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Fetal yawning assessed by 3D and 4D sonography
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mise à jour du
22 novembre 2015
Physiol Behav
2016;153:84-90
Differential organization of male copulatory patterns
in high- and low- yawning-frequency sublines
versus outbred Sprague-Dawley rats
 
Eguibar JR, Cortes C, Toriz CG, Romero-Carbente JC,
González-Flores O, Fernández-Guasti A.  

Chat-logomini

 Tous les travaux de MR Melis & A Argiolas 
Tous les travaux de M Eguibar & G Holmgren
 
Abstract
 
The temporal organization of masculine sexual behavior in rats is highly stereotyped; involving a sequence of mounts, intromissions and ejaculations. Sexual behavior has been described in exogamic and genetically manipulated rodent species. In this work, we compare the male sexual behavior of outbred Sprague-Dawley (SD) to those of rats inbred for high (HY)- and low (LY)- spontaneous yawning frequency. In the first experiment, the percentage of inexperienced rats' ejaculatory behavior is significantly lower in the HY and LY respect to Sprague-Dawley rats. The latency to ejaculate for inexperienced HY was shorter than the LY and SD rats. In the second experiment, we examined the differences between inbred sublines and Sprague-Dawley rats once the subjects had become sexually experienced after four copulatory sessions. HY rats still have slower proportion of ejaculators respect to LY and SD rats. Additionally, postejaculatory latencies were longer for HY rats, with longer intercopulatory intervals and higher number of copulatory bouts that delayed ejaculation. Both sublines show lower copulatory efficiency respect to SD rats. In conclusion, both sublines show alterations in the temporal organization of sexual motor pattern that are due at least partially to strong inbreeding process to select them.
 
 
1. Introduction
The use of selected strains, lines and sublines of rats that differ in their spontaneous frequency of behavioral traits is a powerful tool for studying genetic influences on normal and altered behavior [1]. For this reason, inbred groups of rats are useful models to explore the inter- play between genes and behavior. Male rat sexual behavior consists of a highly stereotyped series of motor patterns, of which timely sequential organization is essential for reaching ejaculation [2]. The masculine cop- ulatory behavior of the rat consists of a series of mounts, intromissions and ejaculations [2]. Mounts are characterized by an approach to the es- trous female rear accompanied by forepaw palpations of the flanks and pelvic thrusting. The intromission behavioral pattern is similar to that of a mount, but finishes abruptly with a quick dismount after penile vagi- nal insertion. Ejaculation is behaviorally characterized as a deep pelvic thrust lasting several seconds during which animals maintain an immo- bile position, followed by a rapid dismount. During a copulatory event, the male rat performs various mounts and intromissions that lead to ejaculation within approximately 10 to 15 min. The number and timing of mounts and intromissions that occur prior to ejaculation are impor- tant measures associated with pregnancy success [3,4]. The time to dis- play the first mount and intromission after introducing a receptive female to the test arena are designated as mount and intromission la- tencies and denote the motivational aspect of copulation [2,4].
 
Furthermore, sexual experience results in highly efficient male rats with ejaculation latencies shorter than 15 min [4]. Additionally, the observa- tion of copulatory behavior is particularly useful to analyze temporal or- ganization patterns (for a review see [5]).
 
Interestingly, some rat strains differ in their expression of mounting, intromission or ejaculation frequencies and timing to ejaculate, suggest- ing that genetic background modulates sexual behavior [6]. For exam- ple, it has been described that male Lewis rats have lower copulatory efficiency and frequently fail to ejaculate, independently of the female partner strain Lewis, Fischer (F344) or Sprague&endash;Dawley (SD) [7]. Addi- tionally, Flinders subline of male rats showed lower proportion of ejac- ulators between resistant as compared to those that are sensitive to cholinergic drugs [8]. Similar findings were found in the Roman low- avoidance (RLA) Wistar line male rats with a decreased sexual perfor- mance respect to Roman high-avoidance (RHA) [9].
 
In our laboratory, we selectively inbred two sublines of Sprague&endash; Dawley rats: the high-yawning (HY) and low-yawning (LY) sublines, with a mean spontaneous frequency of 20 and 2 yawns/h, respectively [10]. We have demonstrated that among rats in the HY subline, yawning and penile erection are correlated; with 50% of the yawns occurring prior to, or following penile erection in a 3 min period [11]. Additionally, HY subline exhibited a disorganized grooming sequence after fur wet- ting or when exposed to a novel environment, with more grooming bouts due to a higher incidence of pauses [12,13]. Furthermore, dams of the HY subline also displayed deficient maternal care associated with a disorganized maternal behavior pattern, which is characterized by shorter latencies to retrieve the first pup and the litter, and higher in- cidence of atypical retrievings from the belly or the legs and re- retrievings when the dams take the pup outside the nest [14].
 
The aims of the present experiments were to analyze the organiza- tion of the copulatory behavior of sexually inexperienced males from the HY and LY sublines. In a second series of experiments, we evaluated the copulatory behavior of HY and LY males with previous sexual expe- rience (four copulatory sessions). For comparison, a group of outbred SD rats was included in both experiments. We hypothesized that the HY and LY males would display deficient sexual performance, relative to the outbred male SD rats.
 
Discussion
In the rat, it has been demonstrated that male sexual performance in adulthood is strongly dependent on maternal care during the first days of life and that stress responses in adulthood are dependent on the ma- ternal care given by the dams. Thus, the high-licking/grooming (LG) dams produce offspring that are resistant to stress and influence their sexual performance by shorter inter-intromission intervals in these males with respect to low-LG dams [30]. Therefore, the male sexual def- icit shown in the present experiments in HY rats could be due to the im- paired maternal care given by the dams [14]. In fact, preliminary experiments revealed that HY males fostered by the LY or SD dams displayed improved sexual performance (data not shown); suggesting an interaction of genetic and epigenetic mechanisms in the deficit in male sexual behavior particularly in the HY rats.
 
Until now, only some selected sublines of rats have been evaluated for their sexual performance. For example, male Flinders rats that are re- sistant to cholinergic agonist- induced increase in central temperature showed poor sexual performance. Similar results were obtained with high-thermal responders to systemic injection of serotonergic 1a sub- type agonists, which also showed poor sexual performance because of longer ejaculation and post-ejaculatory latencies relative to lower ther- mal responders [8,22]. Another recent study revealed that the RLA male rats had poor sexual performance relative to RHA male rats [9].
 
Interestingly, the ejaculation latency is one of the main parameters that differs across different strains or lines/sublines of rats. For example, male Lewis rats have longer ejaculatory latencies than male Fischer or SD rats [7]. Similarly, HY rats showed longer ejaculatory and postejaculatory latencies suggesting that inbreeding alters the mecha- nisms that control them.
 
Another interesting relationship arises from general activity and sexual performance, thus, hyposexual non-copulating males showed hyperactivity in the open-field arena, while males with adequate sexual performance consistently present lower ambulation scores than their counterparts [31]. Remarkably, HY rats show higher ambulation scores associated with a higher proportion of non-copulating males [13,25, and present results] as compared to LY subjects, therefore, hyperactivity and sexual display can be expressions of altered stress responses in the HY subline of rats.
 
Sachs & Barfield [29] suggested that the inter-copulatory intervals and the number of copulatory bouts are essential variables to analyze the internal organization of copulation because they determine the time to reach the ejaculation threshold [29]. It has also been demon- strated that female partners need various intromissions separated with shorter intervals followed by an ejaculation in order to be maxi- mally fertilized [3]. This last evidence might explain why HY rats are less effective at inseminating HY female partners and why HY dams have fewer pups [14,24].
 
The neurobiological bases underlying the slower rate of copulation of HY rats are unknown, but dopamine (DA) may be proposed as a pu- tative candidate. DA serves primarily a facilitator role because of its high concentrations in the medial preoptic area [23,32,33] and in the ventral striatum when the subject intromitted or ejaculate [34]. Additionally, dopaminergic drugs administered systemically or in the medial preoptic area shorten the intromission and ejaculation latencies, as well as the number of intromissions and of sexual bouts before ejaculation; sug- gesting a primary role of this neurotransmitter in male sexual motiva- tion [4,35]. In line with this, a selective D1 agonist, SKF-38393, increased the time spent in a goal compartment with an estrous female and copulatory display, supporting that dopamine enhances sexual mo- tivation by stimulating D1 receptors [36,37]. We have demonstrated a lower concentration of D1 dopamine receptors in the ventral striatum of HY rats as compared to LY rats [38]. Additionally, systemic adminis- tration of SKF 38393 produced more grooming in the HY than in the LY subline [39] suggesting that dopaminergic mechanisms may differ between sublines.
 
Interestingly, when the males of both sublines were allowed to ex- perience seven copulatory sessions, 79% of LY rats ejaculated, while only 53% males of the HY achieved ejaculation (data not shown). That is, even after prior sexual experience, HY males still showed poor per- formance and did not acquire sexual experience efficiently.
 
 
In conclusion, HY rats are a suitable model to analyze the possible causes of the stereotyped motor sequence alterations due to the in- breeding process. HY males showed a disorganized sequence because the number of copulatory bouts is higher and lower intromission ratio that delay ejaculatory threshold respect to that observed in SD rats. Ac- quisition of sexual experience is lower in HY and in a less degree in the LY subline, which could be due to neurobiological changes caused by in- breeding over greater than 80 generations. Therefore, HY are useful be- cause the proportion of non-copulators and sluggish subjects is one order of magnitude higher than SD rats, making it easier to analyze the mechanisms underlying this behavior.