Background

Many psychopharmacological drugs have sexual side effects. Thus: up to 75% of all patients treated with selective serotonin reuptake inhibitors (SSRIs) complain of reduced libido, reduced (or lack of) ability to reach orgasm etc. In males, the latter is associated with prolonged ejaculation latency.

Aim

The purpose of this study was to establish a model of male rat sexual behavior, in order to screen psychopharmacological drugs with regard to sexual side effects.

Methods

Sexually active male rats were treated with paroxetine (a SSRI) for 4 weeks, and their sexual behavior was quantified. Both precopulatory and copulatory behavioral parameters were measured once a week. All behavioral test sessions were recorded on video tapes and later scored using a simple event recorder program for PCs. The program was able to score number of events, latency times, and duration - all by pressing pre-assigned keyboard keys. In the preference test the male rat could choose between proximity to a female rat in heat or one not in heat. This was done in a test chamber (50x50cm) with two side chambers attached. Side chambers contained incentive animals separated from the male test animal by grids. Video recording was done dorsally. Number of visits to each proximity zone was measured as well as total duration of visits in each zone. On this basis the time spent per visit in each zone and time ratios of preference were calculated. Copulatory activity and efficiency of the males was measured as well. Male test animals were habituated to the test chamber (50x50cm) and then introduced to a female rat that had been brought in heat and tested for appropriate sexual behavior. Tests began with introduction of female rat and ended with first mount of the second copulatory series. Video recording was done laterally. The number of mounts and intromissions were measured as well as latency times for the first mount, first intromission and ejaculation of the first copulatory series and latency time for the first intromission of the second copulatory series. In addition to these data the duration of the post-ejaculatory interval (PEI) was calculated.

Discussion

The sexual behavior of the male rat is highly stereotyped, readily elicited in the laboratory, consistent in an individual over time, and sensitive to experimental intervention. At the same time it is a non-invasive model of emotionality using a naturally occurring behavior. This model has many advantages and could be used in a variety of ways.