Release of dopamine in the ventral tegmental area of rat

In this preliminary report we showed that 3,4-dihydroxyphenylacetic acid (DOPAC), the major metabolite of dopamine (DA), is present in the ventral tegmental area. This finding indicates that in the ventral tegmental area, which contains the cell bodies of dopaminergic neurons of the mesocortical and mesolimbic DA systems, DA may be released by a mechanism similar to that operating in the nerve endings. However, haloperidol, which increases DOPAC levels in the substantia nigra, failed to do so in the ventral tegmental area. The results support the contention that DA neurons in the ventral tegmental area have distinctive features from nigral DA neurones.     

Alpha-MSH injected into the substantia nigra or intraventricularly alters behavior and the striatal dopaminergic activity

Rats were injected with 1 μg of alpha-melanocyte stimulating hormone (α-MSH) into the third ventricle and locally in the ventral tegmental area and in different regions of the substantia nigra. The modifications produced on grooming behavior and locomotion as well as on the dopamine content of the nucleus accumbens and the caudate putamen, were studied. Both intraventricular peptide administration and microinjections into the ventral tegmental area induced excessive grooming and a significant increase of the locomotor activity. The dopamine content of the nucleus accumbens and caudate putamen was markedly reduced. Injections of the peptide into the substantia nigra pars compacta failed to induce excessive grooming but did provoke a slight increase in locomotor activity and a smaller change in caudate dopamine content than that observed by injections in the ventral tegmental area or in the third ventricle. Dopamine levels in the nucleus accumbens were not changed. Finally, the injections of α-MSH into the lateral substantia nigra did not produce either biochemical or behavioral changes.The results suggests that α-MSH can modify, directly or indirectly, the striatal dopaminergic activity and that the behavioral alterations observed such as excessive grooming, could be mediated by the activation of the dopamine cells from the ventral tegmental area, that in turn may provoke a significative release of dopamine at the caudate putamen nucleus as well as in nucleus accumbens.     

Different Effects of Opiate Withdrawal on Dopamine Turnover,Uptake, and Release in the Striatum and Nucleus Accumbens

The purpose of these experiments was to further characterize changes in dopaminergic function that follow withdrawal from chronic opiate treatment. Withdrawal after treatment to a maximum dose of 120 mg/kg of morphine did not alter dopamine concentrations in the substantia nigra, ventral tegmental area, striatum, or nucleus accumbens; but did decrease concentrations of DOPAC and the ratio of DOPAC to dopamine in the lateral striatum and nucleus accumbens. Uptake of tritiated dopamine was diminished for withdrawn slices obtained from the striatum with no effect observed for tissue from the nucleus accumbens. Deficits of in vitro release of tritiated dopamine also occurred following withdrawal, with the nucleus accumbens being sensitive to dependence produced by a lower dose of morphine. In conclusion, opiate withdrawal produces a complex pattern of effects on dopaminergic function that is specific for the striatum and nucleus accumbens.     

Habenular modulation of dynorphinergic systems in rat ventral mesencephalon

Bilateral electrolytic lesion of the striatonigral pathways (which convey massive afferents to the substantia nigra) caused a marked lowering of alpha-neo-endorphin (alpha-Neo) and dynorphin A(1-8) [Dyn A(1-8)] levels in the substantia nigra without affecting the alpha-Neo content in the ventral tegmental area. Moreover, unilateral infusion of the axon sparing neurotoxin ibotenate into the striatum, but not into the substantia nigra, decrease these two opioid peptides in the substantia nigra on the side ipsilateral to the lesion, failing to modify the alpha-Neo levels in the ventral tegmental area. Bilateral electrolytic lesion of the habenula augmented alpha-Neo content in the substantia nigra and ventral tegmental area at 8-30 days postlesion without affecting the nigral Dyn A(1-8). These results add further support to the view that alpha-Neo- and Dyn A(1-8)-containing neurons projecting to the substantia nigra originate in the striatum and descend through striatonigral pathways. The present data provide evidence that the habenula may participate in the regulation of the activity of alpha-Neo-immunoreactive neurons in the substantia nigra and ventral tegmental area.     

Regulation of Rat Dopamine Transporter mRNA and Protein by Chronic Cocaine Administration

This study describes a direct comparison of dopamine transporter (DAT) mRNA and protein, as well as its binding sites, in tissue from the same animals after chronic cocaine administration. Rats were treated twice daily with 25 mg/kg cocaine or with saline. After 8 days of cocaine administration, changes in DAT mRNA levels in the substantia nigra pars compacta and ventral tegmental area were measured by in situ hybridization, and DAT protein in the striatum was quantified by immunoblotting. Whereas chronic cocaine treatment significantly reduced levels of DAT mRNA in the substantia nigra pars compacta and ventral tegmental area as compared with vehicle-treated controls, cocaine treatment did not alter DAT protein levels in the striatum. Furthermore, the density of DAT binding sites was also measured in the striatum by quantitative autoradiography using two DAT radioligands, 33-(4-[125I]iodophenyl)tropane-2-carboxylic acid methyl ester ([125I]RTI-55) and [3H]propanoyl-3beta-(4-tolyl)tropane ([3H]PTT). Similar to the results of immunoblotting of DAT protein, [1251]RTI-55 and [3H]PTT binding site levels also remained unaltered. These results indicate a dissociation in the regulation of DAT mRNA and its protein levels as a result of cocaine administration in rats. This study also indicates that the DAT ligands [3H]PTT and [125I]RTI-55 provide an accurate assessment of DAT protein levels.     

LOCALIZATION OF GABAERGIC, CHOLINERGIC AND AMINERGIC STRUCTURES IN THE MESOLIMBIC SYSTEM

Abstract— The localization of cholinergic, GABAergic and aminergic structures in the 'mesolimbic' system has been discussed from studies on the topographical distribution of choline acetyltransferase, glutamate decarboxylase and aromatic amino acid decarboxylase in normal rat brain and in brains hemitransected at the level of globus pallidus. The structures analysed included nucleus accumbens, olfactory tubercle, septum, medial forebrain bundle, striatum, substantia nigra, ventral tegmental area and nucleus interpeduncularis.
Choline acetyltranferase was highly concentrated in the nucleus interpeduncularis, but it did also exhibit considerable activity in the nucleus accumbens, the olfactory tubercle and the striatum. The activities did not change after hemitransection. Aromatic amino acid decarboxylase was highly concentrated in the ventral tegmental area, but high activities were also found in the striatum, the nucleus accumbens, the olfactory tubercle and the pars compacta of the substantia nigra. The activity decreased in all areas rostral to the hemitransection. Glutamate decarboxylase was highly concentrated in the dopamine innervated regions, moreso in the limbic structures than in the striatum. Much higher activity was found in the substantia nigra than in the ventral tegmental area. After hemitransection the activity in the substantia nigra was decreased whereas in the ventral tegmental area it was unchanged. Our results thus suggest that dopaminergic cells in the ventral tegmental area do not receive GABAergic fibres from the terminal regions of the ascending dopaminergic fibres. In addition, we found a very high concentration of glutamate decarboxylase in a region traversed by the rostral medial forebrain bundle. Here the activity was mainly confined to the paniculate fraction, probably the synaptosomes. This fraction also displayed a very active high affinity uptake of y-aminobutyric acid.     

Effects of l-Methyl-4-Phenyl-l,2,3,6-Tetrahydropyridine in the Dog: Effect of Pargyline Pretreatment

Adult beagle dogs of either sex were injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-HCl (2.5 mg/kg, i.v.) alone or after pretreatment with pargyline (5.0 mg/kg, s.c., twice), with pargyline alone, or were uninjected. Groups were killed 2 h, 3 weeks, or 3 months after injection, and several brain areas were assayed for biogenic amines and their synthetic and degradative enzymes. MPTP caused a massive and permanent loss of striatal dopamine, tyrosine hydroxylase, and 3,4-dihydroxyphenylalanine decarboxylase activities and the loss of cells within the substantia nigra pars compacta. Dopamine and norepinephrine also were depleted to various degrees in cortex, olfactory bulb, and hypothalamus; however, dopamine beta-hydroxylase activity in cortex was normal. There was no cell loss in the ventral tegmental area or locus ceruleus. The activities of monoamine oxidase (MAO)-A and MAO-B in cortex and caudate were not affected by MPTP. Despite a permanent loss of the nigrostriatal system, the dogs exhibited only a transient hypokinesia lasting 1-2 weeks. Pargyline pretreatment prevented the loss of striatal dopamine and cells from the substantia nigra, but did not prevent a prolonged but reversible decrease in the concentration of dopamine metabolites. It is argued that this apparent inhibition of MAO is due not to suicide inactivation of the enzyme by MPTP, but to reversible inhibition by accumulation of the pyridinium metabolite, 1-methyl-4-phenylpyridinium, selectivity in aminergic terminals.     

Botulinum A Like Type B and Tetanus Toxins Fulfils Criteria for Being a Zinc-Dependent Protease

Abstract: Iron is abnormally accumulated in the substantia nigra pars compacta of patients with Parkinson's disease (PD). Because neuronal and glial iron uptake seems to be mediated by the binding of ferrotransferrin to a specific high-affinity receptor on the cell surface, the number of transferrin receptors could be altered in this disease. The regional distribution of specific binding sites for human ¹²⁵I-diferric transferrin has been studied in the mesencephalon, on cryostat-cut sections from autopsy brains of control subjects and parkinsonian patients by in vitro autoradiography. Densities of binding sites were highest in the central gray substance (˜10 fmol/mg of tissue equivalent), intermediate in the catecholaminergic cell group A8, superior colliculus, and ventral tegmental area, and almost nonexistent in the substantia nigra. The density of ¹²⁵I-transferrin binding sites was not significantly different between parkinsonian and control brains in any region analyzed. These results show that in the mesencephalon the regional density of transferrin binding sites is lowest in the dopaminergic cell groups, which are the most vulnerable to PD, and suggest that iron does not accumulate through an increased density of transferrin receptors at the level of the substantia nigra.     

Effects of methamphetamine on arterioles of rat caudate nucleus and midbrain

No differences in arteriolar metabolic profiles from rat caudate nucleus, ventral tegmental area or substantia nigra were observed between saline-control and methamphetamine HCl-treated (20 mg/kg, i.p. twice daily for 10 consecutive days) animals. Arterioles from the above regions of forebrain and midbrain are metabolically active vessels with a capacity for aerobic and anaerobic metabolism. These results suggest that a high dose of methamphetamine does not alter cerebral arteriolar metabolism in the areas examined.     

Acute reduction of brain substance P induced by nicotine

Ten minutes after a single injection of 0.8 mg/kg nicotine SC (free base) the level of substance P-like immunoreactivity (SPLI) was reduced by 61–73% in rat caudate-putamen, nucleus accumbens, and olfactory tubercle, with smaller and not significant reductions in the frontal cortex, substantia nigra, and ventral tegmental area. The nicotinic receptor antagonist mecamylamine (1.0 mg/kg IP) prevented the reductions in SPLI. The rapidity and the degree of the changes in SPLI after nicotine exceed those previously reported for other agents and implicate substance P neurotransmission as a major component of nicotinic action.Preliminary data were presented at the 17th annual meeting of the American Society for Neurochemistry, Montreal, 1986 (1).     

Effects of Intranigral Substance P and Neurokinin A Injections on Extracellular Dopamine Levels Measured with Microdialysis in the Striatum and Frontoparietal Cortex of Rats

Extracellular levels of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), in the striatum and frontoparietal (sensorimotor) cortex in halothane-anesthetized rats were analyzed simultaneously using in vivo microdialysis. Basal DA levels, measured from the microdialysis perfusate, were 6.4 +/- 0.8 nM (n = 15) in the striatum and 0.9 +/- 0.1 nM (n = 15) in the frontoparietal cortex. Subcutaneous injections of d-amphetamine (2 mg/kg) increased DA levels 10-fold in the striatum and fivefold in the cortex. Injections of substance P (0.07 nmol/0.2 microliters) into the substantia nigra pars reticulata (SNR) increased DA and DOPAC levels approximately 30% in the ipsilateral striatum and approximately 50% in the ipsilateral frontoparietal cortex. Injections of neurokinin A (0.09 nmol/0.2 microliter) into the SNR increased DA and DOPAC levels approximately 30% in the ipsilateral striatum but did not significantly affect DA levels in the ipsilateral frontoparietal cortex, although DOPAC levels were increased by approximately 50%. It is suggested that striatal and cortical DA release is regulated differently by nigral substance P and neurokinin A terminals.     

Chronic treatment with high doses of haloperidol fails to decrease the time course for the development of depolarization inactivation of midbrain dopamine neurons

Using extracellular single unit recording techniques, we investigated the effects produced by chronic treatment with high doses of haloperidol (CHAL, 5 mg/kg/day, s.c.) on midbrain dopamine (DA) neuronal activity. This regimen of HAL treatment produced a time-dependent reduction in the number of spontaneously active DA neurons. Additionally, this dose regimen induced an irregular firing pattern in many of the remaining active DA neurons in both the ventral tegmental area (A10) and substantia nigra pars compacta (A9) regions. These effects were comparable to those obtained previously in rats treated chronically with lower doses of HAL (0.5 mg/kg/day, s.c.). However, there was a greater decrease in the number of spontaneously active DA cells detected in rats treated with high doses of HAL for three weeks compared to those receiving the low doses. On the other hand, higher doses of apomorphine (200 micrograms/kg, i.v.) were required to reverse both the reduction of DA activity and irregular discharge pattern in rats treated chronically with high doses of HAL. In conclusion, the results of the present study substantiate the view that CHAL-induced depolarization inactivation (DI) of DA neurons is a time-dependent process and chronic treatment with high doses of HAL did not shorten the time course required for the development of DI on the majority of midbrain DA neurons.     

Changes in local cerebral glucose utilization associated with Parkinson's syndrome induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the primate

The quantitative 2-[14C]deoxyglucose autoradiographic method was used to map the pattern of alterations in local cerebral glucose utilization associated with the Parkinsonian syndrome induced by the administration of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), to rhesus monkeys. Monkeys treated with the neurotoxin exhibited both behavioral symptoms (e.g. akinesia, rigidity, flexed posture, and eyelid closure) and neuropathological changes (degeneration of the cells of the substantia nigra pars compacta) that closely paralleled those in human Parkinson's disease. Glucose utilization was significantly reduced in the pars compacta of the substantia nigra and in the subthalamus, and increased in the external segment of the globus pallidus. Outside the basal ganglia reductions in glucose utilization were limited to the mediodorsal nucleus of the thalamus, frontal eye fields, and ventral tegmental area. The results of these studies indicate that the profound functional and behavioral deficits in MPTP-induced Parkinson's syndrome are the consequences of highly selective functional changes in a few cerebral structures, mainly within the basal ganglia.     

Haloperidol but Not Clozapine Increases Neurotensin Receptor mRNA Levels in Rat Substantia Nigra

Abstract: We examined the effects of chronic (2 weeks) treatment with a typical neuroleptic, haloperidol (1 mg/kg, s.c.), and an atypical neuroleptic, clozapine (20 mg/kg, s.c.), on neurotensin receptor (NTR) mRNA levels by in situ hybridization histochemistry. Quantitative OD analysis showed haloperidol-induced NTR mRNA levels in the substantia nigra/ventral tegmental area (SN/ VTA) 110% over control levels (significant difference from the control, p < 0.05). In contrast, the same analysis applied to the sections from clozapine-treated animals showed no significant change in NTR mRNA levels compared with matched control sections ( p > 0.05). Thus, chronic treatment with haloperidol but not clozapine resulted in elevated levels of NTR mRNA within the SN/VTA. These results suggest that the high incidence of extrapyramidal side effects of typical neuroleptics could result from changes in NTR expression in the SN/VTA.     

Short- and Long-Term Alterations of Gene Expression in Limbic Structures by Repeated Electroconvulsive-Induced Seizures

Rats were submitted to a series of 10 daily electroconvulsive shocks (ECS). A first group of animals was killed 1 day after the last seizure and a second group 30 days later. Tyrosine hydroxylase (TH) activity was measured using an in vitro assay in the nucleus caudatus, anterior cortex, amygdala, substantia nigra, ventral tegmental area, and locus ceruleus. The mRNA corresponding to this enzyme (TH-mRNA) was evaluated using a cDNA probe at the cellular level in the ventral tegmental area, substantia nigra, and locus ceruleus. Met-enkephalin (MET)-immunoreactivity and the mRNA coding for the preproenkephalin (PPE-mRNA) were assayed in striatum and the central nucleus of the amygdala. The day after the last ECS an increase of TH activity was observed in the ventral tegmental area, locus ceruleus, and substantia nigra in parallel with a similar increase in the amygdala and striatum; in the anterior cortex TH activity remained unchanged. TH-mRNA was increased in the locus ceruleus, evidencing the presence in this structure of a genomic activation. The amounts of MET and PPE-mRNA were unaffected in the striatum but increased in the amygdala. Thirty days after the last ECS we observed a decrease of TH activity in the amygdala and of TH-mRNA amount in the ventral tegmental area. In the locus ceruleus TH-mRNA remained higher in treated animals than in controls whereas TH activity returned to control levels. These results demonstrate that a series of ECS induces an initial increase of the activity of mesoamygdaloid catecholaminergic neurons followed by a sustained decrease through alterations of TH gene expression which could mediate the clinical effect of the treatment.     

Effect of TRH analog (DN-1417) on tyrosine hydroxylase activity in mesocortical, mesolimbic and nigrostriatal dopaminergic neurons of rat brain

Tyrosine hydroxylase (TH) was assayed in eight regions of rat brain following repeated treatment with a TRH analog, DN-1417 (gamma-butyrolactone-gamma-carbonyl-histidyl-prolinamide). Repeated DN-1417 treatment (20 mg/kg/day, IP) for 7 days increased TH activity in the ventral tegmental area and decreased in the prefrontal cortex polar, medial and lateral fields and olfactory tubercles. No significant change in TH activity was found in the nucleus accumbens, striatum and substantia nigra. Kinetic analysis showed that the increased TH activity in the ventral tegmental area was due to an increase in Vmax, but not a change in the apparent Km of TH for a cofactor, 6-methyl-tetrahydropteridine. When TH was assayed at a suboptimal pH and in the presence of a subsaturating cofactor, the striatal TH was activated significantly after DN-1417. In the prefrontal cortex medial field, nucleus accumbens and olfactory tubercles, TH activity assayed under the suboptimal condition was not modified by DN-1417 treatment. These results suggest an intimate involvement of central dopaminergic systems in the actions of DN-1417.     

Messenger RNA encoding the D2 dopaminergic receptor detected by in situ hybridization histochemistry in rat brain

A 30 base synthetic oligonucleotide probe was used to detect the mRNA encoding the rat D2 dopaminergic receptor. On Northern analysis, the probe identified a single species of mRNA of approximately 2.9 kb, present at highest levels in the striatum but also found in the brainstem, neocortex and diencephalon. On sections, neurons containing high levels of the mRNA were detected in the striatum, the substantia nigra pars compacta and the ventral tegmental area. Lower levels of signal were seen over neurons in the hypothalamus, the frontal neocortex, and the globus pallidus.     

Micro topography of Tyrosine Hydroxylase, Glutamic Acid Decarboxylase, and Choline Acetyltransferase in the Substantia Nigra and Ventral Tegmental Area of Control and Parkinsonian Brains

Tyrosine hydroxylase (TH), glutamic acid decarboxylase (GAD), and choline acetyl transferase (CAT) were used as markers for catecholamine, gamma-aminobutyric acid, and acetylcholine containing neurons in human mesencephalon. Their rostrocaudal, mediolateral, and dorsoventral distribution was investigated within the substantia nigra pars compacta (SNC) and pars reticulata (SNR) and in the ventral tegmental area (VTA). TH activity was highest in the caudal, medial, and ventral SNC and in the middle of VTA medio-ventrally. The enzyme activity in SNR was low and uniformly distributed. In SNC as well as SNR, GAD activity was high and greater laterally and in the middle of the rostro-caudal extent. No particular pattern of distribution was observed in VTA. an area with low GAD content. In the substantia nigra, CAT activity was low. A characteristic medio-ventral distribution with a peak of high enzyme activity in the middle of the rostrocaudal extent was observed. In VTA, enzyme levels were high and also concentrated medio-ventrally and in the middle of the area. In parkinsonian brains, the distribution of TH was uniformly affected throughout the rostro-caudal extent. In VTA the enzyme activity was not as reduced as in SNC and SNR; the CAT pattern was only disrupted in a very localized part of SNC but not in SNR and VTA. In all three areas, GAD activity was reduced to a uniformly low distribution.     

左旋千金藤啶碱对不同脑区DA更新率的影响

应用ＨＰＬＣ－ＥＣＤ测定ＤＡ更新率（ＤＯＰＡＣ／ＤＡ）,证明（－）ＳＰＤ对黑质－纹状体、中脑－边缘系统、下丘脑－垂体ＤＡ神经系统的ＤＡ含量影响不明显,却显著增加ＤＯＰＡＣ含量,并显著加强这些脑区的ＤＡ更新率,这可能是通过末梢的ＤＡ自身受体实现的。但（－）ＳＰＤ既不显著影响中脑－前额叶和中脑－扣带回的ＤＡ含量,也不影响其中ＤＯＰＡＣ含量,表明它不影响这些脑区ＤＡ更新率。这可能是由于皮层ＤＡ系统神经末     

Biochemistry of Somatodendritic Dopamine Release in Substantia Nigra: An In Vivo Comparison with Striatal Dopamine Release

Abstract: The somatodendritic release of dopamine in substantia nigra previously has been suggested to be nonvesicular in nature and thus to differ from the classical, exocytotic release of dopamine described for the dopaminergic nerve terminal in striatum. We have compared the effects of reserpine, a compound that disrupts vesicular sequestration of monoamines, on the storage and release of dopamine in substantia nigra and striatum of rats. Reserpine administration (5 mg/kg, i.p.) significantly decreased the tissue level of dopamine in substantia nigra pars reticulata, substantia nigra pars compacta, and striatum. In these brain areas, reserpine-induced reductions in tissue dopamine level occurred within 2 h and persisted at 24 h postdrug. In vivo measurements using microdialysis revealed that reserpine administration rapidly decreased the extracellular dopamine concentration to nondetectable levels in substantia nigra as well as in striatum. In both structures, it was observed that reserpine treatment significantly attenuated the release of dopamine evoked by a high dose of amphetamine (10 mg/kg, i.p.) given 2 h later. In contrast, dopamine efflux in response to a low dose of amphetamine (2 mg/kg, i.p.) was not altered by reserpine pretreatment either in substantia nigra or in striatum. The present data suggest the existence, both at the somatodendritic and at the nerve terminal level, of a vesicular pool of dopamine that is the primary site of transmitter storage and that can be displaced by high but not low doses of amphetamine. The physiological release of dopamine in substantia nigra and in striatum is dependent on the integrity of this vesicular store.