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R4945 --> 896.3 --> The paraventricular nucleus of the hypothalamus (PVN) is an important autonomic control center. It receives afferent inputs from many brain regions, including the median preoptic nucleus (MnPO). The connection between the MnPO and the PVN is particularly important in generating chronic intermittent hypoxia phenotypes such as increased sympathetic activity leading to the development of hypertension. PVN‐projecting MnPO neurons discharge frequency is <5Hz. To gain more insight into the acute change in PVN neuron properties after low‐frequency stimulation, whole‐cell patch‐clamp recordings were performed on PVN neurons. Adult 250‐350g male rats were injected bilaterally in the PVN with 100 nL retrogradely transported adeno‐associated virus encoding Channelrhodopsin (AAVrg‐CaMKIIa‐hChR2(H134R)‐mCherry) or with AAVrg‐CAG‐tdTomato as control. Three weeks after the injections, the rats were anesthetized with isoflurane (2‐3%) and sacrificed to prepare horizontal brain slices containing the PVN and MnPO. Postsynaptic currents were recorded from PVN neurons in whole‐cell voltage clamp configuration (Vhold=‐60 mV) under constant bath perfusion of normal aCSF (2‐3 ml/min). Axon terminals in the PVN were stimulated with 5Hz LED‐generated blue light (470nM) pulses of 50‐ms duration, 5 seconds off/on for a total of 1 min, delivered using optical fiber directed to the MnPO. Photo‐evoked currents were measured during 5 min before and after the photo‐stimulation train. Amplitude and frequency of spontaneous currents were compared before and after stimulation as well. At the end of each recording, cells were characterized as type I (magnocellular) or type II (parvocellular) PVN neurons based on the presence of transient outward rectification. Data were analyzed offline using Easy Electrophysiology v2.3.3 software. For both cell types, 5 Hz optogenetic stimulation caused a significant reduction in the optogenetic‐evoked current amplitude during the first 15 minutes after stimulation (before stimulation 94.88±2.85 %, n=9 cells vs. 15 minutes after stimulation 67.52±6.15 %, n=9. P=0.0027) before returning to baseline values. Post‐stimulation spontaneous postsynaptic current amplitude and frequency decreased in type II PVN neurons from retrograde ChR2 animals (pre‐stimulation amplitude 100±0.62 % vs. post‐stimulation amplitude 86.50±0.54 %, P=0.0371; pre‐stimulation frequency 3.82±1.7 Hz, post‐stimulation frequency 2.396±1.2 Hz, P= 0.0385) but not in type I PVN neurons from retrograde ChR2 animals or cells from control animals. Kinetic profiles of spontaneous current in type I and II PVN neurons did not change after 5 Hz optogenetic stimulation. The results suggest that low‐frequency stimulation discriminately alters spontaneous presynaptic neurotransmitter release and possibly postsynaptic responsiveness in PVN neurons. Additional experiments will be needed to specifically stimulate PVN afferents from the MnPO. [ABSTRACT FROM AUTHOR]

R4328 --> 896.2 --> Chronic intermittent hypoxia (CIH) has been shown to alter the response of neurons in Median Preoptic nucleus (MnPO) to activation of cardiovascular inputs. Our previous results indicate that CIH enhances spontaneous presynaptic neurotransmitter release while also increasing postsynaptic responsiveness in MnPO. In other systems, BNDF/TrkB signaling has been shown to facilitate excitatory neurotransmission, so we tested its role in the increased MnPO excitation triggered by CIH. Data were collected from PVN‐projecting MnPO neurons which play an important role in CIH‐induced hypertension. Adult 250‐350g male rats were injected bilaterally in the PVN with 200 nL retrograde adeno‐associated virus (pAAV‐CAG‐tdTomato). Three weeks after the injections, the rats were exposed to a 7‐day intermittent hypoxia protocol (6 min cycles; 3 minutes of 21% oxygen, 3 min of 10% oxygen maintenance at 10% oxygen for 8 h during the light phase). Normoxic controls were exposed to room air. At the end of the protocol, the rats were anesthetized with isoflurane (2‐3%) and horizontal brain slices of MnPO were prepared. Miniature Excitatory Postsynaptic Currents (mEPSCs) were recorded using whole cell voltage clamp configuration from PVN‐projecting MnPO neurons. The mEPSCs were recorded with the holding potential of ‐60 mV in the presence of a GABAa receptor antagonist (SR 95531 hydrobromide, 25 µM), tetrodotoxin (1µM), and a glycine receptor antagonist (strychnine, 3 µM) in aCSF. Data were analyzed off‐line using Synaptosoft software. Differences in mEPSCs properties, such as peak amplitude, frequency, decay time, area, and cell capacitance were analyzed by ANOVA and Tukey multiple comparison tests. The results showed that CIH significantly increased mEPSCs frequency (Hz: CIH 1.32 ± 0.09 vs Norm 0.83 ± 0.09, p=5E‐04), decay time (ms: CIH 8.01 ± 0.28 vs Norm 6.64 ± 0.36, p=0.004), area (pA.ms: CIH 63.85± 3.65 vs Norm 50.27 ± 3.6, p=0.01), and cell capacitance (pF: CIH 31.55 ± 1.8 vs Norm 25.34 ± 1.95, p=0.02). The contribution of BDNF/TrkB signaling to these CIH effects were tested using K252a and K252b, two structurally related kinase receptor inhibitors. MnPO slices were pre‐incubated with either K252a or K252b (200nM) for 30 min before recording. Neither K252a nor K252b influenced mEPSCs of MnPO neurons from normoxic slices. Both K252a and K252b significantly affected CIH‐induced changes mEPSCs but at different magnitudes. The K252a significantly reduced the effects of CIH on frequency (Hz: K252a 0.46 ± 0.05, p=1E‐08), decay time (ms: K252a 6.07 ± 0.34, p=1E‐04), area (pA.ms: K252a 43.26 ± 3.55, p=5E‐04), and cell capacitance (pF: K252a 19.59 ± 1.61, p=1E‐04;). In addition, K252a also significantly decreased mEPSCs peak amplitude in CIH neurons (pA: CIH 14.87 ± 0.41 vs K252a 13.27 ± 0.39, p=0.03). While K252b pretreatment also affected the same parameters, the changes produced by K252a were significantly greater. These studies suggest a role for BDNF/TrkB signaling in CIH induced changes in MnPO but additional experiments will be required to validate the specificity of our results. [ABSTRACT FROM AUTHOR]

R3592 --> Studies have shown that the median preoptic nucleus (MnPO) contributes to hypertension associated with chronic intermittent hypoxia (CIH), a model of the hypoxemia associated with sleep apnea. Virally mediated lesions of MnPO neurons prevent the development of a sustained hypertension associated with CIH. To gain more insight into the properties of excitatory transmission to MnPO neurons develops in CIH, whole cell patch clamp recordings were from MnPO neurons brain slices from rats exposed to 7 days of CIH (6 minute cycles; 3 minutes of 21% oxygen room air pumped in, 90 seconds of nitrogen pumped in to lower the chamber O2 to 10% oxygen, and then 90 seconds of maintenance at 10% oxygen) for 8 h during the light phase or were normoxic controls. Slices were perfused with oxygenates artificial cerebrospinal fluid and the MnPO was visually identified. Miniature excitatory postsynaptic currents (mEPSCs) were recorded in the presences of 25 µm SR95531 (GABAA antagonist) and 1 µm TTX (block Na+ channel‐mediated action potentials) using a conventional whole cell patch clamp configuration. The mEPSCs were collected over a 4 min period and amplitude and frequency were compared between cells obtained from slice prepared from normoxic control rats (NORM) or rats exposed to CIH. CIH was associated with a significant increase in mean amplitude (CIH 17.15 ± 0.65 pA, n=19 cells; NORM (15.6 ± 0.6 pA; n=18 cells, P <0.05). Similarly, mean frequency was significantly elevated after CIH (CIH 4.05 ± 0.5 Hz, n=19 vs NORM 2.56 ± 0.37 Hz, n=18; p<0.05) and associated with a significant leftward shift in the cumulative probability of inter event intervals. The results suggest that CIH simultaneously increases enhances spontaneous presynaptic neurotransmitter release while also increasing postsynaptic responsiveness in MnPO. These presynaptic and postsynaptic changes in MnPO that are associated with CIH may represent mechanism contributing to CIH hypertension. [ABSTRACT FROM AUTHOR]