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The Journal of Neuroscience, December 3, 2008, 28(49):13296-13302; doi:10.1523/JNEUROSCI.2843-08.2008

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Behavioral/Systems/Cognitive
New Perspectives on β-Adrenergic Mediation of Innate and Learned Fear Responses to Predator Odor

Fabrício H. M. Do Monte,¹ Newton Sabino Canteras,² Daniel Fernandes,¹ Jamil Assreuy,¹ and Antonio P. Carobrez¹

¹Departamento de Farmacologia, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis-SC 88040900, Brazil, and ²Departamento de Anatomia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo-SP 05508900, Brazil

Correspondence should be addressed to Antonio P. Carobrez, Departamento de Farmacologia, Universidade Federal de Santa Catarina, Campus Trindade, Florianópolis-SC 88040900, Brazil. Email: adepadua{at}farmaco.ufsc.br

In the present study, we investigated the role of noradrenergic transmission in unconditioned and conditioned responses to predatory threats. First, we examined the effects of systemically injected β-blockers on unconditioned and contextual conditioned response to cat odor. The centrally acting β-blocker (propranolol) was able to impair unconditioned responses, as well as the acquisition of the contextual fear to cat odor; however, the peripherally acting (nadolol) was not effective. Next, we examined the neural substrate underlying the noradrenergic modulation of the defensive response to cat odor and focused on the dorsal premammillary nucleus (PMd), because it represents the hypothalamic site most responsive to predatory threats and, at the same time, presents a dense plexus of noradrenergic fibers. We were able to see that propranolol significantly reduced PMd–Fos expression in response to cat odor and that β-adrenoceptor blockade in the PMd, before cat odor exposure, reduced defensive responses to the cat odor and to the cat odor-related environment. We have also shown that β-adrenoceptor blockade in the PMd, before the exposure to cat odor-related context, impaired the contextual conditioned responses. Overall, the present results provide convincing evidence suggesting that central noradrenergic mediation is critical for the expression of unconditioned and contextual conditioned antipredatory responses. We have further shown that the PMd appears to be an important locus to mediate these β-adrenoceptor effects.

Key words: noradrenergic system; β adrenoceptors; β-blockers; cat odor; defensive behavior; contextual fear

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Received June 19, 2008; revised July 29, 2008; accepted Oct. 22, 2008.

Correspondence should be addressed to Antonio P. Carobrez, Departamento de Farmacologia, Universidade Federal de Santa Catarina, Campus Trindade, Florianópolis-SC 88040900, Brazil. Email: adepadua{at}farmaco.ufsc.br

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