Overexpression of neuronal RNA-binding protein HuD increases reward induced reinstatement of an instrumental response

Abstract

The neuronal RNA-binding protein HuD is involved in synaptic plasticity and the molecular mechanisms of learning and memory. Previously, we have shown that HuD is upregulated after both spatial and addiction-associated forms of learning, such as conditioned place preference. However, what role HuD plays in non-drug dependent learning and memory is not fully understood. In order to elucidate the role that HuD plays in non-drug appetitive behavior, we assessed mice over-expressing HuD (HuD_OE) throughout the forebrain on the acquisition of an instrumental response for a non-sucrose food reward utilizing a touch-screen paradigm. Next, we examined whether HuD level would alter the extinction or reward-induced reinstatement of responding. We found that HuD_OE acquired and extinguished the instrumental response at rates similar to control littermates with no significant alterations in secondary measures of motor behavior or motivation. However, HuD_OE reinstated their responding for food reward at rates significantly higher than control animals after a brief presentation of reward. These results suggest that HuD positively regulates the reinstatement of natural reward seeking and supports the role of HuD in forms of learning and memory associated with seeking of appetitive rewards.

Keywords: HuD; Post-transcriptional regulation; RNA binding protein; Reward seeking.

Figure 1:. Touch-screen acquisition, extinction and reinstatement paradigm.

(A) During acquisition, mice are trained to respond via lever press to receive a food pellet reward concomitant with magazine light and tone by touching 1 of 2 white square stimuli on a touch-sensitive screen. (B) During extinction stimuli appear automatically on screen every 10 seconds and touch responses do not produce reward or secondary reinforcers (C). For reinstatement, mice are primed for 6 trials via automatic delivery of reward and secondary reinforcers. Reinstatement of responding is measured over the following 54 unrewarded trials.

Figure 2:. Overexpression of HuD does not alter rate of acquisition of an instrumental response for food reward.

(A) All mice significantly decreased time to complete acquisition sessions and HuD_OE mice showed rates similar to controls. (B) Genotypes did not differ on total sessions to reach acquisition criterion (C) HuD_OE did not significantly alter total average latency to respond to the stimuli or retrieve non-sucrose food reward after a response during acquisition. (Data are Means ±SEM).

Figure 3:. HuD_OE mice show normal extinction of instrumental response.

(A) HuD_OE and control mice showed similar rates of extinction measured by total trials omitted across sessions (B) No differences were seen between genotypes on sessions to reach extinction criterion (C) HuD_OE had similar latencies to touch stimuli when they responded to non-rewarded trials and did not differ on latency to check the reward magazine after a response. (Data are Means ±SEM).

Figure 4:. HuD overexpression significantly increases responding during reward induced reinstatement.

(A) HuD_OE mice did not respond at higher rates than controls during the brief (6 trial) rewarded priming trials but responded significantly more during the remainder of the session. (B) Responding during reinstatement was significantly higher in HuD_OE versus controls compared to the number of responses on the preceding session of extinction. (C) HuD_OE did not differ from controls on latency to responds or check the reward magazine either during primed or unrewarded trials. (*p<.01 versus control animals; Data are Means ±SEM).