Direct hypertonic stimulation of the rat supraoptic nucleus increases c-fos expressionin glial cells rather than magnocellular neurones.
We investigated whether hypertonicity acts directly on supraoptic neurones to activate c-fos expression. Hypertonic artificial cerebrospinal fluid was infused into the supraoptic nucleus (SON) via a microdialysis probe implanted 24 h previously. The rats were decapitated after 90 min for immunohistochemistry with a Fos protein antibody. Direct hypertonic stimulation increased Fos protein expression in glial cells, identified by glial fibrillary acidic protein immunoreactivity, but not in magnocellular neurones. Similarly, with in situ hybridisation c-fos mRNA expression was predominantly seen in glial cells. Fos expression in SON neurones was stimulated by systemic hypertonicity even with a microdialysis probe in the SON, and magnocellular neurones expressed Fos after direct microinjection of cholecystokinin-8S into the SON. Thus, while direct hypertonic stimulation of SON neurones activates secretion of vasopressin and oxytocin, the c-fos gene is not activated, unlike following systemic hypertonic stimulation. This indicates that excitation of neuronal electrical and secretory activity does not necessarily lead to activation of the c-fos gene. Activation of c-fos expression in glial cells by direct hypertonic stimulation may reflect their role in regulating brain extracellular fluid composition.
Ludwig
M
M
Department of Physiology, University Medical School, Teviot Place, Edinburgh EH8 9AG, UK. mludwig@srv2.med.ed.ac.uk
Johnstone
L E
LE
Neumann
I
I
Landgraf
R
R
Russell
J A
JA
D000818:Animals; D002766:Cholecystokinin / Q000494:pharmacology; D005260:Female; D015870:Gene Expression; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D007124:Immunoenzyme Techniques; D017403:In Situ Hybridization; D009457:Neuroglia / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D012462:Saline Solution, Hypertonic; D013495:Supraoptic Nucleus / Q000187:drug effects / Q000378:metabolism*
D005904:Glial Fibrillary Acidic Protein; D016760:Proto-Oncogene Proteins c-fos; D012462:Saline Solution, Hypertonic; D002766:Cholecystokinin