Galanin was discovered at the Karolinska Institute in Sweden. Professor Viktor Mutt and Kazuhiko Tatemoto isolated it from a pig small intestine in 1980. After succeeding in demonstrating that galanin was biologically active in 1983, its structure was determined at the Karolinska Institute and first mentioned in a publication that same year.
What is galanin?
Galanin is a peptide – a molecule composed of amino acids linked together by peptide bonds. Peptides are divided into three categories according to the number of amino acids they contain: Oligopeptides (less than 10), Polypeptides (10 – 100) and Proteins (more than 100). Galanin consists of 30 amino acids in humans and 29 amino acids in all other species in which it has been detected so far. It thus belongs to the polypeptides. Galanin acts as a neurotransmitter, i.e. a substance that transmits, amplifies or modifies stimuli from one nerve cell to another. It plays a role in regulating numerous physiological functions. These include controlling the movement of the gastrointestinal tract, releasing and inhibiting other neurotransmitters and hormones, and influencing the activity of the pancreas. The galanin family includes a total of four peptides. They mediate their action with the help of receptors. Currently, three receptors of galanin are known: GalR1, GalR2, and GalR3.
Function, action, and tasks
Galanin often has inhibitory effects, for example, on pain processing or the release of the happiness hormone serotonin and noradrenaline, which stimulates the sympathetic nervous system. In an in vitro experiment, galanin was shown to inhibit the release of insulin. In addition to the waking and sleeping rhythms, the neuropeptide also regulates food intake. In an experiment with rats, it was shown that there is a connection between the desire to consume high-fat foods and the concentration of galanin in the hypothalamus, the part of the brain responsible for controlling the autonomic nervous system. Consumption of high-fat foods leads to increased formation of galanin in the hypothalamus. This increase in concentration in turn leads to an increased need to eat high-fat foods. In healthy individuals, however, there are counteracting mechanisms that interrupt this cycle. An inhibitory effect of galanin on gastric acid secretion has also been discovered. In humans, it also delays gastric emptying by reducing its movement. Galanin plays a special role in the maturation of the mammary glands and the formation of breast milk. In an experiment on this subject, mice were used whose gene responsible for galanin formation had been deactivated. Although these animals were viable and could reproduce without problems, they were subsequently unable to suckle their young. In the same experiment, it was also found that the animals with the defective galanin gene had difficulty digesting high-fat foods. If damage or inflammation occurs in the body to neurons or the nervous system, this leads to increased production of galanin. It is believed to have a protective effect on neurons and nerves and promotes the formation of new neuron cells.
Formation, occurrence, properties, and optimal levels
The synthesis of galanin takes place in neurons in the hypothalamus, the spinal cord, the placenta, and the limbic system, the part of the brain responsible for drive behavior and emotions, among others. Galanin is formed by first reading the preprotein from a gene on the eleventh chromosome, which is then cleaved by an enzyme called signal peptidase. Galanin is formed from this proprotein by further cleavage. Its three different receptors act in the central nervous system, the anterior pituitary gland, the pancreas, the stomach and the smooth intestinal muscles. Levels of galanin can vary from person to person and fluctuate from day to day. In women, it is also particularly dependent on the quantity of sex hormones produced. When higher amounts of estrogen and progesterone are produced by the ovaries, this elevated hormone concentration leads to increased formation of galanin in the brain. The extent of these fluctuations was shown in a cancer study in which the concentration of galanin in serum was measured in sick and healthy subjects.In the healthy control group, the values varied between approximately 10 and 40 nanograms per milliliter. In the cancer patients, it was significantly higher.
Diseases and disorders
A link between galanin levels and cancer has been established several times. For example, galanin is now considered a characteristic feature of malignant, distant tumor-forming breast cancer tumors. Animal studies showed that galanin can have both inhibitory and growth-promoting effects on cancer cells. Activation of the GalR1 receptor generally antagonizes tumor tissue proliferation, while activation of the GalR2 receptor can both inhibit and enhance growth. It also suggests a link of galanin with diseases such as Alzheimer’s, epilepsy and eating disorders, alcohol addiction and depression. Actually, galanin has a protective effect on nerve cells. In the case of Alzheimer’s, however, it appears to play a key role in the progression of the disease. Initially, the brain tries to defend itself against the disease by increasing the release of the neuropeptide. At a certain point in the course of the disease, however, the effect then reverses, according to a study by Waschington University Medical School, and contributes to the loss of important brain functions. Evidence that galanin levels may be an actual cause of the onset of Alzheimer’s has not yet been found. Researchers at Princeton University, using studies on rats, found that galanin levels affect chronic drinking. Galanin promotes the consumption of alcohol, and this consumption leads to increased production of galanin, creating a cycle that is thought to play a major role in the development of addictive drinking behavior. According to another study, galanin, especially when paired with stress, also plays a central role in the development of depression. If galanin production is disturbed, e.g. due to a genetic defect, this can further promote anxiety disorders. For example, mice lacking the neuropeptide show stronger anxiety behavior than their peers whose bodies can produce galanin.
