Circadian Rhythm in Pineal N‐Acetyltransferase Activity: Rapid Phase Reversal and Response to Shorter than 24‐Hour Cycles (IV)

Abstract

N-Acetyltransferase (NAT) is an enzyme whose rhythmic activity in the pineal gland and retina is responsible for circadian rhythms in melatonin. The NAT activity rhythm has circadian properties such as persistence in constant conditions and precise control by light and dark. Experiments are reported in which chicks (Gallus domesticus), raised for 3 weeks in 12 h of light alternating with 12 h of dark (LD12:12), were exposed to 1-3 days of light-dark treatments during which NAT activity was measured in their pineal glands. (a) In LD12:12, NAT activity rose from less than 4.5 nmol/pineal gland/h during the light-time to 25-50 nmol/pineal gland/h in the dark-time. Constant light (LL) attenuated the amplitude of the NAT activity rhythm to 26-45% of the NAT activity cycle in LD12:12 during the first 24 h. (b) The timing of the increase in NAT activity was reset by the first full LD12:12 cycle following a 12-h phase shift of the LD12:12 cycle (a procedure that reversed the times of light and dark by imposition of either 24 h of light or dark). This result satisfies one of the criteria for NAT to be considered part of a circadian driving oscillator. (c) In less than 24-h cycles [2 h of light in alternation with 2 h of dark (LD2:2), 4 h of light in alternation with 4 h of dark (LD4:4), and 6 h of light in alternation with 6 h of dark (LD6:6)], NAT activity rose in the dark during the chicks' previously scheduled dark-time but not the previously scheduled light-time of LD12:12. In a cycle where 8 h of light alternated with 8 h of dark (LD8:8), NAT activity rose in both 8-h dark periods, even though the second one fell in the light-time of the prior LD12:12 schedule.(ABSTRACT TRUNCATED AT 250 WORDS)

Clonidine in vivo mimics the acute suppressive but not the phase‐shifting effects of light on circadian rhythm of serotonin N‐acetyltransferase activity in chick pineal gland

“…recently been the subject of intensive investigations [Binkley et al, 1981[Binkley et al, , 1987Binkley, 1983;Robertson and Takahashi, 1988b;Zatz, 1989;Zatz and Mullen, 1988a,b;Zatz et al, 19881. In the present study, a more detailed analysis of the circadian clock regulating melatonin biosynthesis in chick pineal gland has been carried out. Furthermore, in parallel experiments the effects of light and clonidine on the rhythm in vivo of pineal NAT activity was examined.…”

Circadian Fluctuation of Catecholamines in the Cockroach Brain-Subesophageal Ganglion Complex detected by HPLC-ECD

“…Apart from the gross anatomy of the circadian system, however, the neurochemical mechanisms of information transmission within the circadian system in terms of neuro-hormones, neurotransmitters or neuromodulators have not been sufficiently investigated in them (e.g., Evans, 1980;Brown and Nestler, 1985;Takeda et al, 1985). This is a great setback in the study of the circadian system when one envision a rapid progress in the research after melatonin has been identified as a modulatory agent in the vertebrate circadian system (Deguchi, 1979;Binkley et al, 1987). The recent arrival of HPLC with electrochemical detector (ECD) has, however, opened an avenue for research on the role of neurotransmitter monoamines in the circadian clock mechanism in insects, where their contents in tissue samples must be minute.…”