Effects of the co-administration of mirtazapine and paroxetine on serotonergic neurotransmission in the rat brain. Inhibitory effect of serotonergic drugs on contractile response of the rat vas deferens to electrical nerve stimulation: in vivo study. Regulation of phosphorylation of cyclic AMP response element-binding protein by paroxetine treatments. Rx drugs

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Eur Neuropsychopharmacol. 2000 May;10(3):177-88.
Effects of the co-administration of mirtazapine and paroxetine on serotonergic neurotransmission in the rat brain.

Besson A, Haddjeri N, Blier P, de Montigny C.

Neurobiological Psychiatry Unit, McGill University, 1033 Pine Avenue, West Montreal, Quebec, Canada.

The alpha(2)-adrenoreceptor antagonist mirtazapine, which is also a 5-HT(2), 5-HT(3) and H(1) receptors antagonist and the selective serotonin (5-HT) reuptake inhibitor paroxetine are effective antidepressant drugs which enhance 5-HT neurotransmission via different mechanisms. The present studies were undertaken to determine whether the mirtazapine-paroxetine combination could induce an earlier and/or a greater effect on the 5-HT system than either drug alone. Using in vivo electrophysiological paradigms, the firing activity of dorsal raphe 5-HT neurons was decreased by 70% in rats treated with paroxetine (10 mg/kg/day, s.c.) for 2 days and was back to normal after 21 days. In contrast, a 2-day treatment with mirtazapine (5 mg/kg/day, s.c.) did not alter the firing of 5-HT neurons whereas it was increased by 60% after 21 days of treatment. A low dose of mirtazapine (5 mg/kg/day, s.c.x2 days) failed to offset the decremental effect of paroxetine on the 5-HT neuron firing activity, but a higher dose (10 mg/kg/day, s.c.x2 days) did attenuate the decremental effect of paroxetine. In the dorsal hippocampus, neither mirtazapine (5 mg/kg/day, s.c.) nor a paroxetine (10 mg/kg/day, s.c.) treatment altered the responsiveness of 5-HT(1A) receptors to microiontophoretically-applied 5-HT. Both in controls and in rats treated for 2 days with paroxetine alone, the administration of the 5-HT(1A) antagonist WAY 100635 (25-100 microg/kg, i.v.) did not change the firing activity of dorsal hippocampus CA(3) pyramidal neurons. However, WAY 100635 increased significantly the firing activity of these neurons in rats treated with mirtazapine alone but to a greater extent with both mirtazapine and paroxetine for 2 days. After 21 days of treatment, WAY 100635 increased to a greater degree the firing rate of CA(3) pyramidal neurons in rats which received the combination over rats given either drug alone. It is concluded that the mirtazapine-paroxetine combination shortened the delay in enhancing the tonic activation of postsynaptic 5-HT(1A) receptors and produced a greater activation of the postsynaptic 5-HT(1A) receptors than either drug given alone. The present results suggested that mirtazapine may have a faster onset of action than a SSRI, and that the co-administration of mirtazapine and paroxetine may accelerate the antidepressant response and as well as being more effective than either drug alone.

online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10793320&dopt=Abstract

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J Urol. 2000 Jun;163(6):1988-91.
Inhibitory effect of serotonergic drugs on contractile response of the rat vas deferens to electrical nerve stimulation: in vivo study.

Kim SC, Seo KK, Han JH, Lee MY.

Department of Urology and Physiology, College of Medicine, Chung-Ang University, Seoul, Korea.

PURPOSE: To evaluate, in vivo, the inhibitory effects of certain serotonergic drugs on the contractile response of the rat seminal tract to electrical stimulation of the hypogastric nerve. MATERIALS AND METHODS: Twenty-five Sprague Dawley rats (250 to 300 gm. each) were equally divided into 5 groups based on experimental agent; normal saline, clomipramine, sertraline, paroxetine, and fluoxetine. The hypogastric nerve was electrically stimulated and the intraluminal pressure of the vas deferens was measured, both pretreatment and 30 minutes after intravenous injection of four different doses (0.1 to 20 x the therapeutic dose) of each agent. Variations of responses relative to the time after administration of each agent (at 10- and 20-fold concentration) were also observed. RESULTS: All serotonergic drugs caused dose-dependent inhibition of elevation in intraluminal pressure of the vas deferens (p <0.05). The inhibitory effect of clomipramine was significantly better (p <0. 05) than that of fluoxetine at a 1-fold dose, while no significant differences were noted among clomipramine, sertraline and paroxetine. At doses of 10- and 20-fold, clomipramine had the strongest inhibitory effect, followed by sertraline and paroxetine, then fluoxetine (p <0.05). No differences were found in the inhibitory effects of the drugs studied, as a function of the time after injection. CONCLUSIONS: Clomipramine was the most potent drug for inhibition of elevation in intraluminal pressure of the rat vas deferens induced by electrical stimulation of the rat hypogastric nerve. The stronger inhibitory effect of clomipramine than the selective serotonin reuptake blockers suggests a possible peripheral action of clomipramine in addition to its central serotonergic action.

online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10799244&dopt=Abstract

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Clin Neuropharmacol. 2000 Mar-Apr;23(2):106-9.
Regulation of phosphorylation of cyclic AMP response element-binding protein by paroxetine treatments.

Morinobu S, Russel DS, Sugawara S, Takahashi M, Fujimaki K.

Department of Psychiatry and Neurosciences, Hiroshima University School of Medicine, Japan.

The present study was undertaken to examine the effect of paroxetine, a selective serotonin reuptake inhibitor, on the phosphorylation of cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) in the rat brain. Single administration of paroxetine significantly induces the phosphorylation of CREB in the rat frontal cortex and hippocampus in a time-dependent manner. Repeated administration of paroxetine attenuates CREB phosphorylation in response to acute paroxetine challenge. These findings suggest that the enhancement of intracellular signal transduction after the activation of serotonin receptors may be attenuated after chronic paroxetine treatment, and this attenuation may be, at least in part, involved in the therapeutic efficacy of paroxetine.

online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10803801&dopt=Abstract

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