SEXUAL BEHAVIOR

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SEXUAL BEHAVIOR
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Hormonal communication
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Principles of hormonal action

• Frequently act in a gradual fashion.
• Often take days to act or to wear off.
• Change frequency or intensity of behavior.
• Not a switch.
• Reciprocal effect
• Behavior can affect hormone release.

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Principles of Action

• Multiple effects on multiple targets.
• Estrogen?brain (mult. areas), uterus, bone, fat
• Chemical structure similar across species
• Require receptor to mediate effect
• Frequently genomically mediated
• Some fast membrane effects
• Pulsatile secretion

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Principles of Action

• Multiple effects on multiple targets.
• Estrogen?brain (mult. areas), uterus, bone, fat
• Chemical structure similar across species
• Require receptor to mediate effect
• Frequently genomically mediated
• Some fast membrane effects
• Pulsatile secretion

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Pulsatile release
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Types of Hormones

• Steroid hormones
• Lipid molecules, derived from cholesterol
• Gonads (testes, ovaries, adrenals)
• Protein peptide hormones
• Amino acid chain, large or relatively small
• Brain, pituitary, many organs/glands

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Classes of sex steroids

• Androgens
• Estrogens
• Progestins/progestogens
• Corticosteroids

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Structures synthetic pathways for sex steroids
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Structures synthetic pathways for sex steroids
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Steroids influence gene expression
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Synthesis and release of oxytocin
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GnRH control of gonadotropin secretion
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Mode of action of protein and peptide hormones
such as GnRH
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Influence of gonadotropins on the testis
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Estrogen production
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A 28-day menstrual cycle
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Hormonal basis of the menstrual cycle
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Menstrual cycle
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Hormones and the menstrual cycle

• Background
• Female fetus Oogonia proliferate ? 4-5 M _at_ 5
  months gestation.
• Mitosis stops, prophase of meiosis begins.
• Replication and lining up of chromosomes
• Girl is born with 2M primary oocytes

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Asexual Reproduction - mitosis
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Sexual reproduction Meiosis prophase
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Sexual reproduction Meiosis I
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Sexual reproduction Meiosis II
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Hormones the menstrual cycle

• Follicular phase
• FSH ? 1 or 2 follicles develop.
• Early negative feedback by E ? decreases FSH
• But, granulosa cells are multiplying increasing
  their FSH receptors ? hi E levels for 2 days
• Something magic happens! Positive feedback ? LH
  (and FSH) surge.

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Stages of follicular development
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Hormones and the menstrual cycle

• Follicular phase (cont.)
• For 12 40 yrs, granulosa cells nourish oocyte,
  prevent 1st meiotic div.
• Via gap junctions
• LH blocks gap junctions primary oocyte divides
  ? secondary oocyte polar body
• Follicle ruptures and secondary oocyte is
  released into abdom. cav., swept up by cilia and
  muscular contractions into fallopian tubes, where
  fertilization can occur.
• Still no 2nd meiotic division unless fertilized.

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Hormones the menstrual cycle

• Luteal phase (After ovulation)
• LH maintains corpus luteum (remnant of follicle)
  ? Progesterone
• P ? further thickening of endometrium dense,
  protein-rich secretion
• Cervical mucus ? thick, impenetrable

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Secondary oocyte w/ zona pellucida cumulus cells
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Hormones the menstrual cycle

• If fertilization conceptus implants and begins
  to secrete hCG (takes the place of LH in
  maintaining corpus luteum).
• 12-14 days necessary to let conceptus implant
  and start secreting hCG.

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Hormones the menstrual cycle

• If no fertilization E P ? negative feedback ?
  GnRH decreases ? corpus luteum degenerates
• E P fall ? endometrium breaks down ?
  menstruation

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4 STAGES OF REPRODUCTIVE BEHAVIOR

• Sexual attraction
• Appetitive behaviors
• Proceptivity
• Copulation
• Receptivity in females
• Mounts, intromissions, ejaculation in males
• Refractory phase

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4 STAGES OF REPRODUCTIVE BEHAVIOR

• Sexual attraction
• Attractivity
• Role of estrogen in females
• Coordinates fertility and attractiveness
• Sex skin swelling in some primates

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Sexual swellings of female baboons
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4 STAGES OF REPRODUCTIVE BEHAVIOR

• Sexual attraction
• Pheromones

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Atlas moth, Attacus atlas
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4 STAGES OF REPRODUCTIVE BEHAVIOR

• Sexual attraction
• Males
• Size, strength, territory, nest, money, lack of
  physical imperfections

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SURVIVAL OF THE SPECIES REQUIRES REPRODUCTIVE
SUCCESS. NEANDERTHALS FAILED!
MANY ANIMALS ADVERTISE REPRODUCTIVE STATUS WITH
COLOR
MALE VERVET MONKEY
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• Sexual attraction
• Males
• Counterintuitive antlers, peacock tails, dark
  manes, bright colors

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4 STAGES OF REPRODUCTIVE BEHAVIOR

• Appetitive behaviors (motivation)
• Proceptivity in females
• Hopping, darting, ear-wiggling in rats
• Eye contact and proximity
• Timing of most copulation is determined by female.

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4 STAGES OF REPRODUCTIVE BEHAVIOR

• Appetitive behaviors
• Males
• Birds elaborate songs and/or nests
• Proximity to female

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• Appetitive behaviors
• Tests
• Bar-pressing, hurdles, bi-level apparatus, X-maze
• Confounds

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4 STAGES OF REPRODUCTIVE BEHAVIOR

• Copulation
• Receptivity in females
• Rats a few hours every 4 or 5 days
• Lordosis necessary for copulation
• Rats spontaneous ovulators but need patterned
  stimuli to induce luteal phase/pregnancy
• Monkeys social variables

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4 STAGES OF REPRODUCTIVE BEHAVIOR

• Copulation
• Males mounts, intromissions, ejaculation
• Great variability among and within species re.
  stimulation needed for ejaculation
• Dogs begin to ejaculate as soon as intromission
  is achieved.
• Rats 7-10 brief intromissions before ejaculation
• Rats copulation accompanied by fever (PGE2?)

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4 STAGES OF REPRODUCTIVE BEHAVIOR

• Refractory phase (absolute, relative)
• Ultrasonic song in male rats (absolute r.p.)
• Function? Cool brain? Stay away?
• Sleep EEG (absolute r.p.)
• Coolidge effect (relative r.p.)
• Locks and Beagles
• Facilitation of ex copula erections in rats after
  first few ejaculations
• Pair bonding in prairie voles

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Neural circuitry in females

• Proceptivity
• Nucleus accumbens (NAc)
• Jill Becker Copulation is rewarding, and
  dopamine is released in NAc, only if female
  controls pace.
• Medial preoptic area (mixed effects)
• Axons to midbrain locomotor area ? hop dart
• Some neurons fire only during proceptive
  behavior others, only during lordosis.

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Neural circuitry in femalesMesolimbic dopamine
tract
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Neural circuitry in females

• Receptivity
• Lordosis posture necessary for copulation in
  most mammals

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Neural circuitry in females

• Ventromedial nucleus of hypothalamus (VMH)
• Essential for lordosis
• Estrogen (E) implants in VMH ? restore
  copulation in ov-x females
• E increases dendritic tree
• E ? progesterone (P) receptors
• Norepinephrine release during copulation

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Neural circuitry in females

• Periaqueductal gray (PAG)
• Convert slow hormonal effects to rapid copulation
• Axons from MPOA and VMH ? prolactin (PRL),
  substance P, and gonadotropin releasing hormone
  (GnRH) into PAG.
• All facilitate lordosis

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Neural circuitry in females

• Lower brain stem
• Medullary reticular formation
• Integrates sensory input and adjusts posture
• Lateral vestibular nuclei
• Detects head movement (ear wiggling)

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Neural circuitry in females

• Spinal cord
• Receives sensory input and controls back muscles
• Receives coordination from medulla

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Neural circuitry in males

• General motivation/activation
• Mesolimbic dopamine tract

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Mesolimbic dopamine tract
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Mesolimbic dopamine tract

• Dopamine is released in nucleus accumbens (NAc)
  as soon as male detects female.
• (Pfaus Phillips, 1991)
• Dopamine is increased in satiated males during
  Coolidge effect.
• (Fiorino et al., 1997)
• Cross-sensitization from amphetamine to sexual
  behavior
• (Fiorino Phillips, 1999)

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Nigrostriatal dopamine tract
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Nigrostriatal dopamine tract

• Dopamine increased in dorsal striatum only after
  copulation had begun.
• Therefore, implicated in motor activation, but
  not sexual motivation.
• (Pfaus Phillips, 1991)

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Neural circuitry in males

• Sensory input
• Vomeronasal organ
• Main olfactory system
• Genitosensory input

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Neural circuitry in the male

• Medial amygdala
• Receives input from both vomeronasal organ and
  main olfactory bulb
• Has copious androgen and estrogen receptors

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Neural circuitry in the male

• Medial preoptic area MPOA
• Main integrative site
• Lesions abolish male sexual behavior in fish
  through primates
• Stimulation ? erection, ejaculation, dud?stud
• Receives input directly or indirectly from all
  senses
• Abundant estrogen and androgen receptors
• Sends output back to sources of input can
  influence its own input

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Neural circuitry in the male

• Dopamine in the MPOA is important for male sexual
  behavior.
• Dopamine agonists in MPOA facilitate copulation
  and genital reflexes.
• Dopamine antagonists impair copulation, genital
  reflexes, and sexual motivation.
• Local periventricular (A14) neurons supply the
  dopamine.

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Dopamine in MPOA

• Intact males, T-replaced castrates, some 1-week
  castrates
• DA rose in presence of female and during
  copulation.
• All 2-week castrates a few 1-week castrates
• DA was low throughout.

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Castrates Basal extracellular DA low, but tissue
DA is high
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Nitric oxide
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Block NO synthase ? block DA release during
copulation
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Nitric oxide in MPOA

• Castrates had fewer NO synthase neurons in MPOA
  than intact or testosterone-treated castrates.

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Dopamine in MPOA

• Large lesions of the amygdala abolished
  copularion.
• A dopamine agonist in MPOA restored copulation.

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Smaller medial amygdala lesions block DA increase
in response to female basal levels normal.
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MPOA summary

• Dopamine in MPOA facilitates all aspects of
  copulation.
• Dopamine is released as soon as a male detects an
  estrous female.
• Testosterone increases both basal dopamine and
  permits the increase in response to a female.
• It does so by increasing nitric oxide synthesis.

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MPOA summary

• A major input to the MPOA is the MeA.
• Large lesions of the amygdala abolished
  copulation, which was restored with a dopamine
  agonist in the MPOA.
• Smaller lesions of MeA impaired copulation and
  prevented the dopamine response to a female.
• Normal basal levels of dopamine sufficient for
  suboptimal copulation.

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Output from MPOA

• Paraventricular nucleus (PVN)
• Oxytocin neurons to spinal cord ? erection and
  ejaculation

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Output from MPOA

• Periaqueductal gray (PAG) of midbrain
• Reciprocal connections with MPOA
• Many steroid receptors
• Projects to nPGi
• Nucleus paragigantocellularis (nPGi) in medulla
• Serotonin-containing axons ? lumbosacral spinal
  cord.
• Lesions facilitate copulation and genital
  reflexes.
• Potential site for inhibitory effects of SSRI
  antidepressants

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Spinal cord

• Sensory input motor output
• Ejaculation generator
• Excitatory inputs from PVN and MPOA
• Inhibitory input from nPGi

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Summary

• Sexual attraction is promoted by estrogen in
  females and, to some extent, androgens in males.
• Sexual motivation is also promoted by gonadal
  hormones, mesolimbic dopamine tract, MPOA in
  both sexes.
• Copulation Females VMH?PAG?medulla? spinal
  cord?lordosis.
• Estrogen? progesterone receptors, norepinephrine
  release in VMH also PRL, GnRH, substance P to
  PAG.

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Summary

• Copulation Males Vomeronasal main olf. sys.?
  MeA ? MPOA (DA) ? PVN (reflexes), PAG nPGi
  (inhibitory) ? spinal cord.
• Parasympathetic system ? erection (also secretion
  of seminal fluids)
• Sympathetic system ? seminal emission and
  ejaculation (may also contribute to erection)

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References

• Bale, T.L., Davis, A.M., Auger, A.P., Dorsa,
  D.M., McCarthy, M.M. (2001) CNS Region-specific
  oxytocin receptor expression Importance in
  regulation of anxiety and sex behavior. J.
  Neurosci., 21, 2546-2552.
• Becker J.B., Rudick C.N., Jenkins W.J. (2001)
  The role of dopamine in the nucleus accumbens and
  striatum during sexual behavior in the female
  rat. J. Neurosci., 21, 3236-3241.
• Dominguez, J., Riolo, J. V., Xu, Z., Hull, E.
  M. (2001). Regulation by the medial amygdala of
  copulation and medial preoptic dopamine release.
  J. Neurosci., , 21, 349-355.
• Fiorino, D. F., and Phillips, A. G. (1999).
  Facilitation of sexual behavior and enhanced
  dopamine efflux in the nucleus accumbens of male
  rats after D-amphetamine-induced behavioral
  sensitization. J. Neurosci. 19, 456-463.
• Fiorino, D. F., Coury, A., and Phillips, A. G.
  (1997). Dynamic changes in nucleus accumbens
  dopamine efflux during the Coolidge effect in
  male rats. J. Neurosci. 17, 4849-4855.
• Hull, E.M., Du, J., Lorrain, D.S., Matuszewich,
  L. (1995). Extracellular dopamine in the medial
  preoptic area Implications for sexual motivation
  and hormonal control of copulation. J. Neurosci.,
  15, 7465-7471.
• Pfaus, J. G., and Phillips, A. G. (1991). Role of
  dopamine in anticipatory and consummatory aspects
  of sexual behavior in the male rat. Behav.
  Neurosci. 105, 727-743.
• Polston, E., Heitz, M., Barnes, W., Cardamone,
  K., Erskine, M.S. (2001) NMDA-mediated
  activation of the medial amygdala initiates a
  downstream neuroendocrine memory responsible for
  pseudopregnancy in the female rat. J. Neurosci.,
  21, 4104-4110.