Growth Hormone Effects on the Membrane Excitability of Ventral Premammillary Nucleus Neurons
Presentation Number: SAT 430
Date of Presentation: April 1st, 2017
Thais T Zampieri*1, Marina Augusto Silveira1, Isadora C Furigo1, Edward Owen List2, John J Kopchick2, Jose Donato Jr.3 and Renata Frazao1
1University of Sao Paulo, Sao Paulo, Brazil, 2Ohio University, Athens, OH, 3University of Sao Paulo, Sao Paulo - SP, Brazil
Despite its classical effect as a key factor for body growth, growth hormone (GH) is involved in several cellular and metabolic processes. Our group has recently demonstrated that GH induces the JAK2/STAT5 signaling pathway in several hypothalamic structures (1). Among these areas, the ventral premammillary nucleus (PMV) is particularly responsive to GH. PMV neurons regulate reproduction and motivated behaviors. To determine the effects of GH on the membrane excitability of PMV neurons, whole-cell patch-clamp recordings were performed in hypothalamic slices of adult male mice (8-12 weeks). In the first set of experiments, we observed that human GH (hGH; 1μg/μL) caused a hyperpolarization in most of PMV neurons (8 out 10 cells, change in resting membrane potential [RMP]: - 7.1 ± 0.7 mV; 36% decrease of input resistance [IR]). Because hGH presents a molecular conformation that is able to activate both GH and prolactin (PRL) receptors (R), we next recorded PMV neurons of brain-specific GHR deficient mice (Nestin GHR KO). Interestingly, when recording from Nestin GHR KO brain slices, we observed a hGH dependent-depolarization in most of recorded PMV neurons (6 out 10 cells; change in RMP: + 6.3 ± 1.3 mV; 62% decrease of IR). These divergent results might be caused by the activation of PRLRs. Therefore, we investigated the effects of PRL (250nM) on the membrane excitability of PMV neurons using wild-type C57BL/6 mice. PRL induced a depolarization in most of recorded PMV neurons (5 out 7 cells; change in RMP: + 9.5 ± 1.0 mV; 10 % increase of IR). To confirm our previous observation that GHR activation causes an inhibitory effect on PMV neurons, we used porcine (p) GH (pGH, 5μg/μL) as a specific activator of GHR. Surprisingly, the membrane excitability of PMV neurons was neither hyperpolarized nor depolarized by pGH (10 cells, change in RMP: -0.3 ± 0.4 mV; no change of IR), even though the biological activity of pGH was confirmed by the robust induction of pSTAT5 in the PMV. In summary, our results suggest that the activation of PRLRs, either by PRL or hGH, exerts an excitatory effect on the membrane excitability of PMV neurons. Although our findings indicate that hGH induces a hyperpolarization of PMV neurons via GHR activation, since this effect was absent in brain-specific GHR deficient mice, we were not able to reproduce the hGH effect using a specific GHR agonist (pGH). Therefore, further studies will be important to demonstrate whether PRL and GH may interact to produce complex effects on the membrane excitability of PMV neurons.
Nothing to Disclose: TTZ, MAS, ICF, EOL, JJK, JD Jr., RF