Electrophysiological Evidence of Mediolateral Functional Dichotomy in the Rat Accumbens during Cocaine Self-Administration II: Phasic Firing Patterns

• Published in: The European journal of neuroscience Vol. 31; no. 9; pp. 1671 - 1682
• Main Authors: Fabbricatore, Anthony T., Ghitza, Udi E., Prokopenko, Volodymyr F., West, Mark O.
• Format: Journal Article
• Language: English
• Published: 01.05.2010
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/j.1460-9568.2010.07230.x

In the cocaine self-administering rat, individual nucleus accumbens (NAcc) neurons exhibit phasic changes in firing rate within minutes and/or seconds of lever presses (i.e. slow phasic and rapid phasic changes, respectively). To determine whether neurons that demonstrate these changes during self-administration sessions are differentially distributed in the NAcc, rats were implanted with jugular catheters and microwire arrays in different NAcc subregions (Core, Dorsal Shell, Ventromedial Shell, Ventrolateral Shell or Rostral Pole). Neural recording sessions were typically conducted on Day 13 - 17 of cocaine self-administration (0.77 mg/kg/0.2mL infusion; fixed-ratio 1 schedule of reinforcement; 6 hr daily sessions). Pre-press rapid phasic firing rate changes were greater in lateral accumbal (core, ventrolateral shell) relative to medial accumbal (dorsal shell, rostral pole shell) subregions. Slow phasic pattern analysis revealed that reversal latencies of neurons that exhibited change + reversal patterns differed mediolaterally: medial NAcc neurons exhibited more early reversals and fewer progressive/late reversals than lateral NAcc neurons. Comparisons of firing patterns within individual neurons across time bases indicated that lateral NAcc pre-press rapid phasic increases were correlated with tonic increases. Tonic decreases were correlated with slow phasic patterns in individual medial NAcc neurons, indicative of greater pharmacological sensitivity of neurons in this region. On the other hand, the bias of the lateral NAcc towards increased pre-press rapid phasic activity coupled with a greater prevalence of tonic increase firing may reflect particular sensitivity of these neurons to excitatory afferent signaling and perhaps differential pharmacological influences on firing rates between regions.