Light-Dark Entrainment of Circadian Activity Rhythms of the Diurnal Indian Palm Squirrel (Funambulus pennanti)

A recent focus of chronobiological studies has been to establish diurnal models as alternatives to the more frequently used nocturnal rodents. In the present study, light-dark (LD) entrainment characteristics were examined in one diurnal species, the Indian palm squirrel ( Funambulus pennanti ). Palm squirrels showed strongly diurnal locomotor activity rhythms (~ 88 percent) under light-dark (LD) cycles, with activity bimodally distributed during the L phase. In comparison to a dim LD cycle, exposure to a bright LD cycle caused a phase advance in the onset of activity, an increase in daily activity levels and an increase in the duration of activity. Percentage diurnality, however, did not vary between bright and dim LD cycles. Activity rhythms reentrained in significantly fewer days after an 8 hour phase delay of the LD cycle compared to an 8 hour phase advance. In both cases, the direction of reentrainment followed the direction of the LD shift. When exposed to single light pulses (1 hour) presented at the same time each day, 6/7 squirrels entrained. Under a skeletal photoperiod cycle (2 x 1 hour light pulses each day), 6/8 squirrels showed stable entrainment. The remaining squirrels exhibited rhythm splitting, with each component synchronising in an unstable manner with one of the light pulses. Under entrainment to single light pulses and to the skeletal photoperiod cycle, the phase angle of entrainment was negatively correlated with t. Finally, when exposed to a skeletal scotoperiod cycle (2 x 1-hour dark pulses each day), only 3/8 squirrels entrained, while the others free-ran. Two of the entrained squirrels showed spontaneous phase reversals during entrainment. As with other species, the activity rhythm of palm squirrels appears to be controlled by two separate self-sustaining oscillators. The strongly diurnal nature of palm squirrels make them a promising diurnal model for studies examining endogenous and exogenous influences on circadian functioning.     

Pineal, Photoperiod and Gonadal Function in the Indian Palm Squirrel, Funambulus pennanti

Effects of morning and evening injections of pineal 5-methoxyindoles (MI), melatonin (aMT) and 5-methoxytryptamine (MT), for 60 continuous days, were observed on the testes of sham-operated (SO) and pinealectomized (Px) Indian palm squirrel, Funambulus pennanti maintained under different photoperiods during the gonad active phase. Long photoperiod (LP) of 14L:10D appeared stimulatory to the testes and caused a significant increase in the weight and seminiferous tubule diameter of both SO and Px animals, as compared to the animals under natural day-length (NDL). Short photoperiod (SP) of 10L:14D had an inhibitory influence and reduced the testes weight and its tubule diameter. aMT and MT injections during evening hours significantly reduced testes weight and tubule diameter of SO and Px animals under NDL, LP and SP. However morning injections, under all conditions, were without any significant effect. The results suggest an inhibitory effect of aMT and MT, under above photoperiodic conditions, on the testes of this tropical mammal. The time of administration of the MI is important in the expression of the effect.     

Effect of Single Low Intensity Light Pulse Exposure and Melatonin Treatment on the Circadian Variation of Melatonin in Indian Palm Squirrel Funambulus pennanti

The endogenous circadian rhythm of melatonin in mammals provides information regarding the resetting response of the mammalian circadian timing system in response to the changes in light dark cycle. Photoperiodic changes are reported to have acute and chronic effect on melatonin rhythm. Our aim in present experiment was to study the effect of single light pulse of low intensity on the circadian variation of melatonin in Indian palm squirrel. A short pulse of 5min was given to the animals at 22:55 h on day 16th in natural photoperiodic condition of long day length (LD ~ 13.55:10.05) and melatonin levels were estimated at every 4-h interval on ZT scale on day 17th (DD). Observations suggest that the light pulse given on day 16th suppressed the melatonin level on day 17th (DD). Besides this, it was also found that there was phase delay in the peak value of melatonin. Further, we tested the ability of single melatonin injection on the light pulse induced phase shift of acrophase of melatonin in this species F. pennanti. We injected the single physiological dose of melatonin (25 microgram/100 g body wt.) just 5 min prior to the commencement of light pulse (22:50 h) on day 16 and melatonin levels were estimated on day 17th as above. Injection of melatonin prior to light pulse altered the suppressing and phase shifting effect of light in terms of peak concentration of melatonin in squirrels. Above data may lead us to conclude that the biological clock mechanism controlling circadian rhythm of melatonin in this rodent is in response to the phase shifting effect of light and acute melatonin treatment. Further, we may suggest that single melatonin injection has the capability to entrain melatonin rhythm but a dose dependent study is required to facilitate the suggestion.     

Effect of Single Low Intensity Light Pulse Exposure and Melatonin Treatment on the Circadian Variation of Melatonin in Indian Palm Squirrel Funambulus pennanti

The endogenous circadian rhythm of melatonin in mammals provides information regarding the resetting response of the mammalian circadian timing system in response to the changes in light dark cycle. Photoperiodic changes are reported to have acute and chronic effect on melatonin rhythm. Our aim in present experiment was to study the effect of single light pulse of low intensity on the circadian variation of melatonin in Indian palm squirrel. A short pulse of 5min was given to the animals at 22:55 h on day 16th in natural photoperiodic condition of long day length (LD ~ 13.55:10.05) and melatonin levels were estimated at every 4-h interval on ZT scale on day 17th (DD). Observations suggest that the light pulse given on day 16th suppressed the melatonin level on day 17th (DD). Besides this, it was also found that there was phase delay in the peak value of melatonin. Further, we tested the ability of single melatonin injection on the light pulse induced phase shift of acrophase of melatonin in this species F. pennanti . We injected the single physiological dose of melatonin (25 microgram/100 g body wt.) just 5 min prior to the commencement of light pulse (22:50 h) on day 16 and melatonin levels were estimated on day 17th as above. Injection of melatonin prior to light pulse altered the suppressing and phase shifting effect of light in terms of peak concentration of melatonin in squirrels. Above data may lead us to conclude that the biological clock mechanism controlling circadian rhythm of melatonin in this rodent is in response to the phase shifting effect of light and acute melatonin treatment. Further, we may suggest that single melatonin injection has the capability to entrain melatonin rhythm but a dose dependent study is required to facilitate the suggestion.     

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.     

Significance of Nonparametric Light Effects in Entrainment of Circadian Rhythms in Owl Monkeys (Aotus Lemurinus Griseimembra) by Light-Dark Cycles

In a total of 12 adult Colombian owl monkeys, Aotus lemurinus griseimembra, the significance of nonparametric light effects for the entrainment of the circadian system by light-dark (LD) cycles was studied by carrying out (a) phase-response experiments testing the phase-shifting effect of 30-min light pulses (LPs) of 250 lx applied at various phases of the free-running circadian activity rhythm (LL 0.2 lx) and (b) synchronization experiments testing the entraining effect of 24-h single LP photoperiods consisting of 30-min L of 80 lx and 23.5-h D of 0.5 lx (sP 0.5) and skeleton photoperiods consisting of two 30-min LPs of 80 lx, given against a background illuminance of 0.5 lx either symmetrically at 12-h intervals (PP 12:12) or asymmetrically at 9- and 15-h intervals (PP 9:15). The phase-response characteristics in Aotus, as evidenced by the phase-response curve, generally correspond to those of nocturnal rodents, proving that this neotropical simian primate chronobiologically is a genuine nocturnal species. When free-running with a spontaneous period close to 24 h (24.3 ± 0.1 h), the PP 12:12 produced entrainment in only two of five owl monkeys, whereas the sP 0.5 entrained four of them. The PP 9:15, however, brought about stable entrainment of the circadian rhythms of locomotor activity, feeding activity, and core temperature in all animals tested (n = 8). Changes in phase position of the activity time with the endogenous rhythm entrained by a PP 12:12, by an sP 0.5, or by a PP 9:15 give evidence that both LPs of a skeleton photoperiod contribute to the phase setting of the circadian system. When free-running with a considerably lengthened spontaneous period (τ ≥ 25.5 h), even the sP 0.5 and the PP 9:15 failed to entrain the owl monkeys' circadian rhythms, whereas a 24-h photoperiod with a very long LP of 3 h caused entrainment. The results indicate that in Aotus lemurinus griseimembra, in addition to the nonparametric light effects, parametric light effects play a significant role in the entrainment of circadian rhythms by LD cycles.     

The pineal gland of the Indian palm squirrel, Funambulus pennanti (Wroughton)

In the adult palm squirrel, F. pennanti the pineal is a club shaped, elongated structure with a connective tissue capsule. It consists of various types of pinealocytes, glial cells, neurons, nerve fibres, blood vessels and connective tissue. Two types of pinealocytes could be identified by light microscopy. They are large rounded with centrally placed nucleus, and small rounded pinealocytes. They have medium sized processes stainable with Alcian blue, periodic acid Schiff and Nissl methods. The pinealocytes are not stainable with bromophenol blue. However, they are moderately stainable with PAS, Sudan black and Baker's acid hematin. Neurons are seen either singly or in groups with axonal processes. Cystic cavities often lined by cells are a normal feature of adult squirrel pineal, and the lining cells are both pinealocytes and glial cells. Often neuronal endings are seen terminating on these lining cells. PAS positive globules were also seen inside the cysts. In some squirrel pineals, fibrous cysts with an inner core of cells are also seen. Occasionally groups of lymphocytes were also encountered in the pineal. In the fetal pineal, the cells are both larger and smaller ones and arranged in a cortex and medulla pattern and no cystic cavities are seen. The third ventricle enters the base of the pineal as pineal recess.     

Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle

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Circadian Rhythms of Locomotor Activity in Lycosa tarentula (Araneae, Lycosidae) and the Pathways of Ocular Entrainment

Lycosa tarentula is a ground-living spider that inhabits a burrow where it awaits the appearance of prey or conspecifics. In this study, circadian rhythms of locomotor activity were examined as well as the ocular pathway of entrainment. Thirty-three adult virgin females were examined under constant darkness (DD); all of them exhibited robust circadian rhythms of locomotor activity with a period averaging 24.1h. Fourteen of these spiders were studied afterwards under an LD 12:12 cycle; they usually entrained to in the first or second day, even when the light intensity was as low as 1 lx. During the LD cycle, locomotor activity was generally restrained to the darkness phase, although several animals showed a small amount of diurnal activity. Ten males were also examined under LD; they were also nocturnal, but were much more active than the females. Seven females were examined under constant light (LL); under this they became arrhythmic. Except for the anterior median eyes (OMAs), all the eyes were capable of entraining the locomotor activity to an LD cycle. These results demonstrate that under laboratory conditions and low light intensities locomotor activity of Lycosa tarentula is circadian and in accordance with Aschoff's 'rule'. Only OMAs are unable to entrain the rhythm; the possible localization of circadian clock is therefore discussed.     

Circadian Rhythms of Locomotor Activity in Lycosa tarentula (Araneae,Lycosidae) and the Pathways of Ocular Entrainment

Lycosa tarentula is a ground-living spider that inhabits a burrow where it awaits the appearance of prey or conspecifics. In this study, circadian rhythms of locomotor activity were examined as well as the ocular pathway of entrainment. Thirty-three adult virgin females were examined under constant darkness (DD); all of them exhibited robust circadian rhythms of locomotor activity with a period averaging 24.1h. Fourteen of these spiders were studied afterwards under an LD 12:12 cycle; they usually entrained to in the first or second day, even when the light intensity was as low as 1 lx. During the LD cycle, locomotor activity was generally restrained to the darkness phase, although several animals showed a small amount of diurnal activity. Ten males were also examined under LD; they were also nocturnal, but were much more active than the females. Seven females were examined under constant light (LL); under this they became arrhythmic. Except for the anterior median eyes (OMAs), all the eyes were capable of entraining the locomotor activity to an LD cycle. These results demonstrate that under laboratory conditions and low light intensities locomotor activity of Lycosa tarentula is circadian and in accordance with Aschoff's 'rule'. Only OMAs are unable to entrain the rhythm; the possible localization of circadian clock is therefore discussed.     

Antigonadotropic activity of pineal gland of the Indian palm squirrel Funambulus pennanti

Bioassay of the pineal extract of F. pennanti was performed in immature female mice which was previously sensitized with human chorionic gonadotrophin. Reduction of ovarian and uterine weights indicated an antigonadotropic nature of the pineal gland of this animal.     

Cytology of the hypophysis, pars anterior of the Indian five-striped palm squirrel, Funambulus pennanti (Wroughton)

By employing various staining techniques the pituitary cells of the squirrels, Funambulus pennanti, can broadly be divided into 'acidophilic', 'basophilic' and 'amphophilic' types. The acidophilic cell types include somatotrophs and lactotrophs. The basophilic cell types include thyrotrophs, folliculotrophs and interstitiotrophs while the amphophilic cells are recognized as corticotrophs. The identification of the pituitary cells and their histochemical characteristics are described at the light microscopical level. Attempt has been made to interpret the cells identified in the present study on a comparative and tinctorial basis.     

Entrainment of Melatonin Rhythms in Rams By Symmetrical Light-Dark Cycles of Different Period Length

The objective of this study was to investigate the entrainment of melatonin rhythms in rams using symmetrical light-dark cycles of different period length. Five groups of six He de France rams were kept in 12L: 12D for 7 weeks and then (i) 12L: 12D, (ii) 11L: 11D, (iii) 10L: 10D, (iv) 13L: 13D and (v) 14L: 14D for a further 3 weeks. Environmental factors other than the light dark cycle were not controlled. The onset and offset of the plasma melatonin rhythm in DD after 3 weeks of the respective light treatments was assessed for 48 hr, immediately after transferring to DD. The duration of secretion in DD was positively related to the length of the previous dark phase. The phase of the melatonin rhythm with respect to the anticipated dark phase suggested entrainment with no change in phase-relationship to the zeitgeber by 12L: 12D and 13L : 13D. Entrainment with a phase-delay or a phase-advance was apparent after 11L: 11D and 14L: 14D, but the individual rhythms were not all synchronized with respect to each other after 10L: 10D. Activity recordings for 2-3-week periods during 12L: 12D, 10L: 10D and 14L: 14D all showed a major 24-hr component at all times, with activity during the light phase in 12L: 12D. It appears that melatonin may be readily desynchronized from overt activity-rest cycles in sheep. The upper and lower entrainment limits are probably greater than 28 hr and close to 20 hr cycles, respectively.     

Acetylcholinesterase-positive intrapineal neuronal system in the palm squirrel Funambulus pennanti (Wroughton)

A well-developed acetylcholinesterase (AChE)-positive neuronal system could be demonstrated in the pineal organ of the palm squirrel. There are two longitudinal nerve tracts which run all along the margin of the pineal organ from its distal to proximal regions. These nerve tracts are confluent distally. Another short, but deep tract was seen in the middle part of the pineal organ which joins one of these tracts. A large number of AChE-positive neurons whose processes actually form the tracts are present all along the pineal organ. They are distinguished into multipolar and pseudounipolar/unipolar neurons. A few neurons seen outside the nerve tract form a network of nerve fibres among the pinealocytes and also link the main tracts. The nerve tracts appear wavy, irregular and tortuous. A large number of round ring-like bodies seen in close association with neuronal perikarya and nerves may represent the axo-somatic and axo-dendritic contacts.     

Social Cues Accelerate Reentrainment of Circadian Rhythms in Diurnal Female Octodon Degus (Rodentia-Octodontidae)

Previous studies paired diurnal Octodon degus undergoing/phase advances (phase-shifters) with those entrained to a light-dark (LD) cycle (donors). Results included opposite outcomes of male and female social cues on resynchronization following 6-h advances in females, but no effect of social cues on male resynchronization. The first experiment determined if social cues could influence resynchronization rates of circadian rhythms in male and female degus following a 6-h phase delay of the LD cycle. Female phase-shifters resynchronized temperature and activity rhythms 20–35% faster when housed with either entrained (donor) females or males compared with females housed alone. No significant differences in resynchronization rate for phase-shifting males existed between test conditions. This experiment extends the previous finding that females, but not males, respond strongly to donor cues to increase resynchronization rates in the presence of light. A second experiment determined that accelerated resynchronization rates of female phase-shifters housed with female donors were due to social cues directly affecting the circadian system rather than the result of social masking. On the day following resynchronization with or without a female donor present, phaseshifters were transferred individually to constant conditions (DD). The temperature and activity rhythms of female phase-shifters free-ran from the point at which resynchronization occurred for both the control and experimental females. Thus, social cues accelerate true reentrainment, not masking, of the circadian system in the presence of a LD cycle in female degus. Donor cues from females enhance reentrainment after advances and delays, but the effect of male donor cues is dependent on the direction of the phase shift.