PHOTO BY:Large Flowering Sensitive Plant (Mimosa grandiflora), Dragon Arum (Dracunculus vulgaris); Temple of Flora, Robert John Thornton
"The object of this work is to trace in as perspicacious a manner as possible the philosophical principles of botany, from the earliest times, up to the present period, and by faithful and well executed engravings of the several subjects of the investigation, to render this curious and interesting inquiry level to everyone's comprehension."—Robert John Thornton
In 1797, an influential physician, wealthy heir, and botanic enthusiast named Dr. Robert John Thornton (1768-1837) undertook the tremendous task of producing a flower book that would establish Britain as the preeminent publisher of artistic and scientific works. An exploration into the "philosophical principles of botany," the florilegium(book of flowers) would dazzle royal subscribers with patriotic allegories, and daunt contemporary French illustrators with exquisite full-color plates. In homage to the great Swedish naturalist, it was titledThe New Illustration of the Sexual System of Linnaeus. While its ambitious publication—largely self-funded, hugely expensive, and unsurpassed in grandeur of the period—would fall short of its initial prospectus, and ultimately leave its author in financial ruins, it would also be celebrated as one of the most spectacular works of botanic literature and illustration ever produced.
A Group of Tulips. Plate 25. Published on May 1st, 1798, this was the first print of the book. Note the windmill in the background of the romantic Dutch landscape.
The last, and most famous, of the book's three volumes wasThe Temple of Flora(1799-1807), a folio of thirty-two botanical portraits (the entire work can be downloadedhere, courtesy of the Missouri Botanical Garden's archive). Thornton commissioned a host of English masters to paint and engrave the intaglio plates, which were a combination of mezzotint, aquatint, line and stipple engraving, finished with watercolor. The plants were curated as a selection of the most exotic species that were arriving on Britain's shores from all corners of the globe.
Unlike his contemporaries, who tended to illustrate botanic specimens on austere plain backgrounds, Thornton staged his plants in dramatic landscapes that carried the grandiose gestalt of the book, if not its scientific accuracy. These habitats were ostensibly not incorrect, though charming creative liberties were occasionally taken. For example, Thornton writes of the cereus flower (Selenicerus grandiflorus), "Each scenery is appropriated to the subject. Thus in the night-blooming Cereus you have the moon playing on the dimpled water, and the turret-clock points XII, the hour at night when this flower is in its full expanse." While it is true that the cereus does open after sunset, an English churchyard is an unlikely natural habitat, but one that creates a lovely sense of place. It's a wonderfully grand approach to aflorilegium, and one for which Thornton can hardly be faulted, if we regard the book as less a scientific reference, and more a magnificent work in the canon of eighteenth-century Romanticism, when there was not a hard divide between art and science.
The commentary, written by Thornton, is no less extraordinary. The reader's journey through lavish and exotic landscapes is narrated by exuberant swathes of text that meander among science, religion, mythology, and politics. Some of Thornton's "Explanations" (as he calls them) are written as traditional descriptions of the floral species, while others are poetic allegories of British nationalism. Thorntonwritesof the rose: "Nature has given her a vest of purest white, and also imperial robes of the brightest scarlet; and that no rude hand should tear her from her rich domain, she is protected by a myriad of soldiers, who present on every side their naked and sharp swords against the daring invader." England is personified as the rose, and Napoleon Bonaparte as the "daring invader." And the blue Egyptian water lily, painted into a hazy dawn over the Nile River, is accompanied by an account of British Admiral Sir Horatio Nelson's victory in the Battle of the Nile, with a list of defeated French ships. Thornton was less concerned with each plant as a scientific specimen, and more interested in what the plants meant to Britain.
Blue Egyptian Water-Lilly (Nymphaea Coerulea). Plate 46.
The Temple of Flora is perhaps the most famousflorilegiumfrom the golden age of botanical illustration: a charming collection of deliberately idiosyncratic flower portraits that became the portrait of a nation. Lack of funding prevented the book from being published in full during Thornton's life and it wasn't until 2008 that a full-size and complete fascimile was produced, by theFolio Society. The production details would have certainly pleased Thornton: The book is quarter-bound in Nigerian goatskin with cloth sides, has 232 pages with nine preliminary monochrome plates, five preliminary color plates, and 29 flower illustrations, measuring 22½" x 18¼" and weighing a hefty 28 pounds.
Aesculapius, Ceres, Flora, and Cupid, Honouring the Bust of Linnaeus. Plate 17.
This is Oxytocin. It is a mammalian neuropeptide hormone best known its roles in sexual reproduction, but has been found to have a role in various behaviors, including orgasm, social recognition, pair bonding, anxiety, and maternal behaviors. For these reasons, it has come to be known as the "love hormone."
— with Daviid ORtega Baro.
Oxytocin in a nine amino acid peptide that is synthesized in hypothalamic neurons and transported down axons of the posterior pituitary for secretion into blood. Oxytocin is also secreted within the brain and from a few other tissues, including the ovaries and testes. Oxytocin differs from antidiuretic hormone in two of the nine amino acids. Both hormones are packaged into granules and secreted along with carrier proteins called neurophysins.
Physiologic Effects of Oxytocin
In years past, oxytocin had the reputation of being an "uncomplicated" hormone, with only a few well-defined activities related to birth and lactation. As has been the case with so many hormones, further research has demonstrated many subtle but profound influences of this little peptide, particularly in regards to its effects in the brain. Oxytocin has been implicated in setting a number of social behaviors in species ranging from mice to humans. For example, secretion or administration of oxytocin in humans appears to enhance trust and cooperation within socially-close groups, while promoting defensive aggression toward unrelated, competing groups.
Oxytocin has been best studied in females where it clearly mediates three major effects:
Stimulation of milk ejection (milk letdown): Milk is initially secreted into small sacs within the mammary gland called alveoli, from which it must be ejected for consumption or harvesting. Mammary alveoli are surrounded by smooth muscle (myoepithelial) cells which are a prominant target cell for oxytocin. Oxytocin stimulates contraction of myoepithelial cells, causing milk to be ejected into the ducts and cisterns.
Stimulation of uterine smooth muscle contraction at birth: At the end of gestation, the uterus must contract vigorously and for a prolonged period of time in order to deliver the fetus. During the later stages of gestation, there is an increase in abundance of oxytocin receptors on uterine smooth muscle cells, which is associated with increased "irritability" of the uterus (and sometimes the mother as well). Oxytocin is released during labor when the fetus stimulates the cervix and vagina, and it enhances contraction of uterine smooth muscle to facilitate parturition or birth.
In cases where uterine contractions are not sufficient to complete delivery, physicians and veterinarians sometimes administer oxytocin ("pitocin") to further stimulate uterine contractions - great care must be exercised in such situations to assure that the fetus can indeed be delivered and to avoid rupture of the uterus.
Establishment of maternal behavior: Successful reproduction in mammals demands that mothers become attached to and nourish their offspring immediately after birth. It is also important that non-lactating females do not manifest such nurturing behavior. The same events that affect the uterus and mammary gland at the time of birth also affect the brain. During parturition, there is an increase in concentration of oxytocin in cerebrospinal fluid, and oxytocin acting within the brain plays a major role in establishing maternal behavior.
Evidence for this role of oxytocin come from two types of experiments. First, infusion of oxytocin into the ventricles of the brain of virgin rats or non-pregnant sheep rapidly induces maternal behavior. Second, administration into the brain of antibodies that neutralize oxytocin or of oxytocin antagonists will prevent mother rats from accepting their pups. Other studies support the contention that this behavioral effect of oxytocin is broadly applicable among mammals.
While all of the effects described above certainly occur in response to oxytocin, doubt has recently been cast on its necessity in parturition and maternal behavior. Mice that are unable to secrete oxytocin due to targeted disruptions of the oxytocin gene will mate, deliver their pups without apparent difficulty and display normal maternal behavior. However, they do show deficits in milk ejection and have subtle derangements in social behavior. It may be best to view oxytocin as a major facilitator of parturition and maternal behavior rather than a necessary component of these processes.
Both sexes secrete oxytocin - what about its role in males?Males synthesize oxytocin in the same regions of the hypothalamus as in females, and also within the testes and perhaps other reproductive tissues. Pulses of oxytocin can be detected during ejaculation. Current evidence suggests that oxytocin is involved in facilitating sperm transport within the male reproductive system and perhaps also in the female, due to its presence in seminal fluid. It may also have effects on some aspects of male sexual behavior.
Control of Oxytocin Secretion
The most important stimulus for release of hypothalamic oxytocin is initiated by physical stimulation of the nipples or teats. The act of nursing or suckling is relayed within a few milliseconds to the brain via a spinal reflex arc. These signals impinge on oxytocin-secreting neurons, leading to release of oxytocin.
If you want to obtain anything other than trivial amounts of milk from animals like dairy cattle, you have to stimulate oxytocin release because something like 80% of the milk is available only after ejection, and milk ejection requires oxytocin. Watch someone milk a cow, even with a machine, and what you'll see is that prior to milking, the teats and lower udder are washed gently - this tactile stimulation leads to oxytocin release and milk ejection.
A number of factors can inhibit oxytocin release, among them acute stress. For example, oxytocin neurons are repressed by catecholamines, which are released from the adrenal gland in response to many types of stress, including fright. As a practical endocrine tip - don't wear a gorilla costume into a milking parlor full of cows or set off firecrackers around a mother nursing her baby.
Both the production of oxytocin and response to oxytocin are modulated by circulating levels of sex steroids. The burst of oxytocin released at birth seems to be triggered in part by cervical and vaginal stimulation by the fetus, but also because of abruptly declining concentrations of progesterone. Another well-studied effect of steroid hormones is the marked increase in synthesis of uterine (myometrial) oxytocin receptors late in gestation, resulting from increasing concentrations of circulating estrogen.
Oxytocin (Greek, “quick birth”) is a mammalian hormone that also acts as a neurotransmitter in the brain.
In humans, oxytocin is thought to be released during hugging, touching, and orgasm in both sexes. In the brain, oxytocin is involved in social recognition and bonding, and may be involved in the formation of trust between people and generosity. [1][2][3]
In women, it is released in large amounts after distension of the cervix and vagina during labor, and after stimulation of the nipples, facilitating birth and breastfeeding, respectively. Synthetic oxytocin is sold as medication under the trade names Pitocin and Syntocinon as well as generic oxytocin.
Actions of oxytocin within the brain
Oxytocin secreted from the pituitary gland cannot re-enter the brain because of the blood-brain barrier. Instead, the behavioral effects of oxytocin are thought to reflect release from centrally projecting oxytocin neurons, different from those that project to the pituitary gland. Oxytocin receptors are expressed by neurons in many parts of the brain and spinal cord, including the amygdala, ventromedial hypothalamus, septum and brainstem.
Sexual arousal. Oxytocin injected into the cerebrospinal fluid causes spontaneous erections in rats,[12] reflecting actions in the hypothalamus and spinal cord.
Bonding. In the Prairie Vole, oxytocin released into the brain of the female during sexual activity is important for forming a monogamous pair bond with her sexual partner. Vasopressin appears to have a similar effect in males.[13] In people, plasma concentrations of oxytocin have been reported to be higher amongst people who claim to be falling in love.[citation needed] Oxytocin has a role in social behaviors in many species, and so it seems likely that it has similar roles in humans.
Autism. A 1998 study found significantly lower levels of oxytocin in blood plasma of autistic children.[14] A 2003 study found a decrease in autism spectrum repetitive behaviors when oxytocin was administered intravenously.[15] A 2007 study reported that oxytocin helped autistic adults retain the ability to evaluate the emotional significance of speech intonation.[16]
Maternal behavior. Sheep and rat females given oxytocin antagonists after giving birth do not exhibit typical maternal behavior. By contrast, virgin female sheep show maternal behavior towards foreign lambs upon cerebrospinal fluid infusion of oxytocin, which they would not do otherwise. [17]
Increasing trust and reducing fear. In a risky investment game, experimental subjects given nasally administered oxytocin displayed “the highest level of trust” twice as often as the control group. Subjects who were told that they were interacting with a computer showed no such reaction, leading to the conclusion that oxytocin was not merely affecting risk-aversion.[18] Nasally administered oxytocin has also been reported to reduce fear, possibly by inhibiting the amygdala (which is thought to be responsible for fear responses).[19] There is no conclusive evidence for access of oxytocin to the brain through intranasal administration, however.
Affecting generosity by increasing empathy during perspective taking. In a neuroeconomics experiment, intranasal oxytocin increased generosity in the Ultimatum Game by 80% but has no effect in the Dictator Game that measures altruism. Perspective-taking is not required in the Dictator Game, but the researchers in this experimental explicitly induced perspective-taking in the Ultimatum Game by not identifying to participants which role they would be in.[20]
According to some studies in animals, oxytocin inhibits the development of tolerance to various addictive drugs (opiates, cocaine, alcohol) and reduces withdrawal symptoms.[21]
Preparing fetal neurons for delivery. Crossing the placenta, maternal oxytocin reaches the fetal brain and induces a switch in the action of neurotransmitter GABA from excitatory to inhibitory on fetal cortical neurons. This silences the fetal brain for the period of delivery and reduces its vulnerability to hypoxic damage.[22]
Certain learning and memory functions are impaired by centrally administered oxytocin.[12]. Also, systemic oxytocin administration can impair memory retrieval in certain aversive memory tasks. [23]
MDMA (ecstasy) may increase feelings of love, empathy and connection to others by stimulating oxytocin activity via activation of serotonin 5-HT1A receptors, if initial studies in animals apply to humans.[24]
Peripheral (hormonal) actions of oxytocin
The actions of oxytocin are mediated by specific, high affinity oxytocin receptors. The peripheral actions of oxytocin mainly reflect secretion from the pituitary gland.
Letdown reflex – in lactating (breastfeeding) mothers, oxytocin acts at the mammary glands, causing milk to be ‘let down’ into a collecting chamber, from where it can be extracted by compressing the areola and sucking at the nipple. Sucking by the infant at the nipple is relayed by spinal nerves to the hypothalamus. The stimulation causes neurons that make oxytocin to fire action potentials in intermittent bursts; these bursts result in the secretion of pulses of oxytocin from the neurosecretory nerve terminals of the pituitary gland.
Uterine contraction – important for cervical dilation before birth and causes contractions during the second and third stages of labor. Oxytocin release during breastfeeding causes mild but often painful uterine contractions during the first few weeks of lactation. This also serves to assist the uterus in clotting the placental attachment point postpartum. However, in knockout mice lacking the oxytocin receptor, reproductive behavior and parturition is normal.[4]
The relationship between oxytocin and human sexual response is unclear. At least two non-controlled studies have found increases in plasma oxytocin at orgasm – in both men and women.[5][6] The authors of one of these studies speculated that oxytocin’s effects on muscle contractibility may facilitate sperm and egg transport.[5] Murphy et al. (1987), studying men, found that oxytocin levels were raised throughout sexual arousal and there was no acute increase at orgasm. [7] A more recent study of men found an increase in plasma oxytocin immediately after orgasm, but only in a portion of their sample that did not reach statistical significance. The authors noted that these changes “may simply reflect contractile properties on reproductive tissue.”[8]
Due to its similarity to vasopressin, it can reduce the excretion of urine slightly. More important, in several species, oxytocin can stimulate sodium excretion from the kidneys (natriuresis), and in humans, high doses of oxytocin can result in hyponatremia.
Oxytocin and oxytocin receptors are also found in the heart in some rodents, and the hormone may play a role in the embryonal development of the heart by promoting cardiomyocyte differentiation. [9][10] However, the absence of either oxytocin or its receptor in knockout mice has not been reported to produce cardiac insufficiencies.[4]
Modulation of hypothalamic-pituitary-adrenal axis activity. Oxytocin, under certain circumstances, indirectly inhibits release of adrenocorticotropic hormone and cortisol and, in those situations, may be considered an antagonist of vasopressin. [11]
Drug forms of oxytocin
Synthetic oxytocin is sold as medication under the trade names Pitocin and Syntocinon and also as generic oxytocin. Oxytocin is destroyed in the gastrointestinal tract, and therefore must be administered by injection or as nasal spray. Oxytocin has a half-life of typically about three minutes in the blood. Oxytocin given intravenously does not enter the brain in significant quantities – it is excluded from the brain by the blood-brain barrier. There is no evidence for significant CNS entry of oxytocin by nasal spray. Oxytocin nasal sprays have been used to stimulate breastfeeding but the efficacy of this approach is doubtful[25].
Injected oxytocin analogues are used to induce labor and support labor in case of non-progression of parturition. It has largely replaced ergotamine as the principal agent to increase uterine tone in acute postpartum haemorrhage. Oxytocin is also used in veterinary medicine to facilitate birth and to increase milk production. The tocolytic agent atosiban (Tractocile) acts as an antagonist of oxytocin receptors; this drug is registered in many countries to suppress premature labour between 24 and 33 weeks of gestation. It has fewer side-effects than drugs previously used for this purpose (ritodrine, salbutamol and terbutaline).
Some have suggested that the trust-inducing property of oxytocin might help those who suffer from social anxieties, while others have noted the potential for abuse with confidence tricks. [26]
Synthesis, storage and release of oxytocin
Oxytocin is made in magnocellular neurosecretory cells in the supraoptic nucleus and paraventricular nucleus of the hypothalamus and is released into the blood from the posterior lobe of the pituitary gland. Oxytocin is also made by some neurons in the paraventricular nucleus that project to other parts of the brain and to the spinal cord.
In the pituitary gland, oxytocin is packaged in large, dense-core vesicles, where it is bound to neurophysin I as shown in the inset of the figure; neurophysin is a large peptide fragment of the larger precursor protein molecule from which oxytocin is derived by enzymatic cleavage.
Secretion of oxytocin from the neurosecretory nerve endings is regulated by the electrical activity of the oxytocin cells in the hypothalamus. These cells generate action potentials that propagate down axons to the nerve endings in the pituitary; the endings contain large numbers of oxytocin-containing vesicles, which are released by exocytosis when the nerve terminals are depolarised.
Oxytocin is also synthesized by corpora lutea of several species, including ruminants and primates. Along with estrogen, it is involved in inducing the endometrial synthesis of Prostaglandin-F2alpha to cause regression of the corpus luteum.
Oxytocin and vasopressin are the only known hormones released by the human posterior pituitary gland to act at a distance. However, oxytocin neurons make other peptides, including corticotropin-releasing hormone (CRH) and dynorphin, for example, that act locally. The magnocellular neurons that make oxytocin are adjacent to magnocellular neurons that make vasopressin, and are similar in many respects.
References
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