The “love hormone” is oxytocin , and we think of it quite often (the last time was quite recently, in connection with the coronavirus). Initially, it was studied as an obstetric hormone, but now only specialists remember this function. We usually hear that oxytocin (which works both as a hormone and as a neurotransmitter) enhances social connections. With oxytocin, we want to communicate even more with our children, lovers and friends; it helps to be faithful, increases attraction, emotional and physical, etc.
On the other hand, the same oxytocin increases not only love, but also anxiety and distrust. It all depends on the social context, on who is next to us: close and dear people, or unpleasant strangers. Researchers at the University of California at Davis write in PNAS that the effect of oxytocin also depends on which part of the brain it works in.
Most of it is synthesized in the hypothalamus, but also some oxytocin is produced by neurons in the terminal stripe nucleus (BNST), a brain structure closely associated with the amygdala, or amygdala. The amygdala works with emotions, and the associated BNST plays a large role in responding to frightening, stressful signals. BNST has been studied extensively in relation to addictions and depressive and anxiety disorders that develop in the presence of constant stress.
Experiments on mice have shown that the more oxytocin appears in the BNST neurons, the more the mice become anxious due to social stress (that is, presumably, due to squabbles with other mice). Moreover, even if there was no stress, and the BNST neurons were simply stimulated with oxytocin, the mice still became anxious. Naturally, in anxiety, there is no time for social connections – in such a state you will treat others with distrust, apprehension, fear.
This is not the first time that other functions of the “love hormone” have been found. For example, last year we wrote that it is used not only by “social” neural circuits, but also by those involved in learning, motivation, processing of olfactory and gustatory signals, etc. On the other hand, something similar happens with serotonin, which called the “hormone of happiness” – it turned out that it can cause not only happiness, but also depression, depending on which neurons it acted on .
All this once again convinces us that everything is more complicated in the brain (even in a mouse), and that names like “love hormone” or “neurotransmitter of happiness” should be treated with caution.