Striatal DA Levels Research Articles

Neuroprotection of rapamycin in lactacystin-induced neurodegeneration via autophagy enhancement

The ubiquitin–proteasome system (UPS) and the autophagy-lysosomal pathway (ALP) are the two most important cellular mechanisms for protein degradation. To investigate the role of autophagy in reversing neuronal injury, the proteasome inhibitor lactacystin was used to cause UPS dysfunction in differentiated PC12 cells and in C57BL/6 mice and rapamycin was used as an autophagy enhancer. The results showed that rapamycin pre-treatment attenuated lactacystin-induced apoptosis and reduced lactacystin-induced ubiquitinated protein aggregation in differentiated PC12 cells. The observed protection was partially blocked by the autophagy inhibitor 3-methyladenine. Furthermore, post-treatment of mice with rapamycin significantly attenuated lactacystin-induced loss of nigral DA neurons and the reduction of striatal DA levels. The lactacystin-induced high molecular ubiquitinated proteins were also attenuated by rapamycin treatment in vivo. In addition, as a chemical compound, rapamycin caused an increase of bcl2 protein level and blocked the release of cytochrome c from mitochondria to cytosal. We concluded that the neuroprotective effect of rapamycin is partially mediated by autophagy enhancement through enhanced degradation of misfolded proteins and autophagy enhancement may be considered to be a promising strategy to prevent diseases associated with misfolded/aggregated proteins, such as Parkinson's disease.

7‐Nitroindazole Protects Striatal Dopaminergic Neurons against MPP+‐Induced Degeneration

The neuropathological hallmark of Parkinson's disease (PD) is the selective degeneration of dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNc). In this study, using a microdialysis technique, we investigated whether an inhibitor of neuronal nitric oxide synthase (nNOS), 7-nitrindazole (7-NI), could protect against DAergic neuronal damage induced by in vivo infusion of 1-methyl-4-phenylpiridinium iodide (MPP(+)) in freely moving rats. Experiments were performed over 2 days in three groups of rats: (a) nonlesioned, (b) MPP(+)-lesioned, and (c) 7-NI pretreated MPP(+)-lesioned rats. On day 1, control rats were perfused with an artificial CSF, while 1 mM MPP(+) was infused into the striatum for 10 min in the other two groups. The infusion of the MPP(+) produced a neurotoxic damage of the SNc DA neurons and increased striatal DA levels. On day 2, 1 mM MPP(+) was reperfused for 10 min into the striata of each rat group and DA levels were measured as an index of neuronal cell integrity. The limited rise of DA following MPP(+) reperfusion in the MPP(+)-lesioned rats was due to toxin-induced neuronal loss and was reversed by pretreatment with 7-NI (50 mg/kg, intraperitoneally) on day 1, indicating a neuroprotective effect by inhibiting NO formation. These results indicate that neuronally derived NO partially mediates MPP(+)-induced neurotoxicity. The similarity between the MPP(+) model and PD suggests that NO may play a significant role in its etiology.

Potential neuroprotective effect of low dose whole-body γ-irradiation against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic toxicity in C57 mice

Low dose whole-body γ-irradiation is recently reported to confer neuroprotection against optic nerve crush and contusive spinal cord injury. Here, we extended the study and investigated whether the pretreatment of a single low dose whole-body γ-irradiation may have a preventive effect in MPTP-induced model of PD. One week after the last MPTP treatment, HPLC determination of striatal dopamine and immunostaining for tyrosine hydroxylase (TH), CD11b and GFAP to detect dopamine neurons and associated glial reaction in the substantia nigra pars compacta (SNpc) were performed. MPTP treatment reduced striatal DA levels significantly; nigral TH immunoreactivity was reduced to a lower extent; robust gliosis was also observed in SNpc. We found that 3.5 Gy irradiation but not 5.5 Gy restores the level of DA and its metabolites decreased by MPTP. However, there was no difference in the number of TH positive neurons between 3.5 Gy irradiated and saline treated mice after MPTP treatment. Irradiation also did not have obvious influence on microgliosis and astroglial reaction induced by MPTP treatment. In conclusion, the results presented here demonstrated that low dose whole-body γ-irradiation renders neuroprotection against MPTP-mediated damage of striatal dopaminergic nerve fibers, though it does not seem to influence the MPTP-induced reduction of SNpc dopaminergic neurons and associated glial responses.

Hypothyroidism alters striatal dopamine release mediated by 3,4-methylenedioxymethamphetamine (MDMA, ecstasy)

Microdialysis cannulas were surgically implanted into the striatum of thyroparathyroidectomized (TX) and sham rats in order to determine differences in dopamine release and core body temperature following MDMA administration. Rats were subsequently treated with MDMA (10 mg/kg, s.c.), and striatal DA levels were monitored at 20 min intervals, as well as core temperature every 30 min. Sham rats responded to MDMA with a characteristic hyperthermic response and significant increases in extracellular dopamine. Conversely, TX rats responded to MDMA with a hypothermic response and failed to demonstrate a similar increase from basal dopamine levels. On the basis of these data, thyroid hormones are not only important in the thermogenic effects of MDMA but also appear to have an auxiliary role in MDMA-induced striatal dopamine release.

Neurochemical correlates of sparing from motor deficits in rats depleted of striatal dopamine as weanlings.

The behavioral and neurochemical effects of striatal DA depletions were investigated in rats lesioned as weanlings (Day 27) or as adults (250-300 g). Administration of 6-OHDA into the medial forebrain bundle resulted in comparably large (> or = 95%) depletions of tissue levels of DA in both age groups. As expected, rats depleted of DA as adults exhibited marked deficits in motoric behavior and body weight regulation that persisted for the 8 days of postsurgical observation. In contrast, rats depleted of DA as weanlings were spared from such deficits, and their behavior closely resembled that of age-matched controls. Microdialysis studies revealed dialysate levels of striatal DA that paralleled these age-dependent behavioral differences. At a time when age-related behavioral differences were still quite pronounced (5-6 days postsurgery), basal DA levels were reduced by 80% of control values in rats lesioned as adults whereas basal DA levels in rats lesioned as weanlings were unchanged relative to their controls. Finally, adults depleted of striatal DA as weanlings were no more sensitive to the movement-impairing effects of intrastriatal sulpiride (3.0 or 10.0 micrograms/hemisphere) infusions than were control rats. These data suggest that weanlings compensate for large, but incomplete, denervation of striatal DA with markedly enhanced release and turnover from residual terminals. This developmental plasticity may prevent the occurrence of behavioral deficits soon after the lesion and also the supersensitivity to the challenging effects of DA antagonists as animals grow into adulthood.

Biogenic amines in striatum of rats that had been treated with ethanol, and their brains later stored in different temperatures.

The purpose of this study was to investigate how ethanol pretreatment and storage temperatures of brain striatum affect levels of biogenic amines in this tissue. Adult Wistar male rats were injected with 25% ethanol (5.0 g/kg i.p.) while the control rats were administered i.p. with the same volume of saline. Two hours later the rats were decapitated, their brains removed, and the striatum separated. Each striatum was divided into three parts: one part was immediately frozen on dry ice and kept at -70 degrees C; a second fragment was kept in a household refrigerator (+4 degrees C); and the third fragment was kept at +22 degrees C. Twenty-four hours later, levels of DA, DOPAC, HVA, 3-MT, 5-HT, and 5-HIAA in the striatum were assayed by HPLC/ED. Immediately after decapitation; ethanol levels were assayed in the serum of ethanol-pretreated and saline-pretreated rats using gas chromatography. Our results indicate that levels of striatal DA, DOPAC, and HVA in saline-pretreated rats decreased significantly when the storage temperature of the striatum was raised from -70 degrees C, through +4 degrees C, to +22 degrees C, while levels of striatal 5-HT and 5-HIAA remained constant within the temperature range tested and levels of 3-MT fluctuated. In ethanol-pretreated rats, striatal levels of DOPAC, HVA, and 5-HIAA were increased in all three storage temperatures, while levels of DA, 5-HT, and 3-MT were decreased in those temperatures. Those decreases were most profound in striatal samples kept at +22 degrees C. We conclude that concern about possible interactions between drugs and biogenic amines should be exercised.

The Role of Dopamine Receptors in Regulating the Size of Axonal Arbors

Factors that regulate terminal arbor size of substantia nigra pars compacta (SNpc) neurons during development and after injury are not well understood. This study examined the role of dopamine receptors in regulating arbor size. Terminal arbors were examined in mice with targeted deletion of the D1 or D2 dopamine receptor [D1(-/-) and D2(-/-) mice, respectively]. Terminal trees were also examined after treatment with receptor blockers and after partial SNpc lesions. Immunohistochemistry was performed, and the number of SNpc neurons and dopaminergic terminals in the striatum was estimated. The number of dopaminergic SNpc neurons were reduced in D1(-/-) and D2(-/-) mice. Density of dopaminergic terminals was unchanged in D1(-/-) mice and increased in D2 (-/-) mice. Steady-state striatal DA and DOPAC levels revealed that dopamine activity was enhanced in D2(-/-) mice but reduced in D1(-/-) mice. Two months after partial SNpc lesions, striatal terminal density was normal in both wild-type and D1(-/-) mice but reduced in D2(-/-) mice. Administration of DA receptor antagonists resulted in larger terminal arbors in D1(-/-) and wild-type mice, whereas D2(-/-) mice showed no change in terminal density. Functional blockade of the D2R during development or in the adult brain results in increased axonal sprouting. Partial SNpc lesions resulted in compensatory sprouting, only in mice with functional D2R. These results suggest that individual dopaminergic axons in D2(-/-) mice have reached maximal arbor size. We conclude that the D2 receptor may play a role in modulating the extent of the terminal arbor of SNpc neurons.

Pramipexole inhibits lipid peroxidation and reduces injury in the substantia nigra induced by the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in C57BL/6 mice

Pramipexole has been showed to protect cultured dopaminergic (DAergic) cells against free radical-induced cytotoxicity. To test if pramipexole is protective against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-mediated nigral DAergic injury in vivo and if such protection is related to inhibition of lipid peroxidation, DAergic function and lipid peroxidation were determined in MPTP-treated C57BL/6 mice. We reported that MPTP administration induced a 38.1% increase of lipid peroxidation product thiobarbituric acid reactive substance (TBARS) in nigra, a 46.7% decrease of tyrosine hydroxylase -positive nigral DAergic neurons and a 59.4% reduction of striatal DA levels. However, pramipexole treatment significantly inhibited the TBARS production by 76%, and attenuated the MPTP-induced decreases in nigral DAergic neurons and striatal DA levels by about 50%. This study suggests that pramipexole can inhibit free radical-mediated lipid peroxidation and protect MPTP-induced nigral injury.

Role of nerve terminal L-type Ca 2+ channel in the brain

The microinjection of Bay K 8644 (BAYK), an L-type Ca 2+ channel stimulant, into rat caudate putamen dose-dependently potentiated locomotor activity. DA receptor antagonists significantly blocked BAYK-induced hyperactivity. Striatal DA levels as detected by microdialysis increased 140 fold above steady state levels 20 min after BAYK administration into caudate putamen. This increase was not influenced by a Na + channel blocker. Pretreatment with 1,4-dihydropyridine (DHP) L-type Ca 2+ channel antagonists, but not nifedipine, into caudate putamen significantly blocked the BAYK induced-hyperactivity and DA efflux. The lowest level of intracellular DA detected by fluorohistochemistry coincided with the highest level of extracellular DA. These results indicate that the extraordinary DA release is regulated by a subtype of L-type Ca 2+ channel that is present in the nerve terminal.

GBR-12909-induced self-injurious behavior: role of dopamine

A regimen of repeated administration of GBR (10 or 20 mg/kg/day, i.p., for 4 days) to female Sprague-Dawley rats induced a dose-and time-related increase in the incidence of self-injurious behavior (SIB) that consisted of injury to body areas, paws and tail. The treatment regimen decreased striatal DA and DOPAC levels. Dopaminergic denervation with 6-hydroxydopamine (6-OHDA) or D1 DA antagonist, SCH-23390 or D2 DA antagonist, spiperone, blocked the GBR-induced SIB. Male rats were less sensitive than female rats to exhibit a comparable incidence of SIB. Taken together, the study reveals that repeated administration of GBR induces SIB that is dependent on the integrity of nigrostriatal dopaminergic system and the presence of D1 and/or D2 DA receptors.

Behavioral and neurochemical changes induced by aging in dopaminergic systems of male and female rats

Changes induced by aging in dopaminergic activity of male and female rats were compared by behavioral and neurochemical methods. Young (3 months) and old (23 months) rats were used. Aging decreased animal activity in the open field and increased apomorphine-induced stereotyped behavior. No differences in open field data were observed between males and females. Young and aged female rats had higher striatal DA and HVA levels than males; aging induced a decrease in both striatal DA and HVA levels in males, but not in females. No changes in HVA/DA ratios were observed among the different groups. These results show that aging reduces nigrostriatal activity as well as nigrostriatal DA levels. Furthermore, they indicate that time course events related to aging differ between males and females.

Spontaneous functional recovery from parkinsonism is not due to reinnervation of the dorsal striatum by residual dopaminergic neurons

Cats exposed to MPTP experience severe motor deficits that spontaneously recover after 4–6 weeks. This recovery occurs despite a persistent deficit (approximately 95%) in dorsal striatal DA levels. To determine whether residual DA neurons that previously did not innervate the dorsal caudate nucleus (CD) have innervated this area in recovered MPTP-treated animals, HRP was injected into the dorsal lateral and dorsal medial CD and the locations of retrogradely labeled neurons in ventral mesencephalon were mapped in normal and recovered MPTP-treated cats. Tyrosine hydroxylase (TH) positive cells were also counted in ventral mesencephalic DA-containing cell groups in normal, symptomatic, and recovered MPTP-treated cats. Results showed no difference in the pattern of HRP labeling in normal and recovered cats except for the loss of labeled substantia-nigra pars compacta (SNc) cells in MPTP-treated cats. Cell counts revealed no significant difference in the degree of TH-positive cell loss in all ventral mesencephalic areas studied in both symptomatic and recovered cats. The results suggest that spontaneous recovery of gross motor function in MPTP-treated cats is most likely not dependent upon reinnervation of the dorsal striatum from residual DAergic neurons.

β,β′-Iminodipropionitrile-induced persistent dyskinetic syndrome in mice is transiently modified by MPTP

Chronic administration of iminodipropionitrile (IDPN) is known to produce a persistent dyskinetic syndrome. Recent neurochemical reports seem to point out the dopaminergic system as having an important role in mediating IDPN syndrome. In order to identify a possible role for the nigrostriatal dopaminergic pathway in determining at least some aspects of the IDPN-induced dyskinetic syndrome, we used the neurotoxin, 1-methyl, 4-phenyl,1,2,3,6-tetrahydropiridine (MPTP), as a tool for investigating which aspects of the IDPN-related syndrome could be due to enhanced dopaminergic activity in the neostriatum. In mice made permanently dyskinetic with IDPN, MPTP administration produced dramatic and biphasic effects on all behavioral patterns characteristics of the dyskinetic syndrome. Six weeks after the syndrome occurred, IDPN failed to produce any change in striatal DA levels with respect to controls. By contrast, IDPN seems to reduce striatal levels of extraneuronal metabolites of DA. These data suggest that the activity of the nigrostriatal dopaminergic pathway does not play a leading role in the maintenance of IDPN-related syndrome. The transient modification of all behavioral parameters immediately after MPTP administration could be explained by acute effects of MPTP on other dopaminergic areas which are not permanently lesioned by this neurotoxin, or by the acute effects of MPTP on the release of other neurotransmitters.

Diurnal monoamine variation in young and old rats: a microdialysis study.

The levels of striatal extracellular DA, DOPAC, HVA and 5-HIAA significantly decreased in aged rats compared to young adults. The magnitude of age-related reduction was greater in dopaminergic than serotonergic substances. The levels of striatal extracellular monoamines in young adult rats showed significant diurnal variations. On the other hand, these substances of aged rats, except for HVA, did not exhibit significant diurnal variations. Enriched environment housing increased levels of striatal extracellular DOPAC in aged rats, but did not influence on the age-related changes of diurnal variations in the striatal extracellular monoamines.

Dissociation between biochemical and behavioral recovery in MPTP-treated mice

Injection of a low dose of haloperidol, that has no obvious behavioral effects in normal mice, produces akinesia, catalepsy, and somatosensory neglect in MPTP-treated mice. These neuroleptic-induced sensorimotor impairments are exhibited soon after MPTP treatments and coincide with a decrease in both striatal DA and DOPAC levels. DA and DOPAC content gradually return to near-control levels over a 3–5 month period. Interestingly, while the haloperidol-induced somatosensory deficits declined in parallel with the rise in DA and DOPAC levels, the motor deficits persisted for up to 5 months after MPTP administration. These data suggest subtle differences in the neurochemical mediation of these behaviors and that the persistence of neuronal impairments may not necessarily be revealed by near-normal transmitter levels.

Reactivity to amphetamine in perinatally undernourished rats: behavioral and neurochemical correlates.

Adult rats deprived at perinatal age and then rehabilitated on balanced chow were treated with a multiple amphetamine (AMPH) schedule (2 mg/kg/48 hr) and submitted, on days of injections, to an open-field test. Throughout 11 sessions, deprived rats showed a progressive increase of locomotor activity as compared with controls. Stereotyped activity evaluated during the AMPH treatment did not differ between control and deprived animals. No differences were detected in basal values of the dopaminergic function measured in naive control and deprived animals. By the end of the multiple AMPH treatment, a reduction of striatal DA and DOPAC levels together with a lower apparent DA turnover rate was detected in deprived animals. Besides, DA receptor binding was significantly increased in striatum from deprived rats as compared with controls. These results demonstrate that a repeated AMPH treatment, that was unable to alter the normal behavior of control rats, produced in early undernourished animals a progressive sensitization to AMPH effects, in addition to significant changes in the striatal dopaminergic function.

Striatal and hypothalamic neurotransmitter changes during ethanol withdrawal in mice

The alterations in striatal and hypothalamic GABA, DA and its metabolites DOPAC and HVA, and in hypothalamic NE were investigated immediately after ethanol removal and during the withdrawal phase following 10 or 30 days of chronic ethanol administration. After 10 days of ethanol, GABA levels were increased immediately after ethanol removal in both the corpus striatum and the hypothalamus. The concentration of striatal DA was increased at days 2 and 3 of withdrawal and was unchanged at any other time. There was no change in the concentration of DOPAC and HVA in the hypothalamus at any time during withdrawal. Striatal DOPAC and HVA levels were increased only at day 7 of withdrawal after 10 and 30 days of ethanol feeding which was associated with a return of striatal DA to control levels. The concentration of NE in the hypothalamus was increased at days 1, 2 and 7 of withdrawal. After 30 days of ethanol, striatal GABA was increased only at day 7 of withdrawal whereas striatal DA levels were only increased at days 2 and 3 of withdrawal. Hypothalamic NE was markedly increased at days 2, 3 and 7 of withdrawal. The increase in DA concentration associated with no change in DOPA accumulation following inhibition of DOPA decarboxylase and a decrease in the striatal disappearance of DA after alphamethylparatyrosine (α-MT) suggests the presence of a hypodopaminergic state. On the other hand an increase in the disappearance of NE in the hypothalamus after α-MT suggests an increased NE turnover and a hyperadrenergic state during withdrawal. The increase in striatal GABA at day 7 of withdrawal after 30 days of ethanol may be a rebound phenomenon and may reflect the presence of a hypogabaergic state which has been shown to occur during ethanol withdrawal.

Comparative study of central dopaminergic properties of RU 29717 (N-propyl-9-oxaergoline) and pergolide

RU 29717, a 9-oxaergoline derivative, has been compared with pergolide in a variety of biochemical and behavioural tests indicative of dopaminergic (DAergic) activity. RU 29717 and pergolide have a similar affinity for DA receptors labelled by [ 3H]spiroperidol or [ 3H]dihydroergocryptine ([ 3H]DHEC) by using striatal or arterior pituitary membranes respectively. Both compounds stimulate the striatal DA-sensitive adenylate cyclase and inhibit the activity of this enzyme in dispersed cells from the neurointermediate lobe of the pituitary gland. In anterior pituitary cells in primary culture, they decrease prolactin release with the same efficacy. In vivo, they exert a long-lasting inhibition of the reserpine-induced hyperprolactinemia. They equally retard the α-MPT-induced disappearance of striatal DA and increase striatal acetylcholine levels. In behavioral models, the similarity between RU 29717 and pergolide is also evident: they induce contralateral circling in animals lesioned unilaterally with 6-OHDA, produce stereotyped behaviour and have emetic activity within the same dose range. Therefore, RU 29717, like pergolide, is a potent direct acting DAergic agonist. In experimental models used to investigate this activity at the striatal or the anterior pituitary levels the compounds present a similar profile of action.

Circling behaviour induced by dopamine releasers and/or uptake inhibitors during degeneration of the nigrostriatal pathway

A number of compounds which induced ipsilateral circling behaviour in rats with chronic unilateral 6-hydroxy-dopamine (6-OHDA) destruction of the nigrostriatal dopamine (DA0 pathway through their postulated DA-releasing and/or uptake-inhibiting properties, have been tested 24 h after a 6-OHDA lesion. Under these conditions, in contrast to chronically lesioned animals, d- or l-amphetamine, mazindol, HR 370, nomifensine and benztropine still induced ipsilateral turns. The monoamine oxidase inhibitor pargyline was inactive and the DA receptor agonist apomorphine induced a mild contralateral circling response at high doses only. The contralateral circling response to d-amphetamine was hardly antagonized by a high dose of α-methyl-p-tyrosine (AMT), and was increased by reserpine. Striatal DA levels were increased in the lesioned side and restored to normal values after d-amphetamine, in contrast to methylphenidate. Ipsilateral turns recorded with chronically lesioned rats were strongly decrease by AMT except in the case of p-chloroamphetamine, methylphenidate and pipradrol. The response of reserpinized rats was decreased except with d-amphetamine and its N-methyl derivative. It was concluded that drugs inducing contralateral turns during degeneration of the nigrostriatal DA pathway predominantly release newly-synthetized DA independently of nerve impulse flow whilst ipsilateral turns are either triggered by inhibiting of DA uptake or by the release of the reserpine-sensitive pool of DA, both on the intact side. This last effect may require a normal nerve impulse flow. This method thus provides the first direct behavioural evidence of differences in the mode of action of drugs interfering presynaptically with DA.

Is glycine an inhibitory synaptic transmitter in the substantia nigra?

Nigral tissue accumulated 14C-glycine by an energy-, temperature- and sodium-dependent mechanism; the transport process was inhibited by small neutral amino acids and had an apparent K m of 143 μM and V max of 787 nmol/g/min. Re-release of accumulated 14C-glycine was initially extremely rapid (40% in first 5 min) and subsequently accelerated by +40 mM K + in a Ca 2+-dependent manner. Intranigral kainate (0.25 μg) lowered the levels of striatal DA (63%)_and nigral GABA (25%) ipsilaterally, but not nigral glycine. Injections of glycine or strychnine (10–100 μg) into one SN induced slow ipsiversive or contraversive turning respectively. The evidence for glycine as a neurotransmitter in SN is discussed.