Cocaine's effects on neuroendocrine systems: clinical and preclinical studies

This review examines the effects of cocaine on the neuroendocrine system and summarizes findings from clinical studies of cocaine abusers and preclinical studies in rodents and rhesus monkeys. The effects of acute and chronic cocaine administration on anterior pituitary, gonadal, and adrenal hormones are described, and the functional consequences of chronic cocaine exposure are discussed. Many of cocaine's acute effects on the endocrine system are consistent with its actions as a monoamine reuptake inhibitor. Acute cocaine administration stimulates release of gonadotropins, ACTH, and cortisol or corticosterone and suppresses prolactin levels. It has been difficult to detect changes in basal levels of most hormones or alterations in hormone responsiveness to a challenge dose of cocaine or other agents after chronic cocaine treatment. Interpretation of clinical data is often complicated by polydrug abuse involving opiates and alcohol as well as cocaine. However, preclinical studies of the effects of chronic cocaine exposure on integrated neuroendocrine function have revealed disruptions of the estrous cycle in rats and the menstrual cycle in rhesus monkeys. Furthermore, the menstrual cycle disorders observed in rhesus monkeys parallel those reported in women who abuse cocaine. Much remains to be learned about cocaine's interactions with the endocrine system and the consequences of cocaine abuse for reproductive function.

Effects of kappa opioids on cocaine self-administration by rhesus monkeys

Kappa opioid agonists attenuate some neurochemical and behavioral effects of cocaine and are being considered as potential treatments for cocaine dependence. The present study examined the effects of two kappa opioid agonists, the benzomorphan ethylketocyclazocine (EKC) and the arylacetamide U50,488, on cocaine self-administration in rhesus monkeys. Monkeys responded for 0.032 mg/kg/injection cocaine (i.v.) and 1 g banana-flavored food pellets during alternating daily sessions of cocaine and food availability. Chronic treatment for 10 consecutive days with EKC (0.0032-0.032 mg/kg/hr) or U50,488 (0.032-0.1 mg/kg/hr) dose-dependently decreased self-administration of cocaine unit doses at the peak of the cocaine dose-effect curve (0.01 and 0.032 mg/kg/injection). These decreases in cocaine self-administration were often sustained throughout the 10 days of treatment. Doses of EKC and U50,488 that decreased cocaine self-administration usually decreased food-maintained responding as well. In addition, EKC and U50,488 often produced emesis and sedation during the first few days of treatment, although tolerance appeared to develop rapidly to these effects. In general, EKC produced fewer undesirable effects than U50,488 at doses that decreased cocaine self-administration. The kappa antagonist norbinaltorphimine (3.2 mg/kg) did not affect responding maintained by cocaine or food. However, both norbinaltorphimine (3.2 mg/kg) and the opioid antagonist naloxone (1.0 mg/kg/hr) blocked the effects of EKC and U50,488. These results indicate that chronic administration of EKC and U50,588 produce a dose-dependent, kappa receptor-mediated and often sustained decrease in cocaine self-administration. However, these kappa agonists also produce undesirable behavioral effects that may complicate their use as treatments for cocaine dependence.

The effects of chronic cocaine self-administration on the menstrual cycle in rhesus monkeys

Clinical studies suggest that cocaine disrupts reproductive function, but because cocaine abusers often abuse opiates and alcohol, it has been difficult to determine the contribution of cocaine alone. The effects of chronic cocaine self-administration on menstrual cycle duration and basal levels of progesterone were examined in eight female rhesus monkeys and compared with the effects of occasional administration of single cocaine doses (0.4 or 0.8 mg/kg) in six otherwise drug-free controls. All monkeys had normal ovulatory menstrual cycles before cocaine exposure. Monkeys self-administered cocaine (0.10 mg/kg/injection) and food (1 gm banana pellets) in 4 daily sessions on a second-order schedule (fixed ratio 2 [variable ratio 16:S]). Cocaine intake was limited to 8 mg/kg/day. During the first cocaine exposure (256-776 days), monkeys self-administered 3.51 (+/- 0.77) to 7.41 (+/- 0.27) mg/kg/day. During the second cocaine exposure (103-623 days), monkeys self-administered 6.18 (+/- 0.77) to 7.41 (+/- 0.27) mg/kg/day. In these prospective longitudinal studies, 48% of the menstrual cycles were of abnormal duration in the cocaine self-administration group, whereas only 6% of the menstrual cycles were abnormal in the control group. There were 19 episodes of amenorrhea (61-190 days of no menses). During cocaine self-administration, approximately one-third of the menstrual cycles were anovulatory with low mid-luteal progesterone levels of 2.04 (+/- 0.6) to 4.13 (+/- 0.5) ng/ml. Over 25% of menstrual cycles were anovulatory during cocaine withdrawal with mid-luteal progesterone levels below 5 ng/ml. These data indicate that chronic cocaine exposure can disrupt the menstrual cycle in rhesus monkeys and that menstrual cycle abnormalities often persist during cocaine withdrawal. These data are consistent with clinical studies and reports of cocaine-induced disruption of the estrous cycle in rodents.

Age-related reduction in functional MRI response to photic stimulation

Many functional imaging studies have demonstrated age-related alterations in cerebral blood flow during the resting state. However, few studies have addressed possible differences in functional response to cerebral activation. We assessed the response of visual cortex to photic stimulation in 9 normal elderly subjects and 17 normal younger subjects with blood oxygenation level dependent functional magnetic resonance imaging. We found that the amplitude of response in elderly subjects was significantly decreased compared to younger subjects (2.5 +/- 1.0% versus 4.0 +/- 1.6%, p = 0.01), suggesting a reduction in functional activation or an age-related alteration in the coupling of blood oxygenation to focal activation.

Effects of alcohol ingestion on estrogens in postmenopausal women

OBJECTIVE

To determine if moderate alcohol drinking increases circulating estradiol levels in postmenopausal women who are taking estrogen replacement.

DESIGN

Randomized, double-blind, placebo-controlled crossover study of the effects of alcohol ingestion on plasma estradiol and estrone.

SETTING

Inpatient Clinical Research Center.

PARTICIPANTS

Twelve healthy postmenopausal women receiving oral estrogen (estradiol, 1 mg/day) and progestin (medroxyprogesterone acetate) replacement therapy were compared with 12 postmenopausal women who were not using estrogen replacement therapy (ERT).

INTERVENTION

Each group drank alcohol (0.7 g/kg) and an isoenergetic (isocaloric) placebo (randomized sequence) on consecutive days. Women who were taking ERT were studied during the estrogen-only portion of their replacement cycle, and estrogen was administered each evening at 2100 hours.

MAIN OUTCOME MEASURE

The impact of alcohol ingestion on plasma estradiol and estrone levels.

RESULTS

Alcohol ingestion lead to a 3-fold increase in circulating estradiol in women on ERT; however, alcohol did not change estradiol significantly in control women who were not on ERT. In women using ERT, estradiol levels increased from 297 to 973 pmol/L (81 to 265 pg/mL) within 50 minutes (P<.001) during the ascending limb of the blood alcohol curve and remained significantly above baseline for 5 hours (P<.001). No significant increase in circulating estrone was detected in either group. However, estrone levels decreased after alcohol and placebo in women on ERT (P<.05). Blood alcohol levels did not differ significantly in women who used ERT and those who did not. Peak blood alcohol levels of 21 mmol/L were attained in each of the 2 groups within 50 to 60 minutes after drinking began. Changes in estradiol were significantly correlated with changes in blood alcohol levels on both the ascending (P<.001) and descending (P<.001) limb of the blood alcohol curve.

CONCLUSIONS

Acute alcohol ingestion may lead to significant and sustained elevations in circulating estradiol to levels 300% higher than those targeted in clinical use of ERT. Potential health risks and benefits of the interactions between acute alcohol ingestion and ERT should be further evaluated.

Effects of the structurally novel opioid 14 alpha, 14' beta-[dithiobis [(2-oxo-2,1-ethanediyl)imino]]bis(7,8-dihydromorphinone) on schedule-controlled behavior and thermal nociception in rhesus monkeys

The in vivo pharmacology of the structurally novel opioid 14 alpha, 14' beta-[dithiobis[(2-oxo-2,1-ethanediyl)imino]]bis(7,8-dihydromorphinon e) (TAMO) was examined in rhesus monkeys with assays of schedule-controlled behavior and thermal nociception. TAMO (0.032-1.8 mg/kg) produced dose-dependent decreases in response rates maintained under a fixed-ratio 30 schedule of food delivery (n = 3) and increases in tail-withdrawal latencies in a warm-water tail-withdrawal procedure (n = 3). Both the rate-decreasing and antinociceptive effects of TAMO (1.0 mg/kg) were maximal after 40 to 80 min and lasted at least 160 min. Pretreatment with the mu-selective opioid antagonist quadazocine (0.001-0.1 mg/kg) antagonized the effects of TAMO and shifted the TAMO dose-effect curves to the right. Schild analysis yielded in vivo apparent pA2 values (mean +/- S.E.M.) of 8.8 +/- 0.072 and 8.7 +/- 0.40 for quadazocine antagonism of the rate-decreasing and antinociceptive effects, respectively, of TAMO, which suggests that the effects of TAMO were mediated by mu-opioid receptors. In addition, quadazocine (0.1-1.0 mg/kg) reversed the behavioral effects of TAMO (1.0 mg/kg) when quadazocine was administered immediately after TAMO had attained its maximal effect. Twenty-four-hour pretreatment with 1.0 mg/kg TAMO did not significantly after the rate-decreasing or antinociceptive effects of fentanyl or the rate-decreasing effects of morphine. The dose-effect curve for morphine antinociception was shifted 4-fold to the right 24 hr after pretreatment with 1.0 mg/kg TAMO. However, 24-hr pretreatment with an equiactive dose of morphine (10.0 mg/kg) also produced a small (2-fold) but significant rightward shift in the dose-effect curve for morphine antinociception. Twenty-four-hour pretreatment with 1.8 mg/kg TAMO had no effect on the antinociceptive effects of U69,593 (0.0032-0.1 mg/kg). These results suggest that TAMO acts as a reversible mu agonist with a relatively slow onset and a duration of action and relative efficacy similar to those of morphine in rhesus monkeys. Twenty-four hours after TAMO administration, the highest doses of TAMO that could be safely administered produced little or no mu antagonist effects and no kappa antagonist effects.

Acute and chronic effects of flupenthixol on the discriminative stimulus and reinforcing effects of cocaine in rhesus monkeys

It has been proposed that the relatively nonselective dopamine receptor antagonist flupenthixol may be useful in the treatment of cocaine dependence. Drugs used in the treatment of cocaine dependence are administered chronically; however, most preclinical studies have examined only the acute effects of flupenthixol treatment on the effects of cocaine. Consequently, the purpose of the present study was to compare the effects of acute and chronic treatment with flupenthixol (0.0032-0.032 mg/kg) on the discriminative stimulus and reinforcing effects to cocaine in rhesus monkeys. One group of six monkeys was trained to discriminate 0.4 mg/kg cocaine (i.m.) from saline in a two-lever, food-reinforced, drug discrimination procedure. A second group of four monkeys was trained to respond for 0.032 mg/kg/injection cocaine (i.v.) and 1-g banana-flavored food pellets during alternating daily cycles of cocaine and food availability. Neither acute nor chronic treatment with a low dose of flupenthixol (0.0032 mg/kg) significantly altered the discriminative stimulus or reinforcing effects of cocaine. Higher doses of flupenthixol (0.01-0.032 mg/kg) produced a surmountable blockade of both the discriminative stimulus and reinforcing effects of cocaine, shifting the dose-effect curves for both cocaine discrimination and cocaine self-administration up to 0.5 log unit to the right. However, doses of flupenthixol that altered cocaine discrimination also decreased response rates. Similarly, doses of flupenthixol that decreased cocaine self-administration also often decreased rates of food-maintained responding. Consequently, nonselective behavioral effects of flupenthixol may have contributed to its effects on cocaine discrimination and self-administration. Moreover, the effects of flupenthixol on cocaine discrimination and self-administration diminished over time. After only 3 to 5 days of chronic treatment, flupenthixol did not consistently shift the cocaine discrimination dose-effect curve to the right. Similarly, rates of cocaine self-administration that were initially decreased by flupenthixol often recovered partially or completely during a 10-day regimen of chronic flupenthixol treatment. These results suggest that flupenthixol may have limited utility in the long-term treatment of cocaine dependence.

Preclinical evaluation of pharmacotherapies for treatment of cocaine and opioid abuse using drug self-administration procedures

Drug abuse is a major public health problem, and the relationship between intravenous drug abuse and AIDS underscores the need for more effective treatment medications. Animal models of drug self-administration are useful to systematically evaluate new treatment medications and predict clinical efficacy. This review summarizes the status of preclinical evaluations of medications for treatment of cocaine and opiate abuse. The basic drug self-administration methodology and the rationale for experimental designs and outcome criteria are described. Studies of the effects of dopamine or opioid receptor agonists and antagonists as well as medications used clinically for other indications on drug self-administration are critically examined. Where possible, the degree of concordance between clinical and preclinical studies of drug abuse treatment medications is discussed. We conclude that drug self-administration models are valuable for preclinical assessment of medication efficacy, and we recommend some strategies to further improve evaluation procedures. The discovery of more effective medications for substance abuse treatment should be facilitated by recent advances in behavioral science, pharmacology, neurobiology and medicinal chemistry.

Effects of the putative dopamine D3 receptor agonist 7-OH-DPAT in rhesus monkeys trained to discriminate cocaine from saline

These studies were designed to evaluate the effects of the putative dopamine D3 receptor agonist 7-hydroxy-N,N-di-n-propyl-2-aminotetraline (7-OH-DPAT), alone and in combination with cocaine, in four rhesus monkeys trained to discriminate cocaine (0.4 mg/kg, IM) from saline under a fixed-ratio 30 schedule of food presentation. Under these conditions, cumulative doses of cocaine (0.013-1.3 mg/kg) produced a dose-dependent and complete generalization to the training dose of cocaine in all monkeys, while producing only minimal effects on response rates. The discriminative stimulus effects of cocaine were antagonized by the non-selective dopamine receptor antagonist flupenthixol (0.018 mg/kg, IM) in all four monkeys. The effects of 7-OH-DPAT (0.01-1.8 mg/kg) were inconsistent across monkeys. In two of the four monkeys (monkeys L990 and L958), 7-OH-DPAT consistently and completely generalized to cocaine and decreased response rates in a dose-dependent manner. Both the cocaine-like discriminative stimulus effects and rate-decreasing effects of 7-OH-DPAT were antagonized by flupenthixol in these two monkeys. Pretreatment with low doses of 7-OH-DPAT (0.01-0.032 mg/kg) had no effect on the cocaine dose-effect curve in monkeys L990 and L958; however, higher doses of 7-OH-DPAT (0.032-0.32 mg/kg) shifted the cocaine dose-effect curve to the left. In the other two monkeys (monkeys 150F and 89B036), 7-OH-DPAT produced a dose-dependent decrease in response rates but did not consistently generalize to cocaine. Flupenthixol did not antagonize the rate-decreasing effects of 7-OH-DPAT in these two monkeys, and pretreatment with 7-OH-DPAT (0.1-0.32 mg/kg) produced a decrease in response rates but had no effect on the cocaine dose-effect curve. Time-course experiments revealed that 7-OH-DPAT (0.32 mg/kg) displayed a slower onset and a longer duration of effect than the training dose of cocaine. Finally, the D3/D2 dopamine agonist quinpirole completely generalized to cocaine in three monkeys, and partially in the fourth monkey. Quinpirole showed the highest potency in those monkeys in which 7-OH-DPAT consistently generalized to cocaine. The results of the present study suggest that, in rhesus monkeys, 7-OH-DPAT produces cocaine-like effects and may modulate the discriminative stimulus effects of cocaine in some monkeys.

Impact of maternal alcoholism on separation of children from their mothers: findings from a sample of incarcerated women

Patterns of maternal child co-residence among 25 alcoholic women incarcerated for drunk driving are examined. Two-thirds of these mothers reported significant periods of time, not due to incarceration, when minor children did not reside with them. Fewer than half of the placements were mandated by child-protective services. Having two or more children while actively alcoholic or residing with a substance abuser correlated strongly with separate residence.

Effects of cocaine on pulsatile activity of hypothalamic-pituitary-adrenal axis in male rhesus monkeys: neuroendocrine and behavioral correlates

Cocaine stimulates the hypothalamic-pituitary-adrenal (HPA) axis in rodents and in humans. This study examined the acute effects of cocaine (0.4 and 0.8 mg/kg) and saline placebo on pulsatile adrenocorticotropic hormone (ACTH) and cortisol release in seven male rhesus monkeys. Pulsatile ACTH and cortisol release were evaluated with an intensive (2-min) venous blood sampling procedure and cluster analysis. In addition, the behavioral responses to cocaine were analyzed to assess the relationship between HPA axis activation and behavior. Although analysis of group data revealed significant (P < .05) increases in pulse amplitude and incremental peak height of ACTH and cortisol release after cocaine (0.8 mg/kg) administration, examination of individual data indicated that this effect was not consistent across all monkeys. Cocaine (0.8 mg/kg) increased ACTH plasma levels within 4.7 +/- 1.3 min (P < .05) and amplitude-related characteristics (P < .05) of pulsatile ACTH and cortisol release only in those animals that subsequently showed behavioral stimulation (high responders: n = 3). The frequency of pulsatile ACTH and cortisol remained unchanged by cocaine. Cocaine (0.8 mg/kg) decreased the mean amplitude of ACTH peaks with no changes in pulsatile cortisol release in the four monkeys that showed no behavioral stimulation (low responders). These differences in pulsatile ACTH and cortisol release patterns after cocaine could not explained by different plasma cocaine levels. Peak plasma cocaine levels averaged 63.1 +/- 13.4 and 78.0 +/- 21.4 ng/ml within 2 min after lower dose and 183.3 +/- 52.3 and 204.3 +/- 50.8 ng/ml after higher dose of cocaine in high- and low responder groups, respectively (P > .05; N.S.). Base-line cortisol, but not ACTH, levels were higher (P < .05) in low responders before administration of 0.8 mg/kg of cocaine. Peak and valley characteristics of base-line cortisol release were higher in low responders than in high responders and an inverse relationship was found between basal cortisol levels and postcocaine ACTH release and behavior. In summary, cocaine stimulated the pulsatile ACTH and cortisol release by increasing the amplitude of secretory episodes in behaviorally responsive monkeys.

Brain alcohol detectability increase with repeated administration in humans: a proton spectroscopy study

Proton MRS was used to detect brain alcohol after repeated alcohol exposure in human subjects. MRS detectability measurements were made after administration of an alcoholic drink (0.6 g/kg alcohol) and after an identical drink administrated 6 h later. Between-drink differences in the methyl proton triplet resonance of ethyl alcohol were assessed at statistically equivalent and near-peak blood alcohol concentrations (reflecting brain alcohol concentrations) and statistically equivalent internal standard N-acetyl resonance areas after Drinks 1 and 2, respectively. Brain alcohol detectability was not altered in TE 30-ms spectra but was increased in all five subjects after Drink 2 by an average of 70% in TE 270-ms spectra (p < 0.01). This was accompanied by significant between-drink differences in subjective ratings of alcohol's effects, suggestive of induction of acute alcohol tolerance. These findings suggest increased brain alcohol detectability in TE 270-ms spectra after repeated alcohol exposure that may reflect acute alcohol tolerance.

Naloxonazine antagonism of levorphanol-induced antinociception and respiratory depression in rhesus monkeys

The mu-opioid receptor antagonist effects of naloxonazine on levorphanol-induced thermal antinociception and respiratory depression were examined in rhesus monkeys. Levorphanol (0.032-3.2 mg/kg) produced dose-dependent increases in tail-withdrawal latencies from 50 degrees C water in a warm-water tail-withdrawal assay and dose-dependent decreases in ventilation in both air and 5% CO2 mixed in air. Naloxonazine (0.1-3.0 mg/kg) antagonized both the antinociceptive and ventilatory effects of levorphanol to a similar degree, and the antagonist effects of naloxonazine were greater after 1 h than after 24 h. Under all conditions, the antagonist effects of naloxonazine were fully surmountable. Schild analysis of the antagonist effects of naloxonazine after 1 h pretreatment in the antinociception assay yielded a pA2 value of 7.6 and a slope of -0.50; by comparison, quadazocine yielded a pA2 value of 7.5 and a slope of -1.05. These results suggest that naloxonazine acts as a potent and fully reversible mu-opioid receptor antagonist with a moderately long duration of action in rhesus monkeys. In addition, these results suggest that the antinociceptive and ventilatory effects of mu-opioid receptor agonists in rhesus monkeys are mediated by pharmacologically similar populations of mu opioid receptors.

Antinociceptive effects of cocaine/opioid combinations in rhesus monkeys

This study characterized the antinociceptive effects of cocaine alone and in combination with mu, delta, and kappa opioids in rhesus monkeys. The shaved tails of four rhesus monkeys were exposed to warm water (42, 46, 50, 54, and 58 degrees C), and tail withdrawal latencies (20 sec maximum) from each temperature were determined. The temperature that produced a tail withdrawal latency of 10 sec (T10) was interpolated, and drug-induced changes in the T10 value (delta T10) were calculated. Dose-dependent increases in delta T10 were produced by cocaine (0.032-1.8 mg/kg), the high efficacy mu agonist fentanyl (0.001-0.1 mg/kg), the intermediate efficacy mu agonist morphine (0.1-18 mg/kg), the low efficacy mu agonist nalbuphine (1-32 mg/kg), and the kappa agonist U69,593 (0.0032-0.1 mg/kg). The delta agonist BW373U86 (0.56 mg/kg) produced no effect. Relative maximum effects, determined from the maximum delta T10 values produced by each drug, were fentanyl > or = (5,7,8 beta)-N-methyl-N[2-(1-pyrrolidinyl)1-oxaspiro[4,5]dec-8- yl]benzeneacetamide > morphine > nalbuphine > or = cocaine > BW373U86. When individual doses of cocaine (0.1-1.8 mg/kg) and morphine (0.32-10.0 mg/kg) were combined, cocaine produced a dose-dependent increase in the effects of each dose of morphine, and the antinociceptive effects of most cocaine/morphine combinations were significantly greater than the antinociceptive effects of either cocaine or morphine alone. Cocaine (1.8 mg/kg) was also combined with nalbuphine (1.0, 10 mg/kg), fentanyl (0.001, 0.032 mg/kg), BW373U86 (0.56 mg/kg) and U69,593 (0.0032-0.056 mg/kg). Cocaine/nalbuphine combinations produced effects markedly greater than either drug alone.

Buprenorphine-induced alterations of cocaine's reinforcing effects in rhesus monkey: a dose-response analysis

Buprenorphine reduces cocaine self-administration by rhesus monkeys, opiate- and cocaine-dependent men and polydrug abusers, but the mechanisms underlying these cocaine-opiate interactions are not well understood. In the present study, the effects of daily placebo or buprenorphine (0.1, 0.3 and 1.0 mg/kg) treatment on cocaine self-administration (0.001-0.3 mg/kg/inject) were examined in five cocaine-experienced rhesus monkeys. Saline and each of six cocaine doses were available in an irregular order. Responding for cocaine (or saline) and food was maintained on a second order FR4 (VR 16:5) schedule of reinforcement. During placebo treatment, the daily number of cocaine injections increased as the unit dose was increased and then decreased at higher doses. Cocaine doses that maintained the highest rates of responding during placebo treatment were more resistant to buprenorphine's effects. The typical increase in response rate during the first five cocaine injections of a session also was attenuated by buprenorphine. The ascending limb of the cocaine dose-response curve was shifted downward and approximately one log unit to the right during low-dose buprenorphine treatment (0.1 mg/kg/day). In contrast, individual response rates for food pellets were unaffected. We conclude that buprenorphine selectively decreases self-administration of some unit doses of cocaine at doses that have minimal effects on food-maintained responding.

Relationship between the discriminative stimulus effects and plasma concentrations of intramuscular cocaine in rhesus monkeys

The relationship between the discriminative stimulus effects and plasma pharmacokinetics of cocaine was evaluated in six rhesus monkeys trained to discriminate cocaine (0.4 mg/kg, IM) from saline under a FR30 schedule of food presentation. The same monkeys were tested in two procedures. In a cumulative dosing procedure, five cumulative doses of cocaine (0.013-1.3 mg/kg) were administered and discriminative stimulus effects were evaluated 10 min after the administration of each dose. Cocaine plasma concentrations were measured in separate sessions using the same doses and interdose intervals. In a single dosing procedure, the time-courses of the discriminative stimulus effects and plasma concentrations of cocaine were assessed after the administration of cocaine (0.4 mg/kg). A close correspondence between cocaine's discriminative stimulus effects and plasma concentrations was obtained in both procedures. Cocaine was virtually undetectable in plasma at doses that produced saline-appropriate responding (0.013 and 0.04 mg/kg), whereas increasing plasma concentrations were measured at doses that produced primarily cocaine-appropriate responding (0.13 mg/kg or higher). The time-course of the discriminative stimulus effects of cocaine was characterized by a rapid onset (within 1-3 min post-cocaine) and offset (within 20-60 min post-cocaine). Peak plasma levels were obtained at 10 min post-cocaine. No differences in plasma concentrations were found 10 min after the administration of a cumulative versus a single dose of cocaine 0.4 mg/kg (mean, 75.8 and 74.0 ng/ml, respectively). Cocaine plasma concentrations lasted longer than its discriminative stimulus effects. The results of the present study confirm that the cumulative dosing procedure used yields plasma concentrations of cocaine that are similar to the concentrations obtained after single cocaine dosing.

Effects of cocaine and corticotropin-releasing factor on pulsatile ACTH and cortisol release in ovariectomized rhesus monkeys

Cocaine stimulates ACTH secretion by a corticotropin-releasing factor (CRF)-dependent mechanism in male rats, rhesus monkeys, and humans. To determine the generality of this effect, we examined the effects of acute cocaine administration on the pulsatile release of ACTH and cortisol in three ovariectomized (OVX) rhesus monkeys and compared its effects to stimulation with CRF. Venous blood samples were collected at 2-min intervals for 60 min before and after iv administration of cocaine (0.4 and 0.8 mg/kg) and CRF (1.0 and 10 micrograms/kg). Cluster analysis procedures were used to evaluate the pulsatile characteristics of ACTH and cortisol release. After placebo administration, an ACTH pulse frequency of 3 peaks/h was detected. After cocaine administration, plasma cocaine levels peaked at 92 +/- 3.0 and 201 +/- 60 ng/mL within 2 min. However, in contrast to normal intact males, cocaine did not stimulate the pulsatile release of ACTH in OVX females. Cocaine (0.4 mg/kg) decreased ACTH incremental peak height and valley levels compared with pre-cocaine values, and a higher dose of cocaine produced no changes in ACTH release. Bolus injection of a low dose of CRF (1.0 micrograms/kg, iv) significantly increased ACTH incremental peak height (P < 0.05), and a higher dose of CRF (10 micrograms/kg) increased ACTH peak amplitude, percentage increase in peak amplitude, area under the peaks, and incremental peak heights as well as ACTH valley level and nadir (10 micrograms/kg, iv) (P < 0.05). ACTH pulse frequency did not change after CRF or cocaine administration. Pulsatile release of cortisol was 2.7 peaks/h under placebo conditions and did not change after cocaine or CRF administration. Cortisol pulse amplitude was increased after low and high doses of CRF. High doses of CRF (10 micrograms/kg) also increased the mean level of cortisol valleys. In summary, we found that CRF but not cocaine stimulated pulsatile ACTH and cortisol release in OVX rhesus monkeys. The profound ACTH response to CRF challenge suggests that the CRF sensitivity and the ACTH release capacity of the anterior pituitary corticotroph cells were intact. The lack of stimulatory effects of cocaine on the hypothalamic-pituitary-adrenal axis in OVX monkeys, in contrast to normal male monkeys, may reflect the absence of gonadal steroids.

A primate model of polydrug abuse: cocaine and heroin combinations

Abuse of cocaine-opiate combinations ("speedballs") reported clinically was simulated in a rhesus monkey model of simultaneous cocaine and heroin self-administration. The reinforcing effects of nine cocaine-heroin combinations (cocaine [0.001, 0.01 and 0.10 mg/kg per injection i.v.] and heroin [0.0001, 0.001 and 0.01 mg/kg per injection i.v.]) were evaluated for 10 days on a second-order fixed ratio of 4 (variable ratio of 16:S) schedule and compared with self-administration of cocaine and heroin alone. Dose-effect curves for cocaine-heroin combinations usually were similar to those for cocaine and heroin alone, and intermediate doses maintained equivalent high levels of drug self-administration. No toxic effects were observed. In drug discrimination studies, cocaine (0.004-1.3 mg/kg) substitution resulted in a dose-dependent generalization to the training dose (0.4 mg/kg i.m.) in all five monkeys. Heroin substitution (0.01-1.0 mg/kg i.m.) resulted in dose-dependent and complete generalization to cocaine in three of five monkeys. Heroin pretreatment (0.1-0.18 mg/kg i.m.) did not change the cocaine discrimination dose-effect curve. Pretreatment with an opiate antagonist, quadazocine (0.1 mg/kg i.m.), had no effect on the discriminative stimulus effects of cocaine but antagonized the cocaine-like discriminative stimulus effects of heroin. Pretreatment with a dopamine antagonist, flupenthixol (0.018 mg/kg), antagonized the discriminative stimulus effects of cocaine but did not affect the cocaine-like effects of heroin. These findings demonstrate the feasibility of maintaining self-administration of cocaine-heroin combinations and suggest that cocaine and heroin have similar reinforcing and discriminative stimulus effects in rhesus monkeys.

Improved regional cerebral blood flow in chronic cocaine polydrug users treated with buprenorphine

Chronic cocaine and polydrug abuse have been associated with regional abnormalities in cerebral perfusion. The authors have previously demonstrated that these abnormalities are partially reversible after drug addiction treatment with buprenorphine. This study was designed to separate the effect on cerebral perfusion of abstinence from drug use from that of buprenorphine directly.

METHODS

Fifteen cocaine- and heroin-dependent men were studied with 99mTc-hexamethylpropyleneamine oxime (HMPAO) brain SPECT. The men, all part of an inpatient drug abuse treatment research program, were randomly assigned after detoxification to receive placebo or either 6 or 12 mg daily buprenorphine treatment. SPECT studies were performed at baseline, after maximum dosage was reached and after tapering off the study drug. Studies were compared visually with regard to the number and location of perfusion defects by reviewers blinded to treatment assignment.

RESULTS

Subjects receiving buprenorphine had a significant reduction in the number of defects per study between baseline and maximum buprenorphine dose as compared with those receiving placebo (decrease of 4 +/- 5.4 versus increase of 4.8 +/- 4.7, p = 0.006). These differences were dose-related. Improvement with buprenorphine was temporary, with return to baseline after tapering off.

CONCLUSION

Buprenorphine treatment, and not abstinence from drug use alone, leads to improvement in regional cerebral perfusion abnormalities in chronic cocaine- and heroin-dependent men.

Role of delta opioid receptors in the reinforcing and discriminative stimulus effects of cocaine in rhesus monkeys

The role of delta opioid receptors in the self-administration and discrimination of cocaine by rhesus monkeys was evaluated using the delta opioid antagonist naltrindole and the delta opioid agonist BW373U86 [(+/-)-4-((alpha R*)-alpha-((2S*,5R*)-4-Allyl-2,5-dimethyl-1- piperazinyl)-3-hydroxybenzyl)-N,N-diethylbenzamide dihydrochloride]. In the self-administration studies, monkeys were trained to respond for food (1 g banana pellets) or cocaine (0.032 mg/kg/injection, i.v.) under a second-order FR4(VR16:S) schedule of reinforcement during multiple daily food and drug sessions. Substitution of saline or other unit doses of cocaine (0.001-0.1 mg/kg/injection) for the maintenance dose of cocaine yielded typical inverted-U shaped dose-effect curves relating unit dose of cocaine to the number of saline or drug injections per day. The unit dose of cocaine available during drug sessions had little effect on food-maintained responding. In the drug discrimination studies, monkeys were trained to discriminate 0.4 mg/kg cocaine (i.m.) from saline in a two-lever, food-reinforced drug discrimination task. Cumulative dosing with cocaine (0.004-1.3 mg/kg) produced a dose-dependent generalization to the training dose of cocaine without consistently altering response rates. Initial experiments with naltrindole (0.1-3.2 mg/kg, i.v. or i.m.) produced effects in some monkeys suggesting that naltrindole may have antagonized the effects of cocaine under both procedures. In the drug self-administration studies, treatment with at least one dose of naltrindole for 10 consecutive days decreased self-administration of a unit dose of cocaine at the peak of the ascending limb of the cocaine dose-effect curve (0.01 mg/kg/injection) in three of four monkeys. In the drug discrimination studies, treatment with at least one dose of naltrindole shifted the cocaine dose-effect curve 1/2 log unit to the right in two of four monkeys. However, naltrindole did not alter the effects of cocaine in all monkeys under either procedure. Furthermore, in the monkeys in which naltrindole was effective, the cocaine-antagonist actions of naltrindole were not replicable and were not monotonically related to dose. When the delta agonist BW373U86 (0.001-0.032 mg/kg/inj, i.v.) was substituted for cocaine in one monkey in which naltrindole decreased cocaine self-administration, BW373186 was not self-administered. In addition, BW373U86 (0.0032-0.32 mg/kg, i.m.) neither generalized to cocaine nor potentiated the effects of cocaine in the drug discrimination procedure. These results suggest that delta opioid receptors play, at best, a minor and inconsistent role in the reinforcing and discriminative stimulus effects of cocaine in rhesus monkeys.

The acute effects of cocaine on anterior pituitary hormones in ovariectomized rhesus monkeys

Cocaine stimulates a rapid release of gonadotropins in intact rhesus males and females and human males and enhances synthetic luteinizing hormone-releasing hormone (LHRH), stimulated luteinizing hormone (LH) and follicle-stimulating hormone (FSH). This report describes the effects of acute cocaine administration on basal and synthetic LHRH-stimulated anterior pituitary hormones [LH, FSH and prolactin (PRL)] in five ovariectomized female rhesus monkeys. Integrated blood samples were collected every 10 min for 40 min before i.v. administration of cocaine (0.4 or 0.8 mg/kg) or an equal volume of vehicle control solution and for 110 min after cocaine or placebo administration. Synthetic LHRH (100 micrograms i.v.) was administered 10 min after cocaine or placebo-cocaine injection. In contrast to previous observations in rhesus and human males and in early follicular and midluteal phase rhesus females, cocaine did not change basal levels of gonadotropins or PRL in long-term ovariectomized females. LHRH stimulated a significant and sustained increase in LH (P < .01) within 20 min and FSH (P < .05) within 40 min after placebo-cocaine administration. LHRH also stimulated significant increases in LH and FSH after 0.4 and 0.8 mg/kg cocaine administration. Significant increases in LH (P < .05) and FSH (P < .01) were measured 10 min sooner after 0.8 mg/kg cocaine than after placebo-cocaine, but cocaine did not significantly increase the magnitude or duration of LHRH-stimulated increases in gonadotropins in ovariectomized females as it did in follicular phase females. Basal PRL levels (3.6 +/- 0.2 and 5.5 +/- 0.7 ng/ml) did not change after administration of cocaine alone.(ABSTRACT TRUNCATED AT 250 WORDS)

The concordance of pulsatile ultradian release of adrenocorticotropin and cortisol in male rhesus monkeys

The ultradian release of ACTH and cortisol was investigated in six male rhesus monkeys (Macaca mulatta) with an intensive (2-min) blood-sampling procedure to investigate micropulsatile hormone secretory patterns. A sensitive and specific immunoradiometric assay was used to measure plasma ACTH concentrations. An objective pulse detection algorithm (Cluster) was used to assess the pulsatility of ACTH and cortisol release. The temporally coincident release of ACTH and cortisol was also examined. Venous blood samples were collected (over < 15 s) every 2 min for 120 min beginning at 1300 h. The number of ACTH peaks (3.2 peaks/h), interpulse intervals (19 +/- 2.4 min), and pulse amplitudes (9.7 +/- 1.6 pmol/L) in rhesus monkey were similar to corresponding measures of ACTH release in humans (3.3 peaks/h, 18 +/- 0.8 min, and 4.7 +/- 1.0 pmol/L, respectively). The number of cortisol peaks (2.3 peaks/h), interpulse interval (26 +/- 8.6 min), and other characteristics of pulsatile cortisol release were also determined. There was a 32.4% exact concordance of ACTH with cortisol peaks (11 of 34; P < 0.001). Fifty-six percent of ACTH peaks (19 of 34) were followed by a cortisol peak within 10 min (P < 0.02). There was a significant correlation between the ACTH and coincident cortisol pulse amplitudes (P < 0.0001). The amplitudes of ACTH peaks coincident with cortisol peaks at 0 min time lag were significantly higher than ACTH peaks not temporally coupled with cortisol peaks. Our data indicate that 1) high frequency, low amplitude micropulsatile ACTH secretion in rhesus monkeys is very similar to the high frequency ACTH rhythm in humans; 2) temporally concordant ACTH and cortisol release episodes may be amplitude coupled; and 3) an adequate incremental ACTH pulse amplitude may elicit a concurrent cortisol release episode from the adrenal cortex. These data suggest that the rhesus monkey is a potentially useful model for the study of neuroendocrine control of ACTH release.