Effects of kappa opioid agonists alone and in combination with cocaine on heart rate and blood pressure in conscious squirrel monkeys

As kappa agonists have been proposed as treatments for cocaine abuse, the cardiovascular effects of the kappa opioid receptor agonists ethylketocyclazocine (EKC) and enadoline were investigated in conscious squirrel monkeys. Both EKC and enadoline increased heart rate with little effect on blood pressure. This effect appeared to be specific for kappa receptors as the mu opioid agonist morphine did not mimic the effects of the kappa agonists. The opioid antagonist naltrexone, at a dose of 1.0 mg/kg, blocked the effect of EKC. An action at both central and peripheral receptors may be responsible for the heart rate increase following kappa agonist treatment. The ganglionic blocker chlorisondamine partially antagonized the effect of EKC on heart rate, suggesting central involvement, while the peripherally-acting agonist ICI 204,448 ((+/-)-1-[2,3- (Dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride) also increased heart rate, supporting a peripheral site of action. When given in combination with cocaine, EKC produced effects that were sub-additive, suggesting that the kappa agonists may be used safely as cocaine abuse treatments.

Hyponatremia in marathon runners due to inappropriate arginine vasopressin secretion

PURPOSE

Exercise-associated hyponatremia (EAH), as defined by a blood sodium concentration [Na+] less than 135 mmol/L, may lead to hypotonic encephalopathy with fatal cerebral edema. Understanding the pathogenetic role of antidiuresis may lead to improved strategies for prevention and treatment.

METHODS

Normonatremic marathon runners were tested pre- and post-race for creatine kinase, interleukin-6, cortisol, prolactin, and arginine vasopressin. Similar testing also was carried out in runners with encephalopathy caused by EAH, including 2 cases with fatal cerebral edema.

RESULTS

Normonatremic runners (n = 33; 2001) with a mean 3% decrease in body weight showed a 40-fold increase in interleukin-6 (66.6 +/- 11.9 pg/mL from 1.6 +/- 0.5 pg/mL, P = .001), which was significantly correlated with increases in creatine kinase (r = 0.88, P = <.0001), cortisol (r = 0.70, P = .0003), and prolactin (r = 0.67, P <.007), but not arginine vasopressin (r = 0.44, P = .07). Collapsed runners with EAH (n = 22; 2004) showed a mean blood urea nitrogen less than 15 mg/dL with measurable plasma levels of arginine vasopressin (>0.5 pg/mL) in 43% of cases. Two marathon runners with fatal cerebral edema additionally showed less than maximally dilute urines (>100 mmol/kg/H2O) and urine [Na+] greater than 25 mEq/L.

CONCLUSIONS

Cases of EAH fulfill the essential diagnostic criteria for the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Runners with hypotonic encephalopathy at subsequent races were treated with intravenous hypertonic (3%) saline on the basis of this paradigm, which resulted in rapid clinical improvement without adverse effects. Release of muscle-derived interleukin-6 may play a role in the nonosmotic secretion of arginine vasopressin, thereby linking rhabdomyolysis to the pathogenesis of EAH.

Effects of nalbuphine on anterior pituitary and adrenal hormones and subjective responses in male cocaine abusers

Nalbuphine (Nubain) is a mixed action mu-kappa agonist used clinically for the management of pain. Nalbuphine and other mu-kappa agonists decreased cocaine self-administration in preclinical models. Cocaine stimulates the hypothalamic-pituitary-adrenal (HPA) axis, but the effects of nalbuphine on the HPA axis are unknown. Analgesic doses (5 and 10 mg/70 kg) of IV nalbuphine were administered to healthy male cocaine abusers, and plasma levels of PRL, ACTH and cortisol were measured before and at 10, 17, 19, 23, 27, 31, 35, 40, 45, 60, 75, 105, and 135 min after nalbuphine administration. Subjective effects were measured on a Visual Analog Scale (VAS). Prolactin (PRL) increased significantly within 17 min (P=.04) and reached peak levels of 22.1+/-7.1 ng/ml and 54.1+/-11.3 at 60 min after low and high dose nalbuphine administration, respectively. VAS reports of "Sick," "Bad" and "Dizzy" were significantly higher after 10 mg/70 kg than after 5 mg/70 kg nalbuphine (P=.05-.0001), and were significantly correlated with increases in PRL (P=.05-.0003). However, sedation and emesis were observed only after a 10 mg/70 kg dose of nalbuphine. Interestingly, ACTH and cortisol levels did not change significantly after administration of either dose of nalbuphine. Taken together, these data suggest that nalbuphine had both mu- and kappa-like effects on PRL (PRL increase) but did not increase ACTH and cortisol.

Effects of the CRF1 antagonist antalarmin on cocaine self-administration and discrimination in rhesus monkeys

Cocaine stimulates the rapid release of ACTH, and by inference, CRF in several species, suggesting that the HPA "stress" axis may contribute to the abuse-related effects of cocaine. The effects of a systemically-active CRF(1) receptor antagonist, antalarmin, on cocaine self-administration and cocaine discrimination were examined in rhesus monkeys. Antalarmin's acute (1-10 mg/kg, IV) and chronic (3.2 mg/kg IV) effects on IV cocaine self-administration were studied. The acute effects of 3.2 mg/kg IV antalarmin on the cocaine self-administration dose-effect curve (0.001-0.10 mg/kg/inj) were also examined. The acute effects of antalarmin (5 and 10 mg/kg, IM) on the cocaine discrimination dose-effect curve (0.013-1.3 mg/kg) were examined. Antalarmin did not significantly decrease the reinforcing or the discriminative stimulus effects of cocaine. Acute antalarmin administration produced a dose-dependent but non-significant decrease in self-administration of 0.01 mg/kg/inj cocaine but did not alter the cocaine dose-effect curve. Chronic daily antalarmin treatment did not significantly decrease cocaine-maintained responding. Antalarmin did not significantly alter either the cocaine discrimination dose-effect curve or the time course of the cocaine-training dose. Antalarmin (10 mg/kg) produced sedation, suggesting that it was centrally active, however, it did not attenuate cocaine's abuse-related effects in rhesus monkeys.

Monoamine releasers with varying selectivity for dopamine/norepinephrine versus serotonin release as candidate "agonist" medications for cocaine dependence: studies in assays of cocaine discrimination and cocaine self-administration in rhesus monkeys

Monoamine releasers constitute one class of drugs under investigation as candidate medications for the treatment of cocaine abuse. Promising preclinical and clinical results have been obtained with amphetamine, which has high selectivity for releasing dopamine/norepinephrine versus serotonin. However, use of amphetamine as a pharmacotherapy is complicated by its high abuse potential. Recent preclinical studies suggest that nonselective monoamine releasers or serotonin-selective releasers have lower abuse liability and may warrant evaluation as alternatives to amphetamine. To address this issue, the present study evaluated the effects of five monoamine releasers in assays of cocaine discrimination and cocaine self-administration in rhesus monkeys. The releasers varied along a continuum from dopamine/norepinephrine-selective to serotonin-selective [m-fluoroamphetamine (PAL-353), methamphetamine, m-methylamphetamine (PAL-314), 1-napthyl-2-aminopropane (PAL-287), fenfluramine]. In drug discrimination studies, rhesus monkeys were trained to discriminate saline from cocaine (0.4 mg/kg i.m.) in a two-key, food-reinforced drug discrimination procedure. Substitution for cocaine was positively associated with selectivity for dopamine/norepinephrine versus serotonin release. In drug self-administration studies, rhesus monkeys responded for cocaine (0.01 and 0.032 mg/kg/injection) and food (1-g pellets) under a second-order fixed-ratio 2 (variable-ratio 16:S) schedule. In general, monoamine releasers produced dose-dependent and sustained decreases in cocaine self-administration. However, the dopamine/norepinephrine-selective releasers decreased cocaine self-administration with minimal effects on food-maintained responding, whereas the more serotonin-selective releasers produced nonselective reductions in both cocaine- and food-maintained responding. These results are consistent with the conclusion that dopamine/norepinephrine-selective releasers retain cocaine-like abuse-related effects but may also be capable of producing relatively selective reductions in the reinforcing effects of cocaine.

Effects of the selective delta opioid agonist SNC80 on cocaine- and food-maintained responding in rhesus monkeys

Delta agonists such as SNC80 ((+)-4-[(aR)-a-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide) produce some cocaine-like behavioral effects and warrant evaluation as candidate "agonist" medications for cocaine abuse. The present study examined acute and chronic effects of the systemically active delta agonist SNC80 on cocaine- and food-maintained responding in rhesus monkeys. Acute SNC80 (0.32-3.2 mg/kg, i.m.) pretreatment dose-dependently decreased cocaine self-administration (0.0032 mg/kg/injection), but doses of SNC80 that decreased cocaine self-administration also decreased food-maintained responding. In chronic studies, SNC80 (0.32-3.2 mg/kg/h, i.v.) was delivered for 7 days, and food or cocaine (0.01 mg/kg/injection) was available during 4 daily components of food availability and 4 daily components of drug availability. Chronic SNC80 (1.8 mg/kg/h) tended to decrease cocaine self-administration but produced greater reductions in food-maintained responding. A higher dose of 3.2 mg/kg/h SNC80 eliminated both cocaine- and food-maintained responding and produced profound sedation in one monkey and was not tested in other monkeys. These findings indicate that SNC80 produced dose-dependent and non-selective reductions in cocaine self-administration. These results suggest that SNC80 is unlikely to be useful as a treatment for cocaine dependence.

Effects of gender and menstrual cycle phase on food-maintained responding under a progressive-ratio schedule in cynomolgus monkeys

Clinical and preclinical data suggest that fluctuations in ovarian steroid hormones across the menstrual/estrous cycle influence spontaneous feeding behavior in females. The effects of gender, menstrual cycle phase, and ovarian hormone fluctuations on food-maintained responding under a progressive-ratio schedule were investigated in four female and three male cynomolgus monkeys. Females were studied across 21 menstrual cycles, and ovulatory cycles were defined by analysis of ovarian steroid hormone levels. Data were analyzed for the early and mid-follicular phase and the mid- and late luteal phase of the menstrual cycle. Progressive-ratio break points for food were significantly higher in males than in females (p < 0.01). However, progressive-ratio break points did not vary consistently as a function of menstrual cycle phase during ovulatory cycles. There were no systematic patterns of progressive-ratio break points in anovulatory menstrual cycles. Only one female monkey reached significantly higher break points during the mid- and late luteal phases in comparison to the mid-follicular phase of the menstrual cycle (p < 0.05). There was also a significant positive correlation between progressive-ratio break points and progesterone levels and a significant negative correlation with estradiol in that monkey. Although fluctuations in ovarian steroid hormones may influence food consumption under some conditions, consistent patterns of food-maintained responding were not detected during ovulatory menstrual cycles in cynomolgus monkeys.

Effects of low- and high-nicotine cigarette smoking on mood states and the HPA axis in men

The acute effects of smoking a low- or high-nicotine cigarette on hypothalamic-pituitary-adrenal (HPA) hormones, subjective responses, and cardiovascular measures were studied in 20 healthy men who met American Psychiatric Association Diagnostic and Statistical Manual IV criteria for nicotine dependence. Within four puffs (or 2 min) after cigarette smoking began, plasma nicotine levels and heart rate increased significantly (P<0.01), and peak ratings of 'high' and 'rush' on a Visual Analogue Scale were reported. Reports of 'high', 'rush', and 'liking' and reduction of 'craving' were significantly greater after smoking a high-nicotine cigarette than a low-nicotine cigarette (P<0.05). Peak plasma nicotine levels after high-nicotine cigarette smoking (23.9+/-2.6 ng/ml) were significantly greater than after low-nicotine cigarette smoking (3.63+/-0.59 ng/ml) (P<0.001). After smoking a low-nicotine cigarette, adrenocorticotropin hormone (ACTH), cortisol, dehydroepiandrosterone (DHEA), and epinephrine did not change significantly from baseline. After high-nicotine cigarette smoking began, plasma ACTH levels increased significantly above baseline within 12 min and reached peak levels of 21.88+/-5.34 pmol/l within 20 min. ACTH increases were significantly correlated with increases in plasma nicotine (r=0.85; P<0.0001), DHEA (r=0.66; P=0.002), and epinephrine (r=0.86; P<0.0001). Cortisol and DHEA increased significantly within 20 min (P<0.05) and reached peak levels of 424+/-48 and 21.13+/-2.55 ng/ml within 60 and 30 min, respectively. Thus cigarette smoking produced nicotine dose-related effects on HPA hormones and subjective and cardiovascular measures. These data suggest that activation of the HPA axis may contribute to the abuse-related effects of cigarette smoking.

Effect of GABA agonists and GABA-A receptor modulators on cocaine- and food-maintained responding and cocaine discrimination in rats

Recent studies indicate that GABAergic ligands modulate abuse-related effects of cocaine. The goal of this study was to evaluate the effects of a mechanistically diverse group of GABAergic ligands on the discriminative stimulus and reinforcing effects of cocaine in rats. One group of rats was trained to discriminate 5.6 mg/kg cocaine from saline in a two-lever, food-reinforced, drug discrimination procedure. In two other groups, responding was maintained by cocaine (0-3.2 mg/kg/injection) or liquid food (0-100%) under a fixed ratio 5 schedule. Six GABA agonists were tested: the GABA-A receptor agonist muscimol, the GABA-B receptor agonist baclofen, the GABA transaminase inhibitor gamma-vinyl-GABA (GVG), and three GABA-A receptor modulators (the barbiturate pentobarbital, the high-efficacy benzodiazepine midazolam, and the low-efficacy benzodiazepine enazenil). When tested alone, none of the compounds substituted fully for the discriminative stimulus effects of cocaine. As acute pretreatments, select doses of midazolam and pentobarbital produced 2.2- to 3.6-fold rightward shifts in the cocaine dose-effect function. In contrast, muscimol, baclofen, GVG, and enazenil failed to alter the discriminative stimulus effects of cocaine. In assays of cocaine- and food-maintained responding, midazolam and pentobarbital decreased cocaine self-administration at doses 9.6- and 3.3-fold lower, respectively, than those that decreased food-maintained responding. In contrast, muscimol, baclofen, and GVG decreased cocaine self-administration at doses that also decreased food-maintained responding. Enazenil failed to alter cocaine self-administration. Together with previous studies, these data suggest that among mechanistically diverse GABA agonists, high-efficacy GABA-A modulators may be the most effective for modifying the abuse-related effects of cocaine.

Effects of the mixed-action kappa/mu opioid agonist 8-carboxamidocyclazocine on cocaine- and food-maintained responding in rhesus monkeys

The present study evaluated the effects of 8-carboxamidocyclazocine (8-CAC), a novel mixed-action kappa/mu agonist with a long duration of action, on food- and cocaine-maintained responding in rhesus monkeys to assess the potential utility of 8-CAC as a medication for the treatment of cocaine dependence. The effects of acute and chronic (10 days) 8-CAC were examined in rhesus monkeys responding under a multiple schedule for both cocaine and food reinforcement. Acute 8-CAC (0.032-0.56 mg/kg, i.m.) dose-dependently eliminated cocaine-maintained responding in all three monkeys. However, doses of 8-CAC that decreased cocaine self-administration typically also decreased food-maintained responding, and 8-CAC-induced decreases in cocaine self-administration diminished during chronic 8-CAC treatment. These results confirm that 8-CAC acutely decreases cocaine self-administration. However, non-selective effects of 8-CAC on food-maintained responding and tolerance to 8-CAC effects on cocaine self-administration may limit its potential for the treatment of cocaine dependence.

Development of a Rationally Designed, Low Abuse Potential, Biogenic Amine Releaser That Suppresses Cocaine Self-Administration

Convergent lines of evidence support a dual deficit model of stimulant withdrawal, where reductions in synaptic dopamine (DA) and 5-hydroxytryptamine (serotonin) (5-HT) contribute to dysphoria, drug craving, and relapse. Thus, we predicted that a nonamphetamine compound with substrate activity at DA and 5-HT transporters (i.e., a dual DA/5-HT releaser) would be an effective medication for treating stimulant addictions. Ideally, this type of medication would alleviate withdrawal symptoms, suppress cocaine self-administration, and lack side effects commonly associated with central nervous system stimulants. In the present work, more than 350 compounds were screened in vitro for activity as substrate-type releasing agents at DA, 5-HT, and norepinephrine transporters. These efforts identified PAL-287 (1-napthyl-2-aminopropane) as a nonamphetamine compound with potent substrate activity at biogenic amine transporters. In vivo microdialysis in rats demonstrated that PAL-287 (1-3 mg/kg i.v.) increased extracellular DA and 5-HT in frontal cortex, but effects on 5-HT were somewhat greater. PAL-287 induced substantially less locomotor stimulation than (+)-amphetamine, a drug that increases only extracellular DA. Administration of high-dose (+)-methamphetamine or (+/-)-3,4-methylenedioxymethamphetamine to rats produced long-lasting depletion of cortical 5-HT, whereas PAL-287 (18 mg/kg i.p. x 3) did not. PAL-287 displayed little or no reinforcing properties in rhesus monkeys trained to self-administer cocaine, yet PAL-287 produced a dose-dependent decrease in responding for cocaine when infused at a dose of 1.0 mg/kg/h. Collectively, the findings reported here demonstrate that nonamphetamine monoamine releasing agents such as PAL-287 might be promising candidate medications for the treatment of stimulant dependence.

Effects of the mixed mu/kappa opioid nalbuphine on cocaine-induced changes in subjective and cardiovascular responses in men

Kappa opioid agonists functionally antagonize some abuse-related and locomotor effects of cocaine, and reduce cocaine self-administration by rhesus monkeys. We compared the cardiovascular and subjective effects of acute doses of the mu/kappa opioid nalbuphine alone (5 mg/70 kg, intravenous (i.v.)), with cocaine alone (0.2 mg/kg, i.v.), and with nalbuphine+cocaine in combination, under placebo-controlled, double-blind conditions. Subjects met American Psychiatric Association Diagnostic and Statistical Manual (DSM-IV) criteria for current cocaine abuse. Nalbuphine serum levels exceeded 50 ng/ml within 10 min after injection, and cocaine plasma levels exceeded 130 ng/ml within 4 min. Cocaine's pharmacokinetic profile did not change after concurrent nalbuphine administration. The nalbuphine+cocaine combination was safe and without synergistic effects on heart rate and systolic or diastolic blood pressure. Moreover, the addition of cocaine did not increase the subjective effects of nalbuphine. Visual Analog Scale (VAS) ratings of High, Euphoria, Stimulated, and Good Effect were equivalent after nalbuphine+cocaine and nalbuphine alone, and both were significantly higher than after cocaine alone (area under the curve analysis) (p<0.05-0.01). Peak VAS ratings of High, Stimulated, Good Effect, and Drug Effect were also significantly higher after nalbuphine+cocaine than after cocaine alone (p<0.01). Addiction Research Center Inventory (ARCI) scores were equivalent for nalbuphine+cocaine and nalbuphine alone, but the PCAG, MBG, and amphetamine scores were significantly higher after both nalbuphine+cocaine and nalbuphine alone than after cocaine alone (p<0.01-0.003). Thus, there were no additive interactions between nalbuphine and cocaine on cardiovascular, subjective, or drug level measures after acute administration.

The effects of cocaine on gonadal steroid hormones and LH in male and female rhesus monkeys

Cocaine stimulates significant increases in estradiol, testosterone (T), and luteinizing hormone (LH) in rhesus monkeys, but the temporal interactions between the gonadal steroid hormones and LH have not been determined. The effects of i.v. cocaine (0.8 mg/kg) or saline placebo administration on estradiol, T, and LH were compared in follicular phase female and male rhesus monkeys. Samples for hormone analysis were collected at 2-min intervals for 20 min, then at 10-min intervals for 50 min. Peak plasma cocaine levels were detected at 4 min and pharmacokinetic analyses showed no significant gender differences. Baseline hormone levels were equivalent before saline and cocaine administration, and saline did not alter LH or estradiol levels. In females, when baseline estradiol levels were low (< 100 pg/ml), LH increased significantly within 8 min after cocaine administration (P < 0.05), but when baseline estradiol levels were high (> 100 pg/ml), LH levels did not change significantly after cocaine administration. Estradiol and T increased significantly after LH, within 16 min after cocaine administration (P < 0.01-0.001). In males, significant LH increases were detected at 16 min after cocaine administration (P < 0.05-0.001), but estradiol and T did not change significantly. Thus, cocaine may stimulate significant increases in estradiol and T in females but not in males. These rapid hormonal changes may contribute to cocaine's abuse-related effects, as well as to disruptions of the menstrual cycle during chronic cocaine administration.

Kappa-opioid receptors are differentially labeled by arylacetamides and benzomorphans

Using Chinese Hamster Ovary cell membranes that stably expressed the human kappa-opioid receptor, we investigated the hypothesis that kappa(1)- and kappa(2)-opioid receptors, historically defined by their pharmacological selectivity for either arylacetamides or benzomorphans are, in fact, different affinity states or binding sites on the same kappa-opioid receptors. Receptor binding studies showed that GTP gamma S potently inhibited [3H](5 alpha,7 alpha,8 beta)-(+)-N-methyl-N-(7-[1-pyrrolidinyl]-1-oxaspiro [4.5]dec-8-yl)-benzeneacetamide (U69,593) binding, compared to virtually no inhibition of [3H]bremazocine binding. Saturation binding experiments showed a three-fold decrease in [3H]U69,593 affinity in the presence of GTP gamma S, but GTP gamma S had no effect on [3H]bremazocine affinity. The kappa-opioid receptor antagonist nor-binaltorphimine had a four-fold higher affinity for [3H]U69,593-labeled receptors than for [3H]bremazocine-labeled receptors. Functional selectivity studies, measuring the stimulation of [35S]GTP gamma S agonist-induced binding, showed a significantly higher U69,593-induced G protein-receptor activation in comparison to the stimulation observed with bremazocine. These results suggest that pharmacologically defined 1 kappa-opioid receptor subtypes may be different affinity states of the same receptor.

Effects of chronic methadone treatment on cocaine- and food-maintained responding under second-order, progressive-ratio and concurrent-choice schedules in rhesus monkeys

The effects of chronic infusion with saline or methadone (0.032-1.0 mg/kg/h) were examined on cocaine- and food-maintained responding in rhesus monkeys using three procedures. In one procedure, cocaine injections (0.0032-0.032 mg/kg per injection) and food pellets were available under a second-order schedule during alternating daily sessions. During saline treatment, cocaine maintained a dose-dependent increase in the number of cocaine injections per day, and monkeys usually responded for the maximum number of pellets. Methadone dose-dependently decreased cocaine self-administration, and methadone doses that decreased cocaine self-administration had variable effects on food-maintained responding. In the second procedure, 0.032 mg/kg per injection cocaine or food pellets were available under a progressive-ratio schedule. During saline treatment, cocaine and food maintained similar break points. Methadone produced a dose-dependent and non-selective decrease in break points maintained by both cocaine and food. In the third procedure, cocaine injections (0-0.1 mg/kg per injection) and food pellets were available under a concurrent-choice schedule. During saline treatment, increasing unit doses of cocaine produced a dose-dependent increase in cocaine choice. Methadone had little effect on the cocaine choice dose-effect curve up to doses that eliminated responding. These results provide little evidence to suggest that chronic methadone altered the reinforcing effects of cocaine; rather methadone appeared to non-selectively decrease rates of operant responding.

Effect of gonadectomy and gonadal hormone replacement on cocaine self-administration in female and male rats

Both sex and gonadal steroid hormones may influence the abuse-related behavioral effects of cocaine under some conditions, but there is considerable inconsistency in the literature. In the present study, rats were trained under a fixed ratio (FR) 5 schedule of food presentation and were then allowed to self-administer cocaine (1.0 mg/kg/injection) until behavior stabilized. Subsequently, complete dose-effect functions for cocaine self-administration (0.032-3.2 mg/kg/injection) were determined in female and male rats before and after gonadectomy, and in gonadectomized female and male rats before and during chronic treatment with estradiol or testosterone, respectively. Sex, gonadectomy, and gonadal hormones did not alter the shape or position of dose-effect functions for cocaine self-administration. These results suggest that sex, estrogen, and testosterone levels are not critical determinants of cocaine's reinforcing effects in rats under these conditions. This study differed from earlier studies in that complete dose-effect functions for cocaine were determined. These findings suggest that the behavioral training history, the unit dose of cocaine, and the schedule of reinforcement are important variables in studies of sex and gonadal hormone effects on cocaine self-administration.

Sex differences in thermal nociception and prostaglandin-induced thermal hypersensitivity in rhesus monkeys

The present study examined thermal nociception in 4 male and 4 female rhesus monkeys. In the first experiment, monkeys were tested 5 days/week for 4 consecutive weeks in a warm-water, tail-withdrawal assay of thermal nociception. Thermal nociception did not vary by sex or menstrual cycle phase. However, male monkeys tended to be slightly more sensitive to thermal stimuli than female monkeys in the follicular phase of the menstrual cycle. Thermal nociception did not correlate with estradiol or progesterone levels in female monkeys. In the second experiment, thermal hypersensitivity was induced by administering prostaglandin E(2) (0.0032 to 0.1 mg subcutaneously) into the tail. Prostaglandin E(2) produced slightly greater thermal hypersensitivity in male than in follicular phase female monkeys, but male and luteal phase female monkeys did not differ, and there was not a significant difference between follicular and luteal phase female monkeys. Exposure to the behavioral procedures produced similar increases in blood levels of the stress-related hormones adrenocorticotropic hormone and cortisol in male and female monkeys, which suggests that measures of thermal nociception or thermal hypersensitivity were not confounded by sex differences in stress responses. These results suggest that sex and gonadal hormone levels have only a minor influence on thermal nociception or thermal hypersensitivity in rhesus monkeys.

PERSPECTIVE

These modest effects of sex and gonadal hormone levels on measures of pain in non-human primates could be interpreted to support the hypothesis that sex differences in pain perception in humans are due more to sociocultural factors than to a biological imperative.

Brain alcohol detectability in human subjects with and without a paternal history of alcoholism

OBJECTIVE

This study examined the putative effects of a paternal history of alcoholism on the apparent detectability of brain alcohol in human subjects.

METHOD

Brain to blood ethanol ratios in two cohorts of men were determined, using proton magnetic resonance spectroscopic imaging in a brain voxel (2 x 2 x 2 cm) containing the putamen. The men were light drinkers with a positive (n = 8) or a negative (n = 8) paternal history of alcoholism and were given an alcohol dose of 0.8 g/kg body weight.

RESULTS

In both groups, brain alcohol detectability was less than 100%. No significant difference (p = .37) was found in the brain/blood ethanol ratios of the two groups. However, subjective assessments of feeling the extreme effects of alcohol and the extent of intoxication ("how drunk") were highly correlated with a paternal history of alcoholism, with the paternal history negative group reporting significantly more intense feelings of intoxication.

CONCLUSIONS

A review of existing literature evidence and data obtained in this study indicate that brain alcohol detectability via magnetic resonance spectroscopic imaging is less than 100%. There were no significant differences in brain alcohol detectability between paternal history positive and paternal history negative men. Differences in the Subjective High Assessment Scale ratings between the two groups, however, indicate the importance of a genetic influence on the subjective response to alcohol.

Sex differences in opioid antinociception in rhesus monkeys: antagonism of fentanyl and U50,488 by quadazocine

Sex differences have been observed in the antinociceptive effects of opioids in rodents and rhesus monkeys. Sex differences in the affinity of opioid ligands for opioid receptors may contribute to these findings. To test this hypothesis, the relative affinity of the competitive opioid antagonist quadazocine for mu and kappa opioid receptors was determined in rhesus monkeys using in vivo pA(2) analysis. The antinociceptive effects of the mu opioid agonist fentanyl and the kappa opioid agonist U50,488 were determined alone and after pretreatment with quadazocine in 4 females and 4 males using a warm-water tail-withdrawal assay of thermal nociception. The relative potency of quadazocine antagonism of fentanyl and U50,488 in females and males was used to assess sex differences in the relative affinity of quadazocine for mu and kappa receptors. Fentanyl was equipotent in female and male monkeys, and quadazocine was equipotent as an antagonist of fentanyl in females and males. In contrast, U50,488 was significantly less potent in females, and quadazocine was less potent as an antagonist of U50,488 in females. These findings suggest that opioid ligands have similar affinity for mu receptors but lower affinity for at least some kappa receptors in female than in male rhesus monkeys.

Design and Synthesis of Novel Dimeric Morphinan Ligands for κ and μ Opioid Receptors

A novel series of morphinans were synthesized, and their binding affinity at and functional selectivity for micro, delta, and kappa opioid receptors were evaluated. These dimeric ligands can be viewed as dimeric morphinans, which were formed by coupling two identical morphinan pharmacophores (cyclorphan (1) or MCL 101 (2)) with varying connecting spacers. Ligands 6 and 7 with alkyl spacers on the nitrogen position and ligands 8 and 9 in which the two morphinan pharmacophores were coupled by ether moieties at the 3-hydroxyl positions showed significant decrease in affinity at all three opioid receptors. An improvement in the affinity was achieved by introducing an ester moiety as the spacer in the dimeric morphinans. It was observed that the affinity of these ligands was sensitive to the character and length of the spacer. Compound 13 (MCL-139) with a 4-carbon ester spacer, compound 17 (MCL-144) containing a 10-carbon spacer, and compound 19 (MCL-145) with the conformationally constrained fumaryl spacer were the most potent ligands in this series, displaying excellent affinities at micro and kappa receptors (K(i) = 0.09-0.2 nM at micro and K(i) = 0.078-0.049 nM at kappa), which were comparable to the parent compound 2. Ligand 12, a compound containing only one morphinan pharmacophore and a long-chain ester group, had affinity at both micro and kappa receptors almost identical to that of the parent ligand 2. In the [(35)S]GTPgammaS binding assay, ligands 13, 17, and 19 and their parent morphinans 1 and 2 stimulated [(35)S]GTPgammaS binding mediated by the micro and kappa receptors. Compounds 13 and 17 were full kappa agonists and partial micro agonists, while compound 19 was a partial agonist at both micro and kappa receptors. These novel ligands, as well as their interesting pharmacological properties, will serve as the basis for our continuing investigation of the dimeric ligands as potential probes for the pharmacotherapy of cocaine abuse and may also open new avenues for the characterization of opioid receptors.

Ovarian steroid hormone modulation of the acute effects of cocaine on luteinizing hormone and prolactin levels in ovariectomized rhesus monkeys

Cocaine stimulates significant increases in luteinizing hormone (LH) and decreases prolactin levels in gonadally intact rhesus monkeys, but cocaine did not alter plasma levels of these anterior pituitary hormones in ovariectomized females. These findings suggested that ovarian steroid hormones may contribute to the endocrine effects of acute cocaine administration. To test this hypothesis, the acute effects of cocaine and placebo-cocaine on plasma LH and prolactin levels were examined in five ovariectomized rhesus females during three chronic hormone replacement conditions: 1) estradiol (E2beta) treatment (0.0015-0.006 mg/kg/day i.m.), 2) progesterone treatment (0.32 mg/kg/day i.m.), and 3) combinations of progesterone (0.32 mg/kg/day i.m.) and E2beta (0.002 and 0.004 mg/kg/day i.m.). Cocaine (0.8 mg/kg i.v.) did not alter prolactin or LH in ovariectomized monkeys without ovarian steroid replacement. During chronic estradiol treatment, cocaine produced an estradiol dose-dependent decrease in prolactin. Cocaine also decreased prolactin during treatment with progesterone alone and progesterone + E2beta (0.004 mg/kg/day i.m.). Cocaine stimulated a significant increase in LH during treatment with progesterone alone, but not during treatment with progesterone + E2beta, or three of four estradiol treatment doses. Cocaine pharmacokinetics did not differ as a function of hormone replacement conditions. Together, these data suggest that both E2beta and progesterone modulate cocaine's effects on prolactin, whereas E2beta alone and in combination with progesterone, do not facilitate LH release in response to cocaine in ovariectomized rhesus females.

Effects of intravenous cocaine and cigarette smoking on luteinizing hormone, testosterone, and prolactin in men

Cocaine and nicotine have a number of similar behavioral and neurobiological effects. This study compared the acute effects of cocaine and cigarette smoking on luteinizing hormone (LH), testosterone (T), and prolactin. Twenty-four men who met American Psychiatric Association Diagnostic and Statistical Manual criteria for cocaine abuse or nicotine dependence were given intravenous cocaine (0.4 mg/kg) or placebo-cocaine, or smoked a low or high nicotine cigarette under controlled conditions. Placebo-cocaine or low nicotine cigarette smoking did not change LH, T, or prolactin. Peak plasma levels of 254 +/- 18 ng cocaine/ml and 22.6 +/- 3.4 ng nicotine/ml were measured at 8 and 14 min, respectively. LH increased significantly after both i.v. cocaine and high nicotine cigarette smoking (P < 0.01). These LH increases were significantly correlated with increases in cocaine and nicotine plasma levels (P < 0.001-0.003), and high nicotine cigarette smoking stimulated significantly greater increases in LH release than i.v. cocaine (P < 0.05). Testosterone levels did not change significantly after either cocaine or after high nicotine cigarette smoking. After i.v. cocaine, prolactin decreased significantly and remained below baseline levels throughout the sampling period (P < 0.05-0.01). After high nicotine cigarette smoking, prolactin increased to hyperpro-lactinemic levels within 6 min and remained significantly above baseline levels for 42 min (P < 0.05-0.03). The rapid increases in LH and reports of subjective "high" after both i.v. cocaine and high nicotine cigarette smoking illustrate the similarities between these drugs and suggest a possible contribution of LH to their abuse-related effects.