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PSYC 318 Lecture Notes - 5-Ht3 Receptor, Noxious Stimulus, Monoamine Oxidase

Course Code
PSYC 318
Wayne Sossin

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Behavioral Neuroscience II
BNST – Homosexuality & Transexuality
Somatostatin innervation by the amygdala was neurons were quantified in the BNST in the 4
groups (42 subjects).
Men had almost twice as many somatostatin neurons as women.
The number of neurons in the BNST of male-to-female transsexuals was similar to that of the
Week 7, Class 1: Aggressive Behavior
Aggression -Definitions
Aggression: from Latin, ad-gradior – “I move forward” (i.e. approach)
Specific type of approach: approach with intent to harm
‘‘Behavior that inflicts harm and injury or threatens to do so’’ (Berkowitz, 1993)
‘‘Any form of behavior directed toward the goal of harming or injuring another living being
who is motivated to avoid such treatment’’ (Baron and Richardson, 1994)
Aggressive behavior can be critical for species survival (adaptive behavior)
Can be used to obtain food, water, and other resources, including female mates in the case
of males, and to defend its territory, offspring, or social rank (Takahashi and Miczek, 2013)
o Aggressive behavior is sometimes essential for survival
Carries the associated risks of injury or even death
o One has to judge whether to be aggressive or not
The exercise of aggressive behavior is determined by a cost-benefit analysis
When this balance is disrupted and an animal shows an exaggerated level of aggression, the
behavior is no longer adaptive, and it could be called maladaptive or pathological aggression
(i.e. escalated aggression)
o When aggression escalates to dangerous, uncontrollable levels.
Neural control of aggressive behavior: The Hypothalamus
Electrical stimulation of the hypothalamus elicits aggressive behavior in cats
o Two forms of aggressive behavior in cats:
Defensive rage (growling, meowing, yowling, hissing,..)
Obtained when stimulating one particular area
Predatory attack (upon stimulation, the cat will bite an anesthetised rat)
Obtained when stimulating another area
Sometimes called “Quiet Biting”

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Amygdala - Hypothalamus – PAG
Electrical Stimulation Techniques have allowed us to identify different areas of the brain
involved in Aggressive behaviors.
o Amygdala, Hypothalamus, Periaqueductal Grey
o Responses are also mediated by input from the VTA and the mPFC (Medial Pre-
Frontal Cortex)
Control of Defensive Rage:
o Central Nucleus
Basal Nucleus from the Amygdala send projections to Dorsal PAG
o Medial Nucleus sends projections through the Hypothalamus to the Dorsal PAG
o Stimulating the medial hypothalamus in cats thus induces Defensive Rage
Predation Behavior
o Medial Hypothalamus projects to the Lateral Hypothalamus, from there, the signal
goes to the Ventral PAG which controls predation
o Stimulating the Lateral Hypothalamus in cats will induce Predatory Attack
Human Equivalents?
Defensive rage:
Impulsive, unplanned
affective aggression.
Planned, goal-directed
emotionless aggression.
o Cat walks calmly
towards rat before
Black: excitatory
Red: inhibitory
Neural control of aggressive behavior – Role of Dopamine and Serotonin
o The male ‘resident’ rats confronted a smaller naive ‘intruder’ male.
o Dopamine levels increase in the Nucleus Accumbens during and after an aggressive
Resident Intruder Paradigm
o The extended duration of the DA response might reflect the expectation of /
preparation for the possibility of a second fight
Study – 2:
o The male ‘resident’ rats confronted a smaller naive ‘intruder’ male.
o Dopamine levels increase in the prefrontal cortex after an aggressive episode
o The levels of serotonin decreased during and after the fight.

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Nucleus Accumbens – Dopamine reinforces aggressive behavior
D1- and D2-like receptor antagonists were infused into the NAcc of male rats prior to the
Goal-directed aggression Experimental set-up
o In this set-up male mice will nose-poke in a hole for an opportunity to fight an
intruder mice.
o Mice were trained to nose- poke in the assigned active hole a certain number of
times after which the house light was turned on and an intruder is introduced into
the cage.
o Fighting is allowed to take place for a certain period of time after which the house
light dimmed and the intruder Removed.
Both antagonists reduced the motivation to fight in a dose-dependent manner
o However, the drug did not did not alter motor activity indicating that the effects were
not secondary to motor deficits.
o Less nose-pokes per minute with increasing antagonist concentrations
D1- and D2-like receptor antagonists also reduced percent time spent aggressing the
intruder during the encounters.
o Less biting, Less tail-rattling.
Serotonin: Lesioning Midbrain Raphe Nuclei
Raphe nuclei contains the cell bodies of serotonergic neurons which project to different
areas of the brain (hippocampus, amygdala, hypothalamus, …)
o RN is found in the brain stem
Lesioning the midbrain Raphe in male rats decreases the levels of serotonin in the forebrain
and induces intraspecific aggressiveness (towards another male).
Serotonin and aggressive behaviour in non-human primates
In this study, they measured the levels of the serotonin metabolite 5-HIAA in the CSF in male
rhesus monkeys.
4 categories of Aggressive behaviour were described:
1. Displacements
2. Stationary threats
3. Chases
4. Physical assault.
“Escalated Aggression” was defined as the percent of aggressive encounters that were
Chases (dangerous long leaps at great heights between treetops) or Physical Assaults
Low CSF 5-HIAA was associated with an increased probability of initiating aggressive
behaviors that escalated to class 3 or 4.
Serotonin and impulsivity
o Low CSF 5-HIAA was associated with a high proportion of spontaneous, unprovoked
long leaps (associated with impulsive aggressive behavior).
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