Form and Function

Oxytocin

How could I not write about oxytocin? As the "love hormone" and with many implications in birth and breastfeeding, oxytocin is near and dear to me. Oxytocin is both a hormone and a peptide-type neurotransmitter and is produced in the hypothalamus then moved to the pituitary where it is packaged into vesicles. Oxytocin is released when oxytocin cells in the hypothalamus send an action potential along their axons to the pituitary, signaling the pituitary to release the contents of the oxytocin vesicles into the blood plasma by means of exocytosis. Oxytocin, along with vasopressin, are the only hormones to be released at such a distance from the locations where their effect occurs. I suppose it's obvious that this allows synthetic forms of oxytocin such as Pitocin to create uterine contractions when administered by IV or intramuscular injection in the leg, but I'd never really thought of it specifically so I'm finding it interesting. Oxytocin is received by specific oxytocin receptors that are necessary for oxytocin to enter the tissues of the body and produce its intended effect. I found information on pharmaceuticals that act as oxytocin receptor antagonists used for preventing pre-term labor, but no information on whether any type of anagonist is naturally produced in the body. I've suspected that there is simply because I've seen Pitocin given to women in late pregnancy with no effect. No contractions, nothing. Given that oxytocin, in combination with other hormones, is largely responsible for mother-infant bonding immediately after birth, it is probably obvious that there are concerns both about the use of synthetic forms of oxytocin used in birth as well as postpartum care routines that distract the mother from her baby or separate the baby from the mother. Quoting renowned French obstetrician Michel Odent regarding generation of the oxytocin peak that occurs immediately after birth*:

"It is easier if the place is very warm (so that the level of hormones of the adrenaline family is as low as possible). It is also easier if the mother has nothing else to do but look at the baby’s eyes and feel contact with the baby’s skin, without any distraction." and "In the particular case of the hour following birth, in physiological conditions, the high peak of oxytocin is associated with a high level of prolactin, which is also known as the "motherhood hormone." This is the most typical situation for inducing love of babies."

Dr. Odent has an entire book dedicated to the subject of the hormones of birth, breastfeeding, and mothering, titled The Scientification of Love, and hopefully some day I'll get around to reading it.

Histamine

Histamine is an amine-type neurotransmitter that plays roles in immune function, smooth muscle contraction, gastric acid secretion, and vascular permeability. Most histamine is produced and stored in mast cells, particularly in areas where injury is common such as the nose, mouth, feet, and blood vessels. A small portion of the body's total amount of histamine is stored and is active in the brain. When histamine is released it can bind with one of four histamine receptor types. The H₁ receptor is the classic type we think of when we think of histamine, resulting in allergic reactions such as difficulty breathing and hives. This type of receptor is found in smooth muscle, endothelial tissue, and in the brain. The H₂ receptor is found on parietal cells and causes gastric acid to be secreted. The H₃ receptor inhibits release of the neurotransmitters histamine, acetylcholine, norepinepherine, and serotonin. The H₄ receptor is found in the small and large intestines as well as in the thymus, spleen, bone marrow, and basophils. Its function is unknown. After being released, histamine is broken down by the enzyme acetaldehyde dehydrogenase. (I thought this next part was interesting because it goes against common assumptions.) It is not an excess of histamine that is responsible for heightened reactions to common allergens, but a deficiency of acetaldehyde dehydrogenase.

GABA

Gamma-aminobutyric acid (GABA) is an amino acid that acts as the primary inhibitory neurotransmitter in the adult human brain. In some other species or in the immature human brain GABA has a primarily excitatory effect. GABA receptors are found in the membranes of both pre- and post-synaptic neurons. To produce an inhibitory effect, when GABA binds to its receptor sites, either Cl^- flows into the cell or K⁺ flows out, causing hyperpolarization of the cell membrane, and making it more unlikely that an action potential will be fired by that neuron. GABA has more than one type of receptor and many drugs produce their effects by interacting with these receptors. Benzodiazepines (e.g. Xanax, Valium, Rohypnol), for example, bind the alpha and gamma sites of the GABA_A receptor, resulting in sedation, muscle relaxation, decreased anxiety or other effects depending on the specific drug. (I looked into this particular group further because I take small doses of Xanax to fly and thought maybe it would be a good idea to know what was going on in there.) Alcohol, barbituates, some anesthetics, and even the herb valerian also act as GABA agonists.