Reciprocal connections of lateral septal neurons and neurons in the lateral hypothalamus in the rat: a combined phaseolus vulgaris-leucoagglutinin and Fluoro-Gold immunocytochemical study

Reciprocal connections between lateral septal neurons and neurons in the lateral hypothalamus/lateral preoptic area were studied in the rat. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) and the retrograde tracer Fluoro-Gold (FG) were simultaneously injected into the lateral septum. After double-immunocytochemistry, PHA-L-labeled terminals were found in synaptic contact with dendrites of retrogradely FG-labeled neurons in the lateral hypothalamic/lateral preoptic area.

Long-lasting transneuronal dendritic changes of GABAergic neurons in the monkey dentate gyrus following entorhinal cortex lesion

This study analyses dendritic changes of GABAergic neurons in the dentate gyrus of the African green monkey Cercopithecus aethiops upon lesioning of their main afferents, i.e., fibers originating form the entorhinal cortex (EC). Monkeys received a unilateral EC lesion (ECL) under visual control. Four, 10 and 365 days after surgery, GABAergic dentate neurons were immunostained for parvalbumin (PV). In comparison to the contralateral side, immunolabeled dendrites ipsilateral to the lesion appeared to be retracted from the outer portions of the molecular layer at all survival times. Dendritic changes were further analysed using an interactive neuron-tracing system. Whereas immunoreactive cell bodies were not reduced in number, the relative extension of dendrites throughout the dentate molecular layer was reduced by 40% 10 days postlesion (dpl) and recovered only up to 80% 365 dpl when compared with the control side. This was reflected by a decrease of the mean segment length, which included proximal dendrites and was apparent even after 365 dpl. The spread of the dendritic field was initially diminished by 50% and seemed to exhibit a long-lasting reduction. The findings are in line with previous results obtained in the rat, thus, indicating that similar transneuronal changes after ECL occur in the primate dentate gyrus. This may be of importance, since the EC appears to be a very early target area of affection in human neurodegenerative disorders, such as Alzheimer's disease.

Serotonin innervation of enkephalin containing neurones in the rat spinal trigeminal nucleus

Light and electron microscopic immunocytochemistry was used to examine the serotonin (5-HT) innervation of the rat spinal trigeminal subnucleus caudalis. 5-HT-immunoreactive fibres form a dense plexus in lamina I and outer lamina II and synapse with the cell bodies and proximal dendrites of local neurones. Light microscopic double labelling revealed that the 5-HT axons contact enkephalin immunoreactive neurones in both laminae. The 5-fHT electron microscopic results indicate that at least some of these contacts are likely to be synapses. 5-HT axons are therefore in a position to exert a direct action on enkephalinergic interneurones and this may contribute to the analgesic actions of the 5-HT system.

Morphology and birth dates of horizontal cells in the retina of a marsupial

Most eutherian (placental) mammals have two horizontal cell types; however, one type only has been seen in rodents. In order to assess whether one type of horizontal cell or two is a basic mammalian feature, we have examined the morphology of horizontal cells in a marsupial, the quokka wallaby, by Golgi staining or horseradish peroxidase labelling. The birth dates of horizontal cells have also been determined by 3H-thymidine/autoradiography. There are two types of horizontal cell in the wallaby retina. One type has no axon and corresponds to the axonless cell in eutherian species; the other has shorter dendrites, an axon, and an axonal arbor, corresponding to the eutherian short-axon cell. As in eutherian mammals, the dendrites of each horizontal cell type lie in the outer plexiform layer (OPL) and contact cones and the axonal arbor of the short-axon cell contacts rods. The dendrites of the axonless cells are long, with an average length of 250 microns, and each cell has one, sometimes two, short, stubby processes, which branch off a dendrite, traverse the inner nuclear layer, and reach the inner plexiform layer. The dendritic field of these cells is elongated, and dendrites show a preferential orientation at right angles to the trajectory of overlying ganglion cell axons. Short-axon cells have a morphology similar to that seen in other species, although the axonal arbor is relatively small. Both types of horizontal cell are generated in the first phase of retinal cell generation.

Granular layer collaterals of the unipolar brush cell axon display rosette-like excrescences. A Golgi study in the rat cerebellar cortex

The unipolar brush cell (UBC) is a medium-sized neuron located in the granular layer of the cerebellar cortex and morphologically characterized by a single dendritic shaft terminated by a brush-like tuft [Mugnaini and Floris, J. Comp. Neurol., in press]. This neuronal class is mostly encountered in the vestibular part of the cerebellum, although also present in the rest of the vermal folia. The UBC axon, as seen in Golgi impregnated material, has a tortuous course throughout the granular layer and gives off number of collaterals of variable diameter. Some of the axon collaterals enter the white matter only for a short distance, after which they ascend into the granular layer. Astonishingly, some of the thick granular collaterals of these axons display characteristic expansions resembling the rosette excrescences seen on mossy fibers. In our series these rosettes are mostly of the simple type [Palay, S. and Chan-Palay, V., Cerebellar Cortex. Cytology and Organization, Springer, Berlin, 1974], i.e. short swellings with simple globular contours. The exact projection targets and functional effect of the UBC axon and granular rosettes have still to be demonstrated.

The morphology of globus pallidus projection neurons in the rat: an intracellular staining study

The morphology of 23 intracellularly stained projection neurons of rat globus pallidus (GP) was studied in light microscopic preparations. The somatic size of these projection neurons was highly variable. The somatic area ranged from 78 to 353 microns 2. The 23 neurons were divided into aspiny and spiny types, based on the existence of dendritic spines. Sixteen neurons were aspiny and 7 were of the spiny type. The aspiny neurons tended to have a larger soma than the spiny neurons. Fourteen of the 23 projection neurons possessed a discoidal dendritic field with the flat plane parallel to the border between the GP and the neostriatum. All of the 14 neurons having a discoidal dendritic field were of the aspiny type and were located throughout the GP. The other 9 neurons, which include all of the 7 spiny types, had radiating dendritic fields with a variety of shapes and were located only in the medial region of the GP. The axons of a majority (i.e. 21 of 23) of the projection neurons emitted multiple collaterals with large boutons en-passant and boutons terminaux within the GP. The main axons were traced to varying distances from their somata. Four of them were traced into the substantia nigra. Two of these 4 emitted multiple collaterals at various rostro-caudal levels in the entopeduncular nucleus, and all 4 axons had one or two collaterals in the subthalamic nucleus. This study revealed that the rat GP contains two types of projection neurons having different dendritic morphologies. The axon reconstructions indicate that the activity of both types of neurons can influence multiple basal ganglia targets, including the GP itself.

Dystrophic dendrites induced in cultured Purkinje cells by exposure to vinblastine

Organotypic cerebellar cultures were exposed to the mitotic spindle inhibitor, vinblastine, and examined by light and electron microscopy, and electrophysiologically. Purkinje cells in exposed cultures had stunted, varicose dendrites when observed in preparations reacted with antibody to nonphosphorylated neurofilament protein. Ultrastructurally, microtubules were selectively reduced in Purkinje cell dendrites, which contained disarrayed excess smooth endoplasmic reticulum, but no large accumulations of densely packed neurofilaments. Spontaneous cortical discharges were initially increased in vinblastine treated cultures and then ceased, at which time the cultures became unresponsive to electrical stimulation. The vinblastine-induced changes were attributed to impaired intracellular transport secondary to disruption of Purkinje cell dendritic microtubules.

Thoracolumbar sympathetic preganglionic neurons in the dorsal commissural nucleus of the male rat: an immunohistochemical study using retrograde labeling of cholera toxin subunit B

The cell morphology of sympathetic preganglionic neurons (SPNs) in the dorsal commissural nucleus was studied by the retrograde labeling technique using cholera toxin subunit B (CTb) as a tracer. A small amount of an aqueous solution of CTb was injected unilaterally into the major pelvic ganglion of the male rat. Labeled SPNs were detected immunohistochemically using anti-CTb antiserum. Most of the labeled SPNs were observed in L1 to L3, and a very small number in T13. They were observed bilaterally in the sympathetic nuclei, such as the intermediolateral cell column, intercalated nucleus and the dorsal commissural nucleus. A loose network of longitudinally or transversely oriented SPN dendrites was located within the dorsal commissural nucleus itself. The lateral margin of the dorsal commissural nucleus was roughly demarcated by longitudinally oriented dendrites. Together with the dendrites of the SPNs of the intercalated and intermediolateral cell column, laterally oriented dendrites of the dorsal commissural nucleus converged and formed the transverse dendritic bundles in the intermediate zone that connect the dorsal commissural nucleus and the intermediolateral cell column. The transverse dendritic bundles were arranged periodically. The axons of the SPNs in the dorsal commissural nucleus traveled laterally into the transverse dendritic bundles, then turned ventrally near the intermediolateral cell column, and finally entered the ventral funiculus. After rhizotomy of the ventral roots of the upper lumbar cord, labeled SPNs were found only on the side contralateral to the rhizotomy. The dorsal commissural nucleus appears as a compact single cell column, but our results clearly show that this nucleus actually consists of two adjacent parallel columns of cells.

The Purkinje cell in olivopontocerebellar atrophy. A Golgi and immunocytochemical study

Purkinje cells were examined in three familial cases of olivopontocerebellar atrophy (OPCA) by means of the Golgi method, and neurofilament and calcium-binding protein immunocytochemistry. Reduced dendritic arborizations, as seen with different techniques, early formation of axonal spheroids, and abnormal accumulation of phosphorylated neurofilament epitopes in dendrites, somata and axonal spheroids, together with limited formation of proximal spine-like protrusions were the main changes in Purkinje cells. These lesions are unlikely to be the consequence of anterograde degeneration secondary to olivary atrophy, as postulated by some investigators, but probably represent primary damage to Purkinje cells in patients with OPCA. Reduced dendritic arborizations result in a decrease of receptor sites for parallel fibres and deprive granule cells of their main targets. Abnormal accumulation of neurofilaments in somata, dendrites and axonal spheroids may contribute to an abnormal transport and may impair protein turnover in the distal regions of Purkinje cells.

Developmental biology of olfactory sensory neurons

Proliferation, differentiation and death of olfactory neurons occur continually, even in adult animals. New data suggest that growth factors regulate the rate of cell proliferation. Early growth of olfactory axons in embryonic development is accompanied by the migration of epithelial cells from the olfactory placode toward the presumptive olfactory bulb. Maturation and ciliogenesis at the dendritic end of the cell is apparently dependent on a signal(s) from the bulb. The total life span of the neuron depends on maintenance of contact with the bulb. Olfactory life span is normally variable but is curtailed substantially in the absence of the bulb.

Mitral cell dendrites: a comparative approach

Phylogenetically persistent structures such as the mitral cells of the vertebrate olfactory bulb undergo changes in their dendritic arbor in the course of evolution. The morphology of mitral cells and the main elements of the olfactory bulb circuit in all classes of vertebrates are reviewed in this paper. Most of the neuronal elements found in the mammalian olfactory bulb are present in anamniotes. However, in contrast to those of amniotes, the mitral cells of most anamniotes lack basal dendrites, and periglomerular cells are absent in fish. This suggests a different circuitry and therefore drastic changes in the processing of olfactory information within the olfactory bulb. Lateral inhibition, conferred by basal dendrites in anamniotes, must then utilize other mechanisms in anamniotes. Moreover, the marked segregation of olfactory inputs onto mammalian mitral cells is less obvious in mitral cells of anamniotes that lack basal dendrites. The general role of dendrites, including those of mitral cells, is discussed in the light of increasing evidence for dendritic excitability. The evolutionary significance of mitral cell basal dendrites is also discussed.

Morphology of GABAergic neurons in the inferior colliculus of the cat

The goal of the present study was to provide a comprehensive and quantitative description of neurons immunoreactive for gamma-aminobutyric acid (GABA) in the inferior colliculus (IC) of the cat. Neurons were investigated with two different antisera and two different incubation methods. Free-floating frozen or vibratome-cut sections were incubated either with an antiserum to glutamic acid decarboxylase (GAD) or to GABA conjugated to protein with glutaraldehyde. Additional 1.5-microns-thick sections were incubated with the GABA antiserum after embedding and removal of the plastic. Quantitative data were obtained from much of this material. Despite the use of these different antisera and reaction methods, the results obtained were remarkably similar. The results show that GAD- or GABA-positive neurons represent a significant population of cells in the central nucleus of the IC, up to 20% of the neurons. Most of these neurons have large or medium-sized perikarya. In contrast, immunonegative neurons are medium-sized or small. Many GABA-positive neurons had proximal dendrites or somata oriented in parallel to the fibrodendritic laminae of the central nucleus and are presumed to be disc-shaped neurons. Other have an orthogonal orientation and are presumed to be stellate cells. Large GABA-positive neurons form two groups, those with many axosomatic endings and those with few. Collectively, these observations suggest that there are several types of GABAergic neuron in the central nucleus and, by extension, that these may participate in many types of inhibitory circuits.

The differentiation of dentate granule cells following transplantation

Immature cells transplanted into an adult host must adapt to their new environment. In the present study we have shown the dendritic development of dentate granule cells following transplantation. The adult host granule cells were lesioned by a fluid injection into the infragranular cleavage plane of the dentate gyrus. Few, if any, granule cells survived the lesion and the molecular layer (ML) shrank. When allogeneic neonatal granule cells were included in the fluid, the host granule cells were simultaneously killed and replaced. In order to visualize the dendrites, the granule cells were filled with Lucifer yellow (LY) in fixed sections and subsequently immunoreacted with an antibody to LY. The granule cell dendrites in the transplant were shorter in length, had a greater cross-sectional area, had more spines, and were more coiled and bent than control granule cell dendrites. The dendrites in the transplant formed functional synapses as indicated by cytochrome oxidase histochemistry and the transplant prevented xc03some of the ML shrinkage. Acetylcholinesterase (ACHE) xkreaction product increased both in lesioned and in transplant groups. The laminar pattern of ACHE in the control ML was not seen after the lesion and did not return in animals with successful transplants. We conclude that (i) the dendrites of neurons in the transplant adapted to the adult host environment and a shrinking ML with remarkable structural plasticity; (ii) the transplant prevented some of the shrinkage of the ML; (iii) the transplant could not reverse some of the lesion-induced changes in host organization, such as the organization of ACHE inputs to the ML; and (iv) a phenotypically specific population of transplanted neurons can replace traumatically lesioned neurons of the same type even if the host conditions continue to change.

GABAergic boutons establish synaptic contacts with the soma and dendrites of cuneothalamic relay neurons in the rat cuneate nucleus

This study investigates the synaptic relation between gamma-aminobutyric acid-immunoreactive (GABA-IR) and cuneothalamic relay neurons (CTNs) in the rat cuneate nucleus. Retrograde transport of wheat germ agglutinin conjugated with horseradish peroxidase complex (WGA-HRP) was used to label CTNs while anti-GABA immunogold serum was used for the detection of GABA-IR boutons associated with CTNs. With these procedures, immunogold-labelled GABA-IR boutons were found to form axosomatic, axodendritic and axospinous synapses with the WGA-HRP-labelled but immunonegative CTNs. Quantitative estimation showed that the mean ratios of GABA-IR to GABA-immunonegative boutons making synaptic contacts with somata, proximal dendrites, and distal dendrites were 47.9%, 49.1% and 34.7%, respectively. Statistical analysis showed that the incidence of GABA-IR boutons on the somata and proximal dendrites of CTNs was significantly higher than on the distal dendrites. Our results indicate that GABA is the primary inhibitory neurotransmitter in the cuneate nucleus, thereby emphasizing the importance of postsynaptic inhibition on cuneothalamic relay neurons.

Colocalization of somatostatin with GABA or glutamate in distinct afferent terminals presynaptic to the Mauthner cell

The presence of somatostatin in afferent fibers impinging on the goldfish Mauthner (M-) cell was determined using immunohistochemical methods, combined with confocal and electron microscopy, and the relationship of this peptide with inhibitory and excitatory terminals was studied. Somatostatin-reactive boutons were present only on the distal part of the M-cell's lateral dendrite. Somatostatin immunoreactivity was observed in typical large myelinated club endings (LMCEs) corresponding to mixed (electrical and chemical) eighth nerve primary afferent fibers. The axoplasm of these fibers contained dense-core vesicles (DCVs) dispersed among round vesicles. We have made a novel finding that the excitatory transmitter glutamate is present in LMCEs. Colocalization of this amino acid with somatostatin was detected in 75% of these endings using postembedding staining with gold particles of various sizes. The other structures labeled by somatostatin antibody were found to be small vesicle boutons (SVBs), which establish symmetrical synapses and contain a population of pleiomorphic vesicles with DCVs scattered among them. Double labeling with antibodies against glutamic acid decarboxylase and GABA allowed the definition of three types of biochemically characterized terminals: [somatostatin-GABA], [GABA], and [somatostatin]. However, the occurrence of DCVs in SVBs stained for GABA alone suggests that neuropeptides other than somatostatin may also coexist with GABA in this class of boutons. The coexistence of somatostatin with both inhibitory and excitatory neurotransmitters acting on the same region of a postsynaptic cell is discussed in relation to the role postulated for this peptide in synaptic plasticity.

The effect of age on dendrites in the rat superior cervical ganglion

Intracellular injection of a biotinylated probe in fixed superior cervical ganglia followed by confocal microscopy was used to investigate the effects of age on the dendritic arborisation of sympathetic neurons in rats aged 6 wk (young adult), 7 months (fully grown adult) and 24 months (aged). In accordance with other studies considerable dendritic growth was observed during postnatal development. However, in old age dendritic growth did not continue, and significant atrophy was observed. Quantitation of neuronal morphology showed significant reductions in soma size, total dendritic length, number of branch points and total area of dendritic arborisation in old age. Unexpectedly, significant reductions in the numbers of primary dendrites were observed in maturity and in old age. Concomitant with this atrophy there was an increase in age-related morphological abnormalities. The similarities between the atrophy and dendritic abnormalities shown by our aged neurons and those seen in other studies of young adult sympathetic neurons following axotomy or trophic factor deprivation are discussed.

Immunohistochemical localization of substance P receptor in the superior colliculus. A light and electron microscope study in the rat

The superficial layers of the superior colliculus (SC) have been known to contain many axons showing substance P-like immunoreactivity (SP-LI). We, therefore, immunohistochemically examined the distribution of SP receptor (SPR) in the superficial layers of the SC in the rat by using a specific antibody against SPR. The majority of SC neurons with SPR-LI were distributed in the zonal and the superficial gray layers, the rest of them were in the optic layer. Electron microscopy revealed that SPR-immunoreaction products in SC neurons were distributed not only in postsynaptic sites, but also in non-synaptic regions of perikaryal and dendritic profiles.

Pyramidal neurons in layer 5 of the rat visual cortex. III. Differential maturation of axon targeting, dendritic morphology, and electrophysiological properties

This paper describes the early morphological and physiological development of pyramidal neurons in layer 5 of the rat visual cortex in relation to the targets chosen by their axons. Cells were prelabeled by retrograde transport from the superior colliculus or the contralateral visual cortex and intracellularly injected either in fixed slices or after recording in living slices. In the adult, corticotectal cells have thick apical dendrites with an extensive terminal arborization extending into layer 1, and fire characteristic bursts of action potentials when injected with a depolarizing current; interhemispheric cells have slender apical dendrites that terminate without a terminal tuft, usually in layer 2/3, and they display a more regular firing pattern (Kasper et al.: J Comp Neurol, this issue, 339:459-474). At embryonic day E18 (when axons of the two classes of cells are already taking different routes towards their targets) and E21, pyramidal-like cells throughout the cortical plate all have similar soma-dendritic morphology, with spindle-shaped cell bodies and few, short basal dendrites but apical dendrites that all end in distinct tufts in the marginal zone. At postnatal day P3, after the axons of both cell classes have reached their targets, all pyramidal neurons in layer 5 still have distinct terminal arborizations in layer 1, though they vary in complexity and extent. The somata are now more mature (round to ovoid in shape), and the basal dendritic tree has extended. As early as P5, all cells studied could be clearly classified as tufted or untufted (considerably earlier than previously reported; Koester and O'Leary: J Neurosci 12:1382, '92), and these features correlated precisely with the projection target, as in the adult. Measurement showed that although interhemispheric cells lose their terminal tufts, in general the trunks of their apical dendrites do not withdraw but continue to grow, at roughly the same rate as those of corticotectal cells. The two classes of layer 5 pyramidal neurons differentiate from each other in three distinct phases: pathway selection by axons precedes the loss of the apical tuft by interhemispheric cells, and these morphological characteristics are established 10 days before the onset of burst-firing in corticotectal cells. These three steps may be guided by different molecular signals.

Pyramidal neurons in layer 5 of the rat visual cortex. II. Development of electrophysiological properties

Two major classes of pyramidal neurons can be distinguished in layer 5 of the adult rat visual cortex. Cells of the "thick/tufted" type have stout apical dendrites with terminal tufts, and most of them project to the superior colliculus (Larkman and Mason: J Neurosci 10:407, '90; Kasper et al.: J Comp Neurol, this issue, 339:459-474). "Slender/untufted" cells have thinner apical trunks with no obvious terminal tufts, and a substantial proportion of them project to the contralateral visual cortex. These two types also differ in their intrinsic electrophysiological features. In this study we describe the postnatal maturation of the electrophysiological and synaptic properties of layer 5 pyramidal neurons and relate these findings to the morphological development and divergence of the two cell types. Living slices were prepared from the visual cortex of rats aged between postnatal day 3 (P3) and young adults and maintained in vitro. Stable intracellular impalements were obtained from a total of 63 pyramidal cells of layer 5 at various ages, which were injected with biocytin so that morphological and electrophysiological data could be obtained from the same cell. Before P15, injection of a single cell sometimes stained a cluster of neurons of similar morphology, probably as a result of dye coupling. The incidence of such clustering and the number of neurons within each cluster decreased with age. There was no obvious difference in electrophysiological properties between cells in clusters and age-matched, noncoupled neurons. From P5, the apical dendrites of neurons could easily be classified as "thick/tufted" or "slender/untufted." On average, the resting potential became more negative, and membrane time constant and input resistance decreased with age. Electrophysiological differences between the "thick/tufted" and "slender/untufted" cell types did not become apparent until the third postnatal week, after which the "thick/tufted" cells on average had lower input resistances and slightly faster time constants than "slender/untufted" cells. The current-voltage relations of the neurons became progressively more nonlinear during maturation, with both rapid inward rectification and time-dependent rectification or "sag" becoming more prominent. There were also changes in the amplitude and waveform of action potentials, which generally approached adult values by 3 weeks of age. Action potential threshold became more negative, both in absolute terms and relative to the resting membrane potential. Action potentials became larger in peak amplitude and of shorter duration, with both rise and fall times decreasing progressively during development.(ABSTRACT TRUNCATED AT 400 WORDS)

Pyramidal neurons in layer 5 of the rat visual cortex. I. Correlation among cell morphology, intrinsic electrophysiological properties, and axon targets

Previous work has established two structure/function correlations for pyramidal neurons of layer 5 of the primary visual cortex of the rat. First, cells projecting to the superior colliculus have thick apical dendrites with a florid terminal arborization in layer 1, whereas those projecting to the visual cortex of the opposite hemisphere have thinner apical dendrites that terminate below layer 1, without a terminal tuft (e.g., Hallman et al.: J Comp Neurol 272:149, '90). Second, intracellular recording combined with dye injection has revealed two classes of cells: the first has a thick, tufted apical dendrite and fires a distinctive initial burst of two or more impulses, of virtually fixed, short interspike interval, in response to current injection; and the other, with a slender apical dendrite lacking a terminal tuft, tends to have a longer membrane time constant and higher input resistance, and does not fire characteristic bursts (e.g., Larkman and Mason: J Neurosci 10:1407, '90). The present study combined intracellular recording in isolated slices of rat visual cortex and injection of carboxyfluorescein, to reveal soma-dendritic morphology, with prior injection of rhodamine-conjugated microspheres into the superior colliculus or contralateral visual cortex to label neurons according to the target of their axons. This permitted a complete correlation of morphology, intrinsic electrophysiological properties, and identity of the projection target for individual pyramidal cells. Neurons retrogradely labeled from the opposite visual cortex were found in all layers except layer 1 while those labeled from the superior colliculus lay exclusively in layer 5. Within layer 5 interhemispheric cells were more concentrated in the lower half of the layer but extensively overlapped the distribution of corticotectal cells. Every cell studied that projected to the superior colliculus was of the bursting type and had a thick apical dendrite with a terminal tuft. Every cell in this study projecting to the opposite visual cortex was a "nonburster" and had a slender apical dendrite with fewer oblique branches that ended without a terminal tuft, usually in the upper part of layer 2/3. Interhemispheric cells also had rounder, less conical somata and generally had fewer basal dendrites than corticotectal neurons. Many cells with the physiological and morphological characteristics of interhemispheric cells were not back-labeled from the opposite visual cortex, implying that pyramidal cells of this type can have other projection targets (e.g., other cortical sites in the ipsilateral hemisphere).(ABSTRACT TRUNCATED AT 400 WORDS)

Synaptic interrelationships between the optic tectum and the ipsilateral nucleus isthmi in Rana pipiens

The nucleus isthmi is reciprocally connected to the ipsilateral optic tectum. Ablation of the nucleus isthmi compromises visually guided behavior that is mediated by the tectum. In this paper, horseradish peroxidase (HRP) histochemistry and electron microscopy were used to explore the synaptic interrelationships between the optic tectum and the ipsilateral nucleus isthmi. After localized injections of HRP into the optic tectum, there are retrogradely labeled isthmotectal neurons and orthogradely labeled fibers and terminals in the ipsilateral nucleus isthmi. These terminals contain round, clear vesicles of medium diameter (40-52 nm). These terminals make synaptic contact with dendrites of nucleus isthmi cells. Almost half of these postsynaptic dendrites are retrogradely labeled, indicating that there are monosynaptic tectoisthmotectal connections. Localized HRP injection into the nucleus isthmi labels terminals primarily in tectal layers B, E, F, and 8. The terminals contain medium-sized clear vesicles and they form synaptic contacts with tectal dendrites. There are no instances of labeled isthmotectal terminals contacting labeled dendrites. Retrogradely labeled tectoisthmal neurons are contacted by unlabeled terminals containing medium-sized and small clear vesicles. Fifty-four percent of the labeled fibers connecting the nucleus isthmi and ipsilateral tectum are myelinated fibers (average diameter approximately 0.6 microns). The remainder are unmyelinated fibers (average diameter approximately 0.4 microns).

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.

The unipolar brush cell: a neglected neuron of the mammalian cerebellar cortex

We describe with a variant of the Golgi method a new type of neuron that is prominently represented in the granular layer of the mammalian vestibulocerebellum but is presently neglected in all major accounts on the cerebellum. These neurons, here termed unipolar brush cells, are intermediate in size between granule cells and Golgi cells. They typically have a thin and presumably myelinated axon, and a single and stubby dendrite whose tip forms a tightly packed group of branchlets resembling a paintbrush. The branchlets often intertwine with the digitiform claws of granule cell dendrites and are occasionally approached by Golgi cell dendrites, indicating that the unipolar brush cells may share the input of the other granular layer neurons. Branchlets of neighboring unipolar brush cells converging into the same neuropil island also occur. The brush-like tip of the unipolar cell engulfs one or two mossy fiber rosettes to form an extensive synapse that appears to close recurrent loops involving the vestibular nuclei. Positive feedback in these loops could help to explain several motor responses and drive mechanisms of extended duration that are controlled by the ventral cerebellum.

The candelabrum cell: a new interneuron in the cerebellar cortex

A new cell type is described in silver-impregnated sections of the rat cerebellar cortex, uniformly distributed through all the cerebellar folia. The soma is rather small, roughly pyriform, vertically oriented, and squeezed, in a sandwich-like manner, between the Purkinje cell somata. One or two thick dendrites arise from the upper pole of the cell body and course through the entire molecular layer, dividing into a few, slightly oblique, branches that can reach the pia mater. These dendrites are covered with irregularly distributed spines. Some more slender dendrites emerge from the lower part of the cell body, or from the proximal trunk of a molecular dendrite, and spread tortuously for a short distance in the upper granular layer. A thick initial segment emerges directly from the soma or from the proximal portion of a dendrite, the axon winding then horizontally through or just above the Purkinje cell layer. During this horizontal course it gives off vertically oriented beaded branches ascending through the major part of the molecular layer. These branches, rather closely spaced, occupy different parasagittal planes, separated by about 10 to 30 microns. This axonal arborisation can thus be compared with a candelabrum. The peculiar three-dimensional spread of the axonal collaterals suggests a functional relationship between these branches and the dendritic trunks of neighbouring Purkinje cells. A comparative analysis of the morphological differences between this candelabrum interneuron and the other corticocerebellar interneurons found in the vicinity of the ganglionic layer confirms the specificity of this new cell class.

Development of the dendritic fields of layer 3 pyramidal cells in the kitten's visual cortex

The cat's visual cortex is immature at birth and undergoes extensive postnatal development. For example, cells of layers 2 and 3 do not complete migration until about 3 weeks after birth. Despite the importance of dendritic growth for synaptic and functional development, there have been few studies of dendritic development in the cat's visual cortex to correlate with numerous studies of functional and synaptic development. Accordingly, we used the Golgi method to study the development of the dendrites of layer 3 pyramidal cells in the visual cortex of a series of cats ranging in age from 2 days to 3 years. Blocks of visual cortex were impregnated by the Golgi-Kopsch method and sectioned in the tangential plane. Layer 3 pyramidal cells were drawn with a camera lucida and analyzed by Sholl diagrams and vector addition. In kittens < 1 week old, these cells were very immature, with only an apical dendrite and no basal dendrites. Basal dendrites appeared during the second week. By 2 weeks, all of the basal dendrites had emerged from the soma, but they had few branches and were tipped with growth cones. By 4 weeks, they had finished branching but continued to grow in length until, by 5 weeks, they reached their adult size. Examination of the basal dendritic fields in the tangential plane revealed that their dendritic fields were more elongated at 2 weeks than at later ages, perhaps because of their smaller size. The distribution of dendritic field orientations was uniform at all ages except 3 and 4 weeks, when there was a preponderance of fields oriented in the rostrocaudal direction. Because dendritic growth and branching occurred very rapidly over a period that precedes and overlaps with the peak periods of synaptogenesis and of sensitivity to the effects of early visual experience, they may depend on afferent visual activity. The early emergence of primary dendrites, however, suggests that this process is independent of afferent activity. The coincident timing of dendritic branching with the presence of dendritic growth cones suggests that branching may occur at growth cones.