Assessment of penile erection methods in rhesus macaques to model pharmacokinetics of antiretroviral drugs and penile infection with simian immunodeficiency virus

Abstract

Rectal electrostimulation treatment elicits transient but consistent penile erections in macaques. High rigidity following RES treatment demonstrates increased blood flow and may provide a functional model for penile PK evaluations and possibly simian immunodeficiency virus (SIV) transmission under erect conditions.

Do monkeys use sex toys? Evidence of stone tool‐assisted masturbation in free‐ranging long‐tailed macaques

“…To test Prediction #1 (i.e., penile erection should be more closely temporally associated with genital stone‐tapping/rubbing than with any other stone handling patterns), for each subject, we selected all available 1‐min stone handling sequences featuring the beginning of a fully rigid penile erection (Figure 1b; cf. Hayes et al, 2016) exactly 30 s after the beginning of the sequence (i.e., penile erection occurred at mid‐point within the stone handling sequence). Since Prediction #1 tested which behavior preceded the expression of penile erection, 1‐min intervals provided a physiologically relevant time window.…”

“…To test Prediction #2 (i.e., genital stone‐tapping/rubbing should last longer in stone handling sequences featuring penile erection than in stone handling sequences without penile erection, whereas no such differences were expected for other stone handling patterns), for each subject, we selected two 3‐min stone handling sequences, one featuring the beginning of a fully rigid penile erection (Figure 1b; cf. Hayes et al, 2016) exactly 90 s after the beginning of the sequence (i.e., penile erection occurred at mid‐point within the stone handling sequence), and one without penile erection. Since Prediction #2 tested whether certain stone handling patterns lasted longer when the performer was experiencing penile erection, 3‐min intervals provided a good trade‐off between a physiologically relevant time window and data availability.…”

“…based on perceived erection hardness (cf. Hayes et al, 2016) with (a) moderate increase in penile rigidity, but not completely hard, with prepuce still visible, and (b) completely hard and fully rigid penile erection, with prepuce fully visible.…”

“…Occasionally, if penile erection did not reach full rigidity within the observed time period, we included instances of stone handling sequences featuring the beginning of a moderate increase in penile rigidity (Figure 1a; cf. Hayes et al, 2016). The selected stone handling sequences were truncated from longer stone handling sequences, and they were independent (i.e., they belonged to distinct stone handling sequences collected on different days).…”