Occurrence of Neurotransmitters in Living Organisms 221 Discoveries

Historical chronologies of the neurotransmitters' discoveries are represented in Table 2.1. The first neurotransmitters were the catecholamines found by the American scientist John Jacob Abel at the end of the nineteenth century in extracts from animal adrenal glands. During the years 1906-1914, the existence of neurotransmitter compounds were identified not only in animals, but also in fungal extracts which were used as medicinal preparations. The twentieth century was the epoch for the discovery of neurotransmitters, mainly by pharmacologists and animal physiologists related to medicine. The roles of the catecholamine compounds in plants and microorganisms became a subject of interest only after 50-70 years of the twentieth century. Pioneering studies included the investigations of Jaffe, Fluck, Riov, Stephenson, Rowatt, Girvin, and Marquardt (see references in monograph of Roshchina 2001a for more detail).

As can be seen from Table 2.2, the concentration range of the neurotransmitter compounds is similar for all three kingdoms of living organisms, although some organs and specialized cells of multicellular organisms may be enriched in these compounds. Over 40 years ago, Soviet physiologist Koshtoyantz (1963) presented a hypothesis that the neurotransmitters are peculiar to all animal cells independently of their position on the evolutionary tree; this view has been confirmed experimentally, and described in several monographs (Buznikov 1967, 1987, 1990) and review (Buznikov et al. 1996). The presence of the neurotransmitters in animals has now been confirmed for all taxa - from Protozoa to Mammalia. As for bacterial cells, no more than 10-12 species have so far been characterized as containing acetylcholine, catecholamines, and serotonin, although histamine has been found in most species of prokaryotes. The issue of mammalian-type hormones in microorganisms has also been considered (Lenard 1992).

Table 2.1 Discovery of neurotransmitters

Neurotransmitter

In microorganisms

In plants

In animals

Acetylcholine

Dopamine

Norepinephrine (noradrenaline)

Epinephrine (adrenaline)

Serotonin Histamine

Identified independently by Ewins and Dale (1914) in preparations of ergot spur fungus Claviceps purpurea in Great Britain and in bacteria Pseudomonas fluoresceins (Chet et al. 1973) Found in infusoria Tetrahymena pyrifotmis by Gundersen and Thompson (1985). Identified in bacterial and fungal microorganisms by Tsavkelova et al. (2000) Identified in microorganisms by Tsavkelova et al. "(2000)

Found in 1986 by Hsu with co-workers in many bacteria Found in ergot fungi Claviceps purpurea in 1910 by Barger. Dale and Kutscher

In 1947 Emmelin and Feldberg found this substance in stinging trichomes and leaves of common nettle by biological method, based on muscle contraction

In 1944. found in Hetmidium alipes by Buelow and Gisvold

In 1956-1958 found in banana fruits in Sweden laboratories organized by Waalkes and Udenfriend In 1972 found in leaves of banana Musa by Askar et al. (1972)

Found in banana fruits (Musa)

by Bowden et al. (1954) Observed in higher plants by Werle and Raub in 1948

In 1921-1926 the presence of acetylcholine has been established in animals by Loewi and Navratil. But earlier, in 1906 student Reid Hunt (worked in USA laboratory of John J. Abel) discovered it in adrenal extracts of animals

Discovered in 1950-1952 by pharmacologists Arvid Carlsson. Nils-Ake Hillarp and von Euler in Sweeden

Isolated from adrenal gland extracts of animals in 1897-1898 by John J. Abel

Isolated from adrenal gland extracts of animals in 1895 by Polish physiologist Napoleon Cybulski and in 1897 by American John J. Abel

Discovered by Erspamer in 1940 and Rapport et al. in 1948 In 1919 American John Jacob Abel isolated histamine from pituitary extract of animals g o->

Sources: (Kruk and Pycock 1990; Roshchina 1991. 2001a; Kuklin and Conger 1995; Oleskin 2007; Kulma and Szopa 2007)

Table 2.2 Level of neurotransmitters in living organisms

In microorganisms

In plants

In animals

mg/g of fresh mass or *

mmol/L or ** mg/billion

mg/g of fresh mass or *

Neurotransmitter

of cells

mg/g of fresh mass

nM/L or ** nm/day

Acetylcholine

3.0-6.6

0.1-547

0.326-65200 (0.15-0.2 in brain)

Dopamine

0.45-2.13*

1-4000

<0.888*1214-2425**

Norepinephrine

0.21-1.87*

0.1-6,760

0.615-3.23*20-240**

(noradrenaline)

Epinephrine

No data

0.22-3833

1.9-2.46*30-80**

(adrenaline)

Serotonin

0.11-50,000**

0.0017-4000

0.21-0.96

Histamine

0.01-3.75

1 (1.34 - pain reaction for human)

0.5-100

Sources: (Fernstrom and Wurtman 1971; Kruk and Pycock 1990; Hsu et al. 1986; Roshchina 1991, 2001a; Oleskin et al. 1998a, b; Tsavkelova et al. 2000)

Sources: (Fernstrom and Wurtman 1971; Kruk and Pycock 1990; Hsu et al. 1986; Roshchina 1991, 2001a; Oleskin et al. 1998a, b; Tsavkelova et al. 2000)

2.2.1.1 Acetylcholine

In animals, acetylcholine and/or the synthesizing enzyme choline acetyltrans-ferase have been demonstrated in epithelial (airways, alimentary tract, urogenital tract, epidermis), mesothelial (pleura, pericardium), endothelial, muscle and immune cells, mainly in granulocytes, lymphocytes, macrophages, and mast cells (Wessler et al. 2001). Acetylcholine has also been found in Protozoa (Janakidevi et al. 1966a, b). Corrado et al. (2001) showed the synthesis of the molecular acetylcholine during the developmental cycle of Paramecium primaurelia. This neurotransmitter has a negative modulating effect on cellular conjugation. But in these unicellular organisms, the presence of functionally related nicotinic and muscarinic receptors and a lytic enzyme acetylcholinesterase has been established. Moreover, the authors could demonstrate (using immunocytochemical and histochemical methods) that the activity of enzyme choline acetyltransferase, which catalyzed acetylcholine synthesis, was located on the surface membrane of mating-competent cells and of mature, but not nonmating-competent P. primaurelia cells.

Acetylcholine has been well identified as a component of bacteria (its production was discovered in a strain of Lactobacillus plantarum) (Stephenson and Rowatt 1947; Rowatt 1948; Girvin and Stevenson 1954; Marquardt and Falk 1957; Marquardt and Spitznagel 1959). Cell free enzyme(s) participating in the acetylcholine synthesis were also first found in L. plantarum (Girvin and Stevenson 1954).

In the plant kingdom, acetylcholine is found in 65 species from 33 different families (Roshchina 1991, 2001a; Wessler et al. 2001; Murch 2006). Acetycholine was synthesized not only free, but also in a conjugated form as well, in particular as conjugates of cholinic esters with plant auxins (Fluck et al. 2000). Acetylcholine is particularly abundant in secretory cells of common nettle stinging hairs, where its concentration reaches 10-1 M or 120-180 nmol/g of fresh mass. Together with the histamine contained in the secretion, acetylcholine may provoke a pain response and formation of blisters when the plant comes in contact with human skin.

Kawashima et al. (2007) have attempted to compare the concentration of the neurotransmitter acetylcholine in a wide variety of sources using the same experimental conditions, which involved a radioimmunoassay with high specificity and sensitivity (1 pg/tube). The authors measured the acetylcholine content in samples from the bacteria, archaea, and eucarya domains of the universal phyloge-netic tree. The authors compared the concentrations in different groups of bacteria (Bacillus subtilis), archaea (Thermococcus kodakaraensis KOD1), fungi (shiitake mushroom and yeast), plants (bamboo shoot and fern), and animals (e.g., bloodworm and lugworm). The levels varied considerably, however, with the highest acetylcholine content detected in the top portion of bamboo shoot (2.9 jmmol/g), which contained about 80 times of that found in rat brain. Various levels of ace-tylcholine-synthesizing activity were also detected in extracts from the cells tested, which contained a choline acetyltransferase-like enzyme (sensitive to bro-moacetylcholine, a selective inhibitor of choline acetyltransferase). The enzyme activity was found in T. kodakaraensis KOD1 (15%), bamboo shoot (91%), shiitake mushroom (51%), bloodworm (91%), and lugworm (81%). Taken together, these findings demonstrate the ubiquitous expression of acetylcholine and acetylcholine-synthesizing activities among life forms without nervous systems, and support the notion that acetylcholine has been expressed and may be active as a local mediator and modulator of physiological functions since the early beginning of life.

2.2.1.2 Catecholamines

In unicellular organisms, biogenic amines are also synthesized. The large amounts of dopamine accumulated by cells of infusoria Tetrahymena pyriformis strain NT-1 and secreted into their growth medium were found to depend primarily upon an extracellular, non-enzymatic conversion of tyrosine to L-dihydroxyphenylalanine (Gundersen and Thompson 1985). Recently, the catecholamines norepinephrine and dopamine have been identified in microorganisms by high-performance liquid chromatography by Tsavkelova et al. (2000). Dopamine in concentrations 0.45-2.13 jmmol/L was found in the biomass of bacteria Bacillus cereus, B. mycoides, B. subtilis, Proteus vulgaris, Serratia marcescens, S. aureus, and E. coli, but was absent in the fungi Saccharomyces cerevisiae, Penicillum chrysogenum, and Zoogloea ramigera. Norepinephrine was found (0.21-1.87 jmmol/L) in the bacteria B. mycoides, B. subtilis, P. vulgaris, and S. marcescens as well as in fungi such as S. cerevisiae (0.21 jmmol/L) and P. chrysogenum (21.1 jmmol/L). It is especially interesting that in many cases, the content of catecholamines in microorganisms is higher than in animals, for example in human, blood norepinephrine is found about

0.04 jmmol/L (Kruk and Pycock 1990). Moreover, it was demonstrated that bacteria, in particular B. subtilis, may release norepinephrine and dopamine out of the cell and, perhaps, by this way possibly participate in intercellular communication both in microorganism-microorganism and bacteria-host.

In plants, catecholamines have been found in 28 species of 18 plant families (Roshchina 1991, 2001a; Kuklin and Conger 1995; Kulma and Szopa 2007). The amount of dopamine found varies during plant development (Kamo and Mahlberg 1984), and sharply increases during stress (Swiedrych et al. 2004). Of particular note is the finding that increased amounts of dopamine (1-4 mg/g fresh mass) are found in flowers and fruits, in particular in Araceae species (Ponchet et al. 1982). This demonstrates the important role of the catecholamines as neurotransmit-ters in fertilization as well as in fruit and seed development.

2.2.1.3 Serotonin

Some microorganisms living within parasitic nematodes are also able to synthesize serotonin (Hsu et al. 1986). In the bacterial flora of the ascarid Ascaris suum, mainly facultative anaerobes (17 species) produced and excreted serotonin into the culture medium of up to 14.32-500.00 jmg/g of fresh mass for Corynebacterium sp. (in the tissues of the helminth itself only 0.25 jmg serotonin per g fresh mass). The concentration of serotonin, in terms of mg serotonin/109 cells for different cultures of microorganisms isolated from helminths is as follows: Klebsiella pneumoniae 8.15, Aeromonas 26.71, Citrobacter 0.58, Corynebacterium sp. 14.32-500.00, Enterobacteria aggiomerans 2.93, Shigella 1.04, Achromobacter xylosoxidans 1.66, Chromobacterium 3.67, Achromobacter 0.15, Acinetobacter 11.79, Streptococcus 37.52, Listeria monocytogens 4.71, and E. coli 3.33. Serotonin has also been found in the yeast Candida guillermondii and bacterium Enterococcus faecalis (Fraikin et al. 1989; Belenikina et al. 1991; Strakhovskaya et al. 1991, 1993). In 1998, Oleskin et al. also established the presence of serotonin in the phototrophic bacterium Rhodospirillum rubrum (1 jmg/billion of cells ~3-12,500 jmg/g of fresh mass) as well as in nonphototrophic bacteria Streptococcus faecalis and E. coli (50 and 3.3 jmg/billion of cells, relatively). The inhibitor of tryptophan hydroxylase, n-chlorophenylalanine, affects the growth of the yeast Candida guillermondii, but not the development of the bacterium E. coli. This suggests that in the latter case, there is an alternative pathway to that found in animals (Oleskin et al. 1998a, b), which is peculiar (Roshchina 1991, 2001a) to plants: tryptophan ^ tryptamine ^ serotonin.

In plants, serotonin is found in 42 species of 20 plant families (Roshchina 1991, 2001a). Besides free serotonin, conjugated serotonins such as N-feruloylserotonin, N-(p-coumaroyl) serotonin, N-(p-coumaroyl) serotonin mono-ß-D-glucopyranoside have been isolated from safflower Carthamus tinctorius L. seed. It should be noted that serotonin in animals (such as rats) may exist in complexes with heparin that prevents the aggregation of thrombocytes (Kondashevskaya et al. 1996).

2.2.1.4 Histamine

Histamine was first found in the ergot fungus Claviceps purpurea (Table 2.1), and subsequently in many bacterial and plant cells by Werle and coauthors (1948, 1949). Since then, it has also been observed in many types of foods as the result of microbial activity. Histamine is one of the biogenic amines formed mainly by microbial decarboxylation of amino acids in numerous foods, including fish, cheese, wine, and fermented products. A number of microorganisms can produce histamine. In particular, bacteria such as Morganella morganii, Proteus sp, and Klebsiella sp. are considered strong histamine formers in fish (Ekici and Coskun 2002; Ekici et al. 2006). Fernandez et al. (2006) summarized the data on the hista-mine content as toxicant in food. Histamine poisoning is the most common food borne problem caused by biogenic amines. At non-toxic doses, this histamine can cause intolerance symptoms such as diarrhea, hypotension, headache, pruritus, and flushes. Just 75 mg of histamine, a quantity commonly present in normal meals, can induce symptoms in the majority. One separate problem concerns the histamine formed by microorganisms in animal pathogenesis. Gram-negative bacterial species such as Branhamella catarrhalis, Haemophilus parainfluenzae, and Pseudomonas aeruginosa have been demonstrated to synthesize clinically relevant amounts of histamine in vitro that implicate the bacterial production of histamine in situ as an additional damage factor in acute exacerbations of chronic bronchitis, cystic fibrosis, and pneumonia. Histamine may also increase the virulence of these bacterial species, unlike some Gram-positive species such as Staphylococcus aureus and Streptococcus pneumoniae (Devalia et al. 1989). Among "non-pathogenic" species, only the Enterobacteriacae, as a group, were found to form hista-mine in significant concentrations.

Significant amounts of histamine have also been observed in higher plants, initially by Werle and Raub in 1948, and subsequently described for 49 plant species belonging to 28 families ranging from basidiomycetes to angiosperms (Roshchina 1991, 2001a). Besides histamine itself, its derivatives N-acetylhistamine, N, N-dimethylhistamine, and feruloylhistamine are also found in plants. Especially high levels are observed in species of the family Urticaceae that could be one of the taxonomic classification signs. The Brazilian stinging shrub Jatropha urens (family Euphorbiaceae) contains 1,250 jmg histamine per 1,000 hairs. The presence of his-tamine in stinging hairs is a protective mechanism that serves order to frighten off predatory animals by inducing burns, pain, and allergic reactions. Under stress conditions, a sharp increase of histamine is observed in plants, as in animals. Ekici and Coskun (2002) have determined the histamine content of some commercial vegetable pickles at the range of 16.54 and 74.91 mg/kg (average 30.73 mg/kg). The maximum value (74.91 mg/kg) was obtained from a sample of hot pepper pickles. The amount of histamine varies according to the phase of plant development. For example, in the marine red algae Furcellaria lumbricalis (Huds.) Lamour, the occurrence of histamine was from 60 to 500 mg/g fresh mass observed in both non-fertile fronds and sexual-expressed parts, in all regions of the thallus of male, female, and tetrasporophyte (Barwell 1979, 1989). The amount of histamine

(in mg/g fresh mass) in the male plant was 90-490 (sometimes up to 1,100), in the female plant 60-120, and in asexual tetra sporophyte 100-500. Especially enriched were the neurotransmitter cells of male plants, as the ramuli were approximately five times higher in histamine than female and asexual plants.

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