5-HT1b receptors in an animal model of depression

After exposure to a 0.8 mA course of uncontrollable shocks, Sprague-Dawley rats can be differentiated into two distinct groups defined in term of their performance in a shock escape paradigm. Learned helpless (LH) rats do not learn to escape a controllable shock while non-helpless (NLH) rats learn this response as quickly as naive controls (NC) rats do. The current experiments were designed to extend our studies of 5-HT receptors in these three groups of rats. The major finding in the present study concerned post-synaptic 5-HT receptor effects in the cortex, hippocampus, septum and hypothalamus of LH rats. These included an up regulation of 5-HT1b receptors in the cortex, hippocampus and septum in LH rats. In contrast, 5-HT1b receptors in the hypothalamus of LH rats were down-regulated. These results implicate serotonergic mechanisms in the behavioral deficit caused by uncontrollable shock with a limbic-hypothalamic circuit serving as a center for adaptation to stress.