Download Pheromones

Chemical Communication Systems
Hormones Have Many Actions in the Body
Hormones are chemicals, secreted by one cell group,
that travel through the bloodstream to act on targets.
Endocrine glands release hormones within the body.
Exocrine glands use ducts to secrete fluids such as
tears and sweat outside the body.
Major Endocrine Structures and Their Functions
The First Experiment in Behavioral Endocrinology
Berthold (1849) found that testes release a chemical into the bloodstream that affects
male behavior and body structure.
Hormones Have Many Actions in the Body
Although Berthold was not aware of it, his experiment also
demonstrated an important aspect of hormonal actions.
The hormone released from the testes (testosterone) must be
present early in life to have such dramatic effects on the
body and behavior.
The brain and body are “organized” by exposure to
hormones early in life, and these changes can be dramatic
and long-lasting.
Later in life, hormones “activate” behaviors, but their effects
tend to be less dramatic and short-lived.
The Influence of a Hormone
“organized” by exposure to hormones early in life
“activate” behaviors, but their effects tend to be less dramatic and short-lived.
Neuroendocrine Cells Blend Neuronal and Endocrine Mechanisms
The Multiplicity of Hormone Action
Testosterone
Thyroxine
Androgen
receptor
Skin
Thyroid receptor
Muscle
Chemical Structures of the Three Main Hormone Types
Chemosensory systems
• Main olfactory epithelium (MOE)
– Detects a broad range of chemicals
– Ciliated olfactory sensor neurons
• Olfactory receptors for general odor information
• Trace amine-associated receptors (TAARs) for pheromone
information
– Circuit from receptors in olfactory epithelium to olfactory bulb and then
to olfactory cortex
• Vomeronasal organ (VNO)
– Detects pheromones
– Circuit from receptors in VNO to accessory olfactory bulb
and then to amygdala and hypothalamus
Chemosensory systems
• Vomeronasal organ (VNO)
– Detects species specific pheromone chemicals
– Microvillar receptor neurons
– Two distinct families of receptors in rodents
• vomeronasal type 1 receptors (V1Rs)
• 100’s of receptor types
– project to the anterior AOB
• vomeronasal type 2 receptors (V2Rs)
– project to the posterior AOB
– responsive to Major Histocompatibility Complex (MHC)
– Distribution and density of receptors varies greatly across
species
The Vomeronasal System
Pheromones
• Secreted or excreted chemical that triggers a social
response in members of the same species
• Used by unicellular organisms “yeast” as well as
multicellular animals “mammals”
• Regulating behavior such as mating, aggression,
and fear
• Influence hormone levels related to puberty or
estrous
• Serve as cues for individual recognition
• Messages are dependent on
– Social identities of the signaller and the receiver
– Gender of the signaller and the receiver
Examples of pheromones
• Major Histocompatibility Complex (MHC)
– MHC proteins are part of the signaling system in the immune system
– Prefer mates with MHC somewhat different from yours
• 2-methylbut-2-enal
– volatile aldehyde in rabbit milk
– induces nipple-searching behavior in pups
– Detected by MOE system
• Methanethiol
– volatile thiol in male mouse urine
– attractant for female mice
• 2,3-dehydroexo-Brevicomin
– volatile testosterone-dependent octane in mouse urine
– modulating receptivity and inducing estrus in female mice
• by altering the hypothalamic secretion of GnR
• which triggers the secretion of gonadotrophic hormones
– follicle stimulating hormone (FSH)
– luteinizing hormone (LH)
– which affect gonadal hormone secretion
Evolution of Pheromone Signaling in Tetrapods
• Aquatic ancestors of all tetrapods
– transition from water to land
– pheromones changed from soluble to:
• volatile: small air borne molecules that signal gender
• non-volatile: large complex proteins that signal
individual identity
– Requires changes to
• mechanisms of release
• sensory anatomy
• receptors
Evolution of Pheromone Signaling in Tetrapods
• In primates
– Increased brain size
• evolution of trichromacy
• increase in social complexity
– Less regulation of behavior from hormone activation
• Reduced influence of pheromones
• Inactivation of the vomeronasal system in catarrhine primates
– Old World monkeys: baboons, macaques, colobus, and so on …
– Apes: gibbons, orangutans, gorillas, chimpanzees, bonobos, and
humans
• How much influence remains in humans?
Human Pheromones
• Controversial because of vestigial VNO and poor replication of
some findings
• For example, compounds from the armpits of women that synchronizes
menstrual cycles in groups of women
• Humans do show sex-specific behavioral and physiological
responses to various odors received through the MOE that
likely qualify as pheromones
• One example is sweat produced by apocrine “sweat” glands
– Contains androstadienone in men
• activates preoptic and ventromedial hypothalamus in women
• affects their endocrine levels, physiological arousal, mood, and
sexual orientation
• Another example is the scent of ovulating women
– Men who smell estrogen-like substance have activation in the
paraventricular and dorsomedial nuclei of the hypothalamus
– Could produce increased levels of testosterone
Human Pheromones
• Trace amine-associated receptors (TAARs)
– In the olfactory system for pheromone information
– mediate aversion or attraction towards
– volatile amines that include
• the mouse odor trimethylamine
– Presented alone, trimethylamine evokes species-specific behaviors.
• the predator odor 2-phenylethylamine
• the death-associated odor cadaverine.
• Humans: 6 genes (TAAR1, TAAR2, TAAR5, TAAR6,
TAAR8, TAAR9)
– Although not all of these are functional