Developmental effects of early-life stress on dopamine D2 receptor and proteins involved in noncanonical D2 dopamine receptor signaling pathway in the prefrontal cortex of male rats

OBJECTIVES

Dopamine neurotransmission is implicated in multiple neuropsychiatric disorders, most strikingly in Parkinson's disease, bipolar disorder, attention-deficit hyperactivity disorder and schizophrenia. In addition to canonical pathway, D2-receptor (D2R) exerts some of its biological actions through regulating the activity of Akt and GSK3, which in turn were found to be altered in several psychiatric illnesses. The present study examined the impacts of maternal separation, an early-life stress model which has been associated with disturbed neurodevelopment and appearance of many psychiatric disorders, on developmental changes in dopamine concentration and the expression of D2Rs, Akt and GSK-3β in the medial prefrontal cortex (PFC; a key target of stress) in adolescent and young adult male rats.

METHODS

Maternal separation was performed 3 h per day from postnatal days 2 to 11. The PFC protein and dopamine contents were determined using western blotting analysis and Eliza, respectively.

RESULTS

Results indicated long-term increases in the prefrontal dopamine levels in stressed adolescent and young adult male rats, accompanied by significant downregulation of D2R as well as upregulation of p-Akt and GSK-3β contents in stressed adolescence compared to controls, with all protein levels that returned to control values in stressed adult rats.

CONCLUSIONS

Our findings suggest that early-life stress differentially modulates prefrontal D2R/Akt/GSK-3β levels during development. Since adolescence period is susceptible to the onset of specific mental illnesses, disruption of noncanonical components of D2R signaling during this critical period may have an important role in programming neurobehavioral phenotypes in adulthood and manipulations influencing Akt/GSK-3β pathway may improve the expression of specific dopamine-related behaviors and the effects of dopaminergic drugs.

Long-Term Decreases in the Expression of Calcineurin and GABAA Receptors Induced by Early Maternal Separation Are Associated with Increased Anxiety-Like Behavior in Adult Male Rats

INTRODUCTION

Early life stress is a well-described risk factor of anxiety disorders in adulthood. Dysfunction in GABA/glutamate receptors and their functional regulator, calcineurin, is linked to anxiety disorders. Here, we investigated the effect of early life stress, such as repeated maternal separation (MS; 3 h per day from postnatal day [P] 2 to 11), on changes in the expression of calcineurin as well as the ionotropic glutamatergic and GABAergic receptors including α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-D-aspartate (NMDA) and GABAA receptors in the hippocampus and prefrontal cortex (PFC) of adolescent (P35) and adult (P62) male Wistar rats and their correlations with anxiety-like behavior in adulthood.

METHODS

The protein levels were assessed by Western blot analysis. Anxiety-like behavior was measured in the elevated plus maze (EPM) and open field (OF) tests.

RESULTS

MS induced a regional transient decrease of glutamate receptors expression at P35, with decreased NMDA and AMPA receptor levels, respectively, in the hippocampus and PFC, suggesting a possible decrease in excitatory synaptic strength. In contrast to glutamate receptors, MS had long-lasting influence on GABAA receptor and calcineurin levels, with reduced expression of GABAA receptor and calcineurin in both brain regions at P35 that continued into adulthood. These results were accompanied by increased anxiety behavior in adulthood, shown by lower percentage of number of total entries and time spent in the open arms of the EPM, and by lower time spent and number of entries in the OF central area.

CONCLUSIONS

Together, our study suggests that GABAA receptors via calcineurin-dependent signaling pathways may play an important role in the expression of stress-induced anxiety-like behavior.

Negative relationship between brain α1A-AR neurotransmission and βArr2 levels in anxious adolescent rats subjected to early life stress

Early-life stress is correlated with the development of anxiety-related behavior in adolescence, but underlying mechanisms remain poorly known. The α_1A-adrenergic receptor (AR) is linked to mood regulation and its function is assumed to be regulated by β-arrestins (βArrs) via desensitization and downregulation. Here, we investigated correlation between changes in α_1A-AR and βArr2 levels in the prefrontal cortex (PFC) and hippocampus of adolescent and adult male rats subjected to maternal separation (MS) and their relationship with anxiety-like behavior in adolescence. MS was performed 3 h per day from postnatal days 2-11 and anxiety-like behavior was evaluated in the elevated plus-maze and open field tests. The protein levels were examined using western blot assay. MS decreased α_1A-AR expression and increased βArr2 expression in both brain regions of adolescent rats, while induced reverse changes in adulthood. MS adolescent rats demonstrated higher anxiety-type behavior and lower activity in behavioral tests than controls. Decreased α_1A-AR levels in MS adolescence strongly correlated with reduced time spent in the open field central area, consistent with increased anxiety-like behavior. An anxiety-like phenotype was mimicked by acute and chronic treatment of developing rats with prazosin, an α_1A-AR antagonist, suggesting α_1A-AR downregulation may facilitate anxiety behavior in MS adolescent rats. Together, our results indicate a negative correlation between α_1A-AR neurotransmission and βArr2 levels in both adults and anxious-adolescent rats and suggest that increased βArr2 levels may contribute to posttranslational regulation of α_1A-AR and modulation of anxiety-like behavior in adolescent rats. This may provide a path to develop more effective anxiolytic treatments.

Pregestational stress attenuated fertility rate in dams and increased seizure susceptibility in offspring

Many studies have found that stress during pregnancy is linked to an increased incidence of epileptic behaviors and reproductive disorders. However, few works have investigated the effect of pregestational stress on seizure susceptibility in the offspring. We investigated the effect of pregestational stress on epileptic behaviors in the offspring as well as fertility rate in dams. The male and female rats were randomly divided into four groups to form a combination of control and stressed groups for each sex. The rats were subjected to predatory stress (exposed to a cat) twice per day for 50 (male) and 15 (female) consecutive days. At the end of the stress procedure, the rats were coupled as follows: both male and female control (M_C-F_C), male stressed/female control (M_S-F_C), male control/female stressed (M_C-F_S), and both male and female stressed (M_S-F_S). Then, the puppies born from these groups were counted and evaluated for pentylentetrazole (PTZ)-induced seizure. There was no significant difference between the male and female pups in each identical group in terms of litter size and epileptic behaviors, except duration of tail rigidity and duration of immobility. The total score of seizure increased in all the stressed groups, but more severely in the M_S-F_S group. However, the onset of the first epileptic behavior and tonic-clonic seizure significantly decreased in the stressed groups. Moreover, fertility rate significantly decreased in the stressed groups compared with the control group, but there was no significant difference in terms of litter size between the groups. These data revealed the impact of pregestational stress during spermatogenesis and oogenesis on fertility rate in dams and epileptic behaviors in the offspring.