BN Unit 2 Exam: defining and measuring MSB

How does the course define "sex"?

The condition by which organisms are categorized as female or male based on chromosomes, hormones, reproductive organs, other morphology, and behavior

How does the course define "sexual behavior"?

Actions directed toward reproduction (bringing the gametes together); also called mating or copulation

How does the course define "male sexual behavior" (MSB)?

All the behaviors necessary and sufficient to deliver male gametes to female gametes

Historically, how was sexual arousal defined?

Equated with motivation: "sexual excitement to such a pitch that the copulatory threshold is attained"

What is a common operational definition of male arousal, and what does it really reflect?

An erect penis in a sexual context; it reflects performance more than motivation

What problem does the phrase "sexual context" raise when defining arousal?

What counts as sexual depends on learning, experience, and expectation

What is an alternative physiological measure of arousal, with one pro and one con?

Genital blood flow. Pro: works in both sexes. Con: hard to interpret when arousal and performance dissociate (e.g., erectile dysfunction)

What three components make up the modern, multidimensional view of sexual arousal?

Physiological responses (genital blood flow, autonomic activation); subjective experience (self-reported desire); cognitive/contextual factors (expectations, learning, meaning)

Can the components of arousal dissociate? Give an example.

Yes — physiological arousal without subjective desire, or desire without genital response

What are the two overlapping processes of MSB?

Sexual motivation (appetitive) and sexual performance (consummatory)

What is sexual motivation (appetitive behavior), with examples?

Behaviors involved in seeking and approaching a partner ("wanting"): courtship displays, orienting toward/following a mate, vocalizations, sniffing, working for access (lever presses, barriers, shocks)

What is sexual performance (consummatory behavior), with examples?

Behaviors of copulation itself ("doing"): mounting, intromission, ejaculation

Can motivation and performance come apart?

Yes — they can dissociate

What does "sex drive" (libido) refer to?

The motivational forces that propel individuals to seek copulation

Which simple organism shows that appetitive/consummatory components are evolutionarily conserved?

C. elegans

What is the Latin origin of "testis"?

testiculus/testis, "to witness"

Give an example of how MSB is quantified experimentally in rats.

Latency to first copulation

What development helped establish a causal role of testosterone in MSB?

The development of synthetic testosterone

What did the rat dose–response graph show about T after castration?

Increasing T doses rescued mating test scores back to (and above) the pre-castration average at ~100–500 µg/day

What are obstruction tests, and give examples?

Tests of sexual motivation where a male must overcome an obstacle to reach an estrous female: physical barrier, electrified floor, moving treadmill, ladder, lever press

How is high sexual motivation inferred from obstruction tests?

The male passes the obstruction quickly or endures great pain to reach the estrus female

What are the three stages of the consummatory phase in rodents?

Mounting → intromission → ejaculation

How is a typical rodent mating test set up?

A male and an estrous female are placed in a glass enclosure

What is mounting?

Assuming a copulatory position without inserting the penis (after investigating the female)

What two measures are recorded for mounting?

Mount latency and inter-mount interval (IMI)

What is intromission?

Entry of the penis into the vagina during a mount (with thrusting in some rodents)

What measure is recorded for intromission?

Inter-intromission interval (if there are multiple intromissions)

What is ejaculation, and what does it look like in rats/mice?

Forceful expulsion of semen through the urethra; involves thrusting, arching the spine, and lifting the forepaws

What three measures are recorded for ejaculation?

Number of intromissions before ejaculation, ejaculatory latency, number of ejaculations

How many times will a rat ejaculate in an unlimited time test?

About 5–8 times

What is the postejaculatory interval (PEI)?

Time between ejaculation and the start of the next copulatory bout (the "refractory period")

What is the absolute refractory period?

A period of complete unresponsiveness to sexual stimuli (and many other stimuli)

What is the relative refractory period?

A period when a new or very potent sexual stimulus may still elicit responsiveness

How long is the PEI in rats vs other rodents?

5–15 minutes in rats; ~30 seconds in some rodents; can be hours or days in others

When is a male rat considered "sexually sated"?

When his PEI exceeds 90 minutes

What four questions define the 16 patterns of mammalian copulation?

Copulatory lock? Thrusting? Multiple intromissions? Multiple ejaculations?

What copulatory pattern do dogs show?

Lock, thrusting, no multiple intromissions, multiple ejaculations

What copulatory pattern do rats show?

No lock, thrusting, multiple intromissions, multiple ejaculations

What copulatory pattern do deer show?

No lock, no thrusting, no multiple intromissions, single ejaculation

After post-puberty castration in rats, how quickly does MSB decline?

Within days

In what order is MSB lost after castration in rats?

Longer latency to mount/intromit → fewer intromissions before ejaculation → can't ejaculate (1–2 weeks) → fewer mounts and intromissions → mounting stops

In what order is MSB restored when castrated rats get T?

Mounting first, then intromissions, then ejaculation

Does castration affect sex drive in rats?

Yes — sex drive (motivation) declines along with performance

What is the difference between maintenance and restoration of MSB with T?

Maintenance: T given right at castration keeps MSB going. Restoration: T given after MSB has already declined

Which requires a higher T dose — maintenance or restoration?

Restoration (lower doses maintain MSB better than they restore it)

Which hormones maintain MSB in castrated male rats, and what do they have in common?

Testosterone and androstenedione (a T precursor); both can be converted to estrogen

Does DHT alone prevent the post-castration decline in rat MSB? Why?

No — DHT cannot be aromatized to estrogen

Give three pieces of evidence for an estrogenic mechanism in rat MSB.

Blocking ERs stops androgens from rescuing MSB; aromatase inhibition (fadrozole) reduces MSB; DHT + estrogen together restore mating

In the mechanistic model, what is testosterone acting as?

A prohormone

In the CNS, what is T converted to, by which enzyme, and what does it do?

Estrogen via aromatase → promotes sexual motivation and mating behavior

In the PNS, what is T converted to, by which enzyme, and what does it do?

DHT via 5α-reductase → maintains penile tactile sensitivity and copulatory reflexes

What are the corpora cavernosa?

Twin tunnels of highly vascular tissue that make up most of the penis body

What is the corpus spongiosum?

The glans and central tissue of the penis that surround the urethra

What is the os penis?

A penile bone (baculum) found in many mammals such as rodents

What do decerebrate rats show about penile reflexes?

They still get erections with appropriate stimulation — the reflexes are spinal

Name the penile reflexes in rats.

Tumescence without glans erection, intense glans erection ("cup"), and penis "flip"

What happens to penile reflexes after castration, and how fast?

Erections, cups, and flips disappear, waning at about 24 hours

How much T is needed to restore penile reflexes?

Much less than typical circulating levels

Which hormone is necessary for penile reflexes?

DHT

What happens to sexual performance when the preoptic area (POA) is lesioned in vertebrates?

Sexual performance is eliminated across all vertebrates

What happens to sexual motivation after POA lesions?

It often remains intact

What do POA lesions show about motivation vs performance?

They dissociate

What happens when the MPOA is electrically or chemically stimulated?

Ejaculation is accelerated and copulatory patterns are facilitated

What is the functional role of the POA in MSB?

An integrative hub: it processes olfactory, auditory, and tactile input plus hormonal signals and turns them into motor output for mating

What triggers dopamine release in the MPOA?

Female cues (not food or other males)

Where does MPOA dopamine come from?

Local hypothalamic DA neurons (incertohypothalamic system), not the VTA

How do castration and T affect MPOA dopamine release?

Castration reduces it; testosterone restores it

What do DA agonists vs antagonists in the MPOA do to copulation?

Agonists facilitate it; antagonists impair it

Is dopamine inside the MPOA linked to motivation or performance?

Performance (consummatory)

What is the pathway linking the MPOA to sexual motivation?

MPOA → VTA → nucleus accumbens

What is the role of VTA dopamine released in the nucleus accumbens?

Drives sexual motivation: approaching and working for access to a female