Rapid and long-term plasticity in the neonatal and adult retinotectal pathways following a retinal lesion

The uncrossed retinotectal projection restricts its terminal fields to the ventral boundary of the visual layers at the rostral tectum during early post natal development. During this critical period, temporal retinal lesions in one eye induce laminar rearrangements in the uncrossed pathway of the intact eye toward the collicular surface previously occupied, almost exclusively, by the crossed retinal axon population. We have compared, using anterograde tracing techniques, the time course and magnitude of the axonal sprouting resulting from retinal lesions in neonates and adults. Early retinal lesions (within the first two post natal weeks) induced extensive and rapid plasticity of the ipsilateral projection 48 h after the lesions. On the third post natal week, similar retinal lesions induced a small reorganization of the intact eye's uncrossed projection within a 3-week survival time. Nevertheless, giving the animals a long-term survival, resulted in an increased plastic capability, suggesting that even after the critical period, intact retinal axons can respond efficiently to injury. The results suggest two phases of axonal reorganization within this subcortical pathway: a rapid plasticity within the critical period and a slow, but continuous plasticity in adulthood.

Management of advanced retinoblastoma

This review provides an update on the current management of advanced retinoblastoma.

[Preliminary results of radiosurgery for uveal melanoma]

OBJECTIVE

To evaluate the clinical value of stereotactic radiosurgery (SRS) for uveal melanoma.

METHODS

From Jan, 1996 to March, 2004, 16 patients with uveal melanoma were treated with SRS, two by one session (35 Gy, 25 Gy) and fourteen by fractionated SRS (30-55 Gy/2-4F/4-16D). The follow-up period ranged from 3 to 100 months (median: 66 months).

RESULTS

All 16 patients were still alive though all were blind in the diseased eye during recent follow-up. Local control rate was 93.4%, 5-year survival rate of 13 patients who have been followed for more than 5 years, was 100% (13/13). However, 7 patients received eyeball enucleation due to corneal ulcer (n = 2), suspicion for uncontrolled tumor (n = 2) and secondary glaucoma (n = 3). One patient developed distant metastasis, though still alive.

CONCLUSION

Fractionated radiosurgery is safe and effective for uveal melanoma. It is indicated for lesions of limited size (longest diameter < 20 mm, depth < 15 mm) located in the posterior pole or behind the equator at the back of the eyeball.

Structural-metabolic organization of field 4 of the cat brain in normal conditions and after unilateral enucleation of the eye

Comparative data on the structural-metabolic organization of field 4 of the cat brain in normal conditions and after unilateral enucleation of the eye are presented. Cytochrome oxidase was detected histochemically. Data were processed by a computerized method using an original video capture system. Data were obtained demonstrating the uneven distribution of enzyme along sublayer IlIb of field 4 in animals with unilateral enucleation. A hypothesis based on published data is suggested whereby the alternation of high- and low-reactive areas is evidence for the ordering of the retinal representations of the right and left eyes in the sensorimotor cortex.

"Finger-tip" cryoprobe assisted enucleation

PURPOSE

To report the use of a new cryotherapy probe to induce proptosis during enucleation surgery.

DESIGN

Interventional case report.

METHODS

Two patients with uveal melanoma and secondary glaucoma were treated by enucleation. A large surface area (70 mm(2)), spatulated, end-freezing cryotherapy probe ("Finger-tip" probes, MIRA, Inc.) was used to induce proptosis during optic nerve transsection.

RESULTS

This new probe offers homogeneous freezing over a relatively large surface area. This new cryoprobe was used to create a large cryo-adhesion on the cornea, for an excellent purchase of the eye during enucleation surgery. Using this adhesion, the eye was lifted, enabling transsection of the optic nerve.

CONCLUSIONS

This report includes photographs of the cryoprobe, the corneal cryo-adhesion, and describes its use for traction during enucleation surgery.

The Collaborative Ocular Melanoma Study

This review provides a summary of the main objectives, significant design features, and major findings and achievements of the Collaborative Ocular Melanoma Study (COMS). It has been written by two ophthalmic oncologists who were not part of the COMS study group; therefore, it represents an extramural view of the trial to supplement summaries published by the COMS investigators. Because the randomized design of the COMS was unique, no attempt is made to make any comparison with the results of previous non-controlled studies.

Multiple periods of functional ocular dominance plasticity in mouse visual cortex

The precise period when experience shapes neural circuits in the mouse visual system is unknown. We used Arc induction to monitor the functional pattern of ipsilateral eye representation in cortex during normal development and after visual deprivation. After monocular deprivation during the critical period, Arc induction reflects ocular dominance (OD) shifts within the binocular zone. Arc induction also reports faithfully expected OD shifts in cat. Shifts towards the open eye and weakening of the deprived eye were seen in layer 4 after the critical period ends and also before it begins. These shifts include an unexpected spatial expansion of Arc induction into the monocular zone. However, this plasticity is not present in adult layer 6. Thus, functionally assessed OD can be altered in cortex by ocular imbalances substantially earlier and far later than expected.

Induction of the candidate-plasticity NGFI-A protein in the adult rat superior colliculus after visual stimulation

In this work, we studied the visually driven expression of the plasticity-related transcription factor NFGI-A in the superficial layers of the rat superior colliculus (sSC) using immunohistochemistry. After dark adaptation, NGFI-A expression was completely down-regulated, indicating this protein is not constitutively expressed in the sSC. Light stimulation for 10 min after dark adaptation was insufficient to induce detectable levels of this protein. But after 30 min of light stimulation, few NGFI-A+ cells were observed in the superficial layers, indicating that the minimal time of stimulation that is sufficient to induce this protein is sometime between 10 and 30 min. The number of NGFI-A+ cells increased progressively, reaching a peak after 90 min. This peak is not reached if animals are returned to darkness after 30 min of stimulation, when a presumable peak in NGFI-A mRNA is reached. Light stimulation of animals in which the retinocollicular or corticocollicular projections were removed revealed that NGFI-A expression is mainly driven by retinal contralateral projections. Removal of corticocollicular projections did not cause any change in the NGFI-A expression in the ipsilateral sSC, in relation to the contralateral (control) sSC, suggesting that this pathway has a minor influence. Our results showed that NGFI-A protein expression in the sSC is entirely dependent on visual stimulation and suggests that the sSC visual circuitry is an interesting model for studies about the involvement of this transcription factor in synaptic plasticity.

[Surgical technique and complications of enucleation]

Enucleation consists of removal of the entire globe and portion of the optic nerve from the orbit. This surgical procedure is generally accepted treatment for intraocular malignancies, a blind painful eye, severely traumatized eye, phthisis bulbi and improvement of cosmetic look. In this review, the authors discuss the current surgical technique of enucleation with orbital implant placement and their complications.

Comparison after 10 years of two 100-patient cohorts operated on for eviscerations or enucleations

PURPOSE

To compare the indications, surgical techniques, and operative outcome between two 100-patient populations operated on for evisceration or enucleation with a 10-year interval.

METHODS

This retrospective study involved 100 patients operated on between 1987 and 1990 (Group 1) compared with another 100 patients operated on between 1996 and 2000 (Group 2). Group 1 included 64 males and 36 females, mean age 49 years; Group 2 included 60 males and 40 females, mean age 53.

RESULTS

In Group 1, 19 eviscerations were performed, versus 55 in Group 2. In both groups, half of the indications for surgery were a painful blind eye. In Group 1, endophthalmia (23%) came second, whereas it was trauma (15%) in Group 2. Sixty-eight patients were implanted in Group 1 (silicone spheres 69%) versus 86 in Group 2 (hydroxyapatite spheres 69%). Twenty spheres (20%) were rejected in Group 1 versus 7% in Group 2.

DISCUSSION AND CONCLUSIONS

The proportion of eviscerations increased in 10 years. The number of endophthalmitis-related operations decreased and trauma-related operations increased. The number of implantations increased with hydroxyapatite as the first choice material instead of silicone. This most likely contributed to reducing the number of rejections.

Myoconjunctival enucleation for enhanced implant motility. result of a randomised prospective study

PURPOSE

Implant motility and cosmetic appearance of the eye after enucleation have remained major considerations whenever mycoconjunctival enucleation is planned. Despite major advances in surgical technique and the availability of a variety of implant materials and shapes, there is lack of consensus on the best material and type of implant. This study was conducted to compare routine and myoconjunctival techniques of enucleation in terms of motility index.

METHODS

Thirty consecutive patients scheduled for enucleation for non-malignant indications were randomly assigned to one of the two groups- routine and myoconjunctival techniques. The postoperative results were compared for the motility of implant and the complications.

RESULTS

The two techniques showed no difference in rates of complications, but implant motility was significantly better with the myoconjunctival technique. Implant extrusion or migration was not seen.

CONCLUSION

We recommend the use of myoconjunctival enucleation for enhanced motility and cosmesis.

Retinoblastoma patients with high risk ocular pathological features: who needs adjuvant therapy?

AIMS

To describe the outcome of patients with non-metastatic unilateral retinoblastoma with high risk histopathological features after primary enucleation, and to clarify the need and results of adjuvant therapy.

PATIENTS AND METHODS

From 1980 to 2001 adjuvant therapy was recommended only to patients with scleral involvement, post-laminar optic nerve involvement (PLONI) with either a positive margin or associated choroidal involvement, or (before 1994) isolated PLONI.

RESULTS

108 of 224 patients had at least one high risk feature (choroidal, scleral, anterior chamber, and/or PLONI). Patients with isolated choroidal (n = 55) or anterior chamber (n = 2) invasion, and most with PLONI without other risk factors (n = 21) were not treated; three relapsed but are long term survivors after intensive therapy. Four with isolated PLONI received adjuvant chemotherapy and none relapsed. Three of 11 with PLONI and concomitant choroidal or scleral involvement who received adjuvant therapy relapsed, versus two of four not treated. Two of five with scleral disease relapsed. All 12 with cut end involvement received adjuvant treatment and none relapsed. In the total group, all four patients who relapsed after adjuvant therapy died.

CONCLUSIONS

Relapsing patients can be rescued with intensive therapy. Those with isolated choroidal or PLONI have a good prognosis without adjuvant therapy. Patients with PLONI with a positive margin have a good prognosis if treated with combined therapy. Those with scleral involvement or PLONI with concomitant choroid disease may benefit from adjuvant therapy.

Influence of non-penetrating glaucoma surgery on aqueous outflow facility in isolated porcine eyes

PURPOSE

To investigate, in vitro, the influence of non-penetrating glaucoma surgery (NPGS) and the influence of tightly suturing the superficial scleral flap on the aqueous outflow facility of isolated porcine eyes.

MATERIALS AND METHODS

The anterior chambers of 12 enucleated porcine cadaver eyes were cannulated and perfused. NPGS was performed by the same surgeon. The overall ocular aqueous outflow facilities were assessed before and after the surgical interventions of NPGS, as well as after scleral flap closure.

RESULTS

The mean (SD) aqueous outflow facility, which was 0.164 (0.014) microl/min/mm Hg before surgery, increased significantly after NPGS to 1.584 (0.217) microl/min/mm Hg, p<0.001. When the superficial flap was closed, the aqueous outflow facility significantly decreased (0.754 (0.107) microl/min/mm Hg, p<0.001) but remained significantly higher than preoperatively (p<0.01). After suturing the superficial flap, the overall resistance increased to 1.625 (0.210) microl/min/mm Hg. The difference in the resistance to outflow before and after flap closure was 0.848 (0.169) microl/min/mm Hg.

CONCLUSION

After NPGS suturing the scleral flap can modulate aqueous outflow resistance. The experimental set up described might provide an efficient model for the technical training of glaucoma surgeries.

Ionotropic glutamate receptor GluR2/3-immunoreactive neurons in the cat, rabbit, and hamster superficial superior colliculus

Ionotropic glutamate receptor (GluR) subtypes occur in various types of cells in the central nervous system. We studied the distribution of AMPA glutamate receptor subtype GluR2/3 in the superficial layers of cat, rabbit, and hamster superior colliculus (SC) with antibody immunocytochemistry and the effect of enucleation on this distribution. Furthermore, we compared this labeling to that of calbindin D28K and parvalbumin. Anti-GluR2/3-immunoreactive (IR) cells formed a dense band of labeled cells within the lower superficial gray layer (SGL) and upper optic layer (OL) in the cat SC. By contrast, GluR2/3-IR cells formed a dense band within the upper OL in the rabbit and within the OL in the hamster SC. Calbindin D28K-IR cells are located in three layers in the SC: one within the zonal layer (ZL) and the upper SGL in all three animals, a second within the lower OL and upper IGL in the cat, within the IGL in the rabbit and within the OL in the hamster, and a third within the deep gray layer (DGL) in all three animals. Many parvalbumin-IR neurons were found within the lower SGL and upper OL. Thus, the GluR2/3-IR band was sandwiched between the first and second layers of calbindin D28K-IR cells in the cat and rabbit SC while the distribution of GluR2/3-IR cells in the hamster matches the second layer of calbindin D28K-IR cells. The patterned distribution of GluR2/3-IR cells overlapped the tier of parvalbumin-IR neurons in cat, but only partially overlapped in hamster and rabbit. Two-color immunofluorescence revealed that more than half (55.1%) of the GluR2/3-IR cells in the hamster SC expressed calbindin D28K. By contrast, only 9.9% of GluR2/3-IR cells expressed calbindin D28K in the cat. Double-labeled cells were not found in the rabbit SC. Some (4.8%) GluR2/3-IR cells in the cat SC also expressed parvalbumin, while no GluR2/3-IR cells in rabbit and hamster SC expressed parvalbumin. In this dense band of GluR2/3, the majority of labeled cells were small to medium-sized round/oval or stellate cells. Immunoreactivity for the GluR2/3 was clearly reduced in the contralateral SC following unilateral enucleation in the hamster. By contrast, enucleation appeared to have had no effect on the GluR2/3 immunoreactivity in the cat and rabbit SC. The results indicate that neurons in the mammalian SC express GluR2/3 in specific layers, which does not correlate with the expression of calbindin D28K and parvalbumin among the animals.

Prolonged expression of c-Fos protein in the lateral habenular nucleus of the Japanese monkey (Macaca fuscata) after eye enucleation

To elucidate the effect of traumatic stress on the lateral habenular nucleus, we investigated the time course of the expression of c-Fos protein in this nucleus of the Japanese monkey (Macaca fuscata) after enucleation of one eye using c-Fos protein immunocytochemistry. c-Fos protein-like immunoreactive neurons were significantly increased; the increase started 1 h after the enucleation and remained high for 3-9 h in the lateral habenular nucleus on both sides. These results suggest that the prolonged expression of c-Fos protein occurred in the lateral habenular nucleus after traumatic stress through multiple transsynaptic activations.

A quantitative study of the neuronal nitric oxide synthase expression in the superficial layers of the adult rat superior colliculus after perinatal enucleation

The level of expression of the neuronal nitric oxide synthase (nNOS) in the retinorecipient layers of rat superior colliculus (SC) was investigated in adult rats after neonatal enucleation using two biochemical methods: (1) measurement of the in vitro specific-activity of NOS by the conversion of [3H]-arginine to [3H]-citrulline and (2) immunochemical analysis by western blotting and densitometry of immunoreactive bands using antibodies that recognise the three prominent isoforms of nNOS, alpha, beta and gamma. A total of 20 Lister rats were used in this study. We have shown that the deprivation of the retinocollicular projections at early postnatal ages induces no significant change in the specific-activity of nNOS. We also have shown that the deafferentation does not significantly influence either the total amount of nNOS in the SC superficial layers or the relative contribution ratio of nNOS isoforms. In conclusion, the expression and activity of nNOS in the SC retinorecipient layers was shown not to be dependent on the presence of retinal afferents during development.

Developmental regulation of spine and filopodial motility in primary visual cortex: reduced effects of activity and sensory deprivation

Dendritic protrusions are highly motile during postnatal development. Although spine morphological plasticity could be associated with synaptic plasticity, the function of rapid spine/filopodial motility is still unknown. To investigate the role of spine motility in the development of the visual cortex and its relation with critical periods, we used two-photon imaging of neurons from layers receiving visual input in developing mouse primary visual cortex and compared motility between control and visually deprived animals. Spine and filopodia motility was prominent during early synaptogenesis (P11-P13) but greatly decreased after P15. This "switch" was coincident with a 2.5-fold increase in protrusion density and spine formation. Spine motility was not regulated during the critical period for monocular deprivation (P19-P34). Moreover, delaying the critical period by dark rearing did not delay the normal developmental decrease of spine motility, but caused a modest further reduction in motility at P28-P35. Dark rearing and enucleation also mildly reduced spine motility before eye opening and dark rearing reduced the proportion of filopodia. We conclude that (1) rapid spine motility is not related to critical period plasticity, but is likely to play a role in early synaptogenesis, and (2) neuronal activity stimulates spine motility during synaptogenesis and promotes the appearance of dendritic filopodia.

Persistence of graded EphA/Ephrin-A expression in the adult frog visual system

Many studies have demonstrated the involvement of the EphA family of receptor tyrosine kinases and their ligands, ephrin-A2 and -A5, in the development of the temporonasal axis of the retinotectal/collicular map, but the role of these molecules in optic nerve regeneration has not been well studied. Noting that the characteristic gradients of the EphA/ephrin-A family that are expressed topographically in the retina and tectum of embryonic chicks and mice tend to disappear after birth, we took as our starting point an analysis of EphA and ephrin-A expression in leopard frogs (Rana pipiens and utricularia), species capable of regenerating the retinotectal map as adults. For the EphA family to be involved in the regeneration, one would expect these topographic gradients to persist in the adult or, if downregulated after metamorphosis, to be reexpressed after optic nerve injury. Using EphA3 receptor and ephrin-A5 ligand alkaline phosphatase in situ affinity probes (RAP and LAP, respectively) in whole-mount applications, we report that reciprocally complementary gradients of RAP and LAP binding persist in the optic tract and optic tectum of postmetamorphic frogs, including mature adults. EphA expression in temporal retinal axons in the optic tract was significantly reduced after nerve section but returned during regeneration. However, ephrin-A expression in the tectal parenchyma was not significantly elevated by either eye removal, with degeneration of optic axons, or during regeneration of the retinotectal projection. Thus, the present study has demonstrated a persisting expression of EphA/ephrin-A family members in the retinal axons and tectal parenchyma that may help guide regenerating fibers, but we can offer no evidence for an upregulation of ephrin-A expression in conjunction with optic nerve injury.

Experience-dependent regulation of the zincergic innervation of visual cortex in adult monkeys

Zinc is packaged in, and released from, a subset of glutamatergic synapses in the mammalian telencephalon where it has been shown to act as a potent neuromodulator. In order to establish the functional role for zincergic neurons in visual cortical function and plasticity we have compared the topographic distribution of zincergic terminals in the primary visual cortex (V1) of normal adult vervet monkeys (Cercopithicus aethiops) to that in monkeys monocularly deprived of visual input for short (24 h) or long (3 months) survival times. In normal animals, staining levels for zinc were highest in layers 1-3, 4b, 5 and 6 and lowest in layers 4a and 4c. The laminar and tangential patterns of zinc staining were complementary to staining patterns demonstrated using cytochrome oxidase (CO) histochemistry. Following 3 months of monocular deprivation by enucleation, levels of zinc staining in layers 3, 4calpha and 6a were heterogeneously reduced, clearly revealing the ocular dominance pattern in V1. When compared with the pattern of CO staining, levels of both CO and zinc were reduced in cortical territory innervated by the enucleated eye. Zinc histochemistry also revealed the ocular dominance pattern after only 24 h of monocular impulse blockade induced by enucleation or intravitreal tetrodotoxin infusion. However, by either means of deprivation for 24 h, levels of zinc were increased in deprived-eye stripes relative to nondeprived-eye stripes. These results indicate that zincergic terminals demarcate distinct compartments in the primate visual cortex. Furthermore, levels of synaptic zinc are rapidly and dynamically regulated, suggesting that zinc and/or zincergic neurons participate in mediating activity-dependent changes in the organization of the adult neocortex.

The eyes suppress a circadian rhythm of FOS expression in the suprachiasmatic nucleus in the absence of light

Photic information transmitted from the eyes to the suprachiasmatic nucleus (SCN) is essential for entrainment of circadian behavioral and physiological rhythms in mammals. Under conditions of constant darkness, these rhythms are maintained by the circadian pacemaker cells of the SCN [Bioessays 22 (2000) 23]. It is possible, however, that even in the absence of light, the eyes, which also contain autonomous circadian pacemakers [Science 272 (1996) 419; Chronobiol Int 16 (1999) 229], modulate circadian rhythms in the SCN. Indeed, it was shown recently that removal of the eyes abolishes an endogenous circadian rhythm within cells of the SCN [Nat Neurosci 6 (2003) 111], a finding that led to the suggestion that specific rhythms of the SCN are driven by input from the eyes. In contrast, we show here that removal of the eyes amplifies a normally dampened endogenous circadian rhythm within the SCN, indicating that the eyes can suppress the expression of specific rhythms within the SCN while promoting others.