Reorganization of GABAergic synapses in the viper optic tectum following retinal deafferentation.

The immunocytochemical analysis of the viper optic tectum was carried out with an anti-gamma-aminobutyric acid (anti-GABA) antiserum following retinal deafferentation for survival times ranging from 10 to 90 days. The ultrastructure of the SGFS neuropil revealed that among the two types of axon terminals, namely pleiomorphic (P) and spherical (S) boutons, a subtype of the latter (S2), corresponding to the retinal terminals, was found to degenerate at varying rates. In most cases, this resulted in the glial engulfment of the presynaptic partner, leaving the postsynaptic differentiation free (FPSD). Beyond the two first months, the asymmetrical freed postsynaptic differentiations (FPSDs) were progressively and partly reafferented by GABA-positive P axon terminals through a sliding process. Three months postoperative, the number of GABA-positive P axon terminals which, in normal animals, establish asymmetrical contacts (1-2%), was found to increase to approximately 10%. The postsynaptic differentiation may represent a mismatched receptor area for the new competing presynaptic partners. The functional implications of such 'axonal terminal sprouting' are discussed.

A preliminary description of the regeneration of optic nerve fibers in a reptile, Vipera aspis.

Crushing or freezing the optic nerve of the viper leads initially to the anterograde degeneration of the optic nerve fibers and to an extensive retrograde demyelination process associated with the degeneration of some retinal ganglion cells. By the 45th postoperative day, regenerating unmyelinated axons can be identified in the damaged region of the optic nerve. These fibers reach the chiasm and the marginal optic tract by the third postoperative month. The radioautographic tracing method shows that some nuclei of the primary visual system begin to be reinnervated by about the 5th postoperative month; this reinnervation was not, however, completely restored in those specimens with the longest postoperative survival of 220 days.

The optic nerve of the viper, Vipera aspis.

A quantitative investigation of the optic nerves of eight adult vipers was carried out, both at the level of resolution of the light microscope by stereological methods, and at the level of resolution of the electron microscope. The majority (87%) of axons are myelinated, and the fibers are organized in fascicles; each bundle of axons is disposed around a central column of glial cells of which the greater proportion (62%) are oligodendrocytes, 33% are astrocytes and the remaining 5% are microglial cells. Estimations of the total number of fibers varied, from 5.37 X 10(4) to 6.96 X 10(4), among the eight specimens. The distribution of diameters of myelinated fibers is well characterized (chi 2 = 16.84, df = 22, 0.9 greater than p greater than 0.5) by a three-parameter lognormal distribution with a mean of 0.735 micron, standard deviation of 0.239 micron, and origin of 0.21 micron. Axon diameter is linearly related (r = 0.60) to the number of electron-dense layers in the myelin sheath. The diameters of unmyelinated fibers are distributed (chi 2 = 1.95, df = 4, 0.9 greater than p greater than 0.5) as a two-parameter lognormal distribution with mean of 0.25 micron and standard deviation of 0.067 micron. A surprisingly large number of myelinated fibers, apparently dispersed at random throughout the nerve, showed anomalies of myelination; two possible explanations, between which it is impossible to discriminate on the basis of the available data, are offered for this state of affairs.

A longitudinal study of the effects of retinal ablation on the organization of the retinal target lamina of the optic tectum in the teleost, Rutilus rutilus.

The optic tecta of 55 Rutilus rutilus were examined at intervals varying from 2 days to 4 years after unilateral retinal ablation. Qualitative ultrastructural examination of the retinal target lamina of the optic tectum (stratum fibrosum et griseum superficiale, SFGS) revealed that an initial period of degeneration and glial reaction, each of which could take one of a variety of forms and which lasted for 1-3 months after ablation, was followed by the temporary formation of heterologous synapses which persisted for a further 1-12 months. This in turn was followed by the degeneration of these synapses during the second year after ablation. Quantitative analysis at the level of the light microscope revealed a shrinkage of the SFGS throughout the level of the light microscope revealed a shrinkage of the SFGS throughout the first 14 postoperative months with no further reduction taking place thereafter. Analysis at the ultrastructural level revealed that this shrinkage was due to the disappearance, and not to the reduction in size, of pre- and postsynaptic profiles accompanied by glial reaction. No signs of collateral sprouting were seen throughout the survival period. Thus, partial deafferentation of the SFGS leads in the long run to a marked impoverishment of its neuronal network, without any apparent compensation.

[Spatio-temporal evolution of optic tract regeneration in Rutilus rutilus]. / Evolution spatio-temporelle de la régénération du tractus optique chez Rutilus rutilus.

Regeneration of the different components of the optic tract of Rutilus takes place at a variable rate and follows a relatively precise pattern. The first optic centres to be reinnervated belong to the lateral thalamo-pretectal group (5 weeks at 14 degrees C after section of the optic nerve), followed by the anterior optic tectum and lateral geniculate nucleus (8 weeks after section), the central regions of the tectum, the suprachiasmatic nucleus and the nucleus of the basal optic root (10-15 weeks after section), and finally the medial thalamo-pretectal nuclei and the caudal regions of the optic tectum (16-25 weeks after section).

The anatomical organization of retinal projections in the shark Scyliorhinus canicula with special reference to the evolution of the selachian primary visual system.

The retinal projections of the shark Scyliorhinus canicula were investigated using both the degeneration technique after eye removal and the radioautographic method following the intraocular injection of various tritiated tracers (proline, leucine, fucose, adenosine). The results showed contralateral projection via different optic tract components (TOM, AOT, TOm, TOl, ROVm, RODm) to various areas and nuclei of the hypothalamus (NSC), thalamus (NODLAT, NODMAT, NTTOM, NOVT, NODPT), pretectum (NOPC, NOCPd, NOCPv), tectum (SFGS, SGI) and mesencephalic tegmentum (AOTMd, NOTMv). Ipsilateral retinal projections were found to arborize within 7 distinct zones at the hypothalamic (NSC), thalamo-pretectal (NODLAT, NTTOM, NOVT, NOPC, NOCpd) and tectal (SFGS) levels. A comparison of the data with those previously obtained in different species of elasmobranchs and batoids indicate the existence of a common and consistent pattern of organization of the primary visual system in all selachians. Many of the discrepancies reported in studies on the organization of selachian retinal projection may be listed to methodological differences and/or interspecies variations in the cytoarchitecture of the different visual centers. Moreover, a comparison of the primary visual system of more primitive squalomorph sharks with that of the more advanced galeomorph sharks and batoids suggests that this system evolved through an increase in the neuronal density of the target structures and transformations in the dendritic configurations of the postsynaptic neurons rather than through an increase in the total number of projection zones.

Fine structure of the optic fiber termination layer in the tectum of the teleost Rutilus: a stereological and morphometric study.

The stratum fibrosum et griseum superficiale (SFGS) of the Rutilus optic tectum, which receives a massive fiber projection from the contralateral retina, was studied by electron microscopy. The qualitative and quantitative analysis of the laterodorsal (LD) portion of the stratum involved both a stereological examination of the different elements and a morphometric study of the various profiles containing synaptic vesicles (PCSVs). The relative volume of each element in the LD SFGS was as follows: myelinated and unmyelinated axons, 6.6%; PCSVs, 38%; dendrites without vesicles, spines, and cell bodies, 41.7%; glia, 10.5%. With the fixation employed, 35% of PCSVs showed spheroidal synaptic vesicles. These profiles could be subdivided into three types: (1) S1 (23.5%) represented optic terminals, since they degenerated after retinal ablation or were labeled after intraocular injection of HRP or [3H] proline. Three subgroups of S1 were identified: S1m--profiles containing clear mitochondria;S1c--profiles that were contiguous with S1m and lacked mitochondria;S1i--isolated profiles without mitochondria. (2) S2 (9.3%) were characterized mainly by their dark mitochondria. (3) S3 (2.2%) corresponded to small nonvisual terminals that were isolated and lacked mitochondria. The PCSVs with pleiomorphic synaptic vesicles (65%) were subdivided into three groups: P1 (38%), P2 (19%), and P3 (8%). P1 and P2 were axonal in nature; P2 could be distinguished from P1 by a greater density of synaptic vesicles. P3 was of dendritic origin. Analysis of synaptic patterns revealed a small number of serial synapses. The presynaptic elements were optic boutons, whereas the intermediate profiles were dendrites with synaptic vesicles (P3). Results are compared with ultrastructural data obtained in the superficial tectal layers of other teleosts and other vertebrate groups.

Long term regeneration of contralateral and induced ipsilateral retinal projections to the remaining optic tectum of Rutilus rutilus.

The regeneration of optic tract fibers hs been investigated in Rutilus kept at 18-20 degrees C, 6-7 months after ablation of one optic tectum and simultaneous section of the optic nerve from the contralateral eye. The labeling of the optic fibers obtained following injection of either tritiated proline or HRP in either of the eyes showed the existence of a normal contralateral retino-tectal projection to strata opticum, fibrosum et griseum superficial (SFGS), griseum centrale, and album centrale. Furthermore, it demonstrated the presence of a conspicuous newly-formed ipsilateral retino-tectal projection to both superficial and deep layers of SFGS in the form of horizontal bands. The partial overlapping of ipsi- and contralateral projections in SFGS was confirmed by a double-labeling technique (HRP and tritiated proline). The results suggest a retinal hyperinnervation of the remaining optic tectum.

A light and electron microscope study of the basal optic system in the reptile Vipera aspis.

The basal optic system of the reptile Vipera aspis was investigated under both light and electron microscopy. The basal optic root (BOR), mainly composed of large diameter myelinated fibers (congruent to 2 micrometers) terminates in he nucleus of the basal optic root (nBOR). The different histological techniques employed disclose a neuronal population distributed in the following three categories: 1) small neurons, of low proportion (21%), have cytological features which allow their classification as Golgi type II neurons, 2) medium-sized neurons (35%) and 3) large multipolar neurons (44%). Both of the latter types of neurons are contacted by optic terminals. Neuroglial elements, astrocytes, oligodendrocytes, and microgliacytes were observed either in an intermediate fascicular or perineuronal satellite position. The neuropil of nBOR is made up of both axonal and dendritic profiles. The dendrites which contain synaptic vesicles (DCSVs) are not numerous (15% of the total population of profiles containing synaptic vesicles, PCSVs) and have the peculiarity of participating in serial and triadic arrangements within glomerulus-like structures where they are postsynaptic to optic terminals. Six types of axon terminals have been identified. Those containing a more or less spheroidal synaptic vesicle population are subdivided in two classes: S 1, the optic terminals being the most numerous (48,5% of the total PCSVs) and S 2 (19% of the total PCSVs). On the basis of density of flattened synaptic vesicles, F type terminals are classified either as F 1 (9%) or F 2 (8%), the first being more densely packed with synaptic vesicles. A very low proportion of terminals (0,5%) comprises a mixed population of large granular vesicles (G) associated with rounded or ellipsoidal synaptic vesicles. Occasionally, gap junctions are observed between an axon terminal and a dendritic profile. The present results show a similarity of synaptic circuitry when compared to bird and mammal nBOR.

The retinofugal pathways in a primitive actinopterygian, the chondrostean Acipenser güldenstädti. An experimental study using degeneration, radioautographic and HRP methods.

Experimental study of the retinofugal pathways in Acipenser güldenstädti was carried out on 109 specimens using 3 experimental tracing methods: Fink-Heimer (after retinal ablation), radioautography (after intraocular injection of tritiated markers) and HRP (after intraocular injection of HRP or iontophoretic deposit of HRP on the optic nerve). The optic fiber was found to partially decussate at the chiasm and to project to 5 contralateral regions: (1) hypothalamus (area optica hypothalami); (2) thalamus (area optica dorsalis thalami, area optica mediale thalami, nucleus thalamicus tractus optici marginalis, nucleus laminaris ventralis); (3) pretectum (nucleus pretectalis ventralis, nucleus commissurae posterioris, nucleus intercalaris lateralis); (4) optic tectum (superficial layers); and (5) mesencephalic tegmentum (area optica accessoria). The ipsilateral component was well developed and innervated the same regions mentioned above. A few contralateral optic fibers crossed again in the posterior commissure and terminated within ipsilateral visual pretectal structures. Although the architecture of the visual centers was less elaborated in this paleopterygian than in neopterygians (holosteans, teleosteans), we observed that the general organization of the retinal contralateral projections in this fish was comparable to that of more advanced actinopterygians. Our results indicate that this pattern was probably set at a very early date, perhaps as soon as the emergence of the chondrostean grade at the beginning of the Devonian.

The retinofugal pathways in the primitive African bony fish Polypterus senegalus (Cuvier, 1829).

Retinal projections were studied using Fink-Heimer and radioautographic methods in Polypterus senegalus, a species which is representative of a small group of African fresh-water bony fish often considered to be very primitive. The large optic nerve showed partial decussation at the chiasm. Two major contralateral tracts were observed: the axillary and marginal optic tracts, with the latter being subdivided posteriorly into the tractus opticus medialis and tractus opticus lateralis. The retina projected onto the: (1) hypothalamus (area optica postoptica); (2) thalamus (nucleus opticus dorsolateralis thalimi, nucleus dorsomedialis thalami, corpus geniculatum laterale, area optica dorsolateralis thalami, area optica ventrolateralis thalami); (3) pretectum (nuclei commissurae posterioris, pretectalis ventralis, pretectalis dorsalis); and (4) optic tectum (stratum marginale, stratum opticum, stratum griseum et fibrosum superficiale, stratum griseum et album centrale, stratum griseum et fibrosum periventriculare). Ipsilateral retinal projections were demonstrated to the same 4 levels and more precisely to the nucleus opticus dorsolateralis thalami, area optica dorsolaterale thalami, nucleus commissurae posterioris, stratum marginale and stratum griseum et album centrale. The existence of a retinal projection to the mesencephalic tegmentum is discussed. Comparing the primary optic system of Polypterus with that of other jawed vertebrates, and particularly with that of other bony fish, indicated that this species possesses a combination of characteristics which are both actinopterygian and sarcopterygian. The phylogenetic significance of this mozaic anatomical arrangement is discussed.

Fine structure of the superficial layers of the viper optic tectum. A Golgi and electron-microscopic study.

The superficial layers of the viper optic tectum, which receive fibers from he retina, were studied using both light and electron microscopes. The optic fibers layer, or stratum opticum, is composed of 200 to 250 tight fascicles containing thin fibers, nearly all of which are myelinated. The main optic terminal layers, the stratum griseum et fibrosum superficiale, the greatest part of the cellular population is composed of small vertically oriented neurons and horizontal nerve cells, many of which are probably local circuit neurons. The neuropil of the stratum griseum et fibrosum superficiale is made up of small nerve elements, including three types of profiles containing synaptic vesicles; 1) boutons with pleiomorphic synaptic vesicles (P), representing over 47% of the total population of profiles containing synaptic vesicles and comprising three subgroups (P1, P2, and P3); 2) boutons with spheroidal synaptic vesicles (S), forming more than 29% of the total populations of profiles containing synaptic vesicles and comprising two categories, S1 and S2 (S2, the more numerous, represents the optic boutons, which make up 22% of the total populations of profiles containing synaptic vesicles); and 3) dendrites with pleiomorphic vesicles, accounting for approximately 23% of the total populations of profiles containing synaptic vesicles. A study of synaptic patterns revealed a large number of serial synapses and a lesser number of triplets or triadic synapses. The presynaptic components are boutons containing spheroidal (S1, S2) or pleiomorphic (P1, P2, P3) synaptic vesicles. The intermediate profile was always a dendrite with synaptic vesicles which frequently belonged to the small neurons of the stratum griseum et fibrosum superficiale. Comparison of the present results with other recent data shows that the synaptic circuitry in the optic tectum of Vipera aspis closely resembles the pattern observed in the optic tectum of other vertebrates, ranging form fish to mammals. However, quantitative differences exist, especially with regard to the proportion of dendrites containing synaptic vesicles. Their number seems to be higher in sauropsidians than in mammals, particularly in primates.

Orthograde and retrograde axonal movement of label and transneuronal transport phenomena after intraocular injection of [3H]adenosine in a poikolotherm vertebrate (Vipera aspis).

The axoplasmic transport of [3H]adenosine (or its related compounds) has been examined radioautographically in the visual system of a poïkilotherm species (Vipera aspis) following an intraocular injection of the nucleoside. It has been found that the axonal transport of the label occurs both in the anterograde directions. Furthermore, a considerable labelling of neuronal bodies as a result of transneuronal transport of tritiated material from the optic endings has been observed, particularly in the primary optic centers. Transneuronal labelling, however, appears less intense than retrograde cell labelling.

[Anatomical study of the afferent pathways of the rostral telencephalon in the Gallus domesticus chick]. / Etude anatomique des afférences du télencéphale rostral chez le poussin de Gallus domesticus L.

The neuroanatomical method involving retrograde axonal transport of horseradish peroxidase (HRP) was employed in the chick Gallus domesticus to investigate ascending projection systems to the rostral telencephalon. Following either extensive or restricted injections of the enzyme into different regions of the latter, differential bilateral or unilateral projections onto the Wulst (hyperstriatum accessorium, hyperstriatum intercalatus superior, hyperstriatum dorsale) were demonstrated from the dorsal thalami complex (nucleus dorsolateralis anterior thalami, pars lateralis). Other nuclei of the dorsal thalamus shown to project to the rostral telencephalon were nuclei, dorsolateralis medialis, dorsolateralis posterior, dorsomedialis anterior, parvocellularis and rotundus. At the level of the mesencephalon, rostral telencephalic projections were found to originate in the substantia grisea centralis, the strata cellulare externum and internum, the lateral reticular formation and the area ventralis. More caudally peroxidase label was localized in the nuclei locus, ceruleus, subceruleus dorsale, subceruleus ventrale and within the principal Vth nucleus. The results obtained using restricted injections of HRP made it possible to more precisely identify the telencephalic projections sites of several of the above areas and nuclei. The data is compared to previous findings regarding ascending projection system in different avian species and some methodological problems in the use of HRP technique are discussed.

[Primary visual centers in the frog (Rana esculenta L.) and the problem of ipsilateral projections. Radioautographic study]. / Les centres visuels primaires chez la grenouille (Rana esculenta L.) et le problème des projections ipsilatérales. Etude radioautographique.

The topographic organization of the frog's primary visual system has been reexamined in Rana esculenta using autoradiographic technique. 10 to 24 hrs following an intraocular injection of tritiated proline, an intense labelling was observed contralaterally in the various retinal projection centres (preoptic area); neuropils of Bellonci; corpus geniculatum of the thalamus; posterior thalamus; posterodorsal preoptic area; magnocellular pretectal nucleus and basal optic nucleus; tectal laminae A to G of Potter), as already described. Furthermore, the presence of a ipsilateral projection within the hypothalamus (preoptic area), the thalamus (neuropils of Bellonci and corpus geniculatum) and the pretectium (posterior thalami neuropil, pretectal optic area) is confirmed. On the other hand, the existence of ipsilateral retinotectal (to Potter's lamina F) and retino-tegmentomescencephalic projections (to the basal optic nucleus), which were thusfar questioned, has been demonstrated.

[Problems posed by the interpretation of peroxidase labelling of various neurons in Cyprinidae]. / Problèmes posés par l'interprétation du marquage peroxydasique de certains neurones chez les Cyprinidés

The origin of a centrifugal visual pathway in Cyprinids could not be demonstrated with the technique involving the labelling of cell bodies by retrograde transport of Horseradish Peroxidase. The hypothalamic labelling following intraocular injection of HRP is localized in neurosecretory structures which take up the enzyme that has passed into the circulatory system. Identical results were obtained following direct intracardiac injection. Thus extreme caution must be taken in attempting to interpret HRP results.