RESUMO
We determined if the dorsal raphe nucleus (DRN) exerts tonic control of basal and stimulated sodium and water intake. Male Wistar rats weighing 300-350 g were microinjected with phosphate buffer (PB-DRN, N = 11) or 1 microg/0.2 microl, in a single dose, ibotenic acid (IBO-DRN, N = 9 to 10) through a guide cannula into the DRN and were observed for 21 days in order to measure basal sodium appetite and water intake and in the following situations: furosemide-induced sodium depletion (20 mg/kg, sc, 24 h before the experiment) and a low dose of dietary captopril (1 mg/g chow). From the 6th day after ibotenic acid injection IBO-DRN rats showed an increase in sodium appetite (12.0 +/- 2.3 to 22.3 +/- 4.6 ml 0.3 M NaCl intake) whereas PB-DRN did not exceed 2 ml (P < 0.001). Water intake was comparable in both groups. In addition to a higher dipsogenic response, sodium-depleted IBO-DRN animals displayed an increase of 0.3 M NaCl intake compared to PB-DRN (37.4 +/- 3.8 vs 21.6 +/- 3.9 ml 300 min after fluid offer, P < 0.001). Captopril added to chow caused an increase of 0.3 M NaCl intake during the first 2 days (IBO-DRN, 33.8 +/- 4.3 and 32.5 +/- 3.4 ml on day 1 and day 2, respectively, vs 20.2 +/- 2.8 ml on day 0, P < 0.001). These data support the view that DRN, probably via ascending serotonergic system, tonically modulates sodium appetite under basal and sodium depletion conditions and/or after an increase in peripheral or brain angiotensin II.
Assuntos
Apetite/efeitos dos fármacos , Ingestão de Líquidos/efeitos dos fármacos , Agonistas de Aminoácidos Excitatórios/toxicidade , Ácido Ibotênico/toxicidade , Núcleos da Rafe/efeitos dos fármacos , Sódio na Dieta , Inibidores da Enzima Conversora de Angiotensina/farmacologia , Animais , Apetite/fisiologia , Soluções Tampão , Captopril/farmacologia , Ingestão de Líquidos/fisiologia , Furosemida/farmacologia , Masculino , Fosfatos , Ratos , Ratos Wistar , Inibidores de Simportadores de Cloreto de Sódio e Potássio/farmacologia , Fatores de TempoRESUMO
We determined if the dorsal raphe nucleus (DRN) exerts tonic control of basal and stimulated sodium and water intake. Male Wistar rats weighing 300-350 g were microinjected with phosphate buffer (PB-DRN, N = 11) or 1 æg/0.2 æl, in a single dose, ibotenic acid (IBO-DRN, N = 9 to 10) through a guide cannula into the DRN and were observed for 21 days in order to measure basal sodium appetite and water intake and in the following situations: furosemide-induced sodium depletion (20 mg/kg, sc, 24 h before the experiment) and a low dose of dietary captopril (1 mg/g chow). From the 6th day after ibotenic acid injection IBO-DRN rats showed an increase in sodium appetite (12.0 ± 2.3 to 22.3 ± 4.6 ml 0.3 M NaCl intake) whereas PB-DRN did not exceed 2 ml (P < 0.001). Water intake was comparable in both groups. In addition to a higher dipsogenic response, sodium-depleted IBO-DRN animals displayed an increase of 0.3 M NaCl intake compared to PB-DRN (37.4 ± 3.8 vs 21.6 ± 3.9 ml 300 min after fluid offer, P < 0.001). Captopril added to chow caused an increase of 0.3 M NaCl intake during the first 2 days (IBO-DRN, 33.8 ± 4.3 and 32.5 ± 3.4 ml on day 1 and day 2, respectively, vs 20.2 ± 2.8 ml on day 0, P < 0.001). These data support the view that DRN, probably via ascending serotonergic system, tonically modulates sodium appetite under basal and sodium depletion conditions and/or after an increase in peripheral or brain angiotensin II.
Assuntos
Animais , Masculino , Ratos , Ácido Ibotênico/toxicidade , Agonistas de Aminoácidos Excitatórios/toxicidade , Apetite/efeitos dos fármacos , Ingestão de Líquidos/efeitos dos fármacos , Núcleos da Rafe/efeitos dos fármacos , Sódio na Dieta , Apetite/fisiologia , Soluções Tampão , Captopril/farmacologia , Furosemida/farmacologia , Ingestão de Líquidos/fisiologia , Inibidores da Enzima Conversora de Angiotensina/farmacologia , Inibidores de Simportadores de Cloreto de Sódio e Potássio/farmacologia , Fosfatos , Ratos Wistar , Fatores de TempoRESUMO
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.
Assuntos
Apetite/fisiologia , Ingestão de Líquidos/fisiologia , Núcleos da Rafe/lesões , Cloreto de Sódio/administração & dosagem , Animais , Traumatismos por Eletricidade/fisiopatologia , Masculino , Ratos , Ratos Wistar , Fatores de TempoRESUMO
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 percent 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 æg 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.