Effects of diphenyl diselenide on depressive-like behavior in ovariectomized mice submitted to subchronic stress: involvement of the serotonergic system.

RATIONALE: The transition to menopause is associated with an increased risk of depressed mood. OBJECTIVES: This study was conducted to investigate whether diphenyl diselenide [(PhSe)2] treatment could reduce the effects of postmenopausal depression-like behavior in ovariectomized female mice submitted to subchronic stress exposure. METHODS: Mice were divided into four groups: sham, (PhSe)2, ovariectomy (OVX), and OVX + (PhSe)2. Animals were ovariectomized/sham-operated and subjected to stress session once a day for 7 days from the fifth to the 11th day after OVX. The behavioral tests (open field, tail suspension (TST), and forced swimming (FST)) were performed on the 14th day after OVX. Mice were treated orally once a day with vehicle (canola oil, 10 ml/kg) or (PhSe)2 (10 mg/kg; 10 ml/kg) 30 min before being exposed to subchronic stress, or from the 11th to the 14th day. Paroxetine (8 mg/kg i.p.) and pargyline (30 mg/kg i.p.) were used as positive controls. The involvement of serotonergic receptor subtypes in the antidepressant-like effect of (PhSe)2 was assessed in the FST using WAY 100635 (0.1 mg/kg s.c.), ritanserin (1 mg/kg i.p.), and ondansetron (1 mg/kg i.p.) as serotonergic antagonists. Monoamine oxidase (MAO) A and B activities were also determined. RESULTS: The prolongation of immobility time in TST and FST in OVX mice submitted to subchronic stress was prevented by (PhSe)2 treatment. Ritanserin and ondansetron blocked the antidepressive-like effect of (PhSe)2, suggesting the involvement of 5-HT(2A/2C) and 5-HT3 receptor subtypes. Both paroxetine and pargyline were effective in reducing the immobility time of stressed OVX mice in the FST. No alterations in locomotor activity were observed. Although (PhSe)2 had inhibited in vitro MAO-A and MAO-B activities, none of the groups presented alterations neither in ex vivo MAO-A nor in MAO-B activity. CONCLUSIONS: (PhSe)2 treatment could influence mood and behavior, indicating a promising role of this organoselenium compound in the management of postmenopausal depressive symptoms.

Pargyline effect on luteinizing hormone secretion throughout the rat estrous cycle: correlation with serotonin, catecholamines and nitric oxide in the medial preoptic area.

The neurons that produce gonadotrophin-releasing hormone (GnRH) are mainly found in the medial preoptic area (MPOA) and constitute a common final pathway to the control of luteinizing hormone (LH) surge on proestrus. The control of GnRH secretion depends on several neurotransmitters, such as serotonin (5-HT), noradrenaline (NA), dopamine (DA) and nitric oxide (NO). The aim of this work was to study the profile of 5-HT, catecholamines and their main metabolites in the MPOA throughout the estrous cycle and their interactions with NO system in this area to control LH surge. For this purpose, the following were evaluated: (I) the effect of pargyline (a monoamine oxidase inhibitor) acute treatment on plasma LH secretion throughout the estrous cycle, correlated with changes of 5-HT, DA and NA content as well as activity and expression of neuronal NO synthase (nNOS) within MPOA; (II) the effect of 5,7-dihydroxitriptamine (a drug that depletes 5-HT) microinjection into MPOA on plasma LH in ovariectomized rats treated with oil, estradiol (E(2)) or E(2) plus progesterone (P(4)). Pargyline prevented LH surge on proestrus without altering its basal secretion. Throughout the estrous cycle, pargyline augmented both 5-HT and DA contents in approximately 300% and NA content in 50% in the MPOA. During proestrus, pargyline stimulated nNOS activity at 9 h and inhibited it at 11 h. nNOS expression was inhibited by pargyline at 15 h. Depletion of 5-HT content in the MPOA increased LH secretion in ovariectomized rats treated with E(2) plus P(4), but it did not modify in rats treated with either oil or E(2). Therefore, the present data show that pargyline treatment can inhibit proestrus LH surge through a mechanism that may involve 5-HT and NO systems in the MPOA. Moreover, the effect of 5-HT in the MPOA for limiting LH surge seems to depend on plasma levels of E(2) and P(4).

Dopamine is metabolised by different enzymes along the rat nephron.

The purpose of this study was to determine the basal levels of dopamine (DA) and to examine the enzymes involved in DA metabolism in different microdissected nephron segments from rat kidneys. Segments were incubated with DA (50 nM) or DA plus monoamine oxidase (MAO) or catechol-O-methyl transferase (COMT) inhibitors. Basal DA levels were higher in the proximal convoluted tubule (PCT, 10.8+/-3.7 pg/mm) and in the medullary collecting duct (MCD, 10.9+/-4.0 pg/mm) than in the medullary thick ascending limb of Henle's loop (MTAL, 4.9+/-0.9 pg/mm) (P<0.05). The percentage of exogenously added DA that was not metabolised was similar in both PCT (67+/-13%) and MCD (65+/-5%) and lower in MTAL (35+/-7%), suggesting that MTAL is a major site of DA metabolism. Inhibition of MAO (pargyline 1 mM) significantly increased the basal content of DA and the percentage of the added non-metabolised DA (to 95+/-10%) in PCT but had no effect on MTAL or MCD. Conversely, inhibition of COMT (nitecapone or Ro-41-0960, both 1 mM) slightly increased the basal levels of DA only in MTAL, whereas the percentage of added DA not metabolised rose to 97+/-10% in MTAL and to 91+/-15% in MCD. COMT inhibition had no effect in PCT. In conscious rats pargyline (50 mg/kg) increased urinary DA from 680+/-34 to 1,128+/-158 ng/d/100 g BW (P<0.01) while nitecapone (40 mg/kg) produced a slight non-significant increment. Our results show that DA is present all along the rat nephron and that renal DA is metabolised continuously and predominantly by MAO in proximal segments, and by COMT in the more distal ones.

Dopamine and serotonin turnover rate in the retina of rabbit, rat, goldfish, and Eugerres plumieri: light effects in goldfish and rat.

The concentration of dopamine, and its metabolites 3,4-dihydroxyphenylacetic and homovanillic acids, as well as serotonin and its metabolite 5-hydroxyindoleacetic acid, were determined in the retina of two teleosts, C. auratus (goldfish) and E. plumieri (mojarra), and two mammals, R. norvegicus (rat) and O. cuniculus (rabbit). The turnover rate of these monoamines were investigated in the four species by the calculation of the ratio monoamine/metabolite as an indirect index, and in goldfish and rat by the inhibition of the synthesis with alpha-methyl-p-tyrosine or p-chlorophenylalanine, by the increase in dopamine or serotonin by the corresponding precursors, 3,4-dihydroxyphenylalanine or 5-hydroxytryptophan, and by inhibition of monoaminooxidase with pargyline. The modulation by light and dark stimulation was studied in the goldfish and the rat. Differences in the concentration and turnover rate were observed among the species. Serotonin concentration was higher in the teleosts. The administration of inhibitors of dopamine and serotonin synthesis differentially decreased the levels of the monoamines in the retina of goldfish and rat. The rate of formation of dopamine and serotonin by the corresponding precursors was much higher in the goldfish than in the rat. Pargyline administration decreased 3,4-dihydroxyphenylacetic and 5-hydroxyindoleacetic acids at different rates and time dependency in the retina of goldfish and rat. Dopamine and serotonin concentration did not exhibit high modifications by the inhibitor, suggesting the function of regulatory mechanisms or additional effect of pargyline at other sites different from monoaminooxidase.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid iodide transport is reduced by administration of monoamine oxidase A inhibitors to rats.

The present work was addressed to study a possible relationship between monoamine oxidase (MAO) and the thyroid iodide transport mechanism. Normal rats treated with clorgyline (a selective MAO-A inhibitor) or tranylcypromine (a non-selective MAO inhibitor) showed a significantly diminished thyroid MAO activity, while deprenyl and pargyline (MAO-B inhibitors) did not modify the thyroidal enzyme activity with respect to the control group. Under these conditions, in vivo iodide transport was reduced both by clorgyline and tranylcypromine administration whereas it remained unchanged after treatment with MAO-B inhibitors. The effect of MAO inhibitors on thyroid MAO activity and in vivo iodide transport was also evaluated in rats treated with exogenous thyrotrophin (TSH) after endogenous TSH secretion blockade produced by T4 administration. In this condition, thyroid MAO activity was significantly lowered by clorgyline and was not modified by deprenyl. In contrast to the results observed in normal rats, in vivo iodide transport in TSH-treated rats remained unaltered after treatment either with clorgyline or deprenyl. MAO activity evaluated in bovine thyroid follicles in primary culture was highly sensitive to low concentrations of clorgyline (< 10 nmol/l) and relatively insensitive to deprenyl, a finding that indicates a predominance of the MAO-A isoform in the follicular cells in culture. When clorgyline (0.1 and 1 mumol/l) or deprenyl (1 mumol/l) were added to the culture medium, no modifications in the active transport of iodide were observed. These results indicate the absence of a direct linkage between thyroid MAO activity and the active iodide transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of tyramine transfer and metabolism using an in vitro intestinal preparation.

The duodenal transfer and metabolism of [3H]tyramine from sacs and perfused segments of rat intestine were determined. In sacs, a linear relationship between the steady-state transfer rate of total tritium and the initial mucosal tyramine concentration was observed, suggesting that the clearance is the same at different concentrations. In duodenal perfusions, there was no significant difference in the amount of total tritium removed between control and everted tissues, whether the flow was 0.2 or 2.0 mL/min. The percentage of [3H]tyramine extracted from the gut lumen depended on the flow rate. About 30-40% of the extracted drug was metabolized; this value decreased to 20% when the rats were pretreated with pargyline. The data support the idea that the transfer mechanism for tyramine is simple diffusion.

Stimulation of the hypothalamo-pituitary-adrenocortical axis by the central serotonergic pathway: involvement of endogenous corticotropin-releasing hormone but not vasopressin.

Many reports indicate that serotonin plays a role in the regulation of the hypothalamo-pituitary-adrenocortical axis. The present study was designed to elucidate whether the activation of the central serotonergic pathway enhances adrenocorticotropin and corticosterone secretion, and if so, whether the CRH and vasopressin neuronal systems could be mediating this effect. Intraperitoneal administration of a low dose of L-5-hydroxytryptophan (an aromatic L-amino acid precursor of serotonin synthesis; 20 mg/kg bw, 30 minutes before the sacrifice) in rats pretreated with pargyline (a brain monoamine oxidase inhibitor, which enhances monoamine activity; 75 mg/Kg bw, 16 hours before the sacrifice) and carbidopa (a peripheral active inhibitor of the decarboxylation of aromatic L-amino acids, which would permit more monoamine precursor to be available to the brain; 50 mg/Kg bw, 90 minutes before the sacrifice) increased ACTH and corticosterone secretion in plasma. Such an effect was partially blocked by metergoline (a serotonin type-1 and-2 receptor blocker; 1 mg/Kg bw, 90 minutes before the sacrifice), but not by spiperone (a serotonin type-2 and dopamine receptor antagonist; 0.5 mg/Kg bw. 90 minutes before the sacrifice). The activation of the central serotonergic system enhanced the CRH content in the median eminence, whereas it decreased the content of this neuropeptide in the medial basal hypothalamus. These effects were fully abolished by metergoline, but not by spiperone pretreatment. The activation of the serotonergic pathway did not influence the vasopressinergic neuronal system. In vitro experiments using hypothalamic-median eminence fragments incubated with serotonin solutions indicate that this monoamine possesses a CRH releasing effect at concentrations of 1 microM or more.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of angiotensin II and bilateral nephrectomy on norepinephrine catabolism in central nervous system.

Effects of angiotensin II (AII) on norepinephrine (NE) catabolism in hypothalamus and medulla oblongata of male rats were studied. 3H-NE uptake, 3H-NE/3H-NE metabolites ratio (NE/MET) and monoamineoxidase (MAO) activity were measured in vitro in both organs. Lack of circulating AII was elicited by means of 48 h bilateral nephrectomy. Pargyline and bilateral nephrectomy increased NE uptake and NE/MET ratio, while in nephrectomized plus pargyline treated groups and additive effect on these results was observed in both organs. All decreased the NE/MET ratio. Pargyline reversed the latter effects of AII. The peptide increased MAO activity in both organs, while bilateral nephrectomy decreased the activity of the enzyme. The results showed that AII modulates NE catabolism by means of MAO activity, eventually at the presynaptic noradrenergic ending sites in the central nervous system.

Uptake and metabolism of 3H-(+/-)-noradrenaline in the isolated perfused rat liver.

The influence of inhibitors of metabolism and uptake of noradrenaline on the 3H-noradrenaline removal from the perfusion fluid by the isolated rat liver was studied. Livers were perfused with 3 nmol/l 3H-noradrenaline and 3H-noradrenaline and 3H-metabolites were determined in effluent, liver and bile. After the perfusion with 14,900 +/- 920 dpm.g-1.min-1 during 90 min, cumulative removal of tritium was 323,574 +/- 63,103 dpm/g. 3H-metabolites recovered from the liver after 90 min perfusion represented 71.1 +/- 9.0% of total metabolite formation. Only the OMDA-fraction appeared in the perfusate; its approach to steady state of efflux was slow. The inhibition either of MAO or COMT changed neither the total removal of tritium nor the 3H-metabolites recovered from the liver. Cocaine (10 mumol/l) reduced the accumulation of 3H-noradrenaline in the liver. The uptake2 inhibitor corticosterone (30 mumol/l) diminished total removal of tritium and the 3H-metabolites recovered from the liver without changing the accumulation of 3H-noradrenaline. The hypothesis of two different compartments, one responsible for the metabolism and the other for the accumulation of the amine is discussed.

Serotonin containing neurons in the retina of the teleost Eugerres plumieri.

The concentration and localization of serotonin was determined in the retina of the teleost Eugerres plumieri by using high performance liquid chromatography (HPLC) and immunohistochemical techniques. Serotonin and dopamine were measured simultaneously, their concentrations in the retina being 77 +/- 8 and 516 +/- 23 ng/mg tissue respectively. Treatment of the animals with pargyline significantly increased the levels of dopamine and serotonin. When retinas were treated with the neurotoxin 5,6-dihydroxytryptamine, the level of serotonin was reduced by more than 90% while the dopamine content only diminished by 20% when compared to controls. By using immunohistochemistry with a monoclonal anti-serotonin antibody it was possible to localize this amine in cell bodies of a population of amacrine cells with processes extending mainly into a thin layer of the most external lamina of the inner plexiform layer. Very few ramifications were seen projecting to the internal lamina of this layer. When visualized in flat mount preparations, dense arborization of fluorescent processes was observed. This is the first direct evidence that serotonin is apparently present in amacrine cells of the retina of E. plumieri with a distribution of the serotonergic terminals similar to goldfish but somewhat different when compared to other species.

Effects of ethylephrine on the rat atrial pacemaker.

Ethylephrine, assayed in isolated rat atria, as a dose-chronotropic response curve showed a typical bell-dome shape of the sympathomimetic amines. Yet, on the same basis, it was less powerful than epinephrine, norepinephrine or isoproterenol. Pretreatment with reserpine provoked supersensitivity and increase in the maximum. As well, previous administration of pargyline to the animals resulted in augmented accelerating effects, either in normal or reserpinized preparations. Cocaine or phentolamine shifted the dose-response curve to the left. On the contrary, propranolol, produced a marked action, decelerating the effects of ethylephrine and also decreased the maxima with higher doses. It is concluded that ethylephrine: a) is a direct-acting sympathomimetic amine; b) it brings beta-receptor stimulation; c) a certain degree of alpha-receptor decelerating effect is also involved; d) it is a good substrate of monoaminoxidase.

[On the mode of action of serotonin in the isolated atrium of the hamster. I. Serotonin: amine of mixed action (author's transl)]. / Sobre el mecanismo de acción de la serotonina en la auricula aislada de hamster. I. Serotonina: amina de acción mixta.

5-hydroxytryptamine (serotonin) produces a positive chronotropic effect in the isolated atrium of the hamster. The characterization of this effect using reserpine pretreatment, propranolol, pargyline, 6-hydroxydopamine or the combination of some of those drugs enable us to conclude that serotonin is an amine of mixed action in the isolated atrium of the hamster, that is, its positive chronotropic effect has a direct component, which is obtained with lower concentrations of agonist and an indirect component through the liberation of endogenous noradrenaline from the sympathetic nerve terminals. The highest concentrations of serotonin are responsible of that component. Pargyline potentiates the indirect component of 5-HT, because inhibition of intraneuronal monoamine oxidase (MAO) avoids the degradation of the noradrenaline released, but it does not potentiate the direct component, indicating that postsynaptic cardiac MAO has little importance in the metabolism of serotonin administered exogenously.