Dopamine D1 receptors involved in locomotor activity and accumbens neural responses to prediction of reward associated with place

Abstract

Predicting reward is essential in learning approach behaviors. Dopaminergic activity has been implicated in reward, movement, and cognitive processes, all essential elements in learning. The nucleus accumbens (NAc) receives converging inputs from corticolimbic information-processing areas and from mesolimbic dopamine neurons originating in the ventral tegmental area. Previously, we reported that in mice, a dopamine D2 receptor knockout (D2R-KO) eliminated the prereward inhibitory response, increased place-field size of NAc neurons, and reduced locomotor activity without marked change in intracranial self-stimulation (ICSS) behavior. The present study investigated the specific contribution of dopamine D1 receptor (D1R) in mediating reward, locomotor activity, and spatial associative processes and in regulating NAc neural responses. In contrast to D2R-KO animals, here we find D1R-KO in mice selectively eliminated the prereward excitatory response and decreased place-field size of NAc neurons. Furthermore, D1R-KO impaired ICSS behavior, seriously reduced locomotor activity, and retarded acquisition of a place learning task. Thus, the present results suggest that D1R may be an important determinant in brain stimulation reward (ICSS) and participates in coding for a type of reward prediction of NAc neurons and in spatial learning.dopamine receptor ͉ nucleus accumbens ͉ spatial learning D opaminergic systems innervate the hippocampal formation (HF), prefrontal cortex, amygdala (AM), and ventral striatum and mediate cognitive processes of working memory and learning (1-6). The nucleus accumbens (NAc) is reliably linked to motivation, locomotion, reward-related processes, and some cognitive functions (1,3,(7)(8)(9). It receives excitatory glutamatergic input from the prefrontal cortex, HF, and AM, as well as a dense converging dopaminergic innervation from the ventral tegmental area (3, 10, 11). Thus, NAc neurons are positioned to recognize context-driven patterns of activation and to relay this information to planning and motor executive systems for appropriate behavioral responses (1,3,7,8,12). Dopamine has profound effects on behavior as highlighted in previous studies (13-16). Nevertheless, the contribution of dopamine D1 receptor (D1R) in assessing reward information at neural level and its link to behaviors such as spatial associative learning remains to be specified. In the present study, we used knockout mice lacking D1R (D1R-KO) and their wild-type (WT) littermates to examine the contribution of this receptor in mediating reward, locomotion, and spatial learning and in regulating neural responses to prediction of reward. These mice were tested for their ability to perform several spatial tasks, including random reward place search task (RRPST) and place learning task (PLT), by using intracranial self-stimulation (ICSS) as rewards (15). To investigate the involvement of D1R functions in reward processing and spatial associative processes, we recorded neural activity from the NAc of D1R-KO mice and their WT litte...

Simultaneous dopamine and single-unit recordings reveal accumbens GABAergic responses: Implications for intracranial self-stimulation

“…In all three cases, the changes in firing rate were time-locked to the stimulation train and concurrent with dopamine release. The firing patterns of NAc neurons during ICS reported here are similar to those reported in mice during ICS (12,29). Similarly, dopamine release evoked by ICS was indistinguishable from the responses observed during noncontingent stimulations.…”

“…Evidence for dopamine's importance in ICS includes the reduced responding in rats with lesions of dopaminergic neurons (34), the blockade of ICS by NAc microinjections of a dopaminergic antagonist (16), and the impaired ICS in D1 knockout mice (12). However, measurements of dopamine release during ICS indicate that it is not a necessary condition for ICS (35).…”

“…In this paradigm, animals lever press to deliver electrical stimulation to select brain regions. Like natural rewards, ICS causes time-locked changes in unit activity in the NAc (11,12).…”

Nucleus accumbens lesions decrease sensitivity to rapid changes in the delay to reinforcement

“…Numerous electrophysiological and imaging studies on rodents, humans and non-human primates have implicated the NACas part of a neural circuit responsible for predicting delayed rewards [14][15][16][17][18][19][20][21][22][23][24][25][26]. The results of the present study provide strong behavioral evidence that the NAC is an essential part of this reward prediction circuit.…”

“…However, these findings were complicated by the observation that lesioned rats had a low preference for the "large" reward even when there was no delay, suggesting that the lesions generally impaired choice behavior rather than directly affecting delay discounting. Because the NAC is part of a circuit involved in predicting the occurrence of delayed rewards [14][15][16][17][18][19][20][21][22][23][24][25][26], it is possible that the lesioned rats in the Cardinal study were less able to track the within session changes in the delay associated with the large reinforcer and generally avoided this option without affecting delay discounting.…”