Role of Peripheral Vision in Brake Reaction Time During Safety Critical Events

The criticality of a rear end event depends on the brake reaction time (BRT) of the driver. Therefore, distracted driving poses greater threat in such events. Evidence accumulation model (EAM) that uses looming of the lead vehicle as main stimuli has shown significant success in estimating drivers’ BR Ts. It is often argued that drivers collect evidence for braking through peripheral vision, especially during off-road glances, and transition to forward. In this work, we have modeled evidence accumulation as a function of gaze eccentricity for off-road glances while approaching safety critical events. The model is tested with real world crash and near crash event data from SHRP2 naturalistic study. Our model shows that linear relation between gaze eccentricity and evidence accumulation rate during off road glances helps to improve EAM estimation in predicting BRT. We have also shown that brake-light onset does not influence EAM in presence of active looming.

0224 Optogenetic Manipulation of Basal Forebrain Parvalbumin Neurons Modulates Vigilant Attention and Rescues Sleep Deprivation Induced Impairments

Introduction Sleep disruption leads to attention impairments, excessive daytime sleepiness, and is a major contributor to accident rates and decreased workplace productivity. The basal forebrain (BF) region has long been associated with promoting cortical arousal and wakefulness. Recently, selective excitation of BF parvalbumin (PV) GABAergic neurons has been shown to produce high frequency cortical activation and brief periods of wakefulness. Here we test the hypothesis that BF PV neurons are involved in vigilant attention using bidirectional optogenetic manipulations in a signaled reaction time task. Methods Brief optogenetic excitation (ChR2) and inhibition (ArchT) of BF PV neurons was applied during a lever release version of the rodent psychomotor vigilance task (rPVT). Mice were trained to hold a lever down to initiate a trial and after a random delay, a 200ms cue light signaled the mouse to quickly release the lever within 1s to receive a sucrose pellet reward. The reaction time between cue light onset and lever release was the primary measure of attentional performance. Sleep deprivation (8h) produced by gentle handling was also investigated. Laser parameters: brief (1s) of continuous (non-pulsatile) laser stimulation was delivered beginning 500ms prior to cue light onset (5mW 473nm blue light for ChR2-mediated excitation; 10mW 530nm green light for ArchT-mediated inhibition). Results BF PV excitation led to faster reactions times (N=6, 14% faster, p<.001), interpreted as an enhancement of attention. Sleep deprivation slowed reaction times (20% slower, p<.01) and BF PV excitation rescued the sleep deprivation induced impairments. BF PV inhibition significantly slowed reaction times (25% slower, p<.02), an effect that resembled the effects of sleep deprivation. Conclusion This is the first demonstration of a role for BF PV neurons in attention and in the attention deficits produced by sleep deprivation. Support T32 HL007901, I01 BX002774, P01 HL095491, R01 MH039683, I01 BX004500, IK2 BX002130, Stonehill College SURE program, I01 BX001356

Conceptual models of entrainment, jet-lag, and seasonality

ABSTRACTUnderstanding entrainment of circadian rhythms is a central goal of chronobiology. Many factors, such as period, amplitude, Zeitgeber strength, and day-length, govern entrainment ranges and the phase of entrainment. Using global optimization, we derive conceptual models with just three free parameters (period, amplitude, relaxation rate) that reproduce known phenotypic features of vertebrate clocks: relatively small phase response curves (PRCs), fast re-entrainment after jet-lag, and seasonal variability to track light onset or offset. Since optimization found multiple sets of model parameters, we can study this model ensemble to gain insight into the underlying design principles. We find that amplitudes control the size of PRCs, that fast relaxation supports short jet-lag, and that specific periods allow reasonable seasonal phase shifts. Arnold onions of representative models visualize strong dependencies of entrainment on periods, relative Zeitgeber strength, and photoperiod.

Peroxisome turnover and diurnal modulation of antioxidant activity in retinal pigment epithelia utilizes microtubule-associated protein 1 light chain 3B (LC3B)

The retinal pigment epithelium (RPE) supports the outer retina through essential roles in the retinoid cycle, nutrient supply, ion exchange, and waste removal. Each day the RPE removes the oldest ~10% of photoreceptor outer segment (OS) disk membranes through phagocytic uptake, which peaks following light onset. Impaired degradation of phagocytosed OS material by the RPE can lead to toxic accumulation of lipids, oxidative tissue damage, inflammation, and cell death. OSs are rich in very long chain fatty acids, which are preferentially catabolized in peroxisomes. Despite the importance of lipid degradation in RPE function, the regulation of peroxisome number and activity relative to diurnal OS ingestion is relatively unexplored. Using immunohistochemistry, immunoblot analysis, and catalase activity assays, we investigated peroxisome abundance and activity at 6 AM, 7 AM (light onset), 8 AM, and 3 PM, in wild-type (WT) mice and mice lacking microtubule-associated protein 1 light chain 3B ( Lc3b), which have impaired phagosome degradation. We found that catalase activity, but not the amount of catalase protein, is 50% higher in the morning compared with 3 PM, in RPE of WT, but not Lc3b−/−, mice. Surprisingly, we found that peroxisome abundance was stable during the day in RPE of WT mice; however, numbers were elevated overall in Lc3b−/− mice, implicating LC3B in autophagic organelle turnover in RPE. Our data suggest that RPE peroxisome function is regulated in coordination with phagocytosis, possibly through direct enzyme regulation, and may serve to prepare RPE peroxisomes for daily surges in ingested lipid-rich OS.

Peroxisome turnover and diurnal modulation of antioxidant activity in retinal pigment epithelia utilizes microtubule-associated protein 1 light chain 3B

The retinal pigment epithelium (RPE) supports the outer retina through essential roles in the retinoid the visual cycle, nutrient supply, ion exchange and waste removal. Each day the RPE removes the oldest ∼10% of photoreceptor outer segments through phagocytic uptake, which peaks in a synchronous burst following light onset. Impaired degradation of phagocytosed OS material by the RPE can lead to toxic accumulation of lipids, oxidative tissue damage, inflammation and cell death. OSs are rich in very long chain fatty acids which are preferentially catabolized in peroxisomes. Despite the importance of lipid degradation in RPE function, the regulation of peroxisome number and activity relative to diurnal OS ingestion is relatively unexplored. Using immunohistochemistry, immunoblotting and catalase activity assays, we investigated peroxisome abundance and activity at 6 am, 7 am (at lights on), 8 am, and 3 pm, in WT mice and mice lacking microtubule-associated protein 1 light chain 3B (LC3B), that have impaired degradation of phagosomes. We found that catalase activity, but not protein expression, is 50% higher in the morning compared with 3 pm, in RPE of WT but not LC3B-/- mice. Surprisingly, we found that peroxisome abundance was stable during the day, however numbers are elevated overall in LC3B-/- mice, implicating LC3B in autophagic organelle turnover in RPE. Our data suggest that RPE peroxisome function is regulated in coordination with phagocytosis, possibly through direct enzyme regulation, and may serve to prepare RPE peroxisomes for daily surges in ingested lipid-rich OS.

Circadian protein regulation in the green lineage I. A phospho-dawn anticipates light onset before proteins peak in daytime

Daily light-dark cycles (LD) drive dynamic regulation of plant and algal transcriptomesviaphotoreceptor pathways and 24-hour, circadian rhythms. Diel regulation of protein levels and modifications has been less studied.Ostreococcus tauri, the smallest free-living eukaryote, provides a minimal model proteome for the green lineage. Here, we compare transcriptome data under LD to the algal proteome and phosphoproteome, assayed using shotgun mass-spectrometry. Under 10% of 855 quantified proteins were rhythmic but two-thirds of 860 phosphoproteins showed rhythmic modification(s). Most rhythmic proteins peaked in the daytime. Model simulations showed that light-stimulated protein synthesis largely accounts for this distribution of protein peaks. Prompted by apparently dark-stable proteins, we sampled during prolonged dark adaptation, where stable RNAs and very limited change to the proteome suggested a quiescent, cellular “dark state”. In LD, acid-directed and proline-directed protein phosphorylation sites were regulated in antiphase. Strikingly, 39% of rhythmic phospho-sites reached peak levels just before dawn. This anticipatory phosphorylation is distinct from light-responsive translation but consistent with plant phosphoprotein profiles, suggesting that a clock-regulated phospho-dawn prepares green cells for daytime functions.

Pregnancy associated plasma protein-aa (Pappaa) regulates photoreceptor synaptic development to mediate visually guided behavior

To guide behavior, sensory systems detect the onset and offset of stimuli and process these distinct inputs via parallel pathways. In the retina, this strategy is implemented by splitting neural signals for light onset and offset via synapses connecting photoreceptors to ON and OFF bipolar cells, respectively. It remains poorly understood which molecular cues establish the architecture of this synaptic configuration to split light onset and offset signals. A mutant with reduced synapses between photoreceptors and one bipolar cell type, but not the other, could reveal a critical cue. From this approach, we report a novel synaptic role pregnancy associated plasma protein aa (pappaa) in promoting the structure and function of cone synapses that transmit light offset information. Electrophysiological and behavioral analyses indicated pappaa mutant zebrafish have dysfunctional cone to OFF bipolar cell synapses and impaired responses to light offset, but intact cone to ON bipolar cell synapses and light onset responses. Ultrastructural analyses of pappaa mutant cones showed a lack of presynaptic domains at synapses with OFF bipolar cells. pappaa is expressed postsynaptically to the cones during retinal synaptogenesis and encodes a secreted metalloprotease known to stimulate insulin-like growth factor 1 (IGF1) signaling. Induction of dominant negative IGF1 receptor expression during synaptogenesis reduced light offset responses. Conversely, stimulating IGF1 signaling at this time improved pappaa mutants’ light offset responses and cone presynaptic structures. Together, our results indicate Pappaa-regulated IGF1 signaling as a novel pathway that establishes how cone synapses convey light offset signals to guide behavior.Significance StatementDistinct sensory inputs, like stimulus onset and offset, are often split at distinct synapses into parallel circuits for processing. In the retina, photoreceptors and ON and OFF bipolar cells form discrete synapses to split neural signals coding light onset and offset, respectively. The molecular cues that establish this synaptic configuration to specifically convey light onset or offset remain unclear. Our work reveals a novel cue: pregnancy associated plasma protein aa (pappaa), which regulates photoreceptor synaptic structure and function to specifically transmit light offset information. Pappaa is a metalloprotease that stimulates local insulin-like growth factor 1 (IGF1) signaling. IGF1 promotes various aspects of synaptic development and function and is broadly expressed; thus requiring local regulators, like Pappaa, to govern its specificity.

Faster than the brain’s speed of light: Retinocortical interactions differ in high frequency activity when processing darks and lights

Visual processing of dark visual stimuli has been hypothesized to occur faster relative to bright stimuli. We investigated the timing, processing, and propagation of neural activity in response to darks and lights, operationalized as light offset and onset, in the human visual system by recording electroretinography (ERG) simultaneously with magnetoencephalography (MEG) in humans. We discovered that dark onset resulted in 75–95 Hz retinal activity that we call the dark retinal oscillatory potential, occurring with the same latency as the analogous but more broadband (55–195 Hz) oscillatory potential at light onset. Both retinal oscillations coupled with subsequent cortical activity of corresponding bandwidths, but cortical responses for darks indeed occurred earlier than for lights. Darks therefore propagate from retina to cortex more quickly than lights, potentially resulting from a thalamic advantage. Furthermore, we found that this propagation is effectuated by high frequency retinocortical coupling of narrow bandwidth for darks but wide bandwidth for lights.

Dosing-Time Dependent Effects of Sodium Nitroprusside on Cerebral, Renal, and Hepatic Catalase Activity in Mice

To investigate the time dependence of sodium nitroprusside- (NPS-) induced oxidative effects, the authors study the variation of the antioxidant enzyme CAT activity in various tissues after the administration of a single 2.5 mg/kg dose of SNP or sodium chloride (NaCl 0.9%). For each of the two dosing times (1 and 13 hours after light onset, HALO, which correspond to the beginning of diurnal rest span and of nocturnal activity span of mice, resp.), brain, kidney, and liver tissues were excised from animals at 0, 1, 3, 6, 9, 12, 24, and 36 h following the drug administration and CAT activity was assayed. The results suggest that SNP-induced stimulation of CAT activity is greater in all three tissues when the drug is administered at 1 HALO than at 13 HALO. Two-way ANOVA revealed that CAT activity significantly (P<0.004) varied as a function of the sampling time but not of the treatment in all three tissues. Moreover, a statistically significant (P<0.004) interaction between the organ sampling-time and the SNP treatment was revealed in kidney regardless of the dosing time, whereas a highly significant (P<0.0002) interaction was validated in liver only in animals injected at 13 HALO.

Inhibitory inputs tune the light response properties of dopaminergic amacrine cells in mouse retina

Dopamine (DA) is a neuromodulator that in the retina adjusts the circuitry for visual processing in dim and bright light conditions. It is synthesized and released from retinal interneurons called dopaminergic amacrine cells (DACs), whose basic physiology is not yet been fully characterized. To investigate their cellular and input properties as well as light responses, DACs were targeted for whole cell recording in isolated retina using two-photon fluorescence microscopy in a mouse line where the dopamine receptor 2 promoter drives green fluorescent protein (GFP) expression. Differences in membrane properties gave rise to cell-to-cell variation in the pattern of resting spontaneous spike activity ranging from silent to rhythmic to periodic burst discharge. All recorded DACs were light sensitive and generated responses that varied with intensity. The threshold response to light onset was a hyperpolarizing potential change initiated by rod photoreceptors that was blocked by strychnine, indicating a glycinergic amacrine input onto DACs at light onset. With increasing light intensity, the ON response acquired an excitatory component that grew to dominate the response to the strongest stimuli. Responses to bright light (photopic) stimuli also included an inhibitory OFF response mediated by GABAergic amacrine cells driven by the cone OFF pathway. DACs expressed GABA (GABAAα1 and GABAAα3) and glycine (α2) receptor clusters on soma, axon, and dendrites consistent with the light response being shaped by dual inhibitory inputs that may serve to tune spike discharge for optimal DA release.