A recent modification of the alcohol dependence model was made to reflect the natural progression of alcohol dependence in which alcohol exposure occurs in a series of extended exposures followed by periods of withdrawal (O'Dell et al., 2004). Chronic exposure to intermittent alcohol vapor exposure elicits even higher alcohol self-administration than continuous vapor (O'Dell et al., 2004), and the intermittent procedure therefore was used to induce dependence in trained animals in the present study. Vapors were delivered on a 14 h on/10 h off schedule for 4 weeks before post-vapor testing began. This schedule of exposure has been shown to induce physical dependence (Richardson et al., 2008). In the chambers, 95% alcohol flows from a large reservoir to a peristaltic pump (model QG-6, FMI Laboratory, Fluid Metering). Alcohol is delivered from the pump to a sidearm flask at a flow rate that can be regulated. The flask is placed on a heater in which the drops of alcohol hitting the bottom of the flask are vaporized. Air flow controlled by a pressure gauge is delivered to the flask and carries
