affiliative and reproductive behaviour

describe the experimental wedding

• oxytocin (love hormone) levels went up

• vasopressin (possession hormone) went down in Nic

• cortisol (stress hormone) was up in Linda before and after the ceremony but went down in Nic after the ceremony

• testosterone levels doubled in Nic

castration and hormone replacement

• testis transplantation restores normal development in roosters

• transplanted testis were not not connected to blood supply or neuronal networks

• their effect was mediated by chemicals released to the blood stream

describe Brinkley’s surgeries

• testis transplant from farm animals to humans with ‘weak sexuality’

• they were successful for some time but ethical, methodological and safety aspects made this unsustainable

what is a hormone?

signalling molecule that can carry messages to distant targets through the blood stream

what is a neurohormone?

a hormone released by neurons; targets neighbouring or distant cells

what is a target?

an organ/cells that can detect hormone(s) and it is affected by it

what are the classes of hormones?

• steroid hormones - derived from cholesterol; can travel across cell membranes

• amine hormones - derived from amino acid tyrosine; cannot cross the cell membrane

• peptide and protein hormones - amino acid chains; cannot cross cell membrane; activate membrane receptors

where are hormones produced?

• sex hormones - females: ovaries for oestrogen and progesterone; male: testes for testosterone

• growth hormone (GH) - pituitary gland

• thyroxine (TH) - thyroid gland

• insulin - pancreas

• adrenaline (ADH) - adrenal gland

what determines genetic sex?

• depends on the sex chromosome carried by the sperm and egg (ovum) that generates them

• depends on the father sperm cells which carry X or Y sex chromosomes

development of sex organs

• all the info to develop bodies of either sex is present in the 22 non-sex and the x chromosomes

• exposure to sex hormones (before and after birth) is responsible for sexual dimorphism

• the Y chromosome controls the development of the glands that produce the male sex hormone

what are the sex organs?

• gonads (ovaries and testes)

• internal sex organs

• external genitalia

key characteristics of gonads

• first to develop - produce ova or sperm and hormones

• sex-determining region Y (SRY) gene (from Y chromosome) express SRY protein that differentiates gonads into testes

• lack of SRY results in ovaries development

key characteristics of internal sex organs

• during first two months of gestation, foetus can develop into either male or female

• at month 3, if testes are present and producing hormones, internal sex organs develop into male ones

• female internal organs do not need presence of any other hormone to develop

key characteristics of external genitalia

• do not need hormonal influence to develop into female organs

• dihydrotestosterone (androgen produced by testes) develops external genitalia into male version

sexual maturation

• secondary sex characteristics develop during puberty and are also influenced by hormones

• hypothalamus release gonadotropin-releasing hormones which stimulates hormone release by testes or ovaries

hormonal control of sexual behaviour

• hormones control sexual development but also interact indirectly with the nervous system to affect sexual behaviour (e.g. menstrual cycle)

• in non-primate females, sexual behaviour is linked to ovulation; primate females can mate at any time during their menstrual cycle

hormones and sexual behaviour in male rodents

• male rodents’ sexual behaviour - mounts, intromission, ejaculation

• depends on testosterone levels - castrated male rats injected with testosterone reinstate sexual behaviour

hormones and sexual behaviour in female rodents

• female rodents’ sexual behaviour - lordosis

• female initiates copulation; when receptive, the male will approach

• sexual behaviour depends on oestradiol and progesterone

neural control of sexual behaviour: tools

• retro-tracing to define the circuit that control sexual organs

• activation of Fos in key brain regions

• identify neurons containing sex hormone receptors

neural control of sexual behaviour: males

• spinal mechanism - men with complete spinal cord transection above 10th thoracic segment can ejaculate

• a group of neurons in the lumbar region (spinal ejaculation generator) lumbar spinothalamic (Lst) cells control ejaculation

• destruction of Lst cells in rats abolishes ejaculation without affecting mounts or intromissions

• brain mechanisms excite or inhibit spinal circuits

neural control of sexual behaviour: females

• do not have a spinal circuit controlling sexual behaviour

describe parental behaviour in mammals

• most mammalian species show parental behaviour

• hormonal and neuronal control mostly base on data from rodents

• most research on maternal behaviour

describe maternal behaviour in rodents

• birth assistance by pulling the pups gently

• nursing

• periodically licks pups’ anogenital region to stimulate urination and defecation

• pups retrieval if they leave or are removed from the nest

• behaviour influenced by prenatal hormones but passage of pups through the birth canal also helps

• hormones can influence behaviour but does not control it

describe paternal behaviour in voles

• few mammalian species show paternal care for the offspring

• monogamous prairie voles share offspring care; polygamous male meadow voles leave female after mating

• size of MPA is less sexually dimorphic in prairie voles than meadow voles

• MPA lesions disrupt paternal behaviour in rats and prairie voles; MPA is also involved in paternal behaviour

what are affiliative behaviours?

• positive social behaviours within the same or different species

• can involve individuals of the same or different sex (formation of pair bonds in voles; prosocial behaviours in humans)

• the neuropeptides oxytocin and vasopressin are key for complex social behaviours

pair bonding in mammals

• only 3-5% of mammals are monogamous

• biparental species - males and females raise the young

hormones influencing pair bonding

• exposure to a partner while injected with VP or OXT increased preference for partner

neurobiology of pair bonds

• associated with the density of VP receptors in the reward areas of the brain

• after mating and cohabitating with a female, male prairie voles tended to spend significantly more time in contact with their partner than the stranger

• overexpression of vasopressin receptor in ventral pallidum enhanced mate preference in meadow voles

how is oxytocin involved in pair bonding?

• OXT receptors are highly expressed in PFC and Nacc in prairie voles

• partner preference in prairie voles is disrupted after blocking OXT or VP receptors

formation of pair bonds in humans

• oxytocin and vasopressin seem to influence pair bonding in humans

• OXT intra-nasal caused relaxation and anxiety reduction in humans

• maternal and romantic love activated regions of the brain rich in vasopressin and oxytocin receptors

role of oxytocin in prosocial behaviour

• administration of oxytocin has subtle effects in social behaviours in humans: trust, empathy, social approach, altruism

• oxytocin has effects on brain regions related to reward and fear related processing

• growing interest in translating oxytocin administration for the treatment of psychiatric conditions

• effects on behaviour are highly influences by individual and contextual conditions

how does oxytocin effect trust?

subjects given oxytocin show significantly higher MU transfer levels

how does oxytocin effect altruism?

• positive correlation between OXT levels and social donation

• no effect in the ecological frame

• OXT increased donations in the social frame but decreased those in the ecological frame

how does oxytocin effect empathy?

• OXT administration increased empathy ratings in all dimensions

how does oxytocin effect social approach?

• OXT administration decreased the social distance that female participants kept between themselves and an unfamiliar (and attractive) male experimenter

role of oxytocin in prosocial behaviour

• expression of OXT and OXT receptors maps into areas involved in anticipatory, appetitive, and aversive cognitive states