[The prenatal development of the tectum mesencephali and substantia nigra in man]. / Prenatal'noe razvitie pokryshki srednego mozga i chernogo veshchestva u cheloveka.

The development of tectum of the midbrain was studied in situ in human 6-11 wks embryos. Using electron microscopy and immunocytochemistry processes that occur in the anlage of tectum of the midbrain at early stages of formation of dopaminergic populations of cells were followed up. Growth of pallium zone due to migration of cells from ventricular zone and their differentiation is proportional to growth of the terms of embryonal development. Proliferating cells were located not only in ventricular zone. Expression of tyrosine hydroxylase was found in 6.5 wks embryos in the fraction of cells that migrated from ventricular zone and was observed only during neuroblast migration. Cells migrate along the radial glia fibres in dorsoventral direction. Microgliocytes with short processes near to vessels located in the vicinity of ventricular zone were found in 7 wks embryos for the first time. Peculiarities of morphogenetic processes participating in anlage of tectum of the midbrain and possible role of microgliocytes in development of embryonal nerve tissue are discussed.

Ultrastructural studies of the primate lateral geniculate nucleus: morphology and spatial relationships of axon terminals arising from the retina, visual cortex (area 17), superior colliculus, parabigeminal nucleus, and pretectum of Galago crassicaudatus.

The electron microscopic autoradiographic tracing method has been used to examine the morphology and postsynaptic relationships of five projections (retina, cortical area 17, superior colliculus (tectal), parabigeminal nucleus, and pretectum) to the dorsal lateral geniculate nucleus of the greater bush baby Galago crassicaudatus. Retinal terminals have been examined in the contralaterally innervated layer of each of the three matched pairs [parvi- (X-cell), magno- (Y-cell), and koniocellular (small, W-cell)] of geniculate layers. These terminals are large and contain pale mitochondria and round vesicles (RLPs). RLPs are presynaptic to juxtasomatic regions of parvi- and magnocellular neurons. In contrast, RLPs innervate more distal regions of koniocellular neurons. Labeled cortical, tectal, and parabigeminal terminals are relatively small and contain round vesicles and dark mitochondria. Cortical terminals in each of the three representative layers are presynaptic to small diameter dendrites. No convergence of cortical and retinal terminals has been seen in any layer. Labeled tectal and parabigeminal terminals are found primarily in the koniocellular layers, but the latter are also seen in all other layers. Tectal and parabigeminal terminals have been observed converging with retinal terminals on dendrites of some koniocellular neurons. Labeled pretectogeniculate terminals contain densely packed pleomorphic vesicles, dark mitochondria, and a dark cytoplasmic matrix. These terminals, which are present in each of the representative layers, are presynaptic to conventional dendrites and profiles containing loosely dispersed pleomorphic vesicles and a pale cytoplasmic matrix.

The spatiotemporal distribution of N-CAM in the retinotectal pathway of adult goldfish detected by the monoclonal antibody D3.

The spatiotemporal distribution of neural cell adhesion molecule (N-CAM) in the retinotectal system of adult goldfish was assessed by immunofluorescence using the monoclonal antibody (Mab) D3 against chick N-CAM. In immunoblots with extracts of cell surface membranes of fish brains, Mab D3 recognized a prominent band at 170K and a weak band at 130K (K = 10(3) Mr). N-CAM immunofluorescence on cells was restricted to the marginal growth zones of the retina and the tectum and, in normal fish, to the youngest axons from the new ganglion cells of the peripheral retinal margin. In fish with previously transected optic nerves (ONS), Mab D3 staining was found transiently on all axons from the site of the cut into the retinorecipient layers of the tectum, but disappeared from these axons 450 days after ONS. Growing retinal axons in vitro exhibited N-CAM immunofluorescence throughout their entire extent, including their growth cones. Glial cells cultured from regenerating optic nerves were, however, unlabeled. These data are consistent with the idea that N-CAM is involved in adhesive interactions of growing axons. The temporally regulated expression of N-CAM on the new retinal axons may contribute to the creation of the age-related organization of the axons in the retinotectal pathway of fish.

[The development of connections in the tecto-thalamo-telencephalic visual system of the brain in 13-day-old chick embryos]. / Razvitie sviazei v tekto-talamo-teléntsefal'noi zritel'noi sisteme mozga 13-sutochnykh kruinykh émbrionov.

Light and electron microscopic studies have been made on degenerative changes in the nervous tissue induced by experimental destruction of the median brain bulb at the 5th day of incubation, in parts of the tecto-thalamo-telencephalic visual system in 13-day chick embryos (in the visual tectum, round nucleus of the thalamus and ectostriatum of the telencephalon). It was shown that to this period tecto-thalamic connections are already formed in the visual system, whereas thalamo-telencephalic connections are, presumably, indirect ones.

[Tecto-thalamo-telencephalic visual system of the brain in 13-day-old chick embryos]. / Tekto-talamo-teléntsefal'naia zritel'naia sistema mozga 13-sutochnykh kurinykh émbrionov.

Light and electron microscopic studies have been made of the nervous tissue in three parts of the tecto-thalamo-telencephalic visual system--i.e. tectum opticum, nucleus rotundus of thalamus and ectostriatum of telencephalon--of 13-day chick embryos. Neuroblasts and neurones at various stages of differentiation were described together with various types of synaptic and nonsynaptic intercellular contacts in the neuropil of these brain structures. Heterochronous maturation of these parts of the visual system in embryogenesis was noted which reflects the level of their phylogenetic maturity. Being phylogenetically more ancient structures, tectum opticum and nucleus rotundus reveal differentiation earlier than ectostriatum which is phylogenetically younger.

Tests of the regenerative capacity of tectal efferent axons in the frog, Rana pipiens.

Experiments were designed to determine if neurons of the ranid optic tectum, a major target of the optic nerve, possess the same regenerative potential as optic axons. Normal tectal efferent (TE) projections were reexamined by using the anterograde transport of 3H-proline and autoradiography (n = 18), bulk-filling damaged TE axons with horseradish peroxidase (HRP; n = 18) and anterogradely transporting wheat germ agglutinin-HRP (n = 8) to label TE axons. Results were similar to reports that used degeneration methods (Rubinson: Brain Behav. Evol. 1:529-561, '68; Lazar: Acta. Biol. Hung. 20:171-183, '69). Following a brainstem hemisection just caudal to the nucleus isthmi (1-20 weeks), the ipsilateral descending TE pathway was autoradiographically examined (n = 20). While all other TE projections appeared normal, there was no detectable ipsilateral descending projection beyond the lesion site. Ascending TE axons were cut at the anterior tectal border by hemisecting the left diencephalon (LDH)--a lesion that also cuts optic axons projecting to the left tectum. There was no indication of TE axonal regeneration with the aid of autoradiography or HRP histochemistry 1-30 weeks postlesion (n = 48) even when the medial diencephalon was intentionally left intact (n = 4). However, in all four cases examined, optic axons regenerated following the same LDH where TE axonal regeneration failed (also see Stelzner, Lyon, and Strauss: Anat. Rec. 205:191A-192A, '83). Local effects of LDH should be similar for both the cut optic and cut TE axons. Other factors were tested that may contribute to the lack of TE axonal regeneration. Our results indicate that optic regeneration itself (n = 8), postaxotomy retrograde cell death of TE neurons (n = 6), deafferentation of the tectum of optic axons, and potential sprouting within tectal targets by intact contralateral TE axons (n = 10) are not critical factors aborting TE axonal regeneration. TE axons filled with HRP at chronic periods after LDH (n = 4) terminate anomalously near the LDH border. Many of these endings are similar to reactive endings or terminal clubs seen after axonal injury in the mammalian CNS. Our results suggest that this disparity in regenerative ability of optic and TE axons may be related to a difference in the responsive ability of these cell types to initiate or maintain axonal elongation after axotomy within the amphibian CNS environment.

The effects of taxol on embryonic chick tectum maintained in culture: an electron microscope study.

Tectal explants from chick embryos, established in culture for 2-3 weeks, were exposed to taxol-enriched media for 1-7 days, fixed, and studied by transmission electron microscopy. Taxol treatment resulted in no apparent disruption of the overall integrity of the organization of the explants nor in grossly increased cell death, but caused marked abnormalities of cytoskeletal elements. Intermediate filaments were increased in number in both neuronal and glial cells and very large numbers of microtubules were present, some aligned below the plasma membrane but most as components of large bundles in neuronal cell bodies and processes. Some such microtubules were associated with a network of intermicrotubule substance, consisting of 10-nm filaments running parallel to the microtubules, in hexagonal arrays surrounding individual microtubules, together with a very fine amorphous or filamentous component which was drawn into thread-like structures that linked the larger filaments to one another and formed the sides of the hexagons. Taxol treatment also resulted in the formation of concentric rings of microtubules separated by cylindrical sheets of electron-dense material. These observations extend previous descriptions of the effects of taxol on cytoskeletal elements, add to growing evidence for heterogeneity of microtubules within neurons, and suggest that taxol may be useful in studies of the functions of cytoskeletal elements and of microtubule heterogeneity in neurons.

Order in the initial retinotectal map in Xenopus: a new technique for labelling growing nerve fibres.

Retinal nerve fibres form an orderly map of visual space in several centres in the vertebrate brain. Such topographic maps are a common feature of central nervous system organization, yet the way in which they develop is poorly understood. Early nerve projections in the fetal and neonatal mammalian brain have been found in several cases to be less restricted than those in the adult, suggesting that nerve fibres may initially form a diffuse set of connections in their target structure from which the adult map is sculpted by the elimination of terminals. Indeed, previous electrophysiological data indicate that the retinotectal map in Xenopus laevis might be initially disorganized. We report here, however, that the retinotectal projection is ordered from the beginning of tectal innervation (stage 39/40). We demonstrate this first autoradiographically by tracing groups of growing ganglion cell axons which we labelled by incubating sectors of eye rudiments, before axonal outgrowth, in 3H-proline and replacing them orthotopically. Separate labelling of dorsal and ventral parts of the initial projection showed that retinal fibres are organized topographically, as in the adult, in the tectal rudiment and throughout much of the pathway. Second, we show that visual responses are ordered in the tectum from the first stage that they can be mapped (stage 40). We conclude that the topographic ordering of retinotectal connections develops as a result of directed axonal outgrowth.

[Comparative study of the neuronal and synaptic organization of the tectum mesencephali in the Caspian (Clemmys caspica Gmel.) and pond (Emys orbicularis L.) tortoises]. / Sravnitel'noe issledovanie neironnoi i sinapticheskoi organizatsii kryshi srednego mozga kaspiiskoi (Clemmys caspica Gmel.) i bolotnoi (Emys orbicularis L.) cherepakh.

The neuronal and synaptic organization of tectum opticum was studied in two species of tortoises (Clemmys caspica Gmel, and Emys orbicularis L.) by means of Nissl, Golgi and electron microscopical methods. The Clemmys caspica tectum differs from that of the Emys orbicularis in a greater diversity of neuronal composition; a greater variety and quantity of cells with short axons, the presence of neurons with relatively short dendrites, in a greater relative thickness of the upper and deep systems of horizontal neurons, in a small number of axo-axonal synapses in sublayer Ia, a more diverse composition of synaptic zones in sublayers IIa and IIb, the presence of axons in layers Ib and IIb with certain species specific features of degeneration, the pattern of localization of tectal ganglionic cell projections. The above mentioned specific features appear to be connected with the species differences of these tortoises.

Possible regulatory function of acetylcholine receptor in maintenance of retinotectal synapses.

alpha-Neurotoxins bind to cholinergic receptor, block transmission, and induce sprouting of retinal terminals in the toad tectum. New connections retain an orderliness that suggests a selective affinity between presynaptic terminals. The results suggest that postsynaptic cells exert a control, associated with receptors, on the growth of presynaptic terminals and on the maintenance of their synaptic connections.

[Ultrastructure of the mesencephalic visual center of the steppe turtle]. / Ul'trastruktura mezentsefalicheskogo zritel'nogo tsentra stepnoi cherepakhi.

A layer-by-layer study of ultrastructural synaptic organization of mesencephalic optic centre (tectum opticum) of T. horsfieldi Gray was made. The predominating type of synaptic contacts is axo-dendritic, however, there are some axo-axonic synapses which are met most frequently in the regions where polysynaptic complexes and glomeneruli (sublayer Ib, sublayer IIa and the upper zone of layer III) are disposed. Axo-somatic contacts are localized virtually in all the neuronic types. In the external layers of the tectum opticum where the terminals of optic afferents are disposed, a considerable morphological variety of nerve terminals is revealed which are distinguished not only by their ultrastructural parameters but also by the character of organization in synaptic complexes at different levels of the cortical plates of the investigated centre.

[Different types of secondary degeneration of visual nerve endings in the midbrain tectum of the steppe turtle]. / Razlichnye tipy vtorichnoi degeneratsii zritel'nykh nervnykh okonchanii v kryshe srednego mozga stepnoi cherepakhi

Along with the commonly known patterns of terminal destruction ("dark", "light", "neurofilamentous"), new types of changes have been revealed, referred to as "vesicular" and "glycogen" trasformation types. Vesicular transformation which may develop according to the dark or light type is characterized by a sharp deformation of synaptic vesicles; glycogen transformation is distinguished by agglutination and disappearance of synaptic vesicles, the inside of the terminal being filled up with glycogen granules. Ultrastructural differences of the terminal degeneration process in different groups of nerve fibers reflect the morpho-functional heterogeneity of the retina ganglion cells and of their axons.

[Period of degeneration and features of the laminar distribution of the visual nerve endings in the midbrain tectum of the steppe turtle (Testudo horsfieldi, Gray)]. / Sroki degeneratsii i osobennosti posloinogo raspredeleniia zritel'nykh nervnykh okonchanii v kryshe srednego mozga stepnoi cherepakhi (Testudo horsfieldi, Gray)

A study of ultrastructural changes in the neuronal terminals of optic fibres at the level of tectum opticum (TO) in different periods after unilateral enucleation has revealed the process of degeneration in the optic system of Testudo horsfieldii as well as in Emysorbicularis L. to take a considerable time: from two weeks to six months. The character of destructive changes and the mode of utilization of desintegrated elements are dissimilar in different groups of retinal axons in the optic nerve and their terminals in TO. A comparison of the degeneration periods and the character of the changes in the optic fibres has made it possible to establish the following approximate correlations: all the nerve terminals of myelinated fibres degenerate after the "dark" type, whereas the terminals of non-myelinated axons are subjected to other kinds of transformations ("light", vesicular", neurofilamentous", "glycogen"). The analysis of the distribution of degenerating nerve terminals in the TO layers has demonstrated that there is a regularity in localization of different nerve terminals at certain levels of TO which is indicative of the layered organization of retino-tectile connections. Considerable differences in the neuronal and synaptic organization of TO have been revealed as well as in the character and the time of destructive changes of retino-tectile fibres after enucleation in T. horsfieldii and E. orbicularis.