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A2 noradrenergic neurons regulate forced swim test immobility

Nam H, Kerman I (2015) A2 noradrenergic neurons regulate forced swim test immobility. Neuroscience 2015 Abstracts 718.10/Y20. Society for Neuroscience, Chicago IL.

Summary: The Wistar-Kyoto rat (WKY) is a well-established animal model of depression- and anxiety-like behavior, characterized by high immobility during the forced swim test (FST) along with a generally inhibited phenotype on related tests of emotional behaviors. Extensive literature indicates that deficits in noradrenergic neurotransmission may contribute to these behavioral traits. Previously, we have reported that the WKY rats are more immobile compared to other rat strains from the beginning of their training phase of the FST, and that they become even more immobile during the testing phase on the next day. We hypothesized that higher immobility during the FST and the greater increase in immobility throughout different phases of the FST are two separate components of rats’ behavior likely mediated by different central mechanisms. We sought to identify the central circuits responsible for these behavioral components by studying activation of neurons within central noradrenergic cell groups during different phases of the FST. The WKY rats along with its parent strain, Wistar rats that experienced either the: 1) 5 minutes training phase (D1), or 2) entire FST (D1 and D2) were compared. Using double-immunocytochemistry for tyrosine hydroxylase and for c-Fos, we determined that within the A2 cell group significantly more noradrenergic neurons were activated in the Wistar than in WKY rats at D1. At D2 WKYs increased their activation of the A2 noradrenergic neurons, and this activation was equivalent to that of the Wistar group. Based on these results, we further investigated the role of A2 cell group during the FST using anti-DBH conjugated saporin (DSAP) to selectively destroy noradrenergic neurons within the area. The Wistar rats treated with DSAP were more immobile during both D1 and D2 of the FST as compared to the rats treated with the vehicle only. Together these data indicate that the A2 noradrenergic cell group regulates FST immobility in rats, and that its activation may contribute to the unique behavioral phenotype of WKY rats. Future experiments aimed at selective activation of A2 noradrenergic neurons will be required to fully elucidate the role of these neurons in mediating behavioral despair and learned helplessness.

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