Stress-Related Changes in Cerebral Catecholamine and Indoleamine Metabolism: Lack of Effect of Adrenalectomy and Corticosterone

The concentrations of catecholamine and indoleamine metabolites were measured in intact and adrenalectomized mice to determine whether adrenal hormones mediate or modulate the stress-induced responses. Thirty minutes of footshock resulted in significant increases of the ratios of the dopamine (DA) catabolite, dihydroxyphenylacetic acid (DOPAC), to DA in prefrontal cortex, nucleus accumbens, striatum, hypothalamus, and brainstem, and of homovanillic (HVA)/DA ratios in nucleus accumbens, striatum, amygdala, and hypothalamus. Ratios of 3-methoxy-4-hydroxyphenylethyleneglycol to norepinephrine (NE) were also increased in prefrontal cortex, nucleus accumbens, septum, amygdala, hypothalamus, hippocampus, and brainstem. The concentration of NE was decreased in amygdala. 5-Hydroxyindoleacetic acid (5-HIAA)/5-hydroxytryptamine (5-HT, serotonin) ratios and free tryptophan were also increased in every brain region. Very similar data were obtained from mice restrained for 30 min. Adrenalectomy resulted in increased HVA/DA ratios in prefrontal cortex and striatum, and 5-HIAA/5-HT in septum. The stress-related changes were largely similar in adrenalectomized mice. Significant interactions between adrenalectomy and footshock treatment occurred in prefrontal cortical DOPAC/DA and hypothalamic NE which was depleted only in adrenalectomized mice, suggesting tendencies for these measures to be more responsive in adrenalectomized mice. Corticosterone administration (0.5-2.0 mg/kg s.c.) which resulted in plasma concentrations in the physiological range did not alter the concentrations of the cerebral metabolites measured in any region. We conclude that adrenal hormones do not mediate cerebral catecholamine or indoleamine metabolism in stress, although adrenalectomy may affect HVA and 5-HIAA metabolism, and there was a tendency for catecholamines to be more sensitive to stress in adrenalectomized animals.     

Effects of sex factors and hemispheric localization on the involvement of serotonin from the frontal cortex, striatum, and nucleus accumbens into the processing of novel and repeatedly presented information in rats

The effects of novel or relevant (a single exposure to experimental chamber) and irrelevant (20 exposures to experimental chamber) stimuli on the levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the frontal cortex, striatum, and nucleus accumbens in the left and right hemispheres were studied in male and female rats. It was found that 5-HT and 5-HIAA contents in the frontal cortex changed in response to neither relevant nor irrelevant stimuli. However, there were hemispheric difference in 5-HT and 5-HIAA in the frontal cortex of intact animals. The level of 5-HT in males and the level of 5-HIAA in females were higher in the left frontal cortex. In females, the level of 5-HIAA in the left striatum decreased in response to the novel stimulus. Sex differences in: a) 5-HT metabolism (increase in the level of 5-HIAA in males and increase in 5-HT in females) and b) lateralization (the striatal 5-HT metabolism in males changed bilaterally and only in the left hemisphere in females) were observed in reactions to irrelevant stimuli. Both in male and female rats, serotonin content in the nucleus accumbens changed only in response to the irrelevant stimuli. The 5-HT level increased in the left and right hemispheres independently of sex, but hemispheric difference was revealed only in females, in which the serotonin level was higher in the left nucleus accumbens. It is concluded that serotonergic neurotransmitter mechanisms are involved in hemispheric and sex differences in selective attention.     

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

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

Rapid, concurrent analysis of dopamine, 5-hydroxytryptamine, their precursors and metabolites utilizing high performance liquid chromatography with electrochemical detection: analysis of brain tissue and cerebrospinal fluid

Assays capable of measuring picomole quantities of dopamine (DA), 5-hydroxytryptamine (5-HT), several of their precursors and metabolites concurrently within 25 minutes were developed utilizing high performance liquid chromatography with electrochemical detection (LCEC). Several parameters of the LCEC were altered in order to separate the compounds while maintaining a short assay time. The final LCEC systems demonstrated biological utility in that the DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and the 5-HT metabolite 5-hydroxy-3-indoleacetic acid (5-HIAA) were detected in rat cerebrospinal fluid; in addition to these compounds, DA and 5-HT were measurable in the striatum, hypothalamus and median eminence of the rat brain. Pargyline decreased the concentrations of DOPAC, HVA and 5-HIAA and increased the 5-HT concentration in all three brain regions, and increased the DA concentration in the striatum. Probenecid increased all three acid metabolite concentrations in the hypothalamus and median eminence, while only the HVA and 5-HIAA concentrations were increased in the striatum. The DA and 5-HT concentrations were unaltered. The LCEC methods described in this paper should be useful in elucidating the mechanisms and roles of 5-HT and DA neurons in experimental paradigms of biological interest.     

Effect of aging on monoamines and their metabolites in the rat brain

Concentrations of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their acid merabolites were assayed in specific brain areas of Wistar rats of various ages. DA and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were significantly lower in striatum and mesolimbic areas of old (24 mos) rats than young adult (3 mos), but not mature (12 mos) rats. The decrease of homovanillic acid (HVA) was significant in mesolimbic areas but not in striatum. Neither cortical NE nor its metabolite methoxydroxyphenylglycol sulphate (MHPG-SO₄) were significantly changed by aging. 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the brainstem showed a tendency to a decrease and increase respectively in aged animals compared with young adults, but the differences were not statistically significant. However, the ratio of 5-HIAA to 5-HT concentrations was significantly higher in aged animals. The conclusion can be drawn that, in these brain areas, DA is more vulnerable to aging than NE and 5-HT, the metabolism of the latter being even enhanced.     

Effects of Chronic Ethanol Consumption and Aging on Dopamine, Serotonin, and Metabolites

Abstract: This study examined the hypothesis that chronic ethanol consumption results in significant abnormalities in both the dopaminergic and the serotonergic system of aged rats. Levels of dopamine (DA), serotonin [5-hydroxytryptamine (5-HT)], 3,4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindole-3-acetic acid (5-HIAA) were determined in brain areas of both the nigrostriatal and mesocorticolimbic DA systems in 5-, 14-, and 24-month-old male Fischer 344 rats. Aging was associated with a reduced concentration of DA in the striatum (ST), ventral tegmental area (VTA), and ventral pallidum (VP) and an increased concentration of 5-HIAA in the ST, globus pallidus, nucleus accumbens, frontal cortex, and VP. In addition, there was an increase in the 5-HIAA/5-HT ratio in all brain areas analyzed. Six weeks of ethanol consumption was accompanied by significant changes in mesocorticolimbic brain areas. In the VTA of 5-month-old ethanol-fed rats DA content was decreased to the levels found in aged rats, e.g., 24 months of age. Ethanol also significantly lowered 5-HT and 5-HIAA contents in the VTA and reduced DOPAC and 5-HIAA levels in the VP. In addition, ethanol blunted the normal age-related increase in 5-HIAA/5-HT ratio in the VTA, VP, and substantia nigra. It is interesting that although the age-related changes were found in both nigrostriatal and mesocorticolimbic brain areas, the ethanol-associated effects were found only in brain areas of the mesocorticolimbic system. The changes in DA and 5-HT function that accompany aging and ethanol consumption may contribute to the problems in motor function and ethanol abuse found in the aged.     

Analysis of γ-Aminobutyric AcidA Receptor Subunits in the Mouse Cochlea by Means of the Polymerase Chain Reaction

Abstract: Unlike 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces consistent decreases in levels of striatal dopamine (DA) with considerably smaller and more variable effects on mouse brain levels of serotonin (5-HT) and norepinephrine (NE), a novel amine-substituted MPTP analogue, 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH₂-MPTP), administered in a standard mouse dosing paradigm for MPTP (20 mg/kg X 4) did not affect striatal DA but led to marked reductions (60–70%) in levels of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), and NE measured in frontal cortex and hippocampus 1 week after treatment. Another 2'-substituted MPTP analogue, 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine, affected cortical and hippocampal 5-HT, 5-HIAA, and NE only minimally, while markedly reducing the DA content in striatum (90%), thus indicating that the substituent (-NH₂ versus -CH₃) at the 2'position is important for the differential effects of these MPTP analogues. In a replication study with a 3-week end point, hippocampal and cortical 5-HT, 5-HIAA, and NE levels remained depressed with no indication of recovery. These results suggest that 2'-NH₂-MPTP may be a novel, regionally selective neurotoxin for serotonergic and norad-renergic nerve terminals.     

Effects of acute 17alpha-methyltestosterone,acute 17beta-estradiol,and chronic 17alpha-methyltestosterone on dopamine,norepinephrine and serotonin levels in the pituitary,hypothalamus and telencephalon of rainbow trout (Oncorhynchus mykiss)

This study investigated: (a) the effects of acute 17alpha-methyltestosterone (MT) or 17beta-estradiol (E(2)) administration on norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3,4, dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) contents in the hypothalamus, telencephalon and pituitary of previtellogenic female rainbow trout Oncorhynchus mykiss, and (b) the effects of chronic MT administration on the levels of these neurotransmitters in these brain regions in immature male rainbow trout. The acute administration of MT induced a significant decrease in pituitary levels of DOPAC as well as in the DOPAC/DA ratio. On the other hand, the acute administration of E(2) induced an increase in pituitary 5-HT levels as well as a decrease in the 5-HIAA/5-HT ratio. In a second experiment, 20 mg MT per kilogram body weight was implanted for 10, 20 or 40 days into sexually immature male rainbow trout. Implanted rainbow trout showed increased testosterone and decreased E(2) levels. In the pituitary, MT induced long-term decreases in NE, DA, DOPAC and 5-HT levels, as well as in the DOPAC/DA ratio. Hypothalamic and telencephalic DA, NE and 5-HT levels were not affected by MT implantation. However, 5-HIAA levels and the 5-HIAA/5-HT ratio were reduced by MT implantation in both brain regions. These results show that chronic treatment with MT exerts both long-term and region-specific effects on NE, DA, and 5-HT contents and metabolism, and thus that this androgen could inhibit pituitary catecholamine and 5-HT synthesis. A possible role for testosterone in the control of pituitary dopaminergic activity and gonadotropin II release is also discussed.     

Asymmetric metabolism of hypothalamic catecholamines alternates with side of ovulation in a lizard (Anolis carolinensis).

We determined levels of monoamines and their metabolites in 2 hypothalami dissected from the right and left hemibrains of 15 females during the right-left alternating ovulatory cycle of Anolis carolinensis. Tissue contents of the following were measured using HPLC and electrochemical (coulometric) detection: dopamine (DA) and its metabolite 2,4-dihydroxyphenylacetic acid (DOPAC), norepinephrine (NE) and its metabolites 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG), and serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA). An asymmetry ratio (AR) was determined by subtracting hypothalamic content (pM/mg) on the larger ovary (LO) side from that on the smaller ovary (SO) side, divided by the sum of the 2 sides (AR = SO - LO/SO+LO). The Ar of MHPG and DHPG both decreased as the largest follicle in the LO grew during the cycle, from greater than 0 (content higher on the SO side) at the beginning of the cycle to less than 0 (content higher on the LO side). The average content of MHPG in the 2 sides significantly increased during the cycle. There were no significant asymmetric changes in hypothalamic DA or DOPAC. The average content of DA increased during the cycle, whereas the content of DOPAC, as well as DOPAC/DA, did not change. The average content of 5-HT increased, and the average metabolite ratio of 5-HIAA/5-HT decreased during the cycle without significant asymmetries. The metabolite ratios of NE and DA, but not 5-HT, were asymmetric on the same side in a given female.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of Serotonin2A and Serotonin2B/2C Receptor Subtypes in the Control of Accumbal and Striatal Dopamine Release Elicited In Vivo by Dorsal Raphe Nucleus Electrical Stimulation

This study investigates, using in vivo microdialysis, the role of serotonin2A (5-HT2A) and 5-HT(2B/2C) receptors in the effect of dorsal raphe nucleus (DRN) electrical stimulation on dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) extracellular levels monitored in the nucleus accumbens (NAC) and the striatum of halothane-anesthetized rats. Following DRN stimulation (300 microA, 1 ms, 20 Hz, 15 min) DA release was enhanced in the NAC and reduced in the striatum. The 5-HT2A antagonist SR 46349B (0.5 mg/kg) and the mixed 5-HT(2A/2B/2C) antagonist ritanserin (0.63 mg/kg) significantly reduced the effect of DRN stimulation on DA release in the NAC but not in the striatum. DA responses to DRN stimulation were not affected by the 5-HT(2B/2C) antagonist SB 206553 (5 mg/kg) in either region. None of these compounds was able to modify the enhancement of DOPAC and 5-HIAA outflow induced by DRN stimulation in either the NAC or the striatum. Finally, in both brain regions basal DA release was significantly increased only by SB 206553. These results indicate that 5-HT2A but not 5-HT(2B/2C) receptors participate in the facilitatory control exerted by endogenous 5-HT on accumbal DA release. Conversely, 5-HT(2B/2C) receptors tonically inhibit basal DA release in both brain regions.     

Effect of barbitone sodium and thiopental sodium on brain dopamine, noradrenaline, serotonin and 5-hydroxyindoleacetic acid content in Arvicanthis niloticus

The quantitative estimation of total dopamine (DA), noradrenaline (NE), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) content in the whole brain tissue of normal Nile grass rat, Arvicanthis niloticus, gives and average of 631 +/- 12 ng DA/g, 366 +/- 12 ng NE/g, 617 +/- 15 ng 5-HT/g and 431 +/- 10 ng 5-HIAA/g fresh brain tissue. The effect of barbitone sodium and thiopental sodium on the total DA, NE, 5-HT and 5-HIAA content in the brain tissue of the Nile grass rat, Arvicanthis niloticus, was studied. The total DA, NE, 5-HT and 5-HIAA contents were determined 5 hr after i.p. injection of different doses of barbitone sodium (20, 40 and 80 mg/ml/100 g body wt) and thiopental sodium (5, 10 and 20 mg/ml/100 g body wt). The effect of different time intervals (1, 10, 30 min, 1, 2.5, 5, 8, 16, 24 and 48 hr) on the total brain DA, NE, 5-HT and 5-HIAA content was investigated after i.p. injection of 40 mg of barbitone sodium and 10 mg of thiopental sodium/ml/100 g body wt. Both barbitone sodium and thiopental sodium caused an increase in DA, NE and 5-HT content and a decrease in 5-HIAA content in the brain tissue of Arvicanthis niloticus. The increase in the whole brain contents of DA, NE and 5-HT after the administration of barbitone sodium and thiopental sodium may be due either to inhibition of transmitter release by an action at the monoamine nerve terminal or to effects causing a decrease in nerve impulse flow. On the other hand, the decrease in 5-HIAA may be due to the decrease in the turnover of 5-HT.     

Altered dopamine turnover in murine hypothalamus after low-dose continuous oral administration of aluminum.

Aluminum, a known neurotoxic substance, has been suggested as a possible contributing factor in the pathogenesis of Alzheimer's disease. Ground-water pollution by aluminum has been recently reported. In the current study groups of 5 male BALB/c mice were administered aluminum ammonium sulfate in drinking water ad libitum at 0, 5, 25, and 125 mg/L aluminum for 4 weeks. At the termination of aluminum exposure, their brains were removed and dissected into cerebrum, cerebellum, medulla oblongata, midbrain, corpus striatum, and hypothalamus. The concentration of norepinephrine (NE), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA), were determined in each brain area. DA, DOPAC, and HVA levels were lower in the hypothalamus of aluminum-treated mice, most notably in the low-dose group, as compared with control. No marked alterations in NE, 5-HT, and 5-HIAA levels were detected in any brain region. Changes in the concentration of DA and its metabolites measured in the hypothalamus suggest an inhibition of DA synthesis by aluminum.     

Postmortem and Regional Changes of Serotonin, 5-Hydroxyindoleacetic Acid, and Tryptophan in Brain

Using a specific and sensitive high pressure liquid chromatographic technique for the measurement of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and tryptophan (TRP), we found that there were no changes in 5-HT or 5-HIAA in the rat cortex when left in situ for 6 h at room temperature or 24 h at 4 degrees C. Only a minimal 14% increase in 5-HT was observed after 24 h at 4 degrees C in the striatum of the same animals. Concentrations of TRP, however, were increased significantly in both brain regions by these postmortem delay procedures. A second study revealed that there were significant regional 5-HT and 5-HIAA concentration differences within the cerebral cortex. The frontal cortex was shown to have the highest concentrations of 5-HT and 5-HIAA. Further, within the frontal cortex, 5-HIAA levels varied, showing apparent progressive rostral to caudal increases. 5-HT concentrations, however, remained constant within the frontal cortex. These results are discussed in reference to the conflicting reports of the previous human suicide and postmortem studies.     

Neurochemical studies on Indian Hypericum perforatum L

The effect of acute administration of 50% standardised ethanolic extract of Indian Hypericum perforatum (IHp) was studied on the rat brain concentrations of monoamines and their metabolites in five different brain regions, viz. hypothalamus, hippocampus, striatum, pons-medulla and frontal cortex by a HPLC technique. IHp extract was administered at the doses of 50 and 200 mg/kg, p.o. and the brain monoamines were assayed after 30 min of the treatment. IHp treatment significantly decreased the levels of serotonin (5-HT) and its metabolite 5-hydroxy indole acetic acid (5-HIAA) and 5-HT turnover in all the brain regions assayed. On the other hand, IHp treatment significantly augmented the levels of norepinephrine (NE) and its metabolite methylhydroxy phenyl glycol (MHPG) and NE turnover in all the brain regions studied. Similarly, the levels of dopamine (DA) were also significantly augmented in the hypothalamus, striatum and frontal cortex. Likewise, the levels of dihydroxyphenyl acetic acid (DOPAC), the major metabolite of DA, were also increased in these brain areas. Pharmacological studies with IHp extract have shown two major behavioural actions, namely, anxiolytic and antidepressant effects. The present findings tend to rationalise these observations, reduced 5-HT activity being consonant with anxiolytic and increased NA and DA activity being consonant with antidepressant action.     

Effect of 3,4-Methylenedioxymethamphetamine on 3,4-Dihydroxyphenylalanine Accumulation in the Striatum and Nucleus Accumbens

The effect of the racemic mixture of 3,4-methylenedioxymethamphetamine (MDMA) on the synthesis of dopamine in the terminals of nigrostriatal and mesolimbic neurons was estimated by measuring the accumulation of 3,4-dihydroxyphenylalanine (DOPA) in the striatum and nucleus accumbens 30 min following the administration of the L-aromatic amino acid decarboxylase inhibitor, 3-hydroxybenzylhydrazine. MDMA produced an increase in DOPA accumulation in the striatum which was greater in magnitude and longer in duration than that in the nucleus accumbens. Although the concentrations of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in both the striatum and nucleus accumbens were reduced 3 h following an injection of MDMA (20 mg/kg), 5-HT and 5-HIAA concentrations were significantly reduced only in the striatum 7 days after the administration of MDMA. Pretreatment with a 5-HT2 antagonist, ketanserin, significantly attenuated the reduction in 5-HT concentration in the striatum 3 h following MDMA administration and completely blocked 5-HT depletion at 7 days post administration. Moreover, ketanserin completely blocked MDMA-induced DOPA accumulation in the striatum. The results obtained in these studies suggest that MDMA activates nigrostriatal dopaminergic pathways via 5-HT2 receptors. In addition, these data are supportive of the hypothesis that dopamine plays a role in MDMA-induced 5-HT depletion.     

Rat brain monoamine and serotonin S2 receptor changes during pregnancy

The concentrations of noradrenaline (NA), dopamine (DA), serotonin (5-HT), and their metabolites were determined in 5 brain areas of non-pregnant, 15 and 20 day pregnant and 4 day post-partum rats. Striatal 5-HT content was significantly lower in 15 and 20 day pregnant rats than in estrous controls. A significant decrease in striatal and frontal cortex 5-hydroxyindole-3-acetic acid (5-HIAA) concentration was observed in 15 day pregnant rats. Significant increases in hypothalamic and hippocampal NA levels were observed at 4 days post-partum. Frontal cortex serotonin S2 receptorKd was reduced in 4 day post-partum rats. There was no significant change in S2 receptorB _max during pregnancy. Levels of progesterone were negatively correlated with striatal DA, homovanillic acid (HVA), 5-HT, and 5-HIAA levels, hypothalamic DA, hippocampal 5-HT, and frontal cortex 5-HIAA values as well as striatal HVA to DA, and HVA to 3,4-dihydroxyphenylacetic acid (DOPAC) ratios and amygdaloid HVA to DOPAC ratios. The limbic neurotransmitter changes might possibly contribute to mood changes which occur during pregnancy and post-partum.     

Regional Differences in 5-Hydroxytryptamine and Catecholamine Uptake in Primary Astrocyte Cultures

The uptake of 3H-labelled 5-hydroxytryptamine (5-HT, serotonin) norepinephrine ([3H]NE), and 3,4-dihydroxyphenylethylamine ([ 3H]dopamine, [3H]DA) was studied in primary astrocyte cultures prepared from the cerebral cortex, corpus striatum, and hippocampal regions of neonatal rat brain. Na+-dependent uptake showed marked regional differences. For [3H]5-HT the magnitude of uptake was corpus striatum greater than or equal to cerebral cortex greater than hippocampus, whereas for [3H]NE the order was hippocampus greater than corpus striatum greater than cerebral cortex. For [3H]DA, only the hippocampal cultures showed significant Na+-dependent uptake. [3H]5-HT uptake was specifically inhibited by 10(-7) M fluoxetine whereas [3H]NE uptake was preferentially inhibited by 10(-7) M desipramine. These results may reflect regional brain specialization and/or different developmental patterns of high affinity uptake of serotonin and catecholamines by astrocytes in situ.     

Release of endogenous dopamine, 3,4-dihydroxyphenylacetic acid,and amino acid transmitters from rat striatal slices

The release of endogenous dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) was measured in superfused striatal slices of the rat and the results compared with data obtained for the release of endogenous (a) DA and DOPAC in the cerebral cortex, nucleus accumbens and thalamus; (b) 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), GABA, and glutamate in the striatum; and (c) GABA, glutamate and 5-HT in the cerebral cortex. In superfused slices of all four CNS regions, there appeared to be a Ca²⁺-dependent, K⁺-stimulated release of endogenous DA. In addition, in slices of the striatum and nucleus accumbens there also appeared to be a Ca²⁺-dependent, 60 mM K⁺ stimulated release of endogenous DOPAC. In the striatum, 16 mM Mg²⁺ was as effective as 2.5 mM Ca²⁺ in promoting the 60 mM K⁺-stimulated release of DOPAC. In addition, 16 mM Mg²⁺ appeared to function as a weak Ca²⁺ agonist since it also promoted the release of DA to approximately 40% of the level attained with Ca²⁺ in the presence of 60 mM K⁺. On the other hand, in the striatum, 16 mM Mg²⁺ inhibited the Ca²⁺-dependent, 60 mM K⁺-stimulated release of GABA and glutamate. Similar Mg²⁺-inhibition was observed in the cerebral cortex not only for GABA and glutamate but also for DA and 5-HT. With the use of -methyl -tyrosine (tyrosine hydroxylase inhibitor), cocaine (uptake inhibitor) and pargyline (monoamine oxidase inhibitor), it was determined that (a) most of the released DA and DOPAC was synthesized in the slices during the superfusion; (b) DOPAC was not formed from DA which had been released and taken up; and (c) DA and DOPAC were released from DA nerve terminals. In addition, the data indicate a difference in the release process between the amino acids and the monoamines from striatal slices since Mg²⁺ inhibited the Ca²⁺-dependent, K⁺-stimulated release of GABA and glutamate and appeared to promote the release of DA and 5-HT.     

Nicotine-Induced Changes in Neurotransmitter Levels in Brain Areas Associated with Cognitive Function

Nicotine, one of the most widespread drugs of abuse, has long been shown to impact areas of the brain involved in addiction and reward. Recent research, however, has begun to explore the positive effects that nicotine may have on learning and memory. The mechanisms by which nicotine interacts with areas of cognitive function are relatively unknown. Therefore, this paper is part of an ongoing study to evaluate regional effects of nicotine enhancement of cognitive function. Nicotine-induced changes in the levels of three neurotransmitters, dopamine (DA), serotonin (5-HT), norepinepherine (NE), their metabolites, homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindoleacetic acid (5-HIAA), and their precursor, L-DOPA, were evaluated in the ventral and dorsal hippocampus (VH and DH), prefrontal and medial temporal cortex (PFC and MTC), and the ventral tegmental area (VTA) using in vivo microdialysis in awake, freely moving, male Sprague-Dawley rats. The animals were treated with acute nicotine (0.5 mg/kg, s.c.) halfway through the 300-min experimental period. The reuptake blockers, desipramine (100 microM) and fluoxetine (30 microM), were given to increase the levels of NE and 5-HT so that they could be detected. Overall, a nicotine-induced DA increase was found in some areas, and this increase was potentiated by desipramine and fluoxetine. The two DA metabolites, HVA and DOPAC, increased in all the areas throughout the experiments, both with and without the inhibitors, indicating a rapid metabolism of the released DA. The increase in these metabolites was greater than the increase in DA. 5-HT was increased in the DH, MTC, and VTA in the presence of fluoxetine; its metabolite, 5-HIAA, was increased in the presence and absence of fluoxetine. Except in the VTA, NE levels increased to a similar extent with desipramine and fluoxetine. Overall, nicotine appeared to increase the release and turnover of these three neurotransmitters, which was indicated by significant increases in their metabolites. Furthermore, DA, and especially HVA and DOPAC, increased for the 150 min following nicotine administration; 5-HT and NE changes were shorter in duration. As gas chromatography experiments showed that nicotine levels in the brain decreased by 75% after 150 min, this may indicate that DA is more susceptible to lower levels of nicotine than 5-HT or NE. In conclusion, acute nicotine administration caused alterations in the levels of DA, 5-HT, and NE, and in the metabolism of DA and 5-HT, in brain areas that are involved in cognitive processes.     

Ventricular Cerebrospinal Fluid Monoamine Transmitter and Metabolite Concentrations Reflect Human Brain Neurochemistry in Autopsy Cases

Concentrations of dopamine (DA), its metabolites 3-methoxytyramine and homovanillic acid (HVA), noradrenaline (NA), its metabolites normetanephrine (NM) and 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxytryptamine (5-HT, serotonin), and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were measured in 14 brain regions and in CSF from the third ventricle of 27 human autopsy cases. In addition, in six cases, lumbar CSF was obtained. Monoamine concentrations were determined by reversed-phase liquid chromatography with electrochemical detection. Ventricular/lumbar CSF ratios indicated persistence of rostrocaudal gradients for HVA and 5-HIAA post mortem. Ventricular CSF concentrations of DA and HVA correlated positively with striatal DA and HVA. CSF NA correlated positively with NA in hypothalamus, and CSF MHPG with levels of MHPG in hypothalamus, temporal cortex, and pons, whereas CSF NM concentration showed positive correlations with NM in striatum, pons, cingulate cortex, and olfactory tubercle. CSF 5-HT concentrations correlated positively with 5-HT in caudate nucleus, whereas the concentration of CSF 5-HIAA correlated to 5-HIAA levels in thalamus, hypothalamus, and the cortical areas. These data suggest a specific topographic origin for monoamine neurotransmitters and their metabolites in human ventricular CSF and support the contention that CSF measurements are useful indices of central monoaminergic activity in man.