Radiation produced avoidance to morphine

Abstract

The effects of two concentrations of morphine solution (eS) Radiation has been demonstrated to function as an unconditioned aversive stimulus (UCS) for avoidance conditioning (GarCia et al, 1955). Although saccharin solution has been used as the conditioned stimulus (CS) in many studies, avoidance conditioning has been obtained utilizing chocolate milk (Kimeldorf et al, 1960) and alcohol (Peacock & Watson, 1964).The above studies produced conditioned avoidance behavior to "naturally" preferred solutions. Given a choice between tap water and morphine solutions, tap water will be the "natural" choice displayed by rats. A technique has been developed (Nichols et aI, 1956) which will train rats to choose morphine solution. The rat then displays opiate directed behavior in a two choice situation. The "trained" preference (morphine solution) gradually reverts to the natural choice of tap water as a function of time; this phenomenon is represented by gradual decrease in morphine consumption over a period of weeks (Nichols et al, 1956;Nichols, 1965). It appeared to be of interest to investigate the modification of opiate directed behavior (which represents a physiological dependency) by avoidance conditioning techniques. Method and ProcedureThe Ss were 18 male Sprague-Dawley rats from the Western Michigan University colony, approximately six months old, with a mean weight of 305. g at the beginning of experimentation.Pre-Irradiation. Morphine dosage began at 9 mg/ kg/day and was increased by 1/2 of the dose of the previous day until 40 mg/kg/day was reached. Increases of 10 mg/kg/day were made until Ss were receiving 110 mg/kg/day, then by 20 mg/kg/day until a level of 210 mg/kg/day was reached. Subcutaneous injections of morphine sulphate were scheduled at 12 h intervals, 9:00 AM and 9:00 PM. The site of injections was alternated between the left and right sides. During the injection series. Ss received tap water for 1 h during every 24 h period, 6 h after the morning injection to avoid association of water availability with the injection of morphine. Wayne Lab Blocks were available at all times. Following cessation of injections, Sa were offered morphine in tap water (0.5 mg/cc) for oral intake in a forced Ten Ss continued to refuse to drink. When no measurable amount of morphine solution had been ingested for seven days, tap water was made continually avallable, but the Ss still did not drink. Using preinjection weight as a base, these Ss had lost 42-45% of their body weight at the time of death. Group 1 was composed of those four Ss which drank a 0.5 mg/cc morphine solution. Group 2 of those four Ss which drank a 0.25 mg/kg concentration.IrradiatIOn. In keeping with the deprivation schedule, Ss were irradiated on the day when morphine only was presented. 2 The radiation (X-radiation) source was a Mathison 140 P K V mobile therapy unit drawing 8 milliamperes and having an 8 in. cone. Exposure was checked by a CD V 746 dosimeter which gave readings in Roentgen (R) units. The radiation chamber was a circular wooden ...