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Show 30 Ethanol Effects on Baseline Firing Ethanol significantly decreased baseline firing in most NAcc neurons (Figure 2.3A, average firing rate after vehicle administration, 4.5 ± 0.3 spikes/s; ethanol, 3.0 ± 0.2 spikes/s, p < 0.001). In order to determine if ethanol differentially affected firing in distinct types of NAcc neurons, we used waveform and firing rate criteria (see Methods) to classify individual neurons into three groups corresponding to putative fast-spiking interneurons (pFSIs), tonically active neurons (pTANs), and medium spiny neurons (pMSNs). While many neurons had properties that conformed well to parameters previously described for specific neuron types, substantial overlap between groups remained (Figure 2.3B). We analyzed ethanol effects in neurons that conformed most stringently to properties described for each neuron type (colored symbols in Figure 2.3B). Ethanol significantly decreased baseline firing rates for all three types of neuron (Figure 2.3C, main effect of ethanol, F (1,568) = 238.7, p < 0.001, main effects of neuron type, F (2,568) = 854.0, p < 0.001, and a significant interaction of subtype and ethanol, F (2,568) = 99.4, p < 0.001; post hoc tests significant for all groups, p < 0.01). Thus, acute ethanol administration broadly suppressed neural firing within the NAcc for all putative neuron types. Overview of Behaviorally-Evoked NAcc Firing We analyzed behaviorally-evoked NAcc firing in 369 neurons recorded in 81 sessions during performance of the delay (n=8 rats) and size (n=6 rats) tasks. Neural responses were heterogeneous, and subsets of neurons responded with increases or decreases in neural firing during most task-related behaviors. We focused specifically on neurons that showed increased firing rates in response to behaviorally relevant events (Table 2.1). Cue-Evoked Responses A subpopulation of NAcc neurons (n=53, ~ 14% of all recorded neurons) showed significantly increased firing rates in response to the reward-predictive cue (light illumination and lever extension) occurring on forced trials. A subset of these neurons encoded anticipated value, |
