AIMS. To describe the state of the art with regard to the physiology of kainate-like glutamate receptors as modulators in glutamatergic excitatory synaptic transmission in the hippocampus. DEVELOPMENT. Kainate receptors modulate the release of glutamate in the hippocampus in the different synapses that have been studied to date. Their activation can produce a decrease or an increase in glutamate release according to the synapse under study and both types of modulation (increase or decrease) can take place even within the same synaptic connection, depending on the agonist concentration reached by the receptors. Thus, in the synapses that are established among the mossy fibres and the pyramidal neurones in region CA3, high concentrations (> 100 nM) of kainate trigger a drop in glutamate release, whereas low concentrations (< 50 nM) give rise to an increased release of the same neurotransmitter. These actions carried out by the kainate receptors are presynaptic and both ionotropic and metabotropic mechanisms have been proposed to explain them.

CONCLUSIONS Kainate receptors act in the hippocampus as modulators of glutamate release, by either increasing or decreasing it. They therefore help to keep the balance of neuronal excitability, also play a part in neuronal plasticity processes (LTP and LTD) and can trigger, under abnormal conditions, a notable imbalance of this excitability and give rise to epileptic-type firing patterns, among other disorders.