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Neurosciences, Loeb Research Institute, Ottawa Civic Hospital, and University of Ottawa, Ottawa, Ontario, Canada K1Y 4E9
To examine ANG II receptors in rat median
preoptic (MnPO) neurons, we used patch-clamp whole cell recordings in a
parasagittal brain slice preparation. Lucifer yellow-filled neurons
displayed a simple morphology with two to three aspiny dendrites.
Bath-applied ANG II (1-2,000 nM for 30 s) induced a response in 37 of 70 cells. In current-clamp recordings, cells displayed a prolonged
(10- to 30-min) depolarizing plateau with action potential discharges and an associated reduction in postburst afterhyperpolarization and
spike frequency adaptation. In voltage-clamp recordings (holding potential 
65 mV), cells displayed tetrodotoxin-resistant inward currents of 7.6 ± 1.9 (n = 5), 9.9 ± 1.9 (n = 9), and 9.2 ± 2.2 pA (n = 6) at 10, 200, and 2,000 nM, respectively. Responses were blockable by pretreatment
with losartan (2 µM; n = 6) but not by PD-123177 (20 µM; n = 3). Net ANG
II-induced current revealed a 7.8 ± 0.9% reduction in membrane
conductance, decreasing but not reversing at hyperpolarized levels.
Neurons expressing a strong hyperpolarization-activated,
time-independent inward rectification were more likely to respond to
ANG II. There was no correlation between the response of a neuron to
ANG II and its response to norepinephrine.
patch-clamp recording; lamina terminalis; morphology; membrane conductance; angiotensin
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