Synaptosomal uptake and release of dopamine in substantia nigra: effects of gamma-aminobutyric acid and substance P

Subcellular and regional localization of mRNA translation in midbrain dopamine neurons

Midbrain dopaminergic (mDA) neurons exhibit extensive dendritic and axonal arborizations, but local protein synthesis is not characterized in these neurons. Here, we investigate messenger RNA (mRNA) localization and translation in mDA neuronal axons and dendrites, both of which release dopamine (DA). Using highly sensitive ribosome-bound RNA sequencing and imaging approaches, we find no evidence for mRNA translation in mDA axons. In contrast, mDA neuronal dendrites in the substantia nigra pars reticulata (SNr) contain ribosomes and mRNAs encoding the major components of DA synthesis, release, and reuptake machinery. Surprisingly, we also observe dendritic localization of mRNAs encoding synaptic vesicle-related proteins, including those involved in exocytic fusion. Our results are consistent with a role for local translation in the regulation of DA release from dendrites, but not from axons. Our translatome data define a molecular signature of sparse mDA neurons in the SNr, including the enrichment of Atp2a3/SERCA3, an atypical ER calcium pump.

Local translation regulates the subcellular proteome in neurons but has not been characterized in midbrain dopamine neurons, cells with large dendrites and axonal arborizations. Hobson et al. investigate messenger RNA localization and translation in midbrain dopamine neurons in the mouse brain, finding ribosomes and dopaminergic mRNAs in dendrites, but not axons.

Compensatory mechanisms in experimental and human parkinsonism: towards a dynamic approach

This paper provides an overview of the compensatory mechanisms which come into action during experimental and human parkinsonism. The intrinsic properties of the dopaminergic neurones of the substantia nigra pars compacta (SNc) which degenerate during Parkinson's disease are described in detail. It is generally considered that the nigrostriatal pathway is principally responsible for the compensatory preservation of dopaminergic function. It is also becoming clear that the morphological characteristics of dopaminergic neurones and the dual character, synaptic and asynaptic, of striatal dopaminergic innervation engender two modes of transmission, wiring and volume, and that both these modes play a role in the preservation of dopaminergic function. The plasticity of the dopamine neurones, extrinsic or intrinsic to the striatum, can thus be regarded as another compensatory mechanism. Recent anatomical and electrophysiological studies have shown that the SNc receives both glutamatergic and cholinergic inputs. The dynamic role this innervation plays in compensatory mechanisms in the course of the disease is explained and discussed. Recent developments in the field of compensatory mechanisms speak for the urgence to develop a valid chronic model of Parkinson's disease, integrating all the clinical features, even resting tremor, and illustrating the gradual evolution of nigral degeneration observed in human Parkinson's disease. Only a dynamic approach to the physiopathological study of compensatory mechanisms in the basal ganglia will be capable of elucidating these complex questions.

NMDA regulation of dopamine release from proximal and distal dendrites in the cat substantia nigra

The NMDA regulation of the dendritic release of [3H]dopamine ([3H]DA) synthesized from [3H]tyrosine was investigated in vitro using a microsuperfusion procedure in the pars compacta (SNC) and the pars reticulata (SNR) of the cat substantia nigra. The spontaneous release of [3H]DA was threefold higher in the SNC than in the SNR and amphetamine (1 microM) enhanced similarly [3H]DA release in both nigral areas. In the absence of magnesium, NMDA (50 microM) stimulated markedly the release of [3H]DA in the SNC and SNR, these effects being completely prevented by MK 801 (1 microM), the NMDA receptor antagonist. The DA uptake inhibitor, nomifensine (5 microM), increased the amount of [3H]DA recovered in SNC (x2) and SNR (x3) superfusates but did not significantly modify the NMDA-evoked responses. The effects of NMDA seen in the absence or presence of nomifensine persisted when the two nigral areas were continuously superfused with tetrodotoxin (1 microM). These results are in favor of the presence of NMDA receptors on dopaminergic dendritic arborizations and indicate that the stimulation of these receptors facilitates in a similar way the release of DA from proximal and distal dendrites.

Determination of release of endogenous dopamine from superfused substantia nigra slices

Dopamine (DA) is synthesized and released not only from the terminals of the nigrostriatal dopaminergic neuronal pathway but also from cell bodies and dendrites in the substantia nigra (SN). In most of the in vitro studies on DA release in the SN, release of exogenously applied 3H-DA has been determined either from slices or from synaptosomes. However 3H-DA has some disadvantages; 3H-DA is taken up and released not only from dopaminergic cells but also from other neuronal elements and radiolabelled DA may not be evenly distributed with the releasable endogenous pool of the amine. Therefore we have developed a method for determination of the release of endogenous DA from superfused guinea pig SN slices. We have used a superfusion system in which 6 slices are placed into a microchamber. Samples of superfusate were collected every 10 min for up to 3 h and biochemical analyses were performed by electrochemical detection preceded by absorption of DA on alumina and chromatography on a cation exchange column. Expected increases of the release of endogenous DA were obtained following D-amphetamine and potassium administration. The data indicate that it is possible to measure endogenous release of DA from guinea pig SN slices with standard HPLC technique and follow the release for a relatively long time.

Organization and physiology of the substantia nigra

A comprehensive review of the literature on the anatomy, electrophysiology and pharmacology of the substantia nigra is presented. A diagram is developed taking into account the interneuronal interactions of neurotransmitters and receptors that control firing rates and neurotransmitter releases. The central features of the diagram are a positive dopaminergic feedforward process and a positive feedback mechanism mediated by extrasynaptic substance P diffusing from striatal terminals to dopaminergic dendrites of the zona compacta neurons. This loop can enhance the transmission of information from the striatum through the pars reticulata output neurons. The loop is controlled at the level of zona compacta neurons by a negative feedback supported by the dendritic release of dopamine and boosted by pedunculopontine activation mediated by muscarinic receptors. The output of the loop is controlled by two negative feedforward processes, both involving GABAergic striatonigral afferents. Application of the model to pharmacological studies of diverse behaviors including seizures, turning, and conditioned behaviors reveals unforseen relationships and may offer insights into, and directions for, further analysis of the mechanisms and functions involved.

Guanine nucleotides regulate the effect of substance P on striatal adenylate cyclase of the rat

Substance P was incubated in an adenylate cyclase assay of a particulate fraction of caudate-putamen tissue of the rat in order to examine the effect of the peptide on D-1 receptor coupled adenylate cyclase in vitro. Substance P did not influence basal adenylate cyclase activity or the stimulation of the enzyme by dopamine. No influence of substance P was seen on the effects of calcium and magnesium chloride as a cofactor of adenylate cyclase. Also the inhibition of adenylate cyclase activity by the dopamine antagonist fluphenazine was not influenced by substance P. However, substance P was able to enhance cyclic AMP formation in the presence of guanosine-imidodiphosphate (Gpp(NH)p), whereas the stimulatory effect of guanosine-triphosphate (GTP) was inhibited by substance P. In our study we suggest that substance P interacts with the guanine nucleotide regulatory subunit without directly affecting D-1 dopamine receptors in the caudate-putamen of the rat.

Peptidergic control of male rat sexual behavior: the effects of intracerebral injections of substance P and cholecystokinin

Behavioral experiments examined the roles of substance P (SP) and cholecystokinin (CCK) in male rat copulatory behavior. Male copulatory behavior was recorded subsequent to injections of different doses of CCK and SP into the medial preoptic-anterior-hypothalamic area (MPOA-AH), caudate/putamen (CP), or the lateral ventricles (LV) in sexually experienced male rats. In the first experiment, three different doses of SP (10, 100, and 200 ng/cannula) injected bilaterally into the MPOA-AH produced marked changes in several components of male copulatory behavior. Latencies were most affected. All three doses significantly shortened the interval to initiate copulation, and the 10 and 100 ng, but not 200 ng dose also significantly reduced ejaculation latencies. Injections of 10 ng of SP into the CP did not affect sexual behavior, while injections into the LV produced changes different from those of MPOA-AH injections. These data argue for some degree of site specificity of the effects of the MPOA-AH injections. Bilateral injections of 10 ng of SP into the MPOA-AH, were incapable of inducing copulatory behavior in castrated rats deprived of testosterone. Injections of an undiluted SP antiserum (2 microliters/cannula) into the MPOA-AH produced a dramatic impairment of male copulatory behavior. These injections significantly lengthened amount, intromission, and ejaculation latencies, while having no effect on the number of mounts or intromissions prior to ejaculation. In contrast, bilateral injections of CCK-8 (10, 100, and 200 ng/cannula) into the MPOA-AH failed to affect any parameter of male copulatory behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and release of dopamine in rat brain: comparison between substantia nigra pars compacts, pars reticulata, and striatum

Dopamine (DA) is synthesized and released not only from the terminals of the nigrostriatal dopaminergic neuronal pathway, but also from the dendrites in the substantia nigra. We have investigated the regulation of the DA turnover, the DA synthesis rate, and the DA release in the substantia nigra pars compacts (SNpc) and pars reticulata (SNpr) in vivo. As a measure of DA turnover, we have assessed the concentrations of 3,4-dihydroxyphenylacetic acid and homovanillic acid. As a measure of the DA synthesis rate, we have determined the 3,4-dihydroxyphenylalanine accumulation after inhibition of aromatic L-amino acid decarboxylase by 3-hydroxybenzylhydrazine. As a measure of DA release, we have investigated the disappearance rate of DA after inhibition of its synthesis by alpha-methyl-p-tyrosine and the 3-methoxytyramine accumulation following monoamine oxidase inhibition by pargyline. Both the DA turnover and the DA synthesis rate increased following treatment with the DA receptor antagonist haloperidol and decreased following treatment with the DA receptor agonist apomorphine in the SNpc and in the SNpr, but the effects of the drugs were less pronounced than in the striatum. gamma-Butyrolactone treatment, which suppresses the firing of the dopaminergic neurons, increased the DA synthesis rate in the striatum (165%), but had no such effect in the SNpc or SNpr. Haloperidol, apomorphine, and gamma-butyrolactone increased, decreased, and abolished, respectively, the DA release in the striatum, but the drugs had no or only slight effects on the alpha-methyl-p-tyrosine-induced DA disappearance and on the pargyline-induced 3-methoxytyramine accumulation in the SNpc or SNpr. Taken together, these results indicate that the DA synthesis rate, but not the DA release, are influenced by DA receptor activity and neuronal firing in the SNpc and SNpr. This is in contrast to the situation in the striatum, where both the DA synthesis rate and the DA release are under such control.

Substance P and neurokinin A regulate by different mechanisms dopamine release from dendrites and nerve terminals of the nigrostriatal dopaminergic neurons

Numerous striatal neurons innervating the substantia nigra contain substance P and/or neurokinin A. In contrast to substance P or neurokinin A, little neurokinin B is found in the substantia nigra. This led us to compare the effects of nigral application of these tachykinins on the release of dopamine from dendrites and nerve terminals of nigrostriatal dopaminergic neurons. Experiments were made in halothane-anesthetized cats implanted with one push-pull cannula in the substantia nigra and another in the ipsilateral caudate nucleus [3H]Tyrosine was delivered continuously to each push-pull cannula and the release of newly synthesized [3H]dopamine measured in the superfusate. Unlike substance P or neurokinin A, neurokinin B (10(-8) M) applied for 30 min into the pars compacta of the substantia nigra was without effect on the release of [3H]dopamine from nerve terminals or dendrites. When either substance P (10(-8) M) or neurokinin A (10(-8) M) was applied into the pars compacta, the release of [3H]dopamine from nerve terminals was enhanced. While neurokinin A also stimulated the dendritic release of [3H]dopamine, this was reduced by substance P. At a lower concentration (10(-9) M), neurokinin A induced similar effects to those observed at 10(-8) M whereas substance P (10(-9) M) stimulated moderately [3H]dopamine release from nerve terminals but did not affect the dendritic release of the [3H]amine. When superfused into the pars reticulata, substance P (10(-8) M) still stimulated [3H]dopamine release from nerve terminals but not from dendrites while neurokinin A (10(-8) M) was without effect either in the caudate nucleus or the substantia nigra. Additional experiments were made to determine whether or not substance P (10(-8) M) or neurokinin A (10(-8) M) act directly on nigral dopaminergic neurons when applied into the pars compacta. The effects of substance P on [3H]dopamine release from nerve terminals and dendrites were prevented when 2-amino-6-trifluoromethoxy benzothiazole (10(-5) M), an antagonist of glutamatergic transmission, was applied continuously into the caudate nucleus. In contrast, the stimulatory effects of neurokinin A on [3H]dopamine release from nerve terminals and dendrites were insensitive to 2-amino-6-trifluoromethoxy benzothiazole (10(-5) M). These results suggest that neurokinin A, but not substance P, acts directly on dopaminergic cells. In the light of previous observations, we propose that the effects of substance P on dopaminergic transmission are mediated by a nigro-thalamo-cortico-striatal loop.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for a tonic facilitatory influence of substance P on dopamine release in the nucleus accumbens

Microinjections of a monoclonal antibody against substance P (SP) into the nucleus accumbens (NAS) increased the concentrations of dopamine (DA) and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the NAS but not in neuroanatomically adjacent areas. SP immunoneutralization in the NAS also reduced the locomotor response to systemically administered D-amphetamine. Microinjections of control antibody did not significantly alter either DA metabolism or D-amphetamine-induced locomotion. These data are consistent with the hypothesis that endogenous SP modulates the release of DA in the NAS.

Stimulatory effect of substance P on the spontaneous release of newly synthesized [3H]dopamine from rat striatal slices: a tetrodotoxin-sensitive process

Striatal slices from the rat were continuously superfused with [3H]tyrosine in order to estimate the release of newly synthesized [3H]dopamine [( 3H]DA). Substance P (SP) and neuromedin K (NKB) stimulated the spontaneous release of [3H]DA when used in concentrations (from 10(-9) M to 10(-7) M). The stimulatory effect of substance P (10(-8) M) was prevented completely when slices were superfused with tetrodotoxin (10(-7) M) or the substance P antagonist (D-Arg1,D-Pro2,D-Trp7,9,Leu11) substance P (10(-5 M) indicating that the response evoked by substance P was mediated by substance P receptors but that these were not located on DA nerve terminals. In addition, substance P did not modify the stimulatory effect of acetylcholine (ACh) (10(-5) M) on the spontaneous release of [3H]DA since the effects of substance P (10(-7) M) and ACh (10(-5) M) were additive.

Evidence for dopamine release and metabolism beyond the control of nerve impulses and dopamine receptors in rat substantia nigra

In rat substantia nigra a biphasic disappearance curve of dopamine (DA) was seen after tyrosine hydroxylase inhibition by alpha-methyl-p-tyrosine (alpha-MT): the initial phase had a fast turnover and a half life of 0.5 h and the later phase had an extremely slow turnover. In contrast to the effects in striatum, neither haloperidol nor apomorphine influenced alpha-MT-induced DA disappearance in the substantia nigra. Furthermore, inhibition of impulse flow by gamma-butyrolactone prevented DA disappearance in striatum but not in the substantia nigra. Measurements of DA and 3-methoxytyramine following treatment with inhibitors of monoamine oxidase (pargyline) and catechol-O-methyl transferase (tropolone) indicated that O-methylation is a more important metabolic pathway in the substantia nigra than in the striatum. The data are interpreted to indicate that the release and metabolism of DA in the substantia nigra are largely beyond the control of nerve impulses and DA receptors. It is suggested that such an arrangement forms an important feature of autoreceptor-mediated feedback control of DA nerve cell activity.

Evidence that [3H]dopamine is taken up and released from nondopaminergic nerve terminals in the rat substantia nigra in vitro

Potassium chloride (25 mM) and (+)-amphetamine (100 microM) both stimulated the release of radioactivity from slices of substantia nigra preincubated with [3H]3,4-dihydroxyphenylethylamine [( 3H]dopamine). Potassium chloride (25 mM) released radioactivity from slices of both zona compacta and zona reticulata. Prior 6-hydroxydopamine (6-OHDA) lesions of one nigrostriatal pathway did not reduce the spontaneous release of radioactivity, or the potassium chloride- or amphetamine-induced release of radioactivity from slices of nigra ipsilateral to the lesion after preincubation with [3H]dopamine. The accumulation of radioactivity following incubation of nigral slices from 6-OHDA-lesioned animals with [3H]dopamine was increased when compared to uptake into slices from intact tissue. In synaptosomal preparations of striatum, nomifensine but not desipramine or fluoxetine inhibited [3H]dopamine uptake. In contrast, nomifensine, desipramine, and fluoxetine all inhibited [3H]dopamine uptake in nigral synaptosomal preparations. Following 6-OHDA lesions of one nigrostriatal pathway the uptake of [3H]dopamine into nigral synaptosomal preparations was unchanged but uptake into striatal preparations was substantially decreased. In contrast, bilateral electrolesions of the dorsal and medial raphe nuclei reduced [3H]dopamine uptake into nigral preparations but not into striatal synaptosomes. The uptake of [3H]5-hydroxytryptamine ([3H]5-HT) into synaptosomal preparations of substantia nigra was abolished by fluoxetine and reduced by desipramine, but was unaffected by nomifensine. In contrast, fluoxetine, desipramine, and nomifensine all inhibited [3H]5-HT uptake into striatal synaptosomal preparations. Following 6-OHDA lesions of one nigro-striatal pathway the uptake of [3H]5-HT into nigral synaptosomal preparations was unchanged but uptake into striatal preparations was reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of release of endogenous dopamine and gamma-aminobutyric acid from rat caudate synaptosomes

Release of endogenous dopamine (DA) and gamma-aminobutyric acid (GABA) from superfused rat caudate synaptosomes was monitored with liquid chromatography with electrochemical detection. Dopamine was analyzed by oxidative detection following alumina extraction while GABA was analyzed with reductive detection following pre-column derivatization with trinitrobenzenesulfonic acid and extraction. Both spontaneous and K+-stimulated (40 mM) release were examined as well as the effect of several possible neuromodulatory agents (DA, GABA, muscimol, ascorbic acid, acetylcholine). The content of GABA in the sample and the amount released by K+ were approximately fifty times those of DA although the relative amounts released by repetitive K+ stimulations were similar. Muscimol and DA significantly attenuated both the spontaneous and stimulated release of GABA while ascorbate and acetylcholine had no effect. Acetylcholine significantly increased both the stimulated and spontaneous release of DA while the other agents had no effect. Dopamine showed an absolute dependence on calcium for stimulated release while GABA exhibited a significant calcium-independent release. These results indicate that profound differences exist in the factors which modulate the release of endogenous DA and GABA.

Substance P immunoreactivity in the post-mortem parkinsonian brain

The amount of substance P immunoreactivity (SPI) was measured by radioimmunoassay from the cerebral cortex, caudate nucleus, putamen, pallidum, substantia nigra, hypothalamus, nucleus accumbens, amygdala and hippocampus from autopsy brains. The whole material consisted of 42 parkinsonian patients and 31 controls. The amount of SPI was significantly decreased in the substantia nigra of the parkinsonian brain. There was also a significant decrease of SPI in the putamen of those parkinsonian patients, who had not received levoDOPA treatment. The levels of SPI in the other brain regions studied did not show any difference between parkinsonian patients and controls. The results obtained suggest that substance P (SP) may have a role in the pathophysiology of Parkinson's disease.

Gamma-aminobutyric acid stimulates the release of endogenous ascorbic acid from rat striatal tissue

Gamma-aminobutyric acid (GABA) was found to induce the release of ascorbic acid from rat striatal homogenates and minces. This release was studied with the use of a rapid superfusion system with an on-line amperometric detector that monitors for the presence of easily oxidized substances (i.e., ascorbate, 3,4-dihydroxyphenylethylamine). The release was found to be calcium-independent and depolarization-dependent. This releasable pool of ascorbate could be replenished through nonstereospecific uptake. The releasing action of GABA was mimicked by the GABA agonist, muscimol, and was completely inhibited by the GABA antagonist, picrotoxin. The structural analogues of GABA, beta-alanine and gamma-hydroxybutyric acid, had no effect. These data indicate that ascorbate release is GABA-receptor mediated and synaptically localized.

Actions of substance P, MIF, TRH and related peptides in the substantia nigra, caudate nucleus and nucleus accumbens

Neurones in the substantia nigra were found to be sensitive to iontophoretically applied substance P, substance P 1-9 methyl ester and substance P 1-9 amide. Substance P 1-2, 4-9 and 5-9 methyl esters, thyrotropin releasing hormone (TRH), Pyroglutamyl-histidyl-2 methyl prolineamide (methyl TRH), Pyroglutamyl-histidyl-2 methyl prolineamide (methyl TRH), histidyl-proline-diketopiperazine (His-Pro) and MSH releasing inhibiting factor (MIF) were without effect on neurones in this area. Thyrotropin releasing hormone (TRH), methyl TRH, His-Pro and MIF were inactive on neurones in the caudate nucleus and nucleus accumbens. Bilateral injections of substance P and substance P 1-9 methyl ester into the ventral tegmental area (VTA) of conscious rats produced locomotor activity, while similar injections of substance P 4-9 and 5-9 methyl esters did not. The locomotor activity produced by amphetamine was prolonged by TRH, while MIF was devoid of such activity. The data suggest that substance P and substance P 1-9 have similar effects in the substantia nigra, although the mechanism of action is unclear. Thyrotropin releasing hormone and MIF probably do not have acute actions in the brain areas tested.

Gamma-aminobutyric acid can both inhibit and facilitate dopamine release in the caudate nucleus of the rabbit

Slices from rabbit caudate nucleus were preincubated with [3H]dopamine and then superfused and stimulated electrically. gamma-Aminobutyric acid (10-4) and 10(-3) mol/L increased both the basal and the stimulation-evoked overflow of tritium. The effects were not changed by picrotoxin and were only slightly reduced by bicuculline. In the presence of nipecotate 10(-3) mol/L, gamma-aminobutyric acid decreased rather than enhanced the basal and the evoked overflow. The inhibition persisted in the presence of bicuculline. Muscimol did not affect, whereas baclofen decreased, the evoked overflow of tritium. Similar results obtained with synaptosomes that were stimulated by 30 mmol/L K+. The results indicate that gamma-aminobutyric acid can both facilitate and depress the release of dopamine. Facilitation occurs after entry of gamma-aminobutyric acid into the dopaminergic terminal axons, whereas inhibition if probably mediated by a receptor site located in the membrane of these terminals.

Dendritic release of dopamine in the substantia nigra

Dopamine can be released in the substantia nigra for the dendrites of nigrostriatal dopaminergic neurones, to be involved there in the self-regulation of the dopaminergic cells, to control the release of neurotransmitters from nigral afferent fibres and to influence the activity of nigral non-dopaminergic cells.