Cue-Dependent Fear Learning Drives Nucleus Accumbens Spine Plasticity.

Area of Science:

• Neuroscience
• Behavioral Neuroscience

Background:

• Nucleus accumbens (NAc) dopamine 2 receptor expressing medium spiny neurons (D2-MSNs) play a role in stress and aversive learning.
• Repeated stress is known to increase excitatory spine density in these neurons, but whether this is due to cue-specific learning or generalized stress is unclear.

Purpose of the Study:

• To investigate whether synaptic plasticity in NAc D2-MSNs is a result of cue-specific learning or generalized stress.
• To dissociate associative plasticity from the effects of foot shock stress.

Main Methods:

• Utilized Pavlovian fear conditioning in Tac1-Cre/Tdtomato mice.
• Dissociated associative plasticity from foot shock stress effects.
• Examined physiological outcomes of acute fear conditioning with and without a cue.

Main Results:

• Acute fear conditioning yielded different outcomes depending on the presence or absence of a cue.
• Seven days of conditioning consolidated cue learning, increasing excitatory transmission frequency and total spine density.
• Repeated foot shock exposure alone did not induce synaptic remodeling.

Conclusions:

• Morphological changes supporting synaptic plasticity on NAc D2-MSNs are driven by cue-dependent learning, not solely by foot shock stress.
• NAc D2-MSNs are proposed to encode learning and responses to threat cues.
• This encoding may contribute to heightened stress responsivity in the future.