Ontogeny of Light‐Induced Decrease of N‐Acetyltransferase Activity in Explanted Chick Pineal Glands

Abstract

The ontogeny of chick pineal serotonin N-acetyltransferase (NAT) activity was investigated in explanted chick pineal glands at 4, 10 and 21 d of age. Nocturnal levels of the enzyme and the response of the enzyme to light exposure were determined in pineal glands maintained in short-term culture at each age. The results indicate that nocturnal NAT activity was increased in the glands from older birds. Nocturnal levels of NAT activity at the time of the initiation of the experiment were threefold greater in glands from 21-d-old birds as compared to that in glands from 4-day-old chicks. The response to light was similar in all three ages examined; light induced a significant decrease in NAT activity within 60 min in explanted glands from 4-d-old chicks and within 180 min in the glands from the 10- and 21-d-old chicks. A paradoxical transient increase in enzyme activity occurred immediately (within 5 min) following light exposure which was significant in the glands from the youngest chicks, and present, but more variable, in the older chicks. These data indicate that the nocturnal enzyme activity is greater in glands from older birds, but that light exposure of explanted glands initiates a transient rise followed by a decrease in NAT activity at all three ages.

Effects of light and an alpha-2-adrenergic agonist on serotonin N-acetyltransferase activity in chick pineal gland

“…The half-time for light-induced inhibition of nocturnal enzyme activity in intact chick pineal glands is in agreement with previous studies from this laboratory (Rudeen et al, 1990), but is much slower than that observed in pineal glands from adult chickens (Binkley et al, 1975). Binkley et al (1975) demonstrated a half-time for light induced inhibition of NAT in adult birds exposed to light at the mid-point of the nocturnal regime to be approximately 10min.…”

“…Animals were maintained under these conditions for three days before use. Previous studies indicate that NAT activity in explanted pineal glands from chicks at this age is sensitive to light inhibition (Rudeen et al, 1990). At the end of the acclimation period, each chick was decapitated, and the pineal gland was removed using aseptic techniques.…”

Ontogeny of the Daily Profile of Plasma Melatonin in European Starlings Raised under Long or Short Photoperiods

“…For example, in rats, day-night differences in NAT gene expression in the pineal become apparent at postnatal day 5, shortly before rhythmical changes in NAT activity are detected (Pfeffer and Stehle, 1998). However, in birds, or at least in precocial birds, there is evidence for rhythmicity in pineal NAT mRNA (Herichová et al, 2001), NAT activity (Binkley and Geller, 1975;Herichová et al, 2001;Rudeen et al, 1990), and pineal melatonin content (Herichová et al, 2001;Zeman et al, 1992) before hatching. Interestingly, although chick embryos incubated on a long photoperiod show a rhythm in plasma melatonin, embryos on a short photoperiod do not, and have consistently low melatonin (Zeman et al, 1999).…”