8-OH-DPAT attenuates isoproterenol- but not forskolin-stimulated accumulation of cAMP in mediobasal hypothalamus

Cellular and molecular mechanisms of action of ovarian steroid hormones II: Regulation of sexual behavior in female rodents

Female sexual behaviors in rodents (lordosis and appetitive or "proceptive" behaviors) are induced through a genomic mechanism by the sequential actions of estradiol (E2) and progesterone (P), or E2 and testosterone (T) at their respective receptors. However, non-steroidal agents, such as gonadotropin-releasing hormone (GnRH), Prostaglandin E2 (PGE2), noradrenaline, dopamine, oxytocin, α-melanocyte stimulating hormone, nitric oxide, leptin, apelin, and others, facilitate different aspects of female sexual behavior through their cellular and intracellular effects at the membrane and genomic levels in ovariectomized rats primed with E2. These neurotransmitters often act as intermediaries of E2 and P (or T). The classical model of steroid hormone action through intracellular receptor binding has been complemented by an alternative scenario wherein the steroid functions as a transcription factor after binding the receptor protein to DNA. Another possible mechanism occurs through the activation of second messenger systems (cyclic AMP, cyclic GMP, calcium), which subsequently initiate phosphorylation events via diverse kinase systems (protein kinases A, G, or C). These kinases target the progesterone receptor (PR) or associated effector proteins that connect the PR to the trans-activation machinery. This may also happen to the androgen receptor (AR). In addition, other cellular mechanisms could be involved since the chemical structure of these non-steroidal agents causes a change in their lipophobicity that prevents them from penetrating the cell and exerting direct transcriptional effects; however, they can exert effects on different components of the cell membrane activating a cross-talk between the cell membrane and the regulation of the transcriptional mechanisms.

Serotomide and safflomide modulate forskolin-stimulated cAMP formation via 5-HT1 receptor

Serotomide (trans-N-caffeoylserotonin) and safflomide (trans-N-caffeoyltryptamine) belong to serotonin-derived phenylpropenoid amides found in plants. In this paper, serotomide and safflomide were investigated to determine their effects on serotonin receptor 5-HT1 in the renal epithelial (OK) cells, due to their structural similarity to 5-HT1 receptor ligands. At the concentration of 10 microM, serotomide was able to inhibit forskolin-stimulated cAMP formation in the OK cells by 31% (p<0.019). The inhibition was repressed by Nan-190 and spiperone (5-HT1 antagonists), suggesting that serotomide suppresses cAMP formation via binding to 5-HT1 receptors in the OK cells. Meanwhile, safflomide could not inhibit forskolin-stimulated cAMP formation at the same concentration (10 microM), but repress the inhibition of forskolin-stimulated cAMP by serotonin agonists (e.g., serotonin and 8-OH-DPAT) by 31% (p<0.018), suggesting that safflomide may block 5-HT1 receptors in a similar way to Nan-190 and spiperone. All together the data indicate that serotomide and safflomide may be potent compounds that respectively act to activate and to block 5-HT1 receptors on OK cells.

Concomitant activation of adenylyl cyclase suppresses the opposite influences of CB(1) cannabinoid receptor agonists on tyrosine hydroxylase expression

The CB(1) cannabinoid receptor shows complex interactions with intracellular signalling partners, and responses to cannabinoid ligands are likely to be influenced by concomitant inputs modifying the overall tone of signalling cascades. This appears even more relevant as we previously evidenced opposite regulations of tyrosine hydroxylase (TH) expression by the two common cannabinoid agonists HU 210 and CP 55,940. Therefore, we studied the consequences of manipulating adenylyl cyclase activity with forskolin on the regulation of TH gene transcription in neuroblastoma cells (N1E-115). Reporter gene experiments performed with the luciferase sequence cloned under the control of modified fragments of the TH gene promoter revealed that the AP-1 consensus sequence is essential for cannabinoid-mediated regulation of TH expression. Consistently, inhibition of PKC totally blocked the responses mediated by both HU 210 and CP 55,940. In addition, forskolin which boosts adenylyl cyclase activity remarkably modified the responses to the cannabinoid agonists. Thus, in these conditions, both agonists efficiently reduced TH gene promoter activity, a response requiring functional PKA/CRE-dependent signallings. Finally, the modulations of the promoter were inhibited in pertussis toxin treated cells, suggesting that responses to both agonists are mediated through G(i/o)-dependent mechanisms. Emphasising on the importance of functional selectivity at GPCRs, these data demonstrate that the concomitant activation of adenylyl cyclase by forskolin strongly influences the biochemical responses triggered by distinct cannabinoid agonists. Together our results suggest that the physiological modulation of TH expression by cannabinoid agonists in dopaminergic neurons would be influenced by additional endogenous inputs.