Dopamine In Caudate-putamen Research Articles

Neuroprotective effects of acetyl-l-carnitine (ALC) in a chronic MPTP-induced Parkinson’s disease mouse model: Endothelial and microglial effects

Parkinson’s disease (PD) is a progressive motor disease with clinical features emerging due to degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc), which project to the caudate putamen (CPu) where they release dopamine (DA). The current study investigated whether acetyl-l-carnitine (ALC) could ameliorate the pathology seen in an in vivoin vivo chronic 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced mouse model of PD. Four treatment groups were included: 1) CONTROL receiving probenecid (PROB; 250 mg/kg) only, 2) MPTP (25 mg/kg) + PROB, 3) MPTP + ALC (100 mg/kg), and 4) ALC alone. MPTP-induced losses in tyrosine hydroxylase and DA transporter immunoreactivity in the SNc and CPu were significantly reduced by ALC. HPLC data further suggests that decreases in CPu DA levels produced by MPTP were also attenuated by ALC. Additionally, microglial activation and astrocytic reactivity induced by MPTP were greatly reduced by ALC, indicating protection against neuroinflammation. Glucose transporter-1 and the tight junction proteins occludin and zonula occludins-1 were also protected from MPTP-induced down-regulation by ALC. Together, data suggest that in this model, ALC protects against MPTP-induced damage to endothelial cells and loss of DA neurons in the SNc and CPu, suggesting that ALC therapy may have the potential to slow or ameliorate the progression of PD pathology in a clinical setting.

Neuroprotective effect of the chemical chaperone, trehalose in a chronic MPTP-induced Parkinson's disease mouse model

Parkinson's disease (PD) is a progressive motor disease of unknown etiology in the majority of cases. The clinical features of PD emerge due to selective degeneration of dopamine (DA) neurons in the substantia nigra pars compacta (SNc), which project to the caudate putamen (CPu) where they release DA. In the current in vivo mouse model study, we tested trehalose for its ability to protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced damage to DA neurons. Trehalose is a naturally occurring disaccharide present in plants and animals and appears capable of protecting cells against various environmental stresses. The effect of trehalose is likely due to its action as a pharmacological chaperone which promotes protein stability. In the present study, there were four treatment groups: saline only (control); probenecid only; MPTP+probenecid; and trehalose+MPTP+probenecid. MPTP-induced losses in tyrosine hydroxylase and DA transporter immunoreactivity in the ventral midbrain SNc and CPu were significantly reduced by trehalose. Decreases in CPu dopamine levels produced by MPTP were also blocked by trehalose. Microglial activation and astrocytic hypertrophy induced by MPTP were greatly reduced by trehalose, indicating protection against neuroinflammation. These effects are commensurate with the observed trehalose sparing of motor deficits produced by MPTP in this mouse model. Two tight junctional proteins, ZO-1 and occludin, are downregulated following MPTP treatment and trehalose blocks this effect. Likewise, the glucose transporter-1 that is expressed in brain endothelial cells is also protected by trehalose from MPTP-induced down-regulation. This study is the first to demonstrate using fluoro-turoquoise FT gel perfusion techniques, the protection afforded by trehalose from MPTP-induced damage to microvessels and endothelial and suggests that trehalose therapy may have the potential to slow or ameliorate PD pathology.

Dopaminergic and behavioral correlates of progressive lesioning of the nigrostriatal pathway with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

A number of neurotoxin- and gene-based rodent models of acute neurodegeneration of nigrostriatal dopamine (DA) neurons are used to study Parkinson's disease (PD). The rapid degeneration achieved by many of these current models limits the capacity of the model to develop pathogenic mechanisms and display the various stages of motor degradation representative of the human Parkinsonian condition. Chronic rodent models have been the only ones to reproduce these characteristics, yet do not show correlated progress of DA loss with multiple stepwise behavioral deficits as seen in humans. In the present study, we have developed a progressive model of increasing DA loss and motor dysfunction via progressively increased administration of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), in the C57Bl/6J mouse. Mice were administered a daily (5 d/wk) dose of MPTP that increased weekly over the course of 4 weeks (4 mg/kg, 8 mg/kg, 16 mg/kg and 32 mg/kg). Each treatment group was tested for exploratory and motor behavioral changes after every week leading up to their final dose, as well as changes in tyrosine hydroxylase immunoreactivity (TH-ir) of the substantia nigra pars compacta (SNpc) and caudate putamen (CPu). We detected a 24% decrease in the mean number of TH-ir SNpc neurons/section after 1 week, and a 62% decrease after 4 weeks as compared to the vehicle group. CPu TH-ir began at a 35% loss after 1 week and increased to a 74% loss after 4 weeks compared to the vehicle group. CPu DA content showed an initial decrease of 20% after 1 week, and a final decrease of 70% following week 4 versus the vehicle group. Free-standing rears (versus wall-assisted rears, in a cylinder), decreased from 35% to 8% of total rears as the dose of MPTP increased from 4 mg/kg to 32 mg/kg, respectively. However, motor impairment as measured by a Parallel Rod Activity Chamber test was not significant until week 4 at 32 mg/kg compared to the vehicle group. The present study is the first to show stepwise progression of behavioral deficits which correlate with gradual dopaminergic decline in the nigrostriatal pathway. This progressive lesioning regiment may be appropriate for future investigation of pathogenic mechanisms and various intervention therapies in PD.

Age-dependent effects of κ-opioid receptor stimulation on cocaine-induced stereotyped behaviors and dopamine overflow in the caudate–putamen: an in vivo microdialysis study

κ-Opioid receptor stimulation attenuates psychostimulant-induced increases in extracellular dopamine in the caudate–putamen (CPu) and nucleus accumbens of adult rats, while reducing cocaine-induced locomotor activity and stereotyped behaviors. Because κ-opioid receptor agonists (e.g., U50,488 or U69,593) often affect the behavior of preweanling rats in a paradoxical manner, the purpose of the present study was to determine whether κ-opioid receptor stimulation differentially affects dopaminergic functioning in the CPu depending on age. In vivo microdialysis was used to determine whether U50,488 (5 mg/kg) attenuates cocaine-induced dopamine overflow in the dorsal CPu on postnatal day (PD) 17 and PD 85. In the microinjection experiment, cocaine-induced stereotyped behaviors were assessed in adult and preweanling rats after bilateral infusions of vehicle or U50,488 (1.6 or 6.4 μg per side) into the CPu. Results showed that U50,488 attenuated the cocaine-induced increases in CPu dopamine overflow on PD 85, while the same dose of U50,488 did not alter dopamine dialysate levels on PD 17. Cocaine also increased stereotyped behaviors (repetitive motor movements, behavioral intensity scores, and discrete behaviors) at both ages, but adult rats appeared to exhibit more intense stereotypic responses than the younger animals. Consistent with the microdialysis findings, bilateral infusions of U50,488 into the dorsal CPu decreased the cocaine-induced stereotypies of adult rats, while leaving the behaviors of preweanling rats unaffected. These results suggest that the neural mechanisms underlying κ-opioid/dopamine interactions in the CPu are not fully mature during the preweanling period. This lack of functional maturity may explain why κ-opioid receptor agonists frequently induce different behavioral effects in young and adult rats.

Human methamphetamine pharmacokinetics simulated in the rat: behavioral and neurochemical effects of a 72-h binge.

Bingeing is one pattern of high dose methamphetamine (METH) abuse which involves continuous drug taking over several days and can result in psychotic behaviors for which the brain pathology remains poorly-defined. A corresponding animal model of this type of METH exposure may provide novel insights into the neurochemical and behavioral sequelae associated with this condition. Accordingly, to simulate the pharmacokinetic profile of a human METH binge exposure in rats we used a computer-controlled, intravenous METH procedure (dynamic infusion) to overcome species differences in METH pharmacokinetics and to replicate the human 12-h plasma METH half-life. Animals were treated over 13 weeks with escalating METH doses, using dynamic infusion, and then exposed to a binge in which drug was administered every 3 h for 72h. Throughout the binge, behavioral effects included unabated intense oral stereotypies in the absence of locomotion and in the absence of sleep. Decrements in regional brain dopamine, norepinephrine and serotonin levels, measured at 1 and 10 h after the last injection of the binge, had, with the exception of caudate-putamen dopamine and frontal cortex serotonin, recovered by 48 h. At 10 h after the last injection of the binge, [3H]ligand binding to dopamine and vesicular monoamine transporters in caudate-putamen were reduced by 35% and 13%, respectively. In a separate METH binge treated cohort, post-binge behavioral alterations were apparent in an attenuated locomotor response to a METH challenge infusion at 24h after the last injection of the binge. Collectively, the changes we characterized during and following a METH binge suggest that for humans under similar exposure conditions, multiple time-dependent neurochemical deficits contribute to their behavioral profiles.

Lack of the DNA Repair Enzyme OGG1 Sensitizes Dopamine Neurons to Manganese Toxicity During Development

Onset of Parkinson's disease (PD) and Parkinson-like syndromes has been associated with exposure to diverse environmental stimuli. Epidemiological studies have demonstrated that exposure to elevated levels of manganese produces neuropathological changes localized to the basal ganglia, including neuronal loss and depletions in striatal dopamine content. However, understanding the mechanisms associated with manganese neurotoxicity has been hampered by the lack of a good rodent model. Elevated levels of 8-hydroxy-2'-deoxyguanosine (oxo8dG) have been found in brain areas affected in PD. Whether increased DNA damage is responsible for neuronal degeneration or is a mere epiphenomena of neuronal loss remains to be elucidated. Thus, by using mice deficient in the ability to remove oxo8dG we aimed to determine if dysregulation of DNA repair coupled to manganese exposure would be detrimental to dopaminergic neurons. Wild-type and OGG1 knockout mice were exposed to manganese from conception to postnatal day 30; in both groups, exposure to manganese led to alterations in the neurochemistry of the nigrostriatal system. After exposure, dopamine levels were elevated in the caudate of wild-type mice. Dopamine was reduced in the caudate of OGG1 knockout mice, a loss that was paralleled by an increase in the dopamine index of turnover. In addition, the reduction of dopamine in caudate putamen correlated with the accumulation of oxo8dG in midbrain. We conclude that OGG1 function is essential in maintaining neuronal stability during development and identify DNA damage as a common pathway in neuronal loss after a toxicological challenge.

Methamphetamine-induced loss of striatal dopamine innervation in BDNF heterozygote mice does not further reduce D3 receptor concentrations.

Depletion of dopamine (DA) reduces D(3) receptor number, but D(3) receptor expression is also regulated by brain-derived neurotrophic factor (BDNF). We took advantage of transgenic heterozygous BDNF mutant mice (+/-) to determine if reduced BDNF and loss of DA fibers produced by methamphetamine were additive in their impact on D(3) receptor number. We assessed selective markers of the dopaminergic system including caudate-putamen DA concentrations and quantitative autoradiographic measurement of tyrosine hydroxylase (TH) levels, DA transporter (DAT), and DA D(3) receptor binding between vehicle and methamphetamine-treated BDNF +/- and their wildtype (WT) littermate control mice. Caudate-putamen DA concentrations, TH and DAT levels were significantly reduced following methamphetamine treatment in both WT and BDNF +/- mice. The extent of methamphetamine-induced reduction in TH and DAT was greater for the WT than BDNF +/- mice and DAT levels were also decreased to a greater extent in nucleus accumbens of WT as compared to BDNF +/- mice. Lower D(3) receptor existed in caudate-putamen and nucleus accumbens in BDNF +/- mice and these differences were not affected by methamphetamine treatment. Taken together, these results not only substantiate the importance of BDNF in controlling D(3) receptor expression, but also indicate that a methamphetamine-induced depletion of DA fibers fails to produce an additive effect with lowered BDNF for control of D(3) receptor expression. In addition, the reduction of D(3) receptor expression is associated with a decreased neurotoxic response to methamphetamine in BDNF +/- mice.

Appetite restored with dopamine

Striatal dopamine can effect specific feeding behaviors, reports a recent Neuron article. Mice born with dopaminergic-cell deficits in tyrosine-hydroxylase are so severely hypoactive and hypophagic that they die of starvation by one month. Using virus-assisted gene therapy in these mice, University of Washington researchers found that restoring dopamine production in the caudate putamen (CPu) restores feeding on normal chow and preference for palatable diets. Mice injected in the nucleus accumbens (NAc) still won't eat normal chow, but they do prefer palatable diets. These differences in either eating for sustenance or eating for pleasure might also reflect larger distinctions in behavior motivation, because CPu dopamine restores nest-building behavior, whereas NAc dopamine increases exploratory behavior. Injections in either area did not fully reverse coordination or movement deficits in these mice, but this study could shed light on dietary and motivational issues that often accompany motor deficits in Parkinson's disease.

Caudate-putamen dopamine and stereotypy response profiles after intravenous and subcutaneous amphetamine.

We compared the behavioral and caudate-putamen extracellular dopamine responses following intravenous (3.6 mg/kg) and subcutaneous (8 mg/kg) amphetamine administration using 2-min microdialysate sampling intervals, and doses of the drug selected to achieve comparable maximal brain concentrations. Following intravenous amphetamine, dopamine peaked within the first 2 min, then declined with a first-order decay rate of 0.018+/-0.007 min(-1). Following subcutaneous amphetamine, dopamine achieved maximum concentrations at 9 min and remained near peak levels for about 30 min before declining with a first-order decay rate of 0.019+/-0.008 min(-1). Maximal brain amphetamine levels and peak dopamine concentrations were equivalent following either route of drug administration. In contrast to the short latency to maximal extracellular dopamine, the onset of oral stereotypies was delayed until about 30 min following both routes of drug administration. Furthermore, in contrast to the behavioral response to amphetamine, apomorphine administration resulted in the rapid appearance of oral stereotypies within 5-10 min after drug administration. These results suggest that although caudate-putamen dopamine receptor activation may be a critical factor in the expression of focused oral stereotypies, other effects of amphetamine may interfere with the ability of animals to exhibit these behaviors.

An Escalating Dose/Multiple High-Dose Binge Pattern of Amphetamine Administration Results in Differential Changes in the Extracellular Dopamine Response Profiles in Caudate-Putamen and Nucleus Accumbens

Amphetamine (AMPH)-induced psychosis is most frequently associated with a chronic high-dose "binge" or "run" pattern of stimulant abuse, generally preceded by a period of gradually escalating doses of the drug. We showed previously that animals subjected to such a regimen of AMPH administration developed, over multiple daily binges, a unique pattern of behavioral response that included a decrease in stereotypy and a pronounced increase in locomotion. Because of the involvement of mesolimbic and mesostriatal dopamine (DA) pathways in locomotion and stereotypy, respectively, we hypothesized that a persistent shift in the relative magnitude of caudate-putamen (CP) and nucleus accumbens (NAC) DA transmission may contribute to this altered behavioral profile. To test this hypothesis, we examined CP and NAC extracellular DA in response to multiple high-dose AMPH binges. Our results revealed that with multiple binges the CP DA response but not the NAC response developed a profound tolerance/tachyphylaxis to the drug-induced increase in extracellular transmitter. These differential regional response alterations seem to correspond to the shift in the relative expression of stereotypy and locomotion. We hypothesize that changes in DA synthesis, perhaps mediated by regionally specific adaptations in DA autoreceptor function, contribute to the differential extracellular transmitter response profiles, and suggest that these neurochemical changes may have important implications for the mechanisms underlying the addictive and psychotogenic properties of AMPH.

Nitric oxide regulation of methamphetamine-induced dopamine release in caudate/putamen

A possible role for NO modulation of dopamine (DA) release in the caudate/putamen (CPU) during methamphetamine (METH) exposure was investigated using in vivo microdialysis in rats. Inclusion of the nitric oxide synthase (NOS) inhibitors N G-nitro- l-arginine (NOARG), N G-nitro- l-arginine methyl ester (L-NAME) or D-NAME (less potent inhibitor) in the microdialysis buffer prior to METH minimally affected basal levels of DA, DOPAC or HVA in CPU microdialysate. However, L-NAME and NOARG produced concentration-dependent decreases of up to 64% (100 μM) in CPU DA levels in microdialysate during exposure to four doses of METH (5 mg/kg i.p./2h), with lesser effects on DOPAC or HVA. Reversal of the NOARG inhibition was produced by inclusion of 500 μM of either l-arginine or l-citrulline in the microdialysate. D-NAME (100 μM) minimally affected levels of DA or metabolites. Paradoxically, inclusion of from 20 to 2 μM of the NO x generators isosorbide dinitrate (ISON) or sodium nitroprusside (SNP) in the microdialysis buffer decreased DA and DOPAC levels in microdialysate during METH exposure. This paradox might result from the concentrations of NO x produced by SNP or ISON being great and not regionally specific resulting in inhibition of DA release and/or synthesis while the NO generated endogenously during METH exposure may have localized and site-specific actions. Alternatively, NO x may inhibit NOS or other enzymes in the NO synthesis pathway, thereby reducing levels of an intermediate (other than NO) which potentiates DA release. In their entirety, our results indicate that NO generation in the CPU may augment the release of DA during METH exposure.

Abnormal rat brain monoamine metabolism in iron deficiency anemia

Iron deficiency in rats produces numerous alterations in brain metabolism as assessed by in vitro techniques. We used a new method of in vivo microdialysis to study the effect of acute iron deficiency anemia on rat brain monoamine metabolism. This method was used to sample extracellular fluid from an implanted microdialysis probe in the caudate putamen from freely moving animals. Method validation experiments showed that steady-state levels of dopamine, norepinephrine, and their metabolites were obtained only after 5 to 7 days of surgical recovery and with prior perfusion of the brain region. Caudate putamen dopamine was significantly increased 30% and 40% in fasted light-exposed and 2-hr-fed dark-exposed iron deficient anemic rats (hemoglobin in vitro demonstrations of down-regulation of dopamine D 2 receptors, they also suggest that uptake and processing of monoamines is significantly perturbed by iron deficiency.

Altered monamine metabolism in caudate-putamen of iron-deficient rats

The effect of iron deficiency on brain monoamine metabolism using in vivo microdialysis techniques has not been previously reported. We, therefore, examined the monoamines, dopamine and norepinephrine, and their metabolites at steady state by in vivo microdialysis in rat brain caudate-putamen in 11-week-old iron-deficient anemic (hemoglobin < 7 g/dl) and control rats (Hb > 14 g/dl). Caudate-putamen dopamine (DA), dihydroxyphenyl acetic acid (DOPAC), and homovanillic acid (HVA) concentrations were increased by 53%, 57%, and 30% ( p < 0.001), respectively, in iron-deficient rats in samples collected over a 4-h period. While diminished numbers of D 2 receptors have been previously reported, the present findings suggest an additional defect in monoamine uptake and catabolism.

Simultaneous real-time correlation of drug effects on dopamine efflux and uptake in rat striatal slices.

An increasing body of evidence suggests that striatal dopamine (DA) terminal areas in the rat (the caudate-putamen (CPu) and nucleus accumbens (NAc)) differ in their DA transport sites [ l ] and possibly DA storage pools [2]. We therefore compared the effects of various drugs acting at each site on the efflux and uptake of DA in CPu and NAc. We used fast cyclic voltammetry (FCV) [3] to electrochemically monitor DA efflux and uptake half-life on a sub-second time scale in these two brain areas. The DA uptake blockers GBR 12935 (GBR: 0.2 pM) and bupropion (Bup: 1 pM), the psychomotor stimulant amfonelic acid (AFA: 0.1 pM) and a putative DA mobiliser (the M2 metabolite of nomifensine (M2: 0.5 pM) [4]) were used in order to probe these suggested differences. Their effects on DA efflux and uptake half-life were measured simultaneously at each site. All experiments were conducted in 350 pm brain slices from male Wistar rats (100-1509) superfused with artificial CSF at 32°C. NAc slices were taken at approximately +10.5 mm vs the interaural line [5] and recordings made in the core of the nucleus. CPu slices were taken from approximately +9.2 mm and recordings made from the dorsolateral region. DA efflux was evoked using alternate single pulse ( lp ) and 5 pulse (5p) trains (0.1 ms, 50 Hz, 10 mA, every 10 min) via a bipolar tungsten electrode. FCV was used to monitor DA efflux and subsequent reuptake at a carbon fibre microelectrode sampling at 2 Hz. Drugs were administered after the third 5p stimulation train and were allowed to equilibrate for two hours. DA efflux and uptake half-life after this period was expressed as a percentage of the mean of the pre-drug period. The data on l p stimulations is not reported here. Figure 1 shows the effects of the drugs on DA efflux and uptake half-life in the CPu. It can be seen that M2, GBR and AFA produced significant increases in efflux in the CPu. Only GBR and AFA had a significant effect on uptake half-life.

Effects of a cold environment or age on methamphetamine-induced dopamine release in the caudate putamen of female rats

Extracellular levels of dopamine (DA) and metabolites as well as serotonin [5-hydroxytryptamine (5-HT)] and 5-hydroxyindoleacetic acid (5-HIAA) were determined in the caudate putamen (CPU) of either 6- or 12-month-old female rats using microdialysis and high-performance liquid chromatography with electrochemical detection (HPLC-ED) before, during, and after four consecutive injections (given at 2-h intervals) of methampetamine (METH). In 6-month-old rats administered 4 × 5 mg/kg METH at an environmental temperature (ET) of 23°C, peak extracellular DA levels (between 50 and 150 ϱg/10 μl) were attained 30–45 min after each dose of METH while dihydroxyphenylacetic acid (DOPAC) decreased steadily after the first doses of METH until it reached a plateau at 50% of control (550−700 pg/10 μl) levels. Increase in 5-HT levles during METH administrations paralleled DA increases while 5-HIAA decreases paralleled DOPAC decreases. The total CPU DA and 5-HT content of these rats was about 65% of control at 3 days post-METH. Reducing the ET to 4°C during dosing decreased the peak and average DA levels attained during the 4 × 5 mg/kg METH administration to about 50% of that observed at a 23°C ET. Increasing the dose to 4 × 10 mg/kg METH (4°C ET) increased peak and average CPU DA levels to 200% that observed during 4 × 5 mg/kg METH at a 23°C ET. However, no significant decreases in total CPU DA content of any rats dosed with METH at a 4°C ET were observed 3 days post-METH. In 12-month-old rats dosed with 4 × 5 mg/kg METH (23°C ET), the peak and average extracellular DA levels were only 30−60% that of 6-month-old rats. However, the CPU DA content of older rats was significantly decreased both 3 (30% control) and 14 (60% control) days post-METH. In summary, METH toxicity may not be predicted solely by the extracellular levels of DA attained during METH administration; age and ET also greatly influence METH neurotoxicity.

Differential effects of mesocortical, mesolimbic, and mesostriatal dopamine depletion on spontaneous, conditioned, and drug-induced locomotor activity

Groups of rats with 6-hydroxydopamine (6-OHDA) lesions of either the medial prefrontal cortex (PFC), nucleus accumbens (NAC), or caudate putamen (CPu) were given daily tests for locomotor activity in photocell cages while food deprived. Two separate groups of NAC-lesioned rats were prepared with either large [NACT (90% NAC dopamine depletion)] or partial [NACP (67% NAC dopamine depletion)] lesions. NACT rats were spontaneously hypoactive whereas NACP rats were hyperactive compared with sham-operated controls. PFC-lesioned rats were also hyperactive compared to their respective controls. Spontaneous locomotor activity in CPu-lesioned rats did not differ from shams. When daily food supplements were paired with the photocell cages, all subjects developed a conditioned locomotor response. During the first few days of conditioning, the response to this conditioning procedure was markedly greater in the NACP group whereas the response in the NACT group was unaffected initially and actually enhanced during the latter days of testing. the locomotor response to the conditioning procedure was unaffected in either the PFC- or CPu-lesioned groups. Both the NACT and NACP lesions attenuated the locomotor response to 1.5 mg/kg d-amphetamine sulphate IP, and the NACT group showed a supersensitive response to 0.1 mg/kg apomorphine HCl SC. PFC or CPu 6-OHDA lesions did not alter the response to either drug. These results differentiate the role of PFC, NAC, and CPu dopamine in spontaneous, conditioned, and drug-induced locomotor activity and further implicate dopaminergic mechanisms of the NAC in the magnitude of the behavioral response to incentive stimuli.

Regional differences in the regulation of dopamine and noradrenaline release in medial frontal cortex, nucleus accumbens and caudate-putamen: a microdialysis study in the rat

Dopamine (DA) and noradrenaline (NA) extracellular levels have been measured by microdialysis in the medial frontal cortex (MFC), nucleus accumbens (NAc) and caudate-putamen (CP) under baseline conditions in awake and halothane-anaesthetized rats, and after application of three types of stimuli which are likely to activate the brainstem catecholaminergic systems: mild stressors (handling and tail pinch), rewarded behavior (eating palatable food without prior food deprivation) and electrical stimulation of the lateral habenular nucleus. Changes were studied with and without uptake blockade (10 μM nomifensine in the perfusion fluid). The influence of calcium concentration (1.2 or 2.3 mM in the perfusion fluid) on DA and NA overflow was tested in some cases. Handling and tail pinch stimulated both DA and NA overflow in MFC, and enhanced NA overflow in NAc. By contrast, these mildly stressful stimuli had only marginal effects on DA overflow in NAc and no effects on either DA or NA overflow in CP. Eating behavior was accompanied by increased DA and NA overflow in MFC but had no effect in NAc. These regional differences were similar also when the manipulations were applied under uptake blockade, which indicates that the more pronounced changes seen in MFC did not simply reflect a more sparse innervation (i.e. lower density of uptake sites) in the MFC compared to the more densely innervated NAc and CP areas. Stimulation of the lateral habenula induced a 2–3-fold increase in NA overflow in both MFC, NAc and CP but had no consistent effect on DA overflow in any region. The effect on NA release was abolished by a transection of the ipsilateral fasciculus retroflexus (which carries the efferent output of the lateral habenula). The results show that the forebrain DA and NA projections to cortical and striatal targets are differentially regulated during ongoing behavior, that the mesocortical and mesostriatal DA systems respond quite differently to stressful and rewarding stimuli; and that the NA projection to MFC (like the dopaminergic one) is more responsive to stressful and rewarding stimuli than the ones innervating the striatum (NAc and CP). The results support the view that environmental stimuli evoking emotional arousal (whether aversive or non-aversive) are accompanied by increased DA and NA release above in all the MFC and only to a minor extent in limbic and striatal areas.

Neuropeptide gene expression in brain is differentially regulated by midbrain dopamine neurons

In situ hybridization was used to study the expression of prepro-neuropeptide Y (NPY), preprosomatostatin (SOM), preprotachykinin (PPT) and preprocholecystokinin (CCK) mRNA in caudate-putamen and frontoparietal cortex of rat brain with unilateral lesion of midbrain dopamine neurons. Neurons expressing NPY and SOM mRNA showed a similar distribution and the expression of both NPY and SOM appears to be regulated by dopamine in a similar fashion. Following a dopamine deafferentation, the numerical density of both NPY and SOM mRNA producing neurons almost doubled in the lesioned caudate-putamen with no change in the average grain density over positive neurons. Hence, in the intact caudate-putamen dopamine appears to suppress expression of these two neuropeptide genes leading to an activation of both NPY and SOM mRNA expression in many non- or low-expressing neurons when the level of dopamine is decreased. In the fronto-parietal cortex, on the other hand, dopamine appears to stimulate NPY and SOM gene expression. Thus, in the absence of dopamine about half of the NPY positive neurons disappeared. However, for SOM the number of positive neurons did not change, but rather most positive neurons appeared to have down-regulated their SOM mRNA expression. No evidence was found for a change in CCK mRNA expression by the dopamine deafferentation, while PPT mRNA expression decreased in the deafferented caudate-putamen. Consequently, dopamine exerts dissimilar effects on the expression of different neuropeptide genes, that in turn do not respond in the same way in different brain regions.

Central catecholaminergic dysfunction and behavioral disorders following hypoxia in adult rats

Wistar male rats, 3–4 months old, were made to breathe for 6 h a sub-lethal hypoxic atmosphere consisting of 8% oxygen and 92% nitrogen. Following this treatment, these rats were subjected to a series of behavioral and biochemical tests starting 30 days and ending at about 180 days after the hypoxic insult. An age-matched control group was subjected to the same series of tests. The following findings were made at the time interval indicated, relative to controls: (1) At 30–35 days, diurnal (3 h) and nocturnal (12 h) locomotor activities decreased by about 25%. (2) At 40–45 days, amphetamine in the dose range of 0.25–1 mg/kg proved less effective in eliciting an increase in motor activity and stereotypic behavior. (3) At about 50 days, apomorphine in the dose range 0.25–0.5 mg/kg caused an increase in stereotypic behavior. (4) At 60–65 days, α-methyl- p-tyrosine at the dose of 50 mg/kg caused a more pronounced hypoactive syndrome and a slower rate of recovery of motor activity. (5) At 75–90 days, performance in the active avoidance test was inferior to that of controls. (6) At 180 days, and one hour after a dose of 200 mg/kg α-methyl- p-tyrosine, the turnover rates of hippocampal norepinephrine and caudate-putamen dopamine were much below control. One may tentatively conclude that one of the effects of hypoxia in adult rats is a lesion producing long-term behavioral disorders which are partly ascribed to dopaminergic and, possibly noradrenergic, dysfunction.

Regional effect of estradiol on rat caudate-putamen dopamine receptors: lateral-medial differences

The effect of a chronic 17β-estradiol (10 μg, b.i.d.) treatment of 2 weeks to ovariectomized rats was investigated on lateral and medial caudate-putamen dopamine receptors. Dopamine D 2 receptors were assayed with [ 3H]spiperone binding to caudate-putamen homogenates or by autoradiography of forebrain sections. Estradiol treatment leads to a significant increase in the density of lateral caudate-putamen dopamine receptors while for the medial dopamine receptors the increase is non-significant. This effect is observed when plasma levels of 17β-estradiol and prolactin are increased. These results indicate that the effect of estradiol on striatal dopamine receptors is heterogeneous and that those in the lateral part are more susceptible to this steroid.