Effect of chronic pretreatment with the sigma ligand JO 1784 on CRF-induced changes in behaviour, neurotransmitter and immunological function in the rat

CRF-1 antagonist and CRF-2 agonist decrease binge-like ethanol drinking in C57BL/6J mice independent of the HPA axis

Recent evidence suggests that corticotropin-releasing factor (CRF) receptor (CRFR) signaling is involved in modulating binge-like ethanol consumption in C57BL/6J mice. In this report, a series of experiments were performed to further characterize the role of CRFR signaling in binge-like ethanol consumption. The role of central CRFR signaling was assessed with intracerebroventricular (i.c.v.) infusion of the nonselective CRFR antagonist, alpha-helical CRF(9-41) (0, 1, 5, 10 microg/1 microl). The contribution of central CRF type 2 receptor (CRF(2)R) signaling was assessed with i.c.v. infusion of the selective CRF(2)R agonist, urocortin (Ucn) 3 (0, 0.05, 0.1, or 0.5 microg/1 microl). The role of the hypothalamic-pituitary-adrenal (HPA) axis was assessed by pretreating mice with intraperitoneal (i.p.) injection of (1) the corticosterone synthesis inhibitor, metyrapone (0, 50, 100, 150 mg/kg) or (2) the glucocorticoid receptor antagonist, mifepristone (0, 25, 50 mg/kg), and (3) by using radioimmunoassay to determine whether binge-like ethanol intake influenced plasma corticosterone levels. Finally, we determined whether the ability of the CRF(1)R antagonist, CP-154,526 (CP; 0, 10, 15 mg/kg, i.p.), to blunt binge-like drinking required normal HPA axis signaling by comparing the effectiveness of CP in adrenalectomized (ADX) and normal mice. Results showed that i.c.v. infusion of a 1 microg dose of alpha-helical CRF(9-41) significantly attenuated binge-like ethanol consumption relative to vehicle treatment, and i.c.v. infusion of Ucn 3 dose-dependently blunted binge-like drinking. On the other hand, metyrapone nonselectively reduced both ethanol and sucrose consumption, mifepristone did not alter ethanol drinking, and binge-like drinking did not correlate with plasma corticosterone levels. Finally, i.p. injection of CP significantly attenuated binge-like ethanol intake in both ADX and normal mice. Together, these results suggest that binge-like ethanol intake in C57BL/6J mice is modulated by CRF(1)R and CRF(2)R signaling, such that blockade of CRF(1)R or activation of CRF(2)R effectively reduces excessive ethanol intake. Furthermore, normal HPA axis signaling is not necessary to achieve binge-like drinking behavior.

Attenuation by a sigma1 (sigma1) receptor agonist of the learning and memory deficits induced by a prenatal restraint stress in juvenile rats

1. Stress during pregnancy results in complex neurochemical and behavioral alterations throughout the offspring lifetime. We here examined the impact of prenatal stress (PS) on memory functions in male and female offspring and report the efficacy of a selective sigma(1) (sigma(1)) receptor agonist, igmesine, in alleviating the observed deficits. 2. Dams received an unpredictable 90-min duration restraint stress from gestational day E17 to E20. Learning was examined in offspring between day P24 and P36 using spontaneous alternation in the Y-maze, delayed alternation in the T-maze, water-maze learning and passive avoidance. 3. Both male and female PS rats showed impairments of spontaneous and delayed alternation performances. Acquisition of a fixed platform position in the water-maze was unchanged in PS rats, but the probe test revealed a diminution of time spent in the training quadrant. Acquisition of a daily changing platform position demonstrated impaired working memory for male and female PS rats. Finally, passive avoidance deficits were observed. 4. Pretreatment with the selective sigma(1) agonist igmesine (1-10 mg x kg(-1) i.p.) reversed the PS-induced learning deficits in offspring rats for each test. The sigma(1) antagonist BD1063 failed to affect performances alone but blocked the igmesine effect, confirming the involvement of the sigma(1) receptor. 5. PS thus induces delayed memory deficits, affecting spatial and nonspatial, short- and long-term memories in juvenile male and female offspring rats. Activation of the sigma(1) neuromodulatory receptor allows a significant recovery of the memory functions in PS rats.

Beneficial effects of the sigma1 receptor agonists igmesine and dehydroepiandrosterone against learning impairments in rats prenatally exposed to cocaine

In utero cocaine (IUC) exposure results in offspring rats in complex neurochemical and behavioral alterations, particularly affecting learning and memory processes. We examined here the impact of IUC exposure on memory functions in male and female offspring rats and report that selective sigma(1) (sigma(1)) receptor agonists are effective in reversing the deficits. Dams received a daily cocaine, 20 mg/kg ip, injection between gestational days E17 to E20. Learning was examined in offspring between day P30 and P41 using delayed alternation in the T-maze, water-maze learning and passive avoidance. Both male and female rats prenatally exposed to cocaine showed delayed alternation deficits and impairments of acquisition of a fixed platform position in the water maze, as shown by higher acquisition latencies and diminutions of time spent in the training quadrant during the probe test. The acquisition of a daily changing platform position also demonstrated impaired working memory. Finally, passive avoidance deficits were observed. Pretreatment with the synthetic sigma(1) agonist igmesine (0.1-1 mg/kg ip) or the neuroactive steroid dehydroepiandrosterone (DHEA 10-40 mg/kg ip) reversed the prenatal cocaine-induced learning deficits in offspring rats for each test. The sigma(1) antagonist BD1063 (1 mg/kg ip) failed to affect performances alone but blocked the igmesine and DHEA effects, confirming the involvement of the sigma(1) receptor. IUC exposure thus results in marked memory deficits, affecting spatial and nonspatial short- and long-term memories in juvenile male and female offspring rats. The activation of the sigma(1) neuromodulatory receptor allows a complete behavioral recovery of the memory functions in prenatally cocaine-exposed rats.

Cannabinoid effects on anxiety-related behaviours and hypothalamic neurotransmitters

The aim of the present study was to examine the effects of the cannabinoid agonist CP 55,940 and the antagonist SR 141716A, alone and in combination, on rat exploratory and anxiety-like behaviour in the holeboard and elevated plus-maze tests. A further aim was to evaluate the effects of these treatments on hypothalamic neurotransmitters. Animals treated with CP 55,940 doses of 0.125 and 0.1 mg/kg exhibited less exploration and an increase in anxiety-like behaviour accompanied by great motor inhibition. No hypoactivity was seen at 0.075 mg/kg dosage, but anxiety and neophobic responses persisted, indicating independent and specific effects. Motor activity effects induced by CP 55,940 were reversed by pretreatment with SR 141716A (3 mg/kg). Surprisingly, when administered on its own, the antagonist also induced a reduction in exploratory parameters and an increase in anxiety-like responses. These apparently similar effects might be caused by different neural mechanisms. Finally, CP 55,940 increased hypothalamic dopamine and serotonin levels. These increases might be involved in the activation of the hypothalamic-pituitary-adrenal axis described for cannabinoids.

Iboga compounds reverse the behavioural disinhibiting and corticosterone effects of acute methamphetamine: Implications for their antiaddictive properties

This study investigated the effects of pretreatment with the putative antiaddictive compound, ibogaine (IBO), and its synthetic derivative, 18-methoxycoronaridine (18-MC), on the changes in behaviour in an elevated plus maze and the changes in corticosterone (CORT) produced by a low dose of methamphetamine (METH). In the elevated plus maze, the acute administration of METH (0.1 mg/kg ip, -20 min) produced an increase in both the number and the duration of open arm entries relative to saline (SAL)-treated controls. No effect of METH administration was observed on the total number of arm entries. These data indicated that METH alone produced either anxiolysis or behavioural disinhibition in this paradigm. More consistent with the latter possibility, the open arm behaviour of METH controls was associated with an increase in plasma levels of CORT, supporting a facilitatory role for CORT in this METH-induced effect. Pretreatment with both IBO and 18-MC (40 mg/kg ip, 19 h earlier) antagonized the behavioural disinhibiting effects of acute METH without altering locomotor activity. In addition, both iboga agents antagonized the increase in CORT produced by METH. These data provide insight into yet another potential mechanism through which iboga compounds may exert their antiaddictive effects, a reversal of the behavioural disinhibiting properties of stimulant drugs. Furthermore, these data indicate that this reversal is related to effects of iboga compounds on the stimulation of neuroendocrine systems by stimulant drugs.

Neuroactive neurosteroids as endogenous effectors for the sigma1 (sigma1) receptor: pharmacological evidence and therapeutic opportunities

Neuroactive neurosteroids, including progesterone, allopregnanolone, pregnenolone and dehydroepiandrosterone, represent steroid hormones synthesized de novo in the brain and acting locally on nervous cells. Neurosteroids modulate several neurotransmitter systems such as gamma-aminobutyric acid type A (GABA(A)), N-methyl-D-aspartate (NMDA) and acetylcholine receptors. As physiologic consequences, they are involved in neuronal plasticity, learning and memory processes, aggression and epilepsy, and they modulate the responses to stress, anxiety and depression. The sigma1-receptor protein was recently purified and its cDNA was cloned in several species. The amino-acid sequences are structurally unrelated to known mammalian proteins, but shared homology with a fungal sterol C8-C7 isomerase. The sigma1-receptor ligands exert a potent neuromodulation on excitatory neurotransmitter systems, including the glutamate and cholinergic systems. Consequently, selective sigma1 agonists show neuroprotective properties and beneficial effects in memory processes, stress and depression. The evidence of a direct interaction between neurosteroids and sigma1 receptors was first suggested by the ability of several steroids to inhibit the binding of sigma1-receptor radioligands in vitro and in vivo. A crossed pharmacology between neurosteroids and sigma1-receptor ligands was described in several physiological tests and behavioral responses. This review will detail the recent evidence for a common mechanism of action between neurosteroids and sigma1-receptor ligands and focus on the potential therapeutic interests of such interaction in the physiopathology of learning and memory impairments, stress, depression and neuroprotection.

The attenuation of learning impairments induced after exposure to CO or trimethyltin in mice by sigma (sigma) receptor ligands involves both sigma1 and sigma2 sites

1. Sigma (sigma) receptor ligands were previously reported to alleviate learning and memory impairments on several pharmacological and pathological rodent models of amnesia. Such effect was demonstrated as involving the sigma1 subtype of sigma receptor. 2. In this study, we characterized the pharmacological effect mediated by sigma ligands on two lesional models of amnesia in mice: (1) the hypoxia-related learning and memory impairment model induced by repeated exposure to carbon monoxide (CO) gas; and (2) the intoxication with trimethyltin (1 mg kg(-1)). 3. The selective sigma1 ligand PRE-084 (1 mg kg(-1)) or the non-selective sigma1/sigma2 compounds DTG (0.1 mg kg(-1)), BD1008 (3 mg kg(-1)), and haloperidol (0.1 mg kg(-1)) reversed significantly the spontaneous alternation deficits observed 7 days after exposure to CO or 14 days after intoxication with trimethyltin. 4. The selective sigma1 receptor antagonist NE-100 (1 mg kg(-1)) was ineffective by itself, but blocked completely the PRE-084 effects, partially the DTG effects, and did not affect the effects induced by BD1008 or haloperidol. 5. A similar pharmacological profile was observed in the step-down type passive avoidance test performed 8 days after exposure to CO. 6. These results show that, in contrast to the previously reported amnesia models, the impairments induced after exposure to CO or intoxication with trimethyltin could be alleviated not only by sigma1 receptor agonists but also by sigma2 agonists. The particular pattern of neurodegeneration observed in these lesional models may explain these differences.

Comparison between the effects of sigma receptor ligand JO 1784 and neuropeptide Y on immune functions

Recent evidence suggests that sigma receptor ligands and neuropeptide Y may act through the same pathways to modulate centrally mediated immune function. The present study demonstrated that both the sigma receptor ligand igmesine: (+)-N-cyclopropylmethy-N-methyl-1, 4-diphenyl-1-yl-but-3-en-1-ylamine, hydrochloride (JO 1784) (10(-7) and 10(-5) M) and neuropeptide Y (10(-9) and 10(-7) M) in vitro significantly reduced neutrophil phagocytosis and decreased mitogen stimulated lymphocyte proliferation. By contrast, central administration of JO 1784 (0.5 and 5 microg/5 microl) significantly reduced the activity of neutrophil phagocytosis, but enhanced lymphocyte proliferation without changing the serum concentration of corticosterone. Neuropeptide Y (10(-9) and 10(-7) M), following intracerebroventricular infusion, also decreased the neutrophil response, but significantly raised the corticosterone concentration. These results indicate that different mechanisms (involving various neurotransmitters and their receptors, changes in the activity of the hypothalamic-pituitary-adrenal axis, or sigma receptor subtypes) may be involved in the central effects of JO 1784 and neuropeptide Y.