Use of a single compartment LCEC cell in the determinations of biogenic amine content and turnover

Chronic binge-like moderate ethanol drinking in rats results in widespread decreases in brain serotonin, dopamine, and norepinephrine turnover rates reversed by ethanol intake

This research was initiated to assess the turnover rates (TORs) of dopamine (DA), norepinephrine (NA), serotonin (5-HT), aspartate, glutamate, and GABA in brain regions during rodent ethanol/sucrose (EtOH) and sucrose (SUC) drinking and in animals with a history of EtOH or SUC drinking to further characterize the neuronal systems that underlie compulsive consumption. Groups of five male rats were used, with two trained to drink EtOH solutions, two to drink SUC and one to serve as a non-drinking control. When stable drinking patterns were obtained, rats were pulse labeled intravenously and killed 60 or 90 min later and the TORs of DA, norepinephrine, 5-HT, aspartate, glutamate, and GABA determined in brain regions. Changes in the TOR of 5-HT, DA, and NA were detected specific to EtOH drinking, SUC drinking or a history of EtOH or SUC drinking. An acute EtOH deprivation effect was detected that was mostly reversed with EtOH drinking. These results suggest that binge-like drinking of moderate amounts of EtOH produces a deficit in neuronal function that could set the stage for the alleviation of anhedonic stimuli with further EtOH intake that strengthen EtOH seeking behaviors which may contribute to increased EtOH use in at risk individuals.

Brain neurotransmitter turnover rates during rat intravenous cocaine self-administration

The turnover rates of dopamine, norepinephrine, serotonin, aspartate, glutamate and GABA were measured in 27 brain regions of rats self-administering cocaine and in yoked cocaine- and yoked vehicle-infused controls using radioactive pulse-labeling procedures to identify brain neuronal systems underlying self-administration. Changes in the activity of heretofore unrecognized dopamine, norepinephrine, serotonin, glutamate and GABA innervations of the forebrain specific to cocaine self-administration were found. This included innervations of the nucleus accumbens, ventral pallidum, lateral hypothalamus and the anterior and posterior cingulate, entorhinal-subicular and visual cortices. Turnover rates also were calculated using metabolite/neurotransmitter ratios which were inconsistent with the pulse-label technologies indicating that ratio procedures are not accurate measures of neurotransmitter utilization. Results with the pulse-label technique provide evidence of the involvement of neuronal systems in cocaine self-administration not previously known, some of which may have a broader role in brain reinforcement processes for natural reinforcers (i.e. food, water, etc.) since drugs of abuse are thought to produce reinforcing effects by modulating activity in these endogenous systems.

Transient alterations in neurotransmitter levels during a critical period of neural development in coho salmon (Oncorhyncus kisutch)

The time of parr-smolt transformation (PST) in salmon is a critical period of brain development during which the olfactory imprinting on the natal stream takes place. PST is associated with a surge of plasma thyroxine. We report here similar surges in the brain content of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), dopamine (DA), norepinephrine (NE), and glutamine (Gln). Other putative neurotransmitters, such as glutamate and aspartate show no such change while gamma-amino-butyric acid (GABA) shows a minor elevation.

Arginine-aspartate and haloperidol-induced neurobehavioral effects in the rat

This study determined the effects, in the rat, of 8-day treatment with arginine-aspartate on haloperidol-induced catalepsy, decrease of locomotor activity and change of striatal dopamine, homovanillic acid (HVA) and dihydroxy-phenylacetic acid (DOPAC) content. Arginine-aspartate was able to attenuate the haloperidol-induced decrease of locomotor activity and to significantly reduce the catalepsy. Moreover, arginine-aspartate treatment itself increased striatal dopamine content and produced a significant decrease of the HVA/dopamine ratio. Pretreatment with arginine-aspartate was able to partially counteract the haloperidol-induced changes of dopamine metabolism: the haloperidol-induced increases of the DOPAC/dopamine and HVA/dopamine ratios were significantly reduced in arginine-aspartate- pretreated rats. These results suggest that the action of arginine-aspartate on haloperidol-induced neurobehavioral effects is probably mediated by interference with striatal dopaminergic innervation.

Rat brain neurotransmitter turnover rates altered during withdrawal from chronic cocaine administration

This experiment utilized neurotransmitter turnover rates to assess the effects of withdrawal from chronic cocaine on the brain. A triad-littermate design was used to evaluate the importance of response dependency on the effects of withdrawal from chronic cocaine administration upon brain biogenic monoamine and amino acid putative neurotransmitter turnover rates. Each member of a triad was exposed to one of three conditions. Cocaine infusions (0.33 mg/inf) were used to engender and maintain lever pressing by one rat under an FR 2 schedule, while the second and third rats received simultaneous infusions of either cocaine or saline, respectively. After a minimum of 15 days exposure to the three treatment conditions and 24 h after the start of the last drug session, the triads were pulse labeled with [14C]glucose, [3H]tyrosine and [3H]tryptophan and killed 60 or 90 min later by total immersion in liquid nitrogen, The frozen brains were removed and dissected at -20 degrees C into 22 areas. The content and specific radioactivities for dopamine (DA), noradrenaline (NA), serotonin (5-HT), aspartate (Asp), glutamate (Glu), glycine (Gly) and gamma-aminobutyric acid (GABA) were determined in each brain region using high pressure liquid chromatography with electrochemical (biogenic monoamines) or fluorescence (amino acids) detection followed by liquid scintillation spectrometry. Turnover rates (TOR) were calculated and compared across treatment conditions. The significant decreases in TOR resulting from chronic cocaine exposure included 5-HT in the frontal cortex, DA in the cingulate cortex, entorhinal-subicular and motor-somatosensory cortices and NA in the inferior colliculus. Significant increases in TOR were also observed which included 5-HT in the preoptic-diagonal band region, DA in the hippocampus and NA in the pyriform and temporal-auditory cortices, the dentate gyrus and brainstem. GABA TOR was also increased in the preoptic-diagonal band region, dentate gyrus and brainstem of both groups receiving cocaine as was Glu TOR in the pyriform cortex and cerebellum. In addition, changes were seen in the rats under the ratio schedule of cocaine self-administration that were not seen in rats receiving yoked-cocaine infusions that included increased TOR of 5-HT in the pyriform cortex, NA in the caudate-putamen and GABA in the pyriform and motor-somatosensory cortices. Decreased 5-HT TO was seen in the motor-somatosensory cortex and dentate gyrus in the rats that had self-administered cocaine compared to the yoked-cocaine infused group. Perhaps the most interesting changes were those seen in the yoked-cocaine group that were reversed in the rats whose responding was maintained by cocaine.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurochemical changes associated with the action of acute administration of diazepam in reversing the behavioral paradigm conditioned emotional response (CER)

Neurotransmitter turnover of biogenic monoamines (dopamine, norepinephrine, and serotonin) and amino acids (glutamate, aspartate, and gamma-aminobutyric acid) was evaluated in rats exposed to the conditioned emotional response (CER) paradigm in the absence (total suppression) or presence of acute 5 mg/kg i.p. diazepam (which reversed suppression and restored normal responding). Based on previous studies of CER, with controls for shock and stimulus histories, the results with respect to the anxiolytic could be divided into several categories: changes in turnover which are associated only with the CER behavior; changes associated only with the drug, diazepam; changes which augmented the effects of the behavior; or changes which were the reverse of those associated with the behavior. Due to the multitude and complexity of the results, not all observations have clear explanations at this time. However, for the CER behavior per se, it is apparent that a combination of neurotransmitters, including some implications about acetylcholine, act in concert to bring about the behavioral suppression. The action of diazepam is more complex, involving the full spectrum of neurotransmitters to bring about its direct and indirect effects.

Lack of serotonin neurotoxicity after intraraphe microinjection of (+)-3,4-methylenedioxymethamphetamine (MDMA)

Systemic administration of 3,4-methylenedioxymethamphetamine (MDMA) produces depletions of serotonin (5-HT) and its primary metabolite, 5-hydroxyindoleacetic acid (5-HIAA), decreases 5-HT reuptake sites and diminishes tryptophan hydroxylase activity in various forebrain regions. MDMA has been shown to be neurotoxic to the fine fibers originating from dorsal raphe (DR) 5-HT neurons but not the beaded fibers from the median raphe (MR) nucleus. In the present experiment, MDMA was microinjected directly into the DR or MR to determine whether differential neurotoxicity developed in the DR versus MR fiber systems as measured by 5-HT levels and immunocytochemistry. Two weeks following stereotaxic injection with either vehicle or (+)MDMA (50 micrograms base in 2 microliters) into the DR or MR, rat brains were assayed for 5-HT and catecholamine content or 5-HT immunocytochemistry. HPLC analysis revealed no significant changes in monoamine or metabolite concentrations in the hippocampus and striatum of rats administered intra-DR or -MR (+)MDMA. Raphe sections stained for 5-HT also did not reveal any apparent neurotoxicity. A single cerebral injection of (+)MDMA does not produce neurotoxicity to 5-HT neuronal systems originating in the raphe, although neurotoxicity of multiple MDMA injections into these raphe nuclei cannot be ruled out.

Serotonergic abnormalities in the central nervous system of seizure-naive genetically epilepsy-prone rats

Seizure predisposition in Genetically Epilepsy-Prone Rats (GEPRs) is characterized by abnormal sensitivity to a number of seizure provoking stimuli. The GEPR model is composed of two independently derived colonies with each exhibiting a characteristic convulsive pattern. In response to a standardized sound stimulus, GEPR-3s exhibit moderate or clonic convulsions while GEPR-9s exhibit more severe tonic extensor convulsions. In order to further characterize the neurochemical abnormalities that underlie seizure predisposition in GEPRs, the current study examined serotonin concentrations in 14 discrete brain areas of controls, GEPR-3s and GEPR-9s. In all areas examined, serotonin concentrations were lower in either one or both GEPR types than in seizure resistant controls. In 6 of the 14 areas both GEPR-3s and GEPR-9s had levels significantly lower than controls. In an additional 7 areas GEPRs had serotonin concentrations of similar magnitude which were significantly lower than control when the GEPR values were combined. In cerebellum, GEPR-3s had significantly lower serotonin concentration than either controls of GEPR-9s while in the striatum, GEPR-9s had significantly lower serotonin levels than either GEPR-3s or controls. In summary, GEPRs have widespread deficits in serotonin concentration and that these abnormalities appear to contribute to the seizure predisposition that characterizes these animals.

Amino acids, monoamines and audiogenic seizures in genetically epilepsy-prone rats: effects of aspartame

It has been suggested that aspartame facilitates seizures in man and animals because phenylalanine, one of its major metabolites, interferes with brain transport of neurotransmitter precursors and alters the synthesis of monoamine neurotransmitters such as norepinephrine, dopamine and/or serotonin. This facilitation is purportedly more likely in subjects predisposed to seizures. One test of this hypothesis would be to administer a wide range of aspartame doses to subjects whose seizure predisposition is dependent on abnormalities in monoaminergic function. Genetically epilepsy-prone rats (GEPRs) have a broadly based seizure predisposition that is based, in part, on widespread central nervous system noradrenergic and serotonergic deficits. Further reductions in the functional state of these neurotransmitters increases seizure severity in GEPRs. Thus, GEPRs appear ideally suited for testing the hypothesis that aspartame facilitates seizures by interfering with central nervous system monoamines. Oral administration of acute (50-2000 mg/kg) or sub-chronic (up to 863 mg/kg/day for 28 days) doses of aspartame did not alter seizure severity in either of two types of GEPRs. Not surprisingly, acute aspartame doses produced dramatic changes in plasma and brain amino acid concentrations. Hypothesized alterations in monoamine neurotransmitter systems were largely absent. Indeed, increases in norepinephrine concentration, rather than the hypothesized decreases, were the most evident alterations in these neurotransmitter systems. We conclude that aspartame does not facilitate seizures in GEPRs and that convincing evidence of seizure facilitation in any species is lacking.

Noradrenergic abnormalities in the central nervous system of seizure-naive genetically epilepsy-prone rats

Norepinephrine (NE) concentrations were measured in 15 discrete areas of the central nervous system of two types of genetically epilepsy-prone rats (GEPRs) and in nonepileptic controls. Both moderate-seizure (GEPR-3) and severe-seizure (GEPR-9) animals had extensive abnormalities in brain NE concentration. Deficits of equal magnitude in GEPR-3s and GEPR-9s were found in the spinal cord, midbrain minus the inferior colliculus, inferior colliculus, hypothalamus, amygdala, hippocampus, occipital + parietal cortex, frontal cortex, and olfactory septum. Because both types of GEPRs share these deficits and share seizure susceptibility, we hypothesize that these areas are candidates for regulation of seizure susceptibility in GEPRs. In addition, because GEPR-9s have more severe seizures than GEPR-3s and because GEPR-9s had greater NE deficits in several brain areas (cerebellum, pons-medulla, thalamus, and possibly the temporal cortex and olfactory bulbs), we hypothesize that these areas may be important in regulation of seizure severity in GEPRs. All animals used in these experiments had been protected from seizure-provoking stimuli and were naive to seizures. Because the abnormalities in NE concentration were present in seizure-predisposed animals that were protected from seizures, we conclude that these abnormalities are important components of the seizure-predisposition characteristic of GEPRs and do not result from seizure experience.

Transport of serotonin from the rat jejunal lumen into mesenteric veins in vivo

The transport of labelled (hot) and non-labelled (cold) serotonin (5-HT) into the mesenteric venous circulation was studied after instillation of test solutions into an isolated jejunal loop of anaesthetized rats. After instillation of [3H]H2O and [14C]5-HT there was an almost parallel appearance of the isotopes in mesenteric venous blood. After instillation of 5-HT a marked early increase of the total amounts of cold 5-HT was observed in mesenteric veins compared with animals instilled with saline only. In a third type of experiment the label was detected in mesenteric venous whole blood after instillation of [3H]5-HT into the gut lumen. After hydrolysis of blood cells and protein precipitation the samples were fractionated and determined for 5-HT and metabolites. Only 5-HT was detected in these fractions. The label was present within 5-HT peaks in three out of eight animals. The experiments indicate rapid transport of 5-HT (or metabolites) across the rat jejunal mucosa. These substances may be bound to a binding protein in platelets since the isotope was detected in whole blood but more seldom in supernatants after hydrolysis and precipitation.

Aspartame fails to facilitate pentylenetetrazol-induced convulsions in CD-1 mice

Concentrations of plasma amino acids and brain monoamines as well as pentylenetetrazol-induced seizures were monitored in CD-1 mice treated with aspartame in acute oral doses from 0 to 2500 mg/kg. One hour after administration aspartame produced increases in plasma concentrations of phenylalanine and tyrosine and modest reductions in concentrations of brain serotonin and 5-hydroxyindole acetic acid. However, these effects of the sweetener had no influence on the convulsive dose fifty (CD50) of pentylenetetrazol. Moreover, aspartame failed to alter the percentage of mice exhibiting seizures when exposed to an approximate CD50 of pentylenetetrazol. Finally, aspartame had no effect on brain norepinephrine or dopamine concentrations. In sharp contrast to previously reported studies, these observations suggest that aspartame, given in heroic doses, does not alter the propensity to seizure activity in CD-1 mice. We conclude that changes in plasma amino acids and brain serotonin produced by large oral bolus doses of aspartame are insufficient to result in functional deficits which might have the capacity to facilitate pentylenetetrazol-induced seizures.

Specific effects of punishment on amino acids turnover in discrete rat brain regions

Specific effects of punishment on the turnover rates of aspartate (Asp), glutamate (Glu) and gamma-aminobutyric acid (GABA) in 14 brain regions were investigated in rats exposed to punishment. Two yoked controls were also used in an attempt to separate the nonspecific effects of response rate, reinforcement density and direct effects of punisher (foot shock). Punished and unpunished littermate rats had similar response rates, and the reinforcement density was almost identical for both groups. A third group (yoked-shock rats) received food and shock independent of responding whenever these were given to the punished rats. When compared to the unpunished rats, the punishment increased the turnover rates of the three amino acids in all brain regions examined except GABA turnover in the caudate-putamen and preoptic-diagonal band. The majority of these changes by the punishment were similar to the effects of the yoked-shock (yoked-shock versus unpunished), although the magnitude of increase by the punishment was mostly larger than that by the yoked-shock. Six changes by the punishment (increase in the turnover rates of Asp in the thalamus, Glu in the hypothalamus and GABA in the cingulate cortex, entorhinal-subicular cortex, dentate gyrus and hypothalamus) appeared to be the specific effects of punishment since the yoked-shock did not affect these parameters. These results suggest that the punishment caused a hyperexcitation of the amino acidergic neurons in the limbic systems, particularly those in Papez's circuit.

Measurement of specific radioactivity of tryptophan labeled with carbon-14 in plasma by high-performance liquid chromatography with a synchronized accumulating radioisotope detector

Measurement of specific radioactivity by a high-performance liquid chromatograph with a synchronized accumulating radioisotope detector was conducted. Accuracy of measurement for an authentic sample containing 0.2 nCi of tryptophan labeled with carbon-14 exceeded 95%. In the case of a plasma sample obtained 120 min following intravenous administration of 15 muCi of labeled tryptophan to a rat, the coefficient of variation was 7.0%.

Lack of an effect of 6-hydroxydopamine lesions of the nucleus accumbens on intravenous morphine self-administration

The neurotoxin, 6-hydroxydopamine (6-OHDA), has been used to selectively destroy dopamine containing neurons in discrete brain regions. Lesions of the nucleus accumbens with this neurotoxin decrease or eliminate cocaine and amphetamine self-administration and either increase or do not affect opiate self-administration in rats with unrestricted access to food and water. This study reports the effects of 6-OHDA lesions of the nucleus accumbens on responding maintained by food, water or morphine (3.3 mg/infusion). Six male rats with continuous access to three response levers were trained on a concurrent chained, fixed-ratio 1, fixed-ratio 9 schedule of reinforcer presentation. After stable patterns of responding were maintained by the three reinforcers, dose-effect curves for morphine were determined by substituting other doses of morphine or vehicle for 24-hour periods. Bilateral sham vehicle or 6-OHDA lesions of the nucleus accumbens were then completed and the effects of the lesion on food, water and morphine intake determined. Dose-effect evaluations were repeated after the lesion. The 6-OHDA lesions did not significantly affect responding maintained by food, water or morphine. The absence of an effect is most likely not the result of an insensitive baseline since other neurotoxin lesions produce long-term and selective decrements in morphine self-administration without affecting food and water responding. Like so many other manipulations, the magnitude of the effect that a neurotoxin lesion can exert on behavior may depend on the specific procedures that are used to maintain responding.

Specific effects of punishment on biogenic monoamine turnover in discrete rat brain regions

Specific effects of punishment on the turnover rates of norepinephrine, dopamine and serotonin (5-HT) in brain regions were investigated in rats exposed to punishment. Two yoked controls were also used in an attempt to separate the non-specific effects of response rate, reinforcement density and direct effects of punisher (foot shock). Punished and unpunished littermate rats had similar response rates, and the reinforcement density was almost identical for both groups. A third group (yoked-shock rats) received food and shock independent of responding whenever these were given to the punished rats. When compared to the unpunished rats, changes in the monoamine turnover rates resulting from the punishment were similar to the effects of yoked-shock with respect to the direction of action in most cases (13 out of 17 changes). These changes may be related to non-specific effects of the shock. Four changes by the punishment were determined to be specific effects of the punishment since the yoked-shock had no effect or changed the turnover to the opposite direction. Among these, increase in 5-HT turnover rate in the frontal cortex (greater than 7-fold) was the largest change. These results and reported effects of drugs which act on serotonergic systems on the punished behavior suggest that the increase in 5-HT neuronal activity in the frontal cortex is involved in the behavioral suppression induced by the punishment.

Effect of chronic naltrexone administration and its withdrawal on the regional activity of neurons that contain norepinephrine, dopamine and serotonin

A method is described that permits the simultaneous quantitation of norepinephrine (NE), dopamine (DA) serotonin (5-HT) and their respective major metabolites, 3-methoxy-4-hydroxy phenylglycol (MHPG), 3-methoxytyramine (3-MT), dihydroxyphenyl acetic acid (DOPAC) and 5-hydroxyindole acetic acid (5-HIAA) in discrete brain regions. The ratio of MHPG/NE, DOPAC/DA and 5-HIAA/5-HT was used to assess the effects of the chronic administration of the narcotic antagonist, naltrexone, and its withdrawal on the regional activity of neurons that contain NE, DA and 5-HT respectively. Chronic administration of naltrexone (8 days) is associated with a significant increase in the ratio of 5-HIAA/5-HT and DOPAC/DA in the frontal cortex and dorsal hippocampus respectively. Under this condition the thalamic concentration of 3-MT in 4 of 8 animals is also significantly elevated. In contrast, the mesolimbic forebrain exhibited a decrease in the MHPG/NE ratio (4 out of 8 animals). One day following naltrexone pellet removal the above ratios, as well as the mean content of 3-MT in the thalamus, returned to control values. At this time the content of 3-MT in the thalamus (5 of 5 animals) and frontal cortex (3 of 9 rats) was appreciably elevated, while its content in the dorsal hippocampus was significantly reduced (6 of 9 rats). These data suggest that the activity of several central monoaminergic neuronal systems are regulated by an opioid input that is tonically active.

Brain norepinephrine and convulsions in the genetically epilepsy-prone rat: sex-dependent responses to Ro 4-1284 treatment

Seizure predisposition in the Genetically Epilepsy-Prone Rat (GEPR) is at least partially dependent on central nervous system noradrenergic deficits. We have previously shown that moderate seizure GEPRs (GEPR-3) experience an increase in seizure severity after receiving Ro 4-1284, a monoamine vesicle inactivating drug. We are now reporting the effect of this drug on severe seizure GEPRs (GEPR-9). Motives for this study were: (a) to determine the effects of further depletion of innately deficient monoaminergic stores on seizure latencies and (b) to investigate whether a previously documented seizure severity difference between the sexes is related to the defective monoaminergic system in these subjects. GEPR-9s with known seizure history were tested for latency to onset of running phase and convulsion 45 minutes after Ro 4-1284 or saline administration. Brain norepinephrine levels were also determined. Ro 4-1284 caused severe depletion of monoamines in all brain areas assayed in both sexes of GEPR-9s and also caused a reduction in the latencies for onset of running and convulsion. The drug-induced norepinephrine depletion across the brain areas surveyed was significantly greater in females than in their male littermates. These observations prompt us to postulate that noradrenergic neurons in female GEPR-9s are functionally different from those in males and that this difference is detected in the differential effectiveness of Ro 4-1284 between the two sexes. Also, the influence of gonadal hormones on seizure predisposition and on the neurochemical actions of Ro 4-1284 may be different in GEPR-9 males and females.

Changes with age in total brain concentrations of biogenic amine neurotransmitters in coho salmon (Oncorhynchus kisutch Walbaum)

Whole brain content of several biogenic amines was determined in two age groups of coho salmon (Oncorhynchus kisutch Walbaum). Brains of presmolt salmon (about 5 months old) were compared to brains of homeward migrants (4 years old). Levels of dopamine and serotonin were significantly higher in the homeward migrants.

Effects of 5,7-dihydroxytryptamine lesions of the nucleus accumbens on rat intravenous morphine self-administration

The role of serotonergic innervations of the nucleus accumbens in the processes maintaining intravenous morphine self-administration were assessed. Pairs of male rat littermates were implanted with intravenous jugular catheters and bilateral injection guide cannulae into the central medial nucleus accumbens, made physically dependent on morphine and then allowed to intravenously self-administer with continuous access. When stable baselines of drug intake were obtained (2-3 weeks), one of each pair received bilateral microinjections of vehicle and the other 5,7-dihydroxytryptamine (5,7-DHT) into the nucleus accumbens. Response independent infusions of morphine were delivered for 24 hours at the previous rate of self-injection and the animals were again allowed to self-administer while drug intake was monitored for thirteen days. The littermate pairs were then sacrificed by immersion in liquid nitrogen, the brains removed at -20 degrees C and frozen sections of the cannulae tract taken for histological assessment. The nucleus accumbens, anterior caudate nucleus and pyriform cortex were removed at -20 degrees C and biogenic monoamine content determined. The 5,7-DHT lesions resulted in a significant increase in drug intake and significantly decreased the content of serotonin (5-HT) and 5-hydroxyindoleacetic acid in the nucleus accumbens (-49% and -30%, respectively) and 5-HT in the anterior caudate nucleus (-14%) and pyriform cortex (-17%). Dose-effect relationships were assessed in four additional animals before and after similar bilateral 5,7-DHT lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting the stability and separation of biogenic amines and their metabolites. Simultaneous measurement by HPLC with electrochemical detection

We describe a simple and sensitive method for the rapid and simultaneous quantification of dopamine, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, serotonin, 5-hydroxyindoleacetic acid, and 5-hydroxytryptophan in the picogram range in small samples of brain tissue. After minimal sample preparation the amines were analyzed utilizing isocratic separation and reversed-phase high-performance liquid chromatography with amperometric detection. The effects of pH and methanol concentration in the solvent on the retention times of the amines on two different C-18 columns were investigated. Stabilities of the amines in solution were determined under various conditions. Light and air were found to be detrimental to the stability of indoles. In the absence of light, their stability was dependent on temperature and the presence of air; however, in the absence of air, light and/or temperature had little effect. The catechols were stable under most of these conditions. The assay has been applied to study the postmortem stability of dopamine, serotonin, and their metabolites in the striatum of rat brain. In the striatum 4 hr after death, the content of dopamine and 3,4-dihydroxyphenylacetic acid decreased by less than 20%, and 3-methoxytyramine increased by 158%, with no changes in serotonin, 5-hydroxyindoleacetic acid, and homovanillic acid.

Acute exposure of rats to air ions: effects on the regional concentration and utilization of serotonin in brain

Exposure to electrically charged gas molecules (air ions) has been reported to influence physiological and behavioral functions in animals and humans although there is controversy as to whether these findings are valid. A popular hypothesis concerning the reported effects of air ions is that alterations in serotonin (5HT) metabolism, particularly in the brain, are involved. We measured the concentration and turnover of 5HT in rats exposed to 5.0 X 10(5) ions/cm3 for up to 66 hours. Contrary to previous reports of other investigators, we were unable to demonstrate any effect of exposure to air ions or associated DC electric fields on the concentration or turnover of 5HT in rats under carefully controlled and characterized exposure conditions.

Reinforcing properties of cocaine in the medical prefrontal cortex: primary action on presynaptic dopaminergic terminals

The presynaptic mechanisms involved in the initiation of cocaine reinforcement were investigated using neurotoxin lesions. Rats were trained to intracranially self-administer cocaine (50 to 90 pmol) into the medial prefrontal cortex and after dose-effect analyses were completed, each rat received a unilateral 6-hydroxydopamine lesion (4 micrograms in 0.2 microliter) at the self-administration site. The lesion selectively decreased dopamine content in the medial prefrontal cortex (-45%) and decreased cocaine-maintained responding to vehicle levels. Lever-pressing could be reinstated by substituting dopamine (300 pmol) but not serotonin for cocaine. Dopamine self-administration was attenuated by including equimolar concentrations of the D2 dopaminergic antagonist sulpiride in the injectate. These results suggest that the initiation of reinforcing neuronal activity in the medial prefrontal cortex appears to result in part through the direct interaction of cocaine with presynaptic reuptake sites associated with dopaminergic nerve endings. The resulting increased synaptic concentration of the neurotransmitter may then interact with postsynaptic D2 binding sites to activate neuronal systems involved in the mediation of this reinforcement.

Effects of adult or neonatal treatment with 6-hydroxydopamine or 5,7-dihydroxytryptamine on locomotor activity, monoamine levels, and response to caffeine

Rats were treated as neonates or adults with desmethylimipramine (DMI) followed by intraventricular 6-hydroxydopamine (6-HDA) or 5,7 dihydroxytryptamine (5,7-DHT). Locomotor activity of treated rats was measured in photocell cages. Neonatal treatment with 5,7-DHT produced hypoactivity during development while neonatal 6-HDA led to hyperactivity. Treatment of adult rats with 5,7-DHT or 6-HDA, while resulting in equivalent monoamine depletions, was without effect on locomotor activity. The dose response function for caffeine was determined in these rats. Depletion of dopamine by either neonatal or adult treatment with 6-HDA decreased caffeine stimulation of locomotor activity. The adenosine receptor agonist l-phenylisopropyladenosine (L-PIA) decreased locomotor activity in all rats in a dose-dependent fashion.

Automated method to estimate catecholamine and indoleamine content and turnover rates

A double-label isotopic method for estimation of the rate of formation of serotonin (5-HT) and dopamine (DA) in mouse striatum, hippocampus and cortex was standardized. Mice received an intravenous pulse injection of [3H]tryptophan (TRP) and [3H]tyrosine (TYR) at 2.5, 5, 10 or 20 min before sacrifice by microwave irradiation. Compounds of interest were separated by automated high-performance liquid chromatography and their contents were determined by electrochemical detection. Programmed collection of the TYR, DA, 5-HT and TRP peaks allowed determination of their radioactivity by liquid scintillation. Conversion of [3H]TYR to [3H]DA was nearly ten times greater in striatum than cortex, whereas the formation of [3H]5-HT from [3H]TRP was similar in striatum, cortex and hippocampus.

Effects of 6-OHDA lesions of the central medial nucleus accumbens on rat intravenous morphine self-administration

The function of dopaminergic innervations of the central medial nucleus accumbens in the processes maintaining intravenous morphine self-administration was assessed by lesioning with 6-OHDA and comparing drug intake with sham-vehicle treated littermates. Localized bilateral lesions of this structure resulted in significant increases in morphine intake shifting the dose-effect relationship to the right with twice the dose necessary to maintain prelesion rates of self-administration. Content of dopamine and dihydroxyphenylacetic acid was decreased in the nucleus accumbens after the lesion, but unchanged in the adjacent pyriform cortex and anterior caudate nucleus-putamen, while serotonin was significantly decreased in the pyriform cortex. High affinity uptake measurements also suggested nucleus accumbens dopaminergic and pyriform cortex serotonergic innervations to be affected by the lesion. The shift to the right in the dose effect relationship after the lesion suggests these neuronal systems to be excitatory to the processes mediating self-administration.

Modification of electroretinograms in dopamine-depleted retinas

The functional role of dopamine in frog retina was examined in a combined neurochemical, immunohistochemical and electrophysiological study. Dopamine and serotonin are the primary monoamines present in the retina and they are localized to amacrine cells which have distinct morphologies. Intravitreal injection of 6-hydroxydopamine was found to produce a selective depletion of retinal dopamine content and elimination of tyrosine hydroxylase-like immunoreactivity. Electroretinograms from 6-hydroxydopamine-treated retinas demonstrated enhanced oscillatory potentials and a lengthening of the b-wave implicit time compared to vehicle control retinas; both of these changes in the electroretinogram were reversed by the dopamine agonist apomorphine. These observations support earlier suggestions that dopamine-containing amacrine cells are part of a retinal feedback system that generates oscillatory potentials and plays a role in light adaptation.

An in vivo steady-state method for the determination of catecholamine biosynthesis in the rat brain using high-performance liquid chromatography with electrochemical detection

A technique is described for the measurement of steady-state catecholamine (CA) synthesis in the rat brain in vivo, using [3H]tyrosine incorporation with high-performance liquid chromatography (HPLC) and electrochemical detection. Adult male rats chronically implanted with lateral intracerebroventricular (i.c.v.) cannulas, were injected i.c.v. with [3H]tyrosine. CA and tyrosine content and specific activity were measured in mediobasal hypothalamus, anterior hypothalamus and striatum. A time-dependent increase in CA synthesis occurred in all tissues over 20 min post-i.c.v. injection. The technique described may prove to be useful in the assessment of central neurotransmitter turnover in various physiological and pharmacological settings.

Simultaneous quantitation of norepinephrine, dopamine and serotonin in brain during and following chronic naltrexone administration

The effects of chronic administration of the narcotic antagonist naltrexone on regional brain levels of norepinephrine, dopamine and serotonin were studied in order to determine whether central monoaminergic neurons are tonically modulated by central opioid systems. Chronic exposure to naltrexone (8 days) is associated with a significant increase in the content of norepinephrine in the mesolimbic forebrain and the content of dopamine in the frontal cortex and striatum. Ten days following naltrexone pellet removal the above levels returned to control values but thalamic dopamine content was reduced 10-fold. These data suggest that the affected brain regions receive an opioidergic input that is tonically active.

Influence of chronic inorganic lead exposure on regional dopamine and 5-hydroxytryptamine turnover in rat brain

The results of previous behavioral studies utilizing chronic exposure to low amounts of inorganic lead (Pb) have suggested alterations in the function of biogenic amine neuronal systems. The following study was performed to provide evidence for the possible bases of these changes in pharmacological responsiveness in exposed animals. Dams were administered 0.2% Pb acetate in drinking water to expose their offspring to Pb via the maternal milk. Males were weaned to the same drinking solution. At 120-140 days a tracer dose of 1.0 mCi L-[3H]2,6-tyrosine (3H-TYR) and 0.5 mCi L-[3H(G)]tryptophan (3H-TRP) was injected through an indwelling jugular catheter, and norepinephrine (NE), dopamine (DA), 5-hydroxytryptamine (5-HT) and their respective precursors and metabolites were quantified by liquid chromatography with electrochemical detection with column eluate collected for liquid scintillation counting. At this level of exposure (blood lead (PbB) at day 90 in exposed animals = 43.1 +/- 1.7 micrograms/dl) no changes were observed in concentration of NE or DA or DA metabolites in any brain region. However, DA turnover was decreased in Pb-exposed animals in nucleus accumbens and frontal cortex. No changes in 5-HT content and turnover were observed in any brain region, but 5-hydroxyindoleacetic acid (5-HIAA) levels were decreased in 6 of the 9 brain regions examined. These findings are consistent with observations of an attenuated behavioral responsiveness to d-amphetamine (AMPH) in exposed animals, and suggest that the changes in DA and 5-HT neurons noted by other workers at higher levels of exposure persist when PbBs are in the range of 40 micrograms/dl.

Rapid automated analysis of biogenic amines and their metabolites using reversed-phase high-performance liquid chromatography with electrochemical detection

A method is described for the rapid automated analysis of: dopamine and norepinephrine; the major dopamine metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid; and the indoles tryptophan, serotonin, and 5-hydroxyindoleacetic acid in less than 0.5 mg of brain tissue. Samples are deproteinized, injected directly onto a reversed-phase high-performance liquid chromatography column, and quantitated using an electrochemical detector with a glassy carbon electrode. High sample stability permits the use of an automatic sample injector at ambient temperatures. Depending upon the column particle size, sample run times are less than 7-12 min. Thus, over 50 duplicate samples can readily be measured in a single day with very little operator attention. The chromatographic system used also resolves epinephrine, and the catecholamine metabolites: 3-methoxytyramine, normetanephrine, and 3-methoxy-4-hydroxyphenylglycol; and with very little modification this assay also could be used to measure these compounds.

Manipulation of mobile phase parameters for the HPLC separation of endogenous monoamines in rat brain tissue

Multi-component mobile phases are common in ion pair reverse phase high performance liquid chromatography for the analysis of endogenous monoamines in rat brain tissue. By examining the effects of each component of a mobile phase on the separation of a number of monoamines and their metabolites, we show how optimization of parameters can achieve and/or maintain a separation both within and between different octadecyl columns. The assay itself is rapid, sensitive, demands minimal sample preparation, and results in complete resolution of the amines. More importantly, the basis for the manipulation of mobile phase components is discussed with regard to practical utilization in selective amine separation. We conclude that knowledge of mobile phase parameters, their mechanism, and manipulation is as important as the assay itself.

Simultaneous measurement of tyrosine, tryptophan and related monoamines for determination of neurotransmitter turnover in discrete rat brain regions by liquid chromatography with electrochemical detection

Concomitant measurement of monoamine neurotransmitter turnover in discrete rat brain areas with the use of radiolabeled amino acid precursors permits simultaneous evaluation of interacting transmitter systems. [3H]Tyrosine and [3H]tryptophan were administered via indwelling catheters to unrestrained rats. Content and specific activity of norepinephrine, dopamine, 5-hydroxytryptamine, and the metabolites dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid in addition to tyrosine and tryptophan were quantified by liquid chromatography with electrochemical detection and liquid scintillation counting. The method employs a simple extraction procedure without prior cleanup for chromatography. Neurotransmitter turnover rates that incorporated tyrosine- or tryptophan-specific activities were found to be two to four times greater than those that did not include them.

Effects of acrylamide on locomotion and central monoamine function in the rat

Male rats receiving acrylamide (ACR) in their drinking water (100 ppm) for a six-week period displayed increased psychomotor stimulation to d-amphetamine (d-A; 1.0 mg/kg SC) under several conditions of handling and drug administration. Following behavioral tests a subset of the animals was sacrificed at 15, 50, 80 and 120 minutes following d-A and the brains removed and dissected for determinations of regional brain levels of several monoamine neurotransmitters and metabolites. ACR rats had elevated levels of 5-hydroxyindoleacetic acid (5-HIAA) in the striatum, septal area, and thalamus. The effect was most pronounced at 15 minutes post-drug with ACR rats not demonstrating a depression in 5-HIAA levels present in controls. Increases in accumben's dopamine and norepinephrine levels, evident after d-A, were of lesser magnitude in ACR-exposed rats. Decreases in dihydroxyphenylacetic acid and homovanillic acid, also evident after d-A, persisted for a longer duration in ACR-exposed rats. Light and electron microscopy of spinal cord, striatum, nucleus accumbens and thalamus did not reveal morphologic abnormalities. Sciatic nerves showed histopathological changes characteristic of multi-focal dying-back peripheral nerve degeneration. It was concluded that acrylamide's effect on the psychomotor stimulant properties of d-A may be related to changes in a serotonergic inhibitory system.