Rat Seeex Flashcards
rat sex and monogamous prairie voles
chick and goat testicles
Absolutely Wild Animal Hormone Studies
Berthold’s castration and hormone replacemenet studies in chicks showed that testis transplantation restores normal development in roosters; the testes were not connected to a blood supply or neuronal network; effect was mediated by chemicals released to the blood stream (hormones!)
Brinkley used goat testes transplantions for human males deemed as having a ‘weak sexuality’
[Reproductive behaviour]
Hormones
- Hormone is a signalling molecule that can carry messages to distant targets through the bloodstream
- Neurohormone if released by neurons; target neighbouring or distant cells
- Target is an organ or cell that can detect the hormone and is affected by it
Hormone Classes:
* steroid hormones - derived from cholesterol, permeate cells (e.g. cortisol)
* amine hormones - derived from tyrosine, cannot permeate cells (e.g. thyroid hormone, TH)
* peptide & protein hormones - amino acid chains, cannot permeate cells but activate membrane receptors (e.g. oxytocin)
Where are they produced?
* ovaries: oestrogen + progesterone
* testes: testosterone
* pituitary gland: growth hormone
* throid gland: thyroxine
* pancreas: insulin
* adrenal gland: adrenaline
[Reproductive behaviour]
Sexual development
Offspring genetic sex depends on sex chromosome carried by sperm (X or Y).
Exposure to sex hormones pre and postnatal is responsible for sexual dimorphism; Y chromosome controls development of glands producing male sex hormones.
Primary Sexual Characteristics
Gonads are first to develop; either testes or ovaries.
* Sex-determining region Y (SRY) gene from Y chromosome expresses SRY protein, which differentiates gonads into testes.
* Lack of SRY means gonads develop into ovaries.
At month 3, if testes present and producing anti-Mullerian hormone and androgens, internal sex organs develop into male genitalia.
If dihydrotestosterone present, develop external male genitalia.
Secondary Sexual Characteristics
Hypothalamus releases gonadotrophin-releasing hormone (GnRH) which stimulates hormone release by testes/ovaries.
Gonadotrophins (testosterone vs estradiol) responsible for development of secondary sexual characteristics in males vs females.
[Reproductive behaviour]
Hormonal control of sexual behaviour
(not sexual development)
e.g. female reproductive cycle (menstrual cycle); FSH - estradiol - LH - ovulation - estradiol + progesterone from corpus luteum
> in non-primate females, sexual behaviour only present during ovulation (heat)
e.g. male sexual behaviour in rats
* mounting
* intromission
* ejaculation
depend on testosterone levels; castrated rats injected with T reinstate sexual behaviour
e.g. female sexual behaviour in rats
* female initiates copulation (approaches male when receptive)
* lordosis (arched back)
depends on estradiol and progesterone; overiectomised rats show no sexual behaviour; inactivate estradiol receptios, no sexual behaviour (allow for mounts but no intromission)
[Reproductive behaviour]
Neural control of sexual behaviour
Methods to investigate neural control of sexual behaviour
* retro-tracing; injecting pseudorebies virus into sexual organs (to define the circuit that controls sexual organs)
* activation of Fos in key brain regions
* identification of neurons containing sex hormone receptors (which brain areas)
Males
* spinal control (absent in females); if complete spinal cord transection above 10th thoracic segment, can ejaculate; lumbar spinothalamic (LSt) cells control ejaculation - destruction abolishes ejaculation without affecting mounting/intromission
* brain mechanisms; excitation vs inhibition of spinal circuits - e.g. medial preoptic area, destruction abolishes sexual behaviour, contains the sexually dimorphic nucleus (males > females)
Females
* no spinal circuit
* brain mechanisms; central circuits - e.g. ventromedial nucleus of hypothalamus (VMH), destruction abolishes sexual behaviour -> periacqueductal grey of midbrain -> medulla
[Parental behaviour]
Maternal behaviour
Examples:
* Nest building is one of the earliest maternal behaviours (during gestation)
* Assist in birth by gently pulling pups
* Nursing
* Periodically lick pups’ anogenital region to stimulate urination/defecation
* Retrieve pups if they leave or are removed from the nest
Hormones can influence maternal behaviour, but cannot control it.
* medial preoptic area is crucial
* VTA-NAcc pathway (reward system) is also necessary; activated when mothers encounter pups
* in lactating females, encountering pups is more rewarding than cocaine (Ferris et al., 2005)
* human mothers show activation of reward system when presented with photos of their babies
[Parental behaviour]
Paternal behaviour
Few mammalian species display paternal care for offspring
e.g. monogamous prairie voles share offspring care VS polygamous meadow voles male leaves female after mating
Size of MPA less sexually dimorphic in prairie voles than meadow voles; MPA lesions disrupt paternal behaviour in rats and prairie voles; MPA involved in paternal behaviour
[Affiliative behaviour]
Pair Bonding
only 3-5% mammals are monogamous
monogamous prairie voles vs polygamous meadow voles
hormonal influence:
* exposure to partner while injected with OXT or VP increased partner-preference
* more time spent with partner when VP and OXT, in males and females
neurobiology:
* pair bonding associated with density of VP receptors in reward areas; as increased sensitivity to hormones (VP receptors similar pattern of expression to dopamine D2 receptor; OXT highly expressed in PFC and Nacc)
* partner preference disrupted after blocking VP/OXT receptors
* overexpression of VP receptors in ventral pallidum increased mate preference in meadow voles
similar effects observed in humans;
* e.g. intranasal OXT caused relaxation and reduced anxiety in humans (Heinrichs et al., 2003)
* e.g. maternal/romantic love activated regions of the brain rich in VP and OXT receptors
