Research on the mechanism of the motor action of dopamine on in vitro isolated rat duodenum]

The study of the direct action of dopamine on the rat duodenum serotoninergic receptors and the parallelism of the results obtained with the motricity curves of this organ in vitro allows us to conclude that dopamine recognizes serotoninergic receptors : the excito- motor effect observed with certain dopamine concentrations on the isolated rat duodenum may be attributed to this action of dopamine on serotoninergic receptors. These results seem in agreement with the observations of other authors.     

Reaction of neurons of the cerebral cingular area in rats to damage of the central monoaminergic systems]

Intracisternal injection of specific neurotoxins 6-oxydopamine and 5,7-dioxytryptamine, producing certain disorders in catecholaminergic and serotoninergic systems respectively, is accompanied with some ultrastructural rearrangements in the proper neurons of the rat cerebral cingular cortex. In the experimental material an essential increase in the amount of intranuclear inclusions--vacuole- and myelin-like--of fibrillar origin is observed. More often than in the control connection of the endoplasmic reticulum with the nuclear membrane is noted. Hypertrophy of cisterns in the Golgi complex, abundance of coated vesicles in its region, dilatation of cisterns of the endoplasmic reticulum are observed. The character of the ultrastructural rearrangements demonstrates certain changes in activity of metabolic processes of these cells, the changes being more pronounced in the case, when the cerebral serotoninergic system is damaged. The reaction of the cerebral cingular zone to injection of neurotoxins is characterized with a selective manifestation and is restricted with certain nervous cells of the II-V layers. According to their ultrastructural organization, these neurons can be considered as stellate and pyramidal.     

Morphological and functional studies on the serotoninergic innervation of the inferior olive

The inferior olive of the cat has, with fluorescence histochemistry, been shown to receive a rich serotoninergic innervation. The distribution of this innervation agrees with the topography of spinal afferent termination as well as the olivo-cerebellar climbing fiber projection. This indicates that different olivary compartments are under different serotoninergic influence. The serotoninergic innervation of the dorsal accessory nucleus (DAO) of the inferior olive of the rat has been identified with electron microscopic radioautography after labelling with 3H-serotonin. The serotoninergic varicosities contain microcanaliculi, tubular-vesicular organelles and large granular vesicles. Few of the serotoninergic varicosities engage in typical synaptic junctions. However, non-junctional varicosities often display other ultrastructural indications of polarity and directed transmitted release. Electrophysiological results indicate that the harmaline-induced tremor, as well as the tremor component of the "serotonin-syndrome", depends on the serotoninergic innervation of the inferior olive. Thus, the sensitivity of different olivary compartments to the induction of rhythmic, synchronous activity by harmaline parallels the distribution of serotoninergic innervation. Neurotoxic destruction of the serotoninergic innervation leads to decreased sensitivity to harmaline. Further, the serotonin receptor agonist 5-methoxy-N,N-dimethyltryptamine, as well as monoamine oxidase inhibition + L-tryptophan loading, leads to rhythmic mass climbing fiber activity in the cerebellum and whole body tremor. A neuromodulatory effect of serotonin on the olivary action potential mechanisms is proposed.     

Ultrastructure of the serotoninergic system of the motor area of the cerebral cortex

Owing to the microscopical investigation, using selective neurotoxin 5,7-dihydroxytryptamine, it has been possible to reveal the serotoninergic system and targets of its innervation in the rat cerebral cortex motor area. The serotoninergic axonal varicosities and synaptic boutons are present in all layers of the neocortex. Their large amount is revealed in the I and II layers. The terminals form contacts with dendrites of small size, sometimes they terminate on the head of the spines, as well as on bodies of neurons in different layers. According to their position and ultrastructural organization these neurons are, perhaps, pyramidal, that is glutamatergic, and those less in their size--refer to interneurons and can be GABAergic ones. Basing on own data and those of the literature, concerning the existence of nonsynaptic link for transmission of serotoninergic effects, a conclusion is made that a coordinating functioning of the synaptic and non-synaptic intercellular integrative mechanisms ensure a wide range of functions of the serotoninergic system in the cerebral cortex.     

A selective inhibitor of serotonin uptake: Lilly 110140, 3-(p-trifluoromethylphenoxy)-N-methyl-3-phenylpropylamine

Lilly 110140 is a highly selective inhibitor of serotonin uptake into synaptosomes of rat brain, unlike previous monoamine uptake inhibitors that also inhibit the uptake of norepinephrine and dopamine. Lilly 110140 should be useful in studying the function of serotoninergic neurons and may be helpful in clariying the role of serotonin in certain types of mental depression.     

Role of the serotoninergic raphe-hippocampus system for the antinocifensive effect of morphine

As revealed in earlier studies, the antinocifensive effect of morphine is brought about, among other things, with involvement of serotoninergic transmission mechanisms. In this context the role of the serotoninergic raphe-hippocampus system has been studied in this paper. Topical microinjections of serotonin into the dorsal hippocampus increased morphine analgesia in a dose-dependent fashion, while application into the striatum had no effect. Morphine injections into the median raphe nucleus in relatively low doses exert an antinocifensive effect which is inhibitable by methysergide. Lysergic acid diethylamide administered into the median raphe nucleus also abolished the effect of morphine in a dose-dependent manner. The results in connection with literature data lend support to the presumed integrative function of the serotoninergic raphe-hippocampus system in the mechanism of antinocifensive action of morphine.     

Study of the stimulating effect of the sympathetic stem on the stomach contraction

Stimulation of the sympathetic stem chest portion induces enhancement rather than suppression of gastric contractions. The activating effect is more obvious under conditions of the alpha- and beta-adrenoreceptors blockade with phenolamine and obsidan, and eliminated with the smooth muscle serotoninoreceptors blocking agent lisergol. The findings suggest that the sympathetic stem includes some serotoninergic neural fibres exerting a strong effect upon gastric and intestinal contractions. A previously unknown serotoninergic part of the vegetative nervous system controlling the internal organs functions, seems to exist in the organism.     

Functional and morphologic organization of stomach vegetative innervation

The functional and morphological organization of stomach vegetative innervation was studied. It is shown, that the sympathetic nerve strengthens vagal stimulation of motor activity of various departments of a stomach. In realization of the phenomenon participate preganglionic serotoninergic fibres transmitting excitation on ganglionic serotoninergic neurons. It is established, that stimulation of a wandering nerve results to degranulation of serotoninergic EC-cells carrying on the surface ganglionic 5-HT3,4-receptors. The irritation of a wandering nerve results in reduction of volume of EC-cells in older age.     

Effect of neurotensin on the behavior of rats with damaged serotoninergic neurons under immobilization stress

It was shown that the immobilization of animals has led to reducing of vertical and horizontal locomotor activity in the "open field" and decreasing of number of conditioned food-procuring reactions into T-maze. The damages of serotoninergic neurons produced via local injections of selective neurotoxin 5, 7-dihydroxytriptamine into dorsal raphe nucleus intensified behavior alterations. Neurotensin administrations reduced effects of neurotoxin: the rats locomotor activity and quantity of conditioned reactions into T-maze were kept at the phone level just after immobilization as well as next two days. The results indicate the important protective significance of neurotensinergic brain structures for ensuring of adaptive behavior of animals with damaged serotoninergic neurons under emotional stress conditions. It is supposed that neurotensin normalizing influences on behavior is connected to a restoration of balance of dopamine-and serotoninergic brain structures interaction.     

NO-Dependent Regulation by Glutamate of Activity of the Serotoninergic System of the Edible Snail Helix lucorum

This work is a continuation of the study on transmitter regulation of the serotoninergic system activity in the brain of the edible snail Helix lucorum, in which serotonin and NO donors have been shown to excite serotoninergic neurons from various snail ganglia (more than 60 of them were studied) and synchronize their activity by activation of the synchronous synaptic inputs. In the current work, it has been shown that glutamate, on the contrary, has an inhibitory and desynchronizing action on the same serotonin-containing neurons by suppressing their own activity and switching off the synchronous synaptic inputs. In the same neurons, another glutamate receptor agonist, NMDA, has a pronounced excitatory effect and activates the synchronous synaptic inputs. The glutamate effects are NO-dependent: the NO donor sodium nitroprusside decreases, switches off entirely, or transforms the glutamate inhibitory effect into the excitatory one. A possible mechanism of interaction of serotonin, glutamate, and NO in regulation of the snail serotoninergic system activity is discussed.     

Mechanisms of synergism of the autonomic nervous system compartments

The realization mechanisms of phenomena of sympathetic nerve potentiation of vagal stimulation of motor activity of duodenal and jejunal intestine, urinary bladder and ureters, uterus and tubes, vas deference and mechanism of sympathetic nerve potentiation of vagal cardioinhibitory action were studied. There were demonstrated that these phenomena were realized with participation of preganglionic serotoninergic nerve fibers transmitting an excitation on ganglionary serotoninergic neurons. It was found an existence of increasing cranio-caudal and decreasing ventro-dorsal gradients of serotoninergic innervation of visceral organs.     

The organization of serotonin-immunoreactive neuronal systems in the brain of the crested newt,Triturus cristatus carnifex Laur.

Summary The distribution of serotonin (5-HT) immunoreactive structures has been investigated in the brain of the crested newt by means of indirect immunofluorescence, and unlabeled antibody peroxidase-antiperoxidase-complex (PAP) or biotin-avidin-system (BAS) techniques. In the newt, the bulk of the serotoninergic system extends from the raphe region of the medulla oblongata, through the isthmus, toward the mesencephalic tegmentum, and is characterized by pyriform neurons mainly located in a subependymal position, close to the midline. Also in the caudal hypothalamus, in addition to some 5-HT-positive adenohypophysial cells, many immunoreactive CSF-contacting neurons are found lining the paraventricular organ and the nucleus infundibularis dorsalis. A rich serotoninergic innervation was observed in the preoptic area and in the habenular complex. Concerning the telencephalon, immunopositive nerve fibers are encountered in the dorsal pallium, primordium hippocampi, striatum and olfactory bulbs. The general organization of serotoninergic systems in the newt brain exhibit close similarities to that described in higher vertebrates.     

Role of the serotoninergic neuron system of the brain stem on the release of thyrotrophic and luteinizing hormone

1. Decrease of brain serotonin concentration, elicited by either parachlorophenylalanine treatment, surgical interruption of the ascending serotoninergic fibres, or by pinealectomy provokes an enhanced release both of TSH and LH. 2. Increased serotonin content of the brain, produced by intraventricular, intrahypothalamic or systemic administration of serotonin, results in a significant inhibition of the release of these two trophic hormones. 3. It is concluded that the serotoninergic neuron system of the brain stem represents an inhibitory mechanism in the neuroendocrine circuit regulating pituitary trophic hormone release.     

Ultrastructural effects of parachlorophenylalanine, 5-hydroxytryptamine and the imipramine group on the nerve processes of the small intestine.

The structure of the nerve fibres in the chronically isolated cat ileum was studied by fluorescence and electron microscopy after imipramine group compounds, parachlorophenylalanine, and 5-hydroxytryptamine treatment. Following treatment with parachlorophenylalanine and imipramine group compounds in the nerve fibres of the small intestine, specific granules were selectively decreased (p less than 0.001) in number. In concordance with ultrastructural observations, a marked diminution of fluorescence intensity was demonstrable in the small intestine. In addition, the number of the granular vesicles was significantly increased following 5-hydroxytryptamine treatment, and yellow fluorescent neurones and processes were observed in the myenteric and submucous plexuses. On the basis of these observations, the serotoninergic nature of certain nerve fibres could be demonstrated.     

Serotonin sensitive adenylate cyclase in horse brain synaptosomal membranes.

In different membranal preparations isolated from horse brain stritum we have shown the existence of an adenylate cyclase system sensitive to serotonin (5-HT). Activation of the adenylate cyclase was determined by measuring cAMP using a radioimmunoassay. This serotoninergic sensitive enzyme is characterized by a high apparent affinity constant (in the nanomolar range), located on synaptosomal membranes. It is inhibited by antiserotoninergic drugs (cyproheptadine, cinanserin, methysergide, LSD), and synergistically activated by GTP. This serotoninergic activation is clearly additive to the activation induced by dopamine. It appears different from the adenylate cyclase system previously described in the literature which is also activated by 5-HT, but which has a low apparent affinity constant (in the micromolar range); the latter is apparently located in non-synaptosomal membranes, and its activation by 5-HT is non-additive to the activation induced by dopamine.The serotoninergic sensitive adenylate cyclase reported in this study, might be related to the serotoninergic binding system which we have previously described which has similar affinity constant, a similar subcellular distribution and which is inhibited in the same concentration ranges by antiserotoninergic drugs. These two systems might represent a synaptosomal serotoninergic receptor complex.     

Beta-adrenergic influences on the firing of raphe dorsalis neurons after neonatal noradrenergic deafferentation in the rat

In Rat, neonatal lesion of the locus coeruleus induces modifications of beta-adrenergic regulations at the level of raphe dorsalis neurons. In normal conditions, the firing of serotoninergic raphe cells is not beta-adrenergic dependent. On the contrary in the lesioned animal, iontophoresis of a beta-blocking agent (DL-propranolol) produces a marked inhibition of the serotoninergic unit firing. Various mechanisms may account for this pharmacological response in the lesioned group: a classical hypersensitivity phenomenon, or the persistence of an immature regulation.     

Increase of the number of bone marrow T-suppressor cells under inhibition of immunogenesis during changes of the activity of the neuromediator system

Increase of serotoninergic system activity and blockade of dopaminergic system activity led to the change of T- and B-lymphocyte distribution in immunocompetent organs of non-immunized animals. Increase of suppressor cel number with Lyt2.2 phenotype was found in bone marrow of C57Bl/6 mice under activation of serotoninergic system (blockade of serotonin reuptake by sertraline) as well as under blockade of dopaminergic system by administration of dopamine autoreceptor agonist--3-PPP. Role of bone marrow in neuro-immunomodulation is discussed.     

Up-regulation of the neuronal serotoninergic phenotype in vitro: BDNF and cAMP share Trk B-dependent mechanisms

The effects of brain-derived neurotrophic factor (BDNF) and cAMP on the neuronal serotoninergic phenotype were studied in primary cultures of E14 rat embryonic rostral raphe. Short treatments (for 18 h) with BDNF or dibutyryl-cAMP induced an almost two-fold increase in the number of serotoninergic neurones and a dramatic extension and ramification of their neurites. These changes were associated with marked increases in the levels of mRNAs encoding the serotonin transporter, the 5-HT1A and 5-HT1B receptors and the BDNF receptor tyrosine kinase B (TrkB). Concomitant blockade of tyrosine kinases by genistein suppressed all the up-regulating effects of BDNF and cAMP on 5-hydroxytryptamine (5-HT) neurones. These findings suggest that an auto-amplifying mechanism underlies the promoting effect of BDNF on the differentiation of serotoninergic neurones through TrkB activation, which is also triggered by cAMP.     

Pharmacological effects of GABA on serotonin metabolism in the rat brain

The pharmacological effects of GABA-related drugs were studied on the serotonin (5-HT) and 5-hydroxyindole-acetic acid (5-HIAA) contents of various regions of the rat brain. These effects were examined in the nuclei raphe dorsalis, magnus and centralis and in structures receiving a dense serotonin innervation such as the habenula complex and subcommissural organ. The GABA agonist, muscimol, increased the 5-HT contents and reduced 5-HIAA levels in structures containing serotoninergic terminals suggesting an inhibitory effect of GABA on the firing of serotoninergic neurons with concomitant reduction of 5-HT utilisation. In contrast, the GABA antagonist, bicuculline, probably stimulated 5-HT turnover since its intraperitoneally administration produced significant increase of 5-HT and/or 5-HIAA levels in the same brain regions. These data are in agreement with a transsynaptic inhibitory control of GABA on serotoninergic neurons. Drugs which inhibit the GABA catabolism such as amino-oxyacetic acid or gamma-vinyl-GABA and which should elevate GABA levels in the synaptic gap were capable of increasing or decreasing the 5-HT and the 5-HIAA levels depending on the experimental conditions. These results suggest that several processes are probably involved in the control of serotoninergic neurons by GABA in the rat brain. Among them, an intracellular effect of GABA on 5-HT metabolism might well occur in cells containing both GABA and 5-HT.     

Interaction of serotonin and nitric oxide (NO) in activation of the serotoninergic system in Helix

Serotonin and the NO donors were shown to induce excitation in all serotoninergic neurones under study and to activate synchronous synaptic input in the Helix brain. The serotonin effects may be blocked by 5,7-DOT and N-monomethyl-L-arginine. The 5,7-DOT blocked activation of the NO-induced synchronous bursts but did not affect their activating effect. The data obtained suggest that serotonin and NO equally regulate the serotoninergic system's function in the snail brain. The effects of serotonin and NO are interconnected and interdependent. A possible role of the NO as a second messenger during serotonin activation and as a serotonin co-transmitter in presynaptic neurones, is discussed.