Biology subjects

Khoo, S. Y.-S.

Publications and source records attributed to Khoo, S. Y.-S..

3 recordsLinked to original sources

bioRxiv2022

Metabotropic glutamate group II receptor activation in the dorsal striatum suppresses the motivation for cocaine in rats

After a history of intermittent cocaine intake, rats develop patterns of drug use characteristic of addiction. The dorsal striatum is involved in the increased pursuit of cocaine after intermittent drug self-administration experience. Within the dorsal striatum, chronic cocaine use changes metabotropic glutamate type II receptor (mGlu2/3) density and function. We examined the extent to which activity at these receptors mediates responding for cocaine after intermittent cocaine use. In Experiment 1, male Wistar rats (n = 11) self-administered 0.25 mg/kg/infusion cocaine during 10 daily intermittent access (IntA) sessions (5 min ON/25 min OFF, for 5 h/session). We then examined the effects of intra-dorsal striatum infusions of the mGlu2/3 receptor agonist LY379268 (0, 1, and 3 g/hemisphere) on cocaine self-administration under a progressive ratio schedule of reinforcement. We observed a non-significant tendency for LY379268 to reduce responding for cocaine. In Experiment 2, we used a larger sample of male (n = 11) and female (n = 10) rats. Across 10 IntA sessions, the sexes showed similar levels of cocaine intake. Across the sexes, locomotion significantly increased over sessions, suggesting that rats developed psychomotor sensitization to self-administered cocaine. After 10 IntA sessions, intra-dorsal striatum LY379268 significantly reduced breakpoints achieved for cocaine, active lever presses, and cocaine infusions earned under progressive ratio. LY379268 had no effects on locomotion or inactive lever presses, indicating no motor effects. These results suggest that mGlu2/3 receptor activation in the dorsal striatum suppresses incentive motivation for cocaine, and this holds promise for anti-addiction therapeutics.

neuroscience↗

bioRxiv2022

Does vendor breeding colony influence sign- and goal-tracking in Pavlovian conditioned approach? A preregistered empirical replication

Vendor differences are thought to affect Pavlovian conditioning in rats. After observing possible differences in sign-tracking and goal-tracking behaviour with rats from different breeding colonies, we performed an empirical replication of the effect. 40 male Long-Evans rats from Charles River colonies K72 and R06 received 11 Pavlovian conditioned approach training sessions (or "autoshaping"), with a lever as the conditioned stimulus (CS) and 10% sucrose as the unconditioned stimulus (US). Each 58-min session consisted of 12 CS-US trials. Paired rats (n = 15/colony) received the US following lever retraction. Unpaired control rats (n = 5/colony) received sucrose during the inter-trial interval. Next, we evaluated the conditioned reinforcing properties of the CS, by determining whether rats would learn to nose-poke into a new, active (vs. inactive) port to receive CS presentations alone (no sucrose). Preregistered confirmatory analyses showed that during autoshaping sessions, Paired rats made significantly more CS-triggered entries into the sucrose port (i.e., goal-tracking) and lever activations (sign-tracking) than Unpaired rats did, demonstrating acquisition of the CS-US association. Confirmatory analyses showed no effects of breeding colony on autoshaping. During conditioned reinforcement testing, analysis of data from Paired rats alone showed significantly more active vs. inactive nosepokes, suggesting that in these rats, the lever CS acquired incentive motivational properties. Analysing Paired rats alone also showed that K72 rats had higher Pavlovian Conditioned Approach scores than R06 rats did. Thus, breeding colony can affect outcome in Pavlovian conditioned approach studies, and animal breeding source should be considered as a covariate in such work.

neuroscience↗

bioRxiv2021

Metabotropic group II glutamate receptors in the basolateral amygdala mediate cue-triggered increases in incentive motivation

RationaleReward-associated cues can trigger incentive motivation for reward and invigorate reward-seeking behaviour via Pavlovian-to-instrumental transfer (PIT). Glutamate signaling within the basolateral amygdala (BLA) modulates cue-triggered increases in incentive motivation. However, the role of BLA metabotropic group II glutamate (mGlu2/3) receptors is largely unknown. ObjectivesIn Experiment 1, we characterized cue-triggered increases in incentive motivation for water reward using the PIT paradigm. In Experiment 2, we assessed the influence of intra-BLA microinjections of the mGlu2/3 receptor agonist LY379268 on this effect. MethodsWater-restricted male Sprague-Dawley rats learned to press a lever for water. Separately, they learned to associate one of two auditory cues with free water. On test days, rats could lever press under extinction conditions (no water), with intermittent, non-contingent CS+ and CS- presentations. In Experiment 1, rats were tested under baseline conditions. In Experiment 2, rats received intra-BLA microinjections of LY379268 (0, 3 and 6 g/hemisphere) before testing. ResultsAcross experiments, CS+, but not CS- presentations increased water-associated lever pressing during testing, even though responding was reinforced neither by water nor the CS+. Intra-BLA LY379268 abolished both CS+ potentiated pressing on the water-associated lever and CS+ evoked conditioned approach to the site of water delivery. LY379268 did not influence locomotion or instrumental and Pavlovian response rates during intervals between CS presentations or during the CS-, indicating no motor effects. ConclusionsmGlu2/3 receptor activity in the BLA mediates CS-triggered potentiation of incentive motivation for reward, suppressing both CS-induced increases in instrumental pursuit of the reward and anticipatory approach behaviour.

neuroscience↗