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Intrapreoptically microdialyzed and microinjected norepinephrine evokes different thermal responses.
1Department of Physiology and Biophysics, University of Tennessee, Memphis 38163.
The American Journal of Physiology
|October 1, 1989
Summary
Norepinephrine (NE) causes different core temperature (Tco) changes depending on administration method. Prostaglandin E2 (PGE2) contamination during microinjection may explain the rise, while NE alone causes a Tco fall.
Area of Science:
- Neuroendocrinology
- Thermoregulation
- Pharmacology
Background:
- Norepinephrine (NE) administration into the medial preoptic area (MPO) yields contrasting core temperature (Tco) effects.
- Microinjection of NE typically causes a Tco rise, while microdialysis results in a Tco fall.
- Prostaglandin E2 (PGE2) is a known contaminant in microinjection procedures and may influence thermal responses.
Purpose of the Study:
- To investigate the role of prostaglandin E2 (PGE2) in mediating the differential thermal responses to microinjected versus microdialyzed norepinephrine (NE).
- To determine the site specificity of NE's effects on Tco within the hypothalamus and related areas.
- To elucidate the interaction between NE and PGE2 in the MPO on Tco regulation.
Main Methods:
- Microinjection and microdialysis techniques were used to administer NE and PGE2 into specific brain regions of conscious guinea pigs.
- The prostaglandin synthetase inhibitor indomethacin (Indo) was administered to block PGE synthesis.
- Core body temperature (Tco) was continuously monitored following substance administration.
Main Results:
- Microinjection of NE into the MPO, after indomethacin treatment, prolonged the latency of the Tco rise and, under specific conditions, induced hypothermia.
- Microdialysis of NE into the MPO, lateral septum, and anterior hypothalamus consistently caused Tco falls, demonstrating site specificity.
- Microdialysis of PGE2 into the MPO induced a Tco rise, and co-administration with NE neutralized their respective effects.
Conclusions:
- The findings suggest that PGE2 contamination during NE microinjection contributes to the observed hyperthermic response.
- NE and PGE2 exhibit reciprocal influences on Tco regulation within the MPO.
- The differential thermal effects of NE depend on the administration method and the presence of PGE2, highlighting the complexity of central thermoregulation.