Dopamine agonist signalling in the hypothalamus of female rats is independent of calcium-dependent kinases.

We have previously demonstrated that dopamine agonist, SKF38396 (SKF), can substitute for progesterone in the facilitation of female reproductive behaviour in oestradiol benzoate-primed female rats and mice. We also reported that both progesterone- and SKF-initiated signalling were mediated by the cAMP-dependent protein kinase A signal transduction cascade. As the rapid effects of progesterone are also mediated by calcium-dependent kinases, calcium- and calmodulin-dependent kinase (CaMKII) and protein kinase (PKC), we sought to determine whether SKF-initiated signalling also recruited calcium as a second messenger. We measured the changes in the activation of CaMKII and PKC in the ventromedial nucleus (VMN) of the hypothalamus and preoptic area (POA) of the rat brain, which are the two regions implicated in the regulation of female reproductive behaviour in rodents. We measured the basal activities representing the activation of the kinases by in vivo treatments, as well as the total kinase activities assayed in the presence of exogenous cofactors in vitro. We report that, in contrast to progesterone-initiated signalling, there was no recruitment of calcium by SKF in the hypothalamus, as shown by the absence of changes in CaMKII activities in the VMN and POA. Furthermore, SKF-treatment resulted in a rapid increase in calcium-independent basal PKC activity in the VMN but not the POA. These rapid changes were not the result of changes in PKC protein levels or phosphorylation status. These data indicate that progesterone- and SKF-recruit distinct signalling molecules within the same regions of the brain to activate region-specific signal transduction pathways.