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Paced Mating Behaviour Is Influenced by Duration of Female Post-Ejaculatory Interval. J Sex Med 2022; 19:1506-1516. [PMID: 35995714 DOI: 10.1016/j.jsxm.2022.07.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 06/10/2022] [Accepted: 07/17/2022] [Indexed: 11/22/2022]
Abstract
BACKGROUND Laboratory paradigms that enable the female rat to control the frequency and temporal distribution of sexual stimulation are well-suited to gaining knowledge about female sexual function; however, the variety of procedures used influence the specific behaviors exhibited by female rats and bring uncertainty into the conclusions that can be drawn. AIM In this study, we evaluated the effects of test parameters on the display of paced mating behavior in female rats to develop better preclinical models for exploring female sexual health. METHODS Sexually experienced, estradiol- and progesterone-primed female rats were tested under paced mating conditions to determine whether sexual behavior differed as a function of number of male partners (1 or 3; Experiment 1), the time span between receipt of an ejaculation and the next intromission (ie, the post-ejaculatory interval or PEI; Experiment 2), or the duration of ejaculations (Experiment 3). OUTCOMES Contact-return latency, exit latency, and withdrawal duration after mounts, intromissions, and ejaculations. RESULTS The shorter withdrawal latency after intromission and longer return latency after ejaculation observed in 30-minute paced mating tests is best attributed to the female's PEI. The duration of the PEI is a specific factor that affects the display of paced mating behavior. CLINICAL TRANSLATION Understanding of neurobiological mechanisms and sensory factors influencing sexual behavior learned from these models can be applied to studies of human female sexual health. STRENGTHS & LIMITATIONS Sexual motivation is indicated by analogous behaviors and supported by evolutionarily conserved systems in women and rats, meaning that animal models can be used to identify neurobiological mechanisms subserving these behaviors. Nonetheless, data related specifically to physiological effects of different mating paradigms are needed in future research. CONCLUSION Procedures that mimic naturalistic settings, and thus enable female sexual motivation to drive behavior, are apt for studies aimed at understanding mechanisms supporting female sexual function whereas artificially lengthening the interval between an ejaculation and subsequent intromission may provide a model to study female sexual dysfunction.
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Piergies AMH, Hicks ME, Schwartz JP, Meerts SH. Sexually experienced, but not naïve, female rats show a conditioned object preference (COP) for mating after a single training trial. Physiol Behav 2018; 198:42-47. [PMID: 30290181 DOI: 10.1016/j.physbeh.2018.09.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 09/30/2018] [Accepted: 09/30/2018] [Indexed: 01/23/2023]
Abstract
Female rats with mating experience spend more time with the male rat, exhibit shorter contact-return latency to intromission, and display more proceptive behaviors in the male rat's compartment than during the first mating experience. The present study tested 1) whether mating induced conditioned object preference (COP) is possible with a single conditioning trial and 2) whether a preference is induced for an object associated with the first mating encounter or the fifth mating encounter in female rats. Ovariectomized, Long-Evans female rats were primed with estradiol benzoate + progesterone and either exposed to an empty paced mating chamber for 15 min (Naïve) or received a 15 intromission test of paced mating behavior (Experienced) on four separate occasions before undergoing the COP procedure. Experienced, but not Naïve, female rats developed a COP for a single mating bout, indicating that mating is highly rewarding for sexually experienced female rats. The findings raise questions about the effect of sexual experience on reward regions in the brain, the responsiveness of genital tissue, and learning mechanisms.
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Affiliation(s)
| | - Maurice E Hicks
- Department of Psychology, Carleton College, Northfield, MN 55057, United States
| | - Jacob P Schwartz
- Department of Psychology, Carleton College, Northfield, MN 55057, United States
| | - Sarah H Meerts
- Department of Psychology, Carleton College, Northfield, MN 55057, United States.
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3
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Sinchak K, Dalhousay L, Sanathara N. Orphanin FQ-ORL-1 regulation of reproduction and reproductive behavior in the female. VITAMINS AND HORMONES 2015; 97:187-221. [PMID: 25677773 DOI: 10.1016/bs.vh.2014.11.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Orphanin FQ (OFQ/N) and its receptor, opioid receptor-like receptor-1 (ORL-1), are expressed throughout steroid-responsive limbic and hypothalamic circuits that regulate female ovarian hormone feedback and reproductive behavior circuits. The arcuate nucleus of the hypothalamus (ARH) is a brain region that expresses OFQ/N and ORL-1 important for both sexual behavior and modulating estradiol feedback loops. Within the ARH, the activation of the OFQ/N-ORL-1 system facilitates sexual receptivity (lordosis) through the inhibition of β-endorphin neuronal activity. Estradiol initially activates ARH β-endorphin neurons to inhibit lordosis. Simultaneously, estradiol upregulates coexpression of OFQ/N and progesterone receptors and ORL-1 in ARH β-endorphin neurons. Ovarian hormones regulate pre- and postsynaptic coupling of ORL-1 to its G protein-coupled signaling pathways. When the steroid-primed rat is nonreceptive, estradiol acts pre- and postsynaptically to decrease the ability of the OFQ/N-ORL-1 system to inhibit ARH β-endorphin neurotransmission. Conversely, when sexually receptive, ORL-1 signaling is restored to inhibit β-endorphin neurotransmission. Although steroid signaling that facilitates lordosis converges to deactivate ARH β-endorphin neurons, estradiol-only facilitation of lordosis requires the activation of ORL-1, but estradiol+progesterone does not, indicating that multiple circuits mediate ovarian hormone signaling to deactivate ARH β-endorphin neurons. Research on the role of OFQ/N-ORL-1 in ovarian hormone feedback loops is just beginning. In the rat, OFQ/N may act to terminate gonadotropin-releasing hormone and luteinizing hormone release under positive and negative feedbacks. In the ewe, it appears to directly inhibit gonadotropin-releasing hormone release to mediate progesterone-negative feedback. As a whole, the localization and actions of OFQ/N-ORL-1 system indicate that it may mediate the actions of estradiol and progesterone to synchronize reproductive behavior and ovarian hormone feedback loops.
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Affiliation(s)
- Kevin Sinchak
- Department of Biological Sciences, California State University, Long Beach, California, USA.
| | - Lauren Dalhousay
- Department of Biological Sciences, California State University, Long Beach, California, USA
| | - Nayna Sanathara
- Department of Pharmacological Sciences, University of California, Irvine, California, USA
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4
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Meerts SH, Schairer RS, Farry-Thorn ME, Johnson EG, Strnad HK. Previous sexual experience alters the display of paced mating behavior in female rats. Horm Behav 2014; 65:497-504. [PMID: 24401472 DOI: 10.1016/j.yhbeh.2013.12.015] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Revised: 12/19/2013] [Accepted: 12/26/2013] [Indexed: 11/28/2022]
Abstract
The present study tested whether the display of paced mating behavior in female rats over four weekly tests is affected by sexual experience and whether test parameters, i.e., ending the test based on time or number of stimulations received, influence behavioral changes. In Experiment 1A rats with nonpaced sexual experience returned to the male more quickly overall compared to sexually naïve rats in a 30-min test of paced mating behavior. In Experiment 1B, rats received four weekly 30-min tests with one, different, male rat partner each week. Over the four tests, rats returned to the male significantly more quickly after intromissions, but significantly more slowly after ejaculations. Experiment 2A tested whether sexual experience would influence paced mating behavior in tests with a 15-intromission end criterion and the male replaced after ejaculation. Rats tested weekly under 15-intromission test conditions returned to the male significantly more quickly after intromissions, but no behavioral change was observed after ejaculations. When those same rats were given a 30-min test of paced mating behavior (Experiment 2B), they returned to the male significantly more slowly after ejaculations. Collectively, these data show that sexual experience influences the display of paced mating behavior in female rats and that the test parameters interact with sexual experience to influence the nature of the changes. Sexual experience may facilitate behaviors that promote reproductive success in female rats.
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Affiliation(s)
- Sarah H Meerts
- Department of Psychology, Carleton College, Northfield, MN 55057, USA.
| | | | | | - Elliott G Johnson
- Department of Psychology, Carleton College, Northfield, MN 55057, USA
| | - Helen K Strnad
- Department of Psychology, Carleton College, Northfield, MN 55057, USA
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5
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Clitoral anesthesia disrupts paced copulation in the female rat. Physiol Behav 2014; 123:180-6. [DOI: 10.1016/j.physbeh.2013.10.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Revised: 09/10/2013] [Accepted: 10/18/2013] [Indexed: 11/20/2022]
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6
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Cummings JA, Becker JB. Quantitative assessment of female sexual motivation in the rat: Hormonal control of motivation. J Neurosci Methods 2011; 204:227-33. [PMID: 22120688 DOI: 10.1016/j.jneumeth.2011.11.017] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Revised: 11/10/2011] [Accepted: 11/12/2011] [Indexed: 11/26/2022]
Abstract
While a good deal of information has been garnered in the last few decades regarding the neural and hormonal control of female sexual behavior, literature elucidating these mechanisms with respect to female sexual motivation has been scarce. We believe that one reason for this is the lack of a standardized paradigm that will quantify female sexual motivation while allowing for sexual interaction to occur. Here we describe a two-chambered apparatus that utilizes operant responding (nose poking) to quantify female sexual motivation. During the test, the female exhibits nose pokes to gain access to a sexually active male, with whom she is allowed to mate. Therefore, this apparatus allows for examination of sexual behavior as well as quantification of sexual motivation by assessing the number of nose pokes the female will exhibit within a fixed interval to gain access to the male. We report that hormone priming significantly increases sexual motivation in the female as indicated by the number of nose pokes she will exhibit to gain access to the male. Additionally, hormone primed females enter the male compartment after a shorter period and spend more time in direct contact with the male compared to when they are not hormone primed. In contrast, when females are not hormone primed they spend more time in view, but out of reach, of the male. This paradigm will help to advance the study of female sexual motivation, providing a method for quantifiable assessment of female sexual motivation while allowing for sexual activity to occur.
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Affiliation(s)
- Jennifer A Cummings
- Molecular and Behavioral Neuroscience Institute, University of Michigan, 205 Zina Pitcher Place, Ann Arbor, MI 48109, United States.
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7
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Meerts SH, Boisvert EM, Spjut KA, Clark AS. Paced mating behavior persists in rats with vaginocervical Lidocaine. Physiol Behav 2010; 99:139-41. [PMID: 19840811 DOI: 10.1016/j.physbeh.2009.10.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2009] [Revised: 09/25/2009] [Accepted: 10/08/2009] [Indexed: 01/01/2023]
Abstract
The present study tested whether the topical application of a local anesthetic (Lidocaine) to the vaginocervical region altered the pattern of paced mating behavior displayed by gonadectomized, hormone-primed female rats. Both rats receiving Lidocaine and rats receiving vehicle exhibited the expected lengthening of contact-return latency as the intensity of the mating stimuli increased (mount<intromission<ejaculation). Although rats given Lidocaine versus vehicle received a greater number of intromissions, no other group differences were observed. The present study found no evidence for a change in behavioral responsiveness following the vaginocervical application of Lidocaine.
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Affiliation(s)
- Sarah H Meerts
- Department of Psychological and Brain Sciences, Dartmouth College, Hanover NH 03755, United States
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8
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Camacho FJ, García-Horsman P, Paredes RG. Hormonal and testing conditions for the induction of conditioned place preference by paced mating. Horm Behav 2009; 56:410-5. [PMID: 19646448 DOI: 10.1016/j.yhbeh.2009.07.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2009] [Revised: 07/14/2009] [Accepted: 07/15/2009] [Indexed: 10/20/2022]
Abstract
The ability to control or pace the sexual interaction has important physiological and behavioral consequences for the female rat. Paced mating favors reproduction and induces a positive affective state as revealed by conditioned place preference (CPP). In the present experiment we evaluated: 1) If paced mating induces CPP in naturally cycling females; 2) If females developed a positive affective state if they paced the sexual interaction through a 1- or a 3-hole pacing chamber; 3) If females that mate with the same male without pacing the sexual interaction develop CPP. In the first experiment intact females were divided in 4 different groups; 2 paced the sexual interaction until receiving 1 or 3 ejaculations; the other 2 groups mated, without pacing the sexual interaction, until receiving 1 or 3 ejaculations. Only the group that paced the sexual interaction until receiving 3 ejaculations developed a positive affective state. In experiments 2 and 3 hormonally treated ovariectomized females were used. In experiment 2 females were allowed to pace the sexual interaction through a 1- or a 3-hole pacing chamber: A clear positive affective state was induced in both testing conditions. Finally, in experiment 3 females did not develop CPP for non-paced sex despite the fact that they mated with the same male in the conditioning sessions. These results demonstrate that the pattern of vaginocervical stimulation that the females received by engaging in approach and avoidance behaviors to pace the sexual interaction can induce a positive affective state in naturally cycling females. They also confirm the existence of a threshold of vaginocervical stimulation for paced mating to induce CPP in female rats.
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Affiliation(s)
- Francisco J Camacho
- Instituto de Neurobiología, Universidad Nacional Autónoma de México, Querétaro, Qro., Mexico
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9
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Flanagan-Cato LM, Lee BJ, Calizo LH. Co-localization of midbrain projections, progestin receptors, and mating-induced fos in the hypothalamic ventromedial nucleus of the female rat. Horm Behav 2006; 50:52-60. [PMID: 16546183 DOI: 10.1016/j.yhbeh.2006.01.012] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2005] [Revised: 01/19/2006] [Accepted: 01/19/2006] [Indexed: 11/30/2022]
Abstract
In female rats, sexual behavior requires the convergence of ovarian hormone signals, namely estradiol and progesterone, and sensory cues from the male on a motor output pathway. Estrogen and progestin receptors (ER and PR) are found in neurons in the hypothalamic ventromedial nucleus (VMH), a brain region necessary for lordosis, the stereotypic female copulatory posture. A subset of VMH neurons sends axonal projections to the periaqueductal gray (PAG) to initiate a motor output relay, and some of these projection neurons express PR. Previous studies showed that VMH neurons are activated during mating, based on the expression of the immediate early gene Fos. Many of the activated neurons expressed ER; however, it is not known if such activated neurons co-express PR. Fluorogold, a retrograde tracer, was injected into the PAG of ovariectomized rats to label neurons projecting from the VMH. Hormone-treated animals then were mated, and their brains were immunohistochemically stained for PR and Fos. Of the Fos-positive neurons, 33% were double-labeled for PR, 19% were double-labeled with Fluorogold, and 5% were triple-labeled for Fos, PR, and the retrograde tracer. The majority of triple-labeled neurons were found in the rostral, rather than caudal, portion of the VMH. These results show that PR-containing neurons are engaged during sexual behavior, which suggests that these neurons are the loci of hormonal-sensory convergence and hormonal-motor integration.
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Affiliation(s)
- Loretta M Flanagan-Cato
- Department of Psychology, Institute of Neurological Sciences, University of Pennsylvania, Philadelphia, PA 19104, USA.
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10
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Afonso VM, Bablekis V, Pfaus JG. Sensory mediation of female–male mounting in the rat: II. Role of tactile and conspecific cues. Physiol Behav 2006; 87:863-9. [PMID: 16488455 DOI: 10.1016/j.physbeh.2006.01.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2005] [Revised: 12/17/2005] [Accepted: 01/03/2006] [Indexed: 11/24/2022]
Abstract
Although previous research has shown that olfactory cues mediate female-male mounting (FMM) in the rat, the role of other sensory modalities on FMM has not been investigated. The present study examined the display of female mounting of castrated male rats in bilevel chambers following different tactile or locomotor activity manipulations. Female rats (N = 40) were ovariectomized (OVX), primed with estrogen (E) and progesterone (P), and given either vaginocervical stimulation (VCS), flank/perineum stimulation (FPS), combined VCS and FPS, or general handling, immediately before each test with a castrated male rat for five trials. Compared to handling, the FPS females showed an increase in FMM behavior, whereas females given VCS, or combined VCS and FPS, showed a decrease in FMM behavior. A second experiment examined the effect of a 15-min delay between stimulation and testing using identical experimental and control conditions. There were no significant differences in the amount of FMM behavior between these groups. Finally, OVX rats primed with E and P were tested with castrated males that had been given injections of a ketamine/xylazine anesthetic mixture, saline, or amphetamine, to induce three levels of conspecific locomotor activity: none, moderate, or high, respectively. A positive linear relationship was found between male activity level and FMM. These data indicate that both tactile cues and cues associated with locomotor activity of the stimulus male modulate FMM.
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Affiliation(s)
- Veronica M Afonso
- Center for Studies in Behavioral Neurobiology, Department of Psychology, Concordia University, 7141 Sherbrooke St. W., Montréal, QC, Canada H4B 1R6
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11
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Paredes RG, Agmo A. Has dopamine a physiological role in the control of sexual behavior? A critical review of the evidence. Prog Neurobiol 2004; 73:179-226. [PMID: 15236835 DOI: 10.1016/j.pneurobio.2004.05.001] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2003] [Accepted: 05/14/2004] [Indexed: 11/30/2022]
Abstract
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.
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Affiliation(s)
- Raúl G Paredes
- Instituto de Neurobiología, Universidad Nacional Aunónoma de México-Campus Juriquilla, Querétaro, Mexico
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Erskine MS, Lehmann ML, Cameron NM, Polston EK. Co-regulation of female sexual behavior and pregnancy induction: an exploratory synthesis. Behav Brain Res 2004; 153:295-315. [PMID: 15265625 DOI: 10.1016/j.bbr.2004.01.026] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2003] [Revised: 12/20/2003] [Accepted: 01/11/2004] [Indexed: 11/20/2022]
Abstract
This paper will review both new and old data that address the question of whether brain mechanisms involved in reproductive function act in a coordinated way to control female sexual behavior and the induction of pregnancy/pseudopregnancy (P/PSP) by vaginocervical stimulation. Although it is clear that female sexual behavior, including pacing behavior, is important for induction of P/PSP, there has been no concerted effort to examine whether or how common mechanisms may control both functions. Because initiation of P/PSP requires that the female receive vaginocervical stimulation, central mechanisms controlling P/PSP may be modulated by or interactive with those that control female sexual behavior. This paper presents a synthesis of the literature and recent data from our lab for the purpose of examining whether there are interactions between behavioral and neuroendocrine mechanisms which reciprocally influence both reproductive functions.
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Affiliation(s)
- Mary S Erskine
- Department of Biology, Boston University, 5 Cummington Street, Boston, MA 02215, USA.
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Pfaus JG, Shadiack A, Van Soest T, Tse M, Molinoff P. Selective facilitation of sexual solicitation in the female rat by a melanocortin receptor agonist. Proc Natl Acad Sci U S A 2004; 101:10201-4. [PMID: 15226502 PMCID: PMC454387 DOI: 10.1073/pnas.0400491101] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2004] [Accepted: 05/28/2004] [Indexed: 01/25/2023] Open
Abstract
Disorders of sexual desire affect an estimated 30% of women in North America and Europe, with etiologies based on interpersonal, personal, and physiological factors. There are currently no pharmacological agents approved for use in the treatment of female sexual dysfunction. This is due, in part, to a focus on the effects of experimental drugs on reflexive components of sexual behavior, such as lordosis, in animal models. Here we report that PT-141, a peptide analogue of alpha-melanocyte-stimulating hormone that binds to central melanocortin receptors, selectively stimulates solicitational behaviors in the female rat. This occurs without affecting lordosis, pacing, or other sexual behaviors. PT-141 did not cause generalized motor activation, nor did it affect the perception of sexual reward. A selective pharmacological effect on appetitive sexual behavior in female rats has not been reported previously, and indicates that central melanocortin systems are important in the regulation of female sexual desire. Accordingly, PT-141 may be the first identified pharmacological agent with the capability to treat female sexual desire disorders.
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Affiliation(s)
- James G Pfaus
- Center for Studies in Behavioral Neurobiology, Department of Psychology, Concordia University, Montreal, QC, Canada H4B 1R6.
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Agmo A, Turi AL, Ellingsen E, Kaspersen H. Preclinical models of sexual desire: conceptual and behavioral analyses. Pharmacol Biochem Behav 2004; 78:379-404. [PMID: 15251248 DOI: 10.1016/j.pbb.2004.04.013] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/08/2004] [Revised: 04/01/2004] [Accepted: 04/16/2004] [Indexed: 01/23/2023]
Abstract
The epidemiology, etiology and proposed treatments for the sexual desire disorders are briefly reviewed before turning to an analysis of preclinical models. We suggest that the concept of sexual desire in the human is equivalent to sexual motivation as employed in the scientific literature. Many animal tests for sexual motivation have been described over the years. Most of them are based on the evaluation of the rate or speed of performing learned operant responses. These are not ideal measures for inferring the intensity of sexual motivation. We present a test for sexual incentive motivation, which has been used in male and female rats. No learning is involved, and the test is rather insensitive to variations in ambulatory activity and it does not employ rate measures. A procedure that recently has attracted much attention, paced-mating behavior in the female, does not seem to be as useful as could be expected. In fact, it does not appear to be superior to tests for sexual receptivity (lordosis). The lack of established, clinically efficient treatments for sexual desire disorders makes it difficult to evaluate if any model has predictive validity. However, the model proposed here may be isomorphic and homologous to the human condition.
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Affiliation(s)
- Anders Agmo
- Department of Psychology, University of Tromsø, 9037 Tromsø, Norway.
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Nedergaard P, Sanchez C, Mellerup E. Different roles of 5-HT2A and 5-HT2C receptors in regulation of female rat paced mating behaviour. Behav Brain Res 2004; 149:151-7. [PMID: 15129779 DOI: 10.1016/s0166-4328(03)00215-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Serotonin (5-HT) receptor 2A (5-HT2A) and 2C (5-HT2C) agonists have been reported to facilitate female rat lordosis behaviour. This study investigated the acute effects of the 5-HT2A receptor agonist DOI ((+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane) and the 5-HT2C receptor agonist MK-212 (2-chloro-6-(1-piperazinyl) pyrazine) on paced mating behaviour in a population of sexually receptive female rats in order to explore the role of 5-HT2A and 5-HT2C receptors in the mediation of female rat sexual motivation. DOI (0.5 and 1.0 mg/kg) increased female rat sexual motivation during the first of two consecutive copulatory series seen as a tendency towards a decrease in return latencies following ejaculation and decreased inter-intromission intervals. MK-212 generally increased approach latencies. 0.5 mg/kg MK-212 increased post-ejaculatory exit latency, while 1.0 and 2.0 mg/kg MK-212 increased both post-ejaculatory exit latencies and post-ejaculatory return latencies. The possibility that an increased level of anxiety confounded the effects of MK-212 on sexual motivation behaviour is discussed. The results may support the hypothesis that both 5-HT2A and 5-HT2C receptors are important in regulation of female sexual behaviour.
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Affiliation(s)
- Per Nedergaard
- Laboratory of Neuropsychiatry, Department of Psychiatry, Copenhagen University Hospital, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
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Calizo LH, Flanagan-Cato LM. Hormonal-neural integration in the female rat ventromedial hypothalamus: triple labeling for estrogen receptor-alpha, retrograde tract tracing from the periaqueductal gray, and mating-induced Fos expression. Endocrinology 2003; 144:5430-40. [PMID: 12960097 DOI: 10.1210/en.2003-0331] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The lordosis reflex, a stereotypic posture adopted by female rats during sexual behavior, requires the convergence of a hormonal signal, estrogen, with a descending neural pathway from the ventromedial hypothalamic nucleus (VMH). The VMH contains at least three lordosis-relevant neural populations: estrogen receptor-alpha immunoreactive (ERalpha-IR) neurons, VMH neurons that project to the periaqueductal gray (PAG), and neurons that are ERalpha-IR and project to the PAG. Expression of Fos, a marker for neuronal activation, is increased in the VMH after mating. However, it is unknown which, if any, of these lordosis-relevant populations is activated. The majority of ERalpha-IR and projection neurons were not colocalized. Of the Fos-positive neurons, 41% neither contained ERalpha nor projected to the PAG, and 35% contained ERalpha but did not project to the PAG. Only 25% of Fos-positive neurons projected to the PAG, including projection neurons that expressed ERalpha. Our results suggest that mating activates several distinct VMH neuron types. However, ERalpha-IR neurons are activated to a greater extent compared with the PAG-projecting neurons.
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Affiliation(s)
- Lyngine H Calizo
- Institute of Neurological Sciences, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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Gréco B, Blasberg ME, Kosinski EC, Blaustein JD. Response of ERalpha-IR and ERbeta-IR cells in the forebrain of female rats to mating stimuli. Horm Behav 2003; 43:444-53. [PMID: 12788290 DOI: 10.1016/s0018-506x(03)00028-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Sexual behavior in female rats depends on the action of estradiol on estrogen receptors (ERs) found in particular brain regions. While hormonal regulation of female sexual behavior requires ERalpha, the possible functions of ERbeta remain to be clarified. Mating stimulation has several behavioral and physiological consequences and induces Fos expression in many brain areas involved in the regulation of reproductive behavior and physiology. In addition, some cells in which mating induces Fos expression coexpress ERalpha. To determine whether cells in which Fos is induced by a particular mating stimulus coexpress ERalpha, ERbeta, or both, we used a triple-label immunofluorescent technique to visualize ERalpha-, ERbeta-, and mating-induced Fos-immunoreactivity (Fos-ir) in neurons in which mating stimulation reliably increases Fos expression. Ovariectomized, hormone-primed rats were either unmated, received 15 mounts, or received 15 intromissions. In the rostral medial preoptic area, Fos-ir was induced by mounts alone primarily in cells coexpressing ERalpha-ir, while Fos-ir was induced by intromissions mainly in cells coexpressing both ERalpha-ir and ERbeta-ir (ERalpha/ERbeta-ir). In the dorsal part of the posterodorsal medial amygdala, Fos-ir was induced by intromissions in cells coexpressing ERalpha-ir and ERalpha/ERbeta-ir. However, in the ventral part of the posterodorsal medial amygdala, Fos-ir was induced by intromissions primarily in cells coexpressing only ERbeta-ir. These data suggest that qualitatively different sexual stimuli may be integrated through distinct ER-containing circuits in the rostral medial preoptic area and posterodorsal medial amygdala. The diversity in coexpression of type of ER in cells in different brain areas after various mating stimuli suggests a role for both ERalpha and ERbeta in the integration of hormonal information and information related to mating stimuli.
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Affiliation(s)
- Béatrice Gréco
- Center for Neuroendocrine Studies, University of Massachusetts, Amherst, MA 01003, USA.
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18
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Bennett AL, Blasberg ME, Blaustein JD. Mating stimulation required for mating-induced estrous abbreviation in female rats: effects of repeated testing. Horm Behav 2002; 42:206-11. [PMID: 12367573 DOI: 10.1006/hbeh.2002.1809] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mating stimulation, particularly vaginal-cervical stimulation, causes estrous abbreviation in female rats. In most previous studies, female rats were repeatedly tested for sexual behavior until estrous termination occurred. Thus, it was not clear whether sensory stimulation (e.g., flank stimulation, olfactory cues) received during the repeated testing procedure contributed to estrous abbreviation. In Experiment 1, we determined the effect of premating to two or four ejaculations on the rate of estrous termination when a repeated testing procedure was used. We compared ovariectomized, hormone-primed, female rats receiving (1) four ejaculations, (2) two ejaculations, or (3) no premating. Females premated to either two or four ejaculations showed significantly lower levels of sexual receptivity 12 h later than did nonpremated females. These results confirm that premating induces estrous abbreviation when a repeated testing procedure is used. In Experiment 2, we determined whether the repeated testing procedure was necessary for estrous abbreviation. Ovariectomized, hormone-primed female rats were premated to two ejaculations or not premated. The rats were then tested for sexual behavior repeatedly or only once. Females that were premated and repeatedly tested for sexual behavior showed a statistically significant decrease in sexual receptivity compared to females that were not premated; however, the level of sexual receptivity in premated females did not differ from that in non-premated females when they were tested only once. The results suggest that heat duration is the result of a complex interplay between those factors that promote the expression of sexual receptivity and those that inhibit it.
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Affiliation(s)
- Amy L Bennett
- Center for Neuroendocrine Studies, Neuroscience and Behavior Program, University of Massachusetts, Amherst 01003, USA
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19
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Bennett AL, Gréco B, Blasberg ME, Blaustein JD. Response to male odours in progestin receptor- and oestrogen receptor-containing cells in female rat brain. J Neuroendocrinol 2002; 14:442-9. [PMID: 12047719 DOI: 10.1046/j.1365-2826.2002.00806.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Sensory cues from male rats, such as odours and vaginal-cervical stimulation (VCS), play a modulatory role in female rat sexual behaviour. For example, exposure to male odours and VCS appears to be at least partially responsible for increases in sexual behaviour following repeated mating of oestradiol-primed female rats. Although there is evidence that VCS influences sexual behaviour via a ligand-independent progestin receptor (PR)-dependent mechanism, the mechanism by which odours influence sexual behaviour is not known. We tested the hypothesis that, similar to VCS, the effects of male odours on sexual behaviour are mediated by progestin receptors. Female rats were injected with the progestin antagonist, RU486, or oil vehicle and were then exposed to male-soiled bedding or clean bedding. Although exposure to male-soiled bedding resulted in higher levels of Fos immunoreactivity in brain areas associated with female sexual behaviour, the progestin antagonist did not reduce this effect. Furthermore, there was minimal coexpression of odour-induced Fos and progestin receptors in brain areas associated with female sexual behaviour. Together, these results suggest that the effects of male odours are not mediated by a PR-dependent mechanism. Therefore, we tested the hypothesis that oestrogen receptor (ER)-containing cells are involved in the effects of olfactory cues. Although there was virtually no coexpression of ERbeta and odour-induced Fos in brain areas associated with female sexual behaviour, exposure to male odours slightly increased the number of cells coexpressing ER(alpha) and odour-induced Fos in the posterodorsal medial amygdala. Although, these results do not support the hypothesis that the effects of odours are mediated by a PR-dependent mechanism, they suggest that integration of male odours and hormonal cues may occur in ER(alpha)-containing cells in the posterodorsal medial amygdala.
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Affiliation(s)
- A L Bennett
- Center for Neuroendocrine Studies, Neuroscience and Behavior Program, University of Massachusetts, Amherst, MA 01003-9271, USA
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20
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Abstract
When rats are mated in a traditional mating chamber (with one male and one female) in which the male dictates the pace of the copulatory sequence, males develop a reward state as evaluated by conditioned place preference (CPP). In this mating situation no reward state is induced in females. However, when female rats are able to control (pace) the rate of sexual stimulation, thereby reducing the aversive consequences associated with mating, a clear CPP is observed. In the present study the CPP paradigm was used to determine whether if the reinforced state induced by coital interactions in male rats can be maintained when females pace the sexual interaction. Adult male and female rats were mated in one of two different conditions: (1) where subjects were able to pace their coital interactions or (2) where subjects were not able to pace their sexual contacts. The results showed that when males had control over the sexual interaction they developed a clear place preference while males that mated with females that paced their coital contacts did not develop CPP. Similarly, only females that were able to pace their sexual contacts developed place preference. These results suggest that coital interactions in males, as well as in females, can induce a reward state only when they are able to control the sexual interaction. Under seminatural conditions sexual behavior in rats is highly promiscuous, they mate in groups and repeatedly change partners in the middle of copulation. This behavioral sequence allows both, male and female to control the rate of sexual interaction, assuring the induction of a reward state outlasting the actual performance of coital responses.
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Affiliation(s)
- I Martínez
- Centro de Neurobiología, Universidad Nacional Autónoma de México, Apartado postal 1-1141, Querétaro, Qro, 76001, México
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21
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Bennett AL, Blasberg ME, Blaustein JD. Sensory cues mediating mating-induced potentiation of sexual receptivity in female rats. Horm Behav 2001; 40:77-83. [PMID: 11467886 DOI: 10.1006/hbeh.2001.1664] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Repeated mating of estradiol-primed female rats increases sexual receptivity. Two studies were conducted to determine the contribution of vaginal--cervical stimulation (VCS) to this increase. In the first study, female rats were repeatedly mated for 165 min. The vaginas of half of the females were covered with tape (masked) to prevent intromissions by the males. The remaining females were unmasked. Only females receiving intromissions (unmasked) showed a significant increase in sexual receptivity during repeated mating, suggesting that VCS from intromissions is necessary for repeated mating to increase sexual receptivity. In the second experiment, female rats received either experimentally administered VCS or control scapular stimulation administered with a plastic probe 1 h prior to testing for sexual receptivity. VCS applied in this manner significantly increased sexual receptivity. Together, these findings suggest that VCS from intromissions is one of the primary factors responsible for increases in sexual receptivity following repeated mating.
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Affiliation(s)
- A L Bennett
- Center for Neuroendocrine Studies, Neuroscience and Behavior Program, University of Massachusetts, Amherst, Massachusetts 01003, USA
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22
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Pfaus JG, Smith WJ, Byrne N, Stephens G. Appetitive and consummatory sexual behaviors of female rats in bilevel chambers. II. Patterns of estrus termination following vaginocervical stimulation. Horm Behav 2000; 37:96-107. [PMID: 10712862 DOI: 10.1006/hbeh.1999.1562] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Copulation with intromission or manual vaginocervical stimulation (VCS) shortens the duration that intact female rats maintain lordosis responding during estrus. The present study examined whether VCS could shorten the duration of both appetitive and consummatory measures of female sexual behavior, and whether these effects occur differentially in time and across different hormone priming intervals. Ovariectomized, sexually experienced female rats were administered subcutaneous injections of estradiol benzoate 48 h and progesterone 4 h, before receiving 50 manual VCSs with a lubricated glass rod distributed over 1 h. Control females received sham VCSs distributed over the same time. The females were then tested for sexual behavior in bilevel chambers with two sexually vigorous males (to one ejaculatory series or 10 min with each male, separated by 5 min) 12, 16, and 20 h after VCS. Prior to the final hormone treatment, different groups of females had been given the same hormone treatment either 28, 14, 7, or 4 days before. In females tested at 28- and 14-day hormone intervals, VCS induced both active and passive rejection responses at 12, 16, and 20 h. In contrast, females that received sham VCS displayed relatively normal sexual behavior at 12 h, although by 16 and 20 h these females displayed active and passive rejection. Females tested at 7- or 4-day intervals displayed normal levels of lordosis at all testing times, regardless of VCS treatment. These data indicate that VCS facilitates rejection responses that precede the decrease in lordosis responsiveness. However, the effects of VCS are dependent on the frequency of hormone priming, suggesting that hormone treatment may block some of the long-term inhibitory effects of VCS on female sexual behavior.
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Affiliation(s)
- J G Pfaus
- Center for Studies in Behavioral Neurobiology, Concordia University, Montréal, Québec, H3G 1M8, Canada.
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23
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24
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Abstract
The motivational aspects of female sexual behavior have been evaluated by a variety of methodologies including: the increasing barrier method, the runway procedure, partner preference test, operant behavior and conditioned place preference. When female rats are tested for sexual receptivity under traditional laboratory conditions, usually a small open area, both appetitive and aversive components of the sexual interaction are easily observed. For example, after prolonged testing, subsequent lordosis and the intensity of this response are reduced increasing the rejection behavior by the female. However, when female rats are allowed to pace (control) the rate of sexual stimulation they received, as usually occurs under seminatural and natural conditions, the aversive properties of mating are reduced. The conditioned place preference can be use to measure the positive affect elicited by mating. We have combined pacing and conditioned place preference in an attempt to reduced the possible aversive consequences associated with mating and increase the likelihood of detecting the appetitive effects of coital interaction in female rats. Only female rats that regulated (paced) their coital interactions with a stud male through a two-compartment chamber in which only the female could freely move from one compartment to the other developed a clear place preference. As well, females that received ten or 15 paced intromissions (without ejaculation) also developed place preference. The place preference induce by paced mating is blocked by the systemic administration of naloxone suggesting that opioids are involved in the reward processes associated with paced mating. Paced sexual interactions can induce a positive affect of sufficient intensity and duration to induce conditioning.
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Affiliation(s)
- R G Paredes
- Centro de Neurobiología, UNAM, Queretaro, Qro., Mexico.
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25
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Pfaus JG, Smith WJ, Coopersmith CB. Appetitive and consummatory sexual behaviors of female rats in bilevel chambers. I. A correlational and factor analysis and the effects of ovarian hormones. Horm Behav 1999; 35:224-40. [PMID: 10373335 DOI: 10.1006/hbeh.1999.1516] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
This study investigated measures of sexual behavior displayed by female rats in bilevel chambers, the statistical relationships among the measures, and their dependency on hormone priming. Normative data from a standard 35-min test of sexual behavior were gathered from 82 fully primed sexually experienced Long-Evans females and subjected to multiple correlational and factor analyses. Several consummatory measures of copulation were related significantly, whereas appetitive level changing was statistically independent of consummatory measures. Factor analyses were conducted using orthogonal rotations of correlational matrices derived either from (a) measures of female behavior alone or (b) measures of female and male behavior together. The first analysis revealed five factors that accounted for 84% of the intersubject variance: Receptivity, Pacing, Appetitive Level Changing, Lordosis Reflex, and Solicitation. The second factor analysis with male data included revealed seven factors that accounted for 95% of the intersubject variance: Pacing, Copulatory Rate, Mount Count, Receptivity, Appetitive Level Changing, Solicitation, and Lordosis Reflex. Subsequently, subsets of these females were maintained on different steroid priming regimens (oil, low estrogen, high estrogen, high estrogen and progesterone) prior to a standard test of sexual behavior. Although the expression of all sexual behaviors required estrogen priming, appetitive level changing, solicitation, and pacing required progesterone for their full expression. Finally, appetitive level changing developed following hormone treatment alone, regardless of whether the females received access to sexually active males, inactive castrated males, or other females. Use of bilevel chambers allows complex patterns of sexual behavior to be observed in female rats and may thus facilitate the identification of neurochemical or endocrine mechanisms associated with different aspects of female sexual motivation and performance.
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Affiliation(s)
- J G Pfaus
- Department of Psychology, Concordia University, Montréal, Québec, H3G 1M8, Canada.
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Brandling-Bennett EM, Blasberg ME, Clark AS. Paced mating behavior in female rats in response to different hormone priming regimens. Horm Behav 1999; 35:144-54. [PMID: 10202122 DOI: 10.1006/hbeh.1998.1507] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
A female rat will display a repertoire of behaviors during a sexual encounter with a male rat including sexually receptive (the lordosis response) and proceptive (hopping, darting) behaviors. In addition, when given the opportunity, a sexually receptive female rat will approach and withdraw from the male rat, controlling the timing of the receipt of mounts, intromissions, and ejaculations, a behavior known as paced mating behavior. The present experiments tested the hypotheses (1) that progesterone regulates paced mating behavior, and (2) that multiple hormone regimens used previously to induce sexual receptivity have the same effect on paced mating behavior. Paced mating behavior was assessed in sexually receptive ovariectomized female rats after treatment with: (1) estradiol benzoate (EB; 30.0 mg/kg) followed by a range of doses of progesterone (P; 1.0-8.0 mg/kg), (2) two pulses of unesterified estradiol (E2; 2.0 microg/rat) followed by 1.0 mg/rat of P, and (3) EB alone (5.0 microg/rat) for 6 days. No differences in sexual receptivity or in paced mating behavior were observed across doses of P (1.0-8.0 mg/kg). In contrast, the number of hops and darts per min increased with the dose of P administered. E2 + P administration resulted in slightly, but significantly, lower levels of sexual receptivity along with significantly longer contact-return latencies following an intromission in relation to the other treatment conditions. In addition, female rats exhibited fewer hops and darts per min in response to E2 + P than in response to EB + 8.0 mg/kg of P. The administration of EB alone for 6 days induced levels of receptivity and paced mating behavior indistinguishable from EB + P, while eliciting significantly fewer hops and darts per min than the EB + 8.0 mg/kg P treatment condition. Hormone priming regimen had no effect on the percentage of exits displayed during the paced mating tests in any experimental phase. Dose of P had no effect on paced mating behavior in sexually receptive rats. In addition, P does not appear to be necessary for the display of paced mating behavior following long-term treatment with EB. In contrast, the pulsatile administration of E2 + P induced a different pattern of paced mating behavior in sexually receptive rats.
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Affiliation(s)
- E M Brandling-Bennett
- Department of Psychology, Dartmouth College, 6207 Gerry Hall, Hanover, New Hampshire 03755, USA
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Yang LY, Clemens LG. Influence of male-related stimuli on female postejaculatory refractory period in rats. Physiol Behav 1998; 63:675-82. [PMID: 9523914 DOI: 10.1016/s0031-9384(97)00523-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Female rats "pace" their sexual contacts with the male when tested in situations where they can escape from the male during copulation. The type and quality of vaginocervical stimulation that the females receive during copulation influences their pacing behavior. This study investigated the effect of several male-related stimuli on the female's postejaculatory refractory period (PER). Females were tested in a two-compartment test chamber from which they could escape the male through one of four openings along the bottom of the barrier separating the two compartments. Experiment 1 examined the influence of the seminal plug, the penile cup, and prostate secretions on the female's PER. Results showed that neither the seminal plug, the penile cup, nor prostate secretions contributed to the female's PER. Experiment 2 investigated the relation of pre-ejaculatory intromission frequency, ejaculation duration, and the number of pelvic thrusts during ejaculation to the female's PER. Results indicated that pre-ejaculatory intromission frequency and ejaculation duration but not the number of pelvic thrusts during ejaculation were significantly correlated with the female's PER. In addition, pre-ejaculatory intromission frequency was significantly correlated with ejaculation duration. Partial correlation analysis suggested that pre-ejaculatory intromission frequency affected ejaculation duration which, in turn, influenced the female's PER. This finding was further supported by the evidence that ejaculation duration and the female's PER were significantly shorter in tests in which the male ejaculated on the first or second intromission.
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Affiliation(s)
- L Y Yang
- Department of Zoology, Michigan State University, East Lansing 48824, USA.
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