Specific oxidative stress profile associated with partial striatal dopaminergic depletion by 6-hydroxydopamine as assessed by a novel multifunctional marker molecule

Abstract

Real time oxidative stress in the extracellular compartment of rat striatum was characterized by microdialysis with synthetic non-dialyzable marker molecules composed of linoleic acid, tyrosine and guanosine (N-linoleoyl tyrosine (LT) and N-linoleoyl tyrosine 2′-deoxyguanosyl ester (LTG)). Partial dopaminergic deafferentation was induced by injection of 6-hydroxydopamine (250 μg) to the left lateral ventricle, which depleted ipsilateral striatal dopamine by 46% and dopaminergic cells in left substantia nigra by 44%, 5 weeks after administration. Resting microdialysate dopamine levels in dopamine-depleted striatum were not different from sham-operated rats, although the ratio of oxidized metabolites of dopamine to free dopamine was significantly increased. Hydroperoxide and epoxy products of the linoleoyl portion of LT and LTG were detected in the striatal microdialysate by LC/MS/MS following initial separation by HPLC and were significantly increased in dopamine-depleted compared with control striatum without an increase in guanosine or tyrosine oxidation or nitration. Systemic administration of N-acetyl cysteine (350 mg/kg i.p.) decreased the increment in hydroperoxide and epoxy metabolites to levels not significantly different from control. Oxidation activity towards polyunsaturated fatty acids is present in the extracellular space of partially dopamine-denervated striatum, whereas oxidized glutathione and oxysterol levels in striatal tissue are decreased, possibly indicative of a compensatory response.     

Role of high-affinity dopamine uptake and impulse activity in the appearance of extracellular dopamine in striatum after administration of exogenous L-DOPA: studies in intact and 6-hydroxydopamine-treated rats

The differential behavioral and neurochemical effects of exogenous L-DOPA in animals with intact versus dopamine (DA)-denervated striata raise questions regarding the role of DA terminals in the regulation of dopaminergic neurotransmission after administration of exogenous L-DOPA. In vivo microdialysis was used to monitor the effect of exogenous L-DOPA on extracellular DA in intact and DA-denervated striata of awake rats. In intact striatum, a small increase in extracellular DA was observed after administration of L-DOPA (50 mg/kg i.p.) but in DA-denervated striatum a much larger increase in extracellular DA was elicited. Additional experiments assessed the role of high-affinity DA uptake and impulse-dependent neurotransmitter release in the effect of exogenous L-DOPA on extracellular DA in striatum. Pretreatment with GBR-12909 (20 mg/kg i.p.), a selective DA uptake inhibitor, enhanced the ability of L-DOPA to increase extracellular DA in intact striatum. However, in DA-denervated striatum, inhibition of DA uptake did not alter the extracellular DA response to L-DOPA. Impulse-dependent neurotransmitter release was blocked by the infusion of tetrodotoxin (TTX; 1 microM), an inhibitor of fast sodium channels, through the dialysis probe. Application of TTX significantly attenuated the L-DOPA-induced increase in extracellular DA observed in striatum of intact rats pretreated with GBR-12909. In a similar manner, TTX infusion significantly attenuated the increase in extracellular DA typically observed in striatum of 6-OHDA-lesioned rats after the administration of L-DOPA. The present results indicate that DA terminals, via high-affinity uptake, play a crucial role in the clearance of extracellular DA formed from exogenous L-DOPA in intact striatum. This regulatory mechanism is absent in the DA-denervated striatum. In addition, this study has shown that DA synthesized from exogenous L-DOPA primarily is released by an impulse-dependent mechanism in both intact and DA-denervated striatum. The latter result suggests an important role for a nondopaminergic neuronal element in striatum that serves as the primary source of extracellular DA formed from exogenous L-DOPA.     

Tyrosine content, influx and accumulation rate, and catecholamine biosynthesis measured in vivo, in the central nervous system and in peripheral organs of the young rat. Influence of neonatal hypo- and hyperthyroidism

The influence of neonatal hypo- and hyperthyroidism on different aspects of tyrosine metabolism in the hypothalamus, striatum, brainstem, adrenal glands, heart and brown adipose tissue (BAT) were studied in 14-day old rats. The synthesis rate of catecholamines (CA) was also determined in vivo after the injection of labelled tyrosine. Hypothyroidism increases tyrosinaemia and endogenous tyrosine concentration in the hypothalamus and BAT. Hyperthyroidism decreases tyrosinaemia and endogenous tyrosine levels in the striatum, adrenals and heart. The accumulation rate of tyrosine determined 30 min after an intravenous injection of the labelled amino acid has been determined in the organs, together with the influx of the amino acid, determined within 20s. Hypothyroidism increases tyrosine accumulation rate in all the organs studied, and tyrosine clearance is decreased in the striatum and brainstem; together with an increased tyrosinaemia, this leads to a normal influx. The influx of tyrosine is increased in the hypothalamus. Hyperthyroidism decreases tyrosine accumulation rate in all the organs except the adrenals. These results indicate that the thyroid status of the young rat can influence tyrosine uptake mechanisms, without modifying an organ's tyrosine content. The fact that hypothyroidism increases tyrosine influx in the hypothalamus without modifying it in the brainstem and striatum reflects an heterogeneous reactivity to the lack of thyroid hormones in different brain structures. Neonatal hypothyroidism decreases the CA synthesis rate in the striatum, the heart and the interscapular brown adipose tissue, while synthesis was enhanced in the brainstem and the adrenals. It is likely that these variations in CA synthesis are due to thyroid hormone modulation of tyrosine hydroxylase activity, the enzyme which catalyses the rate limiting step in CA biosynthesis.     

Region - specific alterations in tyrosine hydroxylase activity in rats exposed to lead

Previous studies from our laboratory showed that subchronic exposure to low levels of Pb resulted in significant decrease in dopamine (DA) content, attenuation of stimulus-induced release of DA in the dopaminergic projection area of nucleus accumbens (NA), and alterations in tyrosine hydroxylase (TH) activity in rat whole brain homogenates. The present study reported here was conducted to assess the functional integrity of DA synthesis in different brain regions of rats subchronically (90-days) exposed to 50 ppm Pb by measuring the activity of the rate limiting enzyme, tyrosine hydroxylase, in seven brain regions. In Pb-exposed rats, TH activity was reduced in two of the seven brain regions investigated, i.e., nucleus accumbens (42% reduction) and frontal cortex (61% reduction) when compared to controls. In contrast, Pb exposure did not affect the TH activity in cerebellum, brainstem, hippocampus, hypothalamus and striatum. The changes in TH activity in nucleus accumbens (NA) and frontal cortex (FC) in Pb-exposed rats were further confirmed by Western blot analysis using TH polyclonal antibody. Collectively, these results indicate that low level subchronic Pb exposure may affect TH protein in these brain regions.     

Amphetamine augments action potential-dependent dopaminergic signaling in the striatum in vivo

Amphetamine (AMPH) is thought to disrupt normal patterns of action potential-dependent dopaminergic signaling by depleting dopamine (DA) vesicular stores and promoting non-exocytotic DA efflux. Voltammetry in brain slices concurrently demonstrates these key drug effects, along with competitive inhibition of neuronal DA uptake. Here, we perform comparable kinetic and voltammetric analyses in vivo to determine whether AMPH acts qualitatively and quantitatively similar in the intact brain. Fast-scan cyclic voltammetry measured extracellular DA in dorsal and ventral striata of urethane-anesthetized rats. Electrically evoked recordings were analyzed to determine K(m) and V(max) for DA uptake and vesicular DA release, while background voltammetric current indexed basal DA concentration. AMPH (0.5, 3, and 10 mg/kg i.p.) robustly increased evoked DA responses in both striatal subregions. The predominant contributor to these elevated levels was competitive uptake inhibition, as exocytotic release was unchanged in the ventral striatum and only modestly decreased in the dorsal striatum. Increases in basal DA levels were not detected. These results are consistent with AMPH augmenting action potential-dependent dopaminergic signaling in vivo across a wide, behaviorally relevant dose range. Future work should be directed at possible causes for the distinct in vitro and in vivo pharmacology of AMPH.     

Plant-Derived Neurotoxic Amino Acids (β-N-Oxalylamino-l-Alanine and β-N-Methylamino-l-Alanine): Effects on Central Monoamine Neurons

In the present study the subacute effects of beta-N-oxalylamino-L-alanine (BOAA) and beta-N-methylamino-L-alanine (BMAA) on CNS monoamine neurons in rats were investigated following intracisternal injections or local intracerebral administration into substantia nigra. In vitro effects of BOAA and BMAA on high-affinity synaptosomal uptake of dopamine (DA), noradrenaline (NA), and serotonin (5-HT) were also examined. Intracisternal administration of BMAA decreased NA levels in hypothalamus, whereas no effects were seen on DA or 5-HT levels. Following intranigral injections of BOAA, NA levels tended to decrease in several regions, whereas the DA levels and the levels of DA metabolites were unaffected in all regions analyzed. Loss of tyrosine hydroxylase (TH) immunoreactivity in the intranigral injection sites and the presence of TH-immunoreactive pyknotic neurons near the borders of the injection sites were observed following both BOAA and BMAA treatments. Furthermore, substance P-immunoreactive terminals in substantia nigra pars reticulata were also found to have disappeared within the lesioned area following either BOAA or BMAA injections. Incubations with both BOAA and BMAA (10(-5) M) reduced high-affinity [3H]NA uptake in cortical synaptosomes to 69% and 41% of controls, respectively, whereas the striatal high-affinity [3H]DA uptake and the cortical high-affinity [3H]5-HT uptake were unaffected by BOAA or BMAA. The results demonstrate that both BOAA and BMAA can affect central monoamine neurons, although the potency and specificity of these substances on monoamine neurons when administered acutely into cerebral tissue or liquor cerebri seem to be low. However, the in vitro studies indicate selective effects of both compounds on NA neurons in synaptosomal preparations.     

Effect of 2-guanidinoethanol on levels of monoamines and their metabolites in the rat brain

The contents of monoamines and their metabolites in rat brains 3 hours after the intracerebroventricular injection of 6 mol of 2-guanidino-ethanol (GEt) were measured by HPLC. GEt which is a configurational analogue of 4-aminobutanoic acid (GABA) induced severe running fits and tonic-clonic convulsions as well as epileptic discharges. In GEt-administered rats, dopamine (DA) decreased in the cortex, hippocampus and hypothalamus. 3,4-Dihydroxyphenylacetic acid (DOPAC) increased to about the same level in all brain regions, therefore the distribution of DOPAC appeared to be homogeneous in the brain. The homovanillic acid levels also increased in the striatum and hippocampus. No significant change in the norepinephrine contents was observed in any region. The turnover ratio of DA increased significantly except in the striatum. Serotonin levels increased in the hypothalamus and midbrain by GEt administration, though 5-hydroxyindoleacetic acid levels showed no change in any of the brain regions. These data suggest that the activity of dopaminergic and serotonergic neurons are increased by GEt.     

Effects of Drugs Interfering with Dopamine and Noradrenaline Biosynthesis on the Endogenous 3,4- Dihydroxyphenylalanine Levels in Rat Brain

A chemical assay of 3,4-dihydroxyphenylalanine (DOPA) in nervous tissue is described. The method is based on a rapidly performed isolation of DOPA on small Sephadex G-10 columns, followed by reverse-phase HPLC with a trichloroacetic acid-containing eluent, in conjunction with a rotating disk electrochemical detector. The detection limit of the assay (about 100 pg/tissue sample) permits a detailed investigation of the regional distribution of endogenous DOPA levels in the rat brain. DOPA as well as dopamine (DA) could be quantified in the same chromatographic run. The assay was applied to a study of the effects of alpha-methyl-p-tyrosine, apomorphine, chlorpromazine, clonidine, gamma-butyrolactone, haloperidol, morphine, oxotremorine, pargyline, reserpine, and tyrosine methylester on the concentration of DOPA in the striatum, hypothalamus, frontal cortex, and cerebellum of the rat brain. Drugs known to interact with DA biosynthesis all caused characteristic changes of the DOPA content in the striatum and not in nondopaminergic brain areas. A close correlation existed between drug-induced changes in tyrosine hydroxylase activity and changes in the DOPA content in the striatum. Tyrosine methylester increased DOPA concentrations in all brain areas studied.     

Release of endogenous norepinephrine and dopamine from rat brain regions in vitro

Using radioenzymatic assay procedures, we have measured picomolar amounts of endogenous norepinephrine (NE) and dopamine (DA) released $\text{in vitro}$. The release of NE and DA in response to KCl stimulation was examined in 6 brain regions: cortex, hippocampus, hypothalamus, striatum, combined accumbens-olfactory tubercle, and substantia nigra. NE release was detectable in all regions except striatum. Amounts of NE released by 55mM KCl (expressed as % control) were: cortex (313%), hippocampus (227%), hypothalamus (225%), accumbens-tubercle (278%), s. nigra (155%). KCl stimulated release of DA was detected in 3 regions: striatum (414%), accumbenstubercle (282%), and hypothalamus (312%). DA was measurable in filtrates from the s. nigra but levels in control and KCl stimulated samples were equal. Release of NE and DA was also measured in 12 brain regions after incubation of tissue $\text{in vitro}$ with 10^?4M d-amphetamine sulfate. d-Amphetamine stimulated NE outflow when compared to controls in all regions examined. DA outflow was markedly increased in most regions, especially striatum (287%), hypothalamus (387%) and accumbens-tubercle (670%). d-Amphetamine doubled endogenous DA outflow from the s. nigra.     

Intranasal administration of PACAP: uptake by brain and regional brain targeting with cyclodextrins

Pituitary adenylate cyclase activating polypeptide (PACAP) is a potent neurotrophic and neuroprotectant that is transported across the blood-brain barrier in amounts sufficient to affect brain function. However, its short half-life in blood makes it difficult to administer peripherally. Here, we determined whether the radioactively labeled 38 amino acid form of PACAP can enter the brain after intranasal (i.n.) administration. Occipital cortex and striatum were the regions with the highest uptake, peaking at levels of about 2-4% of the injected dose per gram of brain region. Inclusion of unlabeled PACAP greatly increased retention of I-PACAP by brain probably because of inhibition of the brain-to-blood efflux transporter for PACAP located at the blood-brain barrier. Sufficient amounts of PACAP could be delivered to the brain to affect function as shown by improvement of memory in aged SAMP8 mice, a model of Alzheimer's disease. We found that each of three cyclodextrins when included in the i.n. injection produced a unique distribution pattern of I-PACAP among brain regions. As examples, β-cyclodextrin greatly increased uptake by the occipital cortex and hypothalamus, α-cyclodextrin increased uptake by the olfactory bulb and decreased uptake by the occipital cortex and striatum, and (2-hydropropyl)-β-cyclodextrin increased uptake by the thalamus and decreased uptake by the striatum. These results show that therapeutic amounts of PACAP can be delivered to the brain by intranasal administration and that cyclodextrins may be useful in the therapeutic targeting of peptides to specific brain regions.     

Effects of ethanol on brain monoamine content of spontaneously hypertensive rats (SHR)

Spontaneously hypertensive rats (SHR) were administered either 2.4 g/kg ethanol or an isocaloric glucose daily for 4 weeks and the levels of norepinephrine (NE), epinephrine (EP), dopamine (DA), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in different brain regions were determined. Results indicated a 3-fold increase in NE level in brain stem and hypothalamus and more than 2-fold increase in DA in corpus striatum in alcohol-treated rats as compared to controls. There was a significant increase in the level of DA in the corpus striatum but the levels in cerebral cortex, brain stem and hippocampus were decreased instead. Decreases in 5-HT levels were found in hypothalamus, brain stem, cortex and cerebellum of alcohol-treated brain as compared to untreated controls. These results indicate alterations of the biogenic amine contents in different regions of the SHR brain after chronic ethanol ingestion. Since stimulated release of biogenic amines in the SHR brain has been implicated in the regulation of blood pressure, changes due to ethanol ingestion may be a risk factor in hypertensive patients.     

Effect of 2-Amino-7-Phosphonoheptanoic Acid on Regional Brain Amino Acid Levels in Fed and Fasted Rodents

Abstract: 2-Amino-7-phosphonoheptanoic acid, an antagonist of excitation caused by dicarboxylic amino acids with a selective action on N -methyl-d-aspartate receptors, has been administered in an anticonvulsant dose (1 mmol/kg i.p.) to fed or fasted rats and mice. The drug impaired motor activity in fasted mice. Glucose and amino acids were determined in dissected regions of brain fixed by microwave irradiation. Glucose content was low in the brains of fasted rats and mice but was restored to normal (fed) concentration 45 min after the administration of 2-amino-7-phosphonoheptanoic acid in fasted mice. In fed animals, 2-amino-7-phosphonoheptanoic acid did not change brain aspartate concentration. In fasted animals, aspartate concentration was raised in most brain regions. In fasted rats and mice, 2-amino-7-phosphonoheptanoic acid significantly increased glutamine in rat cortex and mouse striatum, decreased glutamate content in rat striatum, and decreased aspartate concentration in all regions except mouse cortex and striatum. GABA levels were significantly decreased in rat striatum and hippocampus. These changes are consistent with an increased synaptic release of glutamate and aspartate following blockage of their post-synaptic action at selected sites.     

A comparative study of the neurochemical profiles of remoxipride, raclopride and metoclopramide activity]

Effects of intraperitoneal administration of remoxipride (2.4 mg/kg), raclopride (1.2 mg/kg) and metoclopramide (5 mg/kg) on the concentration of monoamines and metabolites in various brain regions, on the DA and serotonin biosynthesis in the striatum and nucleus accumbens, on the K(+)-stimulated DA release from the isolated striatum, on the extracellular levels of DA and metabolites in the striatum of freely moving rats were studied. Remoxipride and raclopride increase DA turnover, biosynthesis and DA release, studied both in vitro and in vivo. Metoclopramide was shown to be more effective in increasing DA turnover and biosynthesis, while exerted less activity in regard to increasing DA release in vivo and failed to affect release in vitro. Possible neurochemical mechanisms underlying pharmacological effects of these drugs are discussed.     

In vivo binding of [11C]tetrabenazine to vesicular monoamine transporters in mouse brain.

The time course of regional mouse brain distribution of radioactivity after i.v. injection of a tracer dose of [11C]tetrabenazine ([11C]TBZ) has been determined. Radiotracer uptake into brain is rapid, with 3.2% injected dose in the brain at 2 min. Egress from the brain is also very rapid, with only 0.21% of the injected dose still present in brain at 60 min. Radiotracer washout is slowest from the striatum and hypothalamus, consistent with binding to the higher numbers of vesicular monamine transporters in those brain regions. The rank order of radioligand binding at 10 min after injection is striatum greater than hypothalamus greater than hippocampus greater than cortex = cerebellum, similar to that found using in vitro assays of the vesicular monoamine transporters. Maximum ratios of striatum/cerebellum and hypothalamus/cerebellum were 2.85 +/- 0.52 and 1.69 +/- 0.25, respectively, at 10 min after injection. Co-injection of unlabeled tetrabenazine (10 mg/kg) or pretreatment with reserpine (1 mg/kg i.p., 24 h prior) was used to demonstrate specific binding of radioligand in striatum, hypothalamus, cortex, hippocampus and cerebellum. Distribution of [11C]TBZ was unaffected by pretreatment with the neuronal dopamine uptake inhibitor GBR 12935 (20 mg/kg i.p., 30 min prior). [11C]Tetrabenazine is thus a promising new radioligand for the in vivo study of monoaminergic neurons using Positron Emission Tomography.     

Modulation of dopaminergic neurotransmission in rat striatum upon in vitro and in vivo diclofenac treatment

Diclofenac (DCF) is a widely used non-steroidal anti-inflammatory drug, which also act as a mitochondrial toxin. As it is known that selective mitochondrial complex I inhibition combined with mild oxidative stress causes striatal dopaminergic dysfunction, we tested whether DCF also compromise dopaminergic function in the striatum. [3H]Dopamine ([3H]DA) release was measured from rat striatal slices after in vitro (2 h, 10-25 micromol/L) or in vivo (3 mg/kg i.v. for 28 days) DCF treatment. In vitro treatment significantly decreased [3H]DA uptake and dopamine (DA) content of the slices. H2O2 (0.1 mmol/L)-evoked DA release was enhanced. Intracellular reactive oxygen species production was not significantly changed in the presence of DCF. After in vivo DCF treatment no apparent decrease in striatal DA content was observed and the uptake of [3H]DA into slices was increased. The intensity of tyrosine hydroxylase immunoreactivity in the striatum was highly variable, and both decrease and increase were observed in individual rats. The H2O2-evoked [3H]DA release was significantly decreased and the effluent contained a significant amount of [3H]octopamine, [3H]tyramine, and [3H]beta-phenylethylamine. The ATP content and adenylate energy charge were decreased. In conclusion, whereas in vitro DCF pre-treatment resembles the effect of the mitochondrial toxin rotenone, in vivo it rather counteracts than aggravates dopaminergic dysfunction.     

Influence of hypo- and hyperthyroidism on the turnover rate of noradrenaline, dopamine and serotonin in various rat cerebral structures]

The effect of chronic treatment with tyroxine (T4) or propylthiouracile (PTU) on the turnover of norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT) has been studied in various areas of the rat brain (brain stem, hypothalamus, striatum and "rest of the brain"). The turnover of NE and DA was determined by the decay in endogenous levels after inhibition of tyrosine hydroxylase by alpha-methylparatyrosine and the turnover of 5-HT was evaluated by the initial accumulation of endogenous 5-HT after inhibition of monoamine oxydase by pargyline. T4 treatment accelerated the release of DA from the striatum but had no significant effects on NA release in the various cerebral areas : nevertheless the NE endogenous level was significantly reduced in the brain stem. PTU treatment delayed the release of DA and NA only from the "rest of the brain". Concerning 5-HT, the only significant variation was observed in the hypothalamus of PTU-treated rats and implied increased turnover. The possible relations between the changes in cerebral monoamines turnover and the behavioural alterations which are observed in thyroid disfunction are discussed.     

Effect of S-adenosyl-L-homocysteine of dopamine catabolism]

1.--The administration of SAH to rats, at physiologically active dose on the sleep, does not change the urinary level of MD and NM. On the other hand, the excretion of DA and NA decreases. 2.--In the brain, SAH does not modify neither the concentration of NA and NM in hypothalamus and thalamus, nor the concentration of DA and MD in corpus striatum. 3.--After intracisternally injection of [14C]DA or [3H]NA, SAH increases the level of [14C]MD and [3H]NM. 4.--Contrary to the studies in vitro, where SAH is an inhibitor of COMT, on the rat it does not seem prevent the methylation of DA and NA.     

Change of dopamine, serotonin and opioid neuromediator systems in the brain of rats adapted to prolonged effect of ethanol

AIM OF THE STUDY: To investigate the effect of in vivo short-term ethanol administration (i.p., 1.5 g/kg, 6 h) on binding characteristics of opioid receptor agonists in rat midbrain, as well as the contents of dopamine, serotonin and their precursors and metabolites in midbrain, striatum and hypothalamus of rats after long-term alcohol consumption. The methods of receptor binding assay and high performance liquid chromatography with electrochemical detection were used. The data obtained suggest that the response of neurotransmitter systems to short-term ethanol administration in different regions of rats brain is not identical. Our findings demonstrate that short-term ethanol administration may modulate dopaminergic transmission in the rat hypothalamus and striatum but this effect may be attenuated by down-regulation of OP, in the midbrain after long-term alcohol consumption. Serotonin system in hypothalamus becomes more sensitive to short-term ethanol administration after the long-term ethanol-containing liquid diet in comparison with control rats. Our results suggest that reinforcing properties of ethanol may be partially mediated by mechanisms involving the ethanol-induced disturbing of dopaminergic metabolism in the midbrain and hypothalamus and serotoninergic metabolism in hypothalamus.     

Effects of Ethanol In Vitro and In Vivo on the Release of Endogenous Catecholamines from Specific Regions of Rat Brain

Blocks of tissue from the hypothalamus, olfactory bulb, or striatum of rats were incubated in vitro to study the basal and potassium-stimulated release of endogenous catecholamines. When ethanol (100-250 mM) was added to these preparations in vitro no changes in release were observed. When ethanol (3.0 g X kg-1) was injected intraperitoneally in vivo, however, and 3,4-dihydroxyphenylethylamine (DA, dopamine) release was measured in vitro at various times after drug administration, significant increases in the basal release and decreases in the potassium-stimulated release were observed in striatum and olfactory bulb. In striatum, these changes showed a more rapid onset and a longer duration than in olfactory bulb. In both brain regions, DA release did not differ from controls at 4-6 h after the ethanol injection, although blood ethanol concentrations remained elevated. This may imply the tissue's acquisition of acute functional tolerance to the drug. Similar increases and decreases in the basal and the potassium-induced release of DA from striatal tissues were also found at 1 h after injection of a lower dose of ethanol (1.0 g X kg-1). In terms of behavior, this lower dose of ethanol produced only mild intoxication and ataxia, in contrast to the loss of righting reflex following the higher dose.     

On the Significance of Tyrosine for the Synthesis and Catabolism of Dopamine in Rat Brain: Evaluation by HPLC with Electrochemical Detection

Abstract: A chemical assay of tyrosine (Tyr) in nervous tissue is described. The method is based on a rapidly performed isolation of Tyr on small Sephadex G 10 columns, followed by reverse-phase HPLC in conjunction with amperometric detection. The method permitted the additional quantification of 3,4-dihydroxyphenylalanine, dopamine (DA), and its acidic metabolites. The method was applied to a study of the effects of γ-butyrolactone, haloperidol, haloperidol in combination with amfonelic acid, morphine, NSD 1015, and tyrosine methylester on the concentration of Tyr in the striatum, frontal cortex, hypothalamus, and cerebellum of rat brain. The effect of tyrosine methylester on DA and its acidic metabolites was investigated in the striatum and frontal cortex. Morphine and NSD 1015 were found to increase Tyr levels. γ-Butyrolactone, haloperidol, and haloperidol combined with amfonelic acid decreased the Tyr content in a manner related to their stimulatory effect on DA biosynthesis. These effects were restricted to DA-rich brain areas. It was concluded that during conditions of increased DA biosynthesis, the Tyr pool still possesses a considerable reserve capacity. The results bring into question the concept that brain Tyr is an important additional factor controlling catechol synthesis during increased tyrosine hydroxylase activity.