The control of water and sodium chloride intake by postingestional and orosensory stimulation in water-deprived rats

Abstract

We investigated the role of oropharyngeal and postingestional stimulation in the control of the intake of water and NaCl solutions by testing water-deprived rats under real- and sham-drinking conditions with water, 0.150, 0.225, and 0.300 M NaCl solutions. A series of real-drinking tests was given until intake stabilized followed by a series of sham-drinking tests with the same solution. When sham intake stabilized the concentration was increased and the series of real- followed by sham-drinking tests was repeated. Intake of water and 0.150 M NaCl in the first sham-drinking test was significantly greater than in the preceding real-drinking test and did not change with real- or sham-drinking experience. In contrast, intake of 0.225 and 0.300 M NaCl in the first sham-drinking test was not significantly greater than in the preceding real-drinking test but increased with sham-drinking experience. Real intake of 0.225 and 0.300 M NaCl following sham-drinking experience with a lower concentration declined significantly with real-drinking experience. These results show that postingestional stimulation plays a direct role in the control of the intake of water and isotonic saline with little or no orosensory contribution. In contrast, conditioned orosensory responsiveness played the central role in the control of the intake of the two hypertonic solutions with little or no direct contribution from postingestional stimulation. Postingestional stimulation, however, played an indirect role by serving as the unconditioned stimulus for the conditioned orosensory control.