SLOW OSCILLATIONS (LESS-THAN-OR-EQUAL-TO-1 HZ) MEDIATED BY GABAERGIC INTERNEURONAL NETWORKS IN RAT HIPPOCAMPUS

Perfusion of rat brain slices with low millimole CsCl elicits slow osc illations of less than or equal to 1 Hz in hippocampal CAI pyramidal n eurons. These oscillations are GABA(A) receptor-mediated hyperpolariza tions that permit a coherent fire-pause pattern in a population of CA1 neurons. They can persist without the activation of ionotropic glutam ate receptors but require adenosine-dependent inhibition of glutamate transmission. In response to external Cs+, multiple interneurons in th e CA1 region display rhythmic discharges that correlate with the slow oscillations in CA1 pyramidal neurons. The interneuronal discharges ar ise spontaneously from the resting potential, and their rhythmicity is regulated by periodic, GABA(A) receptor-mediated hyperpolarizations. In addition, interneurons show periodic partial spikes and neurobiotin coupling, and applications of known gap junctional uncouplers interru pt the Cs+-induced slow rhythm in both CA1 pyramidal neurons and inter neurons. We propose that these slow oscillations originate from a GABA ergic interneuronal network that interacts through reciprocal inhibiti on and possibly gap junctional connection.