic arbor. Dendritic fields are intermediate in size among cat ganglion cells, with diameters typically two to three times those of beta cells. Fields increase in size with distance from the area centralis, ranging in diameter from 70 to 150 microns centrally to a maximum of 700 microns in the periphery. Theta cells have markedly smaller dendritic fields within the nasal visual streak than above or below it and smaller fields nasally than temporally. Dendritic arbors are narrowly bistratified. The outer arbor lies in the lower part of sublamina a (OFF sublayer) of the inner plexiform layer where it costratifies with the dendrites of OFF alpha cells. The inner arbor occupies the upper part of sublamina b (ON sublayer), where it costratifies with ON alpha dendrites. The outer and inner arbors are composed of many relatively short segments and are densely interconnected by branches that traverse the a/b sublaminar border. Experiments combining retrograde labeling with intracellular staining indicate that theta cells project to the superior colliculus and to two components of the dorsal lateral geniculate nucleus (the C laminae and medial interlaminar nucleus). Theta cells project contralaterally from the nasal retina and ipsilaterally from the temporal retina. They apparently correspond to a sluggish transient or phasic W-cell with an ON-OFF receptive field center.     

Morphology of retinogeniculate terminals in the turtle, Pseudemys scripta elegans

The dorsal lateral geniculate complex in turtles receives a bilateral, topographic projection from the retina and projects to the telencephalon. This study examined the morphology of individual retinogeniculate terminals that were filled with horseradish peroxidase by injections in the optic tract or optic tectum. A large number of retinogeniculate terminals were successfully filled and detailed drawings were prepared of 87 terminals. Terminals were classified into three types based on the size and number of varicosities in the terminal, and (if a terminal formed a spatially restricted arbor) the volume of the arbor. Type I retinogeniculate terminals form spatially restricted, large-volume arbors with a low density of large varicosities. Type II retinogeniculate terminals form small volume arbors with a high density of small varicosities. Type III retinogeniculate terminals, in contrast to types I and II, do not form spatially restricted arbors. Rather, they consist of sparsely branched axons that parallel the optic tract and contain scattered en passant varicosities. Plots of the distribution of different terminal types throughout the geniculate complex show that all three terminal types occur throughout the rostrocaudal and mediolateral extents of the complex. However, each terminal type has a preferential distribution with type II terminals being concentrated in the outer half of the neuropile, type I terminals in the inner half of the neuropile, and type III terminals in the cell plate. All three types can arise from axons that continue caudally to terminate in the tectum. These findings raise the possibility that various classes of retinal ganglion cells differ in their mode of termination within the geniculate complex, but the precise relation between the three types of retinogeniculate terminals and the classes of ganglion cells remains to be determined.     

Types of neurons in nucleus olivaris inferior of the European bison

The studies were carried out on the medullae oblongatae of four European bisons. Preparations made by means of the Golgi technique, as well as preparations stained by the Klüver-Barrera methods, were used. Two types of neurons were distinguished in nucleus olivaris inferior of the European bison. Type I (about 90% of neurons) are multipolar cells whose perikaryons measure from 25 to 40 microns. The multipolar cells generate 5-6 thick dendrites which next give off a number of branches. The dendritic tree is ball-shaped. A single long, thin axon arises from the surface of the perikaryon or branches from the initial segment of one of the dendrites. The axon adopts a course along the plane corresponding to the transverse section of brain stem. Type II (about 10% of neurons) are pear-shaped and rounded cells measuring from 25 to 30 microns. These cells generate 2-3 thick dendritic trunks which are concentrated at one pole of the perikaryon. The dendritic tree has a stream-like form. A single short and rather thin axon emerges from the surface of the perikaryon. Its course corresponds to the long axis of brain stem.     

Distribution of dendrites of mitral, displaced mitral, tufted, and granule cells in the rabbit olfactory bulb

To determine the dendritic fields, mitral, displaced mitral, middle tufted, and granule cells in the rabbit olfactory bulb were stained by intracellular injection of HRP. The secondary dendrites of mitral cells were distributed mostly in the inner half of the external plexiform layer (EPL). Those of displaced mitral cells extended mainly into the middle and superficial sublayers in the EPL. The secondary dendrites of middle tufted cells were distributed mostly in the superficial portion of the EPL. Mitral cells extended their secondary dendrites in virtually all directions within a plane tangential to the mitral cell layer (MCL) and thus had a disklike projection field with a radius of about 850 microns. Displaced mitral cells had similar dendritic projection fields in the tangential plane but with somewhat distorted shapes. The secondary dendrites of middle tufted cells had a tendency to extend in particular directions. From the projection pattern of the gemmules on the peripheral processes, granule cells were classified into three types. Type I granule cells had gemmules both in the superficial and in the deep sublayers of the EPL. The peripheral processes of Type II granule cells were confined to the deep half of the EPL. The gemmules of Type III granule cells ere distributed in the superficial half of the EPL. The differing dendritic ramification among mitral, displaced mitral, and middle tufted cells suggests the separation of the dendrodendritic synaptic interactions with granule cells in different sublayers in the EPL. It also suggests a functional separation of the sublayers of the EPL.     

Structure of layer II in cat primary auditory cortex (AI)

The cytoarchitecture, myeloarchitecture, neuronal architecture, and intrinsic and laminar organization of layer II were studied in the primary auditory cortex (AI) of adult cats. The chief goal was to describe the different types of cells and axons to provide a framework for experimental studies of corticocortical connections or of neurons accumulating putative neurotransmitters. A further goal was to differentiate layer II from layer III. Layer II extends from 150-200 micron to about 400 micron beneath the pia and has two subparts. The superficial stratum, layer IIa, has many small, chiefly non-pyramidal neurons, primarily with round or oval perikarya, and a sparse, fine, and irregularly arranged axonal plexus. Layer IIb somata are larger and more densely packed and there is a more developed vertical and lateral axonal plexus. The border with layer III was marked by numerous large pyramidal cells with a thicker apical dendrite with more developed basal dendritic arbors than those of layer II pyramidal cells. Eight varieties of neurons were recognized in Golgi-impregnated material. These included small and medium-sized pyramidal cells, whose apical dendrites often ramified in layer I; bipolar and bitufted cells with polarized, sparse dendritic arbors; small smooth or sparsely spinous multipolar cells with radiating dendrites and small dendritic fields; spinous multipolar cells, whose large dendritic fields had more extensive apical than basal arbors; large sparsely spinous multipolar cells with smooth, robust apical dendrites; tufted multipolar cells with highly developed apical dendrites and some dendritic appendages; and extraverted multipolar cells with a broad, candelabra-shaped dendritic configuration, and with most dendrites oriented at right angles to the pia. The axons of the different cell types had the following general dispositions: those arising from the pyramidal cells could often be traced into the white matter but had many local branches as well; those of the other neurons had more or less extensive local axonal collateral systems and fewer branches which appeared to be corticofugal. However, the complete trajectory of the axons was not always impregnated in the adult material.(ABSTRACT TRUNCATED AT 400 WORDS)     

Morphological and functional types of neurons in cat ventral posterior thalamic nucleus

Neurons in the thalamic ventral posterior (VB) nucleus of the cat were investigated by extracellular and intracellular recording and by anatomical methods involving either the retrograde transport of horseradish peroxidase (HRP) or the intracellular injection of HRP. Two morphological types of neurons could be detected by retrograde labeling from small injections of HRP in the internal capsule adjacent to VB. These two and one other type, judged to be an interneuron, could also be identified by intracellular staining. Type I cells are large, have thick proximal dendrites which branch in a tuft-like manner, and thick, rapidly conducting axons. They possess few or no dendritic appendages. Type II cells are smaller and have slender proximal dendrites which branch dichotomously and thin, slower conducting axons. Those injected intracellularly are covered in fine, hair-like dendritic appendages. Type III cells are small and have thin processes that give rise to many bulbous dilatations and no obvious axon. Type I and type II cells give off slender axon collaterals in the thalamic reticular nucleus but not in VB. Examples of both types of cell could be antidromically activated from the somatic sensory cortex. Type I and type II cells recovered histologically after intracellular recording included examples of most types of receptive field, including several forms of cutaneous and deep fields, as classified by us in a parallel intra- and extracellular study of unit responses. All but one type I cell, however, responded in a transient manner to peripheral stimulation. The remaining type I cell and all members of an admittedly small sample of type II cells responded in a sustained manner. The sample of recovered interneurons and of units that could not be driven antidromically from the cerebral cortex suggested that they, too, included all receptive field types. We conclude that submodality specificity in VB is not represented by morphological specificity in thalamocortical relay cells or interneurons. Some other functional parameter, such as tonic or phasic responsiveness, may be more obviously correlated with relay cell morphology.     

Amygdala afferents monosynaptically innervate corticospinal neurons in rat medial prefrontal cortex

The amygdala provides the medial prefrontal cortex (mPFC; areas 25, 32, and 24b) with salient emotional information. This study investigated the synaptic connectivity of identified amygdalocortical boutons (ACBs; labeled anterogradely following injections of Phaseolus vulgaris leucoagglutinin into the basolateral nucleus of the amygdala), with the dendritic processes of identified layer 5 corticospinal neurons in the rat mPFC. The corticospinal (CS) neurons in the mPFC had been retrogradely labeled with rhodamine fluorescent latex microspheres and subsequently intracellularly filled with biotinylated lucifer yellow to visualize their basal and apical dendrites. Two main classes of mPFC CS neurons were identified. Type 1 cells had apical dendrites bearing numerous dendritic spines with radiate basal dendritic arbors. Type 2 cells possessed apical dendrites with greatly reduced spine densities and a broad range of basal dendritic tree morphologies. Identified ACBs made asymmetric synaptic junctions with labeled dendritic spines and the labeled apical and basal dendritic shafts of identified CS neurons. On average, eight ACBs were closely associated with the labeled basal dendritic arbors of type 1 CS neurons and five ACBs with type 2 CS basal dendrites. The mean Scholl distance of ACBs from CS somata (for both types 1 and 2 cells) was 66 μm-coinciding with a region containing the highest length density of CS neuron basal dendrites. These results indicate that neurons in the BLA can monosynaptically influence CS neurons in the mPFC that project to autonomic regions of the thoracic spinal cord and probably to other additional subcortical target regions, such as the lateral hypothalamus.     

Two types of motoneurons supplying dorsal fin muscles in lamprey and their activity during fictive locomotion.

The location and dendritic morphology of motoneurons supplying the dorsal fin muscles were studied in the lamprey spinal cord (Ichthyomyzon unicuspis). Motoneurons were retrogradely labelled after injection of HRP into the fin muscles or after its application on the cut ends of the ventral roots. HRP-labelled cells were subsequently reconstructed, in the horizontal and/or transverse planes. Fin motoneurons were also injected intracellularly with Lucifer Yellow and their detailed three-dimensional structure was analysed by confocal laser-scanning microscopy. Unlike myotomal motoneurons, which are closely spaced in the lateral cell column, fin motoneurons were distributed along the spinal cord separately or in pairs. They could be distinguished from motoneurons supplying trunk muscles by having a limited number of dendrites in the lateral part of the spinal cord. In addition, some fin motoneurons extend their dendrites into the dorsal column. The motor cells innervating fin muscles were divided into two types based on their dendritic morphology. Type I have a widespread dendritic tree in the rostrocaudal direction and, with few exceptions, completely restricted to the ipsilateral side. A proportion (25%) of these cells have dendrites extending into the dorsal column. Type II fin motoneurons extended their dendrites both ipsi- and contra-laterally. The contra-lateral dendrites pass below and above the central canal. The dendrites send off branches into the dorsal columns on both the ipsi- and the contra-lateral sides. Electron microscopic analysis showed that both type I and type II fin motoneurons receive numerous synaptic contacts from dorsal column axons. During fictive locomotion both types of motoneurons are active in antiphase in relation to myotomal motoneurons and to the main locomotor burst.     

Effects of visual or light deprivation on the morphology, and the elimination of the transient features during development, of type I retinal ganglion cells in hamsters

Intracellular injection of Lucifer Yellow (LY) was used to study the detailed morphology of the normal visually deprived, and light-deprived superior colliculus projecting Type I retinal ganglion cells (RGCs) in hamsters. The soma size of the normal Type I cells ranged from 337 to 583 microns 2 with a mean of 436 microns 2. Two to six primary dendrites were observed in these cells. The mean dendritic field diameter was 495 microns and ranged from 309 to 702 microns. The dendritic field diameter of this population of cells exhibited an eccentricity dependence. Quantitative comparisons between the normal and visually deprived or light-deprived Type I RGCs indicated that the morphology of these three groups of cells were similar to each other in terms of the soma size, dendritic field diameter, branching pattern, and total length of the dendrites. During the normal development of cats and hamsters, several transient features, such as exuberant dendritic spines and intraretinal axonal branches, have been observed in the developing RGCs. The complete elimination of these transient features occurs at about 3 and 2 weeks after the opening of the eyes in cats and hamsters, respectively. In the present study, the hypothesis whether visual experience or light stimulation is required for the elimination of these transient features during development was examined. After studying a total of 115 mature Type I RGCs, which included cells from the normal, visually deprived and light deprived animals, no transient feature was observed. We conclude that visual or light deprivation has no effect on the morphological development of superior colliculus projecting Type I RGCs in hamsters, and the elimination of the transient features on the Type I RGCs during development does not depend on visual experience or light stimulation.