male reproductive behavior Flashcards
sperm cells
modified gametes carrying haploid components of DNA; one cell of the testis
sertoli cells
nourish sperm during maturation, source of androgen-binding protein (sperm need ABP to travel in the blood because androgens are steroids and hydrophobic); source of inhibin (role in negative feedback on AP) and MIH; associated with FSH; located within seminiferous tubules
Leydig cells
source of androgen (testosterone); mediated by LH; located in interstitial tissue in seminiferous tubules
sperm
cycle of production occurs every 2 months; 200-500 million sperm per ejaculate; originate and mature in the seminiferous tubules and epididymis
seminal fluid
- produced by the seminal vesicle and prostate
- serves as an aqueous buffer for sperm transport
- composed of sugars, amino acids, vitamins, prostaglandins–> nourish the sperm
seminal plug
coagulation of semen at the vaginal entrance; prevents leakage
spermatogenesis
LH–> testosterone–> spermatogenesis
- Process:
- spermatogonia (precursor to sperm) undergo mitosis to produce a)other spermatogonia b)primary spermatocytes
- primary spermatocytes under meiosis 1 to produce 2 secondary spermatocytes
- secondary spermatocytes undergo meiosis 2 to produce 4 spermatid
- spermatid mature into sperm
- sperm travel through lumen of the seminiferous tubules to the epididymis–> vas deferens
seminiferous tubules
where the sperm originate and mature
steroidogenesis
the creation of steroids
- testosterone synthesized in the leydig cells under the influence of LH
- (this T acts on the sertoli cells to stimulate spermatogenesis)
aromatization of T->E
testosterone is aromatized to estradiol in the sertoli cells under the influence of FSH
pathway of Testosterone conversion in Leydig (cholesterol)
-LH–> activation of G-coupled protein receptor–> activation of adenylate cyclase and synthesis of cAMP–> PKA activation–> enzyme amplification–> conversion of cholesterol–> pregnenolone–> progesterone–> androstenedione–> testosterone
FSH, sertoli cells, ABP
FSH stimulates the sertoli cells to produce ABP
-FSH acts as a transcription factor (and ultimately translation factor) that leads to the synthesis of ABP
testosterone metabolites
testosteroneandrostenedione
testosterone–> DHT via 5-a reductase
testosterone–> estradiol via aromatase
negative feedback of testosterone
testosterone produced from leydig cells feeds back on the AP and hypothalamus to decrease GnRH, LH, and FSH
negative feedback of inhibin
inhibin produced from sertoli cells feeds back on AP to decrease FSH secretion
male sexual behavior
all behaviors necessary to deliver the sperm to the ova
appetitive phase
all behaviors a male uses to gain access to a female
- aka: courtship, sex drive, appetitive behavior
- seeking sexual encounters, flirting
consummatory phase
time when copulation occurs; sex behaviors
-associated with performance, copulation, potency
sex drive (part of appetitive phase)
associated with motivation; the motivational force that brings individuals to sexual union
obstruction test
one way to measure male motivation/sex drive in rats
-must cross an electrical grid to gain access to a female; time=measurement of motivation
bar pressing
one way to measure male motivation to engage in sex
mount
pelvic contact without penile insertion
intromission
penile insertion, strong dismount, genital grooming
ejaculation
deep thrust, forceful explosion of semen, weak dismount, post-ejaculatory interval
copulatory lock
animals remain attached b/c penis swells in size and cannot physically leave females body
- maintains sperm transport
- bad in nature because it may leave you vulnerable to predators
- only seen in non-prey species, nocturnal species
testosterone maintenance and restoration
- castration and immediate testosterone replacement will MAINTAIN sex behavior in a dose-dependent manner (increasing levels of T bring an ind. closer to pre-castration levels)
- castration+ long wait period (no more free-floating testosterone circulating in the blood)+ T replacement–> RESTORE sex behavior
-independently will restore mounts, intromissions, and ejaculations
effects of castration on sexual behavior
decreased sexual responsiveness, motivation, and performance (decreased sex behavior and sex drive)
- will not investigate females, will not work nor suffer pain to contact them
- species differentiate in how long after castration that sexual behaviors cease
why are higher doses of testosterone needed to restore rather than maintain sex behavior
persistent exposure of the brain and sensory neural tissue to androgens preserves their responsiveness to those hormones (the number of androgen receptors will decrease if not surrounded by circulating androgens)
order of disappearance of sexual behaviors post-castration
- ejaculations
- intromissions
- mounts
how to test effects of hormonal metabolites
- castration, hormonal replacement with metabolite of interest
- inhibition of enzymes (aromatase, 5a reductase)
- injection of agonist, antagonist
- receptor blockers
role of estradiol in male sexual behavior
testosterone effects the maintenance and restoration of male sex behavior only through its conversion to estradiol, and estradiol’s subsequent action
- ACTS ON THE CNS
- DHT does not restore reproductive behavior/maintain it, cannot be converted to estradiol (however, T and androstenedione can)
- will independently restore mounts and intromissions, but NOT ejaculations
role of DHT in male sexual behavior
acts of the periphery to regulate penile sensitivity and responses
- changing penile shapes associated with different hormone levels and stage of reproductive behavior
- **will not restore any mating behaviors UNLESS in conjunction with estradiol
mPOA role in male performance
MPOA lesions eliminates male PERFORMANCE, but not motivation
-MPOA stimulation–> faster ejaculation
mPOA and dopamine
testosterone and estradiol act on the MPOA to release dopamine–> genital reflexes and sex motivation
Elaine Hull: Microdialysis and MPOA
- found that dopamine levels in the MPOA increase in males in the presence of sexually receptive females
- dopamine levels did NOT increase if the female wasn’t in estrus
- drugs that stimulate dopamine synthesis and release–> facilitation of copulation
- drugs that block dopamine–> decrease in M sexual behavior
role of dopamine in male sexual behavior
dopamine removes the tonic inhibition of the MPOA and leads to greater sensorimotor integration
role of the MPOA
integration of internal and external information: auditor, olfactory, tactile cues that are associated with the time of day, **stimuli associated with an estrous female, endocrine state of the male, **memories associated with previous sexual encounters
role of the olfactory bulbs in male sexual behavior
interact for successful mate recognition and sex behavior
- detection of CHEMICAL SMELLS
- blocking of smell–> decreased social and reproductive behaviors
role of the VNO in male sexual behavior
- detection of PHEROMONES
- VNOX eliminates some sexual behaviors in some animals
- detection of non-volatile components of chemosensory stimuli (i.e. urine) to prolong contact with appropriate mating partners (i.e. estrous female)
- nerves from the VNO terminate on the olfactory bulbs
role of the amygdala in male sexual behavior
lesions of the amygdala lead to DECREASED MOTIVATION but do not hinder performance
- receives projections from the VNO and olfactory bulbs
- projects to the MPOA via the stria terminals (lesioning of the ST can also decrease M motivation to engage in copulatory behaviors)
neural circuit mediating male sexual behavior
- information is integrated in the MPOA
- projection to the periaquaductal gray
- projection to the nucleus gigantocellularis
- information transmitted to the spinal cord neurons that project to the pudendal musculature and cells that regulate penile reflexes
testosterone, MPOA, dendritic spine density
Jennifer Swann
- castration leads to decreased dendritic spine density in the MPOA, but not the LPOA
- testosterone injections in the MPOA increase DS number, but not length
- why is this relevant? more dendritic spines–> more connectivity–> more neural activity–> increased likelihood of behavioral activation
testosterone replacement and MPOA responsiveness to urine
- urine of estrous females increases the neural activity in both the olfactory bulbs, VNO, and MPOA
- castration: still neural activity in the olfactory bulbs (implies that chemosensory cues from females are still processed at an early level of sensory input to the brain) but NOT in the MPOA
- testosterone replacement restores MPOA responsiveness to estrous urine
Biological basis of gay rams
oSDN of male-oriented rams 2-3x smaller than in female-oriented rams, of similar size to female rams
-neuron count in oSDN (ewes (fewest)–> male-oriented–> female oriented))
organizational effects of testosterone on the oSDN
sex differences in SDN-POA and mating behavior arise out of exposure and organizational effects of testosterone and estradiol during the perinatal period
-difference in size of the oSDN is NOT impacted by concentrations of hormones in the blood (T and E have organizational, but not activational effects)
timeline of genital vs. brain masculinization
- genitals masculinized days 30-60
- oSDN masculinized days 60-90
- testosterone affects the differentiation of the genitals and brain in different timeframes, so while a ram’s sex is male, varying levels of T exposure may masculize the brain differently and explain why we see differences in sexual partner preference
HPG axis and masculinization of the body and brain: gay rams
HPG axis is established very early in development to maintain homeostasis and ensure there’s enough testosterone produced to complete testicular development and regulate brain masculinization
-kisspeptin stimulates GnRH neurons in the hypothalamus–> stimulate the AP to produce LH–> production of testosterone in the testis–> brain masculinization and testicular development
garter snakes and dissociated reproductive pattern
reproductive behavior does not coincide with maximum gonad size and activity
- copulation occurs when steroid levels and gamete production are low
- produce when there is no free floating testosterone, testes are regressed)
garter snakes: influence by MPOA and pineal (NOT castration, steroids, or gonadotropins)
sexual performance and motivation can be eliminated by lesioning the MPOA or pineal gland: two regions that integrate environmental information that allows the snake to process seasonal information
