Serotonin is a neurotransmitter which is hypothesized to affect mood. Darkness is suggested to affect the serotonin level greatly and hence mood. This work aimed to study the effect of prolonged darkness on serotonin level in blood and detect which method is best to over come its hazardous effect on mood, and whether excess feeding of carbohydrate and chocolate or exercise training or intermittent light exposure or all of them combined together can combate this hazardous effect compared to the use of antidepressant drugs. Seventy rats were included in this study. They were divided into seven groups. The first group was the control group fed on normal chow. The groups from two to seven were subjected to complete darkness for one month. The second group was fed on normal chow. The third group werefed on excess carbohydrate and chocolate. The fourth group its rats were fed on normal chow and subjected all through the month to undergo exercise swimming for fifteen minutes every day in a shallow beaker. The fifth group its rats were fed on normal chow and subjected to light exposure episodes for fifteen minutes twice daily. The sixth group its rats were fed on excess carbohydrate and chocolate and undergo exercise swimming for fifteen minutes in a shallow beaker every day and they were subjected to light exposure episodes for fifteen minutes twice daily. The seventh group was fed on normal chow and its rats were given antidepressant drug Nardil at a dose of 5 mg/day for one month. At the end of the month samples of blood were collected to measure serotonin level and all rats were subjected to drowning in a deep beaker filled with water and time to resist drowning was detected for each group. Rats of each group were sacrificed and histologic slides were made to show the effect of serotonin on the brain tissue. There was significant decrease of the serotonin level and time to resist drowning in the second group compared to control group. There was a non significant increase in the serotonin level and time to resist drowning in the third group as well as in the fourth and fifth compared to the second group. There was a significant increase in the serotonin level and time to resist drowning in the sixth group compared to the second group. There was a non significant increase in serotonin level and time to resist drowning in the seventh group compared to third group as well as with the fourth and fifth groups There was a significant increase in the serotonin level and time to resist drowning in the seventh group subjected to complete darkness and fed on normal chow and given antidepressant drug Nardil at a dose of 5 mg/day for one month compared to the second group fed on normal chow and subjected to complete darkness for one month. There was a significant increase in the serotonin level and time to resist drowning in the sixth group compared to the seventh group. Conclusion: continuous darkness may decrease serotonin level in blood and hence may cause depression. combined effect of eating excess carbohydrates and chocolate and daily exercise for fifteen minutes and exposure to light may be beneficial to increase serotonin level and hence affect mood positively and overcome depression even more than antidepressant drugs.
