*4.6. Microbiota and the BBB*

A variety of neuropsychiatric disorders [anxiety, depression, autism spectrum disorders (ASDs), Parkinson's disease, Alzheimer's disease, and schizophrenia] have been related to microbial-induced BBB dysfunction [91,92], although the mechanism by which the microbiota affects BBB is unknown. Mediation by gut-derived neurotransmitters and bacterial metabolites is conceivable. Rodent models pointed at a link between microbiota dysbiosis and increased permeability of the BBB, further accompanied by behavioral changes [93], while a pathogen-free gut microbiota restored BBB functionality [91].

To summarize this chapter, the data reviewed support the notion that neuroinflammation is a dominant factor which plays a role in the pathophysiology of psychiatric disorders. The field awaits more multidisciplinary efforts to improve basic scientific understanding of whether antidepressant effects might be achieved using therapies for mood disorders that influence neuroinflammation.

## **5. Conclusions**

Although cancer, T2DM, and mood disorders, all belonging to the entity of complex disorders, represent diseases of different symptomatology residing in different tissues, perplexingly, they all exhibit neuroinflammation as a common denominator. This awareness may be translated into practice. It may be suggested that drugs known to alleviate neuroinflammation, such as aspirin or lithium, may be repurposed as add-on treatment in these disorders.

**Author Contributions:** S.A. wrote the original draft; O.D. carried out the initial review and editing; G.A. conceptualized the idea of the review, supervised S.A. and O.D. and finalized the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** The preparation of this review received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

