Fig 1.
CSD experimentally triggered in somatosensory cortex mouse brain slices by puff application of 130 mM KCl.
(A) Raw near infrared transmitted light image of a representative coronal brain slice in which a pipette for applying 130 mM KCl and two extracellular electrodes for LFP recordings were placed in the somatosensory cortex. The image shows the initiation of CSD induced by a puff of KCl; Scale bar 0.5 mm. The other panels (B–E) show the same slice after image processing (subtraction of the background, optimization of the contrast) to highlight the intrinsic optical signal (IOS) during CSD initiation (KCl puff application, (B) and propagation (C–E) at the indicated times; the white wave is the CSD that propagates in the cortex. Scale bar 0.5 mm. (F) Comparison of the propagation speed measured in slices from WT mice and from mice (without optogenetic illumination), showing that there is no difference. (G) LFP recorded during CSD propagation at the two locations indicated in (E) (LFP1 and LFP2), showing the typical CSD DC shift (note the delay of CDS initiation at LFP2 compared to LFP1).
Fig 2.
Effects of the modulation of GABAergic neurons activity and synaptic transmission on CSD propagation speed.
(A) Schematic representation of the effects of optogenetic illumination (BLUE LIGHT) on GABAergic neurons activity and synaptic transmission, and of the effects of isoguvacine (ISO) and gabazine (GBZ) on GABAergic synaptic transmission. Panel A was created in BioRender. Mantegazza, M. (2025) https://BioRender.com/90to28g. (B) CSD propagation speed in WT and VGAT-ChR2-tdtomato expressing slices (pooled) in control (CTRL, same data as in Fig 1); in WT slices perfused with isoguvacine (ISO) or gabazine (GBZ); and in VGAT-ChR2-tdtomato expressing slices exposed to blue light in control (LIGHT) or with gabazine (GBZ + LIGHT). The number of slices (n) is indicated below the x axis. One-way ANOVA (p<0.0001) with Tukey’s post hoc test; the bars indicate significant differences, all with p<0.0001.
Fig 3.
Effects of the optogenetic activation of GABAergic neurons on CSD propagation speed in the same slice.
A. Schematic representation of optogenetic illumination effects on GABAergic neurons activity and synaptic transmission. B. CSD propagation speed in VGAT-ChR2-tdtomato slices before and during illumination with blue light. C. Schematic representation of the combined effects induced by optogenetic illumination and gabazine on GABAergic neurons activity and synaptic transmission. Figs 3A and 3C were created in BioRender. Mantegazza, M. (2025) https://BioRender.com/90to28g. D. CSD propagation speed in VGAT-ChR2-tdtomato slices perfused with rACSF + gabazine before and during illumination with blue light. The number of slices (n) is indicated below the x-axis. Paired Student’s t-test: p<0.0001.
Fig 4.
Illustration of CSD propagation over the propagation axis Q of the neural field model.
The length of Q is 2Lx. CSD initiation occurs at the source point marked in red. Each turquoise dot represents a microcircuit of interconnected excitatory and inhibitory neurons (schematically depicted in the diagram inset in green and blue, respectively). Here cei and cee model the connection weights of excitatory synapses on inhibitory neurons and of excitatory synapses on excitatory neurons (self-coupling), respectively. Similarly, cie and cii model the connection weights of inhibitory synapses on excitatory neurons and of inhibitory synapses on inhibitory neurons, respectively. The effect of excitatory and inhibitory neurons activity on the extracellular potassium concentration is represented by the functions and
, respectively. The influence of the extracellular potassium on excitatory and inhibitory neurons is described by the functions
and
, respectively. Fig 4 was created in BioRender. Mantegazza, M. (2025) https://BioRender.com/hfkou4f.
Fig 5.
(A) Space-time diagrams of the propagation of excitatory and inhibitory population potentials, the expansion of potassium concentration in space and time. (B) CSD propagation over the propagation axis Q. Top: Propagation in terms of average membrane potentials of the excitatory populations. Red horizontal line indicates the threshold detecting the wavefront of the propagating depolarization block. Middle: Propagation in terms of average membrane potentials of the inhibitory populations. Bottom: Expansion of the increasing potassium concentration towards the patch boundaries as the depolarization block propagates.
Fig 6.
Simulation of the effect of the experimental conditions on CSD speed.
(A) Experimental results already displayed in Fig 2, showed here as fold change. (B) Effects of on CSD propagation speed. Increasing
from the value that gives control propagation speed (mimicking ISO) results in a saturation in the speed, which corresponds to the plateau in the plot (green arrow). Decreasing
(mimicking GBZ) results in an increase of the propagation speed (red arrow). The dashed blue line indicates the values of
that produce a speed equal to that observed with GBZ in the experiments (3.7 mm/min). Here
and
. C. Simulation of the modulatory effect of ChR2 activation with blue light on the propagation speed, resulting in an increase in the activity of the GABAergic population and, consequently, also of GABAergic synaptic transmission, which are modeled by increasing c2 and
, respectively, and that do not modify propagation speed. The black arrow indicates the value of c2 used in (B). Here
and
. D. Effects of c2 (extracellular
generated from the GABAergic neurons) on the propagation speed. Increasing c2 results in a moderate increase in the propagation speed. Here
and
. The black arrow indicates the value of c2 used in (B). (E) Simulation of concomitant blocking of
receptors with GBZ and activation of ChR2, modeled by decreasing
and increasing c2, respectively, in which the propagation speed shows a large increase (purple arrow). The dashed blue line indicates the value of the parameters that produce a speed equal to that observed with GBZ in the experiments (3.7 mm/min), the dashed orange line those that produce a speed equal to that observed with GBZ + blue light in the experiments (5 mm/min). The black arrow indicates the value of c2 used in (B). Here
and
.
Fig 7.
CSD was induced in somatosensory cortex slices by applying a puff of KCl 130 mM. CSD waves were visualized by near infrared intrinsic optical imaging (IOS) with a CCD camera. Two micropipettes, placed about 1 mm (LFP1) and 1.5mm (LFP2) away from the site of CSD induction, were used to record LFPs. Drugs to modulate GABAergic neurons’ synaptic activity were applied to the bath. The activity of GABAergic neurons, which expressed ChR2, was induced by optogenetic illumination with blue light (470 nm). The figure was created in BioRender. Mantegazza, M. (2025) https://BioRender.com/6zlclb8.
Fig 8.
(A) Transfer function of a population
with respect to the firing activity
and potassium concentration k. (B) Top view of the maximum and minimum values of the transfer function. The nonlinear regions are ignored.
Fig 9.
Potassium to rate transfer function with respect to the population firing rate
and potassium concentration k.
Regions of the maximum and minimum values are represented by the yellow and blue colors, respectively.
Fig 10.
Bifurcation diagram of one node of the model with respect to .
Blue and red dots show the maximum and minimum values of during the course of simulation. We see that as we decrease
to the values lower than 1.5, the system goes through a bifurcation (black dot) and switches to a regime with propagation waves. Here
,
,
and
.