Suchergebnisse

Morphine and related opioids are the mainstay of analgesic treatment, especially in patients suffering chronic pain. Besides their antinociceptive effects they may also exhibit anxiolytic-like properties that could contribute to pain relief. The pharmacological manipulation of the serotonergic system may not only modulate pain transmission and processing but also other behavioral effects of opioids. The present study aimed to analyze the effect of the concurrent treatment with citalopram, a selective serotonin reuptake inhibitor, on the antinociceptive, locomotor and anxiety-related effects induced by acute and subchronic administration of morphine in mice. Citalopram (15 mg/kg) enhanced the acute antinociceptive effects of morphine when concurrently administered as evidenced by a two-fold increase in the ED for the antinociceptive effect of morphine in the hot-plate test. Chronic studies also revealed that concurrent citalopram treatment (15 mg/kg) delayed the development of tolerance to the thermal antinociceptive effects of morphine. Additionally, morphine-induced hyperlocomotion was potentiated by citalopram as assessed in the open-field test and in the spontaneous activity recording in the home cage, a behavioral outcome to which tolerance or desensitization was not developed. Interestingly, chronic administration of both drugs promoted an anxiolytic effect as evidenced by the increased central activity in the open field test. Future investigations on this pharmacological interaction, such as the possible translational research in clinics, might have consequences in future strategies for the therapeutic management of pain. ; This research was supported by the grant SAF2010-15663 from the Spanish Government (MINECO). ; Peer Reviewed

Morphine and related opioids are the mainstay of analgesic treatment, especially in patients suffering chronic pain. Besides their antinociceptive effects they may also exhibit anxiolytic-like properties that could contribute to pain relief. The pharmacological manipulation of the serotonergic system may not only modulate pain transmission and processing but also other behavioral effects of opioids. The present study aimed to analyze the effect of the concurrent treatment with citalopram, a selective serotonin reuptake inhibitor, on the antinociceptive, locomotor and anxiety-related effects induced by acute and subchronic administration of morphine in mice. Citalopram (15 mg/kg) enhanced the acute antinociceptive effects of morphine when concurrently administered as evidenced by a two-fold increase in the ED50 for the antinociceptive effect of morphine in the hot-plate test. Chronic studies also revealed that concurrent citalopram treatment (15 mg/kg) delayed the development of tolerance to the thermal antinociceptive effects of morphine. Additionally, morphine-induced hyperlocomotion was potentiated by citalopram as assessed in the open-field test and in the spontaneous activity recording in the home cage, a behavioral outcome to which tolerance or desensitization was not developed. Interestingly, chronic administration of both drugs promoted an anxiolytic effect as evidenced by the increased central activity in the open field test. Future investigations on this pharmacological interaction, such as the possible translational research in clinics, might have consequences in future strategies for the therapeutic management of pain. ; This research was supported by the grant SAF2010-15663 from the Spanish Government (MINECO). We thank David Ramos and Raquel Lanza for their technical assistance in handling living animals. We kindly appreciate Belen Palacio support for video footage and editing and Dr. Albert Adell for the critical reading of the manuscript.

This is an open access article distributed under the terms of the Creative Commons Attribution License. ; The activation of G-protein coupled receptors by agonist compounds results in diverse biological responses in cells, such as the endocytosis process consisting in the translocation of receptors from the plasma membrane to the cytoplasm within internalizing vesicles or endosomes. In order to functionally evaluate endocytosis events resulted from pharmacological responses, we have developed an image analysis method -the Q-Endosomes algorithm- that specifically discriminates the fluorescent signal originated at endosomes from that one observed at the plasma membrane in images obtained from living cells by fluorescence microscopy. Mu opioid (MOP) receptor tagged at the carboxy-terminus with yellow fluorescent protein (YFP) and permanently expressed in HEK293 cells was used as experimental model to validate this methodology. Time-course experiments performed with several agonists resulted in different sigmoid curves depending on the drug used to initiate MOP receptor endocytosis. Thus, endocytosis resulting from the simultaneous activation of co-expressed MOP and serotonin 5-HT 2C receptors by morphine plus serotonin was significantly different, in kinetics as well as in maximal response parameters, from the one caused by DAMGO, sufentanyl or methadone. Therefore, this analytical tool permits the pharmacological characterization of receptor endocytosis in living cells with functional and temporal resolution. ; This work was supported by the SAF2010-15663 grant from the Spanish Government (MINECO). ; Peer Reviewed

The activation of G-protein coupled receptors by agonist compounds results in diverse biological responses in cells, such as the endocytosis process consisting in the translocation of receptors from the plasma membrane to the cytoplasm within internalizing vesicles or endosomes. In order to functionally evaluate endocytosis events resulted from pharmacological responses, we have developed an image analysis method –the Q-Endosomes algorithm– that specifically discriminates the fluorescent signal originated at endosomes from that one observed at the plasma membrane in images obtained from living cells by fluorescence microscopy. Mu opioid (MOP) receptor tagged at the carboxy-terminus with yellow fluorescent protein (YFP) and permanently expressed in HEK293 cells was used as experimental model to validate this methodology. Time-course experiments performed with several agonists resulted in different sigmoid curves depending on the drug used to initiate MOP receptor endocytosis. Thus, endocytosis resulting from the simultaneous activation of coexpressed MOP and serotonin 5-HT2C receptors by morphine plus serotonin was significantly different, in kinetics as well as in maximal response parameters, from the one caused by DAMGO, sufentanyl or methadone. Therefore, this analytical tool permits the pharmacological characterization of receptor endocytosis in living cells with functional and temporal resolution. ; This work was supported by the SAF2010-15663 grant from the Spanish Government (MINECO).