Extremely low threshold for photic entrainment of circadian activity rhythms in molossid bats (Molossus molossus; Chiroptera – Molossidae)

Circadian rhythms usually deviate from 24 h and must be synchronized (entrained) to the outer 24 h day by certain environmental periodicities called Zeitgebers. For almost all organisms the most efficient Zeitgeber is the light-dark cycle (LD). In mammals the photic Zeitgeber cues are exclusively received via retinal photoreceptors. It is still in debate whether this circadian photoreception is mediated by rods, cones, and/or other retinal cells. From recent results in mouse mutants a circadian photoreception via non-rod/non-cone retinal receptors was deduced. However, earlier observations in bats indicating a very low threshold for photic entrainment imply that circadian photoreception may be mediated by rod-like receptors. In the present study the threshold for photic entrainment was determined in the neotropical mastiff bat Molossus molossus. Six test animals (3 m, 3 f) were kept isolated in recording cages situated in light-tight and sound-attenuating wooden boxes with a special lighting device on top. Under constant ambient temperature of 25 ± 1°C, relative humidity of 60 ± 5%, and an irregular ad libitum feeding schedule, the bats were exposed intermittantly for longer times to constant physiological darkness (LD-X) or 12:12 h light dark cycles with physiological darkness during the dark time (D) and varying low light-time illuminances (L). Half of the bats had an extremely low threshold for photic entrainment, about 10⁻⁵ lux, while the other individuals’ free-running activity rhythm was entrained by LD cycles with 10⁻⁴, 10⁻² and 10⁻¹ lux in L. The illuminance of only 10⁻⁵ lux is the lowest threshold value for photic entrainment found thus far in vertebrates. Plausibility considerations suggest circadian photoreception via rod-like retinal receptors to be most probably involved in this case.     

Effect of aging on the photic entrainment in the frugivorous bat, Rousettus leschenaulti

Aging disrupted the photic entrainment in old (∼15 years) frugivorous Rousettus leschenaulti bats as natural light - dark (LD) cycles in the field or artificial LD cycles of 12 h of light at 2000 lux and 12 h of complete darkness failed to entrain them (Vanlalnghaka & Joshi 2005; Vanlalnghaka et al. 2005). The results were attributed to the age-related decline in photic sensitivity and/or the period of zeitgeber (T) deviating too much from the free-running period (τ) of bats. In the present study, the old bats were subjected to LD cycles in which the intensity of the photophase was raised to 6000 lux and Ts of 23.2 h and 24.9 h were exactly that of τ in the scotophase of LD cycles and in constant darkness, respectively. These LD cycles also failed to entrain the old bats which unambiguously demonstrates that aging in R. leschenaulti disrupted the integrity of the photic entrainment mechanism.     

Effects of psi-mutations on the Oviposition Rhythm of Drosophila rajasekari

The psi -mutations affected the circadian rhythm of locomotor activity in the early and late strains of Drosophila rajasekari (Joshi, 1999a). The present study was designed to determine the effects of psi -mutations on the oviposition rhythm of the early and late strains. Oviposition rhythms were studied in light-dark cycles of 12 :12 h in which the light intensity of photophase was 0.001, 0.01, 0.1, 1, 10, 100 or 1000 lux. The oviposition rhythm of wild type was unimodal at or above 10 lux with a peak before lights-off, while it was bimodal at lower light intensities. The early strain was unimodal at all light intensities with a peak after lights-on at or above 10 lux, and around the mid-day at or below 1lux. The late strain was rhythmic at 100 and 1000 lux with a peak after the lights-off, weakly rhythmic at 10 lux and arrhythmic at or below 1 lux. Free running period in constant darkness was shortest in the early and longest in the late strain. Threshold light intensity of constant light to generate arrhythmicity was lowest in the early and highest in the late strain, apparently the photic sensitivity of the clock photoreceptors was differentially altered by these mutations. Thus the psi -mutations for locomotor rhythmicity affected the oviposition rhythm too, suggesting that the same circadian oscillator might be controlling these both rhythms.     

Effects of psi-mutations on the Oviposition Rhythm of Drosophila rajasekari

The psi -mutations affected the circadian rhythm of locomotor activity in the early and late strains of Drosophila rajasekari (Joshi, 1999a). The present study was designed to determine the effects of psi -mutations on the oviposition rhythm of the early and late strains. Oviposition rhythms were studied in light-dark cycles of 12 :12 h in which the light intensity of photophase was 0.001, 0.01, 0.1, 1, 10, 100 or 1000 lux. The oviposition rhythm of wild type was unimodal at or above 10 lux with a peak before lights-off, while it was bimodal at lower light intensities. The early strain was unimodal at all light intensities with a peak after lights-on at or above 10 lux, and around the mid-day at or below 1lux. The late strain was rhythmic at 100 and 1000 lux with a peak after the lights-off, weakly rhythmic at 10 lux and arrhythmic at or below 1 lux. Free running period in constant darkness was shortest in the early and longest in the late strain. Threshold light intensity of constant light to generate arrhythmicity was lowest in the early and highest in the late strain, apparently the photic sensitivity of the clock photoreceptors was differentially altered by these mutations. Thus the psi -mutations for locomotor rhythmicity affected the oviposition rhythm too, suggesting that the same circadian oscillator might be controlling these both rhythms.     

Facilitation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor transmission in the suprachiasmatic nucleus by aniracetam enhances photic responses of the biological clock in rodents

This study was designed to test whether the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-facilitating drug, aniracetam, could potentiate photic responses of the biological clock in the suprachiasmatic nucleus (SCN) of rodents. Using the whole-cell patch technique, we first demonstrated that AMPA currents elicited by either local AMPA application or optic chiasm stimulation were augmented by aniracetam in the neurons of the SCN. The AMPA application-elicited increase of intracellular Ca2+ concentration in SCN slices was also enhanced by aniracetam treatment. The systemic injection of aniracetam dose-dependently (10-100 mg/kg) potentiated the phase delay in behavioral rhythm induced by brief light exposure of low intensity (3 lux) but not high intensity (10 or 60 lux) during early subjective night. Under the blockade of NMDA receptors by (+) MK801, aniracetam failed to potentiate a light (3 lux)-induced phase delay in behavioral rhythm. Aniracetam increased the photic induction of c-Fos protein in the SCN that was elicited by low intensity light exposure (3 lux). These results suggest that AMPA receptor-mediated responses facilitated by aniracetam can explain enhanced photic responses of the biological clock in the SCN of rodents.     

Movement and migration of diatoms on sand grains

The motile species of diatoms in a largely non-motile association on grains of sand travel to the surface of the sand when buried, although they move more slowly and less often than species living in silt, and ascend each grain in turn. Diatoms on sand grains from a freshwater lake are found to migrate daily to and from the surface grains, whether in a natural daylight régime or in continuous darkness. They do not leave the surface when exposed to 750 lux of constant illumination although they will at 75 lux. Their movements help to keep them in the photic zone during the day.     

Effect of light intensity on the oviposition rhythm of the altitudinal strains of Drosophila ananassae

The sensitivity of the circadian photoreceptors mediating entrainment of the eclosion rhythm and phase shifts of oviposition rhythm of the high altitude (HA) strain of Drosophila ananassae originating from Badrinath (5123 m above sea level) in the Himalayas was compared with the low altitude (LA) strain from Firozpur (179 m above sea level). Reduced photic sensitivity of the HA strain is regarded as the result of natural selection, which led to the weakening of the coupling mechanism between the circadian pacemaker and light at the high altitude of origin. The present study was designed to determine whether or not the photic entrainment of the oviposition rhythm of the HA strain of D. ananassae is also altered by the high altitude of its origin, and the results are compared with those of the LA strain. The effects of light intensity on the phase angle difference (Ψ), degree of rhythmicity (R), the percent oviposition in photophase, the threshold light intensity (i.e., the intensity at which stable entrainment occurred), and the saturation light intensity (i.e., the intensity beyond which the values of Ψ or amplitude of rhythm remained unaltered) were determined. Entrainment was studied in light-dark cycles in which the light intensity of 12 h of photophase varied from 1 to 1000 lux, and complete darkness prevailed in all scotophases. The oviposition rhythm of the HA strain was arrhythmic from 1 to 90 lux, weakly rhythmic at 95 lux, but rhythmic at or above 100 lux, while that of the LA strain was weakly rhythmic at 1 lux but rhythmic at or above 2 lux. Oviposition of the HA strain occurred mostly in the photophase, while that of the LA strain occurred in the scotophase; as a result, the oviposition medians of the HA strain were around the subjective forenoons while those of the LA strain were around the subjective evenings. The percent of oviposition in photophase increased from 68 to 98 in the HA strain and from 5 to 33 in the LA strain as light intensity increased from 1 to 1000 lux. In the HA strain, the Ψ values were significantly less and values of R and percent oviposition in photophase were significantly more than those of the LA strain at each level of light intensity. Threshold and saturation intensities for Ψ were 100 and 700 lux, respectively, for the HA strain, but just 2 and 45 lux, respectively, for the LA strain. The saturation intensity for R was 650 and 700 lux for the HA and LA strains, respectively. These results extend the confirmation that the reduced photic sensitivity of the HA strain might have been acquired through natural selection in response to environmental conditions at the high altitude of its origin.     

Effect of Light Intensity on the Oviposition Rhythm of the Altitudinal Strains of Drosophila Ananassae

The sensitivity of the circadian photoreceptors mediating entrainment of the eclosion rhythm and phase shifts of oviposition rhythm of the high altitude (HA) strain of Drosophila ananassae originating from Badrinath (5123 m above sea level) in the Himalayas was compared with the low altitude (LA) strain from Firozpur (179 m above sea level). Reduced photic sensitivity of the HA strain is regarded as the result of natural selection, which led to the weakening of the coupling mechanism between the circadian pacemaker and light at the high altitude of origin. The present study was designed to determine whether or not the photic entrainment of the oviposition rhythm of the HA strain of D. ananassae is also altered by the high altitude of its origin, and the results are compared with those of the LA strain. The effects of light intensity on the phase angle difference (Ψ), degree of rhythmicity (R), the percent oviposition in photophase, the threshold light intensity (i.e., the intensity at which stable entrainment occurred), and the saturation light intensity (i.e., the intensity beyond which the values of Ψ or amplitude of rhythm remained unaltered) were determined. Entrainment was studied in light–dark cycles in which the light intensity of 12 h of photophase varied from 1 to 1000 lux, and complete darkness prevailed in all scotophases. The oviposition rhythm of the HA strain was arrhythmic from 1 to 90 lux, weakly rhythmic at 95 lux, but rhythmic at or above 100 lux, while that of the LA strain was weakly rhythmic at 1 lux but rhythmic at or above 2 lux. Oviposition of the HA strain occurred mostly in the photophase, while that of the LA strain occurred in the scotophase; as a result, the oviposition medians of the HA strain were around the subjective forenoons while those of the LA strain were around the subjective evenings. The percent of oviposition in photophase increased from 68 to 98 in the HA strain and from 5 to 33 in the LA strain as light intensity increased from 1 to 1000 lux. In the HA strain, the Ψ values were significantly less and values of R and percent oviposition in photophase were significantly more than those of the LA strain at each level of light intensity. Threshold and saturation intensities for Ψ were 100 and 700 lux, respectively, for the HA strain, but just 2 and 45 lux, respectively, for the LA strain. The saturation intensity for R was 650 and 700 lux for the HA and LA strains, respectively. These results extend the confirmation that the reduced photic sensitivity of the HA strain might have been acquired through natural selection in response to environmental conditions at the high altitude of its origin.     

THERMOCYCLIC AND PHOTOCYCLIC ENTRAINMENT OF CIRCADIAN LOCOMOTOR ACTIVITY RHYTHMS IN SLEEPY LIZARDS,TILIQUA RUGOSA

Australian sleepy lizards (Tiliqua rugosa) exhibit marked locomotor activity rhythms in the field and laboratory. Light-dark (LD) and temperature cycles (TCs) are considered important for the entrainment of circadian locomotor activity rhythms and for mediating seasonal adjustments in aspects of these rhythms, such as phase, amplitude, and activity pattern. The relative importance of 24 h LD and TCs in entraining the circadian locomotor activity rhythm in T. rugosa was examined in three experiments. In the first experiment, lizards were held under LD 12:12 and subjected to either a TC of 33:15?°?C in phase with the LD cycle or a reversed TC positioned in antiphase to the LD cycle. Following LD 12:12, lizards were maintained under the same TCs but were subjected to DD. Activity was restricted to the thermophase in LD, irrespective of the lighting regime and during the period of DD that followed, suggesting entrainment by the TC. The amplitude of the TC was lowered by 8?°?C to reduce the intensity and possible masking effect of the TC zeitgeber in subsequent experiments. In the second experiment, lizards were held under LD 12.5:11.5 and subjected to one of three treatments: constant 30?°?C, normal TC (30:20?°?C) in phase with the LD cycle, or reversed TC. Following LD, all lizards were subjected to DD and constant 30?°?C. Post-entrainment free-run records revealed that LD cycles and TCs could both entrain the locomotor rhythms of T. rugosa. In LD, mean activity duration (α) of lizards in the normal TC group was considerably less than that in the constant 30?°?C group. Mean α also increased between LD and DD in lizards in the normal TC group. Although there was large variation in the phasing of the rhythm in relation to the LD cycle in reversed TC lizards, TCs presented in phase with the LD cycle most accurately synchronized the rhythm to the photocycle. In the third experiment, lizards were held in DD at constant 30?°?C before being subjected to a further period of DD and one of four treatments: normal TC (06:00 to 18:00 h thermophase), delayed TC (12:00 to 00:00 h thermophase), advanced TC (00:00 to 12:00 h thermophase), or control (no TC, constant 30?°?C). While control lizards continued to free-run in DD at constant temperature, the locomotor activity rhythms of lizards subjected to TCs rapidly entrained to TCs, whether or not the TC was phase advanced or delayed by 6 h. There was no difference in the phase relationships of lizard activity rhythms to the onset of the thermophase among the normal, delayed, and advanced TC groups, suggesting equally strong entrainment to the TC in each group. The results of this experiment excluded the possibility that masking effects were responsible for the locomotor activity responses of lizards to TCs. The three experiments demonstrated that TCs are important for entraining circadian locomotor activity rhythms of T. rugosa, even when photic cues are conflicting or absent, and that an interaction between LD cycles and TCs most accurately synchronizes this rhythm. (Author correspondence: david.j.ellis@adelaide.edu.au)     

Unequal coupling between locomotor pacemakers of the German cockroach,Blattella germanica (L.)

Male adult German cockroaches, Blattella germanica (L.), expressed robust locomotor circadian rhythmicity under 28 degrees C and constant darkness (DD) conditions. By surgically severing the connections between the optic lobes and midbrain and their subsequent regeneration, we demonstrated that the locomotor circadian pacemaker was located in the optic lobes and that it controlled the locomotor circadian rhythm through neural pathways. From the results that unilaterally optic tract severed males still showed locomotor circadian rhythmicity (93.1%, n=29) without significantly changing the circadian period (tau) or level of motor activity, we concluded that the right and left optic lobes each contain a circadian pacemaker competent to drive the locomotor circadian rhythm. These two pacemakers were strongly coupled since only one rhythm was expressed when the pacemakers were independently exposed to opposite lighting conditions (DD or LL) at the same time. However, an unequal contribution of each pacemaker in determining the overt circadian period was found under constant dim light (10 lux) conditions, revealing a major-minor coupling relationship between these two pacemakers, so that the unilaterally blinded male expressed either a LL-rhythm with a circadian period of 24.27+/-0.21 h (41.7%, n=24) or a DD-rhythm with a circadian period of 23.43+/-0.19 h (58.3%, n=24). However, higher intensity of photic information (200-300 lux) could overpower this relationship and cause the minor pacemaker to lead the rhythm.     

Photic induction of locomotor activity is correlated with photic habitat in <Emphasis Type="Italic">Anolis</Emphasis> lizards

A variety of ecologically important behaviors, including circadian rhythms and seasonal reproduction, are influenced by non-visual responses to light, yet very little is known about the relationship between photic habitat and non-visual photoreception. Puerto Rican Anolis lizards have diverged into multiple photic niches, making them a good model for non-visual photosensory ecology. We investigated the photic induction of locomotor activity, a non-visual response to light, in four species of Anolis comprising two pairs of closely related, ecomorphologically similar species whose microhabitats differ in solar irradiance. We developed a device for continuous, automated detection and recording of anole locomotor activity, and used it to characterize activity under 12:12 h light–dark cycles. Next, we administered a series of 2-h light pulses during the dark period of the light–dark cycle and measured the increase in locomotor activity relative to baseline dark activity. Five different irradiances (ranging from very dim to daytime levels) were given to each individual lizard on separate nights. As expected, light caused an irradiance-dependent increase in locomotor activity in all four species. The responses at the highest irradiances were significantly greater in species occupying relatively more shaded habitats, suggesting that non-visual photoreception may be adapted to habitat light in Anolis lizards.     

Retinal and extraretinal photoreceptors mediate entrainment of the circadian locomotor rhythm in lizards

Summary The circadian locomotor activity rhythms of 7 species of lizards can readily be entrained (synchronized) toLD12: 12 (30–50 lux: 0) fluorescent light cycles after complete surgical removal of both eyes. Removal of the parietal eye and pineal organ does not prevent entrainment of blinded lizards. Appropriate control experiments established that lightper se, and not low amplitude temperature cycles or other obvious environmental variables, was the entraining stimulus for blinded lizards. In some cases, blocking the penetration of light to the brains of blinded lizards caused them to free-run (express their endogenous circadian rhythm) in the presence of a dim green light cycle, to which they had previously entrained, suggesting that the brain is the site of the extraretinal photoreceptor(s) mediating entrainment. The extraretinal photoreceptor(s) is capable of intensity discrimination since changing the intensity of aLD 12: 12 fluorescent light cycle caused a change in the phase-relationship between the entrained activity rhythm and the light cycle in a blinded gekko. The lateral eyes are also involved in mediating entrainment since removal of the lateral eyes of thoseSceloporus olivaceus which previously entrained to a dim green light cycle [LD 12: 12 (0.05 lux: 0)] caused them to free-run. Also, blinding had noticeable effects on the entrained activity patterns of some species of lizards.I thank Michael Menaker, Jeffrey Elliott, Sue Binkley, Joseph Silver, Ed Kluth, George Wyche, Bruee Rouse, Nancy Leshikar, Lili Mostafavi, Janet Alvis, Celeste Cromack, A. L. Mackey and Jean Rogers for their suggestions and technical assistance. Support for this work was provided by NIH grant HD-03803-02 (to M. Menaker); NSP grant GB-8138 (to M. Menaker); NSF traineeship GZ-1336 (to H. Underwood); and MH traineeship 5T01GM00836-09 (to H. Underwood).     

Tail Regeneration in Normal,Blinded and Pinealectomized Gekkonid Lizards,Hemidactylus flaviviridis,Exposed to Four Different Light Conditions During Three Seasons (Temperatures)

Tail regeneration was followed for 60 days in 1470 normal (NL), blinded (BL) and pinealectomized (PX) gekkonid lizards, Hemidactylus flaviviridis, fed on cockroaches ad libitum and exposed to continuous light of high intensity (2500 lux), continuous light of low intensity (638 lux), 12 h of light (high intensity) and 12 h of darkness and continuous darkness in summer (March – May; cage temperature 30°C) monsoon (August – October; cage temperature 26°C) and winter (November – January; cage temperature 17°C) seasons. A comparative assessment of the new growth (regenerate) showed that the initiation of regeneration, the daily growth, the total length of tail replaced at the end of regeneration and the total percentage replacement of the lost (autotomized) tails were all enhanced by continuous light and depressed by continuous darkness. Furthermore, there was no significant difference between any of the parameters in NL and BL Hemidactylus; however, PX lizards generally showed retardation in the regeneration process. Seasonal differences in tail regeneration were noted—the best regenerative performance was obtained during the summer months and the worst during the winter months, with the regenerative performance during the monsoon season in between. Thermal and photoperiodic influences on tail regeneration in lizards are discussed.     

Interactions between light and melatonin on the circadian clock of mice.

Melatonin and light synchronize the biological clock and are used to treat sleep/wake disturbances in humans. However, the two treatments affect circadian rhythms differently when they are combined than when they are administered individually. To elucidate the nature of the interaction between melatonin and light, the present study assessed the effect of melatonin on circadian timing and immediate-early gene expression in the suprachiasmatic nucleus (SCN) when administered in the presence of light. Male C3H/HeN mice, housed in constant dark in cages equipped with running wheels, were treated with either melatonin (90 microg, s.c.) or vehicle (3% ethanol-saline) 5 min prior to exposure to light (15 min, 300 lux) at various times in the circadian cycle. Combined treatment resulted in lower magnitude phase delays of circadian activity rhythms than those obtained with light alone during the early subjective night and advances in phase when melatonin and light were administered during the subjective day (p < .001). The reduction in phase delays with combined treatment at Circadian Time (CT) 14 was significant when light exposure measured 300 lux but not at lower light levels (p < .05). When light preceded melatonin administration, the inhibition of phase delays attained significance only when the light exposure reached 1000 lux (p < .05). Neither basal nor light-induced expression of c-fos mRNA in the SCN was modified by melatonin administration at CT 14 or CT 22. Together, these results suggest that combined administration of melatonin and light affect circadian timing in a manner not predicted by summing the two treatments given individually. Furthermore, the interaction is not likely to be due to inhibition of photic input to the clock by melatonin but might arise from a photically induced enhancement of melatonin's actions on circadian timing.     

Circadian variations in the differential blood counts of mice under constant (LL) and alternating (LD) light periods

Summary Laboratory mice, offspring of CB6 F₁ s, were maintained at a constant temperature of 21.0 ± 1.0° C and in constant light (LL) of 40 lux or under 12 h of light (40 lux) alternating with 12 h of darkness (LD) for 8 consecutive days. During the following 36 h, tail blood was secured from each mouse at 6-h intervals. From those samples, a differential white blood cell count, based on 100 leukocytes, was made for each animal. The relative numbers of eosinophils, basophils, and monocytes did not fluctuate rhythmically under LL or LD. The per cent distributions of lymphocytes and neutrophils did vary with circadian frequency in both LL and LD (Figs. 1, 2) The peak counts of neutrophils were found in blood sampled near midnight; high counts of lymphocytes were made in smears prepared about 6:00 a.m. and 6:00 p.m.     

The effect of light on melatonin secretion in the cultured pineal glands of Anolis lizards

Melatonin, a hormone produced by the pineal gland, is important for regulating circadian rhythms in many animals. Light at night causes an acute suppression of melatonin in nearly all vertebrate species. A previous study found that light failed to suppress melatonin in the lizard Anolis carolinensis. This is a surprising result given that the Anolis pineal gland is intrinsically photosensitive, is a key pacemaker controlling locomotor activity, and can be directly entrained to a light-dark cycle. To find out if the lack of photic suppression is widespread in the Anolis genus, we investigated the acute effects of light on melatonin secretion in five different species of Anolis using flow-through tissue culture. We administered a two-hour pulse of bright light to isolated pineal glands during the night. The results show photic suppression of melatonin in all five Anolis species, but the suppression is weak relative to that seen in other vertebrates. Moreover, Anolis species differ in the magnitude of the effect. These findings are discussed in the context of vertebrate pineal evolution and the ecology of Anolis lizards. Given their extensive phylogenetic and ecological divergence, Anolis lizards provide a promising system for investigating the ecology and evolution of circadian organization.     

Dopamine antagonist speeds up tail regeneration in lizards exposed to continuous darkness: evidence for prolactin involvement

In earlier studies, we demonstrated that continuous light (LL:LD, 24:0) stimulated tail regeneration whereas continuous darkness (DD:LD, 0:24) and pinealectomy depressed the same in the Gekkonid lizard, Hemidactylus flaviviridis, and, furthermore, exogenous prolactin significantly enhanced the regeneration process in lizards kept in 0:24 LD. However, the regeneration process in animals exposed to 24:0 LD was unaffected by the dopamine agonist, bromocriptine. This study with pimozide, an antipsychotic drug, and a potent dopamine receptor antagonist was conducted to ascertain whether the dopaminergic regulation of prolactin release is operative in lizards, as in mammals, and to provide further evidence for prolactin involvement in regenerative growth. Once daily intraperitoneal injection of 50 micrograms/kg pimozide to H. flaviviridis, 5 days prior to tail autotomy and 50 days thereafter, stimulated the regeneration process in lizards exposed to 0:24 LD. The initiation of regeneration, the total length of new growth (regenerate) produced by Day 50, and the total percentage replacement of the lost (autotomized) tails at the end of 50 days of experimentation were all significantly enhanced in pimozide-treated animals as compared with their counterparts injected with 0.6% sterile saline; in fact, better than saline-injected controls exposed to 24:0 LD of 638 lux intensity. The daily growth rate was also enhanced in pimozide-treated lizards. Interestingly, the pattern of regeneration as well as the final regenerate of pimozide-treated lizards were similar to those observed earlier in ovine prolactin-treated animals exposed to similar experimental photoperiodic schedules.(ABSTRACT TRUNCATED AT 250 WORDS)     

Entrainment to Light of Circadian Activity Rhythms in Tench (Tinca tinca)

The present article analyzes locomotor activity rhythms in Tinca tinca. To that end, three different experiments were conducted on 24 animals (20 g body weight) kept in pairs in 60‐liter aquaria fitted with infrared sensors connected to a computer to continuously record fish movements. The first experiment was designed to study the endogenous circadian clock under free‐running conditions [ultradian 40:40 min LD pulses and constant dark (DD)] and after shifting the LD cycle. Our results demonstrate that tench has a strictly nocturnal activity pattern, an endogenous rhythm being evident in 45.8% of the fish analyzed. The second experiment was conducted to test the influence of different photoperiods (LD 6:18, 12:12, 18:6, and 22:2) on locomotor activity, the results showing that even under an extremely long photoperiod, tench activity is restricted to dark hours. The third experiment examined the effect of light intensity on locomotor activity rhythms. When fish were exposed to decreasing light intensities (from 300:0 lux to 30:0, 3:0, and 0.3:0 lux) while maintaining a constant photoperiod (LD 12:12), the highest percentage of locomotor activity was in all cases associated with the hours of complete darkness (0 lux). In short, our results clearly show that (a) tench is a species with a strictly nocturnal behavior, and (b) daily activity rhythms gradually entrain after shifting the LD cycle and persist under free‐running conditions, pointing to their circadian nature. However, light strongly influences activity rhythms, since (c) the length of the active phase is directly controlled by the photophase, and (d) strictly nocturnal behavior persists even under very dim light conditions (0.3 lux). The above findings deepen our knowledge of tench behavior, which may help to optimize the aquacultural management of this species, for example, by adjusting feeding strategies to their nocturnal behavior.     

Entrainment to light of circadian activity rhythms in tench (Tinca tinca)

The present article analyzes locomotor activity rhythms in Tinca tinca. To that end, three different experiments were conducted on 24 animals (20 g body weight) kept in pairs in 60-liter aquaria fitted with infrared sensors connected to a computer to continuously record fish movements. The first experiment was designed to study the endogenous circadian clock under free-running conditions [ultradian 40:40 min LD pulses and constant dark (DD)] and after shifting the LD cycle. Our results demonstrate that tench has a strictly nocturnal activity pattern, an endogenous rhythm being evident in 45.8% of the fish analyzed. The second experiment was conducted to test the influence of different photoperiods (LD 6:18, 12:12, 18:6, and 22:2) on locomotor activity, the results showing that even under an extremely long photoperiod, tench activity is restricted to dark hours. The third experiment examined the effect of light intensity on locomotor activity rhythms. When fish were exposed to decreasing light intensities (from 300:0 lux to 30:0, 3:0, and 0.3:0 lux) while maintaining a constant photoperiod (LD 12:12), the highest percentage of locomotor activity was in all cases associated with the hours of complete darkness (0 lux). In short, our results clearly show that (a) tench is a species with a strictly nocturnal behavior, and (b) daily activity rhythms gradually entrain after shifting the LD cycle and persist under free-running conditions, pointing to their circadian nature. However, light strongly influences activity rhythms, since (c) the length of the active phase is directly controlled by the photophase, and (d) strictly nocturnal behavior persists even under very dim light conditions (0.3 lux). The above findings deepen our knowledge of tench behavior, which may help to optimize the aquacultural management of this species, for example, by adjusting feeding strategies to their nocturnal behavior.