Sex, Drugs, and the Medial Amygdala: A Model of Enhanced Sexual Motivation in the Female Rat

Being friendly: paced mating for the study of physiological, behavioral, and neuroplastic changes induced by sexual behavior in females

Paced mating in rats is an experimental condition that allows the evaluation of sexual behavior in a way that closely resembles what occurs in seminatural and natural conditions enabling the female to control the rate of the sexual interaction. In conventional non-paced mating tests, females cannot escape from male approaches, which may lead to an unrewarding overstimulation. Paced mating is an alternative laboratory procedure that improves animal welfare and has a higher ethological relevance. The use of this procedure contributed to the identification of physiological and behavioral factors that favor reproduction. Paced mating includes motivational and behavioral components differentiating quantitative and qualitative characteristics that are critical for the induction of the rewarding properties of mating. These positive consequences ensure that the behavior will be repeated, favoring the species' survival. Sexual reward is an immediate consequence of paced mating, mediated mainly by the endogenous opioid system. Paced mating also induces long-lasting neuroplastic changes, including gene expression, synthesis of proteins, and neurogenesis in sex-relevant brain areas. The interest in paced mating is growing since the complexity of its elements and consequences at different levels in a laboratory setting resembles what occurs in natural conditions. In this review, we analyze the classic studies and recent publications demonstrating the advantages of using paced mating to evaluate different aspects of sexual behavior in females.

Methamphetamine-induced vaginal lubrication in rats

BACKGROUND

Based on previous studies of vaginal lubrication as well as our own previously reported interview study of women who self-reported methamphetamine (meth)-induced vaginal lubrication, in the current study we sought to determine the potential dose-response relationship leading to meth-induced vaginal lubrication. We also developed an animal model to study the reported effects and examine potential mechanisms mediating this phenomenon.

AIM

We sought to characterize the effects of meth on vaginal lubrication in an animal model with the aim of providing a potential framework for new mechanisms that incorporate novel therapeutic agents for the treatment of vaginal dryness.

METHODS

Vaginal lubrication was measured via insertion of a preweighed, cotton-tipped swab into the vaginal canal of anesthetized rats following treatment with various doses of intravenous (IV) meth, up to 0.96 mg/kg, and after additional pharmacological manipulations, including administration of a nitric oxide synthase inhibitor and an estrogen receptor antagonist. Plasma signaling molecules, including estradiol, progesterone, testosterone, nitric oxide, and vasoactive intestinal polypeptide, were measured immediately before and at 9 time points after IV meth administration. Blood was collected via a previously implanted chronic indwelling jugular catheter and analyzed by use of commercially available kits per the manufacturer's instructions.

OUTCOMES

Outcomes for this study include the measurement of vaginal lubrication in anesthetized rats following various pharmacological manipulations and plasma levels of various signaling molecules.

RESULTS

Meth dose-dependently increased vaginal lubrication in anesthetized female rats. Meth significantly increased plasma levels compared to baseline of estradiol (2 and 15 minutes after meth infusion) as well as progesterone, testosterone, and nitric oxide (10 minutes after meth infusion). Also, vasoactive intestinal polypeptide decreased significantly compared to baseline for 45 minutes following meth infusion. Our data further suggest that nitric oxide, but not estradiol, is critical in the production of vaginal secretions in response to meth.

CLINICAL IMPLICATIONS

This study has far-reaching implications for women who are suffering from vaginal dryness and for whom estrogen therapy is unsuccessful, as the investigation has demonstrated that meth presents a novel mechanism for producing vaginal lubrication that can be targeted pharmacologically.

STRENGTHS AND LIMITATIONS

This study is, to our knowledge, the first performed to measure the physiological sexual effects of meth in an animal model. Animals were anesthetized when they were administered meth. In an ideal situation, animals would be self-administering the drug to recapitulate better the contingent nature of drug taking; however, this method was not feasible for the study reported here.

CONCLUSION

Methamphetamine increases vaginal lubrication in female rats through a nitric oxide-dependent mechanism.

The Cortico-Limbo-Thalamo-Cortical Circuits: An Update to the Original Papez Circuit of the Human Limbic System

The Papez circuit, first proposed by James Papez in 1937, is a circuit believed to control memory and emotions, composed of the cingulate cortex, entorhinal cortex, parahippocampal gyrus, hippocampus, hypothalamus, and thalamus. Pursuant to James Papez, Paul Yakovlev and Paul MacLean incorporated the prefrontal/orbitofrontal cortex, septum, amygdalae, and anterior temporal lobes into the limbic system. Over the past few years, diffusion-weighted tractography techniques revealed additional limbic fiber connectivity, which incorporates multiple circuits to the already known complex limbic network. In the current review, we aimed to comprehensively summarize the anatomy of the limbic system and elaborate on the anatomical connectivity of the limbic circuits based on the published literature as an update to the original Papez circuit.

Crystallin Mu in Medial Amygdala Mediates the Effect of Social Experience on Cocaine Seeking in Males but Not in Females

BACKGROUND

Social experiences influence susceptibility to substance use disorder. The adolescent period is associated with the development of social reward and is exceptionally sensitive to disruptions to reward-associated behaviors by social experiences. Social isolation (SI) during adolescence alters anxiety- and reward-related behaviors in adult males, but little is known about females. The medial amygdala (meA) is a likely candidate for the modulation of social influence on drug reward because it regulates social reward, develops during adolescence, and is sensitive to social stress. However, little is known regarding how the meA responds to drugs of abuse.

METHODS

We used adolescent SI coupled with RNA sequencing to better understand the molecular mechanisms underlying meA regulation of social influence on reward.

RESULTS

We show that SI in adolescence, a well-established preclinical model for addiction susceptibility, enhances preference for cocaine in male but not in female mice and alters cocaine-induced protein and transcriptional profiles within the adult meA particularly in males. To determine whether transcriptional mechanisms within the meA are important for these behavioral effects, we manipulated Crym expression, a sex-specific key driver gene identified through differential gene expression and coexpression network analyses, specifically in meA neurons. Overexpression of Crym, but not another key driver that did not meet our sex-specific criteria, recapitulated the behavioral and transcriptional effects of adolescent SI.

CONCLUSIONS

These results show that the meA is essential for modulating the sex-specific effects of social experience on drug reward and establish Crym as a critical mediator of sex-specific behavioral and transcriptional plasticity.

Prevalence and associated factors of sexually transmitted infections among methamphetamine users in Eastern China: a cross-sectional study

BACKGROUND

The reported incidence of sexually transmitted infections (STIs) in China has been increasing over the last decades, especially among drug users, which has become one of the main burdens of public health in China. This study was conducted to estimate the prevalence and associated factors of STIs among non-injecting methamphetamine (MA) users in Eastern China.

METHODS

A cross-sectional survey was conducted among 632 MA users in Eastern China in 2017. Demographic characteristics, sexual behaviors, behaviors of MA use and sexual health knowledge were collected through questionnaire. First pass urine specimens were collected and detected for deoxyribonucleic acid (DNA) of Neisseria gonorrhoeae (NG) and Chlamydia trachomatis (CT) with Nucleic Acid Amplification Technology (NAAT), while blood specimens were collected and detected for antibodies of Human immunodeficiency virus (HIV), Herpes simplex virus type-2 (HSV-2), and syphilis with enzyme-linked immune sorbent assay (ELISA).

RESULTS

Among the 632 MA users, 464 (73.42%) were males, 60.92% were < 35 years of age, 546 (86.39%) were Shandong residents. 317 (50.16%, 95% CI 46.26-54.06%) participants were tested positive for at least one kind of STIs, including 242 (38.29%, 95% CI 34.50-42.08%) for HSV-2, 107 (16.93%, 95% CI 14.01-19.85%) for active syphilis, 46 (7.28%, 95% CI 5.25-9.31%) for treated syphilis, 40 (6.33%, 95% CI 4.43-8.23%) for CT, 6 (0.95%, 95% CI 0.19-1.71%) for HIV, and 3 (0.47%, 95% CI 0.06-1.00%) for NG infection. 99 (15.66%, 95% CI 12.83-18.49%) participants were co-infected with two kinds of STIs, including 91 (14.40%, 95% CI 11.66-17.14%) participants were co-infected with HSV-2 and syphilis. 14 (2.22%, 95% CI 1.07-3.37%) participants were co-infected with three kinds of STIs, and 4 HIV positive participants were co-infected with both syphilis and HSV-2. In the multiple logistic regression analysis, the results showed that females (adjusted OR [AOR] = 7.30, 95% CI 4.34-12.30) and individuals ≥ 35 years of age (AOR = 2.97, 95% CI 2.04-4.32) were more likely to test positive for STIs among MA users, whereas participants who acquired sexual health knowledge primarily from the Internet (AOR = 0.57, 95% CI 0.40-0.82) and those whose regular partners did not use drugs (AOR = 0.59, 95% CI 0.37-0.94) were less likely.

CONCLUSIONS

This study found that the prevalence of HSV-2 and syphilis are alarming high among non-injecting MA users in Shandong Province in Eastern China. The prevention and control intervention of STIs among MA users in Shandong were needed, especially on females and MA users ≥ 35 years of age.

Gender Differences in the Relationship between Methamphetamine Use and High-risk Sexual Behavior among Prisoners: A Nationwide, Cross-sectional Survey in Japan

This study aimed to examine the relationship between methamphetamine (MA) use and high-risk sexual behavior among newly incarcerated prisoners in Japan. We conducted a secondary analysis using cross-sectional survey data, which constituted a nationwide prison sample surveyed between July and November 2017. In total, 699 participants (462 male and 237 female prisoners), who completed the self-administered questionnaire during imprisonment were recruited for the study. The prevalence of high-risk sexual behaviors was as follows: inconsistent condom use (78.4% male, 81.7% female), multiple sexual partners (61.3% male, 41.3% female), history of sexually transmitted diseases (14.1% male, 23.6% female), and trading sex for drugs (15.6% male, 17.7% female). A logistic regression analysis showed that MA use during sex increased the likelihood of high-risk sexual behavior in both male (adjusted odds ratio [AOR] = 5.86; 95% confidence interval [CI] = 3.41-10.07) and female prisoners (AOR = 2.58; 95% CI = 1.33-5.00). Additionally, in female prisoners, a history of sharing MA injection (AOR = 1.60; 95% CI = 1.06-2.42) increased high-risk sexual behavior. Our results indicate that harm reduction programs tailored according to the specific necessities of each gender to reduce high-risk sexual behaviors among MA users should be included in Japanese drug policies.

Glutamate in Male and Female Sexual Behavior: Receptors, Transporters, and Steroid Independence

The survival of animal species predicates on the success of sexual reproduction. Neurotransmitters play an integral role in the expression of these sexual behaviors in the brain. Here, we review the role of glutamate in sexual behavior in rodents and non-rodent species for both males and females. These encompass the release of glutamate and correlations with glutamate receptor expression during sexual behavior. We then present the effects of glutamate on sexual behavior, as well as the effects of antagonists and agonists on different glutamate transporters and receptors. Following that, we discuss the potential role of glutamate on steroid-independent sexual behavior. Finally, we demonstrate the interaction of glutamate with other neurotransmitters to impact sexual behavior. These sexual behavior studies are crucial in the development of novel treatments of sexual dysfunction and in furthering our understanding of the complexity of sexual diversity. In the past decade, we have witnessed the burgeoning of novel techniques to study and manipulate neuron activity, to decode molecular events at the single-cell level, and to analyze behavioral data. They pose exciting avenues to gain further insight into future sexual behavior research. Taken together, this work conveys the essential role of glutamate in sexual behavior.

Antidepressant Use During Development May Impair Women's Sexual Desire in Adulthood

INTRODUCTION

Although antidepressants are well known to cause sexual side effects in adults, the long-term effects of antidepressant use during development on adult sexual function is unknown.

AIM

To explore differences in sexual desire and sexual behavior between adults who did vs did not use antidepressants during childhood or adolescence.

METHODS

An online survey of 610 young adults (66% women) assessed childhood and current mental health and use of antidepressants and other psychiatric medications before the age of 16 years and currently, partnered and solitary sexual desire, and frequency of masturbation and partnered sexual activity. Antidepressants were coded into either selective serotonin reuptake inhibitors (SSRIs) or non-SSRI antidepressants.

MAIN OUTCOME MEASURE

Scores on the Sexual Desire Inventory, and self-reported frequency of masturbation and partnered sexual activity.

RESULTS

For women, childhood SSRI use was associated with significantly lower solitary sexual desire, desire for an attractive other, and frequency of masturbation. This was true even when controlling for childhood mental health concerns, current mental health, and current antidepressant use. However, there was no effect of childhood SSRI use on women's partnered sexual desire or partnered sexual activity. There was no significant effect of childhood antidepressant use on men's sexual desire or masturbation. However, in men, childhood use of non-SSRI antidepressants was associated with significantly higher frequency of partnered sexual activity. Childhood use of non-SSRI antidepressants, or nonantidepressant psychiatric medication, was not associated with adult sexual desire or behavior in either women or men.

CLINICAL IMPLICATIONS

It is possible that SSRI use during childhood interrupts the normal development of sexual reward systems, which may be a risk factor for sexual desire dysfunction in adult women.

STRENGTHS & LIMITATIONS

Strengths include a large sample, use of attention checks and validated measures, and careful assessment of childhood mental health history; however, generalizability is limited by a predominantly white, young adult sample. These data are cross-sectional, and therefore, causal explanations for the association between childhood SSRI use and adult sexual well-being should be considered preliminary, warranting replication.

CONCLUSION

These findings point to a critical need for well-controlled, prospective research on possible long-term effects of antidepressant use, particularly SSRI use, on the development of adult sexual well-being. Lorenz TK. Antidepressant Use During Development May Impair Women's Sexual Desire in Adulthood. J Sex Med 2020;17:470-476.

DeepSnap-Deep Learning Approach Predicts Progesterone Receptor Antagonist Activity With High Performance

The progesterone receptor (PR) is important therapeutic target for many malignancies and endocrine disorders due to its role in controlling ovulation and pregnancy via the reproductive cycle. Therefore, the modulation of PR activity using its agonists and antagonists is receiving increasing interest as novel treatment strategy. However, clinical trials using the PR modulators have not yet been found conclusive evidences. Recently, increasing evidence from several fields shows that the classification of chemical compounds, including agonists and antagonists, can be done with recent improvements in deep learning (DL) using deep neural network. Therefore, we recently proposed a novel DL-based quantitative structure-activity relationship (QSAR) strategy using transfer learning to build prediction models for agonists and antagonists. By employing this novel approach, referred as DeepSnap-DL method, which uses images captured from 3-dimension (3D) chemical structure with multiple angles as input data into the DL classification, we constructed prediction models of the PR antagonists in this study. Here, the DeepSnap-DL method showed a high performance prediction of the PR antagonists by optimization of some parameters and image adjustment from 3D-structures. Furthermore, comparison of the prediction models from this approach with conventional machine learnings (MLs) indicated the DeepSnap-DL method outperformed these MLs. Therefore, the models predicted by DeepSnap-DL would be powerful tool for not only QSAR field in predicting physiological and agonist/antagonist activities, toxicity, and molecular bindings; but also for identifying biological or pathological phenomena.