Participation of Neurotransmitters in Chemical Relations Between Organisms

2.3.2.1 Microorganism-Microorganism Relations

Communication between microorganisms through their secretions (extracellular products released) enriched in hormones or neuromediators is proposed in many reports (Kaprelyants and Kell 1996; Kaprelyants et al. 1999; Oleskin et al. 2000;

Kagarlitskii et al. 2003; Oleskin and Kirovskaya 2006; Oleskin 2007). Neurotransmitters participate in the communication with each other for growth, in particular serotonin as an intercellular communication agent accelerating and possibly synchronizing development of the microbial cells. Exogenous serotonin stimulates the growth of yeast Candida guillermondii, and the Gram-positive bacterium Streptococcus faecalis at low concentration near 10-7 M added with a periodicity of 2 h (Strakhovskaya et al. 1993). Photoactivation of the synthesis of endogenous serotonin in cells exposed to UV light at 280-360 nm led to the photostimulation of the same cultivated cells in lag-phase (Strakhovskaya et al. 1991; Belenikina et al. 1991). Exogenous serotonin at 2 x 10-7-10-5 M also accelerates culture growth and induces cell aggregation in E. coli and R. rubrum (Oleskin et al. 1998a, b). Moreover, dopamine and norepinephrine stimulate the growth of E. coli, S. enterica, Y. enterocolitica, and the staphylococci as well as the yeast Saccharomyces cerevisiae (Neal et al. 2001; Kagarlitskii et al. 2003; Oleskin and Kirovskaya 2006; Freestone et al. 2007).

2.3.2.2 Microorganism-Plant Relations

The communications of plant-microorganisms or plant-fungi via neurotransmitters is still a relatively unexplored field. Although the presence of the compounds is documented for some fungi and rhizobial bacteria (Roshchina 2001a), we can only speculate that there is a role for microbial-produced hormones in plant physiology. However, recently Ishihara et al. (2008) found that the rice pathogenic infection by fungi Bipolaris oryzae (the formation of brown spots on the leaves) leads to the enhanced serotonin production as a defensive response. In the defensive mechanism, the tryptophan pathway is involved as well. The pathway enzymes of rice have been characterized (Kang et al. 2007).

2.3.2.3 Microorganism-Animal Relations

Microorganisms may live within an animal organism and have simple symbiotic or parasitic relationships with their host. The example of non-parasitic cooperation can be found in the marine sponge that used acetylcholine and its hydrolyzing enzyme acetylcholinesterase of the associated bacterium Arthrobacter ilicis (Mohapatra and Bapujr 1998). The clinical aspect suggested by microorganism-animal interactions based on hormones is understandably of special interest. Evans with co-workers first reported in 1948 that catecholamines such as epinephrine were able to enhance bacterial infections. Presently, we know that they may stimulate the growth of Gram-negative bacteria (Lyte and Ernst 1992, 1993). The concept of "microbial endocrinology", in which pathogens are considered to exploit the host effector's molecules as environmental signals promoting growth and virulence factor deployment, has been proposed (Lyte 1992; Lyte and Ernst 1993, Freestone et al. 2008a, b). Cells of bacteria and fungi release neurotransmitters (for example norepinephrine and dopamine) out into the matrix of cellular cover as shown, in particular the bacterium Bacillus subtilis, and with the compounds participate in intercellular communication (Oleskin et al. 2000). Matrix contained biopolymers permit low-molecular neurotransmitters to diffuse among the colonial population. In this case, the compounds serve as chemosignals or information agents of short-radius activity. The formulation of the hypothesis regarding the microbial recognition of cate-cholamines produced during periods of stress as a potential mechanism by which bacteria can utilize the host's environment to initiate pathogenic process was formulated in 1992 (Lyte 1992; Lyte and Ernst 1993) and developed (Lyte et al. 1996; Lyte and Bailey 1997; Freestone et al. 2008 a,b) showed that norepinephrine stimulates the growth of low inocula of commensal and pathogenic E. coli in a minimal medium supplemented with serum. Norepinephrine also forms a complex with transferrin-bound iron in blood or serum, and Freestone et al. (1999, 2000) demonstrated that norepinephrine supplies iron for bacterial growth in the presence of transferrin or lactoferrin. Utilization of iron-catecholamine complexes involving ferric reductase activity has also been found for Listeria monocytogenes (Coulanges et al. 1997).

Other examples are changes in the blood and tissue histamine content in rabbits when sensitized with streptococci combined with heart muscle extract (Kozlov 1972) or as well in those of serotonin and histamine in the organs infected with bacterium Bacterium prodigious. The review of Freestone et al. (2008a) reveals that responsiveness to human stress neurohormones is widespread in the microbial world and relates to the new concept of microbial endocrinology.

2.3.2.4 Plant-Plant Relations

In the relationships between different plant species, neurotransmitters may play a role of attractant or repellent for normal coexistence (Roshchina 1991, 2001a). Plant microspores such as vegetative microspores of horse-tail Equisetum arvense from Cryptogam (spore-bearing) plants or various generative microspores (pollens) from Phanerogams (seed-bearing) plants are unicellular structures containing ace-tylcholine, catecholamines and histamine (Roshchina 2001a) and are the specific objects of microbiology having medicinal areas of the interests (Roshchina 2006b), acting as drugs or allergenous agents. An especially significant role of neurotrans-mitter compounds is seen in the pollen-pollen interaction named pollen allelopathy and pollen-pistil relations during pollination that regulate fertilization of certain plant species (Roshchina 2001b, 2007, 2008). Catecholamines stimulate the microspores germination (Roshchina 2001a, 2004, 2009). Fungi and other microorganisms living within many plant cells also appear to release neurotransmitters that act as plant growth regulators. We may only speculate on the biological significance of these observations as yet.

2.3.2.5 Plant-Animal Relations

Participation of neurotransmitters in plant-animal relations has been evidently shown for dopamine (van Alstyne et al. 2006). This is dangerous for marine communities, fisheries, and aquaculture facilities due to similar antiherbivore defense that is the cause of reduced feeding by echinoderms, molluscs, and arthropods (see above in Sect. 2.1.2). Role of neurotransmitters excreted in the plant-animal relations is "terra incognita" as yet.

2.3.2.6 Animal-Animal Relations

Neurosecretion utilizes mechanisms common to all eukaryotic membrane transport, and the process should be a model of the secretion as a whole (Bajjalieh and Scheller 1995). The role of neurotransmitters in the contacts with other organisms may be seen from the effects of the secretions released. For instance, large amounts of dopamine are secreted by cells of infusoria Tetrahymena pyriformis into their growth medium (Gundersen and Thompson 1985). Secretions from cones of Drosophila contain acetylcholine (Yao et al. 2000), and dopamine and norepinephrine are found in the salivary glands and brain of the tick Boophilus microplus (Megaw and Robertson 1974). Exogenous neurotransmitters such as dopamine and serotonin may act as both growth stimulators or as defense agents (Boucek and Alvarez 1970; Yamamoto et al. 1999).

2.3.2.7 Biomediator Role of Neurotransmitters

Non-neurotransmitter functions of the compounds known as neurotransmitters are especially important in the relationships of bacteria and fungi with plants and animals. It appears to be a significant factor in nature. Based on our present knowledge, one could imagine neurotransmitters rather as biomediators that via cellular secretions participate in cell-cell communications in biocenosis, i.e., a group of interacting organisms that live in a particular habitat and form a self-regulating ecological community (Fig. 2.3). We think that information about intracellular location of the compounds and their release within any cell as well as

Biomediator in secretions and excretions

Contacts within cell

Contacts between cells

Life within organisms bacteria in plant bacteria in animal bacteria in microorganism fungi in plant algae in plant fungi in animal algae in animal

Fig. 2.3 Possible relationships with participation of biomediators their effects on the cellular organelles could be useful in the study of cell endocrinology. The role of acetylcholine and biogenic amines as intracellular regulators has been confirmed for sea animals (Buznikov 1990; Buznikov et al. 1996) and some plants (Roshchina 1989, 1990a, b, 1991, 2006a, b). A special case is related to the life of microorganisms within host cell of animal or plant. The release of neurotransmitters should occur within and out the guest cell (independently para-sitar or not). A universal (biomediator) role of neurotransmitters may be a subject of future investigations.

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