Featured Paper of the Month – February 2018.
Learned associations between environmental stimuli and rewards drive learning and motivated behavior. These memories are thought to be encoded by alterations within specific patterns of sparsely distributed neurons called neuronal ensembles that are selectively activated by reward-predictive stimuli. Here we use the Fos promoter to identify strongly activated neuronal ensembles in rat prelimbic cortex (PLC) and assess altered intrinsic excitability following 10 days of operant food self-administration training. First, we selectively ablated Fos-expressing PLC neurons that were active during food self-administration. Selective removal of these neurons decreased food seeking. We then used male FosGFP transgenic rats to assess selective alterations of intrinsic excitability in Fos-expressing neuronal ensembles (FosGFP+) that were activated during food self-administration and compared these to alterations in less activated non-ensemble neurons (FosGFP-). Using whole cell recordings of pyramidal neurons in a brain slice preparation, we found that food self-administration increased excitability of FosGFP+ neurons and decreased excitability of FosGFP- neurons. Increased excitability of FosGFP+ neurons was driven by increased input resistance. Decreased excitability of FosGFP- neurons was driven by increased contribution of small conductance calcium-activated potassium (SK) channels. Injections of the specific SK channel antagonist apamin into PLC increased Fos expression but had no effect on food seeking. Overall, operant learning increased intrinsic excitability of PLC Fos-expressing neuronal ensembles that play a role in food seeking but decreased intrinsic excitability of Fos-negative non-ensembles.
J Neurosci, 37 (36), pp. 8845–8856, 2017, ISSN: 1529-2401 (Electronic); 0270-6474 (Linking).