Nighttime Increase Research Articles

Circadian rhythms in the green sunfish retina.

We investigated the occurrence of circadian rhythms in retinomotor movements and retinal sensitivity in the green sunfish, Lepomis cyanellus. When green sunfish were kept in constant darkness, cone photoreceptors exhibited circadian retinomotor movements; rod photoreceptors and retinal pigment epithelium (RPE) pigment granules did not. Cones elongated during subjective night and contracted during subjective day. These results corroborate those of Burnside and Ackland (1984. Investigative Ophthalmology and Visual Science. 25:539-545). Electroretinograms (ERGs) recorded in constant darkness in response to dim flashes (lambda = 640 nm) exhibited a greater amplitude during subjective night than during subjective day. The nighttime increase in the ERG amplitude corresponded to a 3-10-fold increase in retinal sensitivity. The rhythmic changes in the ERG amplitude continued in constant darkness with a period of approximately 24 h, which indicates that the rhythm is generated by a circadian oscillator. The spectral sensitivity of the ERG recorded in constant darkness suggests that cones contribute to retinal responses during both day and night. Thus, the elongation of cone myoids during the night does not abolish the response of the cones. To examine the role of retinal efferents in generating retinal circadian rhythms, we cut the optic nerve. This procedure did not abolish the rhythms of retinomotor movement or of the ERG amplitude, but it did reduce the magnitude of the nighttime phases of both rhythms. Our results suggest that more than one endogenous oscillator regulates the retinal circadian rhythms in green sunfish. Circadian signals controlling the rhythms may be either generated within the eye or transferred to the eye via a humoral pathway.

Crassulacean acid metabolism, CO2-recycling, and tissue desiccation in the Mexican epiphyte Tillandsia schiedeana Steud (Bromeliaceae)

After 23 days without water in a greenhouse, rates of nocturnal CO2 uptake in Tillandsia schiedeana decreased substantially and maximum rates occurred later in the dark period eventually coinciding with the onset of illumination. Nocturnal CO2 uptake accounted for less than half the total nighttime increase in acidity measured in well-watered plants. With increased tissue desiccation, only 11-12% of measured acid accumulation was attributable to atmospheric CO2 uptake. Plants desiccated for 30 days regained initial levels of nocturnal acid accumulation and CO2 uptake after rehydration for 10h. These results stress the importance of CO2 recycling via CAM in this epiphytic bromeliad, especially during droughts.

Night-time increase of mesospheric ozone measured with ground-based microwave radiometry

During February and March 1985 ground-based microwave observations of the 142.175 GHz ozone line were made to measure the variations of mesospheric ozone during sunset, throughout the night and during sunrise. Data was taken from 2 h before sunset to 2 h after sunrise. The time resolution was approximately 16 min. Above 50 km we observed a rapid ozone increase at sunset and a decrease at sunrise. The time required for both changes (10–90%) was about 1 h. Day-time ozone concentrations in the mesosphere were found to be larger after sunrise than before sunset. After the initial sunset rise the night-time ozone continued to increase at levels above 60 km, while decreasing below this level. The retrieved night to day ozone ratio was maximum (4.2) at 70 km, near the top of the measurement range. No diurnal changes were seen below 45 km.

Anomalous nighttime increase of ion transition height in the equatorial ionosphere during sunspot maximum period

Analysis of ion composition data at 1100 km from the ISS‐b satellite revealed an anomalous nighttime increase of the transition height in the equatorial ionosphere for December solstice conditions. This feature was absent during June solstice. It appears that this anomalous behavior is observed only during high solar activity periods. Possible causes for this behavior are discussed qualitatively.

Relationship of putative nicotinic cholinergic receptors in the suprachiasmatic nucleus to levels of pineal serotonin N-acetyltransferase activity in the normally cycling female, the male, and the ovariectomized rat.

We have examined the nocturnal increase in pineal serotonin N-acetyltransferase (SNAT) activity in the rat and the decrease in activity of this enzyme as a result of exposure of the rats to light during the nocturnal period. In females with normal ovulatory cycles and ovariectomized females, levels of the enzyme were similar during the dark (695 +/- 70 pmol/min/gland vs. 590 +/- 68) or after 20 min of lights on at night (107 +/- 5 vs. 105 +/- 8). Carbachol, a cholinergic agonist, was injected at 2400 hr (EST) into the lateral ventricle of orbitally enucleated rats. The agonist simulated the lights on effect in both intact and ovariectomized rats. Highly purified fractions of alpha-bungarotoxin, a nicotinic cholinergic antagonist were injected into either the third ventricle or bilaterally adjacent to the SCN in intact females, intact males, or ovariectomized rats. These injections had no effect on either the nighttime increase or the lights on inhibition of SNAT. This study makes the following observations: 1) As was previously demonstrated [Illnerova, H. Endocrinol. Exp. 9:141-148, 1975], ovariectomy affects neither the daytime (light period) nor nighttime (dark period) activity of pineal SNAT. This study extends previous work by demonstrating that ovariectomy also has no effect on the lights on at night decrease of SNAT activity. 2) This study confirms that intraventricular infusion of carbachol decreases the nocturnal pineal SNAT activity [Zatz, M., and Brownstein, M.J. Brain Res. 213:438-442, 1981]. 3) This study does not confirm the report that the nicotinic cholinergic antagonist alpha-bungarotoxin prevents the loss of nocturnal SNAT activity induced by turning lights on at night [Zatz, M., and Brownstein, M.J. Brain Res. 213:438-442, 1981].

Light and retinal damage in Nephrops norvegicus (L.) (Crustacea)

Nephrops norvegicus is a burrow-dwelling marine crustacean normally only active in dim light. The eye has typical crustacean rhabdoms each consisting of alternating layers of microvilli. On light adaptation, proximal shielding pigment moves up from the bases of retinula cells to surround the rhabdoms. In dark-adapted eyes the proximal pigment moves proximally to form a band just above the basement membrane. In this position the tapetum is unshielded and it reflects light back into the eye. The only other detectable difference between light- and dark-adapted eyes is a night-time increase in rhabdom volume. Creel-caught animals raised to the surface of Loch Torridon (NW Scotland) were exposed to ambient surface light for periods ranging from 9 min to 5 h. A short exposure (9 min, average intensity 380 μmol m –2 s –1 ) is sufficient to cause damage to the retinula cell layer. It is histologically detectable one month later. Animals fixed immediately after 15 min exposure show evidence of retinula cell breakdown with swelling of cell bodies and nuclei, escape of proximal shielding pigment from the retinula cells and vesiculation of the rhabdoms. After 2 h of illumination the microvilli of the rhabdom are completely disrupted with only membrane whorls remaining; proximal shielding pigment is found deep within the rhabdom. After 6 h of illumination the retinula cell body layer is absent and there is a massive invasion of the eye by haemocytes. By using animals acclimated to a 12 h light–12 h dark cycle (green light, 0.24 μmol m –2 s –1 ) we were able to test the effects of natural day­light (average intensity 180 μmol m –2 s –1 ) on dark- and light-adapted eyes of known physiological state. The animals were kept alive for two weeks after exposure and the percentage area of the retina destroyed was measured from serial wax sections. Dark-adapted eyes have substantial damage (76.74%) after only 15 s but light adaptation prevents damage with a similar exposure. After 5 min exposure, destruction is almost total (light-adapted, 97.16%; dark-adapted, 98.97%). Intensities of 1000 and 250 μmol m -2 s –1 with an artificial tungsten light source gave similar results. Light-adapted eyes are less sensitive than dark-adapted ones and longer exposures cause greater damage. At these relatively high intensities the damage caused by the two light levels is not very different. At lower intensities (10–250 μmol m –2 s –1 ) the amount of damage is proportional to the intensity. By using the tungsten source and 10 s expo­sures we found that dark-adapted eyes are damaged at 25 μmol m –2 s –1 and that light-adapted eyes are affected at 100 μmol m –2 s –1 .

Mid-latitude electron content modelling: The role of interhemispheric coupling

A modelling study of the electron content of the mid-latitude ionosphere and protonosphere has been carried out for solstice conditions using the mathematical model of Bailey (1983). In the model calculations coupled time-dependent O +, H + continuity and momentum equations and O +, H + and electron heat balance equations are solved for a magnetic shell extending over both hemispheres. The inclusion of interhemispheric flow of plasma and of heat balance has enabled us to investigate the role of interhemispheric coupling on the electron content and related shape parameters. The computed results are compared with results from slant path observations of the ATS-6 radio beacon made at Lancaster (U.K.) and Boulder, Colorado (U.S.A.). It has been found that the conjugate photoelectron heating has a major effect on the shape of the daily variation of slant slab thickness (τ) and also on the magnitude of the protonospheric content ( N p ). Some of the main features of τ are closely related to the sunrise and sunset times in the conjugate ionosphere. Also it is found that night-time increases in total electron content ( N T ) and F2 region peak electron density ( N max) in winter are natural consequences of ionization loss at low altitudes causing an enhanced downward flow of plasma from the protonosphere which is coupled to the summer hemisphere. One other important consequence of the coupled protonosphere is that the effects on N T of the neutral air wind are not much different in winter from those in summer.

Age and day-night changes in clonidine-induced analgesia in mice.

Administrations of clonidine hydrochloride (0.1, 1.0 mg/kg) to young, mature, and old mice influenced their response time on a thermally aversive surface (50 degrees C) in an age-dependent manner. This analgesic effect was of short duration. During daytime measurement periods, young and mature mice showed significantly greater analgesic responses than did the old animals. Although all animals were able to perform the appropriate paw-licking response, the old mice displayed tremors and locomotor disturbances after receiving clonidine. These effects were not seen in the younger groups. Both the young and mature animals showed a substantial enhancement of their analgesic responses after receiving clonidine at night, whereas a significant but much reduced nighttime increase in antinociceptive effect was seen in old animals. Yohimbine, but not prazosin, inhibited clonidine-induced analgesia in young animals. Old mice given combinations of clonidine and these adrenergic antagonists showed elevations in response times, accompanied by severe behavioural changes.

Circadian rhythms in the Limulus visual system

A circadian clock in the Limulus brain generates efferent optic nerve activity at night. The endogenous activity begins near dusk, continues during the night, and stops near dawn. Approximately 10 to 20 efferent fibers in each lateral optic nerve trunk fire in close synchrony with one another and with the efferent fibers in the opposite nerve trunk producing bursts of nerve impulses at night. The synchronous bursting activity indicates extensive coupling in the brain among the efferent neurons or among the circadian pacemakers that drive them. The efferent optic nerve activity mediates circadian rhythms in retinal responses. Electroretinograms (ERGs) from both the lateral eyes and median ocelli exhibit circadian rhythms of equal phase. Sectioning the optic nerves abolishes the rhythms. When the animal is kept in darkness, the phase of the rhythm can be shifted by illuminating the lateral eyes but not the median ocelli. The endogenous rhythm persists for at least 1 year in darkness without attenuation and without substantial changes in the circadian period. Across a large population of animals the duration of the circadian period ranges from 22.2 to 25.5 hr, with a mean value of 23.9 +/- 0.7 hr (n = 75). The nighttime increase in ERG amplitude represents a 20- to 100-fold increase in retinal sensitivity. Most of the increased sensitivity results from an increase in the number of photons absorbed by the photoreceptors at night. A small component may be due to an increase in gain. Pulses of current delivered to the lateral optic nerve during the day mimic the effects of endogenous efferent activity and transform the eye to the nighttime state. The Limulus visual system has evolved numerous mechanisms for adapting visual sensitivity to daily fluctuations in the photic environment. A key to understanding the organization of the visual system is the circadian clock and its associated neural circuitry.

On the nighttime increase of NmF2 at Jicamarca on 2–3 February 1965

The conditions of the nighttime increase in NmF2 at the geomagnetic equator are investigated. It is shown that, in an altitude region above 250 km, after 2100 LT, the increase is due to a downward electromagnetic drift when the compression of the plasma associated with the drift overcomes the chemical loss rate.

Sympathetic regulation of circadian rhythm of serotonin N-acetyltransferase activity in pineal gland of infant rat.

The circadian rhythms of serotonin N-acetyltransferase activity in the pineal glands of infant and adult rats were compared. The nighttime increase of N-acetyltransferase activity in the pineals of infant rats was blocked by removal of superior cervical ganglion or by pretreatment with reserpine, l-propranolol, and cycloheximide. Injection of isoproterenol to infant rats markedly elevated pineal N-acetyltransferase activity. When the pineal glands of infant rats were organ-cultured, N-acetyltransferase activity spontaneously increased 7--12 h after the rats were killed. When infant rats were previously denervated or pretreated with reserpine and their pineals were cultured, this spontaneous elevation of N-acetyltransferase activity was abolished, indicating that the transient increase of the enzyme activity in organ culture was due to a liberation of catecholamine from degenerating nerve endings. Additional illumination until midnight prevented the nighttime increase of N-acetyltransferase activity in intact infant rats but not in blinded infant rats. These observations are taken to indicate that N-acetyltransferase rhythm in immature rat pineals is regulated by the sympathetic nerves in the same manner as in adult rat pineals, that the immature rat pineal does not contain a time-keeping system, and that there is no extraretinal light perception in infant rats as far as N-acetyltransferase rhythm is concerned.

Rhodopsin-like photosensitivity of isolated chicken pineal gland

The pineal gland of lower vertebrates such as fish, amphibians and reptiles is primarily a photoreceptor organ and its electrical activity changes in response to environmental lighting, whereas the mammalian pineal gland is a secretory organ and no longer responds to direct illumination. It is uncertain whether the avian pineal gland retains a photoreceptive capability, and also whether the gland is a photosensor involved in the photo-periodic control of reproductive systems and circadian rhythms in birds. Recently, I and other workers have shown that the circadian rhythm of serotonin N-acetyltransferase activity persisted in organ cultures of chicken pineals, indicating the presence of an endogenous circadian oscillator in the gland. Also, the observation that direct illumination of cultured chicken pineals suppressed the night-time increase of N-acetyl-transferase activity suggests that the gland contains a photoreceptor. I report here that the action spectrum of the photosensitivity of the isolated chicken pineal resembles the absorption spectrum of rhodopsin.

Mid‐latitude winter nighttime increases in the total electron content of the ionosphere

A study is made of winter nighttime increases in the total electron content of the ionosphere over the North American region using data from several total electron content stations and from several geostationary satellites for the month of December for the years 1971, 1974, and 1975. The increases are preceded by substorm activity and enhancements in the total electron content of the ionosphere in the auroral regions. Total electron content nighttime increases are accompanied by large increases in the peak density of the F layer and a lowering of the layer height. At mid‐latitudes most of the enhancements occur after midnight (local time) with a marked maximum around 0300 hours (local time). The spatial extent of the enhancements tends to increase with increasing levels of magnetic activity. The enhancements appear to occur at a constant local time, giving an apparent westward motion. The winter nighttime increases are not accompanied by large changes in the plasmaspheric content. Mechanisms to explain the winter nighttime enhancements are discussed. Low mid‐latitude total electron content increases appear to be controlled by mechanisms different from those operating at higher latitudes.

ROLE OF ADENOSINE 3′, 5′‐MONOPHOSPHATE IN THE REGULATION OF CIRCADIAN OSCILLATION OF SEROTONIN N‐ACETYLTRANSFERASE ACTIVITY IN CULTURED CHICKEN PINEAL GLAND

Abstract—When pineal glands of 10–12‐day‐old chicks were organ‐cultured in darkness, serotonin N‐acetyltransferase activity was low during the daytime, increased at midnight and then decreased to the daytime level the next morning. The pattern of increase and decrease of enzyme activity in cultured pineal glands was comparable to the circadian rhythm of N‐acetyltransferase activity in vivo. When pineal glands were kept at a low temperature for 5 h prior to culture, the phase of autonomous rhythm of enzyme activity was delayed. When chicken pineal glands were cultured during the daytime for 6 h, derivatives of adenosine 3′, 5′‐monophosphate (cyclic AMP), cholera toxin, a high concentration of KCl and phosphodiesterase inhibitors increased N‐acetyltransferase activity 3–7‐fold, indicating an involvement of cyclic AMP in the regulation of N‐acetyltransferase activity in chicken pineal gland as has been shown in rat pineal gland. When pineal glands were cultured at night in darkness, cholera toxin or a high KCl did not enhance the night‐time increase of the enzyme activity. Derivatives of cyclic AMP or phosphodiesterase inhibitors enhanced the autonomous night‐time increase of N‐acetyltransferase activity in an additive or more than additive manner in cultured pineal glands. These observations suggest that adenylate cyclase of pinealocytes is inactive during daytime, but is activated at night in darkness, which is transduced to the synthesis of N‐acetyltransferase molecules. Catecholamines suppressed the basal level and the nocturnal increase of N‐acetyltransferase activity via α‐adrenergic receptor. The nocturnal increase of enzyme activity was prevented by cycloheximide or actinomycin D. Cocaine, which stabilizes cell membrane potential or light exposure, blocked the nighttime increase of N‐acetyltransferase activity in cultured chicken pineal glands.

The effect of the release of an artificial discharge of water on invertebrate drift in the R. Wye, Wales

An artificial discharge of water (3.0 m3/sec), over a 48 h period, from an impoundment into the R. Wye did not substantially affect water temperature or concentrations of dissolved oxygen and suspended solids at a site 16 km below the impoundment. However, the load of suspended material on the second day of the release was about 10 times greater than the pre-release load. The total number of drifting macroinvertebrates on the first and second days of the release were about 7 and 3 times greater than the number on the day preceding the release. The initial increase in flow at 15.00 h resulted in an immediate increase in the number of drifting larvae of Rheotanytarsus, a tubicolous chironomid. Subsequently there was an enhanced night-time increase in the total number of drifting invertebrates, particularly the mayfly, Ephemerella ignita (Poda), and this also occurred on the second night of the release. Increases in the number of drifting Rheotanytarsus and Ephemerella, the most abundant invertebrates, resulted in increase in drift density.

Sugarbeet Response to Irrigation as Measured with Growth Sensors1

AbstractMost research with sugarbeets (Beta vulgaris L) under natural field conditions has been concerned with longterm effects of moisture or fertility levels on overall yield and sugarbeet quality. Variations in ambient conditions under which experiments have been conducted, together with the interrelationships of these variables with each other and with plant factors, have resulted in variable and sometimes contradictory results. There is, therefore, a need for more information on the effects of microclimatic and soil conditions on plant growth. In the study herein, root growth sensors that provide a continuous record of sugarbeet root growth were used to study the short‐term growth response of sugarbeets to irrigation and to variations in ambient meteorological and soil conditions.The continuous growth records of two typical irrigated sugarbeet roots were compared at Bushland, Texas, during a 48‐day period, June 25 to August 11, 1970, in a record dry season when there was little interference from rainfall on the effect of irrigation on root growth. The roots received 10 cm of irrigation water on staggered dates so that the growth record of a root not being irrigated at a particular time might be used to interpret the growth response to irrigation of the second root. The soil was slowly permeable, requiring an average of about 3 days for free water to disappear after an irrigation. A slowgrowth period of about 3 days in length occurred after each. irrigation during which time the irrigated root grew more slowly than the unirrigated root. When moisture stress was not extreme at the time of irrigation, a temporary decrease in growth rate actually occurred after irrigation.In general, root growth occurred at night. In the daytime, growth ceased or a shrinkage in circumference occurred which was proportional to the degree of moisture stress. As the need for moisture by the plant increased between irrigations, the increment of nighttime increase in circumference became progressively smaller and that of the daytime shrinkage, progressively greater. By the time the plant showed visual signs of a severe need for irrigation, the net daily growth had approached zero. Some daytime root shrinkage, however, was also noted during the slow‐growth period when the soil moisture content was very high. Although the reasons for the slowgrowth period after each irrigation were not directly determined in this study, logical explanations based on the literature of plant and soil‐water relationships are poor aeration and/or cooling of the soil.

Role of β-adrenergic receptor in the control of serotonin N-acetyltransferase in rat pineal

Publisher Summary This chapter describes a study which examines the role of β-adrenergic receptor in the control of serotonin N-acetyltransferase in rat pineal. N-Acetyltransferase activity increases 50-fold after rats were kept in darkness 4 h at 10 p.m. When rats were kept in continuous lighting until 10 p.m. or rats were kept in darkness for 6 h during daytime, N-acetyltransferase activity did not increase. The result indicates that both, the absence of light and proper setting of endogenous clock are necessary for the nighttime elevation of enzyme activity in the pineal. Reserpine, a drug that depletes catecholamines in the nerve endings, propranolol, a β-adrenergic blocking agent, or cycloheximide, a protein synthesis inhibitor injected into rats before the onset of darkness blocked the nighttime increase in enzyme activity, whereas an α-adrenergic blocking agent or actinomycin D had no effect. These observations indicate that the nocturnal increase in N-acetyltransferase activity is induced by neuro-transmitter released from sympathetic nerve via stimulation of postsynaptic β-adrenergic receptor, and that the increase in enzyme activity is because of synthesis of new enzyme protein.

A Balloon Study of the OH Airglow Emission From Evening Twilight to Sunrise

A balloon-borne interference filter photometer designed to measure the OH band emission at 2 μm was flown from Fort Churchill, Canada, during the night of August 1–2, 1968. Observations of the intensity of the Q branch of the 8–6 band are presented and compared with results obtained with a 1.66 μm OH photometer carried in the same gondola. The morning and evening twilight variations observed are in agreement with those predicted by models based on mesospheric ozone photochemistry. The observed nighttime increase in the OH emission is not predicted by the theoretical models.

Determination of ionospheric electron content from the Faraday rotation of geostationary satellite signals

Calculations using a wide range of model ionospheres (with a peak at 300 km) show that the integrated electron content up to the height of the satellite could be up to four times the value deduced from Faraday rotation measurements. However, using a fixed mean field height of 400 km, the observed Faraday rotation gives the electron content up to a height h F of 2000 km with an accuracy of ±3 per cent. For observations at different magnetic and geographic latitudes, and geostationary satellites at different longitudes, the optimum value of h F varies by only ±200 km. Night-time increases in the height of the ionosphere have little effect on h F , but increase the mean field height to about 470 km. Using a fixed value of 420 km, with h F = 2000 km, gives an accuracy of ±5 per cent under most conditions.

Diurnal rhythmicity in template activity of mouse liver chromatin

A study was initiated to define the basal state of gene expression in the mouse liver prior to an investigation of responses during stress. It was found that: 1. 1. The ability of isolated mouse liver chromatin to be transcribed in vitro is increased when the chromatin is taken during hours of darkness rather than during the day. It is suggested that this night-time increase in template activity is related to the rhythmic pattern in other phenomena of gene expression in the rodent liver. 2. 2. The magnitude of the periodic increase in template activity is diminished in the adrenalectomized animal, suggesting the involvement of glucocorticoid secretion. 3. 3. The extent of the nocturnal rise in activity is not affected by starvation of the mice. A simple hepatic response to periodic ingestion of the diet appears to be an unlikely source of rhythmicity.