The effect of fluorocitrate on transmitter amino acid release from rat striatal slices

In order to study the role of glutamine from glial cells for the synthesis of transmitter amino acids, the effect of the gliotoxic substance fluorocitrate on amino acid release from slices was investigated. In vivo treatment with 1 nmol fluorocitrate reduced the Ca²⁺ dependent K⁺ evoked release of endogenous glutamate and GABA from the slices, whereas the glutamine efflux decreased and alanine efflux increased. The K⁺ evoked release of [³H]d-aspartate increased during fluorocitrate treatment. The latter is consistent with an inhibited uptake ofd-aspartate into glial cells. Incubation of striatal slices with fluorocitrate (0.1 mM) decreased the glutamine efflux and increased the alanine efflux. Similar to the in vivo condition, fluorocitrate increased the K⁺ evoked [³H]d-asparate release, but the K⁺ evoked release of endogenous glutamate and GABA increased rather than decreased. The ratio between the K⁺ evoked release of exogenousd-aspartate to endogenous glutamate increased in both cases. The results suggest an important role of glial cells in the synthesis and inactivation of transmitter amino acids.Special Issue dedicated to Prof. Holger Hydén.     

Distribution of indolealkylamine nerve terminals in the ventricles of the rat brain

Summary The density, distribution and the pharmacologically produced changes of a formaldehyde-induced yellow supra-ependymal fluorescence in the lateral and third ventricles and in the aqueduct of the rat brain are described. The fluorescence consists of small spots or a thin spotted layer just above the ependymal cells. The highest fluorescence densities occur in the areas near the tela chorioidea of the third ventricle and in the interventricular foramen. A high to moderate density occurs in the lateral ventricles and in the aqueduct. Little or no fluorescence is seen above the hypothalamic areas bordering the third ventricle. The fluorescence rapidly fades upon irradiation with violet-blue light, disappears after treatment of the rats with reserpine or p-chlorophenylalanine, is intensified after nialamide or reserpine + nialamide, and does not change after -methyl-p-tyrosine.Electron microscopically supra-ependymal varicose nerves containing small (500 Å) and large (1000 Å) vesicles in the varicosities are observed in areas with supra-ependymal yellow fluorescence. A fine-structural cytochemical technique reveals the presence of a specific, chromaffine, reserpine-sensitive electron dense core in the small and large vesicles.The conclusion is drawn that a characteristically distributed population of supra-ependymal efferent nerve terminals containing an indolealkylamine, most probably 5-hydroxytryptamine, exists in the cerebral ventricles of the rat brain.The skilful assistance of Mr. R. Wybrecht and Mrs. G. Gschwind is gratefully acknowledged.     

In vivo release of endogenous dopamine, 5-hydroxytryptamine and some of their metabolites from rat caudate nucleus by phenylethylamine

The in vivo release of endogenous 3,4-dihydroxyphenylethylamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 3-methoxytyramine (3-MT), and of 5-hydroxytryptamine (5-HT) and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), has been measured in the caudate nucleus of the anesthetized rat. A push-pull cannula was implanted into the brain, and the tissue perfused with artificial CSF or artificial CSF containing 5×10^–4 M phenylethylamine. The perfusate was collected and analyzed for DA, 5-HT and their metabolites by high performance liquid chromatography with electrochemical detection (HPLC-ECD). DA was released by phenylethylamine at rates significantly greater than its basal rate. 3-MT and 5-HT were undetectable in perfusates collected under basal conditions, but could be detected readlly during phenylethylamine stimulation. DOPAC, HVA and 5-HIAA concentrations were not significantly affected by phenylethylamine. The results suggest (1) that phenylethylamine may exert its behavioural effects through increased release of both DA and 5-HT, and (2) that in vivo measurements of the acid metabolites alone may not be indicative of the release of the amines.Special Issue Dedicated to Dr. Abel Lajtha.     

Stereoselective effects of ketamine on dopamine,serotonin and noradrenaline release and uptake in rat brain slices

Ketamine (2-(2-chlorophenyl)-(1-methylamino)-cyclohexanone) is a rapid-acting dissociative general anaesthetic whose hallucinogenic properties have made it a popular drug of abuse. Ketamine comprises two optical isomers, with differing pharmacology. In the present study, the effects of (+)- and (-)-ketamine on stimulated efflux and reuptake of dopamine (DA), noradrenaline (NA) and serotonin (5-HT) were compared in isolated superfused slices of the rat caudatoputamen (CPu), ventral bed nucleus of the stria terminalis (BSTV) or dorsal raphe nucleus (DRN), respectively. Monoamine efflux was elicited by local electrical stimulation (20 pulses, 100 Hz trains) at tungsten microelectrodes and measured at adjacent carbon fibre microelectrodes using fast cyclic voltammetry (FCV). In CPu (+)-ketamine increased stimulated DA efflux and slowed DA reuptake in a concentration-dependent manner (25-200 microM). At 100 microM (+)-ketamine increased DA efflux by 109+/-20% (mean+/-S.E.M., n=13) of control values after 30 min (P<0.001 versus control) and prolonged uptake half-time (t(1/2)) by 76+/-38% (n=9, P<0.001) of control. In contrast (-)-ketamine (100 microM) had no effect on DA efflux or uptake. In DRN, both isomers (100 microM) increased stimulated 5-HT efflux. (-)-Ketamine had a larger effect (P<0.001), an 88+/-15% increase in 5-HT efflux (n=9) versus 46+/-10% (n=8) for the (+)-isomer. The isomers had similar effects on 5-HT uptake, increasing t(1/2) by approximately 200%. No evidence of stereospecificity was seen in BSTV: both isomers had small effects (+)- and (-)-ketamine (100 microM) increasing NA efflux by 43+/-10% (n=7, P<0.001) and 29+/-8% (n=7, P<0.001), respectively. The isomers also had identical effects on NA uptake, each increasing uptake t(1/2) by approximately 100%. In summary, our data show that the optical isomers of ketamine have strikingly different stereospecificity for the monoamine systems and one might predict, therefore, a different psychotomimetic potential.     

Regional distribution of dopamine, 5-hydroxytryptamine,and noradrenaline in the rat vas deferens

The concentrations of dopamine (DA), 5-hydroxytryptamine (5-HT) and noradrenaline (NA) in the rat vas deferens divided in eight or four sections were determined by high performance liquid chromatography with electrochemical detection. Dopamine and NA had the same regional distribution; their concentrations were maximal near the prostatic end and decreased towards the epididymis. The concentration of 5-HT also decreased from the prostatic to the epididimal end, but 5-HT did not follow the same regional distribution as DA and NA. Reserpine (0.02 or 0.2 mg/kg, i.p., 24 hr) and 6-hydroxydopamine (2×80 mg/kg, i.v., 6 days) decreased the contents of DA and NA; the concentrations of both amines were modified to a similar extent. Reserpine also diminished the content of 5-HT. Pargyline (200 mg/kg, i.p., 2 hr) increased the concentration of 5-HT whilep-chlorophenylalanine (300 mg/kg, oral, 3 days) decreased the contents of the amine in some sections of the vas deferens. This study suggests that DA and NA co-exist in the same sympathetic neurons. Some of the 5-HT could be stored in mast cells as previously proposed, but the finding that tissue content of 5-HT changes after inhibiting the deamination or synthesis of the amine suggests that other source(s) of 5-HT distinct from mast cells exist in the rat vas deferens.     

5-HT nerve terminals in the fourth ventricle of the rat brain: Their identification and distribution studied by fluorescence histochemistry and electron microscopy

Summary The occurrence and distribution of supra-ependymal nerve terminals storing serotonin (5-HT) are described for the fourth ventricle of the rat brain. The nerve terminals were identified as monoaminergic 1) fluorescence-histochemically, by the presence of a varicose, formaldehyde-induced fluorescence (FIF) on the free surface of the ependyma, 2) electron microscopically, by the presence of electron dense (chromaffin) cores in small (50 nm) and large (100 nm) vesicles found within the varicose regions of supra-ependymal nerve fibres, and 3) by the absence of both the FIF and chromaffin dense cores after treatment with reserpine. Moreover, the serotonergic nature of these nerve fibres could be concluded from 1) the yellow colour of the FIF, 2) the increased FIF after treatment with nialamide or reserpine+nialamide, 3) the diminished FIF and absence of chromaffin dense cores after treatment with p-CPA, and finally 4) the persistence of the FIF and chromaffin dense cores after treatment with -MPT.A high density of 5-HT nerve terminals occurred throughout the floor of the fourth ventricle and on the floor and roof of the lateral recess. Few 5-HT nerve terminals occurred only on the roof of the fourth ventricle (velum medullare, lamina epithelialis of the tela chorioidea), and the surface of the choroid plexus epithelia was devoid of such nerves. Virtually all nerve terminals in the fourth ventricle appear to be serotonergic.Results presented in part at the Autumn Meeting of the British and Italian Pharmacological Societies, Bristol, 1974 (Lorez et al., 1974). The skilful assistance of Mr. R. Wybrecht, Mr. R. Reese and Mrs. M. Gschwind is gratefully acknowledged.     

Inhibition of the uptake of 5-hydroxytryptamine, noradrenaline and dopamine into rat brain homogenates by various hydroxylated tryptamines

Recent work has shown that intracerebral injections of 5,6-dihydroxytryptamine (5,6-DHT) lead to a fairly selective and long lasting depletion of 5-HT in the rat CNS (BAUMGARTEN, BJORKLUND, LACHENMAYER, NOBIN and STENEVI, 1971; DALY, FUXE and JONSSON, 1973). This effect appears to result from a degeneration of the serotonin-containing neurons (BAUMGARTEN and LACHENMAYER, 1972a). 5,6-DHT does, however, to a lesser extent affect both NA and dopamine (DA) containing nerve terminals (BAUMGARTEN et al., 1971). In an attempt, therefore, to find compounds having a more specific toxic action we have investigated several other hydroxylated tryptamines. In order to obtain information about the differential affinities of these analogues for neuronal uptake sites we have examined their effects on the uptake of [³H]5-HT and (±)-[³H]NA into synaptosomes in homogenates of rat hypothalamus and of [³H]DA uptake into a similar preparation from the rat corpus striatum. It is known that the uptake of these putative transmitters in rat brain homogenates is predominantly into the synaptosome fraction (KANNENGIESSER, HUNT and RAYNAUD, 1973; COYLE and SNYDER, 1969).     

Retrograde signaling and the development of transmitter release properties in the invertebrate nervous system

The dynamics of presynaptic transmitter release are oftern matched to the functional properties of the prostsynaptic cell. In organisms ranging from cats to crickets, evidence suggests that retrograde signaling is essential for matching these presynaptic release properties to individual postsynaptic partners. Retrograde interactions appear to control the development of presynaptic, short-term facilitation and depression. 1994 John Wiley & Sons, Inc.     

The effects of 5-hydroxytryptophan and 5-hydroxytryptamine on dopamine synthesis and release in rat brain striatal synaptosomes.

The effects of 5-hydroxytryptophan (5-HTP) and serotonin (5-HT) on dopamine synthesis and release in rat brain striatal synaptosomes have been examined and compared to the effects of tyramine and dopamine. Serotonin inhibited dopamine synthesis from tyrosine, with 25% inhibition occurring at 3 μM-5-HT and 60% inhibition at 200 μM. Dopamine synthesis from DOPA was also inhibited by 5-HT, with 30% inhibition occurring at 200 μ. At 200 μM-5-HTP, dopamine synthesis from both tyrosine and DOPA was inhibited about 70%. When just the tyrosine hydroxylation step was measured in the intact synaptosome, 5-HT, 5-HTP, tyramine and dopamine all caused significant inhibition, but only dopamine inhibited soluble tyrosine hydroxylase [L-tyrosine 3-monooxygenase; L-tyrosine, tetrahydropteridine oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2] prepared from lysed synaptosomes. Particulate tyrosine hydroxylase was not inhibited by 10 μM-5-HT, but was about 20% inhibited by 200 μM-5-HT and 5-HTP. At 200 μM both 5-HT and 5-HTP stimulated endogenous dopamine release. These experiments suggest that exposure of dopaminergic neurons to 5-HT or 5-HTP leads to an inhibition of dopamine synthesis, mediated in part by an intraneuronal displacement of dopamine from vesicle storage sites, leading to an increase in dopamine-induced feedback inhibition of tyrosine hydroxylase, and in part by a direct inhibition of DOPA decarboxylation.     

Effects of lowering extracellular and cytosolic pH on calcium fluxes, cytosolic calcium levels, and transmitter release in presynaptic nerve terminals isolated from rat brain

We examined the effects of extracellular and intracellular pH changes on the influx of radioactive 45Ca, the concentration of ionized Ca (pCai) as monitored with the Ca-sensitive fluorescent indicator fura-2, and the efflux of dopamine in presynaptic nerve endings (synaptosomes) isolated from rat brain corpora striata and preloaded with [3H]dopamine. Cytosolic pH (pHi) was monitored by loading the synaptosomes with the H+-sensitive fluorescent indicator 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) (see Nachshen, D. A., and P. Drapeau, 1988, Journal of General Physiology, 91:289-303). An abrupt decrease of the pH of the external medium, from 7.4 to 5.5, produced a slow decrease of pHi (over a 5-min period) from an initial value of 7.2 to a steady state level of approximately 5.8. When 20 mM acetate was present in acidic media, pHi dropped as fast as could be measured (within 2 s) to a level similar to that reached (more slowly) in the absence of acetate. It was therefore possible to lower pHi over short time periods to different levels depending on whether or not acetate was present upon extracellular acidification. Extracellular acidification to pH 5.5 (in the absence of acetate) had no significant effect on pCai and dopamine release over a 30-s period (pHi = 6.4). Acidification in the presence of acetate lowered pHi to 5.8 without affecting pCai, but dopamine efflux increased approximately 20-fold. This increase in basal dopamine release was also observed in the absence of extracellular Ca. Thus, intraterminal, but not extracellular, acidification could stimulate the efflux of dopamine in a Ca-independent manner. The high Q10 (3.6) of acid-stimulated dopamine efflux in the presence of nomifensine (which blocks the dopamine carrier) was consistent with an activation of vesicular dopamine release by H+. When synaptosomes were both depolarized for 2 s in high-K (77.5 mM) solutions and acidified (in the absence of acetate), there was a parallel block of 45Ca entry and evoked dopamine release (50% block at pH 6.0 with 0.2 mM external Ca). When acetate was included in the acidic media to further reduce pHi, Ca entry remained blocked, but evoked dopamine release was increased. Therefore, extracellular, but not cytosolic, acidification inhibited the release of dopamine by blocking voltage-gated Ca channels. The stimulation by cytosolic acidification of both basal and evoked dopamine release suggests that vesicular release in resting and depolarized synaptosomes was directly activated by cytoplasmic H+.     

Type-3 ryanodine receptor involved in Ca2+-induced Ca2+ release and transmitter exocytosis at frog motor nerve terminals

Ca(2+)-induced Ca2+ release (CICR) occurs in frog motor nerve terminals after ryanodine receptors (RyRs) are primed for activation by conditioning large Ca2+ entry. We studied which type of RyR exists, whether CICR occurs without conditioning Ca2+ entry and how RyRs are primed. Immunohistochemistry revealed the existence of RyR3 in motor nerve terminals and axons and both RyR1 and RyR3 in muscle fibers. A blocker of RyR, 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8) slightly decreased rises in intracellular Ca2+ ([Ca2+]i) induced by a short tetanus (50 Hz, 1-2s), but not after treatment with ryanodine. Repetitive tetani (50 Hz for 15s every 20s) produced repetitive rises in [Ca2+]i, whose amplitude overall waxed and waned. TMB-8 blocked the waxing and waning components. Ryanodine suppressed a slow increase in end-plate potentials (EPPs) induced by stimuli (33.3 Hz, 15s) in a low Ca2+, high Mg2+ solution. KN-62, a blocker of Ca(2+)/calmoduline-activated protein kinase II (CaMKII), slightly reduced short tetanus-induced rises in [Ca2+]i, but markedly the slow waxing and waning rises produced by repetitive tetani in both normal and low Ca2+, high Mg2+ solutions. Likewise, KN-62, but not KN-04, an inactive analog, suppressed slow increases in EPP amplitude and miniature EPP frequency during long tetanus. Thus, CICR normally occurs weakly via RyR3 activation by single impulse-induced Ca2+ entry in frog motor nerve terminals and greatly after the priming of RyR via CaMKII activation by conditioning Ca2+ entry, thus, facilitating transmitter exocytosis and its plasticity.     

Glyceride lipases in nerve endings of guinea-pig brain and their stimulation by noradrenaline, 5-hydroxytryptamine and adrenaline

1. Combined guinea-pig cortex and cerebellum was shown to contain triglyceride lipase, diglyceride lipase and monoglyceride lipase, which were assayed by the release of [1-(14)C]palmitate from [1-(14)C]palmitoylglycerol esters. Triglyceride lipase and diglyceride lipase were found in all particulate fractions. 2. With osmotically ruptured synaptosomes the rates of release of palmitate from glyceryl tripalmitate and glyceryl dipalmitate were 7-25mumol/h per g of protein and 0.18-0.69mmol/h per g of protein respectively. The logarithm of the rate of hydrolysis of glyceryl monopalmitate increased linearly with the logarithm of protein concentration. The pH optima of triglyceride lipase and diglyceride lipase were between 7 and 8. The pH optimum for monoglyceride lipase was approx. 8. 3. Triglyceride lipase and diglyceride lipase of osmotically ruptured synaptosomes were stimulated by noradrenaline, 5-hydroxytryptamine and adrenaline. Triglyceride lipase of isolated synaptic membranes was stimulated by 0.01-1mm-noradrenaline. Aging of membranes at 0 degrees C decreased activity, which could still be stimulated by noradrenaline. Diglyceride lipase of isolated membranes was stimulated by 1mum-1mm-noradrenaline. The activity of triglyceride lipase in isolated synaptic vesicles was diminished by 1mm-5-hydroxytryptamine.     

Reactive oxygen species induced by presynaptic glutamate receptor activation is involved in [H]GABA release from rat brain cortical nerve terminals

We investigated the production of reactive oxygen species (ROS) as a response to presynaptic glutamate receptor activation, and the role of ROS in neurotransmitter (GABA) release. Experiments were performed with rat brain cortical synaptosomes using glutamate, NMDA and kainate as agonists of glutamate receptors. ROS production was evaluated with the fluorogenic compound dichlorodihydrofluorescein diacetate (H₂DCF-DA), and GABA release was studied using synaptosomes loaded with [³H]GABA. All agonists were found to stimulate ROS production, and specific antagonists of NMDA and kainate/AMPA receptors, dizocilpine hydrogen maleate (MK-801) and 6-cyano-7-nitroquinoxaline-2,3-done (CNQX), significantly inhibited the ROS increase. Spontaneous as well as agonist-evoked ROS production was effectively attenuated by diphenyleneiodonium (DPI), a commonly used potent inhibitor of NADPH oxidase activity, that suggests a high contribution of NADPH-oxidase to this process. The replacement of glucose with pyruvate or the simultaneous presence of both substrates in the medium led to the decrease in spontaneous and NMDA-evoked ROS production, but to the increase in ROS production induced by kainate. Scavenging of agonist-evoked ROS production by a potent antioxidant N-acetylcysteine was tightly correlated with the inhibition of agonist-evoked GABA release. Together, these findings show that the activation of presynaptic glutamate receptors induces an increase in ROS production, and there is a tight correlation between ROS production and GABA secretion. The pivotal role of kainate/AMPA receptors in ROS production is under discussion.     

The depolarization-induced release of cholecystokinin C-terminal octapeptide (CCK-8) from rat synaptosomes and brain slices

Studies on the subcellular distribution of immunoreactive cholecystokinin (CCK) in homogenates of rat cerebral cortex showed that approximately 95% was associated with particulate fractions, including presynaptic terminals (synaptosomes). Chromatography of extracts of tissue and medium from incubated synaptosomes revealed that this material was almost exclusively in the form of COOH-terminal octapeptide (CCK-8), very little CCK-33 being present. There was a wide range of CCK-8 concentrations in synaptosomes from different brain regions (cortex > striatum ? hypothalamus > brain stem). Cerebral cortex synaptosomes were incubated in vitro and showed a complex pattern of CCK-8 release with varying concentrations of tissue: amounts in the medium rose rapidly with increasing synaptosome concentrations, then fell to a plateau at higher tissue values. A mechanism for the rapid disposal of extracellular CCK-8 was associated with synaptosomal fractions. Depolarization-induced (high K⁺) release of CCK-8 was observed with cortex and corpus striatum synaptosomes. A rapid and reversible enhancement of CCK-8 release from cortex slices was observed in response to elevated K⁺. Veratrine also released CCK-8 from cortex slices, although this was not reversible. Stimulus-induced release of CCK-8 from synaptosomes and slices required extracellular Ca²⁺. The storage, release and degradation of CCK-8 by nerve-endings suggest a synaptic function for this peptide.     

Modulation of GABA-augmented norepinephrine release in female rat brain slices by opioids and adenosine

GABA_A receptor activation augments electrically-stimulated release of norepinephrine (NE) from rat brain slices. Because this effect is not observed in synaptoneurosomes, GABA probably acts on inhibitory interneurons to disinhibit NE release. To determine whether opioids or adenosine influence GABA-augmented NE release, hypothalamic and cortical slices from female rats were superfused with GABA or vehicle in the presence and absence of 10 M morphine or 100 M adenosine. GABA augments [³H]NE release in the cortex and hypothalamus. Morphine alone has no effect on [³H]NE release, but attenuates GABA augmentation of [³H]NE release in both brain regions. Adenosine alone modestly inhibits [³H]NE release in the cortex, but not in the hypothalamus. Adenosine inhibits GABA-augmented [³H]NE release in both brain regions. The general protein kinase inhibitor H-7, augments [³H]NE release in both brain regions and may have additive effects with GABA in cortical slices. These results implicate opioid and adenosine interneurons and possibly protein kinases in regulating GABAergic influences on NE transmission.     

P2Y receptor mediated inhibitory modulation of noradrenaline release in response to electrical field stimulation and ischemic conditions in superfused rat hippocampus slices

In this study, the inhibitory regulation of the release of noradrenaline (NA) by P2 receptors was investigated in hippocampus slices pre-incubated with [³H]NA. Electrical field stimulation (EFS; 2 Hz, 240 shocks, and 1 ms) released NA in an outside [Ca²⁺]-dependent manner, and agonists of P2Y receptors inhibited the EFS-evoked [³H]NA release with pharmacological profile similar to that of the P2Y₁ and P2Y₁₃ receptor subtypes. This inhibitory modulation was counteracted by bicuculline and 6-cyano-2,3-dihydroxy-7-nitro-quinoxaline + 2-amino-5-phosphonovalerate and 2-amino-4-phosphonobutyrate. In contrast, the excess release in response to 30 min combined oxygen and glucose deprivation was outside [Ca²⁺] independent, but still sensitive to the inhibition of both facilitatory P2X₁ and inhibitory P2Y₁ receptors. Whereas mRNA encoding P2Y₁₂ and P2Y₁₃ receptor subunits were expressed in the brainstem, P2Y₁ receptor immunoreactivity was localized to neuronal somata and dendrites innervated by the mossy fiber terminals in the CA3 region of the hippocampus, as well as somata of granule cells and interneurons in the dentate gyrus. In summary, in addition to the known facilitatory modulation via P2X receptors, EFS-evoked [³H]NA outflow in the hippocampus is subject to inhibitory modulation by P2Y₁/P2Y₁₃ receptors. Furthermore, endogenous activation of both facilitatory and inhibitory P2 receptors may participate in the modulation of pathological NA release under ischemic-like conditions.     

Role of excitatory amino acids in the direct and indirect presynaptic regulation of dopamine release from nerve terminals of nigrostriatal dopaminergic neurons

Summary In vivo experiments carried out in halothane-anaesthetized cats implanted with push-pull cannulae demonstrated that glutamate (GLU) released from corticostriatal fibers triggers the release of dopamine (DA), even in the absence of activity in nigral DA cells. As shown in vitro, using rat striatal slices or synaptosomes or in vivo in the cat, both NMDA and AMPA receptors subtypes are involved in the GLU-induced release of DA. Beside this direct regulation, GLU also exert several indirect facilitatory and inhibitory controls on DA release, particularly through cholinergic and GABAergic striatal neurons. Indeed, as shown by numerous authors, the GLU-evoked release of DA is markedly reduced in the presence of tetrodotoxin, bicuculline or atropine or by previous kainate- or ibotenate-induced lesion of striatum. Differences in the presynaptic regulation of DA release in striosomal and matrix compartments have also been found with NMDA and acetylcholine. The effect of acetylcholine was of shorter duration in the matrix than in the striosomal-enriched areas. Two opposite indirect regulations of DA release could be demonstrated: one is facilitatory and involves nicotinic receptors, the other is inhibitory, involves muscarinic receptors and mediated, at least in the matrix by dynorphin containing neurons. The NMDA-evoked responses are of larger amplitude and more sensitive to tetrodotoxin in the matrix than in the striosomes. In conclusion, GLU released from corticostriatal fibers, is able to control the release of DA from terminals of nigrostriatal neurons through direct facilitatory mechanisms (NMDA and AMPA receptors), but also through indirect facilitatory and inhibitory local circuits involving cholinergic and GABAergic neurons.     

A reliable and sensitive method for the simultaneous determination of dopamine, noradrenaline, 5-hydroxytryptamine and 5-hydroxy-indolacetic acid in small brain samples

A sensitive and reliable fluorometric method for the simultaneous determination of dopamine, noradrenaline, 5-hydroxytryptamine and 5-hydroxy-indol acetic acid in small samples of brain tissues is described. The procedure is based on solvent extraction; catecholamines are oxidized by the Chang's method and 5-hydroxytryptamine and 5-hydroxy-indol acetic acid determined by reaction with o-phthalaldehyde, alpha-methyl-p-tyrosine causes a negligible interference with the procedure. Results of determination of these amines in different brain areas are reported.