Plasticity of GABAB receptor-mediated heterosynaptic interactions at mossy fibers after status epilepticus

Several neurotransmitters, including GABA acting at presynaptic GABAB receptors, modulate glutamate release at synapses between hippocampal mossy fibers and CA3 pyramidal neurons. This phenomenon gates excitation of the hippocampus and may therefore prevent limbic seizure propagation. Here we report that status epilepticus, triggered by either perforant path stimulation or pilocarpine administration, was followed 24 hr later by a loss of GABAB receptor-mediated heterosynaptic depression among populations of mossy fibers. This was accompanied by a decrease in the sensitivity of mossy fiber transmission to the exogenous GABAB receptor agonist baclofen. Autoradiography revealed a reduction in GABAB receptor binding in the stratum lucidum after status epilepticus. Failure of GABAB receptor-mediated modulation of mossy fiber transmission at mossy fibers may contribute to the development of spontaneous seizures after status epilepticus.