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Role of the cholinergic system within the posterior hypothalamic nucleus (PHN) during simulated hemorrhage
Author(s) -
Dudley Tawny M.,
Martin John R.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a1407
Stimulation of muscarinic receptors in the PHN of rats evokes an increase in mean arterial pressure (MAP) via sympathoexcitation. The current study was undertaken to determine if the cholinergic system within the PHN plays a role in maintaining MAP during hemorrhage. Male Sprague‐Dawley rats (270–330 g) had their left femoral artery catheterized for MAP, heart rate, and pulse pressure measurement, while the right femoral artery was catheterized for blood withdrawal to simulate hemorrhage. Each rat was implanted with a cannula directed to the left PHN for the microinjection of methylatropine (MeATR; 11nmol, 100 nl) or neostigmine (NEOS; 0.6 nmol, 200 nl) to block muscarinic receptors or to inhibit acetylcholine degradation, respectively, within the PHN. Control rats were microinjected with an equal volume of saline. Rats in each group were bled (1.875 ml/kg/min) until MAP was maintained at 40 mmHg. To normalize the values of blood loss, the amount of blood withdrawn from each rat was divided by the weight of the rat (kg), which was then divided by the difference between the pre‐hemorrhage MAP and the final MAP (40 mmHg) for that rat. The average normalized value of blood loss for the MeATR‐ and NEOS‐treated groups were not significantly different from those of the saline‐treated group, nor was the survival rate different between the groups after reinfusion of the withdrawn blood, which was done when MAP fell to 25 mmHg. These results suggest that the cholinergic system within the PHN may not play an active role in the responses evoked by hemorrhage in the anesthetized rat. Supported by an Institutional Graduate Program grant.