Role for Calcium Signaling and Arachidonic Acid Metabolites in the Activity-Dependent Increase of AHP Amplitude in Leech T Sensory Neurons

• Published in: Journal of neurophysiology Vol. 94; no. 2; pp. 1066 - 1073
• Main Authors: Scuri, Rossana, Mozzachiodi, Riccardo, Brunelli, Marcello
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01-08-2005
• Subjects: Animals; Arachidonic Acids - metabolism; Calcium - metabolism; Calcium Channel Blockers - pharmacology; Cyclooxygenase Inhibitors - pharmacology; Electric Stimulation - methods; Ganglia, Invertebrate - cytology; Hirudinea; Hirudo medicinalis; Hirudo medicinalis - physiology; Membrane Potentials - drug effects; Membrane Potentials - physiology; Membrane Potentials - radiation effects; Neurons, Afferent - drug effects; Neurons, Afferent - metabolism; Nifedipine - pharmacology; Patch-Clamp Techniques - methods
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00075.2005

Department of Physiology and Biochemistry "G. Moruzzi," University of Pisa, Pisa, Italy
Submitted 21 January 2005;
accepted in final form 27 April 2005
Previous studies have revealed a new form of activity-dependent modulation of the afterhyperpolarization (AHP) in tactile (T) neurons of the leech Hirudo medicinalis . The firing of T cells is characterized by an AHP, which is mainly due to the activity of the Na + /K + ATPase. Low-frequency repetitive stimulation of T neurons leads to a robust increment of the AHP amplitude, which is correlated with a synaptic depression between T neuron and follower cells. In the present study, we explored the molecular cascades underlying the AHP increase. We tested the hypothesis that this activity-dependent phenomenon was triggered by calcium influx during neural activity by applying blockers of voltage-dependent Ca 2+ channels. We report that AHP increase requires calcium influx that, in turn, induces release of calcium from intracellular stores so sustaining the enhancement of AHP. An elevation of the intracellular calcium can activate the cytosolic isoforms of the phosholipase A2 (PLA2). Therefore we analyzed the role of PLA2 in the increase of the AHP, and we provide evidence that not only PLA2 but also the recruitment of arachidonic acid metabolites generated by the 5-lipoxygenase pathway are necessary for the induction of AHP increase. These data indicate that a sophisticated cascade of intracellular signals links the repetitive discharge of T neurons to the activation of molecular pathways, which finally may alter the activity of critical enzymes such as the Na + /K + ATPase, that sustains the generation of the AHP and its increase during repetitive stimulation. These results also suggest the potential importance of the poorly studied 5-lipoxygenase pathway in forms of neuronal plasticity.
Address for reprint requests and other correspondence: R. Scuri, Dept. of Physiology and Biochemistry "G. Moruzzi", University of Pisa, Via S. Zeno, 31, 56127 Pisa, Italy (E-mail rscuri{at}dfb.unipi.it )