Biology subjects

Snoeren, E. M. S.

Publications and source records attributed to Snoeren, E. M. S..

10 recordsLinked to original sources

bioRxiv2026

Specialized and experience-dependent neural dynamics in the medial amygdala and bed nucleus of stria terminalis upon social and sexual olfactory and tactile cues

The medial amygdala (MeApd) and bed nucleus of the stria terminalis (BNST) are central components of the social behavior network. However, their real-time activity during social and sexual interactions, and their respective contributions to processing olfactory and tactile cues, remain unclear. Here, we used simultaneous dual site fiber photometry to record GCaMP6s signals from the MeApd and BNST in freely behaving male rats during social interaction, copulation, sexual exhaustion, and vaginal occlusion tests. Introduction of a conspecific increased activity in both regions, but the response profiles differed by social context and experience. The MeApd responded robustly to male and female conspecifics, with larger responses to males, whereas BNST activity increased reliably upon female introduction only after sexual experience. During olfactory investigation of a male conspecific, MeApd activity differentiated sniffing of anterior and posterior body regions, while BNST activity showed no comparable spatial selectivity. Neither region showed robust event-aligned responses during sniffing of receptive females. Tactile stimulation during copulation elicited strong calcium responses in both regions. Mounts, intromissions, and ejaculations each triggered significant activity, with ejaculation producing the largest responses. MeApd responses differentiated ejaculation from mounting in sexually naive animals, whereas distinctions in BNST responses emerged primarily after sexual experience. Moreover, responses to intromissions and ejaculations persisted during the final ejaculatory series preceding sexual exhaustion, while responses to mounts were eliminated when vaginal penetration was prevented. Together, these findings identify specialized yet parallel activity dynamics within the MeApd-BNST network. MeApd activity preferentially tracks socially relevant olfactory investigation and the intensity of copulatory sensory feedback, whereas BNST recruitment during sexual behavior is more strongly shaped by sexual experience.

neuroscience↗

bioRxiv2026

Behavioral dynamics of different stages of sexual motivation in male and female rats

Sexual motivation is a complex concept involving both the initial drive to begin mating and the motivation to sustain copulation. Disruptions in sexual motivation are often observed in psychiatric disorders. This study proposes that sexual motivation can be divided into two distinct components: sexual incentive motivation and the drive to sustain copulation. To investigate this, we utilized the Motivation to Continue Copulation (MCC) test, which measures effort (nose pokes) to gain access to a sexual reward, and compared it with the Sexual Incentive Motivation (SIM) test and standard copulation tests. Male and female rats were trained on a fixed ratio (FR) 1 schedule using cheese rewards before transitioning to sexual rewards. After six FR1 sessions, the effort required increased to FR5 and progressive ratio (PR) schedules. Results revealed that sexual incentive motivation, measured by the SIM test, was higher in males after sexual experience, while females maintained consistent levels. In the MCC test, both males and females exhibited increased motivation to continue copulation with experience, but the motivation declined in the 2nd ejaculatory series. These findings demonstrate that sexual motivation comprises distinct components. The MCC test effectively measures the drive to sustain copulation, while the SIM test assesses incentive motivation. This distinction is crucial for advancing behavioral neuroscience and understanding sexual dysfunction in psychiatric conditions.

neuroscience↗

bioRxiv2025

Perinatal fluoxetine exposure increases male rat sexual behavior

Selective serotonin reuptake inhibitors (SSRIs) are commonly prescribed to pregnant women due to their efficacy and safety profile, leading to potential exposure of the developing fetus and infant. Serotonin, which acts as a neurotransmitter in adults and is crucial for regulating male sexual behavior, also serves as a neurotrophic factor during early brain development. Yet, the long-term consequences of perinatal SSRI exposure on adult sexual functioning remain poorly understood. This study investigates the long-term effects of perinatal SSRI exposure on the sexual behavior of adult male rats in a seminatural environment. During pregnancy and lactating, mother rats were administered either fluoxetine (FLX, 10 mg/kg) or a control solution (CTR, 1% Methylcellulose) daily via oral gavage. Upon reaching adulthood, male offspring were assessed for sexual performance in a semi-natural setting, where they lived in mixed-sex groups for eight days. Comprehensive observations of sexual, social, and conflict behaviors were scoring from the first to the last copulatory behavior during the period in which female rats were sexually receptive. Our findings reveal that perinatal FLX exposure significantly increases sexual behavior in adult male rats, as evidenced by a higher total number of copulatory behaviors. This suggests that elevated serotonin levels during early development have enduring consequences for male rat sexual behavior in adulthood, potentially enhancing reproductive strategies and success in naturalistic environments.

neuroscience↗

bioRxiv2024

Behavioral and neural alterations of the ventral tegmental area by Cafeteria diet exposure in rats

The brain reward system is essential for regulating appetitive and consummatory behaviors in response to various incentive stimuli. Junk food, characterized by its high palatability, is particularly associated with the potential for excessive consumption. While prior studies indicate that excessive junk food intake can impact reward circuitry, the precise mechanisms underlying these effects remain elusive. Furthermore, it is unclear whether the functionality of this neural system is similarly altered in response to other natural rewards. In this study, we used fiber photometry combined with a behavioral reward test to investigate the effects of six weeks of excessive cafeteria (CAF) diet consumption on ventral tegmental area (VTA) neural activity and behavioral responses to food and sexual rewards in female rats. Our findings demonstrate that prolonged exposure to a CAF diet reduced the exploration and consumption of food rewards. These behavioral changes were accompanied by attenuated neural activity in the VTA. Similarly, reductions in VTA activity were observed in response to a sexual partner, although no significant behavioral differences were detected during sexual interactions. Moreover, a two-week reversal diet of standard chow proved insufficient to restore VTA neural activity in CAF-exposed animals, which continued to exhibit decreased VTA responses to both food rewards and sexual partners. Our results suggest that prolonged junk food exposure induces desensitization of the VTA, resulting in reduced responsiveness to natural rewards. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/618156v3_ufig1.gif" ALT="Figure 1"> View larger version (79K): org.highwire.dtl.DTLVardef@63c782org.highwire.dtl.DTLVardef@bf2e28org.highwire.dtl.DTLVardef@16f7ad8org.highwire.dtl.DTLVardef@1ea1235_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2024

The temporal copulatory patterns of female rat sexual behavior

Female sexual behavior is a naturally rewarding activity that plays an important role in reproduction and species survival. For female rats, regulating the timing of sexual interactions is essential for optimizing mating satisfaction and enhancing the physiological conditions needed for successful fertilization. So far, traditional research on female sexual behavior has relied on a limited set of behavioral parameters, which has certain shortcomings. To address this, our study aimed to develop a more detailed behavioral framework for assessing temporal copulatory patterns in female rats. We compared fully receptive females and less-receptive females, while also investigating the effects of (R)-(+)-8-OH-DPAT, a 5-HT1A receptor agonist known for its inhibitory impact on female sexual behavior. Additionally, we examined how sexual experience and pacing conditions influence these copulatory patterns. Our results revealed that female rats engage in structured patterns of sexual bouts and time-outs, with higher receptivity leading to more sexual bouts and shorter time-outs. This suggests that sexual bouts can be viewed as an indicator of copulatory intensity, while time-outs reflect motivation to continue mating. Sexual experience did not enhance sexual performance but did result in females receiving more copulatory events from males. Lastly, we found that the conditions under which mating occurs (paced vs. non-paced) may not significantly impact copulatory behavior in fully-receptive females but could be more relevant for less-receptive females. Despite this, paced mating conditions remain preferable for studying female sexual behavior.

animal behavior and cognition↗

bioRxiv2023

CaMKIIa+ neurons in the bed nucleus of the stria terminalis area 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. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/558107v2_ufig1.gif" ALT="Figure 1"> View larger version (45K): org.highwire.dtl.DTLVardef@1000720org.highwire.dtl.DTLVardef@d3ea4aorg.highwire.dtl.DTLVardef@bacac1org.highwire.dtl.DTLVardef@1557163_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

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.

neuroscience↗

bioRxiv2021

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 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 minute 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.

neuroscience↗

bioRxiv2020

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

Gonadal hormones affect neuronal morphology to ultimately regulate behavior. 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 (GDX) male rats were treated with dihydrotestosterone (DHT, 1.5mg) or vehicle (oil) in 3 experimental groups: intact-oil, GDX-oil and GDX-DHT. Spine density and morphology, measured 24 hours after injection, were determined through 3D reconstruction of DiI-labeled dendritic segments. GDX decreased spine density in the MPN, which was rescued by DHT treatment. MeA spine density increased in GDX-DHT animals compared to intact-oil animals. In the NAcSh, DHT decreased spine density, and also rapidly increased the number of pCREB+ cell bodies. These findings indicate that androgen signaling plays a role in the regulation of spine plasticity within neurocircuits involved in motivated behaviors.

neuroscience↗

bioRxiv2019

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.

animal behavior and cognition↗