Altered pupil light and darkness reflex and eye-blink responses in late-life depression.

BACKGROUND: Late-life depression (LLD) is a prevalent neuropsychiatric disorder in the older population. While LLD exhibits high mortality rates, depressive symptoms in older adults are often masked by physical health conditions. In younger adults, depression is associated with deficits in pupil light reflex and eye blink rate, suggesting the potential use of these responses as biomarkers for LLD. METHODS: We conducted a study using video-based eye-tracking to investigate pupil and blink responses in LLD patients (n = 25), older (OLD) healthy controls (n = 29), and younger (YOUNG) healthy controls (n = 25). The aim was to determine whether there were alterations in pupil and blink responses in LLD compared to both OLD and YOUNG groups. RESULTS: LLD patients displayed significantly higher blink rates and dampened pupil constriction responses compared to OLD and YOUNG controls. While tonic pupil size in YOUNG differed from that of OLD, LLD patients did not exhibit a significant difference compared to OLD and YOUNG controls. GDS-15 scores in older adults correlated with light and darkness reflex response variability and blink rates. PHQ-15 scores showed a correlation with blink rates, while MoCA scores correlated with tonic pupil sizes. CONCLUSIONS: The findings demonstrate that LLD patients display altered pupil and blink behavior compared to OLD and YOUNG controls. These altered responses correlated differently with the severity of depressive, somatic, and cognitive symptoms, indicating their potential as objective biomarkers for LLD.

Investigating Arousal, Saccade Preparation, and Global Luminance Effects on Microsaccade Behavior.

Microsaccades, small saccadic eye movements occurring during fixation, have been suggested to be modulated by various sensory, cognitive, and affective processes relating to arousal. Although the modulation of fatigue-related arousal on microsaccade behavior has previously been characterized, the influence of other aspects of arousal, such as emotional arousal, is less understood. Moreover, microsaccades are modulated by cognitive processes (e.g., voluntary saccade preparation) that could also be linked to arousal. To investigate the influence of emotional arousal, saccade preparation, and global luminance levels on microsaccade behavior, emotional auditory stimuli were presented prior to the onset of a fixation cue whose color indicated to look either at the peripheral stimulus (pro-saccade) or in the opposite direction of the stimulus (anti-saccade). Microsaccade behavior was found to be significantly modulated by saccade preparation and global luminance level, but not emotional arousal. In the pro- and anti-saccade task, microsaccade rate was lower during anti-saccade preparation as compared to pro-saccade preparation, though microsaccade dynamics were comparable during both trial types. Our results reveal a differential role of arousal linked to emotion, fatigue, saccade preparation, and global luminance level on microsaccade behavior.

Daily Onset of Light and Darkness Differentially Controls Hematopoietic Stem Cell Differentiation and Maintenance.

Hematopoietic stem and progenitor cells (HSPCs) tightly couple maintenance of the bone marrow (BM) reservoir, including undifferentiated long-term repopulating hematopoietic stem cells (LT-HSCs), with intensive daily production of mature leukocytes and blood replenishment. We found two daily peaks of BM HSPC activity that are initiated by onset of light and darkness providing this coupling. Both peaks follow transient elevation of BM norepinephrine and TNF secretion, which temporarily increase HSPC reactive oxygen species (ROS) levels. Light-induced norepinephrine and TNF secretion augments HSPC differentiation and increases vascular permeability to replenish the blood. In contrast, darkness-induced TNF increases melatonin secretion to drive renewal of HSPCs and LT-HSC potential through modulating surface CD150 and c-Kit expression, increasing COX-2/αSMA+ macrophages, diminishing vascular permeability, and reducing HSPC ROS levels. These findings reveal that light- and darkness-induced daily bursts of norepinephrine, TNF, and melatonin within the BM are essential for synchronized mature blood cell production and HSPC pool repopulation.

Modification of the Fe protein of the nitrogenase of Gloeothece (Nägeli) sp. ATCC 27152 during growth under alternating light and darkness.

The Fe protein of the nitrogenase of the unicellular Cyanobacterium Gloeothece (Nägeli) sp. ATCC 27152 can be resolved by SDS-PAGE into two antigenically detectable components of approximate Mr 38500 and 40000 respectively. The larger form of this protein may be produced by modification of the smaller form. Modification of the Fe protein is promoted under conditions where O2 (but not O2 - or H2 O2 ) has increased access to the enzyme, but does not allow nitrogenase to function under conditions of O2 stress. During growth of Gloeothece under alternating light and darkness, antigenically detectable Fe protein is absent throughout most of the light period. The restriction of nitrogenase activity to the period of darkness is better explained in terms of regulation of nitrogenase synthesis and degradation than by reversible modification of a constant intracellular concentration of Fe protein. However, newly synthesized Fe protein always appeared initially as its larger form, which may be catalytically inactive in aerobic cultures of Gloeothece. Conversion of this form to the smaller, assumed active, form of the Fe protein may be an additional factor in explaining the increase in nitrogenase activity that occurs during the first few hours of each dark phase.