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Fiorani L, Maccarone R, Fernando N, Colecchi L, Bisti S, Valter K. Slow-release drug delivery through Elvax 40W to the rat retina: implications for the treatment of chronic conditions. J Vis Exp 2014:51563. [PMID: 25286223 DOI: 10.3791/51563] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Diseases of the retina are difficult to treat as the retina lies deep within the eye. Invasive methods of drug delivery are often needed to treat these diseases. Chronic retinal diseases such as retinal oedema or neovascularization usually require multiple intraocular injections to effectively treat the condition. However, the risks associated with these injections increase with repeated delivery of the drug. Therefore, alternative delivery methods need to be established in order to minimize the risks of reinjection. Several other investigations have developed methods to deliver drugs over extended time, through materials capable of releasing chemicals slowly into the eye. In this investigation, we outline the use of Elvax 40W, a copolymer resin, to act as a vehicle for drug delivery to the adult rat retina. The resin is made and loaded with the drug. The drug-resin complex is then implanted into the vitreous cavity, where it will slowly release the drug over time. This method was tested using 2-amino-4-phosphonobutyrate (APB), a glutamate analogue that blocks the light response of the retina. It was demonstrated that the APB was slowly released from the resin, and was able to block the retinal response by 7 days after implantation. This indicates that slow-release drug delivery using this copolymer resin is effective for treating the retina, and could be used therapeutically with further testing.
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Affiliation(s)
- Lavinia Fiorani
- Biotechnology and Applied Clinical Sciences Department, University of L'Aquila
| | - Rita Maccarone
- Biotechnology and Applied Clinical Sciences Department, University of L'Aquila
| | - Nilisha Fernando
- ARC Centre of Excellence in Vision Science; John Curtin School of Medical Research, Australian National University
| | - Linda Colecchi
- Biotechnology and Applied Clinical Sciences Department, University of L'Aquila
| | - Silvia Bisti
- Biotechnology and Applied Clinical Sciences Department, University of L'Aquila; ARC Centre of Excellence in Vision Science
| | - Krisztina Valter
- ARC Centre of Excellence in Vision Science; John Curtin School of Medical Research, Australian National University; ANU Medical School, Australian National University;
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Prusky GT, Silver BD, Tschetter WW, Alam NM, Douglas RM. Experience-dependent plasticity from eye opening enables lasting, visual cortex-dependent enhancement of motion vision. J Neurosci 2008; 28:9817-27. [PMID: 18815266 PMCID: PMC6671217 DOI: 10.1523/jneurosci.1940-08.2008] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2007] [Revised: 07/13/2008] [Accepted: 08/21/2008] [Indexed: 12/12/2022] Open
Abstract
Developmentally regulated plasticity of vision has generally been associated with "sensitive" or "critical" periods in juvenile life, wherein visual deprivation leads to loss of visual function. Here we report an enabling form of visual plasticity that commences in infant rats from eye opening, in which daily threshold testing of optokinetic tracking, amid otherwise normal visual experience, stimulates enduring, visual cortex-dependent enhancement (>60%) of the spatial frequency threshold for tracking. The perceptual ability to use spatial frequency in discriminating between moving visual stimuli is also improved by the testing experience. The capacity for inducing enhancement is transitory and effectively limited to infancy; however, enhanced responses are not consolidated and maintained unless in-kind testing experience continues uninterrupted into juvenile life. The data show that selective visual experience from infancy can alone enable visual function. They also indicate that plasticity associated with visual deprivation may not be the only cause of developmental visual dysfunction, because we found that experientially inducing enhancement in late infancy, without subsequent reinforcement of the experience in early juvenile life, can lead to enduring loss of function.
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Affiliation(s)
- Glen T. Prusky
- Department of Physiology and Biophysics, Weill Cornell Medical College, Burke Medical Research Institute, White Plains, New York 10605
- Department of Neuroscience, University of Lethbridge, Lethbridge, Alberta, Canada T1K 3M4, and
| | - Byron D. Silver
- Department of Neuroscience, University of Lethbridge, Lethbridge, Alberta, Canada T1K 3M4, and
| | - Wayne W. Tschetter
- Department of Physiology and Biophysics, Weill Cornell Medical College, Burke Medical Research Institute, White Plains, New York 10605
- Department of Neuroscience, University of Lethbridge, Lethbridge, Alberta, Canada T1K 3M4, and
| | - Nazia M. Alam
- Department of Physiology and Biophysics, Weill Cornell Medical College, Burke Medical Research Institute, White Plains, New York 10605
- Department of Neuroscience, University of Lethbridge, Lethbridge, Alberta, Canada T1K 3M4, and
| | - Robert M. Douglas
- Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, British Columbia, Canada V5Z 3N9
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Abstract
Plasticity of vision mediated through binocular interactions has been reported in mammals only during a "critical" period in juvenile life, wherein monocular deprivation (MD) causes an enduring loss of visual acuity (amblyopia) selectively through the deprived eye. Here, we report a different form of interocular plasticity of vision in adult mice in which MD leads to an enhancement of the optokinetic response (OKR) selectively through the nondeprived eye. Over 5 d of MD, the spatial frequency sensitivity of the OKR increased gradually, reaching a plateau of approximately 36% above pre-deprivation baseline. Eye opening initiated a gradual decline, but sensitivity was maintained above pre-deprivation baseline for 5-6 d. Enhanced function was restricted to the monocular visual field, notwithstanding the dependence of the plasticity on binocular interactions. Activity in visual cortex ipsilateral to the deprived eye was necessary for the characteristic induction of the enhancement, and activity in visual cortex contralateral to the deprived eye was necessary for its maintenance after MD. The plasticity also displayed distinct learning-like properties: Active testing experience was required to attain maximal enhancement and for enhancement to persist after MD, and the duration of enhanced sensitivity after MD was extended by increasing the length of MD, and by repeating MD. These data show that the adult mouse visual system maintains a form of experience-dependent plasticity in which the visual cortex can modulate the normal function of subcortical visual pathways.
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Affiliation(s)
- Glen T Prusky
- Department of Neuroscience, University of Lethbridge, Lethbridge, Alberta, Canada.
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Hooks BM, Chen C. Distinct Roles for Spontaneous and Visual Activity in Remodeling of the Retinogeniculate Synapse. Neuron 2006; 52:281-91. [PMID: 17046691 DOI: 10.1016/j.neuron.2006.07.007] [Citation(s) in RCA: 228] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2005] [Revised: 05/13/2006] [Accepted: 07/11/2006] [Indexed: 11/21/2022]
Abstract
Sensory experience and spontaneous activity play important roles in development of sensory circuits; however, their relative contributions are unclear. Here, we test the role of different forms of activity on remodeling of the mouse retinogeniculate synapse. We found that the bulk of maturation occurs without patterned sensory activity over 4 days spanning eye opening. During this early developmental period, blockade of spontaneous retinal activity by tetrodotoxin, but not visual deprivation, retarded synaptic strengthening and inhibited pruning of excess retinal afferents. Later in development, synaptic remodeling becomes sensitive to changes in visually evoked activity, but only if there has been previous visual experience. Synaptic strengthening and pruning were disrupted by visual deprivation following 1 week of vision, but not by chronic deprivation from birth. Thus, spontaneous activity is necessary to drive the bulk of synaptic refinement around the time of eye opening, while sensory experience is important for the subsequent maintenance of connections.
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Affiliation(s)
- Bryan M Hooks
- Department of Neurology, Neurobiology Program, Children's Hospital, Boston, Harvard Medical School, 300 Longwood Avenue, Boston, Massachusetts 02115, USA
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Townsend M, Liu Y, Constantine-Paton M. Retina-driven dephosphorylation of the NR2A subunit correlates with faster NMDA receptor kinetics at developing retinocollicular synapses. J Neurosci 2004; 24:11098-107. [PMID: 15590926 PMCID: PMC6730286 DOI: 10.1523/jneurosci.1207-04.2004] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2004] [Revised: 10/25/2004] [Accepted: 10/30/2004] [Indexed: 11/21/2022] Open
Abstract
We describe a homeostatic mechanism that limits NMDA receptor currents in response to early light activation of a developing visual pathway. During the second postnatal week of rodent retinocollicular development, the Ca2+-activated phosphatase calcineurin (CaN) mediates a rapid, activity-induced shortening in the decay time of NMDA receptor (NMDAR) currents. We show that protein kinase A acts in opposition to CaN to maintain NMDAR currents with long decay times. The CaN-mediated change is coincident with the initial expression of the NMDAR subunit NR2A. Using NR2A knock-out mice and dialyzing neurons with a constitutively active CaN, we demonstrate that NR2A subunits are necessary for the effect of CaN on NMDAR current kinetics. In wild-type mice, Ser900 of NR2A, previously implicated in CaN-mediated glycine-independent desensitization, becomes chronically dephosphorylated by postnatal day 11 as NMDAR current decay times become faster. Pharmacologically disrupting early photoreceptor-driven activity in the retina eliminates the dephosphorylation of NR2A and prevents the shortening in NMDAR current decay time. These data suggest that the developmental onset of retinal activity increases CaN-mediated dephosphorylation of NR2A subunits newly incorporated into synaptic NMDARs of the superior colliculus, thereby providing a mechanism for the early and rapid reduction of NMDAR current decay time in visual neurons.
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Affiliation(s)
- Matthew Townsend
- Interdepartmental Neuroscience Program, Yale University, New Haven, Connecticut 06520, USA
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Smith AL, Parsons CH, Lanyon RG, Bizley JK, Akerman CJ, Baker GE, Dempster AC, Thompson ID, King AJ. An investigation of the role of auditory cortex in sound localization using muscimol-releasing Elvax. Eur J Neurosci 2004; 19:3059-72. [PMID: 15182314 DOI: 10.1111/j.0953-816x.2004.03379.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Lesion studies suggest that primary auditory cortex (A1) is required for accurate sound localization by carnivores and primates. In order to elucidate further its role in spatial hearing, we examined the behavioural consequences of reversibly inactivating ferret A1 over long periods, using Elvax implants releasing the GABA(A) receptor agonist muscimol. Sub-dural polymer placements were shown to deliver relatively constant levels of muscimol to underlying cortex for >5 months. The measured diffusion of muscimol beneath and around the implant was limited to 1 mm. Cortical silencing was assessed electrophysiologically in both auditory and visual cortices. This exhibited rapid onset and was reversed within a few hours of implant removal. Inactivation of cortical neurons extended to all layers for implants lasting up to 6 weeks and throughout at least layers I-IV for longer placements, whereas thalamic activity in layer IV appeared to be unaffected. Blockade of cortical neurons in the deeper layers was restricted to < or = 500 microm from the edge of the implant, but was usually more widespread in the superficial layers. In contrast, drug-free Elvax implants had little discernible effect on the responses of the underlying cortical neurons. Bilateral implants of muscimol-Elvax over A1 produced significant deficits in the localization of brief sounds in horizontal space and particularly a reduced ability to discriminate between anterior and posterior sound sources. The performance of these ferrets gradually improved over the period in which the Elvax was in place and attained that of control animals following its removal. Although similar in nature, these deficits were less pronounced than those caused by cortical lesions and suggest a specific role for A1 in resolving the spatial ambiguities inherent in auditory localization cues.
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Affiliation(s)
- Adam L Smith
- Nature Reviews Drug Discovery, 4 Crinan Street, London N1 9XW, UK
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Colonnese MT, Shi J, Constantine-Paton M. Chronic NMDA receptor blockade from birth delays the maturation of NMDA currents, but does not affect AMPA/kainate currents. J Neurophysiol 2003; 89:57-68. [PMID: 12522159 DOI: 10.1152/jn.00049.2002] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The activity of the N-methyl-D-aspartate receptor (NR) regulates the composition of excitatory synapses and mediates multiple forms of synaptic and structural plasticity. In the superficial superior colliculus (sSC) of the rat, NR activity is essential for the full refinement of retinotopy during development. We have examined the NR's role in synaptic development by chronically treating the sSC from birth with the competitive antagonist (+/-)-2-amino-5-phosphonopentanoic acid (AP5) released by the slow-release polymer Elvax. Whole-cell voltage-clamp recordings were used to characterize excitatory postsynaptic potentials (EPSCs) in slices from postnatal day (P)12-20 sSC. Chronic NR blockade reduced the ratio of AMPA/kainate receptor (AMPAR) to NR peak current amplitudes of both spontaneous (s)EPSCs and evoked EPSCs. Spontaneous NR current amplitude was increased following treatment, while spontaneous AMPAR currents were identical to those of controls, indicating that the ratio change was due to an increased NR current. Comparison of sEPSC frequency, AMPAR current rectification, and quantitative Western blots indicated that the characteristics of AMPARs at the synapse are normal following AP5 treatment. In the sSC, NR currents show a rapid decrease in decay time on P11 and previous studies in slices indicate this change results from a NR-mediated activation of the phosphatase calcineurin. Consistent with this in vitro finding, the down-regulation failed to occur in sSC chronically treated with AP5 in vivo. Together the present data show that NR function is necessary for subsequent NR current regulation in vivo, but it is not essential for the developmental expression of normal AMPAR currents.
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Affiliation(s)
- Matthew T Colonnese
- Department of Biology, Department of Brain and Cognitive Science, and McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge 02139, USA
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Extended plasticity of visual cortex in dark-reared animals may result from prolonged expression of cpg15-like genes. J Neurosci 2002. [PMID: 11880509 DOI: 10.1523/jneurosci.22-05-01807.2002] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
cpg15 is an activity-regulated gene that encodes a membrane-bound ligand that coordinately regulates growth of apposing dendritic and axonal arbors and the maturation of their synapses. These properties make it an attractive candidate for participating in plasticity of the mammalian visual system. Here we compare cpg15 expression during normal development of the rat visual system with that seen in response to dark rearing, monocular blockade of retinal action potentials, or monocular deprivation. Our results show that the onset of cpg15 expression in the visual cortex is coincident with eye opening, and it increases until the peak of the critical period at postnatal day 28 (P28). This early expression is independent of both retinal activity and visual experience. After P28, a component of cpg15 expression in the visual cortex, lateral geniculate nucleus (LGN), and superior colliculus (SC) develops a progressively stronger dependence on retinally driven action potentials. Dark rearing does not affect cpg15 mRNA expression in the LGN and SC at any age, but it does significantly affect its expression in the visual cortex from the peak of the critical period and into adulthood. In dark-reared rats, the peak level of cpg15 expression in the visual cortex at P28 is lower than in controls. Rather than showing the normal decline with maturation, these levels are maintained in dark-reared animals. We suggest that the prolonged plasticity in the visual cortex that is seen in dark-reared animals may result from failure to downregulate genes such as cpg15 that could promote structural remodeling and synaptic maturation.
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Chronic NMDA receptor blockade from birth increases the sprouting capacity of ipsilateral retinocollicular axons without disrupting their early segregation. J Neurosci 2001. [PMID: 11222646 DOI: 10.1523/jneurosci.21-05-01557.2001] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We have investigated the role of the NMDA glutamate receptor (NMDAR) in the genesis and regulation of structural plasticity during synaptogenesis in the visual layers of the rat superior colliculus (sSC). In this neuropil, three projections compete for synaptic space during development. By fluorescently labeling the projections of both eyes and imaging them with confocal microscopy, we can quantify the sprouting of the ipsilateral retinal projection that follows removal of a portion of the contralateral retinal and/or corticocollicular projection. Using these techniques we have studied the effects of NMDAR blockade under different levels of competition. NMDARs were chronically blocked from birth [postnatal day 0 (P0)] by suspending the competitive antagonist 2-amino-5-phosphonopentanoic acid in the slow release plastic Elvax, a slab of which was implanted over the sSC. Such treatment alone does not impair the normal segregation of the retinal projections. However, if sprouting of the ipsilateral projection is initiated with a small contralateral retinal lesion at P6, this sprouting can be further increased by blocking NMDARs from birth. Sprouting of the ipsilateral retinal projection is also induced by retinal lesions made at P10/P11, but NMDAR blockade does not augment the sprouting induced by this later lesion. However, when combined with simultaneous ablation of the ipsilateral visual cortex, P10/P11 lesions show increased sprouting after NMDAR blockade. These data indicate that P0 NMDAR blockade does not eliminate synaptic competition in the sSC. Instead, early elimination of NMDAR function appears to facilitate sprouting that is gated in a stepwise manner by the other visual afferents.
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