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Interactions between central corticotropin-releasing factor (CRF) and serotonergic systems are believed to be important for mediating fear and anxiety behaviors. Recently we demonstrated that infusions of CRF into the rat dorsal raphe nucleus result in a delayed increase in serotonin release within the medial prefrontal cortex that coincided with a reduction in fear behavior. The current studies were designed to study the CRF receptor mechanisms and pathways involved in this serotonergic response. Infusions of CRF (0.5 microg/0.5 microL) were made into the dorsal raphe nucleus of urethane-anesthetized rats following either inactivation of the median raphe nucleus by muscimol (25 ng/0.25 microL) or antagonism of CRF receptor type 1 or CRF receptor type 2 in the dorsal raphe nucleus with antalarmin (25-50 ng/0.5 microL) or antisauvagine-30 (2 microg/0.5 microL), respectively. Medial prefrontal cortex serotonin levels were measured using in-vivo microdialysis and high-performance liquid chromatography with electrochemical detection. Increased medial prefrontal cortex serotonin release elicited by CRF infusion into the dorsal raphe nucleus was abolished by inactivation of the median raphe nucleus. Furthermore, antagonism of CRF receptor type 2 but not CRF receptor type 1 in the dorsal raphe nucleus abolished CRF-induced increases in medial prefrontal cortex serotonin. Follow-up studies involved electrical stimulation of the central nucleus of the amygdala, a source of CRF afferents to the dorsal raphe nucleus. Activation of the central nucleus increased medial prefrontal cortex serotonin release. This response was blocked by CRF receptor type 2 antagonism in the dorsal raphe. Overall, these results highlight complex CRF modulation of medial prefrontal cortex serotonergic activity at the level of the raphe nuclei.

Psychostimulant use increases anxious behavior, likely through interactions between central corticotropin-releasing factor (CRF) and serotonergic systems. The current study examined whether chronic amphetamine treatment (2.5 mg/kg, 14 days) or withdrawal altered CRF receptor densities in the serotonergic dorsal raphe nucleus (dRN). Amphetamine treatment increased CRF 2 receptor densities in most subregions of the dRN, and CRF 2 receptors were still elevated following 6 weeks of withdrawal. No changes in CRF 1 receptor densities were observed following amphetamine treatment or during withdrawal. Selective increases in dRN CRF 2 receptors may be related to increased anxiety-like behaviors following psychostimulant use. KeywordsSerotonin; Anxiety; Rat; CRF; Dorsal Raphe Nucleus; AmphetamineThe cycle of addiction is thought to be maintained by negative affective symptoms that are manifest upon cessation of drug taking (Koob, 2003). In rats, withdrawal from chronic psychostimulant administration increases anxiety-like and depressive behaviors (Sarnyai et al., 1995;Perrine et al., 2008). Corticotropin-releasing factor (CRF) plays an important role in mediating anxiety behavior (Bale, 2005; Shepard and Meyers, 2008). Activation of CRF receptors can increase serotonergic neuronal activity in the dorsal raphe nucleus (dRN) (Lowry et al., 2000;Pernar et al., 2004) and increases serotonin release in forebrain limbic regions important for anxiety-like behaviors (Amat et al., 2004;Forster et al., 2006;Lukkes et al., 2008). Stress-induced alterations of serotonin release within forebrain limbic regions are suppressed by central CRF receptor antagonism (Price et al., 2002; Mo et al., 2008). Furthermore, intracerebroventricular administration of CRF antiserum reduces anxiety-like behavior of cocaine-treated rats in withdrawal (Sarnyai et al., 1995). Given the relationship between CRF, serotonin activity and anxiety-like behaviors, psychostimulant-induced changes to CRF receptor levels in the dRN could represent an important pathological alteration related to negative affect following psychostimulant use. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript dose and injection schedule were based on preliminary studies showing behavioral sensitization and increased anxiety-like behavior following treatment at 2 weeks withdrawal (Forster et al., 2007). Twenty hours or 6 weeks following the last injection, rats were anesthetized with pentobarbital (100 mg/kg, ip.) and transcardially perfused with...