Effect of Brain Serotoninergic Stimulation on Sodium Appetite of Euthyroid and Hypothyroid Rats

Abstract

The aim of the present work was to investigate the role of the serotoninergic system in the control of sodium appetite of hypothyroid rats (HTR) by administering drugs that affect the serotoninergic activity, and to compare the same homeostatic behaviour in euthyroid rats (ETR) also given these drugs. Fenfluramine (FEN; 5.0 mg kg _1 , I.P.), which releases serotonin in the brain, significantly reduced the intake of 1.8 % NaCl in HTR subjected to water and sodium depletion (depleted) or water, sodium and food deprivation (deprived) by 31 and 45 %, respectively, 120 min after FEN injection, compared to HTR that received vehicle alone. Similarly, administration of FEN to ETR reduced 1.8 % NaCl intake in depleted and deprived rats by 64 and 46 %, respectively. The presynaptic serotonin reuptake inhibitor fluoxetine (20.0 mg kg _1 , I.P.) led to the inhibition of sodium appetite in HTR during the initial 30 min in depleted rats and for up to 60 min post-injection in deprived rats, while sodium appetite inhibition persisted for longer periods in ETR. The 5HT2C receptor agonist mCPP (5.0 mg kg _1 , I.P.) caused a drastic reduction in sodium appetite in HTR and ETR in depleted and deprived rats, respectively, after 120 min. Prior administration of the 5HT2C receptor antagonist LY53857 (5.0 mg kg _1 , I.P.) completely blocked the inhibitory action of mCPP on sodium appetite in both HTR and ETR. In summary, our results suggest that the recruitment of serotoninergic neurons involved in the modulation of sodium appetite seems to be decreased in hypothyroidism due to a probable deficiency in the cerebral signalling pathway.

Chronic excitotoxic lesion of the dorsal raphe nucleus induces sodium appetite

“…It has been postulated that the DRN serotonergic neurons receive viscerosensory inputs concerning renal sodium load and/or ECF volume variations to trigger homeostatic regulation of sodium appetite (6,21,30). This view has not shown).…”

Role of the serotoninergic system in the sodium appetite control

“…In this condition, the ACE inhibitor just acts peripherally. Therefore, the increase of brain ANG I availability provides the manifestation of the sodium appetite through mechanism that requires central conversion of ANG I to ANG II (Elfont et al 1984, Moe et al 1984, Fitzsimons 1998, Badauê-Passos et al 2003.…”

“…Studies carried out in our laboratory led to similar results. Acute systemic treatments with the brain 5-HT releaser, fenfluramine, the selective 5-HT re-uptake inhibitor, fluoxetine or the 5-HT2C receptor agonists, MK212 and mCPP, reduced signifi cantly the hypertonic saline ingestion, in both, fluids and food deprived-rats and sodium-depleted rats as well (Badauê-Passos et al 2003). Intracerebroventricular administration of 5-HT agonists confi rmed the observations obtained with the systemic treatment and introduced the probable participation of another 5-HT receptor.…”

Effect of L-5-Hydroxytryptophan on drinking behavior in Coturnix japonica (Temminck and Schlegel, 1849) (Galliformes: Aves): involvement of renin-angiotensin system

“…Behavior, such as drinking and feeding are constantly monitored by 5-HT-containing neurons in mammals and birds. Studies in our laboratory evidenced the serotonergic neurons influence in the sodium appetite and food and water intake behavior (Badauê-Passos Jr et al, 2003;Olivares et al, 2003;Lima et al, 2004;Cavalcante-Lima et al, 2005a,b;Cedraz-Mercez et al, 2005;Medeiros et al, 2005). In rats, peripheral administration of either 5-HT or its precursor 5-HTP induces water intake via renal renin-angiotensin system (RAS) activation (Rowland et al, 1987), however they display opposed effects when centrally applied.…”