**Abbreviations**

*Melatonin - The Hormone of Darkness and Its Therapeutic Potential and Perspectives*

As shown in **Figure 2**, whole blood 5-HT levels were significantly lower in depressed patients at 8:30 10:30, 12:30, and 14:30. The blood concentration of 5-HT

*Diurnal variation of blood serotonin levels of healthy men and patients of major depression. Ordinate, blood levels of 5-HT; abscissa, time when blood was taken. \*\*p < 0.01 control vs. depression, \*0.05, levels at 8:30 vs.* 

In the group of depression, the lowest value was shown at 8:30 and the level

Platelet 5-HT content is most likely regulated by the platelet transport activity. Variations of 5-HT uptake in depressed patients have been reported by several

Seasonal changes of serotonin (5-HT) uptake in blood platelets from depressed patients and normal controls were studied over a 2-year period to know if seasonal variations were present [26]. A measure of the number of 5-HT uptake sites in normal controls and depressed patients was significantly higher in fall and winter than in spring and summer. The number of 5-HT uptake in the depressed patients was lower than in normal controls throughout the year. Normal controls showed lower number in April and June. A similar trend was present in the depressed patients but

Blood levels of melatonin, 5-HT, cortisol, prolactin, and serotonin uptake by platelets were measured at 08:00 to 08:00 hours of the following day in healthy men in age from 27 to 35 years [27]. The active transport of 5-HT by platelets was shown to be significantly correlated with melatonin blood levels. This finding suggests either a direct effect of melatonin on 5-HT active transport or the influence of the

So far depressive disorders are considered to be associated with various neurobiological alterations like hyperactivity of the hypothalamic-pituitary-adrenal axis, altered neuroplasticity, and altered circadian rhythms. Unfortunately, the causal

the lowest values were found in the month of December.

suprachiasmatic nucleus on serotonin uptake by platelets.

showed a circadian variation.

*10.30 of depressive patients.*

**4. Discussion of part 2**

groups [26–28].

**Figure 2.**

progressively increased to 14:30.

**140**

