Effect of intraventricular administration of noradrenaline and dopamine on the levels of corticosterone in rats and denervation hypersensitivity resulting from intraventricular administration of 6-hydroxydopamine.

The effects of intraventricular administration of noradrenaline (NA) on the resting levels, stress-induced rises and dexamethasone-induced decreases of plasma corticosterone (B) were studied in rats. The effect of pretreatment with intraventricular administration of 6-hydroxydopamine (6-OHDA) on the effects of NA or dopamine (DA), which was injected intraventricularly, was also examined. The results obtained were as follows: 1) Intraventricular administration of 1.0 μg of NA did not cause a decrease in concentrations of plasma B. 2) Ten μg of NA injected intraventricularly resulted in a rise of the levels of plasma B. 3) The stimulating action of centrally administered NA was more marked when the pre-injection concentrations of B were lower. 4) Pretreatment with intraventricular administration of 6-OHDA facilitated the action of intraventricularly administered NA in the regulation of pituitary-adrenocortical functions. The result suggests a development of denervation hypersensitivity caused by the pretreatment. 5) Intraventricular administration of NA did not block stress-induced rises of plasma B. 6) Intraventricular administration of NA counteracted dexamethasone-induced decrements of plasma B. 7) This counteraction was enhanced by pretreatment with intraventricular administration of 6-OHDA. This also suggests a development of denervation hypersensitivity resulting from intraventricular administration of 6-OHDA. 8) Intraventricular administration of 1.0 μg of DA caused no change in the concentrations of plasma B in either control or 6-OHDA treated animals.     

BIMG 80, a Novel Potential Antipsychotic Drug: Evidence for Multireceptor Actions and Preferential Release of Dopamine in Prefrontal Cortex

Abstract: In radioligand binding studies, BIMG 80, a new putative antipsychotic, displayed good affinity at certain serotonin (5-HT_1A, 5-HT_2A, 5-HT₆), dopamine (D₁, D_2L, D₄), and noradrenergic (α₁) receptors. The effect of acute subcutaneous BIMG 80, clozapine, haloperidol, risperidone, amperozide, olanzapine, and Seroquel was then investigated on dopamine release in medial prefrontal cortex, nucleus accumbens, and striatum in freely moving rats using the microdialysis technique. Four different neurochemical profiles resulted from the studies: (a) Systemic administration of BIMG 80, clozapine, and amperozide produced greater percent increases in dopamine efflux in medial prefrontal cortex than in the striatum or the nucleus accumbens. (b) Haloperidol induced a similar increase in dopamine concentrations in the striatum and nucleus accumbens with no effect in the medial prefrontal cortex. (c) Risperidone and olanzapine stimulated dopamine release to a similar extent in all brain regions investigated. (d) Seroquel failed to change significantly dopamine output both in the medial prefrontal cortex and in the striatum. Because an increase in dopamine release in the medial prefrontal cortex may be predictive of effectiveness in treating negative symptoms and in the striatum may be predictive of induction of extrapyramidal side effects, BIMG 80 appears to be a potential antipsychotic compound active on negative symptoms of schizophrenia with a low incidence of extrapyramidal side effects.     

α-Linolenic Acid Dietary Deficiency Alters Age-Related Changes of Dopaminergic and Serotoninergic Neurotransmission in the Rat Frontal Cortex

Abstract: The effects of α-linolenic acid diet deficiency on rat dopaminergic and serotoninergic neurotransmission systems were investigated in the frontal cortex, striatum, and cerebellum of male rats 2, 6, 12, and 24 months of age. The diet deficiency induced a severe decrease in the 22:6n-3 fatty acid levels in all regions and a compensatory increase in n-6 fatty acid levels. A recovery in the levels of 22:6n-3 was observed in deficient rats between 2 and 12 months of age; however, this recovery was lower in frontal cortex than in striatum and cerebellum. In the striatum and the cerebellum, dopaminergic and serotoninergic receptor densities and endogenous dopamine and serotonin levels were affected by aging regardless of the diet. In contrast, a 40–75% lower level of endogenous dopamine in the frontal cortex occurred in deficient rats according to age. The deficiency also induced an 18–46% increase in serotonin 5-HT₂ receptor density in the frontal cortex during aging, without variation in endogenous serotonin level, and a 10% reduction in density of dopaminergic D₂ receptors. Monoamine oxidase-A and -B activities showed specific age-related variations but regardless of the diet. Our results suggest that a chronically α-linolenic-deficient diet specifically affects the monoaminergic systems in the frontal cortex.     

EPC-K1, a Hydroxyl Radical Scavenger,Prevents 6-Hydroxydopamine-Induced Dopamine Depletion in the Mouse Striatum by Up-Regulation of Catalase Activity

We examined the effect of pretreatment with EPC-K1, a potent hydroxyl radical scavenger, on 6-hydroxydopamine (6-OHDA)-induced reduction of dopamine (DA) and its metabolites in the mouse striatum. EPC-K1 was mixed with diet (0.2%, wt/wt) for 1 or 2 weeks, and then 6-OHDA (60 g in 2l of saline solution) was injected intracereberoventricularly. Mice continued to be fed EPC-K1-containing diet for another one week before they were sacrificed. The concentrations of DA and its metabolites in the striatum were measured by high performance liquid chromatography. 6-OHDA reduced the level of DA and its metabolites in the striatum. Pretreatment with EPC-K1 for 2 weeks, but not for 1 week, abrogated the neurotoxic effect of 6-OHDA on striatal concentrations of DA and its metabolites. Measurement of striatal concentrations of thiobarbituric acid reactive substances, glutathione, and malonaldehyde plus 4-hydroxynonenal, and the activities of superoxide dismutase and catalase in EPC-K1 treated mice showed an increase in catalase activity after 2 weeks of such treatment. No other changes in anti-oxidants levels were noted. Our results suggest that EPC-K1 counteracts the neurotoxicity of 6-OHDA by increasing catalase activities.     

Brain mast cells and therapeutic potential of vasoactive intestinal peptide in a Parkinson's disease model in rats: brain microdialysis, behavior, and microscopy

In the present study, the effect of systemically administered vasoactive intestinal peptide (VIP) (25 ng/kg i.p.) was investigated on drug-induced rotational behavior, extra-cellular dopamine levels and histology of corpus striatum in a 6-hydroxydopamine (6-OHDA)-induced rat model of Parkinson's disease. After 15 days of 6-OHDA lesion, apomorphine-induced (0.05 mg/kg s.c.) rotational behavior of the animals significantly increased and extra-cellular dopamine levels of corpus striatum were significantly reduced. VIP reversed the rotational deficits but did not alter the decrease in striatal dopamine levels. On the other hand, histological data indicate that VIP significantly reduced neuronal death and demyelination. Electron microscopic appearance of mast cells showed ultra-structural variety between VIP-treated and 6-OHDA lesioned groups. VIP activates mast cells without any evidence of typical exocytosis, and possibly mast cells could participate in neuroprotection. Our results suggest that systemically administered VIP can attenuate the motor response changes, neuronal cell death, and myelin sheet loss characteristically associated with 12 microg 6-OHDA administration into the rat striatum. Brain mast cells seem to participate in neuronal protection. Possibly, protective cues could be produced by brain mast cells.     

Evidence that Extracellular Concentrations of Dopamine Are Regulated by Noradrenergic Neurons in the Frontal Cortex of Rats

Abstract: Experiments were performed to confirm that noradrenergic terminals regulate extracellular concentrations of dopamine (DA) in the frontal cortex of rats. The effects of 20 mg/kg 1-[2-[bis(4-fluorphenyl)methoxy]-ethyl]-4-(3-phenylpropyl)piperazine (GBR 12909), a selective inhibitor of DA uptake, and 2.5 mg/kg desipramine (DMI) on the extracellular concentrations of DA in the frontal cortex and striatum were studied in rats given 6-hydroxydopamine (6 µg/µl) bilaterally into the locus coeruleus to destroy noradrenergic terminals. GBR 12909 increased dialysate DA similarly in the striatum of vehicle and 6-hydroxydopamine-treated rats, whereas in the frontal cortex it raised DA concentrations only in lesioned animals. DMI raised extracellular DA concentrations in the frontal cortex but not in the striatum of controls. The effect of DMI on cortical DA was abolished by the 6-hydroxydopamine lesion. GBR 12909, at a subcutaneous dose of 20 mg/kg, further increased cortical dialysate DA in rats given DMI intraperitoneally at 20 mg/kg or through the probe at 10⁻⁵ mol/L. The data support the hypothesis of an important regulation of the extracellular concentrations of DA in the frontal cortex by noradrenergic terminals.     

Differential effect of morphine on dopaminergic neurons in frontal cortex and striatum of the rat

Inhibition of dopamine synthesis by a single injection of α-methyl-para-tyrosine (200 mg/kg, i.p.) was complete from 30 to at least 300 min after administration. When morphine (20 mg/kg) was given intraperitonealy 30 min after α-MpT treatment an enhanced decline of dopamine was observed in frontal parts of the cortex but not in the striatum. These results indicate that morphine affects dopaminergic neurons in frontal parts of the cortex in a way differently from those in the striatum of the rat. This may be caused either by a difference in the properties of dopaminergic nerve endings in both structures or by an effect of morphine on the input to the cortical system which is lacking in the striatum.     

Effect of nicotine on extracellular levels of neurotransmitters assessed by microdialysis in various brain regions: Role of glutamic acid

We studied the effect of local administration of nicotine on the release of monoamines in striatum, substantia nigra, cerebellum, hippocampus, cortex (frontal, cingulate), and pontine nucleus and on the release of glutamic acid in striatum of rats in vivo, using microdialysis for nicotine administration and for measuring extracellular amine and glutamic acid levels. Following nicotine administration the extracellular concentration of dopamine, increased in all regions except cerebellum; serotonin increased in cingulate and frontal cortex; and norepinephrine increased in substantia nigra, cingulate cortex, and pontine nucleus. Cotinine, the major nicotine metabolite, had no effect at similar concentrations. The cholinergic antagonists mecamylamine and atropine, the dopaminergic antagonists haloperidol and sulpiride, and the excitatory amino acid antagonist kynurenic acid all inhibited the nicotine-induced increase of extracellular dopamine in the striatum. The fact that kynurenic acid almost completely prevented the effects of nicotine, and nicotine at this concentration produced a 6-fold increase of glutamic acid release, suggests that the effect of nicotine is mainly mediated via glutamic acid release.     

Effects of acute central and peripheral administration of nicotine on ascending dopamine pathways in the male rat brain. Evidence for nicotine induced increases of dopamine turnover in various telencephalic dopamine nerve terminal systems

The actions of intraventicular injections and intravenous infusions of nicotine were studied on dopamine stores and turnover in discrete areas of the forebrain of normal male rats. This was done by measuring the decline of the dopamine stores after tyrosine hydroxylase inhibition using alpha-methyl-tyrosine methyl ester (H44/68). The dopamine concentrations in the various telencephalic dopamine nerve terminal systems were measured using the Falck-Hillarp methodology involving quantitative microfluorimetry. The catecholamine concentrations in the anteromedial frontal cortex were measured biochemically using high pressure liquid chromatography combined with electrochemical detection. Intraventricular experiments. The dopamine levels in discrete areas of nuc. caudatus and nuc. accumbens were significantly reduced even with the lowest dose of nicotine (1 microgram/rat). Intraventricular injections of nicotine in a dose of 100 microgram/rat produced significant increases of dopamine turnover in various types of dopamine nerve terminal systems in the nuc. caudatus, nuc. accumbens and tuberculum olfactorium, and following a dose of 10 microgram/rat increases of dopamine turnover were observed in the medial part of the nuc. caudatus. Furthermore, nicotine (100 microgram/rat) significantly increased noradrenaline but not dopamine turnover within the anterofrontal cortex. Intravenous experiments. The dopamine levels were selectively reduced by nicotine (1000 microgram/kg) in the cholecystokinin positive and negative dopamine nerve terminal systems of the nuc. accumbens. On the other hand, dopamine levels in the anteromedial frontal cortex were increased after this dose of nicotine. Intravenous infusions of nicotine (10-1000 microgram/kg) produced dose-related increases of dopamine turnover in the various dopamine nerve terminal systems analysed in the telencephalon. These effects became significant with a dose of 1000 microgram/kg/h. The dopamine terminals in the nuc. caudatus showed a higher sensitivity to intravenous infusions of nicotine, being affected by 10-100 microgram/kg of nicotine. These findings suggest that relatively low dose of nicotine via an activation of central nicotine-like cholinergic receptors can reduce dopamine concentration and increase dopamine turnover in discrete limbic and striatal areas. These actions may in part represent the neurochemical basis for the rewarding actions of nicotine and for nicotine dependence in man.     

Effects of des-tyr1 -γ-endorphin on dopamine release from various rat brain regions in vitro

In rat striatum, nucleus accumbens and frontal cortex slices 6×10^?8M of the potential neuroleptic peptide des-Tyr-γ-endorphin (DTγE) did not affect basal dopamine release but depressed K⁺-evoked release. Haloperidol at 5×10^?6M increased both basal and K⁺-induced release in striatal and nucleus accumbens slices whereas it increased only basal dopamine release in frontal cortex slices. At 5×10^?8M haloperidol, however, had no effect. It is concluded that DTγE may decrease dopaminergic activity in the brain by depressing depolarization-induced dopamine release, possibly via a presynaptic mechanism.     

Somatostatin Content Increases Following Norepinephrine Depletion in Frontal Cortex of l-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine-Treated Mice

The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on somatostatin (SS)-containing neurons were examined by measuring dopamine, norepinephrine (NE), SS, and SS mRNA in striatum and frontal cortex of C57/B16 mice at various times following treatment with MPTP-HCl (96 mg/kg i.p.). MPTP caused a 70% depletion of dopamine in striatum by 1 day and a 40% depletion of NE in frontal cortex within 3 days. SS content was increased in frontal cortex 4 days later, but not in striatum; there were no changes in SS mRNA. Maprotiline, a specific NE-uptake blocker, prevented both the depletion of NE and the increase of SS in frontal cortex due to MPTP administration. These results support the possibility that NE can regulate SS in frontal cortex and are discussed in terms of the decrease of SS seen in parkinsonian patients with dementia.     

Characteristics of [3H]GBR 12935 Binding in the Human and Rat Frontal Cortex

Binding characteristics of the selective dopamine uptake inhibitor [3H]GBR 12935 have been described for the striatum but not for the frontal cortex. We have developed assay conditions for quantifying [3H]GBR 12935 binding in the frontal cortex. In both the rat and human frontal cortex, the assay required four times more tissue (8 mg/ml) than in the striatum (2 mg/ml). [3H]GBR 12935 binding in the frontal is complex, as it involves multiple binding sites. The high-affinity binding site is sodium dependent and is inhibited by sodium. In human but not in rat frontal cortex, addition of K+ reversed the sodium inhibition. The pharmacological profile of the high-affinity [3H]GBR 12935 binding site is consistent with that of the dopamine transporter, because drugs with the most selective dopamine reuptake blocking activities are the most potent displacers of [3H]GBR 12935 binding. There is a positive correlation between the rat and human inhibitory constants, a finding indicating that there are similar pharmacological profiles across at least these two species. Rats with a 6-hydroxydopamine lesion had a 47% decrease in number of [3H]GBR 12935 binding sites, a result indicating that at least a portion of these sites had been on presynaptic dopamine terminals.     

Analysis of individual CNS protein synthesis

A procedure for labeling rat CNS proteins in vivo which is useful for behavioral and pharmacological studies has been developed. Intraventricular administration of³⁵S-methionine through bilateral indwelling cannulae provided reproducible and highly specific radiolabeling of proteins from frontal cortex (FC), parietal cortex (PC), occipital cortex (OC), striatum (ST), septal nuclei (SN), amygdala (AM), hippocampus (HIP), thalamus (TH), brain stem (BS) and cerebellum (CB). Relative rates of synthesis of over 200 individual proteins were subsequently analyzed by 2DGE. Regional analysis demonstrated increased labeling of a protein of MW 28 kD and pI 6.4 in the hippocampus that was barely detectable in striatum of control rats. In heat-shocked animals, there was increased relative synthesis of the 74 kD Heat Shock Protein in both the septal nuclei and hippocampus.     

Characterization of sulpiride-displaceable 3H-YM-09151-2 binding sites in rat frontal cortex and the effects of subchronic treatment with haloperidol on cortical D-2 dopamine receptors

We investigated the pharmacological properties of the sulpiride-displaceable binding sites labeled by 3H-YM-09151-2 in rat frontal cortex, compared to those in striatum. The IC50 value of ketanserin was 486 nM, which was apparently different from its affinity for the 5HT-2 receptor. Various dopamine antagonists showed almost the same inhibitory effects for binding site in frontal cortex and striatum. Sulpiride-displaceable 3H-YM-09151-2 binding sites were considered to be D-2 dopamine receptors. After subchronic treatment with haloperidol, the D-2 receptor density of frontal cortex (0.55 fmol/mg tissue) increased to the same extent (about 25%) as striatum without significant change in apparent affinity.     

Phencyclidine-Induced Dysregulation of Dopamine Response to Amphetamine in Prefrontal Cortex and Striatum

Phencyclidine (PCP) administration in rodents has been used to model aspects of schizophrenia. One aspect of such treatment has been the enhancement of amphetamine-induced increase of dopamine in the prefrontal cortex and striatum. To further characterize this mechanism rats were treated for 2 weeks with continuous PCP (15 mg/kg per day via Alzet minipump). Rats were implanted with a microdialysis probe into the prefrontal cortex (PFC) or striatum. Amphetamine was administered locally via the dialysis probe during one collection period and changes in extracellular dopamine were monitored. The effect of local administration of the dopamine uptake blocker nomifensine was also measured. Amphetamine (10 M) and nomifensine (10 M) increased the level of dopamine in both the PFC and striatum. PCP administration did not alter the response to amphetamine or nomifensine in the PFC, but reduced this response about 2-fold in striatum. To examine effects of continuous PCP administration on dopamine autoreceptor function, release of [³H]dopamine in response to electrical stimulation and in the presence of a dopamine agonist or antagonist was tested in striatal and prefrontal cortical tissue. Autoreceptor responses were similar in control and PCP-treated tissues. We conclude that the brain region-specific enhancement of dopamine release by peripheral amphetamine administration in rats after PCP is not likely mediated by alterations in the dopamine autoreceptors or changes in the dopamine transporter. The selective local responses of amphetamine indicates heterogeneous regional effects of continuous PCP on NMDA receptor function; effects that influence both regional excitatory responses and the overall dynamics of tonic excitatory/inhibitory inputs to the PFC and striatum.     

Modification of striatal acetylcholine concentration by N6,O2 -dibutyryl adenosine 3',5' -monophosphate in rats injected with chlorpromazine.

Intraventricular administration of 100 μg of dibutyryl cAMP failed to elevate striatal acetylcholine (ACh). Chlorpromazine (CPZ) significantly (p < 0.005) decreased ACh concentration in the striatum. Intraventricular administration of dibutyryl cAMP prior to CPZ prevented the release of ACh, suggesting that cAMP is the substance which mediates dopamine-induced responses to the cholinergic system in the striatum.     

Effects of Zingerone [4-(4-Hydroxy-3-Methoxyphenyl)-2-Butanone] and Eugenol [2-Methoxy-4-(2-Propenyl)Phenol] on the Pathological Progress in the 6-Hydroxydopamine-Induced Parkinson’s Disease Mouse Model

Parkinson’s disease (PD) is characterized by progressive degeneration of dopaminergic neurons in the nigrostriatal system and dopamine (DA) depletion in the striatum. The most popular therapeutic medicine for treating PD, 3-(3,4-Dihydroxyphenyl)-l-alanine (L-DOPA), has adverse effects, such as dyskinesia and disease acceleration. As superoxide (·O₂ ⁻) and hydroxyl radical (·OH) have been implicated in the pathogenesis of PD, free radical scavenging and antioxidants have attracted attention as agents to prevent disease progression. Rodents injected with 6-hydroxydopamine (6-OHDA) intracerebroventricularly are considered to be a good animal model of PD. Zingerone and eugenol, essential oils extracted from ginger and cloves, are known to have free radical scavenging and antioxidant effects. Therefore, we examined the effects of zingerone and eugenol on the behavioral problems in mouse model and on the DA concentration and antioxidant activities in the striatum after 6-OHDA administration and L-DOPA treatment. Daily oral administration of eugenol/zingerone and injection of L-DOPA intraperitoneally for 4 weeks following a single 6-OHDA injection did not improve abnormal behaviors induced by L-DOPA treatment. 6-OHDA reduced the DA level in the striatum; surprisingly, zingerone and eugenol enhanced the reduction of striatal DA and its metabolites. Zingerone decreased catalase activity, and increased glutathione peroxidase activity and the oxidized L-ascorbate level in the striatum. We previously reported that pre-treatment with zingerone or eugenol prevents 6-OHDA-induced DA depression by preventing lipid peroxidation. However, the present study shows that post-treatment with these substances enhanced the DA decrease. These substances had adverse effects dependent on the time of administration relative to model PD onset. These results suggest that we should be wary of ingesting these spice elements after the onset of PD symptoms.     

Differential effects of chronic treatment with haloperidol and clozapine on the level of preprosomatostatin mRNA in the striatum,nucleus accumbens,and frontal cortex of the rat

1. The goal of this work was to determine the effects of typical and atypical neuroleptics on the level of preprosomatostatin messenger RNA (mRNA) in regions of the rat brain innervated by dopaminergic neurons. 2. Quantitative in situ hybridization histochemistry was used to measure the levels of mRNA encoding preprosomatostatin in neurons of the striatum, the nucleus accumbens, and the medial and lateral agranular areas of the frontal cortex in adult rats treated with either haloperidol or clozapine. 3. In untreated animals, the density of neurons containing preprosomatostatin mRNA was higher in the nucleus accumbens than in the striatum and frontal cortex. The intensity of labeling per neuron, however, was higher in the striatum than in the two other areas examined, suggesting that the expression of preprosomatostatin mRNA is differentially regulated in these brain regions. Chronic administration of haloperidol (1 mg/kg for 28 days) induced a significant decrease in the labeling for preprosomatostatin mRNA in neurons of the nucleus accumbens, frontal cortex, and medial but not lateral striatum. Treatment with clozapine (20 mg/kg for 28 days) increased the levels of preprosomatostatin mRNA in the nucleus accumbens but not in the striatum or the frontal cortex. 4. These results support a role for dopamine in the regulation of central somatostatinergic neurons. The differences in the effects of haloperidol, a neuroleptic which induces extrapyramidal side effects, and clozapine, which does not, suggest that somatostatinergic neurons may play an important role in the regulation of motor behavior.     

Destruction of catecholamine-containing neurons by 6-hydroxydopa, an endogenous amine oxidase cofactor

Summary The amino acid, 6-hydroxydopa (6-OHDOPA), found at the active site of amine oxidases, exists as a keto-enol. Exogenously administered 6-OHDOPA is an excitotoxin like-N-oxalylamino-L-alanine (BOAA) and-N-methylamino-L-alanine (BMAA), acting at the non-N-methyl-D-aspartate (non-NMDA)-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor. BMAA and BOAA are causal factors of neurolathyrism in humans. Much exogenously administered 6-OHDOPA is biotransformed by aminoacid decarboxylase (AADC) to the highly potent and catecholamine (CA) selective neurotoxin, 6-hydroxydopamine (6-OHDA). 6-OHDOPA destroys locus coeruleus noradrenergic perikarya and produces associated denervation of brain by norepinephrine-(NE) containing fibers. Opiopeptides and opioids enhance neurotoxic effects of 6-OHDOPA on noradrenergic nerves, by a naloxone-reversible process. An understanding of mechanisms underlying neurotoxic effects of 6-OHDOPA can be helpful in defining actions of known and newfound amino acids and for investigating their potential neurotoxic properties.Abbreviations AADC aminoacid decarboxylase - AMPA -amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid - BOAA -N-oxalylamino-Lalanine - CA catecholamine - L-DOPA L-dihydroxyphenylalanine - DA dopamine - EAA excitatory amino acid - 6-OHDOPA 6-hydroxydopa - 6-OHDA 6-hydroxydopamine - NE norepinephrine - BMAA -N-methylamino-L-alanine - NMDA N-methyl-D-aspartate - S.E.M. standard error of the mean