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Aggressive Behavior. Neuroendocrinology Kevin Kelliher. Aggression. Aggressive Behavior - An Overt behavior with the intention of inflicting damage or other unpleasantness on an other individual (Moyer 1971) (Brain 1979) Self defense (defensive rage and fear mediated attack)

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aggressive behavior

Aggressive Behavior

Neuroendocrinology Kevin Kelliher

  • Aggressive Behavior - An Overt behavior with the intention of inflicting damage or other unpleasantness on an other individual (Moyer 1971) (Brain 1979)
    • Self defense (defensive rage and fear mediated attack)
    • Maternal Aggression
    • Predatory aggression
    • Pup Killing
    • Social Aggression
  • Agonistic Behaviors - interrelated behaviors related to physical conflict between adult members of the same species (social aggression)
    • Fighting
    • Escape
    • Defensive postures
    • Dominance and Subordination
    • Patrol and marking behaviors
aggression and testosterone
Aggression and Testosterone
  • In a number of species increases in aggression have been correlated with rises in testosterone
    • Seasonal changes
    • Puberty
testosterone levels don t always correlate with aggression
Testosterone levels don’t always correlate with aggression
  • High T and aggression in females are not correlated
  • Male hamsters that are no longer in breeding condition will not increase aggressive bouts when injected with T
  • Changes in(or the presence of) Androgen receptors are required for aggression
organization and activation of aggression in mice
Organization and Activation of Aggression in Mice
  • In mice T is required both during development and in adulthood for the display of aggressive behavior.
  • Females treated with T shortly after birth will display high levels of aggression in adulthood
the 5 ht hypothesis
The 5-HT Hypothesis
  • In general reduced levels of 5-HT are correlated with increased aggression
    • 5-HT or its metabolites collected from CSF are found to be lower in more aggressive males
    • Microdialysis can measure changes in 5-HT in specific brain areas at specific times surrounding aggressive episodes
5 ht and fighting
5-HT and Fighting
  • 5-HT is decreased in the Prefrontal cortex after fighting
    • Correlates with decreases in 5-HT in the CSF in more aggressive individuals
  • 5-HT increases slightly in the NA after fighting
    • In some instances when 5-HT agonists increase or antagonists decease instances of aggression this is believed to take place in the striatum
  • 5-HT
caveat to pharmacology
Caveat to Pharmacology
  • Most drugs are not as specific as we would like (act on various receptors)
  • Effects may be secondary to other effects (sedation, motor control)
5 ht 1b
  • Most direct link between 5-HT and Aggression
    • Agonists with a high affinity for anpirtoline 5-HT1B (anpirtoline, CP-94,253 and zomitritan) reduce aggression.
    • 5-HT1B Knockout mice have an aggressive phenotype
  • By contrast dopamine exerts permissive effects on aggressive behavior
    • Changes in mesocorticolimbic can DA occurs before during and after aggressive episodes
    • Changes in dopamine may reflect motivational aspects
  • Acts via mesocorticolimbic pathway but not striatal
    • Changes in DA are not found in striatum in response to aggressive episodes
  • GABA is believed to tonically inhibit aggressive behavior
    • Acting via the GABAA receptor complex
    • GABA levels are inversely correlated with levels of aggression
  • However GABA agonists have bitionic effects on aggression
    • Low doses increase aggression
    • High doses decease aggression
  • GABA likely mediates alcohol induced aggression
    • Alcohol at low concentrations appears to specifically effect GABAA receptors
    • Alcohols effects on aggression mimic the effects of benzodiazepines
    • Low doses tend to increase aggressive behavior whereas high doses decrease aggression (and have sedative effects
vasopressin and social aggression
Vasopressin and Social Aggression
  • Vasopressin has been implicated in a number of agonistic behaviors
    • Scent-marking
    • Patrolling
    • Social fighting
  • There are three known types of vasopressin receptors
    • V2R - in the periphery
    • V1aR and V1bR - Brain receptors (also located in the periphery as well)
v1br and social aggression
V1bR and Social Aggression
  • Male V1bR-KO mice have significantly reduced instances of aggressive behavior
  • Both Latency and number of attacks during a resident intruder test are decreased
social preferences in v1br kos
Social Preferences in V1bR-KOs
  • Social preferences are also altered in V1bRKO mice
    • Male KOs fail to exhibit normal social preferences
    • KOs appear to have reduced motivation for social interaction
olfactory discrimination in v1brkos
Olfactory Discrimination in V1bRKOs
  • Decreased aggression in V1bRKOs is not due to a deficit in Olfactory Discrimination
    • Mice have no apparent olfactory defects
    • KOs can still discriminate between male and female urine
olfactory influences on aggression
Olfactory influences on Aggression
  • In general an intact olfactory system is needed for full expression of social aggression
  • One caveat about bulbectomy studies is that removal of olfactory bulbs have many non olfactory related consequences
  • Is social aggression mediated by the VNO?
    • Lets check….
vomeronasal influences on aggression
Vomeronasal influences on aggression
  • It appears that aggressive behavior is inhibited in TRPc2-KO mice based on number of fighting episodes vs number of mounting episodes
  • Things to think about
    • Fighting is not eliminated (if intruder is not submissive fighting occurs)
    • Is mounting behavior always sexual?
    • If sex discrimination is not altered what other agonistic behaviors may overall mediate so social aggression in these mice.?
ovarian hormones and maternal aggression
Ovarian hormones and Maternal aggression
  • Ovarian hormones can modulate Maternal Aggression
  • Can differ depending on the species
    • Rats E Increases maternal aggression both before and especially after parturition
    • Mice E delays maternal aggression withdrawal facilitates it.
    • P increases aggression prior to parturition no effect after.
  • It is possible that the primary actions of these hormones are in the periphery facilitating sensory mechanisms
sensory input
Sensory input
  • Olfactory
    • Pup odors are facilitory to maternal aggression
    • Intruder odors are required for maternal aggression
  • Somatosensory
    • Nipple stimulation is critical for the display of maternal aggression
  • Auditory
    • Questionable role however ultrasounds from male rats intruders can inhibit aggression (and facilitate mating)
neural correlates
Neural Correlates
  • Markers for neuronal activity label familiar neural circuits during maternal aggression
neural correlates29
Neural Correlates
  • Lesions of various neural circuits alter the expression of maternal aggression
neural circuitry
Neural Circuitry
  • Olfactory bulb -- Sensory (olfactory) cues from both pups and intruder
  • Amygdala -- Integration of sensory cues from both pups and intruder and central responses
  • Peripeduncular nucleus (PPN) -- Somatosensory cues from pups
  • Septum-- Maternal responsiveness in general (Motivation?) in decreased
  • mPOA-- Unknown exact extent but is known to decrease aggression in general
  • VMH-- thought to be critical site for critical site for transmitting to motor output regions
  • PAG-- Tonical inhibits maternal aggression however not part of output since lesions after removal of pups is not effective
neurochemical correlates
Neurochemical Correlates
  • 5-HT - jury is still out hypothesized to decrease maternal aggression based on effects in males on general aggression
    • Some studies found this some did not
    • Equally interesting correlation between low 5-HT in CSF and aggression may be a male phenomena
    • Likely acting at PAG, Raphe Nuclei or Amygdala to inhibit aggression
    • Actions in the septum increase aggression
5 ht and maternal aggression
5-HT and Maternal Aggression
  • In general 5-HT reduces maternal aggression in rats
  • In mice results of 5-HT agonists and antagonists have been mixed
  • And while 5-HT decreases aggresssion in male praire voles (those that are highly paternal) it doesn’t effect maternal aggression
neurochemical correlates33
Neurochemical Correlates
  • GABA -
    • GABA receptor activity suppresses maternal aggression
    • Actions are likely in the VMH and MeA
    • Interestingly PAG activity inhibits maternal aggression but GABA not involved
    • Maternal Aggression could involve an inhibition of GABA transmission in the amygdala and VMH
  • Dopamine -
    • DA tonically inhibits Maternal aggression
    • Lesions of Dopamine Neurons in VTA results in increased maternal aggression
    • 6-OH-DA injected into striatum is unaffected thus likely not involved (in context of DA)
    • Site of action would thus be MH and VMH
neurochemical correlates34
Neurochemical Correlates
  • Oxytocin
    • Hypothesized that OT from PVN inhibits aggression but no real evidence.
    • By contrast OT in Central amygdala increases maternal aggression in hamsters
    • OTs importance for social recognition (olfactory) is most crucial factor
  • Vasopressin
    • Although no specific studies on maternal aggression believed to have similar functions as with male aggression
    • Vasopressin in lateral septum therefore should increase aggressive behavior
    • Unpublished data reports V1bR-KO mice have reduced maternal aggression (but reduced aggression in general)
neurochemical correlates35
Neurochemical Correlates
  • CRH
    • Peripheral infusions of ATCH or ICV injection of CRH reduce maternal aggression
    • Since CRH elevates fear and anxiety it is thought that decreases would be needed to express maternal aggression
  • Opioids
    • Opioids generally decrease maternal aggression
    • Likely mechanism is indirect altering animals general activity/pain sensation or olfactory ability
neurochemical correlates36
Neurochemical Correlates
  • Nitric Oxide
    • Male nNOS-KO mice are highly aggressive
    • By contrast knocking out nNOS in females eliminates attacks
    • Increases in citulline (the byproduct of NO synthesis is observed in the mPOA, SCN and subparaventricular zone in association with maternal aggression
    • How NO is acting is unknown (5-HT ? CRH? AVP?)
no and male aggression
NO and Male Aggression
  • Male nNOS-KO mice are highly aggressive
  • There is a link between nNOS and 5-HT turnover
  • This may be related to a hypo functioning of the 5-HT1A and 5-HT1B receptors
    • 5-HT agonists can decrease aggression in nNOS mice but significantly higher doses are required
    • Reducing 5-HT turnover in the brain of WT mice mimics aggressive phenotype found in KO mice
predatory aggression40
Predatory Aggression
  • A simplified model of the neural circuitry the mediates predatory aggression in the cat
  • Electrophysiological studies suggest monosynaptic projections from the LH to the midbrain tegmentum are responsible for attack behavior
  • Projections from tegmentum connect to motor pathways, trigeminal and facial nerves
modulatory pathways
Modulatory Pathways
  • A number of sites modulate attack behavior
    • Amygdala (annoyingly abbreviated ME here)
    • BNST - often thought to be part of the “extended amygdala”
    • PAG feeds back to the lateral hypothalamus
    • Also Hippocampus, septum and just about any other limbic area you can think of
defensive rage
Defensive rage
  • The Medial Hypothalamus is the critical site for the initiation of defensive rage in cats
  • The primary circuit being MH to the PAG
  • PAG excites brain stem and spinal neurons causing autonomic and motor cascade resulting in behavior
  • Amygdala modulates activity but is not critical for initiation of behavior
vmh and amh
  • Interestingly while the VMH has historically been the site for initiation of defensive rage the source of efferents is the AMH
  • The VMH stimulates the PAG via the AMH