Kisspeptin in the medial amygdala and sexual behavior in male rats

AbstractThe medial amygdala (MeA) is crucial for sexual behavior; kisspeptin (Kiss1) also plays a role in sexual function. Kisspeptin receptor (Kiss1r) knockout mice display no sexual behavior. Recently Kiss1 and Kiss1r have been discovered in the posterodorsal subnucleus of the medial amygdala (MePD). We hypothesised that Kiss1 in the MePD may have an influence on male sexual behavior. To test this we bilaterally cannulated the MePD and infused kisspeptin-10 in male rats. This caused the rats to have multiple erections, an effect specific to Kiss1 receptor activation, because Kiss1r antagonism blocked the erectile response. When Kiss1 was infused into the lateral cerebroventricle, there were no observed erections. We also measured the plasma levels of LH when Kiss1 is infused into the MePD or lateral cerebroventricle; Kiss1 increased plasma LH to comparable levels when infused into both sites. We conclude that Kiss1 has a role in male sexual behavior, which is specific to the MePD

Role of amygdala kisspeptin in pubertal timing in female rats

To investigate the mechanism by which maternal obesity disrupts reproductive function in offspring, we examined Kiss1 expression in the hypothalamic arcuate (ARC) and anteroventral periventricular (AVPV) nuclei, and posterodorsal medial amygdala (MePD) of pre-pubertal and young adult offspring. Sprague-Dawley rats were fed either a standard or energy-dense diet for six weeks prior to mating and throughout pregnancy and lactation. Male and female offspring were weaned onto normal diet on postnatal day (pnd) 21. Brains were collected on pnd 30 or 100 for qRT-PCR to determine Kiss1 mRNA levels. Maternal obesity increased Kiss1 mRNA expression in the MePD of pre-pubertal male and female offspring, whereas Kiss1 expression was not affected in the ARC or AVPV at this age. Maternal obesity reduced Kiss1 expression in all three brain regions of 3 month old female offspring, but only in MePD of males. The role of MePD kisspeptin on puberty, estrous cyclicity and preovulatory LH surges was assessed directly in a separate group of post-weanling and young adult female rats exposed to a normal diet throughout their life course. Bilateral intra-MePD cannulae connected to osmotic mini-pumps for delivery of kisspeptin receptor antagonist (Peptide 234 for 14 days) were chronically implanted on pnd 21 or 100. Antagonism of MePD kisspeptin delayed puberty onset, disrupted estrous cyclicity and reduced the incidence of LH surges. These data show that the MePD plays a key role in pubertal timing and ovulation and that maternal obesity may act via amygdala kisspeptin signaling to influence reproductive function in the offspring

Effect of chronic intra-MePD administration of kisspeptin receptor antagonist on estrous cyclicity and proestrous LH surge.

<p>Representative examples of estrous cycle pattern (A—D) and LH profile (F and G) in rats treated with kisspeptin receptor antagonist (Peptide 234; 2 nmol in 6 μl/d for 14 days, starting on day 1), or vehicle (aCSF, artificial cerebrospinal fluid). Kisspeptin antagonism in the MePD significantly reduced the percentage of rats showing normal estrous cycles (E) as well as incidence of proestrus LH surges (H). *p<0.05 <i>vs</i> control, (n = 7–10 per group).</p

Day of vaginal opening, first estrus and body weight gain following intra-MePD infusion of Kisspeptin receptor antagonist.

<p>Bilateral micro-infusion of a kisspeptin receptor antagonist (Peptide 234; 2 nmol in 6 μl/d for 14 days, starting on postnatal day 21) into the MePD via osmotic mini-pump resulted in a significant delay in puberty onset, evidenced by day of vaginal opening (A), first estrus (B) without any significant change in body weight (C). *p<0.05 <i>vs</i> control, (n = 6–8 per group). Results represent mean ± S.E.M.</p

Confirmation of the cannula position within the MePD.

<p>Diagram from the rat brain atlas of Paxions and Watson [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0183596#pone.0183596.ref028" target="_blank">28</a>] showed the location of the MePD (marked) in relation to the optic tract (dot marked) (A). Cresyl violet stained brain slice in a representative animal showed accurate cannula position within the MePD. Arrow indicates the site corresponding to the tip of cannula (B).</p

Representative photomicrograph of punched brain sections.

<p>Representative photomicrograph of 300 μm thick coronal brain sections stained with crystal violet showing the position of punched posterodorsal medial amygdala (MePD) at approximately -3.14 from bregma (A), hypothalamic arcuate nucleus (ARC) at -3.14 and -3.30 mm from bregma (A and B) and anteroventral periventricular nucleus (AVPV) taken at approximately -0.46 mm from bregma (C). Arrows point to punched brain region. Lateral ventricles (LV), optic tract (ot), third ventricle (3V), and the dorsal third ventricle (D3V) are also indicated. Scale bar; 3mm.</p