Differential expression of 5HT‐1A, α_1b adrenergic, CRF‐R1, and CRF‐R2 receptor mRNA in serotonergic, γ‐aminobutyric acidergic, and catecholaminergic cells of the rat dorsal raphe nucleus

Abstract

The dorsal raphe nucleus (DR) has a topographic neuroanatomy consistent with the idea that different parts of this nucleus subserve different functions. Here we use dual in situ hybridization to describe the rostral-caudal neurochemical distribution of three major cell groups, serotonin (5-hydroxytryptamine; 5-HT), γ-aminobutyric acid (GABA), and catecholamine, and their relative colocalization with each other and mRNA encoding four different receptor subtypes that have been described to influence DR responses, namely, 5HT-1A, α 1b adrenergic (α 1b ADR), and corticotropinreleasing factor type 1 (CRF-R1) and 2 (CRF-R2) receptors. Serotonergic and GABAergic neurons were distributed throughout the rostral-caudal extent of the DR, whereas catecholaminergic neurons were generally restricted to the rostral half of the nucleus. These phenotypes essentially represent distinct cell populations, because the neurochemical markers were rarely colocalized. Both 5HT-1A and α 1b ADR mRNA were highly expressed throughout the DR, and the vast majority of serotonergic neurons expressed both receptors. A smaller percentage of GABAergic neurons also expressed 5HT-1A or α 1b ADR mRNA. Very few catecholaminergic cells expressed either 5HT-1A or α 1b ADR mRNA. CRF-R1 mRNA was detected only at very low levels within the DR, and quantitative colocalization studies were not technically feasible. CRF-R2 mRNA was mainly expressed at the middle and caudal levels of the DR. At midlevels, CRF-R2 mRNA was expressed exclusively in serotonin neurons, whereas, at caudal levels, approximately half the CRF-R2 mRNA was expressed in GABAergic neurons. The differential distribution of distinct neurochemical phenotypes lends support to the idea of functional differentiation of the DR. Indexing termsGABA; tyrosine hydroxylase; serotonin; corticotropin; dual in situ hybridizationThe dorsal raphe nucleus (DR) contains the highest concentration of serotonin neurons in the brain and has extensive ascending projections that innervate most forebrain structures (Steinbusch, 1981). These projection neurons have been shown to regulate a wide variety of physiological responses and behaviors, including sleep-wake states, feeding, nociception, *Correspondence to: Heidi E.W. Day, Department of Psychology and Center for Neuroscience, University of Colorado, Muenzinger Building, Rm. D244, Boulder, CO 80309-0345. E-mail: heididay@psych.colorado.edu. (Jacobs and Azmitia, 1992). In addition, increasing evidence has implicated serotonin in affective conditions, such as depression and anxiety (Kahn et al., 1988;Graeff et al., 1996). NIH Public AccessHowever, the DR is not a homogeneous structure, and serotonin neurons have been classified into subpopulations according to their electrophysiological properties in behaving animals. For example, the activity of type I neurons that make up the majority of serotonergic neurons is correlated with the degree of behavioral arousal and motor activity (Jacobs and Fornal, 1999). In contrast, the firing rate of the small group...

Differential Role of Galanin Receptors in the Regulation of Depression-Like Behavior and Monoamine/Stress-Related Genes at the Cell Body Level

“…Measurements were performed on four sections for the LC (left and right independently), and on 4-6 sections for the DR and MR, and the mean value was calculated for each animal. Since there exist significant anterior-posterior differences in the expression of various genes in the DR (Day et al, 2004), the analysis was performed on sections taken at identical levels of mid-rostral DR, the area projecting to the forebrain (Ungerstedt, 1971;Azmitia and Segal, 1978;Steinbusch, 1981). The DR nucleus was subdivided into lateral (lDR), dorsal (dDR), and ventral (vDR) subnuclei, which were each assessed individually.…”

Restraint stress increases serotonin release in the central nucleus of the amygdala via activation of corticotropin-releasing factor receptors

“…Five vehicletreated rats from experiment 2 had probe placements within the medial amygdala (MeA) adjacent to the CeA. The MeA has also been implicated in restraint-induced activation of the hypothalamus [14]. Therefore, the regional specificity of restraint stress on amygdala 5-HT was assessed by determining the effects of restraint on MeA 5-HT levels, using a one-way ANOVA with one repeated measure followed by Dunnett's posthoc test, as described for experiment 1.…”

“…Corticotropin-releasing factor, acting as a neurotransmitter, is involved in initiating stress responses, partially by modulating serotonergic systems arising from the dRN [3,27]. The CeA is one of the major sources of CRF innervation to the dRN [24], and CRF type 1 and type 2 (CRF 1/2 ) receptors are present in the dRN [14,42]. The release of CRF from the CeA has been detected during stress [30] and CRF administered to the dRN concurrently increases freezing behavior and 5-HT release within the CeA [23].…”

Chronic low dose ovine corticotropin releasing factor or urocortin II into the rostral dorsal raphe alters exploratory behavior and serotonergic gene expression in specific subregions of the dorsal raphe

“…These peptides may respond differently under acute and chronic stress exposure than the serotonergic component. The internal anatomical complexity of the DRN has been more clearly appreciated recently (Rattray et al, 1999, Commons et al, 2003, Abrams et al, 2004, Abrams et al, 2005, Greenwood et al, 2005, Clark et al, 2006, and discrete changes in serotonergic gene expression in subregions of raphe could be sufficient to induce substantial behavioral changes.Of particular note, CRF receptor distribution in DRN is complex and varies by region (Day et al, 2004, Pernar et al, 2004. Recent reports have emphasized the discrete subregional nature of DRN response to both direct and indirect (via the basolateral amygala) exposure to CRF receptor ligands (Forster et al, 2006, Spiga et al, 2006.…”