Abstract
The present study determined the effect of an electrolytic lesion of the dorsal raphe nucleus (DRN) on water intake and sodium appetite. Male Wistar rats weighing 290-320 g with a lesion of the DRN (L-DRN), performed two days before experiments and confirmed by histology at the end of the experiments, presented increased sensitivity to the dehydration induced by fluid deprivation. The cumulative water intake of L-DRN rats reached 23.3 1.9 ml (a 79% increase, N = 9) while sham-lesioned rats (SL-DRN) did not exceed 13.0 1.0 ml (N = 11, P < 0.0001) after 5 h. The L-DRN rats treated with isoproterenol (300 g kg-1 ml-1, sc) exhibited an increase in water intake that persisted throughout the experimental period (L-DRN, 15.7 1.47 ml, N = 9 vs SL-DRN, 9.3 1.8 ml, N = 11, P < 0.05). The L-DRN rats also showed an increased spontaneous sodium appetite during the entire period of assessment. The intake of 0.3 M NaCl after 12, 24, 36 and 72 h by the L-DRN rats was always higher than 20.2 4.45 ml (N = 10), while the intake by SL-DRN was always lower than 2.45 0.86 ml (N = 10, P < 0.00001). Sodium- and water-depleted L-DRN rats also exhibited an increased sodium appetite (13.9 2.0 ml, N = 11) compared to SL-DRN (4.6 0.64 ml, N = 11) after 120 min of observation (P < 0.02). The sodium preference of L-DRN rats in both conditions was always higher than that of SL-DRN rats. These results suggest that electrolytic lesion of the DRN overcomes a tonic inhibitory component of sodium appetite.
Highlights
Serotonergic neurons of the mesencephalic dorsal raphe nucleus (DRN), located in its medial portion, project to prosencephalic regions involved in hydroelectrolytic and cardiocirculatory homeostasis [1,2,3,4]
The results of the present study reveal that electrolytic lesions of the DRN produced an increase in sensitivity to osmotic stimulation by dehydration induced by fluid deprivation and ß-adrenergic stimulation with isoproterenol
This observation is consistent with the hypothesis that neurons of the DRN, which are probably serotonergic, exert a modulatory influence on the thirst related to an increase in the tonicity of extracellular fluid or on the thirst signaled by increased plasma levels of angiotensin II- (ANG II) [4,19,20,21]
Summary
Serotonergic neurons of the mesencephalic dorsal raphe nucleus (DRN), located in its medial portion, project to prosencephalic regions involved in hydroelectrolytic and cardiocirculatory homeostasis [1,2,3,4]. The short and long term, the changes in volume, pressure and sodium concentration in the extracellular fluid, evokes electrophysiological changes in the DRN [7] In this context, it has been shown that the microinjection of serotonergic agonists of the 5HT2A and 5HT2C receptors into the SFO excites angiotensin II- (ANG II) sensitive neurons [8]. Relevant observations have shown that stimulation of the AV3V region by intracerebroventricular (icv) administration of serotonin, serotonin-releasing agents or 5HT2A/2C agonists increases the urinary excretion of sodium [12,13] All of these stimulation conditions under fluid deprivation, cholinergic or angiotensinergic stimulation of the AV3V region and central or systemic ßadrenergic stimulation caused a decrease in water intake [14,15,16]. Spontaneous sodium appetite was investigated in DRN-lesioned rats following a simultaneous offer of water and hypertonic saline for three consecutive days
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Schedule a callMore From: Brazilian journal of medical and biological research = Revista brasileira de pesquisas medicas e biologicas
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