Yoshihiko Chiba

Post-embryonic development of circadian rhythm in the cricket, Gryllus bimaculatus: A rhythm reversal

SummaryLocomotor activity of the male cricketGryllus bimaculatus DeGeer was recorded from the 7th or last (8th) instar nymph. The nymph showed a diurnal rhythm (nymphal rhythm = NR), while the adult, on the contrary, was nocturnal (adult rhythm = AR) (Fig. 1). This rhythm reversal occurred suddenly 3 to 5 days after the imaginal molt, almost simultaneously with the first spermatophore formation and the start of stridulation (calling song) (Fig. 2). In addition to the antiphase relationship, both rhythms also differed in the freerunning period (tau) and wave form. Tauscdd was significantly longer in NR (24.33 h) than in AR (23.91 h) (Fig. 3). AR was characterized by a sharp activity peak in each cycle, which NR, however, lacked (Fig. 1, 3, 6). On the basis of these differences, two possibilities are discussed; one is that NR and AR are separate oscillations and the other is that both are coupled to different phase points of one oscillation.

Characterization of an optic lobe circadian pacemaker by in situ and in vitro recording of neural activity in the cricket, Gryllus bimaculatus

SummaryThe nature of the circadian rhythms of the optic lamina-medulla compound eye complex was examined in male crickets Gryllus bimaculatus by recording the multiple unit activity from the optic lobe in situ and in vitro. In most in situ preparations, the neural activity of the complex was higher during the subjective night than during the subjective day, both under constant light and dark. The same pattern was also obtained from nymphal crickets, suggesting that the properties of the pacemaker are common to both nymphs and adults. In a few cases, both diurnal and nocturnal increments in the activity were simultaneously observed, indicating there are two neuronal groups conveying different circadian information. The circadian rhythm was also demonstrated in the optic lobes in vitro, providing evidence that the optic lobe contains the circadian pacemaker that is capable of generating the rhythmicity without any neural or humoral factors from the rest of the animal.

Light cycle during post-embryonic development affects adult circadian parameters of the cricket (Gryllus bimaculatus) optic lobe pacemaker

Abstract The circadian pacemaker of the cricket Gryllus bimaculatus , driving the locomotor rhythm, has been localized in the optic lobe. The motion of the optic lobe pacemaker could be monitored by recording the efferent neural activity of the optic lobe from the distal cut end of the optic stalk which is a long nerve trunk connecting the medulla and lobula. We compared the circadian rhythm of the optic lobe efferents among the different developmental groups of animals, which were reared under the 24 h light-dark cycle with either of the following three light-to-dark ratios, i.e. 16-8, 12–12 or 8–16 h. Although all animals showed the electrical activity peaking in the subjective night, effects of lengthening the dark phase from 8 to 16 h on the optic lobe pacemaker occurred in the following three ways. (1) The ratio of subjective night-to-day increased about 2 times, (2) the rising phase was lengthened by 3 h, and (3) the rhythms phase to the light cycle advanced by about 4 h. Possible mechanisms and the adaptive significance of these pacemaker plasticity are discussed.

Circadian rhythm in the neurally isolated lamina-medulla-complex of the cricket, Gryllus bimaculatus

Abstract Efferent neuronal activities of the neurally isolated lamina-medulla-complex of the cricket ( Gryllus bimaculatus ) optic lobe were recorded extracellularly from the optic stalk using a suction electrode. The multiple unit activities of the lamina-medulla-compound eye-system exhibited clear circadian rhythms under constant conditions. In constant light, all specimens exhibited a peak discharge frequency in the subjective night, free-running with a period longer than 24 h. On the other hand, either diurnal or nocturnal increase occurred in specimens kept under constant darkness or in insects with optic nerve severed. Removal of the cerebral lobe and/or suboesophageal ganglion did not affect these rhythms. These results may be regarded as almost conclusive evidence that the lamina-medulla-complex involves a neural mechanism, i.e. a circadian oscillator, which can generate periodic activity without any neural input from the other central nervous system structures.

timrit Lengthens Circadian Period in a Temperature-Dependent Manner through Suppression of PERIOD Protein Cycling and Nuclear Localization

ABSTRACT A fundamental feature of circadian clocks is temperature compensation of period. The free-running period of ritsu(timrit ) (a novel allele oftimeless [tim]) mutants is drastically lengthened in a temperature-dependent manner. PER and TIM protein levels become lower in timrit mutants as temperature becomes higher. This mutation reduces per mRNA but not tim mRNA abundance. PER constitutively driven by the rhodopsin1 promoter is lowered in ritmutants, indicating that timrit mainly affects the per feedback loop at a posttranscriptional level. An excess of per + gene dosage can ameliorate allrit phenotypes, including the weak nuclear localization of PER, suggesting that timrit affects circadian rhythms by reducing PER abundance and its subsequent transportation into nuclei as temperature increases.

Chronobiological analysis of a new clock mutant, Toki, in Drosophila melanogaster.

We have isolated a new semidominant clock mutant Toki on the second chromosome in Drosophila melanogaster. This mutant differs from the wild-type Canton-S in several properties as follows. Larger values are obtained in the phase angle difference (phi, the time from lights-off in a 24-hr light-dark cycle to an activity offset), the ratio of activity time to rest time (alpha/rho) and the activity level. The free-running period (tau) is 25.3 hr, one hour longer than in the wild-type. In the phase response curve (PRC), the ratio between the delay and the advance portion is larger and the cross-over point occurs later, although there is no difference in amplitude of the mutants PRC (Type I). The rhythm is more sensitive to the light intensity, becoming obscure in darker condition. Toki interacts with other clock mutations, pers, perL and And, in such a way that tau s associated with these three X-linked mutations are lengthened and phi values become smaller.

Mutual interactions between optic lobe circadian pacemakers in the cricket Gryllus bimaculatus

SummaryThe coupling mechanism between the bilaterally paired optic lobe circadian pacemakers in the cricket Gryllus bimaculatus was investigated by recording locomotor activity, under constant light or constant red light, after the optic nerve was unilaterally severed.1.The majority (about 70%) of the animals showed a locomotor rhythm with 2 rhythmic components; one freerunning with a period of 25.33 ± 0.41 (SD) h and the other with 24.36 ± 0.37 (SD) h under constant light (Fig. 3A).2.Removal of the intact side optic lobe abolished the longer period component (Fig. 4A), while the operation on the operated side caused a reverse effect (Fig. 4B), indicating that the longer and the shorter period components are driven by the pacemaker on the intact and the operated side, respectively.3.The activity driven by a pacemaker was inhibited during the subjective day of the contralateral pacemaker (circadian time 0–10, Fig. 5).4.The freerunning periods of the two components were not constant but varied as a function of the mutual phase angle relationship (Figs. 3A, 7, 8). These results suggest that the 2 optic lobe pacemakers weakly couple to one another and that the cricket maintains a stable temporal structure in its behavior through the phase-dependent mututal inhibition of activity and the phase-dependent freerunning period modulation.

Circadian phase-response curves for light in nymphal and adult crickets, Gryllus bimaculatus

Abstract The circadian locomotor rhythm of the cricket, Gryllus bimaculatus, is regulated by two pacemakers, one located in each optic lamina-medulla complex of the protocerebrum, and is readily entrained to light-dark cycles. We investigated effects of light pulses on nymphal (diurnal) and adult (nocturnal) free-running locomotor rhythms. When a 3 h light pulse was given, adult crickets free-running under constant darkness showed a clear phase shift in a manner dependent on time of day. The phase-response curves for the light pulses showed phase delays in the early subjective night, phase advances in the late subjective night, and little response in the mid-subjective day. Unilateral removal of the lamina-medulla-compound eye complex had no effects on phase-responsiveness to 3 h light pulses, suggesting that the shape of the phase-response curve reflects the property of a single circadian pacemaker. The average free-running period for the operated animal [23.73±0.25 (SD) h, N = 58] was significantly shorter than that of the intact animal [23.86±0.24 (SD) h, N = 99] (t-test, P

Distribution of Circadian Photoreceptors in the Compound Eye of the Cricket Gryllus bimaculatus

Adult male crickets (Gryllus bimaculatus) show a nocturnal circadian locomotor rhythm, which is driven by the pacemaker in the optic lamina-medulla complex and synchronizes to the light-dark (LD) cycle received by the compound eye. To see whether there was any specially differentiated circadian photoreceptor area in the eye, we examined the effect of a partial reduction of various areas of the compound eye, in addition to a removal of the contralateral optic lamina-medulla-compound eye complex, on entrainability of the locomotor rhythm. All operated animals showed a response to the LD cycle in their locomotor rhythm, no matter which area of the eye was left intact: They either stably entrained to an LD cycle or showed a sign of weak entrainment. The capacity for stable entrainment was still retained when only 262 ommatidia were left. Transient cycles needed for re entrainment, following a 6-hr phase advance of the LD cycle, were measured in 20 reduced-eye animals showing clear stable entrainment. They were in inverse proportion to the number of ommatidia in the reduced eye: The fewer ommatidia there were, the more transient cycles were observed (r = -0.76, p < 0.001). These results suggest that almost the whole area of the compound eye may contain circadian photoreceptors, and that the photic information from each ommatidium may additively affect the circadian clock to entrain via neural integration mechanisms.

Photoperiodic entrainment of locomotor activity in crickets (Gryllus bimaculatus) lacking the optic lobe pacemaker

Abstract The locomotor activity of 40 crickets receiving bilateral optic lamina-medulla removal as 7th-instar nymph was recorded under a light cycle and then constant darkness, and the records were analyzed statistically by an autocorrelogram and maximal entropy spectrum method. The activity of the nymphal stage was severely reduced and no rhythmicity was detected for the first few weeks following the operation. After the imaginal moult, activity gradually increased up to 20 times the nymphal activity. About 50% of the adult crickets restored a rhythmicity with peaks in the light phase, unlike the nocturnal rhythm of intact crickets. The synchronization of the activity was probably due to the newly established neural connection between the retina and the cut end of the optic stalk. The onset of the rhythmic activity preceded lights-on, suggesting the involvement of an endogenous mechanism. In constant darkness, a half of the rhythmic cricket lost the rhythmicity. However, 21% of the crickets retained the rhythmicity and the remaining 26% exhibited an ultradian rhythmicity. On the basis of these results, the involvement of moltiple oscillators, outside the optic lobe, in the regulation of the circadian locomotor rhythm is discussed.