CaMKIIa+ neurons in the bed nucleus of the stria terminalis modulate pace of natural reward seeking depending on internal state.

This study aims to investigate the underlying neurobiological mechanisms that regulate natural reward seeking behaviors, specifically in the context of sexual behavior and sucrose self-administration. The role of CaMKIIa+ neurons in the bed nucleus of the stria terminalis (BNST) was explored using chemogenetic silencing and -stimulation. Additionally, the study examined how these effects interacted with the internal state of the animals. Through detailed behavioral analysis, it was demonstrated that CaMKIIa+ neurons in the BNST play a significant role in the regulation of both sexual behavior and sucrose self-administration. Although the behavioral outcome measures differed between the two behaviors, the regulatory role of the CaMKIIa+ neurons in the BNST was found to converge on the modulation of the pacing of engagement in these behaviors in male rats. Moreover, our study confirmed that the internal physiological state of the animal affects how the BNST modulates these behaviors. These findings suggest that different types of natural rewards may recruit a similar brain circuitry to regulate the display of motivated behaviors. Overall, this research provides valuable insights into the neural mechanisms underlying natural reward seeking and sheds light on the interconnected nature of reward-related behaviors in male rats.

Effects of perinatal fluoxetine exposure on novelty-induced social and non-social investigation behaviors in a seminatural environment.

Selective serotonin reuptake inhibitors (SSRIs) are increasingly prescribed as medication for various affective disorders during pregnancy. SSRIs cross the placenta and affect serotonergic neurotransmission in the fetus, but the neurobehavioral consequences for the offspring remain largely unclear. Recent rodent research has linked perinatal SSRI exposure to alterations in both social and non-social aspects of behavior. However, this research has mainly focused on behavior within simplified environments. The current study investigates the effects of perinatal SSRI exposure on social and non-social investigation behaviors of adult rat offspring upon introduction to a novel seminatural environment with unknown conspecifics. During the perinatal period (gestational day 1 until postnatal day 21), rat dams received daily treatment with either an SSRI (fluoxetine, 10 mg/kg) or vehicle. Adult male and female offspring were observed within the first hour after introduction to a seminatural environment. The results showed that perinatal fluoxetine exposure altered aspects of non-social investigation behaviors, while not altering social investigation behaviors. More specifically, both fluoxetine-exposed males and females spent more total time on locomotor activity than controls. Furthermore, fluoxetine-exposed females spent less time exploring objects and specific elements in the environment. The data suggest that perinatal exposure to SSRIs leads to a quicker, less detailed investigation strategy in novel environments and that the alteration is mostly pronounced in females.

Male rat sexual behavior: Insights from inter-copulatory intervals.

The assessment of sexual behavior in male rats with the aim of unraveling underlying neurobiological mechanisms has in the recent decades been reduced to the annotation of mounts, intromissions and ejaculations. To provide a better understanding of the structure and patterns of copulation, it is necessary to extend and tailor the analysis to the natural organization of male rat copulation. This will lead to better formulation of hypotheses about neurobiological underpinnings of behavior. Mounts and intromissions are naturally organized in mount bouts consisting of one or more copulatory behaviors and are interspersed with time outs. We hypothesized that time outs and the post-ejaculatory interval (inter-copulatory intervals) are related and possibly under the control of a common copulatory inhibition mechanism that is the result of penile sensory stimulation. To test this hypothesis, we analyzed sexual behavior in male rats of three different cohorts from three different laboratories. Results showed that the post-ejaculatory interval and mean time out duration are strongly correlated in all cohorts analyzed. In addition, we showed that individual time out duration is at least partially predicted by the sum of sensory stimulation of copulatory components in the preceding mount bout, with more penile stimulation associated with longer time outs. These findings suggest that both time out and post-ejaculatory interval duration may be determined by the magnitude of sensory stimulation, which inhibits copulation. Whether the same neural pathways are involved in the central orchestration of both time outs and the post-ejaculatory interval should be subject to future studies.

Silencing and stimulating the medial amygdala impairs ejaculation but not sexual incentive motivation in male rats.

The medial amygdala (MeA) is a sexually dimorphic brain region that integrates sensory information and hormonal signaling, and is involved in the regulation of social behaviors. Lesion studies have shown a role for the MeA in copulation, most prominently in the promotion of ejaculation. The role of the MeA in sexual motivation, but also in temporal patterning of copulation, has not been extensively studied in rats. Here, we investigated the effect of chemogenetic inhibition and stimulation of the MeA on sexual incentive motivation and copulation in sexually experienced male rats. AAV5-CaMKIIa viral vectors coding for Gi, Gq, or no DREADDs (sham) were bilaterally infused into the MeA. Rats were assessed in the sexual incentive motivation test and copulation test upon systemic clozapine N-oxide (CNO) or vehicle administration. We report that MeA stimulation and inhibition did not affect sexual incentive motivation. Moreover, both stimulation and inhibition of the MeA decreased the number of ejaculations in a 30 min copulation test and increased ejaculation latency and the number of mounts and intromissions preceding ejaculation, while leaving the temporal pattern of copulation intact. These results indicate that the MeA may be involved in the processing of sensory feedback required to reach ejaculation threshold. The convergence of the behavioral effects of stimulating as well as inhibiting the MeA may reflect opposing behavioral control of specific neuronal populations within the MeA.

Effects of gonadectomy and dihydrotestosterone on neuronal plasticity in motivation and reward related brain regions in the male rat.

Gonadal hormones affect neuronal morphology to ultimately regulate behaviour. In female rats, oestradiol mediates spine plasticity in hypothalamic and limbic brain structures, contributing to long-lasting effects on motivated behaviour. Parallel effects of androgens in male rats have not been extensively studied. Here, we investigated the effect of both castration and androgen replacement on spine plasticity in the nucleus accumbens shell and core (NAcSh and NAcC), caudate putamen (CPu), medial amygdala (MeA) and medial preoptic nucleus (MPN). Intact and castrated (gonadectomy [GDX]) male rats were treated with dihydrotestosterone (DHT, 1.5 mg) or vehicle (oil) in three experimental groups: intact-oil, GDX-oil and GDX-DHT. Spine density and morphology, measured 24 hours after injection, were determined through three-dimensional reconstruction of confocal z-stacks of DiI-labelled dendritic segments. We found that GDX decreased spine density in the MPN, which was rescued by DHT treatment. DHT also increased spine density in the MeA in GDX animals compared to intact oil-treated animals. By contrast, DHT decreased spine density in the NAcSh compared to GDX males. No effect on spine density was observed in the NAcC or CPu. Spine length and spine head diameter were unaffected by GDX and DHT in the investigated brain regions. In addition, immunohistochemistry revealed that DHT treatment of GDX animals rapidly increased the number of cell bodies in the NAcSh positive for phosphorylated cAMP response-element binding protein, a downstream messenger of the androgen receptor. These findings indicate that androgen signalling plays a role in the regulation of spine plasticity within neurocircuits involved in motivated behaviours.

The cafeteria diet: A standardized protocol and its effects on behavior.

Obesity is a major health risk, with junk food consumption playing a central role in weight gain, because of its high palatability and high-energy nutrients. The Cafeteria (CAF) diet model for animal experiments consists of the same tasty but unhealthy food products that people eat (e.g. hot dogs and muffins), and considers variety, novelty and secondary food features, such as smell and texture. This model, therefore, mimics human eating patterns better than other models. In this paper, we systematically review studies that have used a CAF diet in behavioral experiments and propose a standardized CAF diet protocol. The proposed diet is ad libitum and voluntary; combines different textures, nutrients and tastes, including salty and sweet products; and it is rotated and varied. Our summary of the behavioral effects of CAF diet show that it alters meal patterns, reduces the hedonic value of other rewards, and tends to reduce stress and spatial memory. So far, no clear effects of CAF diet were found on locomotor activity, impulsivity, coping and social behavior.

Female rat sexual behavior is unaffected by perinatal fluoxetine exposure.

Serotonin plays an important role in adult female sexual behavior, however little is known about the influence of serotonin during early development on sexual functioning in adulthood. During early development, serotonin acts as neurotrophic factor, while it functions as a modulatory neurotransmitter in adulthood. The occurrence of serotonin release, could thus have different effects on behavioral outcomes, depending on the developmental period in which serotonin is released. Because serotonin is involved in the development of the HPG axis which is required for puberty establishment, serotonin could also alter expression patterns of for instance the estrogen receptor ɑ (ERɑ). The aim of our study was to investigate the effects of increased serotonin levels during early development on adult female rat sexual behavior during the full behavioral estrus in a seminatural environment. To do so, rats were perinatally exposed with the selective serotonin reuptake inhibitor (SSRI) fluoxetine (10 mg/kg FLX) and sexual performance was tested during adulthood. All facets of female sexual behavior between the first and last lordosis (behavioral estrus), and within each copulation bout of the behavioral estrus were analyzed. Besides the length and onset of the behavioral estrus and the sexual behaviors patterns, other social and conflict behavior were also investigated. In addition, we studied the effects of perinatal FLX exposure on ERɑ expression patterns in the medial preoptic nucleus, ventromedial nucleus of the hypothalamus, medial amygdala, bed nucleus of the stria terminalis, and the dorsal raphé nucleus. The results showed that perinatal fluoxetine exposure has no effect on adult female sexual behavior. The behavioral estrus of FLX-females had the same length and pattern as CTR-females. In addition, FLX- and CTR-females showed the same amount of paracopulatory behavior and lordosis, both during the full behavioral estrus and the "most active bout". Furthermore, no differences were found in the display of social and conflict behaviors, nor in ERɑ expression patterns in the brain. We conclude that increases in serotonin levels during early development do not have long-term consequences for female sexual behavior in adulthood.

Third-party prosocial behavior in adult female rats is impaired after perinatal fluoxetine exposure.

SSRIs are commonly used to treat pregnant women with depression. However, SSRIs can cross the placenta and affect the development of the fetus. The effects of perinatal SSRI exposure, and especially the effects on social behavior, are still incompletely documented. This study first aims to investigate whether rats show prosocial behavior in the form of consolation behavior. Secondly, it aims to investigate whether perinatal SSRI exposure affects this prosocial behavior. At last, we investigate whether the behavior changed after the rats had been exposed to an additional white-noise stressor. Rat dams received 10 mg/kg/d fluoxetine (FLX) or vehicle (CTR) via oral gavage from gestational day 1 until postnatal day 21. At adulthood, the rat offspring were housed in four cohorts of 4 females and 4 males in a seminatural environment. As prosocial behaviors are more prominent after stressful situations, we investigated the behavioral response of rats immediately after natural aggressive encounters (fights). Additionally, we studied whether a stressful white-noise exposure would alter this response to the aggressive encounters. Our study indicates that CTR-female rats are able to show third party prosocial behavior in response to witnessing aggressive encounters between conspecifics in a seminatural environment. In addition, we showed that perinatal FLX exposure impairs the display of prosocial behavior in female rats. Moreover, we found no signs of prosocial behavior in CTR- and FLX-males after natural aggressive encounters. After white-noise exposure the effects in third party prosocial behavior of CTR-females ceased to exist. We conclude that female rats are able to show prosocial behavior, possibly in the form of consolation behavior. In addition, the negative effects of perinatal fluoxetine exposure on prosocial behavior could provide additional evidence that SSRI treatment during pregnancy could contribute to the risk for social impairments in the offspring.

Perinatal fluoxetine exposure changes social and stress-coping behavior in adult rats housed in a seminatural environment.

The use of selective serotonin reuptake inhibitors (SSRI) during pregnancy has increased tremendously, but the consequences for the offspring remain largely unclear. Several studies have described potential effects of perinatal SSRI-exposure on neurobehavioral outcomes using simplified rodent test set-ups, however these set-ups only assess a small fraction of the behavior. For translational purposes it is important to take the environmental influences into account which children are exposed to in real life. By using a seminatural environmental set-up, this study is the first to assess behavioral outcomes in offspring exposed to perinatal SSRI exposure under seminatural circumstances. Mothers received daily the SSRI fluoxetine (FLX, 10 mg/kg p.o.) or vehicle (CTR) from gestational day 1 until postnatal day 21. To assess the effect of FLX exposure during early development, female and male offspring were behaviorally tested in the seminatural environment at adulthood. Baseline behavior was measured in addition to responses during and after stressful white-noise events. Behavior was observed on two days, day 4 on which females were sexually non-receptive, and day 7, on which females were sexual receptive. Perinatal FLX exposure reduced general activity in females and increased behavior related to a social context in both males and females. After a stressful white-noise event some behaviors switched. Whereas FLX-females switch from resting socially to resting more solitarily, FLX-males show an increase in self-grooming behavior after the stressor and showed more freezing behavior in the open area. We conclude that perinatal FLX exposure leads to alterations in social and stress-coping behaviors in adulthood, when observed in a seminatural environment. Whether these adaptations in behavior are advantageous or disadvantageous remains to be established.

Female Reproductive Behavior.

Reproductive behavior is the behavior related to the production of offspring and includes all aspects from the establishment of mating systems, courtship, sexual behavior, and parturition to the care of young. In this chapter, I outline the hormonal regulation of the estrous cycle, followed by a description of the neural regulation of female sexual behavior. Ovarian hormones play an important role in the induction of ovulation and behavioral estrus, in which they interact closely with several neurotransmitters and neuropeptides to induce sexual behavior. This chapter discusses the latest research on the role of estrogen, progesterone, serotonin, dopamine, noradrenaline, oxytocin, and GABA in female mating behavior. In addition, the most relevant brain areas, such as the preoptic area and the ventromedial nucleus of the hypothalamus, in which these regulations take place, are discussed.

Assessment of sexual behavior in rats: The potentials and pitfalls.

In the field of behavioral neuroscience, it is essential to use the appropriate animal models for the topic of investigation. Using the wrong model can result in false interpretation of the results. In this review we will discuss the animal models used to study sexual behavior, with a focus on rats. We will discuss the potentials and pitfalls of the different paradigms and try to make recommendations on how research in this field could be optimized. Both male and female sexual behavior are discussed, in addition to sexual motivation.

Mate choice could be random in female rats (Rattus norvegicus).

Female mate choice is often investigated in terms of reproductive success in order to understand how male characteristics contribute to sexual attractiveness. Previous studies have found that females rats prefer mating with their first encounter rather than males visited subsequently, suggesting that the rewarding value of this first encounter is enough to reinforce mating with the first partner. Using a multiple chambers paradigm, we allowed female rats to copulate freely with three males placed each in a different chamber. Then, we switched the males' position, and let the female interact with them freely again within the same session. We tested whether female mate choice was relying rather on a preferred male rat or on a preferred mating location. The results showed that females spent most time with the male in the chamber of 1st entry in the beginning, but as soon as male rats switched chambers, the female rat continued to copulate with the new male in the same chamber of 1st entry, instead of mating with her previously preferred male rat. This suggests that the male preference is an artefact of location preference. Therefore, female mate choice seems to be rather random than the consequence of an individual choice based on male characteristics. This finding, although contradictory with the intuitive feeling that mate choice is a crucial feature in sexual and reproductive behavior, is supported by several recent observations. In the coming years, behavioral neuroscience should bring light to the brain processes at work in random mate choice.

A cooperative function for multisensory stimuli in the induction of approach behavior of a potential mate.

Intrasexual competition is an important element of natural selection in which the most attractive conspecific has a considerable reproductive advantage over the others. The conspecifics that are approached first often become the preferred mate partners, and could thus from a biological perspective have a reproductive advantage. This underlines the importance of the initial approach and raises the question of what induces this approach, or what makes a conspecific attractive. Identification of the sensory modalities crucial for the activation of approach is necessary for elucidating the central nervous processes involved in the activation of sexual motivation and eventually copulatory behavior. The initial approach to a potential mate depends on distant stimuli in the modalities of audition, olfaction, vision, and other undefined characteristics. This study investigated the role of the different modalities and the combination of these modalities in the sexual incentive value of a female rat. This study provides evidence that the presence of a single-sensory stimulus with one modality (olfaction, vision, or 'others', but not audition) is sufficient to attenuate the preference for a social contact with a male rat. However, a multisensory stimulus of multiple modalities is necessary to induce preference for the stimulus over social contact to a level of an intact receptive female. The initial approach behavior, therefore, seems to be induced by the combination of at least two modalities among which olfaction is crucial. This suggests that there is a cooperative function for the different modalities in the induction of approach behavior of a potential mate.

Silent or Vocalizing Rats Copulate in a Similar Manner.

Both male and female rats produce 50 kHz ultrasonic vocalizations (USVs) in the presence of a sexual partner and during copulation. Previous studies showed that USVs have no incentive value for rats. In this study, we evaluated the role of USVs in behavior during copulation. Three groups of rats were used: sham males paired with sham females, devocalized females paired with sham males, and sham females paired with devocalized males. During the copulation test, the USVs emitted by the sham rat were recorded and the sexual behavior of both the male and the female were observed. The results revealed that devocalized and sham females showed similar patterns of sexual behavior and no difference was found in the copulatory behavior of devocalized and sham males. Also the behavior of the partner of a sham rat was comparable to the partner of a devocalized rat. In addition, almost no changes in USVs emission were found in the 5 seconds before and/or after a copulatory behavior. It can be concluded that USVs play no important role in rat copulatory behavior at least in sexually naïve rats.

The role of adrenoceptors in the central nervous system in male and female rat sexual behavior.

Three different phases can be distinguished in rats' sexual cycle, the introductory (precopulatory), the copulatory and the executive (ejaculatory) phases. In this review, a new analysis of existing pharmacological data is made, both in male and female rats, in which the different aspects of sexual behavior are taken into account. An effort is made to distinguish pharmacological effects on sexual behavior from a possible physiological role of noradrenaline. In addition, new data on the role of α2-adrenoceptors on female sexual behavior is presented. The new analysis suggests that noradrenaline has a stimulatory role on the executive phase of male sexual behavior, while the introductory and copulatory phases remain unaffected. Adrenoceptors play a role in the regulation of sexual behavior in the medial preoptic area and the lateral septum. In female rats, noradrenaline also does not play a vital role in the introductory phase. Only the lordosis behavior of the copulatory phase is sometimes affected by adrenergic agents, but only under a certain hormonal condition. The medial preoptic area, the ventromedial nucleus, the arcuate ventromedial nucleus and median eminence are involved in the regulation of female sexual behavior. The new data suggest that α2-adrenoceptors play no major role on any indices of female sexual behavior.

The role of odors and ultrasonic vocalizations in female rat (Rattus norvegicus) partner choice.

Intrasexual competition for access to a female mate is believed to be unusual in wild male rats, which suggests that female choosiness could be more important. It has been shown that females spend more time with one male than with others when tested in a multiple partner paradigm. The male of first entry is visited most. The role of ultrasonic vocalizations (USVs) and male odors in the female rat's initial choice to approach one male instead of another are studied in these experiments. In Experiment 1, female rats were allowed to choose between 3 different intact males, whereas in Experiment 2, females could choose between a devocalized male and 2 intact males. Both experiments started with a 15-min period with inaccessible males followed by a 15-min period with accessible males in which the female could copulate with the males of her choice. The results showed that female rats spent more time with the male of first entry over the males visited subsequently. No differences were found in USV subtype patterns emitted by the different males or the time spent sniffing the different males in the period preceding the choice. In addition, the results of Experiment 2 showed that females visited the silent males as much as the vocalizing males. Thus, the present experiments did not offer any evidence suggesting that USVs or individual differences in male odors play any role in female mate choice. Other factors that were not investigated in this study might be involved in female rat mate selection, but it should also be considered that mate selection could be random.

On the role of individual differences in female odor and ultrasonic vocalizations for male's choice of partner.

Intrasexual competition for access to a female mate is believed to be unusual in wild male rats, which suggests that female choosiness could be important. Even if competition is unusual, males still have to inevitably approach one partner first for copulation. In females, it has been shown that females spend longer time with one male compared to the others when tested in a multiple partner paradigm. The male mate preference was investigated in this study. In addition, the role of ultrasonic vocalizations (USVs) and female odors in the male's initial choice to approach one female instead of another was studied in this experiment. Male rats could choose between three different sexually receptive females. The experiment started with a 15-minute period with inaccessible females followed by a 15-minute period with accessible females in which the males could copulate with the females of his choice. The results showed that male rats spent more time with the female of 1st entry over the second or third females visited. No differences were found in USV subtype patterns emitted by the different females or the number of sniff episodes towards the different female chambers. Thus, the present experiments did not offer any evidence suggesting that USVs or individual differences in female odors play any role in male mate choice. Other factors that were not investigated in this study might be involved in male mate selection, but it should also be considered that mate selection could be random.

The incentive value of males' 50-kHz ultrasonic vocalizations for female rats (Rattus norvegicus).

Rats emit ultrasonic vocalizations (USVs) of 22 kHz and 50 kHz before, during, and after copulation. The 50-kHz vocalizations can be subdivided into flat and frequency-modulated (FM) trill calls. In this study, the role of 50-kHz USVs in sexual incentive motivation in female rats was examined. USVs were recorded from sexually active males during the precopulatory phase. In the first two experiments, "full 10-min song," flat-call, and FM-trill-call stimuli were used. In Experiment 1, a combination of complex and trill calls was used as the FM-trill call, whereas a mixture of multistep and upward ramp calls was used in Experiment 2. The auditory stimuli were played back to sexually receptive female rats in a sexual incentive-motivation test. For comparison, the odor of an intact male rat was also used as incentive stimulus. The flat-call stimulus did not induce approach behavior in any experiment, whereas the FM trill showed a short-lived effect in Experiment 2. The females approached the "full song" during the first minute of stimulus exposure in Experiment 1, but not in Experiment 2. When the entire 10-min test period was analyzed, the females in Experiment 1 did not approach the full song more than background noise, though they did so in Experiment 2. The olfactory stimulus, to the contrary, had a clear incentive value in both experiments. In a third experiment, a devocalized male, an intact vocalizing male and a female rat were used as incentive stimuli. The females did not approach a vocalizing male more than they approached a silent male, showing that USVs do not contribute to the male rat's incentive value. Overall, the results of the present series of experiments show that the male rat's USVs do not have any consistent incentive value for the sexually receptive female rat. This sharply contrasts the strong and reliable effect of male odor.

Serotonin 1A receptors and sexual behavior in female rats: a review.

This review focuses on the role of serotonin and especially 5-HT1A receptors in female rat sexual behavior. In addition, the differences and/or similarities with male rats are discussed. Overall, in both males and females 5-HT1A receptors do not appear to be involved in sexual behavior under normal circumstances, but become very important under conditions of elevated serotonin levels. 5-HT1A receptor agonists facilitate sexual behavior in male rats, but inhibit female sexual activity. At first sight, this seems quite conflicting, but could be due to our definitions of different elements of sexual behavior. Three different phases can be distinguished in rats' sexual cycle, the introductory (precopulatory), the copulatory and the executive (ejaculatory) phases. Different mechanisms and brain regions are involved in these phases. If the appropriate phases of males and females are properly compared, the role of 5-HT1A receptors in rats might be more similar than assumed thus far.

Serotonin 1A receptors and sexual behavior in male rats: a review.

Serotonin plays an important role in male sexual behavior. Many studies have been performed on the pivotal role of 5-HT1A receptors in sexual behavior. Overall, 5-HT1A receptors do not appear to be involved under normal circumstances, but become very important under conditions of elevated serotonin levels in sexual behavior. 5-HT1A receptor agonists facilitate ejaculatory behavior in male rats, while inhibiting copulatory behavior. Three different phases can be distinguished in rats' sexual cycle, the introductory (precopulatory), the copulatory and the executive (ejaculatory) phases. Different mechanisms and brain regions are involved in these phases. The mechanisms, brain regions and the possible involvement of 5-HT and 5-HT1A receptors in the appropriate phases in male rat sexual behavior will be discussed in the current review.