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Osmoresponsive units in sheep median preoptic nucleus
R M McAllen1, G L Pennington, M J McKinley
1Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria, Australia.
The American Journal of Physiology
|September 1, 1990
Summary
Neurons in the median preoptic nucleus (MnPO) respond to osmotic changes, similar to neurohypophysial fibers. However, MnPO neurons do not show hemodynamic responses, suggesting a role in osmotic but not hemodynamic control of vasopressin secretion.
Area of Science:
- Neuroscience
- Physiology
- Endocrinology
Background:
- The lamina terminalis is crucial for osmoregulation.
- Understanding neural control of water balance is vital.
Purpose of the Study:
- Investigate single-unit neural activity in the lamina terminalis during osmotic stimulation.
- Compare osmoresponsive neurons in the median preoptic nucleus (MnPO) with neurohypophysial fibers.
Main Methods:
- Recorded single-unit neural activity in alpha-chloralose-anesthetized sheep.
- Administered intracarotid infusions of hypertonic NaCl, sorbitol, and urea.
- Compared neural responses with multiunit recordings of neurohypophysial fibers.
- Tested hemodynamic responses using nitroprusside-induced hypotension.
Main Results:
- 9.9% of studied units in the MnPO were osmoresponsive.
- Responsive MnPO units and neurohypophysial fibers showed similar responses to hypertonic NaCl and sorbitol, but less to urea.
- Both MnPO units and neurohypophysial fibers exhibited slow onset and peak activity.
- Unlike neurohypophysial fibers, MnPO osmoresponsive units did not respond to hypotension.
Conclusions:
- Osmoresponsive MnPO neurons contribute to osmotic, but not hemodynamic, inputs for vasopressin secretion and osmoregulation.
- MnPO neurons play a specific role in sensing osmotic changes for bodily fluid balance.