Alterations in amphetamine stereotypy following acute lesions of substantia nigra

Stereotypy induced by high doses of amphetamine has been related to the ability of this drug to increase the release of dopamine in the caudate nucleus and to block its reuptake. Since amphetamine-stimulated dopamine release in the caudate is blocked by acute lesions of the nigrostriatal pathway, the mechanism by which amphetamine acts to produce stereotypy may be dependent upon intact nigrostriatal impulse flow. The present study examined the involvement of nigrostriatal impulse flow in amphetamine stereotypy by determining the effect of acute, bilateral lesions of substantia nigra pars compacta on measures of stimulant-induced stereotypy and motility. Acute nigral lesions did not significantly alter the stereotypy or motility induced by 3.0 or 6.0 mg/kg amphetamine. These results suggest that the observed behavioral effects of amphetamine do not require an intact nigrostriatal pathway, and thus may involve changes in spontaneous release or reuptake of dopamine rather than in changes in impulse-coupled dopamine release.     

尾核P物质对胃运动的抑制效应系通过黑质,迷走背核经迷走神经所介导

本工作观察损毁下丘脑外侧区,黑质,迷走背核及其传出神经对尾核微量注射Ｐ物质引起的胃肌电快波和胃运动抑制效应的影响。实验结果：该抑制效应不依赖于下丘脑外侧区的完整但可被损毁黑质,迷走背核或迷走上所消除。用利血平耗竭交感神经递质则不影响该效应。这些结果表明：尾核ＳＰ的抑胃效应系通过黑质、迷走背核经迷走神经所传出。     

Role of various amino acids on the modulation of dopamine release from nigro-striatal dopaminergic neurones

The effects of various transmitter amino-acids on the striatal release of 3H-dopamine (3H-DA) were investigated both in vivo in cat and in vitro in rat striatal slices. When applied to the substantia nigra of the anaesthetized cat by means of a push-pull cannula, GABA induced an increase followed by a transient decrease of 3H-DA release in the ipsilateral caudate nucleus; glycine reduced 3H-DA release under similar experimental conditions. When added to the superfusion medium of rat striatal slices, GABA, glutamate and glycine increased the release of the newly synthetized 3H-DA, suggesting that these amino-acids are also directly or indirectly involved in the presynaptic modulation of striatal DA release.     

The Effect of Mesencephalic Lesions on Tyramine and Dopamine in the Caudate Nucleus of the Rat

Abstract: The dopamine (DA)-containing nerve terminals in the caudate nucleus arise from cell bodies located in the substantia nigra (pars compacta), and it is possible that p-tyramine- and m-tyramine-containing neurons may also exist in this nucleus. We have studied the effects of unilateral electrolytic lesions of the pars compacta in rat on levels of DA, p-tyramine, m-tyramine, and homovanillic acid in the caudate nucleus after various survival times. At 12 and 24 h following lesioning the ipsilateral level of p-tyramine was significantly reduced compared with the contralateral side, whereas the concentrations of m-tyramine, DA, and homovanillic acid were significantly increased. Thus, in the short term, the lesion results in an increase in DA turnover, which is accompanied by an increase in m-tyramine levels and a decrease in p-tyramine levels. Similar changes occur following pharmacological treatments (chlorpromazine, d-amphetamine, l-DOPA) that increase DA turnover. At survival times of 2, 11, and 25 days, the ipsilateral concentrations of m-tyramine, DA, and homovanillic acid were reduced along with p-tyramine. These longer-term alterations in amine levels are most likely a consequence of degeneration of nigro-striatal axons. Placement of a lesion 1 mm dorsal to the usual position centering on the pars compacta produced different biochemical changes from those seen after the pars compacta lesion. One day following this lesion the concentration of p-tyramine was slightly reduced; DA was unaffected, but the concentration of m-tyramine was profoundly increased, even more so than after the pars compacta lesion. This could indicate the existence of specific m-tyramine-containing cell bodies located dorsal to the substantia nigra. The results suggest that p- and m-tyramine in the caudate nucleus originate from neurons in or close to the substantia nigra. The results in the short term following the lesion support the observation that there is an inverse relationship between p-tyramine concentration and DA turnover in the caudate nucleus.     

Effects of the unilateral nigral modulation of substance P transmission on the activity of the two nigro-striatal dopaminergic pathways.

The effects of the unilateral nigral application of substance P, 4–11 substance P, LHRH and of antibodies against substance P on the release of ³H-dopamine (³H-DA) in the two caudate nuclei (CN) and the two substantia nigrae (SN) were examined in halothane anaesthesized cats. The animals were implanted with four push-pull cannulae and ³H-DA was estimated in successive superfusate fractions during the continuous delivery of ³H-tyrosine. The unilateral nigral application of substance P or of 4–11 substance P resulted not only in a stimulation of ³H-DA release in the ipsilateral CN, but also in a reduction of the ³H-transmitter release from dendrites in the SN. As previously reported, the unilateral nigral application of antibodies against substance P induced opposite effects i.e. a decreased release of ³H-DA from nerve terminals associated to an increase of the ³H-amine release from dendrites. Surprisingly, in contrast to that previously observed during the unilateral nigral application of dopaminergic glycinergic or GABAergic agonists and antagonists neither substance P (or 4–11 substance P) nor antibodies against substance P affected the release of ³H-DA from nerve terminlas and dendrites of the contraletaral dopaminergic neurons. LHRH, a similar sized peptide was without effect on ipsilateral as well as on contralateral dopaminergic.     

Intracarotid 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Administration: Biochemical and Behavioral Observations in a Primate Model of Hemiparkinsonism

Cynomolgus monkeys received intracarotid injections of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to produce a chronic unilateral model of parkinsonism. Extensive dopamine (DA) depletion was observed in the caudate nucleus and putamen on the side ipsilateral to the injection and this was associated with contralateral tremor, rigidity, and bradykinesia. A dose of 1.25 mg of MPTP caused ipsilateral DA loss of 99.4% in the caudate nucleus, 99.8% in the putamen, and 74.2% in the nucleus accumbens. A dose of 2.5 mg caused ipsilateral DA depletion of 99.3% in the caudate nucleus, 99.5% in putamen, and 90.1% in the nucleus accumbens. The unilateral aspect of the lesion was dose sensitive, with the 2.5-mg dose causing bilateral asymmetric DA depletion. Tissue concentrations of serotonin were not affected by the toxin. These findings confirm that intracarotid injection of MPTP may produce a useful primate model of hemiparkinsonism that can be associated with selective unilateral DA depletion when the appropriate dose of toxin is used.     

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)     

Biotransformation of l-DOPA to Dopamine in the Substantia Nigra of Freely Moving Rats: Effect of Dopamine Receptor Agonists and Antagonists

Abstract: We investigated the effects of continuous intranigral perfusion of dopamine D1 and D2 receptor agonists and antagonists on the biotransformation of locally applied l -DOPA to dopamine in the substantia nigra of freely moving rats by means of in vivo microdialysis. The "dual-probe" mode was used to monitor simultaneously changes in extracellular dopamine levels in the substantia nigra and the ipsilateral striatum. Intranigral perfusion of 10 µ M l -DOPA for 20 min induced a significant 180-fold increase in extracellular nigral dopamine level. No effect of the intranigral l -DOPA administration was observed on dopamine levels in the ipsilateral striatum, suggesting a tight control of extracellular dopamine in the striatum after enhanced nigral dopamine levels. Continuous nigral infusion with the D1 receptor agonist CY 208243 (10 µ M ) and with the D2 receptor agonist quinpirole at 10 µ M (a nonselective concentration) attenuated the l -DOPA-induced increase in dopamine in the substantia nigra by 85 and 75%, respectively. However, perfusion of the substantia nigra with a lower concentration of quinpirole (1 µ M ) and the D1 antagonist SCH 23390 (10 µ M ) did not affect the nigral l -DOPA biotransformation. The D2 antagonist (−)-sulpiride (10 µ M ) also attenuated the l -DOPA-induced dopamine release in the substantia nigra to ∼10% of that of the control experiments. We confirm that there is an important biotransformation of l -DOPA to dopamine in the substantia nigra. The high concentrations of dopamine formed after l -DOPA administration may be the cause of dyskinesias or further oxidative stress in Parkinson's disease. Simultaneous administration of D1 receptor agonists with l -DOPA attenuates the biotransformation of l -DOPA to dopamine in the substantia nigra. The observed effects could occur via changes in nigral GABA release that in turn influence the firing rate of the nigral dopaminergic neurons.     

Differential regulation of somatodendritic and nerve terminal dopamine release by serotonergic innervation of substantia nigra

Nigrostriatal dopaminergic neurons release dopamine from dendrites in substantia nigra and axon terminals in striatum. The cellular mechanisms for somatodendritic and axonal dopamine release are similar, but somatodendritic and nerve terminal dopamine release may not always occur in parallel. The current studies used in vivo microdialysis to simultaneously measure changes in dendritic and nerve terminal dopamine efflux in substantia nigra and ipsilateral striatum respectively, following intranigral application of various drugs by reverse dialysis through the nigral probe. The serotonin releasers (+/-)-fenfluramine (100 micro m) and (+)-fenfluramine (100 micro m) significantly increased dendritic dopamine efflux without affecting extracellular dopamine in striatum. The non-selective serotonin receptor agonist 1-(m-chlorophenyl)-piperazine (100 micro m) elicited a similar pattern of dopamine release in substantia nigra and striatum. NMDA (33 micro m) produced an increase in nigral dopamine of a similar magnitude to mCPP or either fenfluramine drug. However, NMDA also induced a concurrent increase in striatal dopamine. The D2 agonist quinpirole (100 micro m) had a parallel inhibitory effect on dopamine release from dendritic and terminal sites as well. Taken together, these data suggest that serotonergic afferents to substantia nigra may evoke dendritic dopamine release through a mechanism that is uncoupled from the impulse-dependent control of nerve terminal dopamine release.     

Striatal dopamine levels after unilateral lesions of the substantia nigra: evidence for a contralateral decrease

Unilateral electrolytical and chemical (6-hydroxydopamine) lesions in the substantia nigra (SN) of rats were followed 7 days later by considerable bilateral decreases of neostriatal dopamine (DA) levels. Similarly, the DA content of the substantia nigra decreased not only ipsilaterally but contralaterally as well. Positive correlations were found between ipsi- and contralateral nigral DA levels, ipsi- and contralateral striatal DA and between the DA level of the SN and the striatum of the corresponding side both ipsi- and contralaterally to the lesion.     

Dopamine neuron transplants: electrophysiological unit activity of intrastriatal nigral grafts in freely moving cats

Fetal transplants of substantia nigra dopamine (DA)-containing neurons into the caudate nucleus in cats produced functional synaptic connections, as measured by behavioral analysis. Electrophysiological activity of single units from the intrastriatal nigral grafts revealed that these neurons displayed some of the characteristic electrophysiological parameters of DA neurons, i.e., long duration action potentials and tri-phasic waveform. However, these neurons discharged at a faster rate and never displayed the characteristic decremental burst pattern seen in intact, non-grafted animals. These data are the first electrophysiological recordings of grafted DA neurons in freely moving animals.     

Blockade of nociceptin/orphanin FQ transmission in rat substantia nigra reverses haloperidol-induced akinesia and normalizes nigral glutamate release

We recently showed that pharmacological blockade of nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptors located in the substantia nigra stimulates the nigrostriatal dopaminergic pathway and motor behavior (Marti et al. J. Neurosci. 2004, 24, 6659-6666). To investigate whether such motor-stimulating action was dependent on functional dopaminergic transmission, the selective NOP receptor peptide antagonist [Nphe1,Arg14,Lys15]N/OFQ-NH2 (UFP-101) was microinjected into the substantia nigra reticulata of rats made cataleptic by systemic haloperidol administration. UFP-101 reduced haloperidol-induced akinesia as measured by immobility time in the bar test. UFP-101 also induced contralateral turning in cataleptic rats. To investigate the mechanisms involved in the anti-akinetic action of UFP-101, nigral glutamate release was monitored by microdialysis technique. The anti-akinetic action of UFP-101 correlated with normalization of nigral glutamate release, previously elevated by haloperidol injection. We conclude that endogenous N/OFQ in the substantia nigra sustains akinesia generated by impaired DA transmission and subthalamic nucleus overactivation. NOP receptor antagonists may be beneficial in the symptomatic therapy of parkinsonism, via normalization of subthalamonigral glutamatergic transmission.     

D1 and D2 Dopamine Receptors in Human Substantia Nigra: Localization and the Effect of Aging

D1 and D2 receptor densities in human substantia nigra were examined by use of the specific binding of, respectively, [3H]SCH 23390 [R(+)-7-chloro-8-hydroxy-3-[3H]methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3- benzazepine] and [3H]spiperone. A unilateral loss of striato- and pallidonigral pathways by an infarction (n = 4) had no effect on the ipsilateral nigral D2 receptors, but reduced the ipsilateral nigral D1 receptors by 48-60% compared with the intact side. These data suggest that a substantial fraction of D1 receptors in human substantia nigra is located on terminals of striato- and/or pallidonigral neurons, whereas D2 receptors are confined to intrinsic nigral cells. We also examined the effect of aging on the D1 and D2 receptors in substantia nigra obtained from 25 postmortem human brains (age range 19-88 years). The densities of both receptor types were not affected by the aging process. Since nigrostriatal dopaminergic neurons degenerate with aging, these results suggest either that the nigral D2 receptors are up-regulated in response to a progressive depletion of dopamine in the substantia nigra or that, in contrast to the rat, they are not located on dopaminergic neurons.     

Effect of (-)-cathinone, a khat leaf constituent, on dopaminergic firing and dopamine metabolism in the rat brain

The effect of (-)-cathinone (CAT), an alkaloid from khat leaves, on brain dopamine (DA) metabolism and on the firing rate of nigral DA neurons was studied in rats, in comparison with that of d-amphetamine. Like d-amphetamine, CAT (8-40 mg/kg i.p.) decreased DOPAC levels in the caudate nucleus, nucleus accumbens and frontal cortex, without modifying DA concentrations. CAT showed approximately one fifth of the potency of d-amphetamine in this effect. CAT, injected i.v. to unanesthetized, paralyzed rats, inhibited the firing rate of DA neurons in the substantia nigra, pars compacta, showing a similar potency to that of d-amphetamine in this respect. CAT-induced inhibition of dopaminergic firing was reversed by haloperidol.     

Evoked Release of Proteins from Central Neurons In Vivo

Push-pull cannulae were implanted in both substantiae nigrae and caudate nuclei of the halothane-anesthetized cat. The release of total protein, acetylcho-linesterase, and nonspecific cholinesterases was examined. Following direct application of potassium to one substantia nigra, changes occurred in the local release of total protein and acetylcholinesterase, but not nonspecific cholinesterases; changes also were observed in both caudate nuclei and the contralatera/ substantia nigra. The local evoked release of acetylcholinesterase and of total protein differed in the extent to which they were calcium-dependent. Control studies suggest that release of these compounds, both spontaneous and evoked, is related, at least in part, to neuronal activity. The significance of the neuronal release of proteins is discussed.     

Effects of dynorphin (1-8) on movement: non-opiate effects and structure-activity relationship

Cell bodies in the head of the caudate nucleus that synthesize prodynorphin peptides form a substantial projection to the substantia nigra pars reticulata (SNR). The discovery of this pathway suggested an involvement of prodynorphin products in motor control. The effects of unilateral nigral microinjections of prodynorphin products were tested in an in vivo circling model. Dynorphin (1-8), dynorphin (1-7), dynorphin (1-6), dynorphin (2-17) (des-Tyr-dynorphin), and Leu-enkephalin induced spontaneous contralateral circling at 20 nmol doses. The effect of dynorphin (1-8) was dose dependent and was not blocked by pretreatment with naloxone or WIN 44,441-3. These findings clearly demonstrate the dynorphinergic involvement in nigral motor control which may consist of an opioid and a non-opioid component.     

Behavioral and biochemical assessment of time-related changes in globus pallidus and striatal dopamine induced by intranigrally administered neurotensin

Microinjection of neurotensin (NT; 2 and 5 μg) into the substantia nigra zona compacta caused an increase in dopamine (DA) and DA metabolites in the rodent globus pallidus and striatum which persisted for at least 20 hours after peptide administration. Similar NT treatments given unilaterally into the nigra caused circling away from the injected side in amphetamine-pretreated rats, but were without effect when microinjected into saline-pretreated animals. Circling also occurred when the animals were given amphetamine 20 hours after intranigral NT administration. Contralateral rotation was observed with unilateral intranigral injections of gamma-hydroxybutyric acid (GHB; 400 μg) or with lower intranigral GHB doses (250 μg) in amphetamine-pretreated animals. The effects of GHB and NT differed in the manner in which the animals rotated as well as in the profile of DA and DA metabolite changes induced by these drugs. These studies indicated that: (1) dopaminergic functions of the globus pallidus are influenced, like the striatum, by manipulations of the substantia nigra; (2) NT and GHB likely act via different mechanisms to effect nigral dopamine-containing cells; and (3) NT was capable of inducing changes in dopamine neurons which had long term consequences.     

Subcellular distribution of dopamine in substantia nigra of the rat brain: effects of gamma-butyrolactone and destruction of noradrenergic afferents suggest formation of particles from dendrites.

Abstract— The subcellular distribution of dopamine (DA) in substantia nigra from individual male rats was studied with a fractionation procedure on microscale. After differential centrifugation the distribution of DA coincided with that of noradrenaline (NA) which can serve as a marker for synaptosomes in this area. The proportion of DA/NA concentrations was about 1–2 in most fractions. Sixty per cent of nigral DA was found in P₂ (17,000 g). When P, was layered on a continuous density gradient, DA and NA peaked at the density of 1.0–1.2 M-sucrose. Since DA-containing particles covered a relatively broad range on this gradient, particles between 0.7 and 1.3 M-sucrose were collected with a discontinuous density gradient. Sixty per cent of DA from P₂, was found in this subfraction. The particles containing DA could have been derived from dendrites or axon collaterals of nigrostriatal neurones or represent precursor DA in noradrenergic (NA) terminals. The role of collaterals was investigated by comparing the effect of γ-butyrolactone (GBL, 750 mg/kg, 1 h) on DA concentrations in subcellular fractions from substantia nigra and caudate-putamen. In caudate-putamen, GBL produced a marked increase of DA in total homogenates and subcellular fractions except P₃, whereas DA concentrations remained unchanged in all fractions from substantia nigra. This speaks against a contribution from DA terminals. The proportion of DA contained as precursor in NA terminals was analysed after destruction of the NA input to substantia nigra by two methods. A single injection of 6-hydroxydopamine into the IV ventricle decreased nigral NA by 5574, DA only by 17%. Unilateral electrolytic lesions in the pontine tegmentum affected NA concentrations in homogenates and fraction P₂ of the ipsilateral substantia nigra to a much greater extent than DA. From the results obtained with the two approaches, it is estimated that precursor DA in particulate fractions does not exceed 10%. Our observations indicate that dendrites of the DA neurones in substantia nigra can form particles which behave like synaptosomes on density gradients centrifugation; they may be termed ‘dendrosomes’. According to the proportion of DA found in the particulate fractions at least 4040% of nigral DA appear to be localised in dendrites.     

AN ADAPTATION OF THE PUSH-PULL CANNULA METHOD TO STUDY THE IN VIVO RELEASE OF [3H]DOPAMINE SYNTHESIZED FROM [3H]TYROSINE IN THE CAT CAUDATE NUCLEUS: EFFECTS OF VARIOUS PHYSICAL AND PHARMACOLOGICAL TREATMENTS

Abstract— The release of [³H]dopamine ([³H]DA) continuously synthesized from l-[3,5–³H]tyrosine from the caudate nucleus of the cat was estimated in halothane anaesthetized or‘encéphale isolé’animals. For this purpose, an improved superfusion cannula, avoiding tissue damage, was used. The best localization for the tip of the superfusion cannula was found first by determining the topographical distribution of endogenous DA within the caudate nucleus. A rostro-caudal heterogenous distribution of the transmitter was detected. In perfusion experiments, l-[3,5–³H]tyrosine was introduced continuously at a rate of 33μl/min. [³H]DA was the only catecholamine found in serial 15 min fractions as revealed by cochromatography. The spontaneous release of [³H]DA was greater in anaesthetized than in ‘encéphale isolé’ cats; it represented 150 and 100 times the blank value, respectively. Depolarization by K⁺ (30 mm) applied locally in the striatum or by electrical or mechanical stimulation of the substantia nigra caused a transitory increase in [³H]DA release. Conversely, a decrease in nerve activity induced by tetrodotoxin (5 × 10^?-⁷ m) or by electrocoagulation of the substantia nigra was associated with a decline in the amounts of [³H]DA in superfusates. A temporary reduction in [³H]DA release could also be obtained by a short-lasting cooling block of the substantia nigra. As expected, d-amphetamine (10^?-⁵ m) and benzotropine(10^?-⁷ m) added to the superfusing medium increased [³H]DA release. These pharmacological results, as well as the changes in [³H]DA release observed after various manipulations of the activity of dopaminergic neurones, confirms the validity and the high sensitivity of this approach.     

Differential effect of acute and chronic ethanol on dopamine metabolism in frontal cortex,caudate nucleus and substantia nigra

Acute oral administration of ethanol (3.2g/kg) to normal rats increased DOPAC levels and DOPA formation in the caudate nucleus but had no effect in the substantia nigra and frontal cortex and failed to modify dopamine (DA) levels in any of the above brain areas. Complete tolerance to the stimulant effect on DOPA formation developed after chronic ethanol administration (3.2g daily for 60 days). In chronically treated rats, 24 hrs after ethanol withdrawal, DA levels in the frontal cortex were 60% higher than in controls and were unchanged in the substantia nigra and caudate nucleus as were DOPAC levels in all areas studied. At this time, the administration of ethanol caused a long-lasting depletion of DA and a parallel increase of DOPAC levels in all areas analyzed. The results indicate that acute and chronic ethanol release DA stores but, in the acute condition, DA depletion is prevented by increased synthesis.