We have investigated the role of m- and k-opioid receptors in the central control of preovulatory LH and FSH release in the proestrous rat. Animals were anesthetized with chloral hydrate at 14:00 h on proestrus day. Following femoral artery cannulation, they were mounted in a stereotaxic apparatus. Morphine and U-50488H (benzene-acetamide methane sulphonate) were infused intracerebroventricularly either alone or in combination with naloxone and MR1452, respectively. Controls received sterile saline alone. Blood samples were obtained at hourly intervals between 15:00 h and 17:00 h. Plasma LH and FSH levels were measured by radioimmunoassay. Morphine did not significantly change plasma LH levels at 15:00 h and 16:00 h sampling intervals. A significant increase was observed at 17:00 h compared to the controls (p<0.05). U-50488H significantly increased LH levels at 16:00 h and 17:00 h (p<0.05). The co-administration of naloxone and MR1452 with m- and k-agonist had no significant effect on LH levels at any sampling interval. In all groups, LH levels showed a linear rise over the sampling period between 15:00 h and 17:00 h. None of the treatments significantly altered plasma FSH levels which however, declined towards the end of the afternoon surge. In conclusion, we suggest that the secretion of LH and FSH is differentially regulated by m- and k-opioid receptors. It is thought that in all groups chloral hydrate interfered with the LH surge secretory systems., S. Kumru, M. Şimşek, B. Yilmaz, E. Sapmaz, S. Kutlu, S. Sandal, S. Canpolat., and Obsahuje bibliografii
b1_Large number of extracellular signals is received by plasma membrane receptors which, upon activation, transduce information into the target cell interior via trimeric G-proteins (GPCRs) and induce activation or inhibition of adenylyl cyclase enzyme activity (AC). Receptors for opioid drugs such as morphine ( μ-OR, δ-OR and κ-OR) belong to rhodopsin family of GPCRs. Our recent results indicated a specific up-regulation of AC I (8-fold) and AC II (2.5-fold) in plasma membranes (PM) isolated from rat brain cortex exposed to increasing doses of morphine (10-50 mg/kg) for 10 days. Increase of ACI and ACII represented the specific effect as the amount of ACIII-ACIX, prototypical PM marker Na, K-ATPase and trimeric G-protein α and β subunits was unchanged. The up-regulation of ACI and ACII faded away after 20 days since the last dose of morphine. Proteomic analysis of these PM indicated that the brain cortex of morphine-treated animals cannot be regarded as being adapted to this drug because significant up-regulation of proteins functionally related to oxidativ e stress and alteration of brain energy metabolism occurred. The number of δ-OR was increased 2-fold and their sensitivity to monovalent cations was altered. Characterization of δ-OR-G-protein coupling in model HEK293 cell line indicated high ability of lithium to support affinity of δ-OR response to agonist stimulation. Our studies of PM structure and function in context with desensitization of GPCRs action were extended by data indicating part icipation of cholesterol-enriched membrane domains in agonist-specific internalization of δ-OR. In HEK293 cells stably expressing δ-OR-G i 1 α fusion protein, depletion of PM cholesterol was associated with the decrease in affinity of G-protein response to agonist stimulation, whereas maximum response was unchanged., b2_drophobic interior of isolated PM became more “fluid”, chaotically organized and accessible to water molecules. Validity of this conclusion was supported by the analysis of an immediate PM environment of cholesterol molecules in living δ -OR-G i 1 α-HEK293 cells by fluorescent probes 22- and 25-NBD-cholesterol. The alteration of plasma membrane structure by cholesterol depletion made the membrane more hydrated. Unders tanding of the positive and negative feedback regulatory loops among different OR-initiated signaling cascades (μ-, δ -, and κ-OR) is crucial for understanding of the long-term mechanisms of drug addiction as the decrease in functional activity of μ-OR may be compensated by increase of δ-OR and/or κ-OR signaling., H. Ujčíková ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy
The circadian rhythms of many behavioral and physiological functions are regulated by the major circadian pacemaker in the suprachiasmatic nucleus. Long-term opiate addiction and drug withdrawal may affect circad ian rhythmicity of various hormones or the sleep/activity pattern of many experimental subjects; however, limited research has been done on the long -term effects of sustained opiate administration on the intrinsic rhythmicity in the suprachiasmatic nucleus and pineal gland. Here we compared the effects of repeated daily treatment of rats with morphine or methadone and subsequent naloxone-precipitated withdrawal on the expression of the Per1, Per2, and Avp mRNAs in the suprachiasmatic nucleus and on arylalky lamine N-acetyltransferase activity in the pineal gland. We revealed that 10-day administration and withdrawal of both these drugs failed to affect clock genes and Avp expression in the SCN. Our results indicate that opioid-induced changes in behavioral a nd physiological rhythms originate in brain structures downstream of the suprachiasmatic nucleus regulatory output pathway. Furthermore, we observed that acute withdrawal from methadone markedly extended the period of high night AA -NAT activity in the pine al gland. This suggests that withdrawal from methadone, a widely used drug for the treatment of opioid dependence, may have stronger impact on melatonin synthesis than withdrawal from morphine., D. Pačesová, J. Novotný, Z. Bendová., and Obsahuje bibliografii