A precision drinking device for rats tested with water, etonitazene, and ethanol

An inexpensive system for detecting tongue licking and for delivering liquids to rats is described. Liquids were dispensed under a heterogenous chain schedule of reinforcement in which depressions of a lever were required before tongue licking produced liquid delivery. Three rats drank water dispensed by the system at lowest, highest, and midmost valve settings. The volume of water delivered increased logarithmically from 0.00270 ml to 0.01180 ml across valve settings. In additional tests, drug-experienced rats were tested with either 5.0 microgram/ml etonitazene HCl, water, or 8% w/v ethanol available with the valve at its widest setting. More of the drug solutions were consumed than water suggesting that the drugs served as reinforcers. Intakes of both drugs were compared with intakes previously determined in dipper delivery systems using the same rats. This liquid delivery system has several advantageous features in that it is inexpensive to construct, allows quick and easy control of the volume delivered, minimizes evaporation, and, along with the heterogenous chain schedule of reinforcement, insures that liquid is delivered only when oral contact is made with it.