The opiate receptor: a single 110 kDa recognition molecule appears to be conserved in Tetrahymena, leech, and rat

The hormonal system of the unicellular Tetrahymena: a review with evolutionary aspects

The unicellular ciliate, Tetrahymena has receptors for hormones of the higher ranked animals, these hormones (e.g. insulin, triiodothyronine, ACTH, histamine, etc.) are also produced by it and it has signal pathways and second messengers for signal transmission. These components are chemically and functionally very similar to that of mammalian ones. The exogenously given hormones regulate different functions, as movement, phagocytosis, chemotaxis, cell growth, secretion, excretion and the cells' own hormone production. The receptors are extremely sensitive, certain hormones are sensed (and response is provoked) at 10-21 M concentration, which makes likely that the function could work by the effect of hormones produced by the Tetrahymena itself. The signal reception is selective, it can differentiate between closely related hormones. The review is listing the hormones produced by the Tetrahymena, the receptors which can receive signals and the signal pathways and second messengers as well, as the known effects of mammalian hormones to the life functions of Tetrahymena. The possible and justified role of hormonal system in the Tetrahymena as a single cell and inside the Tetrahymena population, as a community is discussed. The unicellular hormonal system and mammalian endocrine system are compared and evolutionary conclusions are drawn.

Durable effect of heat-stress on the hormone production of Tetrahymena. Effect of insulin on the consequences of stress

The unicellular Tetrahymena pyriformis was stressed by 37°C heat for 1 h and its hormone (serotonin, histamine, triiodothyronine) content was measured by immunocytochemical flow cytometry in different time points (immediately after treatment and after 1, 2, 8, 16 weeks). The treatment increased each hormone level for two weeks, however, after 8 weeks the hormone concentration inside the cells decreased and in case of serotonin this was similar in the 16th week, while the other two hormones' level was similar to the control. Insulin further increased the hormone production during treatment, but this effect was not durable. After one week the cells behave similar to those, subjected to heath shock only. The results show that a single stress causes deep and durable changes in the hormone household of Tetrahymena which is influenced by exogenously given insulin only in the acute phase.

Thyrotropin (TSH) regulates triiodothyronine (T3) production in the unicellular Tetrahymena

The aim of the experiments was to study the regulation of triiodothyronine (T3) production in the unicellular Tetrahymena. Untreated and troph-hormone treated specimen were prepared and in different timepoints T3 content was measured and compared by immunocytochemical flow cytometry. 0.1 or 0.001 IU TSH in tryptone-yeast medium stimulated T3 synthesis at 10, 20, 30 min, but does not stimulate after 1 h. The overlapping gonadotropic hormone (GTH) also did it, however only at 10 min. In Losina salt solution (physiological for Tetrahymena) the effect was weaker, however outer amino acid source was not absolutely needed for the production of the hormone. The results show that the TSH regulation of thyroid hormone synthesis (storage, secretion) and troph-hormone overlap can be deduced to a unicellular level. This may allow the hypothesis that the endocrine mechanisms proved at a low level of phylogeny are preserved for the higher ranked organisms.

Effect of different concentrations of serotonin, histamine and insulin on the hormone (serotonin and ACTH) production of Tetrahymena in nutrient-free physiological milieu

Cell populations of Tetrahymena pyriformisGL were kept in nutrient-free (Losina) milieu and treated with different (10(-6)-10(-21)M) concentrations of serotonin, histamine or insulin for 30 min. Following that the hormone (serotonin and adrenocorticotropin (ACTH) content of the cells were measured by immunocytochemical flow cytometric method. Serotonin reduced histamine when applied in 10(-12) and 10(-15)M concentrations, while elevated ACTH levels when applied in 10(-6), 10(-9) and 10(-21)M concentrations. Histamine reduced serotonin concentration at 10(-9)-10(-21)M concentrations and increased ACTH in 10(-6)M. Insulin elevated both hormones' content in each concentration except at 10(-12)M. The results demonstrate that (1) in nutrient-free conditions the hormonal effects differ from that of nutrient-rich (tryptone+yeast) condition; (2) there is an optimal hormone concentration, which causes the strongest effect and this is different for each hormones; (3) the hormone receptors of Tetrahymena are very sensitive; as they react to zeptomolar concentrations. Such small concentration is even more effective than higher ones. Since hormones must become highly diluted in the natural environment of Tetrahymena, it seems that such low concentrations are the actual physiological concentrations.

Investigations on the triiodothyronine (T3)-specificity of thyrotropic (TSH) and gonadotropic (HCG) hormone in the unicellular Tetrahymena

In a previous experiment thyrotropin (TSH) increased the triiodothyronine (T3) production of Tetrahymena and chorionic gonadotropin (HCG) moderately overlapped the effect. At present the production of three amino acid type (histamine, serotonin, epinephrine) and one peptide (endorphin) hormones were studied under the effect of TSH or HCG, in tryptone-yeast (TY) or salt (Losina-Losinsky) medium. The duration of the effect was 10 min. TSH significantly (with almost 20%) decreased epinephrine production in TY medium and HCG similarly decreased epinephrine and increased histamine level. In salt solution TSH as well as HCG decreased the level of serotonin. The results show that at this low level of phylogeny TSH effect is not completely thyroxine-specific, however it is not general. HCG overlaps TSH effect on epinephrine and serotonin production, however its effect is broader. The experiments also demonstrate that the effect of pituitary trop-hormones can be bidirectional in Tetrahymena, as histamine level was increased and epinephrine level was decreased by HCG, in the same cells.

Hormonal effects on Tetrahymena: change in case of combined treatment

In order to approach their natural conditions, populations of Tetrahymena were kept in Losina-Losinky's salt solution for 1 h, than in the tryptone+yeast medium. During this time they were treated with histamine, serotonin or insulin, or with the combinations of these hormones. Effect of the combined treatments on the production of serotonin (5HT), or adrenocorticotropic hormone (ACTH) or triiodothyronine (T₃) by the cells was compared to the effect of single-hormone treatments. Significant differences were seen between the results obtained following the single or combined treatments. There was no summation of the effects, however an elevation or diminution of the hormone production was observed after the combined treatment, as compared with the untreated controls or with the use of one of the hormones in the samples. The experiments demonstrate that there is a hormonal regulation between the Tetrahymena cells and the hormones influence each other's effect.

The effect of opioids and their antagonists on the nocifensive response of Caenorhabditis elegans to noxious thermal stimuli

Opiates modulate nociception in vertebrates. This has also been demonstrated in a number of invertebrate models. Herein, the effect of the opiate morphine and opioid neuropeptides Endomorphin 1 and 2 on the thermal avoidance (Tav) behavior of Caenorhabditis elegans is explored. Adult wild-type C. elegans N2 were collected from NGM plates using M9 buffer and exposed to morphine and endomorphine 1 and 2 in concentrations between 10(-8) and 10(-4) M (2.5 pmol/mg to 25 nmol/mg) for 30 min and tested for Tav. The opioid receptor antagonists Naloxone and CTOP were tested in combination with the drugs. Forty-seven percentage of the morphine exposed worms exhibited a class I response versus 76% of the control group (P < 0.001). Endomorphin 1 and 2 also caused a statistically significant reduction in class I responses, 36 and 39%, respectively. These effects were reversed with Naloxone and CTOP. Thermonocifensive behavior in C. elegans is modulated by opioids.

Effect of stress and stress hormones on the hormone (insulin) binding of Tetrahymena

The unicellular Tetrahymena pyriformis GL produce, store and secrete vertebrate-like hormones. In earlier experiments the effect of different stressors on the hormone levels of Tetrahymena was studied and an elevation of these was found. In the present experiments the hormone binding was investigated, using flow cytometric method. FITC-insulin binding was elevated after concentrated (5, 10, or 20 mg ml(-1)) NaCl or 0.01%, 0.1%, or 0.05% formaldehyde treatment, or after thermal stress (37 degrees C). Serotonin given together with NaCl increased and together with formaldehyde decreased the binding. Histamine always decreased the binding and insulin was indifferent. Four hours after osmotic stress, hormone binding significantly decreased and this was not influenced by hormones. However, 4 h after formaldehyde stress the binding elevated and this was further increased by repeated hormone treatments. The results show that the stress in Tetrahymena provokes an activation of its hormonal system (hormone production and binding), which is differently influenced by exogeneously given hormones.

Effect of femtomolar concentrations of hormones on insulin binding by Tetrahymena, as a function of time

The unicellular ciliate Tetrahymena, contains and binds hormones, characteristic of vertebrates. Earlier experiments demonstrated the effect of extremely low concentrations of hormones. In the present experiments, the effect of various hormones (endorphin, serotonin, histamine, insulin and epidermal growth factor [EGF]) in 10(-15) M, or oxytocin, gonadotropin at 0.001 IU concentrations) on the binding of FITC-insulin was studied by using flow cytometry and confocal microscopy, after 1, 5, 15, 30 and 60 min. Six of the seven hormones promptly decreased the cells' hormone binding capacity, the exception being EGF, and in four cases (endorphin, serotonin, insulin and oxytocin) the reduction was enormous. The decreased binding was durable. However, in the case of endorphin and oxytocin after 30 min, and in the case of serotonin after 60 min the binding returned to the control level. In the case of oxytocin after 60 min, binding significantly surpassed the control level. Histamine returned to the control level after 15 min, but after that the binding became even lower. EGF provoked special behaviour: it increased hormone binding after 30 and 60 min. The results call attention to the extreme sensitivity of Tetrahymena receptors to hormonal inductions and to its quick response ability.

Hormonal imprinting: phylogeny, ontogeny, diseases and possible role in present-day human evolution

Hormonal (chemical) imprinting which was first observed (and named) by us in the seventies of the last century, is a general biological phenomenon which takes place when the developing receptor meets its target hormone for the first time. Under the effect of imprinting, receptors mature and reach their maximal binding capacity. It also influences the cells' hormone production and different functions depending on receptors and hormones. Hormonal imprinting is present already at the unicellular level causing the development of specific receptors and helping the easier recognition of useful or harmful surrounding molecules. The phenomenon is an important factor in the survival of the species, as the effect of imprinting is transmitted to the progeny cell generations. At the same time it possibly helps the selection of molecules which are suitable for acting as hormones in higher ranked animals. In mammals, hormonal imprinting takes place perinatally and determines the function of receptor-signal-transduction systems as well as hormone production for life. However, there are other critical imprinting periods for continuously developing cells. Excess of the target hormones or presence of foreign molecules which are able to bind to the receptors, provoke faulty imprinting in the critical periods with life-long morphological, biochemical, functional or behavioural consequences. As many receptor-bound foreign molecules are used as medical treatments and many such molecules are present around us and inside us as environmental pollutants, they--causing faulty imprinting--are able to predispose the (human) organism to cardiovascular, endocrine, metabolic and cancerous diseases. It seems likely that this effect is connected with disturbance of DNA methylation process in the critical periods of life. There are some signs of the transgenerational effect of faulty imprinting and this could be manifested in the evolution of humans by an epigenetic route.

Morphine alters the selective association between mu-opioid receptors and specific RGS proteins in mouse periaqueductal gray matter

In the CNS, several regulators of G-protein signalling (RGS) modulate the activity of mu-opioid receptors. In pull-down assays performed on membranes from mouse periaqueductal gray matter (PAG), mu-opioid receptors co-precipitated with delta-opioid receptors, Gi/o/z/q proteins, and the regulators of G-protein signalling RGS4, RGS9-2, RGS14, RGSZ1 and RGSZ2. No RGS2, RGS7, RGS10 and RGS11 proteins were associated with the mu receptors in these PAG membranes. In mice, an intracerebroventricular dose of 10 nmol morphine produced acute tolerance at mu receptors but did not disrupt the co-precipitation of mu-delta receptor complexes. However, this opioid reduced by more than 50% the co-precipitation of G alpha i/o/z subunits with mu receptors, and altered their association with some of the RGS proteins at 30 min, 3 h and 24 h after its administration. The association of RGS9-2 with mu receptors diminished by 30-40% 24 h after the administration of morphine, while that of RGSZ2 and of RGSZ1 increased. Morphine treatment recruited RGS4 to the PAG membranes, and 30 min and 3 h after the opioid challenge its association with mu receptors had increased. However, 24 h after morphine administration, the co-precipitation of RGS4 had decreased by about 30%. The opioid produced no change in the membrane levels of RGS9-2, RGS14, RGSZ1 and RGSZ2. Thus, in PAG synaptosomal membranes, a dynamic and selective link exists between, mu-opioid receptors, Gi/o/z proteins and certain RGS proteins.

Immunoanalogue of vertebrate beta-adrenergic receptor in the unicellular eukaryote Paramecium

Cell fractionation, SDS-PAGE, quantitative Western blot, confocal immunolocalization and immunogold labelling were performed to find an interpretation of the physiological response of the unicellular eukaryote Paramecium to beta-adrenergic ligands. The 69 kDa polypeptide separated by SDS-PAGE in S2 and P2 Paramecium subcellular fractions cross-reacted with antibody directed against human beta2-adrenergic receptor. This was detected by Western blotting followed by chemiluminescent detection. Quantitative image analysis showed that beta-selective adrenergic agonist (-)-isoproterenol--previously shown to enhance phagocytic activity--evoked redistribution of the adrenergic receptor analogue from membraneous (P2) to cytosolic (S2) fraction. The relative increase in immunoreactive band intensity in S2 reached 80% and was paralleled by a 59% decrease in P2 fraction. Confocal immunofluorescence revealed beta2-adrenergic receptor sites on the cell surface and at the ridge of the cytopharynx--where nascent phagosomes are formed. This localization was confirmed by immunoelectron microscopy. These results indicate that the 69 kDa Paramecium polypeptide immunorelated to vertebrate beta2-adrenergic receptor appeared in this evolutionary ancient cell as a nutrient receptor.

The neuroendocrine system of annelids

In vertebrates the neuroendocrine system is based on chemical signaling between neural and endocrine structures. Final outcomes may be realized via chemical messengers traveling through circulatory conduits to their specific target sites. This process may rely, in part, on neurosecretion of the signaling molecules. The complexity of this system can be readily visualized when one considers the way in which interactions among classical neurotransmitters, cytokines, growth factors, and neuroendocrine hormones, in combination with autocrine and paracrine communication, can regulate cells and tissues. Apart from the neuroendocrine system there is also neuroimmune communication, consisting of reciprocal signaling between neuroendocrine and immune cells, which use the same molecules to coordinate their activity. Thus, our concept of the neuroendocrine system is constantly growing, despite its complexity, but it may be simply summarized as allowing bidirectional communication between neural and endocrine structures over distances greater than that achieved by synaptic communication. In the light of this, I demonstrate in this review that annelids, which are considered "simple" animals, also possess a neuroendocrine system.

Crosstalk between nervous and immune systems through the animal kingdom: focus on opioids

During the course of evolution invertebrates and vertebrates have maintained common signaling molecules, such as neuropeptides. For example, complete hormonal-enzymatic systems for the biosynthesis of opioid peptides have been found in both the CNS and immune systems of these animals. These signaling molecules have been found in the blood circulation and act as immunomodulators. In vertebrates, release of the signaling molecules occurs during stress (cognitive or pathogens), which triggers the hypothalamo-hypophysial-adrenal axis. Similarly, these neuropeptides are used as messengers to initiate and stimulate the innate immune response in invertebrates. Thus, the crosstalk between nervous and immune systems has an ancient evolutionary origin and the messengers used have been conserved during the course of evolution reflecting their vital importance.

Insulin uptake, localization and production in previously insulin treated and untreated Tetrahymena. Data on the mechanism of hormonal imprinting

Confocal microscopic experiments demonstrate the presence of insulin in Tetrahymena, observed also in earlier experiments. However, there is a broad spectrum of insulin-containing cells from the immunocytochemically insulin-free, to the strongly antibody-reactive ones. During 1 h of insulin treatment (imprinting) the cells gradually bind and take up insulin, and the process is slow. One minute after the start of treatment there is not difference in the number of insulin antibody-reactive cells and amount of insulin. After 5 or 10 min the cells bind and contain more insulin and after 1 h most of the cells are densely packed with the insulin antibody-reactive material. Insulin imprinting accelerates binding and uptake alike: 48 h after imprinting and 1 min after the start of the second treatment, more insulin is present on the surface and inside the cells, than after 10 min in the first-time treated cells. Theoretically, this effect of hormonal imprinting helps to maintain the species by facilitating molecular recognition and binding as well as uptake of useful molecules. The experiments also support previous observations on the parallel receptor-evoking (strengthening) and hormone-producing effect of hormonal imprinting.

Chemotactic selection of Tetrahymena pyriformis GL induced with histamine, di-iodotyrosine or insulin

It has been hypothesized that in phylogeny the encounter between potential signalling molecules and the continously changing cell membrane could result in the formation of a ligand specific receptor. This chemical (hormonal) imprinting is then transmitted to the progeny generations. It is, however, very difficult to know whether the selection of cells with receptor-like patterns or amplification of complete receptor-like patterns led to the formation of the receptor-hormone complex. The new technique of 'chemotactic selection provides a physiological response-guided selection of cells. It also enables the testing of subpopulations with the characteristic selector ligand. We show here that of three chemotactic ligands (histamine, di-iodotyrosine (T2) and human insulin), insulin and T2 selected subpopulations express a significantly high chemotactic response. Since the control medium has a selector capacity itself, we introduced a chemotactic selection coefficient (Chsel) which facilitates the comparison of all groups. Using this factor we found that insulin (Chsel = 1.57), functions as a strong selector and T2 (Chsel = 0.98), was a weak selector. Morphometric evaluation of the cells showed a good correlation between chemotactic responsiveness and morphometric characteristics of subpopulations selected with insulin and histamine. T2 data suggest that the long lasting responsiveness is not general, but might be subpopulation specific.

Prolonged elevation of insulin content in the unicellular tetrahymena after insulin treatment: induction of insulin production or storage?

In the unicellular organism, Tetrahymena, the first encounter with an exogeneously given hormone results in hormonal imprinting. This causes an increase of the binding capacity of receptors and the production of the appropriate hormone in the progeny generations of the treated cell. In the present experiments the quantity (using radioimmunoassay) and localization (using confocal laser scanning microscopy) of the immunologically insulin-like material (hereafter insulin) were studied for 10 days after 4 h or 24 h 10(-6) M insulin treatment (hormonal imprinting). Forty-eight hours after both insulin treatments a high quantity of insulin was present in the cells. This value was also significantly increased after 96 h. After 8 days the difference to the control was significant only in the 24 h treated group. Confocal microscopy (using antibody to pig insulin) localized insulin in the cell body. The oral field contained extremely high quantities of the endogeneous hormone. Insulin treatment (after 48 and 96 h) caused an elevation of insulin content in general, and specific accumulation in the posterior sections of the cell, around the nucleus and in the periphery were observed. Ten days after both treatments only the peripheral region of the cell body and the ciliary row contained more insulin than the control. This means that after insulin treatment the quantity of insulin increases for a lengthy time period which is followed by the expression of insulin in the peripheral region. Insulin contained by Tetrahymena 48 h after imprinting stimulated glucose uptake of rat diaphragm.

Signaling in unicellular eukaryotes

Aspects of intercellular and intracellular signaling systems in cell survival, proliferation, differentiation, chemosensory behavior, and programmed cell death in free-living unicellular eukaryotes have been reviewed. Comparisons have been made with both bacteria and metazoa. The central organisms were flagellates (Trypanosoma, Leishmania, and Crithidia), slime molds (Dictyostelium), yeast cells (Saccharomyces cerevisiae), and ciliates (Paramecium, Euplotes, and Tetrahymena). There are two novel aspects in this review. First, cellular responses are viewed in an evolutionary perspective, rather than from the more prevailing one, in which the unicellular eukaryotes are seen by the mammalian organisms. Second, results obtained with cell cultures in minimal, chemically defined nutrient media at low cell densities where intercellular signaling is strongly reduced are discussed. These results shed light on control mechanisms and their cooperation inside the living cell. Intracellular systems have many common features in unicellular and multicellular organisms.

A lectin-like molecule is discharged from mucocysts of Tetrahymena pyriformis in the presence of insulin

By use of a monoclonal antibody directed against purified lectin from the sponge Geodia cydonium it was demonstrated that the mucocysts of Tetrahymena pyriformis contain a substance immunologically similar to that found in G. cydonium. In extracts of T. pyriformis the monoclonal antibody recognizes a 36 kDa protein; binding could be abolished by adsorption of the antibody with (i) crude extract, (ii) purified lectin from G. cydonium and (iii) a 29 aa long peptide. In addition the data show that 10(-6) M of insulin causes first the release of mucocyst material, which reacts with the lectin antibody, and second its subsequent redistribution on the surface of the somatic cilia and the oral field.

Opioid receptor types for endogenous enkephalin in the thoracic ganglion of the crab, Carcinus maenas

In crustaceans, the endogenous opioid peptides, enkephalins, are known to be concentrated in the thoracic ganglion, although they have been demonstrated in all parts of the nervous system. Bmax and Kd measurements have been obtained for the binding of ligands used to characterize delta- and kappa-type opioid receptors in vertebrates. High- and low affinity binding of [3H] [2-D-Pen5-D Pen] enkephalin ([3H]DPDPE) has been measured with a Kd = 9.2 +/- 2.4 nM, Bmax = 153 fmol/mg, and Kd = 243 +/- 27 nM, Bmax = 1.785 pmol/mg, respectively. In addition a kappa-type receptor with Kd 85.5 +/- 12.6 nM and Bmax = 21.138 pmol/mg protein has been recorded. Binding characteristics of several ligands were monitored. Electrophoretic studies of affinity chromatographically purified receptor fractions revealed a molecular mass of 60 kDa. Isoelectric focusing showed a specific binding of [3H]DPDPE to thoracic ganglion membranes at a pl of 5.5.

Effects of L-alanine and L-alanine peptides on the chemotaxis of tetrahymena: evolutionary conclusions

L-alanine and its peptides (L-Ala-2-6) do not attract or repulse Tetrahymena in a 10(-8) M concentration. In 10(-10) M concentration there is a consistent repellent effect. Twenty four hours after L-alanine or L-alanine-peptides' pretreatment (imprinting) the progeny generation of the cells react differently to the same materials. L-Alanine, L-alanine penta- and hexapeptide in both concentrations are chemoattractant, while L-alanine tetrapeptide is repellent. L-Alanine dipeptide is inert in 10(-10) M and repellent at 10(-8) M concentrations, while L-alanine tripeptide is strongly repellent at 10(-10) M and attractant at 10(-8) M concentrations. This means, that the first encounter (imprinting) with an exogenous amino acid or peptide is decisive to the later reaction of the protozoan cell. The chain length is important in the imprinting, however the reaction is not consistent. The experiments call the attention to the significance of imprinting in the receptor and hormone evolution.

Immunocytochemical verification of the insulin receptor's specificity in the nuclear envelope of Tetrahymena. Comparison with receptors of the plasma membrane

The unicellular Tetrahymena possess hormone receptors in the nuclear envelope similarly to higher rank animals. These receptors bind insulin and their specificity is detectable by monoclonal antibodies developed to insulin. The hormonal (insulin) pretreatment (imprinting) of the cell did not alter the binding capacity of the nuclear membrane, demonstrated by antibody-technique. The specific binding characteristics of the plasma membrane was demonstrated and this was significantly increased following imprinting. In the nucleus of Tetrahymena presence of insulin was not detected by immunocytochemical method.

The opiate system in invertebrates

The presence in diverse species of a similar mode of communication, that of a soluble messenger binding to a receptor, raises the question as to whether the specific components of this system are equally widespread. Do invertebrates use the same hormones and receptors as vertebrates do? Invertebrates ranging from unicellular organisms to insects have been shown to contain opiate-like peptides and binding sites, and they exhibit biological responses to opiates. However, critical genetic data are lacking. It is not known how signal systems arise phylogenetically, but it is conceivable that signal molecules that are already present cause the formation of their own receptors from membrane proteins.

Pharmacological characterization of an opioid receptor in the ciliate Tetrahymena

A pharmacological characterization has been performed of the opioid receptor involved in modulation of phagocytosis in the protozoan ciliate Tetrahymena. Studies on inhibition of phagocytosis by mammalian prototypic opioid agonists revealed that morphine and beta-endorphin have the highest intrinsic activity, whereas all the other opioids tested can only be considered partial agonists. However, morphine (a mu-receptor agonist) is twice as potent as beta-endorphin (a delta-receptor agonist). Furthermore, the sensitivity for the opioid antagonist naloxone, determined in the presence of morphine and beta-endorphin, is very similar to the sensitivity exhibited by mammalian tissues rich in mu-opioid receptors. We suggest that the opioid receptor coupled to phagocytosis in Tetrahymena is mu-like in some of its pharmacological characteristics and may serve as a model system for studies on opioid receptor function and evolution.

Chemotactic properties, cellular binding and uptake of peptides and peptide derivatives: studies with Tetrahymena thermophila

Receptor-mediated binding of leukocyte chemotactic peptide, N-formylMet-Leu-Phe (fMLP), occurs in the ciliated protozoon Tetrahymena thermophila. In vivo labelling of the cells with N-formylMet-Leu-[3H]Phe ([3H]fMLP) shows that the cells bind the ligand with high affinity (KD = 4 × 10(−9) M to 1 × 10(−8) M). Moreover, Scatchard transformations of the binding data show that there are about 5 × 10(5) binding sites per cell on the cell surface. Two fluorescent derivatives of leukocyte chemotactic peptide, N-dansylMet-Leu-Phe (dansMLP) and N-formylMet-Leu-Phe-(N-dansyl-)Lys (fMLPdanLys) compete for the N-formylMet-Leu-Phe (fMLP) binding sites on the cell surface. Moreover, both derivatives have retained significant chemoattracting potentials. Fluorescence from dansMLP, but not from fMLPdansLys and dansyl-beta-endorphin, is internalized preferentially into small vesicles. The differences may, however, reflect that the fluorescence from the dansyl group is strongly quenched by a hydrophilic microenvironment when using the two latter peptide derivatives. In contrast, the dansyl group from dansMLP must be assumed to be embedded in a hydrophobic microenvironment in the vesicular membrane or membrane protein. Rhodamine-labelled bovine serum albumin, egg albumin and cytochrome c as well as dansylated bovine serum albumin, which are poor chemoattractants, are preferentially seen to be internalized into large vesicles (food vacuoles).

Cortical ultrastructure and chemoreception in ciliated protists (Ciliophora)

The ciliated protists (ciliates) offer a unique opportunity to explore the relationship between chemoreception and cell structure. Ciliates resemble chemosensory neurons in their responses to stimuli and presence of cilia. Ciliates have highly patterned surfaces that should permit precise localization of chemoreceptors in relation to effector organelles. Furthermore, ciliates are easy to grow and to manipulate genetically; they can also be readily studied biochemically and by electrophysiological techniques. This review contains a comparative description of the ultrastructural features of the ciliate cell surface relevant to chemoreception, examines the structural features of putative chemoreceptive cilia, and provides a summary of the electron microscopic information available so far bearing on chemoreceptive aspects of swimming, feeding, excretion, endocytosis, and sexual responses of ciliates. The electron microscopic identification and localization of specific chemoreceptive macromolecules and organelles at the molecular level have not yet been achieved in ciliates. These await the development of specific probes for chemoreceptor and transduction macromolecules. Nevertheless, the electron microscope has provided a wealth of information about the surface features of ciliates where chemoreception is believed to take place. Such morphological information will prove essential to a complete understanding of reception and transduction at the molecular level. In the ciliates, major questions to be answered relate to the apportionment of chemoreceptive functions between the cilia and cell soma, the global distribution of receptors in relation to the anterior-posterior, dorsal-ventral, and left-right axes of the cell, and the relationship of receptors to ultrastructural components of the cell coat, cell membrane, and cytoskeleton.

An opioid growth factor regulates the replication of microorganisms

An opioid growth factor (OGF), [Met5]-enkephalin, interacts with the zeta (zeta) opioid receptor to modulate development of eukaryotes. We have found that [Met5]-enkephalin, an endogenous opioid peptide serves to inhibit the growth of S. aureus. This effect on growth involves cell proliferative events and is under tonic control, since potent opioid antagonists accelerate cell replication. Both the OGF and zeta opioid receptor were associated with these microorganisms. Other opioid receptors (mu, delta and kappa) were not detected. OGF also controlled the growth of other bacteria: P. aeruginosa and S. marcesans. These results indicate that OGF and its receptor, known to be important in the regulation of mammalian development, also function in the growth of simple unicellular organisms. We suggest that the endogenous opioid system related to growth originated billions of years ago.

The evolution of hormonal signalling systems

1. A comparative analysis was made of chemosignalling systems responsible for the action of hormones, hormone-like substances, pheromones, etc. in vertebrates--multicellular invertebrates--unicellular eukaryotes. Many common features revealed in structural-functional organization of the above systems give evidence of their evolutionary conservatism. 2. It was shown that some molecular components as well as signal transduction mechanisms similar to those of higher eukaryote hormonal signalling systems are present in such early organisms as bacteria. This allowed a suggestion that the roots of chemosignalling systems are likely to be found in prokaryotes. 3. The evolution of hormonal signalling systems is discussed in terms of current theories of the origin of eukaryotic cell, its organelles and components. A hypothesis is put forward about endosymbiotic genesis of these signal transduction systems in eukaryotes. 4. A possible evolutionary scenario of the formation of hormonocompetent systems is proposed with hormone-sensitive adenylate cyclase complex taken as an example.

Inhibitory effects of 60-Hz magnetic fields on opiate-induced "analgesia" in the land snail, Cepaea nemoralis, under natural conditions

There is accumulating laboratory evidence that magnetic fields can affect a variety of opioid-mediated behavioral and physiological functions in both vertebrates and invertebrates. The present study examined the effects of various durations (0.50, 1.0 and 2.0 h) of exposure to a low intensity (1.0 gauss rms) 60-Hz magnetic field on opioid-mediated aversive thermal ("nociceptive") responses and morphine-induced "analgesia" in the land snail, Cepaea nemoralis, under natural environmental conditions. Exposure to the powerline-related 60-Hz magnetic fields significantly attenuated morphine-induced analgesia and the basal nociceptive responses of Cepaea, with the degree of attenuation being related to the duration of exposure to the magnetic fields. These results with Cepaea show that 60-Hz magnetic fields can affect opioid-mediated behavioral responses outside the laboratory under natural environmental conditions.

Ontogeny of mu-, delta- and kappa-opioid receptors mediating inhibition of neurotransmitter release and adenylate cyclase activity in rat brain

The ontogeny was examined of functional opioid receptors mediating presynaptic inhibition of neurotransmitter release and inhibition of dopamine (DA)-sensitive adenylate cyclase in the rat brain, using highly selective agonists for mu-, delta- and kappa-receptors. On gestational day 17 (E17) strong inhibitory effects of the selective mu-agonist DAGO on the electrically evoked release of [3H]noradrenaline from cortical slices and of the selective kappa-agonist U-50,488 on the electrically evoked release of [3H]DA from striatal slices were found. Electrically evoked release of [3H]acetylcholine from striatal slices was not detectable before postnatal day 7 (P7), but on that day it was already strongly inhibited by the selective delta-agonist DPDPE. Although mu- and delta-opioid receptors coupled to DA-sensitive adenylate cyclase in the striatum are likely to be physically associated in an opioid receptor complex in the adult, they were found to develop asynchronously. Whereas selective activation of mu-receptors with DAGO resulted in an inhibition of D1 dopamine receptor-stimulated adenylate cyclase activity on E17, activation of delta-receptors with DPDPE was not effective until P14. This study confirms the early appearance of mu- and kappa-opioid receptors and the relatively late development of delta-opioid receptors in the rat brain. Most importantly, it shows that in an early stage of development opioids are already able to mediate modulation of noradrenergic (via activation of mu-receptors) and dopaminergic (via activation of mu- and kappa-receptors) neurotransmission processes. Therefore, these opioid receptor types could play a role in brain development and/or developmental disturbances.

Day-night rhythms in the inhibitory effects of 60 Hz magnetic fields on opiate-mediated 'analgesic' behaviors of the land snail, Cepaea nemoralis

There is accumulating evidence that magnetic fields can affect a variety of opioid-mediated behavioral and physiological functions. The present experiments were designed to examine the effects of various durations of day- and night-time exposures to low intensity (1.0 gauss rms) 60 Hz magnetic fields on light (L) and dark (D) period opioid-mediated aversive thermal ('nociceptive') responses and morphine-induced 'analgesia' in the nocturnally-crepuscularly active land snail, Cepaea nemoralis. The snails displayed a LD rhythm in the latency of their aversive (40 degrees C) thermal (nociceptive) responses, showing a significantly greater response latency at night than during the day. Administration of morphine (10 mg/kg/2.0 microliters) elicited significant increases in the thermal response latencies indicative of the induction of analgesia. The snails displayed a significantly greater analgesic response at night than during the day. Exposure (0.50, 2, 12, 48 or 120 h in L or D) to the 60 Hz fields reduced morphine-induced analgesia in both the L and D periods, with the magnetic stimuli having significantly greater inhibitory effects in the D period. The magnetic fields also significantly attenuated the level of the dark period basal nociceptive response latencies, while not affecting the light period responses. In both the L and D periods the degree of attenuation of the analgesic and nociceptive response latencies was related to the duration of exposure to the 60 Hz magnetic fields.(ABSTRACT TRUNCATED AT 250 WORDS)

Evolutionary and comparative aspects of nociception

The ability to detect and respond to aversive environmental stimuli is a basic feature of animals that is expressed in the term 'nociception.' Nociception and nociceptive responses provide an index of the sensitivity of individuals to aversive physical stimuli. Measurements of alterations in nociceptive responses (antinociception and analgesia) are commonly used to monitor the behavioral and physiological status of animals following experimental manipulation that usually, but not always, involve exposure to either noxious, stressful or potentially stressful physical and/or biological stimuli. This review briefly considers: i) the phylogenetic development of nociceptive responses and behaviors ii) evolutionary and comparative patterns of the neuromodulation of nociceptive behaviors by opioid peptides and other nonopioid peptidal regulatory mechanisms; iii) the effects of various biological variables, including; age, development, sex, and temporal factors (biological rhythms) on nociception in rodents.