Functional disturbances in the striatum by region-specific ablation of NMDA receptors

Abstract

To study the role of NMDA receptors in dopamine signaling of the striatum, the brain area that receives glutamatergic inputs from various cortical areas and most dopaminergic inputs, we generated striatum-specific NMDA receptor-deficient mice. The mutant pups showed reduced food intake and retarded growth starting at the second postnatal week and died on approximately postnatal day 20 (P20). The time course of postnatal lethality is similar to that of compound mutant, double knockout of dopamine D1/D2 receptors, or genetically engineered dopamine-deficient mouse. In vivo electrophysiological recordings in the mutant pups showed that frequencies in the range of gamma oscillation were reduced in the striatal circuits. Moreover, the number of functional dopamine receptors in the striatum as measured by D1-and D2-binding experiments was greatly diminished in the mutants as compared with control animals. A consequence of diminished dopamine binding in the striatum manifested in an increase of locomotor activity. The administration of D1/D2 agonists paradoxically reduced the hyperactivity of the mutant mice as compared with an increase in locomotor activity in control mice. These results demonstrate that the NMDA receptor plays an essential role in the integration of dopamine signaling in the striatum and that is required in behavioral function.T he striatum receives glutamatergic projections from virtually all areas of the cerebral cortex and dense dopaminergic projections from the substantia nigra and ventral tegmental area (1, 2). The principal neurons of the striatum, medium spiny neurons (MSNs), are GABAergic projection neurons. These neurons are classified into two groups: the MSNs that express D1 dopamine receptors responsible for a direct pathway and the MSNs that express D2 dopamine receptors responsible for an indirect pathway (3). These MSNs constitute 90-95% of the striatal neuronal population (4) and contain high levels of NMDA receptors (5, 6).During development, dopamine receptor expressions (both D1 and D2) are already abundant by the late embryonic stage, however functional dopamine receptor binding is low at birth and progressively increases to reach adult levels between postnatal day (P)14 and P21 (7). This delayed appearance of functional dopamine receptors in the MSNs of the striatum suggests that maturation of functional dopamine receptors is regulated by an unknown mechanism, other than the mere availability of the dopamine receptor mRNAs.During postnatal weeks, it has been shown that the NMDA receptor-mediated currents develop later in the MSNs compared with other brain regions such as the hippocampus. There is a Ϸ2-fold increase from the first to the third postnatal week (8). Recently, molecular interactions between NMDA receptors and dopamine receptors have been reported. For example, NMDA receptors trap diffusible D1 receptors by direct physical interaction (9-11). The interaction between NR2B, a subunit of the NMDA receptor, and the D2 receptor can also disrupt the association of Ca 2ϩ /cal...

Genetic Deletion of A2AAdenosine Receptors in the Striatum Selectively Impairs Habit Formation: Figure 1.

“…A 2A R protein and mRNA in the striatum of the st-A 2A R-KO mice were shown to be reduced to the background level seen in gb-A 2A R KO mice (Shen et al 2008). A recent study using the Rosa26-Cre reporter line also confirmed the specificity of the striatum-specific expression pattern of this Dlx5/6-Cre transgenic line (Ohtsuka et al, 2008). …”

Severely Impaired Learning and Altered Neuronal Morphology in Mice Lacking NMDA Receptors in Medium Spiny Neurons

“…Mice with a conditional allele of the unique gene Grin1 , which encodes the NR1 subunit, have been crossed to mice expressing Cre recombinase selectively in the striatum. The results of these studies have confirmed that NMDAR currents are absent in neurons lacking NR1 and that LTP cannot be elicited in striatal slice preparations from these animals [18], [25]. However, the behavioral consequences differ in these studies, perhaps due to incomplete knockout of striatal NR1 protein in the mice that were less severely affected [18], or expression of Cre recombinase in striatal interneurons as well as MSNs [26], [27].…”

Selective inactivation of adenosine A2A receptors in striatal neurons enhances working memory and reversal learning

“…Briefly, Dlx5/6-cre(+) transgenic mice in a FVB genetic background were provided (Ohtsuka et al 2008) and cross-bred to Adora2a flox/flox mice in a congenic C57BL/6 genetic background. A Dlx5/6 intron regulatory element drove the embryonic, striatal neuron-specific Cre-mediated deletion of the "floxed" allele (Zerucha et al 2000;Ghanem et al 2003;Ohtsuka et al 2008).…”