Heterogeneous Expression of the Potassium-Chloride Cotransporter KCC2 in Gonadotropin-Releasing Hormone Neurons of the Adult Mouse

Abstract

In mature central neurons, chloride extrusion mediated by the K-Cl cotransporter KCC2 appears to be largely responsible for the Cl(-) driving force that allows gamma-aminobutyric acid(A) (GABA(A)) receptor activation to trigger a hyperpolarization. In its absence, GABA's effect is typically depolarizing and often excitatory. We examined the colocalization of KCC2 and GnRH in adult male and female mice using a combined in situ hybridization-immunofluorescence procedure. We found that KCC2 was localized to approximately 34% of GnRH neurons. This proportion was similar in females and males. However, females exhibited a marked rostrocaudal gradient of colocalization that was not seen in males. By contrast, KCC2 was localized to nearly all vasopressin neurons of the supraoptic nucleus. These results indicate that a substantial fraction of GnRH neurons may be depolarized and excited by GABA(A) receptor activation throughout life, supporting the existence of functionally heterogeneous subpopulations.

Detection and localization of an estrogen receptor beta splice variant protein (ERβ2) in the adult female rat forebrain and midbrain regions

“…Preadsorption of the GnRH antiserum with the full-length GnRH peptide (140-fold excess) eliminated GnRH immunoreactivity. Specificity and population of neurons detected with the GnRH antiserum used in this study were furthermore consistent with that of LR-1, a well-characterized and accepted antibody from Dr. Robert Benoit for GnRH peptide detection (Leupen et al, 2003). The oxytocin antiserum was verified by the manufacturer and in earlier publications through preadsorption with the immunogenic peptide and has been used by this laboratory in a previous ER␤/oxytocin colocalization study (AlMatubsi et al, 1999;Suzuki and Handa, 2005).…”

Steroid modulation of GABAA receptor-mediated transmission in the hypothalamus: Effects on reproductive function

“…Han et al (2002) report that this developmental change does not occur until approximately the time of pubertal onset (postnatal day 31; PN31), while DeFazio et al (2002) do not observe a developmental shift at all and believe that GABA continues to depolarize GnRH neurons even into adulthood. While the discrepancy between these two reports might result from sampling differences as there is a rostral-caudal gradient in the expression of the potassium-chloride cotransporter KCC2 in female mice (Leupen et al, 2003), the common finding is that GABA continues to depolarize GnRH neurons well beyond the age (~PN14) where GABA switches to a hyperpolarizing action in non-GnRH neurons in the hypothalamus/basal forebrain (Han et al, 2002;Defazio et al, 2002). Thus, steroid allosteric modulators that enhance GABA A receptor-mediated responses may have a paradoxical excitatory effect on GnRH neuron firing well into adolescence and perhaps beyond.…”

Diurnal and estradiol-dependent changes in gonadotropin-releasing hormone neuron firing activity

“…The use of mice in studies investigating the GnRH system has increased greatly in recent years (19)(20)(21)(22)(23)(24)(25)(26). Previous studies in mice have used a regimen of ovariectomy followed by injections of estrogen and͞or progesterone at specific times to induce a LH surge (12,27).…”