Unitary inhibition recorded from two synaptically-connected CR
cells
CR interneurons during the late stages of AD were readily identifiable
under ID-DIC during experiments, (in striking contrast to CCK or SST
cells that were not easily visualised), allowing us to perform paired
recording between two CR cells. We performed paired recording in theAppNL-F/NL-F animals only due to the very
technically challenging nature of these experiments, hampered by the age
of the mice. However, supplementary Figure 1(E-F) shows examples of
paired recordings performed in young healthy control rodents.
Consistent with the finding that the sIPSPs recorded in CR cells were
sensitive to α5-SOP002, unitary IPSPs recorded between two CR cells in
SR were also reduced in peak amplitude and width at half amplitude
following bath-application of α5-SOP002 at -55mV (Figure 4E). The
decrease in amplitude and width was: 51.20 ± 7.36 %
(P <0.05, n =3, paired, two-tailed Student’s
t-test) and 28.25 ± 1.02 % (P <0.01, n =3,
paired, two-tailed Student’s t-test) of control IPSPs recorded inAppNL-F/NL-F , respectively. Bath-application of
the α1 subunit-selective agonist, zolpidem did not change the IPSP
properties at these synapses, which was consistent with previous studies
that reported insensitivity to zolpidem at synapses involving
presynaptic dendrite-preferring cells (Ali et al., 2008). Subsequent
addition of the broad spectrum benzodiazepine site agonist, diazepam
(after α5-SOP002) enhanced IPSP amplitude by 186.59 ± 41.45 %
(P <0.05, n =3, one-way ANOVA) and width at half
amplitude by, 37.31 ± 6.71 % (P >0.05, n =3,
one-way ANOVA with post-hoc Bonferroni’s test) of control IPSPs recorded
in AppNL-F/NL-F mice (Figure. 4 (E-F)).
The recorded (putative) CR –expressing interneurons, recovered post-hoc
were usually oval with 2-3 vertically orientated primary beaded
dendrites, usually from opposite poles, with fine axons containing
small/medium sized boutons originated from the soma or a primary
dendrite and ramified quite sparsely in mid-SR, as described previously
(Shi et al., 2019) These cells resembled previously published CR cells
(Gulyas et al., 1996).