Social defeat, a paradigm of depression in rats that elicits 22-kHz vocalizations, preferentially activates the cholinergic signaling pathway in the periaqueductal gray

Abstract

Gene expression profiles in the periaqueductal gray (PAG) of adult Long-Evans rats as a function of a stressful social defeat in inter-male fighting encounters were examined. This social subordination model mimics prototypical behavioral changes that parallel aspects of clinical depression, has been postulated to simulate early changes in the onset of depression in the losers, and has been successfully utilized for the evaluation of antidepressant activity. 22-kHz ultrasonic vocalizations (USVs) have been shown to reflect negative emotional states akin to anxiety and depression. Social defeat is the most robust and reliable method of eliciting these calls. The PAG has been shown to be a key brain region for the generation of 22-kHz ultrasonic vocalizations, and 22-kHz USVs have been shown to be controlled by the mesolimbic cholinergic system. In this present study we examined gene expression changes in the PAG of social subordinate rats compared to dominant rats (that do not exhibit 22-kHz USVs). We found that social defeat significantly altered the genes associated with cholinergic synaptic transmission in the PAG. The most robust of these were the increased expression of the β2 subunit of the nicotinic acetylcholine receptor (CHRNB2) and the T-subunit of acetylcholinesterase (ACHE) in the subordinate animals. These changes were corroborated by qRT-PCR and found to be exclusive to the PAG compared to seven other brain regions examined. These data suggest that cholinergic transmission in the PAG is involved in the generation of 22-kHz USVs and provide potential therapeutic targets for the treatment of affective disorders.

Regional Changes in Gene Expression after Limbic Kindling

“…Individual 45-mer oligonucleotides complementary to sequences of 1178 cloned rat CNS genes (listed in Supplementary Table 1) were spotted in triplicate onto slides. For a full description of the microarray, please see Kroes et al (2006Kroes et al ( , 2007. Microarray and data analysis were conducted as previously described in Kroes et al (2006Kroes et al ( ), (2007.…”

“…For a full description of the microarray, please see Kroes et al (2006Kroes et al ( , 2007. Microarray and data analysis were conducted as previously described in Kroes et al (2006Kroes et al ( ), (2007. Microarray analyses were performed on tissues from individual animals in triplicate.…”

“…Data were LOW-ESS normalized and extensively quality controlled and quantified by BlueFuse (BlueGnome, USA). The data were then analyzed by the Significance Analysis of Microarray (SAM) algorithm (v1.13, Stanford University), using a stringent False Discovery Rate (FDR) of\1%, followed by ontological data mining using GoMiner (Zeeberg et al 2003) to identify enriched pathways, exactly as described in Kroes et al (2006), Kroes et al (2007). Briefly, the SAM analyses utilize an algorithm based on the Student's t-test to derive statistically significantly differentially expressed genes between two groups of samples using a permutationbased determination of the median false discovery rate (FDR).…”

“…To augment the microarray results, qRT-PCR was conducted as previously described (Kroes et al 2006(Kroes et al , 2007. Total mRNA was isolated from the hippocampus and amygdala separately for individual rats (RNeasy, Qiagen, USA), and converted to cDNA (SuperScript Ò III, Invitrogen, USA).…”

Toward the Rapid Treatment of Depression by Selective Inhibition of Central Stress Circuits

“…The autonomic and hormonal stress responses are well known and have recently been reviewed [5,6]. The instinctive behavioral responses include fear [7], freezing [8], agitation and flight [9], aggression [10] and behavioral passivity [11,12]. There is recent speculation that these areas may also trigger the aversive emotional responses of depression in humans including black mood, pessimism, despair, guilt, worthlessness and demoralization, although the evidence for this is still largely indirect [12][13][14].…”