PSYC 310 Lecture Notes - Lecture 6: Blastocyst, Optogenetics, Adenylyl Cyclase
7 May 2018
School
Department
Course
Professor
PSYC 318
Behavioural Neuroscience II
January 17th, 2018
Lecture 4/24: Reinforcement Learning Theory
• Finish up last paper: Natural Neural Projection Dynamics Underlying Social Behavior
o Paper 2 research question: do midbrain dopamine neurons (many of which project to the
nucleus accumbens) play a causal role in promoting social behavior?
o Why is cre-recombinase used so much?
▪ If we want dopamine neurons to express GCaMP protein, why don’t we simply
make
• 1. Viral DNA that encodes GCaMP under a dopamine specific promotor?
o GCaMP is a synthetic protein, fluorescent indicator of neural
activity: they want to get this indicator into dopamine cells
o We know that we can introduce DNA into cells through viruses,
so we know we can make a viral DNA that encodes GCaMP that
only dopamine cells will read
o People have discovered that the dopamine-specific promotor,
and many cell type specific gene promotors, tend to be too long
to fit inside viruses
o If you just take section of promotor that can fit it doesn’t have
perfectly selective expression
o You could manipulate cells at blastocyst stage in development to
make a transgenic animal: this has not happened yet, because
that mouse would be specific and only helpful for recording
neural activity of dopamine neurons, and the GCaMP protein is
always trying to be made better, brighter, and more sensitive to
calcium; every couple of years there is a new GCaMP protein
released
▪ If you were to make a transgenic mouse it probably
would take a year to do it, and then a year later another,
better GCaMP version will have come out and you’d
have to play catch-up and make another mouse
▪ Instead:
• Authors use viral DNA that encodes GCaMP under a generic gene
promotor, but put in condition that cre recombinase has to be present in
order for this DNA to be read
• You need to have a mouse where cre is present in some cells
• They’ve made transgenic mice that have cre under a dopamine specific
gene promotor
• Scientist-designed viral DNA
o Easy to remake virus if GCaMP version gets better
• Combination of cre-dependent virus and transgenic mouse
o Why is cre-recombinase used so much, instead of just putting in the DNA to do exactly
what we want? Why the dual situation of cre-dependent virus and animals expressing cre
in select population of cells?
▪ Practical: often gene promoter fragments too long to fit inside most viruses
▪ Use of cre provides immense combinatorial control
• People have made hundreds of mouse lines where the expression of cre
is restricted to very specific populations of cells: i.e. dopamine, serotonin,
etc.
• Cre-dependent viruses can be reused in any of the different cre mouse
lines
find more resources at oneclass.com
find more resources at oneclass.com
• When you make a cre-dependent virus, that one virus can be used in
hundreds of different mouse lines for a wide array of different studies
o Same dopamine-cre mice can be used to drive expression of any
foreign protein, like GFP, ChR2, GCaMP, etc.
o In this paper: Do the NAc-projecting dopamine neurons selectively fire during social
interactions?
▪ Inject cre-dependent, GCaMP into midbrain of dopamine-cre mice
▪ Aiming for one part of midbrain called VTA which is highly populated with
dopamine neurons
▪ First experiment was to stick fiber optic cable in midbrain and collect light during
behavior
▪ Put optical fiber to collect light into NAc, image calcium transients in dopamine
terminals in the NAc
o Summary of findings
▪ Midbrain dopamine neurons are active both when mice are interacting with other
mice and when they interact with novel objects
• Stimulating or inhibiting midbrain dopamine neurons promotes or
attenuates, respectively, social interactions but these manipulations do
not affect novel object exploration
▪ Selective stimulation of the projection of midbrain dopamine neurons that project
to the NAc promote social interactions
▪ Dopamine input to PFC: very different results
• Doesn’t increase social interactions, tends to promote place aversion,
increase anxiety-like behaviors, seems to be a very different pathway
• Shows that stimulating dopamine cell bodies in the midbrain can cause
all these effects that probably counteract against each other: dopamine
projecting to the NAc is encouraging behavior in one direction, but
dopamine projecting to PFC encourages behavior in another direction
o Next question: what is it about dopamine inputs to the NAc that promotes social
interactions?
▪ Dopamine projections from the midbrain to the accumbens release dopamine,
but have also been demonstrated in many cases also release glutamate and
GABA
▪ When they’re stimulating pathways and increasing social behavior, is it actually
the dopamine release causing this? One way to test that is to start blocking
specific receptors for certain signaling molecules they think are being released
when they stimulate this pathway
▪ If dopamine release in the NAc promotes social behavior, what receptors there
are important?
• What dopamine receptors are in the NAc?
• There are 5 types of dopamine receptors: D1,2,3,4,5
• Many of them are expressed but we often see two main kinds of receptor
expression. In general in the NAc we say 90% of the neurons are
projection neurons
▪ Half projection neurons express D1 receptor, other half D2
• Seems all projection neurons have at least one of these receptors
• Blocking one of these receptors and stimulate dopamine input: do
receptor antagonists block increase in social interaction we were
expecting?
o If dopamine release in the NAc promotes social behavior, what receptors there are
important?
▪ Blocking dopamine D1 receptors in the NAc blocks the increase in social
interaction that is caused by optical dopamine neuron stimulation
o Dopamine neurons can release glutamate and GABA in addition to dopamine, so how
can you be sure that the dopamine D1 receptor is sufficient?
find more resources at oneclass.com
find more resources at oneclass.com
