Fibre photometry
Recombinant AAV vectors (Viral Vector Facility, Zurich Neuroscience
Center, ETHZ/UZH) were used for pathway specific expression. For
calcium-dependent fluorescent GCaMP6 expression in BA-NAc neurons, a
vector encoding GCaMP6 incorporated into a construct with FLEX,
ssAAV-9/2-hSyn1-chI-dlox-GCaMP6m-dlox-WPRE-SV40p(A)
(“rAAV-FLEX-GCaMP6”; 4.2 x 1012 vg/ml, 300 nl) , was
injected unilaterally in the BA (see Stereotactic surgery for retrograde
tracing and fibre photometry). For Ca2+-independent
EGFP expression, as a control to determine whether certain social
behaviours generated movement-related artifacts in the fibre photometry
signal, a vector encoding EGFP incorporated into a construct with
FLEX, ssAAV-9/2-hSyn1-dlox-EGFP(rev)-dlox-WPRE-hGHp(A)
(“rAAV-FLEX-EGFP”; 8.2 x 1012 vg/ml, 300 nl) was
injected unilaterally in the BA. To induce GCaMP6 or EGFPexpression in BA-NAc neurons specifically, a retrograde vector encodingCre-recombinase , rAAV-2-retro-hsyn1-Cre-mCherry
(“rAAV-retro-Cre”; 8.4.1012 vg/ml, 300 nl) was
injected in the ipsilateral NAc. After BA vector injection, a
fibre-optic probe (Ø = 200 nm) was implanted directly above the
injection site (bregma AP -1.8 mm, ML ±3.2 mm, DV -4.9 mm). Stable
adhesion of the fibre-optic probe onto the cranium was achieved as
described previously . Mice were distributed equally in terms of whether
the left or right hemisphere was studied.
Fibre photometry for optical recording of neural activity in freely
moving mice was performed largely as described previously . Briefly, a
laser as excitation light source, a high-sensitivity photoreceiver
(model 2151, New Focus), and customized software for signal processing,
were used. To provide excitation, a 488 nm laser light was focused into
a fibre patch cord and delivered at the optic fibre tip in the BA. The
patch cord was connected via a ceramic sheath to the optic fibre ferrule
on the mouse cranium. Back-propagated GCaMP6 or EGFP fluorescence was
focused on a photoreceiver, and custom-written software code was used
for data acquisition (LABView, 2020). Testing was conducted in an
attenuation chamber equipped with a loudspeaker emitting low-level white
noise. A camera (model C920, Logitech) was fixed to the underside of the
ceiling of the attenuation chamber and allowed for video recording of
the tests on the control PC running LabView. An opening in the ceiling
of the attenuation chamber allowed for the passage of the patch cord. A
modified cage lid was prepared out of transparent Plexiglas and
contained an opening along its length to allow for passage of the patch
cord and free movement of the mouse in the test cage during testing.
Before the testing of each mouse, the cage lid and the divider used to
divide the cage into two compartments were cleaned with 70% ethanol.