Diurnal fluctuation in the enzyme activity and the messenger RNA level of pineal serotonin N-acetyltransferase in normal and hereditary microphthalmic rats

Immunohistochemical detection of tyrosine hydroxylase and concentrations of monoamines in the substantia nigra and hypothalamus of hereditary microphthalmic rats

We compared tyrosine hydroxylase immunoreactivity in the substantia nigra and hypothalamus of hereditary microphthalmic rats with that of normal rats. A considerable number of neuronal cell bodies expressing tyrosine hydroxylase were present in the substantia nigra of the microphthalmic mutant as well as normal rats. Neuronal cells positive for tyrosine hydroxylase in the hypothalamus were fewer than in the substantia nigra in both rats. The concentrations of monoamines (dopamine, noradrenaline, adrenaline, and serotonin) in the substantia nigra and hypothalamus in the microphthalmic mutant were approximately the same as those of normal rats, although the diurnal fluctuation of a few monoamines was observed in normal rats. These results suggest that the metabolic aspects of catecholamine in the substantia nigra and hypothalamus of the microphthalmic mutant rat do not markedly differ from those of normal rats.

Developmental changes in the mRNA levels of IGF-I and its related genes in the reproductive organs of Japanese quail (Coturnix coturnix japonica)

Summary Insulin-like growth factor-I (IGF-I) is involved in the regulation of growth and differentiation of a variety of vertebrate tissues. The biological actions of IGF-I are mediated mainly by the IGF-I receptor (IGF-IR) and partly by the insulin receptor (IR) and modulated by IGF binding proteins (IGFBP). We conducted studies designed to clarify the possible roles of IGF system in the development of the avian reproductive organs. We cloned cDNAs of IGF-I, IGF-IR, IR and IGFBP-2 of Japanese quail and simultaneously measured the expression of these genes in the quail liver, testis and oviduct at different ages using a lysate RNase protection assay. Hepatic IGF-I mRNA levels increased rapidly and remained elevated during the rapid-growing period, which coincided with the period of rapid increase in testicular weight. IGF-I mRNA was detected at each stage of developing testis examined. Its level was high at the early stage and decreased with age. IGFBP-2 mRNA in testis exhibited a similar expression pattern to that of IGF-I, whereas a divergence in IGF-I and IGF-IR gene expression was observed. Both IGF-IR and IR mRNAs increased when the testis grew rapidly and decreased when sexual maturation was almost completed. These results suggest that IGF-I may serve as an autocrine/paracrine regulator as well as an endocrine regulator in the testicular development and function of Japanese quail. In the oviduct, IGF-I, IGF-IR, IR and IGFBP-2 mRNAs were also developmentally regulated. A rapid growth of the oviduct was accompanied by a significant increase in the level of IGF-I mRNA. The expression of genes encoding IGF-IR, IR and IGFBP-2 in the oviduct exhibited a similar developmental change to that of IGF-I. These results suggest that IGF-I mainly works in an autocrine and/or paracrine manner in the oviduct during the development of this organ. The findings of the present study provide further evidence of an important role for IGF system in the development and function of the avian reproductive system.

Effects of restricted food access on circadian fluctuation of serotonin N-acetyltransferase activities in hereditary microphthalmic rats

The characteristics in diurnal fluctuation of serotonin N-acetyltransferase activity were examined in normal and microphthalmic mutant rats of the Donryu strain under ad lib or restricted feeding conditions. Under a 12:12-h light:dark (12-h LD) cycle with free access to food, normal-sighted rats exhibited typical nocturnal increases in the activity of pineal serotonin N-acetyltransferase, being more than 50-fold higher in the dark period than that in the light period, but hereditary blind rats showed nonperiodic change in the pineal enzyme activity in the average, suggesting that the rhythms in individuals have become free-running, asynchronous. When the subjective night or subjective day of the mutants was discerned by active or inactive in the locomotor activity, the pineal enzyme activities in the mutants increased at the subjective night but depressed at the subjective daytime. When food access was restricted only for 6 h in the light period of the LD cycle, normal rats still showed the nocturnal increases in the pineal enzyme activity, but hereditary blind rats manifested a blunt peak in the activity of the pineal enzyme at eating time in the light period. The results suggest that microphthalmic mutant rats maintain the ability to shift and to synchronize their circadian phases induced by restricted access to food, even if they completely lack their optic nerve and visual input to the circadian clock.

Regulation of the expression of serotonin N-acetyltransferase gene in Japanese quail (Coturnix japonica): I. Rhythmic pattern and effect of light

Serotonin N-acetyltransferase [arylalkylamine N-acetyltransferase (AANAT); EC2.3.1.87] is the rate-limiting enzyme in melatonin synthesis, and its activity exhibits a diurnal rhythm similar to that of the melatonin content in the pineal gland and retina of Japanese quail. Studies were conducted to characterize the Japanese quail AANAT cDNA, and to evaluate the expression of AANAT mRNA in the pineal gland, the retina, and other peripheral tissues. The nucleic acid sequence of a 400 bp cDNA clone obtained by RT-PCR manifested 78 and 95% homology compared to the rat and chicken AANAT cDNA, respectively, while the deduced amino acid sequence homology was 82 and 99%, respectively. AANAT mRNA content in a single pineal gland or an aliquot of eye lysate was measured by a micro-lysate protection assay. The expression of AANAT mRNA in the pineal gland and the retina exhibited circadian rhythm with peak levels at night. AANAT mRNA was also detected in the testis, but did not display a rhythmic change over a 24 hr period. AANAT mRNA was not detected in other tissues studied. Darkness during the day did not increase the pineal AANAT mRNA levels. However, unexpected light-exposure for 2 hr just after lights-off blocked the increase in AANAT mRNA, and at midnight remarkably decreased AANAT mRNA by 50%.

Regulation of the expression of serotonin N-acetyltransferase gene in Japanese quail (Coturnix japonica): II. Effect of vitamin A deficiency

Levels of serotonin N-acetyltransferase [arylalkylamine N-acetyltransferase (AANAT); EC2.3.1.87] mRNA, AANAT activity, and melatonin display a rhythmic pattern in both the pineal gland and the retina. It has been shown that vitamin A is required to maintain the rhythm of melatonin synthesis in the pineal gland of Japanese quail. To understand the mechanism underlying the direct relationship among these factors, we developed an assay system sensitive enough to determine AANAT mRNA, AANAT activity, and melatonin content from a single pineal gland of Japanese quail. Positive direct relationships were found among these three parameters. We next deprived Japanese quail of vitamin A by feeding them a vitamin A-free diet supplemented with retinoic acid, and examined the effects of vitamin A deficiency on the expression of AANAT mRNA in the pineal gland and the retina. Vitamin A deficiency reduced both the expression of AANAT mRNA and melatonin content in the pineal gland. Retinal AANAT mRNA rhythm disappeared in vitamin A-deficient quails. Moreover, the responsiveness of the pineal gland and the retina to light was reduced by vitamin A deficiency when compared with the control group.

Effects of restricted food access on diurnal fluctuation of behaviors and biochemical functions in hereditary microphthalmic rats

The characteristics in circadian rhythms of spontaneous locomotor activity, and some metabolic properties were examined in microphthalmic mutant rats of the Donryu strain under ad lib or restricted food access conditions. The growth of microphthalmic rats was retarded compared to that of normal-sighted rats from the same strain. Under a 12:12-h light:dark (LD) cycle with free access to food, normal-sighted rats showed basically nocturnal patterns of the locomotor activity rhythms, but most of microphthalmic rats manifested free-running rhythms and a few of them showed arrhythmic. When food access was restricted only for 6 h in the light period of the LD cycle, the normal and hereditary blind rats generated gradually new patterns of the locomotor activities in which the animals showed to be more active in the light period. Plasma glucose concentration in normal rats showed a peak after food consumption, but microphthalmic mutants exhibited no periodic changes of the glucose levels. Responses of the biochemical parameters of protein and mineral metabolism to restricted food access in the mutants did not differ from those in normal rats. These results suggest that microphthalmic mutant rats show the free-running circadian rhythm of locomotor activity due to a complete lack of their optic nerve and visual input to the circadian clock, but the mutants maintained the ability to shift their circadian phase induced by restricted food access similar to that in control rats, and also that the mutants have almost normal properties of biochemical and physiological functions except for glucose metabolism.