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Lecture 15

HMB200 2014 Lecture 15.pdf
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Department
Human Biology
Course
HMB200H1
Professor
John Yeomans
Semester
Winter

Description
  Lecture  15:  Sex  and  Gender     -­‐ estrogen  is  concentrated  in  the  ventral  part  of  the  brain   –  especially  in  the  hypothalamus,  pituitary,  and  preoptic   area  à  also  in  amygdala,  bed  nucleus,  and  periaqueductal  grey   area     -­‐ removal  of  gonads:  testosterone  goes  down,  sex  drive  goes   down  à  testosterone  is  the  most  important  androgen  for   inducing  male  sexual  motivation   -­‐ medial  preoptic  area  (mPOA)  is  the  sexually  dimorphic  nucleus   à  highest  expression  of  estrodial  receptors   o triggers  puberty  and  sexual  interest   Brain  Regions  for  Sexual  Behaviour   -­‐ most  important  area  in  rodents:  vomeronasal  organ   o accessory  olfactory  system   o where  water  borne  molecules  (pheromones)  can  reach   accessory  olfactory  system   o males  get  very  aroused  by  female  pheromone  odours   o this  pathway  goes  to  accessory  olfactory  bulb,  then   sends  a  direct  projection  to  the  medial  amygdala   o medial  amygdala:  has  direct  olfactory  projections,  lots  of  estrodial  receptors   à  responds  to  sexual   olfactory  signals   -­‐ amygdala-­‐bed  nucleus-­‐preoptic  pathway  is  needed  for  olfactory  triggering  of  male  sexual  arousal     -­‐ Male  sexual  response  is  mediated  by:  dopamine  neurons   o Pathways  from  mPOA  pathways  go  to  dopamine  neurons  (in  the  ventral  midbrain)   o Dopamine  neurons  in  the  VTA  go  to  the  Nigral  striatal  and  mesolimbic  pathways   o These  dopamine  neurons  stimulate  motor  arousal,  sexual  motivation  (chase  females)   o Triggered  by  hypothalamus  arousal   o Pathway  also  goes  down  to  hindbrain  and  spinal  cord  to  trigger  sexual  reflexes  (males:  erection  and   mounting)   o These  pathways  connect  olfactory  stimuli  to  limbic  to  hypothalamic  to  sexual   reflexes   -­‐ Female:  has  to  approach  male  and  provide  the  odours  that  activates  the  males   o Once  male  mounts  her,  she  has  to  expose  her  hind  end   –  lordosis   Estrus  Cycle  of  Rats   -­‐ female  sexual  behavior  occurs  every  4-­‐5  days  in  rats     -­‐ cycle  involves  a  period  of  ovulation  towards  the  end  of  the  cycle   -­‐ this  period  when  the  female  is  receptive:  estrus   -­‐ 2  hormones:  estrogen  followed  by  a  surge  of  progesterone   -­‐ triggers  female  odours  and  ovary  is  ready  for  male  intromissions       -­‐ ovulation  is  triggered  by  mechanical  stimulation  of  the  cervix  by  the  male  penis   à  induced  ovulation  due  to   mechanical  stimulation  of  the  cervix   -­‐ ovulation  only  follows  when  male  intromits  =  release  of  ovum   =  fertilization  enabled     Behavior  of  Females   -­‐ internal  (estrus)  hormones  that  influence  receptivity     -­‐ hypothalamic  and  hormonally  driven   -­‐ when  female  is  in  estrus:  female  approaches  male,  hopping   away  –  male  chases  female   –  male  mounts  female   –  lordosis   posture  (allows  for  mounting)   o controlled  by  descending  pathways  from   hypothalamus     o ventral  medial  hypothalamus  –  axons  to   periaquaductal  grey   o this  ventral  lateral  part  of  the  periaquaductal  grey  –   opiate  receptors  (analgesia)   § where  lordosis  activating  neurons  go  to  spinal   cord  and  brain  stem  to  produce  this  fixed   posture   Sexual  Diversity  in  Humans   • Sexual  behavior  is  influenced  by  genes ,  by  hormones,  by  social  groups  (competition,  fighting  in  males,  etc)   • Male/female  brain  differences  greatest  in  anterior  hypothalamus  and  BNST.   • Rodent  male  brain  has  a  dark  sexually  dimorphic  nucleus,  like  preoptic  area  in  the  female   • Interstitial  nucleus  of  the  anterior  hypothala mus   (INAH)   • Differences  compared  between  heterosexual  females   and  heterosexual  males   • Females  tend  to  have  a  small  nucleus;  males  tend  to   have  a  darker  and  larger  nucleus   • INAH-­‐3  differences  in  some  male  homosexuals.   • BNST  differences  in  a  few  transgendered  ma les.   • Gay  gene  Xq28  not  supported,  however.   • Single  gene  that  causes  homosexuality  has  not  been   supported     Homosexual  Male  Brains   -­‐ had  smaller  nucleus    INAH3   -­‐ large  cluster  of  AIDS  victim  with  smaller  nuclei   Gender  Identity   • do  you  feel  that  you  are  male  or  fe   • transgendered  can  be  heterosexual  or  homosexual  regardless  of  sex   change  operation   • sexual  preference  is  independent  of  their  gender  identity   • relates  to  differences  in  size  of  ben  nucleus  of  strius  terminalis   à   BNST  is  an  amygdala  connected  structure  (part  of  limbic  system)  –   connects  medial  amygdala  with  medial  preoptic  area   • Central  subdivision  (has  most  of  the  estrodial  receptors)   of  BNST   44%  larger  in  males  than  females.   • Male  heterosexuals  had  a  larger  nucleus  and  more  dark  cells   •
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