Schedule-induced polydipsic consumption of hypertonic NaCl solutions: effects of chlordiazepoxide

Rats were exposed to daily, 3-h sessions of schedule-induced polydipsia (SIP) in which either water, hypertonic NaCl solution (1.5% or 2.2%), or concurrent water and 1.5% NaCl were available. Each condition was in effect for several, consecutive weeks. Presession subcutaneous injections of chlordiazepoxide (CDZP) produced dose-related increases in the polydipsic ingestion of both NaCl solutions but had smaller and less certain effects on water consumption. Under the concurrent-fluid presentation condition, CDZP primarily increased NaCl solution consumption. Conditions generating SIP may function to attenuate what might be viewed as the punishing effects of ingesting highly hypertonic NaCl solutions, thereby permitting the chronic self-administration of large, daily amounts. Like many benzodiazepines, CDZP can attenuate the effects of punishment and thereby also increase NaCl solution ingestion. The two sources of punishment attenuation may be additive, with both differentially effecting greater increases in hypertonic NaCl ingestion, compared to water, when both fluids are presented concurrently.