Enhanced excitatory signal propagation in mouse visual cortical slices
Cell-based study · Acute 300-µm visual cortical slices from P14–P28 C57BL/6J mice; layer-4 stimulation and OGB1-AM calcium imaging at 29–31°C. [1]
(+)-Bicuculline increased evoked calcium-signal amplitude and broadened spatial propagation. The largest fitted enhancement occurred in layer 2/3. Alternative GABA_A blockade gave a similar pattern, while glutamate-receptor blockade largely suppressed the response. These data support functional disinhibition of excitatory cortical circuitry; they do not directly measure receptor binding or establish absolute target selectivity.
| Endpoint | Reported result | Reference |
|---|---|---|
| Spatial propagation of layer-4-evoked calcium transients | qualitative imaging result At 5 µM, signal spread across the entire observation area; largest delayed transients appeared in layer 2/3. At 2 µM, amplitude increased slightly and decay slowed. | [1] |
| Bicuculline enhancement of normalized peak calcium fluorescence in six cortical regions | functional fitted EC50 a: 2.0 µM; b: 2.3 µM; c: 2.6 µM; d: 1.8 µM; e: 2.1 µM; f: 2.8 µM | [1] |
| Pharmacological controls for interpretation of signal propagation | qualitative control results With 10 µM bicuculline plus 10 µM CNQX and 50 µM AP5, calcium transients almost disappeared (n=3 slices). Picrotoxin 10 µM produced a similar propagation pattern to bicuculline 5 µM, with differences near horizontal edges (n=4 slices). | [1] |
Literature-Reported Treatment Conditions
- Treatment concentration
- Figure 5 compares control, 2 µM and 5 µM bicuculline, and 10 µM bicuculline with CNQX/AP5. Figure 6 presents the concentration-response series.
- Method
- Bath perfusion; evoked calcium imaging. The 80 µA stimulus designation is a command amplitude; the authors measured smaller, non-square actual currents.
- Co-treatment
- Control comparison: 10 µM bicuculline + 10 µM CNQX + 50 µM AP5; separate picrotoxin comparison at 10 µM.
- Reported limits
- Bicuculline stock solvent and drug-equilibration duration are not specified in the relevant Drugs/imaging methods. Number of animals contributing the n=4 slices is not specified for this experiment. DMSO used for indicator loading must not be assigned as bicuculline vehicle.
Methods and source locations
Compound reported in the paper: (+)-Bicuculline; Compound label in the paper: Bicuculline (Tocris; free base)
Evidence applies to the reported free-base compound in an ex vivo mouse cortical network assay, not to quaternary methyl salts, a universal receptor potency, or therapeutic efficacy.
Results, Blockade of inhibitory synaptic transmission; Figures 5–6; Figure S6; Materials and Methods, Slice preparation, Ca2+ imaging and stimulation, Data analysis, statistics, Drugs
Spatial propagation of layer-4-evoked calcium transients: OGB1-AM calcium imaging; layer 4 stimulation at 80 µA command amplitude; image sequences and peak ΔF/F maps; n=4 slices for bicuculline mean/SEM maps. — Results, Blockade of inhibitory synaptic transmission; Figure 5A–D and caption
Bicuculline enhancement of normalized peak calcium fluorescence in six cortical regions: Hill-equation fits to regional normalized ΔF/F; normalization to stimulus-position amplitude under control; n=4 slices, plotted error bars SEM. Region letters follow Figure 5A. Values are caption-reported fits, not digitized estimates or receptor IC50 values. — Figure 6a–f and caption; Figure 5A region key; Methods, Data analysis
Pharmacological controls for interpretation of signal propagation: Calcium imaging under perfused antagonists; CNQX/AP5 test dependence on excitatory synaptic transmission; picrotoxin provides an alternative GABA_A-blocker comparison. — Results, Blockade of inhibitory synaptic transmission; Figure 5D; Figure S6 and parent caption