Biomedical subjects

M Vidal-Sanz

Publications and source records attributed to M Vidal-Sanz.

At least 19 recordsLinked to original sources

PubMed2003

Evolving neurovascular relationships in the RCS rat with age.

PURPOSE: To examine the course of development of vascular disorders in the Royal College of Surgeons (RCS) rat and how these may lead to retinal ganglion cell loss. METHODS: Whole-mount retinae from RCS rats were first stained for neurofilament protein and then for NADPH-diaphorase staining. A separate group of RCS rats was injected with Type II Peroxidase and the retinae were subsequently processed for peroxidase histochemistry. RESULTS: The first changes in the deep vascular plexus occur as the photoreceptor layer is lost and it comes into close proximity to the retinal pigment epithelial (RPE) cell layer. RPE cells migrate onto retinal vessels, and at such locations vascular complex develop. These are first found ventral to the optic nerve head and then gradually progress over most of the retina. The inner retinal vessels that supply the complexes cross the optic nerve fiber layer and appear to be under tension. They ligate axons, which leads to retinal ganglion cell loss. CONCLUSIONS: These observations show vascular changes can have secondary repercussions for neurons distant from the primary lesion.

Aging↗

PubMed2002

Retinal ganglion cell death after acute retinal ischemia is an ongoing process whose severity and duration depends on the duration of the insult.

In adult Sprague-Dawley rats we have investigated retinal ganglion cell survival after transient intervals of retinal ischemia of 30, 45, 60, 90 or 120 min duration, induced by ligature of the ophthalmic vessels. Animals were killed 5, 7, 14, 21, 30, 60, 90 or 180 days later and densities of surviving retinal ganglion cells were estimated in retinal whole mounts by counting cells labelled with diAsp. This dye was applied, 3 days prior to death, to the ocular stump of the intraorbitally transected optic nerve. We found that retinal ganglion cell loss after retinal ischemia proceeds for different lengths of time. All the ischemic intervals induced loss of retinal ganglion cells whose severity and duration was related to the length of the ischemic interval. Following 30 or 45 min of ischemia, cell loss lasted 14 days and caused the death of 46 or 50%, respectively, of the population of retinal ganglion cells. Sixty, 90 or 120 min of retinal ischemia were followed by a period of cell loss that lasted up to 90 days and caused the death of 75%, 87% or 99%, respectively, of the population of retinal ganglion cells. We conclude that retinal ganglion cell loss after retinal ischemia is an ongoing process that may last up to 3 months after the injury and that its severity and duration are determined by the ischemic interval.

Acute Disease↗

PubMed2001

Retinal ganglion cell death induced by retinal ischemia. neuroprotective effects of two alpha-2 agonists.

We have investigated in adult Sprague-Dawley rats the neuroprotective effects of two alpha-2-selective agonists [AGN 191,103 (AGN) and brimonidine tartrate (BMD)] on retinal ganglion cell (RGC) survival after transient retinal ischemia. RGCs were labelled with Fluorogold (FG) applied to both superior colliculi. Seven days later, 90 min of retinal ischemia were induced in the left eyes by ligature of the ophthalmic vessels (LOV). In one group of animals, vehicle or AGN (0.01 mg/kg) were administered systemically 1 hr before ischemia. In another group of animals, two 5 microl drops of vehicle, AGN (0.05%) or BMD (0.1%) were administered topically in the left eye 1 hr before ischemia. The animals were processed 7 or 21 days later. RGC survival was estimated by counting FG-labelled cells in 12 standard areas of each retina. In control retinas of systemically pretreated animals, mean densities of labelled RGCs were 2372 +/- 49 cells/mm(2) (mean +/- SEM; n = 6). In experimental retinas of systemically pretreated animals, mean RGC densities had decreased 7 days after ischemia to 53% (n = 6) or 81% (n = 6) of control in the groups treated with vehicle or AGN, respectively. Twenty-one days after ischemia, mean RGC densities had decreased to 38% (n = 6) or 79% (n = 6) of control in the groups treated with vehicle or AGN, respectively. In control retinas of topically pretreated animals, mean densities of labelled RGCs were 2208 +/- 29 cells/mm(2) (n = 6). In experimental retinas of topically pretreated animals, mean RGC densities had decreased 7 days after ischemia to 54% (n = 6), 95% (n = 6) or 96% (n = 6) of control in the groups treated with vehicle, AGN or BMD, respectively. These results indicate that pretreatment with a single systemic or topical dose of AGN or BMD can prevent completely the early rapid phase of RGC loss and abolish the delayed RGC loss observed after 90 min of retinal ischemia induced by ligature of the ophthalmic vessels.

Administration, Topical↗

PubMed2001

Neuroprotective effects of alpha(2)-selective adrenergic agonists against ischemia-induced retinal ganglion cell death.

PURPOSE: To investigate in adult rats the effects of two alpha(2)-selective adrenergic agonists (alpha(2)-SAs; AGN 191103 and AGN 190342) on retinal ganglion cell (RGC) survival after transient retinal ischemia. METHODS: RGCs were labeled with a Fluorogold (FG) tracer applied to both superior colliculi. Seven days later, the left ophthalmic vessels were ligated for 60 or 90 minutes. In one group, a single dose of saline or one alpha(2)-SA was administered intraperitoneally (IP) or topically 1 hour before ischemia. In another group, a single dose of AGN 190342 was administered IP, 1, 2, 4, 24, or 72 hours after ischemia. Rats were processed 7, 14, or 21 days later. Densities of surviving RGCs were estimated by counting FG-labeled cells in 12 standard retinal areas. RESULTS: Seven days after 60 or 90 minutes of retinal ischemia, death had occurred in 36% or 47%, respectively, of the RGC population, and by 21 days the loss of RGCs amounted to 42% or 62%, respectively. Systemic pretreatment with an alpha(2)-SA resulted in enhanced survival of ischemic-injured RGCs. Topical pretreatment with an alpha(2)-SA prevented up to 100% of the ischemia-induced RGC loss. Pretreatment with an alpha(2)-SA abolished the secondary slow RGC loss that occurred between days 7 and 21 after ischemia. When administered shortly after ischemia (up to 2 hours) AGN 190342 rescued substantial proportions of RGCs destined to die and diminished slow RGC death. CONCLUSIONS: Pretreatment and early posttreatment with an alpha(2)-SA induces marked long-lasting neuroprotective in vivo protection against ischemia-induced cell death in RGCs.

Adrenergic alpha-Agonists↗

PubMed2000

Microglial cells in the retina of Carassius auratus: effects of optic nerve crush.

To study the morphology and distribution of the retinal microglial cells of the goldfish retina in normal conditions and after optic nerve crush, we have used the nucleoside diphosphatase (NDPase) technique, applied to whole-mounts or sections, for light and electron microscopy. In normal retinas, two populations of NDPase-positive cells were identified: compact cells associated with the retinal vessels on the vitreal surface of the retina and microglial cells in various retinal layers. The microglial cells had a bipolar or multipolar morphology. Bipolar cells were observed in the nerve fibre layer, and multipolar cells were visualised in the ganglion cell layer (GCL), inner plexiform layer (IPL), and outer plexiform layer. The highest densities of multipolar cells were observed in the IPL layer, where they adopted a regular mosaic-like arrangement in which the occasional spaces were occupied by cells of the GCL. After optic nerve crush, we observed an increase in the number of compact cells associated with the vessels and changes in NDPase activity, morphology, and distribution of the retinal microglial cells. These cells showed an increase in NDPase activity in all retinal layers from day 1 to day 15 after axotomy, and retraction of their processes from day 1 to day 7. In addition, the densities of microglial cells increased in the GCL between 2 and 15 days after axotomy, and decreased in the IPL by day 4 after axotomy. These microglial changes resemble those observed in other regenerating and nonregenerating neuronal systems and may reflect a general response of microglia directed to help the regeneration process.

Acid Anhydride Hydrolases↗

PubMed2000

Selective innervation of retinorecipient brainstem nuclei by retinal ganglion cell axons regenerating through peripheral nerve grafts in adult rats.

The pattern of axonal regeneration, specificity of reinnervation, and terminal arborization in the brainstem by axotomized retinal ganglion cell axons was studied in rats with peripheral nerve grafts linking the retina with ipsilateral regions of the brainstem, including dorsal and lateral aspects of the diencephalon and lateral aspect of the superior colliculus. Four to 13 months later, regenerated retinal projections were traced using intraocular injection of cholera toxin B subunit. In approximately one-third of the animals, regenerated retinal axons extended into the brainstem for distances of up to 6 mm. Although axons followed different patterns of ingrowth depending on their site of entry to the brainstem, within the pretectum, they innervated preferentially the nucleus of the optic tract and the olivary pretectal nucleus in which they formed two types of terminal arbors. Within the superior colliculus, axons extended laterally and formed a different terminal arbor type within the stratum griseum superficiale. In the remaining two-thirds of the animals, retinal fibers formed a neuroma-like structure at the site of entry into the brainstem, or a few fibers extended for very short distances within the neighboring neuropil. These experiments suggest that regenerated retinal axons are capable of a highly selective reinnervation pattern within adult denervated retinorecipient nuclei in which they form well defined terminal arbors that may persist for long periods of time. In addition, these studies provide the anatomical correlate for our previous functional study on the re-establishment of the pupillary light reflex in this experimental paradigm.

Age Factors↗

PubMed2000

Death and neuroprotection of retinal ganglion cells after different types of injury.

In adult Sprague-Dawley rats, retinal ganglion cell survival was investigated after intraorbital optic nerve section and after transient ischemia of the retina induced by elevation of the intraocular pressure or by selective ligature of the ophthalmic vessels. The thickness of the inner nuclear and inner plexiform layers was also assessed after transient periods (120 min) of retinal ischemia induced by selective ligature of the ophthalmic vessels. In addition, we have also investigated the neuroprotective effects of different substances in these paradigms. The intraocular injection of brain-derived neurotrophic factor increased RGC survival after retinal ischemia induced by elevation of the intraocular pressure or by selective ligature of the ophthalmic vessels. The caspase-inhibitor Z-DEVD increased retinal ganglion cell survival after optic nerve section and also after 90 min of retinal ischemia induced by selective ligature of the ophthalmic vessels. The peptide Bcl-2 did not increase retinal ganglion cell survival after optic nerve section but increased retinal ganglion cell survival after 60 or 90 min of retinal ischemia induced by selective ligature of the ophthalmic vessels. Finally, BDNF, nifedipine, naloxone and bcl-2 prevented in part the decrease in thickness of the inner nuclear layer and inner plexiform layer induced by selective ligature of the ophthalmic vessels. Our results suggest that retinal ganglion cell loss induced by different types of injury, may be prevented by substances with neuroprotective effects, by altering steps of the cascade of events leading to cell death.

Journal Article↗

PubMed2000

Progressive optic axon dystrophy and vacuslar changes in rd mice.

PURPOSE: To examine how the vascular plexuses in the rd mouse retina are affected by the loss of photoreceptors and how this compares with the Royal College of Surgeons (RCS) rat. To examine whether the profound effects of vascular pathology on retinal ganglion cells (RGCs) and their axons seen in RCS rats are also found in rd mice. METHODS: Vascular patterns were studied in flatmounted and sectioned retinas using either nicotinamide adenine dinucleotide phosphate(NADPH)-diaphorase histochemistry or vessel filling with horseradish peroxidase. Optic axons were visualized using RT97 (an antibody against the 200-kDa neurofilament subunit), and RGCs were labeled by retrograde transport of fluorescence label, the Fluorogold, applied to the superior colliculus. RESULTS: The present study showed that in the rd mouse, similar to the RCS rat, vascular complexes developed in association with retinal pigment epithelial cells at the outer border of the retina. The number and distribution of complexes were very different from the rat, but as in the rat, progressive axonal dystrophy was seen in the optic fiber layer. RGC loss, rather than being local was more broadly distributed, but some, at least, appeared to be secondary to axonal dystrophy caused by vessels supplying vascular formation. CONCLUSIONS: Photoreceptor loss in the rd mouse leads to RGC axonal dystrophy and loss. The lesser degree and different distribution of RGC loss caused by abnormal vasculature associated with vascular formations in the outer retina in the rd mouse may be due to the early atrophy of the deep vascular plexus in this animal.

Animals↗

PubMed1999

Effects of intramuscular injection of botulinum toxin and doxorubicin on the survival of abducens motoneurons.

PURPOSE: To investigate in vivo the survival of abducens motoneurons (AMNs) at different periods of time after a single intramuscular injection of the neurotoxin botulinum toxin A (BTxA) or doxorubicin (DXR). METHODS: In Sprague-Dawley rats, the AMNs were labeled with fluorogold (FG), which was applied intramuscularly in the lateral rectus muscle. The numbers of labeled neurons were determined in adult control animals; in young animals that had received intramuscular injections of 0.125, 0.250, 1, or 2 U BTxA; and in adult rats that had received 100 microg, 200 microg, or 300 microg DXR, at various survival times. RESULTS: In control animals, the numbers of FG-labeled motoneurons were similar to the numbers found by other investigators with the use of other retrogradely transported tracers; motoneuron numbers diminished with time after FG application. The numbers of FG-labeled neurons in the animals that had been injected with BTxA were similar to those found in control animals. However, there were fewer FG-labeled neurons in the animals injected with DXR. CONCLUSIONS: Fluorogold injected into the lateral rectus muscle can be used to label the AMNs. However, this tracer does not persist within the cytoplasm of the labeled neurons for more than 37 days. The intramuscular injection of 0.125, 0.250, 1, or 2 U BTxA does not induce significant motoneuron death in young rats 30, 60, or 90 days after the injection. Doxorubicin injected intramuscularly causes variable amounts of motoneuron death that is related both to the survival period and to the amount of DXR injected.

Abducens Nerve↗

PubMed1998

Ganglion cell loss in RCS rat retina: a result of compression of axons by contracting intraretinal vessels linked to the pigment epithelium.

In the dystrophic Royal College of Surgeons (RCS) rat retina, there is a progressive loss of photoreceptors. As a result, the retinal circulation becomes apposed to the retinal pigment epithelium (RPE) and neovascular formations develop. RPE and inner nuclear layer cells migrate along these vessels towards the retinal ganglion cell (RGC) layer. The retinal layers gradually become disrupted, and some of the RGC axon bundles involute into the retina. These bundles are always associated with blood vessels, and there is evidence of axon damage where they juxtapose. In wholemount preparations of dystrophic retinae (> or =6 months of age), abrupt changes are observed in the trajectory of RGC axon bundles, where they are crossed by circumferential vessels. Degenerative profiles can be seen at these locations. Visualisation of RGCs with Fluoro-gold shows wedge-shaped sectors in the dystrophic retina devoid of labelling, initially in the ventral retina but later spreading dorsally. It is hypothesised that the vessels supplying the neovascular formations contract and pull surface vessels into the retina, thus displacing any axon bundles that lie beneath them into the inner plexiform layer. The contractility may be an intrinsic property of the vessels or it may be conferred by the cells migrating along them. Axonal transport becomes blocked at the points of tension, thereby causing retrograde degeneration of the parent RGCs. Because RGC loss is also a feature of human retinitis pigmentosa, the RCS rat may provide a model to test interventions devised to prevent such loss following photoreceptor degeneration. This model also may be useful for testing methods designed to control blood vessel and matrix formation.

Animals↗

PubMed1998

Extent and duration of recovered pupillary light reflex following retinal ganglion cell axon regeneration through peripheral nerve grafts directed to the pretectum in adult rats.

The functional reinnervation of the olivary pretectal nucleus (OPN) was studied in adult rats with peripheral nerve (PN) grafts bridging the interrupted retinopretectal pathway. Functional recovery was assessed quantitatively using established pupillometry techniques. The effect of intravitreal tuftsin fragment 1-3 (tuftsin 1-3) injections during the grafting procedure was also studied. A total of 53 adult rats received autologous PN grafts connecting the ocular stump of the transected optic nerve to the ipsilateral OPN. The contralateral eye was enucleated to remove the input from that eye to the OPN. A pupillary light reflex was elicited from 35 of the 53 PN-grafted animals and in the best cases, a response was obtained which compared closely to that recorded from control animals. Tuftsin 1-3 was found to increase the rate of recovery of the response. The response amplitude of PN-grafted rats was generally found to diminish with repeated stimulus presentation and also appeared to deteriorate with age. This was in contrast to control animals' responses. However, a PLR could still be elicited in 3 of the 6 animals studied 15 months after PN-grafting. These findings indicate that a near-normal PLR function can be restored using a peripheral nerve graft, but there are a number of factors that are likely to compromise optimal outcome.

Age Factors↗

PubMed1996

Light induced EEG desynchronization and behavioral arousal in rats with restored retinocollicular projection by peripheral nerve graft.

Peripheral nerve (PN) was grafted to sectioned optic nerve and was bridged to the superior colliculus in adult rats. To test functional recovery of restored retinocollicular pathway, we examined cortical electroencephalogram (EEG) and behavioral arousal responses to light stimuli. In eight of 10 recording trials in PN grafted rats (n = 6) and in all of eight trials in normal rats (n = 5), cortical EEGs showed desynchronization to light stimuli. On the other hand, after bilateral sections of the optic nerve (n = 3) EEG desynchronization to light disappeared while it was induced by a white noise. Mean threshold duration of light for EEG desynchronization was significantly longer in the PN grafted rats (440 ms) than in normal rats (173 ms). In three of six trials in PN grafted rats (n = 4), and in four of eight trials in normal rats (n = 4), EEG desynchronization elicited by light stimulus was accompanied by behavioral arousal responses, whereas no behavioral arousal could be induced by light in blind rats (n = 3). These results strongly suggest that visual information processed through the restored retinocollicular pathway was further transmitted to the cerebral cortices and ultimately resulted in behavioral arousal of the PN grafted rats.

Animals↗

PubMed1996

Mechanism of retinal ganglion cell loss in inherited retinal dystrophy.

To study the inner retinal layers in RCS rats, which suffer major loss of retinal photoreceptors during the first 3 months of life, retinal ganglion cells (RGC) were labelled with fluorogold and their axons were immunoreacted with an antibody against neurofilaments. The retinal vessels were stained with horeseradish peroxidase and the RGC layer was stained with methylene blue. Animals more than 6 months of age showed areas devoid of fluorogold-labelled cells that extended from the optic disc to the periphery. The course of the RGC axons was also abnormal and showed tortuosities, dilatations and signs of abortive regeneration at sites where most inner retinal vessels cross the axons. We conclude that some months after photoreceptor degeneration has concluded in dystrophic animals, some retinal vessels compress the RGC axons and cause retrograde degeneration of their parent cells.

Animals↗

PubMed1996

Effects of axotomy and intraocular administration of NT-4, NT-3, and brain-derived neurotrophic factor on the survival of adult rat retinal ganglion cells. A quantitative in vivo study.

PURPOSE: To investigate in vivo the survival of retinal ganglion cells (RGC) 4 to 14 days after optic nerve (ON) transection alone or in combination wih a single intraocular injection of neurotrophin-4 (NT-4), neurotrophin-3 (NT-3), or brain-derived neurotrophic factor (BDNF). METHODS: In adult rats, RGCs were labeled with fluorogold (FG) applied to their main targets in the brain. Seven days later, the left ON was intraorbitally transected, and, in several groups of animals, the left eye received a sham injection or was injected with 5 microliters of 1% bovine serum albumin-phosphate-buffered saline alone or containing 5 micrograms of NT-4, NT-3, or BDNF. Four, 5, 7, 9, 12 and 14 days after ON transection, the retinas were examined under fluorescence microscopy to estimate RGC survival. RESULTS: In control retinas, the mean densities (cells/mm2+/-SEM) of FG-labeled RGCs were 2421+/-55 (n=20). Four days after axotomy, the densities of RGCs were similar to those observed in control retinas, but 5 and 7 days after axotomy, the mean densities had decreased to 2028+/-63 (n=6) and 1568+/-50 (n=6) respectively. In the group of retinas with sham injection, with vehicle alone or with NT-3, RGC densities also decreased by 7 days to 1261+/-71 (n=5), 1506+/-98 (n=10), and 1474+/-125 (n=4), respectively. However, similar densities to those observed in control retinas were observed 7 days after ON transection in the groups of retinas treated with NT-4 (2505+/-91; n=7) or BDNF (2380+/-74; n=7). Fourteen days after axotomy, RGC densities decreased to 521+/-39 (n=10). Comparable densities were found in groups that underwent axotomy and either sham injection (533+/-51; n=5), injection of vehicle (588+/-19; n=10), or NT-3 treatment (634+/-62; n=6). However, at this time, higher densities were observed in the groups treated with NT-4 839+/-39 (n=8) or BDNF 1321+/-120 (n=7). CONCLUSIONS: Axotomy-induced RGC death first appears by day 5 and reaches 80% of the original RGC population by day 12. NT-4 and BDNF administered intraocularly at the time of axotomy exert a neuroprotective effect on axotomy-induced RGC death, thus increasing the population of surviving RGCs and delaying the onset of RGC of axotomy-induced RGC death by approximately 3 days. Intraocular administration of NT-3 did not modify the survival of RGCs after injury.

Animals↗

PubMed1996

Retinal ganglion cell death after different transient periods of pressure-induced ischemia and survival intervals. A quantitative in vivo study.

PURPOSE: To quantitate in vivo retinal ganglion cell (RGC) survival after transient periods of pressure-induced ischemia of the rat retina and after different survival intervals. METHODS: In adult rats, RGCs were labeled with fluorogold applied to their main targets in the brain. Seven days later, in several groups of rats, the left retinas were subjected to transient periods of ischemia of 30, 45, 60, 75, 90, 105, or 120 minutes, respectively, by increasing the intraocular pressure (IOP) of the left eye above systolic values. Five, 7, 14, and 30 days later, the rats were killed, and their retinas were prepared as wholemounts for examination under fluorescence microscopy to estimate RGC survival. RESULTS: The authors found that periods of ischemia of 30 and 45 minutes do not induce RGC death; longer periods of transient ischemia induce the death of a proportion of RGCs, and the proportion increases with the duration of the ischemia; RGC death, which can be observed as early as 5 days after ischemia, continues during the 30-day study period; and periods of ischemia that last 90 minutes or more cause the death of approximately 95% of the RGC population 30 days later. CONCLUSIONS: Increases of the IOP above systolic levels for periods of 60 minutes or more result in RGC loss in the rat retina. Both the duration of the initial transient period of ischemia and the duration of the survival period influence the proportion of RGC death.

Animals↗

PubMed1993

Rapid and protracted phases of retinal ganglion cell loss follow axotomy in the optic nerve of adult rats.

To investigate the short- and long-term effects of axotomy on the survival of central nervous system (CNS) neurons in adult rats, retinal ganglion cells (RGCs) were labelled retrogradely with the persistent marker diI and their axons interrupted in the optic nerve (ON) by intracranial crush 8 or 10 mm from the eye or intraorbital cut 0.5 or 3 mm from the eye. Labelled RGCs were counted in flat-mounted retinas at intervals from 2 weeks to 20 months after axotomy. Two major patterns of RGC loss were observed: (1) an initial abrupt loss that was confined to the first 2 weeks after injury and was more severe when the ON was cut close to the eye; (2) a slower, persistent decline in RGC densities with one-half survival times that ranged from approximately 1 month after intraorbital ON cut to 6 months after intracranial ON crush. A small population of RGCs (approximately 5%) survived for as long as 20 months after intraorbital axotomy. The initial loss of axotomized RGCs presumably results from time-limited perturbations related to the position of the ON injury. A persistent lack of terminal connectivity between RGCs and their targets in the brain may contribute to the subsequent, more protracted RGC loss, but the differences between intraorbital cut and intracranial crush suggest that additional mechanisms are involved. It is unclear whether the various injury-related processes set in motion in both the ON and the retina exert random effects on all RGCs or act preferentially on subpopulations of these neurons.

Animals↗

PubMed1991

Degenerative and regenerative responses of injured neurons in the central nervous system of adult mammals.

In adult mammals, the severing of the optic nerve near the eye is followed by a loss of retinal ganglion cells (RGCs) and a failure of axons to regrow into the brain. Experimental manipulations of the non-neuronal environment of injured RGCs enhance neuronal survival and make possible a lengthy axonal regeneration that restores functional connections with the superior colliculus. These effects suggest that injured nerve cells in the mature central nervous system (CNS) are strongly influenced by interactions with components of their immediate environment as well as their targets. Under these conditions, injured CNS neurons can express capacities for growth and differentiation that resemble those of normally developing neurons. An understanding of this regeneration in the context of the cellular and molecular events that influence the interactions of axonal growth cones with their non-neuronal substrates and neuronal targets should help in the further elucidation of the capacities of neuronal systems to recover from injury.

Animals↗

PubMed1991

Regenerated synapses persist in the superior colliculus after the regrowth of retinal ganglion cell axons.

Synapse formation by retinal ganglion cell axons was sought in the superior colliculus of four adult rats 16-18 months after the optic nerve was transected and replaced by a peripheral nerve graft that guided regenerating RGC axons from the eye to the superior colliculus. The terminals of retinal ganglion cell axons were labelled by intravitreal injections of tritiated amino acids and studied by light and electron microscopic autoradiography. We found that (i) retinal ganglion cell axons had extended from the tips of the peripheral nerve grafts into the superior colliculus for approximately 350 microns; (ii) within the superior colliculus, some regenerated retinal ganglion cell axons became ensheathed by CNS myelin; (iii) retinal ganglion cell terminals formed asymmetric synapses with dendrites of neurons in the superficial layers of the superior colliculus, mainly the stratum griseum superficialis. Regenerated (n = 418) and normal retinal ganglion cell terminals (n = 1775) in the superior colliculus were compared in terms of their size (area, perimeter, and maximum diameter), contacts per terminal, contacts per 10 microns terminal perimeter, and post-synaptic structure contacted (dendritic spine, shaft, or soma). No statistically significant differences in the ultrastructural characteristics of the pre-synaptic profiles were apparent between the two groups. The post-synaptic structures contacted by axon terminals were similar in regenerated and control animals, although there were quantitative differences in the distributions of these contacts among dendritic spines and shafts. These results suggest that the regeneration of retinal ganglion cell axons in adult rats can lead to the formation of ultrastructurally normal synapses in the appropriate layers of the superior colliculus. The re-formed connections appear to persist for the life-span of these animals.

Animals↗