Effect of 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) on monoamine neurotransmitters in mouse brain & heart

The effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was studied on dopamine (DA), norepinephrine (NE), serotonin (5HT) and γ-aminobutyric acid (GABA) neurons in mouse brain and on NE neurons of mouse heart. MPTP (45 mg/kg) was administered s.c. to mice twice daily for 2 consecutive days. This dosage regimen produced a decrease in the forebrain concentrations of DA and NE at 7 and 20 days after injection. In contrast, the forebrain concentrations of 5HT and GABA were not significantly decreased at either time. MPTP administration also produced a marked decrease in the uptake of ³H-DA into striatal slices and ³H-NE into cerebral cortical slices. In contrast, the uptake of ³H-NE into hypothalamic slices and the uptake of ³H-5HT into slices from several brain regions were not altered. MPTP initially reduced the concentration of NE in the heart, but unlike the persistent decreases in the forebrain concentrations of NE and DA, the NE concentration in the heart returned to control levels at approximately 20 days after MPTP administration. These results, showing that MPTP can produce a long lasting and selective decrease in the forebrain concentrations of NE and DA and in the uptake of radioactive DA and NE into brain slices, suggest that MPTP can cause the destruction of catecholamine neurons in mouse brain. In contrast, MPTP administration does not appear to produce long term changes in either 5HT or GABA neurons.     

Ultrastructural relationship between monoamine- and TRH-containing axons in the rat median eminence as revealed by combined autoradiography and immunocytochemistry in the same tissue section

Summary The correlation of dopamine (DA)-, noradrenaline (NA)- or serotonin (5HT)-containing neurons and thyrotropin releasing hormone (TRH)-containing neurons in the median eminence of the rat, as well as the coexistence of monoamines (MA) and TRH in the neurons, were examined by subjecting ultrathin sections to a technique that combines MA autoradiography and TRH immunocytochemistry. The distribution and localization of silver grains after ³H-MA injection were examined by application of circle analysis on the autoradiographs.TRH-like immunoreactive nerve terminals containing the immunoreactive dense granular vesicles were found to have an intimate contact with monoaminergic terminals labeled after ³H-DA, ³H-NA or ³H-5HT infusion in the vicinity of the primary portal capillaries in the median eminence. Synapses between TRH-like immunoreactive axons and MA axons labeled with silver grains, however, have not been observed to date. Findings suggesting the coexistence of TRH and MA in the same nerve terminals or the uptake of ³H-MA into TRH-like immunoreactive nerve terminals, where silver grains after ³H-MA injection were concurrently localized in TRH-like immunoreactive nerve terminals, were rarely observed in the median eminence. Percentages of the nerve terminals containing both immunoreactive granular vesicles and silver grains after ³H-MA injection to total nerve terminals labeled after ³H-MA infusion silver grains were equally very low in ³H-DA, ³H-NA or ³H-5HT, amounting to less than 6.1%.This work was supported in part by grant-in-aid for scientific research from the Japan Ministry of Education (No. 557018).     

The effect of a series of organic cations upon the plasmalemmal serotonin transporter, SERT

The aim of this work was to test the effect of a series of organic cations upon the activity of the plasma membrane serotonin transporter (SERT). The experiments were performed using the JAR cell line that constitutively expresses high levels of SERT, and rat intestine, whose mucosal epithelial cells also express SERT. Initial rates of (3)H-serotonin ((3)H-5HT; 200 nM) uptake were not changed by some of the organic cations tested (guanidine, N-methylnicotinamide, choline, atenolol, caffeine and theophylline), but were slightly (15-30%) inhibited by some other organic cations, at the highest concentrations tested (thiamine (3 mM), cimetidine (1 mM) and tetraethylammonium (3 mM)). On the other hand, some other organic cations reduced, in a concentration-dependent manner, uptake of (3)H-5HT by JAR cells (IC(50)s of 0.3, 1.3, 5.4, 89.3, 460 and 748 microM for quinidine, verapamil, propranolol, amiloride, nicotine and clonidine, respectively). Quinidine, clonidine and amiloride seem to be competitive inhibitors of (3)H-5HT uptake, whereas verapamil, nicotine and propranolol appear to be uncompetitive or non-competitive inhibitors. Moreover, quinidine, verapamil and propranolol trans-inhibited (3)H-5HT uptake, whereas clonidine, nicotine and amiloride were devoid of effect. Finally, these six organic cations were able to significantly increase the serosal-to-mucosal apparent permeability (P(app)) to (3)H-5HT of rat jejunum, ileum and colon. In conclusion, human and rat SERT-mediated transport is inhibited by several distinct organic cations, some of which are therapeutic agents or drugs of abuse. Knowledge on which organic cations interfere with SERT-mediated transport of 5HT will have major implications in tissues where 5HT plays important physiological roles (eg. central nervous system, intestine and placenta).     

Studies on the mechanisms of L-dopa-induced depletion of 5-hydroxytryptamine in the mouse brain

The administration of L-dopa to mice causes an increase in the brain concentrations of dopa and dopamine which is related temporally to a reduction in the brain concentration of 5HT. These effects occur concurrently with a reduction in the conversion of intravenously administered ³H-tryptophan to ³H-5HT without an alteration in the accumulation of ³H-tryptophan in the brain. The L-dopa-induced changes in the brain concentrations of dopa, dopamine and 5HT are not altered by pretreatment with drugs (imipramine, chlorimipramine, benztropine, cocaine) which inhibit the neuronal uptake of amines. Current evidence suggests that L-dopa is decarboxylated in 5HT neurons to dopamine, which displaces 5HT from intraneuronal storage sites.     

Manipulations of synaptic serotonin: discrepancy of effects on serotonin S1 and S2 sites

The effect of repeated treatment (28 day) with D-fenfluramine, a serotonin (5HT) releaser, L-tryptophan, a 5HT precursor, or fluoxetine, a 5HT uptake inhibitor, on 3H-5HT and 3H-spiperone binding in the rat cerebral cortex was investigated. Treatment with fenfluramine and fluoxetine caused a significant decrease in the number of 3H-5HT binding sites (Bmax). Fenfluramine also decreased binding of 3H-spiperone in the cortex, but fluoxetine treatment increased this binding. Treatment with L-tryptophan produced no change in the binding of either 3H-5HT or of 3H-spiperone significantly. The data show that manipulation of synaptic 5HT concentration does not always result in parallel changes in S1 and S2 receptors. This suggests that the 5HT S1 and S2 receptors may be subject to different regulatory mechanisms.     

Dopamine and 5-hydroxytryptamine actions on the cardiac ganglion of the lobster Homarus americanus

The cardioexcitor monoamines dopamine (DA) and 5-hydroxytryptamine (5HT) accelerate bursting by isolated cardiac ganglia of the lobster Homarusamericanus most effectively when they act on a region of the ganglionic trunk anterior to the small cells which have been considered the pacemakers of the system. 5HT may exert its acceleratory action by depolarizing cell processes. Neither the somata nor the spike-initiating zones of the small cells have to be directly exposed to 5HT or DA in order for acceleration to occur. When 5HT is applied selectively to the small cells bursts are prolonged, probably as a result of increases in the duration of the endogenous burst-organizing potentials (driver potentials) generated by these neurons. This action on the small cells can lead to prolonged and intensified bursts of the full ganglion during the onset of 5HT action when the whole ganglion is exposed to the monoamine. Neither DA nor 5HT has a direct effect on the characteristics of large cell (motorneuron) driver potentials. Accepted: 3 September 1997     

3H-5-hydroxytryptamine accumulation by rat brain synaptic vesicles in a membrane-impermeant medium, and selective reduction by 5,7-dihydroxytryptamine

In order to examine possible selectivity of amine uptake by synaptic vesicles, the ATP-stimulated accumulation of 3H-5-hydroxytryptamine (5HT) by synaptic vesicles from rat whole brain was examined in a medium comprised largely of membrane-impermeant anions (d-tartrate). Such media have previously been shown to stabilize vesicular accumulation of several neurotransmitters. Accumulation of 3H-5HT did not occur in tartrate medium alone, but was increased biphasically with increasing concentrations of both potassium phosphate and potassium bicarbonate. At optimal concentrations of each anion (10 mM), stable accumulation of 3H-5HT was observed at 37 degrees (26.1 +/- 1.2 pmol/mg protein; Km 6 X 10(-7) M), which was reduced by greater than 95% in the absence of K2ATP, at 4 degrees C, in the presence of 10(-6) M reserpine, or in the presence of the proton ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). Uptake was significantly antagonized by millimolar concentrations of Na+, Mg++ or Cl-, but was unaffected by ouabain (10(-5) M). Pretreatment of animals with 5,7-dihydroxytryptamine (5,7-DHT) (200 micrograms, intraventricular) 10 days prior to sacrifice reduced endogenous 5HT levels by 70%, while levels of endogenous norepinephrine (NE) and dopamine (DA) were unaffected. Accumulation of 3H-5HT, examined in the presence of 10(-6) M NE to block 3H-5HT accumulation by vesicles from noradrenergic nerve endings, was reduced by 40% in vesicles from treated animals. Vesicular accumulation of 3H-(-)-NE and 3H-DA was unaffected by 5,7-DHT treatment. The data suggest the possibility of preferential accumulation of 3H-5HT by vesicles arising from serotonergic nerve endings.     

Neurosecretion and the Endocrinology of Nereid Polychaetes

The endocrine activity of the nereid brain supports caudal regenerationin young worms and inhibits both the onset and progress of gametogenesisand metamorphosis. A single hormone is believed to influencethese processes. There is also evidence that the nereid brain,like that of many other polychaetes, secretes a tropic hormonethat is indispensable for normal vitellogenesis. It is not knownif the inhibitory and tropic functions of the brain are causedby separate hormones. The cellular origin of this endocrineactivity is unknown. Some cerebral neurosecretory cells haveterminals located in the infracerebral complex on the ventralregion of the brain. The infracerebral complex, which has somefeatures of a neuroendocrine organ, also has epithelioid infracerebralcells, one type of which resembles cerebral neurosecretory cells.The infracerebral complex is undoubtedly hormonogenic but thefunctions and interactions of its various components are unknown.Evidence that cerebral neurosecretory cells of nereids produceneurohormones or control the activity of infracerebral cellsis circumstantial. The neuroendocrine status of this neurosecretorysystem is uncertain in the absence of demonstrated interactionsbetween nervous and non-nervous endocrine tissues.     

Tryptamine transport in rat brain slices: A comparison with 5-hydroxytryptamine

The uptake of [¹⁴C]tryptamine (¹⁴C-T) and [³H]serotonin (³H-5HT) into slices of rat hypothalamus (HT), fronto-parietal cortex (CX), and caudate nucleus (Cau) has been investigated. In all three brain areas, the uptake of³H-5HT at 37°C was much greater than that in an ice-bath at 1.0–1.5°C. In contrast, the uptake of¹⁴C-T at 37°C was not much greater than uptake at 1.0–1.5°C. While markedly different amounts of³H-5HT were accumulated by each of the brain areas studied, the regional uptake of¹⁴C-T was quantitatively similar. In general the uptake of¹⁴C-T was inhibited less than³H-5HT by cocaine, DNP, ouabain, and decreased Na⁺ concentrations. Similarly,¹⁴C-T was less susceptible to serotonin uptake inhibitors except in the caudate. It was concluded that though a common indoleamine uptake system accumulates both T and 5HT, a non-specific low affinity or diffusional process also transports both amines and is predominantly responsible for T, but not 5HT, uptake. The spontaneous release, or wash-out, of¹⁴C-T from the caudate was much faster than that of³H-5HT. In addition, while depolarizing stimuli caused little or no release of¹⁴C-T, large releases of³H-5HT were observed. T, therefore, does not behave like a conventional neurotransmitter.     

Uptake of biogenic amines by glial cells in culture I. A neuronal-like transport system for serotonin

Rat C6 astrocytoma cells take up serotonin (5HT) via a high affinity carrier mediated system with Km of 1 micromolar, and a second component of lower affinity. This high affinity 5HT transport system is rapid, concentrative, and highly sodium and temperature dependent. Chlorimipramine and Lilly 110140 preferentially block the glial 5HT but not NE uptake. This preferential inhibition has previously been shown for synaptosomes and brain slices. Norepinerphrine (NE) and to a lesser extent dopamine (DA) block the glial 5HT uptake, suggesting a partial overlap between the catecholamine and indoleamine glial carrier systems. 5-Hydroxy but not 6-hydroxy dopamine inhibits the high affinity 5HT transport in glia. A variety of ring hydroxylated indoleamine analogs block this glial 5HT transport; of the compounds tested, 5, 7 dihydroxytryptamine is the least effective inhibitor. Phenylethylamine (PEA) and its 0-methylated derivatives block synaptosomal and glial 5HT transport equally well. These observations suggest that cultured C6 cells used as models of glia possess a 5HT transport system which kinetically and pharmacologically resembles a neuronal 5HT transport system.     

The affinity of metergoline for 3H-Serotonin (5HT) binding sites is regulated by guanine nucleotide

100 μM guanine nucleotide Gpp (NH)p reduces the affinity of the serotonergic antagonist metergoline for ³H-5HT binding sites in rat cerebral cortex. This effect is present both in inhibition binding and in saturation experiments. The hypothesis that the interaction of some serotonergic antagonists with ³H-5HT binding sites is regulated by guanine nucleotides is discussed.     

Effects of ascorbic acid on the uptake of serotonin in differentiated neuroblastoma cells

Ascorbic acid causes concentration-dependent and time-dependent effects on [³H]-serotonin (³H-5HT) uptake into differentiated neuroblastoma N-2a cells. Preincubation of cells with ascorbic acid inhibits both passive diffusion and active transport of ³H-5HT (0.1 μM). The kinetic characteristics of the active uptake process change with ascorbic acid treatment, resulting in an increase in the Km from 0.27 μM to 3.0 μM and in the Vmax from 453 to 2369 fmol/min/10⁶ cells. This inhibitory effect of ascorbic acid appears to be due to its reducing properties.     

The anatomy and histology of the nervous system and excretory system of the maldanid polychaetes Clymenella torquata and Euclymene oerstedi

The nervous system of the maldanid polychaetes Clymenella torquata (Leidy) and Euclymene oerstedi (Claparede) (= Caesicirrus neglectus [Arwidsson, '11-'12]) retains its primitive association with the epidermis. It shows only slight metamerism in the presence of larger collections of neurones opposite the parapodia and of larger nerves at the segmental boundaries. Multicellular giant fibers are present in the ventral nerve cord; giant neurones which show a characteristic pattern of distribution in each species are also present. The cerebral ganglia supply nerves to the prostomial wall, nuchal grooves and the wall of the buccal cavity, and a pair of large nerves from the circumpharyngeal connectives also appear to join the buccal system. The organs of special sense are the elongated prostomial nuchal grooves, and prostomial ocelli in Euclymene but not in Clymenella. Statocysts are absent. Four pairs of nephromixia are present. They lie in the aseptate anterior trunk, in chaetigers 5–9 of Clymenella, and 6–10 of Euclymene. The nephridiopores lie at the ventral ends of the neuropodia of chaetigers 6–9 and 7–10, respectively. Each nephromixium consists of coelomostome, tubule and contractile bladder. The wall of the tubule and bladder consists of both excretory and ciliated cells. Most of the cytoplasm of the latter forms a bounding layer at the outer surface. The cytoplasm of the excretory cells contains lipid material and appears to synthesize lipofuscin. The tips of the excretory cells swell, fill with granules, and break off in the form of vesicles which are periodically expelled in clouds from the nephridiopores. Glycogen is present, especially in the ciliated cells of the tubule and coelomostome. Granules of a lipoid nature accumulate in (or between) cells of the nephridia, epidermis, and some regions of the gut, and may be excretory. Lipid granules also appear to be synthesized by coelomocytes which eventually end up in masses in the ventrolateral coelomic cavities of the tail. The nephridia act as gonoducts, but show no seasonal variation in either size or histological structure.     

Neurons with ‘secretory end-feet’-A probable neuroendocrine complex in Nereis

A neuronal complex of unusual cytological character and probable glandular function is located within the cerebral ganglion in Nereidae (Polychaeta). The perikarya form a pair of ganglionic nuclei situated above the optic commissure. Each nucleus gives rise to a tract of stout axons that passes between the anterior and posterior optic nerves and down through the neuropile. Beneath the neuropile the axons separate from each other and branch extensively before terminating on the brain floor as ‘secretory end-feet’. These endings are scattered over a wide area of the inner surface of the brain capsule and exhibit a topographical relationship with the infracerebral gland.     

Quantitative histomorphological studies on the spinal ganglia of the Indian buffalo (Bubalus bubalis)

Spinal ganglia of C3, C7, T5, T12, L2 and L5 spinal dorsal roots were studied. These ganglia vary in their size. Their greatest cross-sectional area was at C7 (2.12 cm2) in the cervical region and at L5 (1.39 cm2) in the lumbar region. The neurons were either spherical or oval in contour. The smallest neurons (mean size 68.50 X 55.64 micrometer) were located in the T5 ganglion, while some of the largest neurons (mean size 79.17 X 63.34 micrometer) were noticed in the C3 ganglion. As for their cross-sectional area, the ganglionic neurons at the L5 level were the largest (3,713.16 micrometer2), while the least value (2,994.60 micrometer2) was noted in T5 ganglionic cells. The amphicytes (satellite cells) were clearly defined. The neuronal cytoplasm revealed finely granular Nissl material. The neurons exhibit a pale-staining, centrally located vesicular nucleus with a prominent nucleolus. Few multipolar cells with eccentric nuclei were noted in the L5 ganglion.     

Fine structure of the cephalic sensory organ in the larva of the nudibranch Rostanga pulchra (Mollusca,Opisthobranchia, Nudibranchia)

Summary The cephalic sensory organ in the veliger larva of Rostanga pulchra is situated dorsally between the rhinophores, emerging as a tuft of cilia. This organ is made up of three types of sensory cells, and based on their morphology have been termed ampullary, parampullary and ciliary tuft cells. The cell bodies of the organ originate in the cerebral commissure, and their dendrites pass to the epidermis as three tracts. Dendrites terminate in the epidermis to form a sectorial field. Axons of these cells run into the mass of neurites in the cerebral commissure but no synapses were observed in this area. Morphological evidence suggests that the cephalic sensory organ may function in chemoreception and mechanoreception related to substrate selection at settlement, feeding, or other behaviors.     

5-Hydroxytryptamine binding to synaptic membranes from rat brain.

The ³H-5HT binding capacity of rat brain synaptic membranes prepared by density gradient centrifugation has been investigated using a rapid ultrafiltration technique. A saturable, high affinity (K_D = 1.10^?9 M), 5HT displaceable binding has been found. It is thermosensitive, temperature dependent and pH dependent. 5HT and related tryptamines are the most effective displacers of bound ³H-5HT, whereas compounds which are not structurally related to 5HT (chlorpromazine, imipramine, cyproheptadine and cinanserine) and other neuro-transmitters (noradrenalin, dopamine) are ineffective. The distribution of 5HT-specific binding sites in the brain is related to serotonergic input. We conclude that these 5HT binding sites might possibly represent 5HT receptor sites.     

Ultrastructure of a cephalic sensory organ in larvae of the gastropod Phestilla sibogae (Aeolidacea, Nudibrachia)

The cephalic sensory organ is a superficial sensory receptor located between the velar lobes at the level of the shell aperture. Three cell types make up this sensory area: (1) six flask-shaped cells bearing numerous cilia; (2) adjacent supporting or accessory cells which have numerous, often branched, microvilli; and (3) vacuolated cells which occupy the center of the area. The flask-shaped cells appear to be the sensory units. These cells have a deep invaginated lumen, with cilia arising from the cell surface in the lumen oriented either toward the base of the lumen or toward the epidermal surface. These cilia, some of which extend slightly above the body surface, are presumed to be non-motile, as they lack (dynein?) arms on the axonemal A tubules and lack striated rootlets. The six flask cells are in intimate contact with the underlying cerebral ganglia and axons from each cell pass into ganglionic tissue. The supporting cells may be sensory, but no direct connection with the nervous system was seen. The function of the central vacuolated cells is not known. This cephalic organ may be a derivative of the original apical tuft of the trochophore stage.     

Platelet serotonin content and uptake in spontaneously hypertensive rats

Platelet serotonin (5-HT) content and uptake were studied in male SHR and WKY at various ages. Blood was withdrawn from the carotid artery under anesthesia and 5-HT levels determined from platelet rich plasma (PRP) using a HPLC technique coupled with an electrochemical detection method. Platelet 5-HT uptake was studied by incubating PRP at 37 degrees C for 10 sec with increasing concentrations of 3H-5HT. Lineweaver- Burk plots of 3H-5HT uptake were linear suggesting simple Michaelis- Menten uptake kinetics. The SHR had more platelets than age-matched controls and consequently a higher blood circulating pool of 5-HT. Nevertheless, the 5-HT platelet levels were similar to those of their age-matched rats. The 5 week-old SHR and WKY had greater numbers of platelets and higher 5-HT platelet levels than the older rats of both strains. The affinity constants (Km) and the maximal velocities (Vmax) of platelet 5-HT uptake did not differ significantly between the 12 week- and the 6 month-old SHR and WKY. These data suggest that the SHR do not show the same impairment in platelet 5-HT metabolism as observed in essential hypertension in man.