Changes in the Metabolic Profile of Melatonin Synthesis-Related Indoles during Post-Embryonic Development of the Turkey Pineal Organ

Abstract

Research on age-dependent changes in pineal activity has been limited almost exclusively to melatonin (MLT). This study determined, for the first time, the alterations occurring in the metabolic profile of MLT synthesis-related indoles during the post-embryonic development period in birds. Turkeys reared under a 12 h light/dark cycle were euthanized at 2 h intervals for 24 h at the ages of 2, 7, 14, and 28 days and 10, 20, 30, and 45 weeks. The results showed prominent changes in the metabolic profile of indoles during development and could be distinguished in four stages. The first stage, from hatching to the age of 2 weeks, was characterized by a decrease in the 5-hydroxytryptophan concentration and an increase in the concentrations of serotonin (5-HT), MLT, 5-methoxyindoleacetic acid, and 5-methoxytryptamine (5-MTAM). During the second stage, around the age of 1 month, the concentrations of N-acetylserotonin (NAS) and MLT reached a maximum. The synthesis and degradation of 5-HT were also the highest. The third stage, around the age of 10 weeks, was characterized by decreased levels of 5-HT (approximately 50%) and 5-hydroxyindoleacetic acid and a high level of 5-MTAM. The last stage, covering the age of 20 to 45 weeks, was characterized by a large decrease in the synthesis, content, and degradation of 5-HT. Despite these changes, there were no prominent differences in the nocturnal levels of NAS and MLT between the third and fourth stages. The concentrations of all tryptophan derivatives showed daily fluctuations until the age of 45 weeks.

Keywords: birds; development; indoles; melatonin; pineal organ; serotonin; turkey.

Figure 1

Activity (means) of tryptophan hydroxylase, TPH (A), aromatic amino acid decarboxylase, AADC (B), arylalkylamine N-acetyltransferase, AA-NAT (C), and N-acetylserotonin O-methyltransferase, ASMT (D) in the pineal organs of turkeys at the ages of 2, 7, 14, 28 days and 10, 20, 30, 45 weeks. The horizontal bar represents the periods of light and dark phases of the daily cycle. The letters on the charts show differences between age groups at each time-point in Duncan’s test. The letters below the charts show differences between time-points within a group in Duncan’s test. The same letters indicate means which are not significantly different. Insert in figure (B) shows AADC activity in the pineal organs of turkeys aged 2, 7, and 14 days at the limited y-axis scale.

Figure 2

Concentration (means) of tryptophan in the pineal organs of turkeys at the ages of 2, 7, 14, 28 days and 10, 20, 30, 45 weeks. The horizontal bar represents the periods of light and dark phases of the daily cycle. The letters on the charts show differences between age groups at each time-point in Duncan’s test. The same letters indicate means which are not significantly different.

Figure 3

Concentrations (means) of 5-hydroxytryptophan, 5-HTRP (A), and serotonin, 5-HT (B), in the pineal organs of turkeys at the ages of 2, 7, 14, 28 days and 10, 20, 30, 45 weeks. The horizontal bar represents the periods of light and dark phases of the daily cycle. The letters on the charts show differences between age groups at each time-point in Duncan’s test. The letters below the charts show differences between time-points within a group in Duncan’s test. The same letters indicate means which are not significantly different.

Figure 4

Concentrations (means) of N-acetylserotonin, NAS (A), and melatonin, MLT (B), in the pineal organs of turkeys at the ages of 2, 7, 14, 28 days and 10, 20, 30, 45 weeks. The horizontal bar represents the periods of light and dark phases of the daily cycle. The letters on the charts show differences between age groups at each time-point in Duncan’s test. The letters below the charts show differences between time-points within a group in Duncan’s test. The same letters indicate means which are not significantly different.

Figure 5

Concentrations (means) of 5-hydroxyindole acetic acid, 5-HIAA (A), and 5-hydroxytryptophol, 5-HTOL (B), in the pineal organs of turkeys at the ages of 2, 7, 14, 28 days and 10, 20, 30, 45 weeks. The horizontal bar represents the periods of light and dark phases of the daily cycle. The letters on the charts show differences between age groups at each time-point in Duncan’s test. The letters below the charts show differences between time-points within a group in Duncan’s test. The same letters indicate means which are not significantly different.

Figure 6

Concentrations (means) of 5-methoxyindole acetic acid, 5-MIAA (A), and 5-methoxytryptophol, 5-MTOL (B), in the pineal organs of turkeys at the ages of 2, 7, 14, 28 days and 10, 20, 30, 45 weeks. The horizontal bar represents the periods of light and dark phases of the daily cycle. The letters on the charts show differences between age groups at each time-point in Duncan’s test. The letters below the charts show differences between time-points within a group in Duncan’s test. The same letters indicate means which are not significantly different.

Figure 7

Concentration (means) of 5-methoxytryptamine, 5-MTAM, in the pineal organs of turkeys at the ages of 2, 7, 14, 28 days and 10, 20, 30, 45 weeks. The horizontal bar represents the periods of light and dark phases of the daily cycle. The letters on the charts show differences between age groups at each time-point in Duncan’s test. The letters below the charts show differences between time-points within a group in Duncan’s test. The same letters indicate means which are not significantly different. The concentration of 5-MTAM was undetectable in the pineal organs of turkeys aged 2 days.

Figure 8

Contents (means) of melatonin, MLT (A), and serotonin, 5-HT (B), at their peak values in the pineal organs of turkeys at the ages of 2, 7, 14, 28 days and 10, 20, 30, 45 weeks.