Effects of Intrahippocampal Nicotine and Neurosteroid Administration on Withdrawal in Voluntary and Chronic Alcohol-Drinking Rats

Early post-natal neuroactive steroid manipulation modulates ondansetron effects on initial periods of alcohol consumption in rats

Neuroactive steroids (NS) such as allopregnanolone are crucial for brain development and adult behaviour. Early post-natal alterations of NS by administering finasteride induce a decrease in the sensitivity to stimulant effects of low alcohol doses, an increase in alcohol consumption, and a decrease in ventrostriatal dopamine and serotonin levels. The aim of the present study is to observe if the effects of the 5HT3 receptor antagonist ondansetron on initial alcohol consumption are modulated by post-natal NS manipulation. For this purpose, allopregnanolone, finasteride, or vehicle was injected from day 5 to 9. In adulthood, a novel object preference test was carried out in order to detect a possible novelty-seeking pattern in our animals, which has been related to vulnerability to drug abuse. The subjects then had access to two bottles (alcohol or control solutions) one hour daily for two consecutive weeks. Ondansetron (0.01 mg/kg, 0.1 mg/kg or vehicle) was administered before the hour of consumption in the initial phase (days 1, 2, 3) of the procedure, and after prolonged alcohol intake (days 11, 12, 13). Results indicated that finasteride animals showed a higher preference to explore the new object, as well as a higher alcohol consumption than the rest of the groups. Moreover, 0.1 mg/kg of ondansetron decreased alcohol consumption, but only in the post-natal finasteride group, suggesting a possible increase in 5HT3 receptor sensitivity in these animals. In conclusion, NS manipulation in crucial stages of development, such as early post-natal periods, seems to play an important role on the effects of ondansetron on alcohol intake and in the vulnerability to develop drug use or abuse.

Sex Differences in Animal Models: Focus on Addiction

The purpose of this review is to discuss ways to think about and study sex differences in preclinical animal models. We use the framework of addiction, in which animal models have excellent face and construct validity, to illustrate the importance of considering sex differences. There are four types of sex differences: qualitative, quantitative, population, and mechanistic. A better understanding of the ways males and females can differ will help scientists design experiments to characterize better the presence or absence of sex differences in new phenomena that they are investigating. We have outlined major quantitative, population, and mechanistic sex differences in the addiction domain using a heuristic framework of the three established stages of the addiction cycle: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation. Female rats, in general, acquire the self-administration of drugs and alcohol more rapidly, escalate their drug taking with extended access more rapidly, show more motivational withdrawal, and (where tested in animal models of "craving") show greater reinstatement. The one exception is that female rats show less motivational withdrawal to alcohol. The bases for these quantitative sex differences appear to be both organizational, in that estradiol-treated neonatal animals show the male phenotype, and activational, in that the female phenotype depends on the effects of gonadal hormones. In animals, differences within the estrous cycle can be observed but are relatively minor. Such hormonal effects seem to be most prevalent during the acquisition of drug taking and less influential once compulsive drug taking is established and are linked largely to progesterone and estradiol. This review emphasizes not only significant differences in the phenotypes of females and males in the domain of addiction but emphasizes the paucity of data to date in our understanding of those differences.

Toll-like Receptors in the Vascular System: Sensing the Dangers Within

Toll-like receptors (TLRs) are components of the innate immune system that respond to exogenous infectious ligands (pathogen-associated molecular patterns, PAMPs) and endogenous molecules that are released during host tissue injury/death (damage-associated molecular patterns, DAMPs). Interaction of TLRs with their ligands leads to activation of downstream signaling pathways that induce an immune response by producing inflammatory cytokines, type I interferons (IFN), and other inflammatory mediators. TLR activation affects vascular function and remodeling, and these molecular events prime antigen-specific adaptive immune responses. Despite the presence of TLRs in vascular cells, the exact mechanisms whereby TLR signaling affects the function of vascular tissues are largely unknown. Cardiovascular diseases are considered chronic inflammatory conditions, and accumulating data show that TLRs and the innate immune system play a determinant role in the initiation and development of cardiovascular diseases. This evidence unfolds a possibility that targeting TLRs and the innate immune system may be a novel therapeutic goal for these conditions. TLR inhibitors and agonists are already in clinical trials for inflammatory conditions such as asthma, cancer, and autoimmune diseases, but their study in the context of cardiovascular diseases is in its infancy. In this article, we review the current knowledge of TLR signaling in the cardiovascular system with an emphasis on atherosclerosis, hypertension, and cerebrovascular injury. Furthermore, we address the therapeutic potential of TLR as pharmacological targets in cardiovascular disease and consider intriguing research questions for future study.

Effects of neonatal allopregnanolone manipulations and early maternal separation on adult alcohol intake and monoamine levels in ventral striatum of male rats

Changes in endogenous neonatal levels of the neurosteroid allopregnanolone (AlloP) as well as a single 24h period of early maternal separation (EMS) on postnatal day (PND) 9 affect the development of the central nervous system (CNS), causing adolescent/adult alterations including systems and behavioural traits that could be related to vulnerability to drug abuse. In rats, some behavioural alterations caused by EMS can be neutralised by previous administration of AlloP. Thus, the aim of the present work is to analyse if manipulations of neonatal AlloP could increase adult alcohol consumption, and if EMS could change these effects. We administered AlloP or finasteride, a 5α-reductase inhibitor, from PND5 to PND9, followed by 24h of EMS at PND9. At PND70 we measured alcohol consumption using a two-bottle free-choice model (ethanol 10% (v/v)+glucose 3% (w/v), and glucose 3% (w/v)) for 15days. Ventral striatum samples were obtained to determine monoamine levels. Results revealed that neonatal finasteride increased both ethanol and glucose consumption, and AlloP increased alcohol intake compared with neonatal vehicle-injected animals. The differences between neonatal groups in alcohol consumption were not found in EMS animals. In accordance, both finasteride and AlloP animals that did not suffer EMS showed lower levels of dopamine and serotonin in ventral striatum. Taken together, these results reveal that neonatal neurosteroids alterations affect alcohol intake; an effect which can be modified by subsequent EMS. Thus, these data corroborate the importance of the relationship between neonatal neurosteroids and neonatal stress for the correct CNS development.

Neonatal finasteride administration decreases dopamine release in nucleus accumbens after alcohol and food presentation in adult male rats

Endogenous levels of the neurosteroid (NS) allopregnanolone (AlloP) during neonatal stages are crucial for the correct development of the central nervous system (CNS). In a recent work we reported that the neonatal administration of AlloP or finasteride (Finas), an inhibitor of the enzyme 5α-reductase needed for AlloP synthesis, altered the voluntary consumption of ethanol and the ventrostriatal dopamine (DA) levels in adulthood, suggesting that neonatal NS manipulations can increase alcohol abuse vulnerability in adulthood. Moreover, other authors have associated neonatal NS alterations with diverse dopaminergic (DAergic) alterations. Thus, the aim of the present work is to analyse if manipulations of neonatal AlloP alter the DAergic response in the nucleus accumbens (NAcc) during alcohol intake in rats. We administered AlloP or Finas from postnatal day (PND) 5 to PND9. At PND98, we measured alcohol consumption using a two-bottle free-choice model (ethanol 10% (v/v)+glucose 3% (w/v), and glucose 3% (w/v)) for 12 days. On the last day of consumption, we measured the DA and 3,4-dihydroxyphenylacetic acid (DOPAC) release in NAcc in response to ethanol intake. The samples were obtained by means of in vivo microdialysis in freely moving rats, and DA and DOPAC levels were determined by means of high-performance liquid chromatography analysis (HPLC). The results revealed that neonatal Finas increased ethanol consumption in some days of the consumption phase, and decreased the DA release in the NAcc in response to solutions (ethanol+glucose) and food presentation. Taken together, these results suggest that neonatal NS alterations can affect alcohol rewarding properties.

Sex and gender-related differences in alcohol use and its consequences: Contemporary knowledge and future research considerations

AIMS

To review the contemporary evidence reflecting male/female differences in alcohol use and its consequences along with the biological (sex-related) and psycho-socio-cultural (gender-related) factors associated with those differences.

METHODS

MEDLINE, PubMed, Web of Science, SCOPUS, PsycINFO, and CINAHL databases were searched for relevant publications, which were subsequently screened for the presence/absence of pre-specified criteria for high quality evidence.

RESULTS

Compared to men, more women are lifetime abstainers, drink less, and are less likely to engage in problem drinking, develop alcohol-related disorders or alcohol withdrawal symptoms. However, women drinking excessively develop more medical problems. Biological (sex-related) factors, including differences in alcohol pharmacokinetics as well as its effect on brain function and the levels of sex hormones may contribute to some of those differences. In addition, differences in alcohol effects on behavior may also be driven by psycho-socio-cultural (gender-related) factors. This is evident by variation in the magnitude of differences in alcohol use between countries, decreasing difference in the rates of alcohol consumption in recent generations and other findings. Evidence indicates that both sex and gender-related factors are interacting with alcohol use in complex manner, which differentially impacts the risk for development of the behavioral or medical problems and alcohol use disorders in men and women.

CONCLUSIONS

Discovery of the mechanisms underlying biological (sex-related) as well as psycho-socio-cultural (gender-related) differences in alcohol use and related disorders is needed for development of personalized recommendations for prevention and treatment of alcohol use disorders and related problems in men and women.

Neonatal allopregnanolone levels alteration: effects on behavior and role of the hippocampus

Several works have pointed out the importance of the neurosteroid allopregnanolone for the maturation of the central nervous system and for adult behavior. The alteration of neonatal allopregnanolone levels in the first weeks of life alters emotional adult behavior and sensory gating processes. Without ruling out brain structures, some of these behavioral alterations seem to be related to a different functioning of the hippocampus in adult age. We focus here on the different behavioral studies that have revealed the importance of neonatal allopregnanolone levels for the adult response to novel environmental stimuli, anxiety-related behaviors and processing of sensory inputs (prepulse inhibition). An increase in neonatal physiological allopregnanolone levels decreases anxiety and increases novelty responses in adult age, thus affecting the individual response to environmental cues. These effects are also accompanied by a decrease in prepulse inhibition, indicating alterations in sensory gating that have been related to that present in disorders, such as schizophrenia. Moreover, behavioral studies have shown that some of these effects are related to a different functioning of the dorsal hippocampus, as the behavioral effects (decrease in anxiety and locomotion or increase in prepulse inhibition) of intrahippocampal allopregnanolone infusions in adult age are not present in those subjects in whom neonatal allopregnanolone levels were altered. Recent data indicated that this hippocampal involvement may be related to alterations in the expression of gamma-aminobutyric-acid receptors containing α4 and δ subunits, molecular alterations that can persist into adult age and that can, in part, explain the reported behavioral disturbances.

K(Ca)2 channels: novel therapeutic targets for treating alcohol withdrawal and escalation of alcohol consumption

Small-conductance, calcium-activated potassium (K(Ca)2) channels influence neuronal firing properties, intrinsic excitability, and NMDA receptor-dependent synaptic responses and plasticity. In this mini-review, we discuss new evidence that chronic alcohol-associated plasticity critically involves K(Ca)2 channels in hippocampus, ventral tegmental area, and nucleus accumbens. K(Ca)2 channel activity can modulate the magnitude of excitation of midbrain dopamine neurons induced by acute alcohol exposure. Emerging evidence indicates that K(Ca)2 channels regulate neuroadaptations to chronic alcohol that contribute to withdrawal hyperexcitability and escalation of voluntary alcohol consumption. Restoring K(Ca)2 channel activity can attenuate the severity of the alcohol withdrawal syndrome in vivo and withdrawal-associated neurotoxicity in vitro. Pharmacological modulation of K(Ca)2 channels can bi-directionally influence drinking behavior in rat and mouse models of voluntary alcohol consumption. Collectively, these studies using various rodent models have clearly indicated a central role for K(Ca)2 channels in the neuroplasticity of chronic alcohol exposure. In addition, accumulating evidence suggests that K(Ca)2 channels are a novel therapeutic target to alleviate the symptoms of alcohol withdrawal and reduce high amounts of alcohol drinking.

Sex differences and ovarian hormones in animal models of drug dependence

Increasing evidence indicates the presence of sex differences in many aspects of drug abuse. Most studies reveal that females exceed males during the initiation, escalation, extinction, and reinstatement (relapse) of drug-seeking behavior, but males are more sensitive than females to the aversive effects of drugs such as drug withdrawal. Findings from human and animal research indicate that circulating levels of ovarian steroid hormones account for these sex differences. Estrogen (E) facilitates drug-seeking behavior, while progesterone (P) and its metabolite, allopregnanalone (ALLO), counteract the effects of E and reduce drug seeking. Estrogen and P influence other behaviors that are affiliated with drug abuse such as drug-induced locomotor sensitization and conditioned place preference. The enhanced vulnerability to drug seeking in females vs. males is also additive with the other risk factors for drug abuse (e.g., adolescence, sweet preference, novelty reactivity, and impulsivity). Finally, treatment studies using behavioral or pharmacological interventions, including P and ALLO, also indicate that females show greater treatment effectiveness during several phases of the addiction process. The neurobiological basis of sex differences in drug abuse appears to be genetic and involves the influence of ovarian hormones and their metabolites, the hypothalamic pituitary adrenal (HPA) axis, dopamine (DA), and gamma-hydroxy-butyric acid (GABA). Overall, sex and hormonal status along with other biological risk factors account for a continuum of addiction-prone and -resistant animal models that are valuable for studying drug abuse prevention and treatment strategies.

The role of progestins in the behavioral effects of cocaine and other drugs of abuse: human and animal research

This review summarizes findings from human and animal research investigating the influence of progesterone and its metabolites allopreganolone and pregnanolone (progestins) on the effects of cocaine and other drugs of abuse. Since a majority of these studies have used cocaine, this will be the primary focus; however, the influence of progestins on other drugs of abuse will also be discussed. Collectively, findings from these studies support a role for progestins in (1) attenuating the subjective and physiological effects of cocaine in humans, (2) blocking the reinforcing and other behavioral effects of cocaine in animal models of drug abuse, and (3) influencing behavioral responses to other drugs of abuse such as alcohol and nicotine in animals. Administration of several drugs of abuse in both human and nonhuman animals significantly increased progestin levels, and this is explained in terms of progestins acting as homeostatic regulators that decrease and normalize heightened stress and reward responses which lead to increased drug craving and relapse. The findings discussed here highlight the complexity of progestin-drug interactions, and they suggest a possible use for these agents in understanding the etiology of and developing treatments for drug abuse.

Effects of moderate chronic ethanol consumption on hippocampal nicotinic receptors and associative learning

A number of studies have reported that ethanol exposure induces changes in different brain systems. The hippocampus is a brain region that is very vulnerable to ethanol exposition, which functionally results in impairment of learning and memory processes reported in heavy drinkers. Hippocampal nicotinic receptors are involved in learning and memory. In this study, we determined the effects of ethanol on the main hippocampal subtypes of neural nicotinic receptors (alpha7 and alpha4beta2) in rats non-selected for alcohol consumption, in order to check for possible changes on these receptors that could be linked with alterations in learning acquisition. Binding assays were carried out with [3H]methyllycaconitine ([3H]MLA) to study the alpha7 and [3H]nicotine to study alpha4beta2 receptors. Auto-shaping, continuous ratio and extinction procedures were used as behavioral tests. The results show that moderate chronic ethanol consumption for 10 weeks produces: (a) a decrease of both hippocampal nicotinic receptor subtypes without alterations in affinity; (b) no differences in behavioral performance between control rats and ethanol-drinking rats in auto-shaping and continuous ratio; (c) an improvement of performance of extinction paradigm. These results indicate that chronic ethanol consumption, at moderate levels, induces changes in hippocampal nicotinic receptors but does not impair acquisition and performance of new associative learning and even improves some kind of paradigms. These results may have implications in the biochemical basis of interactions between alcohol and nicotine and the effects of these drugs on behavior.

Intrahippocampal allopregnanolone decreases voluntary chronic alcohol consumption in non-selected rats

We have recently shown that 0.2 microg of the neurosteroid allopregnanolone (AlloP) administered to the hippocampus induced an anxiolytic-like profile and also reduced alcohol withdrawal symptoms in voluntary and chronic alcohol-drinking rats. The aim of the present work was to study whether the administration of this dose of AlloP could affect alcohol consumption in non-selected rats that have been voluntarily ingesting high doses of alcohol for long periods of time in a limited access procedure. We used a free-choice drinking procedure that involved providing the rats with an alcoholic solution (10% ethanol) at an early age. Alcohol and control rats were assigned randomly to three groups that received an intrahippocampal (dorsal CA1) injection before the period of alcohol consumption after a long history of chronic alcohol intake. The injection groups were AlloP (0.2 microg, 1.26 microM), pregnenolone sulfate (PregS) (5 ng, 24 microM) or vehicle. Blood alcohol concentrations (BAC) were assessed before testing the effects of injections on alcohol consumption. Although AlloP did not eliminate alcohol ingestion, it significantly decreased alcohol consumption. The intrahippocampal administration of PregS, at the dose tested, did not effectively modify alcohol consumption levels. These results indicate that the positive modulation of hippocampal GABA(A) receptors induced by neurosteroids can be an important neurobiological target for reducing chronic alcohol consumption.

Sexual experience of male rats influences anxiety-like behavior and androgen levels

There is a wide body of literature to suggest that sexual experience may influence androgen secretion in various species, in turn, androgens may also influence anxiety. We hypothesized that sexual experience may alter anxiety behavior and secretion of endogenous androgens. Experiment 1: anxiety behavior of rats with a history of sexual experience was compared to that of sexually-inexperienced, naïve male rats. Sexually-experienced rats showed less anxiety-like behavior in the open field and elevated plus maze, and exhibited increased plasma and hippocampal testosterone (T) levels. Experiment 2: the effects of recent sexual experience on anxiety behavior of sexually-experienced male rats, sexually-responsive but inexperienced male rats, and sexually-unresponsive, inexperienced male rats exposed to a receptive female immediately prior to testing was examined. Recent sexual experience significantly decreased anxiety-like behavior in the open field, elevated plus maze, and the elevated zero maze tasks, and tended to decrease anxiety-like behavior in the light-dark task. Rats with recent sexual experience exhibited increased plasma and hippocampal T levels. Experiment 3: to examine the effect of recent sexual experience, anxiety behavior of rats with a history of sexual experience that received sexual experience with a stimulus female immediately prior to testing was compared to that of rats with a history of sexual experience that did not receive sexual experience immediately prior to behavioral testing. Experienced rats that were exposed to a female prior to testing showed decreased anxiety-like behavior in the open field, elevated plus maze, and light-dark transition tasks, and showed increased plasma and hypothalamic, T and 3alpha-diol, and increased hippocampal T. Thus, sexual experience is associated with lower levels of anxiety-like behavior and higher levels of androgen secretion.

Infusions of 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) to the ventral tegmental area, but not the substantia nigra, enhance exploratory, anti-anxiety, social and sexual behaviours and concomitantly increase 3alpha,5alpha-THP concentrations in the hippocampus, diencephalon and cortex of ovariectomised oestrogen-primed rats

Sequential actions of 17beta-oestradiol (E2) and progesterone (P4) in the ventromedial hypothalamus (VMH) and ventral tegmental area (VTA) mediate sexual behaviour of female rodents. In the presence of appropriate environmental stimuli, E2 and P4 can facilitate initiation of sex behaviour (i.e. lordosis), in part through classic actions at intracellular progestin receptors in the VMH. However, the effects of P4 in the VTA to modulate lordosis involve its metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), which can have paracrine effects in the brain to reduce anxiety and stress. We investigated the effects of 3alpha,5alpha-THP infusions to the VTA, and a control site, the substantia nigra (SN), on exploratory, anti-anxiety, social and sexual behaviours (socio-sexual behaviours) and hormone levels in the midbrain and other regions (hippocampus, diencephalon and cortex) that may mediate these functions. Ovariectomised, rats were E2-primed (10 microg, s.c.) at 0 h and were infused with beta-cyclodextrin vehicle or 3alpha,5alpha-THP to the VTA or SN 44-48 h later. Ten minutes after infusions, rats were tested in the open field, plus maze, partner preference, social interaction and paced mating tasks, or served as nontested controls. Infusions of 3alpha,5alpha-THP to the VTA, but not the SN, increased central entries in the open field, open arm time in the plus maze, time spent in proximity to a male, duration of social interaction, incidence and intensity of lordosis, pacing, proceptivity, and anti-conflict behaviour. 3Alpha,5alpha-THP, but not vehicle, infusions to the VTA (but not the SN) also increased 3alpha,5alpha-THP levels in the midbrain, as well as the hippocampus, diencephalon and cortex. Behavioural testing increased levels of the precursor of 3alpha,5alpha-THP precursor, dihydroprogesterone (DHP). Thus, infusions of 3alpha,5alpha-THP to the VTA enhance socio-sexual behaviours and increase 3alpha,5alpha-THP levels in the hippocampus, diencephalon and cortex, and behavioural testing increases DHP levels in brain areas involved in modulating socio-sexual behaviours.