Determination of normetanephrine, 3,4-dihydroxyphenylethyleneglycol (free and total), and 3-methoxy-4-hydroxyphenylethyleneglycol (free and total) in rat brain by high-performance liquid chromatography with electrochemical detection and effects of drugs on regional concentrations

Norepinephrine modulation of heat dissipation in female rats lacking estrogen

Postmenopausal hot flushes are caused by lack of estradiol (E2) but their neuroendocrine basis is still poorly understood. Here, we investigated the interrelationship between norepinephrine and hypothalamic neurons, with emphasis on kisspeptin neurons in the arcuate nucleus (ARC), as a regulatory pathway in the vasomotor effects of E2. Ovariectomized (OVX) rats displayed increased tail skin temperature (TST), and this increase was prevented in OVX rats treated with E2 (OVX + E2). Expression of Fos in the hypothalamus and the number of ARC kisspeptin neurons coexpressing Fos were increased in OVX rats. Likewise, brainstem norepinephrine neurons of OVX rats displayed higher Fos immunoreactivity associated with the increase in TST. In the ARC, the density of dopamine-ß-hydroxylase (DBH)-immunoreactive (ir) fibers was not altered by E2 but, importantly, DBH-ir terminals were found in close apposition to kisspeptin cells, revealing norepinephrine inputs to ARC kisspeptin neurons. Intracerebroventricular injection of the α2-adrenergic agonist clonidine (CLO) was used to reduce central norepinephrine release, confirmed by the decreased 3-methoxy-4-hydroxyphenylglycol/norepinephrine ratio in the preoptic area and ARC. Accordingly, CLO treatment in OVX rats reduced ARC Kiss1 mRNA levels and TST to the values of OVX + E2 rats. Conversely, CLO stimulated Kiss1 expression in the anteroventral periventricular nucleus (AVPV) and increased luteinizing hormone secretion. These findings provide evidence that augmented heat dissipation in OVX rats involves the increase in central norepinephrine that modulates hypothalamic areas related to thermoregulation, including ARC kisspeptin neurons. This neuronal network is suppressed by E2 and its imbalance may be implicated in the vasomotor symptoms of postmenopausal hot flushes.

Hypothalamic monoamine metabolism is different between the diabetic GK (Goto-Kakizaki) rats and streptozotocin-induced diabetic rats

Hypothalamic neuronal activities of noradrenaline, dopamine and serotonin were investigated in the GK (Goto-Kakizaki) rats, a model for type 2 diabetes, and the streptozotocin (STZ)-induced diabetic rats, a model for type 1 diabetes. Each neuronal activity was assessed from a ratio of the concentrations of the major metabolite to those of its precursor monoamine itself or the metabolite concentrations itself. In the GK rats, hypothalamic noradrenaline and dopamine activities were significantly increased, and serotonin activity was unchanged. In the STZ-induced diabetic rats, hypothalamic dopamine and serotonin activities were significantly decreased, and noradrenaline activity was unchanged. In these two diabetic rats, hypothalamic noradrenaline and dopamine activities correlated significantly with serum insulin concentrations, whereas hypothalamic serotonin activity correlated significantly with serum glucose concentrations. These findings suggest that hypothalamic monoamine metabolism of the GK rats is quite different from that of the STZ-induced diabetic rats, and that not only hyperglycemia but also serum insulin concentrations have an influence on the hypothalamic monoamine metabolism in these diabetic rats.

The morphological and neurochemical effects of diffuse brain injury on rat central noradrenergic system

The central noradrenergic system is widely distributed throughout the brain and is closely related to spontaneous motility and level of consciousness. The study presented here evaluated the morphological as well as neurochemical effects of diffuse brain injury on the central noradrenergic system in rat. Adult male Sprague-Dawley rats were subjected to impact-acceleration brain injury produced with a weight-drop device. Morphological changes in locus coeruleus (LC) neurons were examined by using immunohistochemistry for dopamine-beta-hydroxylase, and norepinephrine (NE) turnover in the cerebral cortex was measured by high performance liquid chromatography with electrochemical detection. The size of LC neurons increased by 11% 24 h after injury but had decreased by 27% seven days after injury. Axons of noradrenergic neurons were swollen 24 h and 48 h after injury but the swelling had dwindled in seven days. NE turnover was significantly reduced seven days after injury and remained at a low level until eight weeks after injury. These results suggest that focal impairment of axonal transport due to diffuse brain injury causes cellular changes in LC and that the neurochemical effect of injury on the central noradrenargic system lasts over an extended period of time. Chronic suppression of NE turnover may explain the sustained behavioral and psychological abnormalities observed in a clinical situation.

Differential catecholamine responses to protein intake in healthy and hypertensive subjects

Protein intake-induced natriuresis previously related to increased urinary dopamine excretion was reexamined in an extensive controlled study comparing healthy and hypertensive subjects. In healthy subjects, ingestion of 1 g/kg wt tuna induced natriuresis that was associated, between postprandial hours 1 and 2, with increased plasma tyrosine [191 +/- 13% (mean +/- SE); P < 0.01], 3, 4-dihydroxyphenylalanine (104 +/- 12%, P < 0.05 in plasma; 162 +/- 20%, P < 0.05 in urine), plasma free dopamine (156 +/- 32%; P < 0. 05), and dopamine sulfate (191 +/- 11%, P < 0.001 in plasma; 199 +/- 15%, P < 0.01 in urine) but affected urinary free dopamine excretion only at limits of significance. Hypertensive subjects had less (P < 0.02) natriuresis and, despite comparable plasma tyrosine and dopamine sulfate increases, no increase in plasma and urinary 3, 4-dihydroxyphenylalanine and plasma free dopamine. Their plasma and urinary free epinephrine responses were less (P < 0.05) than the borderline increases in control subjects. Compared with control subjects, they significantly increased plasma 3, 4-dihydroxyphenylalanine sulfate (P < 0.05), epinephrine sulfate (P < 0.05), and the dopamine sulfate-to-free dopamine ratio (P < 0.02). Postprotein natriuresis is thus associated with nutritional priming-induced plasma but not urinary free dopamine increase. Hypertensive subjects have attenuated natriuretic and plasma free dopamine responses and less free epinephrine increase. This may partly result from higher circulating 3,4-dihydroxyphenylalanine, dopamine, and epinephrine sulfoconjugates leaving fewer free amines for biological actions.

Norepinephrine and traumatic brain injury: a possible role in post-traumatic edema

Unilateral cerebral contusion is associated with an early (30 min) increase in norepinephrine (NE) turnover followed by a later (6-24 h) depression of turnover which is bilateral and widespread throughout the brain. Blockade of NE function during the first few hours after traumatic brain injury (TBI) impedes subsequent recovery of function without enlarging the size of the lesion. The current studies were carried out to characterize further the timing of the switch from increased to decreased NE turnover and to investigate the pathogenesis of the delayed recovery of function associated with blocking NE function. Adult male rats had unilateral somatosensory cortex contusions made with a 5 mm diameter impact piston. They were killed after 2 h and their brains analyzed for NE turnover by HPLC with electrochemical detection. In general, NE turnover (the ratio of 3-methoxy-4-hyroxyphenylglycol to NE levels) had returned to sham-lesion control levels in most brain regions by 2 h after either left or right sided contusions. The only exceptions were a persistent 87% increase at the lesion site after right-sided contusions and 22% and 32% increases in the contralateral cerebellum after right- and left-sided contusions, respectively. Blockade of alpha1-adrenoceptors by treatment with prazosin (3 mg/ kg, i.p.) 30 min prior to TBI produced edema in the striatum and hippocampus at 24 h which was not seen saline-treated rats nor in rats where NE reuptake was blocked with desmethylimipramine (DMI; 10 mg/kg, i.p.). DMI increased edema at the lesion site at 24 h, however. These data suggest that the early increase in NE release following unilateral cerebral contusion is protective and that this may act to stabilize the blood-brain barrier in areas adjacent to the injury site. Drugs that interfere with this enhanced noradrenergic function might enhance the damage caused by TBI.

Effect of reserpine on 3-methoxy-4-hydroxyphenylethyleneglycol and 3,4-dihydroxyphenylacetic acid in the hippocampus of depression-model rats: an in vivo microdialysis study

Using in vivo microdialysis, we examined the effect of intraperitoneal injection of reserpine (2 mg/kg) on hippocampal 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and 3,4-dihydroxy-phenylacetic acid (DOPAC), two major metabolites of catecholamine. Responses were examined serially for 12 h in the hippocampus of walking-stress-induced depression-model rats, recovery rats and control rats. Control rats showed a rapid rise followed by a gradual fall of free and total MHPG and a delayed increase of DOPAC in response to reserpine. Depression-model rats showed a significantly blunted biphasic response of free and total MHPG as well as blunted monophasic response of DOPAC compared with control rats. Recovery rats also exhibited a blunted fall response of MHPG. Our findings suggest that the vesicle membrane in the central noradrenaline (NA) neurons could be hyposensitive to reserpine in the depression-model rats.

Early postnatal appearance of enhanced noradrenaline content in the brain of vasopressin-deficient Brattleboro rat; normal adrenoceptor densities and aberrant influences of vasopressin treatment

The course of postnatal development of noradrenaline (NA) and its unconjugated free metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG), as well as the influence on early chronic vasopressin treatment, were investigated in various brain regions of the hereditary vasopressin-deficient (homozygous di/di) Brattleboro rat. In addition, the densities of the adrenergic receptor subtypes were measured in adult brain. Brain NA levels of di/di pups appeared enhanced already at 7 days of age when compared with data of heterozygous (+/di) controls. This was also seen in areas not known to receive a vasopressinergic input, e.g. the frontal cortex. Levels of MHPG also differed between genotypes, but changes were slight and either a decrease or increase, depending on age and region tested. Saturation analyses of alpha 1-, alpha 2-, and beta-adrenoceptor binding on crude membrane preparations of some brain regions revealed no differences in adulthood. Chronic treatment with vasopressin between 6 and 13 days of age reduced the enhanced NA brain levels throughout the brain of the di/di Brattleboro pups. The known vasopressin-mediated enhancement of NA turnover in adult brain was also measurable in +/di pups of this neonatal period (MHPG/NA ratios), indicating the early maturation of the interaction of vasopressinergic and NAergic systems. However, the dose-response in the di/di Brattleboro rat was biphasic with a decrease at a low dose of vasopressin. Since changes were found throughout the brain, it was concluded that vasopressin deficiency had altered the maturation of NA neurons of the locus coeruleus which may be due to the absence of a presumed inhibitory control of vasopressin on synthesis and storage mechanisms at the perikaryal level.

Widespread and lateralization effects of acute traumatic brain injury on norepinephrine turnover in the rat brain

Norepinephrine (NE) has been implicated in recovery of function following traumatic brain injury (TBI). While bilateral decrease in brain NE turnover occur at 6-24 h after TBI, it is unknown what effects unilateral TBI might have on brain NE turnover the first few minutes after injury. Her male Sprague-Dawley rats had unilateral confusions of either the right or left somatosensory cortex produced by an air between piston. At 30 min after TBI, brain NE turnover was assessed by measuring the ratio of 3-methoxy-4 hydroxyphenylglycol (MHPG) to NE levels in various brain regions. Both right and left TBI produced 32-103% increases in NE turnover at the injury site and in the ipsilateral cerebral cortex surrounding, rostral and caudal to the injury as compared to the contralateral, uninjured site or to the homologous sites in uninjured controls. NE turnover was also altered selectively in some brain areas not affected by right TBI. Left TBI decreased NE turnover by 29% in the frontal cortex contralateral to the injury and by 24% bilaterally in the hypothalamus while increasing locus coeruleus NE turnover by 72% compared to uninjured controls. Thus, unilateral cortical TBI produced predominantly ipsilateral increases in cortical NE turnover but variable, bilateral changes in NE turnover in subcortical areas which were dependent upon the side of injury. These subcortical differences may explain some of the lateralized effects of cortical injury on post-injury behavior.

Determination of the catecholamines and serotonin, their precursors tyrosine and tryptophan, and their main metabolites in rat brain using reversed-phase high-performance liquid chromatography with fluorimetric and oxidative amperometric detection in series

A high-performance liquid chromatographic method for the determination of catecholamines and serotonin, their precursors and their main metabolites was developed applied to rat cerebellum, hypothalamus, striatum and cortex. A fluorimetric and an oxidative amperometric detector were used in series. For both detectors, detection limits (25-520 pg) were useful for this application, linearity of standards was excellent (average r greater than 0.9997), between-run precision for sample analytes was generally acceptable (coefficient of variation less than 10% with appreciable concentrations present) and average recoveries of standard additions to sample analytes were better than 90%. Particular attention was paid to peak identification, including both a thorough treatment of retention time agreement of peaks in standards and sample analytes, and a comparison of results for the seven compounds amenable to quantitation by both detectors. Considerable attention was also given to determining the stability of standards and sample analytes under a wide variety of conditions, and practical recommendations were made.

3-Methoxy-4-hydroxyphenylethyleneglycol concentrations in discrete hypothalamic nuclei reflect the activity of noradrenergic neurons

An analytical technique is described which permits the quantitation of picogram concentrations of 3-methoxy-4-hydroxyphenylethylene-glycol (MHPG) in acid hydrolyzed extracts of microdissected regions of the rat brain, and this procedure is used to determine if alterations in the activity of noradrenergic neurons are reflected by changes in the concentrations of MHPG in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the rat hypothalamus. MHPG was not detected in non-hydrolyzed samples of either the PVN or SON, but following acid hydrolysis (heating of samples at 94 degrees C for 5 min in 0.16 M perchloric acid) MHPG was detected in both of these regions. These results indicate that MHPG exists primarily as a conjugate in the PVN and SON. Neurotoxin-induced lesions of the ventral noradrenergic bundle decreased norepinephrine (NE) and MHPG concentrations in the PVN and SON, demonstrating that tissue levels of MHPG in these brain regions are dependent upon the presence of noradrenergic neurons. Electrical stimulation of the locus coeruleus increased MHPG concentrations in the PVN, but not in the SON, whereas electrical stimulation of the medial forebrain bundle increased MHPG concentrations in both of these regions. The alpha 2-adrenergic receptor antagonist idazoxan increased, while the alpha 2-adrenergic receptor agonist clonidine decreased MHPG concentrations in both the PVN and SON, but neither idazoxan nor clonidine altered NE concentrations in these regions. Immobilization of rats in the supine position increased MHPG concentrations in the PVN and SON, and this was accompanied by a decrease in NE concentrations in the SON.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopaminergic abnormalities in borderline essential hypertensive patients

To explore whether an altered metabolic pathway of dihydroxyphenylalanine (DOPA) may be related to some previously observed dopamine abnormalities in borderline hypertension, we measured basal and DOPA-induced (500 mg orally) changes in blood pressure and pulse rate as well as in three hourly plasma and urine samples. We found that borderline hypertensive patients compared with controls 1) showed a higher baseline urinary excretion of methoxytyramine, a marker of exocytotic dopamine release, with a greater DOPA-induced decrease of systolic blood pressure without reflex tachycardia; 2) had in response to DOPA a blunted plasma DOPA and free dopamine increase but an accentuated plasma dopamine sulfate and urinary DOPAC excretion; and 3) eliminated comparable quantities of dopamine in urine despite a lower rise in the glomerular DOPA load. Furthermore, although DOPA elicited natriuresis in both groups, its effect was greater in borderline hypertensive patients, who lacked the urinary sodium correlation with urinary dopamine excretion seen in control subjects. These data are compatible with increased basal exocytotic dopamine release and accelerated neuronal and renal (extraneuronal) dopamine generation from administered DOPA in borderline hypertension. The DOPA-induced hypernatriuresis exceeding augmented dopamine in borderline hypertensive patients, contrasting with the urinary sodium and dopamine correlation in control subjects, suggests that DOPA induced an additional natriuresis in borderline hypertensive patients by a decrease in renal sympathetic tone because of its central inhibition of sympathetic outflow, which also may account for the absence of reflex tachycardia.

Distribution of monoamines in human brain: evidence for neurochemical heterogeneity in subcortical as well as in cortical areas

Norepinephrine, epinephrine, dopamine, serotonin and their major metabolites were measured by high-performance liquid chromatography with electrochemical detection in 49 regions of the human brain. The regional distribution of the different monoamines in the subcortical areas was similar to previous reports. We report here the distribution pattern of the 4 monoamines observed in the cerebral cortex. Regional differences in concentration were observed for norepinephrine, epinephrine and serotonin, with high concentrations in the frontal and parietal regions. However, no regional difference in dopamine concentrations was detected. The possible role of norepinephrine and serotonin as conventional transmitters, and of dopamine and epinephrine as neurotransmission modulators is discussed.

Regional heterogeneity in the distribution of neurotransmitter markers in the rat hippocampus

A detailed neurochemical analysis of the distribution of markers for the most relevant neurotransmitter systems within the rat hippocampal formation has been performed. The hippocampi, obtained from unfrozen brains of male Sprague-Dawley rats were subdissected into tissue parts containing mainly CA1, CA3 or the dentate gyrus, respectively. Each part was further divided into ventral and dorsal halves. In these six hippocampal subregions the concentrations of noradrenaline, dopamine, serotonin, 3-methoxy-4-hydroxyphenylglycol, 5-hydroxyindoleacetic acid and the putative neurotransmitter amino acids glutamate, aspartate, GABA, glycine and taurine, and the levels of somatostatin and neuropeptide Y and the activities of choline acetyltransferase, acetylcholinesterase and glutamate decarboxylase were measured. A marked heterogeneity in the subregional distribution of markers for various neurotransmitter systems within the hippocampal formation was observed. Each neuronal marker was characterized by an individual pattern of distribution. Most of the markers showed a concentration-gradient, increasing from dorsal to ventral; only taurine was more abundant in the dorsal than in the ventral parts and no dorsoventral difference was seen for aspartate, glycine and neuropeptide Y. The highest molar ratios of total 3-methoxy-4-hydroxyphenylglycol to noradrenaline and 5-hydroxyindoleacetic acid to serotonin were found in the dorsal hippocampus. The levels of noradrenaline, GABA and glutamate decarboxylase activity were highest in the dentate gyrus and lowest in CA1. The concentrations of somatostatin were highest in CA1; those of serotonin were highest in CA3. Highest activities of choline acetyltransferase and acetylcholinesterase were found in the dentate gyrus; lowest activities were found in CA3. In CA3 the lowest values of glutamate, aspartate, taurine and somatostatin were also found. The heterogeneity in the distribution of individual neurochemical markers allows insights into possible functional differences of hippocampal subregions and provides a relevant basis for future neurochemical investigations in this brain area.

Microdialysis studies on cortical noradrenaline release: basic characteristics, significance of extracellular calcium and massive post-mortem increase

Extracellular noradrenaline was measured on-line in the cerebral cortex of the freely moving rat by microdialysis coupled to high performance liquid chromatography and electrochemical detection. High potassium concentrations in the perfusion fluid led to a strong increase, whereas tetrodotoxin led to almost undetectable levels of noradrenaline. This shows that noradrenaline in the dialysate was directly derived from active neuronal release. Noradrenaline levels were sensitive to calcium concentrations in the perfusion fluid: from 10% in calcium-free medium to 200% for 10 mM calcium. An overdose of anesthetic caused a 60-fold increase of noradrenaline post-mortem.

Alpha-adrenoceptor involvement in swim stress-induced antinociception in the mouse

Three different intensities of swim stress produced stress-induced antinociception (SIA) in mice which was assessed either by the reduction in the number of abdominal constrictions produced by acetic acid or by an increase in reaction time on a hot-plate. The involvement of alpha-adrenoceptors in the three models of SIA was investigated using selective antagonists. SIA produced by the mild stress of a 30 s warm water swim was attenuated by idazoxan (0.5-1 mg kg-1), and by yohimbine at a dose (1 mg kg-1) which reduced antinociception produced by clonidine (12.5-50 micrograms kg-1). Indoramin (1-2 mg kg-1) did not affect this model of SIA, but reversed phenylephrine induced inhibition of the constrictions. A 3 min room temperature swim increased reaction times on the hot-plate and this naloxone-sensitive SIA was reduced significantly by prazosin (1-2 mg kg-1), idazoxan (0.5-1 mg kg-1) and yohimbine (0.5-1 mg kg-1) but enhanced by clonidine (0.5 mg kg-1) and noradrenaline (NA) (10 micrograms i.c.v.). Mice treated with 6-hydroxydopamine (60 + 60 micrograms i.c.v.) were hypersensitive to the hot-plate and did not develop SIA. Levels of noradrenaline in the brain (minus the cerebellum) were decreased after the room temperature swim SIA. The most severe stress of a cold water swim produced SIA on the hot-plate which was initially naloxone-insensitive.(ABSTRACT TRUNCATED AT 250 WORDS)

Vesicular accumulation of dopamine following L-DOPA administration

In this study, the accumulations of dopamine (DA) and norepinephrine (NE) were measured in the brain tissues and in the synaptic vesicle fractions prepared from whole brain of control rats and rats injected with L-DOPA. In the normal rat brain, a 3-fold increase in DA following L-DOPA administration was followed by a small, but not significant increase in vesicular DA, indicating a restricted vesicular uptake of exogenous DA. At the same time, NE in the vesicular fraction and in the whole brain tissue did not change, suggesting a possible link between DA vesicular uptake of DA and brain NE. However, in rats pretreated with alpha-methyl-p-tyrosine, which significantly (P less than 0.05) reduced DA and NE levels in brain tissues and in the synaptic vesicles, L-DOPA administration led to a significant increase in vesicular DA (P less than 0.05), suggesting that catecholamine depletion may result in greater vesicular uptake of cytoplasmic DA. The increase in vesicular DA was accompanied by increases in tissue and vesicular NE, underscoring again the existence of a link between vesicular uptake of DA and brain NE following L-DOPA administration. The results also demonstrated a large increase in 3,4-dihydroxyphenylacetic acid (DOPAC) following L-DOPA, in the brain tissues but not in the synaptic vesicle, indicating that monoamine oxidase activity is confined to the cytoplasm.

Chlorpromazine-induced alterations in hypothalamic amine metabolism and stress responses in severe cold

To investigate the effects on the central nervous system of severe cold stress with and without chlorpromazine, guinea pigs were treated with chlorpromazine or 0.9% NaCl and exposed to -20 degrees C or +23 degrees C for 1 h. Hypothalamic noradrenaline (NA), dopamine (DA), 5-hydroxy-tryptamine (5-HT), 3-methoxy-4-hydroxyphenyl ethylene glycol (MHPG), homovanillinic acid (HVA) and 5-hydroxy-indoleacetic acid (5-HIAA) were determined by high-performance liquid chromatography. Serum, urinary and vitreous fluid catecholamines, muscle and liver glycogen, and blood glucose were also measured. Chlorpromazine caused distinct hypothermia at -20 degrees C and slight hypothermia at +23 degrees C. The rise in hypothalamic MHPG, 5-HIAA and MHPG/NA and in 5-HIAA/5-HT ratios in the cold indicate increased noradrenergic and serotonergic activity. The latter was inhibited by chlorpromazine and a drug-induced inhibition of noradrenergic neurons could not be ruled out. Chlorpromazine increased the turnover of DA at room temperature and the same tendency was seen in the cold. The hypothermic animals had low serum catecholamines, indicating diminished sympathetic activity. The chlorpromazine-treated cold-exposed animals did not react to the environmental stress by sympathetic activation, as urinary NA and adrenaline were not elevated, but DA was excreted by all the drug-treated animals. Vitreous fluid NA and DA were elevated as an indicator of cold stress, and no drug effect was seen in this fluid.

Effects of chlorpromazine on hypothalamic aminergic neurons and stress responses in moderate cold

Guinea-pigs were treated with chlorpromazine or 0.9% NaCl and exposed to +4 degrees C or +23 degrees C for 2 h. Hypothalamic noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT), 3-methoxy-4-hydroxyphenylethylene-glycol (MHPG), homovanillinic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were determined by high-performance liquid chromatography. Serum and urinary catecholamines, muscle and liver glycogen and blood glucose were also measured. Chlorpromazine caused deep hypothermia at this moderately cold temperature and slight hypothermia at room temperature. Cold increased the activity of noradrenergic and serotonergic neurons, as indicated by the increase in hypothalamic MHPG and 5-HIAA and also the MHPG:NA and 5-HIAA:5-HT ratios. A tendency towards drug-induced inhibition of hypothalamic serotonergic neurons was seen, although this was not significant. A drug-induced inhibition of noradrenergic neurons could not be ruled out. Increased drug-induced turnover of DA was observed in the cold, and a tendency in the same direction was seen at room temperature. Excretion of DA into the urine was induced by chlorpromazine. The hypothermic guinea-pigs had low serum catecholamines, indicating diminished sympathetic activity, but high urinary catechols, a sign of cold stress.

Catecholamine content changes in brain regions of spontaneously hypertensive rats under immobilization stress

We compared the effect of immobilization stress on noradrenaline (NA) and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) content in two brain regions--diencephalon and pons-medulla oblongata--in young and adult spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). In SHR, NA content decreased with time after the onset of the stress, whereas levels of its metabolite MHPG increased. In WKY, NA and MHPG showed no change. The MHPG/NA ratio in both regions increased relative to the duration of the stress in SHR, whereas it remained almost constant in WKY. The rate of increase in the ratio was much higher in the diencephalon of adult (12-week-old) than of young (4-week-old) SHR. In SHR, NA turnover in the brain is readily affected by environmental stress, and these changes in the noradrenergic system may induce or sustain hypertension.

Simultaneous determination of the major acidic metabolites of catecholamines and serotonin in urine by liquid chromatography with electrochemical detection after a one-step sample clean-up on Sephadex G-10; influence of vanilla and banana ingestion

A simple method is described for the simultaneous determination of vanilmandelic acid (VMA), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindole-3-acetic acid (5-HIAA) and homovanillic acid (HVA) in urine. The compounds are isolated by a one-step sample clean-up on Sephadex G-10, separated by ion-pair reversed-phase liquid chromatography and detected electrochemically. A single analysis is completed within 65 min. Sample clean-up did not cause losses of the compounds of interest. The detection limits in urine were 0.4, 0.8, 1.0 and 1.6 mumol/l for VMA, DOPAC, 5-HIAA and HVA, respectively. 3,4-Dihydroxymandelic acid and vanillic acid (VA) were also detectable, but, under the chromatographic conditions used, they were not resolved from interfering components. VA and 5-HIAA could be analysed separately in the Sephadex G-10 eluate if more restrictive sampling conditions were used. Ingestion of bananas caused an increase of VMA, DOPAC, 5-HIAA and HVA in 24-h urine. After ingestion of vanilla an increased excretion of VA was observed, while the excretion of VMA, DOPAC and HVA was unaffected.

Monoamine metabolism and its responses to food deprivation in the brain of Zucker rats

Monoamines and their metabolites levels were simultaneously measured by high-performance liquid chromatography in brain regions of lean and fatty Zucker rats when fed ad lib and deprived of food for 72 hr to evaluate each monoamine metabolism. Metabolite/monoamine ratios were shown for brevity to represent its metabolism. 3-Methoxy-4-hydroxyphenylethyleneglycol/noradrenaline ratios were not affected by the phenotype factor but increased in the cortex of fatty rats and reduced in the midbrain of both phenotypes after fasting; the interaction between phenotype and feeding factors was observed in the cortex and hippocampus. 3,4-Dihydroxyphenylacetic acid/dopamine ratios were increased in the cortex of deprived fatty rats and in the medulla-pons of ad lib-fed fatties compared with lean counterparts and also increased in the striatum of lean rats after food deprivation; the interaction was observed in the cortex, midbrain and medulla-pons. Homovanillic acid/dopamine ratios were decreased in the striatum of deprived fatty rats and in the midbrain and medulla-pons of fatty rats whether deprived or not, but the ratios were not significantly changed by fasting; the interaction was observed in the striatum. 5-Hydroxyindoleacetic acid/5-hydroxytryptamine ratios were reduced in the cortex, striatum and medulla-pons of fatty rats in both feeding states and in the midbrain of deprived fatties, and after food deprivation increased in the cortex and midbrain of lean rats and in the hippocampus of both phenotypes; the interaction was observed in the midbrain.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of a novel type of rotating disc electrode and a flow cell with laminar flow pattern for the electrochemical detection of biogenic monoamines and their metabolites after Sephadex gel chromatographic purification and high-performance liquid chromatographic isolation from rat brain

A novel type of rotating disc electrode and a flow cell with laminar flow pattern were developed and applied to the electrochemical detection of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 3-methoxytyramine (3-MT), noradrenaline, 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid after HPLC of these compounds. The active surface of the rotating disc working electrode was made from solid paraffin (40% wt/wt) and graphite powder (60% wt/wt). The sensitivity of the detector was proportional to the square root of the angular velocity and was practically independent of the flow rate of the mobile phase. The surface of the working electrode was very large (radius = 12 mm), and so the percentage of oxidation was 24-67% (flow rate = 1.0 ml/min), depending on the compound. Electrical noise between 20 and 40 pA and background current of 20-60 nA were observed. In practice, the sensitivity for the detection of the compounds examined here was 8-16 nA/ng, and so a detection limit of 5 pg/injection could be achieved, when the detector was combined with reversed-phase HPLC. Supernatants obtained from the extracts of the tissue samples (nine brain parts of rat brain were studied) were purified by using Sephadex G-10 gel chromatography. Before this procedure, the proteins of the tissue extracts were precipitated by 0.2 M HClO4, and the excess of HClO4 was precipitated by KOH/HCOOH buffer. Simultaneously, the pH of the extracts was set to 2.4 by the above buffer.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylglycol (DOPEG) in microdissected brain structures and the pituitary gland: metabolite changes in the median eminence in response to hyperprolactinemia and suckling

Dopamine (DA), norepinephrine (NE), epinephrine (E), 3,4-dihydroxyphenylglycol (DOPEG) and dihydroxyphenylacetic acid (DOPAC) were determined simultaneously by a radioenzymatic, thin-layer chromatographic assay able to detect 1-10 pg of the parent compounds and 80-120 pg of their metabolites. A localization study of these compounds in 20 micro-dissected hypothalamic and limbic structures and the anterior and posterior pituitary glands of male rats was completed. DOPAC was detectable in 14 of 22 structures with the lowest DOPAC/DA ratio being found in the caudate nucleus (7.1%) and the highest in the medial aspect of the ventromedial nucleus of the hypothalamus (422.0%). There was a higher DOPAC/DA ratio in the lateral (21.5%) than in the medial (11.3%) portion of the median eminence suggesting that a greater portion of released DA in the medial median eminence enters the portal circulation. DOPEG was detectable in 6 of 22 structures with DOPEG/NE ratios ranging from 8% (interstitial nucleus of the stria terminalis, ventral aspect) to 32% (medial median eminence). A poor correlation exists between DOPAC and DA concentrations in the various brain regions while there was a stronger relationship between DOPEG and NE concentrations. Male rats were rendered hyper-prolactinemic for 48 hours with injections of ovine prolactin (oPRL) every 8 hours (4 mg/kg body weight sc). In such rats there was a suppression of endogenous rat PRL (rPRL) secretion, the DOPAC/DA ratio increased 2.2-fold in the medial (MEm) and 1.9-fold in the lateral median eminence (MEl), and the DA concentration in the anterior pituitary also increased 2.6-fold. In 10 day postpartum lactating rats, suckling produced marked increases in serum rPRL but no change in DOPAC/DA ratios in the ME or in the DA concentration in the anterior pituitary. The data reveal a wide range of DOPAC/DA ratios (7-422%) in brain regions containing cell bodies, axons and terminals of the different dopaminergic neuronal tracts in brain and pituitary. Considering the DOPAC/DA ratios in the MEm and MEl, it is suggested that a large perturbation of dopaminergic transmission produces a significant ratio change while a smaller perturbation is not detected by this index of neuronal metabolism.

Effects of different monoamine oxidase inhibitors on the metabolism of L-dopa in the rat brain

The influence of monoamine oxidases A and B on the metabolism of dopamine or the expanded dopamine pool following L-dopa administration remains unclear. This study found that treatment of Sprague-Dawley rats with monoamine oxidase inhibitors strongly affected L-dopa metabolism in the brain, but the influence varied with each individual inhibitor. In animals pretreated with pargyline or clorgyline, L-dopa administration led to huge accumulations of dopamine and significantly raised central norepinephrine concentrations. In contrast, similar L-dopa injections in deprenyl-pretreated rats caused only a moderate rise in dopamine and no change in norepinephrine. There seems to be little relationship between the degree of monoamine oxidase inhibition and the accumulation of catecholamines and their metabolites in the rat brain. The effects of monoamine oxidase inhibitors on dopamine accumulation appeared to occur outside the catecholaminergic neurons since in the animals pretreated with 6-hydroxydopamine, which decreased significantly the content of brain catecholamines, dopamine accumulation following L-dopa administration still remained considerable. On the other hand, the influence of monoamine oxidase inhibitors on brain norepinephrine concentrations seemed to originate in the noradrenergic neurons because norepinephrine increase was greatly reduced in rats treated with 6-hydroxydopamine but was restored when the treatment with 6-hydroxydopamine was accompanied by desimipramine which specifically protects noradrenergic stores.

Hypothalamic monoamines and their catabolites in relation to the estradiol-induced luteinizing hormone surge

Monoamines and non-conjugated catabolites (serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA), 3,4-dihydroxyphenyl-acetic acid (DOPAC), homovanillic acid (HVA), 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG), norepinephrine (NE), and dopamine (DA] were measured in the medial basal hypothalamus (MBH) and preoptic area (POA) of ovariectomized (OVX) and OVX estradiol (E2)-treated rats using high-performance liquid chromatography with electrochemical detection. These E2 treatments were sufficient to induce an LH surge. The use of MHPG/NE ratios as estimates of NE release was validated in the rat hypothalamus by the major decreases of MHPG after injection of the alpha 2-adrenergic agonist, clonidine, and by MHPG increases after the alpha 2-antagonist, yohimbine. The ratio, MHPG/NE, decreased between morning and afternoon in the MBH but not in the POA; there were no differences between OVX and E2-treated rats. Previous studies using a variety of methods indicate that NE turnover increases during LH surges. The present data suggest that unconjugated MHPG is not a sensitive measure of NE release in the rat hypothalamus, but can detect the large changes produced by stimulating or inhibiting the alpha 2-adrenergic autoreceptor. The ratios of DOPAC/DA and 5-HIAA/5-HT in the MBH decreased consistently between morning and afternoon in OVX rats, with or without E2 treatment. This suggests that the release of DA and 5-HT decreases during the day regardless of steroidal milieu.

Modification of dopamine and norepinephrine metabolism in the rat brain by monoamine oxidase inhibitors

The treatment of Sprague-Dawley rats with monoamine oxidase (MAO) inhibitors (pargyline, tranylcypromine) profoundly affects dopamine (DA) and norepinephrine (NE) metabolism in the brain. In these rats injection of L-dopa led to large increases in norepinephrine (NE), normetanephrine (NMN) and 3-methoxytyramine (3-MT) in brain tissues. The response of MAO-inhibited rats to L-dopa contrasted sharply with those not treated with the MAO inhibitor; the latter showed no change in NE, NMN and 3-MT after similar administration of L-dopa. The increase of NE in pargyline-treated rats correlated closely with that of DA in the hypothalamus and in the brain stem. This response was greatly diminished in rats previously treated with the neurotoxin 6-hydroxydopamine, but was restored when the treatment with 6-hydroxydopamine was accompanied by desimipramine. This suggests that noradrenergic neurons were the origin of the NE response. The NMN and 3-MT increases occurring only in the rats treated with a MAO inhibitor were highly correlated. The results suggested that MAO inhibitor may affect entry of DA into catecholaminergic storage where NE synthesis takes place and from where DA is released.

Electrical stimulation of the C1 region of the rostral ventrolateral medulla of the rat increases mean arterial pressure and adrenaline release in the posterior hypothalamus

By using intracerebral dialysis in combination with high performance liquid chromatography and electrochemical detection, extracellular posterior hypothalamic adrenaline, noradrenaline, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid were measured in the anaesthetized rat and changes in their levels monitored following administration of tranylcypromine and electrical stimulation of the rostral ventrolateral medulla. Tranylcypromine (10 mg/kg i.p.) administration decreased basal extracellular 3,4-dihydroxyphenylacetic acid and 5-hydroxyindole acetic acid levels with a simultaneous increase in adrenaline and noradrenaline levels. Electrical stimulation of the C1 area of the rostral ventrolateral medulla increased (+56.6%) extracellular adrenaline levels in the posterior hypothalamus with a simultaneous increase in mean arterial pressure (+48 mm Hg) compared to prestimulation control values. No change was seen in posterior hypothalamic extracellular levels of noradrenaline, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindole acetic acid during the stimulation period. Electrical stimulation of areas close to but outside the C1 region had no effect on either mean arterial pressure or posterior hypothalamic extracellular levels of the amines or the metabolites. The increase in adrenaline levels in the hypothalamus during stimulation of the C1 region supports the evidence for an adrenergic pathway from the rostral ventrolateral medulla to the hypothalamus and suggests that the increase in mean arterial pressure during electrical stimulation to the C1 region may relate to a specific increase in adrenaline levels.

Differential pulse voltammetry in vivo with working carbon fiber electrodes: 5-hydroxyindole compounds or uric acid detection?

Differential pulse voltammetry was performed in rats chronically implanted with carbon fiber electrodes in the caudate (n.Cd) and raphe dorsalis (n.RD) nuclei. The electrochemical signal obtained at the +300 mV potential (peak 3) in animals implanted for more than one week (long term chronic conditions, greater than 7 days) could be dependent upon the extracellular fraction of 5-hydroxyindolacetic acid (5-HIAA) since a single injection of Pargyline is sufficient to suppress it in n.Cd and n.RD. This result was obtained despite the tendency of Pargyline to increase n.Cd and n.RD endogenous concentrations of Uric Acid (UA) measured by High Performance Liquid Chromatography (HPLC). In contrast, in animals implanted for less than one week (short term chronic conditions, less than 7 days) peak 3 recorded in the same structure could be dependent upon extracellular fractions of 5-HIAA and UA since consecutive injections of Pargyline and Allopurinol are necessary to suppress this signal. The source of extracellular UA measured in brain by voltammetry, in such short term chronic conditions, might result from surgical trauma.

Effect of repeated amiflamine administration on serotonergic and noradrenergic neurotransmission: electrophysiological studies in the rat CNS

Amiflamine is a selective and reversible inhibitor of monoamine oxidase (MAO) type A which exerts a preferential effect on serotonin (5-HT) catabolism. The present studies were undertaken to compare the effects of repeated administration of amiflamine (2 mg/kg, twice daily) on several aspects of the functioning of the 5-HT and norepinephrine (NE) systems in the rat CNS. The activity of MAO-A and B was assessed in forebrain slices and the whole brain contents of the neurotransmitters and their metabolites were determined by HPLC after 2-, 7- and 21-day treatments. MAO-A was inhibited by about 50% 2 h after the last dose and its activity was back to normal in rats sacrificed 12 h after the last dose. The activity of MAO-B was unaffected two or 12 h after the last dose. Whole brain concentration of 5-HT was increased to a greater degree than that of NE following repeated administration of amiflamine. These increases in 5-HT and NE were accompanied by decreased levels of their respective metabolites 5-hydroxy-indoleacetic acid and 3-methoxy-4-hydroxyphenylethyleneglycol. The firing activity of dorsal raphe 5-HT neurons, but not that of NE neurons, was markedly decreased 2-6 h after the last dose of a 2-day treatment. However, 2-6 h after a 21-day treatment, the firing activity of 5-HT neurons was back to normal, whereas that of NE neurons was decreased by 30%.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation of total MHPG in the rat brain using a non enzymatic hydrolysis procedure. Effects of drugs

An acid-catalyzed procedure has been used to hydrolyze MHPG-sulfate in homogenates of rat brain. The samples (in 0.4 mol/L perchloric acid) are treated for 3 min. at 100 degrees C in a water bath and aliquots are injected into a reversed phase HPLC system. Detection is achieved fluorimetrically. The absolute detection limit for MHPG is 150 pg, which allows the reliable determination of either free or total MHPG in rat brain in concentrations down to 15 ng/g, using the described procedure. The concentration of total MHPG found in the brains of saline-treated rats are 101 +/- 21 ng/g (mean +/- S.D.) which is in a good accordance with the concentration value for the same samples obtained using a GC-MS method (115 +/- 19 ng/g). Rats treated with clonidine (300 micrograms/Kg, i.p.) or yohimbine (10 mg/Kg, i.p.) showed brain concentrations of total MHPG of 68 +/- 22 ng/g and 299 +/- 85 ng/g, respectively. The utility of this method for the analysis of brain regions or brain nuclei (e.g. locus coeruleus) is also shown.

Effects of yohimbine and idazoxan on monoamine metabolites in rat cerebrospinal fluid

Effects of two alpha 2-adrenoceptor antagonists, idazoxan and yohimbine, on the concentrations of monoamine metabolites in cisternal cerebrospinal fluid (CSF) of freely moving rats were investigated. Both drugs caused a dose-dependent, up to 250% increase in the concentration of 3-methoxy-4-hydroxyphenylglycol (MHPG) in CSF indicating enhanced release, metabolism and turnover of noradrenaline in the central nervous system (CNS). In addition, a similar increase in homovanillic acid (HVA) in CSF was observed, while the level of 5-hydroxyindoleacetic acid was unchanged. The present results demonstrate the usefulness of monitoring drug-induced alterations in noradrenergic activity in the CNS by measurement of free MHPG in repeatedly collected cisternal CSF samples from awake rats. The possibility that the observed increase in the concentration of HVA after the highly specific alpha 2-antagonist idazoxan reflects increased noradrenergic rather than dopaminergic neuronal activity is discussed.

Comparison of free MHPG in rat cerebrospinal fluid with free and conjugated MHPG in brain tissue: effects of drugs modifying noradrenergic transmission

The changes of free 3-methoxy-4-hydroxyphenylglycol (MHPG) in cerebrospinal fluid (CSF) were compared with the corresponding alterations of free and conjugated MHPG in rat brain tissue after various pharmacological treatments modifying noradrenergic neurotransmission. In addition, the effects of the drug treatments on the concentration of noradrenaline (NA) in brain were determined. alpha-Methyl-p-tyrosine (an inhibitor of tyrosine hydroxylase) induced decreases in free and conjugated MHPG in CSF and brain; the free species appeared to decline more rapidly. Reserpine caused similar biphasic changes in free MHPG in CSF and brain but the rapid and transient initial increase in MHPG-SO4 was very weak. Pargyline (monoamine oxidase inhibitor) induced a sharp decline in the concentration of free MHPG in brain and CSF while MHPG-SO4 in brain definitely decreased more slowly. Relatively similar time courses were seen for all three MHPG parameters after administration of MPV-1248 (alpha 2-antagonist) and clonidine (alpha 2-agonist) i.e., increases and decreases, respectively. The present results support the validity of monitoring drug-induced acute changes in central turnover of NA by repeated measurements of free MHPG levels in rat cisternal CSF.

Is 3,4-dihydroxyphenylglycol the major route of central norepinephrine metabolism in rat brain?

Central norepinephrine (NE) metabolism was assessed by measuring 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and 3,4-dihydroxyphenylethyleneglycol (DHPG) in different rat brain areas after saline or probenecid (300 mg/kg) administration. Under probenecid, results showed an increased accumulation of total MHPG and DHPG, and a clear preponderance of DHPG levels over MHPG in almost all the brain areas examined. Estimation of their formation rates confirmed that in basal conditions DHPG is formed more rapidly. This study supports the notion that, without ruling out the importance of MHPG, brain DHPG may be a useful index of central NE activity.

alpha 2-Adrenoceptor agonists decrease free 3-methoxy-4-hydroxyphenylglycol in rat cerebrospinal fluid

The effects of alpha 2-adrenoceptor agonists on the concentrations of monoamine metabolites in cisternal cerebrospinal fluid (CSF) of freely moving rats were determined. Clonidine and two new imidazole derivatives, detomidine and medetomidine, and diazepam (as a control substance) were administered in sedative doses and the concentrations of unconjugated 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) in CSF were monitored for 48 h. The alpha 2-agonists caused a dose-dependent, statistically significant decrease in the concentration of MHPG in CSF compared to the concentration in animals treated with saline or diazepam. Detomidine caused a statistically significant increase in the concentration of 5-HIAA compared to control treatments. The present results demonstrate the usefulness of monitoring drug-induced alterations in central nervous system (CNS) noradrenergic activity by measuring free MHPG in repeatedly collected cisternal CSF samples from freely moving rats. The alpha 2-agonists reduced the concentration of MHPG in CSF, indicating a decreased release, metabolism and turnover of noradrenaline in the CNS.

An automated direct-injection HPLC-method for the electrochemical/fluorimetric quantitation of monoamines and related compounds optimized for the screening of large numbers of animals

An automated, highly stable HPLC system is described allowing the quantitation of monoamines and related compounds with virtually online data processing and statistical evaluation of the mean values of various differently treated groups of animals. The system is highly suited to the screening of drugs involving large numbers of samples. To ensure long-term, uninterrupted performance, two robust chromatographic systems were developed optimized to separate neighboring peaks as widely as possible. This was achieved by using mobile phases of relatively low pH to retard acidic compounds, and optimal concentrations of the ion-pairing reagent to manipulate the retention times of amines on the RP-18 column, resulting also in clearcut separations from the solvent/tissue peak. Direct injection of deproteinized tissue samples, requiring no clean up procedures is used. One faster system allows measurement of the main biogenic amines, metabolites and TRP, whereas another system allows the simultaneous quantitation of DOPA, 5HTP, NA, MOPEG, NMN, A, MN, VMA, DA, 3MT, DOPAC, HVA, 5HT, 5HIAA and TYR. By pretreatment of animals with a decarboxylase inhibitor the latter system offers the possibility of detecting drug effects in the same animal on either dopamine and serotonin turnover or noradrenaline and serotonin turnover, depending on the brain area chosen. The system described has been running for over a year without major disturbance and with minimal technician attendance.

Effects of 6-hydroxydopamine-induced lesions of the paraventricular nucleus, and of prazosin, on the corticosterone response to restraint in rats

In rats, with bilateral lesions of the paraventricular nuclei induced by 6-hydroxydopamine, restraint stress failed to elevate levels of corticosterone in plasma, although the resting levels in lesioned animals were similar to those of control rats. Prazosin inhibited the plasma-corticosterone response to restraint in intact rats, at doses which did not by themselves influence resting hormone levels. These results suggest a positive role for noradrenaline, acting through alpha-adrenoceptors, on the stress-induced output of corticotrophin.

Alterations in the noradrenergic projection to the cerebellum of the dystonic (dt) rat

The genetically dystonic rat (dt) has elevated resting levels of cerebellar norepinephrine (NE) in comparison with phenotypically normal littermates. This difference is not secondary to cerebellar hypoplasia. Increased NE is observed as early as postnatal day 12, when clinical symptoms have become evident. The elevation in cerebellar NE levels in the dt rat involves all cerebellar areas, but is not generalized to all terminal fields of the locus coeruleus. Elevations in cerebellar NE are followed developmentally by a reduction in sensitivity to the NE-depleting effects of reserpine, a change which is also confined to the cerebellum. The effects of amphetamine and the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine were similar in normal and dt rats. Levels of the major cerebellar metabolite of NE, 3-methoxy-4-hydroxyphenylglycol, did not differ between mutant and normal animals. Nor were any changes noted in the number or affinity of beta-adrenergic receptors. These data indicate that there is a regional alteration in NE storage. Cerebellar morphology appears normal in the dt rat, except for a decrease in Purkinje cell size. This change and other evidence of biochemical abnormalities in the Purkinje cells suggest that the alterations in cerebellar NE in the dt mutant may be a secondary response to a functional change in the target neuron for this system, the Purkinje cell.

Repetitive measurement of monoamine metabolite levels in cerebrospinal fluid of conscious rats: effects of reserpine and haloperidol

A simple high performance liquid chromatographic method with electrochemical detection is described for the simultaneous determination of unconjugated 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA), the principal central nervous system (CNS) metabolites of noradrenaline, serotonin and dopamine (DA), respectively, in small samples of cisternal cerebrospinal fluid (CSF) obtained repeatedly from freely moving rats. Amounts of 30-50 microliter of CSF could be collected repeatedly every 30-60 min allowing monitoring of monoamine metabolite concentration levels in CSF under physiological conditions. None of the metabolites showed any clear diurnal variation. A single injection of reserpine caused a prominent elevation in the concentrations of MHPG, 5-HIAA and HVA in CSF. However, after a rapid increase, the concentration of MHPG was decreased by 85% from the control values. Haloperidol caused a 3-fold increase in the concentration of HVA, indicating increased DA turnover in the CNS. The method enables the reliable quantitative determination of three major monoamine metabolites in small samples of CSF from freely moving rats and appears to be a useful tool in the evaluation of the validity of the clinically used research methods of monitoring drug-induced alterations in CNS monoaminergic activity by metabolite measurements in CSF.

Liquid chromatographic determination of free and conjugated 3-methoxy-4-hydroxyphenylethylene glycol with wide-ranging substances related to monoamine metabolism

A simple and sensitive procedure was developed for the simultaneous determination of substances metabolically related to monoamine transmitters including 3-methoxy-4-hydroxy-phenylethylene glycol (MOPEG) in dissected brain regions of rats using high-performance liquid chromatography combined with electrochemical detection. The tissue sample was homogenized in HCl solution. The homogenate was divided into two portions, of which one was used for the assay of MOPEG after enzymatic hydrolysis with sulfatase. A butanol extraction process was performed on the remaining portion to obtain the sample of monoamine transmitters, precursor amino acids, and acidic metabolites. The monoamines and precursor amino acids were finally recovered in HCl solution, while the acidic metabolites shifted into the alkaline buffer from the organic layer. The basic and neutral substances were separated with a 0.1 M sodium citrate/citric acid buffer system (pH 4.0) containing 1% tetrahydrofuran, and the acidic ones with 0.075 M sodium citrate/citric acid buffer (pH 3.5) containing 1% tetrahydrofuran, 10% methanol, and 12% acetic acid. The steady-state concentrations of three monoamine transmitters (noradrenaline, dopamine, and 5-hydroxytryptamine) were determined together with their precursors and metabolites. Changes in the concentrations of these substances were examined for various drugs, of which the effects had been previously confirmed. The changes reflected putative drug effects and demonstrated that the procedure was applicable to the regional determination of monoamines and their metabolically related substances.

The role of noradrenaline in tuning and dopamine in switching between signals in the CNS

Neuronal catecholaminergic activity modulates central nervous function. Specifically noradrenaline can exert a tuning or biassing function whereby the signal to noise ratio is altered. Dopamine activity may promote switching between inputs and outputs of information to specific brain regions. It has been ten years since evidence for a tuning function was advanced for noradrenaline and in the last 5 years the switching hypothesis for dopamine has been tentatively put forward. Recent studies are reviewed to show that while catecholamine activity contributes to neural interactions in separate brain regions that give rise to the organization of different functions, their working principles may be common between species and independent of the nucleus of origin. Behavioral examples are discussed and an attempt is made to integrate this with evidence from intracellular recording studies. It is suggested that the tuning principle in noradrenergic systems is particularly important for the formation of associations and neural plasticity (interference control) and that the switching principle of dopaminergic systems modulates the timing, time-sharing and initiation of responses (program-control).