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Lesions of the MPO or AV3V: influences on fluid intake
M K McGowan1, B Brown, S P Grossman
1Committee on Biopsychology, University of Chicago, IL 60643.
Abstract:
Electrolytic lesions in the MPO of rats had no significant effects on ad lib food and water intake, but impaired the drinking response to 1 M NaCl. Large MPO lesions also produced a persistent increase in plasma osmolality. In Experiment 2, we depleted neurons from the MPO of rats by iontophoretic application of the neurotoxin kainic acid (KA) which destroys nerve cell bodies without damage to fibers of passage. KA-induced neuron depletion in the MPO of rats significantly reduced the drinking response to 1.0 M saline, to 30% PG, and to 30 micrograms/kg isoproterenol. Ad lib water intake and drinking responses to food or water deprivation, to low concentrations (0.5 M) of hypertonic saline, to low concentrations (10% or 20%) of PG, and to systemic administration of 1.5 mg/kg angiotensin II were within the normal range. In Experiment 3, rats with electrolytic lesions that were strictly confined to the tissue immediately surrounding the wall of the anteroventral portion of the third ventricle (AV3V), without invading the MPO displayed normal ad lib food and water intake and plasma osmolality as well as drinking responses to water deprivation, hypertonic saline (0.5 or 1.0 M), angiotensin II (1.5 mg/kg) and isoproterenol (30 micrograms/kg).
Insights
The medial preoptic area (MPO) is crucial for regulating thirst and drinking behaviors. Neuron depletion in the MPO impairs responses to hypertonic saline and other dipsogens.
Area of Science:
- Neuroscience
- Physiology
- Behavioral Science
Background:
- The medial preoptic area (MPO) plays a role in regulating fluid balance and drinking behavior.
- Understanding the specific neural circuits involved in thirst is essential for comprehending homeostatic mechanisms.
Purpose of the Study:
- To investigate the role of the medial preoptic area (MPO) in regulating drinking behavior and fluid intake.
- To determine the effects of MPO neuron depletion on responses to various dipsogenic stimuli.
Main Methods:
- Electrolytic lesions were created in the MPO of rats.
- Neurons in the MPO were depleted using iontophoretic application of kainic acid (KA).
- Drinking responses to various stimuli, including hypertonic saline, polyethylene glycol (PG), isoproterenol, and angiotensin II, were assessed.
Main Results:
- Electrolytic MPO lesions impaired drinking responses to 1 M NaCl and increased plasma osmolality.
- KA-induced MPO neuron depletion significantly reduced drinking responses to 1.0 M saline, 30% PG, and isoproterenol.
- Rats with MPO lesions showed normal drinking responses to water deprivation, lower saline concentrations, and angiotensin II.
Conclusions:
- The medial preoptic area (MPO) is critical for mediating drinking responses to specific dipsogenic challenges, particularly hypertonic stimuli.
- The MPO's role in fluid regulation is specific and does not encompass all thirst-inducing signals or general homeostatic control.