Short-term lithium administration to healthy volunteers produces long-lasting pronounced changes in platelet serotonin uptake but not imipramine binding.

Platelet [3H]-5HT uptake, [3H]-imipramine binding and endogenous 5HT levels were measured in healthy volunteers during short-term (20 days) administration of lithium, and following its withdrawal. The Vmax of [3H]-5HT uptake was significantly decreased during lithium treatment. Following lithium withdrawal, platelet [3H]-5HT uptake (Vmax) remained decreased and was followed by a pronounced rebound effect in some of the subjects for up to 3 months. The affinity constant (Km) of [3H]-5HT uptake was not modified. Binding of tritiated imipramine during the same period and platelet 5HT levels measured till 14 days after withdrawal was not affected by lithium treatment. As lithium is devoid of in vitro effects on both 5HT uptake and imipramine binding, it is concluded that the effects of lithium on the 5HT transporter do not reflect a direct effect on the transporter complex. Our results indicate that lithium-induced changes at the level of 5HT uptake in platelets are not correlated with concomitant variations in platelet 5HT content and can be dissociated from modifications at the level of imipramine binding sites within the macromolecular complex of the 5HT transporter. Moreover, platelet 5HT uptake is apparently modulated by lithium, with a similar pattern in healthy volunteers and in manic-depressive patients.

Changes in human platelet 5 HT level after 1 week of chlorimipramine treatment.

In platelets of six volunteers taking chlorimipramine (50 mg/day) for 1 week, 5-HT levels were markedly decreased at the time of treatment withdrawal, and remained significantly reduced after a 1-week washout. Individual levels in five subjects remained affected during a 3-week washout. The previously reported observations of reduced serotonin concentration in platelets from depressed patients may reflect a residual effect of previous antidepressant treatment.

Platelet serotonin in essential hypertension and in mental depression.

The similarity between the metabolic pathways of serotonin in platelets and serotoninergic nerve endings has often been emphasized. The turnover of serotonin was therefore investigated in two diseases: hypertension (as central serotoninergic neurones appear to modulate central sympathetic nervous activity) and depression (as a central 5-HT-deficiency and a low 3H-imipramine binding on platelets have been described in patients with endogenous depression). Mean platelet 5-HT level was significantly lower in essential hypertensives than in controls. A reduction in platelet 5-HT level was also observed in depression and was more marked in women than in men. Serotonin level was only weakly related to the severity of the diseases. In some hypertensive patients, administration of ketanserin resulted in a reduction of blood pressure without affecting 5-HT level. In depressive patients, maprotiline and chlorimipramine acted differently on 5-HT level but both improved the clinical symptoms.

Reduced platelet serotonin in depression.

Platelet serotonin levels were measured in several psychiatric disorders to determine whether they distinguish among major depressive disorder (one or more depressive episodes and no manic episodes), dysthymic disorder (depressive neurosis), and schizophrenic and paranoid disorders. Serotonin levels in 141 subjects were determined using high performance liquid chromatography with electrochemical detection. Serotonin (5HT) levels in control subjects were significantly lower in males than in females. A marked reduction in 5HT levels, as compared to controls, was found in male and female patients with major depressive disorder, but not in dysthymic disorder. A slight but significant reduction in serotonin levels was found in female schizophrenic patients. The reduction in serotonin levels found in major depressive disorder could not be attributed to chronic antidepressant treatment. Liquid chromatography with electrochemical detection used in the present study permits a large-scale investigation.

Decreased uptake of 3H-serotonin and endogenous content of serotonin in blood platelets in hypertensive patients.

The uptake and content of serotonin in blood platelets were studied in patients with essential hypertension and in five families in which at least one member was hypertensive. Blood was obtained from male and female normotensive volunteers and hypertensive patients who were free of medication. Lineweaver-Burk plots of 3H-serotonin uptake from both control subjects and hypertensive patients were linear, which suggested simple Michaelis-Menten uptake kinetics. The maximal uptake velocity (Vmax) in hypertensive patients was significantly lower than in control subjects (control = 41.7 +/- 3.3 pmol/min/10(8) platelets, n = 17; hypertensive = 26.6 +/- 3.0 pmol/min/10(8) platelets, n = 16; p less than 0.005). The affinity constant (Km) was slightly but significantly lower in hypertensive patients (control = 0.70 +/- 0.08 microM; hypertensive = 0.46 +/- 0.08 microM; p less than 0.05). The serotonin content in blood platelets determined by high pressure liquid chromatography with electrochemical detection was significantly lower in hypertensive patients (control = 165.0 +/- 12.9 nmol/10(11) platelets, n = 29; hypertensive = 105.9 +/- 10.4 nmol/10(11) platelets, n = 27; p less than 0.001). In the five families investigated, the lowered serotonin content was observed in some normotensive members. The reduced number of carriers of serotonin uptake and the slight decrease in the affinity constant observed in platelets of patients with essential hypertension suggest that serotonin metabolism is altered in essential hypertension and that blood platelets may be a useful model in studying the serotonergic modifications at the molecular level.

Nomifensine antagonizes the ouabain-induced increase in dopamine metabolites in cerebrospinal fluid of the rat.

The effect of the Na+, K+-ATPase inhibitor, ouabain, on cerebrospinal fluid dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindolacetic acid (5-HIAA) levels was studied in pentobarbitone-anesthetized rats. An intracerebroventricular injection of ouabain (100 nmol) dramatically increased DOPAC and HVA levels. A dopamine uptake inhibitor, nomifensine (10 mg/kg i.p.) injected prior to ouabain, completely abolished the effect of ouabain on dopamine metabolites. These results are in agreement with the ouabain-induced increase in dopamine efflux described in vitro and favour the role of a carrier-mediated cytosolic release of dopamine.

Probenecid sensitive pathway of elimination of dopamine and serotonin metabolites in CSF of the rat.

CSF was removed at a constant flow rate of 1 microliter/min from the third ventricle of anesthetized rats. Five microliter CSF samples were directly injected every 15 min into a liquid chromatographic system coupled with an amperometric detector. Mean CSF values for free dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindolacetic acid (5-HIAA) were 1.4, 0.9, and 2.6 X 10(-6)M respectively. High doses of probenecid resulted in a linear increase of acidic metabolite concentrations which gave an index of the fractional turnover rates related to the resorption by the weak organic acid carrier. Accumulation rates were 0.24, 0.87, and 1.58 mumol/l/h for DOPAC, HVA and 5-HIAA respectively. This route of elimination was predominant for 5-HIAA while it represented only a small part of total turnover for DOPAC. A high elimination rate constant for HVA validates the use of control levels of this metabolite as an indication of fractional HVA turnover dependent upon probenecid-sensitive carrier.

Central administration of yohimbine increases free 3-methoxy-4-hydroxyphenylglycol in the cerebrospinal fluid of the rat.

The effect of the alpha2-antagonist, yohimbine, on cerebrospinal fluid 3-methoxy-4-hydroxyphenylglycol (MHPG), dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindolactic acid (5-HIAA) concentrations was studied in vivo. Cerebrospinal fluid was removed at a constant flow rate of 1 microliters/min from the third ventricle of rats and directly analysed by liquid chromatography coupled with electrochemical detection. An intracerebroventricular injection of yohimbine (100 nmol) dramatically increased MHPG levels. These results suggest a functional stimulation of alpha-2 adrenoceptors modulating noradrenergic neurotransmission in vivo.

Rapid liquid chromatographic determination of 5-hydroxyindoles and dihydroxyphenylacetic acid in cerebrospinal fluid of the rat.

A stainless steel guide was implanted in the anterior third ventricle of the anesthetized rat and an internal needle shorter than the guide was used to continuously collect cerebrospinal fluid (CSF) at a constant outflow of 1 microliter/min. Five microliter samples were injected directly into a liquid chromatographic column. The mobile phase was adjusted for selective separation of 5-hydroxytryptophan (5-HTP), serotonin (5-HT), dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindolacetic acid (5-HIAA). Electrochemical detection with a limit of 0.05 pmol was used, 5-HTP and 5-HT concentrations were in the 10(-8) M range in controls while DOPAC and 5-HIAA were in the 10(-7) and 10(-6) M range. Brain aromatic amino acid decarboxylase inhibition with high doses of benserazide corresponded to an increased CSF level of 5-HTP. Monoamine oxidase inhibition with tranylcypromine resulted in a diminution of DOPAC and 5-HIAA. L-Tryptophan loading associated with monoamine oxidase inhibition induced an increase in CSF level of serotonin. These pharmacologically induced changes in serotonin and dopamine metabolite levels exemplify the usefulness of these CSF determinations as indices of brain function.

[Inhibitory effect of noradrenaline on dopamine release from the hypothalamus of the rat]. / Effet inhibiteur de la noradrénaline sur la libération de la dopamine par l'hypothalamus du rat.

1. The release of dopamine from the anterior hypothalamic/preoptic region of the anesthetized and artificially ventilated rats was investigated in vivo using a superfusion technique with a push-pull cannula. L-DOPA and pargyline were added to synthetic cerebrospinal fluid superfusing the area. Dopamine was measured by electrochemical detection after separation by liquid chromatography. Dopamine release rapidly reached stable values after the addition of L-DOPA. 2. Serotonin (10-6M) slightly inhibited dopamine release. Other experiments are necessary to characterize this interaction. 3. Lesions of the ventral noradrenergic bundle by a knife cut significantly increased the release of dopamine. 4. This lesion prolonged the apparent half-life of noradrenaline in the AH/PO. 5. Low concentration (10-7M) of noradrenaline inhibited dopamine release when a lesion was performed prior to the superfusion. 6. These data are compatible with a tonic noradrenergic mechanism mediating an inhibitory control of dopamine release in the AH/PO.

[Implication of anterior hypothalamic dopamine in the regulation of arterial pressure]. / Implication de la dopamine de l'hypothalamus antérieur dans la régulation de la pression artérielle.

The anterior hypothalamus is essential for the normal carotid sinus baroreceptor reflex. The dopamine innervation to this region is a projection from the dopaminergic A 14 cell group of the rostral hypothalamus. The anterior hypothalamic/preoptic region (AH/PO) was unilaterally superfused with buffer containing L-DOPA (10(-4) M) and the superfusate analyzed for dopamine using liquid chromatography with electrochemical detection. A stable release of dopamine was analyzed for dopamine using liquid chromatography with electrochemical detection. A stable release of dopamine was obtained within one hour. When the baroreceptor reflex loop was activated, a concomitant increase in dopamine release was observed. Lesions of the ventral noradrenergic bundle by a knife cut significantly increased the release of dopamine for at least two hours. The data are compatible with a tonic noradrenergic mechanism mediating an inhibitory control of dopamine release in the AH/PO. This dopaminergic involvement may play a functional role in blood pressure control.

LCEC monitoring of 5-hydroxyindolic compounds in the cerebrospinal fluid of the rat related to sleep and feeding.

A new technique which allows for both the chronic withdrawal of CSF and continuous recording of EEG sleep patterns and food intake in the freely moving rat is described. Liquid chromatography with electrochemical detection (LCEC) was used for the direct assay of tryptophan metabolites in the CSF. Both 5-hydroxyindolacetic acid (5-HIAA) and 5-hydroxytryptophan (5-HTP) were easily detectable. However, serotonin (5-HT) levels were relatively low and 5-hydroxytryptophol (5-HTPhol) and N-methylserotonin (N-Me-5HT) were undetectable in several cases. The continuous monitoring of 5-HIAA and 5-HTP indicated stable values throughout the 3-hr experiments during which no food or small meals were consumed. In the rat which consumed a large meal, both 5-HIAA and 5-HTP significantly increased following that meal. This increase in metabolites may be the result of an increased availability of tryptophan to the brain as a result of the meal. Although this study is preliminary, the described technique can provide further information about the possible relationship between behavioral (sleep and/or feeding) changes and the concomitant neurochemical fluctuations.

Alpha 1- and alpha 2-adrenoceptors in rat cerebral cortex: effects of neonatal treatment with 6-hydroxydopamine.

Neonatal 6-hydroxydopamine treatment was used to destroy the noradrenergic nerve terminals in rat cerebral cortex and thus give some insight into the in vivo regulation of alpha-adrenoceptor subtypes, which in turn provides information concerning the anatomical localization of alpha 1- and alpha 2-adrenoceptors. Treatment of rats in the neonatal period with 6-OHDA causes an irreversible decrease in noradrenaline levels of the cerebral cortex compared to controls. Differences in [3H]clonidine and [3H]prazosin binding in the cerebral cortex occurred which varied depending upon the time elapsed between denervation and the binding assay. In rats aged 7-14 days there was a 20% decrease in the number of alpha 2-adrenoceptors and a slight increase in alpha 1-adrenoceptors. In older rats (45-50 day old) both types of alpha adrenoceptors were increased. Results of this study indicate that alpha 2-adrenoceptors located on presynaptic noradrenergic terminals represent only a small proportion of the total alpha 2-adrenoceptors in rat cerebral cortex. Increases in the binding capacity after 67-OHDA treatment indicate an up-regulation phenomenon affecting alpha 1-adrenoceptors and alpha 2-adrenoceptors located on structures other than noradrenergic nerve endings.

Effect of neonatal 6-hydroxydopamine treatment on alpha 1- and alpha 2-adrenoceptors in rat cerebral cortex.

Neonatal 6-hydroxydopamine (6-OHDA) treatment was used to destroy the noradrenergic nerve endings in rat cerebral cortex and thus give some insight into the development and regulation of alpha-adrenoceptor subtypes, which in turn provides information concerning the anatomical localization of alpha 1- and alpha 2-adrenoceptors. In cerebral cortex of rats treated in the neonatal period with 6-OHDA, we have observed an irreversible decrease in noradrenaline levels. Differences in 3H-clonidine and 3H-prazosin binding occurred which varied depending upon the time between denervation and the binding assay. In 7-14 day-old rats we observed a 20% decrease in the number of alpha 2-adrenoceptors and a marked increase in alpha 1-adrenoceptors. In older rats (45-50 day-old) both types of alpha-adrenoceptors were increased. Results of this study indicate that alpha 2-adrenoceptors located on presynaptic noradrenergic terminals represent only a minor fraction of the total alpha 2- adrenoceptors in rat cerebral cortex that are lost after denervation. Conversely, noradrenergic denervation resulted in supersensitivity of the alpha 1-adrenoceptors and nonnoradrenergic terminals located on alpha 2-adrenoceptors.

Regional distribution of noradrenaline and dopamine-beta-hydroxylase in the brain of spontaneously hypertensive rats.

The catecholamine concentration and dopamine-beta-hydroxylase activity were determined in several nuclei of the brain of spontaneously hypertensive rats (SHR) compared with Wistar Kyoto (WKY) controls. Catecholamines were measured by using liquid chromatography coupled with electrochemical detection. The threshold of detection was 5 X 10(-14) mole. Dopamine-beta-hydroxylase (DBH) was assayed by a sensitive radioenzymatic assay using tyramine as the substrate. The limit of detection was 5 pmoles of octopamine per sample. Significantly lower noradrenaline content was observed in 4 week-old SHR in some medullary and hypothalamic areas which are involved in cardiovascular regulation. This abnormally was no longer detectable in 12 week-old rats. The changes in catecholamine levels observed in young rats were not observed during the development of deoxycorticosterone-salt hypertension and therefore probably do not represent a compensatory mechanism tending to limit the progressive rise blood pressure. No significant difference in DBH activity was observed between the young SHR and WKY in any brain region measured. The altered relationship between noradrenaline content and DBH activity observed in young SHR when compared to WKY suggests a change in noradrenergic neurones activity and/or structure which could correspond to a genetically transmitted neurochemical abnormality associated with the initiation of hypertension in the SHR.

In vivo dopamine release from the anterior hypothalamus of the rat.

The release of dopamine from the anterior hypothalamic/preoptic region of the anesthetized rat was investigated in vivo using a superfusion technique with a push-pull cannula. Dopamine was measured electrochemically after separation by liquid chromatography. The spontaneous release of dopamine was very low but detectable in some experiments. An inhibitor of monoamine oxidase (pargyline) and the immediate precursor of dopamine (L-DOPA) were added to synthetic cerebrospinal fluid superfusing the area. When these substances were present dopamine release was increased considerably and appeared to be stable for a long period of time. Mechanisms contributing to the formation of newly synthetized dopamine are discussed in relation to the releasing effect of d-amphetamine and the inhibiting effect of calcium-free medium. The functional significance of dopamine release was shown by the increased release of dopamine following an increase in blood pressure obtained by an intraarterial injection of blood. Finally, ventral noradrenergic bundle lesion on the same side of the superfusion site considerably enhanced dopamine release which may indicate an inhibitory control of dopamine release by noradrenergic neurons. Furthermore, this experimental procedure provides valuable means for analyzing the effects of pharmacological as well as other manipulations on the dopamine released from a superfused brain area in vivo.