Bidirectional Modulation of Intrinsic Excitability in Rat Prelimbic Cortex Neuronal Ensembles and Non-Ensembles after Operant Learning

Abstract

Learned associations between environmental stimuli and rewards drive goal-directed 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 activated selectively 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 after 10 d of operant food self-administration training (1 h/d). First, we used the Daun02 inactivation procedure in male FosLacZ-transgenic rats to ablate selectively Fos-expressing PLC neurons that were active during operant food self-administration. Selective ablation of these neurons decreased food seeking. We then used male FosGFPtransgenic rats to assess selective alterations of intrinsic excitability in Fos-expressing neuronal ensembles (FosGFP ϩ ) that were activated during food self-administration and compared these with alterations in less activated non-ensemble neurons (FosGFP Ϫ ). Using whole-cell recordings of layer V pyramidal neurons in an ex vivo brain slice preparation, we found that operant self-administration increased excitability of FosGFP ϩ neurons and decreased excitability of FosGFP Ϫ neurons. Increased excitability of FosGFP ϩ neurons was driven by increased steady-state input resistance. Decreased excitability of FosGFP Ϫ 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 Fosexpressing neuronal ensembles that play a role in food seeking but decreased intrinsic excitability of Fos Ϫ non-ensembles.

Restoration of Kv7 channel mediated inhibition reduces cued-reinstatement of cocaine seeking

“…Taken together, this indicates that training to self-administer drug (cocaine) and nondrug (sucrose) reinforcers produce qualitatively similar reductions in intrinsic inhibition early on, but for drug reinforcers these modifications are persistent even after withdrawal or extinction. These data are consistent with previous studies reporting that drug and nondrug reinforcers produce different cellular adaptations in PL-PFC neurons (Whitaker et al, 2017).…”

“…Activity-induced increases in Fos are considered to represent the integration of neuronal activity driven by numerous synaptic alterations (Cifani et al, 2012;Koya et al, 2012;Whitaker et al, 2017;Ziminski et al, 2017a;2017b). Using cFos-GFP transgenic rats, we observed that cocaine-SA training decreased intrinsic inhibition selectively in cFos/GFP + neurons.…”

“…Fluorescence-guided patch-clamp recordings of GFP +/cells were performed in slices from the cFos-GFP transgenic rats ( Figure 7F) (Whitaker et al, 2017). Where possible, we attempted to sample equal numbers of GFP +/cells from each brain slice.…”

Drug-taking in a socio-sexual context enhances vulnerability for addiction in male rats

“…Future studies will investigate the role that co-activation of these neurons during concurrent Meth and sex plays in enhanced drug-seeking behavior in extinction or reinstatement. It has been demonstrated in both drug-and food-seeking studies that neurons encoding extinction memories versus those encoding reward memories reside in the mPFC (ventral mPFC and dorsal mPFC, respectively) [52,53], and that expression of these memories is abolished when these neurons are selectively lesioned [54,55]. It is likely, therefore, that distinct neuronal ensembles are implicated in the failure to suppress behavior during the initial phases of extinction learning versus during the expression of drug-associated memory in reinstatement in the concurrent Meth/sex animals.…”

The medial prefrontal cortex is required for responding to alcohol-predictive cues but only in the absence of alcohol delivery

“…Although muscimol and baclofen inactivation is widely used, this manipulation may produce a strong inhibitory effect that overwhelms the function of discrete subsets of neurons that could regulate distinct behavioural effects. Indeed, studies have shown that behaviour can be regulated by small ensembles of neurons in a brain area such as the medial prefrontal cortex (Whitaker et al, 2017), and that eliminating different ensembles within the same region can produce dissociable effects on behaviour (Pfarr et al, 2015). A more selective approach may therefore be necessary to parse with greater specificity the contribution of PL and IL subregions to motivated behaviour produced by appetitive Pavlovian conditioning.…”