Chronic antidepressant exposure enhances 5-hydroxytryptamine7 receptor-mediated cyclic adenosine monophosphate accumulation in rat frontocortical astrocytes.
In rat frontal cortical astrocytes, 5-hydroxytryptamine (5-HT), 5-carboxamidotryptamine and 5-methoxytryptamine elicited a concentration-dependent increase of cyclic AMP accumulation, with EC50 values of 137 +/- 7 nM (5-HT), 10.4 +/- 3.9 nM (5-carboxamidotryptamine) and 57.8 +/- 13.6 nM (5-methoxytryptamine). Accumulation of cyclic AMP stimulated by 5-HT (10 microM) was inhibited by methiothepin (IC50 = 21 +/- 13 nM) but not by pindolol, SCH 23390, ICS 205-930 or GR 113808. These pharmacological effects on cyclic AMP formation in astrocytes are consistent with those observed in 5-HT7 receptor binding studies. Indeed, reverse transcription-polymerase chain reaction analysis revealed the presence of 5-HT7 mRNA in astrocytes. Chronic exposure of astrocytes to mianserin (0.05-4 microM) or amitriptyline (1-8 microM) for 3 days produced a concentration-dependent enhancement of 5-HT-stimulated cyclic AMP accumulation, with EC50 values of 0.47 +/- 0.04 microM (mianserin) and 2.5 +/- 0.3 microM (amitriptyline). The enhancement of cyclic AMP accumulation was time dependent, reaching maximal levels within 2 days. Mianserin exposure (2 microM, for 3 days) resulted in a comparable enhancement of cyclic AMP accumulation mediated by 5-carboxamidotryptamine and 5-methoxytryptamine, whereas this treatment had no effect on cyclic AMP production induced by G protein-specific stimulators and catalytic subunit-selective stimulators. The mianserin-induced enhancement of 5-HT-stimulated cyclic AMP accumulation was decreased by methiothepin (IC50 = 15 +/- 8 nM) and significantly attenuated by pretreatment with 5-HT7 receptor antisense oligonucleotides, suggesting that chronic mianserin exposure produces an increase in 5-HT7 receptor activity. Chronic exposure to maprotiline, setiptiline or clomipramine (5 microM, for 3 days) mimicked the effect of mianserin. The enhancement of 5-HT7 receptor activity after chronic antidepressant exposure may be a mechanism underlying the therapeutic effects.
Shimizu
M
M
Department of Psychiatry and Neuroscience, Kure National Hospital, Japan.
Nishida
A
A
Zensho
H
H
Yamawaki
S
S
D000262:Adenylyl Cyclases / Q000378:metabolism; D000639:Amitriptyline / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D000928:Antidepressive Agents / Q000008:administration & dosage / Q000494:pharmacology*; D001253:Astrocytes / Q000201:enzymology / Q000378:metabolism*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D005625:Frontal Lobe / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D008719:Methiothepin / Q000494:pharmacology; D008803:Mianserin / Q000008:administration & dosage / Q000494:pharmacology; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000235:genetics / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D015398:Signal Transduction
D000928:Antidepressive Agents; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D000639:Amitriptyline; D003609:Dactinomycin; D008803:Mianserin; D008719:Methiothepin; D003513:Cycloheximide; D000242:Cyclic AMP; D000262:Adenylyl Cyclases