The synaptic ribbon is a site of phosphatidic acid generation in ribbon synapses

Ribbon synapses continuously transmit graded membrane potential changes into changes of synaptic vesicle exocytosis and rely on intense synaptic membrane trafficking. The synaptic ribbon is considered central to this process. In the present study we asked whether tonically active ribbon synapses are associated with the generation of certain lipids, specifically the highly active signaling phospholipid phosphatidic acid (PA). Using PA-sensor proteins, we demonstrate that PA is enriched at mouse retinal ribbon synapses in close vicinity to the synaptic ribbon in situ. As shown by heterologous expression, RIBEYE, a main component of synaptic ribbons, is responsible for PA binding at synaptic ribbons. Furthermore, RIBEYE is directly involved in the synthesis of PA. Using various independent substrate binding and enzyme assays, we demonstrate that the B domain of RIBEYE possesses lysophosphatidic acid (LPA) acyltransferase (LPAAT) activity, which leads to the generation of PA from LPA. Since an LPAAT-deficient RIBEYE mutant does not recruit PA-binding proteins to artificial synaptic ribbons, whereas wild-type RIBEYE supports PA binding, we conclude that the LPAAT activity of the RIBEYE(B) domain is a physiologically relevant source of PA generation at the synaptic ribbon. We propose that PA generated at synaptic ribbons likely facilitates synaptic vesicle trafficking.     

Quantitative determination of human protein C. Evaluation of a "fast" functional assay in comparison to a "traditional" functional and an immunological assay

A fast functional assay for protein C was evaluated and compared with a traditional functional and an enzyme linked immunosorbent assay in parallel for the same plasma samples derived from 43 healthy subjects, 12 patients with severe hepatic dysfunction, and 23 patients under stable oral anticoagulation. By all three test systems significantly lower levels of protein C were obtained in both groups of patients compared with normal subjects (p less than 0.0001). No significant between - assay differences were found in normal subjects and in patients with hepatic dysfunction; by correlation analysis coefficients higher than 0.8 were calculated between the measurements of the three tests. In patients under stable oral anticoagulation, however, the immunologic test yielded higher values than the traditional (p less than 0.05) and, more pronounced, the fast functional assay (p less than 0.0001); no or only borderline significant correlations between the results were found. In these patients protein C levels measured with the traditional functional assay were in the same range as the activity levels of factors II, VII, IX, and X, whereas the fast functional test yielded significantly lower levels. The presented results indicate that very similar protein C levels were obtained with both functional and the immunologic assay except in patients under oral anticoagulation.     

Spike-triggered reaction-time EEG as a possible assessment tool for driving ability

The impact of interictal epileptic activity (IEA) on driving is a rarely investigated issue. We analyzed the impact of IEA on reaction time in a pilot study. Reactions to simple visual stimuli (light flash) in the Flash test or complex visual stimuli (obstacle on a road) in a modified car driving computer game, the Steer Clear, were measured during IEA bursts and unremarkable electroencephalography (EEG) periods. Individual epilepsy patients showed slower reaction times (RTs) during generalized IEA compared to RTs during unremarkable EEG periods. RT differences were approximately 300 ms (p < 0.001) in the Flash test and approximately 200 ms (p < 0.001) in the Steer Clear. Prior work suggested that RT differences >100 ms may become clinically relevant. This occurred in 40% of patients in the Flash test and in up to 50% in the Steer Clear. When RT were pooled, mean RT differences were 157 ms in the Flash test (p < 0.0001) and 116 ms in the Steer Clear (p < 0.0001). Generalized IEA of short duration seems to impair brain function, that is, the ability to react. The reaction-time EEG could be used routinely to assess driving ability.     

The synaptic ultrastructure in the outer plexiform layer of the catfish retina: a three-dimensional study with HVEM and conventional EM of Golgi-impregnated bipolar and horizontal cells

Synaptic structures between receptors and horizontal and bipolar cells in the outer plexiform layer (OPL) of Golgi-impregnated catfish retina were examined by conventional electron microscopy of serial ultrathin sections and by high-voltage electron microscopy (HVEM) of thick sections. Cone terminals contained multiple synaptic ribbons and rod terminals contained single synaptic ribbons. This observation was used to identify these two types of photoreceptors. The cone horizontal cell, located in the most distal part of the inner nuclear layer (INL), invaginated only cone terminals, whereas the rod horizontal cell, located in the proximal part of the INL, invaginated only rod terminals. Both lateral elements of the triad in the rod terminal originated from a single rod horizontal cell whereas the same structures in the cone terminal were often derived from several cone horizontal cells. Golgi-impregnated catfish bipolar cells were classified into two types based on the differences in their axonal arborization as described by Famiglietti et al. ('77). Axonal endings of type a bipolar cells were located in the distal part, sublamina a, of the inner plexiform layer (IPL), and axonal endings of type b cells were located in the proximal part, sublamina b, of the IPL. Dendrites from type a bipolar cells made direct contact with the synaptic ribbons in both rod and cone terminals whereas those from type b cells made indirect contact with the ribbons in both rod and cone terminals, but rare direct contact with the ribbon in rod terminals were also seen. In addition, bipolar cells made basal junctions or superficial contacts in both rod and cone terminals. The "lateral" processes of bipolar cells invaginating rods penetrated between the rod terminal and rod horizontal cell processes, and made basal junctions with both rod terminals and rod horizontal cells. There was no definitive morphological feature that could be associated with sign-conserving and sign-inverting signal transmission.     

A follow-up survey on seizures induced by animated cartoon TV program "Pocket Monster"

PURPOSE: To identify the short-term outcome of patients who had seizures while watching an animated cartoon TV program, "Pocket Monster," on December 16, 1997. METHODS: One and three years after the incident, questionnaires were sent to physicians of each patient about seizure recurrence, EEGs, and medication. RESULTS: Among 103 patients in whom epileptic seizures occurred during the TV program and information on the outcomes was available, 25 (24%) patients had a history of unprovoked seizures before the incident (Epilepsy Group), and 78 (76%) did not (Non-Epilepsy Group). Twenty-three (22%) patients were reported to have seizures after the incident, and 15 of them had visually induced seizures. Patients of the Epilepsy Group had more seizure recurrence than did those of the Non-Epilepsy Group (56% vs. 9%; p < 0.0001), either for unprovoked (44% vs. 4%; p < 0.0001) or visually induced seizures (28% vs. 9%; p < 0.05). Of nine patients of the Non-Epilepsy Group who had seizures after the incident, only three developed recurrent unprovoked seizures. In the Non-Epilepsy Group, no difference was found in seizure recurrence between patients in whom valproate (VPA) was prescribed immediately after the incident and in those without medication (one of five (20%) vs. seven of 73 (10%); p > 0.05). EEG was performed at least once in 98 patients after the incident. Photoparoxysmal response (PPR) was present in 45 (46%) patients, and spontaneous epileptiform discharges, in 49 (50%). PPR did not have any correlation with recurrence of seizures, neither spontaneous nor visually induced seizures, whereas spontaneous epileptiform discharges showed a good correlation with seizure recurrence (34% vs. 8%; p < 0.01), including visually induced seizures (24% vs. 2%; p < 0.01). CONCLUSIONS: Short-term outcomes showed that 70 (68%) of 103 patients who had a seizure during the incident had no seizures before and during < or = 3 years of follow-up.     

Répercussions de l'hypothyroïdie sur la synaptogenèse dans le cortex cérébelleux du rat

Summary The corrective action of Thyroxine on the deficit of the synaptic density of the molecular layer of the cerebellar cortex was studed quantitatively, in the rat made hypothyroid by propylthiouracile (P.T.U.). In the normal as in the hypothyroid rat, the increase of the synaptic density does not extend over the fifth postnatal week. In the PTU treated animals, during the 2 first postnatal weeks, the administration of 0,25 g/d during the third and 0.50 //d, during the fourth postnatal week brings the synaptic density back to normal. In the PTU treated animals, during the 5 first postnatal weeks, the administration during a week only of 0.50 g/d of LT4 between 1 and 14 days or, of 1 g/d between 15 and 28 days, increases, but does not return to normal the synaptic density. On the contrary, the administration of 1 g/d of LT4 during 1 or even 2 consecutive weeks 28 days later, remains without effect on the synaptic density.After the end of the fourth postnatal week, the deficit of the synaptic density becomes irreversible.

     

Numerical variation in synaptic ribbons of rat pinealocytes under magnetic storm conditions and on calm days

Based on the hypothesis of the magnetoreceptor function of the pineal gland, a comparative study has been made, with electronic microscopy, of the numerical variations of the synaptic ribbons of the pinealocytes (indicating the cellular metabolic activity) of the groups of rats, under magnetic storm conditions and in calm days. In this quantitative study it was established that the incidence of synaptic ribbons per each 20,000 microns 2 of pineal tissue was smaller in the group of animals sacrificed during geomagnetic storms, as compared with the other group of animals sacrificed in calm periods (P less than 0.001). It was suggested that the synaptic ribbons may be morphological indicators of the pineal activity, with respect to the variations of the geomagnetic field.     

"Large cell/anaplastic" medulloblastomas: a Pediatric Oncology Group Study

495 medulloblastomas (MBs) from 6 Pediatric Oncology Group (POG) protocols were reviewed to assess the incidence and prognostic significance of "large cell" and "anaplastic" variants. "Large cell" medulloblastomas (LC MBs) were those with focal or diffuse, large, round neoplastic cells with prominent nucleoli. "Anaplastic" MBs (A MBs) were those with nuclei that were also large but markedly atypical with coarse chromatin and irregular shapes. Twenty-one cases were identified in the combined LC/A MB group, comprising about 4% of all MBs. Survival curves and Kaplan-Meier estimates of survival probabilities were examined separately for the LC/A MB and control groups. The logrank test for detecting poorer survival in the 21 cases was significant (p < 0.0001). Fluorescence in situ hybridization for c-myc showed amplification in 4 of 11 cases of the LC/A phenotype and 1 additional case of high level gain at 8q24 was disclosed by comparative genomic hybridization. Comparative genomic hybridization confirmed c-myc amplification and found evidence for isochromosome 17q in 3 of 4 LC/A cases studied successfully. One additional tumor showed high level gain restricted to 2p13 consistent with n-myc amplification. Monosomy 22, common in atypical teratoid/rhabdoid tumors, was not found. These results suggest that LC/A MB phenotype could be, at least in part, a correlate of c-myc, and possibly n-myc, amplification. The study thus confirms original observations about the LC MB in regard to histological features, immunohistochemical findings, c-myc amplification, cytogenetic findings, and poor prognosis.     

Quantitative analysis of ribbons,vesicles, and cisterns at the cat inner hair cell synapse: Correlations with spontaneous rate

Cochlear hair cells form ribbon synapses with terminals of the cochlear nerve. To test the hypothesis that one function of the ribbon is to create synaptic vesicles from the cisternal structures that are abundant at the base of hair cells, we analyzed the distribution of vesicles and cisterns around ribbons from serial sections of inner hair cells in the cat, and compared data from low and high spontaneous rate (SR) synapses. Consistent with the hypothesis, we identified a “sphere of influence” of 350 nm around the ribbon, with fewer cisterns and many more synaptic vesicles. Although high‐ and low‐SR ribbons tended to be longer and thinner than high‐SR ribbons, the total volume of the two ribbon types was similar. There were almost as many vesicles docked at the active zone as attached to the ribbon. The major SR‐related difference was that low‐SR ribbons had more synaptic vesicles intimately associated with them. Our data suggest a trend in which low‐SR synapses had more vesicles attached to the ribbon (51.3 vs. 42.8), more docked between the ribbon and the membrane (12 vs. 8.2), more docked at the active zone (56.9 vs. 44.2), and more vesicles within the “sphere of influence” (218 vs. 166). These data suggest that the structural differences between high‐ and low‐SR synapses may be more a consequence, than a determinant, of the physiological differences. J. Comp. Neurol. J. Comp. Neurol. 521:3260–3271, 2013. © 2013 Wiley Periodicals, Inc.     

Synaptic ribbons in pinealocytes of olfactory bulbectomized rats under experimental conditions

In previous studies it has been suggested that the increase in the number of synaptic ribbons is parallel to the melatonin forming activity of the pineal gland. The presence of synaptic ribbons in the pinealocytes of rats subjected to experimental manipulations known as enhancers of pineal actions (blindness, blindness + olfactory bulbectomy, blindness + underfeeding and blindness + cold exposure) has been studied. We found a significantly lower number of synaptic ribbons in the pinealocytes of control rats as compared with rats subjected to enhanced pineal actions. Since the latter showed a pineal-dependent gonadal atrophy and low serum estradiol levels, a direct relationship between the number of synaptic ribbons and the functional status of the pineal gland may be established. Thus, our results suggest that the number of synaptic ribbons might be an indicator of pineal activity.     

Single neuron burst firing in the human hippocampus during sleep

Although there are numerous non-primate studies of the single neuron correlates of sleep-related hippocampal EEG patterns, very limited hippocampal neuronal data are available for correlation with human sleep. We recorded human hippocampal single neuron activity in subjects implanted with depth electrodes required for medical diagnosis and quantitatively evaluated discharge activity from each neuron during episodes of wakefulness (Aw), combined stage 3 and 4 slow-wave sleep (SWS), and rapid eye movement (REM) sleep. The mean firing rate of the population of single neurons was significantly higher during SWS and Aw compared with REM sleep (p = 0.002; p < 0.0001). In addition, burst firing was significantly greater during SWS compared with Aw (p = 0.001) and REM sleep (p < 0.0001). The synchronized state of SWS and associated high-frequency burst discharge found in human hippocampus may subserve functions similar to those reported in non-primate hippocampus that require burst firing to induce synaptic modifications in hippocampal circuitry and in hippocampal projections to neocortical targets that participate in memory consolidation.     

Two ribbon synaptic units in rod photoreceptors of macaque,human, and cat

The rod photoreceptor's synaptic terminal (or spherule) uses an elaborate synaptic structure to signal absorption of one or more photons to its postsynaptic targets. This structure includes one or two synaptic ribbons inside the terminal and a pouch-like "invagination" outside the terminal, into which enter a widely variable number of incoming fibers and postsynaptic targets-central elements supplied by rod bipolar cells and lateral elements supplied by horizontal cells. Nonetheless, our three-dimensional reconstructions of this synaptic structure in foveal retina of macaque monkey and peripheral retina of human and cat reveal several features that are highly conserved across species and with eccentricity: 1). every spherule has one invagination; 2). with rare exceptions, every spherule has two ribbon synaptic units with these features: a). on the presynaptic side, each ribbon synaptic unit has a ribbon or part of a ribbon and one trough-shaped arciform density that demarcates its active zone; b). on the postsynaptic side, each ribbon synaptic unit has two apposed lateral elements and one or more central elements; 3). the volume of the extracellular space in the single invagination is small, approximately 0.1 microm(3); and 4). the largest distance from active zone to receptor regions on bipolar cells is small, less than approximately 1.5 microm. With such small dimensions, release of one quantum of transmitter can pulse glutamate to a concentration comparable to the EC(50) of the metabotropic glutamate receptors on the central elements associated with both synaptic units. We speculate that two ribbon synaptic units are required to sustain the high quantal release rate needed to signal a single photon.     

Nicotine as an antiepileptic agent in ADNFLE: an N-of-one study

PURPOSE: To test nicotine patch treatment for a patient with a defined mutation for autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) whose seizures were refractory to standard antiepileptic therapy. METHODS: Open and double-blind trials of nicotine patches in an "n-of-one" study. The double-blind trial comprised periods during which either placebo or nicotine patches were each used for three periods of 2 weeks, randomized in a double-blind manner. RESULTS: In an open study, nicotine patches reduced seizures from 1.65 +/- 2.36 to 0.01 +/- 0.0 seizures per day (p < 0.0001). In a double-blinded placebo-controlled phase, the average frequency of seizures on nicotine versus placebo was 0 +/- 0 versus 0.56 +/- 1.14 seizures per day (p < 0.0001). CONCLUSIONS: Nicotine patches may be of benefit to some individuals with ADNFLE.     

Early degeneration of photoreceptor synapse in Ccl2/Cx3cr1‐deficient mice on Crb1rd8 background

Photoreceptor ribbon synapse releases glutamate to postsynaptic targets. The synaptic ribbon may play multiple roles in ribbon synapse development, synaptic vesicle recycling, and synaptic transmission. Age‐related macular degeneration (AMD) patients appear to have fewer or no detectable synaptic ribbons as well as abnormal swelling in the photoreceptor terminals in the macula. However, reports on changes of photoreceptor synapses in AMD are scarce and photoreceptor type and quantity affected in early AMD is still unclear. Here, we employed multiple anatomical techniques to investigate these questions in Ccl2^?/?/Cx3cr1^?/? mouse on Crb1^rd8 background (DKO rd8) at one month of age. We found that approximately 17% of photoreceptors over the focal lesion were lost. Immunostaining for synapse‐associated proteins (CtBP2, synaptophysin, and vesicular glutamate transporter 1) showed significantly reduced expression and ectopic localization. Cone opsins demonstrated dramatic reduction in expression (S‐opsins) and extensive mislocalization (M‐opsins). Quantitative ultrastructural analysis confirmed a significant decrease in the number of cone terminals and nuclei, numerous vacuoles in remaining cone terminals, reduction in the number of synaptic ribbons in photoreceptor terminals, and ectopic rod ribbon synapses. In addition, glutamate receptor immunoreactivity on aberrant sprouting of rod bipolar cells and horizontal cells were identified at the ectopic synapses. These results indicate that synaptic alterations occur at the early stages of disease and cones are likely more susceptible to damage caused by DKO rd8 mutation. They provide a new insight into potential mechanism of vision function lost due to synaptic degeneration before cell death in the early stages of AMD. Synapse 67:515–531, 2013. © 2013 Wiley Periodicals, Inc.     

Influence of photoperiod on dense-core vesicles and synaptic ribbons of pinealocytes of the Djungarian hamster (Phodopus sungorus)

Summary The ultrastructure of the superficial part of the pineal gland ofPbodopus sungorus was examined. Dense-core vesicles and synaptic ribbons in pinealocytes of animals kept under different photoperiods were counted, revealing marked differences. Pinealocytes of short-day animals compared with long-day animals exhibit an increase of dense-core vesicles coincident with a decrease of synaptic ribbons. It is assumed that the corresponding numerical changes of these organelles are of functional significance in relation to pineal secretory activity.     

Ribeye a-mCherry fusion protein: a novel tool for labeling synaptic ribbons of the hair cell

Synaptic ribbons are presynaptic cytomatrices that are required for efficient transfer of auditory information from hair cells to the central nervous system. In the hair cell, each electron-dense ribbon tethers numerous synaptic vesicles by fine filaments. The ribbon generally resides juxtaposed to the active zone plasma membrane. A dearth of appropriate tools to visualize the ribbon synapse has limited our knowledge of its development. Here we present the design and implementation of a method to visualize synaptic ribbons in hair cells. This scheme uses a tagged version of the protein Ribeye a, which is specific to ribbons. We generate the DNA construct Tg(pvalb3b:ribeye a-mCherry) to transgenically express the fusion protein Ribeye a-mCherry in zebrafish hair cells. The fusion protein localizes to the basolateral surface of the hair cell with a pattern similar to that of a hair cell labeled with an antiserum that recognizes ribeye proteins. Moreover, using this antiserum to label transgenics that express Ribeye a-mCherry, we demonstrate that the fusion protein and antibody-associated fluorescent signals overlap. In addition, ribbons labeled with the fusion protein are proximal to afferent nerve endings. Finally, the fusion protein labels hair-cell ribbons of zebrafish at different developmental time points. These findings indicate that the fusion protein is an effective tool to label ribbons in live and fixed hair cells, which will make it useful in the study of ribbon synapse development and to characterize zebrafish mutants with defects in synapse formation.     

Significance of white matter high intensity lesions as a predictor of stroke from arteriolosclerosis

OBJECTIVES: To determine whether the extent of white matter high intensity lesions (WML) on magnetic resonance imaging (MRI) is an independent predictor of risk for stroke from arteriolosclerosis, and whether serial evaluation of WML can be used to identify patients who are at risk of strokes. METHODS: Prospective follow up with serial MRI scans was done in 89 patients who were either diagnosed as having symptomatic lacunar infarcts or were stroke-free, neurologically normal individuals with headache or dizziness. None had significant stenosis of major cerebral arteries or atrial fibrillation. Multivariable analysis with the Cox proportional hazards model was used to test the predictive value for subsequent stroke of risk factor status at entry and during follow up, lacunar infarction, and the extent of WML (scored from 0 to 16) on the baseline scans. RESULTS: During follow up (mean (SD), 51 (19) months), seven strokes occurred (five lacunar infarcts and two haemorrhages): four in nine patients with severe WML (score 9-16), and three in 40 patients with mild WML (score 1-8) (log-rank test; p < 0.005). None of 40 patients without WML experienced stroke. The extent of WML was an independent predictor of subsequent stroke (relative risk for a 1 point score increase, 1.60; 95% confidence interval, 1.02 to 2.54; p < 0.05). In three strokes among 80 patients without severe WML, two occurred in four patients with an increase in WML score during follow up, and one occurred in the other 76 patients without an increased score (p < 0.0001). CONCLUSIONS: Severe WML at baseline is an independent predictor of risk for stroke from arteriolosclerosis, while progression of WML during follow up may be associated with subsequent stroke in patients with initially mild WML.     

Exercise improves recognition memory and synaptic plasticity in the prefrontal cortex for rats modelling vascular dementia

Objectives: Functional electrical stimulation (FES) may induce involuntary exercise and make beneficial effects on vascular dementia (VD) by strengthening the BDNF-pCREB-mediated pathway and hippocampal plasticity. Whether FES improves recognition memory and synaptic plasticity in the prefrontal cortex (PFC) was investigated by establishing a VD model.

Methods: The VD rats were administered with two weeks of voluntary exercise, forced exercise, or involuntary exercise induced with FES. Sham-operated and control groups were also included. The behavioral changes were assessed with the novel object recognition test and novel object location test. The expression levels of key proteins related to synaptic plasticity in the PFC were also detected.

Results: All types of exercise improved the rats’ novel object recognition index, but only voluntary exercise and involuntary exercise induced with FES improved the novel object location index. Any sort of exercise enhanced the expression of key proteins in the PFC.

Conclusion: Involuntary exercise induced with FES can improve recognition memory in VD better than forced exercise. The mechanism is associated with increased synaptic plasticity in the PFC. FES may be a useful alternative tool for cognitive rehabilitation.     

Postural stability differentiates "lower body" from idiopathic parkinsonism

Introduction - Patients with an akinetic Parkinson syndrome of the lower extremities and a poor response to L-DOPA have been described as "lower body Parkinsonism" (LBP). These patients are characterized by frequent fallings and poor balance. Methods - We have studied body sway with static (force platform) and dynamic (Equitest) posturography in 11 LBP patients, 6 of them revealing deep white matter lesions on MRI and 10 patients with advanced Parkinson's disease (PD) and compared performance with 30 age-matched controls. Results - When standing on a fixed support the postural performance of both patient groups lay within the normal range. The balance of LBP patients worsened in the static testing in the conditions "eyes open on foam" ( p <0.05) and "eyes closed on foam" ( p < 0.0006, of 11 patients falling), whereas the balance of PD patients deteriorated only with "eyes closed on foam" ( p <0.05). Dynamic posturography confirmed these results in 6 different sensory conditions, clearly distinguishing the more unstable LBP patients from PD patients during "standing, eyes closed, foot support sway referenced" ( p < 0.005). Conclusion - We conclude, that postural adjustments in LBP patients are more disturbed than those in PD patients and posturography can be an additional tool for the differential diagnosis of Parkinson syndromes with gait disorders.