neurobiology and neuroscience | Lecture notes Psychology

CHAPTER 12 – PSYC 355

CHAPTER 12

Sex: Evolutionary, Hormonal, and Neural Bases

There are 4 stages of reproductive behavior:

1. Sexual attraction

2. Appetitive behavior

3. Copulation

4. Post-copulatory behavior

- Reproductive behavior is different from sexual

behavior

Stage 1: sexual attraction

- is 1st step in mating behavior for many animals

- Animals emit many stimuli such as visual cues

pheromones  These attract members of the

opposite sex

- Pair bonds: this is a durable and exclusive

relationship between a male and female  there are

2 types of pair bonds: social monogamy and sexual

monogamy, and they are different from each other

- An animal can have social monogamy with

another individual of the opposite sex but engages

in sexual relationships with other animals

- Social monogamy is important for the survival of

the offspring  has evolutionary advantage.

- Oxytocin and vasopressin are implicated in

monogamy and in human pair bonding.

- Females are attracted to particular traits in males

such as feather types in peacock  this is sexual

selection  has evolutionary purposes.

- Sexual selection is the process by which members

of one biological sex chose one from the opposite

sex

& also refers to competition between individuals of

the same sex in order to access other mates from the

opposite sex

- Superior level of genetic fitness looks more

sexually desirable, looks more attractive.

- Females egg release is synchronised with her

fertility peak and readiness to copulate

Stage 2: appetitive behavior

- Establishes, maintains and promotes sexual

interaction.

- Appetitive behavior is species-specific.

- Proceptive behavior is when the females show

appetitive behavior.

 examples in females: ear wiggling, darting and

hopping in female rats.

 examples in males: sniffing, singing, nest

building.

Stage 3: copulation:

1. Coitus is the sexual act

- Involves intromissions (penis in & out of

vagina)

- Male ejaculates semen into female

2. Refractory phase: period during which the

individual cannot do copulation

Here there is a temporary decrease in the sexual

attractiveness of the partner

- Following ejaculation, there is a refractory phase

during which it’s impossible for the male to

ejaculate again

3. Coolidge effect: faster resumption of mating

behavior with a novel partner

- By the Coolidge effect, you can decrease the

refractory phase by introducing a new female to a

male.

- Female that is willing to copulate is called in heat,

or in estrus or sexually receptive

Stage 4: Post-copulatory behavior

- includes parental behavior to nurture offspring

- Copulatory lock is when the penis swells

temporarily and cannot be withdrawn from the

female. Occurs in dogs and some mice.

- There is temporary inhibition of sexual attraction.

- Copulation brings gametes together

- Internal fertilization tales place inside the female

body  here the fusion of sperm and ovum

produces a zygote (fertilized ovum)

- External fertilization tales place outside the

female’s body  example: some fish and

amphibians that release eggs in water.

- The hormonal cycle of female rats is 4-5 days  it

releases an egg every 4-5 days and she display

proceptive behavior synchronized with egg release.

- The proceptive behavior includes ultrasonic

vocalizations to attract male rats  these sounds are

very high pitched and cannot be detected by humans

- after the female emit these ultrasonic

vocalizations, the male is attracted to the female and

starts to mount her and grab her flanks.

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CHAPTER 12 – PSYC 355 CHAPTER 12 Sex: Evolutionary, Hormonal, and Neural Bases There are 4 stages of reproductive behavior:

**1. Sexual attraction

Appetitive behavior
Copulation
Post-copulatory behavior**

Reproductive behavior is different from sexual behavior Stage 1: sexual attraction
is 1st^ step in mating behavior for many animals
Animals emit many stimuli such as visual cues pheromones  These attract members of the opposite sex
Pair bonds: this is a durable and exclusive relationship between a male and female  there are 2 types of pair bonds: social monogamy and sexual monogamy, and they are different from each other
An animal can have social monogamy with another individual of the opposite sex but engages in sexual relationships with other animals
Social monogamy is important for the survival of the offspring  has evolutionary advantage.
Oxytocin and vasopressin are implicated in monogamy and in human pair bonding.
Females are attracted to particular traits in males such as feather types in peacock  this is sexual selection  has evolutionary purposes.
Sexual selection is the process by which members of one biological sex chose one from the opposite sex & also refers to competition between individuals of the same sex in order to access other mates from the opposite sex
Superior level of genetic fitness looks more sexually desirable, looks more attractive.
Females egg release is synchronised with her fertility peak and readiness to copulate Stage 2: appetitive behavior
Establishes, maintains and promotes sexual interaction.
Appetitive behavior is species-specific.
Proceptive behavior is when the females show appetitive behavior.  examples in females: ear wiggling, darting and hopping in female rats.  examples in males: sniffing, singing, nest building. Stage 3: copulation: 1. Coitus is the sexual act - Involves intromissions (penis in & out of vagina) - Male ejaculates semen into female 2. Refractory phase: period during which the individual cannot do copulation Here there is a temporary decrease in the sexual attractiveness of the partner
- Following ejaculation, there is a refractory phase during which it’s impossible for the male to ejaculate again 3. Coolidge effect: faster resumption of mating behavior with a novel partner
- By the Coolidge effect, you can decrease the refractory phase by introducing a new female to a male.
- Female that is willing to copulate is called in heat, or in estrus or sexually receptive Stage 4: Post-copulatory behavior
- includes parental behavior to nurture offspring - Copulatory lock is when the penis swells temporarily and cannot be withdrawn from the female. Occurs in dogs and some mice.
- There is temporary inhibition of sexual attraction. - Copulation brings gametes together - Internal fertilization tales place inside the female body  here the fusion of sperm and ovum produces a zygote (fertilized ovum) - External fertilization tales place outside the female’s body  example: some fish and amphibians that release eggs in water.
- The hormonal cycle of female rats is 4-5 days  it releases an egg every 4-5 days and she display proceptive behavior synchronized with egg release.
- The proceptive behavior includes ultrasonic vocalizations to attract male rats  these sounds are very high pitched and cannot be detected by humans
- after the female emit these ultrasonic vocalizations, the male is attracted to the female and starts to mount her and grab her flanks.

CHAPTER 12 – PSYC 355

When stimulated properly, female rats adopt the lordosis posture to allow intromission
For 6-7 minutes, male and female do 7- intromissions, then male raises the front half of his body up while he ejaculates for 1 or 2 seconds. **Gonadal steroids are important and activate sexual behavior

Male steroids**

Castrated male loses interest in mating because testosterone is no longer produced
mating behavior is restored with testosterone treatment  activational effect of hormones
Activational effect = hormones briefly activate behavior
Up to a certain point called the baseline drive, increasing the amount of testosterone injected to castrated rats will not increase sexual drive past that point.
The higher the drive, the higher the sexual activity 2. Female steroids:
Estrogen produced at the beginning of the ovulatory cycle are important for female proceptive behavior
The subsequent production of progesterone increases proceptive behavior and activates receptivity
Following ovariectomy, estrogen and progesterone treatments restore appetitive behavior. **Lordosis is regulated by the VMH axis through estrogen and progesterone

The ventromedial hypothalamus (VMH) is crucial to the lordosis response through steroid actions.
Estrogen increases dendritic trees of neurons in the VMH.
Estrogen stimulates production of progesterone receptors.
The VMH sends axons to the periaqueductal gray in the midbrain,
Periaqueductal gray projects to the medullary reticular formation.
Medullary reticular formation projects to the spinal cord via the reticulospinal tract.
Male mounting (sensory information) and descending information from the brain (via the spinal cord) evoke lordosis.**
- What evokes lordosis?
  1. sensory input when male mounts
  2. and descending information from the brain via spinal cord
- What are the effects of estrogens?
  1. Affects neurons at VMH.
  2. Affects neurons at periaqueductal grey.
  3. induce production of progesterone receptor The medial preoptic area (mPOA) coordinates male copulatory behavior
- mPOA sends axons to the ventral midbrain and then to the basal ganglia to coordinate mounting
- Axons also project through brainstem nuclei to the spinal cord. - Paragigantocellular nucleus (PGN) has fibers that normally inhibit the erection response; mPOA signals counteract the inhibition.
- Lesions of the mPOA do not interfere with males’ motivation for copulating with females.
- They will still lever press for access to a receptive female, but they seem unable to mount. Pathway as follows 1. Pheromones from the receptive female are detected by the vomeronasal organ 2. mPOA coordinates copulatory behaviour by sending axons to the ventral midbrain 3. Ventral midbrain projects to basal ganglia and then to spinal cord via several brainstem nuclei 4. Paragigantocellular nucleus (PGN, located in the pons) sends serotonergic fibres down to the spinal cord, where they inhibit circuit responsible for penile erection Pheromones guide reproductive behavior of many species - Pheromones are chemical signals that communicate information between animals of the same species to coordinate reproduction - Vomeronasal organ (VNO): specialized receptor cells near to but separate from the olfactory epithelium. It detects pheromones, which activate male arousal
- VNO information is sent to the accessory olfactory bulb, which then projects to the medial amygdala, and in turn to the mPOA.

CHAPTER 12 – PSYC 355

Genital tubercles will become either penis or clitoris. - In females  **the müllerian ducts develop into the oviducts, uterus, and vagina & most of the wolffian system degenerates.
In males**  **the wolffian ducts develop into the epididymis, vas deferens, and seminal vesicles, and the müllerian system shrinks.
2 hormones from the testes masculinize the system of the indifferent gonad, wolffian duct & müllerian duct: Testosterone & AMH.

Testosterone** promotes development of the wolffian system. 2. Anti-müllerian hormone (AMH) causes regression of the müllerian system.

Testosterone also masculinizes other structures  5α-reductase is an enzyme in genital skin that converts testosterone into the more potent dihydrotestosterone (DHT)
DHT is a more potent form of testosterone and is necessary to form male genitalia (penis, scrotum).
Unless the indifferent gonad becomes testes and start secreting hormones, the tissues are females, women are default. **Changes in the sequence of sexual differentiation result in predictable changes in development
Turner’s syndrome:** a person only has one sex chromosome  a single X. -The individual develops as a female, due to lack of the SRY gene, and no masculinizing effects take place. - Congenital adrenal hyperplasia (CAH) (in females) results from exposure to androgens before birth.  Androgens are produced instead of corticosteroids by the adrenal glands, and the newborn has an intersex appearance.  No testes are present, and ovaries are normal, despite the appearance of external genitalia. Dysfunctional androgen receptors can block male masculinization - Androgen insensitivity syndrome (AIS) occurs in XY people whose androgen receptors do not respond to testosterone (don’t detect it) Testes remain internal  Individuals develop mainly as women
- The gene of androgen sensitivity receptor is found in X chromosome.
- Aromatase converts testosterone into estrogen
- Because they have Y chromosome, they also have SRY gene, so they develop testes that secrete AMH and testosterone. But they don’t have androgen receptors so testosterone can’t be detected and can’t be converted to DHT  this causes the external tissue to form labia and clitoris
- At puberty they will develop breasts (caused by high ratio of estrogen to androgen) & because they have testes, they lack ovaries and uterus (because testes secreted AMH)  no menstruation and they are infertile

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