The pineal melatonin rhythm and its regulation by light in a subterranean rodent, the valley pocket gopher (Thomomys bottae).
The daytime and nightime levels of pineal N-acetyltransferase (NAT) activity, hydroxyindole-O-methyltransferase (HIOMT) activity, and melatonin were measured in adult male and female valley pocket gophers, Thomomys bottae. This species was chosen for study because it is a subterranean rodent that inhabits burrows whose openings to the surface are closed. Therefore, under field conditions it is estimated that the pocket gopher spends roughly 99% of its time in absolute darkness in underground burrows. When wild captured pocket gophers were maintained under a light:dark cycle (light intensity during the day of roughly 140 microW/cm2), nightime levels of pineal NAt activity and melatonin content were higher than values measured during the day; on the other hand, HIOMT activity in the pineal gland was similar in the day and at night. When pocket gophers were exposed to an extended light period (220 microW/cm2) 4 hr into the night, the rise in melatonin synthesis normally associated with darkness onset was not inhibited. Also, when gophers were acutely exposed to a light intensity of 400 microW/cm2 for 1 hr beginning 4 hr after darkness onset, neither high nocturnal levels of pineal NAT nor pineal melatonin contents were reduced. Finally, when pocket gophers were exposed to a 600 microW/cm2 light intensity at either 4 hr or 8 hr into the dark period, pineal melatonin synthesis remained elevated at a level comparable to that measured in dark-exposed controls.(ABSTRACT TRUNCATED AT 250 WORDS)
Reiter
R J
RJ
Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio 78284-7762.
Reiter
M N
MN
Hattori
A
A
Yaga
K
K
Herbert
D C
DC
Barlow-Walden
L
L
D000121:Acetylserotonin O-Methyltransferase / Q000378:metabolism; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D008027:Light; D008297:Male; D008550:Melatonin / Q000378:metabolism*; D010870:Pineal Gland / Q000378:metabolism*; D012377:Rodentia / Q000378:metabolism*
D000121:Acetylserotonin O-Methyltransferase; D001191:Arylamine N-Acetyltransferase; D008550:Melatonin