Vasopressin and Oxytocin Neurons - Similar Neurosecretory Cells with Different Patterns of Activity and Hormone Release

Tuesday, February 16, 1999 - 2:00pm - 3:00pm
Keller 3-180
David Brown (The Babraham Institute)
Magnocellular vasopressin (VP) and oxytocin (OT) secreting neurons are co-located in the supraoptic and paraventricular nuclei of the hypothalamus. They have almost all biophysical properties in common, yet they fire and secrete hormone in very different ways.

BIOPHYSICS. They both exhibit action potentials as a result of influx of Na+ ions, followed by a repolarizing outward K+ conductance. There are low voltage, slowly inactivating Ca2+ channels, and also Ca2+ dependent potassium channels, the resulting depolarizing and hyperpolarizing afterpotentials accounting for some aspects of the firing patterns. One major biophysical difference is in intracellular calcium buffering: in most OT cells, intracellular calcium is effectively buffered involving Calbindin, but most VP cells do not exhibit this buffering.

FUNCTION. Both hormones are involved in maintenance of plasma osmotic pressure, VP by involvement in control of water retention, OT in sodium excretion. OT is additionally involved in events associated with reproduction: pulses of OT release are temporally correlated with milk ejections in the lactating female, and uterine contractions during parturition.

PATTERNS OF ACTIVITY AND HORMONE RELEASE. VP cells, when firing slowly (i.e. when mean firing rate (mfr)
Reference: Leng, G, Brown, D (1997) The origins and significance of pulsatility in hormone secretion from the pituitary, J. Neuroendocrinology, 9, 493-513. [review]