SAT-411 Prepubertal Tonic Gamma-Amino Butyric Acid (GABA) Inhibition Is Upstream of Neurokinin B (NKB), Kisspeptin, and Gonadotropin Releasing Hormone (GnRH) Neuronal Network in Male Rhesus Monkeys

The concept that GnRH release during the prepubertal period is under tonic central inhibition is well established in primates. Although it has been reported that the makorin RING finger protein 3 (MKRN3) gene plays a role in this process (1), neuronal substrates responsible for prepubertal tonic inhibition remain unclear. A series of studies in this lab have shown that GABA neurons are consistently inhibitory to GnRH and kisspeptin neurons in female prepubertal rhesus monkeys (2, 3, 4). Because we recently found that release of GnRH, kisspeptin and NKB in prepubertal male monkeys is significantly lower than those in pubertal monkeys and the pubertal increase in release of these neuropeptides is gonadal steroid independent, in the present study, we ask the question of whether GABA neurons play a role in central inhibition of GnRH release before puberty onset in male monkeys. As described previously, a microdialysis probe was inserted into the median eminence of the hypothalamus in 4 gonadally intact prepubertal male monkeys (15.1 ± 1.9 months of age) and the effects of GABA(A) receptor antagonist, bicuculline, on release of GnRH, kisspeptin and NKB were examined. The results indicate that bicuculline at 1 µM, but not vehicle, dramatically stimulated release of GnRH, kisspeptin, and NKB in prepubertal male monkeys. Subsequently, we examined whether the bicuculline-induced release of GnRH and kisspeptin was affected by the presence of NKB antagonist, SB222200, as previously we found that NKB signaling is upstream of kisspeptin and GnRH neurons in male monkeys (5). We found that inhibition of NKB signaling attenuated the bicuculline-induced release of GnRH and kisspeptin, suggesting that NKB neurons, in part, relay inhibitory GABA signals to GnRH and kisspeptin neurons. These results are interpreted to mean that in male monkeys, inhibitory GABA signaling plays a role in central inhibition during the prepubertal period and that inhibitory GABA signaling is upstream of the NKB, kisspeptin, and GnRH neuronal pathway. How “Central GABA Inhibition” is regulated by genes involved in this process, such as MKRN3, remains to be investigated. References: (1) Abreu et al., N Engl J Med. 2013;368:2467-2475. (2) Mitsushima et al., Proc Natl Acad Sci USA. 1994;91:395-399. (3) Keen et al., Endocrinology. 1999;140:5257-5266. (4) Kurian et al., Endocrinology. 2012;153:3331-3336. (5) Garcia et al., Endocrinology. 2018;159:3048-3060. Sources of Research Support: NIH R01 and T32 Grants