Pineal Gland
Paul V. Malven in Mammalian Neuroendocrinology, 2019
Internal perception of the duration of an ambient photoperiod does not depend upon the total duration of light per day, but rather on when the light occurs during the day and how that light entrains the endogenous circadian rhythm (Elliott and Goldman, 1981). As illustrated in Figure 10-5, a second brief (1 sec) pulse of light occurring 14 h after a previous brief pulse (that was apparently perceived as dawn in the circadian oscillator) could entrain the circadian profile of locomotion, and it also retarded the darkness-induced atrophy of testes in some animals (Earnest and Turek, 1983). A similar brief pulse of light occurring 8 h after the end of a once-daily 6-h period of light completely prevented testicular atrophy suggesting that the light of 6 h duration together with an additional 1-sec pulse at 14 h after the perceived dawn could maintain testes as well as a full 14 h of daily light (Earnest and Turek, 1983).
Environmental Modulation of Neuroendocrine Function
George H. Gass, Harold M. Kaplan in Handbook of Endocrinology, 2020
It has been shown that a skeleton photoperiod consisting of brief pulses of light given during the proper time of the circadian rhythm of photoresponsivity can maintain reproductive activity.84 Thus, a period of several hours of light (which is usually interpreted by the animal as a short day and leads to gonadal regression) followed several hours later by a brief pulse of light appears to be interpreted by the animal as a long day in that it maintains gonadal activity. Detailed studies of the various skeleton photoperiods, the diurnal patterns of animals’ locomotor activity, and the endocrine responses indicate that the animals are sensitive to light some 14 h after the natural or artificial sunrise, and their gonadal function can be maintained or activated by as little as 1 min of light exposure during this period of sensitivity, even if they experienced darkness in the intervening hours.203 This observation may explain how day length actually affects neuroendocrine function in this supposedly nocturnally active animal that spends most of its daylight hours in deep underground burrows.
A Review of the Problem of Alcoholism in Siberia
Bernard Segal, Caesar Korolenko in Addictive Disorders in Arctic Climates, 2014
The influence of continental and extracontinental climates are combined with considerable oscillations of atmospheric pressure, and in the far north the situation is aggravated by unusual photoperiodicity (periods of polar nights and days). Climatic conditions are also significantly affected by industrial and municipal pollution. These climatic factors, when linked with the psychological aspects of living in extreme conditions (e.g., the impact on sensory processes and different forms of hyperstimulation), together with an increase in lifespan, all contribute to create high levels of stress.
Early menarche in visually impaired girls: evidence and hypothesis of light-dark cycle disruption and blindness effect on puberty onset
Published in Chronobiology International, 2022
Jorge A. Barrero, Ismena Mockus
Photoperiodicity integrates a physiological response to changes in the regular pattern of the light-dark cycle. Therefore it is understood as an important evolutionary mechanism that has allowed mammals to adapt to the variations in day and night length during different seasons of the year (Oster et al. 2002). Still, evidence for photoperiodic behavior in humans is inconclusive; it has been observed that the reproductive patterning could be affected by daylight exposure (Bronson 2004), yet this photosensitive regulation appears to have attenuated over time (Wehr 2001). Photoperiodism conveys information from the light-dark cycle and photic influx via neuroendocrine signals that converge on melatonin secretion in the pineal gland (Arendt and Middleton 2018; Gorman 2020). The photoperiodic modulation of the HPG axis has been largely attributed to this neurohormone (Bellastella et al. 2014), and while melatonin has shown to be a potential neuromodulator involved in various aspects of female reproduction, its effect on puberty timing remains somewhat unclear (Boafo et al. 2019; Olcese 2020).
Biological variables influencing the estimation of reference limits
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 2018
Mustafa K. Özçürümez, Rainer Haeckel
Table 2 of the supplement gives a representative overview of further measurands with reported seasonal effects on within-subject variation. These differences partly resemble the annual cycle of day and night length. Annual photoperiodicity is one of the strongest seasonal synchronizers and subsumes timing, duration, intensity and spectral composition of light exposure as well as the contrast between daily light intensities and dark periods [98]. Pineal gland triggered mediators modulate primordial biological processes that determine seasonal variations of biochemical functions as well as behavioural patterns [99]. The majority of these processes is driven by the hypothalamic-pituitary-adrenal axis and controls basic body functions such as stress and immune response, digestion, mood and emotions, sexuality, and energy balance. Thus, all measurands coupled to these processes may potentially be influenced by photoperiodicity.
Daytime and season do not affect reinforcement learning capacity in a response time adjustment task
Published in Chronobiology International, 2021
Sina Kohne, Luise Reimers, Malika Müller, Esther K. Diekhof
Meyer et al. (2016) investigated seasonal influences on performance in a working memory and sustained attention task in healthy young adults and could not detect measurable behavioral effects, just as we could not find any relation between season and behavior. However, Meyer and colleagues could demonstrate neurophysiological changes with season. Working memory provoked a maximum response (inter alia in thalamus, prefrontal and frontopolar areas) around autumn and a minimum around spring. For the attention task, the greatest activity (inter alia in the thalamus, amygdala, frontal areas and hippocampus) was found around summer and it was reduced during the winter. Furthermore, neural activity in this task was closely related to photoperiodicity (Meyer et al. 2016). In addition to that, an impairment of the hippocampal long-term potentiation, learning and memory during simulated short days compared to long days was observed in male white-footed mice (Walton et al. 2011). This indicated that the impairment was mediated by photoperiod and the diminishing impact of melatonin on long-term potentiation and cognition (Walton et al. 2011). It may be assumed that season and probably photoperiod might have an influence on neurophysiological processing of various cognitive operations, which may not necessarily be measurable in behavior.
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