Fluoxetine Chronic Treatment Inhibits Male Rat Sexual Behavior by Affecting Both Copulatory Behavior and the Genital Motor Pattern of Ejaculation

Appeasing Pheromones for the Management of Stress and Aggression during Conservation of Wild Canids: Could the Solution Be Right under Our Nose?

Simple Summary

Many canid species are declining globally. It is important to conserve these species that often serve as important predators within ecosystems. Continued human expansion and the resulting habitat fragmentation necessitate conservation interventions, such as translocation, artificial pack formation, and captive breeding programs. However, chronic stress often occurs during these actions, and can result in aggression, and the physiological suppression of immunity and reproduction. Limited options are currently available for stress and aggression management in wild canids. Pheromones provide a promising natural alternative for stress management; an appeasing pheromone has been identified for multiple domestic species and may reduce stress and aggression behaviours. Many pheromones are species-specific, and the appeasing pheromone has been found to have slight compositional changes across species. In this review, the benefits of a dog appeasing pheromone and the need to investigate species-specific derivatives to produce more pronounced and beneficial behavioural and physiological modulation in target species as a conservation tool are examined.

Abstract

Thirty-six species of canid exist globally, two are classified as critically endangered, three as endangered, and five as near threatened. Human expansion and the coinciding habitat fragmentation necessitate conservation interventions to mitigate concurrent population deterioration. The current conservation management of wild canids includes animal translocation and artificial pack formation. These actions often cause chronic stress, leading to increased aggression and the suppression of the immune and reproductive systems. Castration and pharmaceutical treatments are currently used to reduce stress and aggression in domestic and captive canids. The undesirable side effects make such treatments inadvisable during conservation management of wild canids. Pheromones are naturally occurring chemical messages that modulate behaviour between conspecifics; as such, they offer a natural alternative for behaviour modification. Animals are able to distinguish between pheromones of closely related species through small compositional differences but are more likely to have greater responses to pheromones from individuals of the same species. Appeasing pheromones have been found to reduce stress- and aggression-related behaviours in domestic species, including dogs. Preliminary evidence suggests that dog appeasing pheromones (DAP) may be effective in wild canids. However, the identification and testing of species-specific derivatives could produce more pronounced and beneficial behavioural and physiological changes in target species. In turn, this could provide a valuable tool to improve the conservation management of many endangered wild canids.

Behavioral and neurological improvement by Cydonia oblonga fruit extract in chronic immobilization stress rats

It is known that chronic stress is a contributing factor to several physical and mental diseases. In this study, we examined the effect of hydroethanolic extract of Cydonia oblonga fruit (HECO, 300 mg/kg) in chronically immobilized rats on physiological and behavioral parameters by the open field test (OFT), sucrose preference test (SPT), and forced swimming test (FST) and on neurological alterations by analysis of the hippocampal neurogenesis. A daily 6 hr exposure to chronic immobilization stress (CIS) for 21 consecutive days induced anxiety- and depressive-like behaviors in rats' concomitant with decreased weight gain and increased plasma corticosterone (CORT) levels, rats also showed atrophy in the CA3 subregion of the hippocampus and a decreased number of Ki67 and DCX positive cells in the dentate gyrus (DG). Treatment with HECO successfully suppressed the physiological and behavioral markers of the CIS and prevents the structural abnormality and the impaired cell proliferation in the hippocampus. Moreover, the daily administration of HECO improved the mood function in normal rats. Taking together, our findings demonstrate, for the first time, the anti-depressive effect of C. oblonga fruit by enhancing the hippocampal neurogenesis in the rat model of depression.

Serotonin improves behavioral contrast sensitivity of freely moving rats

Serotonin (5-HT) is a neuromodulator secreted from serotonergic neurons located in the pons and upper brain stem in a behavioral context-dependent manner. The serotonergic axon terminals innervate almost the whole brain, causing modulatory actions on various brain functions including vision. Our previous study demonstrated the visual responses of neurons in the primary visual cortex (V1) of anesthetized monkeys were modulated by the activation of 5-HT receptors depending on the response magnitude, in which 5-HT2A receptor-selective agonists enhanced weak visual responses but not strong responses. This observation suggests that the activation of serotonergic receptors modulates neuronal visual information processing to improve the behavioral detectability of a stimulus. However, it remains unknown if 5-HT improves visual detectability at the behavioral level. To investigate this point, visual detectability was measured as contrast sensitivity (CS) in freely moving rats using a two-alternative forced-choice visual detection task (2AFC-VDT) combined with the staircase method. The grating contrast was decreased or increased step by step after a correct choice (hit) or incorrect choice (miss), respectively. CS was evaluated as an inverse value of the visual contrast threshold. The effect of the intraperitoneal administration of fluoxetine (FLX, 5 mg/kg), a selective serotonin reuptake inhibitor, on CS was tested. The CS of rats was significantly higher in FLX than control conditions, and the drug effect showed specificity for the spatial frequency (SF) of a grating stimulus, in which CS improvement was observed at optimal SF but not non-optimal high SF. Thus, we conclude that endogenously-secreted serotonin in the brain improves visual detectability, which may be mediated by vision-related neurons acquiring SF information of the visual stimulus.

The Sexual Motivation of Male Rats as a Tool in Animal Models of Human Health Disorders

Normal or dysfunctional sexual behavior seems to be an important indicator of health or disease. Many health disorders in male patients affect sexual activity by directly causing erectile dysfunction, affecting sexual motivation, or both. Clinical evidence indicates that many diseases strongly disrupt sexual motivation and sexual performance in patients with depression, addiction, diabetes mellitus and other metabolic disturbances with obesity and diet-related factors, kidney and liver failure, circadian rhythm disorders, sleep disturbances including obstructive sleep apnea syndrome, developmental and hormonal disorders, brain damages, cardiovascular diseases, and peripheral neuropathies. Preclinical studies of these conditions often require appropriate experimental paradigms, including animal models. Male sexual behavior and motivation have been intensively investigated over the last 80 years in animal rat model. Sexual motivation can be examined using such parameters as: anticipatory behavior and 50-kHz ultrasonic vocalizations reflecting the emotional state of rats, initiation of copulation, efficiency of copulation, or techniques of classical (pavlovian) and instrumental conditioning. In this review article, we analyze the behavioral parameters that describe the sexual motivation and sexual performance of male rats in the context of animal experimental models of human health disorders. Based on analysis of the parameters describing the heterogeneous and complex structure of sexual behavior in laboratory rodents, we propose an approach that is useful for delineating distinct mechanisms affecting sexual motivation and sexual performance in selected disease states and the efficacy of therapy in preclinical investigations.

Neuroanatomical dichotomy of sexual behaviors in rodents: a special emphasis on brain serotonin

Much of the social behavior in which rodents engage is related to reproduction, such as maintaining a breeding territory, seeking mates, mating, and caring for their young. Rodents belong to the internally fertilizing species that require sexual behavior for reproduction. The dyadic, heterosexual patterns of most mammalian species are sexually dimorphic, but they also share mutual components in both sexes: sexual attraction is reciprocal, sexual initiative is assumed, appetitive behavior is engaged in, and mating involves consummatory and postconsummatory phases in females as well as in males. Serotonin, a phylogenetically ancient molecule, is the most widely distributed neurotransmitter in the brain and its signaling pathways are essential for numerous functions including sexual behavior. Since the late 1960s, brain serotonergic neurotransmission has been considered to exert an inhibitory influence on the neural mechanisms mediating sexual behavior. This contention was based mainly on the observations that a decrease in central serotonergic activity facilitated the elicitation of sexual behavior, whereas an increase in central serotonergic activity attenuated it. However, the discovery of over 14 types of serotonin receptors has added numerous layers of complexity to the study of serotonin and sexual behavior. Evidence shows that, upon activation, certain receptor subtypes facilitate, whereas some others suppress, sexual behavior, as well as sexual arousal and motivation. Furthermore, the role of these receptors has been shown to be different in the male and female sexes. The use of serotonergic pharmacological interventions, mouse strains with genetic polymorphisms causing alterations in the levels of brain serotonin, and animal models with genetic manipulations of various serotonin effectors has helped delineate the fundamental role of this neurotransmitter in the regulation of sexual behavior. This review aims to examine the basics of the components of female and male sexual behavior and the participation of the serotonin system in the modulation of these behaviors, with emphasis on rodents.

Effects of bupropion on the ejaculatory response of male rats

Chronic antidepressant treatment is associated with sexual side effects, particularly affecting the ejaculatory response. Bupropion (BP), an antidepressant inhibiting dopamine/noradrenaline reuptake, seems to have a low impact upon male sexual function. Ejaculation is regulated both at the brain and spinal cord by the spinal generator for ejaculation (SGE). We investigated the effects of chronic BP treatment on ejaculatory behavior and on SGE functioning. Sexually experienced male rats were intraperitoneally (i.p.) injected with BP (7.5 or 15 mg kg(-1)) during 14 days and tested for sexual behavior on days 1, 7 and 14 of treatment; these same males were used to evaluate the functioning of the SGE by recording the genital motor pattern for ejaculation (GMPE). Acute and chronic BP administration did not importantly modify copulatory behavior of male rats. Chronic treatment with the low dose of BP produced deficits in the functioning of the SGE that were restored by activation of the SGE through afferent stimulation. Conversely, chronic treatment with the high-dose of BP disrupted the functioning of the SGE, as the deficits were not compensated by activating the SGE through sensory stimulation. It is concluded that chronic BP at high doses alters the functioning of the SGE.

Sexual side effects of serotonergic antidepressants: mediated by inhibition of serotonin on central dopamine release?

Antidepressant-induced sexual dysfunction adversely affects the quality of life of antidepressant users and reduces compliance with treatment. Animal models provide an instructive approach for examining potential sexual side effects of novel drugs. This review discusses the stability and reproducibility of our standardized test procedure that assesses the acute, subchronic and chronic effects of psychoactive compounds in a 30 minute mating test. In addition, we present an overview of the effects of several different (putative) antidepressants on male rat sexual behavior, as tested in our standardized test procedure. By comparing the effects of these mechanistically distinct antidepressants (paroxetine, venlafaxine, bupropion, buspirone, DOV 216,303 and S32006), this review discusses the putative mechanism underlying sexual side effects of antidepressants and their normalization. This review shows that sexual behavior is mainly inhibited by antidepressants that increase serotonin neurotransmission via blockade of serotonin transporters, while those that mainly increase the levels of dopamine and noradrenaline are devoid of sexual side effects. Those sexual disturbances cannot be normalized by simultaneously increasing noradrenaline neurotransmission, but are normalized by increasing both noradrenaline and dopamine neurotransmission. Therefore, it is hypothesized that the sexual side effects of selective serotonin reuptake inhibitors may be mediated by their inhibitory effects on dopamine signaling in sex brain circuits. Clinical development of novel antidepressants should therefore focus on compounds that simultaneously increase both serotonin and dopamine signaling.