GABAB receptor dependent modulation of sharp wave-ripple complexes in the rat hippocampus in vitro

• GABAB agonist baclofen transiently suppresses sharp wave-ripple oscillations.
• Induction of sharp wave-ripple activity in presence of baclofen is possible.
• Baclofen affects presynaptic Ca2+ dependent transmitter release.
• GABAB antagonist CGP55846 does not increase incidence of SPW-R activity.
• Associative LTP permits delayed aggregation into neural assemblies.

Sharp wave-ripple complexes (SPW-R) are observed in vivo during resting immobility, consummatory behavior and during slow wave sleep, and they have been proposed to support memory consolidation. It has been suggested that GABAergic cells play important roles in controlling incidence of sharp waves and of ripple frequency. We report here that the GABAB agonist baclofen reversibly suppresses SPW-R activity in rat hippocampal slices, presumably affecting the strength of neuronal coupling in the associative network of area CA3. The effect is specific as the GABAB receptor antagonist CGP55846 prevents this effect; however, CGP55846 application had no major effect on incidence of SPW-R. Interestingly, repetitive stimulation in the presence of baclofen is able to induce SPW-R activity, which only appears after washout of baclofen. Our findings suggest that GABA levels through activation of GABAB receptors may be involved in the transition from theta-gamma to SPW-R working mode in the hippocampus.