Dexamethasone and forskolin synergistically increase [Met5]enkephalin accumulation in mixed brain cell cultures.
Possible synergistic effects of the glucocorticoid dexamethasone (DEX, 10(-7) M) and the adenylate cyclase agonist forskolin (FSK, 10(-5) M) on [Met5]enkephalin (ME) accumulation were examined in enriched rat glial cultures and in mixed neuronal/glial cultures. In enriched glial cultures, DEX and FSK each stimulated the accumulation of ME 2-3-fold over basal media levels, but there was little additional stimulation when these agonists were combined. In contrast, mixed neuronal/glial cultures showed only weak responses to DEX or FSK alone, but the combination of these agonists produced a pronounced synergistic effect on media ME accumulation (6-10-fold over basal levels). The DEX effect was mediated via a classical glucocorticoid receptor, since DEX was potent (acting over a concentration range of 10(-11)-10(-7) M), mimicked by corticosterone (10(-6) M), and blocked by the glucocorticoid receptor antagonist RU486. There was a pronounced time lag (2 days) for the synergistic effects of DEX + FSK to develop. In situ hybridization and immunocytochemical studies suggested that astrocytes were the major source for the increased ME production in all mixed neuronal/glial cultures examined. Creating a mixed culture by plating fetal neurons onto confluent, enriched P7 glial cultures inhibited accumulation of ME in the media. DEX + FSK, but neither agonist alone, overcame this neuronal inhibition and increased accumulation of media ME to levels identical to levels in stimulated enriched glial cultures. The net effect was a 6-fold increase in ME accumulation in the mixed neuronal/glial cultures relative to a 2.5-fold increase in the enriched glial cultures. Neuronal inhibition of basal glial ME production could explain the similar synergistic effects of DEX + FSK observed in all mixed neuronal/glial cultures examined, and may be important in suppressing ME production by astrocytes in the brain.
McMillian
M K
MK
Laboratory of Molecular and Integrative Neuroscience, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
Pennypacker
K R
KR
Thai
L
L
Wu
G C
GC
Suh
H H
HH
Simmons
K L
KL
Hudson
P M
PM
Sawin
S B
SB
Hong
J S
JS
D000818:Animals; D001253:Astrocytes / Q000378:metabolism; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology*; D003907:Dexamethasone / Q000494:pharmacology*; D004338:Drug Combinations; D004357:Drug Synergism; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004745:Enkephalins / Q000235:genetics; D005938:Glucocorticoids / Q000494:pharmacology*; D009457:Neuroglia / Q000378:metabolism; D009474:Neurons / Q000378:metabolism* / Q000502:physiology; D011498:Protein Precursors / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats / Q000196:embryology; D011916:Rats, Inbred F344; D011965:Receptors, Glucocorticoid / Q000502:physiology
D004338:Drug Combinations; D004745:Enkephalins; D005938:Glucocorticoids; D011498:Protein Precursors; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; C029992:proenkephalin; D005576:Colforsin; D004744:Enkephalin, Methionine; C027511:enkephalin-Met, Arg(6)-Phe(7)-; D003907:Dexamethasone