Small Multipolar Neurons Research Articles

Different tonotopic regions of the lateral superior olive receive a similar combination of afferent inputs.

The mammalian lateral superior olive (LSO) codes disparities in the intensity of the sound that reaches the two ears by integrating ipsilateral excitation and contralateral inhibition, but it remains unclear what particular neuron types convey acoustic information to the nucleus. It is also uncertain whether the known conspicuous morphofunctional differences and gradients along the tonotopic axis of the LSO relate to qualitative and/or quantitative regional differences in its afferents. To clarify these issues, we made small, single injections of the neuroanatomical tracer biotinylated dextran amine (BDA) into different tonotopic regions of the LSO of albino rats and analyzed the neurons labeled retrogradely in brainstem auditory nuclei. We demonstrate that the LSO is innervated tonotopically by four brainstem neuron types: spherical bushy cells and planar multipolar neurons of the ipsilateral ventral cochlear nucleus, principal neurons of the ipsilateral medial nucleus of the trapezoid body, and small multipolar neurons of the contralateral ventral nucleus of the trapezoid body. Unexpectedly, the proportion of labeled neurons of each type was virtually identical in all cases, thus indicating that all tonotopic regions of the LSO receive a similar combination of inputs. Even more surprisingly, our data also suggest that the representation of frequencies in the LSO differs from that of the nuclei that innervate it: compared to the latter nuclei, the LSO seems to possess a relatively larger portion of its volume devoted to processing frequencies in the lower-middle part of the spectrum, and a relative smaller portion devoted to higher frequencies. J. Comp. Neurol. 524:2230-2250, 2016. © 2015 Wiley Periodicals, Inc.

Neuronal Organization of the Brain in the Adult Amphioxus (Branchiostoma lanceolatum): A Study With Acetylated Tubulin Immunohistochemistry.

Amphioxus (Cephalochordata) belongs to the most basal extant chordates, and knowledge of their brain organization appears to be key to deciphering the early stages of evolution of vertebrate brains. Most comprehensive studies of the organization of the central nervous system of adult amphioxus have investigated the spinal cord. Some brain populations have been characterized via neurochemistry and electron microscopy, and the overall cytoarchitecture of the brain was studied by Ekhart et al. (2003; J. Comp. Neurol. 466:319-330) with general staining methods and retrograde transport from the spinal cord. Here, the cytoarchitecture of the brain of adult amphioxus Branchiostoma lanceolatum was reinvestigated by using acetylated tubulin immunohistochemistry, which specifically stains neurons and fibers, in combination with some ancillary methods. This method allowed reproducible staining and mapping of types of neuron, mostly in brain regions caudal to the entrance level of nerve 2, and its comparison with spinal cord populations. The brain populations studied and discussed in detail were the Retzius bipolar cells, lamellate cells, Joseph cells, various types of translumenal cells, somatic motoneurons, Rohde nucleus cells, small ventral multipolar neurons, and Edinger cells. These observations expand our knowledge of the distribution of cell types and provide additional data on the number of cells and the axonal tracts and commissural regions of the adult amphioxus brain. The results of this comprehensive study provide a framework for comparison of complex adult populations with the early brain neuronal populations revealed in developmental studies of the amphioxus.

Morphology and Innervation of the Human Cremaster Muscle in Relation to its Function

The electromyographic properties of the cremaster muscle (CM) are quite different from other skeletal muscles. It shows excessive spontaneous discharges, and the motor unit shape and firing frequency of the CM muscle differ from that of limb muscles. In this study, CM of six adult cadavers and six orchiectomy specimens were used to reveal the detailed histology of the muscle and provide an anatomophysiological explanation for these unusual electromyographic properties. Routine histochemical stains revealed the CM was composed of several distinct bundles of smooth and striated muscle fibers within connective tissue. The smooth muscle fibers that were more profuse than previously known and were not arranged in layers, but widely dispersed between striated muscle fibers. Bielschowsky silver staining technique, anti-neurofilament and anti-synaptophysin immunostaining showed the presence of multiple motor end-plates observed as a series of small dots or lines running along the striated muscle fibers and several nerve endings on a single muscle fiber. Myosin immunostaining confirmed the CM is a slow-twitch muscle, and alpha-actin smooth muscle immunostaining confirmed the presence of a large number of smooth muscle fibers. There were also small multipolar neurons forming nerve plexuses between smooth muscle fibers. Anti-GFAP immunostaining confirmed the presence of glial cells similar to astrocytes. In conclusion, the findings of this detailed anatomical study showed the CM, widely known as a striated muscle, contains a large number of smooth muscle fibers, and the spontaneous electromyographic discharges are due to the presence of multiple motor end-plates and dense innervation.

The effect of aging on pars compacta of the substantia nigra in rhesus monkey.

This aim of this study was to re-evaluate the types of neurons present in pars compacta of the substantia nigra in the rhesus monkey, and then to determine the effects of aging on the morphology of both the neurons and neuroglial cells. The substantia nigra was therefore examined in Golgi impregnated material, in sections labeled with antibodies to tyrosine hydroxylase and to GABA, and in tissue embedded in plastic for light and electron microscopy. Three types of neurons were encountered: (1) large multipolar neurons with prominent Nissl bodies, (2) bipolar neurons that are medium sized and spindle-shaped, with Nissl bodies confined to the poles of the deeply indented nuclear envelopes, and (3) small multipolar cells with sparse Nissl substance. The large and medium neurons are believed to be dopaminergic and the small neurons GABA-ergic. With age, all of the neurons accumulate lipofuscin, especially the small multipolar neurons. In addition, Marinesco bodies appear within the nuclei of the large multipolar neurons. The dendrites are most severely affected by age; many of them lose organelles and their cytoplasm can become filled with vacuoles, membranous whorls, and dense bodies. In old monkeys many of the astrocytes have inclusions and in the neuropil there is a striking increase in the number of astrocytic processes. Also large spheroids appear. These appear to be derived from astrocytes and they have a core of dense granular material surrounded by a paler peripheral zone of cytoplasm from which processes can extend. Most of the oligodendrocytes have dense inclusions in their cytoplasm and many of the myelin sheaths break down. Microglial cells can become enormously swollen by phagocytosed material. Although both neurons and neuroglial cells are affected by age, no entities that could be construed to be dying neurons were encountered.

Immunocytochemical Localization of the AMPA Receptor Subunits in the Mesencephalic Trigeminal Nucleus of the Rat

The mesencephalic trigeminal nucleus is composed of large (35–50 µm) pseudo-unipolar neurons. Closely associated with them are small (< 20 µm) multipolar neurons. An unique peculiarity of the pseudo-unipolar perikarya is that they receive synaptic input from various sources, which sets them apart from the dorsal root and cranial nerves sensory ganglia neurons. Whereas glutamate is the best neurotransmitter candidate in pseudo-unipolar neurons, glutamatergic input into them has not yet been reported. AMPA glutamate receptors are implicated in fast excitatory glutamatergic synaptic transmission. They have been localized ultrastructurally at postsynaptic sites. This study demonstrates that the pseudo-unipolar neurons of the mesencephalic trigeminal nucleus express AMPA glutamate receptor subunits, which indicates that these neurons receive glutamatergic input. Serial sections from the rostral pons and midbrain of Sprague-Dawley rats were immunostained with antibodies against C-terminus of AMPA receptor subunits: GluR1, GluR2/3, and GluR4. The immunoreaction was visualized with avidin-biotin-peroxidase/DAB for light and electron microscopy. With GluR1 antibody only the smallest multipolar neurons were recognized as immunopositive within the mesencephalic trigeminal nucleus. GluR2/3 stained the pseudo-unipolar neurons intensely within the entire rostro-caudal extent of the nucleus. In addition the former antibody stained small multipolar neurons within the mesencephalic trigeminal nucleus, though with somewhat larger dimensions than those immunoreactive for GluR1. Whereas the overall staining with GluR4 antibody! was scant, those pseudo-unipolar neurons that were stained, were strongly stained. Furthermore, a considerable number of microglial cells within and surrounding the mesencephalic trigeminal nucleus displayed very intense immunoreactivity for GluR4. These results are discussed in the light of the glutamate receptor subunit composition.

Entwicklung, Zytoarchitektonik und Feinstruktur des mesencephalen Trigeminuskerns bei Hauswiederkäuern *

The ontogenetic development and cell differentiation of the mesencephalic trigeminal nucleus (Ntm) is lightmicroscopically examined in 58 bovine embryos and fetuses ranging from 2.4 to 80 cm Crown-Rump-Length (CRL). The cytoarchitecture and fine structure in adult cattle, sheep, and goats are investigated with the aid of light- and electronmicroscopy. At 2.4 cm CRL, the proneurons of the Ntm are detectable for the first time within the ventricular zone of the alar plate, possessing one drop-like cytoplasmic protrusion, whereas at 5 cm CRL, two cell types with differing sizes appear. Up to a CRL of 11.5 cm, the nucleus shows advanced maturation processes and has reached his final position at the border of the mesencephalic central grey. From 26 cm CRL onward, three cell types, and at 34 cm CRL four cell types, are discernible based on their nissl-granule arrangement. The cytomorphological differentiation and the maturation of the cells proceeds until 56 cm CRL, at which point the topographical and cytological characteristics of the Ntm are comparable with those of adult animals. In adult cattle, sheep and goats the Ntm consists of large (40-60 microns) and scarce medium-sized (30-40 microns) neurons with round and oval shapes. Scarcer small (20-25 microns) round and medium-sized multipolar neurons occur. The Nissl bodies are scattered throughout the pericaryon of the large neurons in a dust-like pattern and in the medium-sized neurons in a grained form. Within the cytoplasmic streets, which are situated between the membranes of the rough ER, numerous neurofilaments and mitochondria are detectable. Large Golgi complexes are placed in a perinuclear position. The neurons are also characterized by some somatic spines, and by a moderate distribution of axosomatic synapses, in which axon-endings with flattened synaptic vesicles predominate.

Distribution of neurofilament protein and calcium-binding proteins parvalbumin, calbindin, and calretinin in the canine hippocampus

Neurofilament protein and calcium-binding proteins parvalbumin, calbindin, and calretinin are present in morphologically distinct neuronal subpopulations in the mammalian cerebral cortex. Immunohistochemical studies of the hippocampal formation and neocortex have demonstrated that while neurofilament protein and calbindin are localized in subsets of pyramidal neurons, the three calcium-binding proteins are useful markers to differentiate non-overlapping populations of interneurons. To date, most studies have been performed in rodents and primates. In the present analysis, we analyzed the distribution of these proteins in the canine hippocampus. Neurofilament protein was present in large multipolar neurons in the hilus and in pyramidal neurons in the CA3 field, whereas pyramidal neurons in the CA1 field and subiculum were less intensely immunoreactive. Parvalbumin immunoreactivity was observed in large multipolar neurons in the hilus and throughout the CA3-CA1 fields, in a few pyramidal-shaped neurons in the CA1 field and subiculum, and had a distinct neuropil staining pattern in the granule cell layer and stratum pyramidale of the Ammon's horn. Calbindin immunoreactivity displayed a strong labeling of the granule cells and mossy fibers and was also observed in a population of moderately immunoreactive neurons in the CA1 field and subiculum. Calretinin immunoreactivity was relatively weaker overall. The inner molecular layer in the dentate gyrus had a distinct band of labeling, the stratum lacunosum/moleculare contained a punctate neuropil staining, and there were a few small multipolar neurons in the hilus, CA3-CA1 fields, and subiculum. Comparison of the staining patterns observed in the dog hippocampus with those in human, macaque monkeys and rats revealed that although there are some subregional differences among these taxa, the dog may constitute a valuable large animal model for the study of certain neurological conditions that affect humans, in spite of the phylogenetic distance between carnivores and primates.

Fine structure and synaptic organization of the mesencephalic trigeminal nucleus of the cat: a quantitative electron microscopic study.

The ultrastructure and synaptic organization of the mesencephalic trigeminal nucleus (MTN) were studied in adult cats by transmission electron microscopy and more precisely quantified with an automated image analysis system. Two subpopulations of MTN neurons were identified within the nucleus: large spherical or ovoid (pseudo)unipolar cells amounted to about 60% of the total population that resemble typical primary sensory neurons and small multipolar neurons (estimated 40%), some of which are possibly interneurons. By electron microscopy, most neurons in the MTN proved to have a rich cytoplasm in the perikaryon with abundant rough endoplasmic reticulum, a large number of free ribosomes and polysomes, also well-developed Golgi complex, and numerous mitochondria and neurofilaments indicating a high rate of protein synthesis and axonal transport in these cells. Three types of synaptic contacts were observed in the MTN: axodendritic, axosomatic and axospinic of both symmetric and asymmetric morphology. Most of them (almost 90%) were axodendritic and axodendritic spine. Approximately 70% of axon terminals contained small round vesicles (S-type boutons) whereas the other 30% belonged to the P-type boutons filled with a pleomorphic vesicle population. Axosomatic synapses were comparatively rare accounting for 10% of the total. About two-third of them were of S-type and almost 25% of the remaining third were F-type in which flat synaptic vesicles could be seen, and less than 10% were P- and G-types with granular vesicles.

Types of callosally projecting nonpyramidal neurons in rat visual cortex identified by lysosomal HRP retrograde labeling.

Callosally projecting neurons, labeled following injection of horseradish peroxidase (HRP) into the 17/18a border of the contralateral hemisphere, have been examined by light and electron microscopy. These neurons exhibit two types of horseradish peroxidase labeling: either a diffuse, Golgi-like labeling, or a granular, punctate labeling. The punctate type of HRP-labeling is the predominant form in nonpyramidal neurons, while pyramidal neurons frequently display either diffuse or punctate labeling. Only punctately labeled neurons have been examined in this study. Light microscopic analyses of 1-microns sections show that in the heavily labeled zone at the area 17/18a border approximately 9% of all of the cells in layer II/III are callosally projecting nonpyramidal cells, and 70% of them are callosally projecting pyramidal cells. Light and electron microscopic examinations indicate that the nonpyramidal neurons are a heterogeneous group which consists of small multipolar neurons, large multipolar neurons, small bipolar neurons, and large bipolar neurons. To investigate the ultrastructural appearance of the punctate HRP labeling, selected neurons have been examined in thin sections. In the electron microscope, the tetramethylbenzidine (TMB) reaction product appears as electron-dense crystals, while the diaminobenzidine (DAB) reaction product appears as dark, electron-dense material which fills the lysosomes. These lysosomes occasionally have a halo of reaction product, but often they are not morphologically distinguishable from dark lysosomes present within neurons from control animals in which the darkening results from staining the thin sections with lead citrate and uranyl acetate. However, labeled neurons possess more dark lysosomes than neurons from control animals. These additional dark lysosomes presumably contain the HRP reaction product visible by light microscopy.

Calbindin immunoreactivity in normal human temporal neocortex

Calbindin immunoreactivity in the temporal neocortex was examined in 4 subjects with no neurological, metabolic or malignant disease. The brains were obtained between 1 and 4 h after death and rapidly fixed by perfusion with 4% paraformaldehyde through the carotid arteries, cut into slabs, cryoprotected and stored at −80°C. Sections of the whole left temporal lobe obtained with a freezing microtome were processed free-floating with a well known monoclonal antibody against calbindin according to the peroxidase-antiperoxidase (PAP) method. Calbindin-immunoreactive (CaBP-ir) neurons were found to be local-circuit neurons (interneurons) mainly distributed in the upper cortical layers (layers I, II and III), and were categorized as small multipolar neurons with ascending dendrites ramifying in the molecular layer, small bitufted cells, pyramid-like cells in layer II, horizontal neurons in the molecular layer, multipolar neurons with long descending dendrites, and large double-bouquet cells, some of them exhibiting a very long dendrite with claw-shaped terminals in layer V. Less than 10% of all CaBP-ir neurons were localized in the remaining cortical layers. Pyramidal cells were only very weakly or not stained at all. In addition, CaBP-ir fibres formed a dense plexus in the molecular layer, and vertical bundles 8–10 μm thick and 500–600 μm long, separated by blank spaces 20–40 microns wide were distributed in layers III and V/VI. CaBP-ir neurons and fibres, through their contacts with pyramidal cells, may regulate contralateral and ipsilateral cortico-cortical connections, may control the vertical neuronal inhibition across different cortical layers, and may regulate the excitability of most pyramidal cells through their terminal bouquets ramifying in the molecular layer.

Neuronal typology of the thalamic area triangularis of Gallotia galloti (reptilia, sauria).

In a Golgi study of the area triangularis (AT), a rostral nucleus of the ventral thalamus of Gallotia galloti, we have identified four major neuronal types on the basis of their morphological characteristics: medium-sized fusiforms with two processes, medium-sized fusiforms with three or four processes, small bipolars, and small and medium-sized multipolars. These neurons are characterized by a simple morphology and radial arrangement. Cell size varies from small to medium, and all axons project laterally. These characteristics distinguish AT neurons from those of neighboring nuclei. In addition, we found some evidence of differential topographic distribution of each neuronal type within the nucleus. Medium-sized fusiform neurons with two processes are located in the most ventral part, where they constitute the ventral nuclear limit. Small multipolar neurons prevail in the dorsal and ventromedial parts, and in the rest of the nucleus medium-sized neurons, including both fusiform with three or four processes and multipolar types, are normally found. Finally, we discuss a putative homology of the reptilian AT with a part of the mammalian zona incerta.

Fetal tectum grafted as a cell suspension into the adult rat inferior colliculus

The known structural and functional features of the inferior colliculus provided an advantageous substrate for examining the outcome of neural transplantation. In the present study, tissue from the midbrain tectum of Sprague-Dawley rat fetuses was removed at 15, 16 and 19 days of gestation (E15, E16 and E19), incubated as a dissociated cell suspension for 12 to 15 h in a medium containing True Blue for prelabeling, and injected into the central nucleus of the inferior colliculus (CNIC) of 28 normal male adult conspecifics. Viable tectal grafts were found in 57.5% of host animals with 65.2% located in CNIC. Grafts of E16 tissue had a survival rate of 84.2%, which was twice that of E15 or E19 donors, and there was no difference in graft survival rate in hosts sacrificed up to 6 months after the implantation procedure. Neurons prelabeled with True Blue and counterstained with thionin were identified as uniquely green stained cells in brightfield illumination and brilliant opaque cells in darkfield microscopy. Grafts were organized in tightly packed clusters of cells including large rounded polygonal and smaller cells similar in size to normal CNIC large and small multipolar neurons. Cell morphology of the larger ovoid and fusiform grafted neurons most closely resembled that of typical adult CNIC cell populations; other implanted cell types appeared immature even when host post-implant survival was extended. At longer post-implant intervals graft and host cells further intermingled, and both cellular and fibrous bridges were observed at the interface between host and graft tissue. The present work demonstrates the viability and development of homotypic cells grafted into a central auditory structure utilizing a simple method of prelabeling donor tissue with a fluorescent dye.

Quantitation of catecholamine neurons in the locus coeruleus in human brains of normal young and older adults and in depression

A quantitative study of the morphology and distribution of norepinephrinergic neurons in the human locus coeruleus (LC) is given for normal young and older adult brain. Norepinephrine (NE)-producing neurons are identified by immunocytochemistry of two NE biosynthetic enzymes, tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH), visualized by the peroxidase-antiperoxidase and immunogold-silver-staining methods. TH and DBH immunoreactions yield equivalent results. Both immunocytochemical visualization methods allow detailed analysis of neuronal morphology. The neurons of the human LC fall into four classes: large multipolar neurons with round or multiangular somata, large elliptical "bipolar" neurons, small multipolar neurons, and small ovoid "bipolar" neurons. Though most of the neurons contain neuromelanin pigment, some larger neurons lack pigmentation. Dendritic arborization of all neurons is extensive. Computer-assisted quantitative measurements of the parameters somatic size, dendritic arbor length, surface area, and volume are given. Somatic areas of LC neurons of all four classes are decreased in older adult brain, but dendritic arborization is equally extensive as in the younger. The rostrocaudal length of the LC is approximately 15 mm, and no age-dependent decrease is observed. Computer-assisted mapping of immunoreactive neurons and three-dimensional reconstruction allow division of the LC into rostral, middle, and caudal parts with characteristic distribution of neurons. Small neurons predominate in all parts, but the relative contribution of larger cells decreases in a rostrocaudal direction. A cell loss of 27-37% occurs in older adult brains and to 55% in the brain of a chronically depressed patient without dementia. Cell loss is highest in the rostral part, lower in the middle, and absent in the caudal part, and more small cells are lost than larger ones.

Laminar distribution and morphology of gamma‐aminobutyric acid (GABA)‐immunoreactive neurons in the medial and dorsomedial areas of the cerebral cortex of the lizard Podarcis hispanica

The morphology and laminar distribution of immunolabeled neurons in the medial and dorsomedial telencephalic cortices of the lizard Podarcis hispanica were examined in vibratome sections after preembedding gamma-aminobutyric acid (GABA)-immunocytochemistry. In both cortical areas and at all rostrocaudal levels, GABA-immunoreactive neurons were found in all cortical layers, with the largest number (74%) of GABA-positive cells in layer 3. GABA-positive neurons were classified into pyramidlike, vertical-fusiform, multipolar, and horizontal neurons. Cells that could be so classified were counted in each cortical lamina. In the medial cortex, multipolar and horizontal-bipolar cells dominated layer 1. Layer 2 displayed mainly horizontal and pyramidlike cells at its outer margin and pyramidlike cells at its inner margin. In layer 3, horizontal cells were the prevalent group. In the dorsomedial cortex, layer 1 mainly contained small multipolar neurons (35% of layer-1 cells) in its outer third and vertical-fusiform neurons (37% of layer-1 cells) in its inner two thirds. In layer 2, 47% of the few GABA-positive perikarya were pyramidlike. The largest population of neurons in layer 3 was that formed by multipolar cells (45% of layer-3 cells). Ultrastructural examination revealed that GABA-immunoreactive neurons possessed indented euchromatic nuclei with a central nucleolus. Their cytoplasm contained numerous mitochondria and a very well-developed granular endoplasmic reticulum. Their somata were contacted by numerous unstained boutons making asymmetric contacts and by a few symmetric synapses of GABA-positive terminals. Dendrites of GABA-immunoreactive cells were thin, with irregular outlines, and generally aspinous. Like the somata, dendrites were contacted by many unstained asymmetric synapses. Some dendritic profiles also received symmetric contacts from GABA-positive boutons. GABA-positive terminal-like puncta were found throughout the layers, with a maximal concentration in layer 2. Electron microscopy confirmed that nearly all of the puncta represent GABA-positive terminal boutons. Comparison of GABA-immunoreactive cells in Podarcis with those found in the mammalian hippocampus suggests that these cells may be inhibitory neurons, as in the hippocampus of mammals.

GABA‐like immunoreactivity in the pedal ganglia of Mytilus galloprovincialis: Light and electron microscopic study

The distribution of gamma-aminobutyric acid (GABA)-like immunoreactivity was investigated in the pedal ganglia (PG) of Mytilus galloprovincialis (Mollusca, Bivalvia) with the aid of an antiserum raised against GABA coupled to bovine serum albumin. Examination of whole-mount preparations and serial vibratome and semithin sections showed the presence of different types of immunoreactive neurons. Small unipolar neurons were the most numerous, and were located mainly in the lateral ganglion cortex. A few bipolar and small multipolar neurons were scattered in the cortex, and, more rarely, in the neuropile. Furthermore, two large symmetrical multipolar neurons, the processes of which extended over large fields in the ipsilateral and contralateral neuropile, were consistently observed in each ganglion. Immunoreactive fibers formed networks in the neuropile and ran parallel in the commissure and in all nerves and connectives. The morphology and distribution of neurons and fibers immunostained by the anti-GABA serum were similar to those of GAD-like immunoreactive elements, which indicates that the neurotransmitter and its biosynthetic enzyme are present in the same neurons. Moreover, comparison of serial semithin sections alternatively incubated in postembedding with anti-GABA and antiserotonin sera revealed that immunoreactivity for these two substances was present in different neuronal populations. However, close association between serotoninlike and GABA-like immunoreactive elements was observed in a few PG areas. GABA-like immunoreactivity was demonstrated on ultrathin sections by using secondary antiserum coupled to colloidal gold particles. Labeling was found over somata, fibers, and varicosities containing a distinct type of small (63 nm), pleomorphic, dense-cored vesicle.

Dorsal raphe serotonergic projection to the retina. A combined peroxidase tracing-neurochemical/high-performance liquid chromatography study in the rat

The existence of retinopetal neurons in the rat was verified using a morphological and neurochemical approach. Horseradish peroxidase injected into the posterior chamber of the eye labeled polygonal, ovoid, fusiform and small multipolar neurons in the lateral cell groups of the dorsal raphe nucleus. Very small electrolytic lesions of this region produced after several days of survival a significant decrease in the serotonin content of the retina. These results demonstrate the existence of a centrifugal projection to the retina from the lateral cell groups of the dorsal raphe nucleus and show its probable serotonergic nature. Besides, they also provide a new possibility to explain the presence of serotonin in the retina.

Primary afferent projections to the central octavus nuclei in the elasmobranch, Rhinobatos sp., as demonstrated by nerve degeneration.

Nerve degeneration studies were performed to determine the central projections of the octavus nerve in the guitarfish. Rhinobatos sp. Most first-order octavus nerve afferents are confined to the ventral longitudinal column of the medulla, which consists of four octavus nuclei: the nucleus octavus anterior (NOA), nucleus octavus magnocellularis (NOM), nucleus octavus descendens (NOD); and nucleus octavus posterior (NOP). Central projections of the octavus nerve outside of the ventral octavus nuclear column are to the vestibulolateral lobe of the cerebellum, the large multipolar cells that lie deep to the cerebellar crest of nucleus intermedius, the reticular formation, and the nucleus octavolateralis efferens. In addition, the cytoarchitectural features of the four octavus nuclei have been analyzed: the NOA consists of large spindle-shaped neurons and medium-sized multipolar neurons; the NOM is a small nucleus consisting of very large multipolar neurons; the NOD contains several types of neurons including large spindle-shaped neurons, large multipolar neurons, and polymorphic small and medium-sized neurons; and the NOP contains small spherical and small multipolar neurons evenly distributed throughout the nucleus. On the basis of the morphology of the neurons, the NOA and NOD appear to have subdivisions suggesting a more complex organization of the octavus nuclear column than previously recognized.

The midbrain periaqueductal gray in the rat. II. A Golgi analysis

This study consists of a detailed analysis of neurons in the midbrain periaqueductal gray of the rat utilizing four variants of the Golgi technique. Neurons were classified into three major categories based on soma shape, number of primary dendrites, number of dendritic bifurcations, interspinous distance, axonal origin, and axon trajectory. Neurons in each category were further subdivided into large and small varieties based predominantly on soma size and dendritic patterns. Both quantitative and qualitative data concerning each neuronal type is provided as well as data relating to its relative distribution among the four periaqueductal gray subdivisions. The small bipolar neuron, characterized by its small size and spindle-shaped soma, was the most prominent cell type observed, composing 37% of the impregnated neurons in our material. This cell type was most numerous in the medial subdivision and least prominent in the dorsolateral subdivision. The small triangular neuron composed 23% of the neuronal population and was relatively evenly distributed through the periaqueductal gray. The remaining four cell types include the large and small multipolar neurons, the large fusiform neurons, and the large triangular neurons. Axons originated from either the perikaryon or a proximal dendrite, with a dendritic origin being most common for large and small triangular neurons and large fusiform neurons. The trajectory of axons in single thick coronal sections originating from periaqueductal gray neurons is typically away from the mesencephalic aqueduct. The exact trajectory is dependent on the location of the neuron. Axons arising from cells in the dorsal subdivision usually project in a dorsal or dorsolateral direction while axons of ventrolateral neurons may project dorsally, laterally, or ventrally. In sum, these data indicate a complex level of internal organization of the periaqueductal gray. The results are discussed in terms of previous immunohistochemical studies of neurons in this region.

Immunocytochemical studies of the peptidergic content of fibers and terminals within the lateral spinal and lateral cervical nuclei

As part of a series of studies in which we are attempting to determine the roles of the lateral spinal (LSn) and lateral cervical (LCn) nuclei in somatic sensation, we have examined the fibers and terminals within these nuclei in the rat using the indirect immunofluorescence technique. Eleven antisera were used. Within the LSn, antisera against dynorphin 1-8 (DYN), substance P (SP), and Met-enkephalin (ENK) produced labeling of a large number of processes in all segmental levels examined. Processes labeled with these antisera frequently apposed the cell bodies and dendrites of LSn neurons. Antisera against somatostatin (SOM) and FMRF-NH2 (FMRF) labeled smaller numbers of processes within the LSn. Few, if any, processes in the LSn were labeled using antisera against serotonin, cholecystokinin octapeptide, oxytocin, neurotensin, corticotrophin-releasing factor, and vasoactive intestinal polypeptide. In contrast to the LSn, the LCn contained virtually no labeled processes irrespective of the antiserum employed. An area was found adjacent to the LCn in the medial portion of the dorsal lateral funiculus (DLf) of C2 that resembled the LSn in several of its anatomical characteristics: like the LSn, the medial portion of the C2 DLf contained small multipolar neurons; it was similar to the LSn in its medial-lateral extent; and following staining with each antiserum, the LSn and the medial DLf of C2 contained a similar number of labeled processes. The peptide-containing area in the medial DLf of C2 was found to be continuous with the LSn. We therefore propose that this region is a rostral extension of the LSn.(ABSTRACT TRUNCATED AT 250 WORDS)

The dendritic architecture of the visual pretectal nuclei of the rat: a study with the Golgi-Cox method.

The dendritic architecture of the neurons of the visual pretectal nuclei in the rat was studied with the Golgi-Cox method. The olivary pretectal nucleus (PO) is characterized by distinctive neurons with a gnarled, tufted, richly branched dendritic arbor forming a dense neuropil within the nucleus. The distinct dendritic morphology of the olivary pretectal neurons enables this nucleus to be identified at all levels of the pretectum in Golgi-impregnated preparations. Rostromedially, the PO is surrounded by peripheral neurons whose dendrites wrap around the surface of the PO. The nucleus of the optic tract (NTO) contains three types of cells: (1) superficial horizontal cells whose dendrites extend out transversely; (2) large multipolar neurons whose dendrites spread out predominantly in a transverse plane, and (3) small to medium multipolar neurons with varying dendritic architecture. The posterior pretectal nucleus (PP) is composed predominantly of (1) multipolar cells with horizontally and vertically oriented dendrites extending out transverse to the optic axons; (2) piriform cells with dendrites extending dorsally toward the brachium; and (3) small multipolar neurons. The presence of superficial horizontal and large multipolar neurons in the NTO distinguishes the NTO from the PP in Golgi preparations. The horizontally oriented dendrites of many of the multipolar neurons in the PP give this nucleus an appearance distinct from that of the NTO. The differences in dendritic morphology between the visual pretectal nuclei in the rat permit identification of these nuclei at all levels within the pretectum. The boundaries of these nuclei, as determined in the Golgi-Cox preparations, correlate quite well with the boundaries defined by studying retinal projections (Scalia and Arango, '79).