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Abstract
<p class="first" id="P1">The controls of thirst and sodium appetite are mediated in
part by the hormones aldosterone
and angiotensin II (AngII). The present study examined the behavioral and neural mechanisms
of altered effort-value in animals treated with systemic mineralocorticoids, intracerebroventricular
AngII, or both. First, rats treated with mineralocorticoid and AngII were tested in
the progressive ratio operant task. The willingness to work for sodium versus water
depended on hormonal treatment. In particular, rats treated with both mineralocorticoid
and AngII preferentially worked for access to sodium versus water compared with rats
given only one of these hormones. Second, components of the mesolimbic dopamine pathway
were examined for modulation by mineralocorticoids and AngII. Based on cFos immunohistochemistry,
AngII treatment activated neurons in the ventral tegmental area and nucleus accumbens,
with no enhancement by mineralocorticoid pretreatment. In contrast, western blot analysis
revealed that combined hormone treatment increased levels of phospho-tyrosine hydroxylase
in the ventral tegmental area. Thus, mineralocorticoid and AngII treatments differentially
engaged the mesolimbic pathway based on tyrosine hydroxylase levels versus cFos activation.
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