β-Endorphins are peptides that exert a wide variety of effects throughout the body. Produced through the cleavage pro-opiomelanocortin (POMC), β-endorphins are the primarily agonist of mu opioid receptors, which can be found throughout the body, brain, and cells of the immune system that regulate a diverse set of systems. As an agonist of the body’s opioid receptors, β-endorphins are most noted for their potent analgesic effects, but they also have their involvement in reward-centric and homeostasis-restoring behaviors, among other effects. These effects have implicated the peptide in psychiatric and neurodegenerative disorders, making it a research target of interest. This review briefly summarizes the basics of endorphin function, goes over the behaviors and regulatory pathways it governs, and examines the variability of β-endorphin levels observed between normal and disease/disorder affected individuals.

Alzheimer' s disease is a progressive neurodegenerative disorder affecting a substantial portion of the older population, with the number of afflicted individuals expected to grow with time. Although numerous contributing factors to the disorder have been identified, there is currently no cure or effective prevention method. With the situation as dire as it is, many efforts have been made to shed light on the mechanisms tying diverse contributing factors to the pathogenesis of Alzheimer' s disease. One common neuropathological feature of Alzheimer' s disease is the dysfunction of the blood-brain barrier, which normally maintains brain homeostasis by isolating it from the peripheral circulation and mediating the transport of various bloodborne elements in and out of the brain. An increase in the blood-brain barrier permeability has been observed in Alzheimer' s disease at a level considerably above normal aging. This chapter provides an overview of the effects of aging, the neuroimmune system, inflammation, traumatic brain injury, apolipoprotein E gene ε4 allele, and secreted protein acidic and rich in cysteine (SPARC) protein on blood-brain barrier. The potential