Do rats have orgasms?

Abstract

Background: Although humans experience orgasms with a degree of statistical regularity, they remain among the most enigmatic of sexual responses; difficult to define and even more difficult to study empirically. The question of whether animals experience orgasms is hampered by similar lack of definition and the additional necessity of making inferences from behavioral responses.

Method: Here we define three behavioral criteria, based on dimensions of the subjective experience of human orgasms described by Mah and Binik, to infer orgasm-like responses (OLRs) in other species: 1) physiological criteria that include pelvic floor and anal muscle contractions that stimulate seminal emission and/or ejaculation in the male, or that stimulate uterine and cervical contractions in the female; 2) short-term behavioral changes that reflect immediate awareness of a pleasurable hedonic reward state during copulation; and 3) long-term behavioral changes that depend on the reward state induced by the OLR, including sexual satiety, the strengthening of patterns of sexual arousal and desire in subsequent copulations, and the generation of conditioned place and partner preferences for contextual and partner-related cues associated with the reward state. We then examine whether physiological and behavioral data from observations of male and female rats during copulation, and in sexually-conditioned place- and partner-preference paradigms, are consistent with these criteria.

Results: Both male and female rats display behavioral patterns consistent with OLRs.

Conclusions: The ability to infer OLRs in rats offers new possibilities to study the phenomenon in neurobiological and molecular detail, and to provide both comparative and translational perspectives that would be useful for both basic and clinical research.

Keywords: animals; conditioned preference; dopamine; female; genitosensory; male; opioids; pleasure; sex; ultrasonic vocalizations.

Fig. 1

Nerves (pudendal, pelvic, hypogastric, and vagus) that subserve sexual arousal and orgasm in women and men. B: bladder. C: cervix. CB: corpora spongiosum of the bulbocavernosus. E: epididymis. NTS: nucleus of the solitary tract (brainstem). P: prostate. SV: seminal vesicle. T: testis. U: uterus. ur: urethra. V: vagina. vas: vas deferens. Adapted from Georgiadis, et al. (2012).

Fig. 2

Schematic diagram of the spinal and supraspinal regulation of tumescence (T) and detumescence (D) of the clitoris and penis. Dashed lines are excitatory and solid lines inhibitory for genital blood flow. After De Groat and Steers (1998). LSt neurons that comprise the ejaculation generator in males are located in the lower lumbar cord (see Coolen et al., 2004).

Fig. 3

Sensory stimulation of female (red) and male (blue) rats during sexual interaction. OFS: olfactory stimulation. FLS: flank (tactile) stimulation. VCS: vaginocervical stimulation. CLS: clitoral stimulation. PNS: penile stimulation.

Fig. 4

Ultrasonic vocalizations made by female rats in response to distributed CLS. Left side depicts raw calls. Middle depicts the proportion of total calling during CLS taken by flats, trills, flat-trills, step-ups, and compound calls. Right side depicts median calls in females that receive full hormone priming with estradiol benzoate and progesterone versus no hormone (oil vehicle). *P<0.01.