A variety of data indicate that electrical activity in primary afferent neurons of the dorsal root ganglia (DRG) influences gene transcription. A likely signal cascade linking electrical activity to biochemical responses starts with a change in intracellular Ca2+ ([Ca2+]i). Further, it is clear that the frequency, kinetics, and subcellular location of oscillations in [Ca2+]i can determine the function of this cascade. However, little is known about the control of [Ca2+]i in DRG neurons at physiological temperature or about the identity of the biochemical effectors and how they work. In order to understand activity-dependent control of gene expression, we are proposing experiments that will investigate physiological changes in [Ca2+]i in response to action potential stimulation, the mechanisms that control them, and the response of Ca2+/calmodulin-dependent protein kinase II (CaMKII) to Ca2+ influx. We will investigate three hypotheses. (1) Immobile Ca2+ buffering, active at physiological temperature, restricts the increase in [Ca2+]i caused by Ca2+ influx via voltage-gated Ca2+ channels to the volume near the plasma membrane. (2) At physiological temperature, CICR does not amplify Ca2+ influx and raise bulk [Ca2+]i. (3) Physiological Ca2+ transients are encoded by CaMKII. If the first two hypotheses are correct, then Ca2+ entering via voltage-gated Ca2+ channels is unlikely to raise free Ca2+ in the nucleus. In this case, Ca2+ must interact with a Ca2+-binding protein near the plasma membrane and this complex must influence gene transcription. We will use experiments combining electrophysiological measurements (action potentials and voltage-clamp measurement of Ca2+ currents) with fluorescence measurements of [Ca2+]i. These experiments will investigate Ca2+ influx and Ca2+ buffering at physiological temperature. We will use activity assays to study the increase in autonomous activity of CaMKII in response to resting and activity-dependent Ca2+ influx.