Journal of Neuroscience, Vol 16, 2373-2380, Copyright © 1996 by Society for Neuroscience
Chronic hyponatremia reduces survival of magnocellular vasopressin and oxytocin neurons after axonal injury
J Dohanics, GE Hoffman and JG Verbalis
Department of Medicine, University of Pittsburgh, Pennsylvania 15261, USA.
Axonal injury to hypothalamic magnocellular vasopressin (AVP) and oxytocin
(OT) neurons causes degeneration of a substantial subpopulation of these
neurons. In this study, we investigated the influence of osmolality on this
injury-induced cell death. Normonatremic, chronically hypernatremic, and
chronically hyponatremic rats received pituitary stalk compression (SC),
which causes degeneration of AVP and OT terminals in the neurohypophysis.
Twenty-one days after SC, rats were perfused and hypothalami were serially
sectioned and alternately stained for AVP-neurophysin and OT- neurophysin
immunoreactivities. Normonatremic and hypernatremic rats exhibited a
triphasic pattern of water intake after SC, with peak intakes 3 times
higher than those exhibited by sham-operated normonatremic rats. In
contrast, hyponatremic SC rats exhibited peak water intakes of 600 ml/24
hr, approximately 9-10 times the water intakes of sham-operated
normonatremic rats. In normonatremic rats, SC caused degeneration of 65% of
the AVP neuron population in the SON and 73% in the PVN, but only 31% of
the OT neuron population in the SON and 35% in the PVN. Similar results
were found in hypernatremic rats after SC. However, in hyponatremic rats SC
caused degeneration of 97% of the AVP neuron population in the SON and 93%
in the PVN, and 90% of the OT neuron population in the SON and 84% in the
PVN. Our results, therefore, demonstrate that injury-induced degeneration
of magnocellular AVP and OT neurons is markedly exacerbated by chronic
hypo-osmolar conditions, but neuronal survival is not enhanced by chronic
hyperosmolar conditions.