Golgi study of the anterior dorsal ventricular ridge in a lizard. I. neuronal typology in the adult

Using Golgi techniques we have studied neuronal cell types in the anterior dorsal ventricular ridge (ADVR) of the adult lizard Gallotia galloti. Multipolar, bitufted, and juxtaependymal neuronal forms were found. The multipolar and bitufted neurons are present in both the periventricular and central ADVR zones. Multipolar neurons can be subdivided into multipolar neurons with polygonal somata and four to six main dendritic trunks and multipolar neurons with pyramidal somata and three or more dendritic trunks. The former are the cells most frequently impregnated in the ADVR. In the population of bitufted neurons, we distinguish subtypes I, II, and III according to the number of dendritic trunks that emerge from the somata. Juxtaependymal neurons are restricted to a cell-poor zone, adjacent to ependymal cells. Their dendrites either are orientated parallel to the ventricular surface or extend into the periventricular zone. The dendrites of ADVR neurons have pedunculated spines with knob-like tips. However, such spines do not appear on the somata or on the primary dendritic trunks. The number of spines is scarce or moderate. The periventricular neuronal clusters contain two to five cells. The morphology of these neurons is mainly multipolar, but we also found some bitufted neurons.     

A Golgi study of anterior dorsal ventricular ridge in the alligator,Alligator mississippiensis

The anterior dorsal ventricular ridge was examined in the American alligator, Alligator mississippiensis, with cresyl violet and Golgi-Kopsch preparations. Four cytoarchitectonic areas (lateral dorsolateral, medial dorsolateral, intermediolateral, and lateral) can be distinguished by variations in the density of neurons and their tendency to form clusters of neurons with apposed somata. Three distinct types of neurons are distributed throughout these areas. Juxtaependymal neurons lie near the ventricular surface and have dendritic fields paralleling the ependymal layer. Their dendrites bear a moderate density of spines. Spiny neurons all have stellate shaped dendritic fields and dendrites that bear dendritic spines, but they vary greatly in the density of spines and the thickness of their dendrites. A very spiny variety has a high spine density and relatively thick dendrites. A moderately spiny variety has a moderate spine density and thin dendrites. A sparsely spiny variety has a low spine density and thick dendrites. Aspiny neurons have a relatively large number of dendrites that form a gnarled dendritic field and lack spines.     

Structure of anterior dorsal ventricular ridge in snakes.

Anterior dorsal ventricular ridge (ADVR) is a major subcortical, telencephalic nucleus in snakes. Its structure was studied in Nissl, Golgi, and electron microscopic preparations in several species of snakes. Neurons in ADVR form a homogeneous population. They have large nuclei, scattered cisternae of rough endoplasmic reticulum in their cytoplasm, and bear dendrites from all portions of their somata. The dendrites have a moderate covering of pedunculated spines. Clusters of two to five cells with touching somata can be seen in Nissl, Golgi, and electron microscopic preparations. The area of apposition may contain a series of specialized junctions which resemble gap junctions. Three populations of axons can be identified in rapid Golgi preparations of snake ADVR. Type 1 axons course from the lateral forebrain bundle and bear small varicosities about 1 mu long. Type 2 axons arise from ADVR neurons and bear large varicosities about 5 mu long. The origin of the very thin type 3 axons is not known; they bear small varicosities about 1 mu long. The majority of axon terminals in ADVR are small (1 mu to 2 mu long), contain round synaptic vesicles, and form asymmetric active zones. This type of axon terminates on dendritic spines and shafts and on somata. A small percentage of terminals are large, 5 mu in length, contain round synaptic vesicles, and form asymmetric active zones. This type of axon terminates only on dendritic spines. A small percentage of terminals are small, contain pleomorphic synaptic vesicles, and form symmetric active zones. This type of axon terminates on dendritic shafts and on somata.     

Anterior dorsal ventricular ridge in the lizard: Embryonic development

In lacertids the telencephalic vesicle starts its development at stage E = 30, at which time it is lined by a homogeneous nucleated zone in which particular ventricular zone territories or sulci cannot be distinguished. At stage E = 32 coinciding with the initial development of the anterior dorsal ventricular ridge (ADVR), one may distinguish the ventricular zone b in the dorsolateral wall of the ventricle adjacent to the sulcus lateralis. The ADVR continues growing by incorporation of cells produced in two proliferative zones (zone b and wall of the sulcus lateralis) and appears fully developed in postnatal lizards. Ultrastructural characteristics of young ADVR neurons between stages E-32 and E-33 are typical of those in immature cells. Beginning at stage E-34, some of these neurons appear to be degenerating (pycnotic). Thereafter, neurons of the ADVR develop abundant cytoplasmic organelles and the neuropile grows quickly. Myelination starts in the ADVR between stages E-38 and E-40, but is not observed in other striatal masses in the same period. Vascularization begins and is well developed at E-40. The first synaptic contacts were observed in embryos of stage E=38; they are chiefly axo-dendritic, although some are axo-somatic. Degenerating neurons were found in the ADVR up to hatching. From stage E-40 onward, the ADVR shows a greater and more rapid differentiation than all other striatal nuclei, including the ventral and amygdaloid complex.     

Neuronal types in the spinal dorsal gray of the turtle Chrysemys d'orbigny: a Golgi study

At thoracic and lumbar levels the spinal dorsal gray of young specimens of the turtle Chrysemys d'orbigny consists of a cell-free neuropil and an aggregation of perikarya termed here the lateral column of the dorsal horn (LCDH). Nerve cell clusters also occur in the dorsal commissure. The main neuropil area can be divided into a thin superficial layer containing some myelinated fibers (neuropil area Ib) and a compact core composed of unmyelinated axon terminals, dendritic branches, and thin glial processes (neuropil area II). A looser neuropil area is located at the horn base (neuropil area III). The so-called marginal zone of de Lange represents a fourth synaptic field termed here neuropil area Ia. The LCDH consists of neurons of different size and shape. Two peculiar nerve cell types have been recognized in the dorsal horn: giant and bitufted neurons. The former exhibits a large dendritic arbor, which after passing through neuropil areas II and Ib projects into neuropil area Ia and the adjacent white matter. Most frequently Golgi-stained giant neurons have perikarya and dendritic domains on the same side (ipsilateral giant neurons). There are also heterolateral giant neurons whose dendritic branches invade the opposite horn. Bitufted neurons are characterized by the presence of two main dendritic shafts connecting neuropil area II of both dorsal horns. At neuropil levels the major dendritic branches ramify profusely giving rise to short tortuous terminal processes. Perikarya of bitufted neurons occur in the dorsal commissure. The LCDH also contains many small and medium-sized neurons. These are oriented in two main directions: parallel or radial with respect to the dorsal horn surface. The population of horizontally oriented neurons comprises two subtypes termed here alpha and beta. Radially oriented neurons are pleomorphic, defying precise, unequivocal classification.     

Neuronal organization of the accessory olfactory bulb of the lizard Podarcis hispanica: Golgi study

The neuronal organization of the accessory olfactory bulb (AOB), which receives sensory information from the vomeronasal organ, was described in a squamate reptile (Podarcis hispanica) by means of light microscopy. Using the Golgi-impregnation method, seven neuronal types could be distinguished: Periglomerular cells constitute a morphologically heterogeneous population of small neurons located between and around the glomeruli. The mitral cells are diffusely distributed in the AOB. Their cell bodies are usually located within the mitral cell layer, but some of them could be also observed in the plexiform layers. Mitral cells were classified into three subgroups on the basis of their sizes and dendritic tree morphologies. Thus, the “outer mitral cells” have the biggest cell bodies, and their distal secondary dendrites are mainly distributed rostrocaudally in the external plexiform layer. The “inner mitral cells” have large cell bodies, and their secondary dendrites are distributed dorsoventrally and are located deeper than those of the other two subgroups. The third type, the “small mitral cells,” is the smallest one among mitral cells in the AOB, and from their cell bodies, only two main dendritic trunks arise. The granule cells are composed of several categories based on their different cell body locations and dendritic tree morphologies. Thus, the “superficial granule cells” are located exclusively in the external plexiform layer and have small dendritic fields. The “middle granule cells” have fusiform cell bodies—situated in the internal plexiform layer—and present a wide dendritic projection area. Finally, the “deep granule cells” are distributed throughout the granule cell layer and include a great variety of dendritic tree morphologies. The distribution and morphological features of all neuronal types constituting the AOB of Podarcis were compared with those reported on other vertebrates. The results suggest that the lamination pattern and neuronal organization of the AOB in lizards are more similar to that of mammals than to that of the remaining vertebrates.     

Neuronal differentiation in the thalamic area triangularis of a lizard

Development of neurons in the area triangularis of Gallotia galloti was investigated in Golgi-impregnated brain tissue. Four major neuronal types present in adults were found to originate from two migratory neuroblast types, which were followed from embryonic stage S.32. One type has a thick main medial process, whereas the second type has a long main lateral process. As they migrate toward the periphery of the nucleus, morphological characteristics of maturation appear, including growth cones, filopodia, and outgrowth of axons. Neuroblasts with a main lateral process differentiate into two immature neuronal types, bipolars and pyramidals, observed at S.33 and thereafter. The neuroblasts with a main medial process undergo some somatic translocation through a transitory tangential shaft. Then they develop into monopolar immature forms with a long varicose medial, process, appearing from S.36. onward. Immature bipolar neurons do not experience great changes in their dendritic arborization during development to the adult stage, but pyramidals and monopolars undergo a rapid development of the dendritic tree after S.36. By S.38 archetypes of adult neuronal forms are established. Hairlike appendages first appear on neurons at S.36 They decrease suddenly in S.38 and then proliferate in S.39 when spines first appear. Around the time of hatching, the hairlike appendages begin to disappear and spines become established. Reduction of spines occurs after hatching and continues to the adult stage. Possible influences of several external factors on neuronal maturation are discussed.     

Embryology and cytodifferentiation of the pituitary gland in the lizard Anolis carolinensis

Anolis embryos have limb buds at the time eggs are laid and require about 39 days to complete development at 28°C. Rathke's pouch is present at five days, and the subdivisions of the adenohypophysis are differentiated by ten days after oviposition. The cells of the rostral half of the pars distalis (PD) are derived from the anterior face of Rathke's pouch; cells of the caudal half from the posterior face. Lateral lobe cells differentiate on the lateral margins of the developing caudal PD, and knob-like outgrowths of this tissue attach to the walls of the diencephalon to form the pars tuberalis (PT). Subsequently, the cells of the PT lose their connection with the PD and become a pair of flattened oblong plaques. They reach maximal size in midincubation, and are gradually invaded by nervous elements and incorporated into the walls of the hypothalamus. Electron micrographs demonstrate that the embryonic PT is secretory. Ultrastructurally the pars intermedia (PI) and PD are composed of parenchymous secretory cells in a framework of stellate cells. Stellate cells surround the lumen of Rathke's pouch and are connected laterally by complex junctions that exclude the secretory cells from the luminal surface. They extend in sheet-like processes among the secretory cells to the outer margin of the gland where they form a partial sheath within the basal lamina around the secretory tissue. As development proceeds, the lumen becomes subdivided and the resulting reduced lumina are recognizable as the forerunners of the follicles of the adult adenohypophysis. The cells of the PI are differentiated into secretory or stellate cells halfway through incubation. At this time only half of the cells of the PD can be so classified. Four of the five granulated cell types described in the adult are recognizable by mid-incubation; the fifth cell type (prolactin cell) becomes distinguishable within ten days thereafter, and at hatching appears to be actively synthesizing secretory products.     

Ultrastructure of the cell types of the anterior hypophysis in a lizard. I. Corticotrophs

Corticotrophs of the teiid lizard Cnemidophorus lemniscatus are situated in the rostral zone of the pars distalis. In normal animals, they are usually rounded cells with slightly eccentric vesicular nuclei, especially characterized by a lucent hyaloplasm and medium-sized secretory granules of uniform high density. Granules are almost spherical, with small angular deformations, and closely bounded by a fuzzy membrane. Many cells have only a few or a moderate number of granules, with large areas of cytoplasm devoid of them; in others, granules fill the supranuclear region. The cytoplasm exhibits numerous ribosomes, often in rosettes and mostly free, a series of loosely superimposed cisternae of rough endoplasmic reticulum, small dictyosomes, and elongate mitochondria of light matrix. Metyrapone administration during 2-8 days causes dramatic alterations in corticotrophs; they become hypertrophic and extensively degranulated, with a great development of the endoplasmic reticulum and Golgi apparatus, eventually showing a row of large peripheral granules of uneven structure, enclosed in ample vesicles studded with ribosomes. A lesser degree of hypertrophy and degranulation of corticotrophs appears during the first two weeks after thyroidectomy or gonadectomy, and may be partially attributed to surgical stress. Well granulated enlarged corticotrophs, with hypertrophic endoplasmic reticulum and Golgi apparatus, are probably a result of hormonal imbalance in lizards of both sexes gonadectomized for one or two months.     

Neuronal circuitry for pain processing in the dorsal horn

Neurons in the spinal dorsal horn process sensory information, which is then transmitted to several brain regions, including those responsible for pain perception. The dorsal horn provides numerous potential targets for the development of novel analgesics and is thought to undergo changes that contribute to the exaggerated pain felt after nerve injury and inflammation. Despite its obvious importance, we still know little about the neuronal circuits that process sensory information, mainly because of the heterogeneity of the various neuronal components that make up these circuits. Recent studies have begun to shed light on the neuronal organization and circuitry of this complex region.     

Neuronal subtype specification in the cerebellum and dorsal hindbrain

In the nervous system, there are hundreds to thousands of neuronal cell types that have morphologically, physiologically, and histochemically different characteristics and this diversity may enable us to elicit higher brain function. A better understanding of the molecular machinery by which neuron subtype specification occurs is thus one of the most important issues in brain science. The dorsal hindbrain, including the cerebellum, is a good model system to study this issue because a variety of types of neurons are produced from this region. Recently developed genetic lineage-tracing methods in addition to gene-transfer technologies have clarified a fate map of neurons produced from the dorsal hindbrain and accelerated our understanding of the molecular machinery of neuronal subtype specification in the nervous system.     

The control of avian cephalic neural crest cytodifferentiation. II. Neural tissues.

A series of neural crest transplantations has been performed to (1) analyze whether avian premigratory cranial neural crest cells are pluripotential or restricted to specific developmental pathways and (2) examine the ability of trunk neural crest cells to develop in an environment usually occupied by cranial crest cells. Quail embryos, the cells of which have a unique nuclear marker, were used as donors and chick embryos as hosts. Hindbrain crest cells grafted in the place of diencephalic crest cells failed to form neurons in all but one case, in which a small ectopic ganglion was found. In the reciprocal transplants, neural crest cells emigrating from a segment of forebrain crest tissue grafted in the place of metencephalic crest cells produced trigeminal and ciliary ganglia which were completely normal. Thus, crest cells which normally never form ganglionic neurons will do so if placed in a suitable neurogenic environment. These results prove that premigratory avian cranial crest cells are not restricted to specific developmental pathways, but are initially pluripotential. Trunk crest cells grafted in the place of metencephalic crest cells form neuronal ganglia along the proximal trigeminal motor roots but do not form normal trigeminal ganglia. These root ganglia do not display normal peripheral projections, and placode cells, a normal component of the trigeminal ganglion, form ganglia in ectopic locations. Thus, while trunk crest cells respond to the metencephalic environment and form neurons, their response is different from that of cranial crest cells in the same location. Whether this is due to differences in developmental potential or in initial population size is not known.     

Ultrastructural study of midgut embryonic cytodifferentiation in the phasmid Clitumnus extradentatus Br.

The embryonic cytodifferentiation of Clitumnus midgut occurs very late when compared to that of other tissues in the embryo. It proceeds from hemolymph towards the yolk, first at the level of the muscular–connective tissue sheath, by the appearance of myofilaments in external–then internal–muscle fibers. In the gut epithelium, cytodifferentiation begins with the appearance of infoldings of the basal membranes of the cells. Then, microvilli and continuous junctions form at the apices of the cells. Microvilli appear in crypts, which seem to represent localized dilatations of intercellular spaces. At the level of these crypts, continuous junctions are formed somewhat later than are microvilli. This midgut differentiation coincides with deposition of the third embryonic (first larval) cuticle, and with a high titer of ecdysteroids.     

Accessory oculomotor nuclei of man. II. The interstitial nucleus of Cajal: a Nissl and Golgi study.

The interstitial nucleus of Cajal (INC) is an important premotor centre related to the control of eye and head movements. The aim of the present research was to draw a detailed picture of the cytoarchitecture of the human INC, in particular taking into consideration the morphological features of the neurons and their functional implications. Within the neuronal population, two groups of cells were identified: one group (the most substantial) was made up of small and medium-sized neurons showing different soma shapes and both light and moderate basophilia. The second group consisted of a limited number (about 25%) of large cells dispersed throughout the whole INC, showing polygonal soma and intense basophilia. The hypothesis that these large cells represent a different cellular population inside the INC is advanced. On the basis of the dendritic emergence pattern, two types of cells were identified: multipolar and fusiform cells. The multipolar cells (59%) had small to large nerve cell bodies giving off 2-3 dendrites radiating in all directions. Dendrites and axons were often seen spreading outside the INC. The fusiform cells were small or medium sized and two dendrites emerged from the opposite poles of their elongated perikaryon. Their dendrites and axons always lay inside the INC. The fusiform cells were interpreted as neurons carrying out a mainly local integrative function, while the multipolar cells could also probably carry out an important projective role. The structural data reported are in agreement with the functional studies indicating the INC as both an integrative and a projective center.     

Biochemical studies on rat liver Golgi apparatus. II. Further characterization of isolated Golgi fraction.

Although the preparation of rat liver Golgi apparatus isolated by our method contains appreciable activities of NADH- and NADPH-cytochrome c reductases and glucose-6-phosphatase, these enzymes as well as thiamine pyrophosphatase of the extensively fragmented Golgi fraction are partitioned in aqueous polymer two-phase systems quite differently from those associated with microsomes. Similarly, the partition patterns of acid phosphatase and 5'-nucleotidase of the Golgi fragments differ from those of homogenized lysosomes and plasma membrane, respectively. It is concluded that most, if not all, of these marker enzymes in the Golgi fraction cannot be ascribed to contamination by the non-Golgi organelles. In sucrose density gradient centrifugation the NADH- and NADPH-cytochrome c reductase activities of the Golgi fraction behave identically with galactosyltransferase but differently from the reductase activities of microsomes, again indicating that the reductases are inherently associated with the Golgi apparatus. NADPH-cytochrome c reductase of the Golgi preparation is immunologically identical with that of microsomes. The marker enzymes mentioned above and galactosyltransferase behave differently from one another when the Golgi fragments are subjected to partitioning in aqueous polymer two-phase systems, suggesting that these enzymes are not uniformly distributed in the Golgi apparatus structure.