Interbody lumbar fusion with a threaded cylindrical cage does not appear to have any clinically relevant effects on segmental lordosis, which is maintained within anatomically normal levels. Clinical outcome measures show significant postsurgery improvement, and changes in lordotic angles are not predictive of clinical outcome.

The effects of acute and chronic administration of intramuscular naltrexone (0.1, 0.3, 1.0, and 3.0 mg/kg) on oral ethanol (8%) self-administration were examined. Naltrexone (1.0 mg/kg) effects on the self-administration of ethanol concentrations ranging from 0.5 to 8% (w/v) were also investigated. Rhesus monkeys with substantial histories of drug and ethanol drinking served as subjects. During daily 3-hr sessions, monkeys were presented with ethanol solutions, concurrently available with water, under fixed-ratio reinforcement schedules. Naltrexone decreased the consumption of ethanol (g/kg). Biphasic temporal effects were observed within sessions. Naltrexone dose-dependently decreased the number of ethanol deliveries by a maximum of 56% (n = 18; 3 monkeys x 6 sessions) during the first hour of the session. During the second and third hours, however, ethanol intake recovered such that maximum decreases over the 3-hr session were approximately 27% (n = 18), and the mean decrease was 16% (n = 18). Often marked tolerance was observed, such that the effects of acute naltrexone administration were greater than effects after chronic administration. The self-administration of low ethanol concentrations (< or =2% w/v) was increased in several monkeys, by up to 340%, after naltrexone pretreatment. In summary, the effects of naltrexone on ethanol self-administration, in drug- and alcohol-experienced rhesus monkeys, are not characterized by unitary decreases in measures of ethanol self-administration. Rather, differential naltrexone effects were a function of experimental parameters, including the dose and number of naltrexone injections, the ethanol concentration, and the time point of measurement.

Four rhesus monkeys (Macaca mulatta), maintained at reduced body weight and restricted food availability, had access to a 0.8-mg/ml cocaine solution and vehicle under a concurrent fixed-ratio (FR) 8 schedule. Over days, the cocaine concentration was reduced (0.57, 0.4, 0.2, 0.1, 0.05, 0.025) and then returned, gradually over days, to 0.8 mg/ml. The ratio value was then varied (to 16, 32, 64, 128, and 8). Food access was unrestricted, and the ratio and the concentration manipulations were then repeated. During food restriction cocaine served as a reinforcer for all monkeys, whereas during free feeding cocaine functioned as a reinforcer for 3 of 4 monkeys; with these monkeys, the dose-response curve obtained under free feeding was shifted to the right of that obtained under food restriction. There were no differences in FR response curves obtained during food restriction and unrestricted feeding. These data suggest that food restriction increases cocaine's reinforcing effects and that the higher the cocaine dose, the greater are the reinforcing effects. A demand curve analysis was completed, and data are discussed in terms of microeconomic principles.

No abstract

Monkeys were given a choice between cocaine solutions and water under concurrent fixed-ratio reinforcement schedules. The operant response was spout contact. Six rhesus monkeys served as subjects. The cocaine concentration was varied from 0.0125 to 0.8 mg/ml, and the fixed-ratio value was varied from 8 to 128. Cocaine maintained higher response rates than did water over a wide range of conditions. Response rate and number of cocaine deliveries per session were inverted U-shaped functions of concentration. These functions were shifted to the right as the fixed ratio was increased. The number of cocaine deliveries was more persistent as fixed-ratio value was increased when the unit dose was larger rather than smaller. Cocaine consumption was analyzed as a function of unit price (fixed-ratio value divided by cocaine concentration), and unit price accounted for between 77% and 92% of the variance in cocaine consumption for individual monkeys. The current data support the claim that a drug's reinforcing effects increase directly with dose and underscore the need to gather parametric data when examining the effects of experimental manipulations on a drug-reinforced baseline.