Doublecortin in the Fish Visual System, a Specific Protein of Maturing Neurons

Simple Summary

Doublecortin (DCX) is an essential protein in the development of the central nervous system and in lamination of the mammalian cortex. It is known that the expression of DCX is restricted to newborn neurons. The visual system of teleost fish has been postulated as an ideal model since it continuously grows throughout the animal’s life. Here, we report a comparative expression analysis of DCX between two teleost fish species as well as a bioinformatic analysis with other animal groups. Our results demonstrate that DCX is very useful for identifying new neurons in the visual systems of Astatotilapia burtoni, but is absent in Danio rerio.

Abstract

Doublecortin (DCX) is a microtubule associated protein, essential for correct central nervous system development and lamination in the mammalian cortex. It has been demonstrated to be expressed in developing—but not in mature—neurons. The teleost visual system is an ideal model to study mechanisms of adult neurogenesis due to its continuous life-long growth. Here, we report immunohistochemical, in silico, and western blot analysis to detect the DCX protein in the visual system of teleost fish. We clearly determined the expression of DCX in newly generated cells in the retina of the cichlid fish Astatotilapia burtoni, but not in the cyprinid fish Danio rerio. Here, we show that DCX is not associated with migrating cells but could be related to axonal growth. This work brings to light the high conservation of DCX sequences between different evolutionary groups, which make it an ideal marker for maturing neurons in various species. The results from different techniques corroborate the absence of DCX expression in zebrafish. In A. burtoni, DCX is very useful for identifying new neurons in the transition zone of the retina. In addition, this marker can be applied to follow axons from maturing neurons through the neural fiber layer, optic nerve head, and optic nerve.

Cultures of glial cells from optic nerve of two adult teleost fish: Astatotilapia burtoni and Danio rerio

BACKGROUND

In vitro studies are very useful to increase the knowledge of different cell types and could be the key to understand cell metabolism and function. Fish optic nerves (ON) can recover visual functions by reestablishing its structure and reconnecting the axons of ganglion cells. This is because fish show spontaneous regeneration of the central nervous system which does not occur in mammals. In addition, several studies have indicated that glial cells of ON have different properties in comparison to the glial cells from brain or retina. Consequently, providing an in vitro tool will be highly beneficial to increase the knowledge of these cells.

NEW METHOD

We developed a cell culture protocol to isolate glial cells from ON of two teleost fish species, Danio rerio and Astatotilapia burtoni.

RESULTS

The optimized protocol allowed us to obtain ON cells and brain-derived cells from adult teleost fish. These cells were characterized as glial cells and their proprieties in vitro were analyzed.Comparison with Existing Method(s): Although it is striking that ON glial cells show peculiarities, their study in vitro has been limited by the only published protocol going back to the 1990s. Our protocol makes glial cells of different fish species available for experiments and studies to increase the understanding of these glial cell types.

CONCLUSIONS

This validated and effective in vitro tool increases the possibilities on studies of glial cells from fish ON which implies a reduction in animal experimentation.

Effects of retinoic acid exposure during zebrafish retinogenesis

Retinoic acid (RA) is an important morphogen involved in retinal development. Perturbations in its levels cause retinal malformations such as microphthalmia. However, the cellular changes in the retina that lead to this phenotype are little known. We have used the zebrafish to analyse the effects of systemic high RA levels on retinogenesis. For this purpose we exposed zebrafish embryos to 0.1μM or 1μM RA from 24 to 48h post-fertilisation (hpf), the period which corresponds to the time of retinal neurogenesis and initial retinal cell differentiation. We did not find severe alterations in 0.1μM RA treated animals, but the exposure to 1μM RA significantly reduced retinal size upon treatment, and this microphthalmia persisted through larval development. We monitored histology and cell death and quantified both the proliferation rate and cell differentiation from 48hpf onwards, focusing on the retina and optic nerve of normal and 1μM treated animals. Retinal lamination and initial neurogenesis are not affected by RA exposure, but we found widespread apoptosis after RA treatment that could be the main cause of microphthalmia. Proliferating cells increased their number at 3days post-fertilisation (dpf) but decreased significantly at 5dpf maintaining the microphthalmic phenotype. Retinal cell differentiation was affected; some cell markers do not reach normal levels at larval stages and some cell types present an increased number compared to those of control animals. We also found the presence of young axons growing ectopically within the retina. Moreover although the optic axons leave the retina and form the optic chiasm they do not reach the optic tectum. The alterations observed in treated animals become more severe as larvae develop.

Abstract OT2-3-10: Phase II study of panitumumab, nab-paclitaxel, and carboplatin for patients with primary inflammatory breast cancer (IBC) without HER2 overexpression

Background: Inflammatory breast cancer (IBC) is the most aggressive form of primary breast cancer. The outcome for patients with IBC is bleak despite multimodality treatment approaches. 10-year disease-free survival rates after combined anthracycline and taxane-containing chemotherapy, surgery, and radiation are only 20%–25%. Our recent study found EGFR overexpression, a predictive factor of poor outcome, in 12 of 40 (30%) patients with IBC. Panitumumab has shown activity against EGFR overexpressing breast cancer xenograft model.

Trial design: This is a single center, open-label, phase II study to evaluate the safety and efficacy of panitumumab in combination with preoperative chemotherapy. The treatment regimen consists panitumumab 2.5 mg/Kg given intravenously alone for the first week, followed by weekly panitumumab, nab-paclitaxel (100mg/m2) and carboplatin (2 AUC) (PNC) for 12 weeks. Patients then will receive 5-FU, epirubicin, and cyclophosphamide (FEC) every 3 weeks for 4 cycles prior to surgery.

Eligibility criteria: 1) Histological confirmation of breast carcinoma with pathologic evidence of dermal lymphatic invasion and clinical diagnosis of IBC, including diffuse erythema, heat, ridging, and peau d'orange; 2) Normal HER2 expression; 3) No prior therapies for IBC; 4) Adequate hematologic, cardiac, renal and hepatic functions.

Specific aims: 1) Primary objective is to determine the pathologic complete response (pCR) rate in patients with primary IBC without HER2 overexpression; 2) Secondary objectives are to determine the disease-free survival (DFS), overall survival (OS), the safety and tolerability of PNC regimens and the correlates of pathologic response rate and EGFR expression level.

Statistical methods: 1) Previous studies have shown that this IBC patient population achieved a 13% pCR rate on the standard of care. We assume a beta (0.26, 1.74) prior distribution for the pCR rate. This prior distribution has a mean of 13% and a standard deviation of 19%. 2) We will stop the trial early if P (pCR rate >/= 13%) is < 0.01. If we determine that there is less than a 1% chance that the pCR rate is 13% or more we will consider stopping the trial. 3) Once we have completed the study we will estimate the pCR rate with a 90% credible interval. If we have pCR in 4 of the 40 patients (10%), then our 90% credible interval for the pCR rate will be 4.0–19.6%. If we have pCR in 8 of the 40 patients (20%), then our 90% credible interval for the pCR rate will be 10.6–30.4%. We will also report the posterior probability that the pCR rate is 13% or more. For example, if we have pCR in 8 of the 40 patients (20%), then the probability that the pCR rate is 13% or more is 0.869.

Present accrual and target accrual: To date, 13 patients have been enrolled. Target accrual is 40 patients.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr OT2-3-10.

Immunocytochemical evidence of the localization of the Crumbs homologue 3 protein (CRB3) in the developing and mature mouse retina

CRB3 (Crumbs homologue 3), a member of the CRB protein family (homologous to the Drosophila Crumbs), is expressed in different epithelium-derived cell types in mammals, where it seems to be involved in regulating the establishment and stability of tight junctions and in ciliogenesis. This protein has been also detected in the retina, but little is known about its localization and function in this tissue. Our goal here was to perform an in-depth study of the presence of CRB3 protein in the mouse retina and to analyze its expression during photoreceptor ciliogenesis and the establishment of the plexiform retinal layers. Double immunofluorescence experiments for CRB3 and well-known markers for the different retinal cell types were performed to study the localization of the CRB3 protein. According to our results, CRB3 is present from postnatal day 0 (P0) until adulthood in the mouse retina. It is localized in the inner segments (IS) of photoreceptor cells, especially concentrated in the area where the connecting cilium is located, in their synaptic terminals in the outer plexiform layer (OPL), and in sub-populations of amacrine and bipolar cells in the inner plexiform layer (IPL).

Characterization of Pax2 expression in the goldfish optic nerve head during retina regeneration

The Pax2 transcription factor plays a crucial role in axon-guidance and astrocyte differentiation in the optic nerve head (ONH) during vertebrate visual system development. However, little is known about its function during regeneration. The fish visual system is in continuous growth and can regenerate. Müller cells and astrocytes of the retina and ONH play an important role in these processes. We demonstrate that pax2a in goldfish is highly conserved and at least two pax2a transcripts are expressed in the optic nerve. Moreover, we show two different astrocyte populations in goldfish: Pax2⁺ astrocytes located in the ONH and S100⁺ astrocytes distributed throughout the retina and the ONH. After peripheral growth zone (PGZ) cryolesion, both Pax2⁺ and S100⁺ astrocytes have different responses. At 7 days after injury the number of Pax2⁺ cells is reduced and coincides with the absence of young axons. In contrast, there is an increase of S100⁺ astrocytes in the retina surrounding the ONH and S100⁺ processes in the ONH. At 15 days post injury, the PGZ starts to regenerate and the number of S100⁺ astrocytes increases in this region. Moreover, the regenerating axons reach the ONH and the pax2a gene expression levels and the number of Pax2⁺ cells increase. At the same time, S100⁺/GFAP⁺/GS⁺ astrocytes located in the posterior ONH react strongly. In the course of the regeneration, Müller cell vitreal processes surrounding the ONH are primarily disorganized and later increase in number. During the whole regenerative process we detect a source of Pax2⁺/PCNA⁺ astrocytes surrounding the posterior ONH. We demonstrate that pax2a expression and the Pax2⁺ astrocyte population in the ONH are modified during the PGZ regeneration, suggesting that they could play an important role in this process.

Growth hormone expression in ontogenic development in gilthead sea bream

The pattern of expression of the growth hormone (GH) gene was studied during the early development of gilthead sea bream ( Sparus aurata). The GH transcript was detected from the 2nd day of the larval stage onwards. In the next stages the expression level fluctuated, possibly due to different regulatory factors. The distribution of GH mRNA studied by in situ hybridization (ISH) was found to be pituitary specific. Hybridization signals for GH mRNA were detected for the first time in 4-day-old larvae. Throughout development the cells that express GH mRNA were mainly located in the proximal pars distalis. Mammosomatotroph cells coexpressing GH and PRL were not detected in juveniles or adults. Moreover, the possible involvement of GH in asynchronic growth in cultivation of gilthead sea bream was also examined by ISH. No differences in the distribution of GH cells were observed in the three sizes of juveniles of gilthead sea bream studied. These results suggest that the transcription of GH is involved in the early developmental stages of sea bream and the asynchronous growth-related changes are not due to distinct distribution of GH cells.

Differential expression and cellular localization of somatolactin-1 and -2 during early development in the gilthead sea bream

The patterns of expression of the somatolactin 1 and 2 (SL1 and SL2) transcripts were studied during the early development of the gilthead sea bream (Sparus aurata). Gene expression of SL1 and SL2 were detected in embryos and in larvae, although both transcripts presented different levels of expression. The SL1 transcripts in contrast to the SL2 transcripts presented high expression levels in embryos and younger larvae. Moreover, the SL2 transcripts were slightly present or absence in embryonic stage and the newly hatched larvae, respectively. The differences in the expression levels of SL1 and SL2 in embryos and larvae may be due to the fact that two distinct genes express both isoforms of the protein. Thus, both SLs may play different physiological roles throughout development. Moreover, the hybridization signals for SL1- and SL2-mRNAs were detected in 4-day-old larvae. Both in larvae and adults the somatolactotroph cells co-expressed both transcripts of SL and were located bordering the neurohypophysis in the pars intermedia.

Transient expression pattern of prolactin in Sparus aurata

Using reverse transcription-polymerase chain reaction and in situ hybridization, the expression of the prolactin (PRL) gene was determined during development in gilthead sea bream (Sparus aurata) for the first time. The mRNA for PRL was detected from the second day of the larval stage onwards. This transcript was also located in the adenohypophysial cells, starting at four days post-hatching and was found to be pituitary-specific. Moreover, the possible involvement of PRL in asynchronous growth in the cultivation of gilthead sea bream was also examined. No differences in the distribution of PRL cells were observed in the three sizes of juvenile gilthead sea bream studied. These results suggest that the transcription of PRL is involved in the early development stages of sea bream and that the asynchronous growth-related changes are not due to distinct distribution of PRL cells.

The degenerative and regenerative processes after the elimination of the proliferative peripheral retina of fish

We have analyzed the modifications in the tench (Tinca tinca) retina after the complete cryo-elimination of the proliferative growing zone (PGZ), which participates in the continuous growth of the retina throughout the life of the fish. By using immunohistochemistry and electron microscopy we demonstrated that, after the lesion, degenerative and regenerative processes take place in the PGZ, in the ciliary zone, and in the transition zone located between the PGZ and the central retina. After 120 days postlesion, the PGZ was completely regenerated and its composition was similar to that of the control animals. Numerous proliferative PCNA-positive cells reappeared and new ganglion cells were formed. In the transition zone and the central retina numerous proliferative PCNA-positive cells also appeared. These are arranged, on occasion, as columnar units from the inner to the outer nuclear layer where the rod precursors and the progenitor cells, respectively, were located. The Müller cells, closely associated with these columnar units, appeared to use them as guides to migration during the regenerative process. Notably, modifications occurred in the ciliary zone, whose cells acquired similar characteristics to the PGZ cells. The ciliary zone cells, the Müller cells, the rod precursors, and the proliferative cells located in the inner nuclear layer appear to participate actively in the regeneration of the PGZ.

Co-expression of somatolactin mRNAs in the pituitary gland of gilthead sea bream

The expression of mRNAs of the two types of somatolactin which have been found, up to the present, in the pituitary of gilthead sea bream (Sparus aurata) have been analyzed by in situ hybridization (ISH). The method of non-radioactive ISH, which we optimize in this study, uses oligonucleotides labelled in the 5' end with biotin or dioxygenin as probes. This allows simple and double ISH of high specificity and sensitivity to be performed. The distinct somatolactin oligoprobes used present a strong signal fundamentally in the pars intermedia of the pituitary gland. For the first time we present cells that co-express both the forms of mRNA mentioned above. Moreover, after studying three groups of different sizes, produced by asynchronic growth of the gilthead sea bream in industrial cultivation, we did not find qualitative differences in the levels of expression of the somatolactin gene.

The glial design of a teleost optic nerve head supporting continuous growth

This study demonstrates the peculiarities of the glial organization of the optic nerve head (ONH) of a fish, the tench (Tinca tinca), by using immunohistochemistry and electron microscopy. We employed antibodies specific for the macroglial cells: glutamine synthetase (GS), glial fibrillary acidic protein (GFAP), and S100. We also used the N518 antibody to label the new ganglion cells' axons, which are continuously added to the fish retina, and the anti-proliferating cell nuclear antigen (PCNA) antibody to specifically locate dividing cells. We demonstrate a specific regional adaptation of the GS-S100-positive Müller cells' vitreal processes around the optic disc, strongly labeled with the anti-GFAP antibody. In direct contact with these Müller cells' vitreal processes, there are S100-positive astrocytes and S100-negative cells ultrastructurally identified as microglial cells. Moreover, a population of PCNA-positive cells, characterized as glioblasts, forms the limit between the retina and the optic nerve in a region homologous to the Kuhnt intermediary tissue of mammals. Finally, in the intraocular portion of the optic nerve there are differentiating oligodendrocytes arranged in rows. Both the glioblasts and the rows of developing cells could serve as a pool of glial elements for the continuous growth of the visual system.

Flow cytometry measurement of the DNA contents of G0/G1 diploid cells from three different teleost fish species

BACKGROUND

Although there is a lot information in the literature about genome size in fish, a high variability among data for the same species is reported, being mainly related to methodological aspects. Flow cytometry-based fluorescence measurements of intercalating dyes is the most attractive approach due to its precision, objectivity, high speed, and relative simplicity.

METHODS

We analyze the DNA content of G0/G1 diploid nuclei of three teleost species (Carassius auratus, Tinca tinca, and Danio rerio) using flow cytometry. Forty-three animals were used and up to 50,000 retinal cells were analyzed per sample. Propidium iodide-associated fluorescence was assessed using a FACSCalibur flow cytometer. Standard human leukocytes were used as a reference.

RESULTS

Our results show that C. auratus (3.584 +/- 0.058 pg per nucleus) and D. rerio (3.357 +/- 0.074 pg per nucleus) showed similar DNA contents per cell, whereas it was significantly lower (2.398 +/- 0.038 pg per nucleus) in T. tinca. Interestingly, a low intraspecies variability was observed, the coefficient of variation being 1.608%, 2.198%, and 1.573% for C. auratus, D. rerio, and T. tinca, respectively.

CONCLUSIONS

The methodology used in this study provides an accurate and easy measurement of the genome size of a species.

Quantitative evaluation of the distribution of proliferating cells in the adult retina in three cyprinid species

In the present study, a descriptive and quantitative analysis of all the proliferating cell populations present in the normal adult retina of three cyprinid species (goldfish, zebrafish, and tench) is reported. Evaluation of cell proliferation was performed in proliferating cell nuclear antigen (PCNA)-labeled tissue sections as well as in single-cell suspensions analyzed by flow cytometry. Our results show that the neural progenitors of the inner nuclear layer (INL) of cyprinids continue dividing in adulthood in uninjured retinas. These cells are probably related to the generation of rods in normal retinal growth, as well as in the production of any retinal cell type in regenerating processes. The distributions of both these cells and their presumptive progeny, the rod precursors, differ from one species to another, being homogeneous in zebrafish, displaced to the periphery in goldfish and to the temporal pole in tench. With regard to the cell apposition at the retinal periphery, it seems to be symmetrical in goldfish and zebrafish, based on a homogeneous extension of the peripheral growth zone (PGZ), but asymmetrical in tench, where it presents a significantly lower extension in the ventral retina. The flow cytometry analyses indicate that, overall, the proportion of proliferating cells is significantly greater in zebrafish retina despite the fact that body growth rate is lower in zebrafish than the other two species.

Temperature induces variations in the retinal cell proliferation rate in a cyprinid

We quantitatively evaluate the changes of the proliferative cell populations in the adult tench retinas maintained at 6 degrees C and 20 degrees C by both PCNA antigen detection and flow cytometry-based DNA measurements. Both the overall percentage of S-phase cells in the whole retinas and the number of PCNA-positive cells in each of the retinal layers were significantly lower in the tench kept at 6 degrees C, indicating that temperature affects the retinal germinal cell proliferation.

Non-neuronal cells involved in the degeneration and regeneration of the fish retina

In the present work we show that during the degenerative process occurring after the cryo-elimination of the tench peripheral growing zone many non-neuronal cell types in addition to the resident microglial cells, appear within the affected areas. Some of them are normally found in the retina, such as the retinal pigmented epithelium cells and others originate from extra-retinal tissues. We identified these as granular leukocytes and macrophages. The microglial cells and macrophages, those resident in the sub-retinal space, and the invasive ones, act as phagocytes. The analysis of the injured retina following lesion shows that the invasive macrophages, arising from the scleral extra-retinal tissues, penetrate the neural retina, and migrate from the scleral to the vitreal portion. In contrast those coming from the vitreal extra-retinal tissues migrate in the opposite direction. Moreover, the retinal pigmented epithelium cells present remarkable modifications in their morphology and distribution and enter the neural retina, where they disrupt the surrounding tissue. We have also observed that this cryo-lesion causes an inflammation mediated by a type of granular leukocyte, denominated heterophils which penetrate the neural retina and probably come from the blood supply. Our results suggest that, during the first days after the lesion, the participation of diverse non-neuronal cells removing cell debris from the damaged zone should create a favourable environment allowing the regeneration of the neural retina.

A comparative study of protein kinase C-like immunoreactive cells in the retina

The present study is a morphological and quantitative analysis of protein kinase C-like immunoreactive (PKC-L ir) bipolar cells in the retinas of five different vertebrate species (chicken, tench, zebrafish, goldfish and rat). The morphology of PKC-L-ir bipolar cell axon terminals in fish differs significantly from those of chicken and rat retinas. Fish have bulky terminals whereas chicken and rat have their terminals in the form of small knob-shaped branches. In tench and goldfish, PKC-L-ir bipolar cells gradually decrease in size from the medial (i.e., in tench: mean +/- SD soma area of 30.09 +/- 5.98 microm2) to the peripheral (i.e., in tench: 19.93 +/- 1.73 microm2) retinal regions. This is not observed in chicken, rat or zebrafish where there is more homogeneity in s oma and axon terminal sizes between different retinal regions. Except in chicken, cell density increases from the central (i.e., in tench: mean +/- SD 1795.88 +/- 242.35 cells/mm2) to the peripheral (i.e., in tench: 4295.41 +/- 279.23 cells/mm2) retina. This study provides data that show relevant differences in the PKC-L-ir bipolar morphology and density among birds, fish and mammals. Moreover, these structural variations could mean not only differences in the cellular physiology, but also in the patterns of development and maintenance of the retina in each species.

Growing and regenerating axons in the visual system of teleosts are recognized with the antibody RT97

We have analyzed the immunolabeling with the antibody RT97, a good marker for ganglion cell axons in several species, in the normal and regenerating visual pathways of teleosts. We have demonstrated that RT97 antibody recognizes several proteins in the tench visual system tissues (105, 115, 160, 200, 325 and 335 kDa approximately). By using immunoprecipitation and Western blot we have found that after crushing the optic nerve the immunoreactivity to anti RT97 increased markedly in the optic nerve. In immunohistochemical analysis we also found a different pattern of labeling in normal and regenerating visual pathways. In normal tench RT97 is a good marker for the horizontal cells in the retina, for growing ganglion cell axons which run along the optic nerve from the retina to the optic tectum and of the axon terminals in the stratum opticum and stratum fibrosum and griseum superficiale in the optic tectum. After optic nerve crush, no immunohistochemistry modifications were observed in the retina. However, in accordance with Western blot experiments, in the optic nerve intensely stained groups of regenerating axons appeared progressively throughout the optic nerve as far as the optic tectum. We conclude that the antibody RT97 is an excellent marker of growing and regenerating axons of the optic nerve of fish.

Protein kinase C-like immunoreactive cells in embryo and adult chicken retinas

Morphological evidence of a temporal parallelism between the appearance of the alpha isoform of protein kinase C (PKC) and some processes such as synaptogenesis in the plexiform layers of the chicken retina is offered. Immunostaining experiments were performed throughout embryonic, young and adult chicken life. The results help to understand the development of rod bipolar cells.

Enzyme histochemical identification of microglial cells in the retina of a fish (Tinca tinca)

Histochemistry for nucleoside diphosphatase was used to study the microglial cells in the adult tench retina. An abundant population of microglial cells was located in the vascular membrane, nerve fibre layer, inner and outer plexiform layers and scattered cells were observed in the inner nuclear layer. Rounded and amoeboid cells could be seen close to the vessel in the vascular membrane, bipolar cells in the nerve fibre layer and ramified cells in the rest of the layers. Several microglial forms could correspond to developing cells. The pattern of distribution was similar to that described in other vertebrates, but with several differences, such as the presence of microglial cells in the vascular membrane and inner nuclear layer and the overlap of processes in the plexiform layers.

Response of microglial cells after a cryolesion in the peripheral proliferative retina of tench

We studied the glial response after inducing a lesion in the zone of the peripheral retina of tench, where there is proliferative neuroepithelium. In the retina and optic nerve, the microglial response was analysed with tomato lectin and the macroglial response with antibodies against GFAP and S-100. In lesioned retinas, there was a temporal-spatial distribution pattern of microglia. One day after lesion, primitive ramified cells appeared in the nerve fibre layer. These cells appeared progressively from the vitreal to the scleral layers until day 7 when cells appeared in all layers, with the exception of the outer plexiform layer. From this point, labelling decreased. In the optic nerve, 3 days after lesion, an increase in the number of microglial cells was observed, first in the nerve folds and from day 15 in specific areas of the optic nerve. In the central retina, in the optic nerve head and within the optic nerve itself, the appearance of microglial cells, after the lesion, near the blood vessels, could indicate a vascular origin of microglia, as has been proposed by many authors. However, we cannot discount the idea that some of the reactive microglial cells arise by proliferation of the microglia existing in the normal state. Using GFAP and S-100 antibodies, no important changes in the retina were observed, however in the optic nerve there was response to the lesion. Thus, the macroglial cells appeared to be involved in reorganisation of the optic nerve axons after lesion.

Ultrastructural organization of the optic nerve of the tench (Cyprinidae, Teleostei)

Different parts of the tench optic nerve--the intraocular and intraorbital segments, the chiasm, and the post-chiasmatic segment--were studied using light and electron microscopy. From the head of the optic nerve, a zone of continuous growth constituted by the younger non-myelinated ganglion axons can be differentiated from a mature zone where almost all the axons are myelinated. The transition from one zone to the other is progressive. The area containing only non-myelinated axons is very restricted, and the presence of myelinated and non-myelinated axons in the same fascicle is frequent. In the head of the optic nerve, the growing zone surrounds the central artery. In the intraorbital segment, where the optic nerve is organized as a folded ribbon, the growing edge is surrounded by other mature folds. In the chiasm and in the post-chiasmatic segment of the optic nerve, the organization as a folded ribbon disappears and the youngest axons are situated on the periphery. In the growing zones, the immature astrocytes predominate; in the transition zones, oligodendrocytes, in different stages of maturity, begin to appear. In the mature zone, almost all the glial cells are differentiated, although immature cells can be found. The microglial cells are not abundant and are of the ramified type. Moreover, in contrast to the descriptions of other teleosts, the tench optic nerve is profusely supplied with blood vessels throughout its length.

S-100-positive glial cells are involved in the regeneration of the visual pathway of teleosts

Glial cells in the normal and regenerating visual pathways of Tinca tinca (Cyprinid, Teleost) were studied by labelling with anti-S-100 antibody. In normal fish, S-100-positive bipolar cells were found in the optic nerve, optic tract, and in the diencephalic visual pathways. After crushing the left optic nerve, the distribution and the number of S-100-immunoreactive cells were modified. In the injured nerve, 7 to 15 days after crushing no immunoreactive cell bodies were found in the crushed area, but a greater number of S-100-positive cells were found on both sides of the injured area. Sixty days after crushing, positive cells penetrating the crushed area were observed; the normal pattern was almost restored 200 days after crushing. In the diencephalon, 25 days after crushing, the number of S-100-positive cells increased remarkably and the most intense immunostaining of glial processes was observed 60 days after crushing. The density of S-100-labelled cells decreased after 4 months postcrushing. However, in the optic tectum no changes were observed. The increase of glial cells in the lesioned visual pathway suggests that they could play an important role in axonal regeneration after crushing.

Microglia in normal and regenerating visual pathways of the tench (Tinca tinca L., 1758; Teleost): a study with tomato lectin

We have studied the microglial cells in the normal and regenerating visual pathways of Tinca tinca (Cyprinid, Teleost) by using the lectin from Lycopersicum esculentum (tomato), which, in our case, has been demonstrated as a specific marker for teleost microglia. In the normal fish, there are tomato lectin positive microglial cells in the retina, optic nerve, and optic tectum. Following optic nerve crush, we observed a more extensive labeling of the microglia in the crushed optic nerve and in the contralateral optic tectum affecting the stratum opticum and stratum fibrosum et griseum superficiale. In both cases, there was an increase of rounded and less ramified microglial cells, and granular cells. This response of a more extensive labeling of microglial cells increases to a maximum at 2-3 weeks after the crush; the density of labeled microglial cells decreases after 3 months after crushing. However, in the retina no changes were observed after optic nerve crush. These results suggest that the microglial cells could play an important role in regeneration of fish optic pathway, as other neuroglial cells do.

Volumetric analysis of the telencephalon and tectum during metamorphosis in a flatfish, the turbot Scophthalmus maximus

The telencephalic hemispheres and the optic tectum of the turbot Scophthalmus maximus were analysed volumetrically during metamorphosis. Both brain regions develop an asymmetry coordinated chronologically with metamorphic events that produce asymmetry in the rest of the animal. Furthermore, the brain asymmetries are correlated with, and may be determined by, the side of origin of their primary afferent inputs, such that the more voluminous side of the brain receives these inputs from the zenithal side. After metamorphosis, the telencephalon remains asymmetric, whereas the optic tectum recovers its bilateral symmetry.

Afferent projections from the brainstem to the area hypothalamica dorsalis: a horseradish peroxidase study in the cat

Experiments using the retrograde transport of horseradish peroxidase were performed in order to identify the cells of origin the ascending projections from different brainstem regions to the area hypothalamica dorsalis (aHd) in the cat. The afferent inputs to this area originate mainly from the midbrain and medulla oblongata regions. The main afferent source of the area hypothalamica dorsalis arises from the substantia grisea centralis, where a large number of labeled cells were observed bilaterally, although more abundant on the ipsilateral side. Substantial afferents reach the aHd from the nuclei vestibularis medialis and inferior and the formatio reticularis mesencephali. A modest number of peroxidase-labeled neurons were observed in the nuclei ruber, interpeduncularis, substantia nigra, reticularis gigantocellularis, vestibularis lateralis, cuneatus and gracilis. From the pons, the nucleus raphe magnus sends a weak projection to the aHd. These anatomical data suggest that such area could be involved in visceral, sexual, nociceptive somatosensorial, sleep-waking and motor mechanisms.