Abstract 043: Prorenin Reduces Spontaneous Firing Rate In Cells Expressing Tyrosine Hydroxylase In The Hypothalamic Paraventricular Nucleus

The (pro)renin receptor (PRR) plays essential roles in cardiovascular and metabolic physiology. The tyrosine hydroxylase (TH) neurons in the paraventricular nucleus of the hypothalamus (PVN) have recently emerged as a key metabolic regulator that play functional roles in the regulation of the energy expenditure and metabolism. Using RNAScope in situ hybridization, we found that 95% of TH-containing neurons in the PVN (n=872 cells/3 mice) express the PRR. In this study, we aimed to examine the effects of PRR activation on the firing activity of the TH-containing neurons in the PVN (TH PVN ). We hypothesized that prorenin activation of the PRR increases firing activity of the TH PVN neuron. To test this hypothesis, we performed electrophysiological recordings in loose cell-attached voltage-clamp configuration in PVN slices from mice expressing TdTomato reporter for TH neurons (TH-cre-TdTomato mice). These experiments were carried out to isolate and record spontaneous firing rate (SFR). We abolished all the synaptic transmission by adding a GABA A receptor antagonist (picrotoxin, 50 μM), an antagonist of AMPA/kainate receptors (CNQX, 5 μM), and an NMDA receptor antagonist (D-APV, 50 μM) throughout the recording. The cells were discarded if the access resistance was >15 MΩ or fluctuated more than 15%. At the end of the experiments, tetrodotoxin (1 μM) was added to abolish and confirm neuronal activity. The SFR in TH PVN neurons was significantly decreased after application of prorenin (PR) (4.9 ± 0.87 and 3.2 ± 1.07 Hz, before and after PR, respectively; n = 10, p = 0.006, paired t -test) indicating that PR reduces spontaneous firing activity of the TH PVN neurons. To determine if this effect was due to the prorenin activation of the PRR, we recorded SFR in the presence of PRR antagonist (PRO20). There was no difference in the SFR (5.8 ± 1.58 Hz and 5.9 ± 1.7 Hz, n = 5, p = 0.903, paired t -test) in the TH PVN neurons between PRO20 and PRO20+PR group respectively suggesting that PRO20 blocks the effect of PR in reducing SFR in TH PVN neurons. Our results showed that the prorenin acts on the PRR to reduce the SFR of the TH PVN neurons. We conclude that PRR signaling in the TH PVN neurons might play a role in cardiovascular and metabolic regulation by the modulating the TH PVN neuronal plasticity.