Oxytocinergic regulation of endogenous as well as drug-induced mood.

The interconnections between the serotonin and oxytocin pathways in the brain suggest that changes in oxytocin levels - arising from natural or drug-induced stimuli - lead to measureable changes in mood. In this paper, we review our findings in the context of what is known about the roles of oxytocin and vasopressin in the expression of a range of behaviours. In our first set of studies we investigated whether stimulation of oxytocin and vasopressin receptors, via central or systemic drug administration, would produce behavioural changes indicative of anti-depressant or anxiolytic activity. In our second study we investigated whether oxytocin receptor activation might be implicated in the interoceptive effects experienced with the popular party drug, MDMA ('ecstasy'). Our first study demonstrated that carbetocin, an oxytocin analogue, had anti-depressant actions following systemic and central administration, effects which were blocked by the oxytocin and vasopressin 1A receptor antagonist, atosiban. Carbetocin also had anxiolytic effects in the elevated plus maze. In an evaluation of the complementary nature of oxytocin and vasopressin, we found that systemic administration of desmopressin, a vasopressin analogue, was anxiogenic; its effects blocked by atosiban which on its own produced robust anxiolytic behavioural changes. In our second study, we evaluated MDMA's interoceptive effects using a drug discrimination paradigm. Carbetocin partially substituted for MDMA, while atosiban interfered with MDMA discrimination, suggesting that oxytocin receptor activation contributes to MDMA-related interoceptive cues. The results of these and other clinical and preclinical studies suggest that oxytocin, as well as its closely related counterpart vasopressin, may provide alternative therapeutic targets for the treatment of mood disorders such as anxiety and depression. The possibility that oxytocin release may contribute to the perception of and processes underlying natural and drug-induced behavioural reinforcement offers exciting prospects for future study.

14 beta-O-cinnamoylnaltrexone and related dihydrocodeinones are mu opioid receptor partial agonists with predominant antagonist activity.

14-O-Cinnamoyl esters of naltrexone (6) were synthesized and evaluated in isolated tissue assays in vitro and in vivo in mouse antinociceptive assays. Their predominant opioid receptor activity was mu receptor (MOR) antagonism, but the unsubstituted cinnamoyl derivative (6a) had partial MOR agonist activity in vitro and in vivo. When compared to the equivalent 14-cinnamoylaminomorphinones (5), the cinnamoyloxy morphinones (6) as MOR antagonists had a shorter duration of action and were less effective as pseudoirreversible antagonists. The antinociceptive activity of the cinnamoyloxycodeinones (7) was not significantly greater than that of the morphinones (6), but they exhibited no evidence of any pseudoirreversible MOR antagonism. In both respects, these profiles differed from those of the equivalent 14-cinnamoylaminocodeinones (4).

Neuroendocrine and subjective responses to pharmacological challenge with citalopram: a controlled study in male and female ecstasy/MDMA users.

Despite evidence that +/-3,4-methylenedioxymethamphetamine (MDMA; 'ecstasy') causes persistent alterations to the serotonergic system of animals, evidence for long-term neurological effects of ecstasy/MDMA in humans remains equivocal. The current study assessed serotonin functioning of nine male and 11 female recreational ecstasy polydrug users by measuring neuroendocrine (prolactin, cortisol) responses to pharmacological challenge with the selective serotonin reuptake inhibitor citalopram, compared with nine male and five female cannabis polydrug users and 11 male and 11 female non-drug using controls. A single-blind, randomised, placebo-controlled design was used. Subjective responses, other substance use, mood, personality traits and demographic variables were measured to control for potentially confounding variables. There were no significant differences between ecstasy polydrug users, cannabis polydrug users and non-drug using controls in neuroendocrine or subjective responses to serotonergic challenge, and there were no sex by drug group interactions. There was no relationship between extent of ecstasy use and neuroendocrine functioning, alone or in combination with potential confounding variables. Subjective responses to the pharmacological challenge (nausea, tremor, dry mouth), novelty seeking and lifetime dose of alcohol were the only variables that contributed to one or more of the neuroendocrine outcome variables. These data do not support the premise that recreational ecstasy/MDMA use results in measurable impairment of serotonergic control of endocrine activity.

Role of sex and sex steroids in mediating pituitary-adrenal responses to acute buspirone treatment in sheep.

Systematic characterisation of sex differences in the serotonergic modulation of the hypothalamic-pituitary-adrenal (HPA) axis may assist with our understanding of why stress-related disorders are disproportionately represented in women. In this study, we examined the acute effects of buspirone, a serotonergic 1A receptor subtype agonist, on the endocrine endpoints of adrenocorticotrophin (ACTH) and cortisol secretion in gonadectomised male and female sheep. Each sheep was treated with an acute i.v. injection containing vehicle or buspirone (0.03, 0.1 and 0.3 mg/kg) in the presence and absence of sex steroid replacement (SSR). In males, SSR treatment consisted of testosterone (2 x 200 mg s.c. pellets) and, in females, the mid-luteal phase of the oestrus cycle was simulated by treatment with oestradiol (1 cm s.c. implant) and an intravaginal controlled internal drug release device containing 0.3 g progesterone. ACTH, cortisol, testosterone and progesterone were measured in jugular blood. Basal ACTH levels were higher in males, whereas basal cortisol levels were higher in females, regardless of sex steroid status. The magnitude of the increase in ACTH and cortisol secretion following buspirone treatment was dose-dependent. There were no differences in the ACTH responses of males and females to buspirone treatment, either in the presence or absence of sex steroid replacement. However, although the cortisol response to buspirone was greater in females, there was no discernable effect of sex steroid status in addition to this sex difference on either basal or buspirone-stimulated cortisol release. We conclude that the larger basal and buspirone-stimulated cortisol response measured in females may reflect a sex difference, either in the sensitivity of the adrenal gland to ACTH or in the catecholaminergic innervation of the adrenal gland. The lack of effect of sex and sex steroids in the ACTH secretory response to buspirone may indicate that the sex differences in serotonergic modulation of the HPA axis, as reported previously by our group, were mediated via serotonergic receptor subtypes other than the 1A receptor.

Methocinnamox is a potent, long-lasting, and selective antagonist of morphine-mediated antinociception in the mouse: comparison with clocinnamox, beta-funaltrexamine, and beta-chlornaltrexamine.

The irreversible mu-opioid antagonists beta-funaltrexamine (beta-FNA) and beta-chlornaltrexamine (beta-CNA) are important pharmacological tools but have a kappa-agonist activity and, in the latter case, low selectivity. This work examines whether clocinnamox (C-CAM) and the newer analog, methocinnamox (M-CAM), represent improved long-lasting antagonists for examining mu-opioid-mediated effects in vivo. beta-FNA, beta-CNA, C-CAM, and M-CAM were compared after systemic administration in mice and in vitro. beta-FNA and beta-CNA were effective agonists in the writhing assay, reversible by the kappa-antagonist norbinaltorphimine. Neither C-CAM nor M-CAM had agonist activity in vivo. M-CAM was devoid of agonist action at cloned opioid receptors. All four compounds depressed the dose-effect curve for the mu-agonist morphine in the warm-water tail-withdrawal test 1 h after administration; at 48 h, recovery was evident. In the writhing assay, the dose-effect curve for morphine was shifted in a parallel fashion in the order M-CAM >> C-CAM > beta-CNA > or = beta-FNA. In comparison with their ability to shift the dose-effect curve for bremazocine (kappa) and BW373U86 (delta), beta-CNA was the least mu-selective, followed by C-CAM < beta-FNA < M-CAM. M-CAM (1.8 mg/kg) produced a 74-fold increase in the ED(50) of morphine while showing no effect on bremazocine or BW373U86 dose-response curves. In binding assays, C-CAM and M-CAM were 8-fold selective for mu- over kappa-receptors, whereas beta-FNA and beta-CNA were mu/delta-, but not mu/kappa, selective. However, ex vivo binding assays confirmed the mu-receptor selectivity of M-CAM. M-CAM is thus a potent, long-lasting, and specific antagonist at mu-receptors in vivo that lacks confounding agonist actions.

Glucocorticoid-reinforced responding in the rhesus monkey.

RATIONALE: Glucocorticoids have been reported to have rewarding effects in rats and may lead to drug-seeking behavior in humans under some circumstances. OBJECTIVES: The present study investigated whether glucocorticoids would be self-administered intravenously by rhesus monkeys (Macaca mulatta). METHODS: Ten monkeys, 7 male and 3 female, were maintained on a fixed ratio 10 (30 or 100), time-out 10-s schedule for 0.1 mg/kg methohexital or saline injections. Dexamethasone (0.03-0.3 mg/kg), methylprednisolone (0.1-1.0 mg/kg) and hydrocortisone (0.3-3.0 mg/kg) were periodically substituted for methohexital or saline. RESULTS: Dexamethasone (0.3 mg/kg) was self-administered by all of the male monkeys on the first, but not on subsequent occasions. It was hypothesized that suppression of hypothalamic-pituitary-adrenal (HPA) activity by these exogenous glucocorticoids following their first presentation may have interfered with their reinforcing effects on subsequent evaluation. Subsequently, plasma adrenocorticotropin and cortisol were measured in four male monkeys to ascertain that normal basal HPA activity had resumed prior to each glucocorticoid substitution. Of the ten monkeys that were tested, only one reliably self-administered dexamethasone, methylprednisolone and hydrocortisone, and he did so regardless of whether his basal HPA activity was suppressed. This monkey differed from some of the other monkeys both behaviorally and in his response to intravenous corticotropin releasing hormone. None of the three female monkeys that were tested with selected glucocorticoid doses showed any evidence of glucocorticoid reinforcement on any occasion. CONCLUSIONS: The results indicate that glucocorticoids were not reinforcing to the majority of monkeys in this study; nevertheless, large individual differences may exist in proclivity of monkeys to self-inject these compounds.

Cocaine-reinforced responding in rhesus monkeys: pharmacological attenuation of the hypothalamic-pituitary-adrenal axis response.

Intravenously self-administered cocaine produces a dose-dependent release of adrenocorticotropic hormone (ACTH) and cortisol in male rhesus monkeys. This study investigated whether the acute disruption of cortisol and/or ACTH release had any effect on ongoing cocaine-maintained responding. Four hypothalamic-pituitary-adrenal (HPA) axis inhibitors were examined: etomidate and ketoconazole, both of which are cortisol synthesis inhibitors; astressin, a peptidic corticotropin-releasing factor (CRF) antagonist that binds CRF(1) receptors predominantly in the pituitary gland; and dexamethasone, a highly selective glucocorticoid receptor agonist whose long-lasting effects reduce or abolish the endogenous release of ACTH and cortisol. The reinforcing effects of a range of cocaine doses, with or without pretreatment with an HPA inhibitor, were evaluated using a fixed ratio 30 time-out 10-min schedule of reinforcement in six male monkeys. Blood was sampled before, during, and after self-administration sessions. Self-administration of cocaine increased plasma cortisol and ACTH. Pretreatment with etomidate and ketoconazole dose-dependently inhibited the cocaine-induced rise in cortisol and, at the highest doses, produced a compensatory increase in ACTH release. Astressin and dexamethasone attenuated or abolished cocaine-induced cortisol and ACTH release. Despite the efficacy exhibited by these pretreatments and the variety of mechanisms by which they inhibited the HPA axis, there was no evidence for any change in cocaine-reinforced behavior (response rate or infusion number), an indication that acute changes in the ACTH or cortisol response to cocaine do not play a direct role in modulating cocaine-seeking behavior under these behavioral circumstances.

Effects of response contingent and noncontingent cocaine injection on hypothalamic-pituitary-adrenal activity in rhesus monkeys.

Earlier studies of cocaine's effects on the hypothalamic-pituitary-adrenal (HPA) axis used nonresponse-contingent designs in which the investigator determined dose, timing, and route of administration. It is important to evaluate whether "control" over cocaine delivery is a significant determinant of cocaine's HPA axis effect. This study measured cocaine's effects on plasma adrenocorticotropic hormone and cortisol, using nonresponse-contingent injections followed later by response-contingent cocaine delivery. In addition, the effects of cocaine history on the HPA response to a noncontingent injection of 1 mg/kg of cocaine were measured. HPA effects of corticotropin-releasing hormone (CRF) were also measured. Male and female rhesus monkeys, with surgically placed venous catheters, were tested in their home cages. Up to 13 injections of saline and cocaine (0.01-, 0.03-, 0.1-, and 0.3-mg/kg/injection) were administered at 10-min intervals (nonresponse-contingent condition) and on a fixed ratio 30, time out 10-min schedule of reinforcement. Overall, cocaine delivered response contingently produced larger, more dose-dependent HPA responses than did noncontingent delivery. The HPA response to a 1 mg/kg cocaine infusion in cocaine-naive monkeys was not predictive of the HPA effect of this dose subsequent to acquisition of cocaine self-administration. Overall, male monkeys had larger HPA responses to cocaine than did female monkeys. Finally, the HPA effects of CRF were significantly correlated with those of large cocaine doses delivered nonresponse contingently, but not with response-contingent administration.

Effects of self-administered cocaine on plasma adrenocorticotropic hormone and cortisol in male rhesus monkeys.

This study was designed to examine the effects of self-administered cocaine on hypothalamic-pituitary-adrenal (HPA) axis activity in rhesus monkeys. Initially, basal release of cortisol and adrenocorticotropic hormone (ACTH) was measured in singly housed male and female monkeys (n = 9) over a 24-h period using plasma samples obtained from indwelling venous catheters. Basal cortisol and ACTH levels in both male and female rhesus monkeys demonstrated a circadian pattern of release, with peak levels for cortisol (19.60 +/- 2.16 microgram/dl) and ACTH (19.63 +/- 2.56 pg/ml) measured at 6:00 AM. The nadir for ACTH (6.27 +/- 0.62 pg/ml) occurred at 6:00 PM, preceding the cortisol nadir (5.55 +/- 1.21 microgram/dl) at 9:00 PM. The reinforcing effects of saline, 0.01, 0.03, 0.1, and 0.3 mg/kg/injection cocaine were then evaluated using a fixed-ratio 30, time-out 10-min schedule of reinforcement in seven male monkeys. Blood was sampled before, during, and after self-administration sessions. Self-administration of cocaine produced dose-dependent increases in cortisol and ACTH. One dose of cocaine (0.03 mg/kg/injection), although reliably self-administered, did not produce a significant increase in HPA axis activity. These results indicate that although cocaine dose-dependently increases HPA axis activity, the HPA effect is more likely a consequence of overall cocaine intake than it is an indicator of cocaine doses that are sufficient to maintain self-administration behavior.

3-Alkyl ethers of clocinnamox: delayed long-term mu-antagonists with variable mu efficacy.

In recent years there has been considerable interest in the relationship between clocinnamox (C-CAM) and its methyl ether methoclocinnamox (MC-CAM). While C-CAM appears to be an insurmountable mu-antagonist, MC-CAM has been shown to be a potent partial agonist at mu-opioid receptors. To further investigate this relationship we prepared other ethers of C-CAM and evaluated these in opioid receptor binding assays and in vivo in mouse antinociceptive assays and in morphine-dependent monkeys. In opioid binding assays, the ethers were generally mu-selective with affinity equivalent to that of C-CAM itself. Although they displayed little or no efficacy in vitro, some of the ethers showed substantial agonist activity in the in vivo antinociceptive tests. Two of the ethers, the propargyl ether 7 and the cyclopropylmethyl ether 5, were chosen for more detailed analysis in vivo. 7 was shown to have significant mu-agonist character and was able to substitute for morphine in morphine-dependent monkeys. Interestingly, when this agonist effect abated, 7 displayed long-lasting mu-antagonism. In contrast, 5 displayed little agonist activity in vivo and was characterized as a potent, long-acting mu antagonist. Although further work is needed to determine whether metabolism is a crucial factor in determining the pharmacological profile of these ethers, it is clear that 3-O-alkylation is a useful means of varying the mu efficacy displayed by this class of acyl-substituted 14-aminomorphinones. MC-CAM itself has generated considerable interest as a potential pharmacotherapy for opiate abuse. These analogues with differing mu efficacy but retaining the long-lasting mu-antagonist effects provide further opportunities for the development of treatment drugs.

Receptor reserve and affinity of mu opioid agonists in mouse antinociception: correlation with receptor binding.

In order to quantitate the extent to which opioid agonist potencies obtained in behavioral assays are determined by the apparent in vivo affinity and efficacy of the agonist, the antinociceptive effects of the mu opioid agonists morphine, fentanyl, etonitazene, and NIH 10741 were assessed before and after administration of the insurmountable mu opioid antagonist clocinnamox (CCAM) in a 55 degrees C warm-water tail withdrawal test in Swiss albino mice. Under control conditions, all four mu opioid agonists produced a full antinociceptive response with the following ED50 values (in mg/kg): morphine, 12; fentanyl, 0.47; etonitazene, 0.039; NIH 10741, 0.0051. Analysis of CCAM's effects according to Black and Leff gave the following agonist efficacy or tau values: Morphine, 4; fentanyl 15, etonitazene, 7; and NIH 10741, 59. The respective KA values were (in mg/kg): morphine, 29; fentanyl, 7.3; etonitazene, 0.22; and NIH 10741, 0.30. The major determinant of the experimentally observed ED50 values seemed to be the apparent in vivo affinity of the respective agonist and not its efficacy. KA values (expressed as mol/kg) correlated with the Ki values (in mol/l) obtained with [3H]DAMGO radioligand binding (r = 0.96 for pKA vs. pKi), although being on average 11,000-fold higher. Values for q, the available receptor fraction as determined in the behavioral experiments, correlated strongly (r = 0.96) with the q values determined by ex vivo [3H]DAMGO- and [3H]naltrexone equilibrium binding (i.e., Bmax,clocinnamox/Bmax,control), the relationship approaching unity.

Differential effects of systemically administered nor-binaltorphimine (nor-BNI) on kappa-opioid agonists in the mouse writhing assay.

The opioid antagonist effects of systemically administered nor-binaltorphimine (nor-BNI) were evaluated against the kappa agonists CI-977, U69,593, U50,488, ethylketocyclazocine (EKC), Mr2034 and bremazocine, the mu agonist morphine and the alkaloid delta agonist BW-373U86 in the acetic acid-induced writhing assay in mice. All eight agonists completely and dose-dependently inhibited writhing. Antagonism of CI-977 was apparent 1 h after administration of 32 mg/kg nor-BNI, peaking after 4 h and was maintained for at least 4 weeks; no antagonist effects of nor-BNI were apparent after 8 weeks. Nor-BNI (32 mg/kg) caused little or no antagonism of morphine or BW-373U86 at 1 h and none at 24 h after nor-BNI administration. Subsequently, dose-effect curves for CI-977, U50,488, U69,593, EKC, Mr2034 and bremazocine were determined 24 h after pretreatment with 3.2, 10 and 32 mg/kg nor-BNI. Pretreatment with 3.2 mg/kg nor-BNI produced significant antagonism of all six kappa agonists, suggesting that their antinociceptive effects were mediated at least in part by nor-BNI-sensitive kappa receptors. At higher doses, nor-BNI dose-dependently shifted the agonist dose-effect curves of CI-977, U50,488, U69,593 and bremazocine, but not those of EKC and Mr2034, suggesting that the latter compounds may be producing effects via nor-BNI-insensitive receptors. Mu receptor involvement was demonstrated following a 24 h pretreatment with 32 mg/kg beta-FNA in combination with nor-BNI, which significantly increased the degree of antagonism of Mr2034 and EKC from that seen with nor-BNI alone.2+ off