Inhibitory effect of GnRH on isolated rat uterine muscle contractility

Gonadotropin-releasing hormone (GnRH) modulates auditory processing in the fish brain

Gonadotropin-releasing hormone 1 (GnRH1) neurons control reproductive activity, but GnRH2 and GnRH3 neurons have widespread projections and function as neuromodulators in the vertebrate brain. While these extra-hypothalamic GnRH forms function as olfactory and visual neuromodulators, their potential effect on processing of auditory information is unknown. To test the hypothesis that GnRH modulates the processing of auditory information in the brain, we used immunohistochemistry to determine seasonal variations in these neuropeptide systems, and in vivo single-neuron recordings to identify neuromodulation in the midbrain torus semicircularis of the soniferous damselfish Abudefduf abdominalis. Our results show abundant GnRH-immunoreactive (-ir) axons in auditory processing regions of the midbrain and hindbrain. The number of extra-hypothalamic GnRH somata and the density of GnRH-ir axons within the auditory torus semicircularis also varied across the year, suggesting seasonal changes in GnRH influence of auditory processing. Exogenous application of GnRH (sGnRH and cGnRHII) caused a primarily inhibitory effect on auditory-evoked single neuron responses in the torus semicircularis. In the majority of neurons, GnRH caused a long-lasting decrease in spike rate in response to both tone bursts and playbacks of complex natural sounds. GnRH also decreased response latency and increased auditory thresholds in a frequency and stimulus type-dependent manner. To our knowledge, these results show for the first time in any vertebrate that GnRH can influence context-specific auditory processing in vivo in the brain, and may function to modulate seasonal auditory-mediated social behaviors.

Targeted disruption of LH receptor gene revealed the importance of uterine LH signaling

Numerous previous studies have demonstrated that LH and hCG can directly regulate several uterine functions. We investigated in the present study, whether uterine phenotype in LH receptor knockout animals resulted also from the absence of direct actions of LH in the uterus. The phenotype consisted of marked growth reduction of uterus, decreased thickness of endometrial and myometrial layers, number of endometrial glands, height of luminal epithelium and vascular space. Analysis of uterine gene expression by mouse genome U74Av2 Affymetrix genechips revealed a differential expression of 155 genes by more than 3-fold (range 3-53-fold) between null and wild-type animals. Of these, 89 genes decreased and 66 increased in uterus of null animals. Semi-quantitative RT-PCR confirmed the differential expression of several selected genes. The decreased genes can be clustered into 18 functional families and the increased into 15 functional families. Semi-quantitative RT-PCR, Western blotting and immunocytochemistry demonstrated a decreased expression of ERbeta, PR-A, PR-B and AR in uterus of null animals as compared with wild-type siblings. Twenty-one-day estradiol and progesterone replacement therapy did not normalize the decrease in the number of endometrial glands and several genes that either decreased or increased in expression. The partial success of therapy suggests that direct LH actions could be required to completely normalize the uterus. In summary, findings on the knockout model reaffirm that LH and hCG control uterine functions directly as well as indirectly through increasing ovarian synthesis of steroid hormones and both actions are required for normal uterine biology.

Gonadotropin releasing hormone (GnRH) modulates odorant responses in the peripheral olfactory system of axolotls

Peripheral signal modulation plays an important role in sensory processing. Activity in the vertebrate olfactory epithelium may be modulated by peptides released from the terminal nerve, such as gonadotropin releasing hormone (GnRH). Here, we demonstrate that GnRH modulates odorant responses in aquatic salamanders (axolotls, Ambystoma mexicanum). We recorded electrical field potentials (electro-olfactograms, or EOGs) in response to stimulation with four different amino acid odorants, L-lysine, L-methionine, L-cysteine, and L-glutamic acid. EOG responses were recorded from the main olfactory epithelium before, during, and after application of 10 microM GnRH. This protocol was repeated for a total of three trials with 60-80 min between trials. The effect of GnRH on EOG responses was broadly similar across odorants and across trials. In general, EOG responses were reduced to 79% of the initial magnitude during application of GnRH; in some trials in which glutamic acid served as the odorant, EOG responses were enhanced during the wash period. Although the 4-min inter-stimulus interval did not lead to adaptation of EOG responses during the first trial, we frequently observed evidence of adaptation during the second and third trials. In addition, we found that lower concentrations of GnRH produced a smaller effect. These results demonstrate that GnRH can modulate odorant responses in the peripheral olfactory system.

GnRH in pregnancy

Human trophoblast produce GnRH and its precursor, immunologically and chemically identical to those of hypothalamic origin. Placental GnRH stimulates human chorionic gonadotropin secretion by the syncytiotrophoblast. It is known that GnRH analogue has negative effect on early rat pregnancy and may cause abortion through its action on the corpus luteum. A significant reduction of progesterone production was found in pregnant rats treated with GnRH agonist. GnRH caused a significant decrease in the maximal contraction intensity of non-pregnant and pregnant uterine muscle strip, following the action of oxytocin and acetylcholine. It was observed that treatment of pregnant rat with pharmacological doses of GnRH was able to delay parturition. Experimentally, GnRH significantly inhibited the release of placental prostaglandins E and F and thromboxane B 2 in a dose dependent fashion. Maternal circulating GnRH levels at 25-35 weeks of gestation were significantly higher in women who later had post-term pregnancies. In an other study maternal circulating GnRH concentration was found to be significantly lower in four patients who developed preterm labor and delivery. Low doses of GnRH in pregnant rats produced inhibition of postpartum lordosis behavior.

Leuprolide acetate stimulates smooth muscle of the human reproductive tract

Leuprolide acetate (10(-4) to 10(-5) M) had a stimulatory effect on spontaneous contractions of human myometrium and fallopian tube in vitro. The uterine and tubal tissues were from patients with dysfunctional uterine bleeding that was treated by hysterectomy. Whether the effect of LA on smooth muscle is a component of the mechanism of therapeutic action or an undesirable side effect remains to be determined.