The Influence of a Hormone

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 Glands and Their Functions

The First Experiment in Behavioral Endocrinology

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.

Chemical Communication Systems

Semiochemicals (Gk. semeon, a signal) are chemicals that mediate interactions between organisms. Semiochemicals are subdivided into allelochemicals and pheromones depending on whether the interactions are interspecific or intraspecific, respectively.

The Multiplicity of Hormone Action

Neuroendocrine Cells Blend Neuronal and Endocrine Mechanisms

Organization of Odor Projections in the Brain

The Vomeronasal System

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

• Vomeronasal organ (VNO)– Detects species specific pheromone chemicals– Microvillar receptor neurons– Two distinct families of receptors

• vomeronasal type 1 receptors (V1Rs) project to the anterior AOB• vomeronasal type 2 receptors (V2Rs)

– project to the posterior AOB– responsive to MHC

– Distribution and density of receptors varies greatly across species• Process the information in separate neural pathways which

converge at the amygdala• Both detect semiochemicals which are chemical messengers

of any type such as pheromones and allomones

Linda B. Buck given the Nobel Prize in Physiology or Medicine in 2004 along with Richard Axel for their discoveries of odorant receptors and the organization of the olfactory system.

Catherine Dulac identified pheromone receptors in the vomeronasal organ (VNO) in mice.

Pheromones• Chemical message

– between conspecifics – regulates specific neuroendocrine mechanism in others– usually not consciously detected as odors

• Regulating behavior– reproduction– maternal care– aggression– alarm responses

• Traditionally two types of pheromones– Releasers (Signaling): cause an immediate behavioral response – Primers: cause long-term physiological changes– Recent examples of pheromones have been shown to produce both

of these effects – Better to conceive of these as two mechanisms not two types

• Messages are dependent on– individual identities of the signaller and the receiver – gender of the signaller and the receiver

Examples of pheromone influences• 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

Male pheromone–stimulated neurogenesis in the adult female brain: possible role in mating behavior. Gloria K Mak . (2007) Nature Neuroscience 10:, 1003 - 1011

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

Palaeontology: A firm step from water to landPer Erik Ahlberg and Jennifer A. Clack Nature 440, 747-749 (6 April 2006)

The lineage leading to modern tetrapods includes several fossil animals that form a morphological bridge between fishes and tetrapods. Five of the most completely known are the osteolepiform Eusthenopteron16; the transitional forms Panderichthys17 and Tiktaalik1; and the primitive tetrapods Acanthostega and Ichthyostega. The vertebral column of Panderichthys is poorly known and not shown. The skull roofs (left) show the loss of the gill cover (blue), reduction in size of the postparietal bones (green) and gradual reshaping of the skull. The transitional zone (red) bounded by Panderichthys and Tiktaalik can now be characterized in detail. These drawings are not to scale, but all animals are between 75 cm and 1.5 m in length. They are all Middle–Late Devonian in age, ranging from 385 million years (Panderichthys) to 365 million years (Acanthostega, Ichthyostega). The Devonian–Carboniferous boundary is dated to 359 million years ago18.

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 across all primates?• How much influence in humans?

Human Pheromones• Produced by exocrine glands (discharged outside of the body)

– compounds from the armpits of women that synchronizes menstrual cycles in groups

– Androstenol breaks down to androstenone the most prominent androstene present on male human axillary hair

– able to simulate the human female vomeronasal organ resulting in changes in autonomic activity

• Influences on behavior– play an important role in mammalian social and sexual behavior – more intensive social contact with men– a significant reduction of nervousness, tension and other negative feeling

states – related to rating of attractiveness

• Influences on neuroendocrine system resulting in – Changing levels of andogrens and estrogens which modulate

• facial appearance • body shape

• How can this happen without a functional VNO?– Do not forget about the MOE– Pheromone signaling through the olfactory system

Major Histocompatibility Complex (MHC)• A large set of genes responsible for MHC proteins

– Found in most vertebrates– Are part of the signaling system in the immune system

• Such as : T cells, natural killer cells, macrophages, B cells – MHC proteins are expressed on the surface of cells – MHC proteins are excreted in urine and apocrine secretions

• Important for reproductive success– Parents with similar MHC will have offspring with similar MHC– Parents with different MHC will have offspring with diverse MHC– Diversity of MHC improves survival

• Mate preference based on MHC– Prefer mates with MHC somewhat different from yours – Which Receptors, is this through TARRs in MOE ? – Most evidence from rodents– Some evidence for this in humans

• Judging odor of T-shirts• Could be masked by colognes and perfumes• Disrupted in women using oral contraceptives