Serotonin in depression and Alzheimer's disease: Focus on SSRI's beneficial effects

Abstract

Depression is a complex and pervasive mental health disorder affecting millions globally. Serotonin, a critical neurotransmitter, plays a central role in the pathophysiology of depression. This review explores serotonin's multifaceted role in depression, focusing on its synthesis, bioavailability, receptor interactions, and the impact of various factors, including diet, stress, and gender differences. This review aims to provide a comprehensive understanding of serotonin's role in depression by examining its synthesis and structure, its bioavailability and dietary influences, and its interactions with stress and immune responses. Additionally, it investigates the influence of age, socioeconomic status, and gender on depression, and integrates findings from animal research to elucidate serotonin's impact on mood disorders and cognitive decline. A literature review was conducted using PubMed, Google Scholar, and Embase databases. Key focus areas included serotonin synthesis and receptor interactions, dietary effects on serotonin bioavailability, and the relationship between serotonin, immune responses, and stress. Gender differences, age-related factors, and socioeconomic influences on depression were also examined. Studies were thematically categorized and analyzed to provide a cohesive overview. Our review highlights that serotonin synthesis involves a complex enzymatic process, with recent structural studies revealing intricate receptor interactions. Dietary factors significantly impact serotonin levels, with interventions potentially modulating mood disorders. Stress and immune responses are linked to serotonin dynamics, with chronic stress exacerbating mood disorders and influencing cognitive decline. Animal studies underscore serotonin's role in mood regulation and cognitive function, while human research reveals how age, gender, and socioeconomic factors affect depression. The findings emphasize the need for a multidimensional approach to understanding and treating depression. Various factors, including diet, stress, and immune responses, influence serotonin's role in mood disorders. The review suggests potential therapeutic pathways involving dietary interventions and stress management. Furthermore, gender-specific considerations and the impact of age and socioeconomic status on depression outcomes highlight the need for tailored treatment strategies.

Keywords: Bioavailability; Depression; Gender Differences; Immune Response; Serotonin; Stress.

Figure 1:

This infographic explores how social determinants of health impact serotonin levels. It shows that healthy adults of average socioeconomic status have high serotonin levels, with men having slightly higher levels than women. In contrast, individuals with low socioeconomic status exhibit significantly lower serotonin levels for both men and women. Similarly, obesity results in a significant decrease in serotonin levels for both genders, akin to the reduction seen in low socioeconomic status. Standard deviation for these margins are also depicted. The visual emphasizes how socioeconomic factors and obesity can negatively affect serotonin levels compared to healthy adults of average socioeconomic status. (Drafted by BioRender).

Figure 2:

This infographic illustrates serotonin levels across different life stages using a bar graph. Both men and women have similar serotonin levels in childhood, with men having slightly higher levels. During adolescence, serotonin levels decrease for both genders, with a more significant drop in women. In adulthood, men maintain their adolescent serotonin levels, while women experience further decline, especially during pregnancy, postpartum, and depression, where their levels are significantly lower. In old age and post-menopause, men’s serotonin levels decrease slightly from adulthood, whereas women’s levels are as low as those experienced during pregnancy or depression in adulthood. Standard deviation for these margins are also depicted. This visual representation highlights the fluctuations in serotonin levels influenced by age, gender, and specific life conditions. (Drafted by BioRender).

Figure 3:

This infographic details the structure and function of serotonin. It starts with the conversion of tryptophan to 5-HTP by tryptophan hydroxylase, followed by the transformation of 5-HTP into serotonin by AADC. The infographic also depicts tryptophan being released from a neuron as a neurotransmitter. It highlights promoters of serotonin synthesis, such as a high tryptophan diet, light exposure, exercise, positive social interactions, and vitamin D. Conversely, it also illustrates inhibitors, including a low tryptophan diet, stress, inflammation, alcohol and substance abuse, and sleep deprivation. This visual guide emphasizes the factors influencing serotonin production and release. (Drafted by BioRender).

Figure 4:

This infographic explores how various comorbidities impact serotonin secretion. It illustrates that tryptophan cannot be converted to serotonin. Comorbidities such as depression, chronic stress, neurodegenerative disorders, and Alzheimer’s Disease lead to decreased serotonin synthesis and release. This reduction in serotonin levels subsequently results in a decreased immune response. The visual representation highlights the connections between these health conditions, serotonin synthesis, and immune function. (Drafted by BioRender).

Figure 5:

This infographic highlights the various benefits of SSRIs. It emphasizes that SSRIs boost serotonin levels and enhance its availability, effectively treating depression and anxiety. Additionally, SSRIs are noted for delaying cognitive impairment and fostering long-lasting positive social behaviors. It also mentions that Celexa and Lexapro both offer therapy with less side effects. This visual representation underscores the multifaceted advantages of SSRI treatment in managing mental health conditions. (Drafted by BioRender)