Antagonism of Serotonin 5-HT1A Receptors Potentiates the Increases in Extracellular Monoamines Induced by Duloxetine in Rat Hypothalamus

Abstract: In the current study we examined the effects of coadministration of a serotonin 5-HT_1A antagonist, (±)-1-(1 H -indol-4-yloxy)-3-(cyclohexylamino)-2-propanol maleate (LY 206130), and a dual 5-HT and norepinephrine (NE) uptake inhibitor, duloxetine, on extracellular levels of NE, 5-HT, dopamine (DA), 5-hydroxyindoleacetic acid, and 3,4-dihydroxyphenylacetic acid in rat hypothalamus microdialysates. LY 206130 (3.0 mg/kg, s.c.) alone significantly increased NE and DA levels by 60 and 34%, respectively, without affecting 5-HT levels. Duloxetine administration at 4.0 mg/kg, i.p. alone produced no significant changes in levels of 5-HT, NE, or DA. In contrast, when LY 206130 and duloxetine were coadministered at 3.0 mg/kg, s.c. and 4.0 mg/kg, i.p., respectively, 5-HT, NE, and DA levels increased to 5.7-, 4.8-, and threefold over their respective basal levels. These data demonstrate that antagonism of somatodendritic 5-HT_1A autoreceptors and concomitant inhibition of 5-HT and NE uptake with duloxetine may promote synergistic increases in levels of extracellular 5-HT, NE, and DA in hypothalamus of conscious, freely moving rats.     

Effect of 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) on monoamine neurotransmitters in mouse brain & heart

The effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was studied on dopamine (DA), norepinephrine (NE), serotonin (5HT) and γ-aminobutyric acid (GABA) neurons in mouse brain and on NE neurons of mouse heart. MPTP (45 mg/kg) was administered s.c. to mice twice daily for 2 consecutive days. This dosage regimen produced a decrease in the forebrain concentrations of DA and NE at 7 and 20 days after injection. In contrast, the forebrain concentrations of 5HT and GABA were not significantly decreased at either time. MPTP administration also produced a marked decrease in the uptake of ³H-DA into striatal slices and ³H-NE into cerebral cortical slices. In contrast, the uptake of ³H-NE into hypothalamic slices and the uptake of ³H-5HT into slices from several brain regions were not altered. MPTP initially reduced the concentration of NE in the heart, but unlike the persistent decreases in the forebrain concentrations of NE and DA, the NE concentration in the heart returned to control levels at approximately 20 days after MPTP administration. These results, showing that MPTP can produce a long lasting and selective decrease in the forebrain concentrations of NE and DA and in the uptake of radioactive DA and NE into brain slices, suggest that MPTP can cause the destruction of catecholamine neurons in mouse brain. In contrast, MPTP administration does not appear to produce long term changes in either 5HT or GABA neurons.     

Synthetic analgesics and other phenylpiperidines: effects on uptake and storage of dopamine and other monoamines mouse forebrain tissue

The neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can induce degeneration of dopamine (DA) and other central monoamine neurons, leading to Parkinson's disease-like effects in man, monkey, and mouse. MPTP and other substituted phenylpiperidines related to synthetic analgesics including alphaprodine and meperidine were evaluated for potency vs. uptake of 0.1 microM tritiated DA, norepinephrine (NE), or serotonin (5HT) in synaptosomal preparations of mouse striatum or cerebral cortex. The most potent inhibitor of the uptake of 3H-DA was N-methyl-4-phenylpyridinium ion (MPP+; IC50 = 1 microM, Ki = 0.4 microM), a metabolite of MPTP; its effect was competitive and reversible. Other analogs of MPTP: the N-ethylindole AHR-1709, N,N-dimethyl-MPTP, and N-methyl-4-phenylpiperidine were all more potent than MPTP against 3H-DA uptake. N-dealkylation and N-propyl substitution, as well as pyridine ring substitution, decreased affinity for DA uptake while 3',4'-dihydroxyphenyl substitution increased potency and selectivity for catecholamine uptake, and quarternarization of the pyridine ring also increased potency against DA uptake. Active compounds showed higher potency against the uptake of NE than of DA. MPP+ was also more potent than MPTP in releasing endogenous DA from striatal synaptosomes (EC50 = 3 vs. 30 microM), but did not release the cytoplasmic markers tyrosine hydroxylase and lactate dehydrogenase (LDH). In contrast to MPTP, synthetic phenylpiperidine analgesics, their potential metabolites and the experimental neuroleptic agent AHR-1709 all failed to deplete striatal DA in vivo, even if active in vitro against DA uptake.     

Monoamine Interactions Measured by Microdialysis in the Ventral Tegmental Area of Rats Treated Systemically with (±)-8-Hydroxy-2-(Di-n-Propylamino)tetralin

Abstract: The effect of (±)-8-hydroxy-2-(di- n -propylamino)tetralin (8-OH-DPAT), a selective serotonin 5-HT_1A agonist, on levels of extracellular norepinephrine (NE), dopamine (DA), and 5-HT (measured simultaneously) was investigated by microdialysis in the ventral tegmental area (VTA) of freely moving rats, and their behavioral activity was monitored. At 50 µg/kg s.c., 8-OH-DPAT reduced 5-HT levels but enhanced NE and DA levels in VTA dialysate. These effects were not altered by pretreatment with systemic idazoxan (5 mg/kg i.p.), a selective α₂ antagonist, or local sulpiride (10 µ M ), a selective D₂/D₃ antagonist. At 500 µg/kg s.c., 8-OH-DPAT further enhanced or more persistently reduced dialysate NE or 5-HT content but had little effect on dialysate DA content. Its DA level-increasing effect could be seen dramatically with local infusion of cocaine (30 µ M ) and, to a lesser extent, sulpiride (10 µ M ). Depletion of endogenous 5-HT with p -chlorophenylalanine attenuated both the 5-HT level-reducing and DA level-enhancing effects of 8-OH-DPAT without affecting its maximal NE effect and the locomotor-stimulatory effect. Partial depletion of endogenous NE with N -(2-chloroethyl)- N -ethyl-2-bromobenzylamine failed to change the monoamine response but diminished the locomotion induced by 8-OH-DPAT. These results suggested that (a) the low dose of 8-OH-DPAT may act at presynaptic 5-HT_1A receptors to modulate 5-HT and DA release, while acting at postsynaptic 5-HT_1A receptors to modulate NE release; (b) the high dose of 8-OH-DPAT may activate D₂ receptors to offset its DA level-increasing effect; and (c) the locomotor-stimulatory effect of 8-OH-DPAT might be mediated primarily by postsynaptic 5-HT_1A receptors and the NE system.     

Cocaine-like neurochemical effects of antihistaminic medications

The pattern of activation of dopamine (DA) neurotransmission in the nucleus accumbens (NAc) of rats produced by H₁ histamine antagonists which have behavioral effects like those of psychostimulant drugs was examined. Diphenhydramine and (+)-chlorpheniramine were compared with triprolidine, a potent and selective H₁ antagonist and (−)-chlorpheniramine which is less active than its enantiomer at H₁ receptors. Affinities of the drugs to DA, serotonin, and norepinephrine transporters at H₁ receptors and potencies for DA uptake inhibition in striatal synaptosomes were determined to assess mechanisms by which the compounds increased DA levels. Intravenous diphenhydramine (1.0–3.0 mg/kg) (+)- and (−)-chlorpheniramine (1.0–5.6 mg/kg) but not triprolidine (1.0–3.0 mg/kg) elicited a cocaine-like pattern of stimulation of DA transmission with larger effects in the NAc shell than core. The absence of stereospecific effects with chlorpheniramine enantiomers along with the lack of an effect with triprolidine suggest that the effects on DA transmission were not related to H₁ receptor antagonism. Although in vivo potencies were not directly related to DA transporter affinities, it is hypothesized that actions at that site modulated by other actions, possibly those at the serotonin transporter, are primarily responsible for the neurochemical actions of the drugs on DA neurotransmission and might underlie the occasional misuse of these medications.     

Uptake of biogenic amines by glial cells in culture I. A neuronal-like transport system for serotonin

Rat C6 astrocytoma cells take up serotonin (5HT) via a high affinity carrier mediated system with Km of 1 micromolar, and a second component of lower affinity. This high affinity 5HT transport system is rapid, concentrative, and highly sodium and temperature dependent. Chlorimipramine and Lilly 110140 preferentially block the glial 5HT but not NE uptake. This preferential inhibition has previously been shown for synaptosomes and brain slices. Norepinerphrine (NE) and to a lesser extent dopamine (DA) block the glial 5HT uptake, suggesting a partial overlap between the catecholamine and indoleamine glial carrier systems. 5-Hydroxy but not 6-hydroxy dopamine inhibits the high affinity 5HT transport in glia. A variety of ring hydroxylated indoleamine analogs block this glial 5HT transport; of the compounds tested, 5, 7 dihydroxytryptamine is the least effective inhibitor. Phenylethylamine (PEA) and its 0-methylated derivatives block synaptosomal and glial 5HT transport equally well. These observations suggest that cultured C6 cells used as models of glia possess a 5HT transport system which kinetically and pharmacologically resembles a neuronal 5HT transport system.     

N-phenylalkyl-substituted tropane analogs of boat conformation with high selectivity for the dopamine versus serotonin transporter

A series of N-phenylalkyl-substituted tropane analogs of boat conformation was synthesized, and these tropanes were evaluated for their ability to inhibit high affinity uptake of dopamine (DA) and serotonin (5-HT) into striatal nerve endings (synaptosomes). Some of these compounds exhibit high affinity for the DA transporter with a 5-HT/DA transporter selectivity ratio of >50.     

Monoamine Neurotransmitter Metabolism and Locomotor Activity During Chemical Hypoxia

The effects of hypoxia on metabolism of 5-hydroxytryptamine (5-HT or serotonin) and 3,4-dihydroxyphenylethylamine (DA or dopamine) were compared with those on open-field activity in male CD-1 mice. Chemical hypoxia was induced with NaNO2. Hypoxia did not alter striatal concentrations of DA, 5HT, Trp, Tyr, 5-hydroxyindoleacetic acid, or homovanillic acid. However, NaNO2 (75 mg/kg) reduced the rates of conversion of [3H]Tyr to [3H]DA (-41%) and [3H]Trp to [3H]5-HT (-39%). Hypoxia also reduced dihydroxyphenylacetic acid (DOPAC) levels (-27%) and DOPAC/DA ratios (-20%). Open-field behavior, as measured in an automated activity monitor, decreased in a dose-dependent fashion with 75-150 mg/kg of NaNO2 (-35 to -90%). Comparison with previous studies suggests that the syntheses of dopamine, serotonin, and the amino acids are equally vulnerable to hypoxic insults but may be less sensitive than the synthesis of acetylcholine.     

<Emphasis Type="Italic">Cynomorium songaricum</Emphasis> Extracts Functionally Modulate Transporters of γ-Aminobutyric Acid and Monoamine

Cynomorium songaricum Rupr. (SY) is a central nervous system-oriented herb material that has actions of anti-dementia, anti-epilepsy, and anti-stress. It is unclear whether SY would be biologically active in functionally regulating neurotransmitter transporters. Here, we assessed these potential actions using Chinese hamster ovary cells expressing γ-aminobutyric acid (GABA) transporter (GAT-1), dopamine transporter (DAT), norepinephrine transporter (NET), or serotonin transporter (SERT) (i.e. G1, D8, N1, or S6 cells, respectively). It was shown that SY extracts, such as SYw, SYa, SYp, SYc, SYe, and SYb (SY water, ethanol, petroleum ether, chloroform, ethyl acetate, and n-butyl alcohol extract, respectively) increased dopamine/norepinephrine (DA/NE) uptake by corresponding D8/N1 cells and decreased γ-aminobutyric acid/serotoin (GABA/5HT) uptake by corresponding G1/S6 cells; wherein, the potency or efficacy of SYc for up-regulating DA/NE uptake and that of SYb for inhibiting GABA/5HT uptake were relatively stronger. Additionally, GABA/5HT-uptake inhibition by SY extracts were also seen in cortical synaptosomes, and DA/NE-uptake enhancement by SYc was dependent on the activity of DAT and NET. Thus, SY extracts especially SYc and SYb are novel neurotransmitter-transporter modulators functioning as DAT/NET activators and/or GAT-1/SERT inhibitors.     

Selective stimulation of serotonin2c receptors blocks the enhancement of striatal and accumbal dopamine release induced by nicotine administration

The effects of acute and repeated nicotine administration on the extracellular levels of dopamine (DA) in the corpus striatum and the nucleus accumbens were studied in conscious, freely moving rats by in vivo microdialysis. Acute intraperitoneal (i.p.) injection of nicotine (1 mg/kg) increased DA outflow both in the corpus striatum and the nucleus accumbens. Repeated daily injection of nicotine (1 mg/kg, i.p.) for 10 consecutive days caused a significant increase in basal DA outflow both in the corpus striatum and the nucleus accumbens. Acute challenge with nicotine (1 mg/kg, i.p.) in animals treated repeatedly with this drug enhanced DA extracellular levels in both brain areas. However, the effect of nicotine was potentiated in the nucleus accumbens, but not in the corpus striatum. To test the hypothesis that stimulation of 5-HT (5-hydroxytryptamine, serotonin)(2C) receptors could affect nicotine-induced DA release, the selective 5-HT(2C) receptor agonist RO 60-0175 was used. Pretreatment with RO 60-0175 (1 and 3 mg/kg, i.p.) dose-dependently prevented the enhancement in DA release elicited by acute nicotine in the corpus striatum, but was devoid of any significant effect in the nucleus accumbens. RO 60-0175 (1 and 3 mg/kg, i.p.) dose-dependently reduced the stimulatory effect on striatal and accumbal DA release induced by an acute challenge with nicotine (1 mg/kg, i.p.) in rats treated repeatedly with this alkaloid. However, only the effect of 3 mg/kg RO 60-0175 reached statistical significance. The inhibitory effect of RO 60-0175 on DA release induced by nicotine in the corpus striatum and the nucleus accumbens was completely prevented by SB 242084 (0.5 mg/kg, i.p.) and SB 243213 (0.5 mg/kg, i.p.), two selective antagonists of 5-HT(2C) receptors. It is concluded that selective activation of 5-HT(2C) receptors can block the stimulatory action of nicotine on central DA function, an effect that might be relevant for the reported antiaddictive properties of RO 60-0175.     

dl-N-methyl-3-(o-methoxyphenoxy)-3-phenylpropylamine hydrochloride, Lilly 94939, a potent inhibitor for uptake of norepinephrine into rat brain synaptosomes and heart.

dl-N-Methyl-3-(o-methoxyphenoxy)-3-phenylpropylamine hydrochloride, Lilly 94949, is a potent inhibitor for uptake of norepinephrine (NE) into synaptosomes of rat brain with inhibitor constant (Ki) value of 1.8 × 10⁻⁷M. Lilly 94939 profoundly reduces the $\text{in vivo}$ accumulation of radioactivity from labeled NE in heart with ED₅₀ value of 1.5 mg/kg i.p. The inhibitory effects of the compound in synaptosomes and heart are most profound within 15 min of an intraperitoneal injection of Lilly 94939 at 10 mg/kg but much deminished at the 4th hr. These properties are in great contrast with its trifluoromethyl analog, Lilly 110140, which has previously been reported as a selective inhibitor of serotonin uptake in synaptosomes and without any effect on the accumulation of radioactivity from labeled NE in heart.     

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.     

Glutamatergic Control of Dopamine Release in the Rat Striatum: Evidence for Presynaptic N-Methyl-D-Aspartate Receptors on Dopaminergic Nerve Terminals

The N-methyl-D-aspartate (NMDA) receptor-mediated regulation of the release of newly synthesized [3H]dopamine [( 3H]DA) was studied in vitro, both on rat striatal slices using a new microsuperfusion device and on rat striatal synaptosomes. Under Mg2(+)-free medium conditions, the NMDA (5 X 10(-5) M)-evoked release of [3H]DA from slices was found to be partly insensitive to tetrodotoxin (TTX). This TTX-resistant stimulatory effect of NMDA was blocked by either Mg2+ (10(-3) M) or the noncompetitive antagonist MK-801 (10(-6) M). In addition, the TTX-resistant NMDA-evoked response could be potentiated by glycine (10(-6) M) in the presence of strychnine (10(-6) M). The coapplication of NMDA (5 X 10(-5) M) and glycine (10(-6) M) stimulated the release of [3H]DA from striatal synaptosomes. This effect was blocked by Mg2+ (10(-3) M) or MK-801 (10(-5) M). These results indicate that some of the NMDA receptors involved in the facilitation of DA release are located on DA nerve terminals. These presynaptic receptors exhibit pharmacological properties similar to those described in electrophysiological studies for postsynaptic NMDA receptors.     

Localization of rat striatal monoamine oxidase activities towards dopamine,serotonin and kynuramine by gradient centrifugation and nigro-striatal lesions

Subfractionation of the crude synaptosomal-mitochondrial fraction of rat striatum in a continuous sucrose gradient in a zonal rotor led to the following results. The distribution pattern of monoamine oxidase (MAO) activity towards dopamine (DA) was very similar to the pattern of MAO activity towards serotonin (5HT), but differed from the pattern of MAO activity towards kynuramine (KYN). As 5HT is specifically deaminated by MAO-A while KYN is a common MAO substrate, this supports earlier suggestions that in rat striatal preparations DA is deaminated preferentially by MAO-A. The patterns of the MAO activities towards DA and 5HT were clearly dissimilar, despite considerable overlap, to the patterns of tyrosine hydroxylase (TH) and DOPA decarboxylase (DD) activity, both marking the presence of striatal dopaminergic synaptosomes. The peak activities were separated and all patterns were symmetrical without showing a shoulder. This indicates that rat striatal MAO activity towards DA and 5HT is not specifically or for the greater part localized in dopaminergic terminals. We also investigated the effects of electrolytic and 6-hydroxydopamine lesions of the substantia nigra, both causing extensive degeneration of striatal dopaminergic terminals as appeared from the large decrease of striatal TH and DD activity. However, neither type of lesion induced a reduction of the MAO activity towards any of the substrates used. It is concluded towards DA and 5HT (probably MAO-A activity) present in dopaminergic terminals is very low compared with the total activity of this enzyme in rat striatal tissue.     

ATP-regulated neuronal catecholamine uptake: a new mechanism

Uptake of the catecholamines (CA), dopamine (DA) and norepinephrine (NE) into synaptosomes prepared from rat and bovine brains was potentiated by ATP (from 0.1 to 5.0 mM) in a dose-dependent manner. Other nucleotides, particularly the nonhydrolyzable ATP analogs beta,gamma-imidoadenosine-5'-triphosphate (AMP-PNP) and beta,gamma-methyladenosine-5'-triphosphate (AMP-PCP) also potentiated [3H]DA and [3H]NE uptake. Several endogenous 5'-nucleotide triphosphates (e.g. GTP, UTP and CTP) potentiated [3H]CA uptake, but were less effective than ATP. Among the ATP metabolites, only ADP potentiated uptake whereas AMP and adenosine did not. [3H]Dopamine uptake measured in Krebs bicarbonate buffer had a Km of 2.1 microM and a Vmax of 163.9 pmol/mg prot./min. In presence of ATP, [3H]DA uptake had much higher affinity (Km = 0.56 microM) and larger capacity (Vmax = 333 pmol/mg prot./min) than uptake in absence of added ATP. Furthermore, [3H]DA uptake in presence of ATP had faster rate of uptake, and was independent of temperature while in absence of added ATP it was temperature-dependent. This ATP-dependent [3H]DA uptake was retained by synaptosomal ghosts that were obtained after lysing the striatal synaptosomes and removing their contents of synaptic vesicles and mitochondria. It is proposed that, in addition to the carrier-mediated (neuronal) uptake of CA, there is neuronal uptake that is regulated by ATP and inhibited by cocaine, which may be more relevant for terminating the synaptic action of CA because of its faster rate of uptake and larger capacity.     

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.     

Characterization of D2 receptors and dopamine levels in the thalamus of the rat.

We kinetically characterized D2 receptors in thalami pooled from a group of Sprague-Dawley rats and then determined thalamic levels of dopamine (DA), homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC), and norepinephrine (NE) in relation to a measure of thalamic DA D2 receptor densities in another group of rats. The equilibrium dissociation constant (kd) was estimated as 0.1 nM by three independent methods, while the Bmax for thalamic D2 receptors was found to be 6.4 fmol/mg p using 3H-spiperone as ligand and ketanserin to occlude 5HT2 binding. Kinetic constants were in agreement with previously reported kinetic data from rodent caudate-putamen. This suggests that thalamic D2 receptors are similar to D2 receptors from other brain areas. Mean thalamic levels of DA (22.6 ng/mg p), DOPAC (1.19 ng/mg p) and HVA (0.31 ng/mg p) concur with previous reports of a sparse distribution of thalamic DA neurons. D2 receptor densities were positively correlated with DA metabolites DOPAC (P less than .05; r = 0.423) and HVA (P less than .05; r = 0.368), but not DA or NE. These results establish fundamental characteristics of thalamic DA neurotransmission to assist in the investigation of behavioral pharmacology of this area.     

Caffeine and regional brain monoamine utilization in mice

Caffeine (100 and 200 mg/kg, 30 min., i.p.) selectively altered the regional utilization of monoamines in the brains of mice. This depended upon the specific neurotransmitter and metabolite studied. Caffeine increased serotonin (5HT) utilization a dramatic ten-fold in the OB but decreased 5HT utilization in the HT. No 5HT changes were seen in other brain regions. Caffeine markedly increased norepinephrine (NE) utilization in the olfactory bulbs (OB), olfactory tubercles (OT), prefrontal cortex (PC), amygdala (AMY), hypothalamus (HT) and hippocampus (HC). Caffeine increased dopamine (DA) utilization in the OB, OT, PC, septum (SP), HT and thalamus (TH) but by various metabolic routes. The selective regional alterations in monoamine utilization produced by caffeine may be relevant to caffeine's central stimulatory effects. Limbic structures are predominantly involved. These changes may have important clinical and research implications. For example, the profound effect of caffeine on OB monoamines indicates that it may serve as a meaningful tool in olfactory research, including the bulbectomy model. Caffeine may also be useful in other limbic system behavioral models.     

Treatment with GM1 Ganglioside Restores Striatal Dopamine in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine-Treated Mouse

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 30 mg/kg i.p. daily for 7 days, was administered to mice. This dosage regimen resulted in an approximately 50% reduction of striatal dopamine (DA) level. Chronic administration of GM1 ganglioside (II3NeuAc-GgOse Cer), beginning between 1 to 4 days after terminating MPTP dosing, resulted in partial restoration of the striatal DA level. From dose- and time-response studies, it appeared that 30 mg/kg i.p. of GM1 administered daily for approximately 23 days resulted in an approximately 80% restoration of the DA level and complete restoration of the 3,4-dihydroxyphenylacetic acid (DOPAC) content. This dosage of GM1 also restored the turnover rate of DA in the striatum to near normal. Discontinuing GM1 treatment resulted in a fall of DA and DOPAC levels to values found in mice treated with MPTP alone. There was no evidence for regeneration of nerve terminal amine reuptake in the GM1-treated mice as evaluated by DA uptake into synaptosomes. Our biochemical findings in animals suggest that early GM1 ganglioside treatment of individuals with degenerative diseases of dopaminergic nigrostriatal neurons might be fruitful.     

A possible role of nitric oxide in the regulation of dopamine transporter function in the striatum.

Brain microdialysis and high-performance liquid chromatography with electrochemical detection were used to study the effect of the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) on striatal dopamine (DA) release in the anesthetized rat. Systemic administration of L-NAME (10 mg/kg, i.p.) significantly decreased the resting release of DA. The peak effect (23% decrease) was reached 45 min after injection. The inactive enantiomer D-NAME (10 mg/kg, i.p.) or the vehicle (saline, 5 ml/kg i.p.) had no effect on the striatal DA level. Neither treatment altered significantly the concentration of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). To investigate the possible involvement of the DA uptake system L-NAME was injected also in the presence of the DA uptake inhibitor nomifensine. Local application of nomifensine (10 microM in the dialysate medium) increased the extracellular concentration of DA to about eight-fold of the basal value and stabilized it at this higher level. Under these conditions L-NAME (10 mg/kg, i.p.) was not able to alter the striatal DA level. Neither nomifensine nor L-NAME caused any change in the level of DOPAC and HVA. Our data suggest that endogenously produced nitric oxide may influence the activity of the DA transporter which effect may have special importance in the regulation of extracellular transmitter concentration in the striatum.