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

Abstract

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.

Keywords: GnRH; androgens; polycystic ovary syndrome; puberty.

Figure 1.

Confirmation of PNA phenotype. A-C. Individual values and median + the interquartile range (IQR) for age at vaginal opening (VO; A) and body mass at VO (B). Individual values and mean ± SEM for anogenital distance in adulthood (AGD, C). D, Representative estrous cycles over 14d. P, proestrus; D, diestrus; E, estrus (top, vehicle; bottom, PNA). E, Individual values and mean ± SEM for days in each cycle over 14d. Statistical parameters are in Table 1.

Figure 2.

Recording quality and passive property parameters. A-D, Individual values and mean ± SEM for input resistance (A), compensated series resistance (B), capacitance (C), and holding current (D). Numbers and statistical parameters are in Table 2.

Figure 3.

Characterization of the transient potassium current. A, Representative traces illustrating mathematical isolation of the transient current (right) by subtracting the −40mV prepulse traces in the middle panel from the −100mV prepulse traces in the left panel. Only three voltage-steps are shown for clarity. B, C, Individual values and mean±SEM for maximum current (B) and current density (C). D, Voltage-dependence of inactivation (left) and activation (right). Fraction of maximum refers to normalized current for inactivation and normalized conductance for activation. Boltzmann fits of the mean data are shown for each group. E-H, Individual values and mean±SEM V_0.5 activation (V_0.5 act, E), V_0.5 inactivation (V_0.5 inact, F), inactivation slope factor (G), and activation slope factor (H). For B, C and E-H, two-way ANOVA/Fisher’s LSD; statistical parameters are in Table 3; tx = treatment. Error bars are often within the size of the symbol.

Figure 4.

Characterization of the time dependence of inactivation and recovery from inactivation of the transient current in GnRH neurons. A, E, Representative traces illustrating the time dependence of transient current inactivation (A) and recovery from inactivation (E). Only three voltage-steps are shown for clarity (bottom). B, F, Current was normalized to the maximum and plotted as a function of time (B, inactivation; F, recovery). The solid lines represent the double exponential equation evaluated using the mean fast and slow time constants for each group. C, D, G, H, Individual values and mean±SEM for the fast time constant of inactivation (inact; C), the slow time constant of inactivation (inact; D), the fast time constant of recovery (recov; G), and the slow time constant of recovery (recov; H). C, D, G, H, two-way ANOVA/Fisher’s LSD; statistical parameters are in Table 4.

Figure 5.

Characterization of the residual potassium current in GnRH neurons. A, Representative traces illustrating the activation of the residual current (top). Only three voltage-steps are shown for clarity (bottom). Individual values and mean±SEM for maximum current at −10 mV. (B), current density (C). D, Voltage-dependence of activation plotted as fraction of maximum conductance; lines are Boltzmann fits of the mean data for each group. Individual values and mean±SEM for V_0.5 activation (V_0.5 act, E), and activation (act) slope factor (F). B, C, E, F two-way ANOVA/Fisher’s LSD. Statistical parameters are in Table 5.