The effect of chronic fluvoxamine on hormonal and psychological responses to buspirone in normal volunteers

We studied the effect of 3 weeks treatment with the selective serotonin reuptake inhibitor (SSRI), fluvoxamine, on hormonal and psychological responses to buspirone, a 5-HT_1A receptor partial agonist which also binds to dopamine receptors, in normal male volunteers. Eleven subjects received buspirone, 30 mg, and placebo before, and in week 3 of fluvoxamine treatment (mean dose 127 mg/day). Placebo and buspirone were given in a balanced order, double-blind. Buspirone significantly elevated plasma prolactin (PRL) and growth hormone (GH) concentrations but had no significant effect on cortisol (CORT) or temperature. Significant psychological effects of lightheadedness, tiredness and difficulty thinking occurred. Fluvoxamine treatment resulted in a nearly 3-fold increase in plasma buspirone with a similar enhancement of the PRL response. In contrast the GH and psychological responses were blunted. The increased buspirone concentrations are likely to be due to inhibition of first pass liver metabolism by fluvoxamine acting on the cytochrome P-450 system. The PRL response is probably mediated by antagonism of pituitary dopamine-D₂ receptors and its enhancement by fluvoxamine treatment may be a pharmacokinetic effect. The blunting of GH and psychological responses suggest that 5-HT_1A receptor function is reduced by chronic fluvoxamine treatment. Received: 15 December 1995/Final version: 29 May 1996     

Plasma serotonin level after 1 day of fluoxetine treatment: a biological predictor for antidepressant response?

Rationale: Antidepressant treatments present a delayed onset of action. Objective: The present study investigated whether plasma or serum serotonin, 5-hydroxytryptamine (5-HT), could predict clinical improvement. Methods: Biological parameters were determined after a 4-week drug-free period (day 0) and 1, 14 and 28 days after the beginning of the treatment with fluoxetine 20 mg daily in depressed patients. Clinical evaluations were assessed on days 0, 14 and 28. Results: One day after a single dose, the mean values of plasma 5-HT (5.4 ± 2.6 nmol/l) and serum 5-HT (484 ± 215 nmol/l) were not statistically different from basal mean values (4.5 ± 2.5 nmol/l and 523 ± 263 nmol/l, respectively). The repeated treatment significantly reduced serum 5-HT to 34% (P = 0.002) and 17% (P = 0.0004) of pretreatment values after 14 and 28 days of treatment, respectively; plasma 5-HT was also reduced significantly to 28% and 15% of pretreatment values (P < 0.05 in both cases). At day 28, four of the eight patients responded by showing a reduction in MADRS score of at least 50% of the baseline score. No correlation was found between pretreatment values of serum or plasma 5-HT and clinical evolution, even if a tendency (P < 0.07) to lower serum 5-HT pretreatment values was observed in responders. Plasma 5-HT after 1 day of treatment was significantly different between responders and non-responders: the plasma 5-HT concentration in responders was 3.4 ± 1.7 nmol/l versus 7.4 ± 1.6 nmol/l in non-responders (P = 0.02). Moreover, plasma 5-HT levels after 1 day of treatment were positively correlated to the final MADRS score (r = +0.89, n = 8, P = 0.003) and inversely correlated to its change from the initial score (r = −0.76, n = 8, P = 0.02). Conclusion: These preliminary data show that fluoxetine and norfluoxetine might influence 5-HT peripheral venous blood parameters and that plasma 5-HT after 1 day of treatment might be a biological predictor for antidepressant response. Received: 10 July 1998/Final version: 12 October 1998     

Sexual segregation in infant mice: behavioural and neuroendocrine responses to d-amphetamine administration

Individual differences arise from both genetic and epigenetic factors. The aim of this study was to test whether pups raised in distinct socio-sexual conditions would show different behavioural and neuroendocrine responses to d-amphetamine (AMPH) administration upon placement in a novel environment. This issue was addressed by testing infant CD-1 mouse pups of both sexes at three different developmental ages [3, 8, or 18 postnatal (PND) days]. These pups were raised from birth in all-male, all-female, or mixed-sex litters. AMPH effects were assessed as a function of the hypothalamic-pituitary-adrenal (HPA) axis activational state using litters that were either maternally deprived for 24 h (DEP) or normally kept with the dam (NDEP). A concomitant maternal behaviour score carried out on selected postpartum days showed that mothers taking care of all-male litters were more often involved in Active nursing than those rearing the mixed-sex ones, whereas the latter were found more often Laying still out of the nest. Basal and stress-induced corticosterone (CORT) secretion was increased in unisexually reared pups following maternal deprivation, an effect limited to PND 3. In general, neuroendocrine and behavioural responses to AMPH were found to be dissociated and were affected by sexual segregation only in conjunction with maternal deprivation. On PND 3, AMPH injection (1 or 3 mg/kg, IP) decreased CORT secretion in deprived unisexually reared subjects without affecting their behaviour. As a whole, behavioural changes due to unisexual rearing were limited to female subjects. On PND 8, unisexually reared females showed, upon maternal deprivation, a generalized shift to the left in the dose-response curve to AMPH for Crossing behaviour, while on PND 18 AMPH-induced stereotypies were considerably reduced in sexually segregated females, especially following maternal deprivation. Thus, maternal deprivation appeared to “sensitize” the monoaminergic system to an AMPH challenge. The individual behavioural and neuroendocrine profiles shown in response to a stressful challenge suggest that changes in social stimulation early during development might produce subtle shifts in the function of selected central monoaminergic systems. Received: 24 February 1997/Final version: 9 May 1997     

Acute hormonal changes after IV citalopram and treatment response in OCD

Rationale Serotonergic pharmacological challenges have failed to produce consensual results in patients with obsessive–compulsive disorder (OCD), suggesting a heterogeneous 5-hydroxytryptamine (5-HT) activity in this disorder. Objectives The aim of this study was to compare the neuroendocrine response to a serotonergic challenge in OCD patient responders (RP) and nonresponders (NR) to serotonin reuptake inhibitors treatment and healthy volunteers. Materials and methods Thirty OCD treatment NR, 30 RP, and 30 controls (CN) matched for sex and age were included. Each subject received 20 mg of intravenous citalopram. Prolactin, cortisol, and growth hormone plasma concentration were measured at times—20, 0, 20, 40, 60, 80, 100, 120, 140, and 160 min after the onset of citalopram infusion. Results Citalopram did not induce anxiety or OCD symptoms in patients. Citalopram was associated with stronger prolactin response in the CN group (maximal percentage variation [max%Δ] = 65.76 ± 105.1) than in NR (max%Δ = 17.41 ± 31.06) and RP groups (max%Δ = 15.87 ± 31.71; p = 0.032; Friedman χ ² = 6.87; df = 2). On the other hand, cortisol response did not differ between CN and RP groups and was blunted in the NR group (NR max%Δ = 20.98 ± 58.14 vs RP max%Δ = 47.69 ± 66.94; CN max%Δ = 63.58 ± 88.4; p = 0.015; Friedman χ ² = 8.60; df = 2). Conclusions Compared to CN, both treatment RP and NR patients showed blunted prolactin response to citalopram, but only NR patients showed an attenuated cortisol response, suggesting a more disrupted central serotonergic transmission in this group.     

The effects of cannabinoids on serum cortisol and prolactin in humans

Background  Cannabis is one of the most widely used illicit substances, and there is growing interest in the therapeutic applications of cannabinoids. While known to modulate neuroendocrine function, the precise acute and chronic dose-related effects of cannabinoids in humans are not well-known. Furthermore, the existing literature on the neuroendocrine effects of cannabinoids is limited by small sample sizes (n = 6–22), heterogeneous samples with regard to cannabis exposure (lumping users and nonusers), lack of controlling for chronic cannabis exposure, differing methodologies, and limited dose–response data. Delta-9-tetrahydrocannabinol (Δ-9-THC) was hypothesized to produce dose-related increases in plasma cortisol levels and decreases in plasma prolactin levels. Furthermore, relative to controls, frequent users of cannabis were hypothesized to show altered baseline levels of these hormones and blunted Δ-9-THC-induced changes of these hormones. Materials and methods  Pooled data from a series of laboratory studies with multiple doses of intravenous Δ-9-THC in healthy control subjects (n = 36) and frequent users of cannabis (n = 40) was examined to characterize the acute, chronic, and acute on chronic effects of cannabinoids on plasma cortisol and prolactin levels. Hormone levels were measured before (baseline) and 70 min after administration of each dose of Δ-9-THC. Data were analyzed using linear mixed models with +70 min hormonal levels as the dependant variable and baseline hormonal level as the covariate. Results  At socially relevant doses, Δ-9-THC raised plasma cortisol levels in a dose-dependent manner but frequent users showed blunted increases relative to healthy controls. Frequent users also had lower baseline plasma prolactin levels relative to healthy controls. Conclusions  These group differences may be related to the development of tolerance to the neuroendocrine effects of cannabinoids. Alternatively, these results may reflect inherent differences in neuroendocrine function in frequent users of cannabis and not a consequence of cannabis use.     

Relationship of disinhibition and aggression to blunted prolactin response to meta-chlorophenylpiperazine in cocaine-dependent patients

Rationale Considerable evidence indicates that serotonergic (5-HT) mechanisms may mediate central effects of cocaine, and disinhibition and aggression. Objective We investigated whether prolactin (PRL) response to meta-chlorophenylpiperazine (m-CPP), a mixed 5-HT agonist/antagonist, differed between abstinent cocaine-dependent patients and controls and whether m-CPP challenge responses were related to measures of disinhibition and aggression. Methods Thirty-five cocaine-dependent African-American subjects who were abstinent for at least 2 weeks and 33 African-American controls underwent assessments of disinhibition and aggression and a challenge with 0.5 mg/kg of oral m-CPP. Results The PRL response to m-CPP was compared between cocaine patients and controls and between subgroups categorized high or low based on disinhibition and aggression measures. Hierarchical regressions were used to determine whether behavioral measures predicted ΔPRL (peak PRL−baseline PRL). The PRL response to m-CPP was significantly diminished in cocaine patients compared to controls. The blunting was more robust in cocaine patients with high disinhibition and aggression. Among cocaine patients, the high-disinhibition subgroup showed greater blunting than the low-disinhibition subgroup and there was a trend for the high-aggression subgroup to be more blunted than the low-aggression subgroup. The subgroups of controls did not differ from each other. A combination of disinhibition and aggression measures significantly predicted ΔPRL in cocaine patients. Conclusion The results indicate that cocaine-dependent patients show disturbances in postsynaptic 5-HT function during early abstinence. It appears that the 5-HT disturbances are more pronounced in the subgroup of cocaine patients with high disinhibition and aggression.     

Use of antisense oligodeoxynucleotide to δ-opioid receptor mRNA in the study of turnover of δ-opioid receptors in the spinal cord of the mouse

Pretreatment of male ICR mice with an antisense oligodeoxynucleotide to δ-opioid receptor mRNA (DOR AS oligo, 163 pmol) given intrathecally (i.t.) once a day for 1–3 days produced a time-dependent attenuation of antinociception produced by i.t.-challenged [D-Ala²] deltorphin II (6.4 nmol), a δ-opioid receptor agonist. The attenuation of the [D-Ala²]deltorphin II-induced antinociception caused by pretreatment with DOR AS oligo given i.t. daily was blocked by co-pretreatment with naltriben (14.5 nmol), a δ-opioid receptor antagonist, but was markedly enhanced by concomitant pretreatment with thiorphan (19.7 nmol) or bestatin (14.5 nmol), which inhibits the degradation of endogenously released Met-enkephalin. Concomitant pretreatment with antiserum to Met-enkephalin, but not with antiserum to Leu-enkephalin, β-endorphin or dynorphin A (1–17), and DOR AS oligo given i.t. daily for 3 days prevented the attenuation of i.t.-challenged [D-Ala²]deltorphin II-induced antinociception caused by the DOR AS oligo pretreatment. Our results support the existence of a turnover of δ-opioid receptors in the mouse spinal cord caused by the release of Met-enkephalin. Received: 9 October 1996/Final version: 6 May 1997     

Temporal effects of nicotine nasal spray and gum on nicotine withdrawal symptoms

Nicotine nasal spray and nicotine gum have been found to be effective in relieving nicotine withdrawal symptoms. In this randomized single-blind study, 91 cigarette smokers were randomly assigned to a single 1 mg dose of active nicotine nasal spray (n = 29), active 4 mg nicotine gum (n = 31), saline placebo nasal spray (n = 16) or placebo gum (n = 15). Following overnight abstinence, subjects repeatedly completed visual analog scales for assessing nicotine withdrawal symptoms over 30 min preceding (time -30 min to time 0) and 120 min following a single dose of study medication. This sequence was performed 3 times during the day. Nicotine withdrawal symptoms were assessed on a 41-point visual analog scale (1 = no withdrawal, 41 = extreme withdrawal). At the initial session only, blood samples for serum nicotine levels were taken at baseline, then at 5, 10, 30 and 120 min following study drug administration. The mean (± SD) age of the subjects was 38.6 (±10.1) years, 48% were females, smoking rate was 24.5 (±7.8) cigarettes per day, and years of smoking was 19.9 (±10.0). A single 1 mg dose of nicotine nasal spray provided more immediate relief for craving for a cigarette compared to a single 4 mg dose of nicotine gum. Serum venous nicotine levels for the active nicotine nasal spray and nicotine gum were comparable at 5 and 10 min while the levels were higher for nicotine gum at 30 and 120 min. Changes in withdrawal symptoms were not found to be related to serum venous nicotine levels. Our findings provide a rationale for the as needed use of nicotine nasal spray to control withdrawal symptoms, possibly in combination with other medications with longer acting effects. Received: 18 February 1998/Final version: 1 May 1998     

Comparison of the pharmacodynamic effects of deflazacort and prednisolone in healthy subjects

  Objective: Deflazacort, a synthetic oxazoline derivative of prednisolone, has been suggested as having major advantages over other glucocorticoids, as it is claimed to cause fewer adverse effects at equivalent antiinflammatory potency. The assumed equipotency ratio of deflazacort versus other glucocorticoids is critical for this assumption. Methods: In a randomized cross-over study we compared the acute effects of deflazacort and prednisolone on serum cortisol, osteocalcin, insulin and blood cells (eosinophils and lymphocytes) in normal subjects. On seven occasions separated by a wash out period ≥ 1 week all participants received placebo, prednisolone (8 mg, 20 mg, 40 mg) and deflazacort (12 mg, 30 mg, 60 mg). The medication was given orally at 20.00 h as a single dose. Blood was collected at 8.00 h before and after each medication. Log (dose) response relationships were calculated and were used to compare the drugs. Results: The following equipotent dose ratios (mg deflazacort: mg prednisolone) were found: osteocalcin suppression 1.54, cortisol suppression 2.27, suppression of eosinophils 1.14 and lymphocytes 2.77. As parallelism between regression curves was rejected, equipotency could not be calculated for insulin. In 3 subjects even the highest dose of deflazacort failed to suppress serum cortisol. Conclusion: Our study highlights the difficulties of establishing equipotency ratios for glucocorticoids. It casts doubts on the generally assumed equipotency dose ratio of deflazacort vs prednisolone, as both for cortisol and lymphocytes the 95% CI was > 1.2. Thus, reduced adverse effects during deflazacort therapy may be a consequence of lower effective glucocorticoid dosage. Received: 11 December 1995 /Accepted in revised form: 16 March 1996     

Inhibition by phospholipid liposomes of the prolactin and cortisol response to insulin hypoglycemia in man

This study was designed to further investigate the purported dopaminergic activity of phospholipid liposomes (PL) prepared from bovine cerebral extracts, and to obtain further indications about their pituitary or suprapituitary site of action. In eight normal subjects, we have studied the effects of PL administration (250 mg as IV bolus plus additional 250 mg infused IV over a 60-min period), compared to placebo, on the prolactin (PRL), cortisol and growth hormone (GH) response to an insulin tolerance test (ITT). In eight additional subjects, the effects of PL on the PRL and TSH response to TRH were evaluated. PL medication blunted the PRL and cortisol response in the ITT: significant differences, with respect to placebo administration, were observed between mean peak PRL values (51.9±13.63 SEM vs 83.4±26.35 ng/ml, P<0.05) and mean cortisol values at 120 min time (20.9±0.67 vs 26.7±2.46 g/dl, P<0.05). In contrast, PL administration did not modify the ITT-related GH rise or the PRL and TSH release in response to TRH. These findings favour the view that PL are endowed with intrinsic biological activity which is dopamine-mediated, and point to the hypothalamus as their primary site of action.     

A neuroendocrine study of 5HT function in depression: evidence for biological mechanisms of endogenous and psychosocial causation

To investigate whether depression is a consequence of disturbed function in 5HT systems, neuroendocrine responses to infusions of the 5HT precursorl-tryptophan (LTP) were studied in patients and controls. After an overnight fast and 60 min bed rest, a solution of LTP (10 g/l) was infused intravenously to a dose of 100 mg/kg over 30 min. Circulating growth hormone (GH), prolactin (PRL), cortisol and tryptophan concentrations were followed from 60 min pre-infusion to 60 min post-infusion. GH responses were attenuated in 23 major depressives (DSM-III) compared with 22 controls and were almost absent in endogenous depressives (New-castle criteria). PRL responses were normal in depressives who had lost more than 3 kg body weight but attenuated in those who had not. GH and PRL responses did not correlate with each other. Reduced basal tryptophan concentrations and more rapid tryptophan clearance were observed in the depressives, but there were no correlations with GH or PRL responses. However, basal cortisol concentrations, which were raised in depressives with chronic psychosocial difficulties, were strongly and inversely predictive of PRL responses in depressives and controls. Blunted GH and PRL responses to LTP appear to be distinct abnormalities in depression which may relate to two processes; (1), an endogenous mechanism indicated by reduced GH responses, and (2), an impairment in 5HT systems, indicated by blunted PRL responses and perhaps caused by raised circulating cortisol or reduced tryptophan concentrations.     

Effects of hot tea, coffee and water ingestion on physiological responses and mood: the role of caffeine, water and beverage type

Psychopharmacological studies using caffeinated beverages or caffeine have rarely considered temporal effects on psychological and physiological function or the specific contribution of caffeine, hot water, or beverage type to the observed effects. The effect of 400 ml hot tea, coffee, and water consumption on systolic and diastolic blood pressure (SBP and DBP), heart rate, skin conductance (a measure of sympathetic nervous system activation), skin temperature, salivary cortisol, and mood were monitored in 16 healthy caffeine-withdrawn (14 h) subjects in a complete crossover design. Beverages were ingested with/without 100 mg caffeine and milk (tea/coffee only). Hot beverage ingestion rapidly increased skin conductance and temperature (+1.7°C) with peak effects observed only 10–30 min post-consumption. Caffeine in the beverage rapidly augmented skin conductance responses but, in contrast to the effect of hot water, reduced the skin temperature response and increased SBP (+2.8 mmHg) and DBP (+2.1 mmHg) 30–60 min post-consumption. Both caffeine and milk addition to beverages independently improved mood and reduced anxiety 30 and 60 min post-consumption. Milk addition had no other effects apart from attenuating the transient increase in physiological responses associated with the drinking phase. There were no effects of beverage consumption on salivary cortisol or of beverage vehicle on salivary caffeine levels, the latter indicating that caffeine pharmacokinetics was similar in both tea and coffee, and not different from caffeinated water. In keeping with this, the responses to tea and coffee ingestion were similar and largely accounted for by the effects of hot water and caffeine. However, tea potentiated the increase in skin temperature compared to coffee and water indicative of a greater vasodilatory response plausibly related to the presence of flavonoids in tea. We conclude that ingestion of hot caffeinated beverages stimulates physiological processes faster than hitherto described, primarily via the effects of hot water and caffeine, but with beverage type and milk playing important modulatory roles. Received: 15 March 1997/Final version: 23 May 1997     

Gender-dependent dissociation between oxytocin but not ACTH, cortisol or TSH responses to m-chlorophenylpiperazine in healthy subjects

m-chlorophenylpiperazine (m-CPP), a serotonin (5-HT) agonist with some selectivity for the 5-HT_2C receptor subtype, which is widely used to examine 5-HT receptor function in human subjects, has been found to induce oxytocin and thyrotropin (TSH) responses in rodents. This study examined whether m-CPP had any effect on plasma oxytocin, TSH and aldosterone concentration in healthy volunteers using a double-blind, placebo-controlled crossover design. Plasma adrenocorticorticotropic hormone (ACTH) and cortisol responses, two generally accepted markers of m-CPP-induced 5-HT receptor activation, were measured in parallel. Male subjects (n = 7) received placebo, 0.25 and 0.5 mg/kg oral m-CPP. In female subjects (n = 5), the effects of placebo and 0.25 mg/kg m-CPP were studied. After placebo, given in the morning, ACTH, cortisol, TSH and aldosterone concentrations decreased over time. m-CPP 0.25 mg/kg avoided decreases in ACTH, cortisol and TSH concentrations; these responses were significant. At the dose of 0.5 mg/kg, m-CPP caused increase in ACTH, cortisol, TSH and aldosterone concentrations. Significant plasma oxytocin responses were found in female subjects only; thus this effect of m-CPP was statistically significantly gender dependent. Other responses to m-CPP were similar in male and female subjects. The present results suggest that there are clear differences, including dose and gender-dependent dissociations, among the 5-HT receptor agonist m-CPP-induced neuroendocrine responses. Received: 6 June 1997/Final version: 27 October 1997     

Lack of effect of the serotonin4 receptor agonist zacopride on ACTH secretion in normal men

Objective: In the present study, we investigated the effect of zacopride on corticotropin (ACTH) and cortisol secretion in healthy volunteers. Male subjects received a single oral dose of placebo, 10 μg zacopride or 400 μg zacopride. Plasma ACTH, cortisol and aldosterone concentrations were measured before and during the 3 h following the administration of the drug. Results: For none of the doses did zacopride cause any modification of plasma ACTH or cortisol levels. In contrast, administration of 400 μg zacopride induced a significant increase in plasma aldosterone levels. Conclusion: Our results indicate that in humans serotonin-evoked stimulation of ACTH secretion is not mediated through serotonin₄ (5-HT₄) receptors. Together with previous findings, these data indicate that the stimulatory effect of 5-HT₄ receptor agonists on aldosterone secretion in man can be ascribed solely to a direct action on glomerulosa cells. Received: 23 October 1995/Accepted in revised form: 13 January 1996     

Detection of the organophosphorus nerve agent sarin by a competitive inhibition enzyme immunoassay

 Two artificial antigens, N ^α N ^ɛ-di(O, O-diisopropyl) phosphoryl L-lysine (DIP)- bovine serum albumin (BSA) conjugate (DIP-BSA) and DIP-KLH (keyhole limpet hemocyanin), were synthesized. Antibodies against sarin (O-isopropyl methylphosphonofluoridate) were obtained after immunization of rabbits with DIP-KLH conjugate. A competitive inhibition enzyme immunoassay (CIEIA) was developed to detect the organophosphorus nerve agent sarin. The antibody solutions could be inhibited by sarin as low as 10^-6 mol/l, and the standard curve was linear over 3 orders of magnitude. The coefficients of intraassay and interassay variation of this method were 5.4–6.2% (n=11) and 8.0–9.5% (n=6) at a sarin concentration range of 10^-3–10^-6 mol/l, respectively. The recovery of sarin in water samples at the concentration of 5×10^-5 mol/l was in the range of 96.8–102.5%. The specificity of the antiserum was assessed by comparing the inhibition induced by sarin with soman, Vx, isopropyl alcohol and isopropyl methyl phosphonic acid. The results showed that less than 5 mmol/l soman, 2 mmol/l Vx, 16 mmol/l isopropyl alcohol and 8 mmol/l isopropyl methyl phosphonic acid did not influence the determination of sarin in water samples. Received: 28 September 1994/Accepted: 2 February 1995     

Trazodone and valproate in patients discontinuing long-term benzodiazepine therapy: effects on withdrawal symptoms and taper outcome

Recent uncontrolled research suggested that trazodone and sodium valproate may be helpful in benzodiazepine (BZ) discontinuation. We therefore undertook a double-blind study to assess whether trazodone and valproate, as compared to placebo, would attenuate withdrawal and facilitate discontinuation in BZ-dependent patients with a minimum of 1 year daily BZ use. Seventy-eight patients, taking a mean dose of 19 ± 17 mg/day of diazepam (or its equivalent), were stabilized for several weeks on their BZ (16 diazepam, 25 lorazepam, 37 alprazolam) and then for 1–2 weeks, pretreated with trazodone, sodium valproate or placebo before being tapered at 25% per week. All treatments were continued for 5 weeks post-taper. BZ-free status was assessed after 5 and 12 weeks post-taper. Neither trazodone nor valproate had any significant effect on withdrawal severity. Peak physician withdrawal checklist change from baseline to peak severity was 16.4 for trazodone, 18.04 sodium valproate and 18.24 placebo (F = 0.10; NS). Taper success rates were significantly effected by both active agents at the 5-week, but not 12-week, assessment. At 5 weeks post-taper, 79% of sodium valproate and 67% of trazodone, but only 31% of placebo patients were BZ-free (χ² = 7.34; df 2; P < 0.03). Major adverse events for trazodone were sedation and dry mouth, and for valproate, diarrhea, nausea and headaches. Received: 27 March 1997/Final version: 9 June 1998     

Nicotine discrimination and self-administration in humans as a function of smoking status

Nicotine’s discriminative stimulus effects may be critical to understanding reinforcement of tobacco smoking. It is not known whether regular nicotine exposure produces tolerance or sensitivity to these effects. In this study, male and female smokers (n = 11) and never-smokers (n = 10) were trained to discriminate 20 μg/kg nicotine by nasal spray from placebo (0) on day 1. On day 2, both groups were tested on generalization of this discrimination across intermittent presentations of 0, 3, 6, 12, and 20 μg/kg nicotine in random order. Quantitative and quantal behavioral discrimination tasks, used in previous research, were employed. On day 3, subjects were instructed to self-administer sprays from the 20 μg/kg nicotine versus 0 bottles in a concurrent-choice procedure. All but one subject (female smoker) learned reliably to discriminate 20 μg/kg nicotine from placebo (≥ 80% correct) on day 1. Nicotine-appropriate responding on day 2 was attenuated in smokers versus never-smokers at 20 μg/kg on the quantitative task and at 12 μg/kg on the quantal task, suggesting tolerance. There was no difference in responding at other doses. Smokers also showed attenuated responses on the subjective measure of “head rush”, which was associated with discrimination responding in both groups. Nicotine self-administration was significantly greater in smokers versus never-smokers, who self-administered nicotine below chance levels, and was inversely related to discrimination behavior in never-smokers but unrelated in smokers. Women smokers showed less change in nicotine-appropriate responding across generalization doses, reported less confidence in discriminating training doses during acquisition on day 1, and tended to self-administer less nicotine on day 3. These results indicate that smokers may become tolerant to the discriminative stimulus effects of nicotine, perhaps promoting increased use. Received: 1 October 1996/Final version: 28 January 1997     

Naltrexone administration affects ad libitum smoking behavior

Endogenous opioid peptides have been implicated in the reinforcement of smoking and opioid antagonists have been examined to determine their role in smoking behavior. To date, the relationship between smoking behavior and chronic opiate antagonist administration during ad libitum smoking has not been investigated. The purpose of this study was to examine the relationships between naltrexone, an opiate antagonist administered orally, and smoking behavior and mood states during ad libitum smoking. A repeated measures experimental design was used. Normal adult male and female volunteers, admitted to the Clinical Research Center, were randomly assigned to naltrexone-treated (n = 22) or placebo-control (n = 21) groups in a double-blind manner. Day 1 was considered acclimation to the unit and day 2 was baseline, or pre-drug administration. On days 3, 4, and 5, subjects received 50 mg naltrexone or a placebo at 0700 and 1600 hours. Plasma nicotine and expired air carbon monoxide levels were measured daily at 1900 hours. Number of cigarettes smoked, mood states, withdrawal symptomatology and self-reported satisfaction with smoking were also quantified daily. Results indicated that plasma nicotine levels (P = 0.005), number of cigarettes smoked daily (P = 0.003) and self-reported satisfaction with smoking (P = 0.043) were significantly lower among those treated with naltrexone, compared to the placebo-control group. Expired air carbon monoxide levels did not differ between the two groups. In addition, mood states and withdrawal symptoms did not differ between groups. These findings suggest that endogenous opioid peptides influence specific smoking behavior variables. Received: 7 November 1997/ Final version: 7 April 1998     

Effects of μ and δ opioid agonists and antagonists on affective vocal and reflexive pain responses during social stress in rats

The present experiments evaluated the influence of intraventricular μ and δ opioid receptors on affective vocal and reflexive responses to aversive stimuli in socially inexperienced, as well as defensive and submissive responses in defeated, adult male Long-Evans rats. Defeat stress consisted of: (1) an aggressive confrontation in which the experimental intruder rat exhibited escape, defensive and submissive behaviors [i.e., upright, supine postures and ultrasonic vocalizations (USV)], and subsequently, (2) protection from the resident stimulus rat with a wire mesh screen for 10–20 min. Defeat stress was immediately followed by an experimental session with tactile startle (20 psi). The μ opioid receptor agonists morphine (0.1–0.6 μg ICV) and [D-Ala²-N-Me-Phe⁴-Gly⁵-ol]-enkephalin (DAMGO; 0.01–0.3 μg ICV), and the δ opioid receptor agonist [D-Pen^2,5]-enkephalin (DPDPE; 10–100 μg ICV) dose-dependently decreased startle-induced USV and increased tail-flick latencies in socially inexperienced and defeated rats. Of greater interest, morphine, DAMGO and DPDPE increased the occurrence of the submissive crouch posture, and defeated rats were more sensitive than socially inexperienced rats to the startle-induced USV-suppressive and antinociceptive effects of morphine and DPDPE. The antinociceptive effects of DAMGO were likewise obtained at lower doses in defeated rats. Finally, the USV-suppressive effects of morphine and DAMGO were reversed with the μ receptor antagonist naltrexone (0.1 mg/kg IP), but the USV-suppressive effects produced by DPDPE were not reversed with the δ receptor antagonist naltrindole (1 mg/kg IP). These results confirm μ, but not δ opioid receptor activation as significant in affective vocal, passive-submissive behavior, as well as reflexive antinociception. Furthermore, similar to previous studies with restraint and electric shock stress, the facilitation of μ opioid effects on vocal responses and antinociception is consistent with the proposal that defeat stress activated endogenous opioid mechanisms. Received: 23 September 1997/Final version: 15 January 1998     

The nitric oxide synthesis inhibitor nitro-L-arginine (L-NNA) attenuates nicotine abstinence syndrome in the rat

Nitric oxide synthesis contributes to opiate tolerance and dependence. Nicotine dependence and abstinence syndrome in the rat appear to involve opiate mechanisms. Therefore, it was postulated that nitric oxide synthase (NOS) activity might be essential for the expression of nicotine abstinence syndrome. Twenty-one rats were rendered dependent by SC infusion of 9 mg/kg per day nicotine tartrate via Alzet osmotic minipump. Rats were pretreated SC with vehicle alone, or with 18 or 30 mg/kg of the NOS inhibitor L-NNA (nitro-L-arginine). Thirty minutes later, rats were challenged by 1 mg/kg of the nicotinic antagonist mecamylamine SC and observed for 30 additional minutes. Rats pretreated with vehicle displayed a total of 68.7 ± 8.0 mecamylamine-precipitated abstinence signs (mean ± SEM), while those receiving 18 or 30 mg/kg L-NNA had 12.7 ± 2.0 and 5.1 ± 1.7 signs, respectively. All three groups differed significantly from one another according to Dunn’s post-hoc procedure. Rats pretreated with L-NNA combined with an excess of the NOS substrate L-arginine had significantly more mecamylamine-precipitated abstinence signs than rats receiving L-NNA combined with D-arginine. Also, D-NNA, which does not selectively bind to NOS, was significantly less effective than L-NNA in preventing mecamylamine-precipitated abstinence syndrome. Additional studies determined the effect of L-NNA on spontaneous nicotine abstinence syndrome. Rats were assessed for abstinence signs at 17 and 20 h after termination of nicotine infusion. They received injections of 9, 18, or 30 mg/kg L-NNA SC or vehicle alone immediately before the 20-h observation; all rats were observed for 30 min. Signs at 20 h (post-injection) as a percentage of signs at 17 h (pre-injection) declined significantly as a function of L-NNA dose. Once again, this effect was attenuated significantly more by co-administration of L-arginine than by D-arginine. The overall pattern of results suggests that nitric oxide synthesis is critical to the expression of nicotine abstinence syndrome. Received: 20 January 1998/Final version: 8 April 1998