brain & behavior ch. 8

hormones/endocrine system

Hormone

Chemical messenger transported through blood to regulate target tissues

Endocrine gland

Releases hormones into the body, usually into the bloodstream

Exocrine gland

Releases substances through ducts, such as sweat or saliva

Berthold's experiment

Reimplanted testes restored male development in castrated roosters, demonstrating chemical signaling

Endocrine communication

Hormones travel through blood to distant targets

Synaptic communication

Neurotransmitters diffuse across a synaptic cleft

Pheromone

Chemical released outside the body that affects the same species

Allomone

Chemical released by one species that affects another species

Three hormone categories

Peptide, amine, and steroid hormones

Peptide and most amine hormone receptors

Membrane metabotropic receptors; effects typically occur within seconds to minutes

Steroid hormone receptors

Intracellular receptors that regulate gene transcription; effects often take hours or longer

Steroid hormone mechanism

Crosses membrane, binds receptor, and changes gene transcription

Testosterone and sexual activity

Normal circulating levels do not directly correlate with amount of sexual activity

Pituitary gland

Endocrine gland connected to and controlled by the hypothalamus

Neuroendocrine cell

Neuron that releases hormones into the circulation

SON

Supraoptic nucleus of the hypothalamus

PVN

Paraventricular nucleus of the hypothalamus

Posterior pituitary hormones

Oxytocin and vasopressin, produced in hypothalamic neurons

Oxytocin functions

Uterine contractions, milk letdown, and aspects of social and reproductive behavior

Vasopressin functions

Water conservation, increased blood pressure, and aspects of social behavior; associated with monogamy in prairie voles

Oxytocin and social recognition

Oxytocin-deficient male mice show impaired recognition of familiar females

Vasopressin and prairie voles

Vasopressin signaling promotes partner preference and correlates with pair bonding

Releasing hormone

Hypothalamic hormone controlling anterior pituitary hormone secretion

Tropic hormone

Anterior pituitary hormone stimulating another endocrine gland

Hypothalamic-pituitary portal system

Blood vessels carrying hypothalamic releasing hormones to anterior pituitary

Negative feedback

Target hormones inhibit further secretion at hypothalamus and/or pituitary

Gonadotropins

Anterior pituitary hormones that selectively stimulate cells of gonads to produce sex steroids and gametes; FSH and LH

Gonadotropin-releasing hormone (GnRH)

Hypothalamic hormone stimulating FSH and LH release from anterior pituitary

FSH in females

Stimulates follicle growth, maturation, and estrogen secretion

FSH in males

Supports sperm production

LH in females

Triggers ovulation by stimulating follicles to rupture, releasing eggs; triggers formation of corpus luteum that secretes progesterone

LH in males

Stimulates testosterone production by the testes

Gonadal hormones are critical for:

triggering reproductive behavior controlled by the brain; gamete production

Sertoli cells

Support sperm development in testes

Leydig cells

Produce and secrete testosterone

Androgens

Class of hormones that promote the development/maintenance of male reproductive organs and secondary sex characteristics; testosterone

Ovulatory cycle

FSH stimulates follicles to grow and secrete estrogens —> induce hypothalamus and pituitary to secrete LH —> triggers ovulation and formation of corpus luteum —> secretes progesterone to maintain uterus for pregnancy

Oral contraceptive mechanism

Synthetic hormones provide negative feedback on the hypothalamus, inhibiting GnRH —> no gonadotropins (FSH/LH) released —> no ovulation

Steroid hormone precursor

Cholesterol; all steroid hormones are made from cholesterol in a step-by-step enzymatic process; ex. cholesterol → progestins → androgens → estrogens

Four stages of reproductive behavior

Sexual attraction, appetitive behavior, copulation, post-copulatory behavior

Sexual attraction

First step in mating behavior, brings males and females together; animals emit stimuli that attract members of the opposite sex; may be synchronized with physiological readiness to reproduce (ex: odors reflecting estrogen levels in females)

Appetitive behavior

Courtship behaviors that establish or maintain attraction; species-specific behaviors

Proceptive female

A female exhibiting behavior that indicates willingness to mate, often characterized by actions that attract males and signal readiness for copulation

Sexual receptivity

State in which an animal is willing to copulate; in heat/estrus; female often the one to choose whether copulation will take place

Refractory phase (copulation)

Period following copulation during which the individual does not recommence copulation; length varies with species

Coolidge effect

Renewed mating interest in response to a novel receptive partner

Post-copulatory behavior

Behavioral patterns after mating, including parental behaviors to nurture offspring; species-specific; lots of variability

Activational hormone effect

Temporary behavioral change caused by hormones acting on an adult nervous system/the administration of a hormone to an adult animal

Five maternal behaviors in rats

Nest building, crouching over pups, cleaning pups, retrieving pups, nursing

Virgin rat response to pups

Initially avoid pups; repeated exposure to smell of pups can produce maternal behavior

Parabiotic preparation

Shared blood supply between mom and pups, demonstrating hormonal preparation for maternal behavior

Hormones involved in maternal behavior

Estrogens, progesterone, oxytocin, and prolactin

Four phases of human sexual response

Excitement, plateau, orgasm, resolution

Refractory period

Period after orgasm when another orgasm or copulation cannot readily occur; men tend to have an absolute refractory phase after orgasm, but not women

Sex determination

Early process establishing whether fetus will develop as male or female

Sexual differentiation

Development of sex-related anatomical and behavioral characteristics

Indifferent gonads

Early fetal gonads not yet differentiated into testes or ovaries

SRY gene

Y-linked gene that directs developing gonads toward testes

Testosterone in fetal development

Promotes Wolffian duct development into male internal reproductive structures

AMH

Anti-Müllerian hormone; causes Müllerian duct regression

5α-reductase

Enzyme converting testosterone into more potent DHT

DHT

Androgen important for full masculinization of external genitalia

Turner syndrome

Single X chromosome, no Y; female development with underdeveloped ovaries

Congenital adrenal hyperplasia (CAH) in XX individuals

Mutations cause female fetuses to be exposed to excess prenatal androgens, may masculinize external genitalia; no testes, normal ovaries; depending on level of exposure, the newborn may have an intersex appearance

Androgen insensitivity syndrome (AIS)

XY fetus with a gene defective for androgen receptors, does not respond to androgens; gonads develop as normal testes due to SRY protein, Wolffian ducts don’t develop; external tissues develop mainly as female

Why is there no uterus in complete AIS?

Testicular AMH causes Müllerian duct regression

5α-reductase deficiency

XY individuals; rare mutation disables 5-α-reductase; develops normal testes and male internal reproductive structures, normal testosterone and AMH; incomplete external masculinization at birth, raised as female until puberty; at puberty, testes produce more testosterone, external genitalia become more masculinized, develop some secondary sex characteristics

What happens at puberty in 5α-reductase deficiency?

Increased testosterone can produce greater masculinization; development of male-leaning secondary sex characteristics

Organizational hormone effect

Lasting neural or behavioral change from steroid hormones during development

Sensitive period

Period during development when organism can be permanently altered by particular experience or treatment; ex: neonatal period, puberty

Organizational hypothesis

Early androgen signaling organizes masculine-typical neural and behavioral development; if the nervous system does not receive an androgen signal, the body will organize itself as female

Sexual dimorphism

Pronounced differences in structure between males and females; also apparent in brain

SDN-POA

Sexually dimorphic nucleus of the pre-optic area in hypothalamus, larger in male than female rats

Evidence for SDN-POA organization

Early androgen exposure enlarges it; adult castration does not reverse its size

SNB

Spinal nucleus of bulbocavernosus; motor neurons associated with penile muscles

Onuf’s nucleus

Human homolog of SNB; men’s are larger

Development of SNB in rats

Rat dams spend more time licking anogenital area of male pups than that of female pups; dam detects androgen metabolites in male pups’ urine, which promotes the development and survival of SNB motor neurons.

Characteristics of AIS women

XY, internal testes, no oviduct/uterus; have vagina and breasts; behave like female, mostly attracted to males; raised as girls and tend to be very feminine; usually strongly identify as female even after learning of condition

Characteristics of CAH females

Described as having more masculine characteristics; as adults, most are heterosexual but more likely than other women to be homosexual

Characteristics of 5-alpha-reductase deficiency

Behave as males as adults

Cloacal exstrophy

A congenital defect where the bladder and genitalia are not properly formed, leading to exposure of internal organs. It often results in significant challenges related to urinary and reproductive function

Characteristics of cloacal exstrophy males with early sex reassigment

Most declared themselves boys; almost all as teenagers reported sexual attraction to girls

Interstitial nuclei of the anterior hypothalamus (INAH)

Nuclei in humans that are seen in the same part of the hypothalamus as the SDN-POA in rats; associated with sexual orientation and gender identity

INAH-3

Human anterior hypothalamic nucleus studied for group differences in sexual dimorphism; larger in men than women; larger in straight men than gay men

Fetal androgen exposure and adult behaviors

In women, measures of these markers indicate that lesbians, on average, were exposed to slightly more fetal androgens than heterosexual women; markers include sound emission from ears, finger length, eyeblink patterns

Fraternal birth order effect

More older biological brothers correlates with higher probability of male homosexuality; mixing of mother’s blood with male infant’s at delivery exposes mother to male-specific proteins, mother may generate antibodies in response, which can transfer to the fetus of her next son