Hyponatremia inhibits sprouting of oxytocinergic axons following bilateral lesions of the paraventricular nucleus in rats.
The external zone of the median eminence in rats contains very few oxytocinergic (OT) fibers. However, 6 weeks after lesioning the paraventricular nucleus (PVN) many OT axons can be found in the external zone, possibly as part of a mechanism compensating for the loss of secretion originating from the PVN. In this study, we investigated whether such structural reorganization of the median eminence occurs in chronically hyponatremic rats, which are known to have significantly inhibited OT and vasopressin (AVP) neurosecretory responses to most physiological stimuli. Normonatremic and chronically hyponatremic rats received bilateral PVN lesions using a rotating knife. One week after PVN lesions both vasopressin-neurophysin (AVP-NP) and oxytocin-neurophysin (OT-NP) staining intensities decreased in the internal zone of the median eminence, and AVP-NP immunoreactivity almost entirely disappeared from the external zone. Six weeks after PVN lesions OT-NP but not AVP-NP immunostaining appeared in the external zone of the median eminence in the normonatremic rats. In contrast, no increase in OT-NP staining occurred in the external zone of the median eminence in the hyponatremic rats by six weeks after PVN lesions. These results indicate that chronic hyponatremia inhibits not only synthesis and secretion of AVP and OT, but also impairs cellular processes involved in the sprouting response normally seen following bilateral PVN lesions in rats.
Dohanics
J
J
Department of Medicine, University of Pittsburgh, PA 15261.
Hoffman
G E
GE
Verbalis
J G
JG
D000818:Animals; D001127:Arginine Vasopressin / Q000008:administration & dosage / Q000494:pharmacology; D001369:Axons / Q000502:physiology*; D002908:Chronic Disease; D004343:Drug Implants; D007010:Hyponatremia / Q000139:chemically induced / Q000503:physiopathology*; D007150:Immunohistochemistry; D008297:Male; D008473:Median Eminence / Q000166:cytology / Q000378:metabolism; D009416:Nerve Regeneration / Q000502:physiology; D010121:Oxytocin / Q000502:physiology*; D010286:Paraventricular Hypothalamic Nucleus / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
D004343:Drug Implants; D001127:Arginine Vasopressin; D010121:Oxytocin