Furlong TM, Carrive P (2005) Hypocretin/orexin neurons and the perifornical hypothalamus play a more important role in contextual fear than in restraint stress. Neuroscience 2005 Abstracts 304.11. Society for Neuroscience, Washington, DC.
Summary: We investigated the role of the neuropeptide hypocretin (Hcrt; also known as orexin) in two different types of stress: conditioned fear to context and restraint stress. For contextual fear, male Wistar rats were tested by re-exposure to a chamber where electric footshocks had previously been administered. For restraint stress, the rats were restrained in tight Plexiglas tubes. In the first study, lesions of the perifornical region of the hypothalamus (PeF; where Hcrt neurons are located) were made with a Hcrt-saporin toxin prior to testing. The cardiovascular response was measured using radio-telemetry. The pressor and tachycardic responses to the context were reduced by 77% and 74% respectively, compared to an intact group (p<0.001, for both comparisons). The lesioned group also displayed significant reductions in freezing (by 67%) and ultrasonic vocalisations (by 74%). In contrast, the cardiovascular response to restraint stress did not differ between the two groups (p>0.5). In the second study, two hours after the tests, the rats were euthanased (200 mg/kg sodium pentobarbitone, i.p) and their brains removed and processed for double immunohistochemical detection of Hcrt and Fos. There was a higher percentage of Hcrt neurons double labeled with Fos after contextual fear (17%) than after restraint stress (6%), which indicates that more Hcrt neurons were active during contextual fear (p=0.024). These studies suggest that the PeF region and Hcrt neurons play a more important role in contextual fear than in restraint stress.
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