B - Sexual Behaviour
Objectives:
To describe appetitive/proceptive behaviours in the male and female rat
To describe the sequential components of both male and female copulatory behaviour
To quantify a lordosis quotient
To quantify paced mating
Introduction:
Being a careful observer of behaviour is essential to being a skilled behavioural neuroscientist. Changes to the nervous system may only produce small changes in behaviour, and therefore it is important to develop skills and techniques to quantify behaviour so that these small changes can be detected. A good behaviour to start with is sexual behaviour, as it is highly stereotyped. Sexual behaviour is essential for the survival of a species, and requires careful coordination of both endocrine activity and behaviour; each of which is controlled by the nervous system. In this lab you will learn to describe appetitive/proceptive behaviours that precede copulation. You will also learn to describe the very stereotyped components of both male (mounting, intromission, ejaculation) and female copulatory behaviour (lordosis).
Procedure:
Preparation:
Rat mating occurs during the night, so the animals will need to be housed in a colony room with a light-dark cycle where the lights go out a few hours before the start of your lab. While male rats will always engage in sexual behavior, female rats are only sexually receptive once every 4-5 days. A variety of approaches can be used to ensure that you have receptive females to work with, which your TA will have performed prior to your lab. 1. Ovariectomized females can be induced to be sexually receptive by giving them an injection of estradiol benzoate (20 pg, SC in sesame seed oil) 48h prior to testing, followed by progesterone (1 mg, SC, sesame seed oil) 4 h prior to testing. 2. Vaginal smears can be taken every day to identify estrus (Jenkins and Becker, 2005) 3. Females can be placed with a male to observe if lordosis appears. Mounting would need to be interrupted immediately so that the female doesn’t become pregnant or pseudopregnant.
We want our females to become pregnant, so the first option is not possible. You TA will likely use approach #3, but depending on experience, the vaginal smear approach is better and may be used.
Test:
If paced mating is to be observed, the female must have a “safe” zone where the male can’t reach her. Two approaches can be used. Have a chamber where the male can be tethered so that he is restricted to one end of the arena. The female should also have an opaque barrier to hide behind. The male will need prior habituation to the tethering, or he will be more interested in the restraint than the female rat during testing (Jenkins and Becker, 2005). Alternatively, two chambers can be used, connected by a piece of PVC pipe large enough to allow the passage of the female rat, but small enough to prevent entry from the male rat. Alternatively, a barrier with appropriately sized holes can be used to dive the arena in two. Small young females and larger, older males will be required in this case.
Position and turn on the video camera. Place the male in the mating arena. If paced mating is to be scored, the male rat may need a physical restraint. Then place the female in the mating arena. Place the female in the mating arena in her end. If only lordosis quotient and a description of proceptive behaviors are to be scored, simply place the male and then the receptive female into the mating arena. Allow mating to progress for 1 hour. For paced mating, if after 30 minutes the female has not entered the male’s side, place her on the male’s side to assess sexual receptivity.
From the video you will need to identify mounts (climbing on, but no insertion of the penis, male simply moves off the female), intromissions (mounting and insertion of the penis, male disengages by springing off the female after a pelvic thrust) and ejaculations (mounting and insertion of the penis, several pelvic thrusts, female disengages). You will need to identify lordosis events (immobility, arched back, dorsiflexion of tail, elevation of head).
To calculate the lordosis quotient, divide the number of lordosis events by the number of male contacts, and multiply by 100% (Jenkins and Becker, 2005).
In paced mating, to calculate percent exits divide the number of exits following coital stimulation by the number of coital stimulations and multiply by 100%. To calculate the return latency, simply measure the time until the female returns to the male’s area. Separate exits and return latencies by the type of coital stimulation that preceded it (mount, intromission, ejaculation) (Jenkins and Becker, 2005).
For describing proceptive and copulatory behavior, make careful notes about the sequences of events. Look for the female to perform the following: hopping, darting, ear wiggling, and lordosis (Erskin, 1989). For males, look at how he orients to the female, touches her and explores her. Note genital exploration and licking, whether of the partner or of the self. Note the sequence and quantity of mounts, intromissions and ejaculations, as well as postcopulatory behaviors (refractory periods).
References:
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