Involvement of dopaminergic mechanisms in the nucleus accumbens core and shell subregions in the expression of fear conditioning

• Published in: Neuroscience letters Vol. 446; no. 2; pp. 112 - 116
• Main Authors: Martinez, R.C.R., Oliveira, A.R., Macedo, C.E., Molina, V.A., Brandão, M.L.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 03-12-2008; Elsevier
• Subjects: Animals; Avoidance Learning - physiology; Biological and medical sciences; Conditioning (Psychology) - physiology; Dopamine - metabolism; Electric Stimulation; Extracellular Fluid - metabolism; Fear - physiology; Fear conditioning; Freezing behavior; Fundamental and applied biological sciences. Psychology; Male; Microdialysis; Neural Pathways - physiology; Nucleus Accumbens - metabolism; Nucleus accumbens core; Nucleus accumbens shell; Rats; Rats, Wistar; Synaptic Transmission - physiology; Vertebrates: nervous system and sense organs; Nucleus accumbens core; Freezing behavior; Nucleus accumbens shell; Microdialysis; Fear conditioning; Dopamine; Central nervous system; Basal ganglion; Catecholamine; Encephalon; Nucleus accumbens; Fear; Neurotransmitter; Conditioning; Tonic immobility
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/j.neulet.2008.09.057

The involvement of dopamine (DA) mechanisms in the nucleus accumbens (NAC) in fear conditioning has been proposed by many studies that have challenged the view that the NAC is solely involved in the modulation of appetitive processes. However, the role of the core and shell subregions of the NAC in aversive conditioning remains unclear. The present study examined DA release in these NAC subregions using microdialysis during the expression of fear memory. Guide cannulae were implanted in rats in the NAC core and shell. Five days later, the animals received 10 footshocks (0.6
mA, 1
s duration) in a distinctive cage A (same context). On the next day, dialysis probes were inserted through the guide cannulae into the NAC core and shell subregions, and the animals were behaviorally tested for fear behavior either in the same context (cage A) or in a novel context (cage B). Dialysates were collected every 5
min for 90
min and analyzed by high-performance liquid chromatography. The rats exhibited a significant fear response in cage A but not in cage B. Moreover, increased DA levels in both NAC subregions were observed 5–25
min after the beginning of the test when the animals were tested in the same context compared with accumbal DA levels from rats tested in the different context. These findings suggest that DA mechanisms in both the NAC core and shell may play an important role in the expression of contextual fear memory.