Fluoxetine induces the transcription of genes encoding c-fos, corticotropin-releasing factor and its type 1 receptor in rat brain.
Fluoxetine is a serotonin re-uptake blocker commonly used to treat endogenous depression. The present experiments were carried out to assess the effects of fluoxetine on c-fos induction throughout the rat brain. In addition, intron-directed in situ hybridization analysis was used to examine fluoxetine regulation of corticotropin-releasing factor heteronuclear gene transcription in the paraventricular nucleus of the hypothalamus. Because the actions of corticotropin-releasing factor are mediated by membrane-bound corticotropin-releasing factor type 1 receptors, we also evaluated the stimulation of such receptors after acute fluoxetine exposure. The immediate-early gene, c-fos, was markedly induced in several telencephalic and diencephalic brain structures. For instance, a strong hybridized signal was apparent 30 min after fluoxetine (10 mg/kg; intraperitoneal) administration in the caudate putamen, septal nucleus, bed nucleus of stria terminalis, anterodorsal preoptic area, paraventricular nucleus, supraoptic nucleus, ventromedial hypothalamus and posterior hypothalamic nucleus. In addition, c-fos-expressing neurons were also evident in discrete amygdaloid nuclei. This nuclear induction was brief in duration, as levels of the immediate-early gene were mostly undetectable 90 min after drug administration. In contrast to the extensive induction of c-fos by fluoxetine throughout the brain parenchyma, elevation of corticotropin-releasing factor heteronuclear RNA levels were confined exclusively to neurosecretory nerve cells of the paraventricular nucleus, with peak levels detected 30 min after fluoxetine exposure. Therefore, the time-course of corticotropin-releasing factor heteronuclear RNA closely paralleled that of c-fos. Significant changes in corticotropin-releasing factor type 1 receptor messenger RNA levels were also observed in the paraventricular nucleus but with a slow incremental biosynthesis of the receptor messenger RNA, as high levels were discernible only 360 min after fluoxetine treatment. Finally, we failed to detect sex-related differences in the acute response to fluoxetine, as both female and male rat brains showed a comparable induction of c-fos, corticotropin-releasing factor heteronuclear RNA and corticotropin-releasing factor type 1 receptor expression within parvocellular neurosecretory nerve cells that govern the stress response. All of these findings are discussed in terms of specific sequences of nuclear events that couple fluoxetine-based serotonin input with changes in gene expression in selective neurons.
Torres
G
G
Department of Psychology, State University of New York at Buffalo, 14260, USA.
Horowitz
J M
JM
Laflamme
N
N
Rivest
S
S
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects*; D003346:Corticotropin-Releasing Hormone / Q000096:biosynthesis* / Q000235:genetics; D005260:Female; D005473:Fluoxetine / Q000494:pharmacology*; D016762:Genes, fos / Q000235:genetics*; D007031:Hypothalamus / Q000378:metabolism; D017403:In Situ Hybridization; D008297:Male; D015347:RNA Probes; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D018019:Receptors, Corticotropin-Releasing Hormone / Q000096:biosynthesis* / Q000235:genetics; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*; D012727:Sex Characteristics; D014158:Transcription, Genetic / Q000187:drug effects*
D003346:Corticotropin-Releasing Hormone; D005473:Fluoxetine; D015347:RNA Probes; D012333:RNA, Messenger; D018019:Receptors, Corticotropin-Releasing Hormone; D017367:Selective Serotonin Reuptake Inhibitors