Chemogenetic tools for modulation of spatial learning in dopamine transporter deficient rats

Abstract

Objectives: We used the chemogenetic tools for the activation of norepinephrine (NE) release in the prefrontal cortex (PFC) of dopamine transporter knockout (DAT-KO) rats. The objective of this study was to evaluate the effect of chemogenetic activation of NE release in the PFC on the performance of a spatial behavior task by DAT-KO rats. The rats DAT-KO rats with deletion of DAT gene were created as a valuable model for persistently elevated extracellular DA levels. The DAT-KO rats show marked behavioral abnormalities: impulsivity, stereotypy and reduced learning ability. Such hyperdopaminergia is thought to be one of the causes of disorders such as schizophrenia, mania and attention deficit hyperactivity disorder (ADHD). The Locus Coeruleus (LC) is a critical area in the brain that plays an important role in control of several physiological and behavioral processes due to the existence of extensive connections to cortical and subcortical structures. Its activity can modulate both norepinephrine and dopamine neurotransmission, particularly in the PFC.

Materials and methods: We used canine adenovirus type 2 (CAV2) to selectively activate LC-NA neurons in DAT-KO rats. The chemogenetic modulation of spatial learning in knockout and wild-type (WT) rats was tested in the Hebb-Williams maze. Variables such as the distance traveled, time taken to reach the goal box, number of errors and the perseverative patterns of activity were analyzed.

Results: Norepinephrine release from the LC to the PFC reduced hyperactive behavioral patterns in rats lacking the dopamine transporter (DAT-KO rats) with spontaneously elevated dopamine transmission. These manipulations in hyperdopaminergic mutants also caused amelioration of cognitive abnormalities in spatial learning task by decrease the perseverative activity and the number of visits to the error zones. Furthermore, chemogenetic activation of NE neurotransmission in these animals significantly improved their performance.

Conclusion: The results obtained in this study highlight an important modulatory role of NE transmission from LC to PFC on hyperactivity and cognitive dysfunctions of hyperdopaminergic DAT-KO rats lacking the dopamine transporter.

Keywords: Hebb-Williams maze; chemogenetic; dopamine transporter; hyperdopaminergia; knockout rats; learning.

Figure 1

Scheme of the Hebb-William maze and its inner wall configurations, used for learning (A) and drug testing (B,C). The location of the start and finish chambers are marked in the opposite corners. Food reinforcement is indicated by a circle.

Figure 2

Comparison of distances traveled (A,B) and duration of test performance (time spent, C,D) in Hebb-Williams maze in DAT-KO and WT rats in DREADD+ (left side, A,C) and DREADD- (right side, B,D) groups. Results are presented as the mean ± SEM; **p < 0.01; ***p < 0.001; ****p < 0.0001; two-way ANOVA, analyzing the genotype factor (DAT-KO or WT); ^#p < 0.05; analyzing the treatment factor (vehicle of Clz administration); ns, p > 0.05.

Figure 3

Comparison of the number of error zone visits (A,B) and the number of the return runs (time spent, C,D) in Hebb-Williams maze in DAT-KO and WT rats in DREADD+ (left side, A,C) and DREADD- (right side, B,D) groups. Results are presented as the mean ± SEM; **p < 0.01; ***p < 0.001; ****p < 0.0001; two-way ANOVA, analyzing the genotype factor (DAT-KO or WT); ^#p < 0.05; analyzing the treatment factor (vehicle of Clz administration); ns, p > 0.05.

Figure 4

Immunofluorescence staining of rat brain LC neurons after administration of CAV PRS hM3D(Gq)-mCherry virus to the PFC (A,B); green fluorescence is DβH-positive neurons (C), red fluorescence is mCherry-positive neurons (D), double-labeled neurons appear yellow-orange (E).