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The mechanism of vulnerability to pediatric low-grade gliomas (pLGGs)-the most common brain tumor in children-during development remains largely unknown. Using mouse models of neurofibromatosis type 1 (NF1)-associated pLGGs in the optic pathway (NF1-OPG), we demonstrate that NF1-OPG arose from the vulnerability to the dependency of Mek-Erk/MAPK signaling during gliogenesis of one of the two developmentally transient precursor populations in the optic nerve, brain-derived migrating glial progenitors (GPs), but not local progenitors. Hyperactive Erk/MAPK signaling by Nf1 loss overproduced GPs by disrupting the balance between stem-cell maintenance and gliogenesis of hypothalamic ventricular zone radial glia (RG). Persistence of RG-like GPs initiated NF1-OPG, causing Bax-dependent apoptosis in retinal ganglion cells. Removal of three Mek1/Mek2 alleles or transient post-natal treatment with a low-dose MEK inhibitor normalized differentiation of Nf1-/- RG-like GPs, preventing NF1-OPG formation and neuronal degeneration. We provide the proof-of-concept evidence for preventing pLGGs before tumor-associated neurological damage enters an irreversible phase.

INTRODUCTION Because treatment and clinical management decisions for children with NF1-OPG remain challenging, we sought to establish evidence-based guidelines. We prospectively enrolled children with newly-diagnosed NF1-OPGs, and gathered standardized clinical neuro-oncology and ophthalmology assessments. METHODS Only children with NF1 and newly diagnosed OPGs, confirmed by central review, were eligible. Indications for obtaining the initial MRI, as well as factors associated with the decision to treat with chemotherapy or observe without treatment, were obtained. Quantitative visual acuity (VA), other ophthalmic features, and imaging were captured at standard time points. Goal enrollment is 250 subjects. RESULTS One-hundred thirty-three children (52% female) from 20 institutions met inclusion criteria, and were included in this preliminary analysis. Eighty-six percent of subjects were able to perform quantitative VA testing at enrollment. The most common reasons for the diagnostic MRI included screening related to NF1 diagnosis (36.8%), ophthalmologic concerns (29.3%), and non-ophthalmologic concerns (24.8%), such as headache. To date, twenty subjects have initiated treatment with chemotherapy, twelve (9%) at the time of the initial OPG diagnosis. Median age at OPG diagnosis was 3.1 years. Age and sex distribution were similar in subjects immediately entering the observation and treatment arms (median age 3.0 versus 3.5 years, respectively). CONCLUSION Most children with NF1-OPGs are observed at time of their initial OPG diagnosis, rather than treated. Importantly, a large proportion of children are able to complete quantitative VA testing at enrollment. Once enrollment is complete, these data will help to establish evidence-based guidelines for clinical management of NF1-OPGs.

BACKGROUND: Prolactin-secreting macroadenomas are generally not life-threatening and often present with visual impairment. Medical management with a dopamine agonist is typically the treatment of choice, which significantly reduces the tumor size and improves symptoms without surgical morbidity. In this report, we present a case of an acidophilic stem cell adenoma (ASCA) that was slowly responsive to medical management, but exhibited marked visual recovery after surgical resection. RESULTS: A 15 year-old previously healthy male presented with significantly decreased peripheral vision but no other neurologic or endocrinologic symptoms. Initial magnetic resonance imaging of the brain/spine revealed a mass in the suprasellar and sellar regions with extension into the cavernous sinus and a prolactin level of 644, leading to a presumptive diagnosis of macroprolactinoma. Medical management with cabergoline resulted in some decrease of the prolactin level, but no radiographic improvement or visual recovery after two months. He subsequently underwent endoscopic endonasal transsphenoidal resection with near-total restoration of his peripheral vision post-operatively and significant improvement of his prolactin level. Pathology was consistent with an ASCA (staining positively with prolactin, growth hormone (a-subunit), and pituitary-specific positive transcription factor 1), a rare pituitary adenoma that tends to be invasive and often requires more aggressive therapy; the patient thus underwent focal consolidative proton beam irradiation. CONCLUSION: This case highlights the importance of considering acidophilic stem cell adenomas in the differential of medically-resistant pituitary macroadenomas and early consideration of resection in cases where significant visual or other symptoms exist, as timely intervention may substantially improve functional outcomes.

Optic pathway gliomas (OPGs) are glial tumors that arise early during development in 15-20% of patients with Neurofibromatosis Type I (NF1). While chemotherapy is often used for patients who have growing tumors and/or vision loss associated with the tumor, a minority of patients have improvement in their vision following treatment. Thus, a new approach to treatment is needed to improve the visual outcomes in this patient population. In our laboratory, we have a Nf1-deficient conditional knockout mouse model that develops optic pathway gliomas around 60 days of age (P60). These mice have associated axon degeneration, loss of retinal ganglion cells, and evidence of vision loss on behavioral testing, thus making this a good model to use in order to identify the optimal therapeutic time window that improves or prevents vision loss. In this study, we treated NF1-deficient mice with a Mek-inhibitor during different developmental time windows and measured response to treatment in terms of nerve cellularity, axon integrity, and retinal ganglion cell loss. We found that response to treatment is highly dependent on when the therapy is initiated during OPG development, and the best response occurred when therapy was initiated early during this process. This study suggests that the timing of therapy initiation is critical for optimal outcomes in NF1-associated OPGs.

One set of missense mutations in the neuron specific beta tubulin isotype 3 (TUBB3) has been reported to cause malformations of cortical development (MCD), while a second set has been reported to cause isolated or syndromic Congenital Fibrosis of the Extraocular Muscles type 3 (CFEOM3). Because TUBB3 mutations reported to cause CFEOM had not been associated with cortical malformations, while mutations reported to cause MCD had not been associated with CFEOM or other forms of paralytic strabismus, it was hypothesized that each set of mutations might alter microtubule function differently. Here, however, we report two novel de novo heterozygous TUBB3 amino acid substitutions, G71R and G98S, in four patients with both MCD and syndromic CFEOM3. These patients present with moderately severe CFEOM3, nystagmus, torticollis, and developmental delay, and have intellectual and social disabilities. Neuroimaging reveals defective cortical gyration, as well as hypoplasia or agenesis of the corpus callosum and anterior commissure, malformations of hippocampi, thalami, basal ganglia and cerebella, and brainstem and cranial nerve hypoplasia. These new TUBB3 substitutions meld the two previously distinct TUBB3-associated phenotypes, and implicate similar microtubule dysfunction underlying both.

Purpose The R345W mutation in EFEMP1 causes malattia leventinese, an autosomal dominant eye disease with pathogenesis similar to an early-onset age-related macular degeneration. In mice, Efemp1R345W does not cause detectable degeneration but small subretinal deposits do accumulate. The purpose of this study was to determine whether there were abnormal responses to light at this presymptomatic stage in Efemp1R345W mice. Methods Responses to light were assessed by visual water task, circadian phase shifting, and negative masking behavior. The mechanism of abnormal responses was investigated by anterior eye exam, electroretinogram, melanopsin cell quantification, and multielectrode recording of retinal ganglion cell activity. Results Visual acuity was not different in Efemp1R345W mice. However, amplitudes of circadian phase shifting (P = 0.016) and negative masking (P < 0.0001) were increased in Efemp1R345W mice. This phenotype was not explained by anterior eye defects or amplified outer retina responses. Instead, we identified increased melanopsin-generated responses to light in the ganglion cell layer of the retina (P < 0.01). Conclusions Efemp1R345W increases the sensitivity to light of behavioral responses driven by detection of irradiance. An amplified response to light in melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) is consistent with this phenotype. The major concern with this effect of the malattia leventinese mutation is the potential for abnormal regulation of physiology by light to negatively affect health.

In a subset of hereditary retinal diseases, early photoreceptor degeneration causes rapidly progressive blindness in children. To better understand how retinal development may interact with degenerative processes, we compared spontaneous and light-evoked activity among retinal ganglion cells in rd1 and rd10 mice, strains with closely related retinal disease. In each, a mutation in the Pde6b gene causes photoreceptor dysfunction and death, but in rd10 mice degeneration starts after a peak in developmental plasticity of retinal circuitry and thereafter progresses more slowly. In vitro multielectrode action potential recordings revealed that spontaneous waves of correlated ganglion cell activity comparable to those in wild-type mice were present in rd1 and rd10 retinas before eye opening [postnatal day (P) 7 to P8]. In both strains, spontaneous firing rates increased by P14–P15 and were many times higher by 4–6 wk of age. Among rd1 ganglion cells, all responses to light had disappeared by ∼P28, yet in rd10 retinas vigorous ON and OFF responses were maintained well beyond this age and were not completely lost until after P60. This difference in developmental time course separates mechanisms underlying the hyperactivity from those that alter light-driven responses in rd10 retinas. Moreover, several broad physiological groups of cells remained identifiable according to response polarity and time course as late as P60. This raises hope that visual function might be preserved or restored despite ganglion cell hyperactivity seen in inherited retinal degenerations, particularly if treatment or manipulation of early developmental plasticity were to be timed appropriately.

Complex alterations in the anatomy of outer retinal pathways accompany photoreceptor degeneration in the rd1 mouse model of retinitis pigmentosa, whereas inner retinal neurons appear relatively preserved. However, the progressive loss of photoreceptor input likely alters the neural circuitry of the inner retina. This study investigated resulting changes in the activity of surviving ganglion cells. Multielectrode recording monitored spontaneous and light-evoked extracellular action potentials simultaneously from 30 to 90 retinal ganglion cells of wild-type ( wt) or rd1 mice. In rd1 mice, this activity evolves through three phases. First, normal spontaneous “waves” of correlated firing are seen at postnatal day 7 (P7) and last until shortly after eye opening. Second, at P14, full-field light flashes evoke reliable responses in many cells, with preferential preservation of off responses. These diminish as photoreceptor degeneration progresses. Third, once light-evoked responses have disappeared in early adulthood, surviving rd1 ganglion cells fire at a much higher spontaneous frequency than normal, sometimes in rhythmic bursts that are distinct from the developmental “waves.” This hyperactivity is sustained well into adulthood, for weeks after photoreceptors have disappeared. Thus striking alterations occur in inner retinal physiology as retinal degeneration progresses in the rd1 mouse. Blindness occurs in the face of sustained hyperactivity among ganglion cells, which remain viable for months despite this activity. On and off responses are differentially affected in early stages of degeneration. While the source of these changes remains to be learned, such features should be considered in designing more effective treatments for these disorders.

Purpose Traumatic brain injury (TBI) frequently leads to chronic visual dysfunction. The purpose of this study was to investigate the effect of TBI on retinal ganglion cells (RGCs), and to test whether treatment with the novel neuroprotective compound P7C3-S243 could prevent in vivo functional deficits in the visual system. Methods Blast-mediated TBI was modeled using an enclosed over-pressure blast chamber. The RGC physiology was evaluated using a multielectrode array and pattern electroretinogram (PERG). Histological analysis of RGC dendritic field and cell number were evaluated at the end of the study. Visual outcome measures also were evaluated based on treatment of mice with P7C3-S243 or vehicle control. Results We show that deficits in neutral position PERG after blast-mediated TBI occur in a temporally bimodal fashion, with temporary recovery 4 weeks after injury followed by chronically persistent dysfunction 12 weeks later. This later time point is associated with development of dendritic abnormalities and irreversible death of RGCs. We also demonstrate that ongoing pathologic processes during the temporary recovery latent period (including abnormalities of RGC physiology) lead to future dysfunction of the visual system. We report that modification of PERG to provocative postural tilt testing elicits changes in PERG measurements that correlate with a key in vitro measures of damage: the spontaneous and light-evoked activity of RGCs. Treatment with P7C3-S243 immediately after injury and throughout the temporary recovery latent period protects mice from developing chronic visual system dysfunction. Conclusions Provocative PERG testing serves as a noninvasive test in the living organism to identify early damage to the visual system, which may reflect corresponding damage in the brain that is not otherwise detectable by noninvasive means. This provides the basis for developing an earlier diagnostic test to identify patients at risk for developing chronic CNS and visual system damage after TBI at an earlier stage when treatments may be more effective in preventing these sequelae. In addition, treatment with the neuroprotective agent P7C3-S243 after TBI protects from visual system dysfunction after TBI.

Purpose Best disease is a macular dystrophy caused by mutations in the BEST1 gene. Affected individuals exhibit a reduced electro-oculographic (EOG) response to changes in light exposure and have significantly longer outer segments (OS) than age-matched controls. The purpose of this study was to investigate the anatomical changes in the outer retina during dark and light adaptation in unaffected and Best disease subjects, and to compare these changes to the EOG. Methods Unaffected (n = 11) and Best disease patients (n = 7) were imaged at approximately 4-minute intervals during an approximately 40-minute dark-light cycle using spectral domain optical coherence tomography (SD-OCT). EOGs of two subjects were obtained under the same conditions. Automated three-dimensional (3-D) segmentation allowed measurement of light-related changes in the distances between five retinal surfaces. Results In normal subjects, there was a significant decrease in outer segment equivalent length (OSEL) of -2.14 μm (95% confidence interval [CI], -1.77 to -2.51 μm) 10 to 20 minutes after the start of light adaptation, while Best disease subjects exhibited a significant increase in OSEL of 2.07 μm (95% CI, 1.79-2.36 μm). The time course of the change in OS length corresponded to that of the EOG waveform. Conclusions Our results strongly suggest that the light peak phase of the EOG is temporally related to a decreased OSEL in normal subjects, and the lack of a light peak phase in Best disease subjects is associated with an increase in OSEL. One potential role of Bestrophin-1 is to trigger an increase in the standing potential that approximates the OS to the apical surface of the RPE to facilitate phagocytosis.

We recorded from on-off direction-selective ganglion cells (DS cells) in the rabbit retina to investigate in detail the inhibition that contributes to direction selectivity in these cells. Using paired stimuli moving sequentially across the cells' receptive fields in the preferred direction, we directly confirmed the prediction of Wyatt and Daw (1975) that a wave of inhibition accompanies any moving excitatory stimulus on its null side, at a fixed spatial offset. Varying the interstimulus distance, stimulus size, luminance, and speed yielded a spatiotemporal map of the strength of inhibition within this region. This “null” inhibition was maximal at an intermediate distance behind a moving stimulus: ½ to 1½ times the width of the receptive field. The strength of inhibition depended more on the distance behind the stimulus than on stimulus speed, and the inhibition often lasted 1–2 s. These spatial and temporal parameters appear to account for the known spatial frequency and velocity tuning of on-off DS cells to drifting contrast gratings. Stimuli that elicit distinct onand off responses to leading and trailing edges revealed that an excitatory response of either polarity could inhibit a subsequent response of either polarity. For example, an offresponse inhibited either an on or off response of a subsequent stimulus. This inhibition apparently is conferred by a neural element or network spanning the on andoff sublayers of the inner plexiform layer, such as a multistratified amacrine cell. Trials using a stationary flashing spot as a probe demonstrated that the total amount of inhibition conferred on the DS cell was equivalent for stimuli moving in either the null or preferred direction. Apparently the cell does not act as a classic “integrate and fire” neuron, summing all inputs at the soma. Rather, computation of stimulus direction likely involves interactions between excitatory and inhibitory inputs in local regions of the dendrites.

PURPOSE In animal models of degenerative photoreceptor disease, there has been some success in restoring photoreception by transplanting stem cell-derived photoreceptor cells into the subretinal space. However, only a small proportion of transplanted cells develop extended outer segments, considered critical for photoreceptor cell function. The purpose of this study was to determine whether photoreceptor cells that lack a fully formed outer segment could usefully contribute to vision. METHODS Retinal and visual function was tested in wild-type and Rds mice at 90 days of age (Rds(P90)). Photoreceptor cells of mice homozygous for the Rds mutation in peripherin 2 never develop a fully formed outer segment. The electroretinogram and multielectrode recording of retinal ganglion cells were used to test retinal responses to light. Three distinct visual behaviors were used to assess visual capabilities: the optokinetic tracking response, the discrimination-based visual water task, and a measure of the effect of vision on wheel running. RESULTS Rds(P90) mice had reduced but measurable electroretinogram responses to light, and exhibited light-evoked responses in multiple types of retinal ganglion cells, the output neurons of the retina. In optokinetic and discrimination-based tests, acuity was measurable but reduced, most notably when contrast was decreased. The wheel running test showed that Rds(P90) mice needed 3 log units brighter luminance than wild type to support useful vision (10 cd/m(2)). CONCLUSIONS Photoreceptors that lack fully formed outer segments can support useful vision. This challenges the idea that normal cellular structure needs to be completely reproduced for transplanted cells to contribute to useful vision.

Detection of light serves many tasks. Independent of form vision, the detection of brightness (irradiance) is used to regulate pupil size,1 entrain circadian rhythms to the day-night cycle,2 and modulate endocrine function.3 Irradiance information is transmitted to central nuclei by a specialized subset of intrinsically photosensitive retinal ganglion cells (ipRGCs).4,5 The response of ipRGCs to light is a composite of their intrinsic melanopsin-generated activity and rod-cone photoreceptor-dependent activation mediated by interneurons of the inner retina.6 However, morphologic and functional specialization among ipRGCs has been identified, and these “ipRGC types” show variation in their projections to central nuclei.7–10 How these differences in ipRGC form, function, and central projections relate to a given irradiance response is not well understood. For instance, the pupillary light reflex and negative masking (a suppression of activity by light) both respond to “lights on” in an irradiance-dependent manner.1,11 However, the effect of outer retina degeneration differs dramatically between these irradiance responses, with a paradoxical enhancement of irradiance sensitivity in negative masking12 and a severe loss of sensitivity in the pupillary light reflex.1,13,14 At the level of the retina, such phenotypic variability could arise from secondary effects of outer retina disease on ipRGCs or from differences in rod-cone input to the different ipRGC types. Although inner retinal circuitry is diverse, all vertical transmission of rod and cone signals to ganglion cells is, at some point, mediated by bipolar cells (BCs).15 Therefore, differences between responses could arise from specificity in bipolar cells mediating rod-cone input. The aim of this study was to determine whether there are differences in inner retinal pathways mediating rod-cone input to functionally distinct irradiance responses and whether such differences could contribute to the divergent effects of outer retinal disease on the different irradiance responses. Negative masking and pupillary light reflex were compared between mice with intact inner-retinal circuitry (wild-type), mice selectively lacking the ON-BC pathway of rod-cone input (Nob4), and mice with degenerate rods and cones (rd1), effectively lacking input to both ON- and OFF-BCs (Fig. 1). Figure 1. Vertical transmission of rod-cone input to ganglion cells. Green: ON pathways. Blue: OFF pathways. Loss of function is indicated by gray shading or cell absence. (A) When rods and cones respond to light, metabotropic or ON-BCs depolarize, and ionotropic ...

In an electrographic model of seizures in the hippocampal slice, both of the N-methyl-D-aspartate (NMDA) antagonists 2-amino-5-phosphonovaleric acid and 5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine maleate (MK-801) prevented the progressive development of seizures but did not block previously induced seizures. Thus, a process dependent on the NMDA receptor-ionophore complex establishes a long-lasting, seizure-prone state; thereafter the seizures depend on non-NMDA receptor-ionophore mechanisms. This suggests that there is an important distinction between epileptogenesis and seizure expression and between antiepileptogenic and anticonvulsant pharmacological agents.