Sex: Evolutionary, Hormonal and Neural Basis

1
Sex Evolutionary, Hormonal and Neural Basis

• 4 Stages of Reproductive BehaviorNeural
  Substrates of Reproductive BehaviorHuman
  ReproductionPheromonesSexual ReproductionReprod
  uctive StrategiesMating and Sexual Selection

2
Stages of Reproductive Behavior - I

• Sexual attraction
• Linked to reproductive cycle
• Sex skin apes and monkeys
• Odors
• Plumage
• Measured male in approaches / time spent
• Appetitive behaviors
• Proceptive - behaviors that establish/maintain
  attraction
• Darting hopping (female), sniffing (male)
  rats
• Elaborate songs nest-building birds

3
Stages of Reproductive Behavior - II

• Copulation / coitus
• Intromission
• Ejaculation
• Refractory phase
• Coolidge effect - shorter refractory phase w/ new
  female
• Post-copulatory phase
• Decreased attraction and appetitive behaviors
• Minutes to months
• Copulatory lock
• Parenting behaviors

4
Fertilization

• Gametes
• Ova sperm
• Zygote
• Fusion of gametes
• External (frogs, fishes) v. internal (mammals
  birds)
• Cloaca
• Oviparity v. viviparity

5
Rat Copulatory Behavior

• Proceptive behaviors
• Darting and hopping, ear wiggling
• Lordosis
• Activational effect
• Testosterone restores mating in castrated males
• Estrogens
• Facilitate proceptive behaviors

6
Steroids in Hypothalamus Female Receptivity

• Ventromedial hypothalamus (VMH)
• Estrogen and progesterone receptors
• Lesions abolish lordosis
• Estrogen implants induce receptivity
• VMH - midbrain (periaqueductal gray) -medullary
  reticular formation - spinal cord(via
  reticulospinal tract)

7
Androgens Male Reproductive Behavior

• Medial preoptic area (MPOA) of hypothalamus
• Steroid neurons
• Lesions abolish male copulation
• Reinstatement of mating w/ androgen implants
• MPOA - ventral midbrain - basal ganglia
  -brainstem - spinal cord (intromission
  ejaculation)
• VNO - amygdala responsible for erections

8
Human Sexual Behavior

• 4 Stages
• Increasing excitement
• Plateau
• Orgasm
• Resolution
• Paragigantocellular nucleus
• Pons spinal cord
• 5-HT neurons inhibit erection /SSRIs sexual
  dysfunction side effects
• Viagara
• Inhibit 2nd messenger enzyme phosphodiesterase-5
• Permissive role of hormones
• Androgens promote sexual interest
• Slight increase in sexual behavior at ovulation
• Major histocompatability complex (MHC)
• Immune-related genes (body odors), women prefer
  similar MHC in mates as fathers

9
Asexual Reproduction / Existence

• Fission
• Parthenogenesis
• Hermaphrodites
• Simultaneous (e.g., snails, slugs fish)
• Spontaneous (e.g., clown fish)

10
Mating Strategies Systems

• Courtship - sexual selection
• Sexual dimorphism
• ___________________________________
• Promiscuity
• Polygyny
• Polyandry
• Monogamy

11
Darwinian - Sexual Selection

• Selective pressures
• Sex-specific
• Adornment / behaviors
• Regulate ovulation (some species)
• Competition / choice

12
Sexual Determination

• Heterogametic v. homogametic
• Reptile
• Sex chromosome
• Egg incubation temperature
• Gonadal differentiation (nature nurture)
• SRY gene on Y chromosome OR XX chromosome
• SRY protein testes / hormonal production
  (testosterone)
• Anti-Müllerian Hormone (AMH)
• Wolffian duct (induction) and Müllerian duct
  (regression)
• T internal organs masculinized
• 5-?-reductase converts T to dihydrotestosterone
  (DHT) to masculinize external genitalia

13
Departures from Sexual Differentiation

• Turners Syndrome (XO)
• No SRY gene
• Immature gonads poorly developed ovaries
• Androgen exposure in-utero masculinizes XX
  individuals
• Increased anogenital distance (rats)
• Decreased ovulatory points and litter size
• Congenital adrenal hyperplasia (CAH)
• Swollen adrenal glands produce excess androgens
• XX individuals external male / internal female
• Androgen insensitivity (AIS)
• Missing androgen receptor gene (X chromosome)
• Gonads develop into testes (produce testosterone
  and AMH),w/out receptors, no Wolffian ducts
• Physically female w/out internal female organs

14
Sexual Dimorphism

• Songbird
• Syrinx (12th cranial nerve - innervated by
  robustus archistriatum (RA) - controlled by
  higher vocal center (HVc)
• Adult androgens (females)
• Enlarge HVc and Robustus archistriatum (RA)
  (brain nucleus)
• POA / SDN-POA
• Different in males slight of control male
  behavior
• Social influences (Celia Moore, 1992)
• Spinal nucleus of the bulbocavernosus (SNB) -
  rodents
• CNTF knock-out mice
• SNB neurons die
• Onufs nucleus (other mammals)

15
Take Home Message

• Stages of reproduction
• Brain and spinal regulation of sex
• Advantages of sexual reproduction
• Hormones
• Sexual strategies / selection
• Gonads / steroids
• Determination, differentiation and development
• Brain regions
• Problems in sexual differentiation
• Sexual dimorphism