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Our previous study showed that the neurosteroid dehydroepiandrosterone sulfate (DHEAS) alters the rewarding effects of cocaine. Because DHEAS is metabolized to androsterone, which has opposite synaptic activity, we wondered about contribution of androsterone to the above phenomenon. Here we examined androsterone’s effect on the rewarding properties of cocaine in CPP test. Male Wistar rats (250–300 g) were used. The CPP procedure consisted of pre-conditioning, conditioning and post-conditioning phases. Drug injections were done i.p. Androsterone alone was rewarding at doses 1 mg/kg and 10 mg/kg, while the dose of 40mg/kg was visibly aversive. Cocaine had a biphasic dose-dependent rewarding effect (inverted U type): the doses 5 and 10 mg/kg were rewarding, while at dose 20 mg/kg, cocaine rewarding effect was lost. Pretreatment with 1mg/kg of androsterone increased the rewarding effect of all cocaine doses, especially the dose of 20 mg/kg, but the rewarding dose of 10 mg/ kg of androsterone had no effect on the rewarding prosperities of cocaine. All doses of cocaine decreased the aversive effect of 40 mg/kg of androsterone. Androsterone per se has a biphasic rewarding-aversive effects in the CPP test and infl uences the rewarding properties of cocaine, which might be explained by two mechanisms: potentiation of reward at low doses and reduction of the aversive effect of the high doses. Funded by EC grant MEXCCT-2006-42371 to M.D. Majewska.
Previous studies showed that high plasma levels of endogenous DHEAS correlated with resiliency and ability of cocaine addicts to maintain prolonged abstinence after the therapy (Wilkins et al. 2005), while addicts treated with high dose of exogenous DHEA used more cocaine that those administered placebo (Shoptaw et al. 2004). Such ambiguous outcomes could be due to mixed actions of DHEAS and its metabolite, androsterone, which have opposite neuronal activities. Here we examined acute effects of both neurosteroids in Porsolt test and their interactions with 5 mg/kg of cocaine – the dose reported to have antidepressive action, but which does not infl uence locomotor activity in the open fi eld. Wistar rats (250-300 g) were used. All substances were injected i.p.; steroids 30 min and cocaine 5 minutes before the test, which measures locomotor activity of rats in narrow water containers. Cocaine at dose 5 mg/kg signifi cantly increased rats’ locomotor activity in the Porsolt test. Neither DHEAS (1, 5, 10, 40, 80 mg/kg) nor androsterone (0,1, 1, 10, 40 mg/kg) per se had any effect on activity in this test. DHEAS dose-dependently potentiated the effect of cocaine, but androsterone had no infl uence on this cocaine action. Acutely administered DHEAS appears to increase antidepressive effects of cocaine, but androsterone has no such infl uence. Funded by EC grant MEXC-CT-2006-42371 to M.D. Majewska.
The neurosteroids, dehydroepiandrosterone sulfate (DHEAS) and androsterone, are implicated in drug addictions. We examined their influence on locomotor activity and reward in male Wistar rats, and on steroid and monoamine metabolism in the hippocampus and striatum. In the open field test, DHEAS injections (10, 40, 80 mg/kg, i.p.) 30 min prior the test had no significant effect on ambulation, but androsterone (10 mg/kg) increased general locomotion and at doses 1-10 mg/kg, increased central field activity, suggestive of an anxiolytic action. In the conditioned place preference test, both steroids had a biphasic effect: DHEAS was rewarding at doses of 10 and 40 mg/kg, but not at 80 mg/kg, while androsterone was rewarding at doses of 1 and 10 mg/kg, but aversive at 40 mg/kg. Monoamine and steroid concentrations were analyzed in homogenates from the hippocampus and striatum of DHEAS and androsterone injected rats. DHEAS reduced the hippocampal dopamine level, increased striatal homovanilic acid (HVA) and decreased the striatal serotonin concentrations. Androsterone did not affect dopamine levels or turnover, but increased noradrenaline concentration and serotonin turnover in the hippocampus. DHEAS administration augmented concentrations of DHEA, pregnenolone, androstendiol and androstentriol in both brain structures, while androsterone injections increased brain levels of androsterone, epiandrosterone, 5a-dihydrotestosterone, and androstandiol. Present data document that although psychobehavioral and neurochemical effects of DHEAS and androsterone differ in several aspects; both neurosteroids have rewarding properties at certain dose ranges, suggesting their likely involvement in addictions, which entail different mechanisms.
DHEAS is endogenous allosteric antagonists of the GABA(A) receptor and has other direct and indirect actions in CNS. It is metabolized to other neuroactive steroids. Prior studies revealed an ambiguous role of DHEA(S) in cocaine dependence, suggesting interactions with cocaine effects in the brain. This preclinical study was undertaken to evaluate direct infl uence of DHEAS on the rewarding effects of cocaine, using the CPP test in rats. Male Wistar rats (250–300 g) were used. The conditioned place preference experiment consisted of preconditioning conditioning and post-conditioning phases. Drug injections were done i.p. only during the conditioning phase. Cocaine had a biphasic dose-dependent rewarding effect (inverted U type). The doses 5 and 10 mg/kg were clearly rewarding, as they increased rats’ preference for cocaine injection site, while at the dose 20 mg/kg, cocaine rewarding effect was lost. DHEAS alone had a similar biphasic rewarding effect (the effect of 40 mg/kg was maximal and statistically signifi cant). Pretreatment of rats with 40 mg/kg of DHEAS before injection of cocaine noticeably changed its rewarding effect, shifting cocaine dose response curve to the left. DHEAS, per se has rewarding properties and it enhances the rewarding effects of low doses of cocaine, but decreases the rewarding effect of higher doses of cocaine. Funded by EC grant MEXC-CT-2006-42371 to M.D. Majewska.
It might seem obvious that pain sensitivity would predict individual, inborn susceptibilities to aversive stimuli and the strength of fear-conditioned responses. Such relationships are based on the assumption that there is a close association between fear-evoked behavioral reactions and the responses to painful, aversive stimuli. However, this problem has not been systematically studied. To this end, we investigated the relationship between pain sensitivity in two pain tests (the ‘tail-flick’ and ‘flinch-jump’ tests) and a conditioned, fear-evoked, freezing response in rats. The results show that there was no correlation between: (1) the conditioned (associative) and the novelty-evoked (non-specific stress-related) fear response and (2) individual differences in pain threshold and fear responses. Furthermore, factor analysis did not group freezing in the conditioned fear test, individual footshock sensibility, or ‘tail-flick’ reaction to painful stimuli together. These results indicate that pain sensitivity and conditioned emotional responses to pain are not directly correlated.
In the present study the effects of a protein synthesis inhibitor, cycloheximide (125 μg, i.c.v.), on the expression and reconsolidation of pentylenetetrazol-induced kindled seizures, were studied in rats. Cycloheximide given repeatedly (every second day) to fully kindled rats, immediately after 4 consecutive sessions of PTZ-seizures, did not modify the strength of subsequent fi ts of convulsions. On the other hand, the protein synthesis inhibitor signifi cantly attenuated the strength of convulsions when the drug was administered 1 h before the PTZ injection, every second day for 5 consecutive experimental sessions. However, when cycloheximide was omitted in a consecutive session, PTZ induced a fully developed fi t of tonicclonic convulsions, indicating that cycloheximide-induced changes in seizure intensity were transitory, not related to a stable modifi cation in the function of neuronal circuits responsible for kindling seizures. The present fi ndings suggest that the mechanisms underlying epileptogenesis are very resistant to modifi cation, and as such, are not the subject to permanent changes even under the infl uence of protein synthesis inhibition. One possible reason may be the depth and multiplicity of changes induced by seizures (i.e. alterations in enzymes, receptors, structural proteins, growth factors, etc.), that may cause permanent biochemical and morphological alterations in the brain that give rise to the kindled seizures.
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