Neural Versus Gonadal GnIH: Are they Independent Systems? A Mini-Review.

Based on research in protochordates and basal vertebrates, we know that communication across the first endocrine axes likely relied on diffusion. Because diffusion is relatively slow, rapid responses to some cues, including stress-related cues, may have required further local control of axis outputs (e.g.

The direct response of the gonads to cues of stress in a temperate songbird species is season-dependent.

The gonadotropin releasing hormone (GnRH) system in the hypothalamus is often considered the final point in integration of environmental cues as they pertain to the reproductive axis. However, cues such as stress and food availability are detectable in the plasma (as glucocorticoid and metabolic fuel fluctuations). Vertebrate gonads express glucocorticoid receptor, therefore we hypothesized that the gonads can detect and respond directly to cues of stress.

Effects of melatonin on peripheral reproductive function: regulation of testicular GnIH and testosterone.

Study of seasonal reproduction has focused on the brain. Here, we show that the inhibition of sex steroid secretion can be seasonally mediated at the level of the gonad. We investigate the direct effects of melatonin on sex steroid secretion and gonadal neuropeptide expression in European starlings (Sturnus vulgaris).

A functional neuropeptide system in vertebrate gonads: Gonadotropin-inhibitory hormone and its receptor in testes of field-caught house sparrow (Passer domesticus).

Unlabelled: Previously, the expression and action of GnIH (Gonadotropin-inhibitory hormone) has been characterized in the hypothalamus and pituitary, respectively. The action of this neurohormone is to inhibit the synthesis and secretion of luteinizing hormone and follicle-stimulating hormone. Several hormone systems identified in the vertebrate brain and classified as neurohormones are synthesized in and have a localized action on the gonads as well.

Neuropeptides in the gonads: from evolution to pharmacology.

Vertebrate gonads are the sites of synthesis and binding of many peptides that were initially classified as neuropeptides. These gonadal neuropeptide systems are neither well understood in isolation, nor in their interactions with other neuropeptide systems. Further, our knowledge of the control of these gonadal neuropeptides by peripheral hormones that bind to the gonads, and which themselves are under regulation by true neuropeptide systems from the hypothalamus, is relatively meager.

The control of reproductive physiology and behavior by gonadotropin-inhibitory hormone.

Gonadotropin-releasing hormone (GnRH) controls the reproductive physiology and behavior of vertebrates by stimulating synthesis and release of gonadotropin from the pituitary gland. In 2000, another hypothalamic neuropeptide, gonadotropin-inhibitory hormone (GnIH), was discovered in quail and found to be an inhibiting factor for gonadotropin release. GnIH homologs are present in the brains of vertebrates, including birds, mammals, amphibians, and fish.

Gonadotropin-inhibitory hormone and its receptor in the avian reproductive system.

Many hormones that are classified as neuropeptides are synthesized in vertebrate gonads in addition to the brain. Receptors for these hormones are also expressed in gonadal tissue; thus there is potential for a highly localized autocrine or paracrine effect of these hormones on a variety of gonadal functions. In the present study we focused on gonadotropin-inhibitory hormone (GnIH), a neuropeptide that was first discovered in the hypothalamus of birds.