Role of dorsal raphe nucleus 5-HT(1A) and 5-HT(2) receptors in tonic immobility modulation in guinea pigs

Tonic immobility (TI) is an innate defensive behavior characterized by a state of physical inactivity and diminished responsiveness to environmental stimuli. Behavioral adaptations to changes in the external and internal milieu involve complex neuronal network activity and a large number of chemical neurotransmitters. The TI response is thought to be influenced by serotonin (5-HT) activity in the central nervous system (CNS) of vertebrates, but the neuronal groups involved in the mechanisms underlying this behavior are poorly understood. Owing to its extensive afferents and efferents, the dorsal raphe nucleus (DRN) has been implicated in a great variety of physiological and behavioral functions. in the current study, we investigated the influence of serotonergic 5-HT(1A) and 5-HT(2) receptor activity within the DRN on the modulation of TI behavior in the guinea pig. Microinjection of a 5-HT(1A) receptor agonist (8-OH-DPAT, 0.01 and 0.1 mu g) decreased TI behavior, an effect blocked by pretreatment with WAY-100635 (0.033 mu g), a 5-HT(1A) antagonist. In contrast, activation of 5-HT(2) receptors within the DRN (alpha-methyl-5-HT, 0.5 mu g) increased the TI duration, and this effect could be reversed by pretreatment with an ineffective dose (0.01 mu g) of ketanserine. Since the 5-HT(1A) and 5-HT(2) agonists decreased and increased, respectively, the duration of TI, different serotonin receptor subtypes may play distinct roles in the modulation of TI in the guinea pig. (C) 2009 Elsevier B.V. All rights reserved.

Downregulation of Melanocortin-4 Receptor during Refeeding and its Modulation by Adrenalectomy in Rats

Melanocortin system and corticotropin releasing hormone (CRH) are implicated in the control of feeding behavior. Besides its anorexigenic effect on food intake, CRH is one of the most important regulators of hypothalamic-pituitary-adrenal (HPA) axis activity. Therefore, there could be an interplay between HPA axis activity and melanocortin system. We investigated the expression of melanocortin-4 receptor (MC4-R) mRNA in the hypothalamus of rats after 14 days of food restriction or after a fasting-refeeding regimen, in sham or adrenalectomized rats. Male Wistar rats were subjected to free access to food or food ingestion restricted for 2 h a day (8-10 AM) during 14d, when plasma corticosterone, ACTH, insulin, leptin concentrations, and MC4-R mRNA expression were determined before and after refeeding. Another set of rats was fasted for 48 h, followed by refeeding during 2 or 4 h on the seventh day after adrenalectomy (ADX) or sham surgery. On the day of the experiment, rats were anesthetized and perfused and the brain processed for MC4-R mRNA by in situ hybridization. Long-term reduction of food intake, either secondary to food restriction or adrenalectomy, reduced body weight gain and also leptin and insulin plasma concentrations. Food ingestion reduced MC4-R expression in the paraventricular nucleus in naive rats subjected to food restriction and also in sham rats fasted for 48 h. However, after ADX, MC4-R expression was not changed by refeeding. In conclusion, the present data indicate that MC4-R expression is downregulated by food ingestion and this response could be modulated by glucocorticoid withdrawal.

Pharmacokinetics of lidocaine and its metabolite in peridural anesthesia administered to pregnant women with gestational diabetes mellitus

Background Peridural blockade with lidocaine, bupivacaine, and fentanyl is an anesthetic procedure extensively used in obstetrics, justifying the pharmacokinetic study of these drugs during labor. Objective To investigate the influence of the physiopathological changes of gestational diabetes mellitus (GDM) on the pharmacokinetics of lidocaine and its metabolite monoethylglycinexylidide (MEGX) in pregnant women subjected to peridural anesthesia. Patients and methods Ten normal pregnant women (group 1) and six pregnant women with GDM (group 2) were studied, all of them at term. The patients received 200 mg 2% lidocaine hydrochloride without a vasoconstrictor by the peridural locoregional route. Maternal blood samples were collected at predetermined times for the analysis of lidocaine and MEGX by chromatography and pharmacokinetic analysis. Results The median pharmacokinetic parameters of lidocaine for groups 1 and 2 (P <= 0.05), respectively, were as follows: for Cmax 879.11 and 1,145.58 ng/ml, AUC(0-infinity) 256.01 and 455.95 wg min(-1) ml(-1), Cl/f/kg 10.61 and 5.64 ml min(-1) kg(-1), and Vd/f/kg 3.26 and 2.19 L/kg. The median pharmacokinetic parameters of MEGX for groups 1 and 2 (P <= 0.05), respectively, were as follows: for Cmax 82.71 and 141.38 ng/ml, Tmax 44.71 and 193.14 min, t(1/2)alpha 7.64 and 59.77 min, alpha 0.097 and 0.012/min, and AUC(0-infinity) 29.91 and 108.23 mu g min(-1) ml(-1). Conclusion The present data permit us to conclude that the apparent clearance of lidocaine and MEGX was reduced in diabetic patients compared to normal women, suggesting that GDM inhibits the CYP1A2/CYP3A4 isoforms responsible for the metabolism of this drug and its metabolite.

Distribution of Bupivacaine Enantiomers and Lidocaine and Its Metabolite in the Placental Intervillous Space and in the Different Maternal and Fetal Compartments in Term Pregnant Women

The aim of this study is to determine the concentrations of lidocaine and its metabolite, monoethylglycine xylidide (MEGX), and of the enantiomers of bupivacaine in maternal and fetal compartments. Ten healthy pregnant women were submitted to epidural anesthesia. Drug concentrations were determined in the maternal vein, fetal umbilical artery and vein, and the placental intervillous space. The highest concentrations of the bupivacaine enantiomers lidocaine and of lidocaine and of its MEGX metabolite were detected in maternal plasma and in the placental intervillous space. The placental transfer was 33% for the (+)-(R)-bupivacaine enantiomer and 31% for the (-)-(S)-bupivacaine enantiomer. For lidocaine and its MEGX metabolite, respective placental transfers were 60% and 43%. Lidocaine concentration in the fetal umbilical vein was 1.46 times higher than in the fetal umbilical artery. The highest concentrations of lidocaine and its metabolite and of the enantiomers of bupivacaine were detected in the placental intervillous space. The higher lidocaine concentrations in the fetal umbilical vein than in the fetal umbilical artery suggest that there was tissue uptake of the drug or drug metabolization by the fetus.