Biomedical subjects

J Rodger

Publications and source records attributed to J Rodger.

At least 19 recordsLinked to original sources

PubMed2006

Changing Pax6 expression correlates with axon outgrowth and restoration of topography during optic nerve regeneration.

Pax6, a member of the highly conserved developmental Pax gene family, plays a crucial role in early eye development and continues to be expressed in adult retinal ganglion cells (RGCs). Here we have used Western blots and immunohistochemistry to investigate the expression of Pax6 in the formation and refinement of topographic projections during optic nerve regeneration in zebrafish and lizard. In zebrafish with natural (12-h light/dark cycle) illumination, Pax6 expression in RGCs was decreased during axon outgrowth and increased during the restoration of the retinotectal map. Rearing fish in stroboscopic illumination to prevent retinotopic refinement resulted in a prolonged decrease in Pax6 levels; return to natural light conditions resulted in map refinement and restoration of normal Pax6 levels. In lizard, RGC axons spontaneously regenerate but remain in a persistent state of regrowth and do not restore topography; visual training during regeneration, however, allows a stabilization of connections and return of topography. Pax6 was persistently decreased in untrained animals but remained increased in trained ones. In both species, changes in expression were not due to cell division or cell death. The results suggest that decreased Pax6 expression is permissive for axon regeneration and extensive searching, while higher levels of Pax6 are associated with restoration of topography.

Animals↗

PubMed2005

cAMP regulates axon outgrowth and guidance during optic nerve regeneration in goldfish.

Increased cAMP improves neuronal survival and axon regeneration in mammals. Here, we assess cAMP levels and identify activated pathways in a spontaneously regenerating central nervous system. Following optic nerve crush in goldfish, almost all retinal ganglion cells (RGC) survive and regenerate retinotectal topography. Goldfish received injections of a cAMP analogue (CPT-cAMP), a protein kinase A (PKA) inhibitor (KT5720), both compounds combined, or PBS (control). RGC survival in experimental groups was unaffected at any stage. The rate of axon regeneration was accelerated by the activator and decelerated both by the inhibitor and by combined injections, suggesting a PKA-dependent pathway. In addition, errors in regenerate retinotectal topography were observed when agents were applied in vivo and RGC response to the guidance cue ephrin-A5 in vitro was altered by the inhibitor. Our results highlight that therapeutic manipulation of cAMP levels to enhance axonal regeneration in mammals must ensure that topography, and consequently function, is not disrupted.

Animals↗

PubMed2005

Eph/ephrin expression in the adult rat visual system following localized retinal lesions: localized and transneuronal up-regulation in the retina and superior colliculus.

Following unilateral optic nerve section in adult PVG hooded rat, the axon guidance cue ephrin-A2 is up-regulated in caudal but not rostral superior colliculus (SC) and the EphA5 receptor is down-regulated in axotomised retinal ganglion cells (RGCs). Changes occur bilaterally despite the retino-collicular projection being mostly crossed. Here we investigate the dynamics of Eph/ephrin expression using in situ hybridization and semi-quantitative immunohistochemistry after localized retinal lesions. Unilateral krypton laser lesions to dorso-nasal retina ablated contralaterally projecting RGCs (DN group); ventro-temporal lesions ablated contralaterally and ipsilaterally projecting RGCs (VT group). Lesions of the entire retina served as controls (Total group). Results are compared to normal animals in which tectal ephrin-A2 and retinal EphA5 are expressed, respectively, as shallow ascending rostro-caudal and naso-temporal gradients. In both SCs of DN and Total groups, tectal ephrin-A2 was up-regulated caudally; in the VT group, expression remained normal bilaterally. Unilateral collicular ablation indicated that bilateral changes in ephrin-A2 expression are mediated via intercollicular pathways. EphA5 expression in the VT group was elevated in the intact nasal region of experimental retinae. For each experimental group, EphA5 expression was also elevated in nasal retina of the opposite eye, resulting in uniform expression across the naso-temporal axis. Up-regulation of ephrin-A2 in caudal, but not rostral, SC suggests the enhancement of developmental positional information as a result of injury. Bilateral increases in retinal EphA5 expression demonstrate that signals for up-regulation operate interocularly. The study demonstrates that signals regulating guidance cue expression are both localized and relayed transneuronally.

Animals↗

PubMed2004

EphA/ephrin-A interactions during optic nerve regeneration: restoration of topography and regulation of ephrin-A2 expression.

During visual system development, interactions between Eph tyrosine kinase receptors and their ligands, the ephrins, guide retinal ganglion cell (RGC) axons to their topographic targets in the optic tectum. Here we show that Eph/ephrin interactions are also involved in restoring topography during RGC axon regeneration in goldfish. Following optic nerve crush, EphA/ephrin-A interactions were blocked by intracranial injections of recombinant Eph receptor (EphA3-AP) or phospho-inositol phospholipase-C. Topographic errors with multiple inputs to some tectal loci were detected electrophysiologically and increased projections to caudal tectum demonstrated by RT-97 immunohistochemistry. In EphA3-AP-injected fish, ephrin-A2-expressing cells in the retino-recipient tectal layers were reduced in number compared to controls and their distribution was no longer graded. The findings, supported by in vitro studies, implicate EphA/ephrin-A interactions in restoring precise topography and in regulating ephrin-A2 expression during regeneration.

Animals↗

PubMed2004

Nutritional and environmental effects on reproduction in small ruminants.

Animals live in environments that are both complex and continually changing, so they have to respond to short- and long-term variations in a wide range of factors, such as photoperiod, nutrition and sociosexual signals. Before they were domesticated, animals developed reproductive strategies that coped with these changes and often took advantage of them. The physiological processes that implement these strategies have been modified to some extent during several millennia of controlled breeding, but most persist. Thus, many genotypes still exhibit profound responses to external inputs, such as the induction of ovulation by sociosexual signals and the doubling of litter size by a change in nutrition. The complexity in these responses is now becoming clearer. For example, with sociosexual signals, we now need to consider the stimulatory effects of males on females, of females on males and of females on females. Similarly, the impact of nutrition has been extended beyond the control of puberty and the production of gametes to include phenomena such as 'fetal programming', with its potentially profound effects on the life-long performance of the animals. Fortunately, our capacity to research these phenomena has been greatly enhanced by technical improvements in hormone assays, molecular and cellular biology, and real-time ultrasound. This has brought us a better understanding of several of the environmental influences on reproduction, including: the cellular processes within ovarian follicles that mediate the effect of nutrition on ovulation rate; the neuroendocrine pathways through which nutritional inputs affect the brain centres that control appetite and reproduction; and the intracerebral pathways through which sociosexual signals (olfactory and non-olfactory) stimulate the reproductive axis. Importantly, we are now beginning to realise that, as well as considering interactions between environmental inputs and genotype, we need to take into account interactions between the environmental factors themselves, just as the animals do. We still have a long way to go for a complete understanding, but we are nevertheless in a position where we can begin to use this information to develop new management systems for our animals to improve their productivity.

Animal Feed↗

PubMed2003

PSA-NCAM is up-regulated during optic nerve regeneration in lizard but not in goldfish.

The addition of polysialic acid (PSA) to neural cell adhesion molecule (NCAM) facilitates axon growth. Here we use Western blots and immunohistochemistry to examine expression of PSA-NCAM during optic nerve regeneration. In lizard, retinal ganglion cell axons become transiently PSA-NCAM positive. By contrast, goldfish RGC axons are PSA-NCAM negative both in normal animals and throughout regeneration with the exception of a PSA-NCAM-positive fascicle arising from newly generated RGCs. Transient sialylation of NCAM in lizard may assist regeneration in the nonpermissive reptilian visual pathway and facilitate the reestablishment of a crude topographic map; down-regulation in the long term may contribute to the breakdown in topography. The lack of sialylation in goldfish presumably reflects the permissive nature of the substrate allowing axon regeneration and the successful reestablishment of a topographic map.

Animals↗

PubMed2003

Training on a visual task improves the outcome of optic nerve regeneration.

Optic nerve regeneration in a lizard, Ctenophorus ornatus, is dysfunctional despite survival of most retinal ganglion cells and axon regeneration to the optic tectum. The regenerated retino-tectal projection at 6 months has crude topography but by 1 year is disordered; visually-elicited behavior is absent via the experimental eye. Here, we assess the influence of training on the outcome of optic nerve regeneration. Lizards were trained to catch prey presented within the monocular field of either eye. One optic nerve was then severed and visual stimulation resumed throughout regeneration. In the trained group, presentation was restricted to the eye undergoing optic nerve regeneration; for the untrained group, the unoperated eye was stimulated. Pupil responses returned in trained but not in untrained animals. At 1 year, trained animals oriented to and captured prey; untrained animals demonstrated minimal orienting and failed to capture prey. Regenerated retino-tectal projections were topographic in the trained but not in the untrained group as assessed by in vitro electrophysiological recording and by carbocyanine dye tracing. In vitro electrophysiological recording during application of neurotransmitter antagonists to the tectum revealed that the level of GABAergic inhibition was modest in trained animals but elevated in the untrained group; responses were mainly AMPA-mediated in both groups. We conclude that training improves the behavioral outcome of regeneration, presumably by stabilizing and refining the transient retino-tectal map and preventing a build-up of tectal inhibition. The results suggest that for successful central nerve regeneration to occur in mammals, it may be necessary to introduce training to complement procedures stimulating axon regeneration.

Animals↗

PubMed2001

Reinnervation of the superior colliculus delays down-regulation of ephrin A2 in neonatal rat.

Although the adult mammalian optic nerve does not regenerate following lesion, in the neonatal rat, retinal ganglion cell (RGC) axons retain the capacity to grow across lesion sites in the brain. Following a brachial lesion at postnatal day 2 (P2), some RGC axons, together with ingrowing cortico-tectal axons, cross the lesion to reinnervate the superior colliculus (SC). Here we use immunohistochemistry to examine expression of the guidance cue ephrin A2 following a brachial lesion. Normal animals show a steady decrease in ephrin A2 immunoreactivity between P5 and P31, with a low rostral to high caudal gradient being evident only at P5. By contrast, after brachial lesion, values are significantly elevated rostrally at P5 and caudally at P12; moreover, a steep rostro-caudal gradient is present at both ages. By P31 values fall to normal levels. Following unilateral enucleation at P2, levels are not significantly different from normal. Our results show that innervation but not denervation triggers increased ephrin A2 expression after a brachial lesion.

Animals↗

PubMed2001

The development and mature organisation of the end-artery retinal vasculature in a marsupial, the dunnart Sminthopsis crassicaudata.

The end-artery retinal vasculature of a marsupial, the fat-tailed dunnart, was defined by India ink injection and studied in wholemounts. In the adult, the vitreal vasculature supplying the ganglion-cell layer has major paired-vessels in a horizontal H shape. These vessels skirt the area centralis and visual streak that are supplied by fine end-loops. A second vascular layer of uniformly distributed endloops arises from the superficial vessels and lies at the inner nuclear/outer plexiform border. During development, vessels enter the eye via the optic nerve head to form the upper vasculature, assuming an essentially mature arrangement prior to the formation of the area centralis and visual streak. Vessels then descend to form the lower bed. Unlike the cat, the dunnart has retinal vessels that are patent throughout development, their growth is interstitial and reductive remodelling is not seen. A retinal end-artery system may have evolved in marsupials because their precocity requires a vasculature that is functional from early stages of development.

Animals↗

PubMed2001

Evidence that regenerating optic axons maintain long-term growth in the lizard Ctenophorus ornatus: growth-associated protein-43 and gefiltin expression.

In the lizard, Ctenophorus ornatus, the optic nerve regenerates but animals remain blind via the experimental eye, presumably as a result of axons failing to consolidate a retinotopic map in the optic tectum. Here we have examined immunohistochemically the expression of the growth-associated protein GAP-43 and the low-molecular-weight intermediate filament protein gefiltin, up to one year after optic nerve crush. Both proteins were found to be permanently up-regulated, suggesting that regenerating axons are held in a permanent state of re-growth. We speculate that, in the lizard, the continued expression of GAP-43 and the failure to switch from the expression of low- to high-molecular-weight intermediate filament proteins are associated with the inability to consolidate a retinotopic projection.

Animals↗

PubMed2001

A randomised phase II study of oxaliplatin alone versus oxaliplatin combined with 5-fluorouracil and folinic acid (Mayo Clinic regimen) in previously untreated metastatic colorectal cancer patients.

The aim of this study was to examine the efficacy and safety of both oxaliplatin as a single agent and oxaliplatin in combination with dailyx5 bolus 5-fluorouracil and folinic acid (5-FU/FA, Mayo clinic regimen) in the first-line treatment of metastatic colorectal cancer (CRC) patients. 73 advanced CRC patients were randomised to receive either oxaliplatin 85 mg/m(2) every 2 weeks (35 patients), or the same treatment combined with 5-FU 425 mg/m(2)/day and FA 20 mg/m(2)/dayx5 days every 4 weeks (38 patients). Treatment was continued until disease progression or unacceptable toxicity. All patients had documented inoperable disease and no previous chemotherapy for advanced disease. Based on the investigators' assessment of best response, objective response rate was 9% (95% confidence interval (CI) 2-24%) in the oxaliplatin arm, and 45% (95% CI 27-64%) in the oxaliplatin+5-FU/FA arm. Median progression-free survival (PFS) was 2 months (95% CI 1.7-2.4 months) in the oxaliplatin arm and 3.9 months (95% CI 2.9-5 months) in the oxaliplatin+5-FU/FA arm. Severe neutropenia was seen in 23% of patients in the oxaliplatin+5-FU/FA arm, and none in the oxaliplatin arm. There were two treatment-related deaths, both in the oxaliplatin+5-FU/FA arm. In the oxaliplatin+5-FU/FA arm, severe diarrhoea, vomiting and stomatitis were seen in 34, 14 and 14% of the patients, respectively. In conclusion, oxaliplatin at a dose of 85 mg/m(2) given every 2 weeks was well tolerated and has limited activity in metastatic CRC, while the combination of this treatment with the full-dose Mayo clinic regimen (5-FU bolus 425 mg/m(2)/day+FA 20 mg/m(2)/dayx5 days every 4 weeks), although active, was unfeasible due to a high level of myelosuppression and gastrointestinal toxicity. Alternative lower dosing or other regimens are to be explored to ascertain the value of bolus 5-FU/FA combined with oxaliplatin.

Adult↗

PubMed2001

Expression of ephrin-A2 in the superior colliculus and EphA5 in the retina following optic nerve section in adult rat.

The vertebrate retina projects topographically to visual brain centres. In the developing visual system, gradients of ephrins and Eph receptors play a role in defining topography. At maturity, ephrins but not Ephs are downregulated. Here we show that optic nerve section in adult rat differentially regulates the expression of ephrin-A2 in the superior colliculus (SC) and of EphA5 in the retina. Expression was quantified immunohistochemically; ephrin-A2 levels were also estimated by semiquantitative reverse transcriptase polymerase chain reaction. In the normal SC, ephrin-A2 was expressed at low levels. At 1 month, levels of protein and of mRNA were upregulated across the contralateral SC giving rise to an increasing rostro-caudal gradient. At 6 months, levels had fallen but a gradient remained. In the retina of normal animals, EphA5 was expressed as an increasing naso-temporal gradient. By 1 month, expression was decreased in far temporal retina, resulting in a uniform expression across the naso-temporal axis. We suggest that denervation-induced plastic changes within the SC modify expression of these molecules.

Animals↗

PubMed2001

Pax genes in development and maturation of the vertebrate visual system: implications for optic nerve regeneration.

Pax genes play a pivotal role in development of the vertebrate visual system. Pax6 is the master control gene for eye development: ectopic expression of Pax6 in Xenopus laevis and Drosphila melanogaster leads to the formation of differentiated eyes on the legs or wings. Pax6 is involved in formation of ganglion cells of the retina, as well as cells of the lens, iris and cornea. In addition Pax6 may play a role in axon guidance in the visual system. Pax2 regulates differentiation of the optic disk through which retinal ganglion cell axons exit the eye. Furthermore, Pax2 plays a critical role in development of the optic chiasm and in the guidance of axons along the contralateral or ipsilateral tracts of the optic nerve to visual targets in the brain. During development Pax7 is expressed in neuronal cells of one of the major visual targets in the brain, the optic tectum/superior colliculus. Neurons expressing Pax7 migrate towards the pia and concentrate in the stratum griseum superficiale (SGFS), the target site for retinal axons. Together, expression of Pax2, 6 and 7 may guide axons during formation of functional retinotectal/collicular projections. Highly regulated Pax gene expression is also observed in mature animals. Moreover, evidence suggests that Pax genes are important for regeneration of the visual system. We are currently investigating Pax gene expression in species that display a range of outcomes of optic nerve regeneration. We predict that such information will provide valuable insights for the induction of successful regeneration of the optic nerve and of other regions of the central nervous system in mammals including man.

Animals↗

PubMed2001

Oxoid aura system as a semi-automated, standard antimicrobial susceptibility test method.

The need for a national strategy for antimicrobial resistance surveillance is well recognised. The diversity of susceptibility testing methods in the UK has led to the development of a standard method by the British Society for Antimicrobial Chemotherapy. Here, use of an early manual-measurement Oxoid Aura system is compared with an in-house, non-standard method. The usefulness of such a system in the evaluation of antibiotic susceptibility data collected for Staphylococcus aureus, including methicillin-resistant S. aureus, is also examined. An automated version of this equipment is now available.

Drug Resistance, Microbial↗

PubMed2000

Transient up-regulation of the rostrocaudal gradient of ephrin A2 in the tectum coincides with reestablishment of orderly projections during optic nerve regeneration in goldfish.

During development, a graded expression of ephrin A2 has been implicated in retinotectal map formation. Here we have examined ephrin A2 expression during optic nerve regeneration in the mature goldfish. In the tecta of normal animals, a gradient of ephrin A2 expression is detected in cell bodies within the stratum fibrosum et griseum superficiale with more immunopositive cells caudally than rostrally. The gradient in the mature animal presumably reflects the plasticity associated with continued retinal and tectal neurogenesis. During optic nerve regeneration, expression throughout the tectum is increased by 1 month as a strong rostrocaudal gradient. The gradient declines to normal by 3 months. The up-regulation of ephrin A2 during optic nerve regeneration is likely to be instrumental in reestablishing the retinotectal map.

Animals↗

PubMed1999

Pax7 is expressed in the capsules surrounding adult mouse neuromuscular spindles.

The multigene Pax family of transcription factors plays an important role in the development of the central nervous system as well as in organ morphogenesis. Expression of one of the members of the family, Pax7, has been described in embryonic muscle and in both embryonic and adult brain. We recently detected Pax7 transcripts in RNA isolated from adult mouse skeletal muscle and brain and here use in situ hybridisation to localise the expression within these tissues. Pax7 expression was observed in neural cells of the brain and in cells of neural crest origin in the inner and outer capsules of neuromuscular spindles. The results suggest that Pax7 may be implicated in the formation and maintenance of neuromuscular contacts within the muscle spindle throughout life.

Animals↗

PubMed1998

Induction of long-term potentiation in vivo regulates alternate splicing to alter syntaxin 3 isoform expression in rat dentate gyrus.

The regulation and specificity of the interactions between the proteins involved in neurotransmitter release are obvious targets for the cellular control of synaptic plasticity. Previous research has identified one of these proteins, syntaxin 1B, as a potential target for mediating the propagation of synaptic plasticity through neural networks. The expression of syntaxin 1B is modified in the hippocampus after the induction of long-term potentiation (LTP) and during learning. Here, we describe the identification of two other members of the syntaxin family from rat brain, syntaxins 3A and 3B, and show that they are generated from the same gene by alternate splicing. In situ hybridization and immunohistochemical staining confirm the expression of syntaxins 3A and 3B in the adult rat brain. The transcripts and proteins show a lower abundance but a similar pattern of expression as syntaxins 1A and 1 B. By using quantitative competitive PCR, we show that the mRNAs that encode syntaxins 1B and 3A are increased in dentate granule cells 6 h after the induction of LTP in vivo, whereas syntaxin 3B mRNA is decreased as rapidly as 30 min, and lasts for at least 6 h, after the induction of LTP. These findings identify coordinated changes in the expression of several syntaxin isoforms with different substrate specificities and suggest that regulation of the splicing machinery by LTP induction is one of the diverse strategies used during the long-term modification of the synapse in the vertebrate nervous system.

Alternative Splicing↗

PubMed1997

Synapsin I and syntaxin 1B: key elements in the control of neurotransmitter release are regulated by neuronal activation and long-term potentiation in vivo.

The messenger RNAs encoding proteins of the exocytotic machinery were measured at different times following the induction of long-term potentiation or increasing neuronal activity in the dentate gyrus of the rat in vivo. In situ hybridization revealed that from the many messenger RNAs that encode proteins involved in regulated exocytosis, only those encoding synapsin I and syntaxin 1B were specifically increased. The levels of messenger RNA encoding both synapsin I and syntaxin 1B were increased on the ipsilateral side of the dorsal dentate gyrus 2 and 5 h following the induction of long-term potentiation. Syntaxin 1B was also increased in the ventral dentate gyrus at the same time-points. On the contralateral side of the dentate gyrus there was an increase in both synapsin I and syntaxin 1B at 5 h only. All of these long-term potentiation-induced changes were prevented when the tetanus was delivered in the presence of the N-methyl-D-aspartate receptor antagonist. (D(-)-2-amino-5-phosphonopentanoic acid. Immunocytochemical staining revealed that protein levels for both synapsin I and syntaxin 1B were elevated in the mossy fibre terminal zone of CA3 5 h after the induction of long-term potentiation. In addition to these plasticity-induced changes, a transient increase in the messenger RNA encoding syntaxin 1B was observed at 2 h in conditions of high intensity stimulation of the perforant path to increase the level of cellular activation, but this change was not maintained even when high intensity stimulation was sustained for 5 h. No changes in either of the messenger RNAs were observed under low frequency stimulation and pseudotetanus at either time-points. These results show that an overall increase in neuronal excitation within a neuronal network can be differentiated from a change in synaptic strength at a specific subset of the synapses, where only synaptic plasticity leads to long-term changes in the expression of selective members of the exocytotic machinery. Altered concentrations of key vesicle proteins may thus provide the means for modulation of neurotransmitter release over long time-periods. The persistent long-term potentiation-induced postsynaptic increase in messenger RNAs encoding these presynaptic proteins has important implications for the propagation of signals downstream from the site of long-term potentiation induction in hippocampal neural networks, and highlights a candidate molecular mechanism for mediating the propagation of synaptic plasticity in such networks.

Animals↗