Diurnal rhythms of serotonin in monkey cerebrospinal fluid

Serotonin concentrations in lumbar and ventricular cerebrospinal fluid (CSF) from rhesus monkeys showed a diurnal variation as measured by a gas chromatographic-mass spectrometric assay. Temporally, CSF serotonin and melatonin diurnal patterns were similar, with concentrations of both rising at the beginning of the dark period and falling to baseline at the onset of lighting. The amplitude of the nighttime serotonin elevations showed marked variation across the seven monkeys studied. A single monkey studied for three consecutive days had temporally and quantitatively consistent melatonin and serotonin concentrations.     

The effect of serotonin given into the lateral ventricle of the brain on serum TSH level in normal and thyroxine-blocked rats

The effect of serotonin given into the lateral ventricle of the brain in rats was investigated. Serotonin was solved in artificial cerebrospinal fluid and administered in three doses: 250 microgram, 50 microgram, 10 microgram. Only the highest dose of serotonin caused a statistically significant increase in serum TSH level 0.5 h after the injection. The possible role of serotonin in the blocking mechanism of thyroid hormones on TSH secretion was also taken into consideration. 50 microgram of serotonin significantly strengthened the lowering effect of 1-thyroxine given 0.5 h before on serum TSH level.     

A comparative analysis of serotonin level in rat platelets,serum, and brain during aging

Serotonin functions as a neurotransmitter in the central nervous system and takes part in vascular tone, gastrointestinal motility, and blood coagulation at the periphery. New data on a correlation between serotonin level in platelets and cerebrospinal fluid (Audhya et al., 2012) have renewed interest in the hypothesis that considers a platelet as a model of serotoninergic neuron. In this study, using high performance liquid chromatography, we compared the serotonin level in platelets, serum and different brain regions in 6- and 24-month-old rats. It was found that serotonin level decreased from 0.768 to 0.359 μg per 10⁹ cells in platelets and increased in midbrain from 0.260 to 0.439 μg per 1 g of wet weight during the animal aging. The differences between young and old animals in the serotonin level in serum and other brain regions were statistically not significant. Hence, despite the attractiveness of the hypothesis considering the platelet as a neuron model the data on the platelet serotonin transport should be extrapolated on the neuronal transport with caution, especially for the aging process.     

Single treatment (hormonal imprinting) of newborn rats with serotonin increases the serotonin content of cells in adults

Hormonal imprinting takes place perinatally at the first encounter between the hormone and its target receptor, causing the finishment of the maturation of receptor-signal transduction system. In the presence of an excess of the target hormone or related molecules faulty imprinting develops with life-long consequences. In earlier experiments single neonatal treatment with minute dose of IL-6 caused also prolonged stimulation of IL-6 production. In the present experiment newborn female and male rats were treated with 20 microg serotonin (hormonal imprinting) and were studied for serotonin content of different cell types in adult age. Serotonin content was measured by flow cytometry and its localization was determined by confocal microscopy. Serotonin content was detected in white blood cells (lymphocytes, monocytes and granulocytes); in lymphocytes, monocytes (macrophages), granulocytes and mast cells of peritoneal fluid and thymic lymphocytes. Serotonin was present in all cell types of control animals studied. Serotonin content extremely elevated in the white blood cells and also increased in the peritoneal cells of neonatally treated female animals. There was no elevation in thymic lymphocytes. The mean values of male animals remained at the control level. The experiments call attention to the life-long effect of the perinatal hormonal imprinting manifested presently in the elevation of serotonin content and point to the gender differences of serotonin imprinting. Considering the role of serotonin in mood and psychiatric diseases, the observations could have some clinical importance.     

Plasma and cerebrospinal fluid concentration of neuropeptide Y, serotonin, and catecholamines in patients under propofol or isoflurane anesthesia

Propofol is a widely used anesthetic for both induction and maintenance of anesthesia during surgery. A strong feeling of hunger has been reported during the early recovery period after propofol anesthesia. We have investigated the effect of propofol on appetite in 10 patients undergoing a craniotomy and in parallel measured neuropeptide Y (NPY), catecholamines, and serotonin levels in the cerebrospinal fluid and plasma during anesthesia. Ten patients anesthetized with a volatile agent (isoflurane) served as a control group. Plasma NPY and catecholamines levels were not affected by surgery at any time. We observed a strong increase in NPY concentrations in the cerebrospinal fluid independently of the anesthetic technique agent used, whereas catecholamines were unchanged. We found that serotonin concentrations decreased significantly in the plasma (but not in the cerebrospinal fluid) of patients treated by propofol when compared with the control group; this decrease was associated with an increase of hunger early postoperatively. We concluded that the proappetite effect of propofol is mediated through a decrease of serotonin at the peripheral level.     

Serotonin-induced cytosolic free calcium transients in cultured vascular smooth muscle cells

Serotonin induced a transient elevation in the levels of cytosolic calcium in cultured rat vascular smooth muscle cells. Ketanserin, a selective antagonist of serotonin 2 receptors, dose-dependently inhibited the elevation of cytosolic calcium induced by serotonin, and ultimately unmasked a serotonin-induced decrease in the levels of cytosolic calcium. These observations show that serotonin has direct and dual effects, that is, it increases and decreases cytosolic free calcium concentrations in vascular smooth muscle cells, in culture. Knowledge of such events is important because serotonergic inhibitors may prove to be useful drugs for treating clinical hypertension and vasospastic disorders.     

A sensitive, fast, durable, highly selective method for the determination of amino acids and biogenic amines in the cerebrospinal fluid and other body fluids and tissues

A sensitive, fast, durable HPLC method with high resolution for the determination of amino acids and some biogenic amines is described. It allows the simultaneous determination of more than 40 substances in the cerebrospinal fluid or other body fluids or tissues. The method allows to measure both, the free and the conjugated amino acids. It detects 5 X 10(-13) g of most amino acids and measures the relevant substances in their physiological concentrations with less than 0.1 ml cerebrospinal fluid. The precision is 1-2%.     

Change inLimnaea stagnalis neuronal response to acetylcholine during intracellular and extracellular perfusion with serotonin

The modifying effect of adding serotonin to the intra- and extracellular environment on the inward currents generated by the cell following intracellular application of acetylcholine was shown during studies on unidentified isolatedLimnaea stagnalis neurons using techniques of intracellular perfusion and voltage clamping. Serotonin inhibited response to achetylcholine in both cases in most of the test neurons. Serotonin intensified this response when applied to the intracellular environment and produced the opposite effect of reducing the amplitude of inward acetylcholine currents when administered extracellularly. Cyproheptadine, the serotonin receptor blocker, inhibited the enhancing effect of serotonin produced by adding this neurotransmitter to the intracellular fluid, but mimicked the inhibitory effects of serotonin on response to acetylcholine, whether added to the intra- or extracellular environment. Findings would suggest the presence of intracellular serotonin receptors in the mollusk neurons; one of their possible functions could be controlling the sensitivity of the cell surface cholinoreceptors.N. K. Koltsov Institute of Developmental Biology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 326–332, May–June, 1986.     

Dopamine and Serotonin Metabolism in Hepatic Encephalopathy

Patients with stupor or coma from fulminant hepatic failure were found to have high cerebrospinal fluid concentrations of homovanillic acid (HVA) and 5-hydroxyindole acetic acid (5-HIAA), metabolites of dopamine and serotonin respectively. Excessive amounts of their precursors—phenylalanine and tyrosine and free tryptophan—were found in the patients'' plasma. Methionine, which participates in dopamine degradation, was also much increased. Similar disturbances were found in patients suffering an acute exacerbation of chronic encephalopathy. These abnormalities would be consistent with other evidence of an increased turnover of serotonin and possibly dopamine in the brain during hepatic encephalopathy.     

Terminal processes of serotonin neurons in the caudal spinal cord of the molly,Poecilia latipinna,project to the leptomeninges and urophysis

Summary The caudal neurosecretory complex of poeciliids has previously been shown to be innervated by extranuclear and intrinsic serotonergic projections. In the present study, immunohistochemical techniques were used to characterize fibers originating from serotonin neurons intrinsic to the caudal spinal cord. Bipolar and multipolar neurons were oriented ventromedially, and contained numerous large granular vesicles. Three types of serotonergic fibers were distinguished based on their distribution and morphology. Intrinsic Type-A fibers branched into varicose segments near the ventrolateral surface of the spinal cord and contacted the basal lamina beneath the leptomeninges. Type-B fibers coursed longitudinally to enter the urophysis, where they diverged and terminated around fenestrated capillaries. Labelled vesicles in Type-A and Type-B terminals were the same size as those in labelled cells and in unlabelled neurosecretory terminals in the urophysis. Type-C small varicose fibers branched within the neuropil of the caudal neurosecretory complex. Serotonin may be secreted into the submeningeal cerebrospinal fluid, the urophysis, and the caudal vein by Type-A and Type-B fibers, whereas, Type-C fibers may be processes of serotonergic interneurons in the neuroendocrine nucleus. The possibility that urotensins I and II or arginine vasotocin were colocalized in the processes of the intrinsic serotonin neurons was investigated immunohistochemically. The negative results of these experiments suggest that serotonin-containing neurons may represent a neurochemically distinct subpopulation in the caudal neurosecretory complex.     

Extractive acylation and mass spectrometric assay of 3-methoxytyramine, normetanephrine, and metanephrine in cerebrospinal fluid

The chemical analysis of 3-methoxytyramine, normetanephrine, and metanephrine in tissues, blood, and cerebrospinal fluid is complicated by the low levels in which they occur and the amphoteric nature of the functional groups, which hampers their isolation from aqueous media. In the present report, we describe a practical and simple method for the routine isolation and derivatization of 3-methoxytyramine, normetanephrine, and metanephrine in high yield from aqueous samples like cerebrospinal fluid. The metabolites are simultaneously derivatized with pentafluoropropionic anhydride and extracted into an organic solvent. After further treatment with pentafluoropropionic anhydride under anhydrous conditions, the samples are ready for GC/MS analysis. The method is able to exploit the theoretical maximal sensitivity available in the electron capture negative-ion chemical ionization mode without any apparent losses during extraction and derivatization, giving limits of detection in the low picogram range. Mean levels of free 3-methoxytyramine, normetanephrine, and metanephrine in human cerebrospinal fluid were 3.77, 5.20, and 0.40 pmol/ml. Assay of pools of squirrel monkey, human, and canine cerebrospinal fluid with and without previous enzymatic hydrolysis demonstrated that the three metabolites occur predominantly in a conjugated form.     

FREE AMINO ACID LEVELS IN THE CEREBROSPINAL FLUID OF NORMAL HUMANS AND THEIR VARIATION IN CASES OF EPILEPSY AND SPIELMEYER-VOGT-BATTEN DISEASE

Abstract— The concentrations of free amino acids in the plasma and cerebrospinal fluid from control subjects and from patients suffering from epilepsy and Spielmeyer-Vogt-Batten disease were determined using an automatic amino acid analyser. It was found that the plasma/cerebrospinal fluid ratio of amino acid concentrations showed the variation in the amounts of free amino acids in epilepsy more clearly than the cerebrospinal fluid levels alone.     

Fluoxetine Partly Exerts its Actions Through GABA: A Neurochemical Evidence

Fluoxetine, as a serotonin re-uptake inhibitor augments serotonin concentration within the synapse by inhibiting the serotonin transporter. The contribution of amino acids has also been shown in depression. We hypothesized that fluoxetine exerts its actions at least in part by intervening brain signaling operated by amino acid transmitters. Therefore the aim of this study is to supply neurochemical evidence that fluoxetine produces changes in amino acids in cerebrospinal fluid of rats. Sprague-Dawley rats were anesthetized and concentric microdialysis probes were implanted stereotaxically into the right lateral ventricle. Intraperitoneal fluoxetine (2.5 or 5 mg/kg) or physiological saline was administered and the probes were perfused with artificial cerebrospinal fluid at a rate of 1 μl/min. In the chronic fluoxetine group, the rats were treated daily with oral fluoxetine solution or inert syrup for 3 weeks. The microdialysis probes were placed on the 21st day and perfused the next day. Fluoxetine was ineffective in changing the cerebrospinal fluid GABA levels at the dose of 2.5 mg/kg but produced a significant increase in the perfusates following injection of 5 mg/kg of fluoxetine (P < 0.05). Oral fluoxetine administration (5 mg/kg) for 21 days also elevated the CSF GABA levels by approximately 2-fold (P < 0.05). l-glutamic acid levels were not affected in all groups. These neurochemical findings show that fluoxetine, a selective serotonin re-uptake inhibitor affects brain GABA levels indirectly, and our results suggest that acute or chronic effects may be involved in beneficial and/or adverse effects of the drug.     

Effects of serotonin1-like receptor agonists on autonomic neurotransmission.

Serotonin1A receptor agonists, 8-hydroxy-2-(di-n-propylamino)tetralin and 10-methyl-11-hydroxyaporphine, inhibited electrical stimulation-induced contraction of the guinea-pig ileum. These agonists also inhibited the pressor and tachycardiac responses to low frequency (0.25 Hz) but not to high frequency (2.0 Hz) electrical stimulation of the sympathetic nervous system in pithed rats. Serotonin1B receptor agonist RU 24969 inhibited pressor and tachycardiac responses to both low and high frequencies of stimulation in pithed rats. In the cat nictitating membrane, serotonin1A receptor agonists did not alter contractions elicited by electrical stimulation (0.1-3.0 Hz). Serotonin not only contracted the cat nictitating membrane but also facilitated contractile responses to low frequency (0.1-1.0 Hz) stimulation. The contractile effect of serotonin in the cat nictitating membrane was blunted by bretylium, methysergide, and ketanserin, but not by metoclopramide. The facilitatory effect of serotonin was antagonized by methysergide, but not by ketanserin, pindolol, propranolol, or metoclopramide. These results suggest that serotonin1A receptors modulate autonomic neurotransmission in the guinea-pig ileum and pithed rats, but not in the cat nictitating membrane. Serotonin contracts the cat nictitating mebrane via serotonin2 subtypes, while facilitating stimulated contractile responses through the serotonin1-like receptors.     

Serotonin has kinin-like activity in stimulating secretion by Malpighian tubules of the house cricket Acheta domesticus

Serotonin stimulates secretion by Malpighian tubules (MT) of a number of insects, and functions as a diuretic hormone in Rhodnius prolixus and in larval Aedes aegypti. Serotonin is here shown to be a potent stimulant of secretion by MT of the house cricket, Acheta domesticus, with an apparent EC₅₀ of 9.4 nmol L⁻¹, although its diuretic activity is just 25% of the maximum achievable with either the native CRF-related peptide, Achdo-DH, or a crude extract of the corpora cardiaca. In this respect, the diuretic activity of serotonin is similar to that of the cricket kinin Achdo-KI, and when tested together their actions are not additive, which suggests they target the same transport process. Consistent with this suggestion, the activity of serotonin is chloride-dependent and is associated with a non-selective stimulation of NaCl and KCl transport. In common with Achdo-KI, serotonin has no effect on cAMP production by isolated MT, and both act synergistically with exogenous 8bromo-cAMP in stimulating fluid secretion, most likely by promoting the release of Ca²⁺ from intracellular stores. A number of serotonin agonists and antagonists were tested to determine the pharmacological profile of receptors on cricket MT. The results are consistent with the diuretic activity of serotonin being mediated through a 5-HT₂-like receptor.     

Determination of tryptophan and several of its metabolites in physiological samples by reversed-phase liquid chromatography with electrochemical detection

A new method for the concurrent assay of three tryptophan metabolites at the picomole level is described. The method has been developed for blood, urine, cerebrospinal fluid, and tissue samples such as whole brain, brain parts, and endocrine glands. Tryptophan itself, serotonin, and 5-hydroxyindoleacetic acid are isolated initially on extraction columns, eluted with a suitable solvent, and injected onto a liquid chromatograph with an amperometric detector. This general approach may be applicable to a variety of other tryptophan metabolites and should be useful in both research and clinical investigations.     

Serotonin; its possible relation to allergic disease

Increased amounts of serotonin as well as histamine have been found in the blood of animals during anaphylactic shock. Certain animals, particularly those in which antihistamines do not prevent anaphylaxis, have been found to have increased quantities of serotonin in the lung tissue during anaphylactic shock. Serotonin is a chemical derived from the amino acid tryptophan, which is widely distributed. It is excreted in the urine as the metabolite 5-hydroxyindoleacetic acid. Serotonin has been found in increased amounts in the blood of patients with carcinoids. The increase of serotonin in the blood and the finding of the excretory product in the urine has become a corroborative sign of the disease. The involvement of serotonin in the production of mental disease is evidenced by the effect of serotonin antagonists, which appear to influence mental behavior.That serotonin antagonists may be of ultimate value in the treatment of allergic disease is a possibility to be considered.     

SEROTONIN—Its Possible Relation to Allergic Disease

Increased amounts of serotonin as well as histamine have been found in the blood of animals during anaphylactic shock. Certain animals, particularly those in which antihistamines do not prevent anaphylaxis, have been found to have increased quantities of serotonin in the lung tissue during anaphylactic shock.Serotonin is a chemical derived from the amino acid tryptophan, which is widely distributed. It is excreted in the urine as the metabolite 5-hydroxyindoleacetic acid. Serotonin has been found in increased amounts in the blood of patients with carcinoids. The increase of serotonin in the blood and the finding of the excretory product in the urine has become a corroborative sign of the disease. The involvement of serotonin in the production of mental disease is evidenced by the effect of serotonin antagonists, which appear to influence mental behavior.That serotonin antagonists may be of ultimate value in the treatment of allergic disease is a possibility to be considered.     

Uptake and Metabolism of Serotonin by Ependymal Primary Cultures

Serotonin uptake and metabolism was studied in ependymal primary cultures. Serotonin uptake was facilitated by two different systems, one of which was the neuronal serotonin transporter SERT, exhibiting a Vmax value of 3.8+/-0.1 pmol x min(-1) x (mg protein)(-1) and an apparent Michaelis-Menten constant of 0.41+/-0.03 microM. The main product of metabolism was 5-hydroxyindole acetic acid, which resulted from the action of monoamine oxidase A. This enzyme showed a maximal rate of 0.85+/-0.02 nmol x min(-1) x (mg protein)(-1) and a Michaelis-Menten constant of 78+/-5 microM. Ependymal cells were able to dispose of extracellular serotonin with initial rates of approximately 600 pmol x min(-1) x (mg protein)(-1) and of 4 pmol x min(-1) x (mg protein)(-1) when challenged with 500 microM and 1 microM extracellular serotonin, respectively. Ependymal cells are concluded to facilitate the "sink" action of the CSF by removing waste compounds upon passing of the fluid from the parenchymal extracellular space into the ventricular system.