Effects of the colour of photophase light on locomotor activity in a nocturnal and a diurnal South African rodent

Many physiological and behavioural responses to varying qualities of light, particularly during the night (scotophase), have been well documented in rodents. We used varying wavelengths of day-time (photophase) lighting to assess daily responses in locomotor activity in the nocturnal Namaqua rock mouse (Micaelamys namaquensis) and diurnal four-striped field mouse (Rhabdomys pumilio). Animals were exposed to three light–dark cycle regimes: a short-wavelength- (SWLC, blue), a medium-wavelength- (MWLC, green) and a long-wavelength light–dark cycle (LWLC, red). Overall, daily locomotor activity of both species changed according to different wavelengths of light: the diurnal species displayed most activity under the SWLC and the nocturnal species exhibited the highest levels of activity under the LWLC. Both species showed an increase in diurnal activity and a decrease in nocturnal activity under the LWLC. These results indicate an attenuated responsiveness to long-wavelength light in the nocturnal species, but this does not appear to be true for the diurnal species. These results emphasize that the effect of light on the locomotor activity of animals depends on both the properties of the light and the temporal organization of activity of a species.http://rsbl.royalsocietypublishinghj2019Mammal Research InstituteZoology and Entomolog

Locomotor activity in the Namaqua rock mouse (Micaelamys namaquensis) : entrainment by light manipulations

The locomotor activity rhythms of wild-caught Namaqua rock mice (Micaelamys namaquensis (A. Smith, 1834)) were examined under four light-cycle regimes to quantitatively describe the daily expression of locomotor activity and to study the innate relationship between activity and the light–dark cycle. Activity was always significantly higher at night than during the day; we note four trends. (1) The LD1 light cycle (12 h light : 12 h dark) established a distinct light-entrained and strongly nocturnal activity rhythm (99.11% nocturnal activity). The activity onset was prompt (zeitgeber time (ZT) 12.2 ± 0.04) and activity continued without any prominent peaks or extended times of rest until the offset of activity at ZT 23.73 ± 0.08. (2) Evidence for the internal maintenance of locomotor activity was obtained from the constant dark cycle (DD) in which locomotor activity free ran (mean = 23.89 h) and 77.58% of the activity was expressed during the subjective night. (3) During re-entrainment (LD2; 12 h light : 12 h dark), a nocturnal activity rhythm was re-established (98.65% nocturnal activity). (4) The inversion of the light cycle (DL; 12 h dark : 12 h light) evoked a shift in activity that again revealed dark-induced locomotor activity (95.69% nocturnal activity). Females were consistently more active than males in all of the light cycles, but only under the DD and LD2 cycles were females significantly more active than males. Although this species is considered nocturnal from field observations, information regarding its daily expression of activity and the role of light in its entrainment is lacking. To the best of our knowledge, this study is the first to report quantitatively on the species’ daily rhythm of activity and to investigate its relationship to the light–dark cycle.Les rythmes de l’activité locomotrice de souris de Namaqua (Micaelamys namaquensis (A. Smith, 1834)) capturées a` l’état sauvage ont été examinés pour quatre régimes de cycle lumineux afin de décrire de manière quantitative l’expression journalière de l’activité locomotrice et d’étudier le lien inné entre l’activité et le cycle lumière–noirceur. L’activité était toujours significativement plus grande la nuit que le jour; quatre tendances ont été notées. (1) Le cycle lumineux LDI (12 h de lumière, 12 h de noirceur) a établi un rythme d’activité distinct entraîné par la lumière et fortement nocturne (activité a` 99,11 % nocturne). Le début de l’activité n’a pas tardé (temps de zeitgeber (ZT) 12,2 ± 0,04) et l’activité s’est poursuivie sans pointe proéminente ou longue période de repos jusqu’a` la fin de l’activité a` ZT 23,73 ± 0,08. (2) Des indications du maintien interne de l’activité locomotrice ont été obtenues du cycle de noirceur constante (DD) dans lequel l’activité locomotrice avait libre cours ( moyen = 23,89 h) et 77,58 % de l’activité s’exprimait durant la nuit subjective. (3) Durant le réentrainement (LD2; 12 h de lumière, 12 h de noirceur), un rythme d’activité nocturne s’est rétabli (activité a` 98,65 % nocturne). (4) L’inversion du cycle lumineux (DL; 12 h de noirceur, 12 h de lumière) a provoqué un changement de l’activité qui révélait encore une fois une activité locomotrice induite par la noirceur (activité a` 95,69 % nocturne). Les femelles étaient uniformément plus actives que les mâles pour tous les cycles lumineux, mais les cycles DD et LD2 étaient les seuls durant lesquels les femelles étaient significativement plus actives que les mâles. Bien que cette espèce soit considérée comme étant nocturne sur la base d’observations de terrain, de l’information concernant l’expression journalière de son activité et le rôle de la lumière dans l’entraînement de cette dernière fait défaut. À notre connaissance, cette étude est la première a` rendre compte de manière quantitative du rythme journalier de l’activité de cette espèce et a` examiner le lien de ce dernier avec le cycle lumière–noirceur.South African Research Chair of Mammal Behavioural Ecology and Physiology and University of Pretoria.http://www.nrcresearchpress.com/cjzhb201

Circadian rhythms of locomotor activity in the reddish-grey musk shrew (Eulipotyphla : Soricidae) from South Africa

The circadian rhythm of locomotor activity in a southern African shrew, the reddish-grey musk shrew Crocidura cyanea was investigated. Thirteen individuals were subjected to three successive light cycles, each cycle lasting approximately 2 weeks: an LD cycle (12 h light/12 h dark), a DD cycle (constant darkness) and a DL cycle (an inverse of the LD cycle). All of the animals exhibited entrainment of their activity to the LD and DL lighting regimes. Locomotor activity of C. cyanea occurred predominantly during the dark phases of the LD cycle and the DL cycle. Under LD, the mean active phase (a) of C. cyanea was 10.8 0.3 h and the total percentage of activity was 78.9% during the dark phase. When subjected to constant darkness, the mean active phase increased to 13.2 01.8 h and all animals expressed free-running rhythms of locomotor activity (mean 1 SD=23.0 0.55 h; range=22.4–23.7 h). On the reverse LD cycle, the mean active phase was lowest (09.3 0.16 h) and the total percentage of activity was 71.5% during the dark phase of the cycle. The reddish-grey musk shrew possesses a strong circadian rhythm of locomotor activity that predominantly occurs during the dark phase and consequently the musk shrew may essentially be considered a nocturnal mammal.The research was supported by a Department of Science and Techonlogy/National Research Foundation South African Research Chair of Mammal Behavioural Ecology and Physiology awarded to NCB. IVDM acknowledges a scholarship from the South African National Research Foundation (NRF). The work was supported by a collecting permit from the Department of Nature Conservation in Limpopo Province.http://www3.interscience.wiley.com/journal/118535410/home-836

Effects of photophase illuminance on locomotor activity, urine production and urinary 6-sulfatoxymelatonin in nocturnal and diurnal South African rodents

Effects of photophase illuminance (1, 10, 100 and 330 lx of white incandescent lighting) on daily rhythms of locomotor activity, urine production and 6-sulfatoxymelatonin (6-SMT; 10 versus 330 lx) were studied in nocturnal Namaqua rock mice (Micaelamys namaquensis) and diurnal four-striped field mice (Rhabdomys pumilio). Micaelamys namaquensis was consistently nocturnal (∼90–94% nocturnal activity), whereas considerable individual variation marked activity profiles in R. pumilio, but with activity mostly pronounced around twilight (∼55–66% diurnal activity). The amplitude of daily activity was distinctly affected by light intensity and this effect was greater in M. namaquensis than in R. pumilio. Only M. namaquensis displayed a distinctive daily rhythm of urine production, which correlated with its activity rhythm. Mean daily urine production appeared to be attenuated under dim photophase conditions, particularly in R. pumilio. The results suggest that the circadian regulation of locomotor activity and urine production possesses separate sensitivity thresholds to photophase illuminance. Micaelamys namaquensis expressed a significant daily 6-SMT rhythm that peaked during the late night, but the rhythm was attenuated by the brighter photophase cycle (330 lx). Rhabdomys pumilio appeared to express an ultradian 6-SMT rhythm under both lighting regimes with comparable mean daily 6-SMT values, but with different temporal patterns. It is widely known that a natural dark phase which is undisturbed by artificial light is essential for optimal circadian function. Here, we show that light intensity during the photophase also plays atheir temporal activity rhythm. key role in maintaining circadian rhythms in rodents, irrespective ofA DST-NRF South African Research Chair of Mammal Behavioural Ecology and Physiology (to N.C.B.) and a scholarship from the University of Pretoria (to I.v.D.M).http://jeb.biologists.org2018-05-30am2017Anatomy and PhysiologyZoology and Entomolog

ENIGMA and global neuroscience: A decade of large-scale studies of the brain in health and disease across more than 40 countries.

This review summarizes the last decade of work by the ENIGMA (Enhancing NeuroImaging Genetics through Meta Analysis) Consortium, a global alliance of over 1400 scientists across 43 countries, studying the human brain in health and disease. Building on large-scale genetic studies that discovered the first robustly replicated genetic loci associated with brain metrics, ENIGMA has diversified into over 50 working groups (WGs), pooling worldwide data and expertise to answer fundamental questions in neuroscience, psychiatry, neurology, and genetics. Most ENIGMA WGs focus on specific psychiatric and neurological conditions, other WGs study normal variation due to sex and gender differences, or development and aging; still other WGs develop methodological pipelines and tools to facilitate harmonized analyses of "big data" (i.e., genetic and epigenetic data, multimodal MRI, and electroencephalography data). These international efforts have yielded the largest neuroimaging studies to date in schizophrenia, bipolar disorder, major depressive disorder, post-traumatic stress disorder, substance use disorders, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, autism spectrum disorders, epilepsy, and 22q11.2 deletion syndrome. More recent ENIGMA WGs have formed to study anxiety disorders, suicidal thoughts and behavior, sleep and insomnia, eating disorders, irritability, brain injury, antisocial personality and conduct disorder, and dissociative identity disorder. Here, we summarize the first decade of ENIGMA's activities and ongoing projects, and describe the successes and challenges encountered along the way. We highlight the advantages of collaborative large-scale coordinated data analyses for testing reproducibility and robustness of findings, offering the opportunity to identify brain systems involved in clinical syndromes across diverse samples and associated genetic, environmental, demographic, cognitive, and psychosocial factors

ENIGMA and global neuroscience: A decade of large-scale studies of the brain in health and disease across more than 40 countries

This review summarizes the last decade of work by the ENIGMA (Enhancing NeuroImaging Genetics through Meta Analysis) Consortium, a global alliance of over 1400 scientists across 43 countries, studying the human brain in health and disease. Building on large-scale genetic studies that discovered the first robustly replicated genetic loci associated with brain metrics, ENIGMA has diversified into over 50 working groups (WGs), pooling worldwide data and expertise to answer fundamental questions in neuroscience, psychiatry, neurology, and genetics. Most ENIGMA WGs focus on specific psychiatric and neurological conditions, other WGs study normal variation due to sex and gender differences, or development and aging; still other WGs develop methodological pipelines and tools to facilitate harmonized analyses of "big data" (i.e., genetic and epigenetic data, multimodal MRI, and electroencephalography data). These international efforts have yielded the largest neuroimaging studies to date in schizophrenia, bipolar disorder, major depressive disorder, post-traumatic stress disorder, substance use disorders, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, autism spectrum disorders, epilepsy, and 22q11.2 deletion syndrome. More recent ENIGMA WGs have formed to study anxiety disorders, suicidal thoughts and behavior, sleep and insomnia, eating disorders, irritability, brain injury, antisocial personality and conduct disorder, and dissociative identity disorder. Here, we summarize the first decade of ENIGMA's activities and ongoing projects, and describe the successes and challenges encountered along the way. We highlight the advantages of collaborative large-scale coordinated data analyses for testing reproducibility and robustness of findings, offering the opportunity to identify brain systems involved in clinical syndromes across diverse samples and associated genetic, environmental, demographic, cognitive, and psychosocial factors

Choosing a course of study

Choosing what to study after matric can cause a considerable amount of anxiety and stress.This video is intended to assist anyone who would like to study further after school, as well as educators, youth workers and parents who support young people in making career and study choices. This video can be used with grade 10 -12 learners to help them start thinking about choosing a course of study

The retinal photoreceptor topography and daily responses to illumination in a nocturnal and a diurnal South African rodent

A number of daily rhythms were investigated under different lighting conditions and the topographical arrangements of visual (rods/cones) and non-visual retinal photoreceptors (ipRGCs) determined, in the Namaqua rock mouse (Micaelamys namaquensis) and the four striped field mouse (Rhabdomys pumilio). The present study provides evidence that M. namaquensis possesses a distinctly nocturnal locomotor activity rhythm that is endogenously entrained by the light-dark cycle, with a near 24h period length. Females also seem to be more active than males, this may be due to females having higher levels of estrogen. The current investigation reveals that M. namaquensis and R. pumilio possess duplex retinas that are rod-dominated, but cone to rod ratios reflect the temporal niches of the species. Micaelamys namaquensis possesses far more rods than cones, whereas R. pumilio possesses a high amount of both rods and cones. Both species also seem to have dichromatic colour vision and although different topographical distributions of the rods, cones and ipRGCs are observed, the adaptive values of these features remain to be elucidated. The ipRGCs are sparsely distributed across the retinas of both species but in R. pumilio they are distinctly concentrated in the dorso-nasal quadrant. The effects of different photophase illuminances on the photoentrainment of various daily rhythms were tested. Across the various photophase illuminances, both species expressed daily activity patterns that are generally typical to the species, but brighter illuminances might be needed to increase diurnal activity in R. pumilio to levels that reflect its activity under natural conditions. The amplitude, but not the temporal expression of daily activity is affected and M. namaquensis seems to be more susceptible to different illuminances than R. pumilio. Unexpectedly, dim photophase lighting reduces daily activity in M. namaquensis. These responses appear to reflect the photoenvironments of the species under natural conditions. Furthermore, day/night urine production values generally reflect the activity patterns of the species. In M. namaquensis, the 6-SMT rhythm is attenuated by a brighter as opposed to a dimmer photophase cycle and likely indicates a sensitivity threshold of the melatonin rhythm that is below 330 lux. Rhabdomys pumilio appears to express an ultradian 6-SMT rhythm with similar mean daily values, yet with different temporal patterns, under both dim and bright photophases. Lastly, the effects of differing photophase wavelengths on the photoentrainment of various daily rhythms were investigated. Long wavelength photophase lighting slightly increases daytime activity in both species. In M. namaquensis, this is probably due to the visual capabilities of the species, but in R. pumilio, lower stress levels under a long wavelength photophase, is the most likely cause. In both species, short wavelength photophase lighting attenuates the overall daily urine production rhythm, while medium and long wavelengths exert similar effects. Furthermore, there is an inverse correlation between the wavelength of the photophase and the level of daily 6-SMT as well as with corticosterone. The results also indicate the involvement of the ipRGCs, in mediating urine, melatonin and corticosterone production in M. namaquensis and in R. pumilio. It is clear that light plays an integral role in adjusting physiology and behaviour in these animals and a wide range of anatomical and physiological features reflect different adaptations according to their respective temporal niches.Thesis (PhD)--University of Pretoria, 2015.Zoology and EntomologyPhDUnrestricte

Water management at a barley brewery

Please read the abstract (Synopsis) in the section, 00front of this documentDissertation (MEng (Environmental Engineering))--University of Pretoria, 2008.Chemical EngineeringMEngunrestricte

Circadian rhythms of locomotor activity in captive eastern rock sengi

We investigated locomotor activity rhythms in the little-studied wild-caught eastern rock sengi (Elephantulus myurus) from Goro Game Reserve, Limpopo Province, South Africa. To assess whether locomotor activity is endogenously entrained by the light–dark cycle, animals (n = 13) were subjected to three different light-cycle regimes: a 12 h light/12 h darkness (LD) cycle, a total darkness (DD) cycle and an inverse of the LD cycle (DL). Ten animals exhibited strong light entrainment under LD1 with the total percentage of activity during the light phase (56.5% 11.9%) significantly higher than during the dark phase (43.5% 11.9%). Eleven animals expressed distinct endogenous free-running rhythms under DD (mean t = 23.6 h 0.6 h; range: 22.9 h–24.5 h), with significant inter-individual variation. Under DL, the total percentage of activity was approximately equal during the light (50.4% 7.8%) and dark phase (49.6% 7.8%). E. myurus was on average active 25% of the 24-h day with a nocturnal–diurnal ratio of 0.8 under LD1 and exhibited locomotor activity under controlled conditions similar to that of closely related species in the wild. In 62% of the animals, activity was highest around dawn, lowest during the afternoon and intermittently expressed throughout the night. Little quantitative data are available on the daily locomotor activity rhythms of sengis particularly in response to the light–dark cycle. This study provides valuable quantitative data on locomotor activity rhythms in E. myurus.A South African Research Chair of Mammal Behavioural Ecology and Physiology and the South African National Research Foundation (NRF).http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-7998ab201