Figure 6.
Integrative Properties of Septo-Habenular Afferent Activity by MHb Neurons
(A and B) Optogenetic stimulation of septal afferents in VGluT2-Cre mice injected with a ChR2-expressing AAV activated a similar groups of fibers as extracellular stimulation. The traces on the left illustrate a typical MHb neuron in which ChR2 activation produced synaptic responses mediated by AMPA and NMDA (clearly visible at +50 mV, top) receptors. The graphs in (A) show that EPSC average amplitudes (left), AMPA rectification indexes (center), and average NMDA/AMPA amplitude ratios (right) were statistically indistinguishable following either optogenetic (Optog., left bar; individual cells depicted as gray points) or extracellular electrical stimulation (Extrac., light gray bars; data already shown in previous figures). In the LCA recording configuration, a 5-s-long blue light stimulation train at 20 Hz distinguished 3 groups of neurons. In the first group (n = 48; B), a dramatic increase in spike rate during the train was followed by strong inhibition in the seconds following the stimulation end (detailed at larger magnification in the inset). Augmentation and post-train inhibition were both blocked by co-application of NBQX and APV, and were replaced by a significant decrease of firing, which was completely eliminated by bath application of the mGluRII antagonist LY341495 (right graphs).
(C) A group of cells (n = 53) is shown, where activation produced dramatic inhibition of the firing rate, which was mGluRII-dependent (right graph).
(D) In several cells (n = 41), ChR2 activation triggered no detectable change in firing.
(B–D) The traces on the left show a typical recording, whereas the time courses of firing changes for all analyzed cells are depicted in the right graphs. Color codes for traces and temporal graphs are black for control, blue for NBQX and APV co-application, and green for LY341495 in the bath either following NBQX and APV (B) or alone (C). Blue lines represent the 5-s-long stimulation trains.
(E) EPSC amplitudes recorded in the whole-cell configuration for a subset of cells in which light trains produced either excitation (Exc.; left bar), only inhibition (Inh.; center bar), or no effect (No; right bar).
Pooled data are represented as mean ± SEM.