Disconnection of basolateral amygdala and insular cortex disrupts conditioned approach in Pavlovian lever autoshaping

Highlights

• Contralateral disconnection of BLA-IC reduced food-cup responding in goal-trackers.

• Contralateral disconnection of BLA-IC reduced lever responding in sign-trackers.

• Ipsilateral disconnection of BLA-IC has no effect on preferred responding in either group.

Abstract

Previously established individual differences in appetitive approach and devaluation sensitivity observed in goal- and sign-trackers may be attributed to differences in the acquisition, modification, or use of associative information in basolateral amygdala (BLA) pathways. Here, we sought to determine the extent to which communication of associative information between BLA and anterior portions of insular cortex (IC) supports ongoing Pavlovian conditioned approach behaviors in sign- and goal-tracking rats, in the absence of manipulations to outcome value. We hypothesized that the BLA mediates goal-, but not sign- tracking approach through interactions with the IC, a brain region involved in supporting flexible behavior. We first trained rats in Pavlovian lever autoshaping to determine their sign- or goal-tracking tendency. During alternating test sessions, we gave unilateral intracranial injections of vehicle or a cocktail of gamma-aminobutyric acid (GABA) receptor agonists, baclofen and muscimol, unilaterally into the BLA and contralaterally or ipsilaterally into the IC prior to reinforced lever autoshaping sessions. Consistent with our hypothesis we found that contralateral inactivation of BLA and IC increased the latency to approach the food cup and decreased the number of food cup contacts in goal-trackers. While contralateral inactivation of BLA and IC did not affect the total number of lever contacts in sign-trackers, this manipulation increased the latency to approach the lever. Ipsilateral inactivation of BLA and IC did not impact approach behaviors in Pavlovian lever autoshaping. These findings, contrary to our hypothesis, suggest that communication between BLA and IC maintains a representation of initially learned appetitive associations that commonly support the initiation of Pavlovian conditioned approach behavior regardless of whether it is directed at the cue or the location of reward delivery.

Introduction

During Pavlovian lever autoshaping, sign-tracking rats preferentially approach and contact the lever, while goal-tracking rats preferentially approach and contact the food cup (Boakes, 1977, Flagel et al., 2007, Hearst and Jenkins, 1974). Two recent studies have provided evidence that goal-trackers rely on representations of the current value of the outcome to promote flexible behavior, whereas sign-trackers inflexibly respond based on initially learned appetitive associations (Morrison et al., 2015, Nasser et al., 2015). Individual differences in behavioral flexibility of sign- and goal-trackers may be rooted in the recruitment of dissociable basolateral amygdala (BLA) pathways known to mediate behavior that relies on stimulus-response versus stimulus-outcome associations. The BLA has reciprocal interactions with more specialized areas including insular cortex (IC) and orbitofrontal cortex (OFC) (Aggleton et al., 1980, Krettek and Price, 1977, McDonald, 1991, McDonald, 1998, Miranda and McGaugh, 2004, Morecraft et al., 1992, Parkes and Balleine, 2013, Shinonaga et al., 1994, Sripanidkulchai et al., 1984). The IC and OFC are two neighboring regions which are critical for representing gustatory associations and the current motivational value of the outcome that is necessary for flexible, stimulus-outcome driven learning and goal-directed action (Baxter et al., 2000, Fiuzat et al., 2017, Grossman et al., 2008, Johnson et al., 2009, Miranda and McGaugh, 2004, Nasser and McNally, 2013, Ostlund and Balleine, 2007, Parkes and Balleine, 2013, Pickens et al., 2003, Piette et al., 2012, Rudebeck et al., 2013, Rudebeck and Murray, 2008, Schoenbaum et al., 1998, Schoenbaum et al., 1999, Schoenbaum et al., 2003, Stalnaker et al., 2007, Zeeb and Winstanley, 2013). Here, we sought to determine the extent to which BLA-IC communication supports ongoing Pavlovian approach behaviors in sign- and goal-tracking rats, in the absence of changes to outcome value.

Amygdala lesion and inactivation studies examining the neurobiological underpinnings of incentive learning processes (for review see: Wassum & Izquierdo, 2015) provide insights into candidate brain circuits that may mediate such individual differences in flexible behavior. We hypothesize that sign- and goal-tracking differences, particularly with relevance for behavioral flexibility, may be rooted in the recruitment of different BLA pathways known to mediate behavior that relies on stimulus-response associations (Hatfield et al., 1996, Setlow, Gallagher et al., 2002, Setlow, Holland et al., 2002) versus stimulus-outcome associations (Hatfield et al., 1996, Johnson et al., 2009, Lichtenberg et al., 2017, Parkinson et al., 2000, Pickens et al., 2003, Schoenbaum et al., 1999, Schoenbaum et al., 2003, Stalnaker et al., 2007). Higher order associative processes including Pavlovian outcome devaluation and second-order conditioning commonly depend on an intact BLA during acquisition of appetitive associative learning. Outcome devaluation studies examining the involvement of BLA in the formation of stimulus-outcome associations show that BLA is not critical for initially acquiring conditioned responding to reinforced cues, but instead for maintaining or adjusting the acquired cue value to support new learning when outcome value changes (Hatfield et al., 1996, Parkinson et al., 2000, Pickens et al., 2003, Johnson et al., 2009). Inactivation, lesion and recording studies demonstrate that BLA encodes and IC/OFC retrieves the current incentive value of the outcome to promote appropriate goal-directed and flexible behaviors (Parkes and Balleine, 2013, Pickens et al., 2003, Rudebeck et al., 2013, Schoenbaum et al., 2003). In Pavlovian outcome devaluation an acquired appetitive cue-outcome association is modified by degrading outcome value, which is then used to flexibly reduce conditioned responding to the previously appetitive cue. The established differences in devaluation sensitivity previously observed in goal- and sign-trackers may be attributed to differences in the acquisition, modification or use of associative information in BLA pathways (Morrison et al., 2015, Nasser et al., 2015). To begin addressing the neurobiological mechanisms mediating tracking-related differences in incentive learning we aimed to determine the extent to which communication of associative information between BLA and IC drives conditioned approach in sign- and goal-tracking rats. We predicted that only in goal-trackers would BLA-IC disconnection disrupt the representation of the initially appetitive association that supports ongoing food-cup approach. Importantly, our speculation on associative representations is based indirectly on previous studies in which behavioral and neurobiological manipulations are made in contexts where S-O and S-R associations are directly probed.

To this end, second-order conditioning studies examining the role of BLA in the formation of stimulus-response associations demonstrate that the BLA is necessary for the initial acquisition of the incentive value of the conditioned stimulus (Hatfield et al., 1996, Setlow, Gallagher et al., 2002). Further, BLA interactions with nucleus accumbens are necessary for using that acquired motivational information to support conditioning to novel cues (Setlow, Holland et al., 2002). Recent work evaluating the role of BLA in supporting conditioned responding during Pavlovian lever autoshaping (Chang et al., 2012a, Chang et al., 2012b), the procedure used to identify sign- and goal- tracking rats (Meyer et al., 2012), demonstrate that the BLA is also necessary for invigorating lever-directed conditioned responding based on previously acquired appetitive associations. Together, studies employing various Pavlovian conditioning procedures demonstrate that BLA is commonly and critically engaged early in learning to drive incentive learning processes. Via its interactions with downstream targets, BLA maintains both stimulus-outcome and stimulus-response associations needed for driving flexibility after manipulations to outcome value and for invigorating conditioned responding, respectively. The present study aims to determine the role for BLA communication with IC for mediating individual differences in appetitive approach that may underlie tracking-related individual differences in higher order processes (Nasser et al., 2015).

Here we test our hypothesis that BLA mediates approach in goal-trackers through interactions with insular cortex, a brain region involved in supporting flexible behavior driven by either stimulus-outcome or action-outcome associations (Ostlund and Balleine, 2007, Parkes and Balleine, 2013, Pickens et al., 2003, Saddoris et al., 2005, Schoenbaum et al., 2003). We use an anatomical asymmetrical disconnection procedure in which we reversibly inactivate the BLA in one hemisphere and IC in the contralateral hemisphere using gamma-aminobutyric acid (GABA) receptor agonists GABA-A + GABA-B receptor agonists (muscimol + baclofen) during Pavlovian lever autoshaping after sign- and goal-tracking behaviors have been established. Because of the overwhelmingly unilateral projections between BLA and IC (Krettek and Price, 1977, Parkes and Balleine, 2013, Sripanidkulchai et al., 1984) contralateral, but not ipsilateral, reversible inactivation of BLA and IC is anticipated to substantially disrupt communication between these two interconnected structures. We include the ipsilateral inactivation groups to verify that effects of BLA and IC inactivation on approach behaviors are due to disrupted communication between these two interconnected structures, and not simply due to unilateral inactivation of these to two brain areas independent of information communicated within the pathways. Notably, the anterior portion of insular cortex we target is often damaged by OFC lesions or recorded from in OFC studies examining associative encoding in rats (Chang, 2014, Gallagher et al., 1999, Ostlund and Balleine, 2007, Pickens et al., 2003, Saddoris et al., 2005, Schoenbaum et al., 2003, Stalnaker et al., 2007).