Microbial Neuroendocrine Hormones
Microbial endocrinology is a recent branch involves intersection of microbiology, endocrinology and neurophysiology. endocrinology deals with interaction between the microorganisms and their host in case of health and disease. Recently, there are many literatures have been published in the field of endocrinology. Most investigations worked on interaction between the bacteria and the stress hormones such as catecholamine, adrenaline, noradrenaline and dopamine. The stress increases the release of adrenaline and noradrenaline and these both hormones suppress the immune system and its function. This could increase the risk of infections. According to this fact, endocrinology provides a tool to understand the nature of the interaction between the microorganisms and the host (animal or human) during the stress. Some published literatures deal with special kind of interaction of the microorganisms and the host. For example, types of bacteria recognize and synthesize nuroendocrine hormones like the hormones of the eukaryotes. These neuroendocrine hormones can interact with the enteric nervous system of enter the circulatory system taking its way to the CNS and the brain hence affect the behavior, food preference and even the appetite.
The human gut microbiota is a wide diverse of approximately 100 trillion microbes in the body which can serve as a metabolic, nutrition, absorption and immune function against pathogens. Dinan et al.  have proposed a new term “psychobiotics”, that probiotics that possess the capacity to deliver therapeutic levels of neurochemicals that could be potentially used to treat psychiatric illness should be termed “psychobiotics” . Bravo et al. [2,3] studied the way by which probiotics may influence host behavior and inflammation. They found that the probiotic could alter emotional behavior of mice. Interestingly, both live and dead probiotics have been shown to be equally efficacious . The microbial endocrinology is not restricted to probiotic microbes but extended to many bacterial species residing in the gut and possess biochemical machinery to synthize neuro endocrorine hormones . Moreover, Lannitti and Patmier  reported that not only live microbial cells having probiotics have shown equal effect  found that probiotics can show antidepressant effect. More studied are required to determine the appropriate environmental conditions to achieve the neuroactive influences .
Neurotransmitters in Microbes
In addition of the effect of the neurotransmitters on the hot the microbial cells are also affected. For example, serotonin stimulated the cellular aggregation and the cellular growth of the bacterial cells of Streptococcus faecalis, Candida guilliermondii  and Saccharomyces cervisea , E. coli K-12 and Rhodospirillium ruhrum . The cell aggregation and microbial growth stimulation serotonin in micromolar and millimolar quantities has been proven. This was applied to both gram positive and Gram-negative bacteria. Interestingly, Oleskin,  described what is called “Supermicroorganisms” which are thought to have become multicellular organisms over the course of evaluation. These neurotransmitters may serve as inhibitors for the microbial aggregation and can be used as protector against the microbial growth .
- Dinan TG, Stanton C, Cryan JF (2013) Psychobiotics: a novel class of psychotropic. Biol Psychiatry 74(10): 720-726.
- Lyte M (2011) Probiotics function mechanistically as delivery vehicles for neuroactive compounds: microbial endocrinology in the design and use of probiotics. Bioessays 33(8): 574-581.
- Bravo JA, Forsythe P, Chew MV, Escaravage E, Savignac HM, et al. (2011) Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proc Natl Acad Sci USA 108(380: 16050-16055.
- Thomas CM, Hong T, van Pijkeren JP, Hemarajata P, Trinh DV (2012) Histamine derived from probiotic Lactobacillus reuteri suppresses TNF via modulation of PKA and ERK signaling. PLoS One 7(2): e31951.
- Komatsuzaki N, Nakamura T, Kimura T, Shima J (2008) Characterization of glutamate decarboxylase from a high gamma-aminobutyric acid (GABA)-producer, lactobacillus paracasei. Biosci Biotechnol Biochem 72(2): 278-285.
- Freestone PP, Lyte M (2008) Microbial endocrinology: experimental design issues in the study of interkingdom signalling in infectious disease. Adv Appl Microbiol 64: 75-105.
- Strakhovskaya MG, Ivanova EV, Fraikin GY (1993) Stimulatory effect of serotonin on the growth of the yeast Candida guilliermondii and the bacterium Streptococcus faecalis. Microbiol 62: 46-49.
- Malikina KD, Shishov VA, Chuvelev DI, Kudrin VS, Oleskin AV (2010) Regulatory role of monoamine neurotransmitters in Saccharomyces cerevisiae cells. Appl Biochem Microbiol 46(6): 672-677.
- Anuchin AM, Chuvelev DI, Kirovskaya TA, Oleskin AV (2008) Effects of monoamine neuromediators on the growth-related variables of Escherichia coli K-12. Microbiol 77(6): 674-680.
- Oleskin AV, Zagryadskaya Yu A, Lisak LV (2013) Effects of biogenic amines on the interactions of fungal hyphae and bacteria. In: Zinchenko VP, Berezhnov AV (Eds.), Reception and intracellular signalling. Emma, Russia, pp. 770-775.
- Balzer I, Poeggeler B, Hardeland R (1993) Circadian rhythms of indoleamines in a dinofl agellate Gonyaulax polyedra: persistence of melatonin rhythm in constant darkness and relationship to 5-methoxytryptamine. In: Touitou Y, Arendt J, Pevet P (Eds.), Melatonin and the pineal gland: from basic science to clinical applications. Excerpta Medica, Amsterdam, Netherlands, pp. 83-186.