Topic: Smoked Heroin and Cocaine Base (Speedball) Combinations Smoked Heroin and Cocaine Base (Speedball) Combinations
Article Critiques – Students are required to submit two article critiques. Each critique must be relevant to issues of chemical use and dependency and its effects. The articles for the critique must come from a peer reviewed journal. Examples of peer reviewed journals include:
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A. Theoretical Article
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2. Summary of Article:
b. Key Points
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Experimental and Clinical Psychopharmacology 1997, Vol. 5, No. 2,113-118 Copyright 1997 by the American Psychological Association, Inc. 1064-l297/97/$3.00 Smoked Heroin and Cocaine Base (Speedball) Combinations in Rhesus Monkeys Adande J. Mattox, Sherry S. Thompson, and Marilyn E. Carroll University of Minnesota, Twin Cities Campus The purpose of this investigation was to compare the self-administration of heroin and cocaine base, alone and in combination, in rhesus monkeys (Macaco mulatto) self-administering a combination of heroin (0.1 mg/kg/delivery) and cocaine base (1.0 mg/kg/delivery) via the smoking route. Smoke deliveries were contingent on completion of a chained fixed ratio (FR; lever press), FR 5 (inhalation) schedule. The lever press FR values (64, 128, 256, 512, and 1,024) represented increasing drug price. Demand functions (Consumption X Price) were obtained for the heroin and cocaine combination and compared with previously determined demand functions for smoked heroin and cocaine alone. As the FR increased and the number of responses emitted increased, the number of drug deliveries decreased. The demand functions were not different for heroin versus cocaine alone or for cocaine alone versus the cocaine-heroin combination. However, the demand for heroin alone was significantly less than the demand for the cocaine-heroin combination, suggesting that smoked cocaine base enhances the behavioral effects of smoked heroin. Heroin and cocaine combinations, also known as speedballs, have a long history of abuse. According to the National Institute on Drug Abuse, the combination of heroin or morphine with cocaine accounted for 15,517 drug-related emergency room mentions in 1994 (U.S. Department of Health and Human Services [USDHHS], 1994), making this combination the second most mentioned drug combination. Further, studies report that 50% to 80% of heroin users are using cocaine (Office of National Drug Control Policy, 1994). Combinations of heroin or morphine with cocaine were also the second most mentioned drug combination after alcohol and cocaine in drug-related deaths (USDHHS, 1995). Thus, the abuse of the speedball combination poses a significant societal and public health issue. Typically, speedball combinations are injected intravenously. In a multistate survey, Diaz et al. (1994) reported that 17% of HIV-positive IV drug users admitted injecting speedball combinations. However, Kramer, Fine, Bahari, and Ottomanelli (1990) reported that 40% of the clients in their drug detoxification units were smoking heroin and crack combinations. The smoking route of self-administration may be more appealing for users, as smoking is seen as more socially acceptable than injecting drugs, and the risk of HIV transmission is decreased. Adande J. Mattox, Sherry S. Thompson, and Marilyn E. Carroll, Department of Psychiatry, University of Minnesota, Twin Cities Campus. This research was supported by National Institute on Drug Abuse Grants R01 DA07716, P01 DA08131, and T32 DA07097. We gratefully acknowledge the technical assistance of Vincent Hunt, Joshua Rodefer, and Lori Listug. A critical review of this article by Joshua Rodefer is also appreciated. Correspondence concerning this article should be addressed to Marilyn E. Carroll, Department of Psychiatry, University of Minnesota, Box 392 U.M.H.C., Minneapolis, Minnesota 55455-0392. Electronic mail may be sent via Internet to email@example.com. It has been hypothesized that heroin and cocaine combinations are self-administered because the coadministration of each of these drugs either enhances the positive effects or offsets the negative side effects of the other. In addition, the combination of the two drugs may produce an effect different from either drug alone (Mello et al., 1995). Ethnographers report that cocaine base (crack) is considered the primary drug, and heroin is added as a “bonus” to ease agitation (Office of National Drug Control Policy, 1995). Further, many new heroin users are crack users who have found that heroin is a way to “come down” from crack. In the laboratory, Foltin and Fischman (1992) evaluated the subjective effects of morphine and cocaine alone and in combination in individuals with histories of both heroin and cocaine use. Many measures did not reveal an interaction; however, there were a few that did. For example, they reported that cocaine alone produced typical stimulant-like effects such as increases in subjective reports of “High” scores and increases in the “A” (amphetamine) scores of the Addiction Research Center Inventory (ARCI). Heroin alone produced typically opiate-like effects such as increases in “Sedation” scores, increases in “High” scores, and increases in opiate symptoms. Morphine in combination with cocaine resulted in an attenuation of cocaine’s increase in “A” scores and of morphine’s increase in sedation. Interestingly, there were increases in “High” scores for the combination that were greater than either drug alone, and cocaine alone increased “I want heroin” scores in these individuals. These data suggest that cocaine and heroin may be interacting to produce different subjective effects than either drug alone. In a recent study of speedball self-administration by Mello et al. (1995), rhesus monkeys were tested with self-administration of IV heroin and cocaine alone and in combination. They reported no enhancement of the reinforcing effects of these drugs in combination. Further, they reported that both cocaine and heroin given singularly 113 114 MATTOX, THOMPSON, AND CARROLL possessed similar reinforcing effects. That the epidemiological data is only weakly supported by the laboratory data may be due to doses used, schedules, species, routes of administration, or other conditions. Research has demonstrated that rhesus monkeys selfadminister cocaine base (Carroll, Krattiger, Gieske, & Sadoff, 1990; Comer, Hunt, & Carroll, 1994; Comer, Turner, & Carroll, 1995) and heroin (Mattox & Carroll, 1996) by the smoking route of administration. One purpose of our study was to demonstrate the feasibility of establishing selfadministration of a cocaine-heroin combination via the smoking route in rhesus monkeys. Currently this is the only experimental model of cocaine or heroin smoking in nonhuman primates. The model appears to closely simulate human behavior as the drug-reinforced behavior is strongly maintained. Cocaine smoking is relatively resistant to behavioral or pharmacological treatment interventions (Comer et al., 1994; Rodefer, Mattox, Thompson, & Carroll, in press), suggesting that the drug functions as a potent reinforcer via the smoking route. A goal of this study was to determine whether the speedball effect would be more strongly expressed with this method than with the IV route that had been used in previous laboratory studies. Another goal was to assess the reinforcing efficacy of cocaine, heroin, and the cocaine-heroin combination, using a behavioral economic analysis of demand. Demand is defined as drug consumption plotted as a function of unit price (e.g., responses/mg) of drug. The demand function is typically characterized by a positively decelerating function (Hursh & Bauman, 1987). A parallel shift upward, a more shallow negative slope of the demand curve, or both, are indicators of increased reinforcing efficacy (Carroll, Rodefer, & Rawleigh, 1995; Hursh, 1991; Hursh & Winger, 1995). For this experiment, demand curves were generated by nonsystematically varying the fixed ratio (FR) required for drug delivery (price) and measuring the number of smoke deliveries (consumption) at each FR. To establish a range of unit prices, we tested monkeys with fixed doses of cocaine, heroin, or the cocaineheroin combination under a range of FR schedules (64— 1,024). We compared demand curves for cocaine alone (1.0 mg/kg/delivery), for heroin alone (0.1 mg/kg/delivery), and for these doses of the cocaine-heroin combination. Method Subjects Six male rhesus monkeys (Macaco mulatto) served as subjects (M-O, M-R3, M-
L1, M-N, M-S2, and M-M4). All subjects had previous experience with cocaine smoking, heroin smoking, or both (Mattox & Carroll, 1996). The monkeys were maintained at 85% of their free-feeding body weights. Body weights were determined by allowing the monkeys to free feed for several weeks and by then calculating 85% of the last three stable weights, which were taken weekly. The free-feeding weights ranged from 10.8 kg to 17.7 kg. Monkeys were weighed every 3-4 weeks. Their cages were steam cleaned every 2 weeks, and cage pans were washed daily. They were housed in their individual operant chambers in a temperature (23 °C)-controHed room under a 12-hr light-dark cycle (lights on from 6:00 a.m. to 6:00 p.m.). Water was freely available from a lip-operated drinking spout, except between 7:30 and 8:30 a.m., when data were collected from the previous day. Monkeys were fed amounts of Teklad monkey chow (e.g., 120-200 g; Bartonville, 1L) to maintain them at their 85% weights at 12:30 p.m. daily. Fresh fruits or other snacks (e.g., raisins) were also available at 1:00 p.m. The experimental protocol (No. 9302017) was approved by the University of Minnesota Institutional Animal Care and Use Committee. Apparatus The monkeys were individually housed in custom-made stainless steel chambers (Lab Products, Maywood, NJ) equipped with an operant work panel on one side that contained one drinking spout, one smoking spout, and a primate lever. The panel contained a solid green stimulus light above the drinking spout on the left to indicate the availability of water. A flashing red light (10 Hz) in the center above the lever designated that the lever-pressing contingency was in effect, while a flashing green light (10 Hz) above the smoking spout on the right indicated initiation of the smoking contingency and delivery of the drug. After the subject completed the lever-pressing schedule requirements, the red stimulus light was extinguished and the right flashing green light was illuminated until five inhalation responses occurred. The drinking and smoking spouts, both cylindrical in shape with a rounded tip, were mounted at the same height (31 cm apart, 48 cm above the chamber floor) directly below their respective stimulus lights. A response lever was located equidistant between the two spouts at 37.5 cm above the chamber floor. The drinking device located on the left side of the chamber consisted of a spout mounted on clear Plexiglas that measured 3.6 cm long, 1.5 cm outer diameter, 1.2 cm inner diameter with a rounded 0.6 cm diameter hole. Lip contacts on the spout resulted in the brief illumination of two white lights located on a clear Plexiglas plate that supported the power cup. The power cup contained the electronic circuitry to activate the drinking spout that allowed liquid to be dispensed from an elevated reservoir by opening a solenoid-operated valve for a fixed period of time. The timing of the spout operation was set to regulate water deliveries at approximately 0.60 ml. The smoking apparatus delivered volatilized drug to the subject at a dose of 1.0 mg/kg/delivery for cocaine base and 0.1 mg/kg/delivery for heroin. The smoking apparatus was also mounted on clear Plexiglas and was a modification of the drinking spout apparatus. The delivery mechanism consisted of a coil of Nichrome wire attached to a machined plug with two pieces of brass tubing, 0.15 cm outside diameter X 5.5 cm in length. The plug had 15 cm of wire with a 2-pin cinch-Jones connector. The connector was plugged into the smoking spout, which contained a vacuum sensor (Model 505-3; Conventry Specialty Corp., Westfield, MA), a 9-pin “D” connector, and a solenoid that regulated the mixture of volatilized drug and air through the spout. The drugs were dissolved in 95% ethanol (100 mg/ml) and stored in 25-ml volumetric flasks with vacutainer tops. The drug solution was dripped onto the Nichrome coils with a 1 ml syringe and 25-gauge needle. To ensure the accurate measurement of the drug, the ethanol was allowed to evaporate for at least 24 hr, leaving the desired dose of drug in dry crystal form on the coil. All coils were weighed before and after the drug application. This heating process vaporized the drug without pyrolizing it. To ensure that the smoke was not deposited in the cage and the monkey received the drag, the coil was heated to approximately 175 °C with a short, high-powered pulse while the monkey was inhaling. Before each trial, the coil was inserted into the smoking spout approximately 1.5 cm from the end of the spout facing the monkey. Inhalation on the spout activated a vacuum switch that sent a signal to the microcomputer control system. Five inhalation responses SPEEDBALL COMBINATIONS IN MONKEYS 115 (FR 5) were required to heat the coil. At the beginning of the fifth inhalation response, the coil was heated. Microcomputers (Microlnterfaces, Minneapolis, MN) controlled the experimental sessions and recorded the data. Detailed descriptions of test chambers (Henningfield & Meisch, 1976), drinking spouts (Meisch & Henningfield, 1977), microcomputers (Carroll, Santi, & Rudell, 1981), and smoking devices (Carroll et al., 1990; Comer et al., 1994; Mattox & Carroll, 1996) have been published. Drugs Cocaine base and heroin HC1 were provided by the National Institute on Drug Abuse (Research Triangle Institute, Research Triangle Park, NC). Ethanol (95%) was obtained from the University of Minnesota Chemical Storehouse. Cocaine base and heroin were mixed weekly and dissolved in 95% ethanol to a concentration of 100 mg/ml (cocaine) or 10 mg/ml (heroin) and stored in a 25-ml volumetric flask with a top from a 3-ml vacutainer. Procedure The subjects were previously trained to smoke cocaine or heroin during daily 4-hr sessions (8:30 a.m.-12:30 p.m.) 7 days per week. Consecutive trials were run, with a maximum of 10 deliveries of the drug. A trial consisted of a 30-min opportunity to complete the schedule requirements. Completed trials were followed by a 15-min time-out. If the response sequence of lever presses and inhalation responses was not completed within 30 min, the trial was considered aborted. If two consecutive trials were aborted, the experimental session was terminated for that day. During the 15-min time-out between each trial, the used coils were replaced with a fresh coil by the experimenter when either the subjects were in the time-out or there was a pause in responding. Before each daily session there was a 60-min time-out starting at 7:30 a.m. During this period, the water volumes from the previous night were recorded and 1,000 ml of fresh water was replaced for the experimental session. The daily experimental session ended at 12:30 p.m. Following the end of the session, the water consumption was measured and replaced with 2,000 ml of water and the subjects were fed. Although most of the monkeys had been previously tested with cocaine base under a range of FR schedules, the demand function for cocaine base was redetermined during this experiment. Thus, order of testing the cocaine base and cocaine-heroin combination demand function were counterbalanced across subjects. The heroin demand function was obtained immediately before this experiment in a previous study (Mattox & Carroll, 1996). The schedule requirement consisted of randomized blocks of FRs. The FRs tested were 64,128, 256, 512, and 1,024. Each FR was tested until 3 days of stable behavior were obtained. Most often the conditions were held constant for 4 or 5 days to obtain 3 stable days; however, occasionally it was necessary to test the condition for up to 10 days. Stability was defined as no steadily increasing or decreasing trend in responses or smoke deliveries. Data Analysis Individual means for number of smoke deliveries and responses per session were taken from the last 3 days of stable behavior from each monkey. We used a two-factor repeated measures analysis of variance (ANOVA) to analyze the effects of FR value and drug condition (cocaine vs. heroin vs. cocaine-heroin combination). Pairwise comparisons were made of heroin versus cocaine, heroin versus cocaine-her
oin combination, and cocaine versus cocaineheroin combination (SuperANOVA, Abacus Software, Berkeley, CA). Results were considered statistically significant if p s .05. Results Figure 1, left graph shows the number of smoked cocaine, heroin, and cocaine-heroin combination deliveries measured at FRs 64, 128, 256, 512, and 1,024. There were FR-related decreases in smoked cocaine self-administration (open squares) such that increases in FR resulted in a decrease in the number of deliveries. At the lowest FR tested, FR 64, the mean number of smoked cocaine deliveries was 9.94 (±0.05). At the intermediate FRs (e.g., 128 and 256), the mean number of deliveries were 9.4 (± 0.4) and 8.2 (±1.2), respectively. There was a 48% decrease in deliveries at FR 512, to 5.2 (±1.7), and at the highest FR tested, FR 1,024, there was an 84% reduction in smoked cocaine self-administration to 1.5 (± 1.1) from the baseline of FR 64. il 10000^ Si _ 1000- II ECocaine Cocaine Plus Heroin 100 1000 10000 100 1000 10000 Drug Price (Fixed Ratio) Figure 1. Left graph: Deliveries of smoked drug are plotted as a function of price, or fixed ratio (64, 128, 256, 512, and 1,024). Right graph: Responses per session for smoked drug are plotted as a function of price, or fixed ratio. Each point is the mean (±SE) for 6 subjects. Each subject’s data point consists of a mean of the last 3 consecutive days of stable behavior. 116 MATTOX, THOMPSON, AND CARROLL The demand curve for heroin is also presented in Figure 1 (open circles). These data were taken from a recently completed heroin self-administration study (Mattox & Carroll, 1996) with the same subjects. Heroin was readily self-administered in all 6 monkeys. There were also FRrelated decreases in smoked heroin self-administration, with increases in FR producing decreases in drug deliveries. The maximum number of smoked heroin deliveries of 9.8 (±0.2) was found at the lowest FR tested, 64. The mean smoked heroin deliveries at FRs 128, 256, and 512 were 8.6 (± 1.3), 6.8 (± 1.6), and 4.2 (± 1.4), respectively. At the highest FR tested, 1,024, there was a mean of 1.2 (±0.5) deliveries of smoked heroin. This represents an 88% reduction in smoked heroin deliveries from the baseline at FR 64. Figure 1, left graph, also shows FR-related decreases in drug deliveries for the cocaine-heroin combination (filled triangles). At the lowest and intermediate FRs (64, 128, and 256), the mean number of heroin and cocaine base deliveries were 10 (±0), 10 (±0), and 9.6 (±0.3), respectively. There was a 36% reduction in drug deliveries at FR 512 and a 64% reduction at the highest FR tested, 1,024, resulting in mean deliveries of 6.4 (±0.9) and 3.6 (±1.4), respectively. The slopes for the three demand curves were —0.93 (cocaine base), -0.72 (heroin), and -0.71 (cocaine-heroin combination), indicating inelasticity (> —1); however, as determined by nonoverlapping 95% confidence limits, they were not significantly different from each other (p > .05). A repeated measures ANOVA of the cocaine alone, heroin alone, and cocaine and heroin in combination conditions revealed significant main effects of drug condition (p < .05) and of ratio requirement (p < .05). Further contrast testing of the drug condition main effect revealed that there was no significant difference between the cocaine alone and the heroin alone conditions, and the cocaine alone and the cocaine-heroin combination did not quite reach statistical significance. However, the heroin alone condition was significantly different from the cocaine-heroin condition (p < .05). This significant difference indicated an increased intensity of demand (parallel shift upward) for the cocaineheroin combination versus the heroin alone condition. The responses per session for smoked heroin and cocaine are presented in the right graph of Figure 1. Again, the heroin data were taken from previous studies from this laboratory (Mattox & Carroll, 1996). For heroin, cocaine base, and the cocaine-heroin combination, there were increases in responding for the drug as the ratio requirement was increased. For heroin, these increases ranged from 626 (±7.9) at FR 64, to 2,181 (±433.6) at FR 1,024, the highest FR tested. Likewise, the range of responses for smoked cocaine base was 636 (±5.9) at FR 64, to 1,597 (±506) at FR 1,024. For the cocaine—heroin combination, the mean number of responses was 640 (±0) at FR 64. Increases in mean responses to 1,280 (±0), 2,447.4 (±61.4), and 3,297.3 (±41.1.1) were found at FRs 128, 256, and 512, respectively. A repeated measures ANOVA of these data revealed significant main effects for the drug condition (p < .05) and for ratio requirement (p < .05). Contrast testing of these main effects indicated that the heroin alone condition was significantly different from the cocaine-heroin combination (p < .05), whereas other pairwise comparisons were not significantly different. Discussion The present findings show that rhesus monkeys readily smoked a combination of cocaine base (1 mg/kg) and heroin (0.1 mg/kg) contingent on a range of response requirements. The data replicated previous findings showing cocaine base (Carroll et al., 1990; Comer et ah, 1995) and heroin (Mattox & Carroll, 1996) smoking under similar experimental conditions. In those studies, when a behaviorally inactive substance was substituted (e.g., lidocaine for cocaine base or loperamide for heroin) responding diminished, indicating that cocaine base and heroin, respectively, were functioning as reinforcers. Although nonpharmacologically active controls were not substituted for the cocaine-heroin combination in the present experiment, it is assumed that the drug combination was functioning as a reinforcer, as it maintained rates of FR responding that equaled or exceeded either drug alone. The present results demonstrated the feasibility of using a primate model for evaluating smoked drug combinations. However, the lack of a robust additive effect of the cocaine-heroin combination, which is consistent with previous literature on IV use (Foltin & Fischman, 1992; Mello et ah, 1995), suggests that the smoking route of administration does not further enhance self-administration of this combination. The behavioral economic analysis of demand revealed that the demand curves for cocaine, heroin, and the cocaineheroin combination were parallel. Because the cocaineheroin combination demand curve was significantly different from the heroin alone curve, and there was no significant interaction, it appeared that the combination produced a parallel shift upward, or an increase in intensity of demand (Hursh, 1991). Responding under the highest unit price showed the largest elevation in demand over cocaine or heroin alone. A limitation of this procedure is that setting the maximum number of deliveries at 10 results in a ceiling effect at the lower unit prices. The demand curves generated by measuring consumption across range of prices (FR values) were positively decelerating functions. The slopes of the three demand curves were not significantly different and ranged from —0.71 to —0.93, which indicates that they were inelastic. However, the elasticities were mixed, showing an inelastic function at lower unit prices and an elastic function at higher unit prices. Overall elasticities can be determined by averaging point to point elasticities or fitting a regression line to the entire curve. Both methods yielded inelastic slopes, and the latter method was used as it has been used more frequently in previous studies. Inelastic demand curves show a proportionally lower decrease in consumption than the relative increase in price. A demand curve for an essential commodity like food would be inelastic or have a slope of less than — 1 (— 1 to 0; Hursh & Bauman, 1987). These findings agree with previous behavioral economic analyses of demand for cocaine (Comer et ah, 1994) that reported a slope of -0.72 for the cocaine alone demand curve. The ability of cocaine to SPEEDBALL COMBINATIONS IN MONKEYS 117 increase the intensity of demand for heroin suggests that its re
inforcing effects were enhanced. Another line of evidence would have been decreased elasticity; however, results are consistent with previous findings of shifts in intensity (parallel increases or decreases) but not elasticity (slope) of demand for drugs when experimental conditions are manipulated (e.g., Carroll & Rodefer, 1993; Carroll et al., 1995; Comer et al., 1994). The enhancement of the heroin demand curve by the addition of cocaine is in agreement with a finding by Foltin and Fischman (1992) of decreased morphine-related reports of “sedated” when a cocaine-morphine combination was given to human participants and compared with morphine alone. This is also consistent with clinical reports indicating that speedball users add cocaine to enhance the effects of heroin (Rosen & Kosten, 1991; Tutton & Crayton, 1993). However, the small magnitude of the effect and the lack of significant enhancement of cocaine’s demand curve by heroin generally agree with recent studies of IV speedball administration in humans (Foltin & Fischman, 1992) and rhesus monkeys (Mello et al., 1995) in that the effect is small and infra-additive, and with many measures the cocaineheroin combinations produced effects similar to either cocaine or heroin alone. In our study the comparison of the demand curve generated by cocaine alone with the cocaineheroin combination curves approached statistical significance. If the data were not censored by the 10-smoke limit, or if more animals were used, then the statistical analysis may have yielded more symmetrical results. Full dose response curves for each drug and combination as well as an analysis of isobolograms are needed to determine whether there was additivity in combining the two drugs. However, such an analysis was beyond the scope of our study, as parametric analyses were directed toward construction of the demand curves that required testing a range of FR values. It should be noted that the unit doses used in the present study were substantially higher than those used in previous studies that tested IV drug. For example, the highest IV doses used in monkeys were 0.1 mg/kg for cocaine and 0.01 mg/kg for heroin (Mello et al., 1995) compared with 1 mg/kg and 0.1 mg/kg, respectively, in our study. Considering the total available doses per session, the amounts for the IV study (8 mg/kg cocaine and 0.8 mg/kg heroin; Mello et al., 1995) were similar to the present smoking study (10 mg/kg cocaine and 1.0 mg/kg heroin). Previous analyses of bioavailability indicated that 95% of the drug is available to the subject (Hatsukami, Keenan, Carroll, Colon, & Gieske, 1990) and blood levels are similar to those found after IV administration (Carroll et al., 1990). There were other differences between studies, such as reinforcement schedule and unrestricted (Mello et al., 1995) versus restricted (present study) feeding conditions that could account for differences in results. There are several interpretations of the apparent speedball effect that was obtained. First, cocaine’s psychomotor stimulant effects may attenuate heroin’s sedative effects. Second, cocaine’s reinforcing effects may have added to the reinforcing efficacy of heroin. Alternatively, cocaine may have diminished the reinforcing effects of heroin, requiring increased responding. However, if this were the case, a decrease in intensity of demand would have been predicted; thus, it is likely that cocaine increased the reinforcing efficacy of heroin by decreasing its aversive effects, by increasing its positive effects, or by a combination of effects. An additional explanation of the enhanced responding maintained by the combination is that the cocaine-heroin combination produced a different drug effect than either drug alone. The lack of a significant difference between cocaine base and the cocaine-heroin combination argues against this hypothesis. However, the inability to show a difference in this regard should be tempered by the limitations of the procedure, specifically, the ceiling effect produced by limiting smoke deliveries to 10 per session. In summary, the data indicate that responding maintained by the drug combination was greater than that for either drug alone, and this difference became more apparent as the cost (FR) of drug increased. References Carroll, M. E., Krattiger, K. L., Gieske, D., & Sadoff, D. A. (1990). Cocaine-base smoking in rhesus monkeys: Reinforcing and physiological effect. Psychopharmacology, 102, 443-450. Carroll, M. E., & Rodefer, J. S. (1993). 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y, Director. Rodefer, J. S., Mattox, A. J., Thompson, S. R., & Carroll, M. E. (in press). Effects of buprenorphine and an alternative nondrug reinforcer, alone and in combination on smoked cocaine selfadministration in monkeys. Drug and Alcohol Dependence. Rosen, M. I., & Kosten, T. R. (1991). Buprenorphine: Beyond methadone? Hospital Community Psychiatry, 42, 347-349. Tutton, C. S., & Crayton, J. W. (1993). Current pharmacotherapies for cocaine abuse: A review. Journal of Addiction Disorders, 12, 109-127. U.S. Department of Health and Human Services, Office of Applied Studies, Substance Abuse and Mental Health Services Administration. (1994). Data from the Drug Abuse Warning Network (DAWN), Series 1, Number 12-A: Annual emergency room data, 1992 (DHHS Publication No. (SMA) 94-2080). Washington, DC: Author. U.S. Department of Health and Human Services, Office of Applied Studies, Substance Abuse and Mental Health Services Administration (1995). Data from the Drug Abuse Warning Network (DAWN), Series I, Number 13-B: Annual medical examiner data, 1993b (DHHS Publication No. (SMA) 95-3019). Washington, DC: Author. Received May 14, 1996 Revision received September 23,1996 Accepted September 24, 1996 New Editor Appointed for Contemporary Psychology: 1999-2004 The Publications and Communications Board of the American Psychological Association announces the appointment of Robert J. Sternberg (Yale University) as editor of Contemporary Psychology, for a 6-year term beginning in 1999. The current editor, John H. Harvey (University of Iowa), will continue as editor through 1998. All reviews are written by invitation only, and neither the current editor nor the incoming editor receives books directly from publishers for consideration. Publishers should continue to send two copies of books for consideration, along with any notices of publication, to PsycINFO Services Department, APA, Attn: Contemporary Psychology Processing, P.O. Box 91700, Washington, DC 20090-1700 or (for UPS shipments) 750 First Street, NE, Washington, DC 20002-4242.