PubMed Health⌕ Search

Biomedical subjects

M Vidal-Sanz

Publications and source records attributed to M Vidal-Sanz.

35 records · Page 2Linked to original sources
PubMed1991

Neuronal and nonneuronal influences on retinal ganglion cell survival, axonal regrowth, and connectivity after axotomy.

In contrast to the abortive regrowth that occurs when axons are interrupted in the adult mammalian CNS, exposure of injured CNS axons to the nonneuronal milieu of a peripheral nerve can lead to extensive axonal elongation. With the application of this experimental approach to the retinocollicular pathway in adult rodents, it has been possible to investigate the influences of neuron-glia and other interactions on the capacity of axotomized CNS neurons to survive injury, to elongate the distances necessary to reach specific targets, and to form connections in the CNS in adult rodents. The results of these investigations indicate that the changed glial environment provided by peripheral nerve grafts permits the guided regeneration of RGC axons to their CNS targets. Back in the CNS glial environment, regenerated axons penetrate their targets for short distances and re-form normal appearing synapses that can excite or inhibit postsynaptic neurons. Further studies will require a better understanding of intrinsic neuronal properties and of the interactions of these neurons with other neurons and with the cellular and noncellular components of the extraneural milieu.

Animals↗
PubMed1990

Synaptic connections made by axons regenerating in the central nervous system of adult mammals.

The restoration of connections in the injured central nervous system (CNS) of adult mammals is hindered by the failure of axons to grow back to their natural fields of innervation. Following transection of the optic nerve of adult rodents, the guided regeneration of retinal ganglion cell (RGC) axons along a transplanted segment of peripheral nerve (PN) has shown that these neurones retain their capacities to form well-differentiated synapses in both normal and abnormal targets. The main aim of this review is to describe the anatomical and functional characteristics of some of these connections and to suggest that their terminal distribution and morphology may be the result of a persistence in these targets of molecular determinants that influence normal connectivity in the intact animal.

Afferent Pathways↗
PubMed1990

Selective impairment of slow axonal transport after optic nerve injury in adult rats.

To investigate cellular responses of injured mammalian CNS neurons, we examined the slow transport of cytoskeletal proteins in rat retinal ganglion cell (RGC) axons within the ocular stump of optic nerves that were crushed intracranially. RGC proteins were labeled by an intravitreal injection of 35S-methionine, and optic nerves were examined by SDS PAGE at different times after injury. In one group of rats, the RGC proteins were labeled 1 week after crushing. From 14 to 67 d after axotomy, the labeling of tubulin and neurofilaments was reduced in relation to other labeled proteins and to the labeling of tubulin and neurofilaments in the intact optic nerve of controls. To determine whether this reduction in labeling was due to an alteration in axonal transport after axotomy, we prelabeled RGC proteins 1 week before crushing. In such experiments, the rate of slow axonal transport of tubulin and neurofilaments decreased approximately 10-fold from 6 to 60 d after injury. Our results cannot be due only to the retrograde degeneration of RGCs and injured axons caused by axotomy in the optic nerve, because fast axonal protein transport and the fluorescent labeling of many axons were preserved in the ocular stumps of these optic nerves. This selective failure of the slow axonal transport of tubulin and neurofilaments may affect the renewal of the cytoskeleton and contribute to the gradual degeneration of RGCs that is observed after axotomy. The alterations in slow transport we document here differ from the enhanced rates we previously reported when injured RGC axons regenerated along peripheral nerve segments grafted to the ocular stump of transected optic nerves (McKerracher et al., 1990).

Animals↗
PubMed1990

Slow transport rates of cytoskeletal proteins change during regeneration of axotomized retinal neurons in adult rats.

To investigate cytoskeletal changes associated with axonal regrowth from damaged nerve cells in the mammalian CNS, we examined the slow transport of axonal proteins during the regeneration of adult rat retinal ganglion cell (RGC) axons. Although normally such RGC axons do not regrow after injury in the CNS, they can extend several centimeters when their nonneuronal environment is changed by replacing the optic nerve (ON) with a grafted segment of peripheral nerve (PN). Proteins transported in axons of RGCs from intact control and PN-grafted animals were labeled by an intraocular injection of 35S-methionine and examined 4-60 days later by SDS PAGE. During RGC regeneration into PN grafts, the transport rate of tubulin and neurofilament increased twofold, whereas that of actin decreased to nearly one third of its normal rate. Thus, in these regenerating RGC axons, all three major cytoskeletal proteins were largely transported within a single rate component rather than in the two separate components (SCa and SCb) normally observed in the intact ON. Furthermore, the 200 kDa neurofilament protein (NF-H) was persistently detected in Western blots during periods of active regeneration, a finding that contrasts with the late appearance of the NF-H during the developmental growth of retinal axons. The changes in slow transport observed during RGC regeneration in adult rats may reflect growth-associated responses of mature CNS neurons during periods of active axonal extension.

Actins↗
PubMed1990

Regrowth and connectivity of injured central nervous system axons in adult rodents.

The capacity of injured nerve cells to regrow and form terminal connections in the CNS of adult mammals was investigated in axotomized retinal ganglion cells (RGCs) of rodents whose optic nerves were substituted by an autologous segment of peripheral nerve. While many RGCs died after axotomy approximately 20% of the surviving RGCs regenerated axons several cm in length. Some of the regenerated RGC axons entered the superior colliculus where they arborized and formed well differentiated synapses that transynaptically excited or inhibited tectal neurons.

Animals↗
PubMed1989

Electrophysiologic responses in hamster superior colliculus evoked by regenerating retinal axons.

Autologous peripheral nerve grafts were used to permit and direct the regrowth of retinal ganglion cell axons from the eye to the ipsilateral superior colliculus of adult hamsters in which the optic nerves had been transected within the orbit. Extracellular recordings in the superior colliculus 15 to 18 weeks after graft insertion revealed excitatory and inhibitory postsynaptic responses to visual stimulation. The finding of light-induced responses in neurons in the superficial layers of the superior colliculus close to the graft indicates that axons regenerating from axotomized retinal ganglion cells can establish electrophysiologically functional synapses with neurons in the superior colliculus of these adult mammals.

Action Potentials↗
PubMed1988

Persistent retrograde labeling of adult rat retinal ganglion cells with the carbocyanine dye diI.

To study the retrograde labeling of intact and axotomized retinal ganglion cells (RGCs) over long periods of time, we applied the carbocyanine dye diI to the superior colliculi (SC) and dorsal lateral geniculate nuclei (dLGN) in adult albino rats and examined the retinas by fluorescence microscopy after different periods of survival. Retrogradely labeled RGCs, which were observed in the retinas as early as 3 days after application of the dye, gradually increased in density so that by 7 days more than 80% of the RGCs were labeled and by 30 days diI-labeled cell densities were similar to those observed after short applications of other tracers. Using short-term retrograde labeling with fast blue (FB) as an independent marker of RGCs, it was determined that these neurons remained labeled with diI for periods of up to 9 months without apparent leakage of the tracer to other retinal cells. In addition, diI labeling persisted in the somata of more than 80% of axotomized RGCs whose contact with the source of label had been interrupted for 3 months. Thus, we propose that retrogradely transported diI is a useful label for quantitative studies of neuronal populations, even after axotomy.

Amidines↗
PubMed1988

Influences of peripheral nerve grafts on the survival and regrowth of axotomized retinal ganglion cells in adult rats.

To investigate the role of extrinsic influences on the survival and growth of axotomized retinal ganglion cells (RGCs) in the mature mammalian CNS, both optic nerves (ONs) of adult rats were transected intraorbitally and, on one side, replaced by an autologous segment of peripheral nerve (PN) that had been left unconnected distally. The survival of RGCs and the regrowth of their cut axons into the PN grafts were assessed using morphometric techniques, neuroanatomic tracers, and immunologic cell markers to identify and count RGCs at times ranging from 15 d to 9 months. It was observed that (1) in the absence of a PN graft, more than 90% of the RGCs died by 1 month after axotomy; (2) between 1 and 3 months after axotomy, survival of RGCs in the PN-grafted retinas was enhanced 2-4-fold; (3) nearly 20% of the surviving RGCs regrew lengthy axons into the grafts; and (4) although the density of surviving RGCs in PN-grafted retinas decreased significantly between 1 and 3 months after axotomy, the densities of RGCs with axons extending into the graft remained relatively stable. These results confirm that in the adult rat retina, neuronal death is a major effect of axotomy near the cell soma. Although such lesions lead to the degeneration of many RGCs, we show that extrinsic influences introduced by the apposition of a PN segment at the time of severing the ON can rescue a substantial number of these neurons. Because the enhanced survival of many axotomized RGCs in the PN-grafted retinas appears to be limited to the first few weeks after injury, while those of RGCs that regenerate axons into the grafts do not show a parallel decline, it is possible that, in these experiments, neuronal viability depends on a spectrum of differently timed influences that may include the early diffusion of critical molecules arising from the graft and the subsequent establishment of more complex interactions with graft components.

Animals↗
PubMed1987

The use of rhodamine-B-isothiocyanate (RITC) as an anterograde and retrograde tracer in the adult rat visual system.

We have used the fluorescent dye Rhodamine-B-Isothiocyanate (RITC) as an anterograde and retrograde marker of retinal neurons in the adult rat. Introduced into the vitreous body, RITC is taken up by retinal ganglion cells and transported anterogradely along their axons. It labels the axons and their terminal arborizations. The dye stains axonal projections for at least 30 days without detectable extracellular leakage or transneuronal passage. Furthermore, the soma and dendrites of retinal ganglion cells can also be labeled retrogradely for at least 30 days when RITC is instilled into the superior colliculus. We conclude that RITC, used previously in studies of chick embryo visual pathways, is also suitable for similar neuroanatomical investigations in the adult rat.

Animals↗
PubMed1987

The use of peripheral nerve grafts to enhance neuronal survival, promote growth and permit terminal reconnections in the central nervous system of adult rats.

During both development and regeneration, the survival of neurones and the growth of axons are controlled by inherent neuronal properties, conditions in the axonal environment, and the establishment of appropriately timed and specific functional contacts. To study the effects of extrinsic influences on the survival, growth and connectivity of axotomized neurones in the mature mammalian CNS, we replaced the optic nerve in adult rats with segments of autologous peripheral nerve (PN) and used morphometric techniques, neuroanatomical tracer substances and immunological cell markers to examine retinal ganglion cells (RGCs), their axons in the PN grafts and their terminals in the superior colliculi (SC) of these animals. We observed that: (1) the survival of axotomized RGCs was enhanced by the PN grafts; (2) in the PN-grafted eyes, approximately 20% of the surviving RGCs regrew their axons into the grafts and (3) some of the RGC axons that regenerated along the PN grafts bridging the eye and the tectum re-entered the SC, arborized and made synaptic contacts with tectal neurones. It is not known if the terminal connections established between RGCs and cells in the SC are appropriate, functional or capable of influencing the long-term survival of their cells of origin.

Animals↗
PubMed1987

Axonal regeneration and synapse formation in the superior colliculus by retinal ganglion cells in the adult rat.

In adult rats, one optic nerve was transected and replaced by a 4 cm segment of autologous peripheral nerve (PN) that linked one eye and the superior colliculus (SC) along a predominantly extracranial course. Retrograde and orthograde studies with the tracers HRP or rhodamine-B-isothiocyanate (RITC), as well as immunocytochemical neuronal labels, indicated the following: (1) Regenerating axons from the axotomized retinal ganglion cells extended along the entire PN grafts, covering a distance nearly twice that of the normal retinotectal projection of intact rats. (2) Some of these axons penetrated the SC and formed terminal arborizations up to 500 microns from the end of the graft. (3) By electron microscopy, the arborizations of these regenerated axons in the SC were seen as small HRP-labeled axonal profiles that contacted neuronal processes in the SC; some of these contacts showed pre- and postsynaptic membrane specializations. These findings indicate that injured retinal ganglion cells in the adult rat are not only able to regrow lengthy axons, but may also form synapses in the SC.

Animals↗
PubMed1985

Responses to light of retinal neurons regenerating axons into peripheral nerve grafts in the rat.

We have recorded unitary activity from axons regenerated into peripheral nerve grafts inserted into the retina of adult rats. Some retinal ganglion cells regenerating axons into these grafts had responses to light similar to those of intact retinal ganglion cells. The number of units that responded to light in these blind-ended grafts declined between 9 and 48 weeks after graft insertion. Axotomized retinal ganglion cells regenerating axons into peripheral nerve grafts thus appear, at least temporarily, to maintain or resume normal function.

Animals↗
PubMed1985

Functional activity of rat brainstem neurons regenerating axons along peripheral nerve grafts.

To investigate activation and discharge patterns of central nervous system neurons that regenerate lengthy axons along peripheral nerve grafts we inserted a 4 cm long autologous segment of sciatic nerve into the dorsolateral medulla oblongata of adult rats. Two to 6 months after grafting, the distribution of the cells of origin of the regenerating axons in many nuclei of the brainstem was documented by retrograde horseradish peroxidase labelling from the cut end of the grafts. Functional properties of neurons regenerating axons into the grafts were studied by recording from single regenerated fibers teased from the grafts. Conduction velocities of graft fibers ranged from less than 1 m/s to 25 m/s (30 degrees C). Spontaneous centrifugal impulse traffic in the grafts included units firing in bursts synchronously with the respiratory cycle. Activity in other units was either elicited or inhibited by natural or electrical stimulation of the periphery. Most units recorded in the grafts were neither spontaneously active nor responsive to stimulation of primary afferents. We conclude that: there are central nervous system neurons projecting into the grafts that respond to both excitatory and inhibitory transsynaptic influences; at least some of the spontaneous and induced activity recorded from axons in the grafts resembles that known for normal nerve cells in the regions of the brainstem from which axonal growth arises; and it is possible that many central neurons regenerating axons into peripheral nerve grafts have significantly reduced or altered synaptic inputs.

Animals↗
PubMed1985

Axonal regeneration from GABAergic neurons in the adult rat thalamus.

Peripheral nerve grafts were inserted into the thalamus in 27 Sprague-Dawley rats. From 6 weeks to 15 months later, horseradish peroxidase (HRP) was applied to the extracranial end of each graft and sections of the brains reacted for peroxidase histochemistry. Of the thalamic neurons that were retrogradely labelled with HRP, more than 80% were located in the reticular nucleus of the thalamus (RNT), a distinct group of nerve cells that contain glutamic acid decarboxylase (GAD)-like immunoreactivity and are presumably GABAergic. By combining immunocytochemistry with HRP histochemistry, it was possible to confirm that the RNT neurons that had grown axons into the peripheral nerves grafts retained their GAD-like immunoreactivity. The apparent selectivity in their regenerative responses of RNT neurons to peripheral nerve grafts may relate to special properties of the neurons that did and did not grow into the grafts.

Animals↗
PubMedDate not supplied

Brimonidine's neuroprotective effects against transient ischaemia-induced retinal ganglion cell death.

PURPOSE: Brimonidine is a lowering pressure agent currently used in glaucoma. This chronic degenerative condition is characterised by neuronal death, and an agent which offers neuroprotection may slow down or impede the progression of neuronal cell death. METHODS: The effects of brimonidine (BMD) on the short- and long-term survival of retinal ganglion cells (RGCs) after transient retinal ischaemia are reported here using a rat model. The fluorescent tracer Fluorogold (FG) was applied to both superior colliculi to retrogradely label RGCs. A ninety-minute period of ischaemia was induced and densities of surviving RGCs were estimated over time by counting FG-labelled RGCs in 12 standard regions of each retina. RESULTS: Seven days after inducing transient ischaemia, there was loss of approximately half of the RGC population. Topical pre-treatment with 0.1% or 0.5% BMD prevented ischaemia-induced RGC death. CONCLUSIONS: These results indicate that optimal neuroprotective effects against the early loss of RGCs are seen with 0.1% or 0.5% BMD. Ischaemia-induced RGC loss continued between day 7 and day 21 in the vehicle treated groups and amounted to approximately 25% of the RGC population. Topical pre-treatment with 0.1% or 0.5% BMD was also effective in reducing the slow loss of RGCs.

Administration, Topical↗