Article Figures & Data
Figures
- Fig. 1.
Effects of ANP on the osmoresponsiveness of MNCs impaled in the supraoptic nucleus (SON) of hypothalamic explants. A, Schematic diagram of experimental setup illustrating the relative positions of MNCs projecting to the posterior pituitary (PP) and of their afferents from osmoreceptor neurons in the OVLT.OC, Optic chiasma. B, Chart recordings of voltage responses recorded in MNCs in response to hypertonic stimulation of the OVLT (bar). Bath application ofANP (150 nm) reversibly blocked the excitatory response of the cell to the hypertonic stimulus. Initial membrane potential was −53 mV in each of the trials shown.
- Fig. 2.
Effects of ANP on the frequency of sEPSPs recorded from MNCs in the SON. A, Bar histograms express the mean (±SEM) normalized frequencies at which sEPSPs occurred in MNCs under isotonic conditions. Note that addition of ANP (75–150 nm) to the solution superfusing the SON did not significantly alter the basal frequency at which sEPSPs were detected in MNCs (90 ± 3% of control; p > 0.05; n = 5).B, Bar histograms express mean (±SEM) normalized changes in sEPSP frequency (Δ sEPSP frequency), relative to the basal rate (% of control), evoked by hypertonic stimulation of the OVLT. Note that the increase in sEPSP frequency observed in ACSF (156 ± 12% of control) was not significantly affected by the inclusion of 75–150 nm ANP in the solution superfusing the SON (147 ± 8%; p > 0.05;n = 5).
- Fig. 3.
Effects of ANP on the amplitude of sEPSPs.A, High-gain voltage excerpts of a recording obtained from a rat MNC in control solution (ACSF) and in the presence of ANP (75 nm). The membrane potential was −63 mV. B, The graph plots the cumulative probability distributions of sEPSP amplitude measured from a different MNC during 60 sec recording segments obtained in ACSF (899 events) and in the presence of 75 nm ANP (809 events).C, Bar histograms plot the mean (±SEM) relative median amplitude (normalized amplitude at 0.5 probability) of the sEPSPs observed in control solutions (ACSF; 100%) and in the presence of 75 nmANP (theasterisk denotes p < 0.01;n = 5).
- Fig. 4.
Effects of ANP on EPSPs evoked by electrical stimulation of the OVLT (arrows). A, Voltage traces showing the reversible decrease in EPSP amplitude in the presence of ANP (75 nm). B, The top graph plots the dose-dependency (dashed line shows IC50 = 3 nm) of the effects of ANP on the relative amplitude of EPSPs evoked by OVLT stimulation. The bottom graph plots the mean input conductance (Gin; relative to control) of cells bathed in the presence of different concentrations of ANP. Closed symbols are single measurements, whereas open symbols are mean values ± SEM; n ≥ 3.
- Fig. 5.
Effects of db-cGMP and glutamate receptor antagonists on EPSPs evoked by electrical stimulation of the OVLT (arrows). A, Superimposed traces showing the EPSP recorded from a cell before (control), during (db-cGMP), and after (wash) bath application of 1 mm db-cGMP. B, Superimposed traces recorded from another MNC illustrate the reversible block of the evoked EPSP by application of CNQX and APV (25 μmeach).
- Fig. 6.
ANP does not affect the responsiveness of MNCs to glutamate receptor activation. A, Chart recordings of voltage responses from a single supraoptic MNC to applications of 25 μmNMDA (bars; top traces) or 30 μmAMPA (bars; bottom traces), recorded in control solution (left panels) or in the presence of 75 nm ANP (right panels). Initial membrane potential was −60 mV in each trial. Action potentials are truncated in this figure.B, Bar histograms plotting the mean ± SEM amplitude of depolarizing responses to NMDA (top) and AMPA (bottom) recorded from three cells.
- Fig. 7.
Inhibitory effects of ANP are presynaptic.A, Voltage responses of an MNC to pairs of electrical stimuli delivered to the OVLT (arrows). InACSF the amplitude of the second EPSP is enhanced relative to the first, reflecting the occurrence of PPF. Thetrace on the right shows the response of the same cell to identical stimuli delivered in the presence of 100 nm ANP. Note that the amplitude of the first EPSP recorded in ANP is attenuated compared with control but that PPF is enhanced.B, The traces shown in Aare superimposed and scaled so that the amplitudes of the first EPSPs match each other. Note the relative enhancement of the second EPSP in the presence of ANP.
