Dopamine release in the nucleus accumbens during sexual behavior in prenatally stressed adult male rats

Prenatal restraint stress downregulates the hypothalamic kisspeptidergic system transcripts genes, reduces the estrogen plasma levels, delayed the onset of puberty, and reduced the sexual behavior intensity in female rats

AIMS

This study investigated the possible relationships between the expression of the Kiss1 and Gpr54 gene expressions and the pituitary-gonadal hormones with the female onset of puberty and sexual behavior. The Kiss1 and Gpr54 gene expressions were examined because they are critical to controlling the hypothalamic activation of GnRH neurons and, in turn, the pituitary-gonadal hormones related to the early onset of puberty and sexual behavior. Further, it was evaluated that the pituitary and gonadal hormones involved in the vaginal opening and the expression of sexual behavior.

METHODS

Pregnant rats exposed to PRS from gestation days 17 to 20 were evaluated for maternal and open-field behaviors. The maternal behavior was analyzed because it may alter brain sexual organization affecting the pups development. It was observed in female pups the physical and development and, in adult age, the open-field behavior, the anxiety-like behavior, the estrous cycle, the sexual behavior, the serum FSH, LH, estrogen, progesterone, and testosterone levels, and the gene expression of kisspeptin protein (Kiss1) and Gpr54 in the hypothalamus.

RESULTS

the maternal and open-field behaviors were unaffected. In the F1 generation, PRS reduced weight at weaning, delayed the day of the vaginal opening and reduced the intensity of lordosis, the estrogen levels, and the Kiss1 and Gpr54 gene expression. These effects were attributed to hypothalamic kisspeptidergic system downregulation of transcripts genes and the reduced estrogen levels affected by the PRS.

Responses and functions of dopamine in nucleus accumbens core during social behaviors

Social behaviors are among the most important motivated behaviors. How dopamine (DA), a "reward" signal, releases during social behaviors has been a topic of interest for decades. Here, we use a genetically encoded DA sensor, GRABDA2m, to record DA activity in the nucleus accumbens (NAc) core during various social behaviors in male and female mice. We find that DA releases during approach, investigation and consummation phases of social behaviors signal animals' motivation, familiarity of the social target, and valence of the experience, respectively. Positive and negative social experiences evoke opposite DA patterns. Furthermore, DA releases during mating and fighting are sexually dimorphic with a higher level in males than in females. At the functional level, increasing DA in NAc enhances social interest toward a familiar conspecific and alleviates defeat-induced social avoidance. Altogether, our results reveal complex information encoded by NAc DA activity during social behaviors and their multistage functional roles.

Neural circuits of social behaviors: Innate yet flexible

Social behaviors, such as mating, fighting, and parenting, are fundamental for survival of any vertebrate species. All members of a species express social behaviors in a stereotypical and species-specific way without training because of developmentally hardwired neural circuits dedicated to these behaviors. Despite being innate, social behaviors are flexible. The readiness to interact with a social target or engage in specific social acts can vary widely based on reproductive state, social experience, and many other internal and external factors. Such high flexibility gives vertebrates the ability to release the relevant behavior at the right moment and toward the right target. This maximizes reproductive success while minimizing the cost and risk associated with behavioral expression. Decades of research have revealed the basic neural circuits underlying each innate social behavior. The neural mechanisms that support behavioral plasticity have also started to emerge. Here we provide an overview of these social behaviors and their underlying neural circuits and then discuss in detail recent findings regarding the neural processes that support the flexibility of innate social behaviors.

Stroke and sexual dysfunction - a narrative review

Sexual function is an essential part of quality of life in adults. However, sexual dysfunction (SD) in stroke survivors is a common but under-recognized complication after stroke. It is frequently neglected by patients and clinicians. The etiology of post-stroke SD, which is multifactorial includes anatomical, physical and psychological factors. Complete return of sexual function is an important target for functional recovery after stroke, so clinicians need to be aware of this issue and take a lead role in addressing this challenge in stroke survivors. Accurate diagnosis and prompt treatment of post-stroke SD should be routinely incorporated into comprehensive stroke rehabilitation. This narrative review article, outlines the anatomy and physiology of sexual function, discusses various factors contributing to post-stroke SD, and proposes directions for future research.

Environmental and genetic contributors to salivary testosterone levels in infants

Transient activation of the hypothalamic-pituitary-gonadal axis in early infancy plays an important role in male genital development and sexual differentiation of the brain, but factors contributing to individual variation in testosterone levels during this period are poorly understood. We measured salivary testosterone levels in 222 infants (119 males, 103 females, 108 singletons, 114 twins) between 2.70 and 4.80 months of age. We tested 16 major demographic and medical history variables for effects on inter-individual variation in salivary testosterone. Using the subset of twins, we estimated genetic and environmental contributions to salivary testosterone levels. Finally, we tested single nucleotide polymorphisms (SNPs) within ±5 kb of genes involved in testosterone synthesis, transport, signaling, and metabolism for associations with salivary testosterone using univariate tests and random forest (RF) analysis. We report an association between 5 min APGAR scores and salivary testosterone levels in males. Twin modeling indicated that individual variability in testosterone levels was primarily explained by environmental factors. Regarding genetic variation, univariate tests did not reveal any variants significantly associated with salivary testosterone after adjusting for false discovery rate. The top hit in males was rs10923844, an SNP of unknown function located downstream of HSD3B1 and HSD3B2. The top hits in females were two SNPs located upstream of ESR1 (rs3407085 and rs2295190). RF analysis, which reflects joint and conditional effects of multiple variants, indicated that genes involved in regulation of reproductive function, particularly LHCGR, are related to salivary testosterone levels in male infants, as are genes involved in cholesterol production, transport, and removal, while genes involved in estrogen signaling are related to salivary testosterone levels in female infants.

Mixing pleasures: review of the effects of drugs on sex behavior in humans and animal models

Drugs of abuse act on the brain circuits mediating motivation and reward associated with natural behaviors. There is ample evidence that drugs of abuse impact male and female sexual behavior. First, the current review discusses the effect of drugs of abuse on sexual motivation and performance in male and female humans. In particular, we discuss the effects of commonly abused drugs including psychostimulants, opiates, marijuana/THC, and alcohol. In general, drug use affects sexual motivation, arousal, and performance and is commonly associated with increased sexual risk behaviors. Second, studies on effects of systemic administration of drugs of abuse on sexual behavior in animals are reviewed. These studies analyze the effects on sexual performance and motivation but do not investigate the effects of drugs on risk-taking behavior, creating a disconnect between human and animal studies. For this reason, we discuss two studies that focus on the effects of alcohol and methamphetamine on inhibition of maladaptive sex-seeking behaviors in rodents. Third, this review discusses potential brain areas where drugs of abuse may be exerting their effect on sexual behavior with a focus on the mesolimbic system as the site of action. Finally, we discuss recent studies that have brought to light that sexual experience in turn can affect drug responsiveness, including a sensitized locomotor response to amphetamine in female and male rodents as well as enhanced drug reward in male rats.

Developmental exposure to corticosterone: behavioral changes and differential effects on leukemia inhibitory factor (LIF) and corticotropin-releasing hormone (CRH) gene expression in the mouse

RATIONALE

Cytokines are found in both the peripheral and central nervous system. There has been increasing interest in their potential role in some of the behavioral features of depressive disorders. Leukemia inhibitory factor (LIF), a proinflammatory cytokine, produces stimulation of adrenocorticotropic hormone (ACTH) secretion in response to emotional and inflammatory stress and recently has been linked to depressive-type behavior. Both the hypothalamic-pituitary-adrenal axis and the immune system, including cytokine-mediated responses, appear to be susceptible to long-term programming during fetal and neonatal development.

OBJECTIVE

The present study was designed to characterize the effects of perinatal exposure to corticostereone on behavior, hypothalamic LIF and corticotropin-releasing hormone (CRH) mRNA expression, and basal plasma corticosterone levels in adult female mice.

METHODS

Corticosterone was added to the drinking water beginning the last week of gestation and continued until weaning. Behavior in the open field and forced swim tests, baseline plasma corticosterone levels, and hypothalamic LIF and CRH gene expression were evaluated in the adult offspring.

RESULTS

Mice exposed to perinatal corticosterone showed increased immobility in the forced swim test and increased locomotor activity in the open field test. Although there were no differences between treatment groups in terms of basal plasma levels of corticosterone or hypothalamic CRH mRNA, LIF mRNA expression was increased in the hypothalamus.

CONCLUSIONS

These results show that perinatal exposure to glucocorticoids can produce long-term behavioral changes and upregulation of central LIF mRNA expression.

Monoamine levels in the nucleus accumbens correlate with male sexual behavior in middle-aged rats

The correlation between monoamine levels in the nucleus accumbens (NAcc) and male sexual behavior was studied in middle-aged rats. Male rats (18-19months) were assigned to three groups: (1) Group MIE consisted of rats showing mounts, intromissions, and ejaculations; (2) Group MI was composed of rats showing mounts and intromissions, but no ejaculation; and (3) Group NC were non-copulators showing no sexual behavior. Young adult rats (4-5months), displaying complete copulatory behavior, were used as the control group. Levels of dopamine (DA), serotonin, and norepinephrine and their metabolites in the NAcc were measured by high-pressure liquid chromatography with electrochemical detection. No difference was seen in DA levels between MIE rats and young controls, whereas DA levels in NC rats were significantly lower than those in both MIE and MI rats. Serotonin levels in NC rats were significantly higher than those in MIE and MI rats. Conversely, norepinephrine levels in NC rats were lower than those in MIE rats. These results suggest that monoamine levels in the NAcc correlate with sexual performance in male rats and that changes in NAcc monoamine levels might affect male sexual behavior in middle-aged rats.

Sexual motivation is demasculinized, but not feminized, in prenatally stressed male rats

Sexual motivation and copulation in male rats are associated with dopamine release in the nucleus accumbens. Demasculinized copulatory behavior has been demonstrated in prenatally stressed adult male rats. We have previously reported that approximately 80% of prenatally stressed male rats do not exhibit copulation and that no significant changes in nucleus accumbens dopamine release are seen during exposure to estrous females. In the present study, we investigated whether prenatal stress affects sexual motivation in these animals as adults. Pregnant Wistar rats were subjected to immobilization stress for two hours daily from day 15-19 of gestation. The prenatally stressed male offspring at the age of 3 months were allowed contact with receptive female rats for a 30 min period per week for 10 weeks; then, between the age of 5 and 6 months, their sexual motivation and copulatory activity were measured. Sexual motivation was measured in terms of sexual partner preference. The number of visits and the duration of each visit to an estrous female (stimulus female) or to a sexually active male rat (stimulus male) were recorded. Compared with control males, prenatally stressed male rats showed a significantly lower number of visits and a shorter duration of each visit to stimulus females. Prenatally stressed males showed no preference for male or female stimulus rats in terms of the number of visits and the duration of each visit, whereas control rats showed a significantly higher number of visits and duration of visits to female stimulus rats than male stimulus rats. A significant decrease in copulatory activity was observed in the prenatally stressed male offspring compared with control male rats, with most of the prenatally stressed males failing to show copulation. In vivo microdialysis experiments were performed on the nucleus accumbens with concurrent observation of sexual behavior. The prenatally stressed rats that did not exhibit copulation showed no significant changes in nucleus accumbens dopamine release during exposure to a stimulus male behind a wire-mesh barrier and the amount of dopamine release remained at the basal levels during actual physical contact. These results, combined with those of our previous report, indicate that sexual motivation in prenatally stressed male rats is demasculinized, but not feminized.

Prenatal treatment with picrotoxin promotes heterotypical sexual behavioral and neurochemical changes in male rat offspring

The effects of maternal prenatal exposure to picrotoxin (0.75 mg/kg S.C. days 16-19 of pregnancy) in male rat offspring were observed. Adult sexually experienced and inexperienced animals were evaluated for heterotypical sexual behavior, as well as the testosterone plasma levels and striatal neurotransmitters. In relation to sexual behavior and analysis of sexual organs, the results showed that animals treated with picrotoxin exhibited a more intense reproductive behavior, and this could be expressed by a significant decrease in the number of mounts and intromissions and increase in the numbers of ejaculation, showed that these males are most motivate for sexual behavior. Testosterone levels as well as weight for sexual organs did not differ from control group. The neurochemical analysis showed that picrotoxin did not alter DA, 5-HT, 5-HIAA and GABA in animals. The DOPAC/DA and HVA/DA relation showed that the treatment increased the DA system activity in animals sexually experienced, as well as promote a decrease in 5-HT/5-HIAA relation, that is known was an inhibitory neurotransmitter system, blockade a male sexual behavior. There are no alterations observed in GABA levels. It's could be explained by suggests that picrotoxin modification DA system activity through GABAergic system, permitting that DA system to be freely active and facilitate the heterotypical behavior of male rats. These results show that the maternal prenatal exposure to picrotoxin produced changes in the neurochemical and sexual behavior of the adult male rats. Also previous heterotypical experience leads to changes in biogenic amine concentrations in these animals.

Could neonatal testosterone replacement prevent alterations induced by prenatal stress in male rats?

The present study was designed to examine whether testosterone replacement is able to prevent some effects of maternal restraint stress--during the period of brain sexual differentiation--on endocrine system and sexual behavior in male rat descendants. Pregnant rats were exposed to restraint stress for 1 h/day from gestational days 18 to 22. At birth, some male pups from these stressed rats received testosterone propionate. The neonatal testosterone replacement was able to prevent the reduction in anogenital distance at 22 days of age observed in pups from stressed pregnant rats as well as prevents the decrease in testosterone levels during the adulthood of these animals. Testosterone replacement in these males also presented an improvement in sexual performance. In this way, testosterone replacement probably through increasing neonatal level of this hormone was able to prevent the later alterations caused by the prenatal stress during the period of brain sexual differentiation.

Sexual behavior, neuroendocrine, and neurochemical aspects in male rats exposed prenatally to stress

The present study was designed to examine some short- and long-term effects of maternal restraint stress--during the period of sexual brain differentiation--on reproductive and endocrine systems, sexual behavior, and brain neurotransmitters in male rat descendants. Pregnant rats were exposed to restraint stress for 1 h/day from gestational days (GDs) 18 to 22. Prenatal stress did not influence the wet weight of sexual organs and the quantity of germ cells in adult male pups; however, these animals showed reduced testosterone levels, delayed latency to the first mount and first intromission, and also decreased number of ejaculations. Additionally, there was an increase in the dopamine and serotonin levels in the striatum. Our results indicate that prenatal stress had a long-term effect on neurotransmitter levels and sexual behavior. In this sense, reproductive problems caused by injuries during the fetal period can compromise the later success of mating as well as the capacity to generate descendants.

Has dopamine a physiological role in the control of sexual behavior? A critical review of the evidence

The role of dopaminergic systems in the control of sexual behavior has been a subject of study for at least 40 years. Not surprisingly, reviews of the area have been published at variable intervals. However, the earlier reviews have been summaries of published research rather than a critical analysis of it. They have focused upon the conclusions presented in the original research papers rather than on evaluating the reliability and functional significance of the data reported to support these conclusions. During the last few years, important new knowledge concerning dopaminergic systems and their behavioral functions as well as the possible role of these systems in sexual behavior has been obtained. For the first time, it is now possible to integrate the data obtained in studies of sexual behavior into the wider context of general dopaminergic functions. To make this possible, we first present an analysis of the nature and organization of sexual behavior followed by a summary of current knowledge about the brain structures of crucial importance for this behavior. We then proceed with a description of the dopaminergic systems within or projecting to these structures. Whenever possible, we also try to include data on the electrophysiological actions of dopamine. Thereafter, we proceed with analyses of pharmacological data and release studies, both in males and in females. Consistently throughout this discussion, we make an effort to distinguish pharmacological effects on sexual behavior from a possible physiological role of dopamine. By pharmacological effects, we mean here drug-induced alterations in behavior that are not the result of the normal actions of synaptically released dopamine in the untreated animal. The conclusion of this endeavor is that pharmacological effects of dopaminergic drugs are variable in both males and females, independently of whether the drugs are administered systemically or intracerebrally. We conclude that the pharmacological data basically reinforce the notion that dopamine is important for motor functions and general arousal. These actions could, in fact, explain most of the effects seen on sexual behavior. Studies of dopamine release, in both males and females, have focused on the nucleus accumbens, a structure with at most a marginal importance for sexual behavior. Since accumbens dopamine release is associated with all kinds of events, aversive as well as appetitive, it can have no specific effect on sexual behavior but promotes arousal and activation of non-specific motor patterns. Preoptic and paraventricular nucleus release of dopamine may have some relationship to mechanisms of ejaculation or to the neuroendocrine consequences of sexual activity or they can be related to other autonomic processes associated with copulation. There is no compelling indication in existing experimental data that dopamine is of any particular importance for sexual motivation. There is experimental evidence showing that it is of no importance for sexual reward.

Effects of Ipomoea carnea aqueous fraction intake by dams during pregnancy on the physical and neurobehavioral development of rat offspring

The effects of daily prenatal exposure to 0.0, 0.7, 3.0 and 15.0 mg/kg of the aqueous extract (AQE) of Ipomoea carnea dried leaves on gestational days 5-21 were studied in rat pups and adult offspring. The physical and reflex developmental parameters, open-field, plus-maze, social interaction, forced swimming, catalepsy and stereotyped behaviors, as well as striatal, cortical and hypothalamic monoamine levels (at 140 days of age) were measured. Maternal and offspring body weights were unaffected by exposure to the different doses of the AQE. High postnatal mortality, smaller size at Day 1 of life, reversible hyperflexion of the carpal joints and delay in the opening of both ears and in negative geotaxis were observed in the offspring exposed to the higher dose of AQE. At 60 and 90 days of age, open-field locomotion frequency was quite different between 0.0 and animals treated with 0.7 and 3.0 mg/kg AQE. No changes were observed in the plus-maze, social interaction, forced swimming, catalepsy, stereotyped behavior and central nervous system monoamines concentrations. Dams treated with the higher AQE dose showed severe cytoplasmic vacuolation in liver, kidney, pancreas and thyroid tissues, in contrast to the mild vacuolation observed in the other experimental groups. No alterations were observed in the histopathological study of the offspring of all experimental groups at 140 days of age. During adulthood, behavior was not modified in offspring exposed to the higher dose of AQE as well as no changes occurred in central nervous system neurotransmitters. The present data show that the offspring development alterations were not severe enough to produce behavioral and central monoamine level changes.

Acquisition of an appetitive behavior prevents development of stress-induced neurochemical modifications in rat nucleus accumbens

In rats, exposure to chronic unavoidable stress produces a decrease in dopamine output in the nucleus accumbens shell that is accompanied by a decreased density of the dopamine transporter and an increased activity of the dopamine-D(1) receptor complex. These modifications have been hypothesized to be adaptive to decreased dopamine output in stressed rats. We investigated whether the learning of an appetitive behavior sustained by palatable food, which is associated with increased dopamine output in the nucleus accumbens shell as measured by microdialysis experiments, would affect the modifications induced by chronic stress exposure on dopamine transporter density and dopamine-D(1) receptor complex activity in the nucleus accumbens. Rats exposed to chronic unavoidable stress after acquisition of the appetitive behavior showed a higher dopamine extraneuronal release in the nucleus accumbens shell than that of stressed animals, and similar to that of control rats. Moreover, previous acquisition of the appetitive behavior prevented development of a stress-induced decrease in dopamine transporter density, measured by [(3)H]-WIN 35428 binding, a stress-induced increase in dopamine-D(1) receptor density, measured by binding of [(3)H]-SCH 23390, and SKF 38393-stimulated adenylyl cyclase activity in the nucleus accumbens. These results support the hypothesis that changes induced in pre- and postsynaptic dopaminergic transmission by chronic stress exposure are related to decreased dopamine output.

Effects of prenatal exposure to deltamethrin on forced swimming behavior, motor activity, and striatal dopamine levels in male and female rats

The effects of prenatal exposure of rat pups to 0.08 mg/kg deltamethrin (DTM) on physical, reflex and behavioral developmental parameters, on forced swimming and open-field behaviors, and on striatal monoamine levels at 60 days of age were observed. Maternal and offspring body weight, physical and reflex development were unaffected by the exposure to the pesticide. At 21 days of age, open-field locomotion frequency and immobility duration of male and female offspring were not different between control and exposed animals. However, male rearing frequency was increased in experimental animals. A decreased immobility latency to float and in general activity after the swimming test in male offspring was observed at adult age; no interference was detected in the float duration during the swimming test. In addition, these animals presented higher striatal 3,4-dihydroxyphenylacetic acid (DOPAC) levels without modification in dopamine (DA) levels and an increased DOPAC/DA ratio. These data indicate a higher activity of the dopaminergic system in these animals. Noradrenaline (NA) levels were increased, while MHPG levels were not detectable in the system studied. Serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) levels, as well as the homovanillic acid (HVA)/DA ratio, were not modified by the exposure to the pesticide. No changes were observed in swimming and open-field behaviors nor were there any changes in striatal monoamines or their metabolites in the female experimental group. In relation to the pesticide formula, the present data showing that prenatal exposure to DTM alters latency to float and the activity of striatal dopaminergic system might reflect a persistent effect of the pesticide on animal motor activity, mainly in males. On the other hand, the decrease in general activity observed in experimental male rats suggests higher levels of emotionality induced by previous exposure to the swimming behavior test in relation to control animals. Data gathered in the present study may be important for the assessment of the safety of pyrethroid insecticides.

Nicotine-induced locomotor activity is increased by preexposure of rats to prenatal stress

Genetic factors are believed to play a predominant role in the individual differences observed in behavioral and pharmacological responses to drugs of abuse. An increasing literature indicates, however, that epigenetic factors can be involved as well. In this report we examined whether developmental changes induced by prenatal stress could alter the way animals respond to the psychostimulant effect of nicotine when adults. The results show that nicotine induces a dose-dependent increase of locomotor activity in both groups, and that prenatally-stressed animals exhibit a higher behavioral response at all doses. This study emphasizes the importance of early environment in the later development of drug-related behavior.

The role of stress in the pathophysiology of the dopaminergic system

In this review, we will examine the most recent preclinical evidence in support of the fact that both acute and chronic stress may have a detrimental impact on the normal function of the dopaminergic system. In recent decades, the term stress has changed its meaning from that of a 'non-specific body response' to a 'monitoring system of internal and external cues'; that is a modality of reaction of the mammalian central nervous system (CNS) which is critical to the adaptation of the organism to its environment. Compelling results have demonstrated that the dopaminergic system is important not only for hedonic impact or reward learning but also, in a broader sense, for reactivity to perturbation in environmental conditions, for selective information processing, and for general emotional responses, which are essential functions in the ability (or failure) to cope with the external world. In this, stress directly influences several basic behaviors which are mediated by the dopaminergic system such as locomotor activity, sexual activity, appetite, and cross sensitization with drugs of abuse. Studies using rat lines which are genetically different in dopamine (DA) physiology, have shown that even small alterations in the birth procedure or early life stress events may contribute to the pathophysiology of psychiatric disorders-in particular those involving central DA dysfunction-and may cause depression or psychotic derangement in the offspring. Finally, the fact that the dopaminergic system after stress responds, preferentially, in the medial prefrontal cortex (MFC), is thought to serve, in humans, as a protection against positive psychotic symptoms, since the increased DA activity in the MFC suppresses limbic DA transmission. However, excessive MFC dopaminergic activity has a negative impact on the cognitive functions of primates, making them unable to select and process significant environmental stimuli. Thus it appears that a critical range of DA turnover is necessary for optimal cognitive functioning after stress, in the response of the CNS to ever-changing environmental demands. Molecular Psychiatry (2000) 5, 14-21.

Sexual experience sensitizes mating-related nucleus accumbens dopamine responses of female Syrian hamsters

We examined the effects of prior sexual experience on extracellular concentrations of dopamine in the nucleus accumbens of female hamsters. Nucleus accumbens dopamine was measured by in vivo microdialysis during mating in female Syrian hamsters that had previously been given six prior sexual encounters with a male, three prior encounters, or were sexually naive. High levels of sexual behavior were observed in all three groups, which were accompanied by increases in dialysate dopamine during periods when the male was present. However, females that received six prior sexual encounters had significantly elevated and prolonged increases in dialysate dopamine compared with those of the sexually naive females or females with only three prior sexual encounters with a male. The data indicate that the mesolimbic system can be sensitized by repeated experiences associated with a motivated behavior.

Facilitation of sexual behavior and enhanced dopamine efflux in the nucleus accumbens of male rats after D-amphetamine-induced behavioral sensitization

Behavioral sensitization caused by repeated and intermittent administration of psychostimulants, such as cocaine and D-amphetamine, is accompanied by enhanced function in limbic-motor circuitry that is involved in the generation of motivated behavior. The present microdialysis study investigated the effect of D-amphetamine-induced sensitization on dopamine (DA) efflux in the nucleus accumbens (NAC) of male rats during sexual behavior. Male rats were given one injection of D-amphetamine (1.5 mg/kg, i.p.) or saline every other day for a total of 10 injections. Three weeks after discontinuation of drug treatment, rats were tested for sexual behavior during a test in which microdialysis was performed. There was an augmented efflux of DA in the NAC of D-amphetamine-sensitized rats compared with nonsensitized control rats when a receptive female was present behind a screen (35 vs 17%). Sensitized rats exhibited facilitated sexual behavior when the screen was removed, as indicated by a significantly shorter latency to mount and an overall increase in the amount of copulatory behavior. Although there was a significant increase in NAC DA concentrations from baseline in both sensitized and nonsensitized rats during copulation, there was a greater increase in DA efflux in the NAC of sensitized rats during the first 10 min copulatory sample (60 vs 37%). These results demonstrate that behavioral sensitization caused by repeated psychostimulant administration can "cross-sensitize" to a natural behavior, such as sex, and that increased NAC DA release may contribute to the facilitation of appetitive and consummatory aspects of this behavior.

Brain N-acetyl aspartate concentrations measured by H MRS are reduced in adult male rats subjected to perinatal stress: preliminary observations and hypothetical implications for neurodevelopmental disorders

The present study was undertaken to determine if the concentration of brain N-acetyl-aspartate (NAA), a putative neuronal marker, is reduced in adult rats subjected to stress during the perinatal period. As the prenatal stressor, pregnant rats were subjected to restraint stress for one hour twice daily from days 14-21 of gestation; stressed offspring were reared by normal dams and studied as adults. As the postnatal stressor, normal pups were reared by prenatally 'stressed' dams and studied as adults. As compared to non-stressed controls (n=6), NAA concentrations were significantly reduced 21 and 25% in left frontal cortex from the prenatal (n=4) and postnatal (n=6) stress groups. respectively. The data suggest that in perinatally stressed adult offspring permanent neuronal damage or loss has occurred. While no direct causal associations between perinatal stress and the developmental of particular disorders can be inferred from these limited data, the effects of perinatal stress on subsequent brain neuropathology are reviewed. particularly in relation to NAA. For hypothesis-generating purposes, the possible relevance of stress and NAA to the neurodevelopmental hypothesis of schizophrenia is discussed in greater detail.

What is the role of dopamine in reward: hedonic impact, reward learning, or incentive salience?

What roles do mesolimbic and neostriatal dopamine systems play in reward? Do they mediate the hedonic impact of rewarding stimuli? Do they mediate hedonic reward learning and associative prediction? Our review of the literature, together with results of a new study of residual reward capacity after dopamine depletion, indicates the answer to both questions is 'no'. Rather, dopamine systems may mediate the incentive salience of rewards, modulating their motivational value in a manner separable from hedonia and reward learning. In a study of the consequences of dopamine loss, rats were depleted of dopamine in the nucleus accumbens and neostriatum by up to 99% using 6-hydroxydopamine. In a series of experiments, we applied the 'taste reactivity' measure of affective reactions (gapes, etc.) to assess the capacity of dopamine-depleted rats for: 1) normal affect (hedonic and aversive reactions), 2) modulation of hedonic affect by associative learning (taste aversion conditioning), and 3) hedonic enhancement of affect by non-dopaminergic pharmacological manipulation of palatability (benzodiazepine administration). We found normal hedonic reaction patterns to sucrose vs. quinine, normal learning of new hedonic stimulus values (a change in palatability based on predictive relations), and normal pharmacological hedonic enhancement of palatability. We discuss these results in the context of hypotheses and data concerning the role of dopamine in reward. We review neurochemical, electrophysiological, and other behavioral evidence. We conclude that dopamine systems are not needed either to mediate the hedonic pleasure of reinforcers or to mediate predictive associations involved in hedonic reward learning. We conclude instead that dopamine may be more important to incentive salience attributions to the neural representations of reward-related stimuli. Incentive salience, we suggest, is a distinct component of motivation and reward. In other words, dopamine systems are necessary for 'wanting' incentives, but not for 'liking' them or for learning new 'likes' and 'dislikes'.

Perinatal treatment with picrotoxin induces sexual, behavioral, and neuroendocrine changes in male rats

The effects of maternal exposure to picrotoxin (PT) during the prenatal and postnatal periods of sexual brain differentiation were studied. Behavioral (sexual behavior), physical (sexual maturation, body, and organ weights) and neurochemical (striatal and hypothalamic monoamine and respective metabolite levels) data were assessed in the offspring of PT-treated dams. The following results were obtained: 1) sexual maturation as measured by the day of testis descent and testis weight comparison was unchanged; 2) a decrease in male sexual behavior occurred, as well as a decrease in body, ductus deferens, and seminal vesicle weights and in plasma testosterone levels of adult male offspring; 3) striatal dopamine (DA) and homovanillic acid (HVA) levels were decreased and hypothalamic norepinephrine (NE) levels were increased. These results indicate that perinatal exposure to PT during the critical periods of male brain sexual differentiation has long-term effects on the reproductive physiology and behavior of male rats.