In Chinese medicine, the term 'Kidney' is an abstract term that encompasses three systemic functions: neurological, reproductive and hormonal endocrine systems. Some of the Kidney essences are used to produce the brain marrow (brain nerves), while some kidney essences produce reproductive cells and hormones. In Chinese medicine, it is believed that the "essence" of the Kidney comes from the parents' reproductive (innate) essence, which is the primordial material for embryonic development. From early childhood, the kidney essence is nurtured by the essence of the food and gradually enriches the human body to grow.
A new study published by the Royal Society has found many similarities between the brain's contents and the scrotum. (1)
Scientists write in their paper: "Brain and testis have the highest number of common proteins, compared with other human body tissues." A team led by biomedical scientist Bárbara Matos from the University of Aveiro in Portugal.
While the brain has highly complex roles - controlling our bodies, receiving and interpreting signals from our sense organs, not to mention thinking and feeling - the human testes have only two main functions - producing sperm and hormones.
The team also took a step back from their work, noting that there may be a reason for the similarities between the proteins produced by the two organs. Previous studies have shown a link between sexual dysfunction and brain disorders and links between intelligence levels and semen quality. But now, they have found an explanation.
The team compared proteins from 33 tissue types, including the heart, gut, cervix, ovaries and placenta, and found that the testes and brain had 13,442 proteins in common. Gene expression studies confirmed this, showing that these two more distantly located organs share the highest number of genes of any organ in the body.
Matos and colleagues found that the most expressed common proteins in these tissues are involved in tissue development and cellular communication. The team explained that these proteins make sense when you consider how surprisingly similar the two tissues are in many ways.
This finding was not surprising, considering that proteins from both organs consume high amounts of energy. Therefore, both organs have specialised cells for supporting the hard-working neurons in the brain and the germ cells in the testes.
"The fact that the highest expression levels are found in the cerebral cortex and testes suggests that these genes may contribute to phenotypic traits that are unique to humans, such as the cognitive ability." The team wrote.
Many of the same receptor and signalling pathways are also found in both tissues. And many of the common proteins are involved in a process called exocytosis. When exocytosis occurs in the brain, cells hand off neurotransmitters between each other, which is also an essential process during fertilisation.
In another study, scientists at Northwestern University have discovered a specific area of the brain where male libido is produced. In this region, a key gene, known as aromatase, determines the strength of male sexual desire. (2)
For the experiment, scientists constructed brain-specific aromatase knockout mice and set up a control group. After selectively knocking out the aromatase gene in the brain, male mice showed a 50 per cent reduction in sexual activity compared to control males, despite their higher blood testosterone levels.
"Male mice with the aromatase gene knockout were partially disinterested in sexual behaviour." Dr Hong Zhao, research associate professor of obstetrics and gynaecology at Northwestern University's Feinberg School of Medicine. Aromatase is a key enzyme in oestrogen production. Estrogen functions in both males and females. Testosterone must be converted to estrogen to drive male sexual desire.
One group of scientists in California have discovered an entirely new connection between the hypothalamus and the testes. This newly discovered neural connection runs through the spinal cord, allowing brain events to affect testosterone secretion much faster than the regular hormonal wiring of the pituitary gland does for testosterone secretion. (3)
1. Matos Bárbara, Publicover Stephen J., Castro Luis Filipe C., Esteves Pedro J. and Fardilha Margarida 2021Brain and testis: more alike than previously thought?Open Biol.11200322200322 http://doi.org/10.1098/rsob.200322
2. David C Brooks, John S Coon V, Cihangir M Ercan, Xia Xu, Hongxin Dong, Jon E Levine, Serdar E Bulun, Hong Zhao, Brain Aromatase and the Regulation of Sexual Activity in Male Mice, Endocrinology, Volume 161, Issue 10, October 2020, bqaa137, https://doi.org/10.1210/endocr/bqaa137
3. Selvage DJ, Rivier C. Importance of the paraventricular nucleus of the hypothalamus as a component of a neural pathway between the brain and the testes that modulates testosterone secretion independently of the pituitary. Endocrinology. 2003 Feb;144(2):594-8. doi: 10.1210/en.2002-220781. PMID: 12538621.