Norepinephrine Metabolism Research Articles

Aldo-keto reductases in norepinephrine metabolism.

Monoamine oxidase (MAO, EC 1.4.3.4) and catechol-O-methyltransferease (COMT, EC 2.1.1.6) are the two primary enzymes responsible for the first step of the metabolism of the catecholamines epinephrine, norepinephrine and dopamine. Catecholamines and their methylated metabolites, produced by COMT, are metabolized to the corresponding aldehyde intermediates by MAO. In the subsequent second step these aldehydes are removed through either their oxidation to acids by aldehyde dehydrogenase (EC 1.2.1.3) or their reduction to alcohols by aldehyde reductase (Kopin, 1985). Here, we focus on the metabolism of norepinephrine and summarize evidences that aldose reductase is the key enzyme responsible for the metabolism of norepinephrine.KeywordsAldehyde DehydrogenaseAldose ReductaseSympathetic Nerve CellAldehyde ReductasePathetic NerveThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Reduced aldehyde dehydrogenase levels in the brain of patients with Down syndrome.

Aldehyde dehydrogenase (ALDH) is a key enzyme in fructose, acetaldehyde and oxalate metabolism and represents a major detoxification system for reactive carbonyls and aldehydes. In the brain, ALDH exerts a major function in the metabolism of biogenic aldehydes, norepinephrine, dopamine and diamines and gamma-aminobutyric acid. Subtractive hybridization studies in Down Syndrome (DS) fetal brain showed that mRNA for ALDH are downregulated. Here we studied the protein levels in the brain of adult patients. The proteins from five brain regions of 9 aged patients with DS and 9 controls were analyzed by two-dimensional (2-D) gel electrophoresis and identified by matrix-assisted laser desorption ionization mass spectrometry. ALDH levels were reduced in the brain regions of at least half of the patients with Down Syndrome, as compared to controls. The decreased ALDH levels in the DS brain may result in accumulation of aldehydes which can lead to the formation of plaques and tangles reflecting abnormally cross-linked, insoluble and modified proteins, found in aged DS brain. Furthermore, we constructed a 2-Dmap including approximately 120 identified human brain proteins.

Effects of the Immunostimulant, Levamisole, on Opiate Withdrawal and Levels of Endogenous Opiate Alkaloids and Monoamine Neurotransmitters in Rat Brain

This report presents evidence that the immunostimulant drug levamisole, (−)-(S)-2,3,5,6-tetrahydro-6-phenylimidazo[2,1-b] thiazole monohydrochloride, produced a significant elevation of endogeneous morphine and codeine levels in brain regions and peripheral organs and attenuated the effects of naltrexone-induced withdrawal in morphine-addicted rats. Levamisole also significantly altered the metabolism of norepinephrine, dopamine, and serotonin in specific brain regions. These results suggest that levamisole’s attenuation of opiate withdrawal may be related to its ability to increase endogeneous opiate alkaloid levels and/or to alter central monoaminergic function. Levamisole does not have significant affinity for opiate receptors. These results raise the intriguing possibility that agents such as levamisole, which elevate the levels of the endogenous opiate alkaloids, might be useful for treating narcotic withdrawal. The mechanism for the immunostimulatory properties of agents such as levamisole and muramyl dipeptide (MDP) have not been established. We suggest that the ability of MDP and levamisole to increase endogenous opiate alkaloids may be related to their immunostimulatory properties.

Whole body, adipose tissue, and forearm norepinephrine kinetics in lean and obese women

We evaluated whole body and regional (subcutaneous abdominal adipose tissue and forearm) norepinephrine (NE) kinetics in seven lean (body mass index 21.3 +/- 0.5 kg/m2) and six upper body obese (body mass index 36.4 +/- 0.4 kg/m2) women who were matched on fat-free mass. NE kinetics were determined by infusing [3H]NE and obtaining blood samples from a radial artery, a deep forearm vein draining mostly skeletal muscle, and an abdominal vein draining subcutaneous abdominal fat. Mean systemic NE spillover tended to be higher in obese (2.82 +/- 0.49 nmol/min) than in lean (2.53 +/- 0.40 nmol/min) subjects, but the differences were not statistically significant. Adipose tissue and forearm NE spillover rates into plasma were greater in lean (0.91 +/- 0.08 pmol. 100 g tissue-1. min-1 and 1.01 +/- 0.09 pmol. 100 ml tissue-1. min-1, respectively) than in obese (0.26 +/- 0.05 pmol. 100 g tissue-1. min-1 and 0.58 +/- 0.11 pmol. 100 ml tissue-1. min-1, respectively) subjects (P < 0.01). These results demonstrate that adipose tissue is an active site for NE metabolism in humans. Adipose tissue NE spillover is considerably lower in obese than in lean women, which may contribute to the lower rate of lipolysis per kilogram of fat mass observed in obesity.

Intracerebroventricular infusion of CRF increases extracellular concentrations of norepinephrine in the hippocampus and cortex as determined by in vivo voltammetry

Previous studies have indicated that intracerebroventricular (i.c.v.) infusions of corticotropin-releasing factor (CRF) activate locus coeruleus (LC) noradrenergic neurons and increase the metabolism and extracellular concentrations of norepinephrine (NE) in several brain regions, suggesting increased release. To examine the temporal aspects and mechanism of the presumed release of NE, CRF was infused i.c.v. and the oxidation current was recorded using carbon fiber voltammetric electrodes placed in rat hippocampus or cortex. The CRF (1 μg, i.c.v.) caused a significant increase of oxidation current with a delay of approximately 5 min, and a peak at approximately 35 min. Similar responses were observed in the medial prefrontal cortex. The hippocampal response was markedly attenuated when CRF was infused into rats pretreated with DSP-4 to deplete NE, suggesting that the observed changes in current resulted from oxidation of NE. The increase of NE-like current did not occur when 25 μg alpha-helical CRF 9–41 (ahCRF) was injected immediately before 1 μg CRF, suggesting that the response was mediated by cerebral CRF-receptors. Subcutaneous pretreatment with the ganglionic blocker, chlorisondamine, at a dose of 3 mg/kg had no effect on the voltammetric response to CRF, but a 6 mg/kg dose completely prevented the response. The β-adrenoceptor antagonists, S-propranolol (5 mg/kg), nadolol (5 and 10 mg/kg), and timolol (5 mg/kg) attenuated the NE response to i.c.v. CRF to varying degrees. When chlorisondamine (3 μg) or nadolol (5 μg) were given i.c.v. before the CRF, the hippocampal responses were not blocked. These results suggest peripheral actions of ganglionic and β-adrenergic blockers. We conclude that peripheral autonomic mechanisms, and probably both central and peripheral β-adrenoceptors, contribute to the increased secretion of hippocampal NE in response to i.c.v. CRF.

Atrial natriuretic factor does not affect norepinephrine catabolism in rat hypothalamus and adrenal medulla

We have previously reported that atrial natriuretic factor (ANF) increases neuronal uptake and endogenous content of norepinephrine (NE) and diminishes neuronal release, synthesis and turn-over of NE in rat hypothalamus and adrenal medulla. The aim of the present work was to study another aspect of NE metabolism and therefore investigate the possible effects of ANF on NE catabolism. The determination of monoamine oxidase (MAO) and catechol- O-methyl transferase (COMT) activity and deaminates metabolites formation were studied in vitro in rat hypothalamus and adrenal medulla slices. Results showed that, in the hypothalamus, 100 nM ANF diminished MAO activity while 10 nM ANF did not modify the enzyme activity. Conversely, 10 and 100 nM ANF reduced MAO activity in adrenal medulla. On the other hand, the atrial factor modified neither COMT activity nor the formation of deaminates metabolites in the hypothalamus and adrenal medulla. Present results as well as previous findings support a putative role for ANF in the modulation of NE metabolism not only in the hypothalamus but also in the adrenal medulla of the rat, affecting the storage, release and uptake of NE but not its catabolism.

Influence of age and gender on iodine-123 MIBG kinetics in normal lung.

Iodine-123 MIBG is a biochemical marker that can be used to monitor pulmonary norepinephrine (NE) metabolism. The purpose of this study was to characterize pulmonary I-123 MIBG kinetics in relation to age and gender. Seventeen healthy volunteers and 14 patients with no cardiac or pulmonary disorders were included in this study (age range: 24 to 88 years, mean age 50.2 +/- 17.6 years; 16 males, 15 females). Planar images were obtained 15 min (early) and 3 h (delayed) after injection of I-123 MIBG (111 MBq). Pulmonary uptake of I-123 MIBG was quantified based on the lung-to-mediastinum ratio (LMR) on early and delayed images. The lung clearance rate (LCR) was calculated form both the early and delayed images. Both early and delayed LMR values increased slightly, although they showed no significant correlations with age. There was a significant inverse correlation between LCR and age (r = -0.57, p < 0.001). Neither LCR nor LMR differed significantly between male and female patients, but the mean age of the men was lower than that of the women. Pulmonary I-123 MIBG kinetics may reflect age-dependent changes in NE metabolism. The effects of age should be taken into account when assessing pulmonary NE metabolism with I-123 MIBG.

Mouse interleukin-6 stimulates the HPA axis and increases brain tryptophan and serotonin metabolism

Neuroendocrine and neurochemical responses were studied following administration of recombinant mouse IL 6 (mIL 6) to mice. Intravenous (iv) or intraperitoneal (ip) injection of mIL 6 caused a rapid and short-lived activation of the hypothalamo-pituitary- adrenocortical (HPA) axis, as indicated by increases in plasma ACTH and corticosterone, with peak responses around 30 60 min. These responses contrast with those to ip mIL-1b which is substantially more potent and induces a greater response which does not peak until about 2 h following ip administration. Unlike IL-1 and lipopolysaccharide (LPS), IL-6 had no detectable effect on norepinephrine metabolism. However, tryptophan concentrations were elevated in most brain regions studied 1 2 h following iv mIL-6, and 2 h following ip mIL-6, significantly later than the peak HPA response. 5-hydroxyindoleacetic acid (5-HIAA) and the ratio of 5-HIAA to serotonin (5-HT) were elevated at around the same time in the brain stem, and occasionally in other brain regions. These responses were observed at doses of mIL-6 as low as 0.25 μg, and near maximal effects were achieved by 0.5 μg. Recombinant human IL-6 elicited similar responses, but was significantly less potent. Heat-treated mIL-6 elicited none of the responses. Serum amyloid A protein (SAA) concentrations were not elevated until 4 h after iv or ip mIL-6 administration, suggesting that the neuroendocrine and neurochemical changes were not secondary to an acute phase protein response. Intracerebroventricular injection of mIL-6 also elevated tryptophan and 5-HIAA in the hypothalamus and brain stem. Pretreatment of mice with the cyclooxygenase inhibitor, indomethacin, or the nitric oxide synthase inhibitor, N-v-nitro-L-arginine methyl ester (L-NAME) did not attenuate the mIL-6 induced neuroendocrine or neurochemical responses. However, the ganglionic blocking drug, chlorisondamine, prevented the increases in tryptophan and 5-HIAA:5-HT ratios. IL-6 may contribute to the HPA and indoleaminergic responses to LPS and IL-1. It is possible that the increases of tryptophan and serotonin metabolism may contribute to some of the biological effects of IL-6.

The role of MAO-A and MAO-B in the metabolic degradation of noradrenaline in human arteries.

1. Segments of human cystic, gastric and ileocolic arteries were obtained from patients undergoing surgery. 2. Segments of arterial tissues, the noradrenaline content of which ranged between 0.27 and 0.52 microg g(-1), were incubated with 0.1 micromol l(-1) [3H]-noradrenaline for 30 min and the accumulation of the amine as well as the formation of metabolites was measured. 3. In all the arteries, oxidative deamination predominated over O-methylation; the mean values of the deaminated and O-methylated metabolites formed for the three arteries were 247.6 and 82.4 pmol g(-1) tissue, respectively. Dihydroxymandelic acid (DOMA) was the most abundant metabolite. 4. Both clorgyline (a selective MAO-A inhibitor) and selegiline (a selective MAO-B inhibitor) reduced the formation of dihydroxyphenylglycol (DOPEG), DOMA and O-methylated-deaminated metabolites (OMDA), and increased that of normetanephrine (NMN). However, clorgyline depressed the formation of DOPEG more than that of DOMA, while selegiline depressed the formation of DOMA more than that of DOPEG. 5. In conclusion, three major differences distinguish the metabolism of noradrenaline by human arteries from that observed in other species: (1) the large predominance of deamination over O-methylation; (2) the extremely high formation of DOMA; and (3) the relative lack of selectivity of clorgyline and selegiline for MAO-A and B, respectively. Since the arterial vessels used were collected from patients older than 60 years, the morphological changes depending on age may explain the increase in DOMA formation.

Determinants of cardiac tyrosine hydroxylase activity during exercise-induced sympathetic activation in humans.

This study assessed whether the mechanisms regulating cardiac norepinephrine (NE) synthesis with changes in NE release are influenced by functions of sympathetic nerves affecting transmitter turnover independently of transmitter release. Differences in arterial and coronary venous plasma concentrations of NE and its metabolites and of dihydroxyphenylalanine (DOPA), the immediate product of tyrosine hydroxylase (TH), were examined before and during cycling exercise. Relative increases during exercise in cardiac tyrosine hydroxylation (as reflected by the %increase in cardiac DOPA spillover) matched closely corresponding increases in NE turnover, but were much lower than increases in NE release. The much larger relative increases in release than turnover of NE were largely attributable to the extensive contribution to transmitter turnover from intraneuronal metabolism of NE leaking from storage vesicles. This contribution remains unchanged during sympathetic activation so that the relative increase in NE turnover is much smaller than that in exocytotic release of NE. To replenish the NE lost from stores during sympathetic activation, TH activity need increase only in proportion to the smaller increase in turnover rather than the larger relative increase in release. The ability to "gear down" increases in tyrosine hydroxylation relative to increases in NE release provides sympathetic nerves the capacity for a more extended range of sustainable release rates than otherwise possible.

An amino acid mixture deficient in phenylalanine and tyrosine reduces cerebrospinal fluid catecholamine metabolites and alcohol consumption in vervet monkeys.

An amino acid mixture devoid of tryptophan, given orally, was previously shown to reduce cerebrospinal fluid levels of tryptophan and 5-hydroxyindoleacetic acid in vervet monkeys, as compared to a control mixture containing all essential amino acids. In the present study, we tested the possibility that a similar amino acid mixture containing tryptophan, but devoid of phenylalanine and tyrosine (the amino acid precursors of catecholamine neurotransmitters), would influence dopamine and noradrenaline metabolism. Five hours after the administration of this mixture to vervet monkeys, cerebrospinal fluid levels of homovanillic acid and 3-methoxy-4-hydroxyphenylethylene glycol were reduced by 27.4% and 26.9%, respectively. Both effects were statistically significant. Plasma tyrosine (-30%) and the ratio of tyrosine to the sum of other large neutral amino acids (sigmaLNAA) were also significantly reduced. The behavioral efficacy of phenylalanine/tyrosine depletion was compared with that of tryptophan depletion in a primate model of voluntary alcohol consumption. All three drinks lowered alcohol consumption, but the effects of the tryptophan-deficient amino acid mixture were not different from those of the balanced amino acid control. The phenylalanine/tyrosine-deficient drink differentially lowered alcohol consumption, consistent with other data in this species and elsewhere implicating dopamine in the rewarding effects of alcohol.

Reproducibility of plasma catecholamine metabolites in normal subjects

Plasma homovanillic acid (HVA) and methoxy-hydroxy-phenylglycol (MHPG) are often used in repeated measurement designs to assess dopamine and norepinephrine metabolism in clinical research. However, only limited data on the reproducibility of these metabolites are currently available. Plasma HVA and MHPG were measured in normal volunteers on five nonconsecutive mornings under fasting conditions and restricted smoking and physical activity. Intraclass correlation coefficients (ICC) for plasma HVA and MHPG across 5 days were determined to be 0.85 and 0.79, respectively. ICC improved to 0.90 for HVA and 0.91 for MHPG when the average of the first 2 days was examined against the average of the last 2 days. Results suggested that under controlled conditions plasma HVA and MHPG measurements have good reproducibility.

Norepinephrine Uptake Is Enhanced in Discrete Telencephalic and Diencephalic Areas and Nuclei in Prehepatic Portal Hypertensive Rats

Several evidences support the hypothesis that central catecholamines may play a significant role in the production and/or maintenance of different alterations that characterize portal hypertension. The aim of the present work was to study the possible modifications in norepinephrine (NE) metabolism in several telencephalic and diencephalic areas rich in NE in experimental prehepatic portal hypertension. NE uptake was studied as an index of NE metabolism. The experiments were carried out in vitro in encephalic areas and nuclei, obtained according to the punch-out technique. Results indicated that portal hypertensive rats showed an enhancement of NE uptake in olfactory bulb (OB), preoptic area (PA), and supraoptic, periventricular, paraventricular, and arcuate nuclei (SON, PeVN, PaVN, and AN, respectively) compared to sham-operated rats. However, no modifications on NE uptake was observed in the median eminence (ME). Present results suggest that the changes observed in central NE uptake may be related to the development and/or maintenance of the portal hypertensive state.

Mechanism of peripheral noradrenergic stimulation by clozapine

In a canine model of diabetes enhanced ventricular vulnerability (VFT) has been associated with reduced myocardial myoinositol and increased release of norepinephrine (NE). To assess the role of the polyol, a dietary supplement of myoinositol was fed for 1 year to a diabetic group. Diabetes was induced with alloxan, 30 mg/kg. Controls (Group 1) were compared with diabetics without (Group 2) and with the inositol supplement (Group 3). After 1 year the animals were anesthetized to assess VFT. Basal heart rate and arterial pressure were comparable. The VFT in Group 1 was 43 ± 2.6 ma, 26.7 ± 2.8 ma in Group 2 (P < 0.02) and 39 ± 3.5 ma in Group 3 (P < 0.02 vs. Group 2). Since the cardiac sympathetic system may promote arrhythmogenesis, the release of NE into the coronary sinus (CS) has been determined. To assess basal NE release serial arterial (A) and (CS) samples were taken at 5 min intervals for 20 min during infusion of 3H-NE. There was no significant difference between the diabetic groups in the level of arterial NE (HPLC). The mean for NEA-CS was higher in Group 2 (−228 ± 33 pg/ml) compared to normals (−75 ± 19 P < 0.02). In Group 3 the mean NE in the coronary venous effluent was −33 ± 9 pg/ml, significantly less than Group 2. Infusion of 3H-NE was attended by significantly higher 3H-NEcslevels in Group 2. While dihydroxyphenylglycol (DHPG) was increased, 3H DHPG was not, suggesting that an impaired uptake mechanism contributed to the increased NEcs. Thus, myoinositol feeding of the diabetic animals was associated with normalization of myocardial vulnerability and NE metabolism.

Possible involvement of norepinephrine transporter activity in the pulsatility of hypothalamic gonadotropin-releasing hormone release: influence of the gonad.

Pulsatile secretion of hypothalamic gonadotropin-releasing hormone (GnRH) is suppressed by alpha-adrenergic antagonists in ovariectomized (OVX) rabbits, thus suggesting that initiation of GnRH pulses requires the presence of norepinephrine (NE) stimulation. Terminals of NE neurons are located in proximity with GnRH cells in the hypothalamus, including the arcuate nucleus-median eminence (AME) region. Synaptic NE molecules may be catabolized or transported back to NE terminals (i.e. reuptake) via specific NE transporter proteins (NET). Thus, the amount of synaptic NE acting on GnRH cells is a function of the rate of NE release, metabolism and reuptake. Hypothetically, the rise and fall of a GnRH pulse may be associated with the similar fluctuations of synaptic NE release and/or NET activity. To test this hypothesis, we examined the effects of AME administration of desipramine (DMI, a specific NET blocking drug) on GnRH release. First, we delivered 0.2-10 mM doses of DMI continuously for 1 h via an AME microdialysis (microD) system into intact male rabbits. We found that each AME-DMI infusion, between dosages of 1 mM and 10 mM, stimulated a GnRH pulse, and that the size of these GnRH pulses were proportional to the dosage of DMI. To confirm the specificity of DMI on NET, we measured catecholamine content in microD samples by HPLC. The temporal (60 min) DMI induced a pattern of NE release that included a rising limb within the first 20-30 min; although NE returned to baseline values within the period of DMI treatment. Neither epinephrine nor dopamine levels were changed by DMI. Second, a median dose of DMI (5 mM) was given by microD for 60 min in four separate rabbit models: gonadal intact females (F-INT), intact males (M-INT), gonadectomized females (F-GDX) and castrated males (M-GDX). Individual microD samples were measured for NE and GnRH. Regardless of gender or gonadal status, 5 mM of DMI concomitantly induced a pulse-like release of NE and GnRH. Furthermore, the response of GnRH to DMI was greater in GDX rabbits than in INT animals of both genders. Third, we administered DMI (5 mM) for 30 min via a push-pull perfusion (PPP) system during four repeated 90 min intervals, in either F-INT or ovariectomized (F-GDX) females, and measured GnRH in PPP samples. In both F-INT and F-GDX, each DMI challenge induced a GnRH pulse. In F-INT, all sequential DMI-induced GnRH pulses were nearly equal in size. In contrast, in F-GDX, the first DMI-induced GnRH pulse was greater than subsequent ones. Collectively, these observations are consistent with the concept of noradrenergic regulation of pulsatile GnRH release, and we conclude that the temporal activity of NET may be an integral part of the mechanism by which GnRH pulses operate.

Role of Cerebral Dopamine and Noradrenaline in the Morphine-induced Locomotor Sensitisation in Mice

The effects of morphine on locomotor activity and cerebral dopamine (DA) and noradrenaline (NA) metabolism were studied in mice treated repeatedly with morphine for 5 days followed by 1, 3, or 5 days of withdrawal. Acute morphine treatment did not increase the locomotor activity of mice withdrawn for 1 day, after withdrawal for 3 days the increase was similar to that in controls, and after 5 days the increase was clearly larger than in controls. In mice withdrawn for 3 or 5 days, but not in control mice, acute morphine significantly elevated striatal 3,4-dihydroxyphenylacetic acid and homovanillic acid concentrations. Acute morphine challenge decreased striatal 3-methoxytyramine in control mice, but did not alter it in mice withdrawn for 3 or 5 days. In mice withdrawn for 3 days acute morphine increased the free 3-methoxy-4-hydroxyphenylethylene glycol in all brain areas studied clearly less than in controls, whereas in mice withdrawn for 5 days the tolerance was found only in the hypothalamus. Our results show that the morphine-induced locomotor hyperactivity is enhanced in mice after sufficiently long withdrawal, when mice are sensitised to the acute morphine-induced increase of DA turnover but the tolerance to morphine’s effects on cerebral NA is disappearing, suggesting that in mice the cerebral NAergic systems, in addition to the DAergic ones, are major determinants of the behavioural response to morphine.

Cognition Enhancing Profile of CR 2249, a New NMDA‐Glycine Site Modulator

Memory processes have been widely studied in recent decades. Unfortunately, although several intriguing hypotheses about the possibility of modulating cognition have been developed, no conclusive result has been obtained (69). Two different neurotransmission models are of major interest in understanding how the brain can acquire and store a single cognitive event (3,23). The main neuronal agents involved in transferring this kind of information seem to be acetylcholine and glutamic acid. These two neurotransmitters are present in all the cerebral areas involved in the memory processes and both are responsible for the stimulation currents linked to the propagation of neuronal signals (1,4). The cholinergic hypothesis of memory ( 3 ) is based on the observation that a marked degeneration of the cholinergic neuronal pathway is often associated with the development of cognitive disorders ( 12). Moreover, it has been reported that one distinctive feature of Alzheimer’s disease (AD) consists of a progressive loss of either cholinergic or adrenergic neurons’ ability to transmit stimuli received from the limbic areas to the cerebral cortex (10,12,21,75). To help preserve high levels of acetylcholine in the synaptic cleft, several antiacetylcholinesterase agents have been synthesized and tested on both biochemical and behavioral models of learning (32,46). Tacrine is certainly the most studied among these agents ( 13). Clinical trials with tacrine revealed some interesting pro-mnemic properties of this compound (42,68), but tacrine exhibits major hepatotoxicity that strongly restricts its use ( 13,73). Donepezil (E2020) is another interesting compound of this family. Two recently published clinical studies (25,63) demonstrate both the efficacy of donepezil in patients with mild-to-moderate Alzheimer’s disease and its relative liver safety. Other potent acetylcholinesterase inhibitors, such as metrifonate and SDZ ENA 7 13, are currently under clinical evaluation (28,62,65). The glutamatergic hypothesis of memory is based on a particular characteristic of the glutamatergic neuronal pathway: long-term potentiation (LTP). LTP was first defined by Bliss and Collingridge (8) as a synaptic memory model expressed as a persistent increase in the size of the synaptic component of the evoked response. The

Δ9-Tetrahydrocannabinol increases prefrontal cortical catecholaminergic utilization and impairs spatial working memory in the rat: blockade of dopaminergic effects with HA966

The present study examined delta 9-tetrahydrocannabinol (THC)-induced alterations in monoamine transmission in the rat forebrain as well as the effects of the enantiomers of 3-amino-1-hydroxypyrrolid-2-one (HA966) on the monoamine response to THC. Activation of dopamine (DA) and norepinephrine (NE) but not serotonin (5-HT) turnover in the prefrontal cortex (PFC) was observed after THC (5 mg/kg i.p.) administration. Both enantiomers of HA966 completely prevented the effects of THC on PFC DA turnover and partially blocked the THC-induced rise in NE metabolism. The cognitive consequences of THC exposure were also examined. THC significantly impaired spatial working, but not reference, memory in rats, and this effect was ameliorated by HA966. Thus, HA966 prevents the THC-induced increases in PFC DA turnover and impairments of prefrontal cortical working memory function. Furthermore, these data suggest that cognitive impairments displayed by marijuana self-administering humans may be related to PFC DA hyperactivity and that HA966 may prevent this effect.

5-hydroxy-3-ethylamino-2-oxindole is not formed in rat brain following a neurotoxic dose of methamphetamine: evidence that methamphetamine does not induce the hydroxyl radical-mediated oxidation of serotonin.

Oxygen radicals have been implicated in the neurodegenerative and other neurobiological effects evoked by methamphetamine (MA) in the brain. It has been reported that shortly after a single large subcutaneous dose of MA to the rat, the serotonergic neurotoxin 5,6-dihydroxytryptamine (5,6-DHT) is formed in the cortex and hippocampus. This somewhat controversial finding suggests that MA potentiates formation of the hydroxyl radical (HO.) that oxidizes 5-hydroxytryptamine (5-HT) to 5,6-DHT, which, in turn, mediates the degeneration of serotonergic terminals. A major and more stable product of the in vitro HO.-mediated oxidation of 5-HT is 5-hydroxy-3-ethylamino-2-oxindole (5-HEO). In this investigation, a method based on HPLC with electrochemical detection (HPLC-EC) has been developed that permits measurement of very low levels of 5-HEO in rat brain tissue in the presence of biogenic amine neurotransmitters/metabolites. After intracerebroventricular administration into rat brain, 5-HEO is transformed into a single major, but unknown, metabolite that can be detected by HPLC-EC. One hour after administration of MA (100 mg/kg s.c.) to the rat, massive decrements of 5-HT were observed in all regions of the brain examined (cortex, hippocampus, medulla and pons, midbrain, and striatum). However, 5-HEO, its unidentified metabolite, or 5,6-DHT were not detected as in vivo metabolites of 5-HT. MA administration, in particular to rats pretreated with pargyline, resulted in the formation of low levels of N-acetyl-5-hydroxytryptamine (NAc-5-HT) in all brain regions examined. These results suggest that MA does not potentiate the HO.-mediated oxidation of 5-HT. Furthermore, the rapid MA-induced decrease of 5-HT might not only be related to oxidative deactivation of tryptophan hydroxylase, as demonstrated by other investigators, but also to the inhibition of tetrahydrobiopterin biosynthesis by NAc-5-HT. The massive decrements of 5-HT evoked by MA are accompanied by small or no corresponding increases in 5-hydroxyindole-3-acetic acid (5-HIAA) levels. This is due, in part, to the relatively rapid clearance of 5-HIAA from the brain and monoamine oxidase (MAO) inhibition by MA. However, the loss of 5-HT without corresponding increases in its metabolites point to other mechanisms that might deplete the neurotransmitter, such as oxidation by superoxide radical anion (O2.-), a reaction that in vitro does not generate 5-HEO or 5,6-DHT but rather another putative neurotoxin, tryptamine-4,5-dione. One hour after administration, MA evokes large depletions of norepinephrine (NE) throughout the brain but somewhat smaller decrements of dopamine (DA) that are restricted to the nigrostriatal pathway. Furthermore, MA evokes a major shift in the metabolism of both NE and DA from the pathway mediated by MAO to that mediated by catechol-O-methyltransferase. The profound and widespread effects of MA on the noradrenergic system, but more anatomically localized influence on the dopaminergic system, suggests that NE in addition to DA, or unusual metabolites of these neurotransmitters, might play roles in the neurodegenerative effects evoked by this drug.

Norepinephrine content in primary and secondary lymphoid organs is altered in rats with adjuvant-induced arthritis

Chemical sympathectomy of secondary lymphoid organs with sparing of the hind limbs exacerbates adjuvant-induced arthritis (AA) in Lewis rats supporting a role for noradrenergic (NA) innervation of the immune system in AA pathology. The present study examines sympathetic innervation of lymphoid organs from Lewis rats 32 days after treatment with complete Freund's adjuvant (CFA) or vehicle using fluorescence histochemistry for localization of catecholamines (CA) and high-performance liquid chromatography with electrochemical detection (LCEC) for measurement for norepinephrine. The thymus from AA rats was significantly reduced in size, while secondary lymphoid organs, i.e. spleen and draining lymph nodes (DLN), were significantly enlarged compared with that seen in vehicle-treated controls. Fluorescence histochemistry revealed no apparent differences in the density of NA innervation, or the intensity of staining in sympathetic nerves in any of the secondary lymphoid organs from AA rats compared with that observed in control animals. However, there was an apparent increase in the density of NA nerve fibers in the thymus of AA rats. Norepinephrine (NE) concentration (pmol NE per g or mg wet weight), in the thymus from AA rats was significantly increased. Conversely, a significant decrease in splenic and lymph node NE concentration was measured in adjuvant-treated animals compared with that seen in vehicle-treated rats. Total NE content (pmol NE per whole organ weight) in lymphoid organs was not altered, except in popliteal lymph nodes (PLN), where it was increased. Collectively, our findings suggest that changes in NA innervation of lymphoid organs from AA rats result largely from increases or decreases in organ mass. Since NE released from NA nerves acts in a paracrine fashion, changes in lymphoid tissue volume that result from enhanced proliferation, migration, or cell death can make a significant difference in the availability of NE for interaction with immune target cells in these organs, even in the absence of a change in NE metabolism. Decreased thymic weight and increased spleen and lymph node weight should increase and decrease NE availability for interaction with target cells, respectively. Additionally, in PLN (a site where the highest concentration of antigen is encountered) an increase in total NE content suggests compensatory changes in NE metabolism.