The effects of a number of short-term exogenous stimuli on pineal serotonin-N-acetyltransferase activity in rats

Abstract

The present study deals with the question as to what extent the sympathetically innervated rat pineal gland is affected by a number of short-term exogenous stimuli given during day-time, as assessed by measuring pineal serotonin-N-acetyltransferase activity (NAT) which is directly proportional to melatonin formation. In male Sprague-Dawley rats kept under LD 12:12 pineal NAT was statistically significantly depressed by physical immobilization for 2 hours, swimming for 15 min in water of 10 and 30 degrees C, exposure for 2 hours to cold (5 degrees C) or heat (40 degrees C), noise (90 db) for 2 hours and hunger for 17 hours. An increase in NAT was noted after swimming for 15 min in water of 20 degrees C. No effect was detectable after 17 hours of thirst or hunger combined with thirst and in one of 2 experiments involving exposure to heat (40 degrees C, 2 hours) and insulin-induced hypoglycemia. In animals kept under continuous illumination for 48 hours, immobilization resulted in a slightly smaller decrease than under LD 12:12 and insulin-induced hypoglycemia led to a striking increase of NAT. As the changes in pineal NAT are brought about by rather strong exogenous stimuli it is suspected that the rat pineal gland during day-time is not very susceptible to ambient factors of normal range.

Melatonin formation in different parts of the guinea-pig pineal complex as assessed over 24 hours

“…Previous studies in rats have shown that short-term exposure to ether has no demonstrable effect on pineal NAT activity (Welker and Vollrath, 1984). Trunk blood was collected and the pineal gland together with the habenular commissure removed from the brain.…”

Swimming Depresses Nighttime Melatonin Content without Changing N-Acetyltransferase Activity in the Rat Pineal Gland

“…Physical immobilization for 2 h reportedly increased NAT activity and melatonin content [9,10] and, in another report, sup pressed NAT activity [27]. Swimming for 2.5 h has been shown to have a dramatic effect on daytime pineal NAT activity if the pineal sympathetic nerve endings have been rendered nonfunctional [16].…”

“…Swimming for 2.5 h has been shown to have a dramatic effect on daytime pineal NAT activity if the pineal sympathetic nerve endings have been rendered nonfunctional [16]. Insulin-induced hypoglyce mia caused an increase in NAT activity and melatonin con tent in the intact rat pineal by 2 h after insulin injection [9,27], while the same treatment was shown to depress NAT activity in another study [27], Hypoglycemia following in sulin administration has been associated with elevated plasma catecholamines [27]. At 1-4 h after lights on, aniReceived: November 20.…”

Melatonin synthesis in the pineal gland of the Richardson's ground squirrel (Spermophilus richardsonii): Influence of age and insulin-induced hypoglycemia

“…Thus, 1. pineal melatonin synthesis in the Richardson's ground squirrel (Reiter et al, 1983) is much less sensitive to light inhibition than is that the pineal gland of the rat (Rollag et al, 1980;Lynch et al, 1981;Webb et al, 1985); 2. although dampened, the pineal melatonin rhythm persists for at least a week when ground squirrels are exposed to continual room light compared to the rat (Rollag et al, 1980;Webb et al, 1985) where suppression of the melatonin cycle immediately follows light exposure of even low intensity; 3. preliminary evidence (unpublished observations) indicates that the melatonin rhythm in the pineal gland of young (30-35 day old) ground squirrels may be may somewhat less robust than that of adult animals unlike in the rat ; 4. stressful stimuli may influence the melatonin cycle in the rat (Lynch et al, 1973(Lynch et al, , 1975(Lynch et al, , 1977Welker and Vollrath, 1984) but this would appear not to be the case in the ground squirrel. This latter statement is based on the observation that when the 24-hour-rhythms of pineal N-acetyltransferase (NAT) activity and melatonin levels are measured within a week after ground squirrels are captured, the cycles are predictably uniform with low values occurring during the day and high levels at night.…”

“…This is interesting from the point of view that wild-captured animals that are caged (multiple animals per cage without access to a burrow) are highly stressed but this seems not to have an impact on what appears to be a normal melatonin cycle. The melatonin cycle of the rat is, at least under certain conditions, readily altered by aversive stimuli (Lynch et al, 1973(Lynch et al, , 1975Welker and Vollrath, 1984;Joshi et al, 1986).…”