Question: What hormone is linked as a stress defense in plants as well as an antidepressant in humans?

Context paragraphs:
Emicerfont: Emicerfont (GW-876,008) is a drug developed by GlaxoSmithKline which acts as a CRF-1 antagonist.  Corticotropin releasing factor (CRF), also known as Corticotropin releasing hormone, is an endogenous peptide hormone which is released in response to various triggers such as chronic stress, and activates the two corticotropin-releasing hormone receptors: CRF and CRF.  This then triggers the release of corticotropin (ACTH), another hormone which is involved in the physiological response to stress.

Kisspeptin: Kisspeptin (formerly known as metastin) is a protein that is encoded by the "KISS1" gene in humans.  Kisspeptin is a G-protein coupled receptor ligand for GPR54.  "Kiss1" was originally identified as a human metastasis suppressor gene that has the ability to suppress melanoma and breast cancer metastasis.  Kisspeptin-GPR54 signaling has an important role in initiating secretion of gonadotropin-releasing hormone (GnRH) at puberty, the extent of which is an area of ongoing research.  Gonadotropin-releasing hormone is released from the hypothalamus to act on the anterior pituitary triggering the release of luteinizing hormone (LH), and follicle stimulating hormone (FSH).  These gonadotropic hormones lead to sexual maturation and gametogenesis.  Disrupting GPR54 signaling can cause hypogonadotrophic hypogonadism in rodents and humans.  The Kiss1 gene is located on chromosome 1.  It is transcribed in the brain, adrenal gland, and pancreas.

Corticotropin-releasing hormone: Corticotropin-releasing hormone (CRH) (also known as corticotropin-releasing factor (CRF) or corticoliberin; corticotropin may also be spelled corticotrophin) is a peptide hormone involved in the stress response.  It is a releasing hormone that belongs to corticotropin-releasing factor family.  In humans, it is encoded by the "CRH" gene.

Effects of stress on memory: The effects of stress on memory include interference with a person's capacity to encode memory and the ability to retrieve information.  During times of stress, the body reacts by secreting stress hormones into the bloodstream.  Stress can cause acute and chronic changes in certain brain areas which can cause long-term damage.  Over-secretion of stress hormones most frequently impairs memory, but in a few cases can enhance it.  In particular, the hippocampus, prefrontal cortex and the amygdala are affected.  One class of stress hormone responsible for negatively affecting memory is the glucocorticoids (GCs), the most notable of which is cortisol.  Glucocorticoids facilitate and impair the actions of stress in the brain memory process.  Cortisol is a known biomarker for stress.  Under normal circumstances, the hippocampus regulates the production of cortisol through negative feedback because it has many receptors that are sensitive to these stress hormones.  However, an excess of cortisol can impair the ability of the hippocampus to both encode and recall memories.  These stress hormones are also hindering the hippocampus from receiving enough energy by diverting glucose levels to surrounding muscles.

Stress in medical students: Stress in medical students is stress caused by strenuous medical programs, which may have physical and psychological effects on the well-being of medical students.  Excessive stress in medical training predisposes students for difficulties in solving interpersonal conflicts as a result of previous stress.  A significant percentage of medical students suffer from anxiety disorders because of the long term effects of stress on emotional and behavioral symptomatology.  This condition has become a focus of concern nationally and globally, therefore the first line of detection and defense from stress are the students themselves.  Students need to be given the tools to recognize and cope with stress, as well as being assured that they will not suffer judgment from others for recognizing their need for help in dealing with stress.  The instructors, advisers and other faculty members who notice the signs of stress in a student need to approach the student in a non-threatening, non-judgmental way, in an effort to help medical students recognize and handle their stress.

Growth hormone 2: Growth hormone 2 (GH2), also known more commonly as placental growth hormone (PGH) or as growth hormone variant (GH-V), is a protein that in humans is encoded by the "GH2" gene.  It is produced by and secreted from the placenta during pregnancy, and becomes the predominant form of growth hormone (GH) in the body during this time.  Its cogener is growth hormone 1 (GH1), or "pituitary growth hormone".

Verucerfont: Verucerfont (GSK-561,679) is a drug developed by GlaxoSmithKline which acts as a CRF-1 antagonist.  Corticotropin releasing factor (CRF), also known as Corticotropin releasing hormone, is an endogenous peptide hormone which is released in response to various triggers such as chronic stress, and activates the two corticotropin-releasing hormone receptors CRH-1 and CRH-2.  This then triggers the release of corticotropin (ACTH), another hormone which is involved in the physiological response to stress.

Stress in the aviation industry: Stress in the aviation industry is a common phenomenon composed of three sources, which are physiological stressors, psychological stressors, and environmental stressors.  Professional pilots can experience stress in flight, on the ground during work-related activities, and during personal time because of the influence of their occupation.  An airline pilot can be an extremely stressful job due to the workload, responsibilities and safety of the thousands of passengers they transport around the world.  Chronic levels of stress can negatively impact one's health, job performance and cognitive functioning.  Being exposed to stress does not always negatively influence humans because it can motivate people to improve and help them adapt to a new environment.  Unfortunate accidents start to occur when a pilot is under excessive stress, as it dramatically affects his or her physical, emotional, and mental conditions.  Stress "jeopardizes decision-making relevance and cognitive functioning" and it is a prominent cause of pilot error.  Being a pilot is considered a unique job that requires managing high workloads and good psychological and physical health.  Unlike the other professional jobs, pilots are considered to be highly affected by stress levels.  One study states that 70% of surgeons agreed that stress and fatigue don't impact their performance level, while only 26% of pilots denied that stress influences their performance.  Pilots themselves realize how powerful stress can be, and yet many accidents and incidents continues to occur and have occurred, such as Asiana Airlines Flight 214, American Airlines Flight 1420, and Polish Air Force Tu-154

Pharmacology of antidepressants: The pharmacology of antidepressants is not entirely clear.  The earliest and probably most widely accepted scientific theory of antidepressant action is the monoamine hypothesis (which can be traced back to the 1950s), which states that depression is due to an imbalance (most often a deficiency) of the monoamine neurotransmitters (namely serotonin, norepinephrine and dopamine).  It was originally proposed based on the observation that certain hydrazine anti-tuberculosis agents produce antidepressant effects, which was later linked to their inhibitory effects on monoamine oxidase, the enzyme that catalyses the breakdown of the monoamine neurotransmitters.  All currently marketed antidepressants have the monoamine hypothesis as their theoretical basis, with the possible exception of agomelatine which acts on a dual melatonergic-serotonergic pathway.  Despite the success of the monoamine hypothesis it has a number of limitations: for one, all monoaminergic antidepressants have a delayed onset of action of at least a week; and secondly, there are a sizeable portion (>40%) of depressed patients that do not adequately respond to monoaminergic antidepressants.  Further evidence to the contrary of the monoamine hypothesis are the recent findings that a single intravenous infusion with ketamine, an antagonist of the NMDA receptor — a type of glutamate receptor — produces rapid (within 2 hours), robust and sustained (lasting for up to a fortnight) antidepressant effects.  Monoamine precursor depletion also fails to alter mood.  To overcome these flaws with the monoamine hypothesis a number of alternative hypotheses have been proposed, including the glutamate, neurogenic, epigenetic, cortisol hypersecretion and inflammatory hypotheses.

Melatonin: Melatonin, also known as "N"-acetyl-5-methoxy tryptamine, is a hormone that is produced by the pineal gland in animals and regulates sleep and wakefulness.  Melatonin is also produced in plants where it functions as a first line of defense against oxidative stress.

Supporting paragraphs: Pharmacology of antidepressants Melatonin
Answer: Melatonin