Differential changes in central monoaminergic metabolism during first and multiple sodium depletions in rats

To investigate the role of central monoamines in the behavior of sodium appetite, serotonergic and dopaminergic metabolism in regions of the forebrain and dorsal hindbrain were measured in sodium-depleted rats. Male Sprague-Dawley rats were sodium depleted by injection of the diuretic-natriuretic drug, Lasix (furosemide, 10 mg), and maintained on a sodium-deficient diet overnight. Rats were tested at a first sodium depletion or after multiple sodium depletions. There were three test conditions: 1) mock depletion consisted of vehicle injection and overnight sodium-deficient diet; 2) sodium depletion alone consisted of Lasix injection and overnight sodium-deficient diet; and 3) intake of NaCl following sodium depletion consisted of 9-min access to 0.3 M NaCl after Lasix injection and overnight sodium-deficient diet. Dopamine (DA), DOPAC, HVA, 5-HT, and 5-HIAA were measured by HPLC in the olfactory tubercle, amygdala-pyriform lobe, n. accumbens, hypothalamus, caudate nucleus, and the dorsal hindbrain. Ingestion of 0.3 M NaCl for 9 min after the first sodium depletion increased 5-HIAA/5-HT ratio significantly in the n. accumbens and amygdala, and increased DOPAC/DA ratio in the n. accumbens and olfactory tubercle compared to the mock treatment. In contrast to the results after the first sodium depletion, rats that ingested 0.3 M NaCl after four or more sodium depletions had no changes in 5-HT and DA metabolism in the forebrain, but they did have a significantly larger 5-HIAA/5-HT ratio in the dorsal hindbrain than mock-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)