Striatal DOPAC Levels Research Articles

Diverging changes in rat striatal extracellular dopamine and DOPAC levels and in frequency-modulated 50-kHz ultrasonic vocalizations rate during repeated amphetamine treatment

One characteristic feature of addictive drugs is their ability to induce, after a single exposure, a lasting sensitization to the next doses; the underlying neuroplastic changes supposedly involve the brain dopamine system. We aimed at identifying putative relationships between alterations in extracellular dorsal striatal dopamine, HVA and DOPAC levels and in frequency-modulated 50-kHz ultrasonic vocalizations rate response during repeated intraperitoneal amphetamine treatment. Measurements were performed before and after amphetamine doses 1, 2, 7 and 8 (Amph1, Amph2, Amph7 and Amph8; treatment days 1, 7, 12 and 23, respectively). Amphetamine was confirmed to induce sensitization of the vocalization response, but an extended recording time (180 instead of 20 min) revealed that sensitization of this response requires more time to develop than hitherto believed. Baseline extracellular dopamine level increased initially, declined after a series of daily amphetamine doses and showed some tendency for recovery after drug withdrawal. Baseline extracellular DOPAC (but not HVA) showed a continuous decline during the treatment. There was no significant change in the integrated short-term (3-h) extracellular dopamine response, whereas the respective DOPAC collection lowered significantly after repeated drug treatment. Extracellular DOPAC is believed to originate mostly from newly synthesized dopamine, hence the declines in its baseline and post-amphetamine levels suggest falling dopamine synthesis. These results indicate that sensitization of the appetitive vocalization response to amphetamine continues despite reduced dorsal striatal dopamine synthesis and involves no changes in amphetamine-induced dopamine release.

Mechanisms of action of paraoxon, an organophosphorus pesticide, on in vivo dopamine release in conscious and freely moving rats

Paraoxon is the active metabolite of parathion, an organophosphorus pesticide which can cause neurotoxic effects in animals and humans. In the present work, we investigated the effects of 5 mM paraoxon on striatal dopamine, DOPAC and HVA levels in conscious and freely moving rats, after treatment with TTX, reserpine, nomifensine, KCl, Ca++-free/EDTA medium, AP-5 or L-NAME. The intrastriatal administration of paraoxon for 60 min, through the microdialysis probe, significantly produced an increase of the dopamine to 1066 ± 120%, relative to basal levels. Administration of paraoxon to 20 μM TTX, 10 mg/kg reserpine or Ca++-free/EDTA medium-pretreated animals decreased the dopamine levels to 73%, 81%, and 70%, respectively, when compared with the effect of 5 mM paraoxon. Infusion of 50 μM nomifensine induced a maximal increase in extracellular dopamine levels to 1435 ± 387%, and when nomifensine was coadministered with paraoxon, striatal dopamine levels increased to 2429 ± 417%, an increase that was ∼230% higher that observed with the administration of the pesticide alone. Coinfusion of KCl and paraoxon produced an increase in extracellular dopamine to 1957 ± 445%, that was significantly higher than that observed with POX or KCl (1104 ± 220%) administered individually. Pretreatment with 650 μM AP-5 or 100 L-NAME reduced the effect of paraoxon on extracellular dopamine levels by 49.1% and 53.7%, respectively. Our results suggest that paraoxon induces dopamine release by a vesicular-, Ca++-, and deporalization-dependent mechanism, being independent of dopamine transporter. In addition, the paraoxon-induced dopamine release is mediated by glutamatergic and nitrergic neurotransmitter systems.

Neuroprotective effects of valproic acid on brain ischemia are related to its HDAC and GSK3 inhibitions

Valproic acid (VA) is an antiepileptic that is also used for the treatment of bipolar disorders. The objective was to evaluate the neuroprotective effects of VA on a brain ischemia model. The groups of male Wistar rats were: SO (sham-operated), ischemic and ischemic treated with VA (25, 50 and 100 mg/kg, p.o.). After anesthesia with ketamine and xilazine, the animals were subjected to clamping of carotid arteries (30 min) and reperfusion. Except for the carotid clamping, the SO group was submitted to the same procedure. On the 7th day, the animals were behaviorally evaluated, euthanized and had their brain dissected for neurochemical and immunohistochemical assays. The data were analyzed by ANOVA and Tukey as the post hoc test. The results showed that VA reversed partly or completely the behavioral (locomotor activity and memory deficits), neurochemical (striatal DA and DOPAC levels, brain nitrite and lipid peroxidation) and immunohistochemical alterations (iNOS, COX-2, HDAC and GSK3) observed in the untreated ischemic group. VA neuroprotective effects are probably related to its anti-inflammatory and antioxidant properties, as well as to HDAC and GSK3 inhibitory effects. These findings stimulate translational studies focusing on VA as a neuroprotective drug to be potentially used in the clinic for several neurological conditions.

Blood withdrawal affects iron store dynamics in primates with consequences on monoaminergic system function

Iron homeostasis is essential for the integrity of brain monoaminergic functions and its deregulation might be involved in neurological movement disorders such as the restless legs syndrome (RLS). Although iron metabolism breakdown concomitantly appears with monoaminergic system dysfunction in iron-deficient rodents and in RLS patients, the direct consequences of peripheral iron deficiency in the central nervous system (CNS) of non-human primates have received little attention. Here, we evaluated the peripheral iron-depletion impact on brain monoamine levels in macaque monkeys. After documenting circadian variations of iron and iron-related proteins (hemoglobin, ferritin and transferrin) in both serum and cerebrospinal fluid (CSF) of normal macaques, repeated blood withdrawals (RBW) were used to reduce peripheral iron-related parameter levels. Decreased serum iron levels were paradoxically associated with increased CSF iron concentrations. Despite limited consequences on tissue monoamine contents (dopamine – DA, 3, 4-dihydroxyphenylacetic acid – DOPAC, homovanillic acid, L-3, 4-dihydroxyphenylalanine – L-DOPA, 5–8 hydroxytryptamine – 5-HT, 5-hydroxyindoleacetic acid – 5-HIAA and noradrenaline) measured with post-mortem chromatography, we found distinct and region-dependent relationships of these tissue concentrations with CSF iron and/or serum iron and/or blood hemoglobin. Additionally, striatal extracellular DA, DOPAC and 5-HIAA levels evaluated by in vivo microdialysis showed a substantial increase, suggesting an overall increase in both DA and 5-HT tones. Finally, a trending increase in general locomotor activity, measured by actimetry, was observed in the most serum iron-depleted macaques. Taken together, our data are compatible with an increase in nigrostriatal DAergic function in the event of iron deficiency and point to a specific alteration of the 5-HT/DA interaction in the CNS that is possibly involved in the etiology of RLS.

Prenatal Curcumin Administration Reverses Behavioral and Neurochemical Effects and Decreases iNOS and COX-2 Expressions in Ischemic Rat Pups

The objectives were to evaluate alterations in ischemic rat pups, from dams administered with curcumin (25 and 50 mg/kg). Ten-day-old male pups were subjected or not (SO) to brain ischemia and reperfusion, for 1, 7, and 14 days (this last group was submitted to behavioral evaluation). After that, pups were euthanized for determinations of striatal DA and DOPAC in SO, ischemic from untreated (ICUD) or curcumin treated (ICTD) dams, as well as hippocampal immunohistochemistry assays for iNOS and COX-2 and cresyl violet staining. At the 14th postischemia day, the ICUD group showed increased locomotor activity and rearing behavior, which were reversed in ICTD animals. ICUD pups presented decreased striatal DA and DOPAC levels, relatively to SO, mainly at the 1st postischemia day, but also at the 7th and 14th days which were partially reversed in ICTD pups. A greater number of viable neurons were observed in ICTD, as related to the ICUD group. Ischemia increased iNOS and COX-2 expressions, in CA1 and CA3 areas, at the 1st, 7th, and 14th postischemia days, and these effects were minimized in ICTD pups. In conclusion, the prenatal curcumin treatment was shown to be neuroprotective where the drug anti-inflammatory and antioxidant effects probably play a role.

Assessment of the abuse potential of MDMA in the conditioned place preference paradigm: Role of CB1 receptors

Numerous reports have highlighted the role of the endocannabinoid system in the addictive potential of MDMA (3,4-methylenedioxy-methamphetamine). A previous report showed that CB1 knockout (KOCB1) mice do not acquire MDMA self-administration, despite developing conditioned place preference (CPP). This contradiction could be due to the particular procedure of place conditioning used. The present work compares MDMA-induced CPP in KOCB1 mice using unbiased and biased procedures of place conditioning. In the unbiased procedure, MDMA induced CPP and reinstatement of the extinguished preference in wild type (WT) mice, but not in KOCB1 mice. In contrast, in a biased protocol of CPP, MDMA produced preference in both types of mice. The anxiolytic response induced by MDMA in the elevated plus maze (EPM) was observed only in KOCB1 mice and may have been responsible, at least partially, for the CPP in the biased procedure. A neurochemical analysis revealed that KOCB1 mice presented higher striatal DA and DOPAC levels in response to MDMA, but no alterations in their levels of monoamine transporters. In line with previous self-administration studies, our data suggest that CB1 receptors play an important role in the reinforcing effects of MDMA, and that the experimental procedure of CPP employed should be taken into account when drawing conclusions.

Haloperidol effects on striatal dopamine and DOPAC levels and subcellular distribution

Signaling involving dopaminergic neurons in the brain is important for determining the saliency of sensory input, the urgency of sensory import, the actual value of an experience as compared to its expected value, and the process of converting motivation to action. Drugs that are antagonists for the dopamine D2 receptor subtype are clinically effective in treating schizophrenia and a variety of other mental conditions. These drugs have a substantial effect on the levels and sub-cellular distribution of dopamine and its major metabolite DOPAC. Currently, there is no quantitative analysis of how these various changes can be accomplished. The goal of this work is to explain how the changes in dopamine and DOPAC levels and subcellular location elicited by the prototypical antipsychotic drug haloperidol occur. A computational model of a dopaminergic striatal varicosity was used. In the model, dopamine can be located in cytosol, vesicles, extracellular compartment, and a DOPAC-synthesis-secretory compartment. DOPAC can be located in cytosol, extracellular, and DOPAC-synthesis-secretory compartment. The model has two distinct sites for dopamine and DOPAC synthesis. The cytosolic site synthesizes dopamine for use in the signaling pool and metabolizes a portion of dopamine that is transiently located in cytosol. The DOPAC-synthesis-secretory complex site is hypothesized to be located on the plasma membrane and to be dedicated to the synthesis of DOPAC to be secreted into the extracellular compartment. The model also has enzymes involved in dopamine and DOPAC synthesis, transporters that move dopamine between compartments, and exocytosis. Haloperidol induces a small increase in extracellular dopamine, a somewhat larger increase in extracellular DOPAC, a larger increase in tissue DOPAC, a large increase in rate of dopamine synthesis, and no change in level of dopamine. The increase in extracellular dopamine was simulated by increasing rate of secretion of dopamine into extracellular space by exocytosis. An increase in synthesis of signaling dopamine was required to maintain the elevated levels of extracellular dopamine. The increase in extracellular DOPAC was simulated by increasing rate of dopamine synthesis in the DOPAC-synthesis-secretory compartment. With only these manipulations, the model failed to match experimental data in terms of increase in total tissue DOPAC and increase in the rate of dopamine synthesis. These discrepancies were resolved by increasing the passive diffusion of dopamine from vesicles to cytosol and further increasing the rate of dopamine synthesis for the signaling pool. Literature data indicate that haloperidol does accumulate in and partially alkalinize amine neurotransmitter storage vesicles, which would increase passive diffusion of dopamine from the vesicles. I conclude that the increases in extracellular dopamine and DOPAC are likely mediated by antagonism of dopamine D2 receptors but that the large increase in tissue DOPAC and much of the increase in dopamine synthesis result from physico-chemical properties of haloperidol rather than block of dopamine D2 receptors. Furthermore, the results suggest dopaminergic varicosities possess a mechanism for monitoring amount of stored dopamine and modulating dopamine synthesis to maintain constant stores.

L-dopa esters as potential prodrugs: effect on brain concentration of dopamine metabolites in reserpinized mice.

The intraperitoneal administration of L-dopa and a series of ester prodrugs of L-dopa to reserpinized mice produced elevations of striatal and tuberculum olfactorium homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) levels. Differences in the pattern of change produced by individual drugs, compared with L-dopa, were observed. Only the phenoxyethyl ester caused elevations of both striatal and tuberculum olfactorium HVA and DOPAC, greater than those measured following L-dopa administration. Overall the m-trifluoromethylbenzyl, phenylethyl, p-chlorophenylethyl and p-methoxyphenylethyl ester prodrugs produced greater elevations of striatal and tuberculum olfactorium HVA, but not DOPAC, compared with L-dopa. The administration of the 2-tetrahydropyranyl-methyl derivative only enhanced striatal HVA and striatal and tuberculum olfactorium DOPAC concentrations. Changes of HVA and DOPAC tissue concentrations following administration of the 2-hydroxypropyl, n-propyl, methyl, ethyl and 2-(1-methoxy)propyl ester prodrugs were comparable with those produced by the administration of L-dopa itself. The alterations in striatal and tuberculum olfactorium HVA and DOPAC levels observed did not correlate with the ability of these compounds to elicit locomotor activity in reserpinized mice.

Preferential Decrease in Dopamine Utilization in Prefrontal Cortex by Zopiclone, Diazepam and Zolpidem in Unstressed Rats

This study has compared the effects of a cyclopyrrolone, zopiclone, a benzodiazepine, diazepam, and an imidazopyridine, zolpidem, on dopamine (DA) and DOPAC levels, and DA utilization (DOPAC/DA ratio) in rat striatum and prefrontal cortex. The endogenous levels of DA were significantly increased by both zopiclone (2.5, 10 and 40 mg kg-1 p.o.) and diazepam (10 and 40 mg kg-1 p.o.) in the prefrontal cortex, whereas striatal DA content was significantly increased only with the highest dose of diazepam (40 mg kg-1 p.o.). Diazepam (10 and 40 mg kg-1 p.o.) decreased cortical level of DOPAC more markedly than striatal levels, whereas zopiclone (40 mg kg-1 p.o.) only slightly decreased striatal DOPAC levels. Zopiclone and diazepam dose-dependently decreased DA utilization, an effect which was more marked in prefrontal cortex than in striatum. This result was confirmed with zolpidem, another benzodiazepine ligand. Zopiclone was most potent at decreasing DA utilization at the cortical level. The diazepam-induced decreases in DA metabolism and utilization were antagonized by Ro 15-1788, suggesting that the effects seen were mediated by specific benzodiazepine receptors. Thus, our results clearly show that ligands acting on the benzodiazepine receptor GABA receptor chloride ionophore complex can decrease the utilization of dopamine in unstressed rats. The preferential decrease in cortical DA utilization induced by benzodiazepine ligands may be compared to the well-known activation by stress of the mesocortical DAergic system.

Age-Related Decrease in Striatal DA Produces Cognitive Deficits in Male Rats

Aging is a process that presents various alterations in physiological, behavioral and neurochemical processes. It causes impairment of CNS functions which lead to changes in memory, cognition and other behavioral performances. Reports have shown that aging causes neurochemical alterations in various physiological functions. The aim of the present study was to evaluate the cognitive changes in relation to process of aging. For this 20 male rats were taken, 10 young (4-6 months) and 10 old (18-22 months). Morris Water Maze (MWM) test was performed to monitor changes in learning and memory while Object-Recognition Task (ORT) was performed to evaluate changes in cognitive function. After behavioral assessment decapitation was done and rat brain was dissected to isolate striatum. Then neurochemical analysis was performed by HPLC-EC to monitor changes in striatal DA and DOPAC levels. Results of behavioral tests showed that aged rats exhibited a significant impairment of long-term memory. While cognitive ability assessed by ORT was also impaired in aged rats. Neurochemical results showed that there was a significant decline in striatal dopamine (DA) concentration while its metabolite DOPAC was significantly increased in aged rats. Hence aging has a significant negative influence on cognitive functions. Age-related behavioral deficits may occur as a result of decline in DA levels in striatum leading to changes in memory and cognitive performance.

Poster 23: Pharmacology of the Dopaminergic Stabilizer Pridopidine (ACR16)

Background 4-[3-(methylsulfonyl)phenyl]-1-propylpiperidine hydrochloride (pridopidine, ACR16) is in development as an agent to target both the motor and behavioral symptoms of Huntington's disease (HD). Pridopidine is a dopaminergic stabilizer, a novel class of drugs that act at dopamine 2 (D2) receptors and display state-dependent behavioral effects. Preclinical studies in vivo suggest that pridopidine has potential efficacy across several clinical domains relevant for HD, including motor function, anxiety, depression, and psychosis. Early clinical studies with pridopidine have been encouraging in terms of reducing HD symptoms, without producing unwanted side effects. Methods Pridopidine was given subcutaneously to male Sprague-Dawley rats. HPLC was used to assess 3,4-dihydroxyphenylacetic acid (DOPAC) levels in brain tissue, and dopamine and noradrenaline levels in brain dialysates. Expression of activity-regulated cytoskeletal protein (Arc) was determined using RT-PCR on brain tissue RNA. Motility meters were used to quantify spontaneous and drug-induced locomotor activity. In vitro D2 radioligand binding and calcium-fluorescence functional studies were performed using human D2 expressing HEK293 cells. Results Pridopidine increased striatal tissue levels of the dopamine metabolite DOPAC (ED50 = 81 μmol/kg) and prefrontal cortex dialysate levels of dopamine and noradrenaline. Arc mRNA in the frontal cortex increased dose-dependently, indicating enhanced N-methyl-D-aspartate receptor-mediated signaling. Pridopidine reduced hyperlocomotion (d-amphetamine: ED50 = 40 μmol/kg; MK801: ED50 = 54 μmol/kg), but preserved spontaneous locomotor activity, confirming state-dependent behavioral effects. In vitro studies with pridopidine revealed surmountable low potency D2 antagonism, no intrinsic activity, and fast recovery of receptor-mediated responses. Conclusions Pridopidine stabilizes psychomotor activity by functional D2 antagonism and strengthening of cortical glutamate functions. Strengthening of cortical glutamatergic transmission may be key to the efficacious in vivo effects of pridopidine in states of hyperdopaminergia and hypoglutamatergia. The dopaminergic stabilizer pridopidine may offer clinical relief of psychomotor symptoms arising from dopaminergic dysfunction in HD.

Progressive Dopaminergic Degeneration in the Chronic MPTPp Mouse Model of Parkinson’s Disease

Parkinson's disease (PD) is characterized by a progressive degeneration of dopamine (DA) neurons and gradual worsening of motor symptoms. The investigation of progressive degenerative mechanisms and potential neuroprotective strategies relies on experimental models of the chronic neuropathology observed in human. The present study investigated the progressive nature of neurodegeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid (MPTPp) chronic mouse model of PD. MPTP (25 mg/kg) plus probenecid (250 mg/kg) were administered twice a week for 5 weeks. We evaluated behavioral deficits (olfactory and motor impairment), neurodegeneration (loss of tyrosine hydroxylase (TH)-positive cells in the substantia nigra pars compacta, SNc), biochemical markers of functional impairment in the caudate-putamen (CPu) (striatal enkephalin mRNA, DA and DOPAC levels), and glial reactivity (CD11b and GFAP immunoreactivity in the SNc and CPu) at progressive time-points (after 1, 3, 7, and 10 administrations of MPTPp). Olfactory dysfunction already appeared after the 1st MPTPp injection, whereas motor dysfunction appeared after the 3rd and worsened upon subsequent administrations. Moreover, starting after three MPTPp injections, we observed a gradual decline of TH-positive cells in the SNc, and a gradual raise of enkephalin mRNA in the CPu. Striatal DA levels reduction was not different among all time-points evaluated, whereas DOPAC levels were similarly reduced after 1-7 MPTP injections, but were further decreased after the 10th injection. Reactive microglia and astroglia were observed in both the SNc and CPu from the 1st MPTPp administration. In the SNc, gliosis displayed a gradual increase over the treatment. After 2 months, TH, DA, DOPAC, and reactive glia in the SNc were still altered in MPTPp-treated mice as compared to controls. By showing a progressive development of behavioral deficits and nigral neurodegeneration, together with impairment of biochemical parameters and gradual increase of glial response, results suggest that the chronic MPTPp protocol is a model of progressive PD, which may be suitable to investigate chronic pathological processes and neuroprotective strategies in PD.

Catalytic metalloporphyrin protects against MPTP-induced Parkinson's disease in mice

Objective:To observe the effects of manganese(Ⅲ)meso-tetrakis(N,N'-diethylimidazolium-2-yl)porphyrin(MnTDM)in treatment of early Parkinson's disease(PD)mouse model induced by subcutaneous injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP)and to discuss its possible mechanism.Methods:Forty male C57BL/6 mice were evenly randomized into 4 groups:MPTP model group(subcutaneous injection of 25 mg/kg MPTP for 3 days).MnTDM +MPTP group(15 mg/kg MnTDM was subcutaneously injected 1 h before MPTP injection).MnTDM control group,and normal saline group.Performance of animals in the pole and swimming test was observed 3 days after the last injection.Levels of dopamine(DA)and its metabolites(3,4-dihydroxyphenylacetic acid [DOPAC] and homovanillic acid [HVA])in the striatum of animals were measured by high-performance liquid chromatography with an electrochemical detector(HPLC-ECD).Thiobarbituric acid(TBA)method was used to examine the levels of malondialdehyde(MDA).Results:Acute injection of MPTP could be used for establishment of PD model.The striatal levels of DA,DOPAC and HVA in MPTP group were significantly lower(P0.01)and the striatal level of MDA was significantly higher(P0.05)than those of the control group.MPTP had no obvious effect on the behavioral performance of the animals in a short term.MnTDM could partly inhibit the above effects of MPTP.Compared with MPTP group,MnTDM+MPTP group had significantly higher DA,DOPAC,and HVA levels and significantly lower MDA level(all P0.05).There was no significant difference in the behavioral indices of animals between the 4 groups.Conclusion:MnTDM can inhibit lipid peroxidation and promote DA production;it has preventive and therapeutic effects on MPTP-induced PD.

Agmatine inhibits morphine-induced locomotion sensitization and morphine-induced changes in striatal dopamine and metabolites in rats

The effects of agmatine on morphine-induced locomotion sensitization and morphine-induced changes in extracellular striatal dopamine (DA) and DA metabolites were studied. The locomotor response to morphine challenge (3 mg/kg, s.c.) was enhanced in rats 3 days after repeated morphine administration, indicating development of locomotion sensitization. In vivo microdialysis demonstrated a significant increase in striatal basal levels of the DA metabolites DOPAC and HVA, but not in DA itself, and an increase in DA response to morphine challenge in rats 3 days after withdrawal. Agmatine (1, 10, 80 mg/kg) inhibited morphine-induced locomotion sensitization and the changes in DA noted above. Idazoxan attenuated the effects of agmatine on locomotion, suggesting that the effects are mediated by imidazoline receptors. In addition, repeated morphine also increased the expression of tyrosine hydroxylase mRNA in the VTA after 4 days of morphine pretreatment, while decreasing the expression of dynorphin mRNA at 3 days after withdrawal. Agmatine inhibited morphine-induced changes in dynorphin, but not in tyrosine hydroxylase mRNA expression. These data suggest that agmatine, likely by activating imidazoline receptors, inhibits morphine-induced locomotion sensitization and morphine-induced changes in extracellular DA and in dynorphin expression. Thus, agmatine deserves further study as an anti-opioid medication.

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.

Effects of some antioxidative aporphine derivatives on striatal dopaminergic transmission and on MPTP-induced striatal dopamine depletion in B6CBA mice

( S)-(+)-boldine, an aporphine alkaloid displaying antioxidative and dopaminergic properties, and six of its derivatives (glaucine, 3-bromoboldine, 3-iodoboldine, 8-aminoboldine, 8-nitrosoboldine and 2,9- O,O′-dipivaloylboldine) were tested for these properties in comparison with their parent compound. All the tested compounds displayed in vitro antioxidative properties equal to or slightly weaker than those of boldine, and equal to or stronger than (±)-6-hydroxy-2,5,7,8,-tetramethylchromane-2-carboxylic acid (Trolox ®), a water-soluble vitamin E analogue, used as a reference compound. All the aporphine compounds tested displaced [ 3H]SCH 23390 and [ 3H]raclopride from their specific binding sites in rat striatum. When tested on dopamine (DA) metabolism in the striatum of B6CBA mice, all the compounds, except 8-aminoboldine, increased striatal levels of DOPAC and HVA, and the HVA/DA ratio, indicating that they cross the blood–brain barrier and that they seem to act as dopamine antagonists in vivo. B6CBA mice were sensitive to the neurotoxic action of MPTP on dopaminergic neurons as indicated by the strongly decreased striatal levels of DA, DOPAC and HVA following administration of MPTP (20 mg/kg, i.p.). Among these aporphine derivatives, only 3-bromoboldine was able to reduce the MPTP-induced decrease of striatal levels of DA and DOPAC, whereas ( R)-apomorphine (5 mg/kg, s.c.) and acetylsalicylic acid (100 mg/kg, i.p.), used as reference compounds, were very active. These data suggest that potent in vitro antioxidative properties and the ability to cross the blood–brain barrier are not sufficient criteria to predict the inhibition of neuronal degeneration induced by MPTP.

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.

Neuroprotective effects of GDNF against 6-OHDA in young and aged rats

In young adult rats, glial cell line-derived neurotrophic factor (GDNF) can completely protect against 6-hydroxydopamine-induced loss of nigral dopamine neurons when administered 6 h prior to the 6-hydroxydopamine. The present study was undertaken to determine if GDNF would provide similar protective effects in aged rats. Male, Fischer 344×Brown Norway hybrid rats of 3, 18 and 24 months of age were given an intranigral injection of GDNF or vehicle followed 6 h later with an intranigral injection of 6-hydroxydopamine. Nigral dopamine neuron cell survival, and striatal and nigral dopamine and DOPAC levels, were evaluated 2 weeks after the lesions. In vehicle treated animals cell survival on the lesioned side ranged from 15 to 27%. GDNF promoted significant cell survival in the nigra of all three age groups; however, the percent survival was lowest in the 24-month-old animals (85% at 3 months, 75% at 18 months, 56% at 24 months). Similarly, dopamine levels in the striatum and substantia nigra on the lesioned side remained significantly greater in the GDNF treated animals compared to the vehicle treated animals. As with the cell survival experiment, the protective effects of GDNF on dopamine levels were less in the 24-month-old animals. GDNF pretreatment also protected against 6-hydroxydopamine-induced reductions in striatal DOPAC levels in all age groups. Overall, these results indicate that GDNF can protect nigrostriatal dopamine neurons against the effects of 6-hydroxydopamine in aged as well as young adult rats. However, the extent of protection is less in the aged (24-month-old) animals.

High frequency stimulation of the subthalamic nucleus increases the extracellular contents of striatal dopamine in normal and partially dopaminergic denervated rats.

The subthalamic nucleus (STN) has come under focus in Parkinson disease (PD) because of recent advances in the understanding of the functional organization of the basal ganglia in normal and pathological conditions. Manipulations of the STN have been described to compensate for some imbalance in motor output of the basal ganglia in animal models of PD and have been proposed as a potential therapeutic target in humans. Indeed, high frequency stimulation (HFS) (130 Hz) of the STN has beneficial effects in severe parkinsonian patients but the precise mechanisms underlying these clinical results remain to be elucidated. To date, very little is known concerning the effect of HFS-STN on striatal dopaminergic transmission. Since it has been reported that dopaminergic medication may be reduced in PD patients under HFS-STN, our goal was to study the effect of HFS-STN on striatal dopamine (DA) transmission by using intracerebral microdialysis in normal and partially DA denervated rats. Our results show that HFS STN induces a significant increase of extracellular DA in the striatum of normal and partially DA lesioned rats while striatal extracellular levels of DOPAC were not affected. We conclude that HFS-STN acts directly and/or indirectly on striatal DA levels in control or partially DA lesioned rats.

The effect of a subchronic post-lesion treatment with (-)-deprenyl on the sensitivity of 6-OHDA-lesioned rats to apomorphine and d-amphetamine.

The effects of a subchronic post-lesion treatment of 14 days with (-)-deprenyl or its solvent on the rotational response to apomorphine (0.1 mg/kg) and d-amphetamine (2.5 mg/kg) in 6-OHDA- and SHAM-lesioned rats were investigated. Rats received a local injection of 6-OHDA (9 microg/0.7 microl) or its solvent into the medial forebrain bundle. Following the (SHAM or 6-OHDA) lesion the animals were randomly assigned to one of the two post-lesion treatment groups, viz. vehicle or (-)-deprenyl (0.1 mg/kg, 2 x day, i.p.) and treated for 14 days. After a wash out period of 6 weeks the number of rotations in response to apomorphine (0.1 mg/kg) and d-amphetamine (2.5 mg/kg) were compared. Seven days following the final behavioural experiments the animals were sacrificed and the striatal dopamine, DOPAC and HVA levels were determined. The (-)-deprenyl-treated 6-OHDA-lesioned rats responded with a reduced number of rotations in response to apomorphine but not to d-amphetamine as compared to vehicle-treated 6-OHDA-lesioned rats. However the two lesion groups did not differ in striatal dopamine, DOPAC and HVA concentrations; the levels were below or close to the detection limit ipsilateral to the 6-OHDA injections. Thus a post-lesion treatment with (-)-deprenyl reduced the dopaminergic supersensitivity without a concomitant increase in striatal dopamine content. The data are discussed in the light of the previously described neurorescue properties of (-)-deprenyl.