Effects of 5,7-dihydroxytriptamine (5,7-DHT) on circadian locomotor activity of the blow fly, Calliphora vicina

The biogenic amine serotonin (5-HT) is a neuromodulator in both vertebrates and invertebrates. It has been shown that serotonin, apart from its distinct effects on behavior, also plays a morphoregulatory role during the ontogeny of the insect's nervous system. The role of serotonin in modulating circadian locomotor activity of the blow fly, Calliphora vicina was explored. Injection of a specific neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), into the hemolymph appeared to significantly reduced the level of locomotor activity and lengthened the period (tau) of circadian rhythmicity. After drug injection in constant darkness flies continued with their free-running rhythm of a locomotor activity, depending on the time of 5,7-DHT injection. This compound causes phase delay when administered in the early subjective day, and phase advance in the late subjective day. This effect is the opposite of the phase response curve obtained for 5-HT injections. This suggests that 5-HT might act as an entraining agent via the output pathway by feedback to clock neurons in the brain. Some of the injected insects regained their normal level of activity after a few days. These findings suggest a potential role for serotonin as modulator of circadian rhythms in insect including regulation of the level of locomotor activity

Locomotor activity rhythms (actograms) of the blow fly, in constant dark at 26 °C (double plotted)

<p><b>Copyright information:</b></p><p>Taken from "Effects of 5,7-dihydroxytriptamine (5,7-DHT) on circadian locomotor activity of the blow fly, "</p><p>Journal of Insect Science 2003;3():-.</p><p>Published online 14 May 2003</p><p>PMCID:PMC524654.</p><p>Copyright © 2003. Open access; copyright is maintained by the authors.</p> It shows unperturbated free-running activity with τ = 20.9 h in the pre-treated fly. On Day 9, 0.5 µg of 5,7-DHT in 1µl of insect saline/ascorbic acid was injected (arrow) in early subjective day. This caused phase delay by a few hours. The level of locomotor activity was greatly reduced and period was lengthened to 21.4h. The reduction in activity level started 2 days after drug injection and after 4 more days normal level of locomotor activity was regained. Periodograms for the appropriate sections of the activity records are shown alongside the actograms. Lines are drawn through activity periods for better visual inspection of the phase shifts

Mean (± SD) length of the period (τ) in hours before and after treatment with 5,7-DHT drug

<p><b>Copyright information:</b></p><p>Taken from "Effects of 5,7-dihydroxytriptamine (5,7-DHT) on circadian locomotor activity of the blow fly, "</p><p>Journal of Insect Science 2003;3():-.</p><p>Published online 14 May 2003</p><p>PMCID:PMC524654.</p><p>Copyright © 2003. Open access; copyright is maintained by the authors.</p> The period after treatment significantly (

Mean locomotor activity (α) per 24 h of recording and coefficient (α/ρ) before injection of 5,7-DHT and after treatment with this compound

<p><b>Copyright information:</b></p><p>Taken from "Effects of 5,7-dihydroxytriptamine (5,7-DHT) on circadian locomotor activity of the blow fly, "</p><p>Journal of Insect Science 2003;3():-.</p><p>Published online 14 May 2003</p><p>PMCID:PMC524654.</p><p>Copyright © 2003. Open access; copyright is maintained by the authors.</p> Both parameters were significantly (

Circadian activity rhythm of the house fly continues after optic tract severance and lobectomy

Under constant conditions, locomotor activity in about 50% of 63 adult Musca domestica continued to be rhythmic after bilateral severance of optic tracts or bilateral lobectomy. Apparently, the optic lobes of Musca do not contain the oscillator for rhythmic control of locomotor activity as has been proposed for other insects. In 20% of the individuals, several circadian components of activity rhythms were found after operation indicating a role of the optic lobes in the coupling of oscillators. The remaining 30% of the flies with severed optic tracts appeared to be arrhythmic. Most of these flies had vacuolized tissue in the central brain. However, disruption of rhythmicity did not correlate with a common pattern of degeneration. Therefore no conclusions can be drawn as to the localization of the circadian control of locomotor activity in the brain. Flies showing an arrhythmic activity pattern could still be synchronized by LD cycles. Activity did not occur solely during the light period as is the case in controls; but was phase delayed by about 6 hr towards the dark period. Since all flies with severed optic tracts could be synchronized by LD cycles, Musca domestica must possess extraocular photoreceptors