Capillary zone electrophoresis with laser-induced fluorescence detection for the determination of nanomolar concentrations of noradrenaline and dopamine: application to brain microdialysate analysis

Determination of catecholamines by capillary zone electrophoresis with laser-induced fluorescence detection was performed on low-concentration samples, which were derivatized with naphthalene-2,3-dicarboxaldehyde to give highly fluorescent compounds. When the borate concentration in the derivatization medium was decreased from 130 to 13 mM, sensitivity for noradrenaline (NA) and dopamine (DA) was greatly enhanced while resolution between these two compounds decreased. A 50 mM borate concentration in derivatization medium was chosen since it provided maximal resolution between NA and DA, together with a high separation efficiency (3.1 million theoretical plates per meter for DA). The injection of 2.4 nL of a NA and DA solution derivatized at 10(-9) M produced peaks with signal-to-noise ratio of 8:1 and 3:1, respectively, corresponding to 1.8 amol of each catecholamine. The calibration curves were linear when NA and DA solutions were derivatized at concentrations ranging from 10(-6) to 10(-9) M. This method was used to determine NA in brain extracellular fluid: a peak corresponding to a basal level of 5 x 10(-9) M endogeneous NA was observed in microdialysates from the medial frontal cortex of the rat, and its nature was confirmed by both electrophoretic and pharmacological validations.     

Noradrenergic and dopaminergic systems in the central nervous system of the hedgehog (Erinaceus europaeus)

The distribution of the noradrenaline (NA)- and dopamine (DA)-containing neuronal structures in the central nervous system of the hedgehog (Erinaceus europaeus), a phylogenetically old mammalian species, was immunocytochemically studied employing antibodies directed against the catecholamines (CA) themselves. Groups of DA cell bodies observed in this study were similar to those present in other species but the distributional map of the NA-containing cell bodies exhibited some peculiarities. Prominent among them were the absence of the A3 group and the paucity of CA cells in the A2 group. DA neurons in the hypothalamus, apart from the densely populated paraventricular and arcuate nuclei, were fewer and less widely distributed than in other species. In the hedgehog mesencepha- Ion, in contrast to what has been described in other species, the major DA cell group was present in the ventral tegmental area. CA immunoreactive fibers were widely distributed in the CNS of the hedgehog. However, similarly to what has been observed in other species, terminal fields of DA neurons were much more restricted when compared to those of the NA neurons. The neocortical DA projection system of the hedgehog appeared less developed but organized similar to that of the rat, and even less developed than that of the primates. The lack of profound regional and laminar variations in the density of cortical NA fibers in the hedgehog enhances the suggestion that the elaboration and differentiation of the NA cortical system parallels the phylogenetic development of the cortex. In the brainstem, interspecies differences in the distribution of the CA fibers were found to concern primarily some hypothalamic areas (medial preoptic area, suprachiasmatic nucleus, arcuate nucleus). Such differences in the thalamus concerned the NA innervation and they were notably present in the visual thalamic nuclei (dorsal lateral geniculate nucleus, lateral posterior thalamic nucleus). In the spinal cord, which was found to receive fewer CA afferents than those found in other species, the density of the DA fibers was much lower than that of the NA axons. In addition to the CNS areas that have been described in other species to receive catecholaminergic innervation, the present study showed that both types of catecholaminergic fibers are distributed in the choroid plexus and along the ventricular wall of the brain ventricles and the central canal of the hedgehog.     

Local non-synaptic modulation of aldosterone production by catecholamines and ATP in rat: implications for a direct neuronal fine tuning

In addition to hypophyseal control, steroid synthesis and secretion in the adrenal cortex is also under direct local neural modulation. We obtained morphological and neurochemical evidence that a substantial proportion of the noradrenergic nerve endings lie in close proximity to zona glomerulosa cells without making synaptic contact, thus providing evidence for a direct local modulatory role of catecholamines in steroid secretion. These noradrenergic neurones, like other noradrenergic neurones in the central nervous system, are able to take up dopamine (DA), convert it partly into noradrenaline (NA) and to release both NA and DA together with the co-transmitter ATP when neuronal activity drives them to do so. These catecholamines and ATP may reach zona glomerulosa cells via diffusion in a paracrine way and modulate the synthesis of aldosterone. The presence of ecto-Ca-ATPases, enzymes that may terminate the effect of ATP, was demonstrated around the nerve profiles indicating that not only ATP but its metabolites (ADP, AMP, adenosine) can also influence the production of aldosterone. These data strongly support the possibility of a paracrine, non-synaptic modulatory role of catecholamines and ATP in the regulation of adrenocortical steroid secretion.     

Objective evaluation of Papanicolaou staining

Altered endothelium-dependent vasodilation has been observed in congestive heart failure (CHF), a disease characterized by a sustained adrenergic activation. The purpose of our study was to test the hypothesis that chronically elevated catecholamines influence the nitric oxide (NO) pathway in the human endothelium. Human umbilical vein endothelial cells (HUVEC) were exposed for 7 days to a concentration of noradrenaline (NA, 1 ng/mL) similar to that found in the blood of patients with CHF. Kinetics of endothelial constitutive NO synthase (ecNOS) and inducible NO synthase (iNOS) activity, measured by [3H]L-arginine to [3H]L-citrulline conversion, and protein expression of ecNOS and iNOS, assessed by Western blot analysis, were unaffected by chronic NA treatment. Furthermore, no changes in subcellular fraction-associated ecNOS were found; this indirectly shows that chronic NA did not cause phosphorylation of the enzyme. Moreover, [3H]L-arginine transport through the plasma membrane was conserved in chronically NA-treated cells. The data demonstrate that prolonged in vitro exposure to pathologic CHF-like NA does not affect the L-arginine: NO pathway in human endothelial cells.     

Local activation of metabotropic glutamate receptors inhibits the handling-induced increased release of dopamine in the nucleus accumbens but not that of dopamine or noradrenaline in the prefrontal cortex: comparison with inhibition of ionotropic receptors

On-line in vivo microdialysis was used to determine the effects of a 16-min handling period on release of dopamine (DA) in the nucleus accumbens and of DA and noradrenaline (NA) in the medial prefrontal cortex of awake, freely moving rats. DA and NA were determined in one HPLC run. Handling resulted in an immediate and strong increase of both catecholamines in the prefrontal cortex. Maximal values for DA were 295%, and for NA 225%, of controls. DA in the nucleus accumbens was also increased (to 135% of controls) but only after a short delay. Local inhibition of ionotropic glutamate receptors by continuous reversed dialysis of the drugs 6-cyano-7-nitroquinoxaline, D-2-amino-5-phosphonopentanoic acid, or dizocilpine did not significantly affect handling-induced increases in cortical DA and NA release. Neither did the agonist of metabotropic glutamate receptors, trans-(1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD), or the GABA-B agonist baclofen. Reversed dialysis of dizocilpine in the nucleus accumbens was equally ineffective, but ACPD inhibited the increase in DA release in this area. Stimulation of metabotropic glutamate receptors in the nucleus accumbens was previously reported to inhibit activation of DA release in that area after stimulation of glutamatergic or dopaminergic afferents. It is concluded that metabotropic receptors in the nucleus accumbens are important for the control of activation of DA release in the accumbens by physiological stimuli but that a similar mechanism is lacking in the prefrontal cortex.     

Monoamine metabolism in different forms of paraphilias

42 persons which commited crime sexual actions were examined in terms of clinical and neurochemical investigations. The sexual behaviours of 31 patients from this group were associated with sexual inclination pathology--with paraphilia. The patients were divided into 2 groups namely with compulsive form of paraphilia (13 individuals) and without compulsive disturbances (18 patients). Both free and conjugated forms of norepinephrine (NA), dopamine (DA), dihyroxyphenylalanine (DOPA) and dihyroxyphenylacetic acid (DOPAC) were measured in serum and daily urine as well as serotonin concentration was estimated in blood plasma and platelets. The rate of 3H-serotonin uptake into platelets (Vmax) was also investigated. It was determined that Vmax, free and especially conjugated forms of NA, DA, DOPAC levels were significantly higher in patients with compulsive forms of paraphilia. It was supposed that monoamine mechanisms may be operated in psychopathological variations of the crime sexual behaviour.     

Changes in plasma dopamine-beta-hydroxylase activity during the perioperative period of cardiac surgery: an index of sympathetic nerve activity

To evaluate the usefulness of plasma dopamine-beta-hydroxylase (DBH) activity as an index of sympathetic nerve activity during cardiac operations, we examined the serial changes in plasma DBH activity, in relation to the plasma noradrenaline (NA) level and hemodynamic parameters, in patients who underwent cardiac surgery. The plasma DBH activity decreased significantly after cardiopulmonary bypass, and remained low during dopamine (DA) infusion until 72 h after the operation. However, recovery of the hemodynamic parameters, being the mean arterial pressure, heart rate and cardiac index, was seen as early as 1-3 h postoperatively. It was therefore assumed that the plasma DBH activity takes a long time to recover after an operation. The time-course changes in the plasma NA level were quite different from the changes in DBH activity, with an apparent negative correlation being observed between them. Thus, there is a possibility that exogenously administered DA, as well as increased plasma NA, might inhibit DBH activity during cardiac surgery. Moreover, since catecholamines are often administered upon completion of cardiac surgery, measurement of the plasma catecholamine level would be inappropriate for evaluating real sympathetic nerve activity. From the results of this study, it is surmised that measurement of the plasma DBH activity could be useful for estimating the intrinsic sympathetic nerve activity of patients who have undergone cardiac surgery.     

Role of catecholamines in release of gonadotrophic hormones in the rabbit

Role of catecholamines (CA) in transmission of neurohormone releasing gonadotrophin (GnHR) from the hypothalamus to hypophysis was estimated on the basis of the hypothalamic catecholaminergic system blockade with 6-hydroxydopamine (6-OHDA) and intraventricular infusions of CA in the rabbit. 6-OHDA administered intraventricularly in doses 200-500 mug caused temporary blockade of ovulation. Intraventricular infusion of noradrenaline (NA) induced ovulation in 50% of animals tested, whereas dopamine (DA) and adrenaline (A), induced ovulation only in very few cases. It seems, that catecholaminergic system participates in transmission of neurohormones to the hypophysis, and NA plays the most important role in this process.     

Behavioral and neurochemical effects of acute and repeated administration of triadimefon in the male rat

The effects of triadimefon (TDF) were examined in male Sprague-Dawley rats. In this study, the acute administration of TDF (100 mg/kg) was found to significantly increase locomotor activity and induce stereotyped behavior. Acute administration of TDF was also found to significantly increase dopamine (DA) and homovanillic acid (HVA) levels while the dihydroxyphenylacetic acid (DOPAC) level remained unchanged in both the nucleus accumbens (NA) and striatal (ST) tissues when compared to control. Furthermore, DOPAC:DA ratios were significantly reduced in both brain regions suggesting an increase in DA turn overrate. On the other hand, in animals receiving repeated TDF administration, only the HVA level was significantly increased in both the ST and NA. TDF neither competed for binding to D2, D3 or D4 DA receptors nor altered the Kd or the Bmax of [3H] SCH 23390 and [3H] spiperone recognition sites associated with striatal D1 and D2 receptors, respectively. Meanwhile, TDF competed with [3H] GBR 12935 for binding to DA transporter sites with strong affinity, but repeated treatment with TDF had no sustained or cumulative effect on the DA transporter system. These results clearly show that acute TDF-induced behavioral effects may not be via binding to DA receptors, but through the interaction with DA transporter binding sites. Also, TDF does not appear to produce cumulative effects in the parameters evaluated.     

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)     

Effects of the antiparkinsonian drug budipine on neurotransmitter release in central nervous system tissue in vitro

The effects of the antiparkinsonian drugs budipine and biperiden on spontaneous and electrically evoked release of dopamine (DA), acetylcholine (ACh), GABA or noradrenaline (NA) were studied in caudate nucleus or cortex slices, respectively, of the rabbit brain. Whereas both drugs (1-10 microM) strongly increased spontaneous [3H]outflow in caudate nucleus slices preincubated with [3H]DA, budipine inhibited but biperiden facilitated the evoked DA release. In the presence of the DA-reuptake inhibitor nomifensine, a significant part of the budipine-induced basal [3H] outflow consisted of unmetabolized DA. Synaptosomal high-affinity uptake of [3H]DA was only weakly affected by budipine and biperiden (IC50 values, 11 and 9 microM, respectively). Budipine enhanced also basal [3H]outflow from cortex slices prelabeled with [3H]NA, however this outflow consisted mainly of NA metabolites even in the presence of cocaine. The evoked release of [3H]ACh in rabbit caudate nucleus slices preincubated with [3H] choline was almost unaffected by budipine but enhanced by biperiden in the absence of further drugs. In the presence of nomifensine, however, budipine inhibited, but biperiden still enhanced, the evoked ACh release. Moreover, both drugs showed antimuscarinic properties in the presence of the ACh esterase inhibitor physostigmine, i.e., they facilitated the evoked ACh release, exhibiting pA2 values of about 6.9 (budipine) and 8.3 (biperiden). Addition of the D2 receptor antagonist domperidone diminished all inhibitory effects of budipine on the evoked ACh release. The evoked overflow of [3H] in caudate nucleus slices preincubated with [3H]GABA was reduced by both budipine and biperiden. It is concluded that both anticholinergic and indirect dopaminomimetic properties contribute to the antiparkinsonian effects of budipine, whereas biperiden exhibits mainly anticholinergic effects. Moreover, both drugs might disinhibit GABA controlled neurons in the central nervous system.     

Mazindol, nomifensine and desmethylimipramine inhibit potassium-induced release of dopamine: effect of stimulus strength

Catecholamine uptake blockers exhibit a second action: They suppress the potassium (K+)-stimulated release of [3H]-dopamine (DA) from rat striatal tissue in vitro. In the present study, a K+ dose-response curve was obtained for the release of both [3H]-DA and endogenous DA from striatal tissue, in the absence and presence of catecholamine uptake blockers. Three drugs were used, namely, mazindol, nomifensine, and desmethylimipramine. The data showed that diminished release in the presence of mazindol or nomifensine was dependent upon the concentration of K+. Marked inhibition of stimulus-induced release of either 3H-DA or endogenous DA was observed at low concentrations of K+ (15 and 20 mM), but not at higher concentrations of K+ (40 and 60 mM). In contrast, the diminished release of DA in the presence of desmethylimipramine persisted over the K+ range of 20-60 mM. These data show that the drug action observed previously was not restricted to a specific neuronal pool of DA that was labelled with [3H]-DA. Further, the data emphasize the importance of the concentration of the depolarizing stimulus when evaluating the effects of drugs on release of catecholamines.     

Interaction of calcium channel blockers with different agonists in aorta from normal and diseased rats

The interactions of calcium channel blockers (CCBs) with noradrenaline (NA), phenylephrine (PE), dopamine (DA) and KCl have been investigated in rat isolated aortic strip. In preparations from control and hypertensive (DOCA-saline) rats chronically treated with verapamil, nifedipine and diltiazem, there was partial inhibition of contractions to NA, PE and DA. However, with nimodipine, there was potentiation of responses. This could be related to the occurrence of different isoforms of L-type calcium channels. In preparations obtained from hyperthyroid rats the concentration-response curves of NA, PE and KCl were shifted to the right with depressed maximal response which could be secondary to the primary effect exerted on the heart. In preparations from L-thyroxine + nimodipine/nifedipine treated rats the concentration-response curves of NA, PE and KCl were shifted to the right and the maxima was depressed suggesting that this may be due to decreased alpha receptor density (NA and PE) and down-regulation of voltage operated channels (KCl).     

Biotransformation of locally applied precursors of dopamine, serotonin and noradrenaline in striatum and hippocampus: a microdialysis study

In vivo microdialysis in freely moving rats was used to study the biotransformation, consisting primarily of decarboxylation by aromatic amino acid decarboxylase (AAAD), of the precursors L-3,4-dihydroxyphenylalanine (L-DOPA), L-5-hydroxytryptophan (L-5HTP), and L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) on extracellular levels of dopamine (DA), serotonin (5HT) and noradrenaline (NA), respectively. The precursors were administered locally through the microdialysis probe into the striatum and into the hippocampus. The different transmitter systems were compared with respect to the ability of the precursors to elevate extracellular levels of their associated transmitter. The basal extracellular concentrations of NA and DA were found to be tetrodotoxin (TTX, a blocker of fast sodium channels) sensitive in striatum and hippocampus, indicating the neuronal origin of the measured transmitters. The extracellular concentrations of 5HT (in hippocampus) were only 60% TTX-sensitive. L-DOPA and L-5HTP showed to be effective precursors of DA and 5HT, respectively, although their formation profile was quite different. The L-DOPA-induced increase in extracellular DA was large and short-lasting, while the L-5HTP-induced increase in 5HT was slower and less pronounced. The relative increase in extracellular DA or 5HT was more pronounced in the brain region where their baseline values were lower, but the absolute amount of transmitter formed from their precursor was similar in both brain regions. L-threo-DOPS was a poor precursor for NA and also failed to influence extracellular DA in striatum, questioning its use in the treatment of freezing gait in late stages of Parkinson's disease.     

Endurance performance in humans: the effect of a dopamine precursor or a specific serotonin (5-HT2A/2C) antagonist

In this study we examined the effect of a dopamine (DA) precursor (L-DOPA) or a serotonin (5-HT) antagonist (Ritanserin) on time to exhaustion. The study had a double-blind, randomised, placebo controlled and cross-over design. Seven moderately trained men performed three tests to exhaustion at 65% Wattmax. Each test was separated by two weeks to allow washout of the drugs (dose: 4 mg/kg Sinemet, and 0.3 mg/kg Ritanserin). Blood lactate, hematocrit, glucose, ammonia, free fatty acids (FFA), growth hormone (GH) and catecholamines were determined before and after exercise. Time to exhaustion did not differ between the three trials. Most of the parameters measured in this study responded as predicted during cycling to exhaustion in man. DA agonism significantly increased heart rate, lactate, and plasma DA values at rest, while other parameters such as FFA, lactate, plasma noradrenaline (NA) and adrenaline (A), and plasma GH showed the highest absolute levels at exhaustion. Ritanserin did not influence basal glucose and heart rate at rest, but this group showed a much lower increase in plasma catecholamine levels. We conclude that under the present conditions, neither a metabolic precursor of DA nor a specific centrally acting 5-HT2A/2C antagonist, when given in two single doses 24 h and immediately before the experiments, influences the time to exhaustion on a bicycle trial at 65% Wattmax.     

Dose-response effects of prostaglandin F2alpha on the rabbit oviduct: reproductive endocrine influence and tachyphylaxis

The mechanism of catecholamine (CA) release induced by transmural stimulation (TS) and the participation of acetylcholine (ACh) in this mechanism were studied using isotonic contraction of excised vas defernse of rats. Furthermore, the inhibitory effect of bretylium (Br) on sympathetic activity was observed. Results: 1) The effects of various kinds of drugs on isotonic contractions induced by TS, exogenous ACh and exogenous noradrenaline (NA) were observed with the results shown in Table 1. The following has been concluded: (1) TS-induced contraction is due to stimulation of the endings of hypogastric nerve (sympathetic nerve), resulting in CA release from adrenergic fiber (AF) and ACh release from cholinergic fiber (CF) in this nerve. (2) The participation of ACh is not indispensable in the CA release from AF induced by TS. (3) Endogenous ACh release from CF by TS brings about CA release under eserine application. (4) CA release by exogenous ACh is not inhibited by ganglion blockade, but is inhibited by atropine, indicating the muscarinic receptor to be in AF endings. 2) Br exerted preferentially the irreversible inhibition on CA release from AF rather than that on ACh release from CF, while it caused a mild reversible inhibition on CA release by exogenous ACh. 3) On the TS contraction that had been abolished irreversibly by Br, NA incubation showed a mild lasting recovery, while methamphetamine (MAP) or calcium (Ca) incubation showed a strong lasting recovery. Furthermore, in this recovery of TS contraction, the incubation with NA or MAP exerted only the recovery of CA release while the Ca incubation exerted the recovery of both CA release and ACH release. It would appear that Br blocks both AF and CF by inhibiting the transmitter-releasing action of Ca.     

In vitro effects on monoamine uptake and release by the reversible monoamine oxidase-B inhibitors lazabemide and N-(2-aminoethyl)-p-chlorobenzamide: a comparison with L-deprenyl

To investigate whether the reversible monoamine oxidase-B (MAO-B) inhibitors lazabemide and Ro 16-6491 have any additional effect on monoamine uptake and release, in vitro experiments were performed on rat forebrain synaptosomes and blood platelets. The effects of the two drugs were compared with those of L-deprenyl, the well-known irreversible MAO-B inhibitor which is reported to affect amine uptake. Both lazabemide and Ro 16-6491 behaved as weak inhibitors of [3H]monoamine uptake by synaptosomes, with a similar rank order of potency for amine uptake inhibition (noradrenaline (NA) > or = 5-hydroxytryptamine (5 HT) > dopamine (DA)). The IC50 values for lazabemide and Ro 16-6491, respectively, were: 86 microM and 90 microM for NA uptake; 123 microM and 90 microM for 5HT uptake; > 500 microM and > 1000 microM for DA uptake. L-Deprenyl (rank order of inhibitory potency: NA > DA > 5 HT) was four to 10 times more potent than either compound in inhibiting [3H]catecholamine uptake (IC50 = NA 23 microM, DA 109 microM), and two to three times less potent in inhibiting 5 HT uptake (IC50 233 microM). Lazabemide and Ro 16-6491 also differed from L-deprenyl in their ability to induce release of endogenous monoamines from synaptosomes. Thus, Ro 16-6491 (500 microM) induced a greater 5 HT release than did L-deprenyl, but was less effective than L-deprenyl in releasing DA. On the contrary, lazabemide was almost completely inactive on either 5 HT and DA release. The differential effect of the three MAO-B inhibitors on synaptosome 5 HT uptake and release was confirmed by [14C]5HT uptake and liberation experiments with isolated rat platelets. The data indicate that the reversible MAO-B inhibitors lazabemide and Ro 16-6491 at relatively high concentrations possess amine uptake-inhibiting properties. With regard to the effects examined, lazabemide markedly differs from L-deprenyl since it does not interfere with DA uptake nor induce amine release from synaptosomes.     

6-Hydroxydopamine lesions of dopaminergic A10 neurons. Long-term effects on the urinary excretion of free and conjugated catecholamines and their metabolites in the rat

Free and conjugated catecholamines (dopamine, noradrenaline, adrenaline) and their methoxylated and/or deaminated metabolites were studied in rat urine after the bilateral destruction of the A10 dopaminergic cell group. Two months after the lesion, dopamine (DA) loss reached 91% in the nucleus accumbens, and was greater than 80% in olfactory tubercles, lateral septum and frontal cortex. At the same time urinary conjugated dihydroxyphenylacetic acid (DOPAC) was decreased by 45% whilst homovanillic acid (HVA) was increased only in its sulfated form (+62%). In contrast, no changes were observed in the free and conjugated forms of urinary DA, 3-methoxytyramine noradrenaline, normetanephrine, adrenaline, vanylmandelic acid, 3-methoxy-4-hydroxyphenylglycol and in the free forms of DOPAC and HVA. The present report confirms and extends our previous findings on the relationships between central dopaminergic activity and urinary deaminated metabolites of DA in the rat. It emphasizes the interest of urinary assays which could provide in vivo information on CNS functions.     

Optimized release of dexamethasone and gentamicin from a soluble ocular insert for the treatment of external ophthalmic infections

The aziridinium ion of ethylcholine (AF64A), a cholinergic neurotoxin, was injected into the right striatum of a rat. The unilateral injection of 10 nmol AF64A reduced the activity of choline acetyltransferase (CAT) and the tissue content of acetylcholine (ACh) in the striatum. The striatal contents of dopamine (DA), norepinephrine (NE), 5-hydroxyindoleacetic acid (5-HIAA) and gamma-aminobutyric acid (GABA) were unchanged. These results suggest that the cholinospecificity in the striatal lesion was induced by the 10 nmol dose of AF64A. The number of N-methyl-D-aspartic acid (NMDA) receptors in the striatum treated with 10 nmol AF64A was determined by a specific binding assay using [3H](+/-)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid ([3H]CPP), a selective ligand for NMDA receptors. The number of the NMDA receptors decreased significantly in the injected area. On the other hand, in a microdialysis using normal rats, the perfusion of 50 microM NMDA into the striatum increased ACh release. The perfusion of 100 microM MK801 which is the specific and non-competitive NMDA receptor antagonist, decreased the basal levels of ACh release and blocked NMDA-elicited ACh release. Taken together, the present results strongly suggest that a population of NMDA receptors exists on cholinergic interneurons within the striatum, and it directly regulates ACh release.     

Effect of ketamine anaesthesia on the content of monoamines and their metabolites in the rat brain

The effects of ketamine anaesthesia (100 mg/kg i.p.) on the content of brain 5-hydroxytryptamine (5HT), 5-hydroxyindoleacetic acid (5HIAA), noradrenaline (NA), dopamine (DA) and homovanillic acid (HVA) were studied in male Wistar rats. Fifteen min after ketamine injection, when the rats were deeply anaesthetized, the 5HT content in many brain regions tended to be increased. An opposite tendency was found in the brain 5HIAA content. In rats treated with probenecid, which markedly lengthened ketamine anaesthesia, the accumulation of 5HIAA was significantly reduced by ketamine. In addition to ketamine anaesthesia, probenecid was found to lengthen thiopental anaesthesia. One hour after the ketamine administration, when the rats were no longer anaesthetized but were excited, the brain NA concentration was increased by 17% (P less than 0.02). The brain DA content was unchanged, but at 15 min and 1 hour after ketamine administration the striatal HVA content was increased by about 55% (P less than 0.05), suggesting an increased turnover of DA. The results suggest that during recovery from ketamine anaesthesia the increased NA content and the increased DA turnover may be associated with the postanaesthetic excitement of the rat, whereas the decreasamine anaesthesia.