Correction: Maternal exposure to dim light at night induces behavioral alterations in the adolescent and adult offspring Wistar rat

Access to electric light has exposed living organisms to varying intensities of light throughout the 24h day. Dim light at night (DLAN) is an inappropriate signal for the biological clock, which is responsible for the circadian organization of physiology.During the gestational period, physiological adaptations occur to ensure a successful pregnancy and optimal fetal development. Environmental maternal conditions, such as disruptions of maternal circadian rhythms, could negatively affect offspring health.We have previously demonstrated that exposure of female Wistar rats to DLAN results in circadian, metabolic, and behavioral alterations. A relevant behavior during adolescence is social play, primarily regulated by the nucleus accumbens (NAc) which is crucial for the proper performance of important behaviors in adulthood.Throughout development, microglia are responsible for the remodeling of diverse brain regions via synaptic pruning. During adolescence, this process occurs within the NAc, where immune-mediated remodeling directly impacts social play behavior.This study investigated the effects of maternal exposure to DLAN or a light-dark cycle (LD) before (5 weeks) and during the gestational period (21-23 days) on the metabolism and behavior of offspring in adolescence and adulthood. Body mass was measured every 5 days from postnatal day 1 (PN1) to PN25 and every 10 days from PN40 to PN90; food consumption was monitored weekly from PN40 to PN90. Social play behavior was evaluated at PN40. The quantification and morphology of microglia in the NAc were measured on PN30. An open field test was conducted at PN60, and anhedonia test was assessed at PN90. Male and female offspring from mothers exposed to DLAN showed increased body mass gain at PN25. DLAN male offspring had lower food consumption, while DLAN females exhibited increased food consumption. In social play behavior, no differences were found between DLAN and LD female offspring. In contrast, DLAN male offspring exhibited a significant decrease in social play behavior compared to LD animals, which was associated with higher numbers of microglia in the NAc that had more ramified morphology. Importantly, at PN90, DLAN offspring presented increased anxiety-like behaviors.These results demonstrate that DLAN exposure induces intergenerational behavioral alterations that persist until adulthood.The circadian system regulates the temporality of physiological and behavioral functions enabling organisms to anticipate and adapt to the changing conditions of the environment (Pilorz et al., 2018). The alternation of the light-dark cycle is the main time cue that synchronizes the mammalian circadian system to the external 24h day (Vetter, 2020). It is estimated that more than 80% of the population worldwide is exposed to nocturnal light (Falchi et al., 2016), which is considered by the World Health Organization as a social determinant of health, that is, a "non-medical factor that influences health outcomes" (WHO, 2022). This abnormal exposure to light during the night affects the organization of circadian rhythms and increase the risk of developing metabolic and emotional disorders like anxiety and depression (Navara and Nelson, 2007).In our everyday environments, we are exposed to various types of artificial light at night each produced by different sources and varying in intensity. Street lamps, light bulbs, illuminated billboards, and windows of commercial buildings emit light that can enter through household windows (Chepesiuk, 2009), becoming a constant source of dim light at night (DLAN). Despite its low intensity (5-30 lux) (Walbeek et al., 2021), exposure to DLAN is associated with sleep disturbances in humans (Cho et al., 2016) and with disruption of the daily sleep-wake cycle (Stenvers et al., 2016), metabolic alterations (Borniger et al., 2014, Fonken et al., 2013), spatial memory impairments (Liu et al., 2022), and depressive and anxious-like behaviors in rodents (Cissé et al., 2016, Fonken andNelson, 2013). We have previously demonstrated that exposing female Wistar rats to DLAN (5-7 lx) for 5 weeks induce the loss of activity and body temperature rhythms, metabolic alterations, low melatonin levels and irregular estrous cycles (Gutiérrez-Pérez et al., 2023), suggesting that DLAN exposure could have an impact on the reproductive and gestational capacity of female rats.During the gestational period, physiological, endocrine, and immunological adaptations occur to ensure a successful pregnancy and optimal fetal development (Chang and Streitman, 2012). Environmental conditions experienced by the mother during gestation significantly impact the developing fetus (Muglia et al., 2022) increasing its vulnerability to chronic diseases later in life (Barker, 2007). This concept is referred to as the developmental origins of health and disease (DOHaD) (Gluckman et al., 2010). Maternal circadian disruption caused by exposure to light at night or changes in the photoperiod, that occur during pregnancy, negatively affects offspring health (Mendez et al., 2016) through mechanisms that have not been determined. However, recent evidence support the role of epigenetic modifications, oxidative stress, melatonin and corticosterone programming (Hsu and Tain, 2020). In primates, constant bright light conditions during the gestational period impair the body temperature rhythms of the offspring (Serón-Ferré et al., 2013). In rodent models, circadian disruption during pregnancy induces a great variety of physiological and behavioral alterations such as: increased body mass, increased adiposity, enhanced response to intraperitoneal glucose (Halabi et al., 2021), cardiac hypertropia (Galdames et al., 2014), disrupted daily plasma melatonin (Mendez et al., 2016) and metabolic rhythms (Dzirbíková et al., 2022), as well as the development of anxiety-like behaviors (Borniger et al., 2014).The development of behavioral disorders in the offspring can lead to depression and anxiety during adulthood (Borniger et al., 2014) which have been associated with alterations in synaptic plasticity processes that take place during critical developmental periods (Marsden, 2013).In rats, an important behavior during adolescence is social play behavior, which is characterized by a series of standardized motor patterns resembling functional behaviors observed in later stages of development, such as sexual behavior, predation, and aggressive peer interactions (Pellis and Pellis, 2017, Panksepp, 1981, Thor and Holloway, 1984). Social interactions during play behavior are critical for social and cognitive development in adulthood (Pellis et al., 2022). In males, but not in females, it has been identified that the dopaminergic pathway in the nucleus accumbens (NAc) that plays an important role in the expression of play behavior is refined through synaptic pruning, mediated by microglial phagocytosis of dopamine 1 receptor (D1r) mainly at PN30. Preventing microglial phagocytosis alters the expression of social play behavior suggesting that the remodeling exerted by microglia during adolescence is crucial for the proper development of social play behavior (Kopec et al., 2018).This study aims to contribute to the DOHaD framework by investigating the intergenerational effects of maternal circadian disruption, due to DLAN exposure on metabolism and behavior of the offspring during adolescence and adulthood. In addition, the expression of the microglial marker IBA-1 was evaluated in the NAc of the adolescent male offspring. Finally, we also analyzed the long-term behavioral effects of maternal DLAN exposure by evaluating anxiety and depressive-like behavior in the adult offspring.Adult female Wistar rats (n=35), weighing 200 to 220g (7-8 weeks old) and male Wistar rats (n=10; 300-350g, 10-12 weeks old), were obtained from the Unidad Académica Bioterio of the Facultad de Medicina, Universidad Nacional Autónoma de México (UNAM). Animals were individually accommodated in transparent acrylic cages measuring 40 cm × 50 cm × 20 cm, positioned atop tilt sensors. The cages were placed within soundproof, well-ventilated activity monitoring system, that can house up to 8 cages each with controlled ambient temperature (22 ± 1 °C), consistent airflow, and controlled illumination conditions of 12:12h light-dark cycle (LD;12h,0lx) where lights on were set at 7:30 h, defined as Zeitgeber time 0 (ZT0), while lights off were set as 19:30 h, defined as Zeitgeber time 12 (ZT12). All rats were left unmanipulated for 7 days for habituation. Nutritional needs were met through ad libitum access to Rodent laboratory chow (Purina 5001, Purina, Minnetonka, MN, USA) and fresh water. All rats remained inside the monitoring system for the entire protocol and only illumination patterns were modified as will be described in the next section.Experiments were approved by the committee for research and ethical evaluation at the Facultad de Medicina, UNAM (FM/DI/070/2023). The use of animals was approved by the "Comité Interno para el Cuidado y Uso de los Animales de Laboratorio" from the Facultad de Medicina, UNAM (023-CIC-2023) and in strict accordance with the Mexican norms for animal handling Norma Oficial Mexicana NOM-062-ZOO-1999, which conforms to international guidelines for animal handling. All efforts were made to minimize the of animals and the rats were in cages in the activity monitoring system and left for 7 days in LD Male rats were only for reproductive and were in LD rats were to of light-dark cycle mothers 0 lx) or exposure at night mothers was light and temperature were measured within each a rats remained in the previously for 5 the of rats from each were with 1 male at a of for for 1 The for each was during this pregnancy and throughout the gestational period (21-23 was by the of in the daily during the day in which were identified was defined as gestational day in the were from the in LD male and female from mothers in LD conditions throughout the entire DLAN male and female from mothers exposed to dim light at night before (5 and during and during pregnancy period (21-23 in postnatal day 0 the mothers and of were placed LD the offspring were and were to 10 (5 and 5 each of LD or DLAN animals from at different The were on and with We series of in each series 5 and 5 were maternal behavior was evaluated in the mothers of series on gain food and social play behavior measured in female and male offspring of the series of male and female LD and DLAN offspring the LD and DLAN male offspring were at for brain and to the of IBA-1 and microglial morphology in the The of the animals were evaluated as on depressive and anxiety-like behaviors were on a glucose test was from the estrous cycle of the female offspring was and a test was on in and females behavior was evaluated on at due to the higher of this behavior at this time of the day et al., The test was in a The mothers were in a acrylic from offspring for et al., the offspring were individually placed and inside the the mother was the for 5 During this interactions were with a The were by the of the the mother the offspring in to from within the to the mother offspring by of maternal the time it for the maternal behavior to mass was monitored every 5 days from to PN25 in and females and every 10 days from PN40 to in and females were not disrupted for body mass measuring during the social play behavior from Body mass gain was by the body mass from the body to each was individually to and the monitoring of while were with were at the time of the day on 24h food was monitored every 10 days from PN40 to in and females 50 of chow food was measured and placed in each at 12 later the food was measured and with and this 12 were in the a was as described in (Gutiérrez-Pérez et al., of a was obtained from the at in and females and an intraperitoneal of of in was glucose were from and levels were with a glucose USA) and glucose the of the estrous was conducted as described in (Gutiérrez-Pérez et al., a was daily at a period of days from to of were the was with and observed at the The estrous cycle was by the in each as previously et al., et al., cycles from to 5 days estrous 1 1 day and days) and have the test was at PN40 in and females a developmental to (Kopec et al., which is by a of behavior The test was conducted between and a period of increased play behavior activity The was illuminated with a light lx) in a was for 24h to the test to play 5 rats of the and different from different were placed in a and a 5 was with a to the social play or in a or on the of rats each and with of behaviors was during the 5 play behavior was as the of previously behaviors were by was in male and female offspring at between and an acrylic cm cm The was illuminated with a light the each was placed in the of the open field and the activity was with a for 5 each the open field was with a the behaviors as of anxiety-like behavior were and of to the were by the of depressive-like behaviors in the adulthood LD and DLAN male offspring and female offspring were exposed for night before the to a 5 of for 24h to to the during the The night before the test rats were of for the at were placed in cages for with 50 of the with 50 of water. We measured the of and in The for was as an of of will to as it is and an not this et al., the of the rats were access to the male offspring of the series of mothers were by an of the animals were and before cardiac we the of for 5 by 5 of in The were and in for and in in and at until were obtained by a The and of the and to were identified to the of the brain in for the postnatal period et al., were at until the and NAc animal were with for 10 to the a with the were at temperature with constant with the to IBA-1 The next the were with and for with a this were with and placed on the were for 5 with and with of of the and of the left from of each animal were obtained with a at and were for IBA-1 the et al., the of IBA-1 were et al., 2012). the was to as a and a was between the IBA-1 and by the we only the IBA-1 in the NAc and process in the NAc were by the to of between microglial and each We evaluated NAc of animals from each where microglial were from the left and NAc and from the The were of the IBA-1 through the a was set until the were was and the from et al., 2014) was to the of microglial each the of the to a for each were to the for each animal as previously by (Liu et al., were presented as the of the were for the Maternal behaviors and social play behaviors and from the were evaluated a The to maternal behaviors and the of to IBA-1 were evaluated with a test was for of of females with or irregular estrous gain and food were analyzed with a for postnatal days (Cissé et al., 2020). The was analyzed with a for time glucose or were analyzed with a for or from All the were by a was defined as All were analyzed and maternal DLAN affects metabolic in the offspring we evaluated body mass gain and food consumption at different before and DLAN male and female offspring exhibited body mass as compared to LD offspring body mass gain was observed in DLAN male and female offspring only at compared to LD offspring and The a significant between postnatal days and PN40 to and females from gain addition, we observed that male DLAN offspring food consumption at as compared to LD rats The a significant between postnatal days and female DLAN offspring exhibited increased food consumption as compared LD females, and this was observed from PN40 until The a significant between postnatal days and also a glucose test for LD and DLAN male and female offspring. were no significant differences in the glucose levels between male and female maternal DLAN exposure alters female offspring estrous we evaluated from We observed that DLAN and LD offspring exhibited estrous cycles with no significant differences in the of irregular rats between maternal DLAN exposure alters offspring behavior during adolescence, we evaluated the social play behavior in the LD and DLAN male and female offspring at PN40. Male DLAN offspring not differences in behavior as compared to male LD offspring In contrast, a significant decrease in and behaviors as well as in the play behaviors were observed in male DLAN offspring as compared to male LD the female offspring were no differences between LD and DLAN animals in and behaviors NAc of male offspring of mothers exposed to DLAN more male rats, during adolescence microglia are responsible for the of the dopamine (D1r) in the NAc, which is an important for the development of social play behavior that is not observed in female rats (Kopec et al., 2018). this and we not significant differences in social play behaviors presented by LD DLAN female rats, we only analyzed the of the male offspring. We observed a significant increase in the of IBA-1 in the NAc and NAc of the DLAN offspring as compared to the LD the IBA-1 of the entire NAc an increased of in the of DLAN offspring as compared to the LD IBA-1 of the DLAN offspring presented a morphology that changes in et al., we analyzed microglial in the NAc of LD and DLAN animals The results from the of microglial between IBA-1 of the NAc of LD and DLAN In contrast, in the NAc microglia of the DLAN offspring showed an increased of at from the of body as compared to the LD In the entire NAc IBA-1 of the DLAN offspring also showed increased of at from the of body as compared to the LD The a significant between or from body for the and the entire NAc the of microglia were significantly increased in the DLAN as compared to the LD male LD male offspring. were no differences in the of between LD and DLAN male offspring During the anhedonia we observed no significant differences in the between LD and DLAN animals the female offspring of the DLAN mothers a of as compared to the LD offspring but were no significant differences in the through the or in behaviors between no significant differences were in the between LD and DLAN offspring maternal can impact on behavioral development of the offspring and 2016), we evaluated the of and the offspring and the to maternal behavior in and We observed that DLAN exposure not maternal behavior and presented the of and the to the maternal behaviors was in the and study that maternal exposure to DLAN has intergenerational effects that in to the offspring with behavioral that can be until adulthood in and offspring presented intergenerational effects from maternal DLAN exposure as we not differences in the estrous cycle in social play behavior as compared to LD offspring. We have previously demonstrated that DLAN exposure female rats in a (Gutiérrez-Pérez et al., However, the intergenerational effects of DLAN on have only been described in and reproductive et al., are to the intergenerational effects of DLAN on Maternal DLAN exposure induce an increase in behavior in the adult female offspring. are consistent with that DLAN exposure during the gestational period to anxiety-like behaviors (Borniger et al., the metabolic effects of maternal DLAN we observed that offspring of exhibited body mass and increased body mass gain at PN25. However, such differences were suggesting a It is that the of maternal to mothers health, the maternal physiological et al., 2022). while showed food females exhibited increased food through development, suggesting to maternal DLAN However, the of significant differences in the and gain that the intergenerational metabolic effects of DLAN impact metabolism in a different recent that gestational DLAN exposure metabolic rhythms of the offspring (Dzirbíková et al., the of the male we observed that maternal exposure to DLAN a significant in social play The expression of this behavior on a to process and which such as the NAc et al., et al., have demonstrated that the remodeling of NAc occur during the adolescence where is a in expression in the developmental in which social play behavior its of expression (Kopec et al., 2018). The remodeling of this is by microglial suggesting that play a critical role in the of the NAc We evaluated the NAc during adolescence, at and observed that this nucleus presented an increased of IBA-1 in the male offspring of DLAN have demonstrated that DLAN microglial and induces oxidative in the (Liu et al., et al., microglial and changes DLAN exposure have been associated with synaptic in is to spatial and memory in (Liu et al., 2022). In to its microglia play an important role in synaptic et al., and can with synaptic plasticity processes social play behavior of male rats (Kopec et al., the morphology of IBA-1 in the NAc of male DLAN are more This morphology has been associated with the of with and et al., and with of phagocytosis of and et al., In with our the exposure of to induce a ramified microglial morphology with higher of et al., 2022), suggesting that microglia be by to which the mothers are during pregnancy with effects postnatal stages such as in microglial morphology were in the of the This dopaminergic primarily from the a crucial pathway in the of and behaviors and such as social play In contrast, the NAc is by from the a in motor and This in the organization of that the and regions results a between the decrease in social play behavior and the increased of IBA-1 in the is a vulnerability in the dopaminergic in response to maternal DLAN In addition, of microglial activity in the NAc and brain in social play behavior are no significant differences were observed in social play behavior between female DLAN and LD it is important to that social play behavior in females in its compared to et al., have that females to aggressive and play patterns compared to this expression a as the to social play behavior are primarily on the standardized motor patterns observed in males, the to and social play behavior patterns in In this it is crucial to more for evaluating motor social play behavior in we not the NAc of the female offspring have that synaptic for social play behavior mediated by microglia during adolescence occur in but not in females (Kopec et al., 2018).This that from synaptic pruning, be in synaptic development and social play behavior in mechanisms is an important for as it could differences in and behavioral development in response to such as DLAN social interactions during adolescence have been associated with long-term behavioral changes in adulthood et al., In with we observed that maternal DLAN exposure induces increased anxiety-like behaviors in male offspring. results are in with the of anxiety-like behavior in the offspring of mothers exposed to DLAN during gestation (Borniger et al., 2014) and with depressive-like behaviors in the offspring of exposed to DLAN (Cissé et al., we also observed increased behavior in the female offspring of DLAN exposed results the effects on behavior of maternal DLAN influences offspring behaviors 2016, 2007). In the study we not differences in maternal between and suggesting that the observed effects in the offspring are not the of alterations in maternal behavior during be to physiological changes experienced by the mothers before or during pregnancy such as circadian disruption due to DLAN exposure (Gutiérrez-Pérez et al., that the effects of exposure to conditions can be to offspring et al., 2020). disruption during gestation offspring development through epigenetic modifications, such as modifications, and (Liu et al., In circadian disruption by during pregnancy in of and of for and development et al., we previously demonstrated that DLAN exposure melatonin plasma levels (Gutiérrez-Pérez et al., This is important not only melatonin is a during pregnancy, various processes for fetal development et al., 2014), but also it plays a role in epigenetic et al., et al., levels from circadian disruption also affect offspring developmental and health, to a higher risk of metabolic and behavioral disorders in later through epigenetic mechanisms 2014, et al., In this maternal circadian disruption due to DLAN in to maternal also fetal development and significantly the epigenetic of offspring and responsible for the and of the long-term intergenerational effects of maternal DLAN exposure and during pregnancy are not and will be the of our presented have significant for circadian such as light at can the developmental programming of to health later in study the to the between epigenetic mechanisms and that to the framework of exposure to artificial light at night an health risk that research and be considered in the development of at a successful pregnancy and the development of diseases in the mothers and the The rats were to the mothers and dim light at night mothers mothers to LD offspring and female from mothers in LD conditions the and DLAN offspring and female from mothers exposed to dim light at night before (5 during and pregnancy postnatal day 0 mothers and of were placed LD NOM-062-ZOO-1999, which conforms to international guidelines for animal handling.