GLANCE: results of a phase 2, randomized, double-blind, placebo-controlled study.

OBJECTIVE: To evaluate the safety and tolerability of natalizumab when added to glatiramer acetate (GA) in patients with relapsing multiple sclerosis. The primary outcome assessed whether this combination would increase the rate of development of new active lesions on cranial MRI scans vs GA alone. METHODS: This phase 2, randomized, double-blind, placebo-controlled study included patients aged 19 to 55 years who were treated with GA for at least 1 year before randomization and experienced at least one relapse during the previous year. Patients received IV natalizumab 300 mg (n = 55) or placebo (n = 55) once every 4 weeks plus GA 20 mg subcutaneously once daily for < or = 20 weeks. RESULTS: The mean rate of development of new active lesions was 0.03 with combination therapy vs 0.11 with GA alone (p = 0.031). Combination therapy resulted in lower mean numbers of new gadolinium-enhancing lesions (0.6 vs 2.3 for GA alone, p = 0.020) and new/newly enlarging T2-hyperintense lesions (0.5 vs 1.3, p = 0.029). The incidence of infection and infusion reactions was similar in both groups; no hypersensitivity reactions were observed. One serious adverse event occurred with combination therapy (elective hip surgery). With the exception of an increase in anti-natalizumab antibodies with combination therapy, laboratory data were consistent with previous clinical studies of natalizumab alone. CONCLUSION: The combination of natalizumab and glatiramer acetate seemed safe and well tolerated during 6 months of therapy.

Extinction of ethanol-induced conditioned place preference and conditioned place aversion: effects of naloxone.

Four experiments examined the effect of naloxone pretreatment on the expression and extinction of ethanol-induced conditioned place preference (experiments 1, 2, 4) or conditioned place aversion (experiments 1, 3). DBA/2 J mice received four pairings of a distinctive tactile (floor) stimulus (CS) with injection of ethanol (2 g/kg) given either immediately before or after 5-min exposure to the CS. A different stimulus was paired with injection of saline. Pre-CS injection of ethanol produced conditioned place preference, whereas post-CS injection of ethanol produced conditioned place aversion. Both behaviors extinguished partially during repeated choice testing after vehicle injection. Naloxone (10 mg/kg) had little effect on the initial expression of conditioned place preference, but facilitated its extinction. Moreover, repeated naloxone testing resulted in the expression of a weak conditioned place aversion to the CS that initially elicited a place preference. In contrast, naloxone (1.5 or 10 mg/kg) enhanced expression of conditioned place aversion, thereby increasing its resistance to extinction. A control experiment (experiment 4) indicated that repeated testing with a different aversive drug, lithium chloride, did not affect rate of extinction or produce an aversion to the CS previously paired with ethanol. These findings do not support the suggestion that naloxone facilitates the general processes that underlie extinction of associative learning. Also, these data are not readily explained by the conditioning of place aversion at the time of testing. Rather, naloxone's effects appear to reflect a selective influence on maintenance of ethanol's conditioned rewarding effect, an effect that may be mediated by release of endogenous opioids. Overall, these findings encourage further consideration of the use of opiate antagonists in the treatment of alcoholism.

Ethanol-induced conditioned place aversion in rats: effect of interstimulus interval.

The purpose of this study was to examine the effect of interstimulus interval (ISI) on ethanol-induced place aversion in rats. Six groups of rats initially received four pairings of a distinctive floor stimulus (CS+) with ethanol (1 g/kg, I.P.) and four pairings of a different floor stimulus (CS-) with saline. Groups -30, -15, -10, -5, 0, and 5 were injected 30, 15, 10, 5, or 0 min before, or 5 min after exposure to the 5 min CS, respectively. After testing for place aversion, all groups were exposed to an additional set of conditioning trials using a higher dose of ethanol (1.5 g/kg). During the first test, only groups 0 and -15 exhibited conditioned place aversion. However, during the second test, all groups showed conditioned aversion except group -30. The results suggest that ethanol's aversive effects dissipate by 30 min postinjection or that it is more difficult to associate those effects with short-duration external stimuli at long backward intervals. In contrast to recent findings with mice, the direction of ethanol-induced place conditioning was not altered in rats exposed to different ISIs.

The effects of naloxone on expression and acquisition of ethanol place conditioning in rats.

Naloxone has been shown to facilitate extinction of ethanol-induced conditioned place preference (CPP) in mice. The present-study extended these findings by examining naloxone's effect on the expression (Experiment 1) and acquisition (Experiment 2) of place conditioning with ethanol in rats. In Experiment 1, after place conditioning with ethanol (1.8 g/kg, I.P.), groups N0, N1.5, and N10 received 0, 1.5, or 10 mg/kg naloxone before testing. As expected, ethanol produced a robust conditioned place aversion (CPA). However, naloxone had no effect on expression of CPA. In contrast to studies with mice, the endogenous opioid system does not appear to be involved in the conditioned motivational effects of ethanol in rats. In Experiment 2, groups SE1 and SE2, NS(1.5), NE(1.5), and NE(10), received ethanol alone (1.2 g/kg), naloxone alone (1.5 mg/kg), naloxone 1.5 mg/kg plus ethanol, and naloxone 10 mg/kg plus ethanol during acquisition, respectively. All naloxone-treated groups exhibited CPA. Moreover, group NE(1.5) showed a stronger CPA than group NS(1.5). The CPA produced by coadministration of naloxone and ethanol was attributed to naloxone's effects on the neural processes underlying ethanol's unconditioned aversive effects, or to other nonspecific effects on ethanol's motivational properties.

Reduced sensitivity to ethanol reward, but not ethanol aversion, in mice lacking 5-HT1B receptors.

Various serotonergic receptor systems are thought to influence the motivational effects of ethanol. This experiment characterized the acquisition of ethanol-induced conditioned taste aversion and ethanol-induced conditioned place reference in mutant knockout mice lacking 5-HT1b receptors. In the taste conditioning procedure, adult homozygous knockout mice (-/-) and homozygous wild-type mice (+/+) received access to 0.2 M NaCl solution, followed immediately by intraperitoneal injection of 0 to 4 g/kg of ethanol. Ethanol produced dose-dependent conditioned taste aversion that was the same in both genotypes. In the place conditioning procedure, knockout and wild-type mice received six pairings of a tactile stimulus with ethanol (2 g/kg, i.p.). A different tactile stimulus was paired with saline. Ethanol produced increases in locomotor activity, with wild-type mice showing higher levels of ethanol-stimulated activity than knockout mice during conditioning trials 5 and 6. Wild-type mice demonstrated conditioned place preference for the ethanol-paired stimulus. In contrast, knockout mice showed no evidence of place conditioning. These results are generally consistent with an important role for serotonergic systems in ethanol reward and specifically indicate that 5-HT1b receptors are important for ethanol's rewarding effects but not for ethanol's aversive effects.

The relative salience of morphine and contextual cues as conditioned stimuli.

Two experiments were conducted to delineate further the properties of conditioning when morphine is used as a conditioned stimulus (CS) in the conditioned suppression of drinking paradigm. Experiment 1 used a test for overshadowing designed to compare the relative salience of contextual cues (metal box) and morphine induced cues (6 mg/kg, IP) as CSs when each was paired with a foot shock unconditioned stimulus (US) in water deprived rats. Six groups (six rats each) were exposed to conditioning procedures during which the conditioning context was present 19 h (groups 1 and 2), 90 min (groups 3 and 4), or 5 min (groups 5 and 6) before shock onset, and morphine (in groups 1, 3, and 5) or saline (in groups 2, 4, and 6) was injected 10 min before shock. Subsequently, the magnitude of suppression of drinking in response to morphine, to the metal box, and to morphine plus the metal box was measured. Only group 1 (19 h group) suppressed drinking in response to morphine, while groups 3-6 suppressed drinking whenever tested in the metal box. The results indicate that morphine cues acted as a CS that elicited suppression of drinking in group 1, and that contextual cues present up to 90 min before morphine cues overshadowed morphine. Experiment 2 showed that expression of the conditioned response to morphine was blocked by naloxone.

Morphine as a conditioned stimulus in a conditioned emotional response paradigm.

A Pavlovian conditioning experiment was conducted to determine whether morphine (6 mg/kg, IP) could act as a conditioned stimulus (CS) when paired with an electric shock unconditioned stimulus (US), and later produce a conditioned suppression of drinking (CR) in water deprived rats. Seven groups were tested for conditioning after exposure to one of the following conditioning procedures: (1) morphine paired with shock; (2) morphine alone with no shock; (3) shock but no morphine; (4) no shock and no morphine; (5) morphine paired with vocalizations of shocked rats; (6) saline paired with shock; (7) saline alone with no shock. Groups 1 and 2 tested whether morphine could act as a CS. Groups 3 and 4 tested for sensitization. Group 5 tested whether exposure to the vocalizations of other rats could act as a US when paired with a morphine CS. Groups 6 and 7 tested whether cues associated with the injection procedure could act as a CS. Only subjects in group 1 showed conditioned suppression of drinking, when compared to control groups. Overall, the results indicate that morphine could act as a conditioned stimulus and that several of the more obvious possible sources of artifact did not significantly contribute to the CR that is produced.

A unique enhancement of associative learning produced by methylenedioxyamphetamine.

The effects of methylenedioxyamphetamine (MDA) on classical conditioning of the rabbit's nictitating membrane response were assessed in four experiments. Experiment 1 established a dose-effect curve for MDA doses of 0, 1, 3, and 10µmol/kg. Both the 3 and 10µmol/kg doses significantly enhanced the rate of learning. Experiment 2 established that the 10µmol/kg dose of MDA had no effect on non-associative determinants of responding to the conditioned stimulus (CS). However, this dose of MDA apparently sensitized the response to the unconditioned stimulus (US). Experiments 3 and 4 assessed the effects of the 10µmol/kg dose of MDA on sensory processing of the CS and US, respectively. MDA had no effect on the intensity thresholds for eliciting responses to either of these stimuli. Thus, the enhanced rate of acquisition observed in experiment 1 cannot be attributed to an increase in nonassociative responding to the CS or to enhanced sensory processing of the CS or US. MDA apparently enhanced the rate of acquisition in experiment 1 by facilitating the association between the CS and US. These findings are unique in that no other hallucinogen we have examined has enhanced acquisition without also affecting either non-associative responding or sensory processing of the CS and US.