Activation of phenotypically-distinct neuronal subpopulations of the rat amygdala following exposure to predator odor

doi:10.1016/j.neuroscience.2010.12.001

Neuroscience

Volume 175, 17 February 2011, Pages 133-144

https://doi.org/10.1016/j.neuroscience.2010.12.001 Get rights and content

Abstract

Exposure of rats to an odor of a predator can elicit an innate fear response. In addition, such exposure has been shown to activate limbic brain regions such as the amygdala. However, there is a paucity of data on the phenotypic characteristics of the activated amygdalar neurons following predator odor exposure. In the current experiments, rats were exposed to cloth which contained either ferret odor, butyric acid, or no odor for 30 min. Ferret odor-exposed rats displayed an increase in defensive burying versus control rats. Sections of the brains were prepared for dual-labeled immunohistochemistry and counts of c-Fos co-localized with Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), parvalbumin, or calbindin were made in the basolateral (BLA), central (CEA), and medial (MEA) nucleus of the amygdala. Dual-labeled immunohistochemistry showed a significant increase in the percentage of CaMKII-positive neurons also immunoreactive for c-Fos in the BLA, CEA and MEA of ferret odor-exposed rats compared to control and butyric acid-exposed groups. Further results showed a significant decrease in calbindin-immunoreactive neurons that were also c-Fos-positive in the anterior portion of the BLA of ferret odor-exposed rats compared to control and butyric acid-exposed rats, whereas the MEA expressed a significant decrease in calbindin/c-Fos dual-labeled neurons in butyric acid-exposed rats compared to controls and ferret odor-exposed groups. These results enhance our understanding of the functioning of the amygdala following exposure to predator threats by showing phenotypic characteristics of activated amygdalar neurons. With this knowledge, specific neuronal populations could be targeted to further elucidate the fundamental underpinnings of anxiety and could possibly indicate new targets for the therapeutic treatment of anxiety.

Research Highlights

▶Exposure of rats to ferret odor induces an innate fear response of defensive burying. ▶Exposure of rats to ferret odor activates discrete CaMKII-positive subpopulations of the basolateral, central, and medial amygdala. ▶A reduction in co-localization of c-Fos with calbindin in the basolateral amygdala was observed in rats exposed to ferret odor.

Section snippets

Animals

Male Long-Evans rats (Harlan Laboratories, Indianapolis, IN, USA), weighing approximately 250–300g were single-housed in an environmentally controlled animal facility on a 12:12 h light: dark cycle with lights on at 0700 hours. Purina rat chow and water were available ad libitum. All experiments were conducted during the light phase, beginning at least 2 h after light phase onset. Animals were housed in an animal facility approved by the Association for Assessment and Accreditation of

Exposure to ferret or noxious odor elicits fear behaviors in naive rats

Rats which had never encountered a predator ferret expressed innate fear-related behaviors upon exposure to the odor of a ferret. One-way analysis of variance (ANOVA) revealed a significant effect of odor exposure on the duration of burying (F_3,38=6.540; P=0.0004) (Fig. 2A) and the latency to begin burying (F_3,38=4.609; P=0.0086) (Fig. 2B). SNK post hoc test revealed that exposure to ferret odor resulted in the expression of robust innate aversive behaviors as indicated by an increase in the

Discussion

Our results indicate that exposure of rats to a either a predator odor or high amounts of a noxious control odor elicits aversive behaviors such as increased defensive burying and a decrease in the latency to bury. Rats which had been exposed to the ferret-scented towel, but not high amounts of butyric acid, expressed increased co-localization of c-Fos, a marker of neuronal activation, with CaMKII in glutamatergic pyramidal neurons in the BLA. Furthermore, the anterior BLA of rats exposed to a

Conclusion

The study presented here enhances our knowledge of the amygdala circuitry involved in the expression of innate fear induced by the odor of a natural predator. We show that distinct neuronal populations in the amygdala are activated by different stressors/anxiogenic stimuli, suggesting that these stimuli activated unique neuronal circuits through this brain area. Such knowledge is important for the fundamental understanding of fear and anxiety and could be used to determine viable targets for

Acknowledgments

This work was funded by an NIMH RO1 (MH063344) and an R21 (AA017361) grant awarded to MAW and JRF. Additionally, we acknowledge funding from Science Undergraduate Research Fellowship (SURF) for EMO and MIH-MBRS-RISE at (Universidad del Este) (UNE) 5R25GM066250 for PBV. The authors wish to thank Dr. Alexander J. McDonald for insightful comments on the content of the manuscript. Thanks to Pumpkin, Zooey, Valentine and Dr. John Hines (Yale University) for supplying ferret-scented towels.

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Cognitive, Behavioral, and Systems NeuroscienceResearch PaperActivation of phenotypically-distinct neuronal subpopulations of the rat amygdala following exposure to predator odor

Abstract

Research Highlights

Section snippets

Animals

Exposure to ferret or noxious odor elicits fear behaviors in naive rats

Discussion

Conclusion

Acknowledgments

Peptides

Pharmacol Biochem Behav

Pharmacol Biochem Behav

Prog Neurobiol

Neurosci Biobehav Rev

Brain Res

Neuroscience

Neurosci Biobehav Rev

Peptides

Neuropsychopharmacology

Prog Neurobiol

Curr Biol

Behav Brain Res

Brain Res

Physiol Behav

Neuroscience

Neuroscience

Brain Res

Brain Res

Neurosci Lett

Prog Neurobiol

Biol Psychol

Neurosci Biobehav Rev

Brain Res

Neuroscience

Neurosci Biobehav Rev

Behav Brain Res

Cognitive, Behavioral, and Systems Neuroscience
Research Paper
Activation of phenotypically-distinct neuronal subpopulations of the rat amygdala following exposure to predator odor