Neurochemical and Neuroendocrine Function during Aging

Phyllis M Wise, PhD

The brain plays a critical role in the transition to reproductive senescence. The virtual lack of ovarian estrogens during the postmenopausal period in women clearly impacts multiple aspects of brain function. We have found that during middle age, the ability of estradiol to modulate the neurochemical events that are required for preovulatory GnRH/LH surges diminishes. The ability of the suprachiasmatic nucleus, the major circadian pacemaker in mammals, to drive diurnal neurochemical events declines, which leads to imprecision in the timing of the GnRH/LH surge.

Estradiol exerts important non-reproductive actions that protect the brain against neurodegenerative conditions. Therefore, its absence during postmenopause leads to increased vulnerability to injury and diseases of the brain. We will test three working hypotheses:

  1. During middle age, attenuation in the diurnal rhythmicity of VIP and/or GABA or responsiveness of GnRH neurons to these neurotransmitters infl uences the synthesis, activation and/or secretion of GnRH
  2. The presence or absence of estradiol infl uences the interactions of these neurotransmitters with GnRH
  3. Estradiol is critical for maintaining normal brain function and for protecting against neurodegeneration associated with disease or injury.

Our results will provide new insights into the cellular and molecular basis of brain aging. They will deepen our understanding of how estradiol modulates the process of brain aging and how its absence impacts brain function. This information is critical in developing new strategies to treat women as they approach the perimenopausal and postmenopausal periods.

Funding Source: National Institute on Aging (NIA)
Contact: Phyllis M Wise, PhD
Ends 7/31/2011

Kisspeptin-GPR54 in the Female Neuroendocrine Axis

Robert A Steiner, PhD

The KiSS-1 gene codes for kisspeptins, which bind to a G protein-coupled receptor known as GPR54. KiSS-1 and GPR54 are expressed in the forebrain, and mutations in the GPR54 gene cause hypo-gonadotropic hypogonadism in humans and mice. Kisspeptins stimulate gonadotropin-releasing hormone (GnRH) and gonadotropin (LH and FSH) secretion, and the KiSS-1 gene is regulated by gonadal steroids, suggesting that signaling through GPR54 plays a critical role in the neuroendocrine regulation of reproduction. In the male mouse, KiSS-1 neurons in the arcuate nucleus (Arc) and anteroventral periventricular nucleus (AVPV) are differentially regulated by testosterone (T), which inhibits KiSS-1 expression in the Arc and stiumlates its expression in the AVPV; these actions are mediated through both androgen and estrogen alpha receptors.

Primary Objectives

1) To determine the physiological significance of kisspeptin-GPR54 signaling the Arc. In this context, we will:

  • Test the hypothesis that KiSS-1 neurons in the Arc play an important role in mediating the negative feedback effect of T on gonadotropin secretion
  • Determine whether kisspeptin-GPR54 signaling is involved in mediating the neuroendocrine effects of metabolic signals

2) To investigate the differences in the physiological function and network organization between KiSS-1 neurons in the AVPV and those in the Arc. Here we will:

  • Evaluate the physiological impact of genetically deleting KiSS-1 gene expression specifically in the AVPV (but not in the Arc)
  • Develop a transgenic mouse that expresses GFP in KiSS-1 neurons and investigate the electro-physiological properties of KiSS-1 neurons in the AVPV and Arc
  • Use double-labeling techniques for in situ hybridization and immunocytochemistry to determine the unique molecular profile and circuitry of KiSS-1 neurons in these two regions

Elucidating the functional significance, regulation and mechanism of kisspeptin's action in the brain may advance our understanding of idiopathic hypogonadotropic hypogonadism and other neuro-endocrine disorders and could provide the scientific rationale for improved therapies to treat precocious or delayed puberty and infertility. It is also conceivable that this knowledge could serve as the basis for the development of new and better strategies for hormonal contraception in men.

Funding Source: NIH
Contact: Robert A Steiner, PhD, (206) 543-8712
Ends 4/30/11

KiSS-1 Signaling and Regulation in the Male Mouse

Robert A Steiner, PhD

The KiSS-1 gene codes for kisspeptins, which have been implicated in the neuroendocrine regulation of reproduction. In the brain, KiSS-1 mRNA-expressing neurons are located in the arcuate (ARC) and anteroventral periventricular (AVPV) nuclei. KiSS-1 neurons in the AVPV appear to play a role in generating the preovulatory GnRH/LH surge, which occurs only in females and is organized peri-natally by gonadal steroids.

Because KiSS-1 is involved in the sexually dimorphic GnRH/LH surge, we hypothesized that KiSS-1 expression is sexually differentiated, with females having more KiSS-1 neurons than either males or neonatally androgenized females. To test this, male and female rats were neonatally treated with androgen or vehicle; then, as adults, they were left intact or gonadectomized and implanted with capsules containing sex steroids or nothing. KiSS-1 mRNA levels in the AVPV and ARC were determined by in situ hybridization. Normal females expressed significantly more KiSS-1 mRNA in the AVPV than normal males, even under identical adult hormonal conditions. This KiSS-1 sex difference was organized perinatally, as demonstrated by the observation that neonatally androgenized females displayed a male-like pattern of adulthood KiSS-1 expression in the AVPV.

In contrast, there was neither a sex difference nor an influence of neonatal treatment in KiSS-1 expression in the ARC. Using double-labeling techniques, we determined that the sexually differentiated KiSS-1 neurons in the AVPV are distinct from the sexually differentiated population of tyrosine hydroxylase (dopaminergic) neurons in this region. Our findings suggest that sex differences in kisspeptin signaling from the AVPV subserve the cellular mechanisms controlling the sexually differentiated GnRH/LH surge.

Funding Source: NIH
Contact: Robert A Steiner, PhD, (206) 543-8712
Ends 3/31/11