Enhancement of calcium-dependent afterpotentials in oxytocin neurons of the rat supraoptic nucleus during lactation

Ryoichi Teruyama, William Armstrong

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

The firing pattern of oxytocin (OT) hormone synthesizing neurons changes dramatically immediately before each milk ejection, when a brief burst of action potentials is discharged. OT neurons possess intrinsic currents that would modulate this burst. Our previous studies showed the amplitude of the Ca2+-dependent afterhyperpolarization (AHP) following spike trains is significantly larger during lactation. In the present study we sought to determine which component of the AHP is enhanced, and whether the enhancement could be related to changes in whole-cell Ca2+ current or the Ca2+ transient in identified OT or vasopressin (VP) neurons during lactation. We confirmed, with whole-cell current-clamp recordings, our previous finding from sharp electrodes that the size of the AHP following spike trains increased in OT, but not VP neurons during lactation. We then determined that an apamin-sensitive medium-duration AHP (mAHP) and an apamin-insensitive slow AHP (sAHP) were specifically increased in OT neurons. Simultaneous Ca2+ imaging revealed that the peak change in somatic [Ca2+]i was not altered in either cell type, but the slow decay of the Ca2+ transient was faster in both cell types during lactation. In voltage clamp, the whole-cell, Ca2+ current was slightly larger during lactation in OT cells only, but current density was unchanged when corrected for somatic hypertrophy. The currents, ImAHP and IsAHP, also were increased in OT neurons only, but only the apamin-sensitive ImAHP showed an increase in current density after adjusting for somatic hypertrophy. These findings suggest a specific modulation (e.g. increased number) of the small-conductance Ca2+-dependent K+ (SK) channels, or their interaction with Ca2+, underlies the increased mAHP/ImAHP during lactation. This larger mAHP may be necessary to limit the explosive bursts during milk ejection.

Original languageEnglish (US)
Pages (from-to)505-518
Number of pages14
JournalJournal of Physiology
Volume566
Issue number2
DOIs
StatePublished - Jul 15 2005

Fingerprint

Supraoptic Nucleus
Oxytocin
Lactation
Calcium
Neurons
Apamin
Milk Ejection
Vasopressins
Hypertrophy
Action Potentials
Electrodes
Hormones

All Science Journal Classification (ASJC) codes

  • Physiology

Cite this

Enhancement of calcium-dependent afterpotentials in oxytocin neurons of the rat supraoptic nucleus during lactation. / Teruyama, Ryoichi; Armstrong, William.

In: Journal of Physiology, Vol. 566, No. 2, 15.07.2005, p. 505-518.

Research output: Contribution to journalArticle

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