Effects of DPDPE (a specific delta-opioid receptor agonist) and naloxone on hypothalamic monoamine concentrations during the pre-ovulatory LH surge in the rat

Abstract

We have investigated the inter-relationship between the opioid and aminergic systems in the control of secretion of the pro-oestrous LH surge and the involvement of d-opioid receptor subtypes in this process. Conscious female rats bearing a cannula in the femoral artery were injected i.p. with a selective d-opioid receptor agonist (DPDPE) either alone or with the opioid antagonist (naloxone) at 1300 h on the day of pro-oestrus. Blood samples were collected hourly between 1500 h and 1900 h, and plasma LH levels were measured by RIA. At the end of this period (1900 h), the animals were autopsied and the concentrations of the amines (noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5HT)) and their metabolites (dihydroxyphenolglycol (DHPG) and 5-hydroxyindoleacetic acid (5HIAA), metabolites of NA and 5HT respectively) were determined by HPLC with electrochemical detection in the medial preoptic area, suprachiasmatic nucleus, median eminence and arcuate nucleus.DPDPE abolished the LH surge and concomitantly decreased hypothalamic NA and DHPG concentrations in all the areas examined. The levels of DA, 5HT and 5HIAA were also reduced in all hypothalamic regions studied, except DA and 5HIAA in the suprachiasmatic nucleus. Naloxone reversed these inhibitory effects of the d-agonist.We conclude that activation of d-opioid receptors may exert an inhibitory effect on LH release. The effect is probably an indirect one mediated by the monoaminergic systems, as they are suppressed by DPDPE in nearly all the hypothalamic regions studied.

Mechanisms underlying δ- and μ-opioid receptor agonist-induced increases in extracellular dopamine level in the nucleus accumbens of freely moving rats

“…Normally, the effects of opioids-including δ-and μ-opioid receptor agonists-are reduced by pretreat- ment with the non-selective opioid receptor antagonist naloxone (6,7). However, caution is necessary when using increasing doses of naloxone to investigate the roles of opioid receptors, because high doses of this compound can produce non-specific effects (8).…”

The Effects of Chronic Asprosin Administration on Sense of Smell and Sexual Behavior in Female Rats

“…Vaginal smears were applied to the study rats that showed 3 regular estrus cycles (4–5 days) before starting the behavioral tests [41]. The vaginal smear sample of each rat was taken at the same time every day (between 10.00 and 12.00) using a pipette filled with 200 µL saline and was then placed on microscope slides and viewed freshly under a light microscope at ×10 and ×40 magnification [42, 43]. Behavioral tests were performed on the rats, which were determined to have a regular cycle, at the 7th and 8th weeks of the injections, when they were in the estrus phase, and in other words, when they were sexually active.…”

“…The degree of lordosis and lordosis ratio are frequently used to evaluate the sexual performance in female rats, an increase in this ratio is considered to be correlated with increased female arousal (31,41,42). Lordosis is the final stage of sexual behavior in female rats [49,50].…”

Activation of opioid μ-receptors, but not δ- or κ-receptors, switches pulmonary C-fiber-mediated rapid shallow breathing into an apnea in anesthetized rats

“…To this end, PBG was injected into the right atrium to evoke RSB in anesthetized and spontaneously breathing rats. This protocol was repeated in three groups of rats (n = 7/group) 5 min after systemic administration of fentanyl (μ-receptor agonist, 8 μg/kg (Brookes et al , 2006)), DPDPE (δ-receptor agonist, 2 mg/kg (Yilmaz et al , 1998)), or U-50488H (κ-receptor agonist, 4 mg/kg (Pei et al , 2006)). Owing to that fentanyl rather than DPDPE or U-50488H was capable of switching the RSB into an apnea in our pilot studies, three-fold higher concentrations of DPDPE and U-50488H were applied in two other rats to ensure no effect of them.…”