A technique for self-injection of drugs in the study of reinforcement

A Procedure Which Produces Sustained Opiate-Directed Behavior (Morphine Addiction) in the Rat

Contrary to naive assumption, animals do not show altered behavior toward opiates after injection. However, a procedure, based on operant conditioning theory, is described which produces sustained opiate-directed behavior (oral morphine addiction) in rats. What is believed to be the first demonstration of relapse in animals was obtained with this method. Examples applying this procedure are given and typical results are shown. This procedure is valuable in that it permits direct experimental attack on many otherwise very difficult problems of addiction. The success of this method in producing sustained opiate-directed behavior in animals has significant implications regarding the development of sustained opiate-directed behavior in man.

Unit-price analysis of opioid consumption by monkeys responding under a progressive-ratio schedule of drug injection

Several reports have indicated that drug consumption in self-administration procedures is a function of the ratio of the instrumental requirement to the dose of drug, a quantity termed unit price. We evaluated three predictions from this unit-price model in a reanalysis of data on opioid self-administration in rhesus monkeys responding under a progressive-ratio schedule (Hoffmeister, 1979). We evaluated whether consumption was inversely related to unit price, and compared the goodness of fit of an equation devised by Hursh, Raslear, Shurtleff, Bauman, and Simmons (1988) to that of a linear model predicting consumption as a function of dose. We also tested whether consumption was constant when the same unit price was comprised of different combinations of dose and instrumental requirement. Consumption declined overall as unit price increased. The equation devised by Hursh et al. and the linear model based on dose fit the data equally well. Drug consumption was not uniform at a given unit price. The analyses suggest limits on the unit-price model as a characterization of drug consumption.

The pneumatic syringe: a simple apparatus for self-administration of drugs by rats

Drug solution is delivered by a syringe operated by a pneumatic cylinder. Recommended delivery volumes are from 10 to 200 microliter. A solid-state control unit is described which can operate two syringes (drug injection and flush), has outputs for recording responses and injections, and can be programmed to provide several schedules of reinforcement. All components are readily commercially available.

Intraventricular self-administration of morphine in naive laboratory rats

Male Wistar rats implanted with cannulae aimed at the left lateral cerebral ventricle were individually maintained in Skinner boxes for 11 consecutive days. Animals were neither predependent on morphine nor shaped to press the operant lever. Experimental animals (n = 7) obtained intraventricular infusions of a 1% morphine HCl solution (2 mul per 5-s infusion) for each lever press while control animals (n = 7) received only the vehicle. Four animals were yoked to experimental animals and received equivalent but non-contingent morphine HCl infusions. The mean number of lever presses per day for the experimental group was significantly higher than for the vehicle control or yoked control groups suggesting that naive rats will work for the positive reinforcing properties of morphine when it is infused centrally.

Drug self-administration and sleep-awake activity in rats dependent on morphine, methadone, or l-alpha-acetylmethadol

Morphine post-dependent rats were prepared with chronic cortical EEG and temporalis muscle EMG electrodes and i.v. jugular cannulae and permitted to self-administer morphine (10 mg/kg/injection) on a fixed-ratio schedule of reinforcement to reestablish and maintain dependence. Morphine was then replaced by methadone or 1-alpha-acetyl-methadol (LAAM) at a dose of 2 and 1 mg/kg, respectively. The rats developed stable patterns of self-administration of each narcotic and maintained the dependent state. The mean (+/- S.E.) interinjection interval was 2.5 +/- 0.1 h for morphine, 1.4 +/- 0.1 h for methadone and 8.8 +- 0.8 H FOR LAAM. The distribution of sleep, REM sleep, and awake within the interinjection interval for the three narcotics was similar. A short phase of behavioral stupor concomitant with EEG slow bursts emerged following the self-injections. This phase was followed by arousal with EEG activation. Sleep and REM sleep then reappeared and predominated before the next injection. LAAM manifested a relatively slow onset of action in comparison with morphine and methadone.