Modeling Human Sexual Motivation in Rodents: Some Caveats

Abstract

Sexual behavior is activated by motivation. An overwhelming majority of experimental studies of the intricacies of sexual motivation has been performed in rodents, most of them in rats. Sometimes it is desirable to generalize results obtained in this species to other species, particularly the human. It is hoped that studies of the neurobiology of rodent sexual behavior may shed light on the central nervous mechanisms operating in the human, and the search for efficient pharmacological treatments of human sexual dysfunctions relies partly on studies performed in rodents. Then the issue of generalizability of the rodent data to the human becomes crucial. We emphasize the importance of distinguishing between copulatory acts, behavior involving the genitals, and the preceding event, the establishment of physical contact with a potential mate. Comparisons between the structure of copulatory behavior in rats and humans show abysmal differences, but there may be some similarity in the underlying mechanisms. The endocrine control of sex behavior is shortly mentioned, and we also compare the effects of the few drugs known to affect both rodent and human copulatory behavior. The stimuli activating sexual motivation, often called desire in the human literature, are examined, and the sexual approach behaviors in rats and humans are compared. There is a striking similarity between these species in how these behaviors respond to drugs. It is then shown that the intensity of sexual approach is unrelated to the intensity of copulatory behavior. Even though the approach is a requisite for copulation, an activity that requires at least two individuals in close physical contact, these two aspects of sexuality do not covary. This is similar to the role of the testosterone in men and male rats: although the hormone is needed for sex behavior, there is no correlation between serum testosterone concentration and the intensity of copulation. It is also pointed out that human sexual behavior is mostly determined by social conventions, whereas this is not the case in rats and other rodents. It is concluded that some observations in rats can be generalized to the human, but extreme caution must be exercised.

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

“…Male sexual behavior can be categorized into either appetitive or consummatory behaviors (reviewed in Hull and Dominguez, 2015;Bialy et al, 2019;Le Moëne and Ågmo, 2019). In rodents, this begins with appetitive sexual behavior where the male examines the face and anogenital region of the female (Angoa-Pérez and Kuhn, 2015), followed by the consummatory sexual behaviors of mounting the female's rear and then intromitting several times until they ejaculate (reviewed in Angoa-Pérez and Kuhn, 2015; Hull and Dominguez, 2015;Bialy et al, 2019).…”

Nature Controls Nurture in the Development of Sexual Orientation, and Voice is Nature’s Agent

“…Due to practical constraints, a large part of our knowledge about the biology of sexual orientation is derived from observing animals. It is important to generalize from animals to humans very cautiously (73,74). Theoretical models and hypotheses, like the model presented here, are crucial stages of the Scientific Method, and are usually employed for optimizing such generalizations and for the exploration of new ideas.…”

Altered Sexual Behavior in Dopamine Transporter (DAT) Knockout Male Rats: A Behavioral, Neurochemical and Intracerebral Microdialysis Study

“…In addition to the above parameters, the total number of mounts (TMF), of intromissions (TIF) and of ejaculations (EF) in the whole 60 min period of copulation, the total copulatory rate (TCR), calculated by dividing the sum of all the activity periods of the male with the female rat (an activity period was defined from the first mount/intromission in a series of copulatory activity until ejaculation in that series) by the sum of all mounts and intromissions of the whole test and the total intromission ratio (TIR) calculated as the TIF divided by the sum of TIF and TMF were also calculated. Moreover, the number of noncontact penile erections (NCPEs), counted during the 30 min period in which the receptive female rat was inaccessible to the male during the microdialysis experiment (see below), was also recorded (Sachs and Barfield, 1976;Melis et al, 2003;Sanna et al, 2014aSanna et al, ,b, 2015aSanna et al, ,b, 2017bSanna et al, , 2019Le Moëne and Ågmo, 2019). Finally, since substantial differences in genital self-grooming, a centrally-mediated, self-directed highly stereotyped behavior that in the context of copulation may indicate self-cleaning and/or self-stimulation (Sachs et al, 1988;Berridge et al, 2005), were observed among the three rat lines during the five copulatory tests, the percent of mounts, intromissions, and ejaculations followed by genital grooming as well as the frequency and duration of genital grooming episodes after mounts, intromissions and ejaculation were recorded for each animal in the first series of copulatory activity during the microdialysis experiment (Sachs et al, 1988).…”