Noxious stimuli produce prolonged changes in the CA1 region of the rat hippocampus

Limbic structures including the hippocampus are thought to be involved in pain though not much is known of their neuronal responses to noxious stimuli. In this report we show that a prolonged and substantial depression of the dorsal hippocampal CA1 pyramidal cell population spike is produced by a brief but intense noxious stimulus applied to the tail of lightly anaesthetized rats. This depression is temperature-dependent and habituates to subsequent noxious stimuli applied more than 1 h later. Further, the depression is absent when noxious heat is applied in the presence of hippocampal theta rhythm.