The effect of pinealectomy on circadian plasma melatonin levels in house sparrows and European starlings.

We determined 24-hr plasma melatonin profiles in intact, sham-pinealectomized, and pinealectomized European starlings (Sturnus vulgaris) and house sparrows (Passer domesticus) in a light-dark (LD) cycle and in constant darkness (DD). In the intact and sham-pinealectomized birds of both species, a melatonin rhythm was found, with low levels during the day and high levels during the night. Pinealectomy abolished the nighttime peak of melatonin in both species; hence, levels were low at all times sampled. This uniform response of plasma melatonin to pinealectomy contrasts with the differential response of circadian activity rhythms to pinealectomy for these two species. In DD, locomotor activity in pinealectomized house sparrows is usually arrhythmic, whereas in starlings a rhythm usually persists. This suggests that in the latter species free-running circadian rhythms are not necessarily dependent on a rhythm in plasma melatonin. The same is true for the synchronized activity rhythm observed in pinealectomized birds of both species in LD, as well as for the damped rhythm that persists in pinealectomized house sparrows following an LD-to-DD transfer. The results are consistent with the hypothesis that the pineal and its periodic output of melatonin constitute only one component in a system of at least two coupled pacemakers. They also suggest that there are species differences in the relative role played by the pineal and other pacemakers in controlling circadian rhythms in behavior.     

Circadian rhythm of ERG in Iguana iguana: role of the pineal

In green iguanas, the pineal controls the circadian rhythm of body temperature but not the rhythm of locomotor activity. As part of a program to investigate the characteristics of this multioscillator circadian system, the authors studied the circadian rhythms of the electroretinographic response (ERG) and asked whether the pineal gland is necessary for the expression of this rhythm. ERGs from a total of 24 anesthetized juvenile iguanas were recorded under four different conditions: (a) complete darkness (DD), (b) dim light-dark cycles (dLD), (c) constant dim light (dLL), and (d) pinealectomized in DD. Results demonstrate that the b-wave component of the ERG shows a very clear circadian rhythm in DD and that this rhythm persists in dLL and entrains to dLD cycles. The ERG response is maximally sensitive during the subjective day. Pinealectomy does not abolish the circadian rhythm in ERG, demonstrating that the oscillator responsible for the ERG rhythm is located elsewhere.     

Period and phase control in a multioscillatory circadian system (Iguana iguana)

The circadian system of the lizard Iguana iguana is composed of several independent pacemakers that work in concert: the pineal gland, retinae of the lateral eyes, and a fourth oscillator presumed to be located in the hypothalamus. These pacemakers govern the circadian expression of multiple behaviors and physiological processes, including rhythms in locomotor activity, endogenous body temperature, electroretinogram, and melatonin synthesis. The numerous, easily measurable rhythmic outputs make the iguana an ideal organism for examining the contributions of individual oscillators and their interactions in governing the expression of overt circadian rhythms. The authors have examined the effects of pinealectomy and enucleation on the endogenous body temperature rhythm (BTR) and locomotor activity rhythm (LAR) of juvenile iguanas at constant temperature both in LD cycles and in constant darkness (DD). They measured the periods (tau) of the circadian rhythms of LAR and BTR, the phase relationships between them in DD (psiAT), and the phase relationship between each rhythm and the light cycle (psiRL). Pinealectomy lengthened tau of locomotor activity in all animals tested and abolished the BTR in two-thirds of the animals. In those animals in which the BTR did persist following pinealectomy, tau lengthened to the same extent as that of locomotor activity. Pinealectomy also delayed the onset of activity with respect to its normal phase relationship with body temperature in DD. Enucleation alone had no significant effect on tau of LAR or BTR; however, after enucleation, BTR became 180 degrees out of phase from LAR in DD. After both pinealectomy and enucleation, 4 of 16 animals became arrhythmic in both activity and body temperature. Their data suggest that rhythmicity, period, and phase of overt circadian behaviors are regulated through the combined output of multiple endogenous circadian oscillators.     

The effects of pinealectomy and blinding on the circadian locomotor activity rhythm in the Japanese newt,Cynops pyrrhogaster

We examined the effects of pinealectomy and blinding (bilateral ocular enucleation) on the circadian locomotor activity rhythm in the Japanese newt, Cynops pyrrhogaster. The pinealectomized newts were entrained to a light-dark cycle of 12 h light and 12 h darkness. After transfer to constant darkness they showed residual rhythmicity for at least several days which was gradually disrupted in prolonged constant darkness. Blinded newts were also entrained to a 12 h light/12 h dark cycle. In subsequent constant darkness they showed free-running rhythms of locomotor activity. However, the freerunning periods noticeably increased compared with those observed in the previous period of constant darkness before blinding. In blinded newts entrained to the light/dark cycle the activity rhythms were gradually disrupted after pinealectomy even in the presence of the light/dark cycle. These results suggest that both the pineal and the eyes are involved in the newt's circadian system, and also suggest that the pineal of the newt acts as an extraretinal photoreceptor which mediates the entrainment of the locomotor activity rhythm.Abbreviations circadian period - DD constant darkness - LD cycle, light-dark cycle - LD 12:12 light-dark cycle of 12 h light and 12 h darkness     

Circadian rhythms of locomotor activity and temperature selection in sleepy lizards, <Emphasis Type="Italic">Tiliqua rugosa</Emphasis>

This study examined whether the daily rhythms of locomotor activity and behavioural thermoregulation that have previously been observed in Australian sleepy lizards (Tiliqua rugosa) under field conditions are true circadian rhythms that persist in constant darkness (DD) and whether these rhythms show similar characteristics. Lizards held on laboratory thermal gradients in the Australian spring under the prevailing 12-hour light : dark (LD) cycle for 14 days displayed robust daily rhythms of behavioural thermoregulation and locomotor activity. In the 13-day period of DD that followed LD, most lizards exhibited free-running circadian rhythms of locomotor activity and behavioural thermoregulation. The predominant activity pattern displayed in LD was unimodal and this was retained in DD. While mean levels of skin temperature and locomotor activity were found to decrease from LD to DD, activity duration remained unchanged. The present results demonstrate for the first time that this species’ daily rhythm of locomotor activity is an endogenous circadian rhythm. Our results also demonstrate a close correlation between the circadian activity and thermoregulatory rhythms in this species indicating that the two rhythms are controlled by the same master oscillator(s). Future examination of seasonal aspects of these rhythms, may, however, cause this hypothesis to be modified.     

Photic entrainment of daily rhythm pattern of locomotor activity in sea bass (Dicentrarcus labrax)

The aim of this study was to evaluate the circadian rhythm of daily locomotor activity in sea bass exposed to three different artificial lighting regimes including 12/12, 24/0, and 0/24 L/D periods, and scheduled daytime feeding. Daily rhythm of locomotor activity during 12/12 L/D was observed, whereas locomotor activity recorded during 24/0 and 0/24 L/D resulted arrhythmic. Statistical differences in mesor values among the photoperiods and between light and dark phases of each photoperiod were found. During the 12/12 and 0/24 L/D, the fish were active mostly during the light phase. During 24/0 L/D, a phase inversion occurred. The results showed that photoperiod is a dominant synchronizer in sea bass, and that the appetite in this fish follows daily rhythms which does not match the imposed feeding schedule, suggesting the absence or the lability of internal process that couples feeding cycles and biological rhythms.     

Locomotor activity rhythm in four wrasse species under varying light conditions

Under controlled laboratory conditions, the locomotor activity rhythms of four species of wrasses (Suezichthys gracilis, Thalassoma cupido, Labroides dimidiatus andCirrhilabrus temminckii) were individually examined using an actograph with infra-red photo-electric switches in a dark room at temperatures of 21.3–24.3°C, for 7 to 14 days. The locomotor activity ofS. gracilis occurred mostly during the light period under a light-dark cycle regimen (LD 12:12; 06:00-18:00 light, 18:00-06:00 dark). The locomotor activity commenced at the beginning of the light period and continued until a little before the beginning of dark period. The diel activity rhythm of this species synchronizes with LD. Under constant illumination (LL) this species shows distinct free-running activity rhythms varying in length from 23 hrs. 39 min. to 23 hrs. 47 min. Therefore,S. gracilis appears to have a circadian rhythm under LL. However, in constant darkness (DD), the activity of this species was greatly suppressed. All the fish showed no activity rhythms in DD conditions. After DD, the fish showed the diel activity rhythm with the resumption of LD, but this activity began shortly after the beginning of light period. The fish required several days to synchronize with the activity in the light period. Therefore,S. gracilis appeared to continue the circadian rhythm under DD. InT. cupido, the locomotor activity commenced somewhat earlier than the beginning of the light period and continued until the beginning of the dark period under LD. The diel activity rhythm of this species synchronizes with LD. Under LL, four of the five specimens of this species tested showed free-running activity rhythms for the first 5 days or longer varying in length from 22 hrs. 54 min. to 23 hrs. 39 min. Although the activity of this species was suppressed under DD, two of five fish showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 38 min. to 23 hrs. 50 min. under DD. Therefore, it was ascertained thatT. cupido has a circadian rhythm. InL. dimidiatus, the locomotor activity rhythm under LD resembled that observed inT. cupido. The diel activity rhythm of this species synchronizes with LD. Under LL, four of seven of this species showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 07 min. to 25 hrs. 48 min. Although the activity of this species was suppressed under DD, three of five fish showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 36 min. to 23 hrs. 41 min. under DD. Therefore, it was ascertained thatL. dimidiatus has a circadian rhythm. Almost all locomotor activity of C.temminckii occurred during the light period under LD. The diel activity rhythm of this species coincides with LD. Under LL, two of four of this species showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 32 min. to 23 hrs. 45 min. Although the activity of this species was suppressed under DD, one of the four fish showed free-running activity rhythms throughout the experimental period. The length of the free-running period was 23 hrs. 21 min. under DD. Therefore,C. temminckii appeared to have a circadian rhythm. According to field observations,S. gracilis burrows and lies in the sandy bottom whileT. cupido, L. dimidiatus, andC. temminckii hide and rest in spaces among piles of boulders or in crevices of rocks during the night. It seems that the differences in nocturnal behavior among the four species of wrasses mentioned above are closely related to the intensity of endogenous factors in their locomotor activity rhythms.     

Daily oscillation in melatonin synthesis in the Turkey pineal gland and retina: diurnal and circadian rhythms

The aim of the present study was to examine arylalkylamine N-acetyltransferase (AANAT) activity and melatonin content in the pineal gland and retina as well as the melatonin concentration in plasma of the turkey (Meleagris gallopavo), an avian species in which several physiological processes, including reproduction, are controlled by day length. In order to investigate whether the analyzed parameters display diurnal or circadian rhythmicity, we measured these variables in tissues isolated at regular time intervals from birds kept either under a regular light-dark (LD) cycle or under constant darkness (DD). The pineal gland and retina of the turkey rhythmically produced melatonin. In birds kept under a daily LD cycle, melatonin levels in the pineal gland and retina were high during the dark phase and low during the light phase. Rhythmic oscillations in melatonin, with high night-time concentrations, were also found in the plasma. The pineal and retinal melatonin rhythms mirrored oscillations in the activity of AANAT, the penultimate enzyme in the melatonin biosynthetic pathway. Rhythmic oscillations in AANAT activity in the turkey pineal gland and retina were circadian in nature, as they persisted under conditions of constant darkness (DD). Transferring birds from LD into DD, however, resulted in a potent decline in the amplitude of the AANAT rhythm from the first day of DD. On the sixth day of DD, pineal AANAT activity was still markedly higher during the subjective dark than during the subjective light phase; whereas, AANAT activity in the retina did not exhibit significant oscillations. The results indicate that melatonin rhythmicity in the turkey pineal gland and retina is regulated both by light and the endogenous circadian clock. The findings suggest that environmental light may be of primary importance in the maintenance of the high-amplitude melatonin rhythms in the turkey.     

Effects of constant darkness and constant light on circadian organization and reproductive responses in the ram

The relationship between circadian rhythms in the blood plasma concentrations of melatonin and rhythms in locomotor activity was studied in adult male sheep (Soay rams) exposed to 16-week periods of short days (8 hr of light and 16 hr of darkness; LD 8:16) or long days (LD 16:8) followed by 16-week periods of constant darkness (dim red light; DD) or constant light (LL). Under both LD 8:16 and LD 16:8, there was a clearly defined 24-hr rhythm in plasma concentrations of melatonin, with high levels throughout the dark phase. Periodogram analysis revealed a 24-hr rhythm in locomotor activity under LD 8:16 and LD 16:8. The main bouts of activity occurred during the light phase. A change from LD 8:16 to LD 16:8 resulted in a decrease in the duration of elevated melatonin secretion (melatonin peak) and an increase in the duration of activity corresponding to the changes in the ratio of light to darkness. In all rams, a significant circadian rhythm of activity persisted over the first 2 weeks following transfer from an entraining photoperiod to DD, with a mean period of 23.77 hr. However, the activity rhythms subsequently became disorganized, as did the 24-hr melatonin rhythms. The introduction of a 1-hr light pulse every 24 hr (LD 1:23) for 2 weeks after 8 weeks under DD reinduced a rhythm in both melatonin secretion and activity: the end of the 1-hr light period acted as the dusk signal, producing a normal temporal association of the two rhythms. Under LL, the 24-hr melatonin rhythms were disrupted, though several rams still showed periods of elevated melatonin secretion. Significant activity rhythms were either absent or a weak component occurred with a period of 24 hr. The introduction of a 1-hr dark period every 24 hr for 2 weeks after 8 weeks under LL (LD 23:1) failed to induce or entrain rhythms in either of the parameters. The occurrence of 24-hr activity rhythm in some rams under LL may indicate nonphotoperiodic entrainment signals in our experimental facility. Reproductive responses to the changes in photoperiod were also monitored. After pretreatment with LD 8:16, the rams were sexually active; exposure to LD 16:8, DD, or LL resulted in a decline in all measures of reproductive function. The decline was slower under DD than LD 16:8 or LL.(ABSTRACT TRUNCATED AT 400 WORDS)     

Seasonal effects of pinealectomy on testicular recrudescence and secretory activity of seminal vesicles in the catfish Heteropneustes fossilis (Bloch)

The effects of pinealectomy on testicular activity and secretory activity of seminal vesicles were examined in the catfish Heteropneustes fossilis under various combinations of photoperiod and temperature during different periods of the annual reproductive cycle. Pinealectomy had no effect on gonadal activity during the preparatory, prespawning and spawning periods of the reproductive cycle. However, during the postspawning period, under long (LD 14:10) or short (LD 9:15) photoperiod at 25° C or at gradually increasing ambient temperature, pinealectomy accelerated testicular recrudescence and secretory activity of the seminal vesicles. Nevertheless. during this period the presence of the pineal facilitated the recrudescence of testes and seminal vesicles in catfish exposed to continuous light (LL), continuous darkness (DD) and 12 hL:l2 hD (LD) at 25° C. These findings suggest that the role of the pineal in catfish reproduction is variable and depends upon the photoperiod and temperature regimes to which the fish are exposed, as well as on the time of the year and the state of the reproductive cycle. The results also suggest that the effects of pinealectomy in catfish are mediated through an influence on the hypothalamo-hypophyseal gonadal axis.     

Seasonal changes in the circadian activity rhythm of light-dark (LD) and completely dark (DD) regimen in the mouse submandibular gland in the presence of light-dark (LD) and completely dark (DD) regimen

Influence of seasons on circadian activity changes and the influence of one and six weeks of DD upon these changes of acid phosphatase (AP) and beta-acetylglucosaminidase (AM) was studied in the submandibular gland of sexually mature male mice. Total enzyme activity was determined in tissue homogenates at four-hour intervals in March, June, October, and February under standard LD12/12 conditions and after one and six weeks of the DD regime. The rhythms were analysed according to cosinor method. Under constant lighting conditions the seasonal differences in the AM circadian activity rhythm were found. AP activity was considerably less influenced by seasonal changes. Both enzyme activity changes were independent of each other and each rhythm was differently influenced by DD. In the case of AM the most pronounced circadian activity changes had the highest amplitude and mesor occurred in summer. The strongest influence of DD upon this enzyme activity rhythm was observed in spring and summer especially after the first week, after six weeks the acrophase returned to the LD group value (spring). In autumn and winter the reaction to DD was different to that of summer and spring. For AP the circadian changes of activity were non-rhythmic in spring, whereas in all other seasons the acrophases occurred almost at the same time in the afternoon. In DD the activity rhythm significantly changed after six weeks. In all seasons, except spring the circadian rhythm of activity was not observed after six weeks of DD. An attempt was made to explain the observed results by the certain kind of genetic memory present in laboratory animals the neurohormonal system of which is influenced by seasonal changes.     

Dissociation between the circadian rhythm of locomotor activity and the pineal clock in the Japanese newt

The circadian locomotor activity rhythm of the Japanese newt has been thought to be driven by a putative brain oscillator(s) subordinate to the pineal clock. The existence of mutual coupling between the pineal clock and the brain oscillator(s) in vivo was examined. We covered the newt's skull with aluminum foil and simultaneously reversed the light-dark cycle, thereby allowing the pineal organ to be exposed to constant darkness while the rest of the animal was exposed to the reversed light-dark cycle. In control animals, whose heads were covered with transparent plastic, the rhythm of synaptic ribbon number in the pineal photoreceptor cells was entrained to the reversed light-dark cycle. Rhythms from newts whose heads were shielded, however, were similar to those observed in the unoperated newts kept under constant darkness. The locomotor activity rhythms of both head-covered animals and control animals were entrained to the reversed light-dark cycle. These data suggest that extrapineal photoreception can entrain the putative brain oscillator(s), but not the pineal clock. Thus, at least in an aspect of photic entrainment, there seems to be little or no mutual coupling between the pineal clock and the putative brain oscillator(s) in the circadian system of the Japanese newt.Abbreviations LD light-dark - DD constant darkness - SCN suprachiasmatic nucleus - SR synaptic ribbon     

Seasonal effects of pinealectomy on the locomotor activity rhythm in the lizard Sceloporus torquatus

Adult lizards (Sceloporus torquatus) were used to test whether seasonal differences in the effects of pinealectomy upon the locomotor activity rhythm exist. Animals were field collected and exposed to artificial light - dark cycles and constant temperature in winter and summer. Free running circadian rhythms under constant temperature and dim red light were monitored using infrared light-crossings. The effects of pinealectomy were assessed by analysing the circadian parameters of free running period and activity - rest ratio in constant darkness or light - dark cycles. Results obtained indicate that pinealectomy changes the free running period of locomotor activity rhythm, irrespective of season, while seasonal differences in activity-rest ratio were detected. Our findings support the hypothesis that seasonal regulation of circadian rhythms in lizards is accomplished, in part, via the output of the pineal gland.     

Daily Oscillation in Melatonin Synthesis in The Turkey Pineal Gland and Retina: Diurnal and Circadian Rhythms

The aim of the present study was to examine arylalkylamine N‐acetyltransferase (AANAT) activity and melatonin content in the pineal gland and retina as well as the melatonin concentration in plasma of the turkey (Meleagris gallopavo), an avian species in which several physiological processes, including reproduction, are controlled by day length. In order to investigate whether the analyzed parameters display diurnal or circadian rhythmicity, we measured these variables in tissues isolated at regular time intervals from birds kept either under a regular light‐dark (LD) cycle or under constant darkness (DD). The pineal gland and retina of the turkey rhythmically produced melatonin. In birds kept under a daily LD cycle, melatonin levels in the pineal gland and retina were high during the dark phase and low during the light phase. Rhythmic oscillations in melatonin, with high night‐time concentrations, were also found in the plasma. The pineal and retinal melatonin rhythms mirrored oscillations in the activity of AANAT, the penultimate enzyme in the melatonin biosynthetic pathway. Rhythmic oscillations in AANAT activity in the turkey pineal gland and retina were circadian in nature, as they persisted under conditions of constant darkness (DD). Transferring birds from LD into DD, however, resulted in a potent decline in the amplitude of the AANAT rhythm from the first day of DD. On the sixth day of DD, pineal AANAT activity was still markedly higher during the subjective dark than during the subjective light phase; whereas, AANAT activity in the retina did not exhibit significant oscillations. The results indicate that melatonin rhythmicity in the turkey pineal gland and retina is regulated both by light and the endogenous circadian clock. The findings suggest that environmental light may be of primary importance in the maintenance of the high‐amplitude melatonin rhythms in the turkey.     

Age-related changes in 24-hour rhythms of norepinephrine content and serotonin turnover in rat pineal gland: effect of melatonin treatment

The 24-hour rhythms of pineal norepinephrine (NE) content and serotonin (5-HT) turnover [estimated from the ratio of 5-hydroxyindoleacetic acid (5-HIAA) to 5-HT] were studied in young (2 months) and aged (18-20 months) Wistar rats killed at 6 different time points throughout a 24-hour cycle. In the first study, significant changes dependent on the time of day were identified, with acrophases in the first half of the activity span for both parameters. Old rats showed significantly smaller mesor and amplitude of the 24-hour rhythm of pineal NE content. They also showed decreased amplitude of the pineal 5-HT turnover rhythm, in the absence of changes in mesor. In old rats, pineal 5-HT and 5-HIAA concentrations were 41-47% of those found in young rats. In a second study, young and old rats received daily intraperitoneal injections of melatonin (30 microg) or vehicle for 11 days at 19.00 h (i.e. 11 h after light on). Analyzed as a main factor in a factorial analysis of variance, both pineal NE content and 5-HT turnover decreased in old rats while pineal 5-HT turnover increased after melatonin treatment. Melatonin treatment augmented the amplitude of the 24-hour rhythm of pineal NE content by 120 and 52% in young and old rats, respectively. The amplitude of the 24-hour rhythm of pineal 5-HT turnover almost doubled after melatonin treatment in young rats and did not change in old rats. Melatonin injection did not modify the rhythm's acrophase. The results indicate that old rats had lower amplitude and lower mesor values of 24-hour variations in pineal NE content and 5-HT turnover. Melatonin treatment only partly restored pineal NE content and was devoid of activity on pineal 5-HT turnover and 5-HT and 5-HIAA concentration in old rats. Impairment of pineal melatonin synthesizing capacity and intrapineal responses to melatonin may underlie pineal aging in rats.     

Locomotor activity rhythm in two wrasses,Halichoeres tenuispinnis andPteragogus flagellifera,under various light conditions

The locomotor activity rhythms were examined by using an actograph with infra-red photo-electric switches for two species of wrasses, (Halichoeres tenuispinnis andPteragogus flagellifera) under various light conditions. InH. tenuispinnis, the locomotor activity of almost all fish under light-dark cycle regimen (LD12:12; 06:00–18:00 light, 18:00–06:00 dark) commenced somewhat earlier than the beginning of light period and continued till somewhat earlier than the beginning of the dark period. This species clearly showed free-running activity rhythms under both constant illumination (LL) and constant darkness (DD). Therefore,H. tenuispinnis appeared to have a circadian rhythm. The length of the circadian period ranged from 23 hr. 30 min. to 23 hr. 44 min. under LL, and was from 23 hr. 39 min. to 24 hr. 18 min. under DD. On the other hand, the locomotor activity ofP. flagellifera occurred mostly in the light period under LD 12:12. The activity of this species continued through LL, but was greatly suppressed in DD, so that none of the fish had any activity rhythm in both constant conditions. It was known from field observations thatH. tenuispinnis burrowed and lay in sandy bottoms, whileP. flagellifera hid and rested in bases of seagrasses and shallow crevices of rocks during the night. In the present two wrasses, it seemed that the above-mentioned difference of noctural behavior was closely related to the intensity of the endogenous factor in the activity rhythm.     

Circadian Locomotor Activity Under Artificial Light in the Freshwater Crab Pseudothelphusa americana

Long-term recordings of locomotor activity were obtained from intact freshwater crabs, Pseudothelphusa americana in constant darkness (DD), constant light (LL) and different light-dark (LD) protocols. Bimodal rhythms were typically observed in this crab when subjected to DD or LD, with bouts of activity anticipating lights-on and lights-off, respectively. Freerunning circadian rhythms were expressed in both DD and LL for longer than 30 days. In DD, we observed that some animals presented different period lengths for each activity component. During LL, activity was primarily unimodal, however spontaneous splitting of the rhythms were observed in some animals. When activity was recorded under artificial long days, the morning bouts maintained their phase relationship but the evening bouts changed their phase relationship with the Zeitgeber. Our results indicate that, bimodal locomotor activity rhythm in the crab Pseudothelphusa americana is variable among organisms. The characteristics of phase relationship with LD and responses to LL for morning and evening bouts, suggest that, locomotor activity could be driven by multiple oscillators, and that coupling between these oscillators may be regulated by light.     

Locomotor Activity Rhythms in Cave Catfishes, Genus Taunayia, from Eastern Brazil (Teleostei: Siluriformes: Heptapterinae)

We studied the locomotor rhythmicity in heptapterine catfishes, genus Taunayia, under free-running conditions (DD) and LD cycles (12:12). Taunayia sp., anophthalmic and depigmented undescribed species from a cave in northeastern Brazil, is the fourth Brazilian troglobitic catfish studied with focus on circadian rhythms. Weak free-running rhythmicity, with absence of significant circadian components, was observed for this species when compared to the epigean, eyed relatives. On the other hand, the studied troglobitic catfishes in general presented significant circadian rhythms under LD cycles, with activity peaks in the night phase probably corresponding to nocturnal activity pattern inherited from their epigean ancestors. However, no residual oscillations were observed after transition from LD to DD. This indicates masking of activity by light-dark cycles. Regression of circadian rhythmicity in the stable, permanently dark subterranean habitat was also observed for other cave fishes. Such regression corroborates the notion that circadian rhythmicity is mainly selected in the epigean environment by ecological factors, namely daily cycles of light and/or temperature.     

Temporal Organization in Locomotor Activity of the Hypogean Loach, Nemacheilus Evezardi, and its Epigean Ancestor

Locomotor activity rhythm in the hypogean population of Nemacheilus evezardi was recorded first under light-to-dark (LD) 12 : 12 h cycle and then DD. The results were compared with that of its epigean counterpart held under comparable regimes. In LD 12 : 12, while hypogean loach exhibited a distinct bimodality in its locomotor activity rhythm, it was altogether absent in the case of epigean population. In hypogean loach, dark-to-light transition peak in LD was observed to free-run under DD. The same was not discernible in case of epigean loach. The locomotor activity rhythm in epigean fish was noticed to free-run in DD either from the dawn peak or dusk peak in LD. It is hypothesized that the hypogean fish still possesses a functional oscillator underlying its overt circadian rhythm in locomotor activity. The ecophysiological significance of these findings is yet to be fully understood.     

Inconsistency in the expression of locomotor and ERG circadian rhythms in the German cockroach, Blattella germanica (L.).

ERG recordings from German cockroaches showed that the amplitude of light-evoked responses have a circadian rhythmicity in adult males that coincided with the locomotor circadian rhythm. The peak of the response occurred during the subjective night, and the circadian period was less than 24 h under DD condition. In contrast, although the locomotor circadian rhythm was masked by the development of ovaries and pregnancy in females, their visual responses displayed circadian rhythmicity. This inconsistency in expression of locomotor and visual sensitivity circadian rhythms in females implied separate pacemakers for these two overt rhythms. After severing the optic nerves, changes in ERG amplitude of the operated cockroaches still displayed a circadian rhythm under DD condition, demonstrating that the visual sensitive pacemaker was located in the eye and independent from the locomotor pacemaker.