piperidines and repinotan-hydrochloride

5-HT(1A)-R-agonist repinotan was shown to counteract a morphine-induced ventilatory depression but had pronociceptive effects at small doses (0.2 μg/kg). It remained to be clarified (1) whether a moderate dose of repinotan, sufficient to stimulate spontaneous breathing, impairs antinociception if plasma concentration decreases over time, and if (2) moderate doses prevent ventilatory depression if given before the opioid.. A dose-response curve of the repinotan effects on spontaneous minute ventilation during continuous remifentanil infusion in anesthetized rats was established to identify moderate doses: (1) tail-flick reflex latencies to assess nociception were recorded until 60 min after cessation of a continuous remifentanil infusion with or without a concomitant moderate repinotan dose (10 μg/kg), and (2) remifentanil boluses (2.5 μg/kg) were given after repinotan (10 and 20 μg/kg).. (1) Remifentanil-induced antinociception lasted only 5 min after infusion was stopped (tail-flick reflex latencies; median [interquartile range], 97 [54-100]% of maximum possible effect; P = 0.034), but was extended by repinotan (10 μg/kg) to 30 min (tail-flick reflex latencies, 100 [75-100]% of maximum possible effect; P = 0.031). Repinotan (10 μg/kg) alone did not have any significant antinociceptive effect. (2) The ventilatory depression by remifentanil boluses (2.5 μg/kg; minute ventilation, -65 [-81 to -56]%; P = 0.031, n = 5) was blunted by repinotan (20 μg/kg; minute ventilation, -24 [-53 to 13]%; P = 0.313, compared with the pretreatment level).. Repinotan prevented remifentanil-induced ventilatory depression in spontaneously breathing, anesthetized rats. Although repinotan did not depress nociception itself, it prolonged the profound antinociception after discontinuation of remifentanil infusion.

Topics: Analgesics, Opioid; Anesthetics, Intravenous; Animals; Benzopyrans; Blood Pressure; Dose-Response Relationship, Drug; Heart Rate; Hemodynamics; Hypnotics and Sedatives; Male; Pain Measurement; Piperidines; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT1A; Remifentanil; Respiratory Insufficiency; Respiratory Mechanics; Serotonin Receptor Agonists; Thiazoles

In the rat, postsynaptic 5-hydroxytryptamine2A receptors medial prefrontal cortex control the activity of the serotonergic system through changes in the activity of pyramidal neurons projecting to the dorsal raphe nucleus. Here we extend these observations to mouse brain. The prefrontal cortex expresses abundant 5- hydroxytryptamine2A receptors, as assessed by immunohistochemistry, Western blots and in situ hybridization procedures. The application of the 5-hydroxytryptamine2A/2C agonist DOI (100 microm) by reverse dialysis in the medial prefrontal cortex doubled the local release of 5-hydroxytryptamine. This effect was reversed by coperfusion of tetrodotoxin, and by the selective 5-hydroxytryptamine2A receptor antagonist M100907, but not by the 5-hydroxytryptamine2C antagonist SB-242084. The effect of DOI was also reversed by prazosin (alpha1-adrenoceptor antagonist), BAY x 3702 (5-hydroxytryptamine1A receptor agonist), NBQX (alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate/kainic acid antagonist) and 1S,3S-ACPD (mGluR II/III agonist), but not by dizocilpine (N-methyl-d-aspartate antagonist). alpha-Amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate mimicked the 5-hydroxytryptamine elevation produced by DOI, an effect also reversed by BAY x 3702. Likewise, the coperfusion of classical (chlorpromazine, haloperidol) and atypical antipsychotic drugs (clozapine, olanzapine) fully reversed the 5-hydroxytryptamine elevation induced by DOI. These observations suggest that DOI increases 5-hydroxytryptamine release in the mouse medial prefrontal cortex through the activation of local 5-hydroxytryptamine2A receptors by an impulse-dependent mechanism that involves/requires the activation of local alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate receptors. This effect is reversed by ligands of receptors present in the medial prefrontal cortex, possibly in pyramidal neurons, which are involved in the action of antipsychotic drugs. In particular, the reversal by classical antipsychotics may involve blockade of alpha1-adrenoceptors, whereas that of atypical antipsychotics may involve 5-hydroxytryptamine2A receptors and alpha1-adrenoceptors.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Aminopyridines; Anesthetics, Local; Animals; Antipsychotic Agents; Benzopyrans; Blotting, Western; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists; Fluorobenzenes; Immunohistochemistry; In Situ Hybridization; Indoles; Indophenol; Male; Mice; Mice, Inbred C57BL; Microdialysis; Piperidines; Prazosin; Prefrontal Cortex; Quinoxalines; Receptor, Serotonin, 5-HT2A; Receptors, Serotonin; RNA, Messenger; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Tetrodotoxin; Thiazoles; Time Factors