Number Of Primary Dendrites Research Articles

Morphological changes in the hypothalamic suprachiasmatic nucleus and circadian rhythm of locomotor activity in hereditary microphthalmic rats.

Analysis of circadian locomotor activity, Golgi-Cox impregnation, and immunohistochemistry were studied on the hereditary microphthalmic rat which congenitally lacked the optic nerve. These blind rats showed free-running circadian rhythms in their locomotor activities. Both the normal and microphthalmic rats had similar ultradian rhythms in addition to circadian rhythms. The neuronal cell population and volume of the hypothalamic suprachiasmatic nucleus (SCN) of the microphthalmic rats were 66% and 71% of those in normal rats, respectively. The number of SCN neurons containing vasoactive intestinal peptide-like immunoreactive substance was dramatically decreased to 35% of that in normal rats. Golgi-Cox impregnation revealed that three types of neurons in the SCN of the microphthalmic rats were consistently distinguished as observed in normal rats. Although there were no changes in the numbers of primary dendrites of the SCN neurons in the microphthalmic and normal rats, the number of secondary and tertiary dendrites in the SCN of the microphthalmic rats was smaller than that of normal rats. These observations suggest that the retinal input may be important for normal morphological formation of the SCN during development, but not for the generation of circadian rhythms and ultradian rhythms.

Reactive Astroglia Support Primary Dendritic but Not Axonal Outgrowth from Mouse Cortical Neuronsin Vitro

Reactive astrocytes are thought to be impediments to axon regrowth following injury to the mammalian central nervous system. Axon and dendrite growth, however, appear to be differently controlled by normal astrocytesin vitro.To determine whether reactive astrocytes differ in their ability to support axons or dendrites, embryonic (E18) mouse cortical neurons were cocultured with P4 and P12 rat astroglial cells derived from normal or lesioned cortex. After 5 daysin vitro,axon and dendrite outgrowth from isolated neurons was quantified with double-labeling immunohistochemical techniques. Reactive astrocytes were able to maintain primary dendrite growth, principally primary dendrite number. Axon elongation, however, was significantly reduced on both neonatal and more mature reactive astrocytes. These results indicate that reactive astrocytes may exhibit separate mechanisms to control dendrite and axon growth.

Astroglia demonstrate regional differences in their ability to maintain primary dendritic outgrowth from mouse cortical neurons in vitro

To determine whether glia from different regions of the central nervous system (CNS) initiate or maintain primary dendritic growth, embryonic day 18 mouse cortical neurons were co-cultured with rat (postnatal day 4) astroglial cells derived from retina, spinal cord, mesencephalon, striatum, olfactory bulb, retina, and cortex. Axon and dendrite outgrowth from isolated neurons was quantified using morphological and immunohistochemical techniques at 18 h and 1, 3, and 5 days in vitro. Neurons initially extend the same number of neurites, regardless of the source of glial monolayer; however, glial cells differ in their ability to maintain primary dendrites. Homotypic cortical astrocytes maintain the greatest number of primary dendrites. Glia derived from the olfactory bulb and retina maintained intermediate numbers of dendrites, whereas only a small number of primary dendrites were maintained by glia derived from striatum, spinal cord, or mesencephalon. Longer axons were initially observed from neurons grown on glia that did not maintain dendrite number. Axonal length, however, was similar on the various monolayers after 5 days in vitro. Neurons that were grown in media conditioned by either mesencephalic or cortical glia for the first 24 h followed by culture media from glia of the alternate source for 4 days in vitro confirmed that glia maintained, rather than initiated, the outgrowth of the primary dendritic arbor. These results indicate that glial cells derived from various CNS regions differ in their ability to maintain the primary dendritic arbor from mouse cortical neurons in vitro.

Nasal and temporal retinal ganglion cells projecting to the midbrain: Implications for “blindsight”

We placed pellets of horseradish peroxidase in the superior colliculus of four macaque monkeys and retrogradely labelled the retinal ganglion cells of both eyes. The ratio of labelled cells in the contralateral nasal retina and the ipsilateral temporal retina was no different from the ratio found after implants in the optic nerve, which label the entire afferent pathway. Our finding therefore invalidates the proposal that prominent differences in the properties of "blindsight" in monocular nasal and temporal visual fields arise from differences in the projection from the nasal and temporal retina to the midbrain. We also measured the size of the soma and dendritic field of the labelled ganglion cells (mostly gamma cells) and compared them with those of alpha and beta cells that project to the dorsal lateral geniculate nucleus. Soma size was very close to that of beta cells at all eccentricities but was much smaller than that of alpha cells. Dendritic field size was significantly larger than that of beta cells but was smaller than that of alpha cells. The number of primary dendrites was counted for cells labelled from the midbrain and in samples of alpha and beta cells labelled from the optic nerve. At eccentricities of 3-7 mm there was a consistent and prominent difference between beta and gamma cells. The results show that at intermediate eccentricities even ganglion cells whose distal dendrites are too poorly labelled to reveal their morphological class can never the less be categorized as alpha, beta or gamma by using a combination of soma size and number of primary dendrites. This is particularly useful when attempting to classify retinal ganglion cells following microinjections into selected target nuclei of optic axons.

Structure and function of gustatory neurons in the nucleus of the solitary tract. I. A classification of neurons based on morphological features

Prior investigations in other laboratories have provided convincing evidence that the neurons of the rostral nucleus of the solitary tract (rNST) can be grouped according to their physiological response properties or morphologic features. The present study is based on the premise that the response properties of gustatory neurons are related to, and perhaps governed by, their morphology and connectivity. In this first phase of our ongoing investigation of structure-function relationships in the rNST of the rat, we have used intracellular injection of neurobiotin to label individual physiologically characterized gustatory neurons. A total of 63 taste-sensitive neurons were successfully labeled and subjected to three-dimensional quantitative and qualitative analysis. A cluster analysis using six morphologic features (total cell volume, soma area, mean segment length, swelling density, spine density, and number of primary dendrites) was used to identify six cell groups. Subsequent analyses of variance and posthoc comparisons verified that each of these six groups differed from all others with respect to at least one variable, so each group was "typified" by at least one of the six morphologic features. Neurons in group A were found to be the smallest neurons in the sample. The cells in group B had small somata and exhibited the highest swelling density of any group. Group C neurons were distinguished by dendrites with long, spine-free branches. These dendrites were significantly longer than those of any other group except Group F. The neurons in group D had more primary dendrites than any other group. Group E neurons possessed dendrities with the lowest swelling density but the most spines of any group. The cells in group F were the largest neurons in our sample and possessed the largest somata of any group. Thus overall cell size and density of dendritic spines and swellings were found to be particularly important variables in this classification scheme. Our preliminary results suggest that the number and density of dendritic spines (as well as other morphologic features) may be related to a given neuron's most effective stimulus, indicating that it will indeed be possible to use the criteria established in the present investigation to derive structure-function relationships for gustatory neurons in the rNST.

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 tree 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.

Regional differences in glial-derived factors that promote dendritic outgrowth from mouse cortical neurons in vitro

To determine whether glia from different CNS regions differ in their ability to support axons or dendrites, embryonic (E18) mouse cortical neurons were cocultured with early postnatal (P4) rat astroglial derived from cortex, retina, olfactory bulb, mesencephalon, striatum, and spinal cord. After 5 d in vitro, axon and dendrite outgrowth from isolated neurons was quantified with double-labeling immunohistochemical techniques. Whereas axonal growth was similar on the various monolayers, total primary dendritic outgrowth was nearly threefold greater on glia derived from the cortex, retina, and olfactory bulb than on glia derived from mesencephalon, striatum, or spinal cord. This effect was principally on the number of primary dendrites rather than the elongation of individual dendrites. Similar morphological differences were observed when cortical neurons were grown on polylysine in a noncontact coculture system with glia continuously conditioning the media. This selective promotion of dendrite growth was independent of neuron survival. These results indicate that there are regional differences in the ability of CNS glia to support dendritic growth and that this effect is due, in part, to release of a diffusable factor.

Nerve growth factor enhances the dendritic arborization of sympathetic ganglion cells undergoing atrophy in aged rats.

We have investigated whether dendritic growth can be induced from sympathetic neurons of aged rats by the application of exogenous nerve growth factor to their target tissues. A previous study showed that significant dendritic atrophy (19%) occurs during aging in the sympathetic neurons innervating the middle cerebral artery and that dendritic atrophy correlated with loss of axon collaterals in the same population of neurons. Using retrograde tracing in conjunction with intracellular injection of fixed tissue and confocal microscopy, we now demonstrate that infusion of nerve growth factor over the peripheral processes of the same neurons from aged rats induces significant dendritic (45%) and cell body (60%) growth. However, not all aspects of the dendritic arborization were affected. Primary dendrites and branch points were not altered by nerve growth factor. In contrast, nerve growth factor induced a significant increase in the number of primary dendrites and branch points (100%) of neurons from young adults. Our results demonstrate that sympathetic neurons undergoing dendritic atrophy during aging can exhibit significant dendritic growth in response to the in vivo infusion of nerve growth factor, although the lack of regenerative response displayed by some parts of the dendritic tree leads us to believe that these neurons also show signs of reduced plasticity.

Morphology of developing rat genioglossal motoneurons studied in vitro: Changes in length, branching pattern, and spatial distribution of dendrites

The aim of this study is to describe the postnatal change in dendritic morphology of those motoneurons in the hypoglossal nucleus that innervate the genioglossus muscle. Forty genioglossal (GG) motoneurons from four age groups (1-2, 5-6, 13-15, and 19-30 postnatal days) were labeled by intracellular injection of neurobiotin in an in vitro slice preparation of the rat brainstem and were reconstructed in three-dimensional space. The number of primary dendrites per GG motoneuron was approximately 6 and remained unchanged with age. The development of these motoneurons from birth to 13-15 days was characterized by a simplification of the dendritic tree involving a decrease in the number of terminal endings and dendritic branches. Motoneurons lost their 6th-8th order branches, in parallel with an elongation of their terminal dendritic branches maintaining the same combined dendritic length. The elongation of terminal branches was attributed to both longitudinal growth and the apparent lengthening caused by resorption of distal branches. The elimination of dendritic branches tended to increase the symmetry of the tree, as revealed by topological analysis. Later, between 13-15 days and 19-30 days, there was a reelaboration of the dendritic arborization returning to a configuration similar to that found in the newborn. The length of terminal branches was shorter at 19-30 days, while the length of preterminal branches did not change, suggesting that the proliferation of branches at 19-30 days takes place in the intermediate parts of terminal branches. The three-dimensional distribution of dendrites was analyzed by dividing space into six equal volumes (hexants). This analysis revealed that GG motoneurons have major components of their dendritic tree oriented in the lateral, medial, and dorsal hexants. Further two-dimensional polar analysis (consisting of eight sectors) revealed a reconfiguration of the tree from birth up to 5-6 days involving resorption of dendrites in the dorsal, dorsomedial, and medial sectors and growth in the lateral sector. Later in development (between 13-15 days and 19-30 days), there was growth in all sectors, but of a greater magnitude in the dorsomedial, medial, and dorsolateral sectors.

Early postnatal changes in the somatodendritic morphology of ankle flexor motoneurons in the rat.

The development of locomotor function in the rat spans the first 3 postnatal weeks. We have studied morphological features of the soma and dendrites of motoneurons innervating the physiological flexor muscles of the ankle, tibialis anterior and extensor digitorum longus, by intracellular injection in vitro between the first and ninth postnatal days. We obtained serial optical sections of 96 adequately filled motoneurons in whole-mounted hemisected spinal cords by confocal microscopy, projected them onto a single plane and analysed them morphometrically. On the day after birth, the somatodendritic surfaces of most such motoneurons were covered in growth-associated spiny, thorny or hair-like appendages. These had disappeared from the soma by the fourth postnatal day and from most proximal dendrites by day 7, but were still common distally on day 9. During this period there was little or no net growth of either the soma (which was still much smaller than in the adult) or the dendritic tree. A dorsal dendritic bias was present and 'sprays' of long, loosely bundled dorsal dendrites were often seen. The mean number of primary dendrites remained constant at about eight, and their combined diameter was already significantly correlated with mean soma diameter, as in the adult cat. Thus, the critical neonatal period during which these ankle flexor motoneurons are known to change their electrophysiological properties and to be particularly sensitive to interference with neuromuscular interaction is characterized by major changes in the neuronal surface, presumably linked to synaptogenesis.

A comparison of rat hippocampal mossy cells and CA3c pyramidal cells

1. There is a long-standing debate about whether the large spiny cells in the hilar region of the hippocampus should be classified as pyramidal cells of Ammon's horn or as a distinct cell type of the dentate gyrus. The rationale for grouping these hilar neurons (termed "mossy cells") with pyramidal cells of Ammon's horn is shared characteristics. In the present study we have compared the morphological and physiological characteristics of mossy cells and nearby CA3c pyramidal cells with the use of a rat hippocampal slice preparation. 2. Biocytin-labeled neurons were examined on the basis of soma area, location, shape, number of primary dendrites, extent of dendritic spines, dendritic location, and axon trajectories. Mossy cells had larger soma areas than CA3c pyramidal cells, and they had more large complex spines (thorny excrescences) on their proximal dendrites and somata than CA3c pyramidal cells. Mossy cell dendritic trees and axon collaterals ramified in different regions of the hippocampus than dendrites and axons of CA3c pyramidal cells. 3. Intrinsic physiological properties, and spontaneous and evoked synaptic properties, were measured and compared. Mossy cells had significantly higher input resistances, smaller amplitude burst afterhyperpolarizations, smaller amplitude action potentials, less spike-frequency adaptation, and more anomalous rectification than CA3c pyramidal cells. 4. Mossy cells had spontaneous excitatory postsynaptic potentials (EPSPs) that were significantly higher in frequency and larger in amplitude than CA3c pyramidal cells. A larger proportion of mossy cells than CA3c pyramidal cells responded to perforant path stimulation with depolarizing postsynaptic potentials without any apparent hyperpolarization. Conversely, a smaller proportion of mossy cells than CA3c pyramidal cells responded to perforant path stimulation with inhibitory postsynaptic potentials (IPSPs), and spontaneous IPSPs were more difficult to detect in mossy cells. 5. The intrinsic physiological properties of mossy cells endow these cells with potent excitatory mechanisms but relatively fewer inhibitory control processes than CA3c pyramidal cells. Recordings of spontaneous and evoked PSPs suggest that mossy cells receive more excitatory input and less inhibitory input than CA3c pyramidal cells. These intrinsic and synaptic properties of mossy cells may explain this cell type's exceptional vulnerability to excitotoxic damage by intense afferent stimulation. 6. In summary, mossy cells were significantly different from CA3c pyramidal cells in many of their morphological, intrinsic physiological, and synaptic properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Basic Fibroblast Growth Factor Enhances the Growth of Postnatal Neostriatal GABAergic Neurons in Vitro

Basic fibroblast growth factor (bFGF) significantly enhances the short-term survival of embryonic striatal neurons in vitro but has little effect on the outgrowth of striatal cells compared to neurons from other brain regions. Studies in our laboratory have shown that bFGF protects postnatal striatal cells in vitro from NMDA receptor-induced neurotoxicity. We therefore examined the effects of bFGF on the outgrowth of GABA-containing cells taken from the postnatal (Day 1) caudate-putamen and cultured for up to 3 weeks. In control cultures GABAergic neurons formed three populations based on somatic size and developed the cytoarchitectural features characteristic of dendrites, spines, and axons. In the presence of bFGF (6 p M continuously from the day of plating), small- and medium-sized GABAergic neurons showed significant increases compared to untreated controls in axon-like growth (axon length) at 6 days in culture and in both axon- and dendrite-like neurite growth (axon length and branch order, number of primary dendrites, dendrite length, and dendritic branch order) at 13 and 17 days in culture. Large GABAergic neurons were unaffected by treatment with bFGF. Striatal GABAergic neurons exposed to nerve growth factor (10 ng/ml) were not different from untreated controls. Neuron survival was also unaffected by bFGF treatment at all days in culture examined. Other observations suggested that the neurotrophic effects of bFGF were mediated by a direct action of the growth factor on striatal neurons and not glial cells. First, glial cells (identified by the immunohistochemical localization of glial fibrillary acidic protein) were unaffected by bFGF treatment at the low concentration (6 p M) used to enhance neurite growth, but did significantly proliferate at higher concentrations of bFGF (6 n M). Second, immunoreactive bFGF receptor protein was localized predominantly to the somata and processes of striatal neurons and not to glial cells in the cultures. Finally, when neurons from control cultures were briefly exposed (1 to 4 h) to bFGF at concentrations which were neurotrophic, a marked elevation in the immediate early gene protein c-fos was observed by immunohistochemistry in the nuclei of neurons, including GABAergic cells. Results provide the first direct evidence that bFGF promotes neurite outgrowth in postnatal striatal GABAergic neurons and suggest a major role for this growth factor in striatal cell development and regeneration. Basic FGF most likely mediates its action by binding to bFGF receptors on striatal neurons. The bFGF-stimulated expression of c-fos and probably other early gene proteins in striatal GABAergic neurons may be important in the regulation of gene transcription associated with neurite growth.

Development of commissural neurons in the embryonic rat spinal cord.

Little is known about the development of the various populations of interneurons in the mammalian spinal cord. We have utilized the lipid-soluble tracer DiI in fixed tissue to study the migration and dendritic arborization of spinal neurons with axons in the ventral commissure in embryonic rats. Crystals of DiI were placed in various locations in the thoracic spinal cord in order to label commissural neurons within the dorsal horn, intermediate zone, and ventral horn at E13.5, E15, E17, and E19. Seven different groups of commissural interneurons are present in the spinal cord by E13.5. Migration is relatively simple with groups occupying a position along the dorsoventral axis roughly corresponding to their position of origin along the neuroepithelium. By E15, commissural cells are near their final locations and exhibit characteristic morphology. One striking feature is the tendency of cells with similar morphology to cluster in distinct groups. By E19, at least 18 different types of commissural interneurons can be identified on morphological grounds. Although the situation is complex, some generalities about dendritic morphology are apparent. Commissural neurons located in the dorsal horn are small and have highly branched dendrites oriented along the dorsoventral axis. In more ventral regions, commissural neurons are larger and possess dendritic arbors oriented obliquely or parallel to the mediolateral axis with long dendrites extending toward the lateral and ventral funiculi. The number of primary dendrites of most groups is set by E15 and dendritic growth occurs in the transverse plane by lengthening and branching of these primary processes. This study demonstrates that a large number of classes of commissural interneurons can be recognized on the basis of characteristic morphologies and locations within the dorsal horn, intermediate zone and ventral horn of the embryonic rat spinal cord. This finding is consistent with the fact that commissural neurons project to many different targets and mediate a variety of different functions. The demonstration that dendritic arbors of spinal interneurons with characteristic morphologies can be conveniently labelled with DiI should prove useful in future studies on the development of specific circuits in the mammalian spinal cord.

Morphological analysis of the neurons in the area of the hypothalamic magnocellular dorsal nucleus of the guinea pig.

In the guinea-pig hypothalamus, a group of enkephalinergic cells forms a well-circumscribed nuclear area called the magnocellular dorsal nucleus (MDN). This nucleus gives rise to a prominent projection to the lateral septum: the hypothalamo-septal enkephalinergic pathway. In the present study, MDN neurons visualized by Golgi impregnation were subjected to morphological analysis in order to define the potential segregation of cellular types within the MDN. This study was complemented by additional observations of MDN neurons intracellularly injected by Lucifer yellow (LY) or horseradish peroxidase (HRP) during the in vitro incubation of hypothalamic slices. The following results were obtained from the analysis of 200 neurons: 163 Golgi-impregnated cells plus 37 injected cells (LY = 14; HRP = 23). Thirteen HRP-injected cells were precisely located in the MDN and 10 were located in the perifornical area surrounding the MDN. Four different cellular types were identified. Type-I neurons (41%) displayed a globular perikaryon, a variable number of primary dendrites that were poorly ramified, no preferential orientation, and an axon emerging from the perikaryon. Type-II neurons (30.5%) had a triangular perikaryon, three well-ramified primary dendrites, an orientation perpendicular to the third ventricle, and an axon emerging from the perikaryon. Type-III neurons (22%) exhibited a spindle-shaped perikaryon, two opposed well-ramified primary dendrites, an orientation perpendicular to the third ventricle, and an axon emerging from a primary dendrite. Type-IV neurons (6.5%), showed a globular perikaryon, a variable number of primary dendrites, poorly ramified dendrites, an orientation parallel to the third ventricle, and an axon whose orientation could not be identified. Neurons labeled after intracellular injection belonged to the first three cellular types.

Morphometric analysis of phrenic motoneurons in the cat during postnatal development

The dendritic geometry of 20 phrenic motoneurons from four postnatal ages (2 weeks, 1 and 2 months, and adult) was examined by using intracellular injection of horseradish peroxidase. The number of primary dendrites (approximately 11-12) remained constant throughout postnatal development. In general, postnatal growth of the dendrites resulted from an increase in the branching and in the length and diameter of segments at all orders of the dendritic tree. There was one exception. Between 2 weeks and 1 month, the maximum extent of the dendrites increased in parallel with the growth of the spinal cord; however, there was no increase in either combined dendritic length or total membrane surface area. In addition, there was a significant decrease in the number of dendritic terminals per cell (59.8 +/- 9.3 vs. 46.4 +/- 7.4 for 2 weeks and 1 month, respectively). The distance from the soma, where the peak number of dendritic terminals per cell occurred, ranged from 700-900 microns at 2 weeks and 2 months to 1,300-1,700 microns in the adult. The diameter of dendrites as a function of distance from the soma along the dendritic path increased with age. The process of maturation tended to increase the distance from the soma over which the surface area and dendritic trunk parameter (sigma d1.5/D1.5) remained constant. The three-dimensional distribution of dendrites was analyzed by dividing space into six equal volumes or hexants. This analysis revealed that the postnatal growth in surface area in the rostral and caudal hexants was proportionately larger than that in either the medial, lateral, dorsal, or ventral hexants. Strong linear correlations were found between the diameter of the primary dendrite and the combined length, surface area, volume, and number of terminals of the dendrite at all ages studied.

Administration or deprivation of nerve growth factor during development permanently alters neuronal geometry

We investigated whether the administration or deprivation of a neuronal growth factor during development can permanently alter the dendritic architecture of sensitive neurons. Nerve growth factor (NGF) or NGF antiserum treatment in the first 2-3 postnatal weeks markedly affected the survival, size, and dendritic arborization of mouse sympathetic ganglion cells acutely. Six months after the completion of treatment, the number of surviving neurons, cell body size, and higher order dendritic branching had changed considerably from their values at 3 weeks, suggesting that these parameters remain malleable throughout postnatal life. However, the number of primary dendrites, a fundamental determinant of organization within sympathetic ganglia, was permanently altered by the neonatal treatment protocol. The idea emerging from this study is that NGF influences the elaboration of primary dendrites by sympathetic ganglion cells only during a critical developmental period. In maturity, NGF acts as a "maintenance" factor necessary for normal neuronal function and survival, but neurons lose the capacity to respond with wholesale rearrangements of dendritic architecture.

Dendritic and synaptic properties of collicular neurons: A quantitative light and electron microscopical study of Golgi‐impregnated cells

The present study deals with a light- and electron microscopic morphometric analysis of Golgi-impregnated neurons in the superior colliculus of rats with the purpose to unravel inter- and intralaminar differences in their dendritic and synaptic organization. In particular, layer IV was studied and compared with its boundary layers III and V. The results show that collicular cells in layer IV basically form a homogeneous population with respect to the number of primary dendrites, the total length of impregnated dendrites, and the diameter, ellipticity, and orientation of dendritic fields and somata of Golgi-impregnated neurons. Somata of reconstructed small cells in layer III and IV as well as V have all a similar density of about 40 synaptic contacts per 100 microns2 surface. However, the cell bodies of large multipolar cells in layer V have a slightly but significantly larger synaptic density (about 50 per 100 microns2). Dendrites of large and small collicular cells had no significantly different synaptic densities (43 and 48 per 100 microns2, respectively). In conclusion, the present results show only minor dendritic and synaptic differences between individual cells in the same layer, as well as in neighboring layers, which implies a low degree of cellular and synaptic intra- and interlaminar differentiation. It is discussed that this organization differs markedly from that in other visual centers, including the collicular homologue, the tectum of lower vertebrates, and the mammalian visual cortex, where pronounced inter- and intralaminar differentiations exist. Such an organization may provide a framework of laminar specificity by which distinct cell types may select a restricted set of input out of all information available. The present quantitative investigation suggests that a similar framework is not present in the superior colliculus.

Early development of the human thalamus: Golgi and Nissl study

Qualitative and quantitative parameters of the early neuronal development of the thalamus were examined in human embryos and fetuses ranging in age from 5–16 gestational weeks (g.w.) using Nissl stained and Golgi impregnated tissue. In the earliest period analyzed, from 5–6 weeks of gestation, dorsal and ventral parts of the human thalamus were poorly differentiated structures forming the sides of the third ventricle. At 6 g.w., the prospective thalamic anlage consisted of the ventricular (VZ), the intermediate (IZ) and the marginal zones (MZ). The neurons in the VZ were bipolar and radially arranged to the ventricular surface. From 6–8 gestational weeks detached bipolar or branched bipolar cells with horizontal or oblique orientation were encountered in the IZ and occasionally in the MZ. In the period between 10–14 weeks of gestation, segregation of neurons into different thalamic nuclei began. The lateral geniculate nucleus, centrum medianum and mediodorsal nucleus were the first to be distinguished. In comparison with the previous period, the neurons throughout the rostro-caudal axis of the thalamus were more differentiated, with a higher number of primary dendrites that were often bifurcated. This resulted in various shapes of immature neurons: simple uni- and bipolar (type 1), branched uni- and bipolar (type 2) and young multipolar (type 3). In addition, the first spines were frequently observed on dendrites at 12 weeks of gestation. At 14–16 weeks of gestation, segregation of the neurons into thalamic nuclei continued. The neurons exhibited further dendritic differentiation that followed the caudo rostral gradient. For the first time, multipolar neurons, especially in the caudal part, could be subdivided into two classes: multipolar with a ‘bushy’ appearance, the result of many primary dendrites with several bifurcations and ‘simpler’ multipolar neurons with fewer and less branched primary dendrites. Neuronal differentiation was further expressed by an increase in the total dendritic length and somatic surface, up to six and three times, respectively, from the earliest period analyzed to 16 weeks of gestation. Dendritic length increased initially by the formation of new primary branches and their elongation and secondly by formation of higher branch orders. At 16 g.w., a group of immature cells were observed dorsally, on the frontal sections through the rostral thalamus. Its ganglionic eminence origin is discussed.

Reduced branching and length of dendrites detected in cervical spinal cord motoneurons of wobbler mouse, a model for inherited motoneuron disease

The Wobbler mouse (wr) has been proposed as a model for human inherited motoneuron disease (infantile spinal muscular atrophy). The primary defect is thought to be in the motoneurons. Therefore we undertook a survey of the qualitative and quantitative changes occurring in the cervical spinal motoneurons of Wobbler mice during a late stage of the motoneuron disease compared with age- and sex-matched normal phenotype (NFR/wr) littermates. The Rapid Golgi Method was applied. In control and Wobbler mice, four types of neurons were identified according to their dendritic patterns: multipolar, tripolar, bipolar, and unipolar cells. Unipolar cells were observed more often in the Wobbler specimens than the controls and may represent a final stage in the degeneration of other cell types with greater numbers of primary dendrites. Medium (300-999 microns 2) and large (greater than 1,000 microns 2) impregnated neurons (presumably alpha-motoneurons) showed strong indications of cell degeneration, including statistically significant reductions in the measurements for dendritic length, distribution, and branching, as well as the number of spines. In contrast, the small (less than 300 microns 2) neurons showed only mild signs of degeneration, including slight reductions in dendritic length, but no significant differences appeared in the distribution and branching of dendrites, or in the number of spines. Instead, a small increase could be detected in the number of primary and secondary dendritic branches emanating from the small neurons, as well as in the number of dendritic spines. These findings suggest that sprouting may occur to a slight extent. Although previous studies document that swelling with subsequent vacuolation of motoneurons is the predominant feature characterizing the Wobbler disease, the mean soma area (microns 2) calculated for the impregnated neurons of the Wobbler specimens showed no significant difference from the controls. It is hypothesized that the advanced signs of the Wobbler motoneuron disease are primarily reflected in the degeneration of the dendrites and spines on the medium and large alpha-motoneurons. The small neurons (presumably a mixed population of gamma-motoneurons, interneurons, and Renshaw cells) possess dendrites and spines that seem to be less affected, and instead show signs of sprouting.

Quantitative and morphometric analysis of Langerhans cells in non-exposed skin in renal transplant patients

Renal transplant recipients have a high incidence of cutaneous complications such as neoplasia and viral or fungal infections. Morphologic alterations of epidermal Langerhans cells (LC) have furthermore been described in these patients. Since these changes have been mainly found in sun-exposed skin, a direct effect of immunosuppressive therapy remains a matter of discussion. A quantitative and morphometric study of epidermal LC in non-exposed skin was performed in 28 renal transplant patients (RTP). RTP were divided in two groups according to immunosuppressive treatment: group A; azathioprine + prednisone (14 cases) and group B; cyclosporine + prednisone (14 cases). Twenty sex-age matched non-immunosuppressed patients acted as controls (group C). Epidermal sheets were obtained by incubation in EDTA and stained for ATPase activity and with the monoclonal antibody T6 (CD1) using the avidin-biotin peroxidase method. Langerhans cells were counted using a calibrated graticule (400x) and expressed as the mean number of LC/mm2. The mean area of the LC and the number of primary dendrites (pd) and secondary dendrites (sd) were determined with a morphometer adapted to an Apple II computer. The mean number of positive cells in controls was: ATPase, 677 +/- 157; T6, 695 +/- 164. Patients in group A had the maximum reduction in both ATPase and T6 LC density (ATPase, 339 +/- 142; T6, 402 +/- 194). Patients in group B had an intermediate reduction in the number of LC (ATPase, 494 +/- 121; T6, 529 +/- 112).(ABSTRACT TRUNCATED AT 250 WORDS)