Development and prenatal exposure to androgens alter potassium currents in gonadotropin-releasing hormone neurons from female mice.

Pulsatile gonadotropin-releasing hormone (GnRH) release is critical for reproduction. Disruptions to GnRH secretion patterns may contribute to polycystic ovary syndrome (PCOS). Prenatally androgenized (PNA) female mice recapitulate many neuroendocrine abnormalities observed in PCOS patients. PNA and development induce changes in spontaneous GnRH neuron firing rate, response to synaptic input, and the afterhyperpolarization potential of the action potential. We hypothesized potassium currents are altered by PNA treatment and/or development. Whole-cell patch-clamp recordings were made of transient and residual potassium currents of GnRH neurons in brain slices from 3-week-old and adult control and PNA females. At 3 weeks of age, PNA treatment increased transient current density versus controls. Development and PNA altered voltage-dependent activation and inactivation of the transient current. In controls, transient current activation and inactivation were depolarized at 3 weeks of age versus in adulthood. In GnRH neurons from 3-week-old mice, transient current activation and inactivation were more depolarized in control than PNA mice. Development and PNA treatment interacted to shift the time-dependence of inactivation and recovery from inactivation. Notably, in cells from adult PNA females, recovery was prolonged compared to all other groups. Activation of the residual current occurred at more depolarized membrane potentials in 3-week-old than adult controls. PNA depolarized activation of the residual current in adults. These findings demonstrate the properties of GnRH neuron potassium currents change during typical development, potentially contributing to puberty, and further suggest PNA treatment may both alter some typical developmental changes and induce additional modifications, which together may underlie aspects of the PNA phenotype. There was not any clinical trial involved in this work.

GnRH Neuron Excitability and Action Potential Properties Change with Development But Are Not Affected by Prenatal Androgen Exposure.

Gonadotropin-releasing hormone (GnRH) neurons produce the final output from the brain to control pituitary gonadotropin secretion and thus regulate reproduction. Disruptions to gonadotropin secretion contribute to infertility, including polycystic ovary syndrome (PCOS) and idiopathic hypogonadotropic hypogonadism. PCOS is the leading cause of infertility in women and symptoms resembling PCOS are observed in girls at or near the time of pubertal onset, suggesting that alterations to the system likely occurred by that developmental period. Prenatally androgenized (PNA) female mice recapitulate many of the neuroendocrine phenotypes observed in PCOS, including altered time of puberty, disrupted reproductive cycles, increased circulating levels of testosterone, and altered gonadotropin secretion patterns. We tested the hypotheses that the intrinsic properties of GnRH neurons change with puberty and with PNA treatment. Whole-cell current-clamp recordings were made from GnRH neurons in brain slices from control and PNA females before puberty at three weeks of age and in adulthood to measure GnRH neuron excitability and action potential (AP) properties. GnRH neurons from adult females were more excitable and required less current to initiate action potential firing compared with three-week-old females. Further, the afterhyperpolarization (AHP) potential of the first spike was larger and its peak was delayed in adulthood. These results indicate development, not PNA, is a primary driver of changes to GnRH neuron intrinsic properties and suggest there may be developmentally-induced changes to voltage-gated ion channels in GnRH neurons that alter how these cells respond to synaptic input.

Prenatal Androgen Treatment Does Not Alter the Firing Activity of Hypothalamic Arcuate Kisspeptin Neurons in Female Mice.

Neuroendocrine control of reproduction is disrupted in many individuals with polycystic ovary syndrome (PCOS), who present with increased luteinizing hormone (LH), and presumably gonadotropin-releasing hormone (GnRH), release frequency, and high androgen levels. Prenatal androgenization (PNA) recapitulates these phenotypes in primates and rodents. Female offspring of mice injected with dihydrotestosterone (DHT) on gestational days 16-18 exhibit disrupted estrous cyclicity, increased LH and testosterone, and increased GnRH neuron firing rate as adults. PNA also alters the developmental trajectory of GnRH neuron firing rates, markedly blunting the prepubertal peak in firing that occurs in three-week (3wk)-old controls. GnRH neurons do not express detectable androgen receptors and are thus probably not the direct target of DHT. Rather, PNA likely alters GnRH neuronal activity by modulating upstream neurons, such as hypothalamic arcuate neurons co-expressing kisspeptin, neurokinin B (gene Tac2), and dynorphin, also known as KNDy neurons. We hypothesized PNA treatment changes firing rates of KNDy neurons in a similar age-dependent manner as GnRH neurons. We conducted targeted extracellular recordings (0.5-2 h) of Tac2-identified KNDy neurons from control and PNA mice at 3wks of age and in adulthood. About half of neurons were quiescent (<0.005 Hz). Long-term firing rates of active cells varied, suggestive of episodic activity, but were not different among groups. Short-term burst firing was also similar. We thus reject the hypothesis that PNA alters the firing rate of KNDy neurons. This does not preclude altered neurosecretory output of KNDy neurons, involvement of other neuronal populations, or in vivo networks as critical drivers of altered GnRH firing rates in PNA mice.