Knockdown of GABA(A) receptor signaling in GnRH neurons has minimal effects upon fertility.
The amino acid gamma-aminobutyric acid (GABA) is thought to play a key role in shaping the activity of the GnRH neurons throughout embryonic and postnatal life. However, the physiological roles of direct GABA inputs to GnRH neurons remain unknown. Using a Cre-LoxP strategy, we generated a targeted mouse line, in which all (98 +/- 1%) GnRH neurons had the gamma2-subunit of the GABA(A) receptor deleted. Electrophysiological recordings of GABA(A)-mediated postsynaptic currents from green fluorescent protein-tagged GnRH neurons with the gamma2-subunit knocked out (GnRH gamma2 KO) showed that the amplitude and frequency of GABA(A) postsynaptic currents were reduced by 70% (P < 0.01) and 77% (P < 0.05), respectively, and that the response to exogenous GABA was reduced by 90% (P < 0.01). Evaluation of male and female GnRH gamma2 KO mice revealed completely normal fecundity, estrous cycles, and puberty onset. Further investigation with gonadectomy and different steroid replacement regimens showed normal basal levels of LH in both sexes, and a normal estradiol-evoked positive feedback mechanism in females. However, the increment in LH after gonadectomy in GnRH gamma2 KO female mice was double that of controls (P < 0.05) and also more potently suppressed by 17-beta-estradiol (P < 0.05). A similar but nonsignificant trend was observed in GnRH gamma2 KO male mice. Together, these findings show that 70-90% reductions in the normal levels of GABA(A) receptor activity at the GnRH neuron appear to impact upon the estrogen negative feedback mechanism but are, nevertheless, compatible with normal fertility in mice.
Lee
Kiho
K
Centre for Neuroendocrinology, Department of Physiology, University of Otago School of Medical Sciences, P.O. Box 913, Dunedin 9054, New Zealand.
Porteous
Robert
R
Campbell
Rebecca E
RE
Lüscher
Bernhard
B
Herbison
Allan E
AE
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D004958:Estradiol / Q000494:pharmacology; D030762:Estrous Cycle / Q000502:physiology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D025461:Feedback, Physiological / Q000187:drug effects; D005260:Female; D005298:Fertility / Q000235:genetics / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007986:Luteinizing Hormone / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D018345:Mice, Knockout; D009474:Neurons / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D010052:Ovariectomy; D011963:Receptors, GABA-A / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; C546280:Gabrg2 protein, mouse; D011963:Receptors, GABA-A; D049452:Green Fluorescent Proteins; D007987:Gonadotropin-Releasing Hormone; D013779:Tetrodotoxin; D004958:Estradiol; D005680:gamma-Aminobutyric Acid; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D007986:Luteinizing Hormone