Dehydroepiandrosterone in the nucleus accumbens is associated with early onset of depressive-behavior: A study in an animal model of childhood depression

Genetically predisposed and resilient animal models of depression reveal divergent responses to early-life adversity

OBJECTIVE

Early-life adversity (ELA) is one of the strongest predictors of childhood depression that may be exacerbated by a genetic predisposition to develop depression. We therefore investigated the bio-behavioural effects of an early-life stressor in an accepted rodent model of depression.

METHODS

The Flinders sensitive line (FSL) and resistant line (FRL) rats were subjected to an early-life stressor, whereafter their bio-behavioural response during pubertal onset was evaluated. Male and female pups were maternally separated for 3 h per day from postnatal day 02 (PND02) to 17, when they were also weaned. Control animals were left undisturbed, until weaning on PND21. Depressive-like behaviour was analysed on PND21 and reassessed on PND36. Hippocampal monoamine levels, markers of oxidative stress and metabolic markers implicating mitochondrial function were also measured.

RESULTS

On PND21, the non-maternal separation and early weaning (non-MSEW) FSL rats spent 10% more time mobile than their FRL controls in the tail suspension test (TST) yet displayed increased depressive-like behaviour in the forced swim test (FST) on PND36. This depressive-like behaviour coincided with increased hippocampal norepinephrine levels, serotonin turnover and a dysfunctional redox state. Maternal separation and early weaning (MSEW) appeared to initially reduce early-life (PND21) depressive-like behaviour in the TST but then induced depressive-like behaviour on PND36 and increased norepinephrine levels more profoundly in the FRL rats.

CONCLUSION

These findings highlight the need to further investigate the stress response pathway in these animals and that the absence or presence of genetic susceptibility may influence the presentation of ELA effects.

Pre-pubertal, low-intensity exercise does not require concomitant venlafaxine to induce robust, late-life antidepressant effects in Flinders sensitive line rats

A significant number of adolescents are considered insufficiently active. This is of concern considering the negative association between physical activity and major depressive disorder (MDD). There is a lack of approved pharmacological treatment options in this population partly due to limited information on the risks associated with lasting effects during early life. Therefore, interest in non-pharmacological strategies is gaining popularity with low- to moderate-intensity exercise being especially attractive for its antidepressant-like effects and augmentation properties in combination with antidepressants. Early-life development might present a unique "window of opportunity" to induce long-term beneficial effects in individuals treated with central acting drugs, such as antidepressants. Therefore, we investigated the bio-behavioural effects of pre-pubertal, low-intensity exercise (EXE) and/or venlafaxine (VEN) on depressive-like behaviour in juvenile (postnatal day 35 (PND35)) and young adult (PND60) stress-sensitive Flinders sensitive line (FSL) rats. Interventions were introduced during pre-pubertal development, that is PND21-34, followed by a 26-day washout/sedentary period, when bio-behavioural analyses were performed in the early adulthood group. VEN, alone or in combination with EXE, proved ineffective in inducing any bio-behavioural changes in either age group. EXE did not induce early-life antidepressant-like effects, despite increasing frontal serotonin (5-HT) and noradrenaline (NA) levels. Later in life (PND60), pre-pubertal exercise reduced immobility and increased coping behaviours, together with increased cortical 5-HT levels, despite a significant reduction in locomotor activity. These findings emphasize a strong serotonergic basis to the observed delayed antidepressant effects of EXE later in life.

Immediate and long-term antidepressive-like effects of pre-pubertal escitalopram and omega-3 supplementation combination in young adult stress-sensitive rats

Major depressive disorder (MDD) affects a significant number of children and adolescents, yet treatment options for this population remain very limited. Escitalopram (ESC) is one of only two antidepressants approved as treatment for juvenile depression. Still, delayed onset of action, and immediate plus the risk of lasting side effects contribute to low patient adherence, and places the medical prescriber in a difficult situation weighing the potential long-term effects of juvenile treatment against the known consequences of untreated MDD. Research into alternative or augmentation strategies and their long-term effects are needed to improve clinical outcome and better our understanding of the long-term consequences of early-life treatment. We investigated the early-life (postnatal day 35 (PND35)) and lasting (PND60) bio-behavioural effects of pre-pubertal (PND21 to PND34) escitalopram (ESC) administration and/or ω-3 supplementation (OM3) in stress sensitive Flinders Sensitive Line rats. Only ESC treatment showed a strong trend to decrease depressive-like behaviour via significantly increased climbing behaviour on PND35. However, OM3 treatment reduced locomotor activity and increased hippocampal neuroplasticity on PND35, suggesting improved coping behaviour and masking of possible antidepressant-like effects. Reduced locomotor activity lasted into early-adulthood on PND60, despite a treatment-free period from PND35 to PND60. Regardless, early-adulthood antidepressive-like behaviour was only observed in the combination treatment (ESC + OM3) group, despite a significant increase in serotonin turnover, suggesting strong neurodevelopmental process to be involved. Taken together, the combination of ESC and OM3 might induce lasting beneficial neurodevelopmental effects in a stress-sensitive population, suggesting a possible role in current treatment strategies.

Long-lasting effects of fluoxetine and/or exercise augmentation on bio-behavioural markers of depression in pre-pubertal stress sensitive rats

Juvenile depression is of great concern with only limited treatment currently approved. Delayed onset of action, low remission and high relapse rates, and potential long-lasting consequences further complicates treatment and highlights the need for new treatment options. Studies reporting on long-lasting effects of early-life treatment have reported conflicting results, with the pre-adolescent period mostly overlooked. The anti-depressive effect of exercise, as a possible treatment option or augmentation strategy, is dependent on age and exercise intensity. We investigated the immediate (i.e. postnatal day 35 (PND35)) and lasting (PND60 to PND61) effects of pre-pubertal (PND21 to PND34) fluoxetine and/or exercise on bio-behavioural markers of depression and oxidative stress in stress sensitive Flinders Sensitive Line rats. Low, but not moderate, intensity exercise or 5, but not 10, mg/kg/day fluoxetine displayed anti-depressant-like properties at PND35. Pre-pubertal treatment with 5mg/kg/day fluoxetine or low intensity exercise exerted lasting anti-depressive-like effects into adulthood, whereas the combination of these two treatments did not. Furthermore, the combination of fluoxetine plus exercise reduced hippocampal BDNF levels as compared to exercise alone, which may explain the latter findings. In all treatment groups hippocampal SOD activity was significantly increased at PND61, suggesting an increased anti-oxidant capacity in adulthood. In conclusion, the data confirm the anti-depressant-like properties of both early-life fluoxetine and exercise in a genetic animal model of depression. However, optimal lasting effects of early-life interventions may require adjustment of antidepressant dose and/or exercise intensity to developmental age, and that a combination of antidepressant and exercise may not necessarily be augmentative.

Dehydroepiandrosterone Attenuates Cocaine-Seeking Behaviour Independently of Corticosterone Fluctuations

The neurosteroid dehydroepiandrosterone (DHEA) is involved in the pathophysiology of several psychiatric disorders, including cocaine addiction. We have previously shown that DHEA attenuates cocaine-seeking behaviour, and also that DHEA decreases corticosterone (CORT) levels in plasma and the prefrontal cortex. Previous studies have found that rats demonstrate cocaine-seeking behaviour only when the level of CORT reaches a minimum threshold. In the present study, we investigated whether the attenuating effect of DHEA on cocaine seeking is a result of it reducing CORT levels rather than a result of any unique neurosteroid properties. Rats received either daily DHEA injections (2 mg/kg, i.p.) alone, daily DHEA (2 mg/kg, i.p.) with CORT infusion (to maintain stable basal levels of CORT; 15 mg/kg, s.c.) or vehicle (i.p.) as control, throughout self-administration training and extinction sessions. We found that both DHEA-treated and DHEA + CORT-treated groups showed a significantly lower number of active lever presses compared to controls throughout training and extinction sessions, as well as at cocaine-primed reinstatement. DHEA-treated rats showed lower CORT levels throughout the experimental phases compared to DHEA + CORT-treated and control rats. Additionally, we show that DHEA administered to cocaine-trained rats throughout extinction sessions, or immediately before reinstatement, attenuated cocaine seeking. These findings indicate that DHEA attenuates cocaine-seeking behaviour independently of fluctuations in CORT levels.

Behavioral effects of environmental enrichment during gestation in WKY and Wistar rats

Effects of prenatal environmental enrichment (EE) were examined in Wistar Kyoto (WKY) "depressive- and anxious-like" rats and Wistar rats. During gestation, dams lived in standard cages or in EE cages. Their behavior during gestation and lactation was observed. On weaning day, they were tested in the forced swimming test, and corticosterone concentration was measured from their plasma. The offspring, reared in standard environment, were tested as juveniles or young adults in the elevated plus maze, open field and forced swimming tests. Corticosterone concentration in feces was analyzed. EE offspring showed more anxiety-like behaviors and less activity, compared to controls. Effects were more prominent in youth than in adulthood and in Wistar rats more than in WKY. EE lowered corticosterone concentration in young WKY rats' feces. EE induced changes in the dams' behavior during gestation and lactation. These changes in dams' behavior could be mediators of the effects on the offspring.

Monoamines, BDNF, Dehydroepiandrosterone, DHEA-Sulfate, and Childhood Depression-An Animal Model Study

Basal levels of monoamines and DHEA in four main limbic brain regions were measured in prepubertal Wistar Kyoto (WKY) rats (a putative animal model of childhood depression). Basal levels of “Brain-Derived Neurotrophic Factor (BDNF)” were also determined in two regions in the hippocampus, compared with Wistar strain controls. In the second phase, we examined the responsiveness of prepubertal WKY rats to different types of chronic antidepressant treatments: Fluoxetine, Desipramine, and dehydroepiandrosterone sulfate (DHEAS). WKY prepubertal rats exhibited different monoamine levels in the limbic system, reduced DHEA levels in the VTA and lower levels of BDNF in the hippocampus CA3 region compared to controls. In prepubertal WKY rats, only treatment with DHEAS produced a statistically significant decrease in immobility, compared to saline-administered controls in the forced swim test. Wistar controls were not affected by any antidepressant. The results imply that DHEA(S) and BDNF may be involved in the pathophysiology and pharmacotherapy of childhood depression.

Arachidonic acid-containing phosphatidylcholine species are increased in selected brain regions of a depressive animal model: implications for pathophysiology

The Flinders Sensitive Line (FSL) rat is a genetic animal model of depression. Following recent findings that the brain fatty acid composition of FSL is characterised by increased arachidonic acid (AA), we used electrospray tandem mass spectrometry and (1)H-NMR to examine lipid species in different brain areas. Cholesterol and sphingolipids were increased in the hypothalamus of the FSL rats. Furthermore, arachidonic acid-containing phosphatidylcholine (AA-PC) species were elevated with PC16:0/20:4, PC18:1/20:4 and PC18:0/20:4 (p<0.003) increased in the hypothalamus and striatum. In contrast, there was a decrease in some docosahexaenoic acid (DHA)-containing species, specifically PC18:1/22:6 (p<0.003) in the striatum and PE18:1/22:6 (p<0.004) in the prefrontal cortex. Since no significant differences were observed in the erythrocyte fatty acid concentrations, dietary or environmental causes for these observations are unlikely. The increase in AA-PC species which in this animal model may be associated with altered neuropathy target esterase activity, an enzyme involved in membrane PC homeostasis, may contribute to the depressive phenotype of the FSL rats.

Possible involvement of sigma-1 receptors in the anti-immobility action of bupropion, a dopamine reuptake inhibitor

Sigma receptors particularly, sigma-1 subtype is known to modulate the release of catecholamines in the brain and may participate in the mechanism of action of various antidepressants. The present study investigated the possible involvement of sigma receptors in modulating the anti-immobility-like effect of bupropion (a dopamine reuptake inhibitor) using the forced swim test (FST) in mice. Bupropion produced dose-dependent (10-40 mg/kg, i.p.) reduction in immobility period and the ED(50) value was found to be 18.5 (7.34-46.6) mg/kg, i.p. (+)-Pentazocine (2.5 mg/kg, i.p.), a high-affinity sigma-1 receptor agonist, produced synergistic response when it was co-administered with a subeffective dose of bupropion (10 mg/kg, i.p.). On the contrary, pretreatment with progesterone (10 mg/kg, s.c.), a sigma-1 receptor antagonist neurosteroid, rimcazole (5 mg/kg, i.p.), another sigma-1 receptor antagonist, or BD 1047 (1 mg/kg, i.p.), a novel sigma-1 receptor antagonist, reversed the anti-immobility effects of bupropion (20 mg/kg, i.p.). The various modulators used in the study did not show any effect per se on locomotor activity except bupropion which at a higher dose (15-40 mg/kg, i.p.) significantly increased the locomotor activity. The results for the first time demonstrated the involvement of sigma-1 receptors in the anti-immobility effects of bupropion.