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Dopaminergic responsivity during cocaine abstinence: a pilot study
Psychiatry
Research,
77
43:77-85
Elsevier
Dopaminergic Responsivity A Pilot Study
During
Cocaine
Abstinence:
Christopher J. McDougle, Lawrence H. Price, Joseph M. Palumbo, Thomas R. Kosten, George R. Heninger, and Herbert D. Kleber Received November
20. 1991; revised version received April 20, 1992; accepted June 13, 1992.
Abstract. This preliminary study investigated dopamine (DA) function in six hospitalized cocaine-dependent subjects (DSM-III-R) who received 1.5 mg/ kg of active cocaine by mouth, t.i.d., for 3 days followed by 9 days of placebo cocaine. During early and late abstinence from cocaine, plasma growth hormone (GH), homovanillic acid (HVA), prolactin, and 3-methoxy-4_hydroxyphenethyleneglycol responses to the placebo-controlled administration of oral L-dopa 250 mg/carbidopa 2.5 mg (Sinemet@) were measured. Sinemet caused significantly greater placebo-corrected increases in GH and HVA during early as compared with late abstinence. Acute abstinence from cocaine may be associated with increased DA responsivity, which normalizes over time. Key Words. Drug dependence,
Cocaine Ellinwood,
abuse is a major 1988; Johanson
public and
carbidopa,
growth hormone,
homovanillic
health problem in the United Fischman, 1989). The intense
States craving
acid. (Gawin and for cocaine
reportedly occurs during periods of abstinence often leads to continued use and eventual dependence on the drug (Gawin and Ellinwood, 1988; Johanson and Fischman, 1989). Identification of the neurobiologic correlates of cocaine abstinence symptomatology might lead to the development of improved pharmacologic treatment strategies designed to disrupt the binge cycle. A consistent description of the clinical signs and symptoms that emerge in chronic cocaine abusers upon abrupt discontinuation of the drug remains to be elucidated (Brower and Paredes, 1987; Dackis et al., 1987; Kleber and Gawin, 1987a, 1987b). In a naturalistic study of outpatient chronic cocaine abusers, Gawin and Kleber (1986) observed a three-phase sequence of cocaine abstinence symptoms. Phase 1, or “crash,” which lasted 9-96 hours, was characterized by an early l- to 4-hour period of intense craving for cocaine that was associated with dysphoria. Phase 2, or that
Christopher J. McDougle,
M.D., is Assistant Professor of Psychiatry, and Lawrence H. Price, M.D., is Associate Professor of Psychiatry, Yale University School of Medicine and The Connecticut Mental Health Center, Ribicoff Research Facilities, New Haven, CT. Joseph M. Palumbo, M.D., is Associate Director for Research at Stony Lodge Hospital, Briarcliff Manor, NY. Thomas R. Kosten, M.D., is Associate Professor of Psychiatry, and George R. Heninger, M.D., is Professor of Psychiatry, Yale University School of Medicine and The Connecticut Mental Health Center, Ribicoff Research Facilities, New Haven, CT. Herbert D. Kleber, M.D., is Deputy Director for Demand Reduction, Office of National Drug Control Policy, Executive Office of the President, Washington, DC. (Reprint requests to Dr. C.J. McDougle, The Connecticut Mental Health Center, Clinical Neuroscience Research Unit, 34 Park St., New Haven, CT 06519, USA.) 01651781/92/$05.00
0 1992 Elsevier Scientific
Publishers
Ireland
Ltd
78
“withdrawal,” which lasted l-10 weeks, initially consisted of minimal craving that later increased. Phase 3, or “extinction,” which lasted indefinitely, was characterized by episodic craving that was usually triggered by environmental cues. Weddington et al. (1990) recently described results from a study of 12 chronic cocaine addicts who were abstinent throughout a 28-day period of hospitalization. They found that mood disturbances and craving were maximal during the period of continued cocaine use before hospitalization. Over the 28-day period of abstinence, they observed a nonphasic, steady improvement in mood states, craving, and sleep. As the investigators point out, because the study was conducted on a closed inpatient unit, the cocaine addicts were not exposed to cues or stimuli that might induce conditioned responses such as craving. Similarly, in a prospective inpatient study of 22 cocaine-dependent subjects, Sate1 et al. (1991) found that subjective ratings of craving, drug withdrawal, physical discomfort, anxiety, and depression decreased significantly, in a linear fashion, during a 3-week hospitalization. Brain dopamine (DA) function is critically involved in mediating cocaine’s reinforcing properties (Ritz et al., 1987). Preclinical and clinical studies also suggest that a disturbance in central DA function may contribute to the neurobiology of cocaine abstinence symptomatology (Gawin and Ellinwood, 1988). Dackis and Gold (1985) have proposed a “dopamine depletion hypothesis” of cocaine addiction, according to which DA depletion may result from overstimulation of DA neurons, with subsequent excessive synaptic metabolism of DA during chronic cocaine abuse. Dependence of residual synaptic DA on the continuing presence of cocaine could then result in a “denervation’-type supersensitivity upon abrupt cocaine discontinuation. The primary objective of this pilot study was to investigate DA function, in an oral L-dopa 250-mg/carbidopa 25 mg (Sinemet@) challenge paradigm, during early and late abstinence following 3 days of oral cocaine ingestion in chronic cocaine abusers under controlled inpatient conditions. Plasma growth hormone (GH) and plasma prolactin (PRL), which are indirect neurohormonal indexes of DA function, and plasma homovanillic acid (HVA), which is the principal metabolite of DA, were neurochemical variables used to assess DA responsivity in this study. 3-Methoxy-4hydroxyphenethyleneglycol (MHPG), the principal metabolite of norepinephrine (NE), was measured so that the differential effects of Sinemet on DA and NE responsivity could be determined. On the basis of the dopamine depletion hypothesis, we predicted that GH, PRL, and HVA responses to Sinemet would be greater during early abstinence than during late abstinence. To our knowledge, this is the first placebo-controlled investigation of the neurobiologic mechanisms of cocaine abstinence following the controlled administration of cocaine in human subjects. Methods Subjects. The sample consisted of six male inpatient subjects, aged 19-47 years (mean f SD = 33.7 f 11.2 years), who had consented to participate in the study on the Clinical Neuroscience Research Unit of the Connecticut Mental Health Center, New Haven. All subjects met DSM-III-R criteria (American Psychiatric Association, 1987) for a current diagnosis of cocaine dependence based on a direct clinical interview by a research psychiatrist.
79
The primary route of administration for all six subjects was smoking the “free-base” form of cocaine. A minimum “street” cocaine use, by history, of 14 grams during the preceding 3 months, with (1) at least one previous episode of using at least 3 grams within a 5-day period and (2) at least 1 gram/week use for the 2 weeks before admission, was required. One positive urine test for cocaine during the 2 weeks before study entry and upon admission was required. Subjects were excluded from the study if (1) they were currently using other drugs (including opioids, sedative-hypnotics, antidepressants, antipsychotics, or other stimulants), except for marijuana or alcohol, more than twice weekly (based on history and plasma and urine toxicology screens); (2) they had met DSM-III-R criteria for dependence on other drugs, including marijuana or alcohol, within the past year; (3) they had a history of intravenous use of drugs other than cocaine; (4) they presented with a history of serious medical or neurologic illness; or (5) they met DSM-III-R criteria for schizophrenia, schizoaffective disorder, schizophreniform disorder, major depressive disorder, bipolar disorder, mental retardation, or organic mental disorder unrelated to cocaine use. Subjects who satisfied the inclusion and exclusion criteria received a complete physical and neurologic evaluation, including electrocardiography and laboratory tests of renal, hepatic, pancreatic, hematopoietic, and thyroid function. In addition, hepatitis and human immunodeficiency virus screens were performed. Plasma cholinesterase activity was also determined to exclude individuals who might be at risk for cocaine toxicity by virtue of a deficiency. Subjects determined to be medically ill, based on this assessment, were excluded from the study. Subjects were not primarily seeking treatment, but participated voluntarily for monetary remuneration. Subjects were paid upon completion of the study. Procedure. Upon admission, subjects were started on a caffeine-free, vanillylmandelic acidfree diet to minimize dietary effects on catecholamine function. On the day of admission, subjects received an oral cocaine test dose (1.5 mg/kg) in gelatin capsule form to screen for individuals with unusual or idiosyncratic sensitivity to cocaine. Three days after the test dose, subjects began receiving 1.5 mg/ kg of active cocaine by mouth in gelatin capsules, under the direct supervision of the medication nurse, at 9 a.m., 1 p.m., and 5 p.m. for 3 days. Subjects reported that the subjective effects of this dose of oral cocaine were equivalent to approximately 75% of their “free-base” high (Van Dyke et al., 1978). The purpose of this stabilization period was to ensure that all subjects would be withdrawing from a fixed daily dose of cocaine. After 3 days of active cocaine administration, subjects received placebo cocaine for the next 9 days under identical conditions as in the first 3 days. On the day of the cocaine test dose and during the 12 days of active or placebo cocaine administration, electrocardiograms were obtained twice daily to assess any unusual cardiovascular response. Subjects and ward staff were unaware of the active or placebo content of the cocaine capsules throughout the study. To minimize the possibility of covert ingestion of unauthorized drugs during the study, subjects were confined to the locked inpatient unit and visitors were restricted to immediate family members. Each subject received four challenge tests (two active, two placebo) of the DA system with oral Sinemet. The first set of challenge test days occurred during early cocaine abstinence and the second set occurred 2 weeks later during late cocaine abstinence. These time points were l-2 and 15- 16 days, respectively, after the last dose of active cocaine. Each set of challenge test days included random assignment to one active Sinemet test day and one placebo test day. From the time of admission to the time of completion of the last Sinemet challenge test, no psychotropic medication was administered. To ensure that nonstudy drugs were not covertly used by subjects during the protocol, supervised urine specimens were obtained three times a week for assay of illicit drug use. On each challenge test day, the same procedure was used. Subjects fasted overnight for 10 hours and throughout the 5-hour test, which began at 8:30 a.m. Subjects were supine with head elevated throughout the test, except for standing to void and to permit measurement of standing vital signs by a research nurse who was in constant attendance. Subjects were not allowed to sleep. Subjects and research nurses were unaware of the composition of the test
80
dose. Blood was sampled from an antecubital vein through an intravenous catheter kept patent by a slow infusion of normal saline solution. Beginning I hour after insertion of the intravenous catheter, blood was obtained for measurement of plasma GH, HVA, MHPG, and PRL at 30 minutes and 5 minutes before and at 30,60,90, 120, 180, and 240 minutes after the Sinemet or placebo (lactose) dose. Vital signs were monitored frequently throughout the challenge test day. Biochemical Methods. Blood samples were kept on ice for no more than 2 hours before separation of plasma in a refrigerated centrifuge. Plasma was stored at -70 “C until assay. For determination of plasma free MHPG levels, sodium metabisulfite, 0.5 mg, and deuterated MHPG, 200 ng, were added to each plasma aliquot before freezing. Sample preparation followed a modified version of the method of Dekirmenjian and Maas (1974). Measurement of plasma free MHPG was carried out by selected ion monitoring with a quadripolar mass spectrometer with gas chromatographic inlet system. Plasma free HVA was also measured by gas chromatography-mass spectroscopy with deuterated internal standards (Maas et al., 1979). Plasma GH was measured by double antibody radioimmunoassay with materials supplied by NIAMDD. The intra-assay and interassay coefficients of variance were 5Y6 and 7Y& respectively. Plasma was assayed for PRL levels using a radioimmunoassay kit from Clinical Assays, with intra-assay and interassay coefficients of variation of 30/c and 70/c, respectively. All specimens were assayed in duplicate to reduce variance, with resulting values being averaged to yield the reported individual value. Data Analysis. Data from the time points of -30 and -5 minutes did not differ from each other and were therefore averaged to obtain a single baseline value for each variable on each test day. These baselines, which did not differ between test days within each phase of abstinence (early vs. late), were then averaged to yield a single baseline for each variable for each phase of abstinence, with baselines between phases of abstinence compared by paired t test. The area under the curve (AUC) was calculated for GH, HVA, MHPG, and PRL responses to active and placebo Sinemet during each phase of abstinence using the trapezoidal rule, with baselines subtracted from the total. Net change in AUC (A AUC) was defined as the AUC following placebo subtracted from the AUC following Sinemet. Paired t tests were used to evaluate A AUC for each variable within each phase of abstinence, and to compare the difference in A AUC for each variable between each phase of abstinence. Peak change for each variable was calculated by subtracting the baseline value from the highest absolute value following administration of the test dose. Placebo-corrected peak change was calculated by subtracting the peak change after placebo from the peak change after active Sinemet. Peak changes after placebo and active Sinemet, as well as placebo-corrected peak changes, were compared by paired f tests between abstinence phases. Statistical tests of the principal hypotheses (that GH, PRL, and HVA responses to Sinemet would be greater during early than during late abstinence) were one-tailed; all other tests were two-tailed. Significance was set at p < 0.05. Data analysis used SAS (SAS Institute, Inc., 1982) and SPSS (SPSS Inc., 1986) programs.
Results Mean (*SD) baseline MHPG was significantly higher in cocaine addicts during early abstinence compared with late abstinence (4. I f 1.9 /..(g/ 1 vs. 3.6 I!Z 2.2 pg/ 1; t = 2.5, df= 5, p < 0.03). There was a trend for mean (?c SD) baseline GH levels to
be lower in the subjects during early abstinence compared with late abstinence (2.0 k 1.7 pg/l vs. 2.9 + 2.5 pg/l; t = -1.8, df= 5, p < 0.10). There were no significant differences in baseline PRL or HVA levels in cocaine addicts between the two phases. During early abstinence, there were significantly greater AUC responses to
81
Sinemet than to placebo for GH (A AUC, 1959.8 + 1766.2pg min/l,p < 0.04), HVA (A AUC, 55747.0 jz 17439.9 pg min/ 1,p < O.OOOS),PRL (A AUC, -63 1.O + 524.9 pg min/l,p < 0.03), and MHPG (A AUC, 266.7 f. 81.4 ,ug min/l, p < 0.0005). During late abstinence, there were significantly greater AUC responses to Sinemet than to placebo for HVA (A AUC, 45437.9 + 16508.1 pug min/l, p < O.OOl), PRL (-725.5 f 87.5 pug min/l,p < O.OOOl), and MHPG (A AUC, 214.1 k 90.4pg min/l, p < 0.002). No significant change in AUC of the GH response to Sinemet compared with placebo was found (A AUC, 434.0 + 1195.6 pg min/l, NS). When cocaine addicts were compared during early and late abstinence (A AUC, early abstinence) - (A AUC, late abstinence), a significant increase in AUC was found for HVA (10309.1 + 3547.7 pg min/l, p < 0.004, l-tailed) (Fig. 1). A trend
Fig. 1. Effects of oral Sinemet (closed symbols) and placebo (open symbols) on plasma homovanillic acid (HVA) in cocaine subjects during early cocaine abstinence (squares) or late cocaine abstinence (circles)
300:
wo-
+
AcllwlAlE
+
PlAcEEolAlE
Earn
$j
160 MOEo0, EAESUNE
toward a significant l-tailed)
p < 0.08,
10
Eo
W
120
1m
240
increase in AUC was identified for GH (1525.8 + 2256.4pg min/ 1, (Fig. 2). There were no significant changes in AUC for MHPG
Fig. 2. Effects of oral Sinemet (closed symbols) and placebo (open symbols) on plasma growth hormone (GH) in cocaine subjects during early cocaine abstinence (squares) or late cocaine abstinence (circles)
82
(52.6 f 125.8 ,ug min/l, NS, l-tailed) (Fig. 3) or PRL (-94.5 f 542.8 pg min/l, NS, l-tailed) (Fig. 4). During early abstinence, there were significantly greater peak change responses to Sinemet than to placebo for GH (24.9 f 14.6 pg min/l; t = 4.2, df = 5, p < 0.009) HVA(360.0 + 100.6pgmin/l; t= 8.8, df= 5,p
Fig. 3. Effects of oral Sinemet (closed symbols) and placebo (open symbols) on plasma free 3-methoxy-4-hydroxyphenethyleneglycol (MHPG) in cocaine subjects during early cocaine abstinence (squares) or late cocaine abstinence (circles) b.!J-
Fig. 4. Effects of oral Sinemet (closed symbols) and placebo (open symbols) on plasma prolactin in cocaine subjects during early cocaine abstinence (squares) or late cocaine abstinence (circles) 10-S
9-
5z $
7-
6-
5-
-e-
nAcE5oEAw
-.-
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83 PRL (-2.9 + I.5 rug/l; 1 = -4.8, df = 5, p < O.OOS), MHPG (1.3 I& 0.5 ,ug/l; t = 6.2, df = 5,p < 0.002), and a trend for GH (8.6 + 10.6pg/l; t = 2.0, df= 5,p < 0.10). When cocaine addicts were compared during early and late abstinence (placebocorrected peak change, early abstinence) - (placebo-corrected peak change, late abstinence), significant differences were found for GH (16.3 + 16.3 pug/l; t = 2.5, df = 5, p < 0.03, l-tailed) and HVA (34.4 + 37.1 pg/l; t = 2.3, df = 5, p < 0.04, l-tailed), but not for MHPG (0.35 + 0.7 lug/l; t = 1.3, df = 5, NS, l-tailed) or PRL (0.6 + 2.9 pg/l; t = 0.5, df = 5, NS, l-tailed).
Discussion This preliminary investigation suggests that acute abstinence from the regular ingestion of cocaine in chronic abusers may be associated with increased DA responsivity. This functional increase in DA tone during early, as compared with late, cocaine abstinence is reflected by both the significantly increased GH response to Sinemet (which may be consistent with increased presynaptic DA turnover or postsynaptic DA receptor supersensitivity) and by the significantly increased HVA response to Sinemet (which may indicate increased presynaptic DA turnover). The decreased GH and HVA responses to Sinemet challenge 2 weeks after the last dose of active cocaine suggest that DA metabolism may equilibrate during the course of continued cocaine abstinence. The results of this study are consistent with the “dopamine depletion hypothesis” of cocaine addiction (Dackis and Gold, 1985), which predicts that a “denervation”type supersensitivity could result from an abrupt cocaine discontinuation, The increased GH and HVA responses to Sinemet that occurred during early cocaine abstinence in our study may represent a compensatory response of presynaptic and postsynaptic DA neurons to an acute deficiency of synaptic DA. A similar compensatory response was demonstrated in preclinical studies, where the activity of tyrosine hydroxylase, the rate-limiting enzyme for DA synthesis, was found to be increased after exposure to cocaine (Patrick and Barchas, 1977; Taylor and Ho, 1977). That these neurobiologic indexes of DA function were abnormal during early, but not late, abstinence appears to parallel the clinical manifestations of inpatient cocaine abstinence, which involve early alterations in craving, mood, and sleep with a subsequent linear normalization (Weddington et al., 1990; Sate1 et al., 1991). In previous studies, Hollander et al. (1990) administered apomorphine to seven chronic cocaine abusers who had been abstinent from cocaine < 3 days and three cocaine addicts who had last used cocaine > 1 week before the study. After apomorphine, a 580% peak increase in GH, and a 28% peak decrease in PRL were observed, with no significant change in plasma HVA. Significant differences were not found in these neurochemical responses to apomorphine between phases. Lee et al. (1990) administered apomorphine to 16 inpatient cocaine addicts and 8 normal controls. No significant differences were found between patients and controls in GH or PRL plasma levels either at baseline or in response to apomorphine. Because of the wide range of days since last reported use of cocaine (4-39 days), however, neurobiologic abnormalities that occurred during acute abstinence may not have been captured.
84
The results of the current study must be considered preliminary: (1) The small number of subjects and the lack of a healthy control comparison group do not permit definitive conclusions. (2) Marked individual differences in the gastric absorption and attained blood levels of both L-dopa and carbidopa may result in marked variation in the amount of DA available to the brain. (3) Although Sinemet causes reliable decreases in PRL, which are most likely DA-related, the GH increase may reflect NE as well as DA function. (4) Some data indicate that in primates there may not be a close correlation between brain and plasma HVA (Elsworth et al., 1987). At such high plasma levels, the accuracy of the biochemical assay for determining HVA is reduced, and it is possible that the findings may reflect differences in renal clearance of plasma HVA rather than differences in brain DA turnover. Despite the methodologic limitations of the current study, the results suggest that a functional increase in DA metabolism may occur during early but not late abstinence from cocaine in chronic cocaine abusers. Although relatively low and infrequent doses of cocaine were administered in this study compared with naturalistic “street” cocaine use, significant neurobiologic changes were seen after cocaine discontinuation. That these alterations in DA function occurred in a controlled, attenuated laboratory model of “street” cocaine use suggests that neurobiologic changes are surely present in a naturalistic setting where higher and more frequent doses of cocaine are used. Further controlled studies that use more specific probes of the DA system, such as apomorphine, possibly in combination seem warranted. In addition, assessment of with brain imaging techniques, contributions from other neurochemical systems, such as the serotonin and noradrenergic systems, and of interactions between systems, will help in elucidating the complex neurobiology of cocaine abstinence. Acknowledgments. This work was supported in part by grants DA-04060, MH-25642, and
MH-36229 from the U.S. Public Health Service, Bethesda, MD; by the Department of Mental Health, State of Connecticut; and by a National Alliance for Research on Schizophrenia and Affective Disorders (NARSAD) Young Investigator’s Award (C.J.M.). Deborah Herbst, M.S., and Sally Trufan assisted in the data analysis. Elizabeth Kyle, A.S., prepared the manuscript.
References American Psychiatric Association. DSM-III-R: Diagnostic and Statistical Manual of Mental Disorders. 3rd ed., revised. Washington, DC: American Psychiatric Press, 1987. Brower, K.J., and Paredes, A. Cocaine withdrawal. (Letter) Archives of General Psychiatry,
44~297, 1987.
Dackis, C.A., and Gold, M.S. New concepts in cocaine addiction: The dopamine depletion hypothesis. Neuroscience and Biobehavioral Review, 9:469-477, 1985. Dackis, C.A.; Gold, M.S.; and Sweeney, D.R. The physiology of cocaine craving and “crashing.” (Letter) Archives of General Psychiatry, 44:298-299, 1987. Dekirmenjian, H., and Maas, J.W. MHPG in plasma. Cfinica Chimica Acta, 52:203-208, 1974.
Elsworth, J.D.; Leahy, D.J.; Roth, R.H.; and Redmond, D.E., Jr. Homovanillic acid concentrations in brain, CSF and plasma as indicators of central dopamine function in primates. Journal of Neural Transmission, 6851-62, 1987.
85 Gawin, F.H., and Ellinwood, E.H., Jr. Cocaine and other stimulants: Actions, abuse, and treatment. New England Journal of Medicine, 318:1173-l 182, 1988. Gawin, F.H., and Kleber, H.D. Abstinence symptomatology and psychiatric diagnosis in cocaine abusers: Clinical observations. Archives of General Psychiatry, 43: 107-l 13, 1986. Hollander, E.; Nunes, E.; DeCaria, C.M.; Quitkin, F.M.; Cooper, T.; Wager, S.; and Klein, D.F. Dopaminergic sensitivity and cocaine abuse: Response to apomorphine. Psychiurry Research, 33:161-169, 1990. Johanson, C.-E., and Fischman, M.W. The pharmacology of cocaine related to its abuse. Phurmucologicul Reviews, 41~3-52, 1989. Kleber, H.D., and Gawin, F.H. [In reply] to Brower, K.J. and Paredes, A. Archives of General Psychiatry, 44:298, 1987~. Kleber, H.D., and Gawin, F.H. [In reply] to Dackis. Archives of General Psychiatry, 44:299-300, 19876. Lee, M.A.; Bowers, M.M.; Nash, J.F.; and Meltzer, H.Y Neuroendocrine measures of dopaminergic function in chronic cocaine users. Psychiatry Research, 33:151-159, 1990. Maas, J.W.; Hattox, S.E.; and Martin, D.M. A direct method for determining dopamine synthesis and output of dopamine metabolites from brain in awake animals. Journal of Neurochemistry, 32:839-843, 1979. Patrick, R.L., and Barchas, J.D. Potentiation by cocaine of the stimulus-induced increase in dopamine synthesis in rat brain striatal synaptosomes. Neurophurmucology, 16~327, 1977. Ritz, M.C.; Lamb, R.J.; Goldberg, S.R.; and Kuhar, M.J. Cocaine receptors on dopamine transporters are related to self-administration of cocaine. Science, 237:1219-1223, 1987. SAS User5 Guide: Statistics, 1982 Edition. Cary, NC: SAS Institute, Inc., 1982. Satel, S.L.; Price, L.H.; Palumbo, J.M.; McDougle, C.J.; Krystal, J.H.; Gawin, F.; Charney, D.S.; Heninger, G.R.; and Kleber, H.D. The clinical phenomenology and neurobiology of cocaine abstinence: A prospective inpatient study. American Journal of Psychiatry, 148:1712-1716, 1991. SPSS User5 Guide. 2nd Edition. Chicago, IL: SPSS, Inc., 1986. Taylor, D., and Ho, B.T. Neurochemical effects of cocaine following acute and repeated injection. Journal of Neuroscience Research. 3:95-101, 1977. Van Dyke, C.; Jatlow, P.; Ungerger, J.; Barash, P.G.; and Byck, R. Oral cocaine: Plasma concentrations and central effects. Science, 200:21 I-213, 1978. Weddington, W.H.; Brown, B.S.; Haertzen, C.A.; Cone, E.J.; Dax, E.M.; Herning, R.I.; and Michaelson, B.S. Changes in mood, craving, and sleep during acute abstinence reported by male cocaine addicts: A controlled, residential study. Archives of General Psychiatry, 47:861-868, 1990.
Research,
77
43:77-85
Elsevier
Dopaminergic Responsivity A Pilot Study
During
Cocaine
Abstinence:
Christopher J. McDougle, Lawrence H. Price, Joseph M. Palumbo, Thomas R. Kosten, George R. Heninger, and Herbert D. Kleber Received November
20. 1991; revised version received April 20, 1992; accepted June 13, 1992.
Abstract. This preliminary study investigated dopamine (DA) function in six hospitalized cocaine-dependent subjects (DSM-III-R) who received 1.5 mg/ kg of active cocaine by mouth, t.i.d., for 3 days followed by 9 days of placebo cocaine. During early and late abstinence from cocaine, plasma growth hormone (GH), homovanillic acid (HVA), prolactin, and 3-methoxy-4_hydroxyphenethyleneglycol responses to the placebo-controlled administration of oral L-dopa 250 mg/carbidopa 2.5 mg (Sinemet@) were measured. Sinemet caused significantly greater placebo-corrected increases in GH and HVA during early as compared with late abstinence. Acute abstinence from cocaine may be associated with increased DA responsivity, which normalizes over time. Key Words. Drug dependence,
Cocaine Ellinwood,
abuse is a major 1988; Johanson
public and
carbidopa,
growth hormone,
homovanillic
health problem in the United Fischman, 1989). The intense
States craving
acid. (Gawin and for cocaine
reportedly occurs during periods of abstinence often leads to continued use and eventual dependence on the drug (Gawin and Ellinwood, 1988; Johanson and Fischman, 1989). Identification of the neurobiologic correlates of cocaine abstinence symptomatology might lead to the development of improved pharmacologic treatment strategies designed to disrupt the binge cycle. A consistent description of the clinical signs and symptoms that emerge in chronic cocaine abusers upon abrupt discontinuation of the drug remains to be elucidated (Brower and Paredes, 1987; Dackis et al., 1987; Kleber and Gawin, 1987a, 1987b). In a naturalistic study of outpatient chronic cocaine abusers, Gawin and Kleber (1986) observed a three-phase sequence of cocaine abstinence symptoms. Phase 1, or “crash,” which lasted 9-96 hours, was characterized by an early l- to 4-hour period of intense craving for cocaine that was associated with dysphoria. Phase 2, or that
Christopher J. McDougle,
M.D., is Assistant Professor of Psychiatry, and Lawrence H. Price, M.D., is Associate Professor of Psychiatry, Yale University School of Medicine and The Connecticut Mental Health Center, Ribicoff Research Facilities, New Haven, CT. Joseph M. Palumbo, M.D., is Associate Director for Research at Stony Lodge Hospital, Briarcliff Manor, NY. Thomas R. Kosten, M.D., is Associate Professor of Psychiatry, and George R. Heninger, M.D., is Professor of Psychiatry, Yale University School of Medicine and The Connecticut Mental Health Center, Ribicoff Research Facilities, New Haven, CT. Herbert D. Kleber, M.D., is Deputy Director for Demand Reduction, Office of National Drug Control Policy, Executive Office of the President, Washington, DC. (Reprint requests to Dr. C.J. McDougle, The Connecticut Mental Health Center, Clinical Neuroscience Research Unit, 34 Park St., New Haven, CT 06519, USA.) 01651781/92/$05.00
0 1992 Elsevier Scientific
Publishers
Ireland
Ltd
78
“withdrawal,” which lasted l-10 weeks, initially consisted of minimal craving that later increased. Phase 3, or “extinction,” which lasted indefinitely, was characterized by episodic craving that was usually triggered by environmental cues. Weddington et al. (1990) recently described results from a study of 12 chronic cocaine addicts who were abstinent throughout a 28-day period of hospitalization. They found that mood disturbances and craving were maximal during the period of continued cocaine use before hospitalization. Over the 28-day period of abstinence, they observed a nonphasic, steady improvement in mood states, craving, and sleep. As the investigators point out, because the study was conducted on a closed inpatient unit, the cocaine addicts were not exposed to cues or stimuli that might induce conditioned responses such as craving. Similarly, in a prospective inpatient study of 22 cocaine-dependent subjects, Sate1 et al. (1991) found that subjective ratings of craving, drug withdrawal, physical discomfort, anxiety, and depression decreased significantly, in a linear fashion, during a 3-week hospitalization. Brain dopamine (DA) function is critically involved in mediating cocaine’s reinforcing properties (Ritz et al., 1987). Preclinical and clinical studies also suggest that a disturbance in central DA function may contribute to the neurobiology of cocaine abstinence symptomatology (Gawin and Ellinwood, 1988). Dackis and Gold (1985) have proposed a “dopamine depletion hypothesis” of cocaine addiction, according to which DA depletion may result from overstimulation of DA neurons, with subsequent excessive synaptic metabolism of DA during chronic cocaine abuse. Dependence of residual synaptic DA on the continuing presence of cocaine could then result in a “denervation’-type supersensitivity upon abrupt cocaine discontinuation. The primary objective of this pilot study was to investigate DA function, in an oral L-dopa 250-mg/carbidopa 25 mg (Sinemet@) challenge paradigm, during early and late abstinence following 3 days of oral cocaine ingestion in chronic cocaine abusers under controlled inpatient conditions. Plasma growth hormone (GH) and plasma prolactin (PRL), which are indirect neurohormonal indexes of DA function, and plasma homovanillic acid (HVA), which is the principal metabolite of DA, were neurochemical variables used to assess DA responsivity in this study. 3-Methoxy-4hydroxyphenethyleneglycol (MHPG), the principal metabolite of norepinephrine (NE), was measured so that the differential effects of Sinemet on DA and NE responsivity could be determined. On the basis of the dopamine depletion hypothesis, we predicted that GH, PRL, and HVA responses to Sinemet would be greater during early abstinence than during late abstinence. To our knowledge, this is the first placebo-controlled investigation of the neurobiologic mechanisms of cocaine abstinence following the controlled administration of cocaine in human subjects. Methods Subjects. The sample consisted of six male inpatient subjects, aged 19-47 years (mean f SD = 33.7 f 11.2 years), who had consented to participate in the study on the Clinical Neuroscience Research Unit of the Connecticut Mental Health Center, New Haven. All subjects met DSM-III-R criteria (American Psychiatric Association, 1987) for a current diagnosis of cocaine dependence based on a direct clinical interview by a research psychiatrist.
79
The primary route of administration for all six subjects was smoking the “free-base” form of cocaine. A minimum “street” cocaine use, by history, of 14 grams during the preceding 3 months, with (1) at least one previous episode of using at least 3 grams within a 5-day period and (2) at least 1 gram/week use for the 2 weeks before admission, was required. One positive urine test for cocaine during the 2 weeks before study entry and upon admission was required. Subjects were excluded from the study if (1) they were currently using other drugs (including opioids, sedative-hypnotics, antidepressants, antipsychotics, or other stimulants), except for marijuana or alcohol, more than twice weekly (based on history and plasma and urine toxicology screens); (2) they had met DSM-III-R criteria for dependence on other drugs, including marijuana or alcohol, within the past year; (3) they had a history of intravenous use of drugs other than cocaine; (4) they presented with a history of serious medical or neurologic illness; or (5) they met DSM-III-R criteria for schizophrenia, schizoaffective disorder, schizophreniform disorder, major depressive disorder, bipolar disorder, mental retardation, or organic mental disorder unrelated to cocaine use. Subjects who satisfied the inclusion and exclusion criteria received a complete physical and neurologic evaluation, including electrocardiography and laboratory tests of renal, hepatic, pancreatic, hematopoietic, and thyroid function. In addition, hepatitis and human immunodeficiency virus screens were performed. Plasma cholinesterase activity was also determined to exclude individuals who might be at risk for cocaine toxicity by virtue of a deficiency. Subjects determined to be medically ill, based on this assessment, were excluded from the study. Subjects were not primarily seeking treatment, but participated voluntarily for monetary remuneration. Subjects were paid upon completion of the study. Procedure. Upon admission, subjects were started on a caffeine-free, vanillylmandelic acidfree diet to minimize dietary effects on catecholamine function. On the day of admission, subjects received an oral cocaine test dose (1.5 mg/kg) in gelatin capsule form to screen for individuals with unusual or idiosyncratic sensitivity to cocaine. Three days after the test dose, subjects began receiving 1.5 mg/ kg of active cocaine by mouth in gelatin capsules, under the direct supervision of the medication nurse, at 9 a.m., 1 p.m., and 5 p.m. for 3 days. Subjects reported that the subjective effects of this dose of oral cocaine were equivalent to approximately 75% of their “free-base” high (Van Dyke et al., 1978). The purpose of this stabilization period was to ensure that all subjects would be withdrawing from a fixed daily dose of cocaine. After 3 days of active cocaine administration, subjects received placebo cocaine for the next 9 days under identical conditions as in the first 3 days. On the day of the cocaine test dose and during the 12 days of active or placebo cocaine administration, electrocardiograms were obtained twice daily to assess any unusual cardiovascular response. Subjects and ward staff were unaware of the active or placebo content of the cocaine capsules throughout the study. To minimize the possibility of covert ingestion of unauthorized drugs during the study, subjects were confined to the locked inpatient unit and visitors were restricted to immediate family members. Each subject received four challenge tests (two active, two placebo) of the DA system with oral Sinemet. The first set of challenge test days occurred during early cocaine abstinence and the second set occurred 2 weeks later during late cocaine abstinence. These time points were l-2 and 15- 16 days, respectively, after the last dose of active cocaine. Each set of challenge test days included random assignment to one active Sinemet test day and one placebo test day. From the time of admission to the time of completion of the last Sinemet challenge test, no psychotropic medication was administered. To ensure that nonstudy drugs were not covertly used by subjects during the protocol, supervised urine specimens were obtained three times a week for assay of illicit drug use. On each challenge test day, the same procedure was used. Subjects fasted overnight for 10 hours and throughout the 5-hour test, which began at 8:30 a.m. Subjects were supine with head elevated throughout the test, except for standing to void and to permit measurement of standing vital signs by a research nurse who was in constant attendance. Subjects were not allowed to sleep. Subjects and research nurses were unaware of the composition of the test
80
dose. Blood was sampled from an antecubital vein through an intravenous catheter kept patent by a slow infusion of normal saline solution. Beginning I hour after insertion of the intravenous catheter, blood was obtained for measurement of plasma GH, HVA, MHPG, and PRL at 30 minutes and 5 minutes before and at 30,60,90, 120, 180, and 240 minutes after the Sinemet or placebo (lactose) dose. Vital signs were monitored frequently throughout the challenge test day. Biochemical Methods. Blood samples were kept on ice for no more than 2 hours before separation of plasma in a refrigerated centrifuge. Plasma was stored at -70 “C until assay. For determination of plasma free MHPG levels, sodium metabisulfite, 0.5 mg, and deuterated MHPG, 200 ng, were added to each plasma aliquot before freezing. Sample preparation followed a modified version of the method of Dekirmenjian and Maas (1974). Measurement of plasma free MHPG was carried out by selected ion monitoring with a quadripolar mass spectrometer with gas chromatographic inlet system. Plasma free HVA was also measured by gas chromatography-mass spectroscopy with deuterated internal standards (Maas et al., 1979). Plasma GH was measured by double antibody radioimmunoassay with materials supplied by NIAMDD. The intra-assay and interassay coefficients of variance were 5Y6 and 7Y& respectively. Plasma was assayed for PRL levels using a radioimmunoassay kit from Clinical Assays, with intra-assay and interassay coefficients of variation of 30/c and 70/c, respectively. All specimens were assayed in duplicate to reduce variance, with resulting values being averaged to yield the reported individual value. Data Analysis. Data from the time points of -30 and -5 minutes did not differ from each other and were therefore averaged to obtain a single baseline value for each variable on each test day. These baselines, which did not differ between test days within each phase of abstinence (early vs. late), were then averaged to yield a single baseline for each variable for each phase of abstinence, with baselines between phases of abstinence compared by paired t test. The area under the curve (AUC) was calculated for GH, HVA, MHPG, and PRL responses to active and placebo Sinemet during each phase of abstinence using the trapezoidal rule, with baselines subtracted from the total. Net change in AUC (A AUC) was defined as the AUC following placebo subtracted from the AUC following Sinemet. Paired t tests were used to evaluate A AUC for each variable within each phase of abstinence, and to compare the difference in A AUC for each variable between each phase of abstinence. Peak change for each variable was calculated by subtracting the baseline value from the highest absolute value following administration of the test dose. Placebo-corrected peak change was calculated by subtracting the peak change after placebo from the peak change after active Sinemet. Peak changes after placebo and active Sinemet, as well as placebo-corrected peak changes, were compared by paired f tests between abstinence phases. Statistical tests of the principal hypotheses (that GH, PRL, and HVA responses to Sinemet would be greater during early than during late abstinence) were one-tailed; all other tests were two-tailed. Significance was set at p < 0.05. Data analysis used SAS (SAS Institute, Inc., 1982) and SPSS (SPSS Inc., 1986) programs.
Results Mean (*SD) baseline MHPG was significantly higher in cocaine addicts during early abstinence compared with late abstinence (4. I f 1.9 /..(g/ 1 vs. 3.6 I!Z 2.2 pg/ 1; t = 2.5, df= 5, p < 0.03). There was a trend for mean (?c SD) baseline GH levels to
be lower in the subjects during early abstinence compared with late abstinence (2.0 k 1.7 pg/l vs. 2.9 + 2.5 pg/l; t = -1.8, df= 5, p < 0.10). There were no significant differences in baseline PRL or HVA levels in cocaine addicts between the two phases. During early abstinence, there were significantly greater AUC responses to
81
Sinemet than to placebo for GH (A AUC, 1959.8 + 1766.2pg min/l,p < 0.04), HVA (A AUC, 55747.0 jz 17439.9 pg min/ 1,p < O.OOOS),PRL (A AUC, -63 1.O + 524.9 pg min/l,p < 0.03), and MHPG (A AUC, 266.7 f. 81.4 ,ug min/l, p < 0.0005). During late abstinence, there were significantly greater AUC responses to Sinemet than to placebo for HVA (A AUC, 45437.9 + 16508.1 pug min/l, p < O.OOl), PRL (-725.5 f 87.5 pug min/l,p < O.OOOl), and MHPG (A AUC, 214.1 k 90.4pg min/l, p < 0.002). No significant change in AUC of the GH response to Sinemet compared with placebo was found (A AUC, 434.0 + 1195.6 pg min/l, NS). When cocaine addicts were compared during early and late abstinence (A AUC, early abstinence) - (A AUC, late abstinence), a significant increase in AUC was found for HVA (10309.1 + 3547.7 pg min/l, p < 0.004, l-tailed) (Fig. 1). A trend
Fig. 1. Effects of oral Sinemet (closed symbols) and placebo (open symbols) on plasma homovanillic acid (HVA) in cocaine subjects during early cocaine abstinence (squares) or late cocaine abstinence (circles)
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increase in AUC was identified for GH (1525.8 + 2256.4pg min/ 1, (Fig. 2). There were no significant changes in AUC for MHPG
Fig. 2. Effects of oral Sinemet (closed symbols) and placebo (open symbols) on plasma growth hormone (GH) in cocaine subjects during early cocaine abstinence (squares) or late cocaine abstinence (circles)
82
(52.6 f 125.8 ,ug min/l, NS, l-tailed) (Fig. 3) or PRL (-94.5 f 542.8 pg min/l, NS, l-tailed) (Fig. 4). During early abstinence, there were significantly greater peak change responses to Sinemet than to placebo for GH (24.9 f 14.6 pg min/l; t = 4.2, df = 5, p < 0.009) HVA(360.0 + 100.6pgmin/l; t= 8.8, df= 5,p
Fig. 3. Effects of oral Sinemet (closed symbols) and placebo (open symbols) on plasma free 3-methoxy-4-hydroxyphenethyleneglycol (MHPG) in cocaine subjects during early cocaine abstinence (squares) or late cocaine abstinence (circles) b.!J-
Fig. 4. Effects of oral Sinemet (closed symbols) and placebo (open symbols) on plasma prolactin in cocaine subjects during early cocaine abstinence (squares) or late cocaine abstinence (circles) 10-S
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83 PRL (-2.9 + I.5 rug/l; 1 = -4.8, df = 5, p < O.OOS), MHPG (1.3 I& 0.5 ,ug/l; t = 6.2, df = 5,p < 0.002), and a trend for GH (8.6 + 10.6pg/l; t = 2.0, df= 5,p < 0.10). When cocaine addicts were compared during early and late abstinence (placebocorrected peak change, early abstinence) - (placebo-corrected peak change, late abstinence), significant differences were found for GH (16.3 + 16.3 pug/l; t = 2.5, df = 5, p < 0.03, l-tailed) and HVA (34.4 + 37.1 pg/l; t = 2.3, df = 5, p < 0.04, l-tailed), but not for MHPG (0.35 + 0.7 lug/l; t = 1.3, df = 5, NS, l-tailed) or PRL (0.6 + 2.9 pg/l; t = 0.5, df = 5, NS, l-tailed).
Discussion This preliminary investigation suggests that acute abstinence from the regular ingestion of cocaine in chronic abusers may be associated with increased DA responsivity. This functional increase in DA tone during early, as compared with late, cocaine abstinence is reflected by both the significantly increased GH response to Sinemet (which may be consistent with increased presynaptic DA turnover or postsynaptic DA receptor supersensitivity) and by the significantly increased HVA response to Sinemet (which may indicate increased presynaptic DA turnover). The decreased GH and HVA responses to Sinemet challenge 2 weeks after the last dose of active cocaine suggest that DA metabolism may equilibrate during the course of continued cocaine abstinence. The results of this study are consistent with the “dopamine depletion hypothesis” of cocaine addiction (Dackis and Gold, 1985), which predicts that a “denervation”type supersensitivity could result from an abrupt cocaine discontinuation, The increased GH and HVA responses to Sinemet that occurred during early cocaine abstinence in our study may represent a compensatory response of presynaptic and postsynaptic DA neurons to an acute deficiency of synaptic DA. A similar compensatory response was demonstrated in preclinical studies, where the activity of tyrosine hydroxylase, the rate-limiting enzyme for DA synthesis, was found to be increased after exposure to cocaine (Patrick and Barchas, 1977; Taylor and Ho, 1977). That these neurobiologic indexes of DA function were abnormal during early, but not late, abstinence appears to parallel the clinical manifestations of inpatient cocaine abstinence, which involve early alterations in craving, mood, and sleep with a subsequent linear normalization (Weddington et al., 1990; Sate1 et al., 1991). In previous studies, Hollander et al. (1990) administered apomorphine to seven chronic cocaine abusers who had been abstinent from cocaine < 3 days and three cocaine addicts who had last used cocaine > 1 week before the study. After apomorphine, a 580% peak increase in GH, and a 28% peak decrease in PRL were observed, with no significant change in plasma HVA. Significant differences were not found in these neurochemical responses to apomorphine between phases. Lee et al. (1990) administered apomorphine to 16 inpatient cocaine addicts and 8 normal controls. No significant differences were found between patients and controls in GH or PRL plasma levels either at baseline or in response to apomorphine. Because of the wide range of days since last reported use of cocaine (4-39 days), however, neurobiologic abnormalities that occurred during acute abstinence may not have been captured.
84
The results of the current study must be considered preliminary: (1) The small number of subjects and the lack of a healthy control comparison group do not permit definitive conclusions. (2) Marked individual differences in the gastric absorption and attained blood levels of both L-dopa and carbidopa may result in marked variation in the amount of DA available to the brain. (3) Although Sinemet causes reliable decreases in PRL, which are most likely DA-related, the GH increase may reflect NE as well as DA function. (4) Some data indicate that in primates there may not be a close correlation between brain and plasma HVA (Elsworth et al., 1987). At such high plasma levels, the accuracy of the biochemical assay for determining HVA is reduced, and it is possible that the findings may reflect differences in renal clearance of plasma HVA rather than differences in brain DA turnover. Despite the methodologic limitations of the current study, the results suggest that a functional increase in DA metabolism may occur during early but not late abstinence from cocaine in chronic cocaine abusers. Although relatively low and infrequent doses of cocaine were administered in this study compared with naturalistic “street” cocaine use, significant neurobiologic changes were seen after cocaine discontinuation. That these alterations in DA function occurred in a controlled, attenuated laboratory model of “street” cocaine use suggests that neurobiologic changes are surely present in a naturalistic setting where higher and more frequent doses of cocaine are used. Further controlled studies that use more specific probes of the DA system, such as apomorphine, possibly in combination seem warranted. In addition, assessment of with brain imaging techniques, contributions from other neurochemical systems, such as the serotonin and noradrenergic systems, and of interactions between systems, will help in elucidating the complex neurobiology of cocaine abstinence. Acknowledgments. This work was supported in part by grants DA-04060, MH-25642, and
MH-36229 from the U.S. Public Health Service, Bethesda, MD; by the Department of Mental Health, State of Connecticut; and by a National Alliance for Research on Schizophrenia and Affective Disorders (NARSAD) Young Investigator’s Award (C.J.M.). Deborah Herbst, M.S., and Sally Trufan assisted in the data analysis. Elizabeth Kyle, A.S., prepared the manuscript.
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Dackis, C.A., and Gold, M.S. New concepts in cocaine addiction: The dopamine depletion hypothesis. Neuroscience and Biobehavioral Review, 9:469-477, 1985. Dackis, C.A.; Gold, M.S.; and Sweeney, D.R. The physiology of cocaine craving and “crashing.” (Letter) Archives of General Psychiatry, 44:298-299, 1987. Dekirmenjian, H., and Maas, J.W. MHPG in plasma. Cfinica Chimica Acta, 52:203-208, 1974.
Elsworth, J.D.; Leahy, D.J.; Roth, R.H.; and Redmond, D.E., Jr. Homovanillic acid concentrations in brain, CSF and plasma as indicators of central dopamine function in primates. Journal of Neural Transmission, 6851-62, 1987.
85 Gawin, F.H., and Ellinwood, E.H., Jr. Cocaine and other stimulants: Actions, abuse, and treatment. New England Journal of Medicine, 318:1173-l 182, 1988. Gawin, F.H., and Kleber, H.D. Abstinence symptomatology and psychiatric diagnosis in cocaine abusers: Clinical observations. Archives of General Psychiatry, 43: 107-l 13, 1986. Hollander, E.; Nunes, E.; DeCaria, C.M.; Quitkin, F.M.; Cooper, T.; Wager, S.; and Klein, D.F. Dopaminergic sensitivity and cocaine abuse: Response to apomorphine. Psychiurry Research, 33:161-169, 1990. Johanson, C.-E., and Fischman, M.W. The pharmacology of cocaine related to its abuse. Phurmucologicul Reviews, 41~3-52, 1989. Kleber, H.D., and Gawin, F.H. [In reply] to Brower, K.J. and Paredes, A. Archives of General Psychiatry, 44:298, 1987~. Kleber, H.D., and Gawin, F.H. [In reply] to Dackis. Archives of General Psychiatry, 44:299-300, 19876. Lee, M.A.; Bowers, M.M.; Nash, J.F.; and Meltzer, H.Y Neuroendocrine measures of dopaminergic function in chronic cocaine users. Psychiatry Research, 33:151-159, 1990. Maas, J.W.; Hattox, S.E.; and Martin, D.M. A direct method for determining dopamine synthesis and output of dopamine metabolites from brain in awake animals. Journal of Neurochemistry, 32:839-843, 1979. Patrick, R.L., and Barchas, J.D. Potentiation by cocaine of the stimulus-induced increase in dopamine synthesis in rat brain striatal synaptosomes. Neurophurmucology, 16~327, 1977. Ritz, M.C.; Lamb, R.J.; Goldberg, S.R.; and Kuhar, M.J. Cocaine receptors on dopamine transporters are related to self-administration of cocaine. Science, 237:1219-1223, 1987. SAS User5 Guide: Statistics, 1982 Edition. Cary, NC: SAS Institute, Inc., 1982. Satel, S.L.; Price, L.H.; Palumbo, J.M.; McDougle, C.J.; Krystal, J.H.; Gawin, F.; Charney, D.S.; Heninger, G.R.; and Kleber, H.D. The clinical phenomenology and neurobiology of cocaine abstinence: A prospective inpatient study. American Journal of Psychiatry, 148:1712-1716, 1991. SPSS User5 Guide. 2nd Edition. Chicago, IL: SPSS, Inc., 1986. Taylor, D., and Ho, B.T. Neurochemical effects of cocaine following acute and repeated injection. Journal of Neuroscience Research. 3:95-101, 1977. Van Dyke, C.; Jatlow, P.; Ungerger, J.; Barash, P.G.; and Byck, R. Oral cocaine: Plasma concentrations and central effects. Science, 200:21 I-213, 1978. Weddington, W.H.; Brown, B.S.; Haertzen, C.A.; Cone, E.J.; Dax, E.M.; Herning, R.I.; and Michaelson, B.S. Changes in mood, craving, and sleep during acute abstinence reported by male cocaine addicts: A controlled, residential study. Archives of General Psychiatry, 47:861-868, 1990.