In the mature brain calcium ions play pivotal roles in transmembrane and intracellular transmission of signals. Thus, calcium is involved in numerous neuronal functions including neurotransmitter release, enzyme regulation, modulation of neuronal excitability, gene expression, microtubular transport or synaptic plasticity. Many of these calcium-dependent processes are mediated or modulated by a number of cytosolic calcium-binding proteins. All nerve cells contain the calcium-binding protein calmodulin. Other CaBPs are restricted to certain nerve celltypes, i.e. parvalbumin, calbindin and calretinin.