AB016.Cholinergic enhancement reduces the temporary shift in perceptual eye dominance induced by a few hours of monocular occlusion

Background:A few hours of monocular deprivation with a diffuser eye patch temporarily strengthens the contribution of the deprived eye to binocular vision.This shift in favour of the deprived eye is characterized as a form of adult visual plasticity.Studies in animal and human models suggest that neuromodulators can enhance adult brain plasticity in general.Specifically,acetylcholine has been shown to improve certain aspects of visual function and plasticity in adulthood.We investigated whether a single administration of donepezil(a cholinesterase inhibitor)could further augment the temporary shift in perceptual eye dominance that occurs after two hours of monocular patching.Methods:We conducted three experiments to investigate whether donepezil enhances the shift in perceptual eye dominance induced by monocular patching.In each experiment,healthy adults completed two experimental sessions while taking either donepezil(5 mg,oral)or a placebo(lactose)pill.In experiment 1 we patched the non-dominant eye for 2 hours and measured ocular balance with a binocular phase combination task.In experiment 2 we patched for one hour to investigate whether donepezil shortens the amount of time necessary to observe a shift in ocular dominance.In experiment 3 we patched for 2 hours and measured ocular balance with a binocular rivalry task to see if the effect of donepezil was comparable across the two tasks.We calculated AUCs for the shift in perceptual eye dominance across five time points after removing the patch to compare our treatment conditions in each experiment.Results:Donepezil significantly reduces the magnitude and duration of the shift in perceptual eye dominance produced by both 2(P<0.01)and 1 hours(P<0.05)of monocular patching when measuring ocular balance with a binocular phase combination task.Donepezil also reduces the magnitude of the shift in ocular dominance when measuring balance with a binocular rivalry task.Conclusions:Previous studies have demonstrated that cholinergic potentiation enhances adult brain plasticity.Because of this,we hypothesized donepezil would further augment the strength of the deprived eye after patching.Our study demonstrates that enhanced cholinergic potentiation actually interferes with the consolidation of the perceptual eye dominance plasticity induced by several hours of monocular deprivation.These results contribute to the growing evidence that cholinergic potentiation enhances certain forms of adult brain plasticity at the expense of others.

AB006.Longitudinal effects of an optic nerve injury on behavioural measures of visual functions

Background:Visual deficits,caused by ocular disease or trauma,can cause lasting damage.However,recent research has focused on neural plasticity as a means to regain visual functions.In order to better understand the involvement of neural plasticity and reorganization in partial vision restoration,we aim to evaluate the partial recovery of a visual deficit over time using two behavioural tests.In our study,a partial optic nerve crush(pONC)serves as an induced visual deficit,allowing for residual vision from surviving cells.Methods:Visual functions in C57BL/6 mice was measured using two behavioural tests prior to a bilateral pONC,then at various time points after the pONC.In this study,two injury intensities were used:a high intensity pONC with the full force of self-closing forceps,and a low intensity pONC,in which a calibrated space was left between the forceps at the closed position.The two behavioural tests consisted of the optomotor reflex(OMR)and the visual cliff(VC)tests.The OMR test measures the mouse’s tracking reflex in response to moving sinusoidal gratings.The VC test,on the other hand,evaluates exploratory behaviour,by simulating a cliff to observe the animal’s sense of depth perception.After the behavioural evaluation,surviving retinal ganglion cells were counted.Results:The high intensity pONC resulted in a total loss of visual acuity as measured by the OMR test,with no improvement in the following 4 weeks.However,the light intensity pONC showed the same initial loss,but recovery was observed as of day 3,and results in 40-60%recovery after 4 weeks.With the VC test,mice with intact vision will avoid the deep end,opting to spend more time in the shallow end.However,after both high and low intensity pONCs,this preference is no longer observed.Both groups show a return to the shallow end preference at day 14,though the low intensity pONC group showed a stronger preference similar to baseline performance.The percentage of surviving retinal ganglion cells was higher with the low intensity(68%)than with the high intensity(17%)pONC.Conclusions:There is evidence of visual recovery at the behavioural level following a pONC,though very little recovery was observed following a high intensity pONC,and only with the VC test.Therefore,a certain amount of residual retinal input may be required for recovery at the behavioural level.

AB067.Cholinergic enhancement of short-term patching in healthy adults

Background:Patching an eye for a period of 2 hours results in a period of plasticity where inter-ocular balance shifts in favor of the patched eye.Acetylcholine has been shown to improve visual function and augment adult neural plasticity.Here we evaluate whether administering the cholinesterase inhibitor donepezil enhances the magnitude or duration of the patching induced shift in ocular balance.Methods:We used a double-blind drug treatment design to test the effect of donepezil and patching on the shift in ocular balance.We used a well-known binocular phase combination task to measure ocular balance before and after treatment.Results:Our results demonstrate that donepezil does not enhance,and may actually reduce the magnitude and duration of the patching-induced shift in ocular balance.Conclusions:Patching induced adult neural plasticity does not appear to be modulated by the cholinergic system,however,increased dose or longer drug administration periods may yield significant results.Future studies on binocular rivalry are in the pipeline.

AB010. The effect of visual conditioning on cortical map plasticity:a wide-field calcium imaging study

Background:Visual conditioning can refine the response of neurons in the visual cortex and higher visual and cognitive processing of a presented stimulus.This process results in increased sensitivity for that stimulus.The development of new optical imaging technology in the field of neuroscience has led to important advances,notably to better define the functional organization and plasticity of visual areas.The objective of this project is to determine the effect of daily visual conditioning with an oblique sinusoidal grating on the distribution and amplitude of cortical responses.For this,we use wide-field calcium imaging on awake mice,allowing for the observation of responses to a stimulus throughout the entire cortex in real time.Methods:C57BL/6 mice,expressing the GCaMP6s calcium reporter gene,are used to longitudinally measure neuronal activity via wide-field calcium imaging.Spontaneous activity at rest,as well as cortical responses to visual stimuli consisting of sinusoidal networks with orientation(0,30°,60°and 90°),spatial frequency(0.03,0.12,0.24 and 0.48 cpd)and contrast(100%,75%and 50%)variables are recorded to establish cortical maps,as well as tuning curves.Subsequently,the baseline function of the cortex,as well as the cortical representation of visual stimulation(30°or 90°,0.03 cpd and a contrast of 50%,75%and 100%)are studied in the animal before,during,and after daily monocular conditioning,consisting of a specific sinusoidal network(30°,0.03 cpd and 100%)over a period of 7 days.The variations in intensity and activation specificity of various visual cortical areas are calculated according to the visual conditioning and compared to an orientation stimulus for which the animal has not been conditioned(90°).Results:The cortical activation curves show a greater sensitivity of response for stimuli having horizontal or vertical gratings(0 and 90°)than for oblique gratings(30°and 60°)at low spatial frequencies(0,0.3 and 0.12 cpd).However,this trend does not occur with high spatial frequencies(0.24 and 0.48 cpd).Finally,although the intensity of activation varies in a way that is not proportional to the contrast of the stimulation,it would have no influence on the perception of the orientation of the stimuli.Conditioning at a 30°stimulus results in greater activation of the primary visual cortex and some extra-striate visual areas,as well as greater amplification of the ipsilateral cortical responses to the presentation of the visual stimuli.Conclusions:In conclusion,the results demonstrate that visual conditioning would allow for plasticity and consolidation of higher visual pathways.

AB029.The role of inducible nitric oxide synthase in deleterious effects of Kinin B1 receptor in diabetic retinopathy

Background:Overexpression of inducible nitric oxide synthase(iNOS)has been reported in diabetic retinopathy(DR).The kinin B1 receptor(B1R)is also overexpressed in DR,and can stimulate iNOS via Gαi/ERK/MAPK pathway.We previously showed that the topical administration of a B1R antagonist,LF22-0542,significantly reduces leukocyte infiltration,increased vascular permeability and overexpression of several inflammatory mediators,including iNOS in DR.Thus,the aim of this study was to determine whether the pro-inflammatory effects of B1R are attributed to oxidative stress caused by the activation of iNOS pathway in order to identify new therapeutic targets for the treatment of DR.iNOS and B1R being absent in the normal retina,their inhibition is unlikely to result in undesirable side effects.The approach will be no invasive by eye application of drops.Methods:Diabetes was induced in male Wistar rats(200-230 g)by a single intraperitoneal injection of streptozotocin(STZ,65 mg/kg b.w).One week later,rats were randomly divided into four groups(N=5)and treated for one week as follows:Gr 1:control rats treated with the selective iNOS inhibitor(1,400 W,0.06μM twice a day by eye-drops×7 days),Gr 2,STZ-diabetic rats treated with 1,400 W,Gr 3:control rats received a selective B1R agonist[Sar(D-Phe8)-des-Arg9-BK,100μg twice a week]by intravitreal injections(itrv)and treated with 1,400 W,Gr 4:STZ-diabetic rats+B1R agonist+1,400 W.At the end of treatment and two weeks post-STZ,three series of experiments were carried out to measure vascular permeability(by Evans blue dye method)and the expression of vasoactive and inflammatory mediators,including iNOS,VEGF-A,VEGF-R2,IL-1β,Cox-2,TNF-α,bradykinin 1 and 2 receptors and carboxypeptidase M/kininase 1(by Western Blotting and qRT-PCR).The nitrosative stress(nitrosylation of proteins)was also assessed by Western Blotting.One-way Anova test with Bonferroni post hoc was used for statistical analysis.Results:STZ-diabetic rats showed a significant increase in retinal vascular permeability(22.8μg/g Evans blue dye per g of fresh retinas,P=0.016)compared with control rats and control treated rats(17.2 and 16.8μg/g respectively).The injections of B1R agonist amplified the increase of vascular permeability which was normalized by the 1,400 W.The overexpression of inflammatory markers was also normalized by the 1,400 W in STZ-diabetic rats received or not the B1R agonist.Conclusions:These results support a contribution of iNOS in the deleterious effects of B1R in this model of diabetic retinopathy.Hence,iNOS inhibition by ocular application of 1,400 W may represent a promising and non-invasive therapeutic approach in the treatment of diabetic retinopathy.

AB021.The effect of anti-VEGF on retinal inflammation and its relationship with the Kinin system in a rat model of laser-induced choroidal neovascularization

Background:The neovascular aged-related macular degeneration(AMD)is the leading cause of legal blindness in the elderly.It is presently treated by anti-VEGF intravitreal injection in order to stop the neovascularization.In seeking of more efficient treatments to prevent retinal damage,it has been proposed that the kinin-kallikrein system(KKS),a key player in inflammation,could be involved in AMD etiology.However,the role of kinin receptors and their interaction with VEGF in AMD is poorly understood.Methods:In order to address this question,choroidal neovascularization(CNV)was induced in the left eye of Long-Evans rat.After laser induction,anti-VEGF or IgG control were injected into the vitreal cavity.Gene expression was measured by qRT-PCR,retinal adherent leukocytes were labelled with FITC-Concanavalin A lectin,vascular leakage by the method of Evans blue and cellular localisation by immunohistochemistry.Results:The number of labelled adherent leucocytes was significantly increased in laser-induced CNV compared to the control eye.This was significantly reversed by one single injection of anti-VEGF.Extravasation of Evans blue dye was significantly increased in laser-induced CNV eyes compared to control eyes and partially reversed by one single injection of anti-VEGF or by R954 treatment.The mRNA expression of inflammatory mediators was significantly increased in the retina of CNV rats.Immunodetection of B1R was significantly increased in CNV eyes.B1R immunolabeling was detected on endothelial and ganglion cells.Conclusions:This study is the first to highlight an effect of the kinin/kallikrein system in a model of CNV that could be reduced by both anti-VEGF therapy and topically administered B1R antagonist R-954.

AB058.A longitudinal study on the effects of the optic nerve crush on behavioural visual acuity measures in mice

Background:Visual deficits,caused by ocular disease or trauma to the visual system,can cause lasting damage with insufficient treatment options available.However,recent research has focused on neural plasticity as a means to regain visual abilities.In order to better understand the involvement of neural plasticity and reorganization in partial vision restoration,we aim to evaluate the partial recovery of a visual deficit over time using three behavioural tests.In our study,a partial optic nerve crush(ONC)serves as an induced visual deficit,allowing for residual vision from surviving cells.Methods:Three behavioural tests-optokinetic reflex,object recognition,and visual cliff-were conducted in 9 mice prior to a bilateral,partial ONC,then 1,3,7,14,21,and 28 days after the ONC.The optokinetic reflex test measured the tracking reflex in response to moving sinusoidal gratings.These gratings increase in spatial frequency until a reflex is no longer observed,i.e.,a visual acuity threshold is reached.The object recognition test examines the animal’s exploratory behaviour in its capacity to distinguish high versus low contrast objects.The visual cliff test also evaluates exploratory behaviour,by simulating a cliff to observe the animal’s sense of depth perception.All three tests provide an estimate of the rodent’s visual abilities at different levels of the visual pathway.Results:The partial optic nerve crush resulted in a total loss of visual acuity as measured by the optokinetic reflex.The deficit did not show improvement during the 4 following weeks.Despite the visual cliff test showing a non-significant decrease in deep end preference 1-day post ONC,though this was not the case for subsequent test occasions.The object recognition test showed no significant trends.Conclusions:In conclusion,the optokinetic reflex test showed a significant loss of function following the visual deficit,but no recovery.However,a complimentary pilot study shows visual recovery using lighter crush intensities.The spatial visual function does not seem to be affected by the ONC,suggesting that the object recognition and visual cliff tests,in their current design,may rely on somatosensory means of exploration.