Pineal rhythm of N-acetyltransferase activity and melatonin in the male badger, Meles meles L, under natural daylight: relationship with the photoperiod

Effects of irradiation on the sensitivity of melatonin release to norepinephrine in cultured pineal bodies of rats

We measured levels of basal and norepinephrine (NE) -induced melatonin release in cultured pineal bodies of rats just after and 2 days after irradiation (20 or 200 Gy) or sham-irradiation. On the day of irradiation, basal and NE-induced melatonin release were not affected by irradiation. Two days after irradiation, basal melatonin levels in both irradiated groups were significantly lower than those in control group, whereas NE-induced melatonin levels in the irradiated groups were higher than those in the control group. These results suggested that irradiation decreases basal melatonin synthesis in pineal glands but that melatonin response to NE is increased after irradiation.

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)