title: Phosphatidylinositol 4,5-bisphosphate (PIP2) modulates afterhyperpolarizations in oxytocin neurons of the supraoptic nucleus.
abstract: Afterhyperpolarizations (AHPs) generated by repetitive action potentials in supraoptic magnocellular neurons regulate repetitive firing and spike frequency adaptation but relatively little is known about PIP2's control of these AHPs. We examined how changes in PIP2levels affected AHPs, somatic [Ca2+]i, and whole cell Ca2+currents. Manipulations of PIP2levels affected both medium and slow AHP currents in oxytocin (OT) neurons of the supraoptic nucleus. Manipulations of PIP2levels did not modulate AHPs by influencing Ca2+release from IP3-triggered Ca2+stores, suggesting more direct modulation of channels by PIP2. PIP2depletion reduced spike-evoked Ca2+entry and voltage-gated Ca2+currents. PIP2appears to influence AHPs in OT neurons by reducing Ca2+influx during spiking.
  
  
  
  Oxytocin (OT)- and vasopressin (VP)-secreting magnocellular neurons of the supraoptic nucleus (SON) display calcium-dependent afterhyperpolarizations (AHPs) following a train of action potentials that are critical to shaping the firing patterns of these cells. Previous work demonstrated that the lipid phosphatidylinositol 4,5-bisphosphate (PIP2) enabled the slow AHP component (sAHP) in cortical pyramidal neurons. We investigated whether this phenomenon occurred in OT and VP neurons of the SON. Using whole cell recordings in coronal hypothalamic slices from adult female rats, we demonstrated that inhibition of PIP2synthesis with wortmannin robustly blocked both the medium and slow AHP currents (ImAHPand IsAHP) of OT, but not VP neurons with high affinity. We further tested this by introducing a water-soluble PIP2analogue (diC8-PIP2) into neurons, which in OT neurons not only prevented wortmannin's inhibitory effect, but slowed rundown of the ImAHPand IsAHP. Inhibition of phospholipase C (PLC) with U73122 did not inhibit either ImAHPor IsAHPin OT neurons, consistent with wortmannin's effects not being due to reducing diacylglycerol (DAG) or IP3availability, i.e. PIP2modulation of AHPs is not likely to involve downstream Ca2+release from inositol 1,4,5-trisphosphate (IP3)-triggered Ca2+-store release, or channel modulation via DAG and protein kinase C (PKC). We found that wortmannin reduced [Ca2+]iincrease induced by spike trains in OT neurons, but had no effect on AHPs evoked by uncaging intracellular Ca2+. Finally, wortmannin selectively reduced whole cell Ca2+currents in OT neurons while leaving VP neurons unaffected. The results indicate that PIP2modulates both the ImAHPand IsAHPin OT neurons, most likely by controlling Ca2+entry through voltage-gated Ca2+channels opened during spike trains.
authors.affiliation: Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA.
authors.forename: Matthew K
authors.identifier: 0000-0001-6960-7685
authors.initials: MK
authors.lastname: Kirchner
authors.affiliation: Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Foehring
authors.affiliation: Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA.
authors.forename: Lie
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA.
authors.forename: Giri Kumar
authors.initials: GK
authors.lastname: Chandaka
authors.affiliation: Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA.
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Callaway
authors.affiliation: Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Armstrong
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010121:Oxytocin / Q000502:physiology; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000037:antagonists & inhibitors / Q000502:physiology*; D017207:Rats, Sprague-Dawley; D013495:Supraoptic Nucleus / Q000187:drug effects / Q000502:physiology*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D019269:Phosphatidylinositol 4,5-Diphosphate; D010121:Oxytocin; D000077191:Wortmannin
keywords: PIP2; after-hyperpolarization; after-hyperpolarization current; caged calcium; calcium; oxytocin